1. Mechanical damage
The mechanical damage of the sliding bearing means that the alloy surface of the bearing bush has different degrees of groove marks. In severe cases, metal peeling occurs on the contact surface and a large area of random scratches occurs; in general, the contact surface damage and ablation phenomenon exist simultaneously.
The main cause of mechanical damage to the bearing is that it is difficult to form an oil film on the bearing surface or the oil film is seriously damaged.
2, bearing cave erosion
Under the repeated action of the sliding bearing in the cylinder pressure impact load, the surface layer is plastically deformed and hardened by hardening, and the local deformation loss ability is gradually formed, and the grain is gradually formed and expanded continuously. Then, as the wear debris falls off, a hole is formed in the loaded surface layer. . Generally, when cavitation occurs in the bearing bush, the pit first appears, and then the pit gradually expands and causes cracking at the interface of the alloy layer, and the crack spreads in the parallel direction of the interface until peeling off.
The main reason for the cavitation of the sliding bearing is that the oil flow is strongly disturbed due to the sudden change of the cross section of the structural elements such as the oil groove and the oil hole, and bubbles are formed in the vacuum region where the oil flow is disordered, and then the bubble collapses due to the pressure rise. eclipse. Cavitation is generally found in the high load area of the bearing, such as the lower bearing of the main bearing of the crankshaft.
3, fatigue pitting
Bearing fatigue pitting refers to the overheating of the bearing and the excessive bearing clearance due to over-loading of the engine, resulting in fatigue damage, fatigue pitting or fatigue shedding in the middle of the bearing.
Most of this damage is caused by overload, excessive bearing clearance, or unclean lubricating oil and foreign matter mixed in the interior. Therefore, when using, care should be taken to avoid overloading the bearing. Do not operate at too low or too high speed; adjust the engine to a steady state when idling; ensure normal bearing clearance and prevent engine speed from being too high or too low; check and adjust cooling The working condition of the system ensures that the working temperature of the engine is suitable.
4, bearing alloy corrosion
The bearing alloy corrosion is generally the area where the lubricating oil is not pure. The chemical impurities (acid oxides, etc.) in the lubricating oil cause the bearing alloy to oxidize to form an acidic substance, causing the bearing alloy to partially fall off and form irregular micro holes or small concaves. pit. The main reason for the corrosion of the bearing alloy is improper selection of lubricating oil, poor corrosion resistance of the bearing material, or rough engine operation and high temperature.
5, bearing burning
There is a slight convex metal surface between the journal and the bearing friction pair, which forms a local high temperature. In the case of insufficient lubrication and poor cooling, the bearing alloy is blackened or partially melted. This fault is often caused by the over-tightening of the journal and the bearing; the insufficient pressure of the lubricating oil can easily cause the bearing to burn out.
6, the bearing goes outside the circle
The outer circle of the bearing is the relative rotation of the bearing in the seat hole. After the bearing goes out of the circle, it not only affects the heat dissipation of the bearing, but also causes the alloy on the inner surface of the bearing to ablate, and it also damages the back of the bearing and burns the bearing in severe cases. The main reason is that the bearings are too short, the crown is damaged, the processing or installation does not meet the specifications.
It can be seen that it is very important to understand the damage and characteristics of bearings in many industries.
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