Selection and characteristics of oil-free self-lubricating bearing in casting
In order to solve the lubrication problems of high temperature, low speed, heavy load, heavy dust, water flushing and shock vibration in mechanical equipment, oil-free self-lubricating bearings are selected.
1. The structure of the bearing Self lubricating bearing is a composite bearing with a solid lubricant friction area of 25-65%, which is made by developing orderly arranged cavities on the metal friction surface bimetallic bearing of the bearing matrix, embedding molybdenum disulfide, graphite and other linear bearings into a composite self-lubricating slider embedded in a metal sleeve.
The solid self lubricating slider can work normally at a high temperature of 280 ℃. However, due to its low mechanical strength, weak bearing capacity of the copper bushing, it is easy to deform. Embedding it in the metal hole groove can restrain this shortcoming, forming a metal part that plays a bearing role and a self-lubricating slider that plays a lubricating role.
The lubrication mechanism of the self-lubricating bearing is that during the sliding friction between the shaft and the sleeve, a part of the self-lubricating material molecule transfers to the metal surface of the shaft, fills the tiny uneven surface, and forms a relatively stable solid lubricating film, which causes the friction between the solid lubricating films and prevents the adhesion wear between the shaft and the sleeve.
This reasonable combination combines the respective complementary advantages of copper alloy and non-metallic antifriction materials, and is especially suitable for use under the special working conditions of oil-free, high temperature, high load, low speed, anti fouling, anti-corrosion, and strong radiation environments, as well as in the special working conditions of water or other solutions that can not add lubricating grease at all.
2. The proportion of the area occupied by the self lubricating slider to the surface area is related to the running speed and bearing strength, and the running speed is low; The pressure bearing strength is high, and the metal area should be larger.
For example, the area of the self lubricated slider of the traveling wheel bearing of the ingot grabbing trolley is about 25%, and the bearing of the spindle shaft of the ingot pulling mechanism should be fully lubricated with low bearing strength. The area of the self lubricated slider is about 65%.
3. As for the technical requirements of the bushing material, the bushing shall be made of alloy copper. The bushing shall have a high hardness, generally requiring heat treatment, and its hardness shall not be lower than HRC45.
4. Geometric shape and inlay requirements of self lubricating slider. There are two shapes of self lubricating slider, namely, column shape and rectangle shape. The self lubricating slider can adopt column shape according to its area, and vice versa. No matter what shape, it must be firmly embedded to prevent falling off during operation.
5. The fit clearance between the bushing and the shaft is about 10 times of the linear expansion coefficient of the self lubricating slider.
In order to adapt to the bearing temperature change, the clearance between the shaft and the bushing has increased from 0.032~0.15MM for the original metal piece four stage dynamic fit (D4/DC4) to 0.45~0.5MM.
The self lubricating slider protrudes 0.2~0.4MM from the bushing metal at one side of the friction pair. In this way, the bearing will be fully lubricated during the initial running in period, reducing the consumption of power driving power.
6. Advantages of oil-free self-lubricating bearings
A. No oil lubrication or little oil lubrication, applicable to places where oil cannot be added or it is difficult to add oil, and no maintenance or little maintenance can be carried out during use;
B. Good wear resistance, small friction coefficient and long service life;
C. It has an appropriate amount of elastic-plastic, which can distribute the stress on a wider contact surface and improve the bearing capacity;
D. The static and dynamic friction coefficients are similar, which can eliminate the creeping at low speed, thus ensuring the working accuracy of the machine;
E. It can reduce vibration and noise of machinery, prevent pollution and improve working conditions;
F. The transfer film can be formed during operation to protect the grinding shaft, without shaft seizure;
G. The hardness of the grinding shaft is low, and the untempered shaft can be used, thus reducing the processing difficulty of related parts;
H. Thin wall structure, light weight, can reduce the mechanical volume;
1. The bushing is made of brass and can be used in corrosive medium.