Sliding bearings used in engines are generally divided into two types: one is a lining type thin-walled bearing, which is similar to a tile commonly known as a bearing bush; the other is a bushing, also known as a copper sleeve, which is in the shape of a hollow cylinder. The lining type thin-walled bearing is mainly used to support the crankshaft and the connecting rod of the engine; the bushing is mainly used for supporting the camshaft journal and the piston pin. This paper mainly describes the lining type thin-walled
bearings (bearings).
Early damage form
This natural damage is unavoidable during normal use of the bearing due to wear and tear until it eventually loses its ability to work and ends its service life. However, if the bearing is prematurely worn or damaged due to improper adjustment of the engine assembly, poor quality of the lubricating oil or poor use conditions, it is an early damage caused by man. Early damage not only greatly reduces the service life of the bearing, but also affects the normal operation of the engine. According to the long-term experience of diesel engine maintenance, the common forms of early damage of sliding bearings are mechanical damage, bearing cavitation, fatigue pitting, corrosion and so on.
(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 cavitation
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 corrosion of the bearing alloy is generally that 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.
