·Table of Contents
·Terrestrial and Marine Transportation
A dynamic and quantitative method for measuring wheel flats and abrasion of trainsQibo Feng, Jianying Cui, Yan Zhao, Ying Pi, Yongping Teng
(Dept. Of Physics, Northern Jiaotong University, Beijing 100044,P. R . of China)
Wheel flats and other kinds of irregularities or defects on any wheel tread of trains are one of the main causes that threaten safety of trains. There are several methods at present to measure wheel flats. However, almost all these methods are qualitative, and can not get the values of the wheel flats, not to mention to get the values of the wheel abrasion. A totally new method to measure dynamically and quantitatively wheel flats is put forward in this paper, and both the values of wheel flats and abrasion in any tread of trains can be got when a train passes through the measuring device. The measurement system mainly consists of several sets of parallelogram mechanisms, displacement transducers and data collecting and processing system, and it was installed in the railway site. Through a lot of in-situ experiments, the accuracy of about 0.2mm in the measurement of both wheel flat and abrasion can be obtained by the system when the moving speed of a train is less than 15km per hour.
Key Words : Wheel flat, Abrasion, dynamic measurement and train wheels.
The true running status of wheels in a wheel/rail system plays an important role, as any defects in treads of wheels will lead to significant vibration and noise. Especially, wheel flats will cause unacceptable additional varying loads on both wheel set bearings and rail tracks, and on some occasions, this great load can lead to rail fractures or even break rails [1~2]. So, how to measure correctly and quantitatively the value of wheel flats is a key problem that must be solved in the development of high-speed and heavy-load trains, and it has not been solved properly up to now. Currently, there are several methods of measuring wheel flats [3~5], such as using the accelerometers or gauges to measure the vertical impulse acceleration or force caused by the wheel flat. However, these methods are qualitative, they can not get the values of wheel flats. Moreover, the impulse force or acceleration impacting on the rail is influenced greatly by many other factors such as the speed, the weight of the train and the type and the quality of the rail etc., which makes it impossible to get exactly the values of wheel flats. How to quantitatively measure both the wheel flat and wear is a common concern among researchers in the field of railway safety technology, and it is the main objective of this paper.
|Fig 1: Schematic illustration of measuring the wheel flat and abrasion|
|Fig 2: Configuration of measuring wheel flat and abrasion of a train|
|Fig 3: A. Ideal signals. B. Signals got by an X-Y recorder. C. Signals got by the computer|
|Fig 4: Ideal signals when a vehicle passes through two transducers|
Table one is a typical measurement report form given by the system when a train passes through the measurement device. In fact, due to adverse circumstances, the signals are greatly different from ideal ones, which produces a little difficulty in the data processing. The main tasks for data processing are to find the flat spot and calculate the values of both wheel flats and abrasion, to give the correct positions where all these defects are located. Finally, the computer will print out a report from to the people on duty, giving the locations and the values of both wheel flats and abrasion that exceed the limits.
|Date:02/02/99, Time:05:07, Train Code:2129, Average speed:24Km/h, Total number of vehicle tanks:62, Total number of engine tanks:2, Recorded file:E2020507.dat|
|Number of car tanks||Number of wheels||Number of wheels||Flat Values(mm)|
|By our system||By people|
|Table 1: Experiment results|
This system works very well when the moving speed of a train is less than 15Km per hour. Theoretically, the lower the speed of a train, the higher the measurement accuracy. By comparing the results given by our system and the measurement results given by the technician using a traditional special micrometer, it is found that the measurement errors for both wheel flats and abrasion is 0.2mm. However, there is a great impulse force acting on the long beam at the moment the flange top collides with the beam if the speed is high, which causes a vibration in the parallelogram and makes the flange top not contact with the long beam. In such cases, the measurement base is lost, and the wheel flat can not be found out. To avoid this, some vibration absorber and damping system must be added to the parallelogram mechanism, and this is under development.
|© AIPnD , created by NDT.net|||Home| |Top||