During the rolling process, the roller is subjected to bending, friction, impact and other effects, which mainly cause roller surface peeling and roller surface wear. Therefore, the roller surface is generally required to have high strength, hardness, wear resistance and fatigue limit. These surface properties are not only related to the material of the roller, but also to the surface treatment process of the roller. The surface treatment process of the roller mainly includes the roller integral quenching process, induction heating quenching process, surfacing process, thermal spraying process, thermal spraying process and laser surface modification process.
Overall quenching process
Integral quenching is to uniformly heat the roller as a whole to the austenitizing temperature for quenching, and at the same time, the roller neck is protected by insulating materials to ensure that it maintains good toughness. The overall quenching process will cause high residual compressive stress on the roller surface, which makes the roller have the disadvantages of shallow hardened layer, weak matrix and poor accident resistance.
Induction heating quenching process Induction heating quenching process is to use high-frequency AC magnetic field to heat the roller twice in succession, so that the surface of the roller is quickly heated to above the critical temperature, and then quickly cooled to obtain martensite. Usually, the roller is heated twice in succession by two power frequency induction coils, and the roller is heated successively by a power frequency induction coil and a medium frequency induction coil to ensure the depth of the heating layer and the uniformity of the temperature. At present, the dual-frequency quenching machine tool of OSB Company in Belgium is commonly used in China. For example, Changzhou Metallurgical Machinery Plant, Wuhan Iron and Steel, and Baosteel have introduced this product. The dual-frequency quenching machine tool produced by Beiman Special Steel is mainly produced in China. However, the induction heating quenching process is limited to a certain depth of the surface layer, and the internal temperature of the roller is still low, so it cannot be guaranteed that all quenching surfaces can obtain a uniform surface quenching layer, etc., which limits the development of the process to a certain extent.
Overlaying process
After the roller is damaged, its surface needs to be repaired. Overlaying process is a commonly used repair process, which is to melt the metal by electric welding or gas welding and pile it on the surface of the roller. Although the surfacing process can ensure the wear resistance of the roller, the whole process is too complicated, the productivity is low, and the technical requirements for workers are high. At the same time, the roller will produce pores, cracks, slag inclusions and other problems during surfacing.
Thermal spraying process
The thermal spraying process is to spray the molten or semi-molten spraying material on the surface of the roller at high speed to form a micro-metallurgical bonding or mechanical bonding coating. Due to the low bonding strength between the coating and the substrate, mainly mechanical bonding, there are gaps and residual stresses in the coating, which makes the toughness and cutting processability of the roller poor. At the same time, the material utilization rate is low during the spraying process, and there is a certain harm to the health of workers during the operation.
Thermal spraying process
The thermal spraying process is based on the thermal spraying process. After the spray layer is remelted, the spray layer and the substrate surface material reach a molten state, and then a tighter metallurgical bonding layer is further formed. The specific method is to first spray the self-fluxing alloy powder on the substrate, and wet the substrate surface and melt it into the substrate without melting the substrate to form a metallurgical bond, forming the required dense spray welding layer. The metallurgical bond between them is formed by mutual sintering and diffusion between the liquid alloy and the solid substrate surface to form a new layer of surface alloy. Thermal spraying can be regarded as a combination of alloy spraying and metal surfacing. It overcomes the shortcomings of low bonding strength and low hardness of thermal spraying layers. At the same time, due to the use of high-alloy powder, the spraying layer has a series of special properties that are not available in general surfacing.
Laser surface modification process
Laser strengthening is to irradiate the roller with a high-density, high-capacity laser beam to instantly increase the surface temperature of the roller, thereby causing the surface structure of the roller to be modified. Therefore, it has a series of advantages such as high automatic control accuracy of the heat treatment area, highly refined structure of the strengthening area, small thermal deformation of the workpiece, and the use of point processing or line scanning processing to obtain a discrete strengthening surface layer with the same softness and hardness, strong and tough. Laser phase change hardening, laser melting, laser cladding, laser alloying, laser texturing and other process means are usually used to change and optimize the surface structure of the roller, so as to effectively improve the hardness and wear resistance of the roller surface, thereby increasing the service life of the roller.
With the development of smelting technology, the manufacturing technology and surface treatment process of rollers have been rapidly developed. In order to improve the production and manufacturing technology of rollers, our scientific and technical personnel and manufacturers work together to improve the production and manufacturing technology of rollers and strive to catch up with the world’s advanced level.
