Abstract: This article analyzes the causes of vibration patterns in rolling mill grinding from the aspects of grinder, workpiece, and grinding wheel. By optimizing the grinding process parameters, the surface quality of rolling mill grinding has been improved, and the defects of grinding vibration patterns have been eliminated.
Keywords: grinding machine; Grinding; Vibration pattern; roll
0. Introduction
The production of cold-rolled strip steel with high surface quality largely relies on rollers with high surface grinding quality. During the grinding process of a certain cold rolling mill, there were frequent occurrences of straight strip-shaped vibration defects on the roll surface, which were further transmitted to the surface of the steel strip during the rolling process, seriously affecting the surface quality of the product.
1. Causes of grinding vibration patterns
Grinding vibration patterns are generally visible under lateral light observation when the rolling mill rotates at low speed. The reason for this is that during the grinding process, the grinding wheel vibrates at a certain frequency relative to the rolling mill. There are many factors that cause this vibration, and the grinding machine, workpiece, grinding wheel, and grinding parameters are closely related to it. As the grinding parameters of the factory have been solidified and used for many years, the main reasons are mainly investigated from the aspects of grinding machine, workpiece, and grinding wheel.
2. Analysis of Reasons for Grinding Machines
2.1 Torva and bracket
(1) The fixing bolts of the bracket must be tightened;
(2) The upper (side) support must be leveled to avoid contact between the curved surface and the roll neck, which may cause unstable rotation of the rolling mill;
(3) The lower support has a slight curvature, with the outer side higher and the inner side lower, and maintaining the outer 2/3 as the center of contact for the rolling mill;
(4) Scrape off the black spots on the Tova, which are contact points caused by high-temperature oxidation;
(5) Check if the contact surface between the Tova and the Tova adjustment device is good (using red lead powder), and smooth the high point with sandpaper.
2.2 Grinding wheel spindle
(1) The radial and axial runout of the grinding wheel spindle, as well as the concentricity of the spindle cone, must be less than 0.005mm;
(2) Check for high points and rust on the cone surface of the grinding wheel spindle, and use metallographic sandpaper to smooth it out;
(3) Check the tightness of the grinding wheel spindle belt, it should not be too tight or too loose.
2.3 Headframe
(1) Check if there is any abnormal noise during the operation of the auscultation head frame bearing, and inspect the tightness of the head frame belt;
(2) Check the contact between the head frame dial and the claw. It is best to cover the dial contact surface with a certain thickness of rubber to ensure stable transmission.
2.4 Tailstock
During the grinding process, the contact between the tailstock and the rolling mill should be appropriately loose. If it is too loose, the rolling mill may move axially, and if it is too tight, the rotational force of the rolling mill cannot be released, which can easily cause vibration.
2.5 Guide rails
(1) Check the wear of the guide rail based on the grinding pattern status of the guide rail;
(2) The level gauge is used to detect the longitudinal and transverse levels of the guide rail, with a requirement of less than ± 0.01mm;
(3) Check the cleanliness and liquid level of the guide rail oil: the liquid level of the V-rail guide rail oil should be controlled at 2/3 of the height of the V-plane; The oil level of the flat track guide rail is about 5mm above the track surface, and the oil level of the middle screw lubrication guide rail is controlled at about half of the observation window.
2.6 Screw and Nut
(1) Check the wear condition of the screw surface;
(2) Check the level of the screw, requiring it to be less than 0.05mm;
(3) Move the grinding wheel holder back and forth, measure the vibration of the lead screw, and ensure that the vibration is less than 0.5mm;
(4) Check the tightness of the mother screw belt;
(5) Check the cleanliness of the guide rail oil, with a focus on checking for metal shavings and water ingress in the oil.
3. Analysis of reasons related to workpieces
The main influencing factor on the workpiece is the circular runout tolerance of the roll neck, which is required to be less than 0.005mm and not exceed 0.01mm at most. Excessive runout can easily cause grinding vibration.
4. Analysis of reasons related to grinding wheels
(1) Check for any changes in the material and hardness of the grinding wheel. A hard grinding wheel can easily cause grinding vibration.
(2) Check the static and dynamic balance characteristics of the grinding wheel. The centrifugal force generated by the imbalance of the grinding wheel causes the grinding wheel to vibrate, with a frequency equal to the rotation frequency of the grinding wheel. This vibration directly acts on the workpiece, producing vibration patterns equal to the rotation frequency of the grinding wheel.
(3) Check the flange of the grinding wheel. When the flange of the grinding wheel does not make good contact with the cone surface of the grinding wheel spindle, the grinding process will cause irregular oscillation of the grinding wheel, resulting in wheel jumping.
5. Optimize grinding process to improve grinding surface quality
Through a detailed inspection of the above factors, it was found that the grinding machine screw of the factory had a concave groove of 0.5mm, severe vibration, and an amplitude of 5mm; there were obvious wear marks on the surface of the screw, and a large amount of metal debris was found in the guide rail oil; The local wear of the grinding wheel rack guide rail is more obvious, and the track surface pattern is partially ground flat. Therefore, it is judged that the vibration pattern is mainly caused by the wear of the screw and guide rail. Due to the fact that the replacement of the screw and the scraping of the guide rail need to be handled during the large and medium maintenance period of the grinder, in order to ensure the quality of the roller grinding, the grinding parameters of the roller have been optimized, and the grinding vibration patterns have been basically eliminated, meeting the production needs.
(1) Reduce the grinding current and drag plate lateral movement speed in each stage of rough, medium, and fine grinding.
(2) Add several polishing procedures and perform grinding wheel refinement before polishing, with a feed rate of 0.03mm and 8-10 times of grinding.
(3) Set the grinding wheel speed and rolling mill speed to undergo periodic changes during the grinding process, with a variation amplitude of 8-10% and a variation period of about 60 seconds, in order to change the regularity of vibration and achieve significant results.
6. Conclusion
The grinding quality of rolling mills not only relies on high-precision grinding machines, but also requires operators to have sufficient skill levels. With changes in equipment conditions, they need to flexibly adjust and optimize grinding parameters to achieve good surface processing quality and avoid various grinding defects.
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