RTM Composites » Molding Processes

Making Closed Molding Simple, Just Say When…

John Moore — Mon, 19 Oct 2020 16:23:42 +0000

There are times in life when things are rather subjective or can change from time to time, one such scenario could be while dining. The waiter reaches over your salad with their pepper grinder hovering and says, “Just Say When” implying you tell them when to stop grinding pepper on top of your salad.

How much pepper you choose to add to your salad is up to you. In contrast, when injecting a mold with resin there is a set volume the mold can accept. Overfilling or underfilling the mold can have impacts on part quality, production performance, and the health of the molding operation, let alone lowering profits and wasting money.

When reviewing many closed molders’ general practices it revealed that the volume of resin injected into their molds is inconsistent. The impact of that inconsistency is driving excessive cost and reducing tool life.

This article addresses both the factors that prevent the RTM/LRTM or Vacuum Infusion mold from consistently filling and the solution to gain control over this vital element of the closed molding injection process.

First, we’ll consider the methods used to halt the resin injection once the mold is filled. Then we’ll review the variables that are driving the apparent need to change the resin fill volume on the molding floor.

RTM, LRTM, and Vacuum Infusion (VARTM) Closed Molding

When it comes to the critical production step of filling a mold with resin, there must be a predetermined control on the volume of resin that is injected into the mold. There shouldn’t be a “variance” in the injection volume between molding cycles. Unlike pepper on a salad, the time to say “when” for total resin injection volume is set by the closed cavity volume and not subject to change.

Too often “when” to stop the injection on the molding floor is when the mold is overfilled with resin and is witnessed at the vent, causing resin waste, mold stress, excessively thick parts, and post mold rework.

Resin Waste Goes Back to the Historical Beginnings

Brief History on Controlling Resin Injection Volume

Before the 1980s Operators Kept Count

Back in the early 1980s and prior, the composite industry relied on the operator to know how many “strokes” of resin were to be pumped into the mold by “listening” to the pump and counting strokes as the mold filled, assuming they did not lose count, the operator would halt or stops the injection at the moment the mold was filled.

The Mid-1980s Brought the Stroke Counter

The stroke counter keeps track of strokes throughout an injection and halts the injection when the predetermined count is reached.

Each time a different mold is presented to the injection system, the stroke counter must manually be reset from the previous injection and updated with the predetermined count to match the current mold.

This is done by an operator who often refers to a handwritten value scribbled down on the mold near the injection point, or sometimes in an injection journal/notepad. Though the stroke counter is an upgrade from the operator listening and keeping count, it still unnecessarily opens the injection process to human error and is considered obsolete with today’s simplified technology.

The 1990s and the Mold Protection Guard

The 1990s brought the Mold Protection Guard or MPG, which worked in unison with a pump speed setting—similar to how the count is preset within the stroke counter. The motivation for the MPG was influenced by the higher injection pressures used during the 90s within the RTM process.

The MPG acts as a regulator for the resin pump, restricting airflow to the pump when the pressure exceeded the set limit. Though the MPG is a pressure control, it began exposing the need for what is now understood as flow control.

Though the MPG provided a solution for the higher pressure environments of RTM it’s inadequate for today’s lighter molding process, such as LRTM and VARTM.

2020 Modern-Day Solution is RFID Technology

Today’s advancements in technology have brought many improvements to the composite industry, one of which is radio-frequency identification or RFID as it’s more commonly known as.

Using unique RFID tags that are directly attached and assigned to each mold, a modern meter mix injection system has enough insight and understanding to allow an operator to start the injection with a single button press. Massively reducing and removing human operator error.

Each RFID tag is linked with a mold and backed by a predetermined recipe within the injection system. The operator uses the RFID reader, which is normally attached to the injection wand, by setting the tag on the reader and pressing start. The injection machine knows exactly which recipe to use and ultimately how many “strokes” to put into the mold. However precise control over stroke count is only the beginning when using recipes.

Mold Link by JHM Technologies, Inc. is an RFID tag solution for modern-day production environments and is available on the Infuser line of injection systems. Mold Link has been leading innovation with RFID technology in the composite industry, truly opening the doors to a precise, repeatable, and predictable production process in a cost-effective way.

Stroke Counter Compared to Mold Link

Today, JHM Technologies, Inc. Infusatrol Mold Link technology is a far superior method of controlling resin volume in each mold when compared to the earlier alternatives of using a manual stroke counter.

Several steps are involved for the operator to program the stroke counter which is prone to human error and suffers from no means to confirm process compliance on the floor.

Reliable and repeatable production is simple with Mold Link

Each mold count, or recipe, is held in the “Infusatrol” Infuser machine memory with no need for the operator to program each digit manually.

Each time the Injection System is connected to a mold, the Mold Link tag attached to that mold is placed on the Mold Link reader and then the operator simply presses the “start” button which instantly sets the counts to fill the mold automatically without concern of human error. This takes a huge weight of responsibility off the operators.

Coming to Terms With Injection Process Variables

How do you Determine the Stroke Count for a Mold?

The stroke count should be a factor of the total mold cavity volume less than the volume of the fiber. Using a common fiber load as an example: If the composite laminate is to have 30% by weight fiber, then the fiber “volume” would be ~17% of the mold cavity volume leaving ~83% plus any injection feed line volume to divide by 100 CC to calculate the needed stroke counts for the mold injection. This value shall then be the set volume needed for the mold fill.

Stroke Counts Variances

Often, the number programmed manually into the stroke counter is handwritten on the top side of each mold for the operator reference. Molders with a documented process will have a stroke count documented in their written process, yet in practice, the documented number of counts may well not be the amount injected currently on the molding floor.

The reason for the variance in pump stroke counts is an important topic not professionally managed in today’s closed molding processes. However, the volume variances have a direct impact on the molded part quality, mold life/maintenance, and true production throughput.

Understanding Variances in Stroke Count for a Mold

Injection volume for a mold should not change unless the fiber load or the mold has physically changed. The variance is a lack of process controls!

Let us peek behind the curtain into a real-world production example of closed molding today.

When visiting an RTM, LRTM, or VARTM closed molding plant you will most often see numbers written on the backside of the molds indicating counts for resin injection volume. Those counts can be accompanied by other counts that had been scribbled out some time ago, usually by a previous operator.

What this shows is the amount of resin pumped into the mold has changed as molding issues appear on the molding floor. As the issue(s) are worked through, the operator will change the stroke count value, in most cases adding additional strokes of resin volume.

The White Elephant in the Room That Most Molders Ignore

If the mold has not been modified in size, nor fiber volume changed, then how can the “volume” of resin needed to fill the mold change? The part cavity volume does not change, so unless fiber volume changes, the precise same amount of resin to fill the mold from part 1 to part 1000 or more should be a constant—it shouldn’t change.

What are the concerns if the stroke counts are changed?

Resin Cost – The stroke of a professional injection systems count volume is ~ ¼ pound of resin (100 CCs). For every 4 counts over the actual needed amount to fill the mold the waste is nearly a pound of resin which can cost from $1.00 to $2.00 per pound. It is, however, not too uncommon to find molds that are overfilled by far more than 4 counts. The waste of 1 to 2 or more pounds of resin per part becomes a substantial cost very quickly.

Note: A recent survey of several Molder’s asking; what is your resin inventory variance when audited? The responses were normally that variance is far greater than 17% higher than BOM usage. Which is to say, it takes >117% of the planned bill of materials for the resin to fill the molds. Highlighting at minimum, molders are paying >17% more for their resin than needed due to pumping in more resin that the mold can hold.
Mold Life – If you stop and think about it, if the mold cavity volume were filled with the correct dry fiber, and then as an example; to fill the remaining cavity (part area) were say 10 pounds of resin. Yet, the operator pumped in an additional 1.7 pounds of resin, what happened in the mold part cavity? The mold was forced to increase in cavity volume and thus the only way to do so is to open the mold and make a thicker part. This forces the mold open which puts heavy stress on the mold and is often witnessed in cracking of the mold surface.
Part Post Mold Rework – When the mold is forced open, we are faced with the added cost found in resin waste and mold life reduction/maintenance, we are also faced with far more post-mold rework of the parts produced.

Controlling Injection Pressure

All immediately agree that injecting resin into a closed mold at “too high” of pressure is going to force the mold open. Yet, what is not well understood is how little pressure is needed to open the mold. Many have put trust in the injection equipment to have the “Mold Protection Guard” or MPG. Not realizing the MPG was designed back in the early 1990s when the typical injection was a higher pressure than what is common in today’s light structure tooling.

The MPG is an extremely limited form of “flow control” yet as a means of simple explanation, has been introduced as a “pressure control”.

MPG function is like holding down on the gas pedal while “pumping” the brake to control the Car’s speed.

To better illustrate how the MPG worked, it can be likened to pressing down on the gas and then trying to tap the brake at the same time in an attempt to control the speed of the car. While the concept would have some level of control it is easy to see that adjusting the pressure on the accelerator—gas pedal in this analogy—is a much more practical and elegant means to control the car speed.

Deeper Insight Into Injection Pressure

Professional Injection systems use an 11 to 1 power ratio between the compressed air pressure powering the powerhead air motor and the actual resin pressure exiting the resin fluid section of the pump with lighter duty pumps use a 7 to 1 ratio.

The resin pump ratio is the factor of the air motor piston diameter compared to the resin pump rod diameter. The reciprocating action of the piston pump is driven by the air motor piston connected directly to the resin pump rod, the area of the air motor piston is either 7 or 11 times larger than the resin pump rod. This factor then amplifies the resin pump output pressure by the factor of the difference.

The resin pump displaces resin in both the up and down stroke as the air motor reciprocates.

Note: The shorter the pump stroke the more often the pump needs to reverse direction, it is the moment at the top and bottom of the stroke where the potential to affect the “resin and catalyst” mix ratio is most vulnerable. The equipment manufacturers will shorten the pump stroke to reduce their cost in manufacturing the pump, yet at the cost of the molder.

Referring to the resin pump power ratio, and using the lower 7 to 1 example, should the resin pump be fed with 10 psi of air pressure, the static resin delivery pressure would be 70 psi.

Considering a lightweight LRTM mold upper for instance, such as those built today weigh 10 pounds, or less, per square foot of mold area.

If we look at just one square foot of mold and consider that there are 144 square inches within that 12″ x 12″ area. If we were to apply only 10 psi resin pressure to the mold in that 1 sq/ft area we would have a lifting force equal to 1,440 pounds. Realizing the resin pump with as little as 10 psi air supply pressure amplifies the resin static pressure to 70 psi we can easily see the mold has no means to remain closed, even with the mold flange having a vacuum area and initially the mold cavity having a regulated vacuum, still the forces possible in the resin delivery easily outweigh the clamping forces.

With just 10 psi of resin injection pressure, we can lift the mold upper 144 times over. This fact is usually overlooked when determining how to control the injection process.

Understanding how little injection pressure is required to open a mold, we now start to have insights into the primary cause of variance in mold fill volume. Yet, it is still common in the industry to allow the operator to simply add more strokes. Resulting in wasted resin, unneeded mold stress and wear, and post-mold rework of parts.

The Rise and Fall of Zero Injection Pressure (ZIP)

In 2001, JHM Technologies, Inc. began controlling the injection process on the foundation of injection “pressure” alone. Pressure sensors were installed within the mold cavity. This feature opened the door to confirm the vacuum level in the mold cavity for processes such as LRTM, confirmed the vacuum cavity level before injection, and also provided a “set point” of maximum dynamic resin pressure to which the injection system could react to. Some equipment manufacturers still follow this path having been motivated by the Zero Injection Pressure (ZIP) technology.

A new industry acronym was created with ZIP RTM technology, which represents the process of maintaining the injection pressure below “gain” to the outer atmospheric pressure, working to hold the mold cavity closed during the injection process. The leap in additional process control with ZIP technology over the MPG technology was immediately realized and patent applications were granted in Europe while pending in the USA as acceptance of the process grew.

The Composite Fabricator Magazine featured the ZIP molding technology on the front cover of their March 2003 edition. This feature article was to highlight the advancements of JHM Technologies, Inc. patented Zero Injection Pressure gain to atmosphere process (ZIP RTM). From 2001 to 2004 JHM supplied many different molding applications with the ZIP technology in which the pressure within the cavity was to be maintained below the external clamping atmospheric force.

Ultimately the ZIP technology was abandoned as we realized it’s not possible to prevent the mold from opening during the injection process using pressure control alone, especially as we worked to push the envelope on the speed of injection.

What was learned during the ZIP phase also shed light on a reason using MPG alone wasn’t enough for controlling the mold closure during the injection.

There comes a very fine point when the mold begins to open, it in effect “pops” this is the point in which even if the injection process is paused, the upper often cannot settle back down on the Z plane mold stops. Once this happens the mold cavity has opened increasing the part thickness and requirement for the additional resin to fill the mold, as well as the loss of control of the resin flow path which resulted in air entrapments or dry spots found in the part when the mold was opened.

Control Flow Rate and use Pressure as a Governor, Infusatrol

Using the knowledge learned from working with pressure alone as the control, we reflected on other injection processes especially that of thermoplastic injection in which the flow rate is the focus of the process control.

The Infusatrol injection control software was developed with proprietary algorithms to manage the air over hydraulic resin pressure provided by the injection system. This allows accurate control of the injection flow rate and monitoring the injection pressure in real-time. This state-of-the-art control has been working to provide users of the Infuser series of injection systems with an extremely competitive advantage over molders attempting to blindly control their process through the belief and faith in the MPG alone.

With Infusatrol, should the injection pressure limit be exceeded, the Infuser will momentarily stop and automatically reset the flow rate setting to a lower value and then ramp up to the new lowered flow rate. The purpose is again to hold on to a constant dynamic flow rate yet react to the pressure exceeding a set limit.

Using Infusatrol the upper mold half may be so light it is a nylon or silicone rubber film and no rigid structure at all and control over the flow rate is still available.

The Progression to a Simpler, Repeatable, and Modern Solution

The MPG sensor is accompanied by a second operator setting for “pump speed” control, which is simply the regulated air pressure feeding the resin pump. The first limitation of the MPG sensor is the fact it requires several PSI in resin pressure to push the diaphragm up and to send a signal to choke off the air supply to the resin pump air motor. Then once it does trigger, and the air supply to the resin pump is restricted, the resin pump slows, yet the same pump speed setting remains. Again, like holding the gas pedal down as it were. As the resin pressure in the feed line to the mold drops from the resin pump restriction, the MPG diaphragm returns to allow the pump to be fed with air pressure again, yet the “pump speed” regulator remains constant so again the pressure builds in the mold.

The trouble is, that for the same reason the ZIP technology was abandoned, the mold often has “popped” and actually the back pressure from the resin feed drops as the mold opens and the added cavity opening allows the resin to flow easier into the mold, while simultaneously losing control of the resin flow front leading edge and resin flowing in the path(s) of least resistance. At this point, the MPG is doing nothing and the pump is flowing at the pump speed setting.

This phenomenon can be witnessed using the Infusatrol controls, in real-time the actual flow rate and the actual resin feed pressure is displayed on the control screen. As the mold continues to fill, the actual resin pressure steadily rises, as the flow rate is held at the predetermined set point.

