Industry News
A Preliminary Analysis of the Heating Mechanism of Sliding Bearings
As a supporting component of the rotating body, sliding bearings are widely used in high-speed and heavy-duty equipment due to their strong load-bearing capacity, no limit on speed and service life. They are used to support the rotating body. When they reach the condition of liquid lubrication, the sliding friction coefficient is quite low and the power consumption is relatively small, so they are highly favored by users; But when the processing accuracy and installation accuracy are insufficient, it can cause heating or even burning, often causing people to suffer greatly. Previously, there have been many introductions on the direct causes of its fever. Now, we will mainly provide a deeper introduction and analysis of its fever mechanism for readers' reference.
1. Design verification method for sliding bearings
The design of sliding bearings requires that the pressure per unit area must be less than the allowable pressure per unit area, or the heat generated by sliding bearings must be less than the allowable heat generation, that is, the heat dissipation capacity of sliding bearings must be greater than the heat generated by themselves. The equation can be expressed as:
Where:
P - pressure per unit area of sliding bearings
[p] Allowable pressure per unit area of sliding bearings
V - Linear velocity of sliding bearings
Pa - Total pressure of sliding bearings
Da - diameter of sliding bearing
Length of sliding bearing
N -- Speed of sliding bearings
From the above equation, it can be seen that the pressure p per unit area is affected by the bearing diameter da, bearing length la, and total pressure pa. When the equipment generates vibration or other additional loads, the total pressure increases, and the pressure per unit area increases accordingly. The pressure per unit area is proportional to the total pressure; When the inner diameter or length of the bearing changes, the pressure per unit area also changes and is inversely proportional to it. For sliding bearings in operation, although the diameter, length, and total load have been determined, the actual contact area between the shaft and the bearing varies, and the actual contact area will only be smaller than the nominal size. For example, the shaft and bearing cannot reach the nominal size in the arc length direction due to the influence of tile clearance and other factors; The contact in the length direction is the same. When the axial contact between the shaft and the bearing is short, the pressure per unit area increases. In short, the pressure per unit area is inversely proportional to the diameter of the bearing and the length of the bearing.
2. Heating mechanism of sliding bearings
The above analysis shows the relationship between the pressure per unit area of sliding bearings and the total load, bearing diameter, and bearing length, as well as the forms of change. The following analysis introduces the results generated when the pressure per unit area changes.
We know that the shaft and sliding bearing are a pair of friction pairs, belonging to sliding friction. Friction will generate heat, and the amount of heat generated is proportional to the frictional force and the speed of motion; High friction, high heat generation, fast speed, and high heat generation. Friction force is directly proportional to positive pressure and friction coefficient. From a design perspective, the total load is determined. After determining the diameter and length of the bearing, the pressure per unit area is also fixed. If these conditions are met during operation, the bearing will not generate heat, but the operation is variable. When the total load increases, the actual contact arc length, and the actual contact length change, the pressure per unit area will increase. This is a problem. In fact, the friction coefficient also increases with the increase of pressure per unit area. Once the friction coefficient increases, the frictional heat will increase. Once the heat is generated to the point where the frictional heat exceeds the amount that can be dissipated, the balance is broken, and the bearing will generate heat. In fact, when the pressure per unit area increases, the friction coefficient increases rapidly, as shown in the table below.
From the table, it can be seen that as the pressure acting on the bearing increases, its friction coefficient increases because the frictional work is equal to the product of the friction coefficient, positive pressure, and motion speed. When the contact is poor, the contact area decreases and the pressure increases; When the total load of the equipment increases during vibration, its pressure will also increase, so the friction coefficient will increase, the heat generation will increase, and the sliding bearing will inevitably generate heat. So any decrease in contact accuracy and increase in load under any circumstances will lead to an increase in local pressure on the sliding bearing, which in turn increases the friction coefficient and causes the bearing to heat up. In order to avoid friction between the shaft and the end of the bearing caused by the inflexibility of the ball surface tile, some units open the tile mouth very wide. Although this solves the problem to a certain extent, in a sense, it actually increases the force on the unit area of the bearing, which shortens the bearing life and reduces its ability to resist risks. When the bearing is moved by wind and grass, it will heat up, which is not conducive to stable operation. Some units reduce the contact area between the spherical tile and the tile seat very small in order to improve the flexibility of the spherical tile, especially for the spherical tile with a groove in the middle. Only a small part of the groove contacts on both sides, and the friction force will increase significantly, which is not conducive to the activity of the spherical tile. Although the enormous pressure did not cause collapse, there will always be local high points pressed in, just like rooting on both sides of a bridge, which further increases the stability of the spherical tiles. Therefore, in equipment management and maintenance, it is best to meet the design requirements as much as possible. For some parts with low processing accuracy, manual methods should be found to make up for them and meet the design requirements.
The coefficient of friction is not only related to pressure, but also to the speed of motion. The following is the relationship between speed and coefficient of friction.
From the above table, it can be seen that the friction coefficient of the equipment is very high when it is started. After running, the friction coefficient decreases, but the change is relatively small within a certain range. The magnitude of the change is relatively different from the influence of pressure on the friction coefficient. Therefore, when cement heats up in the kiln, the method of reducing the kiln speed is often used. Although it is effective, most of it cannot change the fate of heating. That is the reason. Some units operate well before shutdown, but when they start up, the tiles become hot or even partially burned, which is actually caused by high friction during startup. At this time, not only is the friction high, but the lubrication conditions also do not meet the requirements, especially for equipment without static pressure startup. On the other hand, when it comes to braking, it's different. The coefficient of friction increases from small to large, making it difficult for equipment running at high speeds to stop instantly, even with the use of holding brakes. In the past, the inertia principle was commonly used to explain why trains traveling at high speeds find it difficult to brake. In fact, the coefficient of friction also has an impact, at least extending the stopping time.
3. Conclusion
Through analysis, the relationship between friction force, friction coefficient, and pressure changes, as well as the relationship between friction coefficient and motion speed, can be obtained. This explains the mechanism of damage to the bearings during equipment start-up and heating of the bearings when contact accuracy is low, and why high-speed trains have difficulty braking.
2025 September 4th Week Marginal Product Recommendation:
Margianl LCB Plastic Clip Linear Bushings：
Made of high anti-wear material EPB13;
2.Maintenance-free, self lubricating;
3. Chemical resistant;
4. Dust resistant and quit running;
5. Installation by force fitting;
6. The E10 inner tolerance ensues only after the press fit.
