Machine Design

Bearing Lubed With Solid Thrives Where Standard Designs Fail

The dark line around the inner race of the spherical plain bearing from Tribology Systems Inc., is its solid lubricant. Some bearings of this design have a 20-year projected life without relubing.

A patented cage design and self-contained lubricant film lasts longer than traditional lubricants in bearings of all kinds. These improved bearings were first developed for solid-lubricated hybrid-ceramic bearings in gas-turbine engines. Conventional drybearing designs had been tried there without success. The cage in them suffered the most damage at high speeds using dry solid lubricants.

One key to the new bearing's success is a cage design called Aerofloat. The developer says it creates little interference with ball or roller motion. The geometry of the guide-land surfaces in the cage is optimized to generate hydrodynamic lubricant films that reduce friction to low levels. Also, increasing pocket clearances in the orbiting direction avoids most rolling-element contact with the pocket surfaces, thereby reducing cage-pocket contact forces an order of magnitude lower than standard cage designs.

The improved cage subjects lubricant films at the load-carrying contacts in the bearing to less severe microskidding than in standard bearings. Research shows this skidding is the primary source of lubricant failure and reduced bearing life.

Long-term endurance tests run with the improved bearing design project service life to over 20 years. For the application, a test machine simulated operating conditions of the bearing in service and reproduced conditions that failed existing designs. Test results demonstrating seizure-free operation at several times higher load and speed than in the actual application.

The same lubrication concepts combined with a lubricant-film replenishing device, called Ringlube, have produced a specialty spherical plain bearing. It's targeted at high-speed vehicles and fits the same envelope as industry-standard designs. Unlike conventional bearings, it does not require regreasing in service and has an estimated life of 20 years.

Solid-lubricated Ringlube hybrid-ceramic ball bearings have also been used in high-vacuum applications tolerating high speed and high-impact loads. Another is for an aircraft-engine valve. It works at 700°F under high thrust load. Bearings for this application used solid-lube Aerofloat cages, tool-steel rings, and ceramic balls.

This information supplied by Tribology Systems Inc., Warminster, Pa.

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