If however, the flow rate setting is too high, then resin pressure will continue to rise, should the pressure exceed the “upper limit” setting for pressure, then Infusatrol will halt the resin pump momentarily, reset the flow rate setting to a lower value and then begin flowing at the lower pump speed setting. However, if the upper limit setting for resin pressure is set too high and allows the resin to be pumped into the mold at the same flow rate setting, the “actual” resin pressure will drop. This indicates the mold has been opened making it easier for the resin to flow into the expanded mold.

This insight allows for the maximum pressure limit to be set low enough to prevent the mold from opening and yet allows for the flow rate to be maximized to allow filling the mold, without opening, at the fastest rate possible. To take this control to a greater level, the Infusatrol can have multiple “steps” during injection which trigger at different stroke counts during the fill, as the mold fills, the flow rate and pressure limit can have a different setting. This allows for rapid injection at the beginning and to progressively slow the flow rate as the mold continues to fill.

Through the combination of Mold Link, automated flow rate, and pressure control provided by Infusatrol, today’s molders are operating with modern technology leaving behind the obsolete 1980 and 1990s level of control as critically needed today in the competitive global market that we live in.

Simplify Your Process Today

Take control and simplify your injection process today with today’s industry leading technology. Remove operator error and improve production throughput, automate reporting and reduce waste, drastically reduce post-mold rework, all while extending the life of your molds.

All of those features and more are available with Infusatrol on the Infuser series injection systems. The Infuser injection system is competitively priced against the competitors while being the only injection system which pays for itself in reduced material costs, mold maintenance, and post-mold part rework.

JHM Technologies, Inc. has a full line of meter mix injection systems for polyesters, vinyl esters, epoxies, and urethanes. Systems ranging from the industrial Flow Master to the PRG Servo used in the aerospace applications with 2 component epoxies at 300 degrees held within a 1% mix ratio all while taking advantage of the Infusatrol injection software.

JHM Technologies, Inc. is the oldest manufacturer in North America for RTM injection systems. The product line was built specifically for the advancement and to serve the RTM molders worldwide.

To simplify and gain control of your molding process visit www.rtmcomposites.com/contact or call +1 810-629-6515 and speak with the team who has over 40 years of hands on molding experience.

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Vacuum Infusion is not a Direct Replacement for Open Mold or RTM

John Moore — Thu, 14 Apr 2016 00:33:50 +0000

The various low pressure closed molding processes continue to retain the interest of the molding community. Often however what is presented as new and “what everyone is converting too” is simply an introduction to a method that has been in practice for many years.

Today, we see the interest in vacuum infusion has gained the spotlight focus, especially with the offering of high tear strength silicone and latex materials used to produce the reusable “bags”. This has brought a level of economics not previously available by users of nylon film and butyl tape.

Over the years, vacuum infusion was thought of as a “slower”, low volume process as compared to open mold or even resin transfer molding which has been recognized as a medium volume process method.

Today, we see a trend to promote the use of the vacuum infusion process using reusable upper bags be it, silicone or latex, as a direct replacement for both open mold or RTM processes. Interesting as that is, the direct comparison shows some profound differences.

Standard Expectation

Still to this day the majority of products produced using FRP are using the open molding process; that is speaking of the conventional industries—industrial, recreational, medical, heavy truck, and aftermarket automotive markets. The conventional industries alone account for the majority use of unsaturated poly / vinyl esters and fiberglass composites in the market.

In that light, the fiber to resin ratio is often found to be ~30% fiber and 70% resin by weight, with a very common general purpose thickness of 1/8″ (3mm) in terms of a typical laminate profile.

First Notable Difference

Notable Difference With the Open Mold Process

In the open molding process to achieve a 1/8″ thickness one simply indicates to the operator, or robot, how many passes to make with the chopper gun or how many layers of a particular fiber to lay down. While here the target thickness is controlled in general by the operator as he can add too many or too few passes, or have too high of a resin content and so on, typically we are not coming up with thin laminate. The open mold industry on average has a thicker than required 1/8″ laminate, accounting for much of the experienced materials variance and waste.

While what we see pulled from the open mold process is typically close to the nominal prescribed thickness, if anything randomly too thick, while negative details can be said about the “B” side finish and uniformity. We find the typical open molded part performs well within spec tolerance.

Notable Difference With the RTM Process (RTM, LRTM, HP-RTM)

Alternatively, when we consider RTM closed molding (RTM, LRTM, HP-RTM), we see that by the fact we have a mold with two rigid halves, the actual molding tool part cavity sets the part thickness, here we can then load the mold with the prescribed dry fiber at the same weight as the open mold, inject the resin, and produce a part that performs similar to the open molded part in terms of physical strengths, especially comparing that of stiffness (flex modulus)—which initially is the first obvious factor in perceived strength.

RTM closed molding (RTM, LRTM, HP-RTM) produces a repeatable part which is near absolute thickness uniformity and consistency. This is made possible by having the molding tool’s part cavity set the part thickness and the injection system precisely controlling the injected resin. The operator in this process measures and lays the dry fiber in the mold cavity prior to injection. In comparison to the “expected standard” using that of open mold as the reference, 30% fiberglass and 70% resin by weight at 1/8″ laminate we produce a molded product with the same physical properties as open mold, yet with uniformity and consistency in material usage from molding to molding—injection to injection.

Notable Difference With the Vacuum Infusion (VARTM)

Now, if however, we were to load the same dry fiber / weight as used in the open mold or RTM ridged mold method into a single sided ridged mold with an upper half of either nylon film, silicone or latex rubber, then inject resin into the mold, we will find that the produced product is not the same thickness as the open mold product or other various forms of RTM. In the infusion process the thickness is a factor of dry fiber thickness and it’s compaction factor under vacuum. Unlike in open mold where the thickness is controller by the operator, or in an RTM process where the thickness is controlled by the mold tooling cavity, the infusion process produces a part with a thickness controlled by the fiber’s compaction under vacuum.

At the same fiber loading per square foot of area we are seeing a reduce in resin usage and a much greater fiber content in the vacuum infusion process – when compared to open mold or an RTM process. Initially the reduction of resin is seen as a major benefit, primarily for its cost savings. However we immediately find that our produced parts are now far more flexible, which is not always accepted within the products specification.

In consideration that the majority of the products produced are not what we would compare to an optimized or “engineered” laminate, we are seeing many stumble into the assumption that using the infusion process offers a reduction in resin use at the same fiber weight all with the benefit of closed molding at lower mold cost to RTM. At least this is what is being said when introduced to the “new” process of vacuum infusion. In the end the thinner, more flexible product may be acceptable for some in the industry, it’s often found to be too thin and too flexible.

Overcoming the thin laminate is a simple fix. Simply adding fiber layers or other “bulking” media to the dry fiber will result in stiffening up the final product. Yet, the added fiber material may void the savings in resin reduction and or set the bill of material for that product at a premium over the open mold or an RTM process methods.

Surface Finish

The second notable difference when comparing the moldings from open mold to closed molding is the final part surface. Again, using open mold as a “standard of acceptance” and processes methods using non heated tooling, we can say that the open molded part surface will have less fiber print than that of a closed molded part.

This is in part due to the fact that in open mold, the resin is curing often in two steps having a “skin coat” initially applied and rolled out over the gel coat, then a “bulk” layer applied to build to final thickness. Where in the various closed molding process of RTM or vacuum infusion the resin is all cured to final thickness in one step, resulting in a more rapid cure and typically showing more fiber print and other similar imperfections.

This is especially true of the vacuum infusion process where the dry fiber is packed tightly to the gel coat which is cured well enough to withstand the styrene from the molding resin and not alligator, yet still soft enough to be imprinted by the fibers pressed tightly to the gel back side surface. There is again a simple solution to surface finish in both the vacuum infusion and RTM. With the use of veil, low profile resins, and or barrier coats we are able to produce a premium surface finish. Yet, again adding these additional materials increases the products bill of materials, and may exceed the perceived cost reductions.

Surface finish is often one of the first struggles we see with customers in the industry who have transition to the vacuum infusion process. Followed by the thinner, more flexible part they’re quick to deters them from their assumption that the product molded using the vacuum infusion process was a direct replacement for the open mold or an RTM process.

Comparison Summary

Lets review for a moment. We can use the open mold process as the standard for expectation in terms of “feel” for flexibility and “sight” for surface finish, by changing laminate schedule we can meet the feel of stiffness in vacuum infusion by increasing the fiber pack volume, and in both RTM and vacuum infusion we can achieve a premium surface finish with use of veils and barrier coats and low profile resins.

What this article is meant to highlight at this point; is that transitioning into closed molding is not simply adding a bag to an open mold tool and expecting it will produce an equal product. Or even transition between vacuum infusion and an RTM process to produce equal products. Equal transitions can be made at the expense of changes in the material. Which will directly affect the final cost of the product—generally costing more than open mold in terms of pound for pound material costs of the product.

Now to be certain we clarify, our discussion here is based on an industry that for the most part is not working to finite standards. The mass volume of products produced is in open mold and the majority of those parts are produced based on anecdotal material selection. It’s quite possible, and well known, that using any of the process we can achieve specific structural and aesthetic properties. The goal of this article is to bring attention to the majority of molders with their goals of keeping the bill of materials as close as possible, and produce a final product that is inline with their accustom open mold “standard”. Naturally the faster production of RTM and even vacuum infusion with reusable bags offsets tooling and or bag cost, the focus here is on perception of materials and results in the final molded product.

The Toolbox of Processes Methods

The open molding process, while very common method of molding an FRP product, is only one of several “tools” of the trade as it were. That is precisely the point, each process method should be viewed as a “tool” one of many in our molder’s toolbox.

Each process method—tool—of molding has advantages and disadvantages; no part can only be molded one way, yet often the most practical way is limited to one or two of the “tools” in our process methods toolbox.

If you however consider process methods such as vacuum infusion, RTM, and open mold as “tools” then when one considers how to produce a particular product in FRP, they can reach into their toolbox of methods with a complete understanding of how each method is going to yield a given result.

This is the ideal manner to view the process selection. Never should we view methods as “new” or “up and coming” the way everyone is moving and so on… yet too often this is exactly how the decision is made to produce a product. The second is to view strictly by the cost of the mold, which is another discussion altogether. For example, vacuum infusion “tooling” is ~25% less than an RTM process tooling while open mold tooling is ~45% of RTM—though often overlooked is the final cost depends on the production cycles per shift as well as other factors, not just the initial tooling cost.

It is true, you can use a blade tipped screwdriver as a chisel, yet for the most part a blade tipped screwdriver is neither a chisel nor a pry bar, it is a tool to be used with a slotted head fastener. So it is with each of the molding processes.

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Composite Manhole Process Development

John Moore — Fri, 27 Mar 2015 18:20:19 +0000

Edge boil is all too common when you’re molding FRP manhole covers—particularly those striving for the H20/H25 and C250/EN124 standards. Due to the size, fiber density, and required resins, optimizing the injection process of FRP manhole covers often plague molders with expensive labor-intensive post-mold work. Edge boil occurs—in this case—when the center of the part reacts and cures at a faster rate than the outer edge. This reaction generates exothermic heat causing the styrene on the outer perimeter, which has not yet fully cross-linked, to boil.

Using the Infusatrol™ injection software controlling the Infuser PRG automated injection system, JHM Technologies, Inc. developed a solution by programming the catalyst ratio to progressively decrease as the resin filled the mold. Progressively decreasing the catalyst during injection insured a far more even cure, removing edge boil, pits, and ferning! Using this method provided additional ideal characteristics! The center mass is thicker, slowing the exothermic heat generation. Slowing of the exothermic generation allows the outer edge to progress further in cure before the full extent of the heat is generated – despite the fact that the perimeter resin has had as much as 6 minutes lead time over the last resin entering the mold.

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An Affordable, Production Ready Carbon Fiber Process is Here

John Moore — Thu, 09 Oct 2014 20:53:11 +0000

Weight to strength ratio along with its aesthetic appearance has always made carbon fiber an attractive material choice. However due to it’s excessive startup costs and molding complexities it has been out of reach for many. Molding carbon fiber reinforced composites (CFRP) has mostly been dedicated to the aerospace industry along with other low volume niche` applications. In recent years the automotive sector has joined in on molding CFRP with high-end steel tooling. While high-end steel tooling may prove to be an effective cost model for high volume applications, majority of the vehicles or applications that benefit from the advantages of carbon fiber are currently low volume niche` applications.

Molding CFRP is not new, however due to the lack of innovation it’s still dedicated for being used for low to moderate volume production. Typical methods being either prepreg with very high material and tooling cost — with at best 1 cycle per day in production – or vacuum infusion with similar production speeds but only one smooth finished side.

Requested Solution

We were challenged to create a package that provided low cost entry to CFRP molded class “A” surface panels. The solution had to include low cost tooling, the ability to run in extended daily production, minimum of 1 part per 2 hours, and ultimately meet speeds of 15 minutes or less. All while maintaining a surface quality as though it was molded in match metal tooling on both the “A” and “B” sides of the part.

Solution Provided

Leveraging our 30+ years of experience and using tooling design from the LRTM process in combination with elements from HP-RTM, we developed a packaged solution — far exceeding expectations —, which was used to produce the door skin example shown here. Included in the package was cost effective tooling and equipment, along with complete process training.

The example tool shown here is first part off of the mold without any process refinement! The door skin is shown with “as molded” carbon fiber “A” surface, primer, and finally top coated sections. It should be noted that there is no coating applied to the carbon fiber in the mold. The part contains 1448 grams of Momentive epoxy 035/038 resin system and 1730 grams of carbon fiber. Resulting in fiber volume fractions of 48% and a nominal part thickness of 2mm. Total weight of the door skin is 7 pounds, which far lighter than any comparable steel door outer — averaging 14.38 pounds.

Using the developed package along with the included Infuser Servo® injection system, a precise automated injection of 1448 grams of resin was injected into the mold in less than 90 seconds. The tooling used to create the example part is a “soft” FRP mold set (LRTM) with replaceable “A” cavity side mold surface, allowing for the “A” mold to be replaced at an affordable cost of $710. Complete startup cost for tooling came to $16,729.

As Molded “A” Side

As Molded “B” Side

This part and more will be at our booth #3648 during CAMX 2014 in Orlando, Florida!

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As close to Fire and Forget as it gets for VARTM

John Moore — Fri, 15 Aug 2014 22:28:18 +0000

MTI® hose – “As close to Fire and Forget as it gets for VARTM“

The MTI® hose is a spiral tube with an outer jacket that allows for resin to be stopped at the edge of the tube by the barrier jacket, yet air can still pass by.

The beauty of this technology is the fact that the positive resin pressure does not enter the negative pressure within the vacuum spiral tube environment.

This barrier maintains the differential pressure allow for the hydraulic resin pressure to be optimized thus forcing the entrapped atmosphere within the laminate to still find the low pressure of the vent tube and thus produces a higher density void free laminate without the need for an autoclave.

To see the MTI® in action, watch the few second video below. There you will see the resin in direct contact with the MTI® Tube jacket yet the atmosphere (air) from within the laminate still escaping by.

