Search

In cold strip rolling control system, rolling force and forward slip are the prerequisites for the model setting calculation, and the deformation resistance and friction coefficient are the main parameters that affect their predictions. A new method based on objective function is first proposed in this paper to improve the calculation accuracy of rolling force and forward slip, and the deformation resistance and friction coefficient are taken as optimisation variables. Using the multi-population co-evolutionary algorithm to solve the objective function, the required rolling force and forward slip are obtained. The pre-set values of rolling force and roller line speed are compared with the actual measured ones in a 1450 mm five-stand tandem cold mill and other researcher’s method. Results show that the calculated values are in fair agreements with the on-line measured ones, and the thickness and flatness accuracy of the final product are improved.

An artificial neural network (ANN) optimized by genetic algorithm (GA) is an established prediction model of bending force in hot strip rolling. The data are collected from factory of steel manufacture. Entrance temperature and thickness, exit thickness, strip width, rolling force, rolling speed, roll shifting, target profile, and yield strength of strip are selected to be independent variables as network inputs. MATLAB software is utilized for establishing GA-ANN model and achieving the purpose of obtaining the bending force as results of setup model, as well as the GA method is used to optimize the initial weights and biases of the backpropagation neural network. Mean absolute error (MAE), mean absolute percentage error (MAPE), root mean squared error (RMSE), and correlation coefficient are adapted to evaluate the performance of the model. The predictive results are compared with the measured results to verify the accuracy of the GA-ANN prediction model. It is found that the optimization effect is the best with the population size 40 crossover probability of 0.7 and the mutation probability of 0.05 at the same time, the fitness function value can reach 80.7. In addition, the ANN architecture 9-11-1 trained with Bayesian regulation “trainbr” function has the best performance with mean absolute error of 0.01 and correlation coefficient of 0.983. With a deeper understanding of neural networks through the analysis of the GA-ANN model, the proposed model can be flexibly used for on-line controlling and rolling schedule optimizing.

In order to improve the threading stability and the head thickness precision in tandem hot rolling process, an adaptive threading strategy was proposed. The proposed strategy was realized by the rolling characteristics analysis, and factors which affect the rolling force and the final thickness were determined and analyzed based on the influence coefficients calculation process. An objective function consisting of the influenced factors was founded, and the disturbance quantity was obtained by minimizing the function with the Nelder-Mead simplex method, and the proposed adaptive threading strategy was realized based on the calculation results. The adaptive threading strategy has been applied to one 7-stand hot tandem mill successfully, actual statistics data show that the predicted rolling force prediction in the range of ±5.0% is improved to 97.8%, the head thickness precision in the range of ±35 μm is improved to 98.5%, and the threading stability and the head thickness precision are enhanced to a high level.

Controlling the looper height and strip tension is important in hot strip mills because these variables affect both the strip quality and strip threading. Many researchers have proposed and applied a variety of control schemes for this problem, but the increasingly strict market demand for strip quality requires further improvements. This work describes a dynamic matrix predictive control (DMC) strategy that realizes the optimal control of a hydraulic looper multivariable system. Simulation experiments for a traditional controller and the proposed DMC controller were conducted using MATLAB/Simulink software. The simulation results show that both controllers acquire good control effects with model matching. However, when the model is mismatched, the traditional controller produces an overshoot of 32.4% and a rising time of up to 2120.2 ms, which is unacceptable in a hydraulic looper system. The DMC controller restricts the overshoot to less than 0.08%, and the rising time is less than 48.6 ms in all cases.

The rolling force model was the core factor for the control system of the cold rolled sheet, the prediction accuracy affect the final flatness and the strip thickness directly. A novel approach for the rolling force prediction of cold rolled sheet was first proposed based on the plastic mechanics, in which the cylindrical velocity field was used to analyze the metal flow in the deformation region by the upper bound analysis in this paper. The analysis solution of rolling torque, rolling force and stress state coefficient are obtained by minimizing the total power which contain the internal plastic power, frictional power, shear power and tense power. Moreover, the effects of frictional factor, reduction ratio and the tense on the location of neutral point and stress state coefficient are discussed, respectively, and the validity of the proposed model was verified by comparing with the traditional models. The calculation process was programed and applied in the control system of one 1450 mm cold tandem mill successfully, the prediction results was in good agreement with the actual measured ones, and deviation proportion in the range of ±10.0% reached 97.3%, it can meet the requirements of the control system in cold rolling process.

