Opti mization and Model of Laminar Cooling Control Systemfor Hot Strip Mills

The structure of laminar cooling control system for hot rolling was introduced and the control mode, cooling strategy, segment tracking and model recalculation were analyzed. The parameters of air/water cooling models were optimized by regressing the data gathering in situ, and satisfactory effect was obtained. The coiling temperature can be controlled within ±15℃.

Cooling Efficiency of Laminar Cooling System for Plate Mill

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.

Development of the laminar flow cooling control system of the No.3 hot strip rolling line at Baosteel

The coiling temperature of the hot strip rolling process plays an important role in strip quality control. The newly-built laminar flow cooling control system was independently developed by Baosteel. L2 conducts totally dynamic control （L1 only executes the result from L2, and does not conduct any dynamic control ）. The system has many advantages, such as quick real-time control, accurate model calculation, quick response after self-adaptation, etc. Compared with the 2050 mm hot strip rolling line,the new system can satisfy the strict cooling requirements of high strength steel, silicon steel and heavy plates because of its newly-developed technologies of cooling rate control, strip cooling by sections and proportion-integral-differential coefficient （PID） feedback fuzzy control.

Self-Learning and Its Application to Laminar Cooling Model of Hot Rolled Strip

The mathematical model for online controlling hot rolled steel cooling on run-out table （ROT for abbreviation） was analyzed, and water cooling is found to be the main cooling mode for hot rolled steel. The calculation of the drop in strip temperature by both water cooling and air cooling is summed up to obtain the change of heat transfer coefficient. It is found that the learning coefficient of heat transfer coefficient is the kernel coefficient of coiler temperature control （CTC） model tuning. To decrease the deviation between the calculated steel temperature and the measured one at coiler entrance, a laminar cooling control self-learning strategy is used. Using the data acquired in the field, the results of the self-learning model used in the field were analyzed. The analyzed results show that the self-learning function is effective.

Element Tracking Strategies for Hot Strip Laminar Cooling Control

Feedforward control is the core to control function in the cooling process of hot strip. One of the most important tasks in feedforward control is to determine the arrival time of the strip at various locations on the runout table for effective control. Based on the principles of element tracking and tracking strategies for variable rolling speed and constant rolling speed, a simple diagonal tracking method for an existing hot strip mill was proposed and tested. The test results show that the proposed strategies are effective for improving tracking control.

Optimization of Heat Flux Coefficient Determination for Laminar Cooling Control

A new heat flux coefficient model and improved refreshing rules were introduced for optimizing coiling temperature model.The off-line simulation of the new strategy was performed by laminar cooling intelligent software,and the on-line application shows that the control of coiling temperature has been improved significantly.

PREDICTION OF CARBON CONCENTRATION AND FERRITE VOLUME FRACTION OF HOT-ROLLED STEEL STRIP DURING LAMINAR COOLING

A phase transformation model was presented for predicting the phase fraction transformed and the carbon concentration in austenite for austenite to ferrite transformation during laminar cooling on run-out table in hot rolling strip mill. In this model, the parameter k in Avrami equation was developed for carbon steels. The wide range of chemical composition, the primary austenite grain size, and the retained strain were taken into account. It can be used to predict the ferrite volume fraction and the carbon concentration in austenite of hot-rolled steel strip during laminar cooling on run-out table. The coiling temperature controlling model was also presented to calculate the temperature of steel strip. The transformation kinetics of austenite to ferrite and the evolution of carbon concentration in austenite at different temperatures during cooling were investigated in the hot rolled Q235B strip for thickness of 9.35, 6.4, and 3.2mm. The ferrite volume fraction along the length of the strip was also calculated. The calculated ferrite volume fraction was compared with the log data from hot strip mill and the calculated results were in agreement with the experimental ones. The present study is a part of the prediction of the mechanical properties of hot-rolled steel strip, and it has already been used on-line and off-line in the hot strip mill.

