Description: Sheet Molding Compound (SMC)

Sheet molding compound (SMC) consists of a doughy material composed of  chopped glass fiber rovings, 0.75-2” in length, fillers (e.g. calcium carbonate, low profile additives, catalyst, catalyst aids, and a thermoset resin, normally a polyester based thermoset, epoxy or vinyl ester resin.  The long fibers present in this material provide good stiffness and impact resistance.  The initial paste has a viscosity near the 40,000-100,000 cps range.  SMC is then packaged and placed into storage for 1 to 2 days allowing the resin to advance to achieve viscosities in the range of 60,000 to 750,000 poise.  The thickening during this time period is usually assisted with additives like magnesium oxide, magnesium hydroxide, or calcium hydroxide.  The aged SMC is then weighed, and placed into a heated compression mold (250-350^oF) which under pressure (500-2500 psi) forms a composite part.  Typical compression molding cycle times of 30 seconds to several minutes are possible with thicker parts requiring more dwell/curing time. 

 

 

 

 

 

 

 

 

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SMS line specification

                                       

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