Bearing as the main components of the locomotive, traction motor and axle box bearing, in particular, its function plays an important role in transportation safety, locomotive running online, once the fault of the bearings, will cause the whole trains can not run, blocking transportation trunk line, especially the passenger train fails, the negative impact is bigger, once the locomotive bearing failure occurs at the same time, the locomotive repair is very difficult, so as to prevent or reduce the locomotive bearing fault occurs, transportation is very important to the security of locomotive, can in front of the bearing loading would have detected the problems of bearing,The emphasis of this paper is to ensure that the qualified bearing fittings are mounted. 

Bearing failure

Bearing damage, often is not a single cause, but under the effect of several aspects comprehensive, under harsh operating conditions to produce vicious circle, cause serious loss bearing, so after the accident, it is often difficult to determine is caused by what, also give us relevant measures to bring certain difficulties, convenient for discussion, first from several aspects to analyze the causes of bearing failure. 

(1) abnormal wear of bearing

A when the bearing is used for a period of time, certain defects and scars occur in the inner ring, rolling body, cage, outer ring and raceway of the bearing, resulting in poor lubrication of the bearing and resulting in the bearing heating, which will lead to :(1) the dilution of bearing lubricating oil.(2) accelerate the fatigue of the material and reduce the hardness.As a result of the above reasons, and further form a vicious cycle, accelerated overheating and the bearing burning damage.Serious bearing inner ring displacement, rolling body out of the circle, impact heat, and finally fused together.Therefore, when running on the line, if the bearing is found to be seriously hot, smoke, do not stop, but should maintain the operation to the front station, because the superheated bearing is in melting state at the moment, once the parking cooling can no longer walk, block the positive line. 

B of locomotive bearing oil for maintenance is very important, especially for bearing the right amount of fuel can guarantee good lubrication bearing, too much of the lack of oil and gas, are easy to cause bearing failure, and poor lubrication oil and less likely to cause bearing heating, and much more likely to cause a stir overheating, so in the maintenance of oil to appropriate, at the same time the clean bearing grease is also very important, once the fall into the other impurities in the oil and water, will affect the normal clearance and building must be the oil film. 

The long service time of c bearing is too long to exceed the service life of the bearing, which is easy to cause fatigue of the material. In addition, the material is deformed due to the strong impact effect, resulting in stripping and grinding of the roller and raceway surface, resulting in poor lubrication and increased vibration. 

(2) impact of installation on bearing

The interference of the inner ring of bearing a is not consistent with the fit clearance of the shaft, which is also easy to cause bearing failure. The large interference is easy to cause the bearing inner ring to crack due to the excessive tensile stress, and the small interference is also easy to cause the bearing inner ring to "relax". 

B bearing assembly improper cooperate clearance fit, also easy to cause bearing failure, small clearance is easy to cause the roller and raceway friction heat, with the rising of the temperature, the bearing inner ring, rolling body, cage, outer ring, the temperature of the end cover is not the same, there is a temperature difference between each other, thus expanding quantity is slightly different, also can make further reduce the tolerance clearance, according to the bearing heating.If the clearance is too large, the vibration of the roller will increase, which will aggravate the impact of the roller and raceway. Meanwhile, it is easy to cause uneven distribution of internal load, reducing the load bearing roller, and excessive load of the central roller. 

C. When assembling the bearing, the bearing is not in accordance with the technological requirements. The copper hammer is used to impact the bearing, resulting in the deformation of the cage.  

3. Detection and diagnosis of bearing faults

At present domestic adopt bearing fault detection approach roughly measuring temperature, noise and vibration parameters of the method, by using the method of measuring temperature, noise is easy, but the lack of effective preventive action, once in the running high bearing temperature and noise is very big, it was generally supposed that the locomotive bearing has reached to more serious damage.The method of measuring vibration parameters is to test the bearing when the locomotive is in minor repair. It is a simple and practical detection method because it is convenient and simple to obtain and collect information in the detection and is more suitable for the popularization and use of the middle repair section. 

There are two main diagnostic methods for locomotive bearing:

A simple diagnosis of locomotive bearing. 

