Russian Rail Shop Competition Results
Application of Bearing Diagnostics in Railway Repair Shops
Automatic System for Rolling Element Bearings Diagnostics
Our company, VAST, Inc., has developed an automatic system for diagnostics of rolling element bearings called DREAM (Diagnostic Rolling Element Analysis Module) which has been introduced in many branches of industry and transport including railways . The system consists of IBM PC compatible personal computer, a means of envelope spectra measurements, and software, DREAM. The input data for the system are the dimensions of the bearings, rotation speed and envelope spectra. Using this data system automatically identifies both type and severity of 12 different bearing defects and gives a condition prediction for a period up to 6 months by a single measurement. The system works automatically without need for operator interference in the diagnostic process. This enables even an operator not qualified in diagnostics to process up to several dozen bearing spectra per hour. The system was developed in 1992 and, since that time, was installed on more than 200 enterprises in Russia and in the West.
The Current Situation on Russian Railroads
Currently, there are no formal regulations adopted concerning methods and means of vibrodiagnostics of rolling element bearings although some railway divisions and repair shops have introduced diagnostics for:
Hot Bearing Detectors (HBD) are also widely used for wayside control of box bearings on both subway and railways.
|Figure 1. Diagnostic stands for wheel pairs of locomotives or rail cars. The wheelpair is rotated from an external drive allowing the bearings to be diagnosed. For locomotive wheel pairs, the gears are also diagnosed.|
The condition of the rolling element bearings is a vital element for the efficiency of the locomotive and railway car operation. A study of repair cases during several years showed that 44% of the cases of unplanned repairs of electric locomotives were due to the failure of bearings and gearboxes and that these repairs took about 58% of all unplanned repair time because bearing and gearbox repair is the most complicated and time consuming of all the railway work. The financial losses of the railroad due to the occasional failure of these units exceeded the price of the installation of the diagnostic complex based on the DREAM software by 6 times. This means reducing the number of unpredicted failures by 20% will cover all the installation and acquisition costs of the diagnostic complex.
In 1997, the Russian railway ministry adopted plans to introduce PC based automatic diagnostic systems for rolling element bearings, gears, and electric machines in railway repair shops. Currently, one such system based on DREAM software is in use in Kemerovo. First, a locomotive is lifted. Then, 42 accelerometers are temporary mounted (7 measurement points on each of 6 wheel pairs). Next, the wheels are rotated by the locomotive motors and the measurements are conducted. Two locomotives are diagnosed during one working shift.
|Figure 2. Diagnostic stand for a locomotive. The locomotive is lifted, allowing the wheels to be rotated by their own motors and the accelerometer is mounted on the gearbox bearing case.|
|Figure 3. Diagnostic stand for locomotive. The locomotive is lifted allowing the wheels to be rotated by their own motors and the accelerometer is mounted on the wheel bearing case.|
Another system currently in use is for diagnostics of wheel
pairs before and after repair using special stands. Currently, in
Russia, there are about 300 such stands that are ideal for our
automatic systems. They can be equipped either with a PC based
systems or portable data-collector systems.
Tests Conducted at the TTC, USA
In June, 1996, during a meeting for the Improved Wayside Freight Car Roller Bearing Inspection program which is sponsored by the Association of American Railroads and Federal Railroad Administration at the Transportation Technology Center in Pueblo, CO, USA, a DREAM system was tested on recordings made from faulty bearings on a special test stand at the TTC. A portable computer with an analog to digital converter board was used to acquire the vibration data. The bearings under investigation were type F bearings rotated at a frequency equal to 80 miles per hour train speed and fully loaded. The DREAM system found defects of outer and inner races and rollers. Examples of envelope spectra and defect identification are presented on figures 4-5.
Figure 4a(above). An envelope spectrum of a bearing
measured by the diagnostic system. The system automatically
determines the measurement settings determined by the bearing
dimemsions and the rotating speed of the bearing.
Figure 4b(above). Diagnostic screen made by the system in automatic mode.
Figure 4c(above). Photo of the bearing under test courtesy TTC.
Figure 5a, b, c(below).
Figure 5a(above). Bearing envelope spectrum measured by the diagnostic system.
Figure 5b(above). Diagnostic screen made by the system in
Figure 5c(above). Photo of the bearing under test courtesy TTC.
Case stories from Ekaterinburg division of the Russian railway
The first case was on a ChS-2 type locomotive. The investigation was carried out because of the increased vibration noise in the region of a small gear in the transmission. It was suspected that the gear was severely worn along with the bearings. After the measurements and diagnostics with DREAM, it was found that the bearings were good condition and did not need to be changed. After disassembling the gearbox this diagnosis was confirmed by visual inspection.
The next case was August 31, 1994. Bearings in the main electric motor of the same type of locomotive were diagnosed. The program automatically identified a severe cage wear defect and spalls of the rolling elements and recommended that the bearing be replaced.
A third case involved diagnostics of two bearings in the wheel box. After the measurements, severe wear of the outer race of one on the bearings was diagnosed. Because there were no other defects found, DREAM gave a prediction for 2 days safe operation. This prediction made possible the postponement of the repair of the bearing until the railway car could be brought to the maintenance shop. Moreover, the bearing was not replaced. As the defect was on the of outer race (fixed race), the race was just 180 degrees rotated and re-mounted in place. Now, the load was applied on good bearing surface and a prediction was made using DREAM for safe operation for the next month.
|Figure 6. Proposed test stand allowing wheels to be loaded in the same direction as normal.|
After testing DREAM on the Ekaterinburg division of Russian railway at the Sverdlovsk passenger locomotive depot, the following conclusions were made:
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