As the basis for a flatness control system, flatness actuator efficiency describes an actuator’s control ability, but it is difficult to obtain an actuator efficiency factor accurately through rolling tests because of the complicated subsidiary facilities of the mill. This paper proposes a novel simulation approach that is applied to obtain the actuator efficiency factors in terms of work roll bending, intermediate roll bending, and intermediate roll shifting for a six-high Universal Crown Control mill (UCM mill). A three-dimensional (3D) finite element model of the mill was developed to simulate the dynamic strip rolling process. The validation of rolling experiments shows that this model has enough precision, where the relative error of strip thickness between simulated values and actual values is less than 1.0%. The effects of the actuators on strip thickness profile, crown, edge drop, and elongation difference of longitudinal fibers were investigated. In the case of different actuator parameters, the curves of actuator efficiency factors were obtained and quantitatively descripted by truncated Legendre orthogonal polynomials. The mechanism of flatness control was studied based on an analysis of the actuator’s influence rule on the elastic deflection of rolls and 3D distribution of rolling pressure. The results indicate that the curves of actuator efficiency factors have a symmetrical upside-down v-shaped distribution and contain the quadratic and quartic flatness components. The actuator efficiency factors of intermediate roll shifting have a nonignorable variation with the change of actuator parameters. This study is the first attempt to obtain actuator efficiency factors for UCM mill using an elastic–plastic finite element method.

A parabolic velocity field is proposed to get the minimum required rolling force in hot rolling process, the equal area yield criterion is used to calculate the plastic deformation power, the collinear vector inner product method is used to get friction power, the analytical equation of strip rolling power functional is obtained, and the required rolling force was calculated by minimizing the power functional. Meanwhile, the location of neutral point, shape factor, and stress state coefficient are discussed. The accuracy of the proposed theoretical model is examined through comparing with the experimental measured ones and online measured ones, it shows good agreement, the relative error of rolling force is less than 9.1%, and the proposed model is considered to be effective in hot tandem rolling process.

Automatic control systems for tandem cold rolling are constantly being applied due to consumers’ requirements: good flatness and surface finish, accurate strip thickness, and consistent metallurgical properties. And those requirements are related to accurate prediction of the roll force directly. A novel analytical approach to predict roll force in tandem cold rolling is proposed based on elastic and plastic mechanics. A hyperbolic sine velocity field is firstly proposed to get the required minimum roll force in plastic deformation zone in this paper. The field, Inscribed Dodecagon (ID) yield criterion and the co-line vector inner product method are applied to integrate the analytical expression of total deformation power functional. The values of roll torque, roll force and stress effective factor are obtained considering the effect of roll flattening on the roll force. A good agreement between theoretical predictions of roll force and other researchers’ models, especially on-line measured roll force in a tandem cold rolling plant, verifies that the proposed mathematical model is efficient and stable, and the model can be considered to be applied in cold rolling. Besides, the effects of rolling parameters on location of neutral point and stress effective factor are discussed respectively.

A new sine velocity field is proposed to analyze total power in the roll gap for rolling in hot strip finishing mill. The field and linear geometric midline yield criteria are used to calculate the plastic deformation power, and the collinear vector inner product method is used to get friction power. Then analytical equation of strip rolling power functional is obtained. Finally, the roll force and torque can be calculated by minimizing the power functional. In the model, average deformation resistance is determined by the thermo-mechanical coupled analysis. The prediction accuracy of the proposed model is examined through comparing with the on-line measured results in a hot strip finishing mill. It shows that the predicted roll forces are in good agreement with the measured ones, and the maximum error is less than 12 %. Moreover, the effects of various rolling conditions, such as thickness reduction, friction factor, and shape factor, on roll force, location of neutral angle, and stress-state coefficient are discussed systematically.

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.

The interstand tension control is one of the most important ways to meet tight tolerances for strip product quality during tandem cold rolling process. Using coordinate analysis and parabolic approximation for the mass flow balance principle, the strip velocities eliminating the use of forward slips and backward slips were calculated. In order to reduce the effect of roll eccentricity on the tension measurement, a filter based on bilinear transformation was designed. Applying a first-order Taylor series approximation, the transfer function matrix model of interstand tension stress was derived. The actual measurements on-site and the final calculation results showed that the established model had high calculation accuracy and was beneficial for interstand tension control of tandem cold rolling process.

