Interface - The Journal of Wheel/Rail Interaction

CONSTANT CONTACT SIDE BEARINGS

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

One conclusion of this testing was that metal capped side bearings provided superior performance by increasing operating speeds with a higher and more consistent level of friction at the CCSB/car body interface. More importantly, the AAR concluded that in many cases the long travel CCSBs actually improved curve negotiation, from a wheel load equalization and L/V standpoint, despite the modest increase in truck turning resistance. In addition, long travel side bearings improved car negotiation of track irregularities such as those found in the dynamic curving requirement of Chapter XI. As a result of this testing, the AAR modified the CCSB mandate to require long travel metal capped CCSBs, effective January 1, 2003. The AAR also expanded the mandate to include certain classes of rebuilt and reclassified cars.

What are long travel side bearings? Normal gap style side bearings allow approximately 1/4 inch of travel at the side bearing when the car body rolls and the side bearing is at its nominal set-up height. As seen in Figure 4, standard travel CCSBs allow 1/4 - 5/16 inches of travel at the side bearing before the car body roll is limited by solid stops. Very simply, long travel CCSBs allow 5/8 inches, or twice as much travel.

Miner Enterprises, Inc., developed the first long travel side bearing, the TCC-II series, in 1991, in response to an industry need for a CCSB that was more forgiving, from set-up standpoint, on articulated intermodal cars. Articulated connectors have multiple surfaces that wear and can cause the male side of the connector to drop in relationship to the female side. This reduction in height is transferred to the side bearings on the male side of the connector, as seen figure 5. Through testing at TTCI, TTX concluded that this extra travel not only provided more flexibility with set-up height, it also improved negotiation of entry and exit spirals. Subsequently, TTX experimented with the long travel at other locations on articulated cars and found improvements there as well. TTX then incorporated long travel in stand-alone intermodal and autorack cars. Since that point, long travel benefits have been realized in almost every car type.

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