Cold Strip Mill Research Articles

Fixed‐time prescribed performance optimization control for the speed and tension system of the cold strip rolling mill with output constraints

SummaryFor the speed and tension system of the reversible cold strip rolling mill with output constraints, parameter perturbations and load disturbance, a fixed‐time prescribed performance optimization control method is proposed based on disturbance observers in this article. First, the disturbance observers are constructed to estimate the system's unmatched uncertainties, and the observer errors can converge in fixed time. Second, a time‐varying logarithmic barrier Lyapunov function (TLBLF) is given and combined with the command filtered backstepping approach, the fixed‐time control and the prescribed performance control to complete the controller designs for the speed and tension system of the cold strip rolling mill, which make the system states converge in fixed time and are always constrained within predefined ranges. Third, particle swarm optimization‐gray wolf optimization (PSO_GWO) hybrid intelligent algorithm is used to optimize the main control parameters of the designed controllers, which further improves the convergence speed and steady‐state accuracy of the rolling mill system. Theoretical analysis proves that the proposed control method can ensure the closed‐loop system is stable in fixed time. Finally, the simulation comparison study is carried out by using the field actual data of a reversible cold strip mill system, and the simulation results verify the effectiveness of the proposed control method.

Research on the effect of thickness difference of weld seam on strip breaking during rolling in PL-TCM

At the entry of the pickling and tandem cold strip mill (PL-TCM), the unreasonable cut length of the head and tail of the strip often causes a thickness difference between the weld surfaces of the front and back strip, resulting in a weld seam with thickness difference after welding. This can easily lead to strip breaking at the weld seam in the cold rolling process. In this paper, a finite element model of roll and strip with weld seam is established to investigate the mechanism of strip breaking at weld seam due to thickness difference. By simulating the working conditions in the rolling process for weld seam with different thickness differences, the evolution of the stress state of the weld seam in the rolling process under each working condition is analyzed. The influence of thickness difference in the rolling process of the weld seam is revealed, and the effect of thickness difference on the risk of strip breaking at weld seam during the rolling process is further discussed. According to the research results, the optimization method of strip head and tail shear length was designed and applied to the industrial site. After application, the accident rate of strip breaking is reduced and the effect is as expected.

Development of On-line Model of Forward Slip on Tandem Cold Strip Mill

Development of On-line Model of Forward Slip on Tandem Cold Strip Mill

FEM Analysis for Asymmetric Bending Roll of Roll Process in Four-High Mill

Accurate prediction for the deformation of the roll system is a key to improve the accuracy of the preset model and on-line control model of strip cold rolling processes. A non-linear finite element contact model to simulate the roll system deformation has been developed for4h cold strip rolling mill. Roll process of 4-high cold strip mill is simulated and analyzed by 3D elastic-plastic FEM on the bases of software ANSYS. In the model, the elastic deformation of work roll and backup roll, the plastic deformation of the strip and the pressure of strip and the work and the backup roll were taken into account. Results show that the work roll HYPERLINK "javascript:showjdsw ('showjd_0','j_0')" asymmetric bending is the most effective mean in these strip shape controlling means. The calculated roll gap profile is close to the measured values. This model can improve the accuracy of final products through a correct preset model and on-line control model of strip.

Symmetry variable taper work roll technology for silicon steel profile control in hot strip mills

ABSTRACT Strip profile control in the hot rolling process plays an important role in guaranteeing high-precision profiles for silicon steel production in cold strip mills. A symmetry variable taper (SVT) work roll for the downstream finishing stands of hot strip mills is designed, which can be used for long stroke reciprocating shifting of work rolls, resulting in decreased edge drop and more uniform work roll wear contour. A finite element simulation model of 4-high mill based on ABAQUS was established, which improved the control characteristics of each process parameter for the strip profile when using the SVT work roll. The actual production data of the 1580 hot strip rolling mill equipped with SVT work rolls showed that the crown C25 of non-oriented silicon steel was reduced by about 5%, the edge drop was reduced by more than 15%, and the crown qualified rate was increased by 10%.

Development of innovative production technology of automotive high quality in the conditions of cold rolling mill

The main tendency of ferrous metallurgy development is improvement of automotive sheet quality and production of the new steel grades which meet the requirements of the international standards. The studied subject is continuous cold strip mill 2500. Analysis of the defects for emulsion spots and spotted carburization showed that their distribution is irregular across the strip width. In the world practice, there are various ways to remove the lubricating and cooling liquid from the rolled strip during the production of automotive sheet by a cold rolling mill. Special modern systems are developed by both foreign and domestic firms are used to remove cooling lubricant from the strip. But significant disadvantage of such solutions is high cost. So, the rational solution of this problem is the development of an innovative technology for removing the cutting compound based on the principle of blowing with minimum amount of compressed air. The article describes an innovative system for cleaning the strip from the residues of the lubricating-cooling liquid in the production of an automotive sheet on the four-stand cold rolling mill 2500 and calculation of parameters. The implementation of improved automotive sheet production technology will reduce the compressed airflow more than 2.5 times, compared with the current system and significantly to expand the range of products.

