Interface - The Journal of Wheel/Rail Interaction

CONSTANT CONTACT SIDE BEARINGS

Making the Case for Long Travel Constant Contact Side Bearings (continued)

An extra 5/16 inches of travel may not seem like much, but the added travel is significant when decoupling the car from track crosslevel differences. As shown in Figure 6, a standard travel CCSB can “go solid” entering and exiting a curve. This causes the car body weight to be transferred to the high side of the rail, resulting in wheel unloading and high lateral over vertical (L/V) loads. Gap style side bearings would produce the same type of wheel unloading and L/Vs, because the travel is essentially the same. In contrast, long travel side bearings provide enough flexibility to not “go solid,” resulting in better wheel load equalization and modest L/Vs.

Over the years, the rail industry has experienced a number of costly derailments due to high-speed stability and car body roll. In 2004, TTCI and a consortium of tank car owners and side bearing manufacturers conducted tests to evaluate the effects of CCSBs on tank car roll. Five side bearings were tested, including the original gap style block design. Vertical wheel loading was significantly improved in the twist and roll section of track at TTCI by using elastomeric long travel CCSBs. This improvement was enough to pass the minimum wheel unloading levels required by Chapter XI because of the long travel and the CCSB vertical damping, which was achieved using designs with elastomeric springs. High-speed stability was confirmed at speeds up to 70 mph. As a result of this testing, the AAR mandated long travel CCSBs on all existing tank cars as of April 2005.

Bill O'Donnell is Manager of Product Engineering for Miner Enterprises, Inc.

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