Intermediate Roll Research Articles

Energy analysis of third-octave-mode chatter in tandem cold rolling

Mill chatter has become a complicated issue in the cold tandem rolling process due to the demand for higher rolling speeds and thinner specifications. The third-octave-mode chatter is a prominent vibration form that leads to serious product degradation and equipment damage. This study aims to investigate the energy generation and transmission of the mill-strip system during third-octave-mode chatter using the upper bound method and power flow approach. To obtain the strip forming power, a parabolic cross-section dynamic velocity field is used, which is considered more appropriate for the unsteady rolling process. Additionally, a new linear yield criterion, called the golden section (GS) yield criterion, is established to simplify the integration of internal plastic deformation power. The energy transmission and dissipation in the mill structure are analyzed using a finite element power flow model. The energy distribution variations affected by the rolling speed and time are discussed in detail, and the main cause of vibration intensification is explained. Since the intermediate roll shifting (IRS) has a significant influence on mill stiffness, the energy transfer concerning IRS is also investigated. The results are consistent with previous research. Furthermore, it is concluded that reducing IRS and improving mill stiffness are effective ways to promote mill stability and critical rolling speed.

Roll profile and roll shifting strategy for silicon steel edge drop control in cold rolling CVC mill

The cold rolling CVC rolling mill, which is a primary piece of equipment for producing thin-gauge nonoriented silicon steel, lacks suitable edge drop control methods. To construct a theoretical system for high-quality edge drop control of CVC rolling mills, this study focused on a 1780 mm CVC cold continuous rolling mill at a specific factory. Using ABAQUS software, a finite element model was constructed to simulate and validate the production process. Work roll profiles were developed to enhance the mill's edge drop control capability for silicon steel, effectively preventing issues related to excessive edge tensile stress caused by strip misalignment. Additionally, a multistand simulation model was developed to analyse the edge drop and curvature control capabilities of different mill stands. Based on the buckling theory under high tension conditions, an intermediate roll shifting strategy was developed for edge drop control in a cold continuous rolling CVC rolling mill. Field applications have shown that this research effectively reduces edge drop issues, improving the pass rate by 25.1 %, thus confirming the effectiveness of this study.

Vertical vibration model for the roll system of a six-high rolling mill based on the Timoshenko beam theory

During the production of cold-rolled strips, the high-speed operation of rolling mills generates vibrations that significantly impact the production efficiency, the strip quality, and the rolling mill service life. Therefore, investigating the vibration characteristics of rolling mills is of paramount importance. Previous studies predominantly treated the rolls as point masses, overlooking variations in the vibrations along the lengths of the rolls. In this study, the working, intermediate, and backup rolls were regarded as continuous elastic bodies, and they were simplified as Timoshenko beams. The modal superposition method was used to solve the vertical vibration equations for the rolls of a six-high rolling mill; thus, the natural frequencies and modal shapes for the rolls were obtained for both free and forced vibrations. A finite-element model validation confirmed that the accuracy of the novel Timoshenko beam six-high rolling mill vibration model introduced in this paper is significantly higher than that of the traditional Euler beam model when the roller length-to-diameter ratio is relatively small. Further analysis based on this model indicates that the forced vibration of the rolls is primarily influenced by fluctuations in rolling force. The amplitude of forced vibration is affected by factors such as the friction coefficient in the deformation zone, rolling speed, and cumulative rolling distance of the work rolls. These findings provide a precise representation of the characteristics of forced vibrations in rolling mills and offer valuable theoretical insight to ensure stable rolling mill operation.

Flatness defect control during cold rolling of SUS430 stainless steel

Abstract A statics finite element (FE) model as well as a dynamics FE model for Sendzimir mill have been established. It is in order to solve the bilateral wave defect caused by loose edge rolling during the cold rolling process with SUS430 stainless steel strip. The profile and flatness control effects are quantitatively analyzed by adjusting various roll contour configurations such as work roll crown, the second intermediate idler roll crown, the first intermediate roll taper depth and taper length. The coupling relationship between strip edge-drop and flatness under different roll contour configurations has been studied to analyze their effects on flatness defect control. The first intermediate roll taper depth is the most effective way to control edge wave. The first intermediate roll taper depth has been adjusted from 0.4 mm to 0.6 mm in the industrial production line. The overall profile has been improved by 21.5 %. The deviation of residual stress at strip edges has been reduced by 32.9 %. An excellent flatness defect control result has been achieved for the industrial production of SUS430 stainless steel. The present work is responsible for providing a theoretical basis and practical experience for the flatness defect control technology of a Sendzimir mill.

