Hand Lay-Up or Contact Molding

Mat n. A fabric or felt of glass or other reinforcing fibrous material cut to the contour of a mold, for use in reinforced-plastics processes such as matched-die molding, hand lay-up, or contact-pressure molding. The mat is usually impregnated with resin just before or during the molding process. 

Hand Lay-Up (Contact Molding). A layer of liquid resin is applied to the surface of the mold. A layer of glass fiber mat (low strength) or fabric (high strength) is hand laid over it. Liquid resin is poured over it, and brushed or rolled (squeegeed) into it. The process is repeated to build up the desired thickness of the product. The assembly is allowed to stand until cured. 

Molds for hand lay-up (as well as others such as spray-up, contact molding, thermoforming, and casting) are usually made of TS polyester or epoxy shell set in a cradle made of a material such as steel angle. They can usually be made in-house, on a model of the product that could be made from an inexpensive material that can be shaped or sculpted, such as plaster, balsa wood, or expanded polystyrene, sealed and coated with a release agent. 

Hand Lay-uplSpray up Spray up and open contact molding (hand lay-up) in one-sided molds is one of the cheapest and most common process for making fiber composite products. Typical products are boat hulls and decks, truck cabs and fenders. In a typical open mold application, the mold is first waxed and sprayed with gel coat and cured in a heated oven at about 49°C. In the spray up process, after the gel coat is cured, catalyzed resin (usually polyester or vinyl ester at 500-1,000 cP viscosity) is sprayed into the mold, along with chopped fiber. A secondary spray up layer imbeds the core between the laminates (sandwich construction). Then it is cured, cooled, and removed from the reusable mold. In hand layup processing, continuous fiber strand mat and other fabrics such as woven roving are manually placed in the mold. Each ply is sprayed with catalyzed resin (1,000-1,500 cP) and the resin is worked into the fiber with brush rollers to wet-out and compact the laminate. 

Includes simultaneous heat and high-pressure matched metal die molded compounds only. Excludes low-pressure or low-temperature curing processes such as open-mold (hand lay-up, spray-up, contact bag, filament winding), encapsulation, lamination, and so on. 

This is the basic hand lay-up process, and the resin is in contact with air. The wet lay-up hardens at room temperature. A smooth exposed surface can be achieved by covering the surface with a plastic film which can be removed after cure. Boat hulls, lorry cabs, or similar objects are molded in a female mold while water or chemical tanks must be molded over a male mold as a smooth inside surface is needed for them. 

Vacuum molding n. This type of molding is used to mold fiberglass-reinforced plastics. The method allows molding without high temperatures and pressures. In this technique, layers of reinforced media are applied to the mold by hand. Resin is either sprayed or brushed on after each layer is positioned. The flexible sheet (usually cellophane or polyvinyl acetate) is placed over the lay up. Joints and seals are sealed and a vacuum causes the b to collapse over the face of the product not contacting the mold. The resultant pressure tends to eliminate voids and forces out any excess resin or entrapped air. Madox DM (1998) Handbook of physical vapor deposition (PVD) processing. Noyes Data Corporation, New York. 

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