EFFECTS OF MATERIAL AND PROCESSING CONDITIONS ON THE SHRINKAGE OF AN INJECTION MOLDED LIQUID SILICONE RUBBER PART

摘要

An injection molded liquid silicone rubber (LSR) part was investigated for better understanding of how material properties, typical processing conditions, and packing affect shrinkage. This work showed no direct correlation between material durometer and shrinkage. In-flow shrinkage was greater than cross-flow shrinkage, but the diametric shrinkage was twice the in-flow shrinkage. Small (1%) increases in shot size significantly reduced shrinkage, whereas injection velocity and cure time had no direct effect on shrinkage. Packing of LSR parts is possible, with higher pack pressures and shorter pack times decreasing shrinkage. As expected, higher mold temperatures produced greater shrinkage, but this effect was offset by packing of the part near the gate.