What is the rolling process of rolling mill and rolling mill?

Rolling process \ x0d \ x0d \ Generally, the rolling process of a single stand 20-high cold rolling mill can be divided into feeding, threading and reversible rolling; Unload \x0d\ rewind in three stages. Twenty-high rolling mill, especially Sendzimir twenty-high rolling mill, has large rolling tension; After the tension of the steel strip is applied by the coiler/uncoiler before and after the rolling mill, the rolling process begins, and before that, it is the feeding and threading stage. \x0d\ Feeding and threading stage: generally, the steel coil is sent to the uncoiler drum by the feeding trolley; Floating uncoilers are often used for uncoiling, \x0d\ to ensure that the steel strip is always in the center of the rolling mill; The floating uncoiler is controlled by the universal hydraulic cylinder of the photoelectric centering device; Straighten the uncoiled steel strip with a straightener (three-roller straightener or five-roller straightener); Some rolling mills are equipped with cutting heads of hydraulic shears; The steel strip passes through the coiler in front of the machine with an upward swinging guide table and is directly sent to the 20-high rolling mill; Then, the uncoiler continues to feed the steel strip forward through the rolling mill until it is sent to the coiler jaw behind the uncoiler, and the jaw clamps the lead wire of the steel strip and winds it on the drum for 2-3 times, then the tape feeding is stopped and the tape threading is finished. \x0d\ Reversible rolling stage: After the threading, first place the upper and lower work rolls (the work rolls have been removed when threading), then align the rolling line, close the closed door of the rolling mill, press down the front platen of the rolling mill, press down the steel strip with the wiper on the outlet side, start the lubrication cooling system of the rolling mill to supply liquid, press down the steel strip of the rolling mill, rotate the coiler to give tension to the steel strip, and enter the rolling line with a thickness gauge and a speedometer before and after the rolling mill. \x0d\ In the rolling process, if defects are found at the edge of the steel strip, which will affect high-speed rolling, when the defective parts pass through the rollers; \x0d\ The operator presses the button on the console to input the defect position signal into the AGC system. When the rolling is about to end, the mill will slow down. When the tail of the steel strip reaches the coiler position in front of the rolling mill, the unit will stop and the first pass will end. The thickness gauge and speedometer exit the rolling line \x0d\, the rolling mill is pressed down and lifted, the tension of the steel strip is released, the supply of cooling lubricant is stopped, and the platen is lifted. \x0d\ During the second rolling, the steel strip moves in the opposite direction, and the positions in front of the machine and behind the machine are exchanged. When the second job starts, the coiler runs in the opposite direction \x0d\ and sends the head of the front steel strip to the jaw of the front coiler drum. After the jaw clamps the head, the front coiler rotates to wind the steel strip \x0d\ on the drum for 2-3 turns; Then, the cooling lubricant is supplied to the rolling mill, and the rolling mill is pressed down, and the rear coiler is driven to give the rear \x0d\ tension. Thickness gauges and speedometers before and after the rolling mill enter the rolling line, and the unit starts secondary rolling. \x0d\ Starting from the second pass, rolling is carried out between the coiler in front of the machine and the 20-high mill. After the automatic gauge control (ACC) system of rolling mill is put into operation, full automatic control can be realized. When the defective steel passes through the roll during rolling, the rolling mill will automatically slow down. At the end of rolling, the rolling mill will stop automatically. \x0d\ Generally, a reversible mill rolls odd passes, but when the front and rear coilers are extended coilers, even passes can be rolled, that is, even passes can be uncoiled at the uncoiler side of the mill. \x0d\ Generally, it is necessary to replace the work roll before the pass rolling of finished products to obtain high quality and special requirements for the surface quality of strip steel. After each pass of finished product rolling, the rolling mill stops, presses down and picks it up, the thickness gauge and speedometer exit the rolling line, the rolling mill stops supplying cooling lubricant, the coiler presses down, or the uncoiler is lifted by the car