Validation Testing of Bearing Temperature Differentials and Identification of Root Causes on Selected Union Pacific Railroad Hot and Warm Trend Set-Outs

This paper is the summary report on work started in 2007, and initially introduced in a presentation at the joint ASME – TTCI Bearing Symposium in Chicago in September of 2007 [1]. The identification of the root cause(s) for “warm bearing trend” temperatures has also been the subject of other technical papers [2, 3]. Traditional railroad journal bearing hot box detector (HBD) systems monitor journal bearing temperatures, and typically provide an alarm based on a measured in-service bearing absolute temperature, or against a programmed “delta” over the ambient temperature level. More recently, bearing operating temperatures have been statistically analyzed for temperature “trending”, and identification of temperature “outliers”, or bearings which display a higher temperature relative to the majority of bearings in the same train. AAR rules now facilitate the removal from service of bearings which either: 1) exceed traditionally defined limits, or 2) meet the statistical criteria set forth by these newly established AAR industry rules, to ideally prevent or eliminate “burn off journals” and potential derailments. This study is focused on testing of railroad journal bearings that were removed from service for “Why Made Code 50” (an “overheated” journal bearing), and exhibited no visually obvious external signs of distress. Dynamic testing and a corresponding tear down investigation to determine the root cause(s) for the elevated temperature was performed for the trend and mate bearings. This dynamic rig testing and corresponding investigation(s) have resulted in the determination of a significant and potential root cause for warm trend bearings.