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The efficiency of the flatness actuator is the cornerstone of the strip steel flatness control system and is pivotal in maintaining the quality of the strip shape and microstructure properties in commercial strip steel. However, the fluctuation in the thermal crown of the work rolls during the cold rolling process significantly impacts strip flatness quality. Obtaining real-time updates on the thermal crown alterations of the work rolls presents notable difficulties. Hence, the actual efficiency of the flatness actuator measured in the cold rolling environment fails to consider the effects of the work rolls' thermal crown, undermining the control precision of strip shape. Exploring the mechanism through which the thermal crown of the work rolls influences strip shape is therefore crucial. This would allow for determining the efficiency of the flatness actuator, accounting for the work rolls' thermal crown. In this research, an innovative approach is utilized, where FEM is used to create a highly accurate model. This model encapsulates the temperature-stress-strain field. This model effectively elucidates the time-varying influence of the hot roll shape on the strip shape, enabling the derivation of a dynamic strip flatness actuator efficiency curve for work roll bending and other actuators in the nonstationary rolling process. In addition, it addresses common challenges encountered in strip shape control during tandem cold rolling, such as the roll change stage and acceleration/deceleration stage.> [ABSTRACT FROM AUTHOR]

An accurate description of the metal flow behavior during wedge zone deformation is key to the stability of the endless strip production rolling process. To predict the flatness distribution based on the law of volume invariance, a flatness calculation model of the wedge zone during the flying gauge change (FGC) process was established by considering the metal transverse flow. Furthermore, the effect of different rolling parameters on the flow of metal in the wedge zone was investigated using a combination of this model with a 3D finite element model. In addition, the influences of the reduction rate, roll crown, and friction coefficient on the flatness and metal lateral flow were analyzed and discussed. Finally, the numerical results provided by the finite element model were compared with the computed results of the flatness distribution to illustrate the effectiveness and stability of the proposed model. [ABSTRACT FROM AUTHOR]

To investigate the edge drop control characteristics of the roll contour on the taper segment of a taper-work roll, a three-dimensional roll stack-strip-tension coupling model was established with the finite element method, and the simulation model was verified using experimental data. The effects of the taper-work roll shifting (T-WRS) for different contours on the edge drop, center crown, flatness, and nonuniformity of the rolling pressure field unevenness were studied. The results indicated that the thickness difference caused by the combination of the roll contour and the work roll shifting (WRS) effectively compensated for the edge drop caused by the elastic deformation of the roll was the main way for T-WRS to reduce edge drop. Increasing the height of the roll contour inserted into the strip could significantly improve the edge drop control ability. However, it would also lead to increasing the trend of M-mode waviness defects and increase the peak of rolling pressure and the unevenness of the contact pressure between the rolls. Therefore, a novel approach for the roll contour evaluation was proposed by constructing the multi-objective function of the taper-work roll shifting. With edge drop control as the primary goal, the optimal range and suitable range of the WRS for different roll contours were calculated for the first stand of the tandem cold mill. [ABSTRACT FROM AUTHOR]

The strips with good flatness after finish rolling will have flatness defects such as edge wave after run-out table cooling. These defects are caused by the residual stress due to inhomogeneous thermal and microstructural behaviors during the cooling stage. The traditional residual stress control methods rely too much on experience, resulting in poor control effect and poor universality. Therefore, this study proposed two residual stress control methods based on model calculation: water flow central crown and center wave compensation control. The former is mainly based on controlling the uniformity of strip transverse temperature and microstructure. The latter is mainly controlled by mutual compensation of internal stresses. In this paper, the mathematical models of water flow central crown cooling and critical center wave compensation stress were established, respectively. Meanwhile, a post-buckling model of hot-rolled strip was established to calculate the aim flatness value at exit of finishing mill under critical compensation stress. Furthermore, a fully coupled finite element model based on temperature, phase transitions, and stress was developed and it was verified using experimental data. Finally, the above two residual stress control methods were realized in the finite element model. The results showed that the two methods can reduce the residual stress and improve the flatness, and the application of center wave compensation control is more effective. [ABSTRACT FROM AUTHOR]

Chatter is a major problem that restricts production efficiency and product quality in the cold rolling process at high speed. Although many research studies have focused on relating rolling parameters to mill stability, information about the roll-stack in the axial direction and the strip in the width direction have not yet been considered due to the limitations of modeling methods. This paper proposes a new finite element model for the Universal Crown Control mill (UCM mill) with an improved Timoshenko beam used to investigate the influence of flatness control actuators on the mill stability. A dynamic rolling force calculation formula coupled with a mixed lubrication model is obtained. Then, the structure–process coupling model is established to simulate the rolling process at both steady and unsteady states. The results show that the work roll bending (WRB) has the greatest impact on the critical speed, followed by the intermediate roll shifting (IRS) and the intermediate roll bending (IRB). During vibration, the distribution of the friction stress varies rapidly, and a negative forward slip appears, which exacerbates vibration. Furthermore, the analysis of the energy dissipation in the rolling interface illuminates the vibration mechanism. Therefore, this study contributes to mechanism improvement and chatter suppression in the cold rolling process. [ABSTRACT FROM AUTHOR]