Asymmetric Shape Control Ability and Mutual Influence of the S6-High Cold Rolling Mill

The control of the asymmetric shape of strips has always been an important and difficult part of the production of cold rolling strips. In this paper, the S6-High cold rolling mill is taken as the research object. A finite element model of this mill is constructed using ABAQUS 2022 software, and a multistage working condition simulation analysis is carried out. The independent effects of asymmetric Intermediate Roll Bending (IRB) and asymmetric Intermediate Roll Shifting (IRS) on the strip shape are investigated by constructing an asymmetric convexity evaluation index. The equivalent relationship between the asymmetric roll bending and the asymmetric roll shifting was determined by analysing the coupling effect of the benchmark bending and shifting rollers on their asymmetric shape control characteristics. The on-site application shows that optimizing the amount of preset asymmetric shape control can significantly improve the asymmetric situation of the shape, providing theoretical guidance for the asymmetric shape control of the S6-High cold rolling mill.

Design of intermediate roll contour and analysis of regulation ability on strip shape of 18-High mill

Design of intermediate roll contour and analysis of regulation ability on strip shape of 18-High mill

Generation mechanism of high-order waves in wide titanium strip under the control of the first intermediate taper roll of a 20-high mill

Generation mechanism of high-order waves in wide titanium strip under the control of the first intermediate taper roll of a 20-high mill

Research on the control strategy of coning amount and ASU adjustment considering profile and high-order flatness cooperative control

ABSTRACT In the production of a 20-high mill, high-order flatness defects occur frequently. To achieve collaborative control of the profile and high-order flatness of a 20-high mill, an integrated coupling model of the roll system and strip has been established based on ABAQUS software. It has been found that as the coning amount of the intermediate taper roll increased, the profile evaluation index C25 decreased, while the work roll axis exhibited high-order deflection deformation, which could lead to the generation of high-order flatness defects. Subsequently, a novel control strategy of the coning amount and backup roll segmented reduction (ASU) control adjustment has been proposed to ensure that the profile evaluation index C25 meets the requirements while eliminating the risk of high-order flatness defects caused by roll shifting (coning amount) control. The specific combination form of the control strategy has been determined by using the particle swarm optimisation (PSO) algorithm. The Industrial application results show that the maximum compressive stress in the area 75 mm-300 mm away from the edge can be reduced by more than 40% after using the novel control strategy.

Research on the mechanism and law of strip tilt induced by cold rolling intermediate roll shifting

ABSTRACT Ensuring product quality requires the accurate detection of strip flatness during cold rolling. For cold rolling mills with intermediate roll shifting control, the uneven stiffness induced by the shifting process can cause the strip to tilt in the mill, which can affect the accuracy of strip flatness detection. In this study, the strip tilt is defined, and a finite element model of the S6-high mill is constructed using ABAQUS software to study the strip’s deflection and flattening behaviour during the rolling process and the effect of different rolling process parameters on the strip tilt. The specific spatial position of the rolls during the rolling process is also examined, and the main structure of the mill is identified as the primary cause of strip tilt. This research provides a theoretical basis for the strip’s absolute position change in the rolling process, which can enhance the measurement accuracy of flatness detection roll in the future.

Research on the generation and control of high-order flatness during the controlling of titanium strip profile by the intermediate taper roll in a 20-high mill

Research on the generation and control of high-order flatness during the controlling of titanium strip profile by the intermediate taper roll in a 20-high mill

Optimization of Multi‐Segment Work Roll Profile for 1340 mm HC Tandem Cold‐Rolling Mills Based on DBSCAN and NSGA‐II Algorithms

To address issues with saturated work roll bending force (WRB), maximum contact pressure between the work roll and intermediate roll (QWI), and challenging flatness lifting in a four‐stand, six‐high tandem cold mill with a 1340 mm width, the density‐based spatial clustering of applications with noise algorithm and the non‐dominated sorting genetic algorithm II are used for optimal design and online application research of a five‐segment work roll profile. When compared to a flat roll and a parabolic roll profile with a maximum crown of 15 μm, the optimized roll profile decreases the secondary crown of the roll gap (CW2) by 5.99 and 1.055 μm, respectively, and the fourth crown of the roll gap (CW4) by 0.21 and 0.39 μm, respectively. Additionally, QWI in the field of roll gap crown adjustment decreases by 1.04 and 0.445 kN mm−1. Industrial testing shows that the average integrated value of flatness in rolling the four extreme specifications of 1340 mm tandem cold‐rolling mills lowers by 2.65 IU following the application of the new roll profile, and the average reduction of WRB in the last stand is 2.215 MPa.

