Development of advanced shape control technology f

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The development of advanced technology of shape control of cold rolled strip in the world

shape control is the core control of cold rolled strip processing, that is, the length and width are one of the technologies of 1200 mm and 60 mm respectively. In recent years, with the continuous progress of science and technology, advanced shape control technology has been emerging and improving day by day. The development of shape control technology has promoted the equipment progress and industrial upgrading of cold rolled strip industry, Production efficiency and benefits have been greatly improved

concept of shape

1 basic concept of shape

shape refers to the warpage of plate and strip intuitively, and its essence is the distribution of residual stress in the plate and strip. As long as there is residual stress in the plate and strip, it is bad shape. If the residual stress is not enough to cause the strip to warp, it is called "potential" bad shape; If the residual stress causes the strip to be unstable and warped, it is called "apparent" bad shape

2 plate shape expression method

plate shape expression method includes relative length difference expression method, waveform expression method, tension difference expression method and thickness relative change expression method. The first two methods are commonly used in the production control process

3 common shape defects and analysis

common shape defects include edge waves, melting intermediate waves at about 96 ℃, 10000 US dollars) unilateral waves, two rib waves and composite waves, which are mainly caused by uneven extension of all parts of the strip during rolling, resulting in internal stress

in order to obtain high-quality rolled strip, the roll gap must be adjusted at any time to suit the plate crown of the incoming material, and the influence of various factors on the roll gap must be compensated. For strips with different widths, thicknesses and alloys, only with an optimal crown can the roll produce an ideal target shape. Therefore, the essence of flatness control is to control the bearing roll gap. Unlike thickness control, which only needs to control the opening accuracy at the midpoint of the roll gap, flatness control must control the shape of the full roll gap within the width span of the rolled piece

leading factor on shape control

as we all know, the main factors affecting shape include the following aspects:

(1) the change of rolling force

(2) change of convexity of incoming plate

(3) crown of original roll

(4) plate width

(5) tension

(6) roll contact state

(7) change of roll thermal crown

advanced technologies of shape control

to improve and improve the level of shape control, we need to start from two aspects: one is from the aspect of equipment configuration, such as adopting advanced shape control means, increasing mill stiffness, etc; The second is from the aspect of process configuration, including the determination of the original crown of the roll, the amount of deformation and the distribution of passes

conventional flatness control methods mainly include roll bending control technology, roll tilting control technology and segmented cooling control technology. In recent years, some special control technologies, such as roll drawing technology (HC Rolling Mills and UC series rolling mills of Shimadzu, Beijing landmaker and other companies in Japan), roll rising technology (VC rolling mills and IC rolling mills), rolling force distribution control technology (DSR dynamic flatness roll) and roll edge thermal spray technology, have been widely used. Here, several typical technologies are briefly introduced

The HC Rolling Mill is a new 6-high rolling mill jointly developed by Hitachi and Nippon Steel in the 1970s. HC (high crown) refers to high-performance roll crown. Based on the ordinary 4-high mill, a pair of axially movable intermediate rolls are installed between the support roll and the work roll, and the axial movement direction of the intermediate rolls is opposite

through the analysis of the roll deflection of the ordinary 4-high mill, the harmful contact area between the work roll and the backup roll beyond the width area of the rolled piece leads to the excessive deflection of the roll. This deflection depends not only on the rolling force, but also on the width of the rolled piece. On the other hand, when the bending force is applied to the work roll, the deflection of the roll will be constrained by the support roll at the part beyond the width of the rolled piece. HC Rolling Mill eliminates the harmful contact zone between the support roll and the work roll through the transverse movement of the intermediate roll, improves the shape control ability of rolling, and can be applied to the rolling of any width strip. At present, HC Rolling Mill has developed many forms, such as HCM 6-high rolling mill driven by intermediate roll; Hcmw 6-high mill with intermediate roll and work roll moving; Hc-cvc rolling mill with intermediate roll profile curve; And HCW, UCM, uvmw, MB, uc2~uc4 and other improved rolling mills

Advantages of

hc rolling mill:

* strong shape control ability, which can better adjust the shape without too much roll bending force

* it can eliminate the harmful contact part between the support roll and the edge of the work roll, and reduce the thinning and fission tendency of the edge

* due to the small working roll diameter (about 30% smaller than the ordinary 4-high mill), the reduction can be increased, the rolling with large reduction can be realized, and the energy consumption can be reduced

* the use of standard non convexity rolls can meet the rolling of strips of various widths and reduce the spare parts of rolls

since the 1970s, more than 200 HC mills have been built all over the world, and they are still a popular model until now

2 curved roll technology

* CVC roll shape control

cvc roll shape control technology was developed by German Sigmar Demag company in 1980. CVC (coutinuously variable crown) originally means continuous variable convexity. After more than 20 years of development and improvement, CVC mill has developed many types, which are widely used in the production of cold rolled strip. The combination of advanced control strategy and control means 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, and the positions of the upper and lower rolls are inverted by 180 degrees. When the initial phase of the curve is zero, an equidistant S-shaped parallel roll gap is formed. Through the roll movement mechanism, the upper and lower CVC rolls move relatively synchronously, and the continuously changing positive and negative convexity contours can be generated at the roll gap, so as to adapt to the process. Under different conditions, the rolls can be quickly, continuously Arbitrarily change the requirements of roll gap crown

