Four-high Mill Research Articles

Study on roll shape control characteristics of electromagnetic control sleeve support roll

The paper proposed a new type of electromagnetic control support roll to obtain a better ability of controlling the plate shape. According to the principle of induction heating, the bulge shape of the support roll and the contact pressure between the rolls are changed to control the crown of the work roll. To analyze the shape control characteristics of the electromagnetic control sleeve support roll, the roll system model of the four-high mill was established and the no-load bulging experiment was carried out. The simulation results show that under different roll sleeve thickness, current frequency and current intensity, the bulge amount of support roll, contact pressure between rolls and work roll crown increase with heating time, but the growth rate gradually decreases to zero. The bulge of the support roll, the contact pressure between the rolls, the crown of the work roll change quasi-linearly with the current frequency and parabolically with the current intensity. The bulging amount of the support roll and contact pressure decrease with the increase of the thickness of the roll sleeve, and the crown of the work roll increases first and then decreases. This paper verifies the feasibility of adjusting the shape of roll gap by electromagnetic control sleeve support roll, which provides a basis for multi-zone joint control.

Vibration monitoring and analysis of strip rolling mill based on the digital twin model

A vibration monitoring method of strip rolling mill based on the digital twin model was proposed which could effectively reduce the structure complexity and test cost of the traditional monitoring system. Firstly, the coupling vibration mechanism model of the dynamic characteristics of roll system and bearings of four-high mill was established. Secondly, the digital twin model of strip rolling mill vibration was built based on the mechanism model. At the same time, the traditional monitoring test of the rolling mill was carried out to verify the accuracy of the digital twin model. Through analyzing the experimental results, it could be found that the roll system is vibrating intensely with the increase of rolling force obvious fluctuation. Finally, based on the above research results, the corresponding measures were put forward to suppress the rolling mill vibration. In conclusion, the rolling mill vibration monitoring theory based on the digital twin model provided the technical support and theoretical basis for improving equipment operation stability and reducing testing costs.

Influence of Work Hardening on the Surface of Backup Rolls for a 4-High Rolling Mill Fractured during Rolling Campaign.

Backup rolls are the main tool in a four-high rolling mill; the rolling forces applied in load cells promote the fatigue of the material due to mechanical contact between backup rolls and work rolls. This work investigated the causes of recurrent failures in backup rolls, with cracking always initiated on the surface of the roll body and finishing in the main radius between neck and roll body. Aiming to find the causes of failure, visual inspection and morphology of the fracture were performed, complemented with mechanical tests of hardness on the stress concentration area, in addition to validating the results by applying the finite element method, using ANSYS Mechanical Static Structural Software. It was concluded that the fatigue crack initiated on the surface of BUR due to work hardening continued growing up over the fatigued material, creating beach marks, and finally, a fracture occurred in the main radius of BUR due to stress concentration. The work hardening is the main cause of spalling on BURs and other mechanical components exposed to mechanical contact.

Rolling in Nondriven Rollers of Four-High Mill Stands

Rolling in Nondriven Rollers of Four-High Mill Stands

The Simplifying the Calculation of the Strip Profile during Rolling in a Four-High Mill Stand

The task of simplifying the calculation of deformation of the rolls and the strip profile during rolling in a four-high (quatro) stand has been formulated and stated in the article. The design and computer experiment results on the basis of which nonlinear approximations have been obtained for simplified calculation of the transverse rigidity moduli of the roller unit of the quarto finishing stand of the wide - strip hot mill 2500 have been described. The calculation of the transverse rigidity moduli of the roller unit of the quarto finishing stand is performed depending on the rolling force and the regulating force.

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.

