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Spray-up - Winona State University

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SPRAY-UP
WHAT IS SPRAY-UP?
one or more continuous fiberrovingsfed through a chopperfiberrovingsare cut to predetermined lengthschopped fibers are propelled into resin streamresin and chopped fibers are deposited simultaneously on moldrolled by hand with serrated rollers"automated wet lay-up" (however fibers not continuous)YouTube video
ADVANTAGES OF SPRAY-UP
rapid lay-upability to fabricate large, complex shapes where forming and fitting of mat or fabric would be difficult
REINFORCING FIBER AND RESIN SYSTEM
E-glass rovingpolyester resinbase resin (includes crosslinking agent, usually styrene)catalyst (initiator)accelerator
SPRAY-UP SYSTEM COMPONENTS
pumps for resin and/or catalystpressure pots for catalystspressure pots for flushing solventschopper for fiber reinforcementvarious air regulators and gauges for controlboom and dolly assembly or chassisvarious hoses for transporting materialsgun assembly for dispersing materialscompressed air source
RESIN SYSTEM MIXING METHODS
external mixresin/catalystresin and catalyst/resin and accelerator (two-pot system)internal mixresin/catalyst (catalyst injection)air-atomized - addition of air into the gun to disperse resin mixairless (flow coaters) - hydraulic pressure to disperse resin mix
CHOPPERS
chops continuous fiber roving in lengths typically 0.5 in. - 2.0 in.driven by small air motor, speed can be controlled by valvesexhaust usually ducted into the chopper chamber to thrust chopped roving toward resinchopper comprised of two rollersone made of rubber or urethane (cottwheel)one made of aluminum with fitted slots to hold razor blades (cutter wheel)air motor drives either wheel with the roving passing between the two wheels
WHAT SHOULD BE CONSIDERED IN SELECTING A SPRAY-UP SYSTEM?
resin/fiber output - rate the gun to the anticipated operation (capabilities up to 30 lbs/min glass/resin mixture)gun weight and balance - continuous operation should not cause undue discomfort to the operatorcontrols (gun triggers, resin and catalyst flow controls) - conveniently located and easy to use (ideal gun is one which can be operated with one hand)spray head adjustment - correct, rapid alignment of the resin nozzle's output contacting the chopped rovinggun cleaning and maintenance -simple gun design with a limited number of partscan be dismantled with standard toolspacking and gaskets will not be damaged by solvents or other materials usedresin metering devices - if large quantities of resin are to be handled continuously consider the metering controlparts availability - manufacturer stocks replacement parts
FABRICATION PROCESS
gun calibration (collect resin and chopped roving for 15 sec in separate bags)if gel coat spray thin pass of resin (no chopped roving)usually start spray passes at bottom of mold using horizontal spray patternoverlap about one-third to assure uniform layerfollow horizontal layer with vertical layer, if possible (will yield best uniform laminate)gun head 18 - 24 in from the mold surfacemost outputs and operators maintain 0.050 in nominal thickness per pass
ADDITIONAL PROCESSING IS NEEDED AFTER CHOP IS APPLIED TO MOLD
best laminate - one pass, roll out, let gel, continuerolled by hand with serrated rollers (aluminum or plastic) to remove air, compact the fibers and smooth the surfacestart rolling near center and work to edgeswhere reinforcement bridges female contours work down into contours by pulling fibers from edge to center of female contourmale molds easier to spray-up and roll out, however usually more fiber and resin overspray (waste) on floorcure will be similar to wet lay-up

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Spray-up - Winona State University