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Failure judgment of angular contact ball bearings in manufacturing

wallpapers Industry 2020-11-20
In the manufacturing industry, the most commonly used spindles are high-speed precision angular contact ball bearings, which rotate at high speeds and sometimes generate high heat. If this phenomenon is not eliminated in time, it will lead to overheating of angular contact ball bearings and increase the temperature of the corresponding parts of the machine tool to produce thermal deformation. In severe cases, the main shaft and tailstock will not be equal in height, which will not only affect the accuracy and processing accuracy of the machine tool itself. , And it will burn out the bearing.
 
Rated fatigue life
 
Rated fatigue life refers to the total number of revolutions when a group of bearings of the same model is operated under the same conditions, and 90% of the angular contact ball bearings are free from peeling caused by rolling fatigue. When the speed is constant, the total operating time is often used to express the rated fatigue life. When studying the life of a thrust ball bearing, one should not only consider the fatigue life but also consider several service limits based on the performance of the bearing. For example, the grease life of grease lubricated bearings. The noise life, wear life, etc., have different usage limits depending on the application. Therefore, the empirical limits are often selected in advance. Therefore, it is difficult to know the real cause of the damage only by investigating the damage of the angular contact ball bearing. However, if you know the use of the thrust ball bearing machinery, operating conditions, the structure around the bearing, understand the situation before and after the accident, combined with the damage state of the bearing and several reasons, you can prevent similar accidents from happening again.
 
Judgment on the availability of angular contact ball bearings
 
It is mainly determined by considering the degree of bearing damage, mechanical performance, importance, operating conditions, and the period until the next maintenance. If there are the following defects, they can no longer be used and must be replaced with new thrust ball bearings. There are cracks or gaps in any of the inner ring, outer ring, rolling element, and cage. Wear failure is one of the common failure modes of various types of bearings. According to the form of wear, it can usually be divided into the most common abrasive wear and adhesive wear. We can judge whether the bearing has reached wear failure through the following techniques:
 
1. Oil film resistance diagnosis technology
 
Features: The same criteria can be used for different working conditions. Diagnosing abnormalities such as surface peeling, indentation, and cracking is poor.
 
Application: Suitable for occasions where the rotating shaft is exposed.
 
2. Vibration diagnosis technology
 
Features: Vibration diagnosis technology is widely used; online monitoring can be realized; diagnosis is fast, and diagnosis theory is mature.
 
Application: It is especially suitable for fault monitoring of angular contact ball bearings in rotating machinery.
 
3. Ferrograph diagnostic technology
 
Features: The machine does not need to be disassembled; the investment is low and the effect is good; the early fatigue failure of the oil-free bearing can be found; the wear mechanism can be studied.
 
Application scope: Suitable for fault diagnosis of angular contact ball bearings lubricated with lubricating oil, but difficult for bearings lubricated with grease.
 
 
4. Temperature diagnosis technology
 
Features: Simple diagnosis; better judgment of bearing burn.
 
Application range: Suitable for simple routine diagnosis of bearings in machines.
 
5. Optical fiber monitoring and diagnosis technology
 
Features: The optical fiber displacement sensor has high sensitivity; the signal is extracted directly from the surface of the oil-free bearing, which improves the signal-to-noise ratio; it can directly reflect the manufacturing quality, surface wear, load, lubrication and clearance of the angular contact ball bearing.
 
Application: Suitable for machines where the sensor can be installed in the bearing housing.
 
6. Acoustic emission diagnostic technology
 
Features: fast and easy diagnosis; online monitoring.
 
Application scope: New technologies developed in recent years are rarely used in bearing condition monitoring.
 
 
When picking oil-free bearings by hand during the inspection process, wash away the sweat from your hands and apply high-quality mineral oil before proceeding. Pay special attention to rust prevention during the rainy season and summer. Under certain special operating conditions, angular contact ball bearings can obtain a longer life than traditional calculations, especially under light load conditions. These special operating conditions are when the rolling surfaces (tracks and rolling elements) are effectively separated by a lubricating oil film and limit contaminants that may cause surface damage. In fact, under ideal conditions, the so-called permanent bearing life is possible.
 
As soon as the angular contact ball bearing rotates, the raceway surfaces of the inner ring and the outer ring are in rolling contact with the rolling elements, so the running track is a dark surface, and the running track attached to the raceway surface is not abnormal. Load conditions, so when disassembling the oil-free bearing, please pay attention to and observe the running track of the raceway surface.

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