Temperature Profiles of Railroad Tapered Roller Bearings With Defective Inner and Outer Rings

In the railroad industry, monitoring the condition of key components such as bearings and wheels is vital to ensure the safe transport of goods and commodities. Bearing seizures are amongst the most dangerous types of failures experienced by trains because they occur unexpectedly and may lead to costly derailments. Current bearing health monitoring techniques include tracking the temperature and acoustic emissions given by the bearings. Although temperature histories of railroad tapered roller bearings are readily available, the literature does not provide information relating the temperature profiles to the severity of the bearing defect. The study presented here investigates the correlation between temperature profiles and bearing defect severity measured by the size of spalls present on bearing outer (cup) and inner (cone) rings. The temperature data used for this study was acquired from defective and healthy bearings that were run at various operating load and speed conditions. The data presented here provides the railroad industry with a greater understanding of the thermal behavior of defective bearings, which can be used to assess the future needs of bearing condition monitoring systems. INTRODUCTION AND BACKGROUND Conventional bearing health monitoring systems rely on the bearing outer ring (cup) temperature emissions detected by wayside infrared devices known as hot-box detectors (HBDs). HBDs take a snapshot of the bearing temperature at designated wayside detection sites which, depending on the track, may be spaced as far apart as 65 km (~40 mi). If a bearing is found to be operating at temperatures greater than 94.4°C (170°F) above ambient conditions, the HBD will trigger an alarm and the suspect bearing will be removed from service for later disassembly and inspection. An extension of this practice is the tracking of bearing temperatures and comparing each bearing temperature to the average temperature of all the bearings on the same side of the train. Bearings running at temperatures higher than the average, as detected by multiple HBDs, are said to be “warm trending” and are flagged without the HBD being triggered [1]. Bearings that are identified in this manner are removed from service for later disassembly and inspection. In most cases, the cause of bearing overheating may be attributed to one of several modes of bearing failure such as spalling, water contamination, loose bearings, broken components, damaged seals, incorrect mounting procedures, etc. However, there have been several documented cases where the bearings removed do not exhibit evidence of any of the common causes of bearing failure. These latter bearings are classified as “non-verified” bearings. According to data collected by Amsted Rail from 2001 to 2007, an average of nearly 40% of bearing removals are non-verified. This figure approached 60% in 2003 and 2004, and never dropped below 24% during the period from 2001 to 2007. In other words, a considerable percentage of bearings pulled from service based on HBD readings have no discernable defects. Researchers have placed special emphasis on this warm trending phenomenon because it leads to unnecessary and