An ultrasoft seal cushions delicate components and keeps dust from infiltrating displays in handheld electronics.
Compression force deflection versus Shore hardness
Rogers Corp., Rogers, Conn., reports the hardness characteristics of its Poron family of urethane foams using ASTM D3574. This standard describes procedures for evaluating "Flexible Cellular Materials Slab, Bonded, and Molded Urethane Foams." In this test method hardness is determined by Compression Force Deflection (CFD), Test C.
CFD is an engineering measurement expressed in pounds-force-per-square inch (psi). It is merely the force required to compress a material a fixed percentage. Rogers Corp.'s High Performance Foams Div. has chosen 25% compression to characterize various grades of Poron microcellular urethanes.
CFD measurements are a useful tool for making
material selections and are also available in compression values other than 25%. The conventional Shore hardness measurements provide only relative information. For example, a material with a Shore "A" 5 rating is softer than one with Shore "A" 10 but says nothing about how much compression force is needed to fill a gap or make a tight seal.