Fiberglass spray lay-up process

Spray-Up also known as chop method of creating fiberglass objects by spraying short strands of glass out of a pneumatic gun. This method is used often when one side of the finished product is not seen, or when large quantities of a product must be made cheaply and quickly without regards to strength.Corvette fenders and boat dinghies are commonly manufactured this way.

It is very different from the hand lay-up process. The difference comes from the application of the fibre and resin material to the mould. Spray-up is an open-moulding composites fabrication process where resin and reinforcements are sprayed onto a reusable mould. The resin and glass may be applied separately or simultaneously "chopped" in a combined stream from a chopper gun. Workers roll out the spray-up to compact the laminate. Wood, foam, or other core material may then be added, and a secondary spray-up layer embeds the core between the laminates. The part is then cured, cooled, and removed from the mould.

Applications include making of custom parts in low to medium volume quantities. Bathtubs, swimming pools, boat hulls, storage tanks, duct and air handling equipment, and furniture components are some of the commercial uses of this process.

The basic reinforcement material for this process is glass-fibre rovings, which are chopped to a length of 10 to 40 mm and then applied on the mould. For improved mechanical properties, a combination of fabric and chopped fibre layers is used. The most common material type is E-glass, but carbon and Kevlar rovings can also be used. Continuous strand mat, fabric, and various types of core materials are embedded by hand whenever required. The weight fraction of reinforcement in this process is typically 20 to 40% of the total weight of the part. The most common resin system used for the spray-up process is general purpose or DCDP polyester; isophthalic polyesters and vinylesters are also sometimes used. Fast-reacting resins with a pot life of 30 to 40 minutes are typical. The resin often contains a significant amount of filler. The most common fillers are calcium carbonates and aluminium trihydrates. In filled resin systems, fillers replace some of the reinforcements; 5 to 25% filler is used by weight.

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