Work Roll Bending Research Articles

3D FEM analysis of strip shape during multi-pass rolling in a 6-high CVC cold rolling mill

A 3D elastic–plastic finite element method (FEM) model of cold strip rolling for 6-high continuous variable crown (CVC) control rolling mill was developed. This model considers the boundary conditions such as accurate CVC curves, total rolling forces, total bending forces and roll shifting values. The rolling force distributions were obtained by the internal iteration processes instead of being treated as model boundary conditions. The calculated error has been significantly reduced by the developed model. Based on the rolling schedule data from a 1,850-mm CVC cold rolling mill, the absolute error between the simulated results and the actual values is obtained to be less than 10 μm and relative error is less than 1 %. The simulated results are in good agreement with the measured data. The developed model is significant in investigating the flatness control capability of the 6-high CVC cold rolling mill in terms of work roll bending forces, intermediate roll bending forces and intermediate roll shifting values.

Flatness Feed-Forward Control Model Based on Neural Networks

The influence on the shape of the strip from rolling force fluctuations has been analyzed. The combination of intermediate roll bending and work roll bending has been adopted. The principle of rolling force feed-forward control has been analyzed. The feed-forward control model has been established on the basis of neural networks. The model has been successfully applied to a rolling mill and a good effect has been achieved.

FEM Analysis of Profile Control Capability during Rolling in a 6-High CVC Cold Rolling Mill

A 3D elastic-plastic finite element method (FEM) model of cold strip rolling for 6-high continuous variable crown (CVC) rolling mill was developed. The rolling force distributions were obtained by the internal iteration processes. The calculated error has been significantly reduced by the developed model. the absolute error between the simulated results and the actual values is obtained to be less than 10μm, and relative error is less than 1%. The developed model is significant in investigating the profile control capability of the CVC cold rolling mill in terms of work roll bending, intermediate roll bending and intermediate roll shifting.

The Mathematical Models and Simulation on Work Roll Bending Control System of Cold Rolling Mill

The calculated result of the mathematical model based on the conventional transfer function has bigger deviation than the measured. In this paper the mathematical model of the work roll bending is derived. The modeling is different from conventional modeling used many presumptions and linear processing. The modeling calculated accurately the equivalent load spring using the method of influence function. The simulation results agree well with actual data of the bending system.

Manifested flatness defect prediction in cold rolling of thin strips

Flatness defects in thin strip cold rolling are a consequence of roll thermo-elastic deformation, from which heterogeneous strip plastic deformation results. When flatness defects manifest on line, buckling reorganizes the stress field in the pre- and post-bite areas. Comparison with flatness roll measurement requires this effect to be taken into account. A coupled Finite Element Method (FEM) approach is used here to compute stresses and strains in-bite as well as out-of-bite. The detection of buckled (non-flat) areas is demonstrated for a very thin strip cold rolling case. The model is then applied here to two questions, namely the impact on flatness of the heterogeneous temperature field and the effect of friction on optimal setting of a flatness actuator, Work Roll Bending.

Development of HOFC Work Roll Curve for Strip Rolling Mill

The HOFC (High Order Flatness Control) work roll curve was designed using Matlab. It has great flatness control ability, for the roll diameter in the position of the 1/4 roll length can be altered with the changing of angle and index parameters. Combined with the data from a hot strip factory, the elastic deformation of the HOFC work roll was analyzed following the influence coefficient method. The distribution curves of the exit thickness, roll force, work roll bending, pressure between rolls, roll flatting, and roll gap geometry were given under the conditions of different roll parameters. Results show that the HOFC work roll curve can eliminate the high flatness defects, reduce the edge drop, improve the lateral thickness uniformity, and maximize the available cross section of the strip effectively.

Calculation of work roll initial crown based on desired strip profile in hot rolling

The superposition of work roll initial crown, the work roll bending and flattening crown, the work roll wearing crown and the work roll thermal crown makes the final hot strip. In this paper, new models based on numerical method have been obtained to predict the roll force, the work roll wearing crown and the work roll thermal crown utilizing experimental data provided by Mobarake Steel Complex. Meanwhile, the work roll bending and flattening crown has been obtained from finite element method as well as elasticity approach. Then, a computer programing has been written to obtain the work roll initial crown in order to get desired strip profile. This program is called Initial Crown Prediction Software (ICPS). Finally, the obtained initial crowns from ICPS were applied for different stands of hot strip mill of Mobarake Steel Complex, and the strip profile shows a good agreement with the desired one for the mentioned mill.

