Three-phase asynchronous motor journal wear and bearing overheating treatment methods

Journal wear and bearing overheating in three-phase asynchronous motors are two of the most common but related mechanical failures. Journal wear is often the result of an overheated bearing, improper installation, or lubrication failure that worsens the problem. Below I will sort out the solutions to these two types of problems separately to facilitate your comparison.

1. Treatment of journal wear

When dealing with journal wear, different repair processes are mainly selected based on the degree of wear:

Slight wear: If the journal wear is not large, it can be chrome plated or sprayed with a layer of metal, and then machined to the original size with a lathe or grinder. In some emergency situations, the worn area can also be knurled to temporarily restore size.

Severe wear: For severely worn journals, the most common and reliable method is to turn after repair welding. The key points of the operation are: evenly surfacing the journal wear along the circumference (it is recommended that the surfacing thickness be 3mm higher than the original surface), pay attention to avoid pores and slag inclusions, and use a lathe to turn the circle according to the original diameter after cooling.

The wear is particularly serious: If the journal wear is too large, the hot pressing sleeve method can be used. Turn the worn part of the journal into small pieces, and use 35#-45# steel to make a ferrule (thickness is not less than 3-4mm). Heat the ferrule to about 100°C and put it on the journal while it is hot. After cooling and shrinking, turn it to the required size. Please refer to the following table for interference amounts of different shaft diameters:

Note: For the wear caused by the inner ring of the bearing "running on the inner ring" (that is, the inner ring slides on the shaft), when repairing the journal, it is necessary to replace the new bearing and ensure that the matching tolerance between the new bearing and the repaired journal is correct.

2. How to deal with bearing overheating

Bearing overheating usually manifests as the temperature rise of rolling bearings exceeding 55℃ and the temperature rise of sliding bearings exceeding 40℃. When handling, first check the lubrication, then check the mechanical assembly, and finally check the load condition.

Lubrication problem: The space volume of the bearing chamber from about 1/2 to 2/3 is a reasonable amount of grease filling. Too much or too little will cause overheating. At the same time, ensure that the grease is of the correct type, clean and free of impurities. Deteriorated grease needs to be thoroughly cleaned and replaced.

Assembly issues: Check whether the bearing is installed in place and the fit is appropriate. If the fit between the bearing and the shaft is too tight or the fit between the bearing and the end cover is too loose, it will cause heat. At the same time, it is necessary to check whether the end caps or bearing caps on both sides are installed parallel, whether the stop is tight, and whether the axial gap between the bearing cap and the bearing outer ring is too small (if it is too small, you can turn the bearing cap or add a paper pad to adjust).

Shaft and connection problems: Shaft bending will cause the bearing to bear non-pure radial forces and generate heat, requiring alignment or replacement. In addition, the coupling between the motor and the load is not corrected, the belt is too tight, etc., which will also cause the bearing to bear extra load and overheat.

3. Sequence of investigation and processing

If you encounter a problem on site, you can troubleshoot according to this idea:

First, check and adjust lubrication. This is the most common and easiest to deal with, refill with proper amount of clean grease.

Secondly, check the assembly quality. Listen to the bearing for any abnormal noise and feel for vibration. If you suspect that the assembly is too tight or the shaft is bent, you need to disassemble the machine for inspection and measurement.

Finally, deal with journal wear. If the bearing is found to be severely damaged during inspection, after removing the bearing, be sure to measure and repair the journal wear before assembling a new bearing, otherwise the new bearing will soon be damaged.

It should be noted that for medium and large motors, the selection of bearings with reliable quality (such as products from the three major manufacturers of SKF, NSK, FAG or Havalo) is the basis for reducing such failures.

(Source: Electrical Engineering and Intelligent Technology)