No. 37 - Spray-Up Composites

What used to be known as FRP (fiber-reinforced plastic) spray-up came on the scene in the 1950s as a more efficient open-mold laminating system that required less time and labor than hand lay-up for making large composite parts. By the 1960s, it became a widely used method for manufacturing composite boat hulls and decks, RV components, truck cabs and fenders, spa tubs, and showers.

Glass-Mate and Venus Products (later Magnum Venus Products) were early developers of the process which sprayed resin (usually polyester or vinyl ester), catalyst, and chopped fiberglass onto an open mold. In the early 1960s, Glass-Mate introduced a two-pot system with dual nozzles for the “A” side of premixed resin and initiator (usually BPO) and “B” side of resin with promoter (DMA).

A key technical development came in 1967 when Venus introduced the first internal-mix system, which combined the resin and initiator in the spray head. At the same time, open-mold fabricators switched from solid BPO to liquid MEKP as the preferred initiator ingredient because of its relative safety and ease of use. MEKP was a liquid that required no pre-mixing and was easier to dispense than BPO. A limiting factor for internal mix, however, was that cured resin had to be flushed from the system to prevent hardening in the spray gun.

Easy-to-use external systems that sprayed resin and MEKP initiator separately outside the head were developed at about the same time. These systems avoided the need for solvent flushing.

In the late 1970s, companies like Glas-Craft and Binks unveiled airless systems that made use of industrial spray-painting technology. These were capable of dispensing high-pressure (1200-psi) fluids at high output and offered an improvement in transfer efficiency over the former air-atomized technology, which produced more overspray and fumes.

The 1980s saw the introduction of airless/air-assist systems that utilized lower (400- to 600-psi) fluid pressure. This technology combined airless delivery with external shaping air to form a spray pattern. It was yet another improvement for spray-up in terms of higher transfer and reduced emissions.

In the mid-1980s, Venus was one of the first to develop a “flow coater” that dispensed catalyzed resin through multiple spray-tip orifices that produced a stream of large droplets rather than an atomized spray. Resembling a shower head, this type of system greatly reduced styrene emissions but initially was suited only to hand lay-up saturation and not chopped-glass spray-up.

In the late 1990s, several companies—including Venus, Magnum Industries, GS Manufacturing, and Glas-Craft—extended the technology by offering flow-coat systems with glass-chopping capability.