I was recently asked this question…
We have been experiencing problems with excessive flash on a new silicone part. We are injecting a liquid silicone into a mold and letting it set. Could you give any insite to what may be causing this problem?
lash is a common issue that must be dealt with in silicone injection molding. The low viscosity of the silicone prior to curing allows it to get out of the smallest spaces of the mold including the parting line, mold vents, and ejector pins. In order to prevent flash in silicone injection molding a few different things can be done to counteract the problem.
First, ensure your shot size is not to large. An excessively large shot size will contribute to flash because the silicone expands as it cures. Unlike traditional injection molding the mold does not usually need to be 95-98% full during first stage fill. Second, check your mold tonnage and ensure both platens are evenly applying the appropriate force. This can be verified with spotting fluid. Also, try increasing the mold temperature or preheat the silicone more prior to injection. This should reduce your curing and cycle times and also increase the silicones viscosity in the mold.