We have made countless carbon & epoxy parts using the MTI® hose never had a bad part and the physical properties are matching those needed in production OEM Automotive applications for which the composite tooling is being made for. This process is used to prove out the part design and laminate properties. We find we can use select resins from Momentive molding at temperatures of 160℉ with post mold post curing, then matching the properties of the fast cure HP-RTM resins proposed for actual OEM production.

The MTI® hose is available within our store!

Purchase MTI® hose

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Today…You Can Create Your Mold as Easy as Making a Part!

John Moore — Thu, 24 Jul 2014 16:03:48 +0000

In the late 90′s there were two innovative tooling methods to address the shortcomings of “soft” FRP Tooling as used for the “RTM” molding process at that time. These were the VEC and MIT technologies. VEC brought rapid and even temperature control using a tank of water as the mold base. The VEC tool was also far less structure as compared to the typical RTM tools of that time due to the support the tank of water provided, thus reducing the cost of the VEC mold since the tanks were common to several mold shapes.

Mold Insert Skin Tooling (MIT)

The MIT process method offered a “Mold Insert Skin” that allowed the mold cavity half to be “resurfaced” instantly. Soon however, it was clear that having extra MIT skins would allow for process steps such as Gel Coating, Fiber Loading and De-Molding to be done simultaneously while another part was in the actual mold set being injected and curing. The results proved that a MIT mold set could then increase productivity by as much as 270% by having as many as five mold skins rotating in the tool set. It should be said, that the construction of a FRP mold is made of tooling gel coat and fiber reinforced tooling resin, yet historically these materials were permanent as the mold surface by the mold building process attaching the mold base structure directly to the said mold surface mold laminate. MIT simply separates the mold surface laminate from the mold structure in a precise manner. This method has been used on a variety of parts ranging in size from a Baseball Cap to a 21′ Boat Hulls and Decks. Today, this innovative tooling design has been given some new enhancements, in the past the lower half (bolster) of the production tool set was needed to make new skins So production was lost while the lower mold half was making new MIT skins. Now, using a combination of the OSM Glass Master used to make the cavity and an LRTM upper mold matched to the Glass Master we make the MIT Skins using the LRTM process. This new molded MIT skin then fits perfectly and is vacuum locked into the production mold lower “bolster” to create a lower mold half. Today we have in effect enabled the LRTM process to make new tool surfaces, as easy as, making a part at a comparable cost. Naturally the MIT Skin is made with Tooling Gel Coat and Tooling Resin with fiber reinforcement, yet cost is far more comparable to a part then making whole mold set. Having the ability to simply mold a new mold skin completely off line at a very nominal cost is proving to completely change the economics of FRP soft tooling allowing for dramatic reduction in post mold finishing as was historically common as the life of the mold developed surface imperfections that were transferred to each subsequent molding produced. What we find what makes this possible is the precise injection control provided by the JHM Technologies Infuser PRG injection system. While this same process control has proven useful in reducing cost in making of production parts, it is now proving to allow the cost of tooling and tool replacement to be far more attractive as well.

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Tip: Mold Process Troubleshooting

John Moore — Thu, 21 Mar 2013 00:13:38 +0000

The key to repeatable molding process control in a RTM or LRTM tool is to have ACCURATE cavity thickness calibration. Most obvious consideration one would normally make is to use sheetwax of the same thickness desired for the final part thickness. For instance if a 1/8” (.125”) part thickness is desire for the final part then it would be assumed that 1/8” wax be used, this however has proven NOT to provide an accurate 1/8” part thickness in the end. The reason is when the upper mold is produced, it lifts the sheetwax during the curing process and thus the part cavity is not the predicted, often the 1/8” part turns out to be between .115” to .160” as the Upper is distorted by the wax lift. This problem plagued the closed mold builder for many years with various attempts to correct proving less than consistent results. The problem with a cavity that is not accurate has little to do with the needs of the final molded part, as often ones feel it is less than a top priority, it is critical however to controlling the resin flow path. In accurate mods produce parts with air voids and dry spots, not to mention heat shrink and cracking in radii. The solution is to build the upper mold while clamped under vacuum. This begins with the total laminate thickness wax applied in two layers with the first layer typically 1/3 the total then the final layer the remaining 2/3 of the total part thickness desired. The technique of applying the wax and then the precise method of applying vacuum during the upper mold construction is a large portion of the JHM Technologies mold building schools held in Fenton Michigan. The first layer of wax is cut into 6” squares and applied with prescribed gaps on all four sides to create a series of vacuum channels for vacuum communication. The top layer of wax is applied in full size 12” x 24” sheets with the seams tightly sealed. The use of the 6” squares is consistent in both small and large molds. The results of using the proven technique taught, is high part cavity accuracy achieving very predictable resin flow without resulting in dry spots or voids in the final part moldings.

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Process Troubleshooting: Air Pockets Causing Mold Defects

John Moore — Thu, 29 Nov 2012 15:32:26 +0000

Quite often we are sent photos or actual parts to determine root cause and solution for prevention of various part defects. In this example, a base seat of a chair was sent which exhibits gel-coat breaking away exposing a void beneath. The actual root cause was air trapped between the gel-coat and the laminate during the injection process. This is due to the “air” not being compressed or encroached by the resin. To properly eliminate this molding defect there needs to be resistance to the leading edge of the resin flow path and that resistance must remain as the resin passes through these corner radii of the part. This effect can also be enhanced if the resistance continues beyond the radii towards the exit vent. To best understand, the air resides in the mold at the atmospheric pressure it was when the mold was closed. When the resin begins to fill the mold is displaces the air, yet the air can find “hiding” places such as radii or top of pockets in the part geometry that are not forcefully filled with resin during the injection process. If however the leading edge of the resin flow path cannot migrate through the fiber fast enough so to speak the resin behind the leading edge looks for alternative paths. In the school here we try and illustrate like a crowd of people all rushing for a door, if those in the front aren’t moving fast enough those in the back start to push and shove others look around for another way to go. Same holds true of the hydraulic resin flow path, in the case the front is not passing through the glass fiber fast enough, then the resin behind looks for other areas to fill, this then finds “air” pockets, once the resin begins to compress the air in the pocket, the air resists the change in its atmospheric pressure increasing and thus inherently rushes to the lower pressure area of the exit vent. So the ultimate solution is to fill the mold cavity cossectionally with fiber at a density needed to provide the needed structure of the final composite. Then control the FLOW RATE to keep that resin flow front flowing in a “wave” from the top to bottom mold surfaces. This requires that first the mold have accurate crossection, then the fiber be loaded in such a manner as to have enough “Loft” to fill the crossection. The the operator must be certain the fiber is stretched to fit the mold shape and NOT rely on the mold closer to form the fiber. Yet, what do you do if the crossection changes or is NOT accurate? Then additional fiber must be placed as needed tightly against the gel coat before forming the nominal glass layer.

As shown here the strips of fiber are pressed well into the radii, then the top layer of fiber is placed and formed over them.

Now as the resin fills the mold, with a controlled flow rate the mold will NOT open, the fiber will be filling the crossection and the resin leading flow front will create a wave that encroaches on the air within chasing the air to vent(s). Any air missed by the leading flow front will be encroached as the hydraulic pressure of the flowing resin exceeds the atmospheric pressure of any bubble and thus that bubble of air will pass through to the nearest vent of lower pressure.

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RTM, LRTM, & VARTM Glossary

John Moore — Mon, 12 Oct 1998 18:54:13 +0000

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A-

Ablative Plastic: Material that absorbs heat (with low material loss and char rate) through a decomposition process (pyrolysis) that takes place at or near the surface exposed to the heat. ABS: Acrylonitrile Butadiene Styrene (Thermoplastic Resin). Abrasion: Wearing away by friction. Glass is highly resistant to abrasion by other materials, but can be damaged through contact with itself. A lubricant is used during processing and fabrication to prevent abrasion. Accelerated Test: Procedure in which conditions are increased in magnitude to reduce the time required to obtain a result. To reproduce in a short time the deteriorating effect obtained under normal service conditions. Accelerator (Promoter): A highly active oxidizing agent suspended in a liquid carrier used in conjunction with a catalyst to produce internal heat in a liquid plastic to cure it. Examples are diethylaniline, cobalt naphthanate and cobalt octoate. Acetone: (Styrene solubility) – The percentage of the sizing on the glass fiber that is dissolved off the strand in acetone (or styrene) after soaking in the solvent. Acoustic Emission: Measure of integrity of a material, as determined by sound emission when a material is stressed. Ideally, emissions can be correlated with defects and/or incipient failure. Acrylic: Thermoplastic polymer made by the polymerization of esters of acrylic acid and its derivatives. Activator: See Accelerator. Actual End Count: The number of bundles or splits that are actually counted in one doff of roving. (This is less than the theoretical end count due to splitting efficiencies of less that 100%). Addition polymerization: Chemical reaction in which simple molecules (monomers) are added to each other to form long-chain molecules (polymers) without forming byproducts. Additive: Any number of materials used to modify the properties of polymer resins, such as plasticizers, initiators, light stabilizers and flame-retardants. Adhesive: Substance capable of holding two materials together by surface attachment. Adhesive can be in film, liquid, or paste form. Admixture: Addition and homogeneous dispersion of discrete components, before cure. Aggregate: Hard, coarse material usually of mineral origins in composite tools. Also used in flooring or as a surface medium. Aging: Effect on materials of exposure to the environment. The process of exposing materials to an environment for an interval of time. Air-bubble: Void air entrapment within and between plies of reinforcement or within a bond line or encapsulated area; localized, non-interconnected, spherical in shape. Air Splice: The coupling between two roving doffs which is made by a jet of air entwining/snarling the two strands together. The air splice is used instead of a knot. Air Vent: Small outlet to prevent entrapment of gases in a molding or tooling fixture. Alligatoring: Visible cosmetic defect in exposed gel coat which looks like wrinkled or alligator skin. Alloy: In plastics, a blend of polymers or copolymers with other polymers or elastomers under selected conditions. Ambient: Surrounding environmental conditions, such as pressure, temperature, or relative humidity. Angle-Ply Laminate: Laminate having fibers of adjacent plies oriented at alternating angles. An Isotropic: Exhibiting different properties when tested along axes in different directions. See An isotropic laminate and Isotropic An Isotropic Laminate: One in which the properties are different in different directions. Antioxidant: Substance that, when added in small quantities to resin, prevents oxidative degradation and contributes to the maintenance of its properties. Antistatic Agents: Agents that, when added to a molding material or applied to the surface of a molded object, make it more conducting, thus hindering the fixation of dust or the buildup of electrical charge. Arimid: Type of highly oriented organic material derived from polyamide but incorporating aromatic ring structure. Used primarily as a high-strength, high-modulus fiber. Kevlar and Nomex are example of arimid. Arc Resistance: Ability to withstand exposure to an electric voltage. The total time in seconds that an intermittent arc may play across a plastic surface without rendering the surface conductive. Ash Content: Proportion of the solid residue remaining after a reinforcing substance has been incinerated (charred or intensely heated). Aspect Ratio: Ratio of length to diameter of a fiber. A-Stage: Early stage in the polymerization reaction of certain thermosetting resins (especially Phenolic) in which the material, after application to the reinforcement, is still soluble in certain liquids and is fusible. Also called resole. See B-Stage and C-Stage ASTM: American Society of Test Methods. Autoclave: Closed vessel for conducting and completing a chemical reaction or other operation, under pressure and heat. Autoclave Molding: Process in which, after lay-up, winding, or wrapping, and entire assembly is placed in a heated autoclave, usually 50 to 200 psi. Additional pressure permits higher density and improved removal of volatiles from the resin. Lay-up usually vacuum bagged with a bleeder and release cloth. Autosprueâ„¢: Automatic gate at the inlet sprue of the mold which eliminates the need to remove the resin supply during the injection process for flushing. See: Autosprue Axial Winding: In filament-wound reinforced plastics, a winding with the filaments parallel or at a small angle to the axis (0ï¿½ helix angle).

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B-

Bagging: Applying an impermeable layer of film over an uncured part and sealing the edges so that a vacuum can be drawn. Bag Molding: Process in which the consolidation of the material in the mold is affected by the application of fluid or gas pressure through a flexible membrane. Balanced Construction: Equal parts of warp and fill in fiber fabric. Construction in which reactions to tension and compression loads result in extension or compression deformations only, and in which flexural loads produce pure bending of equal magnitude in axial and lateral directions. Balanced Laminate: Composite laminate in which all laminate at angles of 0ï¿½ and 90ï¿½ occur only in + or – pairs (not necessarily adjacent) and are symmetrical around the centerline. Ball: See Roving Band Width: In filament winding, the width of the reinforcement as it is applied to the mandrel. Barcol-Shore Rockwell Hardness: This is a property of material which describes its ability to be indented. The Rockwell method for measuring hardness forces a steel point into the material and then measures the penetration of the point. The different letters in the Rockwell reading describe the shape of the point and the load applied during the test. Units – Rockwell units with the appropriate suffix letter. The letter and number cannot be separated. Higher numbers with the same letter indicate harder materials. Harder materials have more resistance to penetration by another substance. Bare Glass: The glass as it flows from the bushing in fiber form, before a binder or sizing is applied. Batch Oven: Large temperature-controlled oven, used to heat-clean rolls of glass fiber fabric. Batt: Felted fabrics. Structures built by the interlocking action of compressing fibers, without spinning, weaving, or knitting. Beam: A spool, on which is wound a number of parallel ends of singles or plied yarns, for use in weaving or similar processing operations. Beaming: Operation in which many ends of yarn from a creel are combined on a section beam. Bearing Strength: Maximum bearing stress that can be sustained. Also, the bearing stress at that point on the stress-strain curve where the tangent is equal to the bearing stress divided by n% of the bearing hole diameter. Bearing Stress: Applied load in pounds divided by the bearing area. Maximum bearing stress is the maximum load in pounds sustained by the specimen during the test, divided by the original bearing area. Bed: The result of the chopping operation. A mat of chopped glass fibers that is deposited onto a layer of resin mix on a carrier film under the chopper. Bias Fabric: Warp and fill fibers at an angle to the length of the fabric. Biaxial Load: Loading condition in which a laminate is stressed in two different directions in its plane. A loading condition of a pressure vessel under internal pressure and with unrestrained ends. Biaxial Winding: In filament winding, a type of winding in which the helical band is laid in sequence, side by side, with crossover of the fibers eliminated. Bi-directional: Reinforcing fibers that are arranged in two directions, usually at right angles. Bi-directional Laminate: A reinforced plastic laminate with the fibers oriented in two directions in its plane. A cross laminate. Binder: A coating applied to the surface of a chopped glass mat or preform which is then cured. The binder holds the previously sized glass bundles or ends together in the roving operation into a stable shape or form. Birdnest: A large collection of continuous glass bundles which is tangled up and will not run through the guide eye into roving creel. In the field, a large tangled collection of roving which does not run through the tube or guide eyes to the chopper. Bismaleimide (BMI): Type of polyamide that cures by an addition rather than a condensation reaction, thus avoiding problems with volatiles formation, and which is produced by a vinyl-type polymerization of a pre-polymer terminated with two maleimide groups. Intermediate in temperature capability between epoxy and polyamide. Blade Packing: Glass bundles or chopper fuzz which build up and pack between the blades of a chopper. This blade packing can cause poor choppability. If it falls off, it usually does not wet-through, and this can cause blisters or porosity. Blanket: Fiber or fabric plies that have been laid up in a complete assembly and placed on or in the mold all at one time (flexible bag process). Also, the form of bag in which the edges are sealed against the mold. Bleeder Cloth: Woven or non-woven layer of material used in the manufacture of composite parts to allow the escape of excess gas and resin during cure. The bleeder cloth is removed after the curing process and is not part of the final composite. Blister: Flaw either between layers of laminate or between the gel coat film and laminate. BMC: Bulk Molding Compound (Thermoset). Bobbin: The spool or shipping package on to which textile yarns are wound. Bond Strength: Amount of adhesion between bonded surfaces. The stress required to separate a layer of material from the base to which it is bonded, as measured by load/bond area. Boron Fiber: Fiber produced by vapor deposition of elemental boron, usually onto a tungsten filament core, to impart strength and stiffness. Braid/Braider: A narrow tubular or flat fabric produced by intertwining a single set of yarns according to a definite pattern. Breakup: See Dispersion. Breathing: Opening and closing of a mold to allow gas to escape early in the molding cycle. Also called “degassing”; sometimes called “bumping” in Phenolic molding. Bridging: Condition in which fibers do not move into or conform to radii and corner during molding, resulting in voids and dimensional control problems. Broad Strand: See Wides or Matchsticks. Broken Strand: See Broken End. Broken End: In the roving operation, a broken or severed strand (bundle) which causes the forming cake to stop running. Broken Fibers: See Fuzz. B-Stage: Intermediate stage in the reaction of certain thermosetting resins in which the material softens when heated and is plastic and fusible buy may not entirely dissolve or fuse. Also called “resistol” or “resitol.” The resin in an uncured prepreg or premix is usually in this stage. Buckling (Composite): Mode of failure generally characterized by an unstable lateral material deflection due to compressive action on the structural element involved. Buildup: Glass bundles or chopper fuzz which collect on the chopper, cot, static bars or machine frame. Bulk Molding Composite (BMC): Thermosetting resin mixed with short strand reinforcement, filler, and so on, into a viscous compound for compression or injection molding. Bundle: A discrete collection of many parallel glass filaments. A collection of individual filaments, a sub-strand. Bushing: Plate with holes through which molten glass is pulled to produce glass fibers. Bushing Tip: Small tapered protrusions on the bottom of bushings each containing an orifice through which molted glass flows, from which continuous filaments are drawn.