Accurate calculation of the heat source in the roll gap during the cold rolling process is the basis for a well-designed coolant system, which is particularly important for reducing roll wear and improving the flatness quality of strip steel. Although many established numerical models have high precision when calculating the work roll temperature, complex modeling processes and large calculation times result in the inability to predict the work roll temperature quickly for the application of automatic control systems. Therefore, the authors developed a new analytical heat source model to calculate the axial temperature distribution of the work roll in the cold rolling process. First, according to the deformation characteristics of strip cold rolling, the deformation zone is divided into a plastic zone and two elastic zones, and the length of each deformation zone is calculated considering the effect of tension. Then, the friction heat generated in the elastic zone is calculated. Second, new exponential velocity and corresponding strain-rate fields satisfying kinematically admissible conditions are proposed to calculate the deformation heat and friction heat generated in the plastic zone. Finally, the work roll temperature prediction model is established by contemplating the heat source of the roll gap, emulsion heat transfer, air cooling, and contact heat transfer with the intermediate roll. By repeatedly optimizing the weighted coefficient d of intermediate principal shear stress on the yield criterion, the maximum error between the calculated results and the actual measured cold roll temperature data was reduced to 3.1%. The effects of the reduction ratio, rolling speed, and resistance to deformation on the deformation heat and friction heat are discussed, and the variation of temperature field of the work roll with time is analyzed quantitatively. [ABSTRACT FROM AUTHOR]

Vertical rolling is an important technique used to control the width of continuous casting slabs in the hot-rolling field. Accurate prediction of vertical rolling force is a core point maintaining rolling-mill equipment. Owing to the limitation of the algorithm in use, the prediction accuracy of most vertical rolling force models based on the energy method can only reach more than 10%. Therefore, it is challenging to optimize the rolling-force model to improve prediction accuracy. An innovative approach for optimizing the calculation of vertical rolling force with a unified yield criterion is presented in this paper. First, the maximal width of a dog-bone region is determined by the slip-line method, and the dog-bone shape is described using a sine-function model. Second, the velocity and corresponding strain-rate fields satisfying kinematically admissible conditions are proposed to calculate the total power of the vertical rolling process. Finally, the analytical solution of the rolling force and the dog-bone-shape model is obtained by repeatedly optimizing the weighted coefficient b of intermediate principal shear stress on the yield criterion. Moreover, the effectiveness of the proposed mechanical model is verified by measured data in the strip hot-rolling field and other models' results. Results show that the prediction accuracy of the vertical rolling force model can be improved by optimizing the value of b. Then, the impacts of reduction rate, initial thickness, and friction factor on dog-bone shape size and vertical rolling force are discussed. [ABSTRACT FROM AUTHOR]

In the routine roll shifting mode, work rolls of the continuous variable crown (CVC) hot strip mill are always in repeated shifting positions, which affects the uniform wear of work rolls. As an available solution to the above problem, a new random shifting mode for CVC work rolls has been developed in this paper. According to the relationship between shifting position and bending force, the new CVC shifting mode shifts work rolls in a random pattern within the limits by randomly changing the bending force, so that the roll shifting is dispersed and the strip shape remains good. The Light Gradient Boosting Machine (LightGBM) algorithm is applied to build the prediction models of CVC shifting to accurately express the relationship between shifting position and bending force. Random search and Bayesian optimization are used to optimize the LightGBM models, respectively. By comparison, LightGBM with Bayesian optimization is recommended to predict roll shifting, which is more accurate and efficient than using random search. The new CVC shifting mode has been implemented by an off-line application in the 1780 mm hot rolling line. The results reveal that the proposed CVC shifting mode can well disperse roll shifting positions and accurately control strip shape. [ABSTRACT FROM AUTHOR]

To study the transverse temperature uniformity with transverse flux induction heating (TFIH) during endless strip production (ESP) rolling, a coupled electromagnetic-thermal finite element model of transverse flux induction heating is established. The initial temperature distribution at the TFIH inlet is taken into consideration, which is the basis of subsequent numerical studies. Magnetic screens are designed to weaken the influence of edge overheating, and the influence of magnetic shielding amounts on temperature uniformity is discussed. Moreover, an evaluation criterion is provided to determine the temperature uniformity. Furthermore, the effect of different shielding amounts on the edge temperature is studied. An ideal temperature distribution at the TFIH outlet is obtained based on a model combining various shielding amounts, and the temperature standard deviation of this method is 2.01% lower than the traditional arrangement of magnetic shielding amounts. Actual data are collected to verify the results of the proposed model. The temperature deviation between the middle and edge is approximately 12°C, and the temperature uniformity is enhanced with the optimized combination of magnetic shielding amounts. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A Correction to this paper has been published: https://doi.org/10.1007/s00170-021-07508-2 [ABSTRACT FROM AUTHOR]