Progress in advanced technology of shape control of cold rolled strip in the world

Shape control is one of the core control technologies for cold-rolled strip processing. In recent years, with the continuous advancement of science and technology, advanced shape control technology has emerged and improved day by day. The development of shape control technology has promoted cold rolling. The equipment industry and industrial upgrading of the strip industry have greatly improved production efficiency and efficiency.

Concept of Shape

1 basic concept of plate shape

The shape of the plate is intuitively referred to as the warpage of the strip, which is essentially the distribution of residual stress inside the strip. As long as there is residual stress inside the strip, it is a bad shape. If the residual stress is not enough to cause the plate to warp, it is called "potential" plate shape defect; if the residual stress causes the plate to be unstable and warp, it is called "apparent" plate shape defect.

2 representation of the shape of the plate

The representation of the plate shape includes various methods such as a relative length difference representation, a waveform representation method, a tension difference representation method, and a thickness relative change amount representation method. The first two methods are more commonly used in the production control process.

3 common shape defects and analysis

Common plate-shaped defects include edge wave, middle wave, single-sided wave, two-ribbed wave and composite wave, etc., mainly due to uneven extension of various parts of the strip during rolling, resulting in internal stress. of.

In order to obtain a high-quality rolled strip, it is necessary to adjust the roll gap of the roll at any time to suit the convexity of the incoming sheet and to compensate for the influence of various factors on the roll gap. For strips of different widths, thicknesses, and alloys, there is only one optimum crown for the rolls to produce the desired target shape. Therefore, the essence of the shape control is the control of the bearing roll gap, and the thickness control only needs to control the opening precision at the midpoint of the roll gap, and the shape control must control the shape of the full roll gap in the width span of the rolled piece.

Leading factor on Shape control

As we all know, the main factors affecting the shape of the plate are as follows:

(1) changes in rolling force;
(2) The change of the convexity of the incoming plate;
(3) the crown of the original roll;
(4) board width;
(5) tension;
(6) Roll contact state;
(7) The change in the thermal crown of the roll.

Advanced Technologies of Shape Control

To improve and improve the shape control level, we need to start from two aspects. First, from the aspect of equipment configuration, such as the use of advanced shape control means, increase the rigidity of the rolling mill; second, from the aspect of process configuration, including the original crown of the roll Determination, deformation and distribution of passes.

Conventional shape control methods mainly include bending roller control technology, tilt roller control technology and segmental cooling control technology. In recent years, some special control technologies, such as roll technology (HC mill and UC series mill), roll technology (VC mill and IC mill), rolling force distribution control technology (DSR dynamic plate roll) and roll edge Advanced shape control technologies such as thermal spray technology are increasingly used. Here, a few of them are briefly introduced.

1 Roller Technology---HC Roller Roller Traverse Shape Control System

The HC mill is a new 6-roll mill jointly developed by Hitachi and Nippon Steel in the 1970s. HC (High Crown) is the high performance roll crown. The rolling mill is based on a conventional 4-roll mill in which a pair of axially movable intermediate rolls are mounted between the support rolls and the work rolls, and the intermediate rolls are moved in opposite directions in the axial direction.

By analyzing the deflection of the rolls of a conventional 4-roll mill, the detrimental contact area between the work rolls and the support rolls beyond the width of the rolled piece results in excessive deflection of the rolls. This deflection depends not only on the magnitude of the rolling force but also on the width of the rolled stock. On the other hand, when a bending force is applied to the work rolls, the deflection of the rolls is constrained by the support rolls beyond the width of the rolled stock. The HC mill is traversed by the intermediate roll, eliminating the harmful contact area between the support roll and the work roll, improving the shape control ability of the roll, and is suitable for rolling of any width strip. The HC mill has been developed in various forms, such as the HCM 6 roll mill with intermediate roll drive; the HCMW 6 roll mill with intermediate rolls and work rolls; the HC--CVC mill with intermediate roll with roll profile; and HCW , UCM, UVMW, MB, UC2 ~ UC4 and other improved rolling mills.

Advantages of the HC mill:

* The shape control ability is strong, and the shape of the plate can be adjusted well without much bending force;
* It can eliminate the harmful contact between the support roller and the edge of the work roll, and reduce the tendency of the side to reduce the book and fission;
* Due to the small working roller diameter (about 30% smaller than the ordinary 4-roll mill), the reduction can be increased to achieve large reduction rolling and reduce energy consumption;
* With standard non-convex rolls, it can meet the rolling of various width strips and reduce the spare parts of the rolls.
* Since the 1970s, more than 200 HC mills have been built in various countries around the world, and it is still a popular model until now.

2 curved roller technology

* CVC roll shape control

The CVC roll shape control technology was developed in 1980 by the German SMS-Demag company. The original meaning of CVC (Coutinuously Variable Crown) is continuous variable crown. After more than 20 years of development and improvement, CVC mill has developed a variety of models, widely used in the production of cold rolled strip. The combination of advanced control strategies and control methods makes CVC technology one of the most advanced rolling technologies in the world. Its control principle is very simple, that is, the upper and lower roll bodies are ground into the same S-shaped CVC curve, the positions of the upper and lower rolls are inverted by 180 degrees, and when the initial phase of the curve is zero, an equidistant S-shape is formed. Parallel roll gap, through the roll swaying mechanism, the upper and lower CVC rolls are synchronously pulsating synchronously, and the continuously changing positive and negative convex contours can be generated at the roll gap, thereby adapting the process to the roll under different conditions. , continuous, arbitrarily change the requirements of the roll gap.