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C-

Cabled Yarn: Yarn that is plied more than once; yarn made by plying two or more previously plied yarns. Carbon: Element that provides the backbone for all organic polymers. Graphite is a more ordered form of carbon. Diamond is the densest crystalline form of carbon. Carbon-Carbon: Composite material consisting of carbon or graphite fibers in a carbon or graphite matrix. Carbon Fiber: Fiber produced by the pyrolysis of organic precursor fibers, such as rayon, polyacrylonitrile (PAN), and pitch, in an inert environment. Carding: The process of untangling and partially straightening fibers by passing them between two closely spaced surfaces which are moving at different speeds, and at least one of which is covered with sharp points, thus converting a tangled mass of fibers to a filmy web. Casting: Process of pouring a mixture of resin, fillers and/or fibers into a mold as opposed to building up layers through lamination. This technique produces different physical properties from laminating. Catalyst (Hardener): A substance which markedly speeds up the cure of a compound by decomposing in the presence of a promoter to release an active oxygen radical. Catalyst content can vary from 0.2% to 2.0% with higher catalyst levels giving faster gel times. Examples are methyl ethyl ketone peroxide, benzoyl peroxide. Catastrophic Failures: Totally unpredictable failures of a mechanical, thermal, or electrical nature. Catenary: A consolidated group of individual strands which, when checked between two fixed points of length, exhibit strands of different lengths. The resulting curve between fixed points of the inextensionable material is defined as catenary. The amount of catenary is measured by the distance between the topmost and lowermost strands when stretched between two fixed points. Caul Plates: Smooth metal plates, free of surface defects, the same size and shape as a composite lay-up, used immediately in contact with the lay-up during the curing process to transmit normal pressure and temperature, and to provide a smooth surface on the finished laminate. Cavity: Space inside a mold in which a resin or molding compound is poured or injected. The female portion of the mold. That portion of the mold that encloses the molded article (often referred to as the die). Depending on the number of such depressions, molds are designated as a single cavity or multiple cavity. Cell: The vertical plane of doffs on a pallet. A pallet may be constructed for 4- or 12-end run-out depending on application. C-Glass: Glass with a soda-lime-borosilicate composition that is used for its chemical stability in corrosive environments. Chalking: Surface phenomenon indicating degradation of a cosmetic surface. Chalking is a powdery film which appears lighter than the original color. Chemical Size: A surface finish applied to the fiber that contains some chemical constituents other than water. Choppability: The ease of chopping/cutting the glass fibers to a uniform length. Clamping Pressure: In injection molding and transfer molding, the pressure that is applied to the mold to keep it closed in opposition to the fluid pressure of the compressed molding material. Cloth: Fiberglass reinforcement made by weaving strands of glass fiber yarns. Clump: A group of chopped bundles of glass fibers which has collected on the SMC machine and then fallen into the bed of glass. The clump produces areas of high glass content which may not wet-through. Coefficient of Thermal Expansion (CTE): How much a material shape will change for each degree of temperature change. Cold Flow: The distortion that takes place in materials under continuous load at temperatures within the working rage of the material without a phase or chemical change. Collet: A spool on which the gathered strands from the bushing are wound for further processing. Compaction: The application of a temporary vacuum bag and vacuum to remove trapped air and compact the lay-up; also in SMC machines for removal of air prior to roll-up. Compatibility: The ability of two or more substances combined with one another to form a homogeneous composition of useful plastic properties; for example, the suitability of a sizing or finish for use with certain general resin types. Composite: Chemical or mechanical bonding of dissimilar materials such as glass fiber and polyester resin, whose cumulative properties are superior to the individual materials. Composite Material: A combination of two or more materials (reinforcing elements, fillers, and composite matrix binder). The constituents retain their identities; that is, they do not dissolve or merge completely into one another although they act in concert. Normally, the components can be physically identified and exhibit an interface between one another. Compounder: Manufacturer who mixes a polymer, fillers, additives and glass fibers, and sells the resulting pellets for injection molding. Compression Molding: A process where a mold is open when the material is introduced and shapes the material by the pressure of closing and by heat. Compressive Modulus: Ratio of compressive stress to compressive strain below the proportional limit. Theoretically equal to Young’s modulus determined from tensile experiments. Compressive Strength: This number describes how much of a nonmoving load a bar can take before it is crushed. Units are normally thousands of pounds per square inch. (103 psi) – Mega Pascals (mPa). Higher numbers indicate stronger materials which can withstand a heavier load before they break. Condensation Polymerization: A chemical reaction in which two or more molecules combine, with the separation of water or some other simple substance. Conductivity: Reciprocal of volume resistivity. The electrical or thermal conductance of a unit cube of any material (conductivity per unit volume). Conformability: Ability of the mat to conform to difficult shapes without causing wrinkles or leaving excessively resin-rich or glass-rich radii, which may craze. Contact Molding: Refers to the use of a single or open mold onto which layers of polymer and reinforcement materials can be applied. Contact molding is characterized by one finished cosmetic side. Cure is either at room temperature using a catalyst-promoter system or by heating in an oven, without additional pressure. Continuous Filaments: Filaments that extend substantially throughout the length of the yarn. Continuous Heat Resistance: This is the maximum temperature the material should be subjected to in a continuous application. Below this temperature the material is acceptable. Above this temperature the material may decompose, melt, or otherwise fail in an application. Units – degrees Fahrenheit (ï¿½F)- degrees Centigrade (ï¿½C). Higher numbers mean that the material can be used continuously at higher temperatures. Continuous Laminating: Process for forming panels and sheeting in which fabric or mat is passed through a resin bath, brought together between covering sheets, and passed through a heating zone for cure. Squeeze rolls control thickness and resin content as the various plies are brought together. Continuous Rovings: Rovings supplies in a package that allows for continuous processing. Continuous Strand: Fiberglass mat of very long individual fibers with a regular crossed pattern loosely held together with a binder. Copolymer: A resin produced by copolymerization, the process where unlike molecules are arranged in alternate sequence in a chain. Core: A low-density material used between two FRP skins. Examples of core materials are end-grain balsa wood, urethane foam, PVC foam and various honeycomb materials. The central member, usually foam or honeycomb, of a sandwich construction to which the faces of the sandwich are attached or bonded. The central member of a plywood assembly. A channel in a mold for circulation of heat transfer media. A device on which prepreg is wound. Coronizing: Continuous heat cleaning and weave setting. Corrosion Resistance: The ability of a material to withstand contact with ambient natural factors or those of a particular artificially created atmosphere, without degradation or change in properties. For metals, this could be pitting or rusting; for or organic materials, it could be crazing. Coupling Agent: Any chemical substance designed to react with both the reinforcement and matrix phases of a composite material to form or promote a stronger bond at the interface. Crazing: Cracking of gel coat or resin due to stress. Region of ultra-fine cracks, which may extend in a network on or under the surface of a resin or plastic material. May appear as a white band. Often found in a filament-wound pressure vessel or bottle. Creel: Glass Fiber Manufacturing – A framework used to hold forming cakes so they can be wound or roved into roving doffs. Creels generally hold 10 to 33 forming cakes which are replaced randomly as they run out as doffs are roved. Composite Fabrication – The area where the pallets of roving are placed and “threaded up” through metal tubes or guide eyes to a chopper. Creep: The slow movement of a plastic material with time. Creep, Rate of: Rate of the slope of the creep-time curve at a given time. Deflection with time under a given static load. Crosslinking: The setting up of chemical links between molecule chains. This occurs in all thermosetting resins. Styrene monomer is a crosslinking agent in polyester resins. C-Stage: The final stage in the reaction of certain thermosetting resins in which the material is practically insoluble and infusible. CTE: see Coefficient of Thermal Expansion. Cure: The crosslinking or total polymerization of the molecules of the resin which alters the properties of the material and changes it from a liquid into a solid. Cure Cycle: The time/temperature/pressure cycle used to cure a thermosetting resin system or prepreg Cure Time: The time required for the liquid resin to reach a cured or fully polymerized state after the catalyst has been added. Curing Agent: A catalytic or reactive agent that, when added to a resin, causes polymerization. Also called hardener. Cut Ends on Doff: Severed ends on the doff which generally are caused by abrasion during shipping or by careless use of a knife when the package is removed from the pallet.

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D-

Damping: The decay with time of the amplitude of free vibrations of a specimen. DAP: Diallyl Phthalate (Thermoset Resin). Daylight: The distance, in the open position, between the moving and fixed tables or the platens of a hydraulic press. In the case of a multi-platen press, daylight is the distance between adjacent platens. Daylight provides space for removal of the molded part from the mold. Deflashing: A finishing technique used to remove the excess, unwanted material (flashing) on a plastic molding. Delamination: Separation of composite layers, either local or covering a wide area. Can occur in the cure or subsequent life. Denier: A direct numbering system for expressing linear density, equal to the mass in grams per 9000m of yarn, filament, fiber, or other textile strand. Density: This is defined as the weight of a material per unit volume. Units – pounds per cubic inch (lb/cu in) grams/cubic centimeter. Higher numbers indicate heavier materials. Note: Density in lbs/cu in, and Specific Gravity are conveniently related by the following ratio:

Density (LB/cu in) Density (gr/cu cm) ——————– = 0.0361 ——————– = 0.9975 Specific Gravity Specific Gravity Density, Fiber: Mass per unit volume of the solid matter of which a fiber is composed, measured under specified conditions.

Dielectric: A nonconductor of electricity. The ability of a material to resist the flow of an electrical current. Dielectric Constant: The ratio of the capacitance of an assembly of two electrodes separated solely by a plastic insulating material to its capacitance when the electrodes are separated by air. Dielectric Heating: The heating of materials by dielectric loss in a high-frequency electrostatic field. Dielectric Strength: This is an electrical property and gives an indication of how well the material acts as an electrical insulator. It describes how much of an electrical voltage can be built up on one side of the material before it is communicated to the other side. Units – Volts per mil of thickness (volts/mil). Higher numbers indicate materials which are better insulators. C means that the material conducts electricity and therefore has no dielectric strength. Dimensional Stability: Ability of a plastic part to retain the precise shape to which it was molded, cast, or otherwise fabricated. Direct-Sized Yarn: Specially formulated sizings on textile yarns that allow them to be resin compatible. Dispersion: The degree to which the roving separates into discrete bundles after being chopped. Good dispersion is characterized by a bed of bundles which are uniform in width. Poor dispersion is characterized by a wide distribution in the widths of various bundles in the bed. Poor dispersion can cause poor wet-through and wet-out. Distortion: Change in shape from that which is intended. Symptomatic of laminating difficulties, curing problems, tooling problems or resin shrinkage. Doctor Blade or Bar: A straight piece of material used to spread resin, as in application of a thin film of resin for use in hot melt prepreg or for use as an adhesive film. Also called paste metering blade. Doff: See Roving Doff Doff Collapse: The failure of the roving doff to maintain its shape and stability during run-out or storage. Doff collapse generally occurs when there is only a 1/2″ to 1/4″ ring of roving left from the original doff. Draft: The taper or slope of the vertical surfaces of a which allow removal of molded parts. Dry Loft: Height of the bed of chopped fibers. Dwell: A pause in the application of pressure or temperature to a mold, made just before it is completely closed, to allow the escape of gas from the molding material.

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E-

E Glass: A family of calcia-alumina-silicate glasses which has a certified chemical composition and which is used for general purposes and most electrical applications. (ASTM D578-90.) Elasticity: That property of materials by virtue of which they tend to recover their original size and shape after removal of a force causing deformation. Elastic Limit: The greatest stress a material is capable of sustaining without permanent strain remaining after the complete release of the stress. A material is said to have passed its elastic limit when the load is sufficient to initiate plastic, or non-recoverable, deformation. Elastomer: A material that substantially recovers its original shape and size at room temperature after removal of a deforming force. Elongation: As mentioned under tensile modulus, when a bar is pulled it gets longer. The elongation tells how much longer it gets before it breaks. Encapsulating: Completely surrounding an object with resin or a fiber resin composite. Sometimes used specifically in reference to the enclosure of capacitors or circuit board modules. End: A single bundle of filaments. End count: An exact number of ends supplied on a ball of roving. Environment: The aggregate of all conditions (such as contamination, temperature, humidity, radiation, magnetic and electric fields, shock, and vibration) that externally influence the performance of an item. Epoxy: A polymerizable thermoset polymer containing one or more epoxide groups and curable by reaction with amines, alcohols, phenols, carboxylic acids, acid anhydrides, and mercaptans. An important matrix resin in composites and structural adhesive. Epoxies generally have higher physical properties than polyester resins. They are also more costly and difficult to process, and less able to withstand sunlight. Even Tension: The process whereby each end of roving is kept in the same degree of tension as the other ends making up the ball of roving. Exothermic Heat: Heat given off during a polymerization reaction by the chemical ingredients as they react and the resin cures. Extend: To add fillers or low-cost materials in an economy producing endeavor. To add inert materials to improve void-filling characteristics and reduce crazing. Extenders: Low-cost materials used to dilute or extend high-cost resins without extensive lessening of properties. Extruder: Machine that pushes molten plastic through small holes to form fibers.