In terms of tandem cold mill productivity and product quality, a multi-objective optimization model of rolling schedule based on cost function was proposed to determine the stand reductions, inter-stand tensions and rolling speeds for a specified product. The proposed schedule optimization model consists of several single cost functions, which take rolling force, motor power, inter-stand tension and stand reduction into consideration. The cost function, which can evaluate how far the rolling parameters are from the ideal values, was minimized using the Nelder-Mead simplex method. The proposed rolling schedule optimization method has been applied successfully to the 5-stand tandem cold mill in Tangsteel, and the results from a case study show that the proposed method is superior to those based on empirical formulae.

As the spring equation is limited to the accuracy of mill stiffness and the linearity of the mill spring curve, the traditional gaugemeter automatic gauge control (GM-AGC) system based on spring equation cannot meet the requirements of practical production. In allusion to this problem, a kind of novel GM-AGC system based on mill stretch characteristic curve was proposed. The error existing in calculating strip thickness by spring equation were analyzed first. And then the mill stretch characteristic curve which could effectively eliminate the influence of mill stiffness was described. The novel GM-AGC system has been applied successfully in a hot strip mill, the application results show that the thickness control precision is improved significantly, with the novel GM-AGC system, over 98.6% of the strip thickness deviation of 3.0 mm class can be controlled within the target tolerances of ±20 μm.

Vertical mill is usually installed on the roughing trains to improve the width of the slab control precision and adjust the shape of edge during hot rolling. Because of the high ratio of width to thickness in edge rolling, the deformation of slab is mainly restricted in a small zone on the edge and this is different from the horizontal rolling. There is not a suitable formula to calculate the edge rolling force. With variable upper limit integration, the GM (Geometrical Midline) yield criterion and mean value theorem, as well as the vector inner product method are used respectively in integration of plastic deformation, shear and friction power terms. Then analytical solutions of slab total power functional and rolling force in edge rolling are obtained. The analytical rolling force of the model is in good agreement with those of data in a strip rolling plant. By this proposed analytical model, it is noted that the calculation time and computer expense are saved, and the precision can satisfy the requirement of production control.

In order to reduce equipment wear and operator pressure, as well as to improve the production efficiency of combined continuous pickling line and tandem cold rolling mill units, four sections’ speeds should be automatically optimized to control the three loopers’ abundance, which include the entry loopers’ entry speed, pickling speed, trimming speed, and tandem cold rolling mill entry speed. According to the optimal speed principle, a new optimization algorithm was proposed based on objective function. In this work, Nelder–Mead simplex method is applied to find the optimal solution by minimizing the objective function. In addition, the calculation of four initial speeds is specified, especially the initial tandem cold rolling mill entry speed. The proposed speed optimization algorithm was successfully applied to a 1450 mm continuous pickling line and tandem cold rolling mill. The acceleration and deceleration are smooth and steady when welding, trimming, or roll changing takes place in practice, the three loopers’ abundance are controlled in suitable range. Results show that the continuous pickling line unit could provide the material in maximum capacity to ensure that the tandem cold rolling mill unit’s production is efficient, and the rolling yield is greatly improved due to the decrease in the number of stops.

Aim at improvement leaching reaction and heat transfer efficiency, A novel self-stirring tubular reactor driven by pressure energy used in bauxite digestion process was presented originally by Northeastern University, which combined the advantages of autoclaves and conventional tubular digestion equipment. Quasi-logarithmic equation between the stirring speed and the various factors was established by dimensional analysis method. The results demonstrated that higher pressure promoted the appearance of more obvious turbulence and improved the mixing effect of media in the reactor. The quasi-logarithmic equation between the stirring speed and the various factors was: N = 356.7053ρ−0.4322μ−0.13546P0.56773H−0.86454

In order to meet the severe requirements of market and reduce production costs of high quality steels, advanced run-out table cooling based on ultra fast cooling (UFC) and laminar cooling (LC) was proposed and applied to industrial production. Cooling mechanism of UFC and LC was introduced first, and then the control system and control models were described. By using UFC and LC, low-cost Q345B strips had been produced in a large scale, and industrial trials of producing low-cost dual phase strips were completed successfully. Application results show that the ultra fast cooling is uniform along the strip width and length, and does not affect the flatness of strips. The run-out table cooling system runs stably with a high precision, and makes it possible for the user to develop more high quality steels with low costs.

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.

