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Case Analysis of Bearing Overheating of Single-stage Hammer

Date:2019-05-20 15:56     writer:admin     Views:

  A single-stage hammer crusher was used for limestone crushing in a cement plant. When the kiln was shut down for overhaul, the crusher was checked and repaired, and the flywheel of the crusher was replaced. After the replacement of the test machine, it was found that the temperature of the flywheel bearing remained high and the alarm was frequent, so the crusher had to stop and inspect. Normal start-up temperature will not exceed 65 C, this test machine less than 20 hours, the temperature of the flywheel bearing measured by the thermometer gun has reached more than 100 C. This article shares the possible causes and corresponding measures in this case.

  After the hot condition of the bearing of the segment hammer crusher, the maintenance personnel tried several maintenance schemes, which had no obvious effect. After comprehensive analysis of the causes and consequences of the fault, the crux of the problem was finally found and the fault was finally solved. Following is the analysis of several possible causes of failure, as well as solutions. 1. Bad lubrication has an important influence on the fatigue life, friction, wear and vibration of bearings. According to statistics, about 40% of bearing damage is related to poor lubrication. Therefore, good lubrication is a necessary condition to ensure the normal operation of bearings. The effects of lubrication on bearings are as follows: (1) reducing friction and wear, prolonging the life of bearings; (2) discharging friction heat to prevent excessive temperature rise of bearings; (3) preventing foreign body intrusion and sealing; (4) preventing metal corrosion. Usually, the main factors causing poor lubrication of bearings are insufficient lubricating grease, impurities in lubricating grease or problems in the quality of lubricating grease, etc. In this case, when the bearing temperature is on the high side, the maintenance personnel used kerosene to clean the bearing, replaced the new grease, and tested the machine and recorded the temperature. It was found that the temperature rise of the rotor bearing did not change significantly before and after the bearing cleaning. It can be determined that the abnormal temperature rise of the fixed end bearing has little relationship with the quality of lubricating grease and lubrication. 2. The working environment of bearing wear crusher is very dusty. When some fine dust enters the high-speed running bearing seat, the grease in the bearing seat deteriorates and lubricates poorly, and then the bearing wears. Bearing continues to operate under wear condition, because of the increase of friction and heat, it will lead to the increase of bearing temperature. After checking the bearings after the shutdown, it was found that most of the lubricating grease in the bearing seat had been lost due to high temperature, slight scratches on the surface of the bearing rollers and blue phenomenon on the outer ring of the bearings. Measuring bearing clearance, it is found that the clearance is small. Bearing clearance is too small, because the grease shear friction loss in the clearance is too large, it will also cause bearing heating; in addition, if the clearance is too small, the amount of oil will be reduced, so that the heat generated by friction can not be taken away, thereby further improving the temperature rise of bearings. For this reason, gaskets are used to adjust bearing clearance to meet the required requirements, and iron chips produced in operation are washed out with water during commissioning. Through the above adjustment, the bearing temperature decreases slightly, but the effect is not obvious. This shows that the bearing clearance and slight wear in this case have a certain relationship with bearing temperature rise, but it is not the main reason. 3 After the above factors are excluded from incorrect installation, the main reason for judging bearing heating should be related to incorrect installation. Whether the bearing is installed correctly or not has a direct impact on its life and the accuracy of the main engine. Therefore, when the bearing is installed, the center line of the shaft and the bearing hole must coincide. If the bearing is installed incorrectly, the accuracy is low, and the bearing has deflection, the moment will be generated when the bearing rotates, which will cause the bearing to heat or wear. In addition, the bearing will also produce vibration, increase the noise, and increase the temperature rise.

  Linear alignment motor bearings and flywheel bearings were used in the field, and it was found that the axes of the two axes were not in the same straight line. The flywheel was replaced only during the overhaul, and the base was not involved, so the inspection and correction of bearing installation were neglected. In order to thoroughly solve the heating problem of bearings, the level of bearing base was also checked, and it was found that the base of motor bearing and flywheel bearing were not on the same plane. Before adjustment, the coaxiality deviation between the crusher rotor and the motor is large, and the two axes are not concentric. Before adjustment, the coaxiality is 0.755mm, which is too large. In addition, the inclination of the end face of motor and crusher shaft before adjustment is 0.0007251, which is too large. This is because in the process of replacing the flywheel, although there is no moving base, the rotor bearings deviate from the original position during installation, so that the concentricity and inclination of the crusher shaft are too large. In addition, the measurement results show that the crusher shaft is higher and not level than the motor shaft. By adjusting the number of gaskets on the bearing base, the coaxiality and inclination of the motor and the crusher are greatly improved. After adjustment, the coaxiality deviation of crusher rotor and motor is reduced to 0.483 mm, which meets the requirement of less than 0.5 mm stipulated in JCJO 3-1990 "Code for Construction and Acceptance of Cement Machinery Equipment"; after adjustment, the inclination of motor and crusher shaft end surface is 0.0002475, which is 34.1% before adjustment, thus reducing the inclination of two axes. In addition, the leveling of motor rotor and crusher rotor is tested and adjusted by the level meter, and then the straightness of motor and crusher center line is checked by the method of pulling wire and lifting weight hammer until the requirement is met.

  Several rubber plates of the coupling were also removed to reduce the stiffness in the connection between the crusher rotor and the motor, so that the deformation in operation can be absorbed by the rubber plate in time, and the friction heat of the crusher rotor in the operation process can be alleviated. After the above adjustments, the machine is tested immediately. The temperature is measured once every 15 minutes, and the test run lasts 3 hours. The bearing temperature is kept within 70 C. Single-stage hammer crusher is a common crushing equipment in cement enterprises. Because of the complex working conditions, sometimes the bearing temperature is too high. Bearing temperature rise is not a special fault, but it dilutes grease and leaks out slightly, and damages bearings severely, causing economic losses to enterprises. There are many reasons for the increase of bearing temperature, which should be excluded one by one according to the specific conditions when adjusting. The main negligence in the process of solving the accident is that there is no change in the base when the flywheel is replaced, so the corresponding inspection and correction are not taken. The accident also reminds us that in the maintenance of equipment, we must carefully operate according to the relevant technical regulations, and check that it meets the requirements of technical parameters before starting up.

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