Causes and diagnosis methods of locomotive rolling bearing faults

This paper introduces the simple diagnosis and precise diagnosis of locomotive rolling bearing,and lists the detection examples.

1 Introduction

Bearing,as the main component of locomotive,especially traction motor and axle box bearing,plays an important role in safe transportation.When the locomotive runs online,once the bearing fails,the whole train will be unable to run and the main transportation line will be blocked,especially when the passenger train fails,which will have a greater negative impact.At the same time,once the locomotive bearing fails,it is very difficult to repair the locomotive.Therefore,it is very difficult to prevent and reduce the occurrence of locomotive bearing failure.It is very important for the safe transportation of locomotives.The key point of this paper{TodayHot}is whether the bearings with hidden trouble can be detected before loading the bearings to ensure the qualified bearing parts get on the train.

2 bearing failure

The serious damage of bearings is often not caused by a single reason,but by the comprehensive action of several aspects,a vicious circle is generated under bad operating conditions,which leads to serious burning of bearings.Therefore,after the accident,it is often difficult to judge what causes it,which brings us some difficulties in formulating relevant measures.For the convenience of discussion,the reasons for bearing failure are analyzed from several aspects.

2.1 Abnormal wear of bearings

2.1.1 When the bearing is used for a period of time,certain defects and scars will occur in the inner ring,rolling body,cage,outer ring and raceway of the bearing,resulting in poor lubrication of the bearing and heating of the bearing,which will lead to:(1)dilution of bearing lubricating oil.(2)Accelerate the fatigue of materials and decrease the hardness.Due to the above reasons,a vicious circle is further formed,which accelerates overheating and causes bearing burning.Serious bearing inner ring displacement,rolling body out of round,collision and heat generation,and finally welded together.Therefore,when running on the line,if{HotTag}finds that the bearing is seriously hot and smoking,do not stop,but keep running to the front station,because the overheated bearing is in a melting state at this moment,and once it is stopped and cooled,it can no longer walk,blocking the main line.

2.1.2 It is very important for locomotive bearings to be oiled and maintained,especially proper oiling can ensure good lubrication of bearings.Lack of oil and excessive oiling can easily lead to bearing failures.Adding less oil can easily lead to poor lubrication of bearings and heating,and adding more oil can easily lead to overheating of mixing.Therefore,proper oiling is required in maintenance,and the cleaning of lubricating grease of bearings is also very important.Once other impurities and moisture fall into grease,it will affect normal clearance and establish necessary oil film.

2.1.3 The service life of the bearing is too long,which will easily lead to the fatigue of the material.In addition,the strong impact will deform the material,which will cause peeling and grinding of the roller and raceway surface,resulting in poor lubrication and increased vibration.

2.2 Influence of Installation on Bearing

2.2.1 The fit clearance between the bearing inner ring and the shaft does not match the interference amount,which is easy to cause bearing failure.The interference amount is large,which is easy to cause the bearing inner ring to crack due to excessive tensile stress,and the interference amount is too small,which is also easy to cause the bearing inner ring to"relax".

2.2.2 Improper clearance fit in bearing assembly will easily lead to bearing failure,and small clearance will easily lead to friction and heat generation between roller and raceway.With the rising temperature,the temperatures of bearing inner ring,rolling body,cage,outer ring and end cover are different,and there is a temperature difference between them,so the expansion amount is slightly different,which will further reduce the fit clearance and increase the heat generation of bearing.If the gap is too large,the vibration of the roller will increase,which will aggravate the impact of the roller and raceway,and at the same time,it will easily cause uneven internal load distribution,less bearing rollers and excessive load of the central roller.

2.2.3 When assembling the bearing,a copper hammer is used to impact the bearing,resulting in deformation of the cage,incorrect installation of the inner and outer rings of the traction motor bearing or other reasons,which makes the axial transverse momentum disappear,causing the bearing shaft to be squeezed to death.

3 bearing fault detection and diagnosis

At present,the methods used to detect bearing faults in China are generally the methods of measuring temperature,noise and vibration parameters.The methods of measuring temperature and noise are relatively simple,but they lack effective preventive effect.Once the bearing temperature is too high and the noise is very high in operation,it is generally believed that the locomotive bearings have reached a relatively serious degree of damage.The method of measuring vibration parameters is to detect the bearing when the locomotive is in the middle and small repair.Because it is convenient and simple to obtain and collect information in the detection,it is more suitable for popularization and use in the middle repair section,and it is a simple and practical detection method.

3.1 Diagnosis method of locomotive bearing

There are two main methods for locomotive bearings:(1)simple diagnosis of locomotive bearings,and(2)precise diagnosis of locomotive bearing resonance demodulation spectrum analysis technology.

