Asymmetric Rolling Conditions Research Articles

Investigation of the features of the formation of the structure of steel 08Yu during asymmetric rolling on a new mill 400

A study of the 08Yu steel structure during cold rolling at a new rolling mill in the Zhilyaev Laboratory of Mechanics of Gradient Nanomaterials of the Nosov Magnitogorsk State Technical University. It has been found that asymmetric rolling in rollers with speeds that differ 5 times and all other things being equal, resulted in the formation of a gradient structure. In the upper part of the strip section on the side where the rolling speed was lower, a uniform structure is observed, which is formed at more than half the strip thickness and consists of ultra-fine practically equiaxial grains of less than 1000 nm in size. The formation of the ultrafine structure is explained by the dynamic recrystallization under the conditions of heating the strip to a temperature of 250–300 ºC during rolling. In the lower part, on the side where the rolling speed was higher, a fibrous structure with smaller fragments up to 200 nm in size within individual fibers is clearly revealed. The hardness after asymmetric rolling compared to symmetrical rolling increased slightly and turned out to be more evenly distributed over the section. The difference in its values of different sections was not more than 15 % compared to symmetrical rolling, where the hardness in the central and perephyrian sections of the strip section differed by about 35 %. It has been found that these asymmetric rolling conditions lead to a simultaneous increase in reduction from 50 to 80 % and a decrease in force of almost 3 times per pass compared to symmetrical rolling, which can be explained by grinding the structure.The study was carried out within the framework of grants from the Russian Science Foundation (No. 20-69-46042 dated May 20, 2020), RFBR (No. 20-38-90097 dated September 3, 2020) and Megagrant (No. 075-15-2021-627 dated June 8, 2021).

Study on the relationship between asymmetrical rolling deformation zone configuration and rolling parameters

A new model for analyzing asymmetrical cold rolling process is proposed by the slab method, which solves the problem of insufficient applicability of existing models in the face of multiple asymmetric rolling conditions. In the new model, six configurations of the deformation zone are proposed as, forward-slip zone + cross-shear zone + backward-slip zone (F + C + B), cross-shear zone + backward-slip zone (C + B), all cross-shear zone (AC), forward-slip zone + cross-shear zone (F + C), all forward-slip zone (AF) and all backward-slip zone (AB). By analyzing the effects of rolling parameters such as reduction rate, roll speed ratio, tension and friction coefficient on the deformation zone configuration, the critical roll speed ratio and critical tension required for different deformation zone configurations are proposed. According to the variations of the critical roll speed ratio and critical tension with different rolling parameters, the deformation zone configuration - rolling parameters relationship diagram is obtained. Based on this diagram, the deformation zone configurations produced by different rolling parameter ranges can be determined, and the reasonable asymmetrical rolling technology can be selected for different production objectives. The proposed model can comprehensively and accurately calculate the rolling pressure, rolling force and torques under various rolling conditions, the calculated values agree well with the experimental results, the maximum error is 9.97%.

Influence of snake rolling on metal flow in hot rolling of aluminum alloy thick plate

Most asymmetrical rolling conditions should not appear in regular rolling processes, but for obtaining large deformations inside aluminium alloy thick plates, the asymmetrical rolling process is the most effective method. Snake rolling is adopted for promoting more deformation inside the plates. For exploring the deformation inside an aluminium alloy thick plate, a finite element model for simulating the process of snake rolling is established and the key influence factors are set as initial thickness, speed ratio and offset distance. The results show that deformation inside of the plate increases obviously while the thickness of plate is less than 300 mm after snake rolling. The speed ratio has a positive effect on promoting deformation partly inside of the plate. On the contrary, the offset distance has a negative influence by affecting the exit thickness. A formula for calculating the exit thickness after snake rolling is proposed and validated by data from the finite element models. Thus, snake rolling is suggested to be used in the downstream pass of hot rough rolling considering that the influence of thickness and the offset distance should be controlled in a reasonable range.

Analysis of mechanical parameters for asymmetrical strip rolling by slab method

An analytical model is proposed to analyze the asymmetrical cold strip rolling by the slab method, and used to easily determine the rolling pressure distribution, roll force, and torque. The effects of asymmetrical rolling conditions including roll speed, roll radius and friction coefficient on rolling pressure, roll force and torque are analyzed separately. The influences of different asymmetrical conditions on rolling pressure distribution are different and unrelated, but will superimpose each other when multiple asymmetrical conditions coexist. An appropriate combination of asymmetrical conditions can improve the non-uniform distribution of roll torques due to the unequal roll speed. The analysis results are in good agreement with experimental measurements and other studies, which verify the accuracy of the proposed model.

