As BRENCO has continued its research into bearing retention, additional areas of the bearing / axle assembly have been identified as requiring attention at the time of bearing installation. Those areas are:
- Mechanical condition of the cap screws
- Mechanical condition of the tapped cap screw holes in the axle
- Axle journal diameter
Cap Screw Condition
Damaged or defective cap screws can reduce the clamp force on the bearing. Mechanical condition of cap screws has received additional emphasis with the revision to Roller Bearing Manual Rule 3.27 to require gaging of all cap screws before return to service. The gaging requirement was effective August 1, 1988, and initial indications from shops using the gage are that large percentages of used cap screws are being rejected. This will probably increase the demand for new cap screws.
As a result of its research into cap screw lubrication, BRENCO discovered that for the same lubricant tested, used cap screws develop lower clamp force than new cap screws in nearly every test pair. Another advantage to new cap screws is that they usually are supplied pre-lubricated by the cap screw manufacturer.
Reductions in bearing clamp force can also be caused by damaged or defective threads in the axle. Incorrectly tapped threads, corrosion, dirt, or metal chips on the threads can cause cap screws to bind on installation and prevent the development of proper bolt tension. We recommend careful inspection of all threaded holes before bearing installation.
AAR research into bearing performance identified undersize axle journals as a common problem area in service. Undersize journals (prohibited by Wheel and Axle Manual Rule 1K4) reduce the interference fit between the journal and the bearing inner ring. The reduced interference fit makes the bearing prone to loose component failure. This appears to be less of a problem where plating of the journal is prevalent, such as the Canadian railroad shops. Journal plating should be considered because of the lower cost compared to new axles.
The best bearing in the world will not last long if installed on a defective axle using defective cap screws or if improper installation procedures are used. In order to assist our customers with proper installation practices, BRENCO has produced a video tape entitled Proper Bearing Mounting Procedures. This tape explains each of the steps required for proper bearing installation and illustrates a number of techniques used to insure proper installation. The tape is available upon request by writing:
BRENCO, Incorporated
Proper Bearing Mounting Procedures
PO Box 389
Petersburg, Virginia 23804
804/732-0202
The Technical Forum is an information resource for the rail industry and is provided as a courtesy of Amsted Rail Group. Suggestions, inquiries or comments are welcomed and should be directed to:
Editor, Technical Forum
BRENCO, Incorporated
P.O. Box 389
Petersburg, Virginia 23804
804-863-1713
Additional copies provided upon request.
BACK TO TECH SHEETS
|
