Low Friction Seal
Freudenberg-NOK Sealing Technologies Simrit has developed a new friction-optimized seal designed to fit in existing standard sealing grooves. Engineered to provide more consistent sealing performance, the combined elastomer/polytetrafluoroethylene (PTFE) system offers low breakaway force, improved durability and temperature resistance for dry running piston type systems such as air brakes or pneumatics, the company said.
According to Freudenberg-NOK, an elastomeric seal typically requires a continuous oil film to operate at the same friction levels as a PTFE seal and the commonly used elastomeric energized PTFE seal can be difficult to install. In dry running conditions, the coefficient of friction for rubber is normally around 1.5 to 2, but can be optimized to a minimum of approximately 0.4 to 0.5 with special designs and materials, whereas for PTFE it is primarily around 0.1 to 0.2 in its natural state. Samples of Freudenberg-NOK’s dual material seal were tested side-by-side verses the traditional elastomeric D-ring type seal at various pressures for dynamic and break away force. The results showed a reduction of overall friction by two times at zero pressure and three times at 145 psi, the company said.
Freudenberg-NOK Simrit said the dual-material seal provides low initial breakaway torque and friction, as well as high-temperature consistency and a comparable installation to that of an o-ring, including direction independence, twist-safe performance and gap extrusion resistance. The new design also offers increased design freedom, as a variance of geometries and diameters are available to minimize friction differences even when utilizing all production tolerances, the company said. The PTFE layer is bonded to an elastomer, which then can be bonded to a solid carrier if required. Additionally, the seal eliminates stick-slip, the effects of rubber aging, the influence of temperature and the effect of hysteresis, the company said.