Flying Gauge Control for a Specified Section Including a Welding Point in a Cold Strip Mill

Flying Gauge Control for a Specified Section Including a Welding Point in a Cold Strip Mill

Identification and optimization for hydraulic roll gap control in strip rolling mill

In order to improve the control performance of strip rolling mill, theoretical model of the hydraulic gap control (HGC) system was established. HGC system offline identification scheme was designed for a tandem cold strip mill, the system model parameters were identified by ARX model, and the identified model was verified. Taking the offline identified parameters as the initial values, online identification using recursive least square was carried out with model parameters changing. For the purpose of improving system robustness and decreasing the sensitivity due to model errors, the HGC system based on generalized predictive control (GPC) was designed, and simulation experiments for traditional controller and GPC controller were conducted. The results show that both controllers acquire good control effect with model matching. When the model mismatches, for the traditional controller, the overshot will increase to 76.7% and the rising time will increase to 165.7 ms, which cannot be accepted by HGC system; for the GPC controller, the overshot is less than 8.5%, and the rising time is less than 26 ms in any case.

Compound control for speed and tension multivariable coupling system of reversible cold strip mill

To weaken the nonlinear coupling influence among the variables in the speed and tension system of reversible cold strip mill, a compound control (CC) strategy based on invariance principle was proposed. Firstly, invariance principle was used to realize static decoupling between the speed and tension of reversible cold strip mill. Then, considering the influence caused by the time variation of steel coil radius and rotational inertia of the left and right coilers, as well as the uncertainties, a CC strategy that is composed of extended state observer (ESO) and global sliding mode control (GSMC) with backstepping adaptive was proposed, which further realized dynamic decoupling and coordination control for the speed and tension system. Theoretical analysis shows that the resulting closed-loop system is global bounded stable. Finally, the simulation was carried out on the speed and tension system of a 1422 mm reversible cold strip mill by using the actual data, and through the comparison of the other control strategies, validity of the proposed CC strategy was shown by the results.

Quantitative Evaluation Method of Shape Indicator for Cold-rolled Strip

Quantitative level evaluation of cold-rolled strip was significant for the shape control and the product structure optimization. Based on the probability statistics method and the shape pattern recognition method, the shape evaluation model of cold-rolled strip was established to evaluate real-time shape of the online strip. The model was embedded in the shape control system, and the online strip shape state was real-time observed whether to meet the technical indicators, so the shape level could be identified and evaluated. Based on the shape evaluation indicators, the shape component could be well controlled to improve the shape hit rate and the control stability, so that the rolled strip shape could meet the technical requirements. At a 1050 cold strip mill, the shape data of the scene typical specifications strip were online collected and real-time evaluated, and the hit of macro shape in less than 8 I was 68.44%, indicating that the mill shape control had considerable room for improvement, as well as the evaluation method was feasible and practical for quantitative evaluation of the strip shape. So the new evaluation model has important guiding significance to increase value-added and reduce product quality objection.

Research and Development of Automatic Control System for High Precision Cold Strip Rolling Mill

The automatic control system is one of the most important parts of improve cold rolling strip precision and increase the automate level. The improved cold strip mill process control system has been developed and successfully applied to several new cold strip production lines. This paper introduces the Key Technical Features and New Technology of the system include the system architecture, hardware configuration and new control algorithms, etc. System operation and actual production proves that the system has the features of shorter commissioning time, convenient maintenance, high reliability, high automatic level and control precision.

Actuator Efficiency Adaptive Flatness Control Model and Its Application in 1250 mm Reversible Cold Strip 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 is used for general flatness control. As the basis of flatness control system, the efficiencies of flatness actuators provide a quantitative description to the law of flatness control. Therefore, the determination of actuator efficiency factors is crucial in flatness control. The strategies of closed loop feedback flatness control and rolling force feed-forward control were established respectively based on actuator efficiency factors. For the purpose of obtaining accurate efficiency factors matrixes of flatness actuators, a self-learning model of actuator efficiency factors was established. The precision of actuator efficiency factors can be improved continuously by the input of correlative measured flatness data. 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 application results show that the self-learning model is capable of obtaining good flatness.

Application of Electro-Hydraulic Servo Systems to Hot Strip Down Coilers

Many kinds of electro-hydraulic servo systems have been applied to rolling mills, such as hot strip mills, cold strip mills, and seamless tube mills, for their quick response, high power, and high positioning accuracy. However, when an electro-hydraulic servo system is applied to a hot strip down coiler, it is found that the controlled object has low natural frequency and is lightly damped, so stable control is very difficult to achieve. In order to overcome these issues, first, the optimal control theory is applied to eliminate these deficiencies [1, 2]. However, the derived control system is found to lack robustness. Control effectiveness is highly influenced by the response of servo valve and the length of the piping between the servo valve and the cylinder in particular. Finally, a novel, practical controlmethod is found and proposed in the process of adjusting the production machine. The novel control method proposed here, based on the “posicast” control proposed by O. J. M. Smith in 1957 [3], has realized a kind of dead-beat control and has been found to be robust because it uses the internal information of the controlled object.