Is in the vibration detection by testing is usually something the size of the vibration parameters, compared with standard (threshold value) to judge the state of bearing, in the simple diagnosis of the locomotive bearing, mainly choose the time domain wave kurtosis coefficient parameters of KV,,,, acceleration RMS Xrms two indicators as fault diagnosis parameters, including kurtosis index KV is a dimensionless parameter, sensitivity to the early failure of bearing, and is not sensitive to operating conditions, when bearing failure of tooth surface work surface, turn every week will have the impact of face defect pulse, the greater the failure, the shock response amplitude, the greater the KV value rise faster,However, with the serious deterioration of bearing fault in the later period, the KV value decreases somewhat, while the value with comparison is the opposite. It is not sensitive enough to the early failure, but rises with the continuous deterioration of bearing fault, and its stability is better.In short, in order to obtain more reliable results 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 better side, but there are also many shortcomings, when the bearing simple diagnosis, there will be the following situations; 

* bearing parameters?Value has fault, but its fault location cannot be determined,

* the bearing itself is fault-free, but due to the assembly of the fault, (such as rotor dynamic imbalance, shaft misalignment collision, etc.). 

* when the sensor is placed on the machine base, the measured fault signals are either strong or weak (the inner ring is the smallest, the roller is strong, and the outer ring is large), thus errors will be generated according to the parameters.Through the analysis of the above three cases, there is no simple diagnosis method to determine the fault of bearing components, and it cannot solve the problem of "depending on the situation of maintenance". Therefore, it is not enough to judge the fault of bearing only through simple diagnosis, but must make precise diagnosis. 

B. Resonance demodulation spectrum analysis technique of locomotive bearing -- precise diagnosis. 

When the bearing surface damage, such as stripping, partial wear, surface corrosion fatigue failure, rolling bearing and Hugh rotation will take turns rolling the surface damage, high speed of inner ring spinning can make this kind of rolling impact, the impact failure caused by longitudinal wave before the material has not yet occurred deformation to launch on the speed of sound, with a steep front waveform and spectrum of the most abundant, with material internal damping, the waves of shock attenuation sharply, so the sensor receives the impact pulse signal. 

The impact pulse waveform similar to rectangle, the failure frequency of rectangular pulse is extremely broad, and bearing system and all kinds of natural frequency of the sensor is very low, so the natural frequency of the bearing system and all kinds of sense organ is a message was covered with fault impact pulse frequency, failure frequency resonance, provoked a bearing system and each kind of sensor with a bandpass filter filter out unwanted low and high frequency noise (such as mechanical vibration and other kinds of noise) only make fault shock pulse excited resonance response waveform through the bearing outer ring or sensor, and the low-frequency fault impact signal amplification and to increase for the vibration system of the response attenuation of high frequency oscillation,The 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. 

Locomotive bearing diagnosis cases

The following case is the fault case of the fourth left axle box bearing of dongfeng 7D0034 locomotive detected on January 27, 2002, bearing type 752732.Test with jl-501 bearing test stand, speed 500 RPM. 

As for the diagnostic parameters detected by the time domain waveform, the kurtosis coefficient is 6.63, and the high kurtosis is also seriously exceeded, so the detection result is unqualified. 

At the same time, it can be seen from the detailed spectrum that the peak value of demodulation spectrum is 60HZ, and the peak intervals of order 1, 2 and 3 are all 60HZ. The frequency of bearing fault parts is calculated according to the locomotive bearing failure frequency table: 500×0.12=60HZ. The fault parts are found to be bearing outer ring from the table. 

5 conclusion

The locomotive rolling bearing diagnosis method described in this paper has been carried out in my section for nearly two years. There are two sets of equipment in my section, jl-201 locomotive bearing diagnosis instrument and jl-501 locomotive bearing diagnosis platform.Jl-201 is mainly used for ground detection of traction motor bearings and wheelset jacking detection of locomotive bearings, while jl-501 is mainly used for dynamic detection of rolling bearings of mid-repair locomotives. 

In the past two years, a total of 2318 sets of bearings have been tested for other sections and this section's medium repair locomotives, and a total of 189 sets of unqualified bearings have been detected. Among them, there has been no bearing failure or machine failure caused by bearing failure in our section since 2001, which has received significant results.