When we use self-lubricating bearings, the self-lubri […]
When we use self-lubricating bearings, the self-lubricating bearings will be damaged due to wear during use. So what are the reasons for these damages?
1. Bearing cavitation
Self-lubricating bearings under the repeated action of the cylinder pressure charge load), the surface layer undergoes plastic deformation and cold work hardness, one-sided loss of deformation strength, gradually forming lines and expanding continuously, and then followed by the fragmentation of wear debris, forming on the loaded surface layer hole. Usually, when the bearing is corroded, pits appear first, and then the pits gradually enlarge and cause the cracking of the alloy layer interface, and the cracks extend along the parallel target of the interface until they peel off.
The key reason for the cavitation of self-lubricating bearings is that the sudden change of the cross-section of structural factors such as oil grooves and oil holes causes severe turbulence in the oil flow. Bubbles are formed in the turbulent vacuum zone of the oil flow, and then the bubbles collapse due to the increase in pressure. Cavitation. Cavitation usually occurs in the high load area of the bearing, such as the lower bearing bush of the main bearing of the crankshaft.
2, the bearing goes outside the circle
The outer circle of the bearing means the relative rotation of the bearing in the seat hole. After the bearing goes outside the circle, it will not only affect the heat dissipation of the bearing, and easily ablate the alloy on the inner surface of the bearing, but also damage the reverse surface of the bearing. The bearing will be destroyed when it is urgent. The main reason is that the bearing is too short, the tenon is damaged, the processing or the installation does not meet the specifications, etc.
3, mechanical damage
Self-lubricating bearing mechanical damage refers to the presence of groove marks of different levels on the alloy surface of the bearing bush. When it is important, metal peeling and large-area messy scratches occur on the contact surface; under normal conditions, contact surface damage and ablation occur at the same time.
The main reason for the formation of bearing mechanical damage is that it is difficult to form an oil film on the bearing surface or the oil film is critically destroyed.
4, bearing alloy erosion
Bearing alloy erosion is usually caused by the impure smooth oil. The chemical impurities (acid oxides, etc.) in the smooth oil oxidize the bearing alloy to produce acidic substances, causing the bearing alloy to fall apart and form tiny cracks or dimples that cannot be avoided. pit. The key reasons for the corrosion of bearing alloys are improper selection of lubricating oil, poor corrosion resistance of bearing raw materials, or excessive work and excessive temperature.
5. Fatigue pitting
Bearing fatigue pitting refers to the overheating of the bearing and the excessive clearance of the bearing due to the idea of overloading, resulting in fatigue damage, fatigue pitting, or fatigue in the middle of the bearing.
This kind of damage is mostly caused by overload, excessive bearing clearance, or dirty oil and foreign matter inside. Therefore, attention should be paid to prevent bearing overload work and not run at insufficient or excessively high speed; when idling, adjust the engine to a stable form; ensure normal bearing clearance to prevent excessive or insufficient engine speed; check and adjust cooling The working conditions of the system ensure that the working temperature of the idea is appropriate.
6, bearing melting
There is a small raised metal surface in direct contact between the journal and the bearing conflict pair, resulting in a one-sided high temperature, and under the condition of insufficient smoothness and poor cooling, the bearing alloy will be black or one-sided sintered. This obstacle is often caused by the tight fit between the journal and the bearing; insufficient lubricating oil pressure can easily destroy the bearing.