Interface - The Journal of Wheel/Rail Interaction

SIDE BEARINGS

Vehicle Side Bearings: Function, Performance and Maintenance (Part 2 of 2)
By Gary Wolf • May 04, 2005

Part 1 of this two-part article explored the importance of roller style side bearings in maintaining proper vehicle performance and how improper maintenance of side bearings can directly affect wheel/rail forces.
Part 2 examines the purpose, types of designs and maintenance of the constant contact, or resilient, side bearing.

The use of constant contact side bearings came into prominence in the 1960s to inhibit the tendency of trucks/bogies to hunt at high speeds. The constant contact side bearing (CCSB), which, as the name indicates, is designed with no clearance between the car body and the bearing itself, prevents truck hunting by developing a small amount of turning restraint at the interface of the truck bolster and the car body. During truck hunting, the bolster rotates as the wheelsets move laterally back and forth between the rails. This small rotation occurs rapidly at a frequency between 1 - 3 Hz. Early CCSB designs used a metal spring to provide a small amount of compressive force upward against the side bearing wear plate.

The A. Stucki Co. pioneered the use of elastomeric elements that could be retrofitted in the standard roller cages. The elastomeric blocks functioned much like a rubber spring and provided several thousand pounds of compressive force against the wear plate (see Figure 1). As the truck bolster tried to rotate, or yaw, at high speed, the friction pressure of the elastomeric block against the wear plate resisted rotation or yawing. This inhibited the hunting tendency. The elastomeric blocks were relatively inexpensive and could be easily retrofitted in a standard side bearing cage, thereby increasing the high speed stability of a car without expensive modifications. Figure 2 shows a typical CCSB installation.

More cars were fitted with CCSBs during the 1970s and 1980s. The rise in intermodal traffic and the need for higher speeds was a driving factor. The development of Doublestack cars in the 1980s brought on new challenges. With shared articulated trucks, four side bearings were located on each bolster, instead of two. This increased the turning resistance of the truck during curving, which, under the right conditions, could increase derailment tendency. The situation was aggravated by the fact that one side (male) of the connector tended to wear faster, closing up the setup height faster.

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