Research and application of non-symmetrical roll bending control of cold rolling mill

The existing research of the flatness control for strip cold rolling mainly focuses on the calculation of the optimum adjustment of individual flatness actuator in accordance with the flatness deviation, which can be used for general flatness control. However, it does not work for some special rolling processes, such as the elimination of ultra single side edge-waves and the prevention of strip break due to tilting roll control overshooting. For the purpose of solving these problems, the influences of non-symmetrical work roll bending and intermediate roll bending on flatness control were analyzed by studying efficiencies of them. Moreover, impacts of two kinds of non-symmetrical roll bending control on the pressure distribution between rolls were studied theoretically. A non-symmetrical work roll bending model was developed by theoretical analysis in accordance with practical conditions. The model was applied to the revamp of a 1250 6-H reversible universal crown mill (UCM) cold mill. Theoretical study and practical applications show that the coordination utilization of the non-symmetrical work roll bending control and tilting roll control was effective in flatness control when there appeared bad strip single side edge waves, especially when the incoming strip was with a wedge shape. In addition, the risk of strip break due to tilting control overshooting could be reduced. Furthermore, the non-symmetrical roll bending control can reduce the extent of uneven distribution of pressure between rolls caused by intermediate roll shifting in flatness control and slow down roll wear. The non-symmetrical roll bending control technology has important theoretical and practical significance to better flatness control.

Edge Drop Constituent Analysis of Cold Rolled Strip

Aiming at the strip edge drop control, the three dimensional finite element roll system models were built. From the point of the burdened load and deformation of the roll system, the reason which caused the strip edge drop and its composing were analyzed, and the critical width was proposed to control the strip edge drop. Based on the FEM analysis and industrial experiment, the VCR (Varying contact backup rolls) matching the EDW (Edge drop control work rolls) was designed and proposed independently. The application of such rolls gives better mill crown control ability, a high performance of work roll bending force and the improved strip edge drop, crown and flatness quality.

Preset model of bending force for 6-high reversing cold rolling mill based on genetic algorithm

The hydraulic roll-bending device was studied, which was widely used in modern cold rolling mills to regulate the strip flatness. The loaded roll gap crown mathematic model and the strip crown mathematic model of the reversing cold rolling process were established, and the deformation model of roll stack system of the 6-high 1 250 mm high crown (HC) reversing cold rolling mill was built by slit beam method. The simulation results show that, the quadratic component of strip crown decreases nearly linearly with the increase of the work roll bending force, when the shifting value of intermediate roll is determined by the rolling process. From the first pass to the fifth pass of reversing rolling process, the crown controllability of bending force is gradually weakened. Base on analyzing the relationship among the main factors associated with roll-bending force in reversing multi-pass rolling, such as strip width and rolling force, a preset mathematic model of bending force is developed by genetic algorithm. The simulation data demonstrate that the relative deviation of flatness criterions in each rolling pass is improved significantly and the mean relative deviation of all five passes is decreased from 25.1% to 1.7%. The model can keep good shape in multi-pass reversing cold rolling process with the high prediction accuracy and can be used to guide the production process.

Adaptive Learning of Bending Force Presetting Model in a Six-High Cold Rolling Mill

In this paper, adaptive learning method of bending force presetting model in a six-high cold rolling mill is introduced. Adaptive learning coefficient of bending force presetting model is calculated by contrast between measured and model calculated actual bending force, then exponential method is used to modify the adaptive learning coefficient to improve the precision of the bending force presetting model. While calculating model calculated actual bending force, Legendre polynomials are used to convert measured flatness data to quadratic and quartic flatness coefficient, then regulating quantity on the quadratic flatness coefficient of intermediate roll bending force and work roll bending force is determined based on their regulate capability. Practical application shows that precision of the bending force presetting model has improved significantly by adaptive learning.

Research and Application of Dynamic Substitution Control of Actuators in Flatness Control of Cold Rolling Mill

AbstractThe work roll bending control has a strong ability to eliminate the symmetrical flatness defects of strip. However, if the incoming strip is coming with severe symmetrical flatness defects, it happens that the position limit of work roll bending is prone to be reached or exceeded during the execution of the displacement, resulting in the residual symmetrical flatness defects without further elimination, as well as a limited flatness control process. Abilities of work roll bending and intermediate roll bending / shifting for flatness control have been analyzed based on the actuator efficiencies for the purpose of solving the problem of work roll bending control reaching threshold. Meanwhile, a self‐learning determination model of actuator efficiency factors, which can be utilized to determine the actuator efficiency factors online accurately, was developed from the measurement data extracted from the rolling mill. Models of intermediate roll bending and intermediate roll shifting substitution control in case of work roll bending control over‐limitation have been developed, in accordance with the practical conditions and the degree of work roll bending over‐limitation. Applications show that the substitution control can play an important role in the residual symmetrical flatness deviation control, which should have been removed completely by the work roll bending control.

A Robust Model for Work Roll Bending Control Reaching Threshold in Flatness Control of Cold Rolling Mill

The work roll bending is one of the most effective flatness actuators in flatness control of cold rolled strips, as a result of its characteristics such as high speed response, powerful effects on the elimination of flatness defects such as edge-waves, central waves and so on. The existing research on flatness control mainly focuses on the calculation of optimal adjustment of individual flatness actuator. However, the final output of a flatness actuator is required to be limited firstly for some special cases. If the incoming strip is coming with big symmetrical flatness defects, it happens that the position limit of work roll bending is prone to be reached or exceeded during the execution of the displacement, resulting in the residual symmetrical flatness defects without further elimination, as well as a limited flatness control process. In order to avoid this situation, substitution control by intermediate roll bending in case of work roll bending control over-limitation have been developed, which is based on actuator efficiencies and in accordance with the practical conditions. Applications show that the substitution control of intermediate roll bending for work roll bending over-limitation can play an important role in the residually symmetrical flatness control.

