Abstract: With the development of social economy, China's transportation industry has developed rapidly, and railway engineering construction has also made great progress. This paper discusses the common faults and countermeasures of rolling bearings for railway freight cars, hoping to improve the economic benefits and operation safety of railway transportation.
Key words: rolling bearing; Common faults; Countermeasures
Introduction
The increasing application range of railway freight cars has further improved the use quality of railway freight cars and raised the safety of freight cars. The application of rolling bearing plays a key role in vehicle operation. Therefore, it is particularly important to take protective measures in advance. Once a fault occurs, its harm and consequences are very serious.
1. Brief introduction of press mounting process
The main process of bearing press mounting is to measure the diameter of bearing inner race and axle journal respectively after the bearing and wheel set are at the same temperature, select and combine them according to a certain amount of interference, and then use CNC hydraulic equipment with automatic curve recording function to press the bearing onto the journal of the wheel set by cold pressing, and hold the pressure for a certain time to make the bearing press in place. In the process of bearing press fitting, the two inner rings of the bearing are pressed into the journal in turn, and the press fitting equipment automatically records the stroke and pressure of the hydraulic cylinder. There are differences in the structure of different types of bearings, but the press fitting process and press fitting curve recording principle are the same.
2 Fault cause analysis
Railway rolling stock bearings are mostly used in locomotives and rolling stock. The bearing structure of rolling stock includes traction motor bearing, axle box bearing, transmission system bearing, power equipment bearing and cooling system bearing, etc., and the axle box bearing of rolling stock is the primary bearing. Short cylindrical roller bearings are mostly used in passenger cars. Tapered roller bearings are mostly truck bearings. The type, layout and function of vehicle bearings are similar to those of locomotive axle box bearings.
2.1 Abnormal sound
The sound of the rolling bearing in good condition is continuous and crisp during rapid rotation, and there is no abnormal sound jamming during repeated rotation. However, if the bearing is inflexible during rotation and accompanied by the sound of rolling body breaking, it indicates that the rolling bearing has serious fault.
2.2 Loose bearing sealing cover
The seal cover is generally not replaced with new products in time during maintenance, resulting in the seal cover is not restored in time after shaping, and the outer ring mouth mostly fits with the seal cover, which will cause loosening. However, the friction between the seal seat and the seal ring increases after the speed is increased, and the seal cover is driven to rotate together, resulting in the looseness of the seal cover. During the train inspection, it is required to only handle the removal of the seal cover. Finally, the looseness of the sealing cover was aggravated without treatment.
2.3 Tonnage skip of press fitting curve
The quality of bearing press-fitting has a direct impact on the safe operation of vehicles. In actual production, it is very common that the displacement-pressure curve jumps at the initial stage of bearing press installation. Although the technical standard does not clearly specify the limit of the weight jump of the bearing press fitting curve, and the analysis shows that the weight jump of the displacement-pressure curve at the initial stage has no impact on the subsequent use of the axle, the product inspection usually determines that the weight jump exceeds 58.8KN (the minimum qualified press fitting force) as the curve abnormality, and the bearing needs to be removed, re-selected and pressed.
2.4 Increased cage breakage
Because the strength of the cage itself is not very high and the processing and manufacturing level is also low, manufacturing defects exist in the cage. Due to insufficient strength, the cage can not meet the needs of railway speed increase and heavy load. The stress of the cage is restricted by the quality of the wheel set tread, so the stress degree of the cage is greatly reduced. It can be seen that the damage to the bearing cage is the tread failure. The harm to the cage will gradually increase with the increase of train speed. The reason is that the impact force depends on the speed of the train, and the impact frequency increases with the increase of the train speed. The harm to bearings is also increasing. Finally, the reason for the cage breakage is that the pressure is too large, the sealing of the seal cover is reduced, and the outside is loose. The grease is thrown out in a large amount during the train operation, and the lubrication effect is gradually lost.
2.5 Loose bolts at shaft end
During the technical maintenance of the train, the train inspector shall check the locking of the axle end bolts and the connecting axle end bolts respectively. If the locking is broken or lost during the inspection, the axle end bolts shall be checked immediately. If the axle end bolts are found to be loose or loose, the axle end bolts shall be immediately removed and replaced.
2.6 Others
In addition, incorrect assembly and use may cause deformation of the cage, increase the friction between the cage and the rolling body, make it stick to the rolling body, and increase the friction between the cage and the inner and outer rings. The vibration and noise are further increased, resulting in bearing damage and failure.
