Bearings are important components in motors. The speed of the bearings will directly affect the performance of the motor. If the speed is too low, the motor cannot be driven, and if the speed is too high, the motor will burn out due to high temperature. According to our understanding of motor bearings, generally speaking, bearing overheating means that the rolling temperature rise exceeds 55°C and the sliding bearing temperature rise exceeds 40°C.
The root cause and solution of excessive temperature of motor bearings:
1. The rolling bearing is not installed correctly, and the matching tolerance is too tight or too loose. The working performance of the rolling bearing depends not only on the manufacturing accuracy of the bearing itself, but also on the dimensional accuracy, geometric tolerance and surface roughness of the matching shaft and hole, as well as the selected matching and correct installation. In general horizontal motors, the assembled rolling bearings only bear radial stress, but if the inner ring of the bearing is too tight with the shaft, or the outer ring of the bearing is too tight with the end cover, that is, when the positive interference is too large, the bearing clearance after assembly is too small, sometimes even close to zero. In this way, the rotation is not flexible and heat is generated during operation. If the inner ring of the bearing is too loose with the shaft, or the outer ring of the bearing is too loose with the end cover, the inner ring of the bearing and the shaft or the outer ring of the bearing and the end cover rotate relative to each other, resulting in frictional heating and overheating of the bearing. In general, the inner diameter tolerance zone of the inner ring of the bearing as a reference part moves below the zero line in the standard. The matching of the tolerance zone of the same shaft with the inner ring of the bearing is much more important than the matching of the tolerance zone with the general reference hole.
2. Improper selection or maintenance of grease, poor quality or deterioration of grease, or mixing with dust and impurities will cause the bearing to heat up. Too much or too little grease will also cause the bearing to heat up, because too much grease will cause greater friction between the rotating part of the bearing and the grease, while too little grease will cause dry friction and heat. Therefore, the amount of grease must be adjusted to about 1/2-2/3 of the volume of the bearing chamber space. Inappropriate or deteriorated grease should be cleaned and replaced with appropriate and clean grease.
3. The axial clearance between the outer bearing cover of the motor and the outer circle of the rolling bearing is too small. Large and medium-sized motors generally use ball bearings at the non-shaft extension end. Roller bearings are used at the shaft extension end so that the rotor can extend freely when it expands due to heat. Since ball bearings are used at both ends of small motors, there should be an appropriate gap between the outer bearing cover and the outer ring of the bearing, otherwise the bearing may be heated due to excessive axial thermal extension. When this phenomenon occurs, the front and rear bearing covers should be removed, or a thin paper pad should be added between the bearing cover and the end cover to form a sufficient gap between the outer bearing cover and the outer ring of the bearing.
4. The end covers or bearing covers on both sides of the motor are not installed correctly. If the end covers or bearing covers on both sides of the motor are not installed in parallel or the stop blocks are not tight, the ball will rotate out of the track and generate heat. The end covers or bearing covers on both sides must be reinstalled flat and fixed with bolts that rotate evenly.
5. The balls, rollers, inner and outer rings, and ball cages are severely worn or the metal is peeled off. The bearings should be replaced at this time.
6. Poor connection with the loader. Including: poor coupling assembly, excessive belt tension, different load machine axis, too small pulley diameter, too far bearing distance, too large axial or radial load, etc. Correct the wrong connection to avoid abnormal force on the bearing.
7. The shaft is bent. At this time, the bearing force of the shaft is no longer a pure radial force, so it will cause the bearing to heat up. Try to straighten the bent shaft or replace it with a new one. Mainly used for motor bearings hardened with soft dry oil or anti-rust paste, they should be immersed in hot engine oil at 100-200℃, clamp the motor bearing with pliers, and brush the oil on the motor bearing with a brush. Soft dry oil or anti-rust paste melts when heated to 100-200℃, and it is easy to flush out from the gap of the motor bearing. Sometimes, as long as the motor bearing is shaken in the oil several times, the oil will flow out from the gap. When cleaning the radial spherical motor bearing of the motor, the ball, bead rack, and inner ring should be turned out horizontally from the outer ring and then immersed in hot oil. When cleaning the short cylindrical roller motor bearing, the roller, bead rack, inner ring and outer ring should also be disengaged. When cleaning with hot oil, the oil temperature should not exceed 200℃. If it is heated directly with an open flame, care should be taken to prevent the oil from burning. The motor bearing should be suspended in the oil pan and sink to the bottom, which will cause overheating and reduce the hardness. The general cleaning method is to soak the motor bearing in kerosene for 5-10 minutes, hold the inner ring with one hand, and turn the outer ring with the other hand, and the dry oil or anti-rust paste on the motor bearing will fall off. Then put the motor bearing into the cleaner kerosene, scrub it with a soft brush, clean the oil stains in the ball and the gap, and then put it in gasoline for cleaning once, and put it on clean paper after taking it out. When cleaning the radial spherical motor bearing and the short cylindrical roller motor bearing, the ball, bead rack, inner ring and outer ring should be disengaged for cleaning. The cleaning of the motor bearings mounted on the shaft mainly relies on the method of pouring oil. The oil stains that are easy to clean are first washed with kerosene and then gasoline; the oil stains that are difficult to clean are first washed with hot engine oil at 100-200℃ and then washed with gasoline. Be sure not to use sharp tools to scrape the hardened oil stains or rust on the motor bearings, so as not to damage the finish of the rolling elements and groove rings of the motor bearings. The cleaned motor bearings are wiped dry with a clean cloth.