Understanding the regulation ability of roll bending on strip shape in a CVC-6 tandem cold mill using a 3D multiple stand FE model

Roll bending is a common technique to regulate the strip shape in tandem cold rolling (TCR), but its regulation ability at each stand is poorly understood at present. In this study, based on a 3D multiple stand elasto-plastic finite element (EPFE) model, the effects of work roll bending (WRB) and intermediate roll bending (IRB) on the strip crown, strip flatness and elastic deformation of work roll (WR) were quantitatively studied at each stand in the TCR. Results show that the regulation abilities of WRB and IRB on the strip crown both show a downward tendency from Stand 1 (S1) to Stand 5 (S5), which both depend on the strip plastic rigidity. Moreover, under various WRBs and IRBs, the strip shape is mainly determined by the elastic deflection of WR in the upstream stand, while it is determined combinedly by the elastic deflection and flattening deformation of WR in the downstream stand. Furthermore, the regulation ability of WRB on the strip crown and quadratic flatness is at least 2.5 times larger than that of IRB. The experimental results show that the developed multiple stand EPFE model can well predict the trend of the quadratic and quartic flatness between coils. These findings help understand the influence mechanism of the roll bending on the strip shape and improve the strip shape by optimising the roll bending in the TCR.

Preset model of bending force in 6-high universal crown tandem cold rolling mill based on symbolic regression

ABSTRACT Highly accurate bending force presetting is a prerequisite to ensure the well flatness of the strip head, however, there are limitations in the preset model used in industrial sites. According to the flatness control characteristics of work roll and intermediate roll bending forces, this paper integrates the historical production data of a 1420 mm 6-high tandem cold rolling mill and establishes a chain model of bending force preset based on symbolic regression, which implements with age-layered population structure genetic programming (ALPS-GPSR). The advantage of symbolic regression models is the ability to obtain explicit mathematical expressions, which is very important in complex industrial production environments. With the application of ALPS-GPSR based bending force preset model in the industrial site, the hit rate of flatness within 6IU in the strip head for three specifications of the strip has increased by 2.86%, 1.61%, and 2.19% respectively on average, achieving a satisfactory result.

Numerical analysis of contact pressure between rolls of Sendzimir mill based on double influence function method and conjugate gradient techniques

This paper established a model for calculating the contact pressure between the rolls of the Sendzimir 20-high mill based on the influence function method with considering the dispersion distribution characteristics of backup rolls. Stone's and Hirschcock's formula are used to calculate the rolling force between the work rolls and the rolling stock. The force balance equations and the moment balance equations of the roll system are established to determine the relationship between the contact pressure of rolls and the rolling force. The deformation-compatibility equation is established by combining the flattening deformation, deflection deformation, and rigid displacement of the rolls and roll crown. The influence function method is used to solve the flattening deformation and deflection deformation between the rolls. The conjugate gradient method is used to solve the contact pressure between the rolls by combining the force balance equation group, the moment balance equation group, and the deformation compatibility equation group of the roll system. The contact pressure between rolls obtained by the model established is compared to that by the finite element method. The results show that the calculation accuracy of the model established in this paper is consistent with that of the finite element method. Significantly, the contact pressure between the backup roll and the second intermediate roll can be accurately calculated by considering the dispersion distribution characteristics of the backup roll, and the computation time can be greatly reduced.

Influence of roll diameter configuration of 20 high mill on roll shifting control characteristics of wide titanium strip cold rolling

In the production of wide titanium strips cold rolled by 20 high mill, when the diameter of the 1st intermediate roll is reduced, the work roll with a large roll diameter will be used to match it, which is called non-standard roll diameter configuration in this study. In order to master the control characteristics of the 1st intermediate roll shifting under non-standard roll diameter configuration, the coupled static model of roll system and strip is established by FEM, and the model is verified by using the corresponding relationship between the change of load roll gap and the change of titanium strip residual stress after cold rolling. The simulation results show that under the same rolling force, the contact stress peaks of non-standard roll diameter configuration in flat area and cone area of the 1st intermediate roll are about 1.44 times and 1.51 times of standard roll diameter configuration respectively. Compared with the standard roll diameter configuration, when the roll shifting amount increases, the longitudinal plastic strain of non-standard roll diameter increases most significantly in the range of 0-300mm from the titanium strip edge. Under the non-standard roll diameter configuration, increasing the roll shifting amount is more prone to occur the high-order buckle problem.

Novel analytical heat source model for cold rolling based on an energy method and unified yield criterion

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.