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F-

Fabrication: The portion of the glass fiber production process where the forming cakes are put into creels and “roved” or fabricated onto doffs. Fabricator: Manufacturer of reinforced plastic products. Fall: The shape of the pattern of chopped fibers as they drop from the chopper to the bed. Fan or Curtain: The chopped bundles which fall or are thrown off the chopper and cot. Fatigue: The failure or decay of mechanical properties after repeated applications of stress. Fatigue tests give information on the ability of a material to resist the development of cracks, which eventually bring about failure as a result of a large number of cycles. Fatigue Life: The number of cycles of deformation required to bring about failures of the test specimen under a given set of oscillating conditions (stresses and strains). Fatigue Limit: The stress level below which a material can be stress cyclically for an infinite number of times without failure. Fatigue Strength: The maximum cyclical stress a material can withstand for a given number of cycles before failure occurs. The residual strength after being subjected to fatigue. Fiber: Reinforcement material which is a major component in a composite matrix. Often, fiber is used synonymously with filament. Fiber Content: The amount of fiber present in a composite. This is usually expressed as a percentage volume fraction or weight fraction of the composite. Fiber Diameter Letter Designation: Fibers are generally classified in hundred thousandths, i.e. a “K” fiber has a mean average diameter of 50+ to 55 height.

Letter Designation

Range of Fiber Diameter Up to and Including

A

.00006 in. (1.50 mi.)

.00010 in. (2.50 mi.)

B

.00010 in. (2.515 mi.)

.00015 in. (3.81 mi.)

C

.00015 in. (3.81 mi.)

.00020 in. (5.08 mi.)

D

.00020 in. (5.08 mi.)

.00025 in. (6.35 mi.)

E

.00025 in. (6.35 mi.)

.00030 in. (7.62 mi.)

F

.00030 in. (7.62 mi.)

.00035 in. (8.89 mi.)

G

.00035 in. (8.89 mi.)

.00040 in. (10.12 mi.)

H

.00040 in. (10.12 mi.)

.00045 in. (11.43 mi.)

J

.00045 in. (11.43 mi.)

.00050 in. (12.70 mi.)

K

.00050 in. (12.70 mi.)

.00055 in. (13.97 mi.)

L

.00055 in. (13.91 mi.)

.00060 in. (15.24 mi.)

M

.00060 in. (15.24 mi.)

.00065 in. (16.51 mi.)

N

.00065 in. (16.51 mi.)

.00070 in. (17.78 mi.)

P

.00070 in. (17.78 mi.)

.00075 in. (19.05 mi.)

Q

.00075 in. (19.05 mi.)

.00080 in. (20.32 mi.)

R

.00080 in. (20.32 mi.)

.00085 in. (21.59 mi.)

S

.00085 in. (21.59 mi.)

.00090 in. (22.86 mi.)

T

.00090 in. (22.86 mi.)

.00095 in. (24.13 mi.)

U

.00095 in. (24.13 mi.)

.00100 in. (25.40 mi.)

NOTE: The letters I and O are not used in this sequence.

Fiber Direction: The orientation or alignment of the longitudinal axis of the fiber with respect to a stated reference axis. Fiber glass: Primarily means glass in fiber form. However, “fiber glass” is also used to describe composite processing and applications. Examples of usage: fiber glass molding plant, fiber glass car. Fiberglass Reinforcement: Major material used to reinforce plastic. Available as mat, roving, fabric, and so forth, it is incorporated into both thermosets and thermoplastics. Fiber Pattern: Visible fibers on the surface laminates or molding. The thread size and weave of glass cloth. Fiber Reinforced Plastic (FRP): A general term for a composite that is reinforced with cloth, mat, strands, or any other fiber form. Filament: A single, threadlike fiber of glass. Filament Winding: Process, which involves winding a resin-saturated strand of glass filament around a rotating mandrel. Filament Yarn: A yarn composed of continuous filaments assembled with or without twist. Fill: The system of yarns running crosswise in a fabric (short for filling). Also known as weft. See Warp. Filler: An inexpensive substance which is added to plastic resins to extend volume, improve properties, and lower cost. Fines: Bundles that have been split apart into smaller bundles which are composed of only a few or single filaments. Fuzz is usually made of fines. Finish: See Size. Fire Retardants: Certain chemicals that are used to reduce the tendency of a resin to burn. Fish Eye: Effect of surface contamination, which causes a circular separation of a paint or gel coat. Flammability: This property describes how fast a plastic material will burn when subjected to a particular ASTM test. In this test, a flame is applied to one end of a strip of material. When the material starts burning the flame is removed and the time to consume a given amount of material is measured. Units – inches per minute (in/min.). Higher numbers indicate that the material will burn faster under conditions of this particular test. S.E. means self extinguishing. If a material is classified as S.E., the specimen stops burning when the flame is taken away. Flash: That portion of the charge, which flows from or is extruded from the mold cavity during the molding. Extra plastic attached to a molding along the parting line, which must be removed before the part is considered finished. Flash Point: Lowest temperature at which a substance gives off enough vapors to form a flammable mixture. Flexible Molds: Molds made of rubber or elastomeric plastics, used for casting plastics. They can be stretched to remove cured pieces with undercuts. Flexural Modulus: This is a number associated with the stiffness of materials. It is used to calculate how far a bar will bend when a bending load is applied to it. Units are normally millions of pounds per square inch. (106 psi) – Giga Pascals (gPa). Higher numbers for materials mean that they are more resistant to deflection when equal thickness are being compared. Flexural Strength: This is also known as bending strength. It describes how much of a nonmoving load can be applied before a bar yields or breaks. Units are normally thousands of pounds per square inch. (103 psi) – Mega Pascals (mPa). Higher numbers mean that material is stronger and can withstand a heavier load. Flow: The movement of resin under pressure, allowing it to fill all parts of a mold. The gradual but continuous distortion of a material under continued load, usually at high temperatures; also called creep. Flow Line: A mark on a molded piece made by the meeting of two flow fronts during molding. Also called striae, weld mark, or weld line. Flow Marks: Wavy surface appearance of an object molded from thermoplastic resins, cased by improper flow of the resin into the mold. Fly: Fibers which fly out into the atmosphere during handling and processing. Foam: Lightweight, cellular plastic material containing glass-filled voids. Typical foams include urethane, PVC, and polyester. Force: The male half of the mold that enters the cavity, exerting pressure on the resin and causing it to flow. Also called punch. Forming: The portion of the glass fiber production process where the fibers are drawn, attenuated from molten glass, and collected in forming cakes. Forming Cakes or “Cakes”: The package of glass fibers which is produced in forming. This package is generally on a tube and is placed on a forming carrier and sent through a drying/curing oven. These “cakes” are subsequently put into a roving creel and collected together into a roving doff. Fracture: The separation of a body. Defined both as rupture of the surface without complete separation of laminate and as complete separation of a body because of external or internal forces. Fracture Stress: The true, normal stress on the minimum cross-sectional area at the beginning of fracture. Fracture Toughness: A measure of the damage tolerance of a material containing initial flaws or cracks. Used in aircraft structural design and analysis. FRP: Acronym for fiber glass-reinforced or fiber-reinforced plastic, polymer or polyester. Fuzz: Creel Fuzz – In glass fiber manufacturing, the broken filaments found around and on a roving creel. Chopper Fuzz – In Composite Fabrication, the broken filaments found around the glass cutter or chopper. See Fines. In the field, the broken filaments found around a roving pallet. Fuzz Plug: Small, broken, compacted filaments of glass which collect inside the guide eye tubes which feed the chopper and cause the glass to stop running through it.

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G-

Gate: Where the molten thermoplastic enters the cavity in the injection molding tool. Gel: A partial cure of plastic resins; a semisolid, jelly-like state similar to gelatin in consistency. Gel: The initial jelly-like solid phase that develops during the formation of a resin from a liquid. A semisolid system consisting of a network of solid aggregates in which liquid is held. Gelation: The point in a resin cure when the resin viscosity has increased to a point such that it barely moves when probed with a sharp instrument. Gel Coat: Surface coat of a specialized, quick-setting polyester resin, either colored or clear, providing a cosmetic enhancement and weather ability to a fiberglass laminate. The gel coat becomes an integral part of the finished laminate. Gel Point: The stage at which a liquid begins to exhibit pseudo-elastic properties. This stage may be conveniently observed from the inflection point on a viscosity time plot. Gel Time: Time required to change a flowable liquid resin into a non-flowing gel. GFRP: Glass fiber-reinforced plastic, polymer or polyester. Glass Blends: When several different fiber types, i.e. different lengths and diameters, are blended in the fiber slurry. Glass Content: Percentage of glass in the compound. Glass Fiber Wet-Process: Process of forming a glass mat on modified papermaking equipment. Glass Transition: Reversible change in the amorphous polymer or in amorphous regions of a partially crystalline polymer from, or to, a viscous or rubbery condition to, or from, a hard and relatively brittle one. Glass Transition Temperature (Tg): The appropriate midpoint of the temperature range over which glass transition takes place. Good Side: Side of a molding in contact with a mold surface. Graphite Fiber: A fiber made from a precursor by oxidation, carbonization, and graphitization process (which provides a graphitic structure). Green: Resin, which has not completely cured and is still rather soft and rubbery. Green Strength: That ability of the material, while not completely cured, to undergo removal from the mold and handling without tearing or permanent distortion. GRP: Glass-reinforced plastic, polymer or polyester. This derivation is commonly used in Europe.

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H-

Hand: The softness of a piece of fabric, as determined by the touch (individual judgment). Hand Lay-up: The process of placing (and working) successive plies of reinforcing material or resin-impregnated reinforcement in position on a mold by hand. Method of molding room temperature curing thermosetting polymers, mainly epoxies and polyesters, in association with glass, mineral, or fiber reinforcements. Catalyzed resin mixtures are sprayed, brushed, or spatulated on a mold. A precut reinforcing layer is laid on the wet resin. After the resin soaks into the reinforcement, subsequent layers are built up to the required thickness and are cured, removed from the mold and trimmed. Some variations of hand lay-up techniques are bag molding, drape molding, vacuum molding and spray-up molding. Typical parts are custom auto bodies and boat hulls. Hardener: A substance or mixture added to a plastic composition to promote or control the curing action by taking part in it. Hard Glass: A roving product that is not very soluble in acetone or styrene which results in the tendency of the individual bundles to retain their integrity (hardness) and not filamentize in the matrix resin. Hard glass is often stiff and brashy. The size is generally less than 40% soluble in acetone. See Soft Glass. Hardness: The resistance to surface indentation usually measured by the depth of penetration (or arbitrary units related to the depth of penetration) of a blunt point under a given load using a particular instrument according to a prescribed procedure. Heat Cleaning: Batch and continuous processes in which organic yarn binder is removed from glass fabrics. Heat Distortion Point: Temperature at which the strength of a material begins to degrade. Now called deflection temperature. Heat Resistance: The property or ability of plastics and elastomers to resist the deteriorating effect of elevated temperatures. Heat Sink: A contrivance for the absorption or transfer of heat away from a critical element or part. Bulk graphite is often used as a heat sink. Heat Distortion Temperature: This is a measurement of the temperature which will cause the material to bend under a give load. It was developed for thermoplastic materials which soften considerably when heated. It has relatively little value as a design figure for thermosetting reinforced plastics. During this test a load is applied in bending to cause 264 psi stress in the material. The temperature of the material is then raised until the material bends one tenth of an inch at the center. Units – degrees Fahrenheit (ï¿½F)- degrees Centigrade (ï¿½C). Higher numbers mean that the material can be heated to a higher temperature before it deflects one tenth of an inch under this arbitrary load of 264 psi. Helical Winding: In filament wound items, a winding in which a filament band advances along a helical path, not necessarily at a constant angle except in the case of a cylinder. Het-Acid Resin: Polyester resin with exceptional fire qualities. High-Pressure Laminates: Laminates molded and cured at pressures not lower than 6.9 MP (1.0 ksi), and more commonly in the range of 8.3 to 13.9 Mpa (1.2 to 2.0 ksi). Homogeneous: Descriptive term for a material of uniform composition throughout. Homopolymer: A compound produced by polymerization. Honeycomb: Manufactured product of resin-impregnated sheet material (paper, glass, fabric, and so on) or metal foil, formed into hexagonal-shaped cells. Used as a core material in sandwich construction. Hoop Stress: The circumferential stress in a material of cylindrical form subjected to internal or external pressure. Hybrid: A composite laminate consisting of laminate of two or more composite material systems. A combination of two or more different fibers, such as carbon and glass or carbon and arimid, into a structure. Hydraulic Press: A press in which the molding force is created by the pressure exerted by a fluid. Hygroscopic: Material that absorbs moisture from the air. Hysteresis: The energy absorbed in a complete cycle of loading and unloading. This energy in converted from mechanical to friction energy (heat).

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I-

Ignition Loss: The difference in weight before and after burning. As with glass, the burning off of the binder or size. Impact Strength-IZOD: A moving load is one that is moving when it strikes a bar. The effect of such a load which is denoted by the work “impact”. The impact strength of a material is a measure of how much energy is absorbed by the bar when it is broken by a moving weight. There are many different test methods for measuring impact. Izod is but one of these methods. Units – foot pounds per inch of width. This is sometimes given as foot pounds per inch of notch. Joules/Meter (J/M). Higher numbers mean that the material will absorb more energy before it is broken by a moving weight. Impact Test: Measure of the energy necessary to fracture a standard sample by an impulse load. Impregnate: In reinforced plastics, to saturate a reinforcement, especially fiberglass, with a resin. Inhibitor: A substance that retards polymerization, thus extending shelf life of a monomer. Also used to influence gel time and exotherm. Initiator: Peroxides used as sources of free radicals. They are used in free-radical polymerization, for curing thermosetting resins, as cross-linking agents for elastomers and polyethylene, and for polymer modification. Injection Molding: Method of forming a plastic to the desired shape by forcing the heat-softened thermoplastic polymer into a relatively cool cavity under pressure or thermosetting polymer into a heated mold. Inorganic Pigments: Natural or synthetic metallic oxides, sulfides, and other salts that impart heat and light stability, weathering resistance, color, or migration resistance to plastics. Insert: An integral part of plastic molding consisting of metal or other material that may be molded into the part or pressed into position after the molding is completed. In-Situ: In place. In the position which it will finally occupy, e.g. molding or forming foam. Interface: A surface that lies between two different materials. Interlaminar: Descriptive term pertaining to an object (for example, voids), event (for example, fracture), or potential field (for example, shear stress) referenced as existing or occurring between two or more adjacent laminae. Interlaminar Shear: Shearing force tending to produce a relative displacement between two laminae in a laminate along the plane of the interface. Intumescent: Fire-retardant technology which causes an otherwise flammable material to foam, forming an insulating barrier when exposed to heat. Irreversible: Not capable of re-dissolving or re-melting. Chemical reactions that proceed in a single direction and are not capable of reversal (as applied to thermosetting resins). Isocyanate Plastics: Plastics based on resins made by the reaction or organic isocyanates with other compounds. Isophthalic: Polyester resin based on isophthalic acid, generally higher in properties than a general purpose or orthothatic polyester resin. Isotropic: Having uniform properties in all directions. Izod Impact Test: A test for shock loading in which a notched specimen bar is held at one end and broken by striking, and the energy absorbed is measured.