3. Condition monitoring technology of rolling bearing
① Vibration signal analysis and diagnosis method. One of the most widely used methods in the monitoring and diagnosis of rolling bearings is the vibration signal analysis and diagnosis method. When the surface of rolling bearing is partially damaged, the bearing will generate periodic broadband pulse excitation signal. The spectrum structure of rolling bearing vibration can be divided into three types. (1) Low frequency spectrum (lower than 1kHz), including fault characteristic frequency of bearing and vibration characteristic frequency caused by machining error. The corresponding fault of the bearing can be diagnosed by analyzing the spectrum line of the low frequency band. (2) Medium frequency spectrum (1~20kHz), the natural vibration frequency of bearing caused by bearing surface damage. Generally, resonance regulation technology is used to obtain vibration signals with high signal to noise ratio, so as to carry out bearing fault analysis. (3) High frequency spectrum (more than 20kHZ) refers to the frequency energy distribution of the bearing damage impact exceeding 20kHZ, mainly including the high frequency part of the signal containing more than 20kHZ. High-frequency signal analysis is usually used as the most common method to diagnose the initial bearing fault. ② Monitoring and diagnosis method of bearing lubrication condition. When the lubrication state of the bearing rolling surface changes, such as from full liquid lubrication? When it comes to dry friction, the direct contact time between metals will continue to increase, the impulse value of bearing will also increase correspondingly, and the oil film resistance will continue to decrease. Therefore, oil film resistance diagnosis method and oil film thickness method are two commonly used methods in monitoring work. ③ Temperature monitoring diagnosis method. As a rotating part, the rolling bearing will generate heat when working. When the bearing is damaged, the bearing temperature will change. Therefore, the bearing temperature monitoring method can be used to diagnose the bearing fault. However, when the bearing temperature is obvious, the fault often has reached a very serious level, so this method is mainly used to assist monitoring and diagnosis methods to ensure that important equipment will not be scrapped.
4 Improvement measures and suggestions
4.1 Measures to avoid weight jump of bearing press fitting curve
(1) It is recommended that the axle design unit improve the axle drawing and increase the length of the axle lead-in section. Effectively improve the fitting relationship between the bearing press fitting and the timing, reduce the press fitting resistance, and have no effect on the effective joint surface of the bearing and the journal, and have little impact on the strength of the axle. (2) When machining the axle, the length of the lead-in section is controlled according to the upper limit of the size, which can effectively increase the included angle between the conical surface busbar of the bearing inner ring and the busbar of the axle lead-in section, and reduce the press-fitting resistance of the bearing and the axle alignment. (3) When machining the inner diameter of the bearing, the transition arc between the inner diameter and the conical surface is controlled as small as possible to reduce the contact area between the bearing inner race and the journal entry section, which can effectively reduce the pressure mounting resistance of the bearing and the axle alignment. (4) Before pressing the bearing, when servicing the axle, check the processing quality of the transition part at the rear of the journal entry section one by one. If the transition is not smooth, use abrasive cloth to polish it first to facilitate the smooth alignment of the bearing with the axle. (5) To improve the processing parameters of axle form grinding, the transition part at the rear of the journal entry section can be changed to form grinding machine, and the arc radius of the transition part can be appropriately increased, so as to increase the included angle between the cone generatrix of the bearing inner ring and the generatrix of the axle entry section, and reduce the resistance force of the bearing and the axle alignment. (3) Strengthen the status inspection of the bearing press-fitting equipment and conduct regular inspection on the diameter of the guide sleeve. On the premise of ensuring the smooth installation and withdrawal of the bearing, the larger the diameter of the guide sleeve is, the more conducive to the smooth alignment of the bearing.
4.2 Sealing cover
When the workers repair or overhaul the vehicle, the interference of the outer ring and seal ring shall be calculated from the interference of the outer ring and seal cover.
4.3 Bearing cage
The manufacturer must improve the technological level. The quality inspection department shall carry out quality supervision and strict control. Strengthen supervision awareness and eliminate manufacturing defects of products. The rigid cage should be replaced with plastic cage. It should adapt to the development of new materials for vehicle speed increase in the future, and the quality of cage should be improved. Strengthen the inspection and repair of wheel sets at all levels, ensure the quality of wheel sets, especially wheel tread, and avoid the impact and damage of tread defects on bearings.
Conclusion
To sum up, it is necessary to be familiar with the fault form and fault development stage of rolling bearing. To master the analysis principle and method of rolling bearing fault diagnosis is the premise of accurate diagnosis of rolling bearing fault.
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2023-03-15