seat roller and pushed against the steel coil, so as to prevent the tail of the steel coil from being completely wound on the drum due to the rotation of the uncoiler. At this point, the reversible rolling process is over. \x0d\ Unwinding and rewinding stage: Unwinding is relatively simple for expanding and contracting reel coilers. First, tie the coil in the radial direction \x0d\ with a strap. The unwinding trolley rises against the coil, the coiler drum shrinks, the jaws open and the coil is supported by the unwinding trolley. The coil unloading trolley and the auxiliary trolley of the coiler move synchronously, and then the coil is unloaded from the coiler. The coil unloading trolley continues to move and sends the coil to the coil storage platform. \x0d\ For the coiler with solid drums at the front and back of the rolling mill, the steel coil cannot be directly unloaded from the drum. Only when the coil is rewound on the expansion coiler can the coil be unloaded. When the solid coiler is used on Sendzimir 20 high-roller mill and Sendewei 20 high-roller mill, the unit is generally equipped with a rewinding mechanism, which transports the finished steel coil together with the solid coiler from the winding position to the rewinding and uncoiling position I, and then rewinds the steel coil from the uncoiler to the rewinder once. Because the rewinding process is carried out outside the rolling zone of the rolling mill, rewinding and rolling can be carried out at the same time without affecting each other. \x0d\ rolling process \ \x0d\1+0 reduction system \ x0d \ rolling mill reduction system should be determined according to the technical parameters of the rolling mill, the mechanical properties of the rolled materials and the quality requirements of the products. At the same time, the high capacity and low consumption of rolling mill should be considered. \x0d\ It is relatively easy to roll high-quality carbon steel with a 20-high mill. The purpose of using 20-high rolling mill is to pursue the high quality of \x0d\ products, with high dimensional accuracy, flatness and surface quality, and to obtain thinner products. \x0d\ carbon steel, especially low-carbon low-carbon steel, on the 20-high rolling mill, the total reduction rate in one pass can reach over 95%, and the reduction rate in each pass can reach 66%. \x0d\ For reversible cold rolling mill, because each pass is rolled on the same stand, the pass reduction ratio distribution is determined by the principle of equal pressure rolling. Generally, the first pass \x0d\ the second pass has the largest reduction rate. With the hardening of rolled strip, the reduction rate of each pass gradually decreases, making the rolling pressure of each pass almost equal. \x0d\ In order to improve the production capacity of the rolling mill, on the premise of making full use of the main drive power of the rolling mill and the coiler before and after the rolling mill, the pass reduction rate should be increased as much as possible and the rolling pass should be reduced. But sometimes, in order to obtain good shape and surface quality and reduce the longitudinal thickness deviation of \x0d\ steel strip, the rolling passes can be appropriately increased. Under the same total reduction rate, the strength of steel strip can be slightly improved by using more rolling passes. The pass reduction rate of finished products has a great influence on the shape, which is generally about 10% \ x0d \. \x0d\ 2 Tension system \x0d\ One feature of cold rolled steel strip is tension rolling; Cold rolling of steel strip cannot be carried out without tension. Tension can reduce the rolling pressure, improve the flatness \x0d\ stabilize the rolling process. Tension system is very important for cold rolled strip. \x0d\ Twenty-high rolling mills (and multi-high rolling mills) use small-diameter work rolls, and the technological feature of the rolling process is large \x0d\ tension rolling. \x0d\ must adopt larger unit tension, because the rolled material has anisotropic physical and mechanical properties, or the work roll has almost no skew within a smaller \x0d\ deformation arc length, so there is an imbalance between pressing down and extending along the width direction of the strip. When the tension redistributes in the area with less pressure, the tension reaches the yield limit, and the well \x0d\ may balance the extension of the strip in the width direction. \x0d\ Actually, when rolling on a multi-high mill, the deformation of metal is the result of the joint action of the roll reduction and the strip tension established by the coiler. \x0d\ The unit tension used in the multi-high mill