In 1962, retail earplug manufacturer McKeon Products, Inc., invented the silicone earplug. Since that time, the company has designed a full range of moldable and pre-molded silicone earplugs for a variety of uses, including for swimming and hearing protection. Its newest earplug, however, presented some manufacturing challenges, so the company turned to Silcotech North America, Inc., a liquid-silicone parts molder, to lead the production.

The Liquid Injection Molding System (LIMS) KE2004-20 silicone product was recently integrated into the production of a next-generation earplug for swimming and hearing protection. The Series’ low durometer (22 Shore A) and low-modulus produced a soft, flexible feel, and its high tear strength (207 ppi) significantly reduced scrap and cycle time.

The product had a thin wall section that needed higher tear strength to withstand the de-molding process.  After prototyping five different molds, the engineering team chose an automatic 16-cavity slide tool with 0.25 mil wall sections for sealing flanges and 5.0 mil wall sections for handle areas.

The part’s geometry and cavity had significant undercuts, so the loads on the material were high during part removal. Parts would break and remain in the cavity. In addition, silicone plating on surfaces required operators to remove the tool from the press for cleaning every two weeks for 6 to 8 hours. Lastly, the tool had to cool down and heat up between production runs.

Redesigning the tool to eliminate the undercut would have cost the company from $70 to 100K, so Silcotech sought out a superior material with sufficient mechanical strength properties to handle the part.

Redesigning the tool to eliminate the undercut was too costly, so Silcotech opted to select a different material that had sufficient mechanical strength to handle the part. To reduce cycle time, Shin-Etsu Silicones of America, Inc., tested its 20 durometer KE2004-20 silicone Liquid Injection Molding System (LIMS) product. The Series’ low durometer (22 Shore A) and low-modulus produced a soft, flexible feel. Its high strength (207 ppi) and release properties eased de-molding – particularly those with thin wall thicknesses – without tearing or generating scrap. In addition to its low hardness and high tear strength, the material’s high viscosity improved handling and flash.

Shin-Etsu sent Silcotech sample test pails to run with the tool, and Silcotech conducted three to four tests. KE2004-20 reduced cycle time by 60%. The number of scrap parts during de-molding was reduced and the same soft feel was maintained. Less plating-out of silicone meant less frequent cleaning. What’s more, the change to the new material was easy because there were no changes to processing parameters.