Feedback Control of the Contour Shape in Heavy-Plate Hot Rolling

This paper deals with the mathematical modeling and feedback control of the contour evolution in heavy-plate rolling. During the rolling process, asymmetric rolling conditions in the lateral direction may lead to a deviation between the actual and the desired plate contour. Such asymmetric rolling conditions are often unknown and hence cannot be compensated in advance. Therefore, a feedback control approach to reduce contour errors during the rolling process is presented. However, the measurement of the plate contour is subject to a transport delay, which complicates the design of feedback controllers. The angular velocity of the plate is also linked with its contour evolution. This is why the delay-free measurement of the angular movement is used in a 2-degrees-of-freedom Smith-predictor structure. The basis for the control approach is a mathematical model describing the nexus between the angular velocity and the contour evolution of the plate. The feedback controller utilizes an upstream and a downstream measurement of the contour and the movement of the plate. Furthermore, a proof of the robust stability of the proposed control concept is presented. Simulation results and measurements from an industrial plant demonstrate that the presented approach can significantly reduce the contour errors of rolled plates.

Automatic Gauge Control under Laterally Asymmetric Rolling Conditions Combined with Feedforward

The most common and well proven control strategy for thickness control in industrial rolling mills is the automatic gauge controller (AGC). However, it is still unclear how to use AGC for the control of asymmetries in lateral direction. How should the controller react to different thickness estimations at both sides of the mill? Such laterally asymmetric rolling conditions may originate from strip track-off, asymmetric friction in the mill stand, or a wedge-shaped entry profile of the strip thickness. In this paper, three control approaches are discussed. Two different setups of AGC are compared and a feedforward (FF) approach is developed for lateral asymmetries of the entry thickness profile. Simulation studies based on a validated mill stand model demonstrate the benefit of combining AGC with a feedforward controller to compensate for asymmetries.

Optimization-based reduction of contour errors of heavy plates in hot rolling

This paper deals with the reduction of top view contour errors in the hot rolling process. Deviations between the actual plate contour and the desired shape may result from asymmetric rolling conditions caused by, e.g., temperature gradients or non-homogeneous input thickness profiles. Under real rolling conditions these disturbances are hard to predict and hence cannot be compensated in a feedforward approach. Therefore, it seems suitable to apply feedback when contour errors occur. This approach essentially requires a measurement of the plate contour and a mathematical model to predict the plate contour after the roll pass. This model is the basis for an optimization-based approach to determine the necessary adjustment of the rolling mill to reduce contour errors. The optimization problem allows to systematically incorporate constraints on the asymmetry of the output plate thickness. Generally, the compliance of the mill stand is not strictly symmetric and may deteriorate the result of the presented approach. The asymmetric compliance results in an asymmetric deflection of the mill stand which is compensated in an empirical approach utilizing the forces applied during the roll pass. Simulation results and measurements of plates rolled during the normal production demonstrate the effectiveness of the proposed method.

Optimization-based estimator for the contour and movement of heavy plates in hot rolling

This paper deals with the estimation of the contour of heavy plates during the hot rolling process. Asymmetric rolling conditions lead to a non-rectangular contour. The reasons for this effect, e.g., temperature gradients or non-homogeneous input thickness profiles, are hard to predict in a real rolling mill. Hence, feedforward compensation of these disturbances is difficult, whereas feedback control could be a suitable means for improving the plate contour. Feedback control essentially requires the actual contour of the plate, which has to be measured or estimated in real-time. The method presented in this paper suggests to capture an image sequence of the plate by means of a thermographic measurement device. In the considered application, an image sequence is required because the whole plate contour cannot be captured by a single image. An optimization-based algorithm takes into account the image data and the restrictions of the plate movement in the rolling gap and uses this information to estimate the actual plate contour. In addition, the algorithm estimates the angular velocity and the speed of the plate. Measurement data from a heavy plate mill is used to validate the effectiveness of the proposed method.

Effect of Additional Shear Stress on Microstructure Evolution of AZ31 Sheet by Differential Speed Rolling

Asymmetric rolling of deformed magnesium alloys sheet can accelerate refine the grain size, reduce the basal texture, and improve the subsequent formability. This happens because the additional shear stress and strain are introduced during the differential speed rolling. This paper investigates the relationship of shear stress and microstructure evolution by the experiment in conjunction with the FEM (Finite Element Method) simulation. The differential speed ratio (1, 1.2 and 1.5) and rolling reduction (8% and 15%) were executed at room temperature. The additional shear strain field is simulated for corresponding asymmetric rolling conditions. The results showed that the additional shear stress and strain were the essential influence factors of microstructure evolution and formability of AZ31 sheet for the differential speed rolling. It is helpful in enhancing and improving the formability of rolled magnesium alloys.

