Brent M. Wilson

A Metallurgical and Experimental Investigation Into Sources of Warm Bearing Trending

In the railroad industry, bearing hot-box detectors are the primary tools utilized for the removal of distressed bearings from service. Current technology has expanded the role of these detectors to monitor bearings that appear to “warm trend” relative to the average temperatures of the remainder of bearings on the train. Several bearings set-out for trending and classified as non-verified revealed that a common feature was discoloration of rollers within a cone assembly. A number of laboratory tests were performed to determine a minimum temperature and environment needed to reproduce these discolorations. In addition, a metallurgical examination concluded that microhardness profiles from discolored rollers exhibited evidence of heating, which lead to softening of the case microstructure, and a reduction in case depth. In order to determine a cause for the internal heat leading to the discoloration of rollers, selected laboratory experiments were carried out in a simulated service environment. Testing focused on exploring certain defects or hypothetical scenarios that may raise the bearing cup temperature above that of normal operating conditions. None of the examined cases resulted in similar roller discolorations to those observed in the trended set-outs. The studies presented in this paper comprise the initial work aimed at determining the root cause of warm bearing trending that some tapered roller bearings experience during service.Copyright

Near-Race Ultrasonic Inspection of Tapered Roller Bearing Components for Non-Metallic Defects

Bearing steel cleanliness is directly linked to failures caused by the interaction of subsurface defects and rolling contact fatigue (RCF). Optical analysis of as-received steel coupled with ultrasonic inspection on finished components minimizes the occurrence of defects in the near race. While useful as a preventative measure, these methods do not ensure that critical areas of components subjected to RCF are free of defects that act as stress concentrators and contribute to premature failure. This presentation provides a brief summary of the current technology and standards utilized in the industry. The deficiencies of the current methods for the particular case at hand are identified and a surface wave scanning method is introduced. The development and production of reference parts for this type of scanning are then discussed. The production method entails both traditional electro-discharge machining (EDM) and femtosecond laser machining (FLM) on finished bearing components such that the reference part microstructure resembles that of a finished part. Experimental results utilizing surface wave scanning are given for two types of assembly-ready bearing components that are then subjected to realistic service loads and mileage to the point of failure. The results of the service life simulations are then correlated with surface wave scanning results and are shown to be in good agreement. This work is anticipated to impact any field in which components are subjected to RCF.Copyright

Implementation of wireless temperature sensors for continuous condition monitoring of railroad bearings

At present there are no existing bearing health monitoring systems capable of continuous monitoring and tracking of railroad bearings on freight cars. Current wayside equipment is used to garner intermittent bearing cup temperatures, which at times could be every 65 km (∼40 mi) or more. Such devices are not designed to provide continuous condition monitoring which would enable users to assess the rate of bearing health degradation and predict when a bearing will require service. To this end, IONX, LLC, a subsidiary of Amsted Rail, Inc., has developed low power Wireless Sensor Nodes (WSNs) which can be retrofitted to existing bearing adapters. The WSNs provide continuous monitoring of bearing temperatures as well as the current ambient temperature. Since the nodes are affixed to the bearing adapter surface, a correlation is necessary to estimate the bearing cup temperature using the measured adapter surface temperature. This paper describes research conducted at The University of Texas-Pan American (UTPA) to devise a reliable mathematical model to correlate both temperatures. Additionally, these wireless nodes are currently in use on ten railroad cars that are part of an Australian fleet. The nodes have been collecting data since March 2010. The acquired data was used to devise and test a series of metrics that can automatically detect distressed bearings and predict time to maintenance. The development of bearing health monitoring metrics and their use to assess bearings in the Australian fleet is also discussed in this paper.© 2011 ASME

Vibration Signatures of Temperature Trended Bearings in Field and Laboratory Testing

Over the past two years, a series of papers have been published concerning bearing temperature trending and a mechanism to explain this troubling phenomenon. In September of 2008, a collaborative field test between The Union Pacific Railroad (UP), Amsted Rail, Rail Sciences Inc. (RSI), and The University of Texas-Pan American (UTPA) was conducted to corroborate the findings of laboratory research and testing. Field and laboratory results confirm that temperature trended bearings exhibit vibration signals that can be distinguished from healthy bearings. Distinct primary frequencies and overtones associated with the axle, cone, cage, and rollers can be readily identified within a bearing vibration signal. In a previous paper, it was demonstrated that a trended bearing exhibits vibrations of higher magnitude. However, all characteristic frequencies appear in both healthy and trended bearings, but those that dominate, i.e., have higher magnitude, are distinct for trended bearings when compared to healthy bearings. The latter can be repeatedly demonstrated in both field and laboratory experiments. Moreover, the current work identifies and distinguishes between the primary bearing frequencies and those linked to roller misalignment, which is known to increase friction and wear, and consequently raise the bearing temperature.Copyright

Bearing Condition Monitoring Using Wireless Technology to Reduce the Risk of Bearing Failure

With the need for rail systems to provide long distance and highly reliable operations, problems that could arise should be quickly detected and addressed such that they do not become major issues. If undetected, sudden component faults can result in costly and difficult repair scenarios, and in the worst case, derailments, which can be catastrophic if they occur in populated areas. One such problem, Bearing Burn-off, can result in significant damage to the cars as well as to the rail infrastructure, often before the symptoms can be detected by rail crews and in most situations by wayside mounted infrastructure. A system developed by IONX for railroad operations is designed to monitor rail car bearings to detect potential burn-off conditions before they arise and before they become destructive. This system is comprised of a Central Monitoring Unit (CMU) and Wireless Sensor Nodes (WSNs) which continuously monitor bearing temperatures as well as the current ambient temperature. The application of various algorithms not only conducts trend analysis to anticipate burn-off events, but also reports events at predetermined temperature limits to provide early warning and immediately actionable feedback to locomotive engineers. With these alerts, the driver or train controller can then decide on the appropriate action to be taken and destructive consequences can be avoided saving operational and infrastructure costs. For this pilot study, a total of ten freight cars and fifteen locomotives were equipped, operated, and monitored for an initial three month period. This paper presents preliminary operational results for these tests demonstrating the benefits of predictive condition monitoring systems in real-world applications.© 2012 ASME

