The temperature of a bearing during operation differs from the temperature in the non-operational state, indicating an increase in temperature when the bearing is in use. The main causes for this increase in temperature can be categorized into two main aspects:
Firstly, external heat conduction. The heat generated by the operation of external mechanical components leads to a general increase in temperature in all parts of the machinery. This heat is conducted to the bearings, resulting in heat generation.
For motors and gearboxes, this occurs mainly in two ways:
1) In the case of motors, the main sources of heat during operation are the windings and the core itself. The well-known heat loss due to copper loss during motor operation is caused by the heat generated when current flows through the wire.
Iron loss refers to the heat generated by the core itself when the magnetic field changes during engine operation. These two parts are the main heat sources of the engine, and this heat is conducted to the bearings through the base, shaft and end cap, causing the bearing temperature to increase.
2) For gearboxes, the meshing of gears causes frictional heat generation. This heat is conducted through the gears, shaft and base. The agitation of the lubricating oil transmitted to the bearings also contributes to the increase in bearing temperatures.
Secondly, the heat generation of the bearings themselves. During bearing operation, the internal environment of the bearing involves rolling friction, sliding friction, loss of drag, sealing friction and other corresponding friction. This friction dissipates in the form of heat, resulting in an increase in the temperature of the bearing itself.
Equipment engineers are deeply concerned about the inherent temperature of bearings, so it is sometimes necessary to estimate bearing temperature. This article presents a simple method to resolve this issue.
Before we start the actual calculations, we can first make a rough estimate of the heating state of the two parts mentioned above. The reason for making such an estimate is that, on site, if specific calculations cannot be carried out, at least a general assessment and understanding of the causes of bearing heating can be made, which will help distinguish whether the site condition is normal. or not.
We know that for bearings, most of the internal friction is rolling friction. The nature of rolling friction dictates that this is a small value. Please note that this is determined by the characteristics of the bearings, otherwise what is the use of bearings?
Don't forget that the purpose of inventing bearings is to reduce friction and decrease torque. The proportion of sliding friction in bearings must be very small, otherwise it cannot be called rolling.
At the same time, the loss of lubrication due to shaking in the bearings, compared with other friction, should also not be a large value. Therefore, the heat generated by the movement of the bearing itself is not the main source of heat, but must be a secondary factor in the overall increase in bearing temperature.
The main factor that causes a significant increase in temperature in bearings is the heat generated by the equipment itself. The heat generated by the equipment itself will be estimated during equipment design. This heat, when transmitted to the bearings considering heat dissipation and other factors, is generally less than or equal to the total heat generated by the equipment itself.
Based on this knowledge, when heating the bearings on site, the temperature distribution of the heated bearings of the equipment can initially be checked, and then consider the heating elements of the bearing itself.
If the bearing temperature is significantly higher than the equipment temperature, this should be a cause for concern, as at this point the heat generated by the bearing has become the main heat source, indicating that the internal friction condition is no longer normal.
Calculating the heat generated by the bearing itself begins with calculating the bearing friction. Normally, the heat generated by the bearing itself can be calculated through its own friction torque, the formula is as follows:
Q=1.05*10 -4 Mn
- M: Total friction torque of the bearing
- n: Bearing rotation speed.
Interested engineers can calculate the proportion of bearing heat in the total heat generation of their equipment. This will facilitate a qualitative and quantitative understanding of the two stages of bearing heat generation.
