Cold Mill Research Articles

Asymmetric Shape Control Theory and Practice in Cold Strip Mills

In cold rolling process, asymmetric shape defects are still a common problem to strip quality. For the mills with inverse symmetry roll shifting system, different roll wear and thermal contour of top roll system and bottom roll system could cause asymmetric shape defects during shifting operation. In this paper, three dimension finite element simulation models of inverse shifting roll system were established to calculate the parameters and to analyze the effects. Based on the idea in the mill engineering that mill style option depended on the product grade, shifting weakness was evaluated and the opinion of limit shifting was suggested. To improve control effect to asymmetric shape defects in cold rolling, shape control system with asymmetric shape control ability is developed, including asymmetric edge drop control at upstream stands and asymmetric flatness control at last stand. The further improvement of asymmetric shape control theory and practice is the key way to reach the higher precision of shape quality in cold strip mills.

Influence of Roll Profile Configuration on High-Strength Strip Flatness Control Performance in Tandem Cold Rolling

According to the characteristic of high-strength strip, the roll profile configuration and change of CVC tandem cold mill are analyzed. Through the establishment of FEM model, the influences of three representative forms of roll profile configuration on high-strength strip flatness control in CVC cold rolling mill are compared, which are conventional back-up roll / CVC intermediate roll, back-up roll with CVC compensation / CVC intermediate roll, VCL+ back-up roll / HVC intermediate roll. Compared with the other two roll profile configuration, the configuration of VCL+ back-up roll / HVC intermediate roll increases 26.74% in crown adjustment domain of roll gap and 22.09% in lateral stiffness of roll gap, decreases 27.43% in contact pressure peak values between rolls. The new roll profile configuration has obtained industrial applications. Production data indicate that the control accuracy of high-strength strip is improved, also the wear of back-up roll. Significant application results have been achieved.

Nonlinear Self-Adaptive Compensation of Screw down System of Tandem Cold Mill

The Screw Down System (SDS) is a typical hydraulic servo control system. It is the key actuator of cold rolling mill. The dynamic performance of SDS has a significant effect on the accuracy of thickness. Hydraulic servo control system is not always optimal and stable due to highly nonlinear and parameter uncertainties. In this paper, the most important nonlinear relating flow and pressure is analyzed. A nonlinear self-adaptive compensation method is designed. Modeling and simulating the hydraulic servo control system of SDS using this method, the numerical simulation results show that the maximum overshoot and static error of the compensated system are more less than that of without nonlinear compensation. The overshoot of the compensated system is less than 10% when the cold strip is rolling. So the thickness tolerance of the cold strip can be guaranteed easily. This self- adaptive compensation method can be used to other hydraulic servo control systems.

Performance Analysis of Asymmetrical Roll Bending for Flatness Control of Cold Rolling Mill

When there appeared catastrophic asymmetrical flatness defects in rolling processes, especially when the incoming strip is with a wedge shape, the tilting roll can hardly eliminate these defects completely. Moreover, the overshooting of tilting roll will lead to strip break. In order to improve the ability of cold rolling mill for asymmetrical flatness defects control, performance of the work roll asymmetrical bending as well as the intermediate roll asymmetrical bending has been analyzed, based on the actuator efficiency factors of them. In addition, for the purpose of obtaining accurate efficiency factors matrixes of actuators, a self-learning determination model of actuator efficiency factors was established in accordance with the practical rolling processes. In this paper, a 1250 single stand 6-H reversible UCM cold mill was taken as the object of this study, with efficiency factors of asymmetrical roll bending analyzed, which provides a theoretical basis for better flatness control. Analysis shows that the asymmetrical roll bending is significant for asymmetrical flatness control.

A Flatness Control System Design Based on Actuator Efficiency Factors for Cold Rolling Mill

In order to improve the flatness of cold rolled strips, strategies of closed loop feedback flatness control and rolling force feed forward control were established respectively, based on actuator efficiency factors. As the basis of flatness control system, efficiencies of flatness actuators provide a quantitative description to the law of flatness control. For the purpose of obtaining accurate efficiency factors matrixes of actuators, a self-learning model of actuator efficiency factors was established. The precision of actuator efficiency factors could be improved continuously by correlative measurement flatness data inputs. Meanwhile, the self-learning model of actuator efficiency factors permits the application of this flatness control for all possible types of actuators and every stand type. The developed flatness control system has been applied to a 1250mm single stand 6-H reversible UCM cold mill. Applications show that the flatness control system based on actuator efficiency factors is capable to obtain good flatness.

Optimization of Rolling Schedule in Tandem Cold Mill Based on QPSO Algorithm

This paper adopts equal relatively load as objective function, and makes every parameter to meet certain restrictive conditions. SUMT algorithm was used to change constraints to non-binding conditions. QPSO algorithm was applied to optimize objective functions to obtain optimal solution. This algorithm was based on classical particle swarm optimization, which, with the conduct of quantum particle, had effective global search capability, good convergence and stability. As a result, reasonable distribution of tandem cold rolling power and full use of equipment capacity were realized, resulting in the improvement of production efficiency.

