Interface - The Journal of Wheel/Rail Interaction

SIDE BEARINGS

Vehicle Side Bearings: Function, Performance and Maintenance (Part 2 of 2)
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Another problem with certain CCSB designs was abrasion wear on the elastomeric blocks. After considerable service, the CCSB blocks tended to crack and abrade on the top surface. This caused the blocks to be ineffective in preventing truck hunting. As you might expect, the more the trucks hunted, the worse the wear became, and the blocks would quickly deteriorate once they started cracking. Also, operation in cold weather could exacerbate this problem, as the blocks became more brittle in sub-zero weather. When the blocks start cracking, irregular surfaces change the frictional characteristic of the blocks. Figure 5 shows cracks forming in the top surface of an elastomeric block.

After considerable service life, the elastomeric material can take a permanent “set,” resulting in loss of preload on the wear plate, and an attendant loss of hunting restraint. Figure 6. shows a comparison of a new metal-capped side bearing with a service worn side bearing exhibiting a permanent set.

Metal Capped CCSBs
To overcome the wear problem with the elastomeric blocks, and to provide a more consistent frictional force on the top surface, metal-capped CCSBs were introduced in the late 1980s. Both the A. Stucki Co. and Miner Enterprises, Inc., developed CCSB designs using a metal cap on top of elastomeric blocks. Stucki introduced designs with a removable metal cap that could be inserted into special indents in the top of the elastomeric blocks. Miner Enterprises introduced TCC designs using a metal cap that was directly bonded on the top of the TecsPak® elastomeric material. Most of the A. Stucki designs could be retrofitted into conventional roller side bearing cages, whereas the Miner design used a proprietary cage unique to their cap design.

Other metal cap designs were developed including roller assist designs. In the roller assist design, a standard steel roller is placed beside the elastomeric element to assist in curving when excessive preload is developed during car leaning in curves.

Maintenance of Constant Contact Designs
Until several years ago, the AAR interchange rules referred to “the manufacturers’ specifications” when it came to maintenance and inspection of constant contact designs. Now, the new Rule 62 states specific guidelines for the maintenance of constant contact designs. Several important provisions of Rule 62 are:

Wear limits, Gaging and Cause for Renewal or Attention:

• Heat damaged or missing elastomer elements.
• Broken or split elastomer elements if exhibiting two or more vertical cracks each greater than 1/2 inch in length.
• Metal caps worn through wear limit indicators, where such indicators exist.
• Repair is required at anytime where height measured is:
– Less than 4-7/8 inches
– Greater than 5-1/4 inches

The reader should consult AAR Rule 62 for other important inspection, measurement and maintenance provisions for both constant contact and conventional roller designs. In addition, both the A. Stucki Co. and Miner Enterprises have produced handy “pocket guides” for identification and maintenance of their respective designs. It is important to remember that the setup height should be closely maintained to the AAR and manufacturer’s specifications in order to prevent the development of excessive turning moments during vehicle curving. Cars with setup heights below 4-7/8 inches can contribute to derailments due to rail rollover or wheel climb. If elastomer elements are missing, split, broken or cracked, they may not be effective in preventing truck hunting, which could lead to high-speed derailment. Either way, the CCSB setup heights should be inspected and closely monitored to ensure proper vehicle performance and reduce the risk of derailments.

Gary P. Wolf is President of Rail Sciences Inc.

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