Reinforced-plastic rotational molding

Important are behaviors associated and interrelated with plastic materials (thermoplastics, thermosets, elastomers, reinforced plastics, etc.) and fabricating processes (extrusion, injection molding, blow molding, forming, foaming, rotational molding, etc.). They are presented so that the technical or non-technical reader can readily understand the interrelationships. 

Focusing collectors are usually cast acrylic Fresnel lenses, or mirrors of aluminized polyester film in frames of aluminum. These reflectors are either enclosed in a bubble of poly(vinyl fluoride) film, or under polycarbonate glazing, which may be covered with a fluorocarbon film to reduce the reflectivity. The absorbers for active systems are copper or aluminum since the temperatures are too high (325—370°C) for plastics. The frames, however, can be molded ABS, high density polyethylene or polyurethane, either solid or structural foam. Polybutylene or chlorinated PVC can be used for piping hot water, and tanks can be made of either reinforced polyester or blow- or rotational-molded, high density polyethylene (12—15). 

The wall-thickness variations that result from such steps are always gradual, with abmpt wall thickness changes being virtually impossible. The maximum recommended thickness buildup, when necessary, is 50 percent of the normal wall thickness for the part. The following recommendations apply to designed wall thicknesses of rotational molded parts a preferred or desirable nominal wall thickness of 1/10 to in., a minimum wall thickness of 0.050 to 0.060 in., a maximum wall thickness of i in., and an optimum thickness of glass-fiber-reinforced plastic parts of f in. 

Michael W. Sowa, Rotational Molding of Glass Reinforced Powdered Polyethylene , 28th Annual Technical Conference, Society of Plastics Engineers, Inc., New York, NY, May 4-7, 1970. 

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