LOW FRICTION MATERIALS FOR UNLUBRICATED PLAIN BEARINGS IN ULTRA HIGH VACUUM,

Chosen pairs of materials were tested in a bearing assembly comprising a vertical shaft, held by a pair of journal bearings, with its lower, pointed end supported on a flat plate. Tested shafts were of stainless steel, Silver steel, pure iron, molybdenum and tungsten carbide. Bearings and plate were of stainless steel, graphite, graphite and molybdenum disulphide, copper, silver, and tungsten carbide. The bearing assemblies were baked under vacuum for some hours at 400 C, and subsequently tested at room temperature in vacua of the order of 10 to the minus 10th power torr. Only the pure iron shaft and pure silver bearings were satisfactory when so tested. The other pairs showed high friction or seizure, after rotating at about 40 r.p.m. for an hour or less. During the early part of each test, the pressure increased, due to the gas liberated from the rubbing surfaces. After test, each shaft was visually examined for damage to the bearing surfaces. Only the iron shaft in silver bearings was almost unmarked. The pivot and plate contacts appeared generally undamaged. Author