Tapered roller bearings are widely used in both the main and nose wheel landing gear assemblies for all types of aircraft. On commercial and military aircraft, these bearings experience high radial loads as the aircraft taxis. During landings, the bearings in all of these aircraft are subjected to shock loads combined with very rapid acceleration.
Most bearings are protected from excessive wear and heat by a lubricant film that actually keeps the bearing rollers separated from the races. But under the high loads and speeds of an aircraft landing, that lubricant film is significantly reduced or lost. Metal-to-metal contact can occur, creating high heat and rapid wear. Scuffing and scoring of the bearing often results.
Once scuffed or scored, the operating torque of the bearing will increase and the correct bearing setting will likely be lost. The bearing will begin to run hotter, shortening its life. It may generate enough heat that the bearing components fuse together, and the bearing could seize.
A Timken aerospace customer was experiencing this bearing scuffing and scoring at the point where the end of the roller contacted the rib of the bearing’s inner ring (race). As a result, the customer had to regularly take their planes out of service for bearing replacement.
Scuffing at rib face
Scuffing at large roller end
The customer wanted to avoid the expense and delay involved in changing the design of the existing wheel assembly geometry. In order to keep their planes flying with less landing gear maintenance, they turned to Timken for a solution.
Timken experts reviewed the Engineered Surfaces Toolbox and selected a coating that was applied to the end of each roller. This coating significantly increased the hardness of the roller end. The resulting bearing assembly provided superior resistance to scuffing and scoring. Because the coatings are so thin, there were no changes to the geometry of the landing gear assembly.
Timken has helped many customers identify appropriate Engineered Surfaces solutions. The various Engineered Surfaces treatments can be used individually or in combination to eliminate problems or enhance equipment performance.
Timken coating on large roller ends