Plate shape and cold-rolled plate shape control
What is plate shape
The so-called plate shape is the flatness of the fingerboard belt. Intuitively speaking, the plate is placed between two ideal plates, if the two sides of the plate and the plate 100% contact, it is considered that the plate is flat, otherwise it is considered that there is an unflatness or wave shape. In the basic concept of plate shape control, the so-called plate shape refers to the warping degree of the plate, which is essentially the distribution of residual stress inside the fingerplate strip. The length difference representation is usually used to describe the shape of the plate quantitatively.
The shape of the plate depends on whether the strip extends equally along the width direction. This condition is determined by the uniformity of billet cross section thickness and roll shape or actual roll gap before rolling.
How to control the shape of modern cold rolling mill
The original roll shape cannot be changed with the change of rolling conditions. And the actual production of rolling conditions are ever-changing, so. In order to compensate the change of roll shape effectively and obtain high-precision products, the roll shape and plate shape must be adjusted and controlled according to different conditions during rolling. At present, the commonly used plate shape control methods include temperature control method and hydraulic roll bending method.
1, temperature control method: also known as hot crown control method, is to artificially cool or heat some parts of the roll, change the distribution of the roll temperature, in order to achieve the purpose of controlling the roll shape. In practice, the coolant section control method is mainly used, that is, the coolant flow and pressure arranged along the length direction of the roll body are controlled in sections, the cooling conditions of each part are changed, and then the hot crown of the roll is controlled. If the middle wave of the rolled part is too large, it means that the coolant flow rate in the middle of the roll body should be increased or the coolant flow rate in the side of the roll should be reduced, so that the hot convexity in the middle of the roll body is reduced. If the rolled piece has bilateral waves, the opposite adjustment is made.
2, hydraulic roll bending method: In order to effectively control the transverse thickness difference and plate shape of the plate belt in a timely manner, a rapid response to the roller gap adjustment method is needed. This purpose can be achieved by using hydraulic roll bending technology and applying pressure from hydraulic cylinder to produce additional bending of work roll or support roll to compensate for changes in roll gap shape caused by changes in rolling pressure and rolling temperature and other process factors. The bending work roll is divided into two ways: positive bending roll and negative bending roll.
3, research and development of new rolling mill
(1) HC rolling mill: The high-performance version control mill is based on the ordinary four-high rolling mill, and a pair of axially movable intermediate shafts are installed between the support roll and the work roll, and it becomes a six-high rolling mill, and the axial movement of the middle roll is opposite.
(2) VC rolling mill: Roll crown can change instantaneously rolling mill, variable crown roll is a combined roll, by the mandrel and sleeve assembly, there is a hydraulic chamber between the mandrel and sleeve, the chamber is filled with pressure variable high pressure oil, with the rolling process conditions change, constantly adjust the pressure of high pressure oil, change the expansion of the roll (that is, roll crown), in order to obtain a good shape.
(3) CVC mill: continuously variable crown mill.
Control of shape of extremely thin cold rolled steel strip
The value of extremely thin cold rolled steel strip is high, but the production is difficult, and various plate shape problems are easy to occur in production, which affects the improvement of product quality. The following reasons are easy to cause the shape defect of extremely thin cold-rolled steel strip:
1. Large fluctuation of bending force.
The 6-roll HC reversible cold rolling mill can improve the shape quality by the bending force. If the bending force fluctuates greatly, it is unfavorable to the adjustment of the shape of the steel strip.
2, uneven thermal expansion of the roll.
In the process of steel strip rolling, there will be a lot of deformation heat, if the roll preheating time is too short, this deformation heat will make the roll thermal expansion, thus changing the original roll shape and affecting the quality of the shape.
3, the rolling pressure is large, is not conducive to the adjustment of the plate shape.
When rolling extremely thin steel coils, check the rolling pressure, the finished product pass rolling pressure exceeds the specified value of 7800kN, resulting in edge wave defects.
4. Large amount of roll steel.
With the extension of the working time of the roll in the mill (the increase of the amount of excess steel), the friction between the work roll and the steel strip causes the roll wear, resulting in the irregular shape of the roll gap, resulting in the shape defect.
Control measure
1. Reduce the fluctuation of bending roller force
The hydraulic oil is tested, and the large particulate matter exceeding the standard is filtered through the oil filter, and the accuracy of the oil product is below 6. The filter element is replaced to ensure the oil accuracy of the bending roll station. In view of the deviation of the zero point of the servo valve, the coil resistance value of the servo valve is measured by using the roll change time, and the resistance value exceeding the standard is replaced. The fluctuation of roll bending force can be controlled, thus reducing the shape defects caused by large fluctuation of roll bending force.
2, improve the uniformity of roll thermal expansion
By optimizing the rolling speed (< 400m/min) and adjusting the preheating time (> 25min), the roll achieves the effect of uniform thermal expansion and improves the shape quality.
3. Optimize rolling and annealing process parameters
The emulsion concentration is increased from 1.0% ~ 2.0% to 1.8% ~ 2.5% by using work roll with hardness ≥93HSD when producing ultra-thin cold rolled steel strip. The holding temperature of the second roll was optimized from 620℃ to 640℃, and the holding time was 8h.
4. Ensure the precision of roll shape
950 mill rolling extremely thin steel strip, the work roll from the original 80 tons reduced to 60 tons, the intermediate roll from the original 120 tons reduced to 100 tons, the production of extremely thin cold rolled steel strip support roll surface pit area ≯50mm2, the number of pits is not more than 3, to ensure the roll profile accuracy.
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