The Effect of Sustained Wheel Impacts on Tapered Roller Bearing Cages

Mechanical damage to tapered roller bearings resulting from wheel impacts is a growing concern in the railroad industry. Repeated impacts can cause plastic deformation, wear, and eventually fatigue in roller bearing cages. A servo-hydraulic system was implemented in order to impact a bearing assembly with 65 g peak acceleration impacts at 6 Hz. Three different cage designs were tested for the Class F and K bearings: the standard steel design, and two polyamide cage designs. Testing was conducted on the three cage designs in impact increments of 10², 10³, 10⁴, 10⁵, 10⁶, and 15×10⁶ cycles. Between each testing increment, cages were removed from a special two-piece cone to inspect damage. Mechanical damage in the forms of plastic deformation and wear were measured by means of their area and depth. Results indicated that although high acceleration impacts were inflicted on the bearing; none of the cages developed fatigue fractures in the roller pocket corners consistent with field failures. However, a large amount of hourglass shaped damage in the roller pockets was recorded. Comparing the three designs revealed that although the polyamide cage designs were lower strength, they were more resistant to plastic deformation and wear than the steel cage design.