Papers by Keyword: Strip Shape

Abstract: High-strength steel is widely applied due to its excellent mechanical properties. However, its high strength in turn brings great difficulties to production and processing such as hot strip rolling owing to the high rolling force, which results in large elastic deformation of roll stack and poses a huge challenge to the control of strip crown and flatness. In this paper, A three-dimensional (3D) elastic-plastic coupled thermo-mechanical finite element (FE) model for hot strip rolling of high-strength steel is developed and then verified experimentally. This model not only calculates the elastic deformation of rolls and plastic deformation of strip simultaneously, but also considers the effect of temperature variation during hot strip rolling. Based on this valid model, the effects of bending force and shifting value of work roll (WR), back-up roll (BR) size, entrance strip crown and rolling force on strip crown have been investigated quantitatively. The results obtained provide valuable guidelines for industrial strip production.

Abstract: High-strength steel is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion than carbon steel. Strip shape is an important factor affecting the strip quality significantly for the rolled products. Because of the complex influence factors of plate shape and profile, shape detection and control technology have not been solved, especially for high strength steel rolling. In this paper, a novel three dimensional finite element simulation of the strip shape and flatness of high strength steel has been proposed. The material constitutive model has been built up based on experimental results through the Gleeble 3800 Thermal Simulator under different temperatures and stain rates. The modelling of roll elastic deformation system, roll gap profile and edge drop has been set up systematically considering the influence of the work roll transverse shifting and roll bending. Results have shown that both higher bending force and more roll shifting will significantly reduce the strip crown, and obtain improved edge drop distribution as well. The proposed numerical model has been validated through hot rolling experiments in 4-high rolling mills.

Abstract: Optimisation of the physical and mechanical properties of cold rolled thin strips is achieved by controlling the rolling parameters. In this paper, the factors affecting the low carbon steel thin strip profile of asymmetrical cold rolling have been studied at a speed ratio of 1.3 without lubricant applied. The effect of rolling parameters on the resulting microstructure was also investigated. It was found that under dry condition, work roll shifting and work roll cross angle can improve the strip profile, and the improvement is more significant with an increase of work roll cross angle rather than that of work roll shifting. A slight change in microstructure was evident with increasing work roll shifting values. In addition, effects of rolling parameters on the strip profile and microstructure have also been discussed.

Abstract: In order to automatically set the shape target curve, a model based on shape control theory is put forward. By coupling the shape forecast model and the shape discrimination model, the practical and strict shape target curve is researched. By combining strip plastic deformation model and rolls elastic deformation model, the shape forecast model is built. The shape discrimination is based on the strip element method. The main idea of the shape target curve is to minimize the shape crown in the first few passes on the condition that the strip is not unstable, in the last two passes to keep the good shape under the natural shape crown. Taking five-pass six-high rolling mill as an example, the convex strip is analyzed. The simulation and calculation results prove the validity and feasible of the shape target curve setting model. This model develops the shape target theory and lays the foundation of application of shape target curve in the rolling process of cold rolling.

Abstract: The harder and thinner strips, such as high strength steel and so on, have been needed to be rolled. When the rolled strip becomes thinner and harder, the unstable state rolling and tail end pinching might occur and so the strip shape measurement during rolling is strongly required under the condition that tension is applied to the strip. Visual-type shape meter, which has been already used, could not measure the strip shape when tension is applied to the strip. Looper Shape Meter, hereinafter referred as LSM, has been developed which could measure the strip shape under the tension. LSM is installed between mill stands and consists of 7 segment rolls along the width direction and a segment roll has two torque meters. LSM could accurately measure the tension distribution along the width direction without hysteresis and is protected with purge air and internal cooling system against severe environment in hot rolling. In order to verify the performance of LSM, the verification test was carried out in laboratory and production line. As a result, enough durability and good results of measured strip shape are obtained. LSM is easily replaced with existing conventional looper and it is expected that LSM contributes to the stable rolling and improve the productivity of rolling.

Abstract: Aim at solving the problem of ribbing defect is found on cold rolling strips which is caused by bad hot strip shape, analyze the reason from the hot rolling process, and study out that there are some reasons such as uneven wear of rolls can lead to ribbing defect. Roll contour, roll shifting model, rolling plan were optimized and got a geart effect: the hot strip shape being better, the production being more stable, the ratio of ribbing defect decreasing obviously (from 2.2% to 0.3%). The quality of their product has been improved a lot.

Abstract: Controlling cold strip profile is a difficult and significant problem has been found in industry during thin strip rolling. At present choosing the new type of strip rolling mill is the one of main methods to control the strip shape quality in cold rolling. The influences of rolling process parameters such as the work roll cross angle and work roll shifting on the strip shape and profile of thin strip are recognised throughout this study. The results show that the roll crossing and shifting is efficient way to control the strip shape. The increase of the work roll crossing angle would lead to improve the strip profile significantly by decreasing the exit strip crown and edge drop. The strip profile would be enhanced if the axial roll shifting was increased. Moreover, the total rolling force was analysed in detail by changing the roll cross angle and axial shifting roll.

Abstract: Shape Set Up (SSU) system is the key technology for Hot Strip Mill (HSM). Precise SSU system is applied to improve the strip quality for HSM. The function of SSU, Setup and Feedback, is introduced. The main mathematic model of strip profile is set up. SSU system strategy is studied of a certain domestic 1700mm HSM. The SSU system is carried out in produce and the measurement data show that strip flatness deviant and strip profile deviant could be controlled in target scope. The study has set a sound base to improve the setting accuracy and develop SSU system for HSM further.

Abstract: This paper focuses on a new type of 8-roll cold rolling mill with the back-up bearing roll. Compared to the traditional 6-roll cold rolling mill, a thick-walled bearing roll is used to multi-support the intermediate roll. By the rack, the fan-shaped gears, the eccentric core shaft and the servo-cylinder, the work roll can be pushed down by this screw down device on the top of the mill; By contrast with the 4(6)-roll mill, this type of mill has some characteristics, such as: the small size of rolls, lighter weight, the fast response for the screw down. The bearing roll is fixed by the supporting blocks placed on the rolling-mill housing. So this mill has large traverse rigidity, and this is propitious to the flatness control. By different means of strip flatness adjustments, such as the intermediate roll shifting, the roll bending and the bearing roll adjusting, the strip flatness can be well controlled. The oil-gas lubrication is used in the bearings of the bearing rolls, and the changing rolls equipment is designed for this type of mill too. A series of this type of mills (as 450, 800, 1250, 1450 series) have been produced since it was developed in 1997. The mills for 1250 and 1450 series have been applied in five-stand cold rolling mill and single stand reversing mill, a rolling speed of 800m/min has been achieved.

Abstract: In this paper, finite element models of the strip shape during cold rolling of ultra thin strip in both symmetrical and asymmetrical rolling cases have been successfully developed, and the strip shape such as the thickness distribution along the strip width has been obtained. The strip shape and edge drop are discussed under both symmetrical and asymmetrical rolling conditions. Simulation results show that the asymmetrical rolling can reduce strip edge drop dramatically. The work roll edge curve also affects strip shape significantly. The developed finite element model has been verified with the experimental values.