Re-reddening on Strip Surface After Water Cooling

After water cooling, there is a big temperature difference between the center and the surface of strip, which leads to the heat transfer from the center to the surface, and the surface temperature can rise in a short time. The finite element method was used to simulate the phenomena of re-reddening on the surface of strip and to analyze the temperature field of hot roiled strip during laminar cooling, and the periodical variation curve of the cooling rate was obtained during water cooling and subsequent re-reddening. The results show that the critical line of the cooling rate is at 1/3 of the half-thickness from the strip surface. The regression model of the relation of rereddening temperature, time, and distance from the surface was obtained in the re-reddening region. Re-reddening regularity on the surface of strip under the condition of different thickness and cooling rate was also studied.

Effect of Laminar Cooling on Phase Transformation Evolution in Hot Rolling Process

The effect of temperature variation owing to the cooling pattern （CP） on the microstructural evolution was investigated by establishing a thermomechanical coupled FE （finite element） model. A set of constitutive equations of phase transformation was implanted into the commercial FE solver MARC through the user defined subroutine CR- PLAW, and the temperature field was calculated by another user defined subroutine FILM. The results show that the final mierostructure is completely bainite phase for CP one, 98% of bainite phase and 2% of ferrite phase for CP two, and 55% of bainite phase, 35% of pearlite phase and 10% of ferrite phase for CP three.

Simulation of Rolling Billet in Oval Pass by Explicit Dynamics Elastic-Plastic FEM

Considering the strip speed during controlled laminar cooling on Baosteel 1580 hot strip mill in China, the influence of strip speed fluctuation on coiling temperature control for the tail and “neck” of the strip was analyzed. The optimization strategies were put forward and proved effective in operation.

Development of New Generation Cooling Control System After Rolling in Hot Rolled Strip Based on UFC

Ultra-fast cooling （UFC） is an advanced technology in hot rolling field. Through this technology, great changes on the run-out table are produced in the strip cooling process. In order to adapt to these changes, a new gen-eration of hot strip cooling control system after rolling was developed based on the UFC basic principle. The system can not only accomplish temperature of UFC delivery side, coiling temperature, cooling rate, etc, and multi-objective accuracy control, but also offer more flexibility and new attractive possibilities in terms of cooling pattern on the run-out table, which could be of prime importance for the production of some difficult steels. In addition, through the time-velocity-distance （TVD） profile prediction combined with speed feed-forward control and coiling temperature feedback control, the coiling temperature control precision can be effectively improved during accelerative rolling in the system. At present, the system has been successfully used in the conventional strip production line and CSP short process production line, and its application effect is perfect.

Improvement of Prediction Method for Strip Coiling Temperature

In order to improve the control precision of strip coiling temperature for hot strip mill,the BP neural network was combined with mathematical model to calculate convective heat-transfer coefficient of laminar flow cooling.The off-line calculated results indicate that the standard deviation of coiling temperature prediction is reduced by 22.84 % with the convective heat-transfer coefficient calculated by BP neural network.The prospects of this method for online application are bright.This method is more helpful to increasing the control precision of coiling temperature for hot strip steel.

Algorithm Design and Application of Laminar Cooling Feedback Control in Hot Strip Mill

Feedback control is one of the most important ways to improve coiling temperature control precision during laminar cooling process.Laminar cooling equipments of a hot strip mill and structure of the control system were introduced.Feedback control algorithm based on PI controller and that based on Smith predictor were designed and tested in a hot strip mill respectively.Practical application shows that the feedback control system based on PI controller plays a limited role in improving coiling temperature control precision.The feedback control system based on Smith predictor runs stable and reliable.When the measured coiling temperature deviates from the target value,it can be adjusted to the required range quickly and steadily by Smith predictor feedback control,which improves the coiling temperature control precision greatly,and qualities of hot rolled strips are improved significantly

FEM Calculation of Work Roll Temperature and Thermal Crown

A new heat flux coefficient model and improved refreshing rules were introduced for optimizing coiling temperature model. The off-line simulation of the new strategy was performed by laminar cooling intelligent software, and the on-line application shows that the control of coiling temperature has been improved significantly.