Mathematical modeling of the contour evolution of heavy plates in hot rolling

This paper deals with modeling of the contour evolution of heavy plates in hot rolling. During the rolling process asymmetric rolling conditions, such as temperature gradients or non-homogeneous input thickness profiles, may lead to a non-rectangular plate contour. A continuum mechanics approach is employed to systematically derive the contour evolution of the plate based on the input and output thickness. The mathematical model covering deviations in two dimensions is solved using methods for plane problems in mechanics. A comparison between the simulated contour evolution and measurement data from a real rolling process indicates the good accuracy of the model. Moreover, the model can be executed within one millisecond on a standard computer which stresses its real-time capability. A short analysis of the main reasons for the generation of camber utilizing the proposed model is presented.

Research on Camber Correction Method of Heavy Plate

In the rolling process of heavy plate mill, the longitudinal extension will result in differences at different positions in the lateral direction of rolling pieces. This difference is affected due to some asymmetric rolling conditions, which lead to the camber. Lateral direction of the plate which is based on image processing algorithm is measured by using plate images acquired during rolling process with the help of linear array camera. In combination to camber correction model deducted and camber feedback control system is developed to realize the automatic correction control for camber of plate during production in this paper. Field applications show that this control method is able to reduce human interference and camber curve rate, which is significant in improving the yield of product.

Finite Element Analysis of Thin Strip Profile in Asymmetric Cold Rolling Considering Work Roll Crossing and Shifting

Cold rolled thin strip has received a great deal of attention through technological and theoretical progress in the rolling process, as well as from researchers who have focused on some essential parameters of strip such as its shape and profile. This paper describes the development of a 3-D finite element model of the shape of thin strip during cold rolling to simulate the cold rolling of WCS (work roll crossing and shifting) in asymmetric rolling. This finite element model considers the asymmetrical rolling parameters such as variations in the diameters of the rolls and the crossing angle as the work roll shifts on the strip during cold rolling. The shape and profile of the strip are discussed in the asymmetrical and symmetrical rolling conditions, while the total rolling force and distribution of stress are discussed in the case where the roll cross angle and axial shifting roll changes. The results can then be used to control the shape and profile of thin strip during rolling.

Analysis of Thin Strip Profile during Asymmetrical Cold Rolling with Roll Crossing and Shifting Mill

Strip profile control during rolling is required to assure the dimensional quality of rolled thin strip is acceptable for customers. Throughout rolling, the strip profile is controlled by using the advanced shape control rolling mill, such as the combination of work roll crossing and shifting during asymmetrical rolling, the one of the valuable methods to control the strip profile quality in rolling process. In this paper, the influences of cold rolling parameters such as the crossing angle and axial shifting value of work rolls on the strip profile are analysed. The strip shape control is discussed under both symmetrical and asymmetrical rolling conditions. The obtained results are appropriate to control the rolled thin strip profile in practice.

An in-line model for predicting front end bending in hot plate rolling and its experimental verification

In this article, we present an in-line model that can be used for predicting the front end bending of a material frequently produced by hot plate rolling under asymmetric rolling conditions. The in-line model was formulated by examining the relationship between asymmetric rolling conditions and front end bending slope and by expressing front end bending slope as a function of asymmetric rolling conditions as well as roll-bite profiles (shape factor and reduction ratio). We also performed a pilot hot plate rolling test to verify the usefulness of the proposed in-line model. Before the rolling test began, a board-shaped specimen that had been heated in a reheating furnace at 1100 °C was half submerged, horizontally, in a bathtub filled with cold water to derive temperature variation of the specimen along the specimen’s thickness direction, which is one of the asymmetric rolling conditions that produce front end bending. Results show that front end bending slopes formulated as a double-linear function of asymmetric rolling conditions as well as roll-bite profiles (i.e. shape factor and reduction ratio) were successful. The proposed in-line model computed immediately the amount of front end bending whenever the roll-bite profiles and asymmetric rolling conditions changed during rolling. The results predicted by the in-line model were within 6.5%–10.3% of the front end bending slopes measured from the pilot hot plate rolling test.

