Inspection of Rolling Bearing Failures and Causes of Failure

Rolling Bearing Failures

Due to its own quality and external conditions, the bearing capacity, rotation accuracy and wear resistance of rolling bearings will change during use. When the performance index of the bearing is lower than the usage requirements and cannot work normally, the bearing will fail or even fail. Once the bearing fails and other unexpected circumstances, the machine and equipment will stop, and various abnormal phenomena such as loss of function will occur. Therefore, It is necessary to find out the cause of the occurrence in the short term and take corresponding measures.

In order to make the bearing maintain its proper performance under good conditions and use it for a long time. The bearing must be inspected and maintained. Inspection and maintenance are very important to prevent failure. During operation, the rolling sound, vibration, temperature and lubricant of the bearing should be checked.

1. The rolling sound of the bearing

One of the noise of rolling bearing is generated by the bearing itself, that is, the inherent noise of the bearing; the other is the noise generated after the bearing is installed, which has nothing to do with the noise of the bearing itself. Some problems can be analyzed by listening to the sound. a) Inherent noise: rolling Sound “Various bearings and rolling friction sounds (cylindrical roller bearings) are inherent sounds of rolling bearings.” The sound of the raceway is produced by the elastic characteristics of the rolling elements when they are in contact with the raceway. When the bearing rotates, the rolling elements are in the rolling It is a continuous and smooth sound made by rolling on the road; abnormal rolling friction sound can make abnormal metal friction sound such as “squeak, squeak”, and it will not make such a sound when it is well lubricated. Therefore, it is not a problem in general, and it is necessary to pay attention only after the noise increases. b) Noise related to bearing manufacturing: including cage noise and vibrato, cage noise mainly occurs in ball bearings and tapered roller bearings, when the bearing rotates due to the vibration of the cage and the collision between the cage and the rolling elements. Make noise. This sound is periodic. Tremolo (various bearings) is a sound with a certain frequency, which is caused by the vibration caused by the large waviness on the raceway surface. c) Noise caused by improper use: it exists for all kinds of bearings. When the bearing raceway surface or rolling element surface is bumped, cratered, and corroded, noise and vibration with a certain period will be generated. When the bearing has dust intrusion during operation, dirt noise will be generated. This kind of noise is not Periodic, also accompanied by vibration, the volume of the sound is not fixed, sometimes absent.

2. Vibration of bearing

The vibration of the bearing has an obvious effect on the failure of the bearing. For example, spalling, indentation, corrosion, cracks, wear, etc. will be reflected in the bearing vibration detection, so by using a special bearing vibration measurement device (frequency analyzer and vibrator, etc. ) can measure the magnitude of the vibration, and the specific situation of abnormal vibration can be inferred from the frequency distribution. The measured values ​​are different due to the operating conditions of the bearing or the installation position of the sensor, so it is necessary to analyze and compare the measured values ​​of each machine in advance. Then determine the judgment criteria.

3. The temperature of the bearing

Usually the temperature of the bearing gradually increases with the operation, and reaches a steady state after 1 to 2 hours. The normal temperature of the bearing varies with the heat capacity, heat dissipation, speed and load of the machine. If the lubrication and installation are not suitable, the bearing temperature It will rise sharply and abnormally high temperature will occur, at this time, it is necessary to stop and take necessary preventive measures.

4. Lubricant

Lubrication has an important influence on the fatigue life and friction, wear, temperature rise, vibration, etc. of rolling bearings. Without normal lubrication, the bearing cannot work. Analysis of the causes of bearing damage shows that about 40% of bearing damage is related to poor lubrication. Therefore, Good lubrication of the bearing is an effective measure to reduce the friction and wear of the bearing. In addition, the lubrication of the bearing also plays a role in heat dissipation, rust prevention, sealing, mitigation of impact, etc. To ensure that the lubricant cannot expire and fail, the selection must be correct .The lubricating of the harvester bearing is divided into oil lubrication and grease lubrication. The oil lubrication of the large model gear box is GL-5 80W90 gear oil; the grease lubrication is generally made of molybdenum disulfide lithium base grease, and the torque increaser is continuously variable. The lower unit must be lubricated with Mobil XHP222 or better.

There are many reasons for bearing failure. In addition to normal fatigue spalling, factors such as failed seals, too small bearing clearance or poor lubrication caused by tight fit can leave special failure traces and failure modes. Therefore, check the failed bearings in the Most of the time, the cause of bearing failure can be found, so that countermeasures can be taken in time. Generally speaking, 1/3 of bearing failure is because the bearing has reached the fatigue spalling period, which is a normal failure; 1/3 is due to premature failure due to poor lubrication. 1/3 The bearing fails prematurely due to contaminants entering the bearing or improper installation. Generally speaking, there are seven common symptoms when the bearing does not operate normally: bearing overheating, bearing noise too high, bearing life too low, and vibration , The performance requirements of the machine cannot be met, the bearing is loose on the shaft, and the shaft is difficult to rotate.

Typical causes of seven common symptoms: grease, lubricating oil expired failure or wrong type selection; grease is too full or oil level is too high; bearing clearance is too small; bearing housing inner hole is not round, bearing housing is twisted and deformed, supporting surface Uneven, the inner diameter of the bearing box hole is too small; the interference of the contact oil seal is too large or the spring is too tight; there are two fixed bearings on one shaft, and the bearing clearance becomes smaller due to the expansion of the shaft; the tightening sleeve is too tight; the bearing The box hole is too large and the force is unbalanced; the coaxiality of two or more bearings is not good; the anti-loosening snap ring is in contact with the bearing; the contact oil seal is severely worn, resulting in the leakage of lubricating oil; the diameter of the shaft is too large. As a result, the inner ring of the bearing expands seriously, reducing the bearing clearance; because the material of the box hole is too soft, the hole diameter becomes larger after being stressed, causing the outer ring to slip in the box hole; the oil level is too low, and the grease in the bearing box is insufficient; Sundries, sand, carbon powder or other contaminants enter the bearing housing; water, acid, paint or other contaminants enter the bearing housing; debris and other debris in the bearing housing are not removed before the bearing is installed; the shaft diameter is too small, Insufficient locking of the clamping sleeve; scratches on the rolling elements due to slippage (due to rapid start); shaft bending due to unreasonable shoulder size; shaft shoulder rubbing against bearing seal cover; shaft shoulder at the inner joint of bearing housing Twisting of bearing outer ring due to too small area; Twisting of bearing seals; Twisting of shaft and bearing inner sleeve; ; The contact oil seal is severely worn, resulting in the leakage of lubricating oil; the bearing clearance is too large to cause the shaft to vibrate.

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