Spray-up is another alternative for open mould wet lay-up processes. It helps to automate the application of the matrix resin and reinforcement fibre layers, thereby reducing the time period required in the manual lay-up procedure.

As shown in this picture, in a spray-up process, chopped fibres, together with the liquid matrix resin, are sprayed onto an open mould surface until the desired thickness of the composite lamination is obtained by successive layers. Spray-up may also be used in applying the gel coat to the mould surface beforehand lay-up and spray-up processes.

The equipment necessary in the spray-up process includes a spray gun, a glass fibre chopper attachment and a pumping system. The chopper attachment delivers continuous roving and cuts them into short fibres.

Generally, chopped fibres have a length of between 25 and 75 mm, and they are added to the matrix resin stream as it exits the spray gun nozzle. This type of mixing leads to random orientation of the fibres in the layer, whereas in hand lay-up fibres may be oriented.

After the application of the catalysed resin mixture and chopped fibres through the spray gun onto the open mould surface, rolling will be necessary to compact the laminate as in hand lay-up.

Manufacturers use hand rollers or automated rolling systems. Usually, hand rolling is adequate for smaller parts, whereas automated rolling systems are preferred for larger parts with flat surfaces.

Bibliographical Reference:

Handbook of Composite Fabrication – Page 59

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