Preparation before grinding of rolls
The rolls removed from the mill should be cooled to room temperature before grinding (if necessary, the rolls can also be cooled with grinding fluid).
1. Before grinding the rolls, use the top to centre the rolls and then use the stand to square them. The purpose is to keep the vertical and horizontal bus lines of the roll parallel to the centre line of the grinding wheel to ensure roll grinding accuracy. In the alignment process, it is difficult to adjust the lower support point because it is not in a vertical position. Two detection points should be used to detect the displacement of the roll in the vertical and horizontal directions at the same time during the alignment process, so that the alignment can be faster and more accurate. The difference in diameter between the two ends of the roll should be taken into account during the alignment, and the difference should be added during the adjustment.
2. Axial positioning
After squaring the roll, a special plastic block should be placed between each of the two tops and the roll, which is a cushion for easy rotation between the top and the roll to prevent the roll from moving axially during grinding.
3. Roll grinding
Roll grinding is generally divided into three stages: rough grinding, medium grinding and fine grinding.
Coarse grinding is mainly aimed at removing the hardened layer and visible defects on the surface of the rolls. Rough grinding requires grinding off the excess surface layer as far as possible within a short period of time, which is in principle strong grinding, with a larger grinding wheel size and a coarser surface roughness. The grinding wheel travels at a speed of 2/3 of the wheel width.
Due to the high loss of the grinding wheel during rough grinding, in order to improve the grinding efficiency and to ensure that the roll shape and surface roughness of the grinding rolls are uniform, the ammeter should be constantly observed during operation so that the grinding is carried out at a relatively constant current.
The middle grinding is to remove the walking marks of the rough grinding and to prepare the roll shape for the fine grinding. Fine grinding is to obtain the final desired surface roughness of the rolls. For medium and fine grinding rolls, it is generally important to use different grinding wheels according to the requirements of the rolling process and to choose the right grinding wheel. The walking speed of the grinding wheel during fine grinding is 1/5 of the width of the grinding wheel.
To obtain the ideal surface roughness of the rolls, the number of revolutions of the grinding wheel and the rolls and the amount of wheel feed should be matched properly. In order to avoid heating of the roll neck and vibration of the roll, the rough and medium grinding of the roll should not be too high.
The key to fine grinding is to control the surface roughness, both to meet the requirements of the rolling process and to ensure that the surface roughness of the roll is uniform. To do this, it requires the grinding machine operator from the rough grinding to the whole process of fine grinding, balanced and effective control of the roll's transverse feed and the roll's longitudinal walk, a reasonable choice of the number of revolutions of the roll and the number of revolutions of the grinding wheel.
The modernisation of roll manufacturing technology and roll grinding machines provides good conditions for roll grinding, but not with two good rolls and modern roll grinding machines, it is always possible to grind out qualified rolls. To ensure that each pair of rolls can fully meet the requirements of rolling and technology, it ultimately depends on the careful and meticulous operation of skilled roll grinding machine operators.