depends on the physical and mechanical properties of the material, the degree of cold work hardening, the thickness of the strip and its edge quality. General unit Zhang Liwei 20%-70%. \x0d\ In order to realize the large unit tension and total tension required by the stable rolling process, it is necessary to set up a coiler with \x0d\ high power drive in the multi-high mill. Generally, the motor power of the coiler of a 20-high rolling mill reaches 70% ~ 80% of the main drive power of the rolling mill, and some even reach 100%. \x0d\ The tension of each pass is determined as follows. Generally speaking, when rolling for the first time, because the coiling tension of pickling line is less than \x0d\, in order to avoid scratching the surface due to the dislocation between steel strips, the root of post-tension of the first line is less than the coiling tension of pickling line. \x0d\ In order to increase the post-tension of the first rolling, a pressure plate is arranged at the entrance side of the twenty-high rolling mill to increase the post-rolling tension; Pre-tension can be freely determined according to process requirements. In the subsequent rolling passes, the varieties and specifications of rolled steel strips should be excavated one by one, either the front tension \x0d\ is greater than the back tension, or the back tension is greater than the front tension. Generally, the pre-rolling tension of the previous pass is taken as the post-rolling tension of this pass, and the unit pre-rolling tension of \x0d\ is greater than the unit post-rolling tension. There are two kinds of pre-tension (coiling tension) of finished products. For the expansion and contraction reel coiler, since the steel coil can be unwound directly on the coiler, and the steel coil can be directly wound in the hood furnace for close annealing, the coiling tension should be reduced during annealing to prevent sticking. When the coiling tension is less than 50Mpa, the probability of annealing bonding is very low, but the low coiling tension will affect the production capacity of the rolling mill. For the solid reel coiler, because it needs rewinding, small tension (10-40 MPa) can be used for rewinding, so large tension can be used for rolling, which can improve the production capacity of the rolling mill. The tension of pass \x0d\ should be adjusted at any time according to the shape, especially when the rolled strip is thin. When there are waves in the middle of the material, the tension should be reduced to prevent the edge of the belt from being torn or broken; When the strip produces edge waves, the tension can be increased appropriately. \x0d\ 3 Determination of speed system \x0d\ Rolling speed should be increased as much as possible within the allowable speed range of the rolling mill according to the capacity of the equipment, so as to improve the production capacity of the rolling mill; At the same time, when the rolling speed increases, the rolling pressure decreases accordingly. \x0d\ Generally, low rolling speed is adopted in the first pass, because the reduction in the first pass is large. If rolling at high speed, the roll will heat up sharply, and the service life of the roll will be affected because of the poor cooling conditions of the roll of the multi-high rolling mill. In addition, due to the large deviation of the longitudinal thickness of the blank, the shape of the blank is not completely consistent with the shape of the roll, so it is necessary to adjust the blank at the beginning of rolling, which requires a low speed; At the same time, the capacity of the main motor can not be satisfied with high speed and large reduction ratio. After \x0d\, the rolling speed is determined according to the power of the screw-down system, the tension system and the main motor, so that the energy of the main motor can be exerted. \x0d\ During the start-up and braking of each rolling pass, there is a speed-up and speed-down process respectively. In the rolling process, the speed adjustment should be as small as possible to ensure the stability of rolling \x0d\ the uniformity of thickness deviation. \x0d\ 4-roll profile \x0d\ Because of the rigidity and zero crown design of the 20-roll mill frame and various effective means to adjust the roll profile, \x0d\ 20-roll mill can use flat rolls without roll crown for rolling. According to the requirements, the working roller \x0d\ the second intermediate roller can also be equipped with a crown roller. The first intermediate roller is always a flat roller, but its head is tapered for axial adjustment of the roller; The backup bearing of the backup roller cannot have a convex surface.