“How do Surfacing Veils Promote a Resin-Rich Surface?“

The surface veil creates the conditions for the resin to be dispersed more evenly on the surface. Instead of resin-rich pockets, they are more evenly distributed on the surface of the product.

“What is a Surfacing Veil?“

A surface veil is a veil that is made in such a way that it absorbs resin quickly and easily. The properties that promote this rapid wet-out also limit resin shrinkage.

For the purposes of this article and related presentations, all examples refer to a continuous glass veil. Veils of different materials offer a variety of options for different applications. Specific materials include polyester fiber synthetic veils, polyacrylonitrile fiber veils, aramid fiber veils, paper veils, chopped glass veils and continuous glass veils. Contact us for free samples. Discussing these materials here implies further discussion of barrier coatings and LPAs. Each option has its own advantages, disadvantages and overall effect. In this discussion, continuous glass veils offer the widest range of applications and provide the best surface.

In this case, a continuous glass veil is a veil with uniformly dispersed individual glass fibers.

A typical glass veil consists of 25 micron filaments. Each filament is independent of the other and held in place by a lightweight resin binder. The dispersion of these filaments is sufficiently consistent to provide a contradictory balance of bulk and density.

By contrast, standard chopped reinforcement mats or braided rovings use 25 micron filaments that are densely packed together. This density promotes fiber reinforcement but hinders rapid and uniform resin flow.

In a lamination scheme, a surface veil can be placed between the gel coat and the reinforcement pad.

“How does the Surface Veil Work? “

In the case of a surfacing veil, the uniformly dispersed fibers have two exclusive and independent objectives.

The first objective is resin flow. The veil has individual fibers that form invisible conduits on the surface of the laminate. The density of the roving woven mat or chopped strand mat hinders the flow of the resin. Resin flows easily to the surface due to the fast wetting properties provided by the veil

On a flat surface, pour equal parts polyester resin into two small pools. Place a 96-ounce piece of woven roving in the resin and the wet-out time for about a minute. Drop a 30-gram glass veil onto the resin and the wet-out time is less than a second.

The contrast is obvious, with more glass and density in the woven roving. However, this is also the point of this comparison. Resin flows easily through the veil. The high amount of glass and high density in the reinforcement hinders wet-out of the resin.

The second objection is to limit resin shrinkage. We have previously observed that sufficiently uniform, uniformly dispersed fibers can achieve a paradoxical balance between bulk and density. It is this uniform density on the surface that limits the shrinkage of the resin. This is a property of density.

Visualize resin-rich pockets in woven rovings. The three-dimensionally woven structure leaves resin-rich pockets, which are unavoidable. The apparent result of this situation is the printout. Resin shrinks, but glass doesn’t. The print is very obviously due to a large number of resin-rich pockets.

The same phenomenon occurs with veils, but to a much lesser extent. The resin-rich pockets are defined by the gaps between the filaments in the veil. Unlike woven rovings, however, where resin-rich pockets can measure an eighth of an inch between bundles of filaments, resin-rich pockets in surface veil are absent. That said, there’s no way to use a tape measure for comparison. These are real resin-rich pockets is a stretch.

“Why a Resin-Rich Surface? “

A consistent resin-rich surface is key to the longevity of the laminate. External sources attacking the laminate will shorten its useful life. Whether the attack is to the surface or beyond, a laminate will not stand the test of time if it is not properly protected. The resin-rich surface is its protective layer

The lack of resin-rich surfaces means high porosity. There are no two ways to solve this problem. Porosity is the doom of laminates.

Paved roads are porous. That’s doom for Detroit’s I-75, which thaws every spring. Water seeps and pours from cracks in the pavement. Potholes appear when water freezes. Even as our highway paving technology continues to improve, potholes are still inevitable every spring thaw.

The composites industry does have the technology to increase the porosity of laminates. Surface yarn, which allows uniform resin flow over the surface while allowing limited resin shrinkage over the surface, is this technique.

Even after accounting for all variables; environmental conditions, mold conditions, glass to resin ratio, gel coat thickness, and proper catalyst ratio; porosity due to resin shrinkage is still unavoidable, including the opening mold process.

