Spray-up techniques

Thermoforming is faster and higher fiber contents can be achieved than they can for the spray-up technique. Moreover, if continuous strand mat is used in thermoforming, it can be combined with patches of directional reinforcement. The major drawback with thermoforming is the relatively high level of waste material. 

FIGURE 2.44 (a) Basic hand lay-up method, (b) Spray-up technique. 

To increase the production rate, spray-up technique is used instead of a hand lay-up technique. This technique employs a multiple-headed spray gun. The resin mixture and chopped fibres are discharged simultaneously by using the spay gun on the surface of the mould where they are deposited to a uniform thickness. Sheets, storage vessels, auto body parts, boat hulls, truck bodies and building components are made using this process. 

This process has been described in a previous chapter as a means to process unreinforced resins. Fibre-reinforced composites can be fabricated in a similar way. The resin and fibre can be combined by usual hand lay-up or spray-up techniques. Glass fibre content up to 70 wt% or 50 vol% can be achieved for fibre composites processed by this technique. Press moulding offers obvious advantages like fast cycle time, good finish, structural integrity and high reinforcement content. 

By layup and spray-up techniques, large- and short-run reinforced items are fabricated. Examples include boats of all kinds, dune buggies, all-terrain vehicles, custom auto bodies, truck cabs, horse trailers, motor homes, housing modules, conCTete forms, and playground equipment... 

Most manufacturers use spray guns and pumping systems to have a more rapid and consistent mix to wet out the laminate, where highly accurate metering systems can also be used and automated tape-laying machines have been developed recently, as discussed in the part on spray-up techniques. 

Various techniques have been developed for speeding up the contact moulding process. Of most importance is the spray-up technique (Fig. 2). The cutting of random mats... 

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