Strip Flatness Research Articles

Approach for designing and developing high-precision integrative systems for strip flatness detection.

In this paper, we propose an approach for designing and developing high-precision integrative systems for strip flatness detection. Algorithms are developed for camera calibration, which are more accurate than the general method calculating all the camera parameters. On the basis of this method, a detection system is developed including an integrative device for easy calculation and repeated usage. On-site experiment results confirm that the proposed method works well under hostile environmental conditions in mills.

Study on CCD laser scanning flatness measurement method for hot rolled strip

To provide a flexible calibration method and make an accurate machine vision (MV) based flatness measurement strategy a reality in routine production line, an area scan charge coupled device (CCD) laser stripe scanning approach is presented. The applicability of the proposed method is not tied to the strip exclusively. First, we devise an automatic laser stripe imaging quality evaluation method through analysing the characteristics of the image grey gradient of laser stripe, which is a prerequisite for precisely extracting the laser stripe modulated information in hot or reflective object surface; second, a fast system calibration method is designed based on the area scan CCD imaging principle and spatial measurement technologies; here, the practical calibration is an indispensable technique for MV based measurement with large field of view in modern steelmaking lines. The proposed method performs competitively with the state-of-the-art as seen from the comparison of the experimental results. Through online testing, this method also showed considerable promise for hot rolled strip flatness measurement. However, the scheme for eliminating the influence of vibrations related to different applications is not taken into account in the current work.

THE FEATURES OF TEMPERATURE FIELD OF STEEL STRIPES UNDER HOT ROLLING

The study of temperature distribution across the width of stripes in the HRM 2000 line was carried out in collaboration of OJSC “NLMK” Hot Rolled Stock Manufacture specialists with students and lecturers of the Lipetsk State Technical University. The investigations were made with the use of portable thermal imager BALTECH TR-1400. Surface temperature increasing was found from the right edge of the strip to the left while rolling. The temperature distribution asymmetry across the width of the strip is one of the reasons of camber, wedging and fl atness of hot-rolled strips.

Optimization of flatness of strip during coiling process based on evolutionary algorithms

In this paper, an optimization study was conducted for improving flatness of the strips during coiling process. The evolutionary optimizer coded by MATLAB is used for reducing axial inhomogeneity of the stress distribution and the maximum compressive stress calculated by Love’s elastic solution within a thin strip during the coiling process which might cause irregular surface profile of the strip. An improved differential evolution (DE) method employing opposition-based concept is newly proposed in the present work and is used along with several well-established evolutionary algorithms (EAs) to obtain the optimal processing parameters such as spool geometry and coiling tension of the strip coiling process. It was found that the newly proposed differential evolutionary algorithm outperformed other EAs according to the present study. This kind of optimization studies will be helpful in reducing the edge wave defects during the strip coiling process to improve product quality.

Research on Distribution of Residual Stresses of Cold Rolled Sheet Distorted Area Based on ANSYS

Based on the value of longitudinal distribution of the residual stresses in the strip with the cold rolled strip in different forms under stress loading, this paper establishes a finite element model. According to the simulation analysis on different stress curve functions and under some coefficient combining conditions of different stress curve functions, it is discovered that the stress acting lengths and the features are completely different under the actions of even-degree and odd-degree stress functions, and under the even-degree function, the residual stresses are distributed evenly at the far end of the strip, and the length location of the point where the residual stresses tends to be stable on the strip are linearly related to the strip width; under the odd-degree function, the residual stresses are distributed linearly in the horizontal direction of the strip while without any changes along the strip length. According to the analysis results of the strip's shear stress, a little strip shear stress is not enough to produce deformation. The result of this paper has profound guiding significance for cold-rolled strip flatness closed-loop control. Only with different control strategies for different flatness deviations after fitting, can the quality of the strip steel flatness be improved more effectively, thereby reducing the impact of the lag in flatness detection on the strip flatness control as far as possible.

Production of flat electrical steel with superlow magnetic losses

The influence of the chemical composition of steel (its Al, Si, and Sb content) on its texture and magnetic properties is studied, with a view to developing a production technology for high-alloy isotropic electrical steel (containing up to 3% Si) with superlow magnetic losses (P1.5/50 ≤ 2.70 W/kg for strip of rated thickness 0.50 mm and P1.5/50 ≤ 2.50 W/kg for rated thickness 0.35 mm) and a high degree of flatness (nonplanarity class 1 according to State Standard GOST 21427.2, with discrepancies no greater than 2 mm). Alloying with aluminum and antimony improves the texture of the final steel and hence greatly reduces the magnetic losses. The influence of cold rolling and recrystallization annealing of the flatness of the final strip is discussed.

