Effect of Air Release Agents on Performance Results of Fabric Lined Bushings

A configuration of a plain (sliding) bearing system is the use of a reinforced fabric comprising a woven structure of polytetrafluoroethylene (PTFE) and other fibers integrated with a phenolic resin system used to both encapsulate the fibrous materials and provide adhesion to metallic and other substrates. This construction promotes dimensional stability and improves thermal conductivity. These PTFE linings offer exceptionally low coefficient friction. The bushing is recommended for high loads when combined with low surface speeds. These fully self-lubricating bushings offer good contamination resistance, no stick-slip and excellent cold flow resistance. This technique has shown longer life of 7 to 10 times that of standard steel-backed, bronze-sintered and PTFE overlay. Proprietary self-lubricating PTFE fibers are applied directly to the steel. This polytetrafluoroethylene is woven onsite and applied directly to the steel. The woven liner is compressible and able to absorb distortions in mating surfaces. PTFE fabrics processed with phenolic resins can entrap air within the cured fabric liner. The entrapped air has the potential to affect bearing performance by reduction of bonding area and reduction in load carrying capabilities. Air release agents can be used to limit the amount of air entrapment within the liner system.

The intent of this research is to determine what, if any, affect the addition of commercially available air release agents would have on PTFE bearing performance. Experimental wear testing at various static and dynamic bearing conditions with and without contamination (de-ice fluid), including at high temperature (325ºF) were conducted on eighteen specimens. Peel strength test were also conducted. All these tests were conducted based on prevalent industry standards.   

Parameters of static load resistance (deflection and permanent set) and loaded torque were found to be unaffected by the use of an air release agent when compared to baseline articles manufactured without such air releasing agents. Results showed that by integration of a commercially available air release agent into the processing of a PTFE based, phenolic resin bearing liner system, one can reduce variability and help stabilize wear performance. Specimens prepared with air release agent showed improved oscillation (fatigue) test results. Further, air release agent also resulted in a 35% increase in peel strength performance when tested per industry standard methods. Contamination with de-ice fluid showed no negative performance results. While the investigations here used only one ratio of additive among all tested bearings, but other concentrations are possible. Authors would like to pursue additional studies in near future to determine the amount of air release agent that can reliably be added to remove the maximum air release without affecting the overall bearing performance. By finding this a threshold of additive will also be determined.