1、 Mechanical damage
In severe cases, metal peeling and large areas of messy scratches may occur when in contact with the surface. Under normal circumstances, mechanical damage to bearings refers to the appearance of uneven grooves on the alloy surface of the bearing shell. The primary reason for the mechanical damage of bearings caused by contact surface damage and erosion is that the outer surface of the bearing is difficult to form an oil film or the oil film is severely damaged.
2、 Bearing cavitation
The outer layer undergoes plastic deformation and cold work hardening, and the sliding bearing is subjected to repeated effects of cylinder pressure impact loads. Partially losing the ability to deform, gradually forming patterns and continuously expanding, and then following the falling of debris, the outer layer under load forms cavities. Usually, when the bearing shell experiences pitting corrosion, pits first appear, and then these pits gradually expand, leading to cracking of the alloy layer interface. The cracks expand along the parallel direction of the interface until the fall stops. The primary cause of pitting corrosion in sliding bearings is due to the sudden modification of the cross-section of layout elements such as oil grooves and oil holes, which leads to intense oil flow imbalance. The vacuum zone with oil flow imbalance forms bubbles, which then collapse and cause pitting corrosion due to increased pressure. Cavitation usually occurs in the high load area of bearings, such as the lower bearing shell of the crankshaft main bearing.
3、 Fatigue pitting corrosion
Due to engine overload operation, bearing fatigue pitting refers to. Overheating of the bearing operation and excessive clearance of the bearing can cause fatigue damage, fatigue pitting, or fatigue induced falls in the middle of the bearing. This type of damage is mostly caused by overloading, excessive bearing clearance, unclean lubricating oil, or foreign objects mixed inside. Therefore, when using it, attention should be paid to preventing bearing overload operation and not operating at too low or too high a speed; When idling, adjust the engine to a stable condition; Ensure normal bearing clearance to prevent engine speed from being too high or too low; Check and adjust the operating condition of the cooling system to ensure that the engine’s operating temperature is appropriate.
4、 Corrosion of bearing alloy
The chemical impurities (such as acidic oxides) in the lubricating oil oxidize the bearing alloy and generate acidic substances. Corrosion of the bearing alloy is usually caused by impure lubricating oil. Causing the bearing alloy to partially fall, resulting in irregular micro cracks or small pits. The primary cause of corrosion in bearing alloys is improper selection of lubricating oil, poor corrosion resistance of bearing materials, and perhaps rough engine operation or excessively high temperatures.
5、 Bearing melting
The components are in high temperature, and there are slight raised metal surfaces in direct contact between the shaft neck and the bearing contact pair. Under conditions of insufficient lubrication and poor cooling, the bearing alloy may turn black or partially melt. This problem is often caused by the tight cooperation between the journal and the bearing; Insufficient lubricating oil pressure can also lead to bearing burnout.