In a recent test by the National Composites Center, the porosity of two identical samples was compared. Sample A has no surface veil; sample B has a surface veil.

Except for the surface veil, these samples are identical. Because of this, no elaboration is needed other than to note that the laminate contains 20 mil gel coat, vinyl ester resin, 54 oz braided roving and was prepared with 14 psi vacuum assist. For photographic reasons, the specimens are made with an intentionally matte finish. These tests were performed to provide visual evidence of gel coat behavior with and without a veil.

The cured samples showed no difference in surface profile by eye or touch.

However, when the samples were measured on the stylus profilometer, significant differences were found. Sample A, without the veil, measured an average roughness of 4500. Sample B with the veil, measured an average roughness of 28.

Stylus profilometers measure the average roughness or RA of vertical profiles. It does not measure an “A” grade finish. The RA value is equal to 1/10,000 of an inch. Sample A without the veil was 45/10,000 inches and Sample B was 28/1,000,000 inches, a difference of 160 times. It’s not reading 160%. This is read as unveiled specimens are 160 times rougher than veiled specimens.

Or for easier visualization, sit in a chair next to the Renaissance Center in downtown Detroit. Look down at the ground. That’s with a veil. look up. That is the veil without the surface. This visualization compares the 4.6-foot height to the Renaissance Center’s 747-foot height. 4.6/747=160.

This extreme and simple example shows the difference in porosity between laminates with and without a veil.

It should also be noted that this profilometer test was on a laminate with 20 mil of gel coat. If a laminate is to be produced with no gel coat, and painted at a later time, we need to keep in mind that the porosity will be greater with no gel coat and no veil. When this porous surface has paint applied to it, porosity will still be an issue.

We should also note that this profiler test was done on a laminate with a 20 mil gel coat. If the laminate is produced without the gel coat and painted later, we know that the porosity will be greater without the gel coat and veil. Porosity remains an issue when this porous surface is painted.

The resin-rich surface also acts as a barrier against attack on the laminate. The most common of these attacks are UV rays and corrosion.

When corrosion is related to auto parts, road salt may be the first thing that comes to mind. Early Corvettes took advantage of this. Nobody rust.

Today, advances in paint systems and metal fabrication, plus the use of thermal plastics and SMC has widened the playing field. The Corvette’s rust-free bragging point can also be used by Saturn.

Beyond the outer body, other unseen components of the automobile are moving toward composites. A pultruded drive shaft for instance is a good example. While cosmetics are not at issue, the protection of this drive shaft is at issue.

In the pultrusion process, the introduction of a facing yarn will reduce porosity and increase the barrier against corrosion.

The corrosion barrier will protect the drive shaft from such attacks as road salt and transmission fluid.

Under the hood, items such as heat shields, battery trays, and valve covers come in contact with a myriad of chemicals.

Every day, new ideas for a wide variety of composite parts become reality in the R&D laboratory. Any and all of these components will come into contact with corrosive materials.

“A Corrosion Barrier Becomes a Necessity “

UV rays can also attack composite components. The composite laminate is well protected by a surface veil with UV resistance and anti-aging.

The effect of UV attack is color degradation through oxidation and ultimately a chalky and delaminated surface.

The class “A” finish is ideally the most recognized of a surfacing veil. And in the automotive industry, class “A” finish is King.

Surfacing veil is the ingredient that best reduces printout. A class “A” finish cannot be attained when printout is present.

The wearability and durability of composite laminates are greatly improved with veils. It is part of the “A” class finish requirements. A surface veil applied to the laminate improves smoothness and eliminates paint popping.

“Where else Can I Improve the Surface? “

When discussing corrosion, the pultrusion process was mentioned. Such as pultrusion drive shafts. While cosmetics are not critical in this component, an improved surface with a veil is essential to prevent corrosion attacks.

The SMC process traditionally does not require a veil. But laying a veil will improve the surface. If there is color degradation in the cured SMC part, mold temperature is likely to be the culprit. The glass veil will balance the mold temperature and give the cured SMC part the desired consistent appearance.

