Compression Molding Compounds

Compression molding compounds are available to support a broad range of applications for molded rubber gaskets, cushioning pads and custom rubber components. Stockwell Elastomerics compression molds small to mid-range production requirements on-site at its Philadelphia facility to service requirements for high performance silicone and fluorosilicone gaskets, along with specialty applications in the technology sectors. The compression molding materials are mixed off-site to maintain the cleanliness of the molding facility and stored cold to extend the shelf life of the catalyzed compound.

Silicone rubber compounds are inventoried from 25 to 80 durometer Shore A. These are gum base silicones, also called high consistency rubber compounds, in contrast to the 2-part liquid silicone rubber compounds that support the liquid injection molding processes. Most of these gum silicone compounds are methyl vinyl based, which can be formulated for high elongation, flex, tensile and tear properties for mechanically demanding applications and withstand temperatures from -100°F to 500°F. Phenyl based silicones are intended for very low temperatures, down to -130°F that can be required in rubber gaskets for laboratory instrumentation and aerospace applications. Gum based silicones for compression molding can be formulated to meet a number of industrial and military specifications such as ZZ-R-765 and AA-59988.

Fluorosilicone rubber compounds are primarily chosen because of their ability to resist fuels and chemicals and function over the broad temperature range that silicones typically exhibit. Stockwell Elastomerics inventories the 40 and 60 durometer Shore A compounds that are certified to Mil-R-25988 (Mil-DTL-25988). Other 40, 50, 60 and 70 durometer fluorosilicone compounds meeting AMS and commercial specifications are also available. Stockwell Elastomerics frequently molds fluorosilicone into 12″ x 12″ sheets from .062″ to .500″ thick for customers requiring only a few square feet of material to support fast turn / low volume gasket requirements.

Specialty Silicone Compounds / Compression Molding Materials

Electrically conductive compounds such as electrically conductive nickel-graphite filled silicone, silver plated aluminum filled silicone and carbon filled conductive silicone are used in the compression molding of EMI shielding gaskets and components to promote ESD protection. The nickel-graphite filled compounds are specified most frequently as the shielding effectiveness values exceed 100 dB over a broad frequency range and has excellent value for its relative cost. Nickel-graphite filled silicones are available in 30, 40, 55, and 65 durometers and nickel-graphite filled fluorosilicone is available in 60 durometer. Stockwell Elastomerics can help customers select the compound that best suits specifications.

Thermally conductive silicone compounds are available for molded thermal interface pads used in electronics and thermally conductive gaskets used in medical sterilization and heat sealing. These compounds generally have a higher density due to the additional of special fillers required to enhance thermal conductivity. The available durometers are rather firm; 60, 70 and 80 Shore A.

Platinum cure silicone compounds, also referred to as addition cure silicones, are formulated for high strength and purity. The purity or “clean” is the primary selling point for these compounds, hence they are most frequently used in the medical and food industries. The platinum cure silicones also tend to exhibit high tear strength properties.

Viton™ fluoroelastomer rubber compression molding compounds are readily available if your application is best served by these chemically inert materials. Stockwell Elastomerics has 65 durometer Viton™ A, and 70 and 80 durometer fluoroelastomer compounds for seals in analytical instrumentation and similar technology equipment where chemical contact is anticipated.

Silicone compounding resources: Stockwell Elastomerics is pleased to be associated with Specialty Silicone Products as a strategic vendor partner for many compression molding compounds. Along with the materials, Stockwell Elastomerics receives certifications of analysis that include most physical properties to ensure that customers receive a high quality molded component.

Why only silicone, fluorosilicone and fluoroelastomers? Stockwell Elastomerics invested heavily to support on-site liquid injection molding of silicone rubber over the past few years. The organic rubber compounds such as EPDM, Buna-N (Nitrile), neoprene and natural rubber no longer serve customers’ needs. Stockwell Elastomerics would be glad to provide referrals for those seeking a viable source for molded organic elastomerics.

Special rubber sheets: Stockwell Elastomerics frequently receives requests for compression molded sheets in non-standard gauges to support rapid prototype development for aerospace equipment, instrumentation and medical equipment. 12″ x 12″ and 14″ x 14″ sheet molds are available to serve these needs. Silicones and fluorosilicones can be compression molded into sheets from .062″ thick through .500″ thick. Finished gaskets can then be water jet cut or die cut from the sheets.

Viton™ is a trademark of The Chemours Company FC, LLC.