Cold rolling roll defects and treatment measures

1. Vibration marks
In the rolling process of strip steel, the strip surface often appears a light and dark, and the direction of the strip movement is perpendicular to the strip strip, the defect of this strip steel is called strip vibration. Practice has proved that the cause of the vibration of this strip steel is mostly from the roll, that is, the roll vibration is copied to the strip surface.
1.1 Causes of roll vibrations
The causes and manifestations of roll striations are as follows: the roll striations caused by the vibration of the grinding wheel spindle are distributed on the roll surface in a spiral shape; The roll vibrations caused by poor shape of the grinding wheel or poor threshing of the grinding wheel are distributed on the surface of the roll in a spiral shape. The spacing of the vibrations can usually be measured by the rotational speed of the roll and the rotational speed of the grinding wheel, and then compared with the actual situation, it can be accurately identified as the grinding wheel vibrations. Roll vibration marks are distributed on the rolling surface in the form of parallel to the roll bus bar due to the poor contact of the roll carrier (support). Roll vibration marks are distributed parallel to the roll bus bar due to the poor shape of the tailstock center; The distribution of roll vibration marks caused by poor rotation of the head frame is parallel to the roll bus; The roll vibration pattern caused by resonance between the vibration of the grinding wheel head frame and the vibration of the headboard is distributed on the rolling surface in the form of parallel bus.
1.2 Elimination method of roll vibration marks
To eliminate rolling stripes, first of all, to eliminate the abnormal vibration source, and then choose the grinding method according to the obvious degree of vibration stripes. Obvious vibromarks should be eliminated from rough grinding, and non-obvious vibromarks can be eliminated from semi-rough grinding.

2, roll printing
① The expression form and cause of roll marks. The main manifestations of rolling and radial printing are radial pinholes, dents, indentations and holes. An irregularly distributed dent on the rolling surface, generally circular, with the surface state or texture of the roll usually retained within the dent, usually caused by some debris (foreign matter) entering the bite zone or contact friction between rollers. The preventive measures include: identifying the source of debris, cleaning the frame, improving the process lubrication and cooling conditions, improving the surface quality and cutting edge quality of the pickling coil, increasing the surface hardness and hardening depth of the work roll, and rationally distributing the hardness difference between the work roll and the intermediate roll.

②The elimination method of roll marks. Roll marks are removed by grinding or turning according to different degrees of roll marks.

3. Knife flower
3.1 The cause of roll cutting is caused by the mismatch between the rotation speed of the roll, the rotation speed of the grinding wheel, the longitudinal movement speed of the Z axis and the feed amount of the grinding wheel. Sharp edge of the grinding wheel or the edge of the grinding wheel caused by defects; The number of semi-fine grinding passes is not enough, and the defects of rough grinding passes are not eliminated. Grinding pass due to excessive load caused by the knife flower: roll crown is too large will also produce the knife flower.

3.2 Preventive measures and elimination methods of roll cutter flower ① Preventive measures. According to a=, the rotation speed of the roll, the longitudinal moving speed of the Z axis, the feed amount of the grinding wheel and the rotation speed of the grinding wheel are reasonably configured. Where, a is the grinding amount (mm); Vw is the workpiece circular speed (m/min); Vs is the wheel circle speed (m/s); Ap is the amount of back cutting tool (mm); Ds is the diameter of grinding wheel (mm); Dw is the workpiece diameter (mm); m is the number of effective grinding edges per unit length around the grinding wheel. Chamfer the edge of the sharp grinding wheel and grind the tail seat of the defective grinding wheel until the defect disappears. Select the standard grinding program according to different roll types, grinding in strict accordance with the standard grinding program, every start to jump to the next grinding program, to ensure that the previous step of grinding defects are eliminated. Under the premise of ensuring that the defects of the semi-finishing pass are eliminated, the number of passes and load of the finishing pass are controlled, and the softer grinding wheel is selected or the crown of the grinding wheel is reduced.
The elimination method of roll cutting flower. The method of repeated grinding is generally used to eliminate roll cutting.

4, crack

① the cause of roll crack. When rolling or the hot roll is grinding, it is easy to crack because of the local stress concentration: the rolling mill breaks the strip and other accidents lead to cracks; The uneven thickness of the incoming material causes the roll to be impacted in the rolling process, which causes the roll to crack due to excessive rolling force in a short time. Roll fatigue crack.

② Elimination method of roll crack. In order to prevent the roll from falling flesh or larger defects caused by cracks, it must be treated in time and ensure that the cracks are removed clean. When grinding, check the roll carefully, and mark the end of the rolling neck if there is a crack, so as to facilitate the next inspection. If the crack is small, the naked eye can not determine whether the crack has been worn out after grinding for a period of time, then it is necessary to do imaging test or flaw detection to determine whether the crack has been worn out, and continue grinding if it still exists; If the crack is large and deep, it is still obvious after a long time of grinding, fixed-point cut-in grinding can be carried out to determine the depth of the crack.