A NUMERICAL SIMULATION OF STRIP PROFILE IN A 6-HIGH COLD ROLLING MILL

Shape control is always a key issue in the six-high rolling mill, in which the shifting of the intermediate roll and the work roll have been used to enhance the shape control capability. In this paper, a finite element method (FEM) model has been developed to simultaneously simulate the strip deformation and the roll stack deformation for the six-high rolling mill. The effects of the work-roll bending, the shifting of the intermediate roll and the work roll on the strip crown and edge drop are discussed in details. Results have shown that both higher bending force and more roll shifting will significantly reduce the strip crown. The edge drop is also reduced with the bending force and the roll shifting.

Mechanics of Asymmetric Rolling of Thin Strip with Effect of Work Roll Edge Contact

Asymmetric rolling of thin strip has become important due to a significant decrease of rolling force, which contributes to obtain the extremely thin strip, to reduce the rolling passes, and to save the energy by a decrease of anneal treatment. In asymmetric rolling of thin strip, edges of work rolls may contact and deform when no or small work roll bending force is applied. Work roll edge contact forms a new deformation feature. In this paper, the effects of initial thickness of strip and friction coefficient on the rolling pressure, roll edge contact length and strip crown during asymmetric rolling of thin strip with work roll edge contact effect has been discussed, and the calculated rolling force with work roll edge contact is compared with the measured value.

A time-encoded signal-processing approach to fault classification of an electrohydraulic pressure control system and its application to a hot steel strip rolling mill

A technique is presented whereby time domain signals may be classified in terms of four shape parameters. These parameters are processed to create a condition indicator, its variation being used to identify system faults. In this study, the leakage flowrate and a faulty servo-valve are identified on a pressure control system and a comparison is made with a conventional fast Fourier transform approach and a commercial software package, time-encoded signal processing and recognition. A new code, CARCODE, is then applied to 28 servo-valve-controlled work roll bending circuits on a seven-stand hot steel strip rolling mill and a simple graphics presentation is developed to aid real-time condition monitoring.

CARCODE for Time Encoded Signal Processing and fault trending of the Work Roll Bending hydraulic control systems on a 7-stand Hot Steel Strip Rolling Mill

CARCODE for Time Encoded Signal Processing and fault trending of the Work Roll Bending hydraulic control systems on a 7-stand Hot Steel Strip Rolling Mill

Computer analysis for the prediction of a strip profile in cold rolling

In the present work, a software is developed on windows environment in C++ using analytical methods to predict the strip thickness distribution in the transverse direction. For this purpose, the rolling equations are solved analytically along the length of arc of contact, while a numerical approach is used to determine the load distribution across the width. The procedure takes into account elastic deformations of work rolls and back-up rolls, the effect of roll flattening and the effect of work roll bending. It considers various situations, i.e., whether chamber is given or not to the work roll, back-up roll. Computations have been performed for various realistic ranges of rolling parameters. Using the data available from the literature regarding likely temperature distribution of the work roll, the program incorporates the expected thermal expansion of rolls and is capable of not only predicting the strip profile but also suggesting the magnitude of optimum camber, which would result in best possible flatness of strip under the given set of rolling conditions.

The effect of the work-roll bending force on the roll force in a hot-strip mill

The effect of work-roll bending force on the roll in a hot-strip mill has been investigated to enable the making of a more precise roll-force prediction for the finish mill set-up. The relationship between the applied bending force and the corresponding increase in roll force was obtained from the work-roll bending test under the contact roll condition, the test result showing that only a proportion of the bending force was transmitted to the load cell, the proportion decreasing with increasing preset roll force. This relationship was refined further by a stiffness calibration between the workpiece and the work-roll bending system. The bender-compensated prediction of the roll force for ultra-low carbon steel and Nb-added steel showed improved accuracy, with about 20% decrease in terms of the standard deviation of the predicted roll-force values against the measured values.

Improved flatness in cold rolling of copper foils

Cold-rolled copper foils in thicknesses between 10 μm–100 μm have many ranges of applications, as for example in the electronic industries for flexible printed circuits boards (PCB) and for cable wrapping and shielding. A good flatness of the foils is important, especially for the PCB-foils which are surfaced after rolling. Normal shape defects, such as centre buckles and long edges, are today detected efficiently by commercial shape meters. Flatness is controlled by, for example, work-roll bending and thermal crowning of the rolls. However, in the rolling of copper foils a special kind of out-of-flatness occurs, which is impossible to detect and control by normal systems for shape control. This kind of defect is characterized by an evenly distributed pattern of small buckles. In the present work it is supposed that this phenomenon is related to a variation in forward slip along the barrel of the roll. This in turn is due to various friction conditions at different locations along the contact between the rolls and the foil. According to a theoretical model advanced by the authors, the variation in forward slip can be decreased for certain combinations of entry- and exit-tensions. The applicability of the model that has been developed for improving the flatness has been confirmed in industrial production.