10
2023
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08
Problems and Treatment of Roll Easily in Cold Rolling
In the rolling process of strip steel, strip steel surface often appear a light and dark, and strip steel movement direction perpendicular to the stripe, the strip steel defect is called strip steel vibration pattern. Practice has proved that most of the causes of the vibration grain of this strip steel come from the roll, that is, the vibration grain of the roll is copied to the surface of the strip steel.
1. Vibrato
In the rolling process of strip steel, strip steel surface often appear a light and dark, and strip steel movement direction perpendicular to the stripe, the strip steel defect is called strip steel vibration pattern. Practice has proved that most of the causes of the vibration grain of this strip steel come from the roll, that is, the vibration grain of the roll is copied to the surface of the strip steel.
The Cause of 1.1 Roll Vibraation
The causes and manifestations of roll chatter marks mainly include the following points: roll chatter marks caused by the vibration of the grinding wheel spindle, which are distributed on the roll surface in the form of spirals; Roll chatter marks caused by poor grinding wheel shape or poor grinding wheel threshing are distributed on the roll surface in the form of spirals. Usually, the spacing of chatter marks can be measured by the rotation speed of the roll and the rotation speed of the grinding wheel and then compared with the actual situation, it can be accurately judged that the grinding wheel chatter; The chatter marks of the roll caused by the poor contact of the roll bracket (bearing tile) are distributed on the roll surface in the form of parallel to the roll bus. The chatter marks of the roll caused by the poor tip shape of the top of the tailstock are distributed parallel to the roll bus. The chatter marks of the roll caused by the poor rotation of the head frame, the distribution of the vibration pattern is parallel to the generatrix of the roll; the vibration of the grinding wheel head frame and the vibration of the head box produce resonance between the vibration of the roll, which is distributed on the roll surface in the form of parallel to the generatrix.
The Method of Eliminating the Vibration Pattern of 1.2 Roll
To eliminate the roll chatter, the first is to eliminate the abnormal vibration source, and then choose the grinding method according to the obvious degree of the chatter. Obvious chatter lines should be eliminated from the rough grinding, and unobvious chatter lines can be eliminated from the semi-rough grinding.
2. Roll printing
① The manifestation and cause of roll printing. Roller roll printing is mainly manifested as pinholes, dents, indentations and holes on the roller surface. The irregularly distributed dents on the surface of the roll are generally round, and the surface state or the texture of the roll is usually retained in the dents, which are generally caused by some debris (foreign matter) entering the bite zone or mutual contact friction between the rolls. The preventive measures are: identify the source of debris, clean the frame, improve the process lubrication and cooling conditions, improve the surface quality of the pickling coil and the quality of the shearing edge, increase the surface hardness and hardening depth of the work roll, and rationally configure the work roll and the middle roll The hardness difference.
The elimination method of roller printing. The roll print is removed by grinding or turning depending on the extent of the roll print.
3, knife flower
Cause of 3.1 Roller Blowing
The knife flower caused by the mismatch of the rotation speed of the roller, the rotation speed of the grinding wheel, the longitudinal movement speed of the Z axis and the feed amount of the grinding wheel; The knife flower caused by the sharp edge of the grinding wheel or the defect of the edge of the grinding wheel; The knife flower formed by the insufficient number of semi-fine grinding passes and the failure to eliminate the defects of the rough grinding passes; The knife flower caused by the excessive load of the fine grinding pass; roller crown is too large will also produce knife flower.