Model Software Package Development for Laminar Cooling Process in Hot Mill

The use of computer simulation techniques in the control system design of the laminar cooling process in a hot mill can significantly reduce the development cost while ensuring maximum production safety. The case-based modelling strategy was proposed and implemented in a software package. The functional structure of the software package was discussed in detail. The interfaces and functions of the software package were introduced. The results of industrial experiments can be directly visualized in the software package, allowing accurate and instant comparison of the model predictions with real measurements. The software package provides the simulation platform for research into advanced modelling and control strategies of the laminar cooling process in a hot rolling mill.

Intelligent Control on Hot Strip Coiling Temperature

A new intelligent control scheme for hot strip coiling temperature is presented. In this scheme, the prediction mode1 of finishing temperature and the presetting model of main cooling zone are establish based on BP neural network, the feed-forward open-loop control model of main cooling zone is constructed based on T-S fuzzy neural network, a new improved structure of T-S fuzzy neural network is developed, and the feedback close-loop control model of precision cooling zone is obtained based on fuzzy control. The effectiveness of the proposed scheme has been demonstrated by computer simulation with a satisfactory result.

A Kind of Plate Laminar Cooling Strategy With High Response and Steady Precision

After Smith Predictor being used to laminar cooling system, the control law for integral regulators is introduced. New notion of plate sample length is given for evading the delay time varying with the roll table speed. It is found that the integral algorithm is more controllable for system regulating process and has better steady state precision. Compared with the traditional control strategies, the new control law has faster response speed and higher steady state precision. The controller can be regulated in shorter time and the response is faster than that of routine controller and it can effectively eliminate the oscillatory instability. Owing to its easy realization and high stability, it has been applied to a plate mill. The accuracy of finish cooling temperature can be controlled within ± 10 ℃.

Semisolid Slurry Preparation of Die Steel with High Chromium Content

The control model of laminar cooling system for hot strip, including air-cooling model, water-cooling model, temperature distribution model along thickness direction, feedforward control model, feedback control model and self-learning model, was introduced. PID arithmetic and Smith predictor controller were applied to feedback control. The sample of model parameter classification was given. The calculation process was shown by flow chart. The model has been proved to be simple, effective and of high precision.

Hot Rolled Strip Re-reddening Temperature Changing Law during Ultra-fast Cooling

Temperature deviation between surface and the center of hot rolled strip is formed during ultra-fast cooling （UFC）. Surface temperature would rise when temperature deviation goes up to an extent, and strip re-reddening phenomenon will appear. Strip re-reddening affects the stability of strip microstructure, property and temperature control precision. Thus, it is necessary to conduct research on re-reddening temperature changing law to improve strip property and temperature control precision. Strip temperature trends for various strip thicknesses and ultra-fast cooling rates were obtained by numerical calculation method. Re-reddening temperature, temperature deviation between surface and center, and boundary layer position changing law were obtained. By comparison, some conclusions were obtained： UFC re-reddening temperature and laminar cooling （LC） re-reddening temperature were linear to ultra-fast cooling rate respectively. Ultra-fast cooling rate affected UFC re-reddening temperature greatly, but it had little effect on LC re-reddening temperature. Equations which were used to calculate UFC re-reddening temperature, LC re-reddening temperature and maximum temperature deviation were obtained. The position of boundary layer stayed in 1/4 strip thickness.

An On-line Finite Element Temperature Field Model for Plate Ultra Fast Cooling Process

Taking the element specific-heat interpolation function into account, a one-dimensional （l-D） finite ele- ment temperature field model for the on-line control of the ultra fast cooling process was developed based on the heat transfer theory. This 1-D model was successfully implemented in one 4 300 mm plate production line. To improve the calculation accuracy of this model, the temperature-dependent material properties inside an element were considered during the modeling process. Furthermore, in order to satisfy the real-time requirements of the on-line model, the variable bandwidth storage method and the Cholesky decomposition method were used in the programming to storage the data and carry out the numerical solution. The on-line application of the proposed model indicated that the devia- tion between the calculated cooling stop temperature and the measured one was less than ± 15 ℃.