Why Composites – Overview
Within the last several years, the term “composites” has been used to cover a wide variety of formulated compounds: from wood-fiber composites and concrete composites to thermoplastic and thermoset composites. By adding additional ingredients to a standard base formula, the resulting composite acquires a new set of properties with a wider range of capabilities. These new composite materials offer designers and engineers many advantages in the development of new products and the improvement of existing products.
Applied Composites Corp specializes in the manufacture of thermoset reinforced composites and utilizes the compression molding process to produce products for a wide variety of industries.
Sheet Molding Compound:
Sheet molding compound (SMC) is fiberglass reinforced composite material, produced in a “sheet” format.
The process begins when continuous strand fiberglass (also called a “roving”) is chopped into desired lengths (usually under 2”). The strands are deposited onto a bottom layer of paste made from resin and filler. The paste and fiberglass strand travel through the processing machine, on a carrier film. A top layer of resin and filler paste sandwiches the fibers to the bottom layer of paste and is covered by a top layer of the carrier film. The “fiber and paste sandwich” is then compacted by a series of rollers to make a continuous sheet of the molding compound.
SMC is made of 3 basic components: the base resigns system (polyester, vinyl ester, epoxy, phenolic or polyimide), the reinforcements (fiberglass, graphite, aramid), and additives which include inert fillers, pigments, UV stabilizers, catalysts, inhibitors, and thickeners.
While there is basically no limit to the number and types of formulations that can be produced, it is important to prioritize the desired properties for the product. This helps to ensure that the optimum material system is achieved within the economic guidelines of the program.
Compression molding primarily uses thermoset composite resin systems, which use heat to form and permanently set the shape of a part. Once the resin is cured, the part cannot be reformed, making the process irreversible.
Compression molding uses matched steel molds to compress a weighed “charge” of sheet molding compound (SMC) into a new and specific shape. The two halves of the mold, which are mounted in a hydraulic molding press, are closed around the charge. The combination of heat (300 degrees) and pressure (1000 PSI) caused the thermoset material to cure in the mold. Molding cycles will range from well under 1 minute to over 5 minutes, depending on the size and cross-sectional thickness of the part. The mold is then opened, and the part is removed.