Sheet Molding Compound (SMC) is used in compression molding - often of larger parts - where higher mechanical strengths need to be achieved. Glass reinforcement is between 10% and 60%, and glass length is slightly longer than Bulk Molding Compound (BMC) - between 1/2-inch and 1-inch (25mm).
As with BMC, thermoset sheet molding compound is a mixture of polymer resin, inert fillers, fiber reinforcement, catalysts, pigments and stabilizers, release agents, and thickeners. Manufacture of sheet molding compound is a continuous in-line process. The material is sheathed both top and bottom with a polyethylene or nylon plastic film to prevent auto-adhesion. The paste is spread uniformly onto the bottom film. Chopped glass fibers are randomly deposited onto the paste. The top film is introduced and the sandwich is rolled into a pre-determined thickness. The sheet is allowed to mature for 48 hours.
Sheet molding compound can be molded into complex shapes. High mechanical properties and excellent surface appearance, and excellent electrical insulation make sheet molding compound ideal for automotive Class A body panels, high-strength electrical parts, business equipment cabinets, personal watercraft, and various structural components.
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