Liquid Silicone Rubber Becomes Solution for Challenging Molded Valve

By: Angel Kinsey, Engineering Services

Dymotek is a custom manufacturing company that specializes in injection molding of thermoplastic and liquid silicone rubber materials (LSR).  We are often challenged by a customer that has an application where a flexible material is required.  Our experience in working with thermoplastic elastomers (TPE), rubbers (TPR), and urethanes (TPU) as well as liquid silicone rubber (LSR) makes us uniquely qualified to guide the customer to a material that best fits their application.

We were recently challenged with a drinking valve application that was attempted to be manufactured by another molder.  The valve needed to meet the design requirements for flexibility and fit and seal with a mating polypropylene cap. TPE was the material selected by the customer. Many grades were tried but the end results were not favorable. A molded part that met the design criteria and was free of defects was unachievable with a TPE.  The customer brought the application to Dymotek.

Dymotek’s team of engineers was able to quickly see that a TPE material was not the correct material for the application.  A new prototype mold was built for liquid silicone rubber and two grades supplied by Wacker were trialed to find the optimized molded part fit and seal. A Wacker Elastosil LR 3003/60 A/B, 60A durometer material, proved to have the ideal processing characteristics to produce a stress free molded product that consistently met the requirements for flexibility, fit and seal. The flow characteristics of the LSR material provided the solution to address the processing challenges for the molded valve.

The lesson learned here is the application must be carefully considered before selecting a material.  In general, if a TPE can be utilized it will be less expensive (both in resin and finished piece cost) and require a shorter mold manufacturing lead time.  LSR’s raw material tends to be a little more expensive and there are fewer mold manufacturers with the knowledge and capability of manufacturing molds.  Compression set, sensitivity to molded-in stress, variable wall thickness, and very thin wall sections are all strong indicators that an application may be best suited to LSR.



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