The effect of sustained wheel impacts on tapered roller bearing cages

Mechanical damage to tapered roller bearings resulting from wheel impacts is a growing concern in the railroad industry. Repeated impacts can cause plastic deformation, wear, and eventually fatigue in roller bearing cages. A servo-hydraulic system was implemented in order to impact a bearing assembly with 65 g peak acceleration impacts at 6 Hz. Three different cage designs were tested for the Class F and K bearings: the standard steel design, and two polyamide cage designs. Testing was conducted on the three cage designs in impact increments of 102 , 103, 104, 105, 106, and 15times106 cycles. Between each testing increment, cages were removed from a special two-piece cone to inspect damage. Mechanical damage in the forms of plastic deformation and wear were measured by means of their area and depth. Results indicated that although high acceleration impacts were inflicted on the bearing, none of the cages developed fatigue fractures in the roller pocket corners consistent with field failures. However, a large amount of hourglass shaped damage in the roller pockets was recorded. Comparing the three designs revealed that although the polyamide cage designs were lower strength, they were more resistant to plastic deformation and wear than the steel cage design

Multiple Frequency Ultrasonic Detection of Subsurface Near-Race Inclusions for Improved Fatigue Life Performance

The importance of steel cleanliness for the performance of tapered roller bearings has been clearly established and has led to on-going improvements in steel production methods. The presence of non-metallic impurities within the steel can result in hard/brittle inclusions that may serve as initiation sites for damage due to sub-surface rolling contact fatigue (RCF) if the inclusions lie within the near-race of the bearing components due to the high mechanical stress present. Current inspection standards define steel cleanliness with respect to bulk inclusion morphology, which limits inspection to a small area that may or may not be representative of the entire steel heat. In this presentation, ultrasonic surface wave methods are described for detecting subsurface inclusions directly on finished bearing inner and outer rings. We expand on our previous work to exploit the different inspection depths that can be achieved with different measurement frequencies. The impact of the different inspection depths is quantified through simulated service life testing with heavy axle loading conditions. For this study, bearing components were first subjected to ultrasonic surface wave testing at three different frequencies to identify near-race inclusions. The simulated service life testing was then used to assess the onset and propagation of RCF failure. RCF spall initiations correlated highly with the positions identified by the ultrasonic inspections suggesting that this approach has a predictive potential. However, additional research is needed to establish the specific criteria needed for such predictions with respect to the inclusion location along the race, the depth from the race surface, the inclusion morphology and the inclusion mechanical properties. This work is anticipated to improve the understanding of RCF damage initiation which will lead a higher level of safety for railroad operations.Copyright

Tracking of Spall Deterioration on Tapered Roller Bearings

Fatigue spall initiation is one of the major modes of premature bearing failure. The spall initiation is often exacerbated by the presence of impurities in the near-surface region (∼400 μm) of the bearing raceways. Once a spall initiates, it can propagate rapidly, leading to abnormal bearing operation and possible catastrophic failure if not detected early. Testing performed at the University of Texas-Pan American (UTPA) has focused on ultrasonically scanned tapered roller bearings found to have inclusion content within 400 μm of the surface of the raceways. These bearings undergo accelerated service life tests in which spall initiation is detected and tracked over time while documenting spall growth. The work presented here provides several study cases that document the spall initiation and propagation on ultrasonically scanned tapered roller bearing components. Results show that spalls generally initiate on locations corresponding to sites of subsurface inclusions, and they grow many times their original size within relatively short operating periods. The study also shows that spalls tend to initiate and propagate at a faster rate on bearing cups (outer rings) than on cones (inner rings).Copyright

Use of On-Board Hand Brake Monitoring to Prevent Freight Car Wheel Damage and Improve Maintenance and Safety

This paper discusses the benefits of using on-board hand brake sensors to determine whether a freight car hand brake is applied or released in service. Unreleased hand brakes are a significant source of wheel tread damage, which can lead to wheel removals, and in extreme cases can cause damage and derailments. Also, hand brake-related accidents are a significant cause of North American railroad accidents. Wheel tread damage and wayside wheel impact load detectors (WILD) are reviewed, along with AAR why made codes for wheel removals. Wheel failures and other wheel impact associated damage are discussed, along with operational considerations for hand brakes. Further, on-board sensors in general, and hand brake sensors in particular, are described in detail and service data from monitored cars is presented. Additionally, possible safety and operational improvements related to use of hand brake sensors are discussed, along with comments on the use of sensors to assist with proactive maintenance of freight cars.Copyright

Predicting Railway Tapered Roller Bearing Life Using Measured Residual Stress and Retained Austenite Data

A predictive life tool for case-carburized railcar tapered roller bearings, called the Service Load Factor (SLF), makes use of residual stress and retained austenite data to assess the condition of bearings as a result of service history. It is well known that the interaction between retained austenite transformation and the development of residual stresses are primary factors contributing to cone bore growth and decreased resistance to raceway spalling. This paper attempts to quantify these changes throughout the life of a bearing to provide insight into the predicted remaining service life of the bearing. Also, this paper will cover the use of the SLF as a failure analysis tool in order to quantify bearing damage due to shifted lading or worn adapters.Copyright