Influence of intermediate roll shifting on strip shape in a CVC-6 tandem cold mill based on a 3D multi-stand FE model

Intermediate roll shifting (IRS) is widely used for improving the strip shape in the six-high tandem cold mill, but most related studies are limited to a single stand. To fill the knowledge gap, a three-dimensional (3D) multi-stand elastic–plastic finite element (FE) model was developed for a continuously variable crown (CVC)-6 tandem cold mill using data transfer, which was then validated by industrial experimental results. Based on this FE model, the effects of the IRS on the strip crown, strip flatness, loaded roll gap profile and contact normal stress between rolls at each stand were quantitatively analysed. The results show that from Stand 1 (S1) to Stand 5 (S5), the regulation ability of the IRS on the strip crown shows a decreasing trend, which depends on the strip plastic rigidity; in contrast, the regulation ability on the quadratic flatness experiences an obvious increase from S1 to Stand 4 (S4), then a drop at S5, while the IRS exerts little effect on the quartic flatness and quartic crown of the loaded roll gap. Moreover, the most uniform distribution of contact normal stress emerges at different IRSs from S1 to S5. These findings can contribute to a better understanding of the role of the IRS in controlling the strip shape during tandem cold rolling (TCR).

Transverse thickness profile control of electrical steel in 6-high cold rolling mills based on the GA-PSO hybrid algorithm

In order to meet the shape control requirements of “dead flat” transverse thickness profile of electrical steel sheet in cold rolling process, the 3D finite element model (FEM) for roll stacks and strip of 6-high tandem cold rolling mills (TCMs) was built with the developed Edge Drop Control Work Rolls for Non-shifting (EDW-N). The efficiency curves of the work roll bending (WRB), the intermediate roll bending (IRB), and the intermediate roll shifting (IRS) in cold rolling process are obtained for transverse thickness profile control performance. The control strategy of multi-stand and multi-variable profile and flatness control actuators, i.e., WRB, IRB, and IRS of stands 1 ~ 5 in 6-high TCMs is proposed based on the GA-PSO hybrid algorithm with better optimization ability. The results show that the control strategy can fully exploit the shape control ability and achieve the high precision control for transverse thickness profile of 6-high TCMs. The industrial application on the production gives remarkable results that the rate of the measured strip crown less than 7 μm increased from 38.58 to 67.74% for electrical steel sheet in the 1420-mm 6-high TCMs. The control strategy has applied to the production successfully.

Research on High‐Precision Transverse Thickness Difference Control Strategy Based on Data Mining in 6‐High Tandem Cold Rolling Mills

To meet the “dead flat” transverse thickness profile requirement of electrical steel strip in 5‐stand 6‐high universal crown mill (UCM) tandem cold rolling mills, a random forest predictive model for electrical steel strip profile is established to reduce the dimension of the data and make predictions for the strip transverse thickness difference (TTD), based on the collected and processed real‐time data of the steel strip transverse thickness profile and multi‐methods of the industrial production mills. The control strategy of multi‐methods including positive and negative hydraulic work roll bending system (WRB), positive hydraulic intermediate roll bending system (IRB), and hydraulic intermediate roll shifting system (IRS) of different stands in 5‐stand 6‐high mills is proposed by comprehensively considering association rules mining which shows the optimal combination of ranges of key control parameters and analysis of 5‐stand 6‐high mills with the developed edge drop control work rolls for non‐shifting of work rolls (EDW‐N) with divided width groups technology on stand No. 1 and No. 2. The strategy is continuously and stably applied to 1420 mm 5‐stand 6‐high UCM tandem cold rolling mills and shows remarkable results. The rate of TTD less than or equal to 7 μm increases from 38.58% to 67.74%.

Efficient Three-Dimensional Model to Predict Time History of Structural Dynamics in Cold Rolling Mills

Abstract Introduced is a new physics-based three-dimensional (3D) mathematical model capable of efficiently predicting time histories of the nonlinear structural dynamics in cold rolling mills used to manufacture metal strips and sheets. The described model allows for the prediction of transient strip thickness profiles, contact force distributions, and roll-stack deformations due to dynamic disturbances. Formulation of the new 3D model is achieved through a combination of the highly efficient simplified-mixed finite element method with a Newmark-beta direct time integration approach to solve the system of differential equations that governs the motion of the roll-stack. In contrast to prior approaches to predict structural dynamics in cold rolling, the presented method abandons several simplifying assumptions and restrictions, including 1D or 2D linear lumped parameter analyses, vertical symmetry, continuous and constant contact between the rolls and strip, as well as the inability to model cluster-type mill configurations and accommodate typical profile/flatness control mechanisms used in industry. Following spatial and temporal convergence studies of the undamped step response, and validation of the damped step response, the new model is demonstrated for a 4-high mill equipped with both work-roll bending and work-roll crown, a 6-high mill with continuously variable crown (CVC) intermediate rolls, and finally a complex 20-high cluster mill. Solution times on a single computing processor for the damped 4-high and 20-high case studies are just 0.37 s and 3.38 s per time-step, respectively.