Liquid silicone rubber

The views of Bernie Stritzke, MedPlast, on the liquid silicone rubber (LSR) fluid delivery system, press injection units, tooling, materials, and two-shot molding, are presented. The LSR molding process involves a two-part system consisting of part A containing a platinum catalyst and part B containing a silicone hybrid crosslinker and an inhibiter to afford reasonable mixed pot life. Part A and B drums are placed near an injection molding machine, while pumps similar to grease pumps deliver the room temperature material at a 1:1 ratio to the static mixer. Variable ratio machines are available that offer the molder the ability to fine tune hardness, when parts A and B have different durometers. The static mixer combines part A with part B by dividing and shearing the stream of material repeatedly through a series of mix elements.