* UPC roll shape control

upc mill is a universal shape control mill developed by German MDS. It is another roll traverse mill that can improve the shape after HC and CVC technology. The principle is to grind the work roll of the ordinary 4-high mill into a cigar shape, and the large and small ends are arranged opposite to each other to form a roll gap with different convexity

the number of UPC rolling mills put into production is less than that of HC Rolling Mills and CVC rolling mills. The first to use UPC technology are Krupp 1250 rolling mills in Germany and 2000 rolling mills in Finland

3 cross roll technology - - PC rolling mill roll cross flatness control

pc (pair cross) originally meant that the rolls crossed in pairs, that is, rolling mill roll cross flatness control technology. The design principle of the roll crossover system is the same as that of the work roll with crown. By adjusting the cross angle of the roll, the roll gap is larger the farther away from the roll center, and the shape of the roll gap is controlled

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

CR = se sc= (BR) ^2/(2dw)

where: Cr - equivalent crown

b---- width of rolled piece

se---- central roll gap

r---- roll deflection angle

dw---- roll diameter

sc ---- edge roll gap

common roll crossing systems are:

* support roll crossing system with only support roll crossing

* work roll crossover system with only work roll crossover

* each group of work rolls is parallel to the axis of the support roll, and the upper and lower roll systems intersect

4 roll expansion technology - VC flatness variable crown support roll flatness control technology

vc (variable crown) originally means variable crown support roll, which was successfully developed by Sumitomo Metal Company of Japan in 1977. The roll of the rolling mill is a roll sleeve type roll, which is mainly composed of mandrel, roll sleeve, sealing oil cavity, oil circuit, rotary connector and high-pressure pump station

The principle of controlling the flatness of VC roll is relatively simple. There is a sealed oil cavity between the roll sleeve and the mandrel. By changing the pressure in the oil cavity, even if the backup roll changes the roll shape (roll crown), the pressure in the oil cavity has a linear relationship with the diameter swell within a certain range, and it can be adjusted steplessly. Therefore, it can participate in the closed-loop flatness control system

vc has many advantages:

* reduce the number of roll changes of the backup roll and avoid storing multiple rolls of different roll types

* can compensate roll wear and hot roll shape

* in the acceleration and deceleration stages of strip rolling, the rolling force fluctuation and roll crown change caused by the change of rolling speed can be effectively compensated

* the transformation is convenient, and only VC roller is needed to replace the original support roller

but VC also has limitations:

* it is difficult to manufacture VC rollers

* it is difficult to maintain the high-pressure rotary joint and oil cavity seal

* the range of adjusting roll crown is small

5 rolling force distribution control technology - DSR dynamic flatness roll high-precision flatness control

dsr dynamic flatness roll high-precision flatness control (i.e. rolling force distribution control) technology was introduced by French VAI clecim company in the 1990s. It is mainly composed of static roll core, rotating roll sleeve, 7 plunger hydraulic cylinders, thrust pads and electro-hydraulic servo valves

dsr dynamic flatness roll is mostly used for the support roll of four high mill, which can be used in pairs or alone. Its working principle: according to the comparison between the actual curve measured and calculated by the shape meter and the target shape curve, a group of deviations are obtained. Through seven separately regulated hydraulic screwdown cylinders, the corresponding rolling force is distributed to the strip along the whole bandwidth through the rotating roll sleeve to control the shape (flatness) with high precision

The high-precision flatness control of DSR dynamic flatness roll has outstanding advantages and is a historic leap of high-precision flatness control actuator. It is mainly manifested in that:

* can eliminate symmetrical and asymmetric flatness defects

* shape control does not affect thickness control

* it can dynamically and accurately control the shape of the plate

the key to give full play to the high-precision flatness control ability of DSR mode lies in the measurement accuracy, calculation accuracy and the accuracy of converting deviation into servo valve control signal of flatness meter system. Generally, the flatness meter should reach the measurement accuracy of 1I unit

dsr has outstanding advantages, but its structure is relatively complex, overhaul and maintenance are difficult and expensive, so it has not been widely popularized at present

in China, DSR technology is the first to be applied in Shanghai Baosteel 2030 Cold Rolling Mill. The four roll 2300 cold rolling mill under construction in Zhengzhou cold rolling plant of Aluminum Corporation of China Henan Branch has also introduced this 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 flatness control is also popular in the world. It has the characteristics of small production and short transformation cycle, and is more suitable for the transformation of existing equipment. This advanced roll thermal spray flatness control technology is developed by Australian Industrial automation service company. The system is composed of computer control software and edge thermal spray system. Two thermal spray devices are installed on both sides of the roll, and several nozzles are installed on each device. The control range of each nozzle is 25mm. Spray heating is implemented when the rolling mill is working. The system effectively solves the flatness defect of edge tension caused by roll thermal crown during high-speed rolling, and improves the

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