The ever-changing field of regulations and findings with food related materials results in the change of food product design. To provide safe, reliable products, many producers seek options that will follow future FDA regulation and provide a cost effective solution. New processes, such as two shot molding with liquid silicone rubber and other substrates, provide solutions that were unseen even a couple years before.
To follow the new BPA-free regulation put forward, a new material was selected, but it did not provide the structural integrity required for normal use. A new seal was designed to fix the structural flaw and provided proper sealing. With the need for both structural support and a proper sealing surface, two materials had to be determined that not only were BPA-free but that also bonded well together.
After material research, a true two shot component of PBT (polybutylene terephthalate) and LSR (liquid silicone rubber) was designed. Following FDA regulations, both materials are BPA-free and pass other required tests.
The support needed by the product would be provided by an inlayed PBT ring. Tight tolerances are needed to ensure that deformation is not an issue, since the component supports a connection in its application. By carefully managing the mold flow through multiple gate locations, a uniform part that meets the narrow tolerances is produced. The part is produced with a tolerance of plus or minus 0.06 mm on an inner diameter of 45.80 mm. For the 49.60 mm outer diameter, a tolerance of plus or minus 0.1 mm was achieved.
The LSR was over molded onto the part to form the seal needed. For the actual over molding, a true two shot rotation mold was selected for the many benefits it would provide to the finished product. A benefit of the rotating mold is that the part is never removed for the core. Without the part being transferred from one core to the next, there is no chance of damage due to misalignment when the part is reinserted. Since the part is never removed from the core, a longer cooling time is possible, which allows the tolerances to be held so tightly.