Two-Color, Dual-Hardness LSR Molding

At the recent K 2007 show in Dusseldorf, a Swiss custom molder illustrated the trend toward multi-component molding with liquid silicone rubber (LSR). Silcotech AG of Stein am Rhein, molded a baby pacifier that combined two colors and hardnesses of LSR in one part. The two materials were injected sequentially in one cycle without opening the mold, using proprietary tooling technology (apparently involving a mold action). One material was an 80 Shore A green LSR from Momentive Performance Materials (U.S. office in Wilton, Conn.). The other was a clear, 40A LSR from Wacker Silicones (Adrian, Mich.). The part was being molded for PickMed of Kufstein, Austria, on a 110-ton, all-electric Arburg Allrounder 470A with two dual-component pumping systems. A single-cavity cold-runner mold was being used for prototyping, but as many as four cavities could be used in commercial production. A Wittmann robot demolded the part with the aid of ejector pins and air assist because of the part’s 3- to 4-mm undercut. Cycle time was 57.3 sec but may be shortened with further optimization. Silcotech also molds multi-component LSR parts at its Bolton, Ont., plant in Canada. According to v.p. Isolde Boettger, an example is keypads that contain conductive and non-conductive LSRs of different hardnesses. Silcotech: (905) 857-9998 . www.silcotech.ca

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