Research of Strip Flatness Control Based on Legendre Polynomial Decomposition

A traditional least squares has negatively a clear physical significance in the process of strip flatness pattern recognition and it is too complex in calculation to be suitable for industrial controller to realize. In this paper we deduced the basic model of strip flatness pattern recognition based on Legendre polynomial. Under this mode, there are three out- standing advantages: The integral value along the width direction of strip shape is 0, which satisfies the condition of equi- librium in the residual stress. Each component of polynomial corresponds to steer roller, bending roller and step cooling control respectively, which makes the physical meaning clear. Operational calculation is suitable for industrial controller. The simulation shows that calculation time-consuming dropped from average 0.012 s to average 0.002 s. Also practice in the real world had proved that this method is effective and applicable.

Effect of Edge Masking on Residual Stress of Hot-Rolled Strip on Run-Out Table

A numerical model including thermal and microstructural model is established for precisely prediction of residual stress of hot-rolled strip on run-out table. Temperature and phase transformation fraction are coupled and formulated for the calculation of thermal and transformation expansion that could induce internal stress. Residual stress for hot-rolled strip before and after coiling are calculated using C++ program. Influence of edge masking on residual stress is analyzed. It is concluded that edge masking makes the strip flatness better after coiling.

Calculation and Analysis of Tandem Cold Rolling Force Parameters

In order to improve the accuracy of rolling force parameters,the elastic deformation and pressure between rolls of tandem cold rolling are calculated using divided element method in this paper. Bland-Ford model is used to calculate the rolling force, and the lengths of flattening contact arcs of each element are calculated. Considering the flattening contact arc lengths and tensile stress synthetically, rolling force parameters are calculated iteratively. Then the corresponding procedure is developed, and the distribution of rolling force, pressure between rolls and tensile stress are calculated with this procedure. The results are basically consistent with the measured data, and it will be useful to thermal crown calculation and strip flatness control.

Bending Force Preset Model Based on Optimal Algorithm

The reasonable bending force preset has a deep impact on strip flatness and yield. In this article, the optimal objective function bending force is established. The impact of roll thermal expansion and roll wear on roll gap crown is analyzed. The optimal bending force model is established. Rosenbrock algorithm is adopted by the model to solve the optimal bending force .The strip flatness control deviation is effectively decreased by the calculated bending force. The yield is increased markedly. The model has been applied into a 1450mm five-stand cold rolling process control system successfully and a good effect is achieved.

Effects of processing parameters on elastic deformation of the coil during the thin-strip coiling process

It is well known that axial inhomogeneity of the stress distribution within a thin-strip causes defects such as edge waves and center buckling during the thin-strip coiling process. In the current study, an analytical model was utilized to investigate the effects of processing parameters such as strip crown, spool geometry, and coiling tension on the elastic stress distribution and deformation of the strip during the coiling process. In the present investigation, the elastic modulus was introduced as a function of temperature and axial distance for better simulation of the process. According to the present analyses, it was found that improvement of the strip flatness might be achieved by suppressing the strip crown, increasing the thickness of the spool with the shape of a swollen hollow cylinder, and lowering the coiling tension with transient increase at the beginning stage of the coiling process only. This study will be helpful for better understanding of identifying the proper processing parameters during the coiling process.

Effect of Mid-Roll Shift on the Strip Flatness for CVC 6-H Mill

In order to obtain the best position of mid-roll shift, this paper studies the effect of different mid-roll shift position on the strip flatness of CVC 6-H mill. Strip element variation method and influence function method are put forward to analyze the effect of mid-roll shift on strip flatness. The results show the CVC 6-H mill is able to get good strip shape. The best shift position is obtained from the calculation results. The conclusion has a good significance for the practical application.

Flatness Assessment System of Ultra-Wide Tandem Cold Rolling Mill

Many complex waviness defects occur during the production process of ultra wide TCMs, flatness idex I can not meet the demands of analyzing these problems. Therefore flatness pattern recognition considering cubic patterns is introduced to provide a flatness evaluation parameter. Combining the calculation methods and statistical methods of evaluation parameters, a flatness assessment system is programmed with Matlab GUI, which provides functions such as representing the flatness of previous strips, recognizing the flatness error and making statistics. After verifying of actual flatness measured value, the system is proved to be effective, which provides theoretical basis and data support for mastering the flatness quality and optimizing flatness control parameters.

Novel curved roll contour technology for profile control in hot strip mills

The combination of variable crown contour and work roll shifting is a prominent and efficient tool for strip profile and flatness control in hot strip mills. The design principle of variable crown contour has great influence on the control performance. In this paper, the development on variable crown contour is carried out in depth, and a novel curved work roll contour consisting of a piecewise smooth curve with quadratic parts is developed to make the relationship between crown adjustment capacity and strip width strictly linear in a certain width range. This characteristic enhances the crown adjustment capacity of mills, and makes them more powerful for profile control, especially for narrow strip. Meanwhile, the equivalent crown of work roll is linearly proportional to its shifting position, which will definitely facilitate the profile and flatness control system. Additionally, an optimisation model is proposed to find the optimal contour coefficient to decrease the axial force and diameter difference of work roll. Compared with some conventional curved contour technology which its crown adjustment capacity is proportional to the square of strip width, this novel contour has a stronger crown adjustment capacity for both wide and narrow strip, thus, promising to apply in hot strip mills to enhance the overall performance of mills in profile control. The industrial application of this new contour technology shows the percentage, which strip head crown is within 0·05±0·02 mm, is up to 95·6% after being used on the upstream stands of the hot stainless strip rolling mills.

