Problems and treatment of rolls that are prone to occur during cold rolling

In the process of cold rolling, the roll has a great influence on the three indicators of strip steel output, plate surface quality and cost consumption per ton of steel. Defects in the use of cold-rolled rolls will cause the quality of batches to be degraded or even scrapped, resulting in lower yields and possibly damage to related equipment. Therefore, domestic cold rolling manufacturers pay great attention to the research on the use of rolls, and are committed to effectively reducing the consumption of cold rolling rolls. Aiming at the common defects of the rolls in the field production of stainless steel cold rolling of a certain steel, this paper briefly analyzes the causes of common roll defects and proposes treatment measures.

cold rolling

In the initial stage of production of a cold rolling mill of a steel, the surface defects of the rolls brought great trouble to the production, which greatly affected the product quality and production rhythm. Roll surface defects mainly include chatter marks, roll marks, knives, cracks and spalling, which will affect the product surface. Exploring the causes and solutions of these defects is of great significance to on-site production.

 

Vibration pattern

 

During the rolling process of strip steel, stripes with alternating light and dark often appear on the surface of strip steel, which are perpendicular to the direction of strip steel movement. This strip steel defect is called strip steel chatter pattern. Practice has proved that most of the vibration lines of the strip come from the rolls, that is, the vibration lines of the rolls are copied to the surface of the strip.

 

1.1 Causes of roll chatter lines

 

The causes and manifestations of roll vibration lines are mainly as follows: roll vibration lines caused by vibration of the grinding wheel spindle, and the vibration lines are distributed on the surface of the roll in a spiral form; roll vibration lines caused by poor shape of the grinding wheel or poor threshing of the grinding wheel. The grains are distributed on the surface of the roll in a spiral form. Usually, the distance between the vibration marks can be measured by the rotational speed of the roll and the rotational speed of the grinding wheel, and then compared with the actual one, it can be accurately judged that it is the grinding wheel chatter; due to the roll bracket ( The vibration pattern of the roll is caused by the poor contact of the supporting shoe, and the vibration pattern is distributed on the surface of the roll in the form of being parallel to the busbar of the roll; the vibration pattern of the roll caused by the poor shape of the tip of the tailstock, the distribution of the vibration pattern is parallel to the busbar of the roll; The vibration pattern of the roll caused by the poor rotation of the headstock, the distribution of the vibration pattern is parallel to the busbar of the roll; the vibration pattern of the roll caused by the resonance between the vibration of the grinding wheel headstock and the vibration of the headstock is distributed parallel to the busbar on the roll surface.

 

1.2 Elimination method of roll chatter marks

 

To eliminate the roll vibration pattern, the first is to eliminate the abnormal vibration source, and then select the grinding method according to the obvious degree of the vibration pattern. Obvious vibration lines should be eliminated from rough grinding, and insignificant vibration lines can be eliminated from semi-coarse grinding.

 

Roll printing

 

①The manifestations and causes of roll marks. The roll marks are mainly manifested as pinholes, dents, indentations and holes on the roll surface. Irregularly distributed dents on the surface of the roll, generally in the shape of a circle, the surface state or the texture of the roll is usually retained in the dent, generally caused by some debris (foreign matter) entering the bite area or contact friction between the rolls. The preventive measures are: identify the source of debris and foreign matter, clean the frame, improve the lubricating and cooling conditions of the process, improve the surface quality and trimming quality of the pickling coil, increase the surface hardness and hardening depth of the work roll, and reasonably configure the work roll and the intermediate roll. difference in hardness.

 

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

 

Knife flower

 

3.1 Reasons for the occurrence of roll knives

 

The knife pattern caused by the mismatch between the rotational speed of the roll, the rotational speed of the grinding wheel, the longitudinal movement speed of the Z-axis and the feed amount of the grinding wheel; the knife pattern caused by the sharp edge of the grinding wheel or the defect of the edge of the grinding wheel; semi-finishing grinding The number of cuts is not enough, and the cuttings formed by the defects of the rough grinding passes are not eliminated; the cuttings are caused by the excessive load of the fine grinding passes; the roll crowns are too large, which will also produce cuttings.

 

3.2 Preventive measures and elimination methods of roll knives

 

①Precautionary measures. According to a= reasonably configure the rotational speed of the roll, the longitudinal movement speed of the Z axis, the feed amount of the grinding wheel, and the rotational speed of the grinding wheel. Among them, a is the grinding amount (mm); Vw is the peripheral speed of the workpiece (m/min); Vs is the peripheral speed of the grinding wheel (m/s); Ap is the amount of back cutting (mm); Ds is the diameter of the grinding wheel (mm) ; Dw is the diameter of the workpiece (mm); m is the number of effective grinding points within the unit length of the grinding wheel circumference. Chamfer the sharp edge of the wheel and tailstock the defective wheel until the defect disappears. Choose a standard grinding program according to different roll types and strictly follow the standard grinding program. Every time you start to jump to the next grinding program, you must ensure that the defects of the previous grinding are eliminated. Under the premise of ensuring that the defects of the semi-finishing pass are eliminated, control the number of passes and load of the finishing pass, and select a softer grinding wheel or reduce the convexity of the grinding wheel.

 

②The elimination method of roll knife flower. Generally, the method of repeated grinding is used to eliminate the rolling cutter.

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