New 50-Durometer 3A Silicone Resists Flex-Fatigue, Tearing, Low Temperatures
Important: This article contains additional information about SSP's flex-fatigue resistant silicones.
Specialty Silicone Products (SSP) has developed a 50-durometer silicone that meets the full requirements of A-A-59588, Class 3A, Grade 50. The elastomer, SSP-2523-T, combines low-temperature resistance with high tear strength and flex-fatigue resistance. SSP-2523-T is supplied as uncured ready-to-mold compounds, compression-molded sheets, and continuous rolls for gasket fabrication.
A-A-59588, Class 3A and Flex-Fatigue Resistance
The A-A-59588 standard is published by the U.S. General Services Administration (GSA) and contains six alphanumeric classes or sections. Each class specifies multiple material properties, but 3A is one of only two classes with requirements for flex-fatigue resistance. (The other is Class 3B.) Each A-A-59588 class also contains numbered grades (e.g., 50) that correspond to the silicone’s Shore A durometer.
Silicones resist a wide range of service temperatures, but these elastomers don’t always offer strong flex-fatigue resistance – a measure of a material’s ability to withstand repeated flexing or bending. Flex-fatigue resistance is especially important in military and aerospace applications, where harsh environments and excessive temperature cycling can also contribute to elastomeric fatigue.
Silicones that meet the full requirements of A-A-59588, Class 3A must pass the DeMattia Flex Resistance Test, a dynamic test that measures crack growth in inches over thousands of flexural cycles. As the data sheet for SSP-2523-T shows, this elastomer has a typical flex-resistance of 0.35-in. over 10,000 cycles. That’s less than the maximum allowable value of 0.50-in. for crack growth.
Resistance to Tearing and Low Temperatures
SSP-2523-T also meets A-A-59588, Class 3A, Grade 50 requirements for tear resistance or tear strength, a measure of how well a material can resist tearing. As the data sheet for SSP-2523-T shows, this military and aerospace silicone has a typical Tear-B, ppi of 237. That’s well-above the minimum Tear B, ppi of 175 in the GSA’s published specification.
Importantly, SSP-2523-T also resists low temperatures. In the A-A-59588, Class 3A, Grade 50 specification, there are two low-temperature requirements: brittle point at -90° C and torsional stiffness at -75° C. SSP-2523-T passed all five test for low-temperature brittleness and met the maximum requirement (15) for torsional stiffness.