Poor lubrication is an important cause of bearing failure, accounting for more than one-third of bearing failures. During the use of bearings, poor lubrication is a problem that many engineers need to face. This article introduces the knowledge of bearing problem diagnosis and analysis related to poor bearing lubrication.

General mechanism of bearing poor lubrication

Lubrication mainly plays a role in reducing friction in bearings. A general lubricant separates the friction pair by forming a lubricating oil film between the two surfaces of the bearing in relative motion, thereby reducing friction. For rolling bearings, the rolling elements and raceways are separated. If the lubricating oil film completely separates the rolling elements from the road, it is in a hydrodynamic lubrication state, which is a very good lubrication state. The so-called poor lubrication is essentially that the lubricating oil film does not separate the rolling elements from the raceways. When the bearing rolls, the metal is in direct contact with the metal, thus accelerating the failure of the bearing. For the specific lubrication mechanism, you can refer to a series of bearing application technical books written by the author, all of which are explained in detail. This article only gives a general description.

"Symptoms" of Poor Bearing Lubrication

It can be seen from the above that the essence of poor bearing lubrication is that the oil film does not completely separate the rolling elements and the raceways. In other words, there is direct contact between the rolling elements and the raceways. When the bearing is rolling, there is direct friction between metal and metal inside the bearing.

In a well-lubricated state, there is no direct metal friction inside the bearing, and the overall friction is small, so the heat generated by friction is small. In the case of poor lubrication state of the bearing, the bearing lubricating film is destroyed, the bearing metal is in direct contact, the friction increases, and the heat generated by the bearing operation becomes larger. Therefore, the phenomenon of high bearing temperature will occur. It is often said that the bearing heats up.

Other failures of the bearing will also cause the temperature of the bearing to rise and generate heat. What is the difference between these states and the temperature change caused by simple poor lubrication?

The simple poor lubrication here refers to the poor lubrication itself, and its essence is the poor basic performance of the lubricating medium, mainly the problem of lubricating viscosity. When simple poor lubrication begins to appear, there is no other problem with the bearing, so only the friction between the rolling body and the raceway surface is abnormal, and the bearing surface does not cause serious damage in a short period of time, only the rolling friction increases and the temperature rises. At this point an increase in bearing temperature can be observed. However, since all components of the bearing are in good condition, the vibration of each component of the bearing has no abnormality in its characteristic frequency. The on-site observation is that the temperature of the bearing is rising, but other status information such as vibration is normal.

Failure Analysis of Bearing Poor Lubrication

Poor lubrication results in direct metal-to-metal contact between the bearing rolling elements and the raceway, so surface-originated fatigue or surface degradation occurs between the bearing rolling elements and the raceway surface. As shown below:

The surface roughness of the raceway in the figure changes, and the bearing begins to show surface degradation. If it is purely poor lubrication (contamination issues are not included here), the metal surface may develop into a state of surface fatigue, initially showing a non-uniform mirror surface, and then surface peeling.

Treatment of poor bearing lubrication

There are many factors that cause poor bearing lubrication, such as pollution and other factors. The poor lubrication mentioned in this article refers to simple poor lubrication, and the influence of pollution and other factors will be introduced in subsequent articles.

As mentioned earlier, the simple poor lubrication of the bearing is mainly due to the fact that the viscosity of the bearing cannot meet the requirements for forming a lubricating film. If there is poor lubrication at this time, the factors affecting the viscosity of the lubricant should be adjusted according to the situation.

Poor lubrication may be related to lubrication selection when the equipment has just completed the manufacturing stage. When poor lubrication occurs, check the selection of lubrication, filling of lubrication and other processes. Ensure that the bearing lubrication in the equipment is selected correctly and the oil quantity is correct.

In the problem of poor lubrication during the operation of the equipment, the equipment was originally in good condition, but suddenly there are indications of poor lubrication. Then it is necessary to examine the factors that affect the lubrication during this process. For example, whether the temperature fluctuates; whether there is a relubrication operation; whether there is pollution entering; whether there is a mixture of grease and other factors.

At the early stage of improper lubrication indications, correcting the lubrication problem in time can avoid early failure of the bearing. At this time, the bearing may not be damaged, and the lubrication is corrected, and all failure indications will be solved.

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