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J-

Jackstrawing: Visual effect of glass fiber turning white in a cured laminate. It may not effect the strength of a laminate, but could indicate air entrapment or water contamination.

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K-

Kevlar: An organic polymer composed of aromatic polyamides having a para-type orientation (parallel chain extending bonds from each aromatic nucleus). Knitted Fabric: A textile structure produced by interlooping one or more ends of yarn or comparable material. Knot: The means of joining the strands of two doffs of roving. The knot is generally a reduced triple loop surgeon’s knot, square knot or overhand knot.

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L-

Laminat: Composite material system made with layers of fiber reinforcement in a resin. Sometimes used as a general reference for composites, regardless of how made. Laminate: Primarily means a composite material system made with layers of fiber reinforcement in a resin. Sometimes used as a general reference for composites, regardless of how made. Examples of usage: laminate consumption by market, compression-molded laminate. Laydown: A characteristic of the bed of chopped glass fibers which relates to the degree of uniformity in thickness that the bed exhibits across the width of the chopped pattern. Layer: The horizontal plane of doffs on a pallet. A pallet usually has four layers of twelve doffs each. (Also see Cell). Lay-up: Act of building up successive layers of polymer and reinforcement. Layers of catalyzed resin and fiberglass or other reinforcements are applied to a mold in order to make a part. The reinforcing material placed in position in the mold. The process of placing the reinforcing material in position in the mold. The resin-impregnated reinforcement. Liquid-Crystal Polymer: A newer thermoplastic polymer that is melt process able and develops high orientation in molding, with resultant tensile strength and high-temperature capability. Load-Deflection Curve: A curve in which the increasing tension, compression, of flexural load are plotted on the ordinate axis and the deflections caused by those loads are plotted on an abscissa axis. Loom: A mechanical device that interlaces fibers at right angles with varying degrees of weave construction (weight, thickness and design). More modern looms are air jet but rapier and more traditional shuttle equipment is still in use. Loom Beam: A large, flanged cylinder onto which all warp yarns are wound and from which yarns enter the loom. Loop: Small open place in the strands due to the excessive length of one or more strands. Loss on Ignition: Weight loss, usually expressed as percent of total, after burning off an organic sizing from glass fibers, or an organic resin from a glass fiber laminate. Low-pressure Laminates: Laminated, molded, and cured using pressures from 400 psi down to and including the pressure obtained by mere contact of the plies. Lubricant: A material added to most sizing to improve the handling and processing properties of textile strands.

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M-

Mandrel: The core tool around which resin-impregnated paper, fabric, or fiber is wound to form pipes, tubes, or structural shell shapes. Manipulator: Highly efficient system which eliminates the need for a press screw driven frame structure that opens and closes the mold in a controlled line of draw to prevent tool damage. See Megaject Pro. Mat: A fibrous material for reinforced plastic consisting of randomly oriented chopped filaments, short fibers (with or without a carrier fabric), or swirled filaments loosely held together with a binder. Matched Metal Molding: A reinforced plastics manufacturing process in which matching male and female metal molds are used (also called compression molding) to form the part, with time, pressure, and heat. Matrix: The resin component of a polymer composite. Both thermoplastic and thermoset resins may be used, as well as metals, ceramics, and glasses. The plural is matrices. Mat Strength: Ability of the mat to resist being pulled apart under tension during impregnation and molding. Matchsticks: Strand-to-strand adhesion. A matchstick is a wide bundle that has 3 to 4 times as many filaments in it as do the majority of the bundles in the bed. Matrix: Term used to describe the resin component of a polymer composite. An example of usage would be: “The glass fibers are reinforcing a polyester matrix.” The plural is matrices. Mechanical Properties: The properties of a material, such as compressive and tensile strengths, and modulus, that are associated with elastic and inelastic reaction when force is applied. The individual relationship between stress and strain. Melamine: Thermoset resin. Metallic Fiber: Manufactured fiber composed of metal, plastic-coated metal, metal-coated plastic, or core completely covered by metal. Microballoons: Microscopic bubbles of glass, ceramic or Phenolic, used as a filler or to create syntactic foam or putty mixtures. Microcracking: Crack formed in composites when thermal stresses locally exceed the strength of the matrix. Mil: The unit used in measuring the diameter of glass fiber strands ( 1 mil = 0.001 in.). Milled Fiber: Continuous glass strands hammer milled into very short glass fibers. Useful as inexpensive filler or anti-crazing reinforcing filler for adhesives. M.I.Tâ„¢: See Multiple Insert Tooling. MPG: See Mold Protection Guard. Modulus, Initial: The slope of the initial straight portion of a stress strain or load-elongation curve. Modulus of Elasticity: Describes a material’s ability to bend without losing its ability to return to its original physical properties. Moisture: The amount of volatiles on the glass expressed as a percentage of the total weight. Moisture Content: The amount of moisture in a material determined under prescribed conditions, and expressed as a percentage of the mass of the moist specimen, that is, the mass of the dry substance plus the moisture present. Mold: The cavity or matrix into or on which the plastic composition is placed and from which it takes form. The tool used to fabricate the desired part shape. Molded Edge: An edge that is not physically altered after molding for use in final form, and particularly on that does not have fiber ends along its length. Molding: The forming of a polymer or composite into a solid mass of prescribed shape and size. Molding Cycle: The period of time required for the complete sequence of operations on a molding press to produce one set of moldings. Molding Pressure: The pressure applied to the ram of an injection machine or compression or transfer press to force the softened plastic to fill the mold cavities completely. Mold Protection Guard: Mold protection guard. Prevents the over pressurization of the RTM mold during the injection process. See MPG. Mold-Release Agent: A lubricant, liquid, or powder (often silicone oils and waxes), used to prevent sticking of molded articles in the cavity. Multiple Insert Tooling: Low risk, high output composite tooling breakthrough. MIT tooling technology offers the composite molder quick-change multiple mold surfaces without multiple tooling costs. As each surface is an exact clone of its counterpart the replication of mold cavity accuracy, and therefore molded part, is guaranteed. See What is M.I.T?

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N-

Non-Air-Inhibited Resin: Resin in which the surface cure will not be inhibited or stopped by the presence of air. Non-Woven Fabric: A textile structure produced by bonding or interlocking of fibers, or both, accomplished by mechanical, chemical, thermal, or solvent means and combinations thereof.

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O-

Orange Peel: Gel coated or painted finish, which is not smooth and is patterned similar to an orange’s skin. Organic: Matter originating in plant or animal life or composed of chemicals of hydrocarbon origin, either natural or synthetic. Orientation: Position with relation to flow of polymer in mold. Orthophthalic Resin: Polyester resin based on Orthophthalic acid, also known as a general purpose resin (GP). Overlay Sheet: A non-woven fibrous mat (of glass, synthetic fiber, and so forth) used as the top layer in a cloth or mat lay-up, to provide a smoother finish, minimize the appearance of the fibrous pattern, or permit machining or grinding to a precise dimension. Also called surfacing mat. Overspray: A specially formulated binder applied to texturized yarn that helps retain the bulk of the yarn after texturizing.

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P-

PBT: Polybuthlene Therephthalate (Thermoplastic Polyester Resin). PET: Polyethylene Terephthalate (Thermoplastic Polyester Resin). Phenolic Resin: Thermosetting resin produced by the condensation of an aromatic alcohol with an aldehyde, particularly of phenol with formaldehyde. Used in high-temperature applications with various fillers and reinforcements. Pigment: A colorant added to gel coat or resin. Pinholes: Small holes on the exposed gel coated surface. They are about the diameter of common pins and may be easily counted. Plastic: Material that contains as an essential ingredient an organic polymer of large molecular weight, hardeners, fillers, reinforcements, and so forth; is solid in its finished state, and, at some stage in its manufacture or its processing into finished articles, can be shaped by flow. Made of plastic. A plastic may be either thermoplastic or thermoset. Plasticizers: Material incorporated in a plastic to increase its workability and flexibility. Normally used in thermoplastics. A lower molecular weight material added to an epoxy to reduce stiffness and brittleness, thereby resulting in a lower glass transition temperature for the polymer. Plied Yarn: A yarn formed by twisting together two or more single yarns in one operation. (Synonyms: folded yarn, formed yarn.) Plug: A composite industry name for a pattern or model. Ply: The number of single yarns twisted together to form a plied yarn; also the number of plied yarns twisted together to form a cord. The individual yarn in a plied yarn or in a cord. One of several layers of fabric. Poisson’s Ratio: The ratio of transverse strain to axial strain during axial load. Polyester Combination Yarn: A polyester/fiber glass hybrid yarn. Polyester (Unsaturated): Product of an acid-glycol reaction commonly blended with a monomer to create a polymer resin. In its thermosetting form it is the most common resin used in the FRP industry. Polymer: Chain molecule composed of many identical groups, commonly found in plastics. Polymerization: Chemical bonding of polymer molecules during the curing reaction. Porosity: Entrapped gas bubbles or voids in a gel coat film. Post Bake: See Post Cure. Post Cure: A heat cycle a roving doff goes through after fabrication. This is generally used to help “set” the ribbon on the outside of the doff to improve the doff’s stability and resistance to package collapse. PPO: Polyphenylene Oxide (Thermoplastic Resin). PPS: Polyphenylene Sulfide (Thermoplastic Resin). Prepreg: Either ready-to-mold material in sheet form or ready-to-wind material in roving form, which may be cloth, mat, unidirectional fiber, or paper impregnated with resin and stored for use. The resin is partially cured to a B-stage and supplied to the fabricator, who lays up the finished shape and completes the cure with heat and pressure. The two distinct types of prepreg available are (1) commercial prepregs, where the roving is coated with a hot melt or solvent system to produce a specific product to meet specific customer requirements, and, (2) wet prepreg, where the basic resin is installed without solvents or preservatives but has limited room-temperature shelf life. Pressure Bag: A membrane which conforms to the inside of a laminate laid up on a mold. The membrane or bag is then inflated applying pressure which consolidates and densifies the laminate. Print Through: Distortion in the surface of a part which allows the pattern of the core or fiberglass reinforcement to be visible through the surface. Also known as print out, telegraphing or read through. Pultrusion: Continuous process for manufacturing composites that have a constant cross-sectional shape. The process consists of pulling a fiber-reinforcing material through a resin impregnation bath and through a shaping die, where the resin is subsequently cured. Putty: Thickened mixture of resin made by adding fillers and reinforcing fibers.

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Reaction Injection Molding (RIM): Process for molding polyurethane, epoxy, and other liquid chemical systems. Mixing of two to four components in the proper chemical ratio is accomplished by a high-pressure impingement-type mixing head, from which the mixed material is delivered into the mold at low pressure, where it reacts (cures).

Re-Chop: Bundles which have clung to the chopper or cot which are chopped again into shorter lengths. Re-chop causes excessive chopper fuzz as the strands are cut and mashed into smaller bundles.

Reinforced Molding Compound: Compound consisting of a polymer and a reinforcement fiber or filler supplied by raw material producer in the form of ready-to-use materials. Reinforced Plastics: Molded, formed, filament-wound, tape-wrapped, or shaped plastic parts consisting of resins to which reinforcing fibers, mats, fabrics, and so forth, have been added before the forming operation to provide some strength properties greatly superior to those of the base resin. Reinforced Reaction Injection Molding (RRIM): A reaction injection molding with a reinforcement added. See Reaction Injection Molding. Reinforcement: Strong material bonded into a matrix to improve its mechanical properties. Reinforcements are usually long fibers, chopped fibers, whiskers, particulates, and so forth. The term should not be used synonymously with filler. Release Agent: Compound used to reduce surface tension or adhesion between a mold and a part. Resin: Solid or pseudosolid organic material, usually of high molecular weight, that exhibits a tendency to flow when subjected to stress. Most resins are polymers. In reinforced plastics, the material used to bind together the reinforcement material. See Matrix and Polymer. Resin-Rich Area: Localized area filled with resin and lacking reinforcing material. Resin-Starved Area: Localized area of insufficient resin, usually identified by low gloss, dry spots, or fiber showing on the surface. Resin Tearing: Separation of pigments in a gel coat affecting cosmetic appearance. Resin Transfer Molding (RTM): A process whereby catalyzed resin is transferred or injected into an enclosed mold in which the fiberglass reinforcement has been placed. See RTM within the site. Ribbon: The propensity of the glass bundles to “stick” together and act as a strand or end. RIM: see Reaction Injection Molding. Roving Doff or “Doff”: The final product sold to the customer. It was made by roving or pulling together a group of forming cakes (the number of which depends upon the product being made). Roving: A collection of untwisted strands wound together into a doff (ball). Also another name for the fabrication process step. RP: Reinforced plastic, polymer or polyester. RRIM: See Reinforced Reaction Injection Molding. RTM: See Resin Transfer Molding. See also RTM within the site. RTM Light: See Vacuum Molding. See also VM within the site. RTP: Sometimes used to distinguish reinforced thermoplastic from reinforced thermosetting plastic. Rule-of-Mixtures: When combined, the properties of the composite material is some combination of the properties of the two constituent materials. The composite property equals the amount of the fiber property multiplied by the volume percentage of fiber, plus the amount of matrix property multiplied by the volume percentage of matrix. Run-Out: The process of pulling the glass from the doff to the chopper. Runner: The channel through which thermoplastic material moves through a mold.

