Small oil-free bearings

Abstract

An investigation was made of materials that may be suitable for use as oil-free bearings in aircraft clocks and similar instruments between —55° and +70° C, to replace lubricated jewels 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 periodically during shelf storage. Materials included in the investigation were plastics, plastics with fillers, impregnated metals, and impregnated carbon. Friction tests were made with an inclined-plane type of static-friction apparatus, and with shafts rotating in loaded journal bearings, at temperatures from —55° to +70° C. With bearings of typical materials stored on steel shafts, the effect of shelf storage on static friction was investigated. Wear tests were made with loaded bearings on %-inch-diameter rotating shafts made of different types of steel. With oscillating ^-inch-diameter shafts and 1,000-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-thrust bearings made of typical bearing materials. The performance of oil-free bearings in 18 timepieces was investigated.