BEARINGS AND LUBRICANTS FOR AIRCRAFT TURBINE ENGINES 550014
The paper describes the bearing and lubricant problems inherent in aircraft turbine engines; these problems are severe because of the occurrence of high rotative speeds and an extremely broad temperature range (including high temperatures as one end of the range). It is indicated that the materials currently used in rolling contact bearings for turbine engines are temperature limited to such an extent that completely new materials are now under consideration. Some data are presented which show acceptable friction and wear properties of some materials for rolling contact bearings and their cages (separators, retainers) at high speeds and at high temperatures. For liquid-lubricated-bearings, considerable improvement in the limiting speeds of rolling contact bearings appears possible with proper cage and bearing design. The design principle involves providing easy flow paths for the lubricant through the bearing.
The broad temperature range also imposes a temperature limitation problem on the lubricants. Synthetic lubricants have a considerably higher limiting temperature than the petroleums. For the higher temperatures, solid or gaseous lubricants are under consideration because of better thermal stability. Solids, such as MoS2 and graphite have been effective in lubrication of rolling contact bearings at high temperatures (500° to 1000° F). Similarly gases have been used as lubricants at high temperatures. Preliminary studies of the externally pressurized air bearing at 1000° F showed that a nonrotating bearing supported loads in a stable manner at this temperature.
The data and discussions of the paper show that there are bearing and lubricant materials which show promise for use at the high speeds and high temperatures of aircraft turbine engines. Considerable research is required, however, in laboratory apparatus, in full scale equipment under simulated conditions and in turbine engines.