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close up liquid silicone molding Moldmaker explores new lsr Molding technologies can liquid silicone rubber (lsr) be overmolded onto polypropylene? is there a cleaner and more reliable way to heat lsr injection molds? Affrmative answers to both questions were revealed by Roembke Mfg. & Design, Inc., Ossian, Ind., at a recent open house to celebrate its 35th anniversary and to showcase its capabilities as a leading LSR moldmaker. The company (roembke.com), led by founder and CEO John Roembke and president Greg Roembke, demonstrated its pursuit of innovation with two new projects: 1) overmolding LSR onto PP; and 2) molding with pressurized hot water instead of oil or electric cartridge heaters. The event also included a technical presentation by Engel Machinery North America, York, Pa., on extending its novel "Xmelt" expansion molding process from thermoplastics to LSR. Roembke helped Engel document the tighter shot-to-shot consistency of this process on an Engel press in Roembke's shop equipped with X-melt software—data that were presented in a feature article in last month's issue of Plastics Technology. Roembke supports LSR tooling and process R&D; with its unusually large (for a moldmaker) stable of LSR injection presses: fve of its own (30 to 200 tons) from Engel (engelglobal.com/ na) and Arburg Inc., Newington, Conn. (arburg.com); as well as two on temporary consignment—a Sodick Plustech two-stage screw/plunger V-line machine from Plustech Inc., Schumburg, Ill. (plustech-inc.com); and an all-electric Fanuc Robotshot from Milacron Inc., Batavia, Ohio (milacron.com). OVERMOLDING LSR ONTO PP Up to now, LSR has been overmolded mainly onto engineering thermoplastics like nylon and PBT, which can withstand the 300-400 F mold temperatures required to cure LSR. Although new LSR materials have been developed to cure at low temperature with UV light, Roembke and its development partners demonstrated that it can be done with conventional heat curing as well. PP water vial is molded in a two-shot Engel victory combi press in a prototype mold at Roembke. PP is injected in the right-hand cavity and then transferred by a robot to the left-hand cavity where the LSR plug is overmolded into the bottom center of the vial. PP vial from Endetec is used for sampling water quality. Overmolded LSR plug (circular insert at center of the vial's base) is a critical element for UV optical detection of bacterial growth after incubation. Overmolding LSR onto PP is a rare feat because of the 340 F cure temperature of the LSR, above the 245 F HDT of the PP. Water-soluble packet of bacterial growth medium (lower right) is inserted into the vial by a six-axis robot. Plastics technology february 2013 11