AUSTRIA-based Elmet debuts its new production approach for the processing of liquid silicone rubber (LSR), which cures under UV-light from a LED source, at the K 2013 held in Düsseldorf, Germany.
According to Elmet, this method eliminates the high curing temperatures required for conventional heat-curing LSR grades. Thermoplastics with a low melting point, including polypropylene (PP), polyethylene (PE) or polymethyl methacrylate (PMMA), are suitable for two-component injection moulding with LSR as the soft component, whereas otherwise materials providing higher temperature resistance at higher prices are required, such as polyamide (PA) or polybutylene terephthalate (PBT). Thus, a broad diversity of new applications is opened up in the production of hard/soft composites using LSR as the soft component.
An application example is a soap dish made of translucent polypropylene (PP) which has a directly molded-on silicone support base. For making this item, ELMET had developed a complete production system in cooperation with the machine manufacturer Engel and the raw materials supplier Momentive. This solution was then built on a turnkey basis.
One key element of the system is an innovative injection mould operating in a standard injection moulding machine , such as an e-mac170/50 made by Engel. In this mould, which has steel sealing surfaces on both mould halves, the molding is initially produced from UV-transparent PP. After demolding and relocating this PP part to a higher mold region, the LSR base is then injection-molded onto it. Afterwards, the silicone component is exposed to UV light through the PP article for curing.
The light sources used in this application are rugged LED lamps which are noted for their long service life. Moreover, the activation point and ON time duration of these LEDs can be accurately matched to the curing reaction so as to minimize energy input and cycle time.
The system is equipped with the new air-powered injection unit for the LSR component. Integrated into the machine control system, it provides a very precise, repeatable injection pressure and velocity for exceptional process stability. The space-saving TOP 1000 Mini metering system is another novelty; it delivers an accurately metered amount of LSR into the injection unit. The cross-linking agent and dye are introduced using a standard additives line.