Case study on bearing overheating of single-section hammer-type crusher in cement plant,3 reasons and treatment measures

Date: 2019-06-17 Views:

Limestone crushing in cement plant adopts single-stage hammer crusher. During the inspection and maintenance of primary kiln shutdown, the crusher was inspected and maintained, and the flywheel of the crusher was replaced;After replacing the test run, it is found that the temperature of the flywheel bearing is high, the alarm is frequent, and it has to stop for inspection.

The temperature will not exceed 65 ℃ during normal startup. The temperature of the flywheel bearing measured by the temperature measuring gun is above 100 ℃ for less than 20h. This paper is to share the possible causes and corresponding treatment measures in this case.

After the bearing of the section hammer crusher is over-heated, the maintenance personnel have tried several maintenance schemes, without obvious effect; after the result of the failure of the comprehensive analysis, the crux of the problem is finally found, and finally the problem is solved. The following are several cause analyses that may lead to a failure, as well as solutions.

 

1、 Poor lubrication


Lubrication has an important influence on the fatigue life, friction, wear and vibration of bearings. According to statistics, about 40% of the bearing damage is related to poor lubrication. Therefore, good lubrication is a necessary condition to ensure the normal operation of the bearing.
 

The effect of lubrication on bearings is as follows:


(1) reduce friction and wear and prolong the life of bearings;

(2) drain the friction heat to prevent the bearing temperature from rising too high;

(3) to prevent foreign bodies from invading and to play a sealing role;

(4) Prevent the corrosion of the metal.

 



The main factors that cause the poor lubrication of the bearing are the shortage of grease and grease, and the problem of the quality of impurities or grease in the grease. In the case, after the bearing temperature was high, the maintenance personnel cleaned the bearing with kerosene, replaced the new grease, and conducted the test machine and the temperature record, and 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 temperature rise of the fixed end bearing is not related to the grease quality and the lubrication condition.
 

2、Bearing wear


The working environment of the crusher is large, when part of the fine dust enters the bearing seat which runs at high speed, the grease in the bearing seat is spoiled and the lubrication is poor, and then the bearing can be worn out. The bearing continues to run in wear state, because of the increase of friction and heat, which will lead to the increase of bearing temperature.

After the shutdown, it was found that most of the lubricating grease in the bearing seat had been lost due to high temperature, and there had been a slight scratch on the surface of the bearing rolling body, and the outer ring of the bearing had blued. The clearance of bearing is measured and it is found that the clearance is small. When the clearance of the bearing is too small, the friction loss of the grease in the clearance is too large, which will also cause the bearing to heat up; in addition, when the clearance is too small, the oil quantity will be reduced and the heat generated by the friction will not be taken away, thus further increasing the temperature rise of the bearing.

Therefore, the gasket is used to adjust the bearing clearance to meet the prescribed requirements, and the iron chips produced in operation are washed out with water during trial operation. Through the above adjustment, the bearing temperature is slightly reduced, but the effect is not very obvious. This shows that the bearing clearance and slight wear are related to the temperature rise of the bearing, but not the main reason.

 

3、 incorrect installation


After excluding the above factors, the main reason to judge the bearing heating should be related to the installation error. Because the bearing installation is correct or not, it has a direct impact on its life and main engine accuracy. Therefore, when the bearing is installed, the center line of the shaft and bearing hole must coincide.

If the bearing is not installed correctly, the precision is low, and the bearing has deflection, the torque will be produced when the bearing rotates, which will cause the bearing to heat up or wear; in addition, the bearing will also produce vibration, noise increase, and the temperature rise will also increase.

The linear correction motor bearing and flywheel bearing are used in the field, and it is found that the axis of the two shafts is not in the same straight line. The flywheel was only replaced during the overhaul, and the base was not involved, so the inspection and correction of bearing installation were ignored. In order to completely solve the heating problem of the bearing, the level of the bearing base is also checked, and it is found that the base of the motor bearing and the flywheel bearing are not in the same plane.

Before adjustment, the coaxiality deviation between rotor and motor of crusher is large, and the two shafts are not concentric. Before adjustment, the coaxiality is 0.755mm, which is too large, and the inclination of the end face of motor and crusher shaft before adjustment is 0.0007251, which is too large. This is because when the flywheel is replaced, although there is no moving base, the rotor bearing deviates from the original position in the installation process, so that the concentric degree and inclination of the crusher shaft are too large.

In addition, it is known from the measurement results that the shaft of the crushing machine is higher than that of the motor shaft, and it is not horizontal. By adjusting the number of gaskets on the bearing base, the coaxiality and inclination of the motor and the crusher are greatly improved. The coaxiality deviation between the rotor and motor of the adjusted crusher is reduced to 0.483mm, which meets the requirements of less than 0.5mm stipulated in JCJO3-1990 Code for Construction and acceptance of cement Machinery and equipment, and the inclination of the end face of the motor and the crusher shaft is 0.0002475, which is 34.1% of that before adjustment, thus reducing the tilt degree of the two shafts.

In addition, the level of the level is used to detect and adjust the levelness of the motor rotor and the crusher rotor, and then the straightness of the motor and the center line of the crusher is checked by the method of pulling the weight by the pull wire until the requirements are met.

Several rubber plates of the coupling are also removed in order 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 and heat generation of the crusher rotor in the running process can be reduced. After the above adjustment, the temperature of the machine is measured once per 15min, and the bearing temperature is stable within 70 ℃ for 3 hours.

Single-stage hammer crusher is a common crushing equipment in cement enterprises. Due to complicated working conditions, the bearing temperature may be too high. Although the bearing temperature rise is not a special fault, the lubricating grease is diluted and leaked;The bearing will be damaged, causing economic loss to the enterprise. There are a lot of reasons for bearing temperature rise, which shall be excluded according to specific conditions during adjustment.

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