Today, cold runner technology is the standard in silicone processing. Liquid silicone rubber solidifies at temperatures of 170° C to 200° C and, once cross-linked, cannot be melted down and reused. In conventional injection molding, the molten material is injected through a runner into the heated mold containing the product’s negative mold. As the runner lies directly against the mold, it reaches temperatures at which the silicone, which is still in the sprue at the end of the injection process, also begins to cross-link. In the process, a large amount of material has to be scrapped. Using cold runner technology, the cooled injection runner is separated from the mold by an insulating plate to avoid the loss of unused material. This prevents premature cross-linking of the silicone and considerably reduces scrap.
The valve gate makes additional significant material savings possible: After the elastomer has been injected through the runner into the mold, a valve closes the nozzle interrupting the material flow directly at the product. So there are no annoying sprue marks that need to be removed in further processing steps. This not only saves time, but also additional energy resources.