Allowable variation of cold-rolled strip transverse profiles in high tension

The formation mechanism of the cold-rolled strip shape with high tension was studied. An advanced method to calculate the allowable variation of strip transverse profiles was established by the strip buckling criterion, which can be more properly used in cold rolling. With this method, the aim allowable variation of the product strip transverse profile and the required transverse profile range of incoming strips can be reached. Besides, this method has been successfully applied in a domestic tandem cold mill, and the transverse profile range of incoming strips suggested with this method is more practicable and complete. Consequently, the good performance is acquired.

Analysis of Actuator Performance Based on Actuator Efficiency in Flatness Control of Cold Rolling Mill

In order to improve the flatness of cold rolled strips, the accurate knowledge of actuator performance in flatness control is required. As the basis of flatness control, efficiencies of flatness actuators provide a quantitative description to the law of flatness control. In this paper, a 1250 single stand 6-H reversible UCM cold mill was taken as the object of this study, with efficiency factors of individual actuators analyzed for better flatness control. For the purpose of obtaining accurate efficiency factors matrixes of actuators, a self-learning determination model of actuator efficiency factors was established in accordance with the practical rolling processes. The actuator efficiency factors can be determined and improved continuously by the self-learning model with correlative measurement flatness data input. With this study, performance of actuators in flatness control of UCM cold rolling mill has been obtained, which provides a theoretical basis for better flatness control.

The Integrated Robust Control of Interstand Strip Tension for Tandem Cold Rolling Mill

We describe an integrated tension controller design for a tandem cold rolling mill in steel plants. To achieve stable rolling and ensure strip quality, it is very important to control the tension of the cold rolling mill. Previous researches examined only the operation of a single stand. But it is not sufficient to examine the operation and effect of whole stands because the operation is wholly interdependent. To solve the problem, this paper proposes an integrated control strategy for tension control of tandem cold mill, the full stand model for the tension system of a tandem cold mill is built, and the interaction of all the stands is analyzed. Then applying the method of μ-synthesis design a integrated robust tension controller. Simulation with the practical data proves the integrated robust tension controller can achieve more robust performance than that of typical industrial approach.

Compensation Model for Shape Measuring of Cold Strip Rolling

Some unavoidable factors in the process of cold strip shape measurement interfere with the shape meter, so the shape measuring results cannot reflect the true shape of the strip and the measuring precision is low. The influences of the measuring error of the strip edges, the transverse temperature difference of the strip, the deflection of shape detection roller, and the shape of the strip coil on the shape measuring results were analyzed in detail, and the corresponding compensation models were established. The simulation calculation and analysis were carried out on a cold strip mill, and a number of disciplinarian cognitions were obtained.

Strip flatness modelling including buckling phenomena during thin strip cold rolling

This paper describes the application of a steady state elastic–viscoplastic finite element model to the prediction of strip flatness and out of bite buckling during cold rolling of thin strips. This model is applied here to the last stand of a tinplate tandem cold mill. Results show that strip buckling reshuffles the non-homogeneous strip velocity profile just at the roll bite exit; strip stresses inside the roll bite are little impacted, so that roll stack deformation and roll force profile are not modified. The paper focuses on 'latent strip flatness', i.e. the profile in the transverse direction of the stress in the rolling direction. The profile predicted by the model far downstream the roll bite is in good agreement with shapemeter measurements only if strip buckling (i.e. manifest flatness) just at the roll bite exit and its interaction with the roll bite are considered, using a strong coupling of bite model and post-bite buckling model.

A New Optimal Control of a Tandem Cold Metal Rolling Process

In tandem cold mill, a strip is flattened by stands of rolls to a desired thickness. In the process, there exists thickness disturbance and hardness disturbance, which will affect the export thickness of the strip. In order to solve these problems, control system adopt a new control strategy wherein a state-dependent Riccati equation is utilized. In the third part of this paper, the new technique which uses the state-dependent Riccati equation method for controlling the tandem cold rolling is tested by simulations. The results of these simulations are included in the evaluations which show successful control during the passage of the weld.

The Effect of Entrance Temperature on Texture and Microstructure Development in Cold Mill Rolled 85/15 α-Brass

With the entrance temperature at 300°C, cold mill rolling produced deformation texture transition from brass type to copper type in worked 85/15 α-brass. From the texture and TEM scale microstructure evidence, it is suggested that, rather than deformation twinning, recovery and easy cross slip favor in the deformation process, as the interior working temperature falls into the texture transition range proposed by Tranchant.

