Sheet molding compound, processing

J. Ferrarini, D. M. Longnecker, N. N. Shah, J. Feltzin, and G. G. Greth, Development of a Unique Method for the Preparation of High Quality SMC, 33rd Annual Technical Conference, R-P/C Institute, SPI, P. 1, Section 9-D (1978). ITP , interpenetrating thickening process. Sheet molding compounds based on SINs. Polyurethane/styrene-polyester. 

Compounds based on S—EB—S usually contain polypropylene, which improves solvent resistance and processibility and raises upper service temperatures. Compounds intended for use in the automotive industry are able to survive 1000 hours air exposure at temperatures of 125°C with only minor changes in properties (54). Very soft compounds have been developed to replace foam mbber for interior trim parts. In this and similar applications, these soft compounds are usually insert molded over polypropylene or metal and then coated with flexible polyurethane paint (55). Other automotive applications include products intended for sound deadening, flexible air ducts, and gear shifter boots, as well as improving the properties of sheet molding compounds. 

With these properties and values the finite difference technique was used to model the curing process in sheet molding compound (SMC) plates using a heat balance with an exothermic reaction as... 

In Europe, car manufacturers first used a half product, a sheet molding compound (SMC) made of sheets of fibers pre-impreg-nated with resin. In the USA they used a different process named RIM (Reaction Injection Molding) which allowed the bumper to be painted the same color as the rest of the structure. 

Depending on the resin preparation, the material in or around a mold can be cured with or without heat, and commonly without pressure. Curing needs include room temperature conditions, heat sources, vacuum bags, pressure bags, autoclaves, etc. An alternative is to use preimpregnated, B-stage TS polyester or sheet molding compound (SMC), but in this case heat is applied with low pressure via a impermeable sheet over the material. This process can produce compact... 

Special types of glass fiber for specific processes (Chapters 4 and 5), such as sheet molding compound (SMC), pultrusion, and reinforcement of thermoplastics, is a marked trend in current development. Examples follow ... 

Products such as sheet molding compounds (SMCs) and BMCs are usually manufactured by a two-stage process, in which resin, fillers and other additives are first mixed to a paste and then combined with fiber reinforcement, according to the required form of compound. For continuous production of SMC, the paste is thickened and metered by... 

Low-pressure SMC Low-pressure sheet molding compounds can present problems due to difficulty in controlling the chemical thickening process at low viscosity levels, and achieving a dry, tack-free easily handled compound without any resin separation. New technology from Union Carbide is claimed to overcome this, offering wide process latitude for thickener control, with dry easily handled compounds of stable viscosity. 

---