Shore 70A Silicone Rubber

Shore 70A Silicone Rubber: The Firm, High-Strength Grade

Shore 70A silicone rubber is the firmest grade in regular commercial use, offering the highest tensile strength (8–12 MPa) and tear resistance (22–35 kN/m) of the standard hardness range. It provides dimensional rigidity under compressive load, making it the grade of choice for structural sealing, cable jacketing, high-pressure gaskets, and applications where the rubber must maintain its cross-sectional shape under sustained mechanical loading.

At Shore 70A, silicone rubber feels similar to a firm automotive tire sidewall — significantly stiffer than mid-range grades but still fully elastomeric and resilient. Elongation at break of 150–300% remains sufficient for installation stretching and dynamic cycling.

Primary Applications

Spark plug boots and ignition components: Shore 70A HTV compounds with high dielectric strength (20–25 kV/mm) are the standard for ignition system boots. The firm hardness resists deformation under the snap-fit retaining force of the spark plug connector and withstands continuous exposure to engine heat up to 200 °C and oil vapor.

Cable jacket extrusion: Shore 70A silicone cable compounds are continuously extruded and vulcanized for industrial, automotive, and military cable jackets. The firm hardness provides abrasion resistance during cable pulling and installation, while the thermal rating (−60 °C to +200 °C continuous) enables use in environments that would degrade PVC or thermoplastic elastomer jacketing.

High-pressure gaskets and seals: For flange gaskets and static face seals operating at pressures above 10 bar, Shore 70A provides the rigidity needed to resist extrusion from the joint under bolt load. Shore 50A or softer grades can extrude and creep at high gasket stresses.

Automotive engine seals: Valve cover gaskets, cam cover seals, and oil pan gaskets exposed to hot engine oil and continuous 200 °C operating temperatures. Shore 70A resists compression creep over the engine service life (typically 150,000–200,000 km / 10+ years).

Industrial rollers: Shore 70A silicone-covered printing and textile rollers provide a balance of hardness for dimensional stability and silicone's inherent release surface properties.

Processing Shore 70A

Shore 70A HTV is processed by compression molding, transfer molding, and extrusion. The higher cross-link density requires slightly higher mold temperatures (165–185 °C) and longer cure times than softer grades to ensure complete vulcanization throughout the section. Post-cure at 200 °C for 4 hours is recommended for peroxide-cured grades to remove residual by-products and achieve final mechanical properties.

Comparison with Shore 50A and Shore 30A

Shore 70A provides higher tensile and tear strength than Shore 50A but reduced elongation, making it more resistant to mechanical damage during handling but less conformable to irregular sealing surfaces. Shore 30A is preferred wherever sealing force must be minimized or soft contact is required; Shore 70A is preferred wherever mechanical load-bearing or extrusion resistance is needed.

Certification and Compliance

Food-contact grades (FDA 21 CFR 177.2600, LFGB): available in platinum-cured, post-cured white and colored variants. Cable compounds typically comply with RoHS and halogen-free flame retardancy requirements. Automotive grades are validated against ASTM D1418, ASTM D2000 M2HH, or OEM-specific material specifications.

Contact us to verify certification documents and request Shore 70A samples for your application.