Today, let’s look at the damage characteristics of engine journal bearings.
The mechanical damage of NSK imported bearing refers to the groove on the alloy surface of bearing bush. In severe cases, the metal on the contact surface will fall off and scratch a large area randomly. Generally, contact surface damage and ablation exist at the same time. The main reason of bearing mechanical damage is that it is difficult to form oil film on the bearing surface or the oil film is seriously damaged.
Under the repeated action of pressure impact load in the cylinder, plastic deformation and cold work hardening occur on the surface of sliding bearing, the local deformation capacity of NSK imported bearing is lost, and the grain gradually forms and continues to expand. A cavity layer is formed on the bearing surface and the wear particles fall off. In the process of pitting corrosion, pitting pits appear first and then expand gradually, resulting in interfacial cracking of alloy layer. The crack propagates along the parallel direction of the interface until peeling.
Fatigue pitting corrosion of NSK imported bearing refers to fatigue damage, fatigue pitting corrosion or fatigue falling off in the middle of the bearing due to engine overload, bearing overheating, bearing clearance and other reasons. This damage is mostly caused by overload, excessive bearing clearance, or unclean lubricating oil and mixed with foreign matters. Therefore, attention shall be paid to avoid bearing overload operation, and the speed shall not be too low or too high; Adjust the engine to a stable state at idle speed; Normal bearing clearance shall be ensured to prevent the engine speed from being too high or too low; The working state of the temperature drop system shall be checked and adjusted to ensure that the operating temperature of the engine is appropriate.
The corrosion of NSK imported bearing alloy is generally caused by impurities in lubricating oil. Chemical impurities (such as acid oxides) in the lubricating oil oxidize the bearing alloy and produce acidic substances, which makes the bearing alloy fall off and form irregular microcracks or pits. The main causes of bearing alloy corrosion are improper selection of lubricating oil, poor corrosion resistance of bearing materials, rough engine operation and high temperature.
There is a small convex metal surface between the journal and the bearing friction pair, forming a local high temperature. When the lubrication is insufficient and the temperature drop is poor, the bearing alloy blackens or partially melts. This tight journal lubrication is usually caused by bearing combustion.
The outer ring of NSK inlet bearing indicates that the bearing has relative rotation in the seating hole. After the bearing enters the outer ring, it will not only affect the heat dissipation of the bearing, but also the alloy on the inner surface of the bearing is easy to ablate, and the rear surface of the bearing will be damaged, which will burn the bearing in serious cases. The main reason is that the bearing is too short, the tenon is damaged, and the processing or installation does not meet the specifications.