On the heating of bearings

High bearing temperature is a common and harmful fault of rotating equipment, which will reduce the service life of the bearing and increase the maintenance cost. When the temperature rises rapidly and exceeds the standard, it is easy to cause unplanned outage or load reduction operation of the unit, which has a great impact on economic benefits. Therefore, it is the guarantee for the continuous and safe operation of the equipment to quickly determine the cause of the fault and take appropriate measures to solve it.

Common causes of high bearing temperature

1) Poor lubrication. If the lubrication is insufficient or excessive, the quality of lubricating oil does not meet the requirements, deteriorates or has impurities;

2) Not enough cooling. If the pipeline is blocked, the cooler is not suitable and the cooling effect is poor;

3) The bearing is abnormal. If the bearing is damaged, the bearing assembly process is poor, and the clearance adjustment of each part of the bearing box does not meet the requirements;

4) It vibrates a lot. For example, the alignment process of coupling is poor and does not meet the requirements, the rotor has dynamic and static imbalance, poor foundation rigidity, virtual foundation, rotating stall and surge.

resolvent

When the bearing temperature is high, the following problems should be solved first:

1) Improper oil filling, too little or too much lubricating grease

Oil the bearing box regularly according to the requirements of the work. Sometimes high temperature occurs after the bearing is oiled, which is mainly due to excessive oiling. At this time, the phenomenon is that the temperature continues to rise, after reaching a certain point (generally 10 ℃ ~ 15 ℃ higher than the normal operating temperature), it will remain unchanged, and then it will gradually decline.

2) The grease on the bearing does not meet the requirements or is contaminated

Improper selection of lubricating grease makes it difficult to form a uniform lubricating oil film, which can not reduce the internal friction and wear of the bearing, and the bearing temperature rises due to insufficient lubrication. When different types of grease are mixed, chemical reaction may occur, resulting in deterioration and caking of grease, reducing the lubricating effect. Grease contamination will also increase the bearing temperature. Dust will fall in the process of grease filling, resulting in grease pollution, which will lead to the deterioration of grease in the bearing box, damage the bearing lubrication and increase the temperature.

Therefore, proper grease should be selected. During the maintenance, the bearing box and bearing should be cleaned. The oil filling pipeline should be checked and dredged. Different types of grease should not be mixed. If other types of grease are replaced, the original grease should be cleaned first; Grease shall be added regularly during operation and maintenance, and the grease shall be properly kept to prevent moisture and dust.

3) Not enough cooling

Check whether the pipeline is blocked, and whether the inlet oil temperature and return water temperature exceed the standard. If the cooler selection is not appropriate, the cooling effect is poor, and can not meet the use requirements, timely replacement or parallel installation of new cooler should be carried out. Axial flow induced draft fan should also check the insulation and sealing of the core tube.

4) Check the alignment of the coupling and the bearing after confirming that the above problems do not exist

The alignment of the coupling meets the process standard. During the alignment of axial-flow induced draft fan and hydraulic coupling, the problem of thermal expansion of equipment in operation should also be considered. The bearing box of the induced draft fan rises due to the expansion of the impeller; During the operation of the hydraulic coupling, the temperature rises, the bearing box expands, and the bearing rises. Therefore, the timing motor should be higher, and the reserved amount should be determined according to the characteristics of the equipment and the temperature parameters in operation.

The inspection of bearings mainly includes the following points:

1) Quality of bearing

During the disassembly of the bearing box, first of all, check whether the lubricating grease has bad conditions such as deterioration, caking and impurities, which is an important basis for judging the cause of bearing damage. Secondly, check the bearing for bite and wear; Check the surface finish of the inner and outer rings, rolling elements and cages of the bearing, and check whether there are cracks, rust, peeling, pits, overheating discoloration and other defects, and measure whether the bearing clearance exceeds the standard; Check whether the shaft sleeve is worn, pitted or peeled. If so, replace it with a new bearing.

2) Fit of bearing

When the bearing is installed, the fit between the inner diameter of the bearing and the shaft, the outer diameter and the shell is very important. When the fit is too loose, the relative sliding of the fit surface will occur, which is called creep. Once creep occurs, it will damage the wear surface, the shaft or the shell, and the wear powder will invade into the bearing, causing heating, vibration and damage. When the interference is too large, the outer diameter of the outer ring will become smaller or the inner diameter of the inner ring will become larger, reducing the internal clearance of the bearing. In order to select the suitable fit, we should consider the nature of the bearing load, size, temperature conditions, the rotation of the inner ring and outer ring.

3) Adjustment of fit clearance of bearing parts

When the bearing clearance is too small, the bearing will be heated due to the large shear friction loss of grease in the clearance. At the same time, when the clearance is too small, the amount of oil will be reduced, and there is no time to take away the heat generated by friction, which will further improve the temperature rise of the bearing. However, if the clearance is too large, the dynamic characteristics of the bearing will be changed and the rotor will be unstable. Therefore, it is necessary to select the verified bearing clearance according to different equipment and service conditions.