The cause of the heating of cylindrical roller bearings on the service life

• Shanghai Zhio Technology Co.,Ltd 
• 2023-08-29

Overheating of the microstructure after quenching can be observed on the rough mouth of the bearing part. But to accurately judge the degree of its overheating must observe the microstructure. If coarse acicular martensite appears in the quenched structure of GCr15 steel, it is a quenched superheated structure. The reason for the formation may be the overall overheating caused by the quenching heating temperature is too high or the heating and holding time is too long; it may also be due to serious banded carbides in the original structure, forming local martensitic needle-like thick in the low-carbon area between the two bands, localized overheating. The retained austenite in the superheated structure increases and the dimensional stability decreases. Due to the overheating of the quenched structure and the coarse crystals of the steel, the toughness of the parts will be reduced, the impact resistance will be reduced, and the life of the bearing will also be reduced. Severe overheating can even cause quenching cracks
If the quenching temperature is too low or the cooling is not good, a tortenite structure exceeding the standard will be produced in the microstructure, which is called underheating structure, which reduces the hardness and wear resistance sharply, which affects the life of cylindrical roller bearings. Cracks formed by internal stress during quenching and cooling are called quenching cracks. The reasons for this crack are: due to the high quenching heating temperature or the rapid cooling, the thermal stress and the structural stress of the metal mass and volume change are greater than the fracture strength of the steel; the original defects of the working surface (such as surface fine cracks or scratches) Severe surface decarburization and carbide segregation; insufficient or untimely tempering of parts after quenching; excessive cold stamping stress caused by previous processes, forging folds, deep Turning tool marks, sharp edges and corners of oil grooves, etc. In short, the cause of quenching cracks may be one or more of the above factors, and the existence of internal stress is the main reason for the formation of quenching cracks. The quenching crack is deep and slender, the fracture is straight, and the fracture surface has no oxidation color. It is often a longitudinal straight crack or annular crack on the cylindrical roller bearing ring; the shape of the bearing steel ball is S-shaped, T-shaped or annular. The organizational characteristics of quenching cracks are that there is no decarburization on both sides of the cracks, which is obviously different from forging cracks and material cracks.
During the heat treatment of bearing parts, there are thermal stress and tissue stress. This internal stress can be superimposed or partially offset, which is complex and changeable, because it can vary with the heating temperature, heating speed, cooling method, cooling speed, and shape of the part. and size changes, so heat treatment deformation is inevitable. Knowing and mastering its changing law can make the deformation of cylindrical roller bearing parts in a controllable range, which is beneficial to the production. Of course, the mechanical impact during the heat treatment will also deform the part, but this deformation can be reduced and avoided with improved operations.
Internal factors mainly refer to the three major factors that determine bearing quality, such as structural design, manufacturing process and material quality.
The metallurgical quality of bearing materials used to be a major factor affecting the early failure of rolling bearings. With the advancement of metallurgical technology (such as vacuum degassing of bearing steel, etc.), the quality of raw materials has been improved. The proportion of raw material quality factor in bearing failure analysis has dropped significantly, but it is still one of the main influencing factors of bearing failure. Whether the material is selected properly is still a factor that must be considered in bearing failure analysis.
The manufacture of cylindrical roller bearings generally goes through multiple processing processes such as forging, heat treatment, turning, grinding and assembly. The rationality, advancement and stability of each processing technology will also affect the life of the bearing. Among them, the heat treatment and grinding processes that affect the quality of the finished bearing are often more directly related to the failure of the bearing. In recent years, the research on the metamorphic layer of the bearing working surface shows that the grinding process is closely related to the bearing surface quality.
The main task of bearing service life analysis is to find out the main factors causing bearing failure according to a large number of background materials, analysis data and failure forms, so as to propose improvement measures in a targeted manner, prolong the service life of bearings, and avoid cylindrical roller bearings. Sudden early failure occurs.