Preventive measures and elimination methods of 3.2 roller knife flower
① Preventive measures. According to a = reasonable configuration of the rotation speed of the roll, the longitudinal movement speed of the Z axis, the feed of the grinding wheel, the rotation speed of the grinding wheel. Among them, a is the grinding amount (mm);Vw is the circumferential speed of the workpiece (m/min);Vs is the circumferential 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 edges in the unit length of the grinding wheel circumference. Chamfer the edge of the sharp grinding wheel and grind the tailstock of the defective grinding wheel until the defect disappears. Select the standard grinding procedure according to different roll types, and grind in strict accordance with the standard grinding procedure. Every time you start to jump to the next grinding procedure, you must ensure that the defects of the previous grinding are eliminated. Under the premise of ensuring that the defects of semi-fine grinding passes are eliminated, the number and load of fine grinding passes are controlled, and a softer grinding wheel is selected or the convexity of the grinding wheel is reduced.
The elimination method of roller knife flower. Generally, the method of repeated grinding is used to eliminate the roller knife flower.
4. Cracks
① Cause of roll crack. When the roll is rolling or when the hot roll is grinding, it is easy to produce cracks due to local stress concentration; the rolling mill has accidents such as broken belt and twisted steel, which leads to cracks; the uneven thickness of incoming materials leads to the impact of the roll in the rolling process, which makes the roll crack due to excessive rolling force in a short time; the fatigue crack of the roll.
The elimination method of roll crack. In order to prevent the roll from falling meat or larger defects caused by cracks, it must be handled in time and ensure that the cracks are removed clean. Carefully check the roll during grinding. If any crack is found, mark it at the end of the roll neck to facilitate the next inspection. If the crack is small, the naked eye cannot determine whether the crack has been ground after grinding for a period of time. At this time, imaging test or flaw detection is required to determine whether the crack has been ground. If the crack is large and deep, it is still obvious after long-term grinding, fixed point plunge grinding may be performed to determine the depth of the crack.
5, peeling (off meat)
Roll spalling refers to the phenomenon that a certain area of the roll body is separated from the roll body.
5.1 roll surface spalling
① During rolling due to broken strip, tail flick, steel strip overlap, etc., the steel card or slip, the contact area of the roller surface caused by thermal shock, so that the roller surface produce different degrees of burns, resulting in stress concentration factors on the roller surface. If the rolling stress acting on the roll is greater than the tensile strength of the roll, the surface cracks may be dispersed during the rolling cycle and cause the roll to peel off.
② high cycle fatigue spalling, under the skin crack initiation of this way, generally in the two intermediate and support rolls in the more common, and usually no mill accident will occur. Generally speaking, this type of fatigue fracture is described as "brittle" type spalling, indicating that the entire process is initiated under the roll skin. The number of stress is very important, even if the stress is lower than the strength of the roll material, but due to repeated action can also lead to crack initiation, that is, fatigue cracks lead to spalling. Since very small cracks are distributed parallel to the tangent line of the roll surface, fatigue propagation of high cycle contact stress can occur in many places in the stress region. Repeated cyclic stresses then diffuse these cracks to the surface until spalling occurs.
5.2 roll roll end off meat
Abnormality of the thrust bearing of the rolling mill leads to meat loss at the end of the roll; the wrong position or abnormality of the roll changing trolley of the rolling mill leads to abnormal situation during roll changing, resulting in meat loss at the end of the roll; lifting or other unexpected circumstances, resulting in impact and damage at the end of the roll.
Treatment of 5.3 Roll Spalling
The surface of the roll shall be subject to rough grinding and flaw detection until the defects are eliminated. As for the peeling of the roll end, the slight peeling shall be treated by grinding, and the roll shall be scrapped for serious peeling.
6. Towa India
① Causes of roll bearing printing. Roller bearing printing generally exists on rolls with small diameter and need to be supported by roll body brackets during grinding. Rollers with bearing printing in cold rolling mills generally include work rolls, one middle and two middle rolls of 20-roll mills. Towa printing is caused by burrs produced by uneven Towa, impurities in Towa material, or grinding wheel abrasive grains, iron filings and other impurities are mixed between Towa and the roll, which scratch the roll surface during grinding.
The elimination method of roller bearing printing. The general use of pad paper, half-way grinding or repeated grinding to eliminate Towa print.
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