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Heat treatment is a key process in the manufacturing process of automotive bearings. Its processing quality and raw materials are two important factors affecting bearing life. Below, the author based on his own work experience and knowledge, from the automotive bearing materials, heat treatment design, heat treatment process, heat treatment equipment, heat treatment technology and heat treatment development direction, etc., to briefly explain the automotive bearing heat treatment technology.
First, the bearing material
The quality of the material is the most important factor determining the life of the bearing. The gap between China's automotive bearings and foreign countries, material is the main factor, followed by bearing design, process level and process equipment. Although we revised the GB/T18254 standard, the standard of “high-quality high-carbon chrome bearing steel†was added, and the requirements for carbide, segregation, oxygen content and inclusions were improved, but it was subject to domestic steel mill smelting technology and cost. Other factors, such as full implementation, still have great difficulty.
With the wide application of vacuum degassing, China's bearing steel has greatly improved in the control of oxygen content, which is close to foreign level. However, there are still large gaps in carbide uniformity, mesh carbide control, inclusion control, etc., which leads to the inherent shortage of domestic automotive bearing quality, bearing life, reliability and consistency are inferior to foreign bearings.
China's bearing materials are widely used in GCr15 steel and GCr15SiMn steel, with a single variety. There is no report on the research and development of special materials for automotive bearings. Bearing steel manufacturers rarely cooperate with bearing manufacturers.
Second, bearing design and process
1. Individualized, differentiated design lacks
The advanced bearing design should be based on the service environment of the bearing, adopting individualized and differentiated design to meet the actual working conditions of the bearing. Domestic bearing individualization and differentiated design are still insufficient. In addition, the heat treatment design of the bearing is also an important factor affecting the life of the bearing. The bearings contain four large parts: the outer ring, the inner ring, the rolling elements and the cage. Foreign advanced bearing enterprises have different hardness requirements for inner and outer rings and rolling elements. Many top domestic manufacturers of automotive bearings have begun to try this, but they are subject to the general industry standard for bearings, "Technical Conditions for Heat Treatment of High Carbon Chromium Bearing Steel Rolling Bearing Parts" The range of hardness requirements is limited in the hardness design of bearing parts. At the same time, the domestic bearing heat treatment process and equipment level are also factors that affect the realization of individualized and differentiated design. In short, China's automotive bearing design is in an extensive stage compared with foreign advanced enterprises. Many sub-fields have not carried out special research. Most of the imitation designs, less independent design, are more lacking in the technical reserve of bearing design.
2. CQI-9 quality standard promotion
The heat treatment quality of bearing parts is an important factor in determining bearing life. At present, the major domestic automobile bearing manufacturers have been able to basically guarantee the quality of heat treatment of parts, but they pay insufficient attention to the precise control of heat treatment process parameters, the use of quenching medium and the guarantee capacity of heat treatment equipment, resulting in the quality stability of heat treatment of bearing parts compared with foreign countries. Big gap. The CQI-9 quality standard that has been widely implemented by foreign advanced enterprises is limited to the selective trial of individual enterprises in China, and it also contains factors that should be reviewed by foreign companies. Therefore, the comprehensive and conscious implementation and promotion of CQI-9 quality standards should be the only way for domestic bearing manufacturers to improve the quality of heat treatment and meet or exceed the advanced level of foreign countries.
3. Application of new energy-saving technologies
At present, most domestic bearing manufacturers still use the traditional heat treatment quenching and tempering process: 820 ~ 860 °C quenching, oil quenching and tempering below 200 °C. The entire process is about 4.5 to 5.5 hours. The process has been in use for nearly forty or fifty years. With the increasing demand for energy saving and environmental protection, as a bearing heat treatment industry for large energy consumers, it has also begun to study and improve the classical heat treatment process of bearings. The core of the research is to change and improve the quenching and tempering temperature and shorten the process time. At the same time, try to use non-oil quenching medium, such as salt bath, water-soluble medium, etc., to expand the heat treatment processing range, so that the heat treatment deformation is more regular. Enterprises such as the stern shaft, the slab shaft and the Luo axis have tried in these aspects and have achieved certain results.
In addition, the normalizing treatment after forging, the current use of forging heat after normalizing the process has been widely used in China, saving a lot of energy, but there is still a lack of clear process specifications, energy is utilized, the quality of normalizing is very unstable. Need to have special equipment to solve the problem of quality stability. 1 2 3 Next page
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Bearings are an important mechanical foundation connector and are used in a wide range of applications in the machinery industry. It can be said that there are bearings where there is a rotation. As the main means of transportation for people in the modern society, the automobile industry has also become a major pillar industry in China, and bearings also play an important role. Many of the car's security components, such as the steering gear, engine and gearbox, can be seen in the bearing. As a branch of the bearing, the automotive bearing has special properties such as bearing, impact resistance and high-speed rotation. Its performance has an important impact on the safety of passengers, drivers and the vehicle itself.