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SAN: Styrene Acrylonitrile (Thermoplastic Resin). Sandwich Constructions: Panels composed of a lightweight core material, such as honeycomb or foamed plastic, to which two relatively thin, dense, high-strength or high-stiffness faces or skins are adhered. S Glass: A family of magnesium-alumina-silicate glasses with a certified chemical composition which conforms to an applicable material specification and which produces high mechanical strength. Scrim: A light, woven or non-woven fabric with relatively large openings between the yarns, used as reinforcement for paper and other products. Secton Beam: A flanged cylinder onto which yarn is drawn and accumulated from yarn bobbins or packages. Serving: Wrapping of yarn around a product in one or more layers, to form a protective covering. Sewing Thread: A flexible, small diameter yarn or strand, usually treated with a surface coating, lubricant, or both, intended to be used to stitch one or more pieces of material or an object to a material. Shear: Engineering term referring to forces applied normal to the surface of a given material. The movement between plies of a laminate is referred to as interlaminate shear. Sheet Molding Compound (SMC): Composite of fibers, usually a polyester resin, and pigments, fillers, and other additives that have been compounded and processed into sheet form to facilitate handling in the molding operation. Shelf Life: Allowable storage time before a product must be used. Single Yarn: The simplest strand of textile material suitable for operations such as weaving, knitting, etc. Size: The treatment applied to the glass fiber to allow the resin and glass to adhere to one another. Also allows glass fiber to be conveniently handled. Skein: A loose coil of roving or strands which is generally used as a Quality Control sample. Skin Coat: First layer of laminate next to the gel coat. Slashing: The method of applying size to a width of warp yarns on a continuous basis. Slink: Glass bundles which are thrown off the chopper or cot during the chopping operation. Sliver: A term used to describe the geometry of a fibrous glass reinforcement in the forming operation, e.g., 2K37 S/2 meaning a configuration in forming which makes a nominal fiber diameter in the “K” range which is 3700 yards to a pound and is split into two discrete bundles in the forming cake. Sluffing: See Doff Collapse. SMC: See Sheet Molding Compound. Snarl: See Birdnest. Soft Glass: A roving product whose sizing is moderately soluble in acetone or styrene which results in the tendency of the bundles to open readily or filamentize the matrix resin. The size is generally between 50% and 80% soluble in acetone. Solid: The amount of sizing on the glass expressed as a percentage of the total weight. Specific Gravity: This describes the weight of a material in relation to the weight of an equal volume of water. For example, a material with a Specific Gravity of 2.0 weighs twice as much as an equal volume of water. Units – Because specific gravity is a ratio of values for two materials, there are no units. Higher numbers indicate heavier materials. Specific Heat: (Thermal Capacity) – This defines how much heat is needed to raise the temperature of one pound of material one degree Fahrenheit. Units – BTUs per pound per degree Fahrenheit (BTA/LB/ï¿½F) – Joules/Kilogram Kelvin (J/KgK). Higher numbers means that it takes more input heat energy to raise the temperature of a material. Splice: The joining of two ends of yarn by intertwining, knotting, overlapping or adhering them together. Split: One bundle. Spray-Up: Technique in which a spray gun is used as an applicator tool. In reinforced plastics, for example, fibrous glass and resin can be simultaneously deposited in a mold. Sprue: Connector between the runner and the nozzle in the injection molding machine. Splitting Efficiency: A ratio of the actual number of ends divided by the theoretical number of ends in a roving doff. Expressed as a percentage. Staple: Filaments produced in short lengths from the bushing (usually less than 17 inches), to be gathered into strands or sliver. SeeContinuous Filament. Static: The buildup of an electrical charge which causes the chopper roving to “cling” or stick to the chopper, line and/or people. The static level is quantified by measuring the electrical field strength in kilovolts per inch. Sticker: See Trapped End. Strand: In the roving process or shop – a primary group of bundles gathered together in a creel. A strand is that which is pulled out of a doff. A plurality of drawn and elongated individual filaments combined together to form an individual strand. Strands are held together and protected by the sizing. Strand Count: U.S. Yardage System: the length, in hundreds of yards, of a single strand having a mass of one pound. European TEX System: the mass, in grams, of a strand 1000 meters in length. Strand Integrity: Relating to the ability of the size to keep all the filaments of a bundle stuck together during chopping. Good strand integrity is required for good flow in or wet-through and wet-out on the mold. Structural Reaction Injection Molding (S-RIM): Evolution of two other plastic molding processes-RIM and RTM. S-RIM uses the fast polymerization reactions of RIM-type polymers, its intensive resin mixing procedures, and its rapid resin injection rates. S-RIM also employs preforms like RTM to obtain composite mechanical properties. Styrene Monomer: A water-thin liquid monomer used to thin polyester resins and act as the crosslinking agent. Surfacing Mat: Very thin mat, usually 180 to 510 mm (7 to 20 mil) thick, used primarily to produce a smooth, resin-rich surface on a reinforced plastic laminate, or for precise machining or grinding. See Veil. Surfactant: Chemicals used to modify or change the surface of a layer of resin or polymer. Usually used to form a film on a curing resin, producing a tack-free surface.

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Tack: Surface stickiness. Tack Free: Surface, which is not sticky after cure. Tangent Modulus: Slope of the line at a predefined point on a static stress-strain curve, expressed in force per unit area per unit strain. This is the tangent modulus at that point in shear, tension, or compression, as the case may be. Tape: A narrow fabric with a mass per unit area of less than 0.5 kg/m 2 (0.1 LB/ft2) for each 25.4 mm (1 in.) of width and which is used primarily for utilitarian purposes. Tensile Elongation: Engineering term referring to the amount of stretch a sample experiences during tensile strain. Tensile Load: Load applied away from and to opposite ends of a given sample. Tensile Modulus: When a bar is pulled in tension, it has to get longer. The tensile modulus is used to calculate how much longer it will get when a certain load is applied to it. Units are normally millions of pounds per square inch. (10 6 psi) – Giga Pascals (gPa). Higher numbers indicate materials which will not elongate as much as others when they are being compared under equal tensile loading conditions. Tensile Strength: This number describes how large a nonmoving load a bar can withstand before it breaks due to elongation. Units are normally thousands of pounds per square inch. (103 psi) – Mega Pascals (mPa). Higher numbers indicate materials which can withstand a stronger pull before breaking. Tensile Stress: Normal stress caused by forces directed away from the plane on which they act. Tension Device: A mechanical or magnetic device that controls tension. TEX: A unit for expressing linear density, equal to the mass in grams of 1 km of yarn, filament, fiber or other textile strand. Texturized Glass Yarn: A yarn processed from continuous filament yarn in such a manner to induce bulk to the yarn by disorientation of the filaments. Thermal Coefficient of Expansion: This is a measurement of how much the length of a material will change when the material is heated or cooled. The value given is based on the inch as a unit. The number given shows how much this inch of material will increase if the temperature of the material is raised one degree Fahrenheit. Units – inches per inch per degree Fahrenheit (in/in/ï¿½F) – Meters/Meter/ï¿½C. Higher numbers mean that the material will expand or lengthen more for each degree rise in temperature. Smaller numbers indicate relative stability to changes in temperature. Thermal Conductivity: This property is known as the K factor. It is a measure of the transfer of heat by conduction. It tells how much heat is transferred from one side of a plate to the other side. It is measured as BTUs (units of heat in the English system) per hour per unit area (square feet) for a thickness of one inch and a temperature difference of one degree Fahrenheit between both sides of the plate. Units – BTU/hr/sq/ï¿½F/inch. – Watt/(Meter Deg Kelven) W/MK. Higher numbers mean that the material will absorb more energy before it is broken by a moving weight. Thermoplastic: Capable of being repeatedly softened by an increase of temperature and hardened by a decrease in temperature. Applicable to those materials whose change upon heating is substantially physical rather than chemical and that in the softened stage can be shaped by flow into articles by molding or extrusion. Thermoplastic Polyesters: Class of thermoplastic polymers in which the repeating units are joined by ester groups. The two important types are (1) polyethylene terephthalate (PET), which is widely used as film, fiber, and soda bottles; and (2) polybutylene terephthalate (PBT), primarily a molding compound. Thermoset: A material that will undergo a chemical reaction caused by heat, catalyst, etc., leading to the formation of a solid. Once it becomes a solid, it cannot be reformed. Thermosetting Polyesters: Class of resins produced by dissolving unsaturated, generally linear, alkyd resins in a vinyl-type active monomer such as styrene, methyl styrene, or diallyl phthalate. Cure is effected through vinyl polymerization using peroside catalysts and promoters or heat to accelerate the reaction. The two important commercial types are (1) liquid resins that are cross-linked with styrene and used either as impregnants for glass or carbon fiber reinforcements in laminates, filament-wound structures, and other built-up constructions, or as binders for chopped-fiber reinforcements in molding compounds, such as sheet molding compound (SMC), bulk molding compound (BMC), and thick molding compound (TMC); and (2) liquid or solid resins cross-linked with other esters in chopped-fiber and mineral-filled molding compounds, for example, alkyd and diallyl phthalate. Theoretical End Count: The maximum number of bundles that are in a roving doff, e.g., a roving doff made with 18 forming cakes in the creel that were “split out” 4 ways in forming will have 64 theoretical ends. Thickeners: Material added to the resin to thicken it or raise the viscosity index of the resin so that it will not flow as readily. Thixotropic: The property of becoming a gel at rest, but liquifying again on agitation. Tooling Gel Coat: Gel coat formulated for mold surfaces. Transfer: The smooth and successful transition from one roving doff to another during processing. Translucent: Permits a percentage of light to pass but not optically clear like window glass. Trapped End: A loop which was embedded into the roving doff during the roving process which gets stuck during run-out with sufficient tenacity that it prevents the entire strand from running freely to the chopper. Tube Stoppage or Plug: The failure of the glass to run through the metal tubes or guide-eyes from the creel to the chopper. This usually caused by a large knot or small birdnest becoming stuck inside the tube or guide-eye. Turn: One 360ï¿½ revolution of the components around the axis of the strand. Turnaround: The portion of the roving doff where the roving changes direction when it is pulled out of the doff. Twist and Ply Frames: Machines used to twist and ply glass yarns.

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Unidirectional: Strength lying mainly in one direction. A glass reinforcement in which the fiber is oriented in one direction. Untied Ends: The lack of a knot or splice between two doffs, one on top of the other, which prevents successful transfer from the top doff to the bottom doff in a creel par. Untreated: A descriptive term for glass fiber yarns having no applied chemicals or coatings, other than the minimal lubricant or binder used to control intra-fiber abrasion. UV Stabilizer: Chemical compound which improves resistance to degradation from ultraviolet radiation.

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Vacuum Bag Molding: Process in which a sheet of flexible transparent material plus bleeder cloth and release film are placed over the lay-up on the mold and sealed at the edges. A vacuum is applied between the sheet and the lay-up. The entrapped air is mechanically worked out of the lay-up and removed by the vacuum, and the part is cured with temperature, pressure, and time. Also called bag molding. Vacuum Molding: Method of low cost entry into the RTM process through the use of rigid cavity mold half and a semi rigid upper mold have each made of FRP. Ability to produce moldings at rate of 3 to 4 that of open mold with acceptable repeatability but not equal to that of RTM. SeeVM within the site. Veil: Ultra thin mat similar to a surface mat. Vinyl-Coated Glass Yarn: Continuous glass filament yarn, coated with a pigment and plasticized vinyl chloride resin. Vinyl Esters: Class of thermosetting resins containing esters of acrylic and/or methacrylic acids, many of which have been made from epoxy resin. Cure is accomplished as with unsaturated polyesters by CO-polymerization with other vinyl monomers, such as styrene. Viscosity: A measure of the resistance of a liquid to flow. VM: See Vacuum Molding. Also see Vacuum Molding within the site.

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Warp: The yarn running lengthwise in a woven fabric. A group of yarns in long lengths and approximately parallel, put on beams or warp reels for further textile processing including weaving, knitting, twisting, dyeing, etc. Warp Size: Chemicals applied to the warp yarn to improve strand integrity, strength and smoothness in order to withstand rigors of weaving. Weft: the system of yarns running crosswise in a fabric. Also known as fill. Wet-Out: The degree and/or rate at which each individual filament is “wet” or encapsulated by the matrix polymer resin in a composite sheet. Relates to the ability of the polymer matrix resin system to move through the glass fiber bed and to attain complete encapsulation of each individual filament. A measure of the wetability of the sized glass fiber surface. Wet-Process: A process for forming a non-woven web from a water slurry on “papermakingâ€™ equipment. Also known as “wet-laid” or “wet-formed”. Wet-Through: The degree and/or rate of encapsulation of the sized glass fiber bundles in a laminate. The rate and/or degree of which the polymer matrix resin system can flow through the bed of sized glass bundles or strands and encapsulate each bundle of filaments. Wides: A term used to describe bundles of roving which are wider than most of the other bundles in the bed of chopped glass fibers. These usually contain 3 to 4 times as many filaments per bundle as do most of the other bundles in the roving. (See Matchstick). Woven Roving Fabric: Heavy fabrics woven from continuous filament in roving form. Usually in weights between 18-30 oz. per square yard. Wrinkle: Surface imperfection in laminated plastics that has the appearance of a crease or fold in one or more outer sheets of the paper, fabric, or other base, which has been pressed in. Also occurs in vacuum bag molding when the bag is improperly placed, causing a crease.

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Yardage: Similar to Yield, but used to describe the linear density of “bare glass” or an unsized product. Yardage specifies the number of yards of glass required to weigh one pound. It is measured in hundreds. For example, K18 is a K fiber diameter that has 1800 yards in one pound of glass.

Yarn: A generic term for a continuous strand of textile fibers, filaments, or material in a form suitable for knitting, weaving, or otherwise intertwining to form a textile fabric. Yield: Yield refers to the linear density of a roving or yarn and is measured as the number of yards per pound. Yield Point: First stress in a material, less than the maximum attainable stress, at which the strain increases at a higher rate than the stress. The point at which permanent deformation of a stressed specimen begins to take place. Only materials that exhibit yielding have a yield point. Yield Strength: Stress at the yield point. The stress at which a material exhibits a specified limiting deviation from the proportionality of stress to strain. The lowest stress at which a material undergoes plastic deformation. Below this stress, the material is elastic; above it, the material is viscous. Often defined as the stress needed to produce a specified amount of plastic deformation (usually a 0.2% change in length). Young’s Modulus: Ratio of normal stress to corresponding strain for tensile or compressive stresses less than the proportional limit of the material.

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The post RTM, LRTM, & VARTM Glossary appeared first on RTM Composites.