Data mining-based flatness pattern prediction for cold rolling process with varying operating condition

Data-rich environments in modern rolling processes provide a great opportunity for more effective process control and more total quality improvement. Flatness is a key geometrical feature of strip products in a cold rolling process. In order to achieve good flatness, it is necessary to reveal the factors that often influence the flatness quality, to develop a general flatness pattern prediction model that can handle the varying operating condition during the rolling of products with different specifications and to realize an effective flatness feedback control strategy. This paper develops a practical data mining-based flatness pattern prediction method for cold rolling process with varying operating condition. Firstly, the high-dimensional process measurements are projected onto a low-dimensional space (i.e., the latent variable space) using locality preserving projection method; at the same time, the Legendre orthogonal polynomials are used to extract the basic flatness patterns by projecting the high-dimensional flatness measurements into several flatness characteristic coefficients. Secondly, a mixture probabilistic linear regression model is adopted to describe the relationships between the latent variables and the flatness characteristic coefficients. Case study is conducted on a real steel rolling process. Results show that the developed method has not only the satisfactory prediction performance, but good potentials to improve process understanding and strip flatness quality.

Application of Q Learning-Based Self-Tuning PID with DRNN in the Strip Flatness and Gauge System

In view of the process of automatic flatness control and automatic gauge control that is a nonlinear system with multi-dimensions, multi-variables, strong coupling and time variation, a novel control method called self-tuning PID with diagonal recurrent neural network (DRNN-PID) based on Q learning is proposed. It is able to coordinate the coupling of flatness control and gauge control agents to get the satisfactory control requirements without decoupling directly and amend output control laws by DRNN-PID adaptively. Decomposition-coordination is utilized to establish a novel multi-agent system for coordination control including flatness agent, gauge agent and Q learning agent. Simulation result demonstrates the validity of our proposed method.

Dynamic characteristics of cold rolling mill and strip based on flatness and thickness control in rolling process

The dynamic model of cold rolling mill based on strip flatness and thickness integrated control was proposed, containing the following sub-models: the rolling process model, the dynamic model of rolls along axial direction, and the compensation model. Based on the rule of volume flow rate, the dynamic rolling process model was built. The work roll and backup roll were taken as elastic continuous bodies, the effect of shear and moment of inertia were taken into consideration, and then the dynamic model of rolls was built. The two models were coupled together, and the dynamic model of rolling mill was built. In the dynamic model, the thermal expansion of the rolls, the wear of the rolls and other related parameters can not be considered. In order to compensate the dynamic model, the coupled static model of rolls and strip was applied. Then, according to the inner relationship of these models, the dynamic model and the compensation model were coupled, and the dynamic model of rolling mill based on the strip flatness and thickness integrated control was built. The dynamic simulation of the rolling process was made, and the dynamic thickness and the dynamic flatness information were obtained. This model not only provides a theory basis for the virtual rolling, but also provides a platform for the application of advanced control theory.

Development of Mathematical Model for Control Wear in Backup Roll for Hot Strip Mill

The precision of strip flatness depends on several factors; wear of rolls is one of the main variables that have influence on the surface quality of the strip. The wear of the rolls represents a complex friction condition, sometimes the wear in the backup roll is not analyzed because the strip is not in contact with the backup roll; however, after several campaigns of rolling, the wear in the backup roll becomes dangerous because the pressure distribution is not uniform. Investigation of mechanism of the surface deterioration of the backup roll for the hot strip rolling is very important for the development of the automatic strip shape control system used in hot strip mills. A mathematical model is developed considering the Hertzian pressure distribution between two cylinders with parallel axes. It is used in real time for calculating the wear in the backup roll and in this manner take decisions for preventing finished product reworking or damage of equipments, which result in accidents caused by excessive wear in the backup rolls.

The Strategy of Shape Setup Model and the Obtaining of Several Key Parameters in Hot Strip Mill Process

Shape setup model (SSM) plays a critical role to achieve satisfactory precision of strip shape in hot strip mill process (HSMP). In this paper, the process of SSM is introduced, taking 1700mm HSMP line in Ansteel as the research object. Special attention is focused on the gap crown model, which is the foundation of SSM. And the allocation strategy of reference values for mechanical actuators is presented. Then an off-line simulation method is proposed to obtain several key parameters of the model. SSM has been put into practical use and proved to be effective to control strip flatness and profile by high accuracy.

Influence of the cross section of hot-rolled steel on the flatness of cold-rolled strip

A mathematical model is proposed for the shaping of cold-rolled strip from four-roller stands. Model calculations confirm the practical limits on the convexity of the hot-rolled steel’s cross section. Saddle distortion of the strip cross section is discussed.