Dynamic tests on PTFE sliding layers under earthquake conditions

Abstract

The first part of a programme to assess the characteristics of PTFE sliding bearings during earthquake motions is described. Tests were performed on pure PTFE elements sliding on stainless steel. Representative normal loads were applied together with a sliding action, giving a maximum acceleration of 0.2 g and a maximum velocity of 38 cm/sec, i.e. motions equivalent to a moderate to severe earthquake. At 0°C friction was found to have maximum coefficients which fell from 17 to 13% as the normal pressure was increased from 15 to 25 MN/m2. At 20°C corresponding values were reduced to 15 and 10%. Maximum friction generally occurred in the first cycle of loading after which values fell. After 5 cycles the range was typically 9 to 5%. Tests on lubricated PTFE layers showed coefficients of friction less than 2% under the above test conditions; the maintenance of this low value over the years would depend on the effective retention of the grease. It is possible that, by careful design of bearings for higher pressures, and utilizing filled PTFE materials, lower overall friction values for the dry condition may be achieved.