Small oil-free bearings

An investigation was made of materials that may be suitable for usc as oil-free bearings in aircraft clocks and similar instruments between -55 0 and +70 0 C, to replace l ubricated j ewcls that do not give satisfactory operation at subzero temperatures because of congealing of the oil. Another advantage of an oil-free instrument is the freedom from cleaning and oiling p eriodically during shelf storage. Materials included in the investigation were plastics, plastics with fillers, impregnated metals, and impregnated carbon. Friction tests were mad' with an inclined-plane type of static-friction apparatus, and with shafts rotating in loaded journal bearings, at temperatures from -55 0 to + 70 0 C. With bearings of typical makrials stored on steel shafts, the effect of shelf storage on static friction was investigated. Wear tests were made with loaded bearings on X-in ch-diameter rotating sbafts made of different types of steel. With oscillating )/g-ineh-dia meter shafts and I ,OOO-gram loads, wear data were obtained on bearings of the more promising materials. Using an endstone wear testing machine, wear data were obtained for end-tlu'ust bearings made of t.ypical bearing materials. The p erfor mance of oil-free bearings in 18 timepieces was investigated.