Rail hopper cars, which are typically used to transport goods such as coal, grain and other items by railroad, usually each have eight axle-mounted roller bearings. These bearings are subject to various types and degrees of failure, ranging from normal wear to extensive damage due to metal fatigue. Some companies own as many as several thousand of these railcars, thereby necessitating a reliable preventative maintenance program directed at railcar bearing failure. Early detection of potential bearing failure is essential to an effective preventative maintenance program, the purpose of which is to prevent catastrophic failure of bearings in service. Such a failure could result in a major train derailment with attendant possible injury to operating personnel and major damage to equipment.
The term "acoustic emission" is applied to the "shock pulse" which is emitted by material under stress. In a roller bearing, this pulse is generated when, for example, a crack develops in an inner or outer bearing race. Each time a roller crosses the crack it is stressed and a pulse is generated and transmitted into the adjacent mounting structure.
During the past years, work done in the aerospace industry has produced definite data showing a direct relationship between increased acoustic emissions and the onset of bearing failure. Additional research and development in the bearing industry has shown a relationship between certain types of emitted signals and specific types of bearing failure. Moreover, a direct relationship exists between the decibel level of the acoustic emission and the extent of damage existing within a bearing. By measuring, recording, and plotting these emissions, it is possible to determine the condition of a bearing and its rate of deterioration to predict and avoid catastrophic failures.
The current accepted method of testing roller bearings mounted on railcar axles involves removal of the axle-bearing-wheel assembly from the car. A mechanic then grasps the outer race of the bearing, slowly rotates it by hand, and depends upon his sense of feel to determine if any defects are present within that bearing. Should he "feel" a defect, the bearing is then dismantled, inspected, and repaired or replaced if necessary. Obviously, this method depends solely upon the skill of the individual mechanic and does not provide acceptable records for a reliable preventative maintenance program.
The proposed device of the invention for testing axle-mounted roller bearings utilizes the acoustic emission principles described above and involves the use of an apparatus to rotate the bearing being tested. Such a device has been developed to permit rotation of the bearing for subsequent testing by the acoustic emission principle. Use of the device does not require removal of the bearing from the axle or removal of the axle assembly from the railcar.
Numerous devices pertaining to wheel friction indicators, directed primarily to railcars for determining the condition of the bearings are shown in the known prior art. Some examples of such prior art are disclosed in U.S. Pat. Nos. 3,033,018; 3,111,294; 3,116,044; 3,182,513; and 4,016,020. However, equipment for rotating the bearing of a railcar to conduct acoustic emission tests is not disclosed.
There is no roller bearing testing device for axle-mounted roller bearings of a railcar of which we are aware which rotates the bearing of a railcar for the purpose of conducting acoustic emission tests without requiring movement of the railcar along the rail, removal of the bearing from the axle, or removal of the axle assembly from the railcar to carry out such tests.