* UPC roll shape control

UPC rolling mill is a universal shape control rolling mill developed by German MDS. It is a roll traverse rolling mill which can improve the shape of the plate after HC and CVC technology. The principle is to grind the work rolls of the ordinary 4-roll mill into a cigar type, and the large and small heads are arranged oppositely to form a roll gap of different convexity.

The UPC mill was put into production less than the HC mill and the CVC mill. The first to use UPC technology was the German Krupp 1250 mill and the Finnish 2000 mill.

3 Cross Roller Technology---PC Rolling Roller Shape Control

The original meaning of PC (Pair Cross) is the roll-to-roll crossover, that is, the rolling mill cross-plate shape control technology. The design of the roll cross system is the same as that of a work roll with a crown. By adjusting the cross angle of the rolls, the farther the roll is from the center of the roll, the control of the roll gap morphology is achieved.

The cross-equivalent crown of the roll is related to the roll cross angle, the roll diameter and the width of the rolled piece. The relationship is as follows:

Cr=Se-Sc=(br)^2/(2Dw)
Where: Cr ---- equivalent convexity;
b----rolling width;
Se----center roll seam;
r----roller deflection angle;
Dw----roller diameter;
Sc----Edge roll seam.

Commonly used roll cross systems are:

* Only the support roller cross system with the support rollers crossing;
* Work roll crossover system with only work rolls crossed;
* Each set of work rolls is parallel to the axis of the support rolls, while the upper and lower rolls are crossed by a pair of rolls.

4 Rolling Technology - VC Shaped Variable Convex Support Roller Shape Control Technology

VC (Variable Crown) originally intended for the online variable crown support roller, which was successfully developed by Sumitomo Metal Co., Ltd. in Japan in 1977. The roll of the rolling mill is a roll-type roll, mainly consisting of a mandrel, a roll sleeve, a sealing oil chamber, and an oil. Road, rotary connector and high pressure pump station and other components.

The principle of the VC roller control plate shape is relatively simple. A sealing oil chamber is provided between the roller sleeve and the mandrel. By changing the pressure in the oil chamber, even if the support roller changes the roll shape (roll crown), the oil chamber pressure and the diameter are swollen. It has a linear relationship within a certain range and can be adjusted steplessly, so it can participate in the closed-loop shape control system.

VC has many advantages:

* Reduce the number of roll changes of the support roller to avoid storing multiple rolls of different roll types;
* Can compensate for roll wear and hot roll shape;
* In the strip rolling addition and deceleration stage, the rolling force fluctuation and roll crown variation caused by the change of rolling speed can be effectively compensated;
* Easy to change online, just use VC roller instead of the original support roller.

But VC also has limitations:

*VC roller manufacturing is more difficult;
* High-pressure rotary joints and oil chamber seals are difficult to maintain;
* Adjust the roll crown to a lesser extent.

5 Rolling force distribution control technology—DSR dynamic plate roll high-precision shape control

DSR dynamic plate-shaped roller high-precision shape control (ie rolling force distribution control) technology was introduced by French VAI Clecim company in the 1990s, mainly by stationary roller core, rotating roller sleeve, 7 plunger hydraulic The cylinder, the thrust pad and the electro-hydraulic servo valve are partially composed.

DSR dynamic plate rolls are mostly used for the support rolls of four-high mills and can be used in pairs or separately. The working principle: according to the actual curve calculated by the shape meter and the target shape curve, a set of deviations is obtained, and the seven separate pressure-controlled hydraulic pressure cylinders are distributed along the entire bandwidth through the rotating roller sleeve. Rolling force for high-precision plate shape (flatness) control.

DSR dynamic plate-shaped roller high-precision shape control has outstanding advantages and is a historical leap of high-precision shape control actuators. Mainly in:

* Can eliminate symmetry and asymmetry of plate shape defects;
* Shape control does not affect thickness control;
* Can control the shape of the plate with high precision.

The key to making full use of the DSR high-precision shape control capability is that the measurement accuracy, calculation accuracy, and deviation of the shape meter system are converted to the accuracy of the servo valve control signal. The general shape meter should achieve a measurement accuracy of 1I unit.

DSR has outstanding advantages, but its structure is relatively complicated, difficult to repair and maintain, and expensive, so it has not yet been widely popularized.

In China, DSR technology was first applied in Shanghai Baosteel 2030 cold rolling mill. The four-roll 2300 cold rolling mill under construction at Zhengzhou Cold Rolling Mill of China Aluminum Corporation Henan Branch also introduced the technology. The project is expected to be officially put into operation at the end of 2008.

At present, an advanced technology called roll thermal spray plate shape control is popular in the world. It has the characteristics of small production and short cycle, and is more suitable for online transformation of existing equipment. The advanced technology for roll hot plate shape control was developed by Australian Industrial Automation Services, which consists of computer control software and an edge thermal spray system. Two thermal spray devices are installed on both sides of the roll, and each device is equipped with a plurality of nozzles, each of which has a control range of 25 mm, and is spray-heated while the mill is in operation. The system effectively solves the plate-shaped defects of the edge tension caused by the thermal crown of the roll during high-speed rolling, improves the rolling speed, and reduces the probability of breaking.

Conclusion

The shape control is a comprehensive technology. In the production, the advanced control method must be matched with the process parameters to obtain the ideal shape.

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