3.1.1 Simple diagnosis,that is,in vibration detection,the state of bearings is generally judged by testing the size of some vibration parameters and comparing them with the standard values(threshold values).In simple diagnosis of locomotive bearings,two indexes,namely,KV,KV and Xrms,which are time domain kurtosis coefficient parameters,are mainly selected as fault judgment parameters,among which KV is a dimensionless parameter,which is sensitive to early faults of bearings but insensitive to operating conditions.When there is a fault on the working surface of the bearing tooth surface,the impact pulse at the defect of the working surface will be generated every revolution.The bigger the fault is,the greater the amplitude of the impact response will be,and the faster the KV value will rise.However,with the serious deterioration of the bearing fault in the later stage,the KV value will decrease,while with a relatively high value,it is not sensitive to the early fault,but it will rise with the continuous deterioration of the bearing fault,with good stability.In a word,in order to obtain the reliable comparison result of simple diagnosis,it is appropriate to apply kurtosis coefficient and comparison value at the same time,which takes into account the sensitivity and stability of diagnostic parameters.

Simple diagnosis has a good side,but there are also many shortcomings.When simple diagnosis is carried out on bearings,the following situations will occur;(1)the bearing parameters are out of order,but the fault position cannot be determined;(2)the bearing itself has no fault,but is caused by the fault during assembly(such as dynamic unbalance of rotor,misalignment of shaft and rubbing,etc.).(3)When the sensor is placed on the frame,the measured fault signals are strong or weak(the inner ring is the smallest,the roller is stronger and the outer ring is larger),which will lead to errors according to the parameters.Through the analysis of the above three situations,it is found that there is no method to judge the failure of bearing components in simple diagnosis,and the problem of"condition-based maintenance"cannot be solved.Therefore,it is not enough to judge whether there is a failure in bearing diagnosis only through simple diagnosis,and precise diagnosis must be carried out.

3.1.2 Precision diagnosis

When the bearing surface is damaged,such as fatigue peeling,local wear,surface corrosion,etc.,the bearing and rolling idle rotation will crush these surface damaged parts in turn,and the high-speed inner ring rotation will make this rolling impact.The longitudinal wave caused by this fault impact will be emitted at the speed of sound before the material is deformed,with a steep front waveform and extremely rich frequency spectrum.With the internal damping of the material,the longitudinal wave generated by the impact will be rapidly attenuated,so the sensor will receive the impact pulse signal.The waveform of this impact pulse is approximately rectangular,and the failure frequency of this rectangular pulse is extremely wide,while the natural frequencies of the bearing system and various sensors are very low,so the natural frequencies of the bearing system and various sensors are covered by the failure impact pulse frequency,which arouses the resonance of the bearing system and various sensors.Using bandpass filter to filter out unnecessary low and high frequency noise(such as mechanical vibration and other noises)only causes the fault impulse to excite the resonance response waveform of the bearing outer ring or sensor to pass through,and amplifies and improves the low frequency fault impulse signal into the higher frequency response attenuation oscillation of the vibration system.Envelope demodulation amplifies this higher frequency response into an expanded low frequency signal,which is transformed into a low frequency spectrum by the frequency analyzer,that is,the demodulation spectrum.

4 locomotive bearing diagnosis case

The following case is a fault case detected on the fourth left axle box bearing of Dongfeng 7D0034 locomotive on January 27th,2002.The bearing type is 752732.Use JL-501 bearing testing platform to test,and the speed is 500 rpm.

The kurtosis coefficient of the diagnostic parameters detected by the time domain waveform is 6.63,and the high kurtosis is also seriously exceeded,so the detection result is unqualified.At the same time,the refined spectrum shows that the peak shown in the demodulation spectrum is 60HZ,and the interval between the first,second and third order peaks is 60HZ.According to the locomotive bearing fault frequency table,the frequency of the bearing fault position is calculated as 500×0.12=60HZ,and the fault position is found to be the bearing outer ring from the table.In the subsequent decomposition of the bearing,it is found that the raceway of the outer ring is slightly corroded and crushed.

5 concluding remarks

The diagnosis method of locomotive rolling bearing described in this paper has been carried out in our section for nearly two years.There are two sets of equipment in our section:JL-201 locomotive bearing diagnosis instrument and JL-501 locomotive bearing diagnosis table.JL-201 is mainly used for ground detection of traction motor bearings and top wheel detection of locomotive bearings,and JL-501 is mainly used for dynamic detection of rolling bearings of locomotives under repair.In the past two years,a total of 2,318 sets of bearings have been tested for the locomotives in other sections and this section,and 189 sets of unqualified bearings have been detected.Among them,there has been no bearing failure or mechanical damage caused by bearing failure in our section since 2001,and remarkable results have been achieved.