Optimum Design of Rolling Schedule for Tandem Cold Mill Using SLPSO

This paper proposes a new method to optimize cold strip rolling schedule by means of self-adaptive learning based particle swarm optimization (SLPSO). Multiple strategies may be adopted based on their previous behaviors in the searching. This particle swarm optimization version is robust and effective in solving complex problems. Function of power cost was constructed to heuristically direct the SLPSO searching, based on the consideration of power distribution, speed and rolling constraints. The results of simulation demonstrate that SLPSO is more efficient in calculating than others, and provides a new valid method for the intelligent optimum design of scheduling tandem cold strip mill.

Research on New Shape Meter of Cold Rolling Strip

A new strip shaper is developed to avoid the scratch of the strip surface due to different thermal expansion of the traditional detection roller measuring unit effectively. The signal transmission form which is different form the international popular dry slip ring is put forward; the spray wet slip ring is developed to improve the measuring precision and the service life. The signal processing form which is different form the international popular gathering card is put forward and the embedded DSP shape signal processing hardware system is developed to improve the measuring precision and the anti-interference ability. The shape signal processing software system whose function contains error compensation, pattern recognition, establishment of the target shape and the close-loop control calculation is built to implement the intelligentized shape meter. The shape meter has been test chronically on the 1250 mm cold strip mill of Angang Steel Company Limited and the test result indicates that the measuring signal is stable and reliable and the closed-loop control of shape is implemented.

Research on Industrial Shape Meter and its Application

A industrial strip shaper is developed, which mainly consisted of the shape detecting roller, the collecting ring, the DSP shape signal processing board and the shape control model. The structural form which is different from the international popular segmented detection roller is put forward and the entire detection roller inlayed block is developed to avoid the scratch of the strip surface due to different thermal expansion of the traditional detection roller measuring unit effectively. The signal transmission form which is different form the international popular dry slip ring is put forward, the spray wet slip ring is developed to improve the measuring precision and the service life. The signal processing form which is different form the international popular gathering card is put forward and the embedded DSP shape signal processing hardware system is developed to improve the measuring precision and the anti-interference ability. The shape signal processing software system whose function contains error compensation, pattern recognition, establishment of the target shape and the close loop control calculation is built to implement the intelligentized shape meter. The shape meter has been test chronically on the 1250 mm cold strip mill of Angang Steel Company Limited and the test result indicates that the measuring signals were stable and reliable and the close loop control of shape was implemented.

熱延ダウンコイラへの電気油圧サーボシステムの適用

Many kinds of electro-hydraulic servo systems are applied to rolling mills such as a hot strip mill, a cold strip mill and a seamless tube mill because of quick response, high power and high positioning accuracy. However when applying an electro-hydraulic servo system to a hot strip downcoiler, it was found that the controlled object has low natural frequency and is lightly damped so that stable control is very difficult. Optimal control theory has been recognized as a powerful tool for system synthesis in such a case. This paper first shows that the existing design method of optimal control is effective for designing an electro-hydraulic servo controller, in which the proper weighting matrices in the quadratic performance function can be determined directly from a physical model. A new design method is then proposed by which the state feedback gains can be obtained directly based on the characteristics of the controlled object. The effectiveness of the controller is demonstrated experimentally.

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.

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.

Flatness Control Based on Dynamic Effective Matrix for Cold Strip Mills

Steel strips are the main of steel products and flatness is an important quality indicator of steel strips. Flatness control is the key and highly difficult technique of strip mills. The bottle-neck restricting the improvement of flatness control techniques is that the research on flatness theories and control mathematic models is not in accordance with the requirement of technique developments. To build a simple, rapid and accurate explicit formulation control model has become an urgent need for the development of flatness control technique. This paper puts forward the conception of dynamic effective matrix based on the effective matrix method for flatness control proposed by the authors under the consideration of the influence of the change of parameters in rolling processes on the effective matrix, and the concept is validated by industrial productions. Three methods of the effective matrix generation are induced: the calculation method based on the flatness prediction model; the calculation method based on the data excavation in rolling processes and the direct calculation method based on the network model. A fuzzy neural network effective matrix model is built based on the clusters, and then the network structure is optimized and the high-speed-calculation problem of the dynamic effective matrix is solved. The flatness control scheme for cold strip mills is proposed based on the dynamic effective matrix. On stand 5 of the 1 220 mm five-stand 4-high cold strip tandem mill, the industrial experiment with the control methods of tilting roll and bending roll is done by the control scheme of the static effective matrix and the dynamic effective matrix, respectively. The experiment result proves that the control effect of the dynamic effective matrix is much better than that of the static effective matrix. This paper proposes a new idea and method for the dynamic flatness control in the rolling processes of cold strip mills and develops the theory and model of the flatness control effective matrix method.