1 introduction under some service conditions, rolling bearings often fail to reach their calculated life and suffer early damage due to the influence of internal or external factors.Study on Spalling of Outer Race of Cylindrical Roller Bearing
The early damage of rolling bearing is analyzed, in which the spalling of bearing outer race is one of the important factors. Based on the previous test results, this paper analyzes the spalling causes of the outer race of cylindrical roller bearing, and puts forward the corresponding improvement measures.Study on Spalling of Outer Race of Cylindrical Roller Bearing
2 Analysis of previous test results 2.1 macroscopic analysis: the appearance of the bearing outer ring with raceway spalling is inspected.
The spalling area is mostly distributed on one side of the raceway. In the spalling area, there are many dark brown strips with thermal oxidation discoloration on the cylindrical surface of all rollers. On the roller side corresponding to the spalling place of the raceway, the oxidation discoloration is more serious, there are many indentation on the surface, and the end face of one side of the roller is worn and scratched,Study on Spalling of Outer Race of Cylindrical Roller Bearing
There is a slight oxidized discoloration ring near the outer diameter on the end face of the other side, which is light brown.Study on Spalling of Outer Race of Cylindrical Roller Bearing
2. chemical composition analysis analyze the chemical composition of the bearing outer ring, The results are shown in the following table: Table 1 Chemical Composition /% C Mn Si CR s p 1.02 0.36 0.30 1.55 0.013 0.004 2.3 hardness measurement hardness (HRC) measurement results are shown in Table 2: Table 2 outer diameter and inner diameter (raceway surface) hardness value of outer sleeve end face (typeface) end face (non typeface) at ferrule position 61.8,62.8,62.3 62,62 60,60.4,60.4 60.2,60.1 2.4 material quality analysis table 3 microstructure (grade) of non-metallic inclusions (grade).
At present, most foreign bearing materials use vacuum deoxidized steel with oxygen content below 15ppm, while only a few steel plants in China can meet this requirement. Most other steel plants do not have the conditions, resulting in roller material structure greater than grade 4 and many cracks.Study on Spalling of Outer Race of Cylindrical Roller Bearing
In the material quality analysis, the non-metallic inclusions and microstructure were compared and analyzed by YJZ84 standard, and the level of sulfide impurities in the ferrule exceeded the standard. The spalling outer ring was tested. At the peeling source, the metallographic sample was longitudinally ground 0.5mm ~ 1mm away from the source.
It was observed that there were chain brittle inclusions in the range of 0.36mm-0.49mm away from the peeling surface, and there were fine vibration lines
at these inclusions. On the same metallographic sample, there are chain brittle inclusions slightly away from the source and about 0.8mm away from the stripped surface.Study on Spalling of Outer Race of Cylindrical Roller Bearing
The metallographic samples were ground longitudinally along the stripping source, and chain brittle inclusions were also observed at and near the source.
There are micro cracks between the inclusions 0.3mm away from the stripping surface, and there are chain brittle inclusions about 0.56mm long at 0.68mm away from the stripping surface.
The above shows that there are many chain brittle inclusions on the surface of the outer raceway, and some have exceeded the qualification level specified in YJZ84 standard. For the metallographic structure of the outer ring, the microstructure under the stripping surface at the stripping source is fine crystalline martensite + fine needle martensite + fine granular carbide banded distribution + residual austenite + a small amount of dot and needle troostite.
At the edge of the peeling place, although the surface of the raceway is not peeled off, there are parallel cracks under the surface. The structure of the surface of the raceway is fine crystalline martensite + fine needle martensite + fine granular carbide + residual austenite + a small amount of point and needle troostite. With the deepening to the inside, the non martensitic structure increases, but at 3mm from the surface, the non martensitic structure exceeds the specified qualification level.
2.5 the heat treatment quality analysis of ferrule shall be checked according to the heat treatment quality inspection standard of bearing parts.