To analyze and solve the problem of single-side long edge of hot rolled strip in certain domestic factory, the asymmetrical deformation of rolls and strip in asymmetrical stiffness mill stand based on slit beam model, the strip profile and rolling force distribution at the exit of asymmetric stiffness stand mill were calculated using influence function method. Considering the character of in-site equipment and technology, a scheme of adjusting load distribution in finishing mill was made and the experiment was applied. Comparison of strip profile between new load distribution and the old one shows that the method can solve single-side long edge problem well.

In accordance with the feature of pure delay in monitor AGC system for cold rolling mill, a new fuzzy self-tuning PID Smith prediction controller is developed. The position control model is deduced based on a single stand cold rolling mill, and the fuzzy controller for monitor AGC system is designed. The analysis of dynamic performance for traditional PID Smith prediction controller and fuzzy self-tuning PID Smith prediction controller is done by MATLAB toolbox. The simulation results show that fuzzy self-tuning PID Smith controller has stronger robustness, faster response and higher static accuracy than traditional PID Smith controller.

The simplified transfer function diagram block for a monitor automatic gauge control (Mon-AGC) system of strip steel rolling process was investigated. The new notion of strip sample length was given. In this way, the delay time varying with the rolling speed was evaded. After a Smith predictor was used to monitor the AGC system, the control laws were deduced for both proportional and integral regulators. The control strategies showed that by choosing the controller parameter P=∞ for both control algorithms each regulator could compensate the whole strip gage error in the first control step. The result shows that the integral algorithm is more controllable for the system regulating process and has a better steady-state precision than the proportional regulator. Compared with the traditional control strategy, the new control laws have a faster response speed and a higher steady-state precision.

Heat transfer was researched from a perspective of the industry application. On the basis of the first law of thermodynamics, the cooling efficiency was deduced from the change of enthalpy inside hot plate. The relationship between the cooling efficiency and its influencing parameters was regressed from plenty of data collected from the worksite and discussed in detail. The temperature profiles resulting from the online model and the model modified by regressed formulas were presented and compared. The results indicated that the control accuracy of the modified model was increased obviously.

To improve the deficiency of the control system of finish cooling temperature (FCT), a new model developed from a combination of a multilayer perception neural network as the self-learning system and traditional mathematical model were brought forward to predict the plate FCT. The relationship between the self-learning factor of heat transfer coefficient and its influencing parameters such as plate thickness, start cooling temperature, was investigated. Simulative calculation indicates that the deficiency of FCT control system is overcome completely, the accuracy of FCT is obviously improved and the difference between the calculated and target FCT is controlled between −15 °C and 15 °C.

Based on the influence coefficient method, the effect of entry strip crown on the shape of hot rolled strip was analyzed using the software of roll elastic deformation simulation. According to the practical condition of a domestic hot rolled strip plant, the unit strip crown change from the first stand to the last stand was calculated when the entry crown of hot strip varies. The calculated result shows that the entry strip crown does not significantly affect the target strip crown at the exit of the last finishing stand in respect to a fixed strip shape control reference (such as bending force). The calculation was analyzed, and the research is helpful in modeling strip shape setup and shape control.

Hydraulic gap control system is the inner loop of automatic gauge control system, and the dynamics of hydraulic gap control system is the key factor for the high precision gauge control effect. The dynamics of hydraulic gap control system is influenced by a non-linear part since the oil flow of valve port depends not only on the control current but also on the changing rolling force. This influence is compensated by a method with compensation factor based on actual rolling force. The application indicates that the dynamics of the hydraulic gap control system is improved greatly with compensation.

Through the designing of Smith predictor and controller, the second-order engineering optimal controller parameters by fixed-timing sampling are given for the controlled object with pure delay inertia link, and the explicit formulation of control law is derived. Aiming at the problem of delay time changing with rolling speed, the solution strategy of using fixed-length sampling is proposed, and the optimal MN-AGC control strategy based on fixed-length sampling is given. This optimal controller has characteristic of pure integral, whether it is based on fixed-timing sampling or fixed-length sampling.

The automotive control system of hot strip mill’s laminar cooling, including water level control, feedforward control and feedback control of coiling temperature with smith predictor, is introduced. Steady water level can be got by water level control model, which is very important for water flux stabilization and the setup precision of process computer. Feedforward control strategy and feedback control strategy are necessary for the control precision of coiling temperature. This control system has been used on site and good performance has been got, which testifies that this system may be applied on the other hot strip mill’s laminar cooling system.