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New spray-up gun helps FRP fabricators 'clean up their act.' (fiberglass-reinforced plastic)

New Spray-Up Gun Helps FRP Fabricators `Clean Up Their Act'

A new airless/air-assist, external-mix gun for FRP spray-up has been introduced by Binks Manufacturing Co., Franklin Park, III. Material transfer and catalyst mixing efficiencies are said to be improved 20-30% with the new gun, reportedly allowing reduced styrene and other volatile organic compound (VOC) emissions.

Among the gun's special features is a new method of catalyst mixing, which Binks calls "ExACT," for exclusively/external advanced catalyzation technology. In this method, unatomized MEKP is introduced into the resin spray close to the exit point of the resin nozzle, so the resin is hit in its miniscus. This reportedly leads to an even dispersal of the catalyst to all of the edges of the material spray. According to Robert McCullough, general manager of Binks' PRED Div., previous designs either joined the catalyst and resin streams at a point beyond the miniscus, leading to catalyst buildup in the middle of the stream; or joined the streams at a point before the miniscus, which confined the catalyst to the edges of the stream.

The catalyst mixing efficiency of this gun is reportedly 25-30% better than existing external-mix guns. McCullough says that "in order to obtain a gel time similar to the ones obtained with current guns, we have to reduce the catalyst flow by up to about 30%, or else we over-catalyze. With air-atomized catalyst, a substantial portion of catalyst is being lost to the atmosphere."

Air is injected into the stream at the miniscus for air-assist/airless atomization of the resin. Hydraulic atomization pressures have been reduced from 1200-1500 psi to 400-1000 psi with the new gun. Lower atomization pressures are said to result in less "blow-back" from the mold, for improved transfer efficiency and less fume emissions.

Says McCullough, "We have had several tests run whereby a user or material supplier took a mold, covered half of it, and sprayed the other half with a hot-pot or premix batch, then set the gun up for exactly the same catalyzation rate, and sprayed the other half of the mold. The gel times were indentical, which tells us that we have essentially 100% catalyst utilization."

The new gun, model #102-2400, has a separate chopper switch on the trigger, allowing independent operation of resin/catalyst dispensing and glass chopping. The chopper is mounted on dual bolts, to prevent the loosening problems of single-mount guns.

Other features of the gun include larger fluid passages and orifices than previous Binks guns for greater throughput, especially when running vascous materials. The gun is reportedly capable of running heavily filled materials such as syntactic foams. Nozzle sizes range from 0.015 to 0.078 in., with spray angles from 25 [degrees] to 60 [degrees]. Reduced maintenance is expected, thanks to externally spring-loaded needle valves that reportedly don't become clogged with material, and a canted surface on the trigger mechanism that reduces strain on the valve needles. A safety lock helps prevent unintended operation.

The gun is priced at $845 without chopper, and is also available with complete spray/chop systems. (CIRCLE 33)
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Author:Evans, Bill
Publication:Plastics Technology
Date:Oct 1, 1990
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