Rolling process of rolling mill

The rolling process of single stand 20-high cold rolling mill can generally be divided into feeding, threading and reversible rolling. Unloading and rewinding.

Duan. Twenty-high rolling mill, especially Sendzimir twenty-high rolling mill, has large rolling tension; The rolling process is from steel

The belt starts after the tension is applied by the coiler/uncoiler before and after the rolling mill, which is the stage of feeding and threading.

Loading and threading stage: generally, the steel coil is sent to the uncoiler drum by the loading trolley; Floating uncoilers are mostly used for uncoiling.

So as to ensure that the steel strip is always at the center of the rolling mill; The floating uncoiler is controlled by the universal hydraulic cylinder of the photoelectric centering device; open

Straighten the rolled 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.

Reversible rolling stage: after 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 platen in front of the rolling mill, press down the steel strip with the wiper at the exit side, start the lubrication cooling system of the rolling mill to supply liquid, press down the steel strip in the rolling mill, and rotate the coiler to give tension to the steel strip. Then, the thickness gauges and speedometers at the front and rear of the rolling mill enter the rolling line to start the first operation of the unit.

In the rolling process, if the edge of the steel strip is found to be defective, it will affect the high-speed rolling. When the defective part passes through the roll;

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 stop rotating.

Line, the rolling mill is pressed down and lifted, the tension of steel strip is released, the supply of cooling lubricant is stopped, and the pressure plate is lifted.

During the second rolling, the steel strip moves in the opposite direction, and the front and rear positions of the machine are exchanged. After the second work started, the coiler reversed.

Send the head of the front steel strip to the drum clamp of the front coiler. After the jaw clamps the head, the front coiler rotates to send out the steel strip.

Winding 2-3 times on the drum; Then, the rolling mill supplies cooling lubricant, the rolling mill presses down, and the front and rear coilers are driven.

Tension, thickness gauge and speed meter before and after the machine enters the rolling line, and the unit runs to start secondary rolling.

Starting from the second rolling, rolling goes back and forth in the machine between the coiler 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.

Generally speaking, the reversible mill rolls odd passes, but when the coilers before and after the mill are expansion coilers, even passes can be rolled.

Second, even on the uncoiler side of the rolling mill, the coil can be unwound.

Generally, it is necessary to replace the work roll before the pass rolling of finished products, in order to obtain high quality and special requirements of steel strip surface quality.

Quantity. 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.

Unwinding and rewinding stage: for the winding machine with expansion and contraction drum, unwinding is relatively simple. First, the steel coil is bound in the radial direction with a binding belt.

When they are tied together, the coil unloading trolley rises against the coil, the reel of the coiler contracts, the clamping jaw opens, and the coil is fixed by the coil unloading trolley. The coil unloading trolley and the auxiliary pusher of the coiler move synchronously to unload the coil from the coiler, and the coil unloading trolley continues to move to send the coil to the coil storage platform.

For the coiler with solid drums in front and back of the rolling mill, the steel coil can not be directly unloaded from the drum, but can only be rewound.

Steel coils can only be unloaded on the expansion coiler. 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.

Rolling process

1 reduction system

The reduction system of rolling mill should be formulated according to the technical parameters of rolling mill, the mechanical properties of rolled materials and the quality requirements of products.

At the same time, the production capacity of the rolling mill should be high and the consumption should be low.

It is relatively easy to roll high quality carbon steel with a 20-high mill. The purpose of using a 20-high mill is to

The product has high quality, high dimensional accuracy, high shape and surface quality, and the product is thinner.

For carbon steel, especially low-carbon low-carbon steel, on the 20-high mill, the total reduction rate of a rolling pass can reach more than 95%, and the reduction rate of each pass can reach 66%.

For reversible cold rolling mill, because each pass is rolled on the same stand, the reduction ratio distribution of each pass is determined by the principle of equal pressure rolling. Generally, the reduction ratio of the first pass and the second pass is the largest, and with the hardening of the rolled strip,

The pass reduction rate gradually decreases, making the rolling pressure of each pass approximately equal.

In order to improve the production capacity of rolling mill, we must do everything possible under the premise of making full use of the main driving force of rolling mill and coiler before and after rolling mill.

Pass reduction can be increased to reduce rolling passes. But in order to obtain good shape and surface quality, it is sometimes reduced.

The thickness deviation in the longitudinal direction of steel strip can also appropriately increase the number of rolling passes. 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 10%.

About.

2 tension system

One of the characteristics of cold-rolled steel strip is tension rolling; Cold rolling of steel strip cannot be carried out without tension. Tension can be reduced by rolling.

Make pressure, improve shape and stabilize rolling process. Tension system is very important for cold rolled strip.

Twenty-high mills (and multi-high mills) with small work roll diameters are characterized by large rolling process.

Tension rolling.

Because the rolled material has anisotropic physical and mechanical properties, or the unit tension is very small, it is necessary to adopt a larger unit tension.

The deflection of the work roll in the deformation arc length is very small, so there is an imbalance between the reduction and the extension along the width direction of the strip. Under pressure

When the tension redistributes in a small range, the tension reaches the yield limit, and the well may balance the tension of the strip in the width direction.

In fact, when rolling on a multi-high mill, the deformation of metal depends on the roll reduction and the strip tension established by the coiler.

It's over.

The unit tension used by multi-high rolling mill depends on the physical and mechanical properties of the material, the degree of cold working hardening and the strip.

Wood thickness and edge quality. General unit Zhang Liwei 20%-70%.

In order to achieve the large unit tension and total tension required for stable rolling process, it is necessary to set up a multi-high rolling mill.

High power drive coiler. Generally, the motor power of the coiler of the twenty-high mill reaches 70% of the main driving power of the mill.

80%, and some even reached 100%.

The tension of each pass is determined as follows. Generally speaking, the coiling tension of pickling line is relatively low during the first rolling.

Small, in order to avoid scratching the surface due to dislocation between layers of steel strip, the tension root after the first pass is small, which is less than the coiling tension of pickling line.

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-tensioning tank

According to the process requirements. In the subsequent rolling pass, the varieties and specifications of rolled steel strip should be excavated or pre-tension should be adopted.

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.

Tension, the front tension of the unit is greater than the rear tension of the unit. 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 coiler of solid drum, it can be rewound because it needs rewinding.

Small tension (10-40 MPa) is used, so large tension can be used in rolling, which can improve the production capacity of the rolling mill.

The tension of each pass should also 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.

Three-speed system

The rolling speed should be determined according to the capacity of the equipment, and the rolling should be as high as possible within the allowable speed range of the rolling mill.

Speed, in order to improve the production capacity of rolling mill; At the same time, when the rolling speed increases, the rolling pressure decreases accordingly.

Generally, the lower rolling speed is used in the first pass, because the reduction in the first pass is large. If high speed rolling is used again,

System, will make the roll temperature rise sharply, because of the poor cooling conditions of multi-high rolling mill roll, it will affect the roll life; 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.

In the next pass, the rolling speed is determined according to the power of the screw down system, the tension system and the main motor, so that the main motor can

Power comes into play.

The beginning and braking of each pass have a process of increasing speed and decreasing speed respectively. In the process of rolling, as far as possible

Less speed adjustment ensures the stability of rolling, thus achieving the uniformity of thickness deviation.

Four-roll shape

Due to the rigidity and zero crown design of the 20-high rolling mill frame and various effective roll profile adjustment means,

All 20-high rolling mills can use flat rolls without roll crown for rolling. The work roll and that second intermediate roll also

The crown roller can be properly configured; 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.