Some manufacturers design gel coats for smaller-scale products. Diversified Structural Composites, for example, produces the shafts for electric trolling motors for fishing boats.
“It’s a fiberglass-reinforced pultrusion that comes straight out of our die with a gloss, Class A finish,” says Rob Klawonn, company president. “We produce a very uniform, consistent surface finish for a low cost. We also add some UV inhibitors to the resin mix that gives it a long life as a composite outside; they can last 10 to 20 years in a rugged environment while maintaining a good surface finish without powdering or chalking.” A combination of processing techniques, resin chemistry and tool design enables the company to achieve this result, he says.
Putting on the Veil
Surface veils provide an extra layer of protection for composite parts. They are thin, lightweight materials weighing from 17 to 68 grams per square meter.
“With surface veils, we’re basically putting a fiber into a fabric manufacturing process to impart surface smoothness or to block the underlying reinforcements from blooming to the surface when exposed to UV or corrosive chemicals,” says Brandon Ratcliffe, market manager at Precision Fabrics Group. “The use of a veil creates a resin-rich surface layer that enhances the corrosion properties of the FRP composites. A lot of veils are used in FRP corrosion-resistant pipes and corrosion-resistant tanks that hold aggressive corrosive agents to improve durability and longevity.” The fiber choice and the means by which the veil is made into a nonwoven greatly affect processing and end use performance. Veils can also provide UV protection and fire resistance.
Veils fall into three major categories: glass, carbon and synthetic. Glass veils are common in everyday use because they process very easily and wet out well in compatible resin systems. They’re found in flooring and in corrosion-resistant products where the chemicals don’t attack the glass.
Composite manufacturers use carbon veils in niche applications, such as high-temperature caustic services or where the product needs electrical static dissipation. “FRP is highly insulative, which is great for electrical applications but can result in static charge build up in some pipe, tank or ducting applications. Conductive veil is often specified when there is a fire or explosive hazard, because it allows you to ground the equipment and prevent static build up and fires,” Ratcliffe says.
Both glass and carbon veils must be compatible with the resin they’re going to be used in. That’s not the case with synthetic veils. “They are resin agnostic, so you can use them in any resin system,” Ratcliffe says.