The quenching and tempering structure of its outer ring is shown in Table 4. Table 4 depth from surface / mm surface 1.0 2.0 3.0 tissue grade / grade 6 < 7 < 9 3 conclusion 1 From the macro structure, the peeling is on one side of the raceway, which is mainly due to the deviation of the force direction of the bearing in the process of use, resulting in uneven contact between the roller and the raceway, resulting in overload load in the limited area of the bearing raceway, resulting in early fatigue peeling of the raceway of the outer ring of the bearing.
Therefore, during the installation of the rolling bearing, the inclination of the inner sleeve should be avoided to make the rollers contact evenly on the raceway and avoid local overload.
At the same time, during the use of the bearing, the inclination of the bearing should be avoided as far as possible. In addition, the cause of force deviation is also related to the strength of the bearing box and shaft. Due to the poor strength of the supporting box or shaft or the unreasonable coordination between parts and insufficient rigidity, the shaft tilts to the outer sleeve.
In this way, the stress is not distributed in the strong cylindrical wet machining system, and the market prospect is broad. Relevant friends pointed out that the wet machining chip removal and coolant purification system have just started in China, Most machining enterprises still lack understanding of it.
If the system can be popularized and applied, it will produce significant economic and social benefits, and the market prospect is very broad. It is understood that wet machining system has been widely used in foreign industrial developed countries, which has properly solved a series of problems in the process of metal cutting and promoted the development of production.
At present, single machine cooling and lubrication is widely used in China, and centralized cooling and lubrication system is only used in a few factories with advanced technology.
According to the national plan, by 2010, the annual output of automobiles in China will reach 6 million, which requires technical transformation of large engine plants.
Therefore, it is very necessary to promote the application of wet machining system in some mass-produced machining factories and industries such as bearings, motorcycles and tractors.
t can promote China’s mechanical products to enter the international market more and faster, generate foreign exchange for the country, and reduce the import of such equipment.
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The whole width of the outer raceway of the roller bearing is concentrated on one side to form point contact, so it causes one side to peel off.Study on Spalling of Outer Race of Cylindrical Roller Bearing
Therefore, the design should ensure that the bearing housing and shaft have sufficient strength, and make the coordination between various parts reasonable to ensure their stiffness.
2. In the material quality analysis, it is found that there are many chain brittle inclusions and carbide banded distribution outside the spalling source of the outer raceway. Study on Spalling of Outer Race of Cylindrical Roller Bearing
The existence of chain brittle inclusions destroys the continuity of the matrix and is conducive to crack initiation, and the carbide banded distribution is also conducive to crack initiation.
It can be seen that non-metallic inclusions are the internal cause of early spalling of raceway. Study on Spalling of Outer Race of Cylindrical Roller Bearing
Therefore, the metallurgical quality of bearing steel should be strictly controlled.
In addition, through the sampling inspection of the oxygen content of steel, it is found that the oxygen content of some steel is as high as 35ppm, far exceeding the specified standard. Some steels do not take any deoxidation measures, which seriously affects the service life of the bearing.
Therefore, the raw materials of bearings should be strictly controlled and high-quality steel should be selected. Study on Spalling of Outer Race of Cylindrical Roller Bearing
Through the analysis of the heat treatment quality of ferrule, in order to obtain martensite, it is necessary to increase the heating temperature and adopt rapid oil quenching, which brings a series of problems such as stress concentration in heat treatment, such as oil groove, typing and even surface collision, which will lead to stress cracks after heat treatment. Therefore, in order to prevent the accumulation of stress, the foundation should be laid in the turning process before heat treatment. For example, when turning the oil groove and chamfering, the cutting tool should be kept sharp, and the number of words and depth of typing should be reduced.
Take strict precautions against bumps and injuries during the transportation of vehicles and workers. In the process of heat treatment, adjust the heating temperature according to different “wall thickness” as far as possible to control the temperature within the lower limit and cool it fully. As for the organization of heat treatment, the allowable grade shall be determined according to the chemical composition of steel. In addition, the large-area spalling of raceway may also be related to the depth of martensite. The depth of martensite should exceed 3mm. Therefore, how to reduce the amount of martensite within 3mm without causing quenching cracks will be a research topic in the future.