Microstructure and texture evolution of copper processed by differential speed rolling with various speed asymmetry coefficient

The analysis of structure and texture changes in cold-deformed copper by asymmetric rolling with different coefficient of rolls speed asymmetry R (R=2–4), was shown in recent paper. The results were compared to ones obtained for cold rolled copper with equal speed of both rolls (R=1). It was found that the application of asymmetric rolling conditions results in a greater strain hardening than in the case of the classical rolling process (R=1). The results have revealed that increase of the asymmetry coefficient R value, causes presence of higher fraction of high angle boundaries in as-deformed material structure, suggesting the possibility of occurrence of thermally activated processes of structure recovery or mechanical fragmentation of grains. Texture analysis has shown that application of rolling speed asymmetry results in a significant sharpening of the deformation texture (maximum ODF values were twice higher than for normally rolled samples (R=1)). In addition, for the variant with the greatest coefficient of rolling speed asymmetry (R=4), obtained deformation texture was characterized by a relatively low fraction of the typical rolling texture components (the Cu, the Bs, and the S), and significantly increased fraction of the shear texture components.

Modelling of Strip Shape and Profile during Cold Rolling of Ultra Thin Strip

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.

Analysis of Strip Shape in Cold Rolling of Thin Strip

In this paper, finite element models of the strip shape during cold rolling of thin strip in both symmetrical and asymmetrical rolling cases have been successfully developed, and the effects of rolling parameters on strip shape such as the thickness distribution along the strip width have been obtained. The strip edge drop and shape are discussed under both symmetrical and asymmetrical rolling conditions. Simulation results show that the asymmetrical rolling can reduce the strip edge drop dramatically, which is useful in improving the strip shape and reducing the energy cost during cold rolling of thin strip. The developed finite element model has been verified with the experimental value. The obtained results are applicable to control the rolled thin strip shape in practice.

Model–based control of front–end bending in hot rolling processes

This contribution deals with the modeling and control of flatness defects in form of so–called ski–ends which occur during the hot rolling process of heavy plates. These ski–ends are caused by asymmetrical rolling conditions, e.g., different work roll circumferential speeds or vertical temperature gradients. In a first step, a physics–based model for asymmetrical rolling is derived based on the upper bound method for ideal rigid–plastic materials and is validated by means of numerical and measurement data. It turns out that the drive train proves to be the suitable actuator for suppressing the ski–ends. Therefore, an improved underlying multi–input multi–output control concept for the two main drives is presented. Finally, an overall pass–to–pass model–based control concept for the reduction of ski–ends is developed.

A theoretical study on the application of asymmetric rolling for the estimation of friction

In this work, a method for the estimation of friction coefficient is proposed based on the asymmetric rolling operation. Asymmetry is produced by operating the lower and upper rolls at different speeds. A slab method based computer code is developed for estimating the curvature of the rolled sheet under asymmetric rolling conditions. Strain-hardening behavior of the material has been incorporated and Wanheim and Bay's friction model is employed. The developed code is used for solving the inverse problem of estimating the coefficient of friction by measuring the curvature of the rolled sheet under known operating conditions. The simulations show a good potential of the method.

Increase of Lankford Value of Al-Mg-Si Sheets for Automotive Panel Produced by Asymmetric Warm Rolling

To restrain global warming, weight reduction of autobodies is needed for fuel saving and discharge of carbon dioxide (CO2) gas. Usage of light weight aluminum alloy sheets is efficiency for the weight reduction, but the less formabilities comparing with low carbon steel sheets restrict the usage of autobodies applications actually. To improve the formabilities of aluminum alloy sheets, asymmetric warm rolling is studied. The formability of a metallic sheet strongly depends on the textures. Lankford value (r-value), one of the indicators of formability, of recrystallized low carbon steel sheets is high because the density of {111}//ND orientation suitable for deep drawing is high. The texture of conventionally cold rolled and recrystallized aluminum alloy sheets mainly consists of cube texture which is lower r-value and unsuitable for deep drawing. It is well known that similar texture to low carbon steel sheet can be obtained by shear deformation in aluminum alloy sheets. To provide the shear texture in aluminum alloy sheet, asymmetric warm rolling is carried out at 473K-573K with differential roll velocities. A small amount of {111}//ND orientation which is hardly produced by conventionally cold rolling is observed in asymmetric warm rolled aluminum alloy sheets after recrystallizing. Controlling the asymmetric warm rolling conditions, such as rolling temperature, total reduction and asymmetric ratio, higher r-value and deep drawability comparing with conventionally processed aluminum alloy sheets are achieved. Other properties such as strength, elongation, and bendability of asymmetric warm rolled sheets are almost same as those of conventionally processed sheets.