Using Efficiency Function in Analyzing the Ability of Flatness Control for a Cold Mill

Analyzing a mill’s ability of flatness control has two purposes, one is finding the feather of a mill, and the other is making a judgment that whether a flatness error can be eliminated. But using classical method is hard to form a correct judgment when the error is complicated. Based on applying efficiency function in finding the property of each flatness actuator, a new method is developed to describe a mill’s comprehensive ability of flatness control. And we found the factors which contribute to whether a mill can weaken a certain flatness error. Practical application shows the new method is feasible.

Multivariable decoupling robust control for tandem cold mills based on H_∞ mixed sensitivity

The thickness and tension system in tandem cold rolling has the features such as multivariation,strong coupling and uncertainty.To improve its control accuracy and quality,a new robust control scheme based on the invariance-decoupling theory and H∞ mixed sensitivity method was presented.First,a dynamic coupling model for the thickness and tension system was built,and the invariance-decoupling theory was applied to completely decouple the thickness and tension system.Then,for systematic uncertainty of modeling error,parameter perturbation and external disturbance,a robust controller was designed based on H∞ mixed sensitivity method to ensure the robust stability and robust performance of the system.Simulation results show that the thickness and tension system after decoupling is controled better,proving the validity of the algorithm.

Nonlinear Receding Horizon Control of Thickness and Tension in a Tandem Cold Mill with a Variable Rolling Speed

For precise control of tension and thickness in a tandem cold mill in acceleration and deceleration conditions, we develop a nonlinear model including the rolling speed as a time-varying parameter. It is demonstrated in simulation results that nonlinear receding horizon control by real-time optimization achieves satisfactory performance for the nonlinear model.

Tension Reference Optimization in Automatic Gauge and Tension Control for a Tandem Cold Mill

During acceleration and deceleration in cold rolling, variation in friction between a strip and the rolls can adversely affect strip thickness accuracy. Though automatic gauge and tension control is being introduced, constant tension references are insufficient for adequate control over a wide range of rolling speeds. Therefore, we have optimized tension references which vary depending on rolling speed. In order to limit maximum tension to an acceptable value, the optimization problem is composed in a multi level way by using an approximate surface. Moreover, the lowest level optimization problem is decomposed into sub-problems to obtain a solution stably and quickly. Experimental results with a 5-stand tandem cold mill showed a decrease in off-gauge length.

A neural network-based preset generation tool for a steel tandem cold mill

This paper traces the development of a software tool, based on a combination of artificial neural networks (ANN) and a few process equations, aiming to serve as a backup operation instrument in the reference generation for real-time controllers of a steel tandem cold mill. By emulating the mathematical model responsible for generating presets under normal operational conditions, the system works as an option to maintain plant operation in the event of a failure in the processing unit that executes the mathematical model. The system, built from the production data collected over six years of plant operation, steered to the replacement of the former backup operation mode (based on a lookup table), which degraded both product quality and plant productivity. The study showed that ANN are appropriated tools for the intended purpose and that by this instrument it is possible to achieve nearly the totality of the presets needed by this kind of process. The text characterizes the problem, relates the investigated options to solve it, justifies the choice of the ANN approach, describes the methodology and system implementation and, finally, shows and discusses the attained results.

Aluminium rolling: improving production and quality with minimum energy consumption

Improvements in control systems technology and datalogging have allowed improved dynamic control of the factors affecting strip flatness and quality. Modern automatic flatness control systems for aluminium cold and foil mills have the potential to increase productivity and reduce energy consumption significantly. The contribution of coolant spray control to these objectives is summarised.

Prevalence of and risk factors for fatty liver disease in a professional population of Wuhan, China

To explore the prevalence of fatty liver disease (FLD) and its risk factors in a cold steel-rolling mill in Wuhan, China. A cross-sectional survey. In total, 1174 subjects were investigated for FLD (596 exposed workers and 578 controls). FLD was determined by ultrasonography. Height, weight, blood pressure, fasting plasma glucose, serum aspartate aminotransferase (AST), serum triglyceride (TG) and serum hepatitis B surface antigen (HBsAg) were determined by routine laboratory methods. The prevalences of major diseases such as FLD (41.6%), hypertension (21.1%) and high serum TG (42.6%) were higher in the exposed workers than in the controls. The prevalence of FLD was highest among grinding roller workers (50.6%); this was almost four times as high as in the control group (14.7%). Logistic regression analysis indicated that all six types of work (zincing, shearing, tinning, operating grinding rollers, electrics and fitting), as well as high serum TG, high serum AST, hyperglycaemia, hypertension, higher body mass index (BMI) and drinking alcohol were risk factors for FLD. A high prevalence of FLD was found among the exposed workers, and some risk factors, especially different types of work, were related to the prevalence of FLD. High serum TG, high serum AST, hypertension, hyperglycaemia, higher BMI and drinking alcohol were important risk factors for FLD.