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Working surface and center of bearing parts are in condition
发布时间:2021-09-14浏览次数:0

There are great differences in the state, structure and performance requirements of the working surface and center of bearing parts, and the overall heat treatment often makes the two can not take into account, and the potential of the material can not be fully played. The application of material surface strengthening technology can not only better solve the differences between surface and core in structure and requirements, but also can further make the surface to obtain some special working performance, in order to meet the requirements of working surface performance of bearings under specific conditions. This is of great significance in the development of modern science and technology.


The traditional surface strengthening method belongs to the category of heat treatment. The surface strengthening methods developed in modern times, such as laser, electron beam and ion beam, not only apply some high and new technologies to the surface strengthening of materials, but also go beyond the scope of traditional heat treatment and form a new technical field. Therefore, the current surface strengthening technology can form a variety of classification methods from different angles. According to the physical and chemical process of surface strengthening technology, it can be roughly divided into five categories: surface deformation strengthening, surface heat treatment strengthening, chemical heat treatment strengthening, surface metallurgy strengthening, and surface film strengthening.


1. Surface deformation strengthening


Through mechanical methods to make the metal surface layer plastic deformation, so as to form a high hardness and high strength hardening layer, this surface strengthening method is called surface deformation strengthening, also known as work hardening. Including shot blasting, sandblasting, cold extrusion, rolling, cold grinding and impact, explosion impact strengthening, etc. The characteristics of these methods are as follows: the dislocation density of the reinforcing layer is increased, the subcrystal structure is refined, so that the hardness and strength of the reinforcing layer are improved, the surface roughness value is reduced, and the surface fatigue strength of the component is significantly improved and the sensitivity of the fatigue notch is reduced. This strengthening method is simple and effective, there is no obvious boundary between the hardened layer and the matrix, the structure is coherent, and it is not easy to fall off in use. Most of these methods have been applied in bearing industry: the surface impact strengthening of rolling body is the application of this kind of method, and precision rolling has become a new processing and strengthening method of ring.


2 surface heat treatment strengthening


The use of solid phase transformation, through the method of rapid heating on the surface layer of parts for quenching treatment is called surface heat treatment, commonly known as surface quenching. Including flame heating quenching, high (medium) frequency induction heating quenching, laser heating or electron beam heating quenching, etc. The characteristics of these methods are: local surface heating quenching, small deformation of the workpiece; Fast heating speed, high production efficiency; Short heating time, surface oxidation decarbonization is very slight. This method is particularly effective in improving the wear resistance and fatigue strength of large and very large bearing parts bearing certain impact loads.


Chemical heat treatment intensification


Using a certain element of solid diffusion infiltration, to change the chemical composition of the metal surface layer, in order to achieve surface strengthening method is called chemical heat treatment strengthening, also known as diffusion heat treatment. Including boronizing, metalizing, carburizing and carbonitriding, nitriding and nitrogen carburizing, sulfur and sulfur nitrogen carburizing, chrome, aluminizing and chromium-aluminizing, graphitization layer and so on, various, different characteristics. Infiltrate elements or dissolve into the base metal to form a solid solution, or combine with other metal elements to form compounds. In a word, infiltration elements can not only change the chemical composition of the surface layer, but also get different phase structures. The treatment process of carburized bearing steel parts and the surface nitriding strengthening treatment of needle roller bearing sleeve belong to this kind of strengthening method.


4 surface metallurgical strengthening


The surface strengthening technology which uses the re-melting and solidification of the surface metal of the workpiece to get the desired composition or structure is called surface metallurgical strengthening. Including surface autolysis alloy or composite powder coating, surface melting crystallization or amorphous treatment, surface alloying and other methods. It is characterized by rapid heating with high energy density, melting the metal surface layer or alloyed material coated on the metal surface, and then solidification by its own cooling to get special structure or specific performance of the strengthening layer. Depending on the process parameters and methods of surface metallurgy, the special structure may be fine crystalline structure, supersaturated phase, metastable phase, or even amorphous structure.


The rolling bearing industry has done research on the working surface of miniature bearing by laser heating, and the results are good.


5. Surface film strengthening


The application of physical or chemical methods to the metal surface coated with a strengthening film of different properties of the matrix material is called surface film strengthening. It includes electroplating, electroless plating (chromium plating, nickel plating, copper plating, silver plating, etc.) and composite plating, brush plating or conversion processing, also includes the rapid development of new and high technology in recent years: such as CVD, PVD, P-CVD and other vapor deposition film strengthening methods and ion implantation surface strengthening technology (also known as atomic metallurgy technology) and so on. Their common feature is that they can form a film of specific performance on the working surface, in order to strengthen the wear resistance, fatigue resistance, corrosion resistance and self-lubrication of the surface. For example, ion implantation technology strengthens the working surface of bearings, which can significantly improve the wear resistance, corrosion resistance and contact fatigue resistance of the working surface of bearings, so that the service life of bearings can be increased exponentially.




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