Focus on Bearings: New life for old anti-friction bearings
The concept of remanufacturing anti-friction bearings has been known for many years, and when they are processed correctly, the procedure provides additional service life for many bearings.Bearing lif...
June 1, 2002 | By Dave P. Jones, Sr., & Stuart A. Hansen
The concept of remanufacturing anti-friction bearings has been known for many years, and when they are processed correctly, the procedure provides additional service life for many bearings.
Bearing life is expressed as the number of revolutions, or the number of hours at a given speed and load, at which the bearing will operate before any evidence of fatigue develops on the contacting surfaces. Very few bearings reach their intended life due to several factors, including lubrication, contamination, excessive heat, corrosion, misalignment, and improper mounting.
Under load, bearing races and rolling-element surfaces experience deformation and high stress at the point of contact. This condition is dynamic as the bearing rotates and causes the raceways and rolling elements to flex, resulting in fatigue.
In 1987, a study was performed for the National Aeronautics and Space Administration (NASA) in Cleveland, OH by E.V. Zaretsky, titled Effects of Surface Removal on Rolling Element Fatigue, which indicated the stock removal should not be less than 0.05 mm (0.002 in.) with the surface finish maintained to its original specifications. When the fatigued material was removed, the service life of the reground bearing was equal to a new bearing. In no case did a test bearing experience failure attributable to the restoration process.
Since the remanufacturing process is highly technical, the bearing must be closely inspected and evaluated for damage. This will assure the bearing is a candidate for remanufacturing, and will allow it to perform the same as a new bearing.
Anti-friction bearings are designed to support radial loads, thrust loads, or combination loads; all of these types can be remanufactured. The types are designated as tapered roller bearings, cylindrical roller bearings, spherical roller bearings, ball radial bearings, cylindrical roller thrust bearings, tapered roller thrust bearings, and ball thrust bearings.
The remanufacturing process requires the removal of fatigued material from all contacting surfaces, and the calculation of new internal geometry to provide the proper relationship of the new ground surfaces. When raceways are ground, new oversized rollers are required to return the bearing to its original internal clearance. When a bearing race is damaged to the degree that it is not useable, a replacement of that component in conjunction with grinding of the other contacting surface will provide a restored bearing. This process results in a new bearing that will equal the original service life under the same operating conditions.
To provide this type of restoration or remanufacturing process requires a facility and highly trained personnel with the capability to produce new bearings. Removing this fatigued material and the calculation of new internal geometry is only part of the remanufacturing process. It begins with the initial inspection, which includes visual and dimensional gauging for damage.
A report of the findings will sent to the remanufacturer’s engineering department for evaluation and determination of the scope of work required. After the bearing has been remanufactured, it is important to record all the dimensions of the internal geometry to assure that the proper conformity has been established. The bearing is then carefully preserved, wrapped, and boxed to provide for long- term storage.
The life of a remanufactured bearing is equal to a new bearing when operating under the same conditions. The savings are outstanding since the original bearing provides the raw material, the machining, and the heat treatment of the parts used. In addition, the remanufacturing process can greatly reduce delivery time.
Dave P. Jones, Sr., is president, and Stuart A. Hansen is chief executive officer of Rotation Products Corporation, which has the facility and personnel to restore and remanufacture bearings. Rotation is represented in Canada by Cooper-Grainger Canada Inc., Mississauga, Ont. For more information, use the reply number below.