Here's a New Way to Spray FRP with Fillers & Low VOCs.

* Open-mold fabricators of products like bathtubs, spas, and truck hoods now have a more environmentally acceptable way of spraying filled systems. Styrene emissions 50-80% lower than standard airless spray-up and 20-50% lower than flow-coat systems are claimed by some makers of a new style of non-atomized FRP spray equipment. These so-called "impingement" spray systems were the major news in open-mold processing at the recent Composites '99 show in Chicago, sponsored by the Composites Fabricators Association (CFA). All five of the major suppliers of spray-up and flow-coating equipment showed or talked about new impingement systems. Besides low VOCs, they are said to handle fillers-and perhaps even gelcoats--better than flow coaters. But the technology remains somewhat controversial, and the sellers' attitudes toward it appear to range from warmly enthusiastic to neutral or even cool about its prospects.

Larger orifices

The prime mover behind "impingement" spraying is Magnum Industries, Clearwater, Fla. Last spring, Magnum came out with its FIT (Fluid Impingement Technology) system. The original inspiration, it seems, was to find a non-atomized way of spraying filled systems. Flow coaters, which typically have a nozzle with a row of tiny holes (11-18 mils), tend to plug up with filler particles. They aren't used with gelcoats for the same reason. FIT and similar systems have just two larger nozzle orifices (50 to 125 mils) that are said to be immune to plugging.

The tip orifices are angled so that the two streams of internally mixed resin and catalyst converge within a few millimeters' distance to form a flat sheet of liquid. About 8 to 16 in. away from the head, the sheet breaks up into large droplets, much larger than those from a flow coater. There is no external air assist.

FIT and some other impingement systems are pumped at very low pressure--only 15-30 psi, in Magnum's case. Magnum's FIT systems use a 3:1 pump ratio for unfilled systems, 6:1 for filled, and 7:1 or 11:1 for gelcoat. Air consumption is reduced by 35%, Magnum says, and wear on pumps is extended five- or sixfold, according to Tom Headger, manager of manufacturing product development. He adds that changing the angle of the two orifices provides unprecedented flexibility to vary pattern width and also permits adjusting for resin viscosity without having to increase pump pressure and thus raise styrene emissions.

FIT and other impingement systems tend to have a tray or chute extension on the chopper, both to spread out the glass pattern and to lay the glass gently onto the liquid sheet so as not to "blow through" it.

FIT trials at tub/shower producers showed dramatically reduced overspray and bounce-back, Hedger says. Customers reportedly saved as much as 1.5 lb of material per tub. At one spa manufacturer, waste was cut fom 300 lb/day per spray-up station down to 110 lb/day. What's more, Hedger says the FIT system wets out the glass better than a flow coater, and less air entrapment makes for easier roll-out than with a standard spray gun.

In tests conducted at an EPA facility in Research Triangle, N.C., Magnum's FIT system produced significantly lower styrene emissions than either a flow coater or airless/air-assist spray gun. The resin was a DCPD polyester containing 42% styrene. It was sprayed with chopped glass for 75-90 sec at a 24-sq-ft target over a distance of 32 in. Styrene levels were measured with a flame-ionization detector.

Magnum has also published data on tests in its own shop. A DCPD resin with 38% styrene was sprayed with glass for 2 min at a slightly larger target over a slightly shorter distance. Average airborne styrene concentration (measured with Magnum's new EMS-250 electrocatalytic detector) was 16 ppm for FIT, 20 ppm for a flow coater and 60 ppm for an airless/AA spray gun. Also, Magnum sprayed an orthophthalic gelcoat with 33% styrene and recorded 22 ppm emissions with FIT vs. 49 ppm with a standard spray gun.

While most makers of impingement spray systems are skeptical about their applicability to gelcoating, Magnum is "confident," Hedger says. "We have 20 FIT units in gelcoat out in the field and working well, getting low porosity and low air entrapment."

Differing views

Another believer in impingement-type spraying is Mike Keegan, director of sales and marketing of Glas-Craft, Inc. in Indianapolis. He believes the combination of a nonatomized system, the ability to handle fillers, and a more uniform spray pattern than a flow coater (no "cornrow" effect) will make major inroads for impingement systems against both airless spraying and flow coating. Add in the same price as a flow coater and the ability to convert existing flow coaters with just a change of tip, and Keegan foresees quick adoption of the new technology.

Glas-Craft's new V-Force impingement nozzle is an option for its new Indy gun. The gun also accepts a dual-row flow-coat nozzle. The gun has an internal mixing chamber designed along principles similar to a polyurethane high-pressure mix-head. It is followed by a static mixer. Glas-Craft offers pump ratios from 4:1 to 11:1 with the V-Force nozzle.

Glas-Craft has no test data on styrene emissions from the V-Force nozzle, but Keegan says it requires lower pressure than a flow coater and therefore probably creates lower VOC levels. Keegan doesn't believe today's impingement spray systems are necessarily the last word in low-VOC dispensing, but he agrees that they have major advantages over current alternatives.

The CrossFire impingement nozzle is one option on the new "three-in-one" SystemOne low-pressure internal-mix system from Venus-Gusmer, Inc., Kent, Wash. Simplicity, modularity, and easily interchangeable components are said to be hallmarks of this system, which can also be used for standard airless spraying, gelcoating, and flow coating (or FlowChop). Its new stainless-steel SuperPro gun has a slide valve instead of troublesome o-rings. The new SlideDrive catalyst metering system provides infinitely adjustable catalyst settings. An 11:1 pump is standard. It provides pressures from 20 psi for impingement to 40 psi for flow coating or spraying. Venus-Gusmer says the high-ratio pump permits using longer hose sets and running filled, vinyl ester, or low-styrene resins without heating. The bolt-on pump also can be quickly changed.

Venus-Gusmer president Meg Charter believes impingement offers a good alternative to FlowChop in many applications and may have potential for gelcoating. Some customers report that CrossFire provides a uniform spray pattern and rollout capability comparable to airless spraying. But unofficial tests at Venus-Gusmer have raised concerns about whether impingement actually lowers, or perhaps even raises, styrene emissions relative to flow coating. To clarify the issue, Venus-Gusmer is currently testing impingement against flow coating at an independent laboratory.

GS Manufacturing, Costa Mesa, Calif., also offers an "impingement flow" gun, but president Gary Smith says it emits more VOCs than his flow coater. He also does not think his impingement gun is suitable for gel-coating. GS offers this "Uni-Chopper System" with a 4:1 to 9:1 pump. In-line heater and catalyst alarm are options. Smith will introduce a different concept for spraying filled materials this year.

A new impingement system just went into production last month at ITW Poly-Craft, Winter Haven, Fla. It's based on the company's new Flow Master internal-mix gun for flow coating, which is all stainless steel and uses no o-rings. The internal mixing chamber encapsulates the catalyst with resin and is followed by a static mixer. The gun is supplied with a 4:1 to 8:1 pump.