Demystifying the RTM Process

John Moore — Sat, 25 Jul 1998 18:50:52 +0000

Resin Transfer Molding (RTM) is a low pressure, closed molding process which offers high-quality dimensional and surface finish composite moldings using liquid thermoset polymers reinforced with various forms of fiber reinforcements. Typically polymers of Epoxy, Vinyl Ester, Methyl Methacrylate, Polyester or Phenolic are used with fiberglass reinforcement. Other reinforcements are offered for more demanding applications such as Arimid, Carbon and Synthetic fibers either individually or in combination with each other. The matrix selection of polymer and reinforcement, dictates both molding material cost, as well as, molding mechanical and surface finish performance. Along with the polymer and reinforcement the addition of mineral fillers may be added to enhance fire retardantcy, flex modulus and surface finish. Reinforcements are presented in their dry form to the mold in binder-bound chopped mat, random-continuous strand mat, stitched “conformable” mat or woven cloth. The fiber has been either “preformed” to the exact shape of the molding tool in a previous operation or is hand-tailored during the loading process in the molding tool. After the fiber is installed into the mold, a premixed catalyst and resin is injected into the closed mold cavity encapsulating the fiber within. The primary surface of the molding may be gel-coated, a process of spraying the mold surface before installing the fiber. If a gel coat is not required, the exterior finish would be the same from the front to back of the molded part. RTM having the inherent advantage of low-pressure injection usually does not exceed 100 psi of resin injection pressure during the mold-fill process. the most common applications of using the RTM process are molded with a cross-section thickness of 4mm with 30% fiber content by weight of the total laminate. Evolution of the Process During the late1960′s through the early 1970′s the composite industry experienced significant growth, this was driven by two primary industries which were the Marine industry as the boats converted fully from the previous wood materials and the Automotive industry to meet both styling needs and weight reduction of the various exterior body panel components. To meet the rapid market growth, the suppliers of the primary polymer resins and fiber reinforcements developed their products to support the sheet molding compound (SMC) as needed by the automotive industry and the open molding process as needed by the marine manufactures. It should be noted that generally the primary materials of resins and reinforcement for both the SMC and the open molding, as well as, the RTM process are nearly identical, making then primary differences to be found in the actual molding process methods. SMC (Sheet Molding Compound) The SMC process is a high temperature process performed in a matched set of steel molds heated to over 350° (f), the SMC compound is laid in a measured volume in the heated mold with all of the needed, resin, catalyst, mineral fillers and reinforcement premixed into the compound in a previous compounding process, then the mold is forced closed under greater then 2000 psi of pressure squeezing the compound to fill the entire mold cavity rapidly curing within 1 to 3 minutes. Once cured, the mold is opened and the molding is ejected as a finished part needing only minimal surface preparation prior to finish painting. One added key advantage of the SMC process is the ability to mold the part to “net” shape, that is, normally SMC parts are molded to the final net shape of the part which does not then need post mold trimming, this eliminates the need to trim parts after molding and provides the most consistent part to part trim repeatability. The key to justification for the use of the SMC process is SUSTAINED DAILY PRODUCTION VOLUME needs that allows for the tooling cost to be amortized in a favorable manner across the planned production volume rate and life of the part to be produced. Having the ability to produce a finished molding every 3 to 5 minutes enables typical production volumes found in the automotive industry of typically greater then 20,000 units per year to be met and with that volume need, the cost of the steel molds and related high tonnage presses can be justified. Open Molding Process The open mold process is performed in molds made from basically the same resins and fiberglass reinforcements as are the parts produced in the molds. The molds are created over a simple form, may it be a professional CNC cut model or a simple shape hand made of screen covered with bondo body filler, in either case the mold is created by applying a gel-coat over the model, then using sheets of fiberglass wetted with catalyzed resin applied in individual layers built-up by hand until the desired mold thickness is achieved at which time a basic steel or wood frame is fasten to the backside of the mold to provide support and to position in an ergonomic manner for producing parts within. Initially the open mold process was facilitated by brushing a layer of gel-coat into the mold which will create the actual exterior finish of the final molded part. Then sheets of fiberglass mat were wet-out by brushing catalyzed resin over the mat, the wetted resin and fiberglass is rolled tight against the gel-coat and the additional subsequent layers to ensure the air within is rolled out, this is done using a roller similar to a paint roller which is controlled by the operator manually rolling the wetted glass mat to eliminate the entrapped air. Developments in the 1970′s from the equipment suppliers provided equipment to spray the gel-coat and the resin with chopped fiberglass into the mold, which significantly improved the application time, still then the fiber and resin needed to be “rolled” by the operator to eliminate entrapped air and to smooth the backside of the part. The open mold process is able to cure at room temperature, without added heat or pressure, the actual process will require from 4 to 6 hours from start to finish for each molding produced. Meeting the Demand from the 1970′s through 2000 The automotive industry was served well with the SMC process since their volume justified the capital cost associated with the tooling and high tonnage presses required. The marine markets could never justify SMC tooling. The varied Marine models, the need to react to nearly constant product changes and the low volume need of each of the moldings makes the SMC process very impractical for the Marine market offering the open molding as a practical method for their needs. If the volume requires the need for more then one molding per shift then additional molds are created, each at a very nominal cost, so the open molding process can be very flexible in meeting the needs of the marine or similar volume markets. The Orphan Alternative Method – RTM Through-out the evolution of the open mold and SMC processes, there has been an alternative closed molding process. Like the SMC process in which a matched set of tooling (an upper and lower mold half), the resin transfer molding (RTM) process has been available for use in both the automotive and marine markets, as well as, all others. The RTM process was not accepted by the automotive markets due to their need for rapid or high volume production and the marine market also looked the other way due to the added cost in tooling since two mold halves were needed and in the open molding process only a cavity or single half mold is needed. Few RTM Specialists Through the 1980′s to present only a few have specialized in the RTM process methods and tooling designs. Many in the industry would recognize names such as Applicator – Sweden, Plastech T.T. – United Kingdom, JHM Technologies – USA, Pyramid Composites – USA, as leaders in innovation who supply the industry with the “package” of needed tooling, equipment and training to carry out the production molding of RTM products. There have also been a limited number of molders who also adopted the advantages of the RTM process as their methods to supply the various OEM needs in the market, many would also recognize Cincinnati Fiberglass, Nero Plastics, ETM, Able Body, ASC, New Boston Composites all within the USA, various other molders can be found in France, England, Australia and Belgium as well. Within the molder community there are also a number of open molders who have a portion of their production produced one form or another of RTM, this however is generally a smaller portion of their main method which is open molding. Distinguishing the Differences The SMC process produces the highest productivity with the highest surface finish quality. Expected tooling life for a steel tool as used in the SMC process is greater then 100,000 moldings. Open mold, offers the lowest cost tooling, with a exterior finish directly from the mold that meets the needs of a high gloss smooth surface normally well suited for most Marine and general non-automotive surface needs. The lower quality surface as compared to SMC is due to the mold materials (composites versus steel as in SMC). Those in the automotive industry, as well as, others who need to meet a “Class A” exterior surface finish who do not have the volume to justify the SMC process can use the open molding process provided the surface of the molding is sanded, primed and finish painted to meet the finish specifications of the product needs. Additionally, the open mold process by having only a single mold half, the back side of the molding is fully dependant on the skill of the operator to maintain the part thickness and finish smoothness. This then requires many industries to grind by hand the individual parts to fit due to the variance common to the manufacturing process. RTM can enjoy the benefits of steel tooling to achieve the true “Class A” surface finish standards, yet then the economics would make sense to put the mold in a press and form SMC, so the RTM process is typically performed using composite tooling construction materials such as the open molding process. The advantage of having two mold halves eliminates the variance in part thickness common to the open mold method, making the RTM part very comparable in dimensional accuracy and repeatability of the SMC process. Summarizing the differences SMC has enjoyed the high end use in the industry, providing the benchmark for surface finish, production rate and tooling life, carrying the highest capital cost. Open mold, provides a rapid tooling lead time with tools that can easily be changed to meet engineering or marketing needs. The surface finish out of the mold serves many applications with the use of a gel-coat step prior to forming the actual molding laminate, if higher surface finish is needed, then post mold sand, prime and paint can meet the needs of the market. The primary disadvantage is found the operator dependency for part quality and uniformity, as well as, lately VOC emission restrictions. RTM has many advantages to offer, yet since it has not the ability to produce at the rate of the needs for the automotive industry and has tooling cost perceived to be too costly for the marine market, has historically been restricted to only a few niche applications.

Process Comparisons
	SMC	Open Mold	RTM
Raw Material Per pound Cost	$0.85	$0.95	$1.07 to $1.89
Specific gravity	1.3	1.1	1.1 to 1.3
Molding Cycle Time	3 to 5 minutes	6 hours	12 to 90 minutes
Tooling Life*	>100,000	>1,000	>1,000 to 5,000
* Tool life is determined by the quality of the parts produced to meet the dimensional and surface finish standards of the product molded. Parts having the need to meet a “Class A” automotive finish would have a lower expected mold life while applications requiring an “industrial” grade of general industrial finish would have extended tool life.

Material Strengths All of the processes can produce a similar product as far as strength is concerned. It is rare that a product can not be produced in one process due to a strength issue. Selecting the Right Process The selection of the best molding process is first determined by the daily production volume needs. If the daily and long-term production needs can justify the investment cost of SMC tooling and if the molded product surface can be as molded or post mold painted, then the SMC process is the most cost effect method to mold the part. If however the part needs gel-coat as a finish or the volume does not justify the cost of the steel SMC tooling then the open mold or RTM process methods need to be evaluated. Open mold serves well for daily production needs of 1 to 3 parts per shift as long as the part produced can tolerate the part thickness variance and the rough part back side finish. This true as well as if the total VOC emissions using the open mold process does not exceed local restrictions. Current RTM Developments Three primary factors are having a major impact on the use of the RTM process today.

The first is the Environmental agencies have recently reduced the allowable styrene (primary volatile organic compound “VOC” contained with the resins used for SMC, Open mold and RTM) level in the work place to levels that are very difficult to meet using the open molding process.
The second factor is the labor force of today is one that is not interested in working in an open mold environment. Thus the skill level needed to maintain the desired / required product quality and consistency is becoming increasing rare. The result is much higher production cost due to required “re-working” in a post mold operation of the products molded to meet quality standards.
The third factor is the innovation coming from the suppliers of equipment and tooling who have changed the mold design to incorporate the use of vacuum in balance with the injection pressure enabling lower cost tooling through the reduction in tooling structure and previously needed external clamping hardware.

Background to Current Developments The RTM process has been faced with competing with the Open mold and SMC processes, while in most low volume applications the cost of Open Mold tooling has made that process the choice for many applications. The high volume applications have chosen the SMC process. RTM has tried many different tooling methods to both increase tool life and improve surface finish longevity. These efforts have been to use Nickel Shell, Cast Aluminum, then Cut Aluminum. The cut aluminum tooling then led to cut steel and we found ourselves with tooling that equals the cost of SMC tooling so the program may as well go to SMC. All of this tooling effort or change was in reaction to attempting to improve the surface quality of the molded parts, by improving the damage resistance of the mold surface. The RTM process began with Epoxy tooling surfaces, which led to high temperature Polyester tooling gel-coats to improve release and reduce wear caused by sticking. The high temperature polyester was easily damaged which led to the nickel, the nickel was not easily repaired which led to cast aluminum, the cast aluminum had too much porosity to that led to cut billet aluminum, while that was an excellent surface, for only 20% more we could go to cut steel and then we realized that we were way off course as far as tooling cost to make the process competitive with either SMC or Open Mold. What is described above represents the evolution of the process over the 1960′s through late 1990′s. In 1997 an effort between JHM Technologies, Inc. and Plastech T.T of United Kingdom developed the Multiple Insert Tooling (MIT) method of building RTM molds. The purpose was to replace the mold surface as needed at a very nominal cost. This was done by making the mold with the mold surface removable as a separate “skin” of tooling gel-coat and laminate that would be held in the mold base (the Bolster) by vacuum locking the skin tightly into the Bolster. The actual MIT molding process is injected exactly as the RTM process had been carried out for the last 30+ years, it is only now that we have the ability to address the major cost factor, tooling surface finish life. A second advantage came of the MIT tooling design that is the ability to have multiple mold (MIT skins), having multiple skins allowed for many of the process steps to be carried out simultaneously, this has allowed the actual through-put of the mold set to be several times faster, actually about 300% increase in production rate. In the last two years, further developments in the RTM process have born a new innovation originally introduced as “RTM Light”. The RTM Light process has eliminated a major portion of the tooling cost by reducing the backside tooling structure as was needed in the conventional RTM process. The RTM Light process has proved to be the most revolutionary change to the industry in the last 20 years. While MIT has made a major step forward the RTM Light method, by lowering the tooling cost has open the door to the RTM Light process actually competing with Open Mold for total cost, yet yielding a far better molding then open mold having two finish sides and far more repeatable quality. JHM Technologies has taken the RTM Light process and added controls in place that protect the mold from over pressurizing during the injection process which maximizes the molding process. We then took the example of the MIT technology and produced mold cavities as “skins” much in the way as we did with the MIT technology for RTM. The ZIP (Zero Injection Pressure) RTM process as then born. Zero injection pressure is not to mean that there is zero injection pressure within the mold, it is to mean that the internal mold cavity pressure created from the injecting resin is kept BELOW the surrounding atmosphere which is clamping it closed. Unlike the RTM or RTM MIT process where the internal mold cavity pressure can be from 25 to 90 psi, the ZIP RTM process is typically less then 9 psi and with having drawn over ½ of an atmosphere (-.5 bar) from within the mold, the exterior the mold is being clamped with equal or greater force then the injecting resin pressure. The goal and controls of the ZIP RTM process are to maintain less then zero gain in relation to the exterior atmosphere when measuring the internal mold pressure. Virtual Example Illustration of ZIP It is a fact that employing the ZIP RTM principles, one could have just two matching mold skins representing the upper and lower mold halves, those skins could be suspended in mid air, clamp under vacuum and as long as the injection pressure was kept below the exterior atmospheric pressure the mold skins would remain closed and the part could be easily molded within. The only disadvantages to the ZIP RTM process in comparison to the conventional RTM or MIT RTM process is that it takes longer to inject the mold since the pressure is much lower. The advantages are many with the low cost tooling and ability to handle the upper mold half in most cases manually without the need for a press or mold manipulator system. Cost comparison: Part for Comparison- Typical Truck Roof having 1.8 meter width, 1.2 meter length and .3 meter height Materials to be used- Roof to be gel-coated, fiberglass reinforced with 25% by weight fiber, polyester resin filled 23% with calcium carbonate filler. Mold cost: The following comparison is based on single cavity impression mold with internal water lines on both the upper and lower mold halves. The conventional RTM and MIT RTM molds are designed to operate as a “stand alone” tool, or can be clamped in a hydraulic press to enhance clamping force and allowing for reduced injection time. The ZIP RTM mold is designed to be a stand alone mold only.

1) Conventional RTM	- $33,300.00 Expected production rate per 9 hour shift: 12 to 14 in press 8 to 12 stand alone
2) MIT RTM	-$41,400.00 Each added cavity skin -$ 960.00 Expected production rate per 9 hour shift * : 37 to 45 in press 20 to 33 stand aloneMIT RTM License Fee Cost: 5 Year MIT License fee cost 10,000 British Pound Sterling
3) ZIP RTM	$11,700.00 Each added cavity skin $ 960.00 Expected production rate per 9 hour shift * : 11 to 18 stand alone

* Both the RTM MIT and ZIP RTM process methods are listed above with 5 cavity skins to achieve the production rates indicated. It is expected that a ZIP or MIT skin will have a service life between 500 to 1500 molding cycles depending on surface finish needs of the final molding.

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Letter Designation	Range of Fiber Diameter Up to and Including
A	.00006 in. (1.50 mi.)	.00010 in. (2.50 mi.)
B	.00010 in. (2.515 mi.)	.00015 in. (3.81 mi.)
C	.00015 in. (3.81 mi.)	.00020 in. (5.08 mi.)
D	.00020 in. (5.08 mi.)	.00025 in. (6.35 mi.)
E	.00025 in. (6.35 mi.)	.00030 in. (7.62 mi.)
F	.00030 in. (7.62 mi.)	.00035 in. (8.89 mi.)
G	.00035 in. (8.89 mi.)	.00040 in. (10.12 mi.)
H	.00040 in. (10.12 mi.)	.00045 in. (11.43 mi.)
J	.00045 in. (11.43 mi.)	.00050 in. (12.70 mi.)
K	.00050 in. (12.70 mi.)	.00055 in. (13.97 mi.)
L	.00055 in. (13.91 mi.)	.00060 in. (15.24 mi.)
M	.00060 in. (15.24 mi.)	.00065 in. (16.51 mi.)
N	.00065 in. (16.51 mi.)	.00070 in. (17.78 mi.)
P	.00070 in. (17.78 mi.)	.00075 in. (19.05 mi.)
Q	.00075 in. (19.05 mi.)	.00080 in. (20.32 mi.)
R	.00080 in. (20.32 mi.)	.00085 in. (21.59 mi.)
S	.00085 in. (21.59 mi.)	.00090 in. (22.86 mi.)
T	.00090 in. (22.86 mi.)	.00095 in. (24.13 mi.)
U	.00095 in. (24.13 mi.)	.00100 in. (25.40 mi.)
NOTE: The letters I and O are not used in this sequence.