Constant contact side bearing set-up height adjustment and the need for level track

Abstract

This paper is intended to start an industry discussion on the need for a level track requirement during the installation and adjustment of constant contact side bearings (CCSBs). CCSBs provide critical benefits to railcar performance in the form higher operating speeds and improved negotiation of track irregularities. However, if CCSBs are not installed correctly, these performance improvements can be marginalized, maintenance costs can be increased, or in the worst-case scenario, can lead to safety issues. A constant contact side bearing is mounted to the truck bolster and is by definition always in contact with the car body in the form of a compressed spring. However, this compressed spring does not "hold the car up", or in other words, support 100 percent of the car body weight. In fact, pursuant to the AAR side bearing specification M-948, CCSBs can support no more than 85 percent of the car body weight in a light car condition. Obviously, this support is at a much lower percentage when the car is in a loaded condition. The vertical height at which side bearings are installed is one of the most important installation details. This vertical height or set-up height determines how much spring force is exerted against the underside of the car body and how much the side bearing can be compressed before solid stops limit travel. If the set-up height is adjusted on track with a significant cross level difference, resulting CCSB characteristics, namely spring force and travel, can be significantly different from intended. Constant contact side bearing set-up heights need to be adjusted on level track, which is defined and justified in this paper.