The root cause and solution of the high temperature of the motor bearing

Bearing is an important part in the motor. The running speed of the bearing will directly affect the performance of the motor. If the running speed is too low, the motor cannot be brought up. If the running speed is too high, it will cause the motor to burn out at high temperature. Tell everyone, in general, 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 the high temperature of the motor bearing:

1. The rolling bearing is installed incorrectly, and the matching tolerance is too tight or too loose.

The working performance of rolling bearings 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 bearing only bears 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 male interference is too large, the assembly The rear bearing clearance is too small, sometimes even close to zero.

In this way, the rotation is inflexible and heat is generated during operation. If the inner ring of the bearing and the shaft are too loosely fitted, or the outer ring of the bearing and the end cover are too loosely fitted, 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 bearing inner ring, which is used as a reference part, is moved below the zero line in the standard. The fit between the tolerance zone of the same shaft and the inner ring of the bearing is much more important than the fit between the tolerance zone and the general reference hole.

2. Improper selection or maintenance of grease, poor quality or deterioration of grease, or mixed 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 make the rotating part of the bearing have greater friction with the grease, while too little grease will cause dry friction and heat.

Therefore, the amount of grease must be adjusted so that it is about 1/2-2/3 of the space volume of the bearing chamber. Unsuitable or deteriorated grease should be cleaned and replaced with suitable 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. The shaft extension end adopts roller bearings, so that the rotor can be freely extended when it is heated and expanded. Due to the use of ball bearings at both ends of the small motor, there should be proper clearance between the bearing cover and the bearing outer ring, otherwise the bearing may be heated due to excessive thermal extension in the axial direction.

When this phenomenon occurs, the front and rear bearing caps should be removed, or a tissue pad should be added between the bearing cap and the end cap to form a sufficient gap between the outer bearing cap and the bearing outer ring.

4. The end covers or bearing covers on both sides of the motor are not installed correctly.

If the end caps or bearing caps on both sides of the motor are not mounted parallel or the stops are loose, the balls will spin out of the track and generate heat.

The end caps or bearing caps on both sides must be reinstalled flat and secured with evenly rotated bolts.

5. The balls, rollers, inner and outer rings, and ball cages are severely worn or peeled off.

Bearings should be replaced at this time.

6. Poor connection with the loader. Including: poor coupling assembly, excessive belt tension, different axis of load machine, too small diameter of pulley, too far bearing distance, too large axial or radial load, etc.

Correct wrong connections to avoid abnormal forces on bearings.

7. The shaft is bent.

At this time, the bearing force of the shaft is no longer a pure radial force, which will cause the bearing to heat up.

Try straightening the bent shaft or get a new one.

Mainly used for motor bearings hardened by soft dry oil or anti-rust paste, should be immersed in hot oil at 100-200 ℃, clamp the motor bearings with pliers, and use a brush to clean the oil stains on the motor bearings. Soft dry oil or anti-rust paste is heated to 100-200 ℃ to melt, and it is easy to wash out from the gap of the motor bearing. Sometimes as long as the motor bearing is shaken many times in the oil, the oil will flow away from the gap.

When cleaning the radial spherical motor bearing of the motor, the balls, the ball carrier and the inner ring should be turned out of the outer ring laterally and then immersed in the hot oil. When cleaning the short cylindrical roller motor bearing, the rollers, balls and The frame, inner ring and outer ring are disengaged.

During hot oil cleaning, the temperature of the oil should not exceed 200°C. When heating 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 sinking to the bottom will cause overheating and reduce the hardness.

General cleaning method

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, the dry oil or anti-rust paste on the motor bearing will fall off. Then put the motor bearing into relatively clean kerosene, brush with a soft brush, clean the oil stains in the ball and the gap, and then put it in the gasoline to clean it once, take it out and put it on a clean paper. When cleaning the radial spherical ball motor bearing and the short cylindrical roller motor bearing, the balls, the ball carrier, the inner ring and the outer ring should be separated and cleaned.

The cleaning of the motor bearing mounted on the shaft mainly relies on the method of drenching oil. The oil stains that are easy to be cleaned are first used kerosene and then gasoline; the oil stains that are difficult to be cleaned, first rinse with 100-200 ℃ hot oil, and then use gasoline cleaning. Be careful not to scrape the hard grease or rust on the motor bearing with sharp tools, so as not to damage the smoothness of the motor bearing rolling element and groove ring. Clean the motor bearing and dry it with a clean cloth.

Installation and inspection method

1. Before checking the bearing, first take out the old lubricating oil of the inner and outer small caps of the bearing, and then clean the inner and outer small caps of the bearing with gasoline with a brush. After cleaning, clean the bristles or cotton threads, and do not leave them in the bearing.

2. Carefully inspect the cleaned bearings. The bearings should be clean and intact, without overheating, cracks, peeling, groove impurities, etc., the inner and outer raceways are smooth, and the clearances everywhere are qualified. If the support frame is loose, it will cause friction between the support frame and the bearing sleeve. should be replaced with new bearings.

3. The bearing after maintenance should rotate flexibly without jamming.

4. Check that the inner and outer small covers of the bearing should be free of wear, and if there is wear, the cause should be found out and dealt with.

5. The matching between the inner sleeve of the bearing and the shaft should be tightened, otherwise it should be dealt with.

6. When assembling a new bearing, use oil heating or eddy current method to heat the bearing. The heating temperature is preferably 90-100 °C. Set the bearing on the motor shaft under high temperature, and ensure that the bearing is assembled in place. Bearing is hit to avoid damage to the bearing.