“How does Surfacing Veil Increase Efficiency? “

The veil’s claim to fame is cosmetics. So far, we’ve seen how veneers improve and protect surfaces. Surface veils added to the process can also improve efficiency. Resource savings may be time or effort. This is also a hidden benefit.

“Quicker Resin Flow in a Closed Mold “

During the injection of resin into the mold, especially the vacuum-assisted RTM process, resin flow is hindered by densely packed glass fibers. Since resin shrinkage on the surface is already an issue, the veil is likely to be an integral part of the final laminate.

A hidden benefit is when the veil acts as a conduit in the mold. The resin is pulled from one end of the mold to the other, and through this guiding ability, it moves rapidly along the surface. At the same time, the resin on the surface can penetrate into the glass, ultimately reducing the time in the mold.

“Earlier Demold Time for Closed and Open Mold “

Just like the example above, the amount of time the laminate sits in the mold depends on its crafting. That is, fill the mold with resin. Once the glass is sufficiently saturated, the laminate must cure.

“An Open Mold does not Deal with Resin Flow “

In both cases, the synthetic surfacing veil reduces the resin shrinkage of the surface. An advantage for demolded parts. The resin continues to shrink as the exotherm continues to cure the part. The same is true if the part is pulled from the mold ahead of time. The surface veil greatly reduces resin shrinkage, even after the part is pulled early from the mold.

This concept requires great care. Such times need to be tested due to a large number of variables. Even in an open-mold hand spray process, a laminate made at the beginning of the day will not be the same as a laminate made at the end of the day. Variation in resin amount will change cure time.

“Protects Pultrusion Dies “

During pultrusion, glass rovings are drawn through a die. A large amount of glass is loaded into a small area with a lot of pressure.

Adding a synthetic surfacing veil reduces wear on the roving. The veil protects the expensive mold from accelerated deterioration.

“Strengthens the Gel Coat “

The concept of surface veil strengthening the gel coat is very similar to the concept of reinforcement mat strengthening the resin.

Gel coats without a surface veil on laminate are prone to chipping and cracking. Because it is not reinforced. The surface veil is the hidden benefit of enhancing the gel coat.

Regardless of whether the process is open or closed mold, a surface veil fiberglass should be applied to a gel coat that is still tacky or not fully cured. The fiberglass surface tissue keeps each fiberglass independent of each other. These individual glass fibers sink into the gel coat. Once cured, the veil strengthens the gel coat.

“Bonds Gel Coat to Reinforcement “

Just like above, a surface tissue applied to a tacky gel coat will sink into the gel coat. Not the entire fiberglass surface tissue sinks into the gel coat. The remaining work surface mat will combine with the resin that is interacting with the reinforcement mat.

A fiberglass surface mat in a composite laminate between a gel coat and types of glass fiber reinforcement is similar to providing an abrasive surface to a smooth surface before painting. The veil acts as a bridge, interlocking the gel coat with the glass fiber reinforced plaster fabrications.

“CONCLUSION “

In the automotive industry, class “A” surface is King. A poor frp surface profile due to printout is a major obstacle when a class “A” fabric finish is required. A surfacing veil was added to the lamination process. eliminates that obstacle by producing a consistent resin-rich surface.

This resin-rich surface doesn’t just eliminate printouts. It also provides a barrier against chemical and UV corrosion. In addition, the fiberglass surface tissue and resin-rich surface greatly reduces porosity.

Surfacing veil’s relationship with gel coat is an important one. Not only does veil strengthen the gel coat, veil also bonds the gel coat to the reinforcement.

The relationship between the work surface mat and the gel coat is important. The surface veil not only strengthens the gel coat, but also bonds the gel coat to the glass fiber reinforced composites material.

synthetic surfacing veil are also a low-cost addition to the lamination process. For just a few cents, the veil is very attractive because it not only improves the surface but also increases the efficiency of the process and leads to things like reinforced gel coats, earlier demold times and faster resin flow in closed molds(RTM, Infusion Vacuum) and other benefits. This also means that production has been increased.