Ball Bearings Equipped for In Situ Lubrication on Demand

Tag : bearing ball

In situ systems that provide fresh lubricants to ball/race contactson demand have been developed to prolong the operational lives ofball bearings. These systems were originally intended to beincorporated into ball bearings in mechanisms that are required tooperate in outer space for years, in conditions in which lubricantstend to deteriorate and/or evaporate. These systems may also beuseful for similarly prolonging bearing lifetimes on Earth.
Reservoirs have been among the means used previously to resupplylubricants. Lubricant-resupply reservoirs are bulky and addcomplexity to bearing assemblies. In addition, such a reservoircannot be turned on or off as needed: it supplies lubricantcontinuously, often leading to an excess of lubricant in thebearing. A lubricator of the present type includes a porous ringcartridge attached to the inner or the outer ring of a ball bearing(see Figure 1). Oil is stored in the porous cartridge and isreleased by heating the cartridge: Because the thermal expansion ofthe oil exceeds that of the cartridge, heating causes the ejectionof some oil. A metal film can be deposited on a face of thecartridge to serve as an electrical-resistance heater. The heatercan be activated in response to a measured increase in torque thatsignals depletion of oil from the bearing/race contacts.
Because the oil has low surface tension and readily wets thebearing-ring material, it spreads over the bearing ring andeventually reaches the ball/race contacts. The Marangoni effect (asurface-tension gradient associated with a temperature gradient) isutilized to enhance the desired transfer of lubricant to theball/race contacts during heating.
For a test, a ball bearing designed for use at low speed wasassembled without lubricant and equipped with a porous ringlubricator, the resistance heater of which consumed a power of lessthan 1 W when triggered on by a torque-measuring device. In thetest, a load of 20 lb (≈89 N) was applied and the bearing wasturned at a rate of 200 RPM. The lubricator control was turned onat the beginning of the test, turned off for about 800 seconds,then turned on again. As shown in Figure 2, the controlledlubricator stabilized the torque in a low range, startingimmediately after initial turn-on and immediately after resumptionof the lubricator control.
This work was done by Mario Marchetti of National Research Council;William R. Jones, Jr., and Stephen V. Pepper of Glenn ResearchCenter; Mark Jansen of Sest, Inc.; and Roamer Predmore of GoddardSpace Flight Center.