Nanoporous Al sandwich foils using size effect of Al layer thickness during Cu/Al/Cu laminate rolling

The roll bonding technique is one of the most widely used methods to produce metal laminate sheets. Such sheets offer interesting research opportunities for both scientists and engineers. In this paper, we report on an experimental investigation of the ‘thickness effect’ during laminate rolling for the first time. Using a four-high multifunction rolling mill, Cu/Al/Cu laminate sheets were fabricated with a range of thicknesses (16, 40, 70 and 130 μm) of the Al layer. The thickness of the Cu sheets was a constant 300 μm. After rolling, TEM images show good bonding quality between the Cu and Al layers. However, there are many nanoscale pores in the Al layer. The fraction of nanoscale pores in the Al layer increases with a reduction in the Al layer thickness. The finite element method was used to simulate the Cu/Al/Cu rolling process. The simulation results reveal the effect of the Al layer thickness on the deformation characteristics of the Cu/Al/Cu laminate. Finally, we propose that the size effect of the Al layer thickness during Cu/Al/Cu laminate rolling may offer a method to fabricate ‘nanoporous’ Al sandwich laminate foils. Such foils can be used in electromagnetic shielding of electrical devices and noisy shielding of building.

Axial Force Analysis and Roll Contour Configuration of Four-High CVC Mill

In order to analyze the influence of technical parameters on work roll axial force of four-high continuous variable crown (CVC) mill, the deformation analyzing model with top roll system and strip was established based on influence function method. Then a CVC work roll curve designing scheme was proposed and it was carried out on some cold rolling mill considering the requirement of comprehensive work roll axial force minimization. The status of comprehensive work roll axial force is improved considering the rolling schedule that is beneficial to the roller bearing. Corresponding to the newly designed work roll contour, the backup roll end chamfer was designed considering comprehensive performance of interroll stress concentration, comprehensive work roll axial force, and strip shape control ability. The distribution of roll wear with newly designed backup roll contour is more even according to the field application data. The newly established roll configuration scheme is beneficial to four-high CVC mill.

A Roll-Stack Contact Mechanics Model to Predict Strip Profile in Rolling Mills With Asymmetric, Continuously Variable Crown Rolls

Introduced is an efficient new model to compute the roll-stack deflections and contact mechanics behaviors for metal rolling mills with asymmetric roll crowns. The new model expands the simplified mixed finite element (FE) method to consider complex antisymmetric contact conditions of continuously variable crown (CVC) roll diameter profiles designed for use with work-roll (WR) shifting on four-high mills, and intermediate-roll (IR) shifting on six-high mills. Conventional roll-stack deflection models are either more computationally expensive or exploit more simplifying assumptions. Moreover, almost all existing approaches fail to adequately simulate the antisymmetric CVC contact problem required for model-based control of thickness profile and flatness in hot and cold CVC rolling mills. The presented model efficiently captures bending, shear, and flattening deformations while computing contact interference forces, binary contact locations, and net effects of roll and strip crowns. Strip thickness profiles and contact force distributions predicted by the new model are checked against known theoretical solutions, and compared to predictions from large-scale FE simulations for a four-high mill with WR CVC shifting, and a thin-strip six-high mill with IR CVC shifting.

Creating Weldable High-Strength Structural Steel with Nanostructuring

Exploitation of the Arctic calls for the creation of economical high-strength steel capable of operating at low temperatures. Research shows that, to that end, means of controlling the steel structure must be identified, so as to create quasi-isotropic fragmented nanostructure within the metal. The formation of finegrain structure is possible by a combination of intense plastic deformation with recrystallization and phase transformations. To confirm the theoretical and experimental preconditions for this process, experiments are conducted on the Gleeble-3800 instrument and a Kvarto-800 four-high rolling mill. Experimental steel melts with a carbon equivalent Cequ = 0.44–0.87% are investigated. In simulation on the Gleeble-3800 instrument, compressive deformation is applied in two stages: roughing at 1080–1100°C; and finishing at 950 and 820°C. That simulates the deformation cycle in industrial Kvarto-5000 four-high mills. The grain size in the steel is decreased from 6.5 to 2.2 μm after deformation at 950°C and 1.1 μm after deformation at 810°C. Fragments smaller than 500 nm constitute 20–37% of the steel structure. In the steel with Cequ = 0.44–0.65%, the yield point is 500–700 MPa, which is 40% greater than the standard values. In the steel with Cequ = 0.65–0.87%, the yield point is 700–1150 MPa. These values are obtained with increase in nickel content in the steel to 3%. At higher Ni concentrations, no improvement in yield point is seen. After rolling on the Kvarto-800 mill, with Cequ = 0.60–0.87% in one pass (with 70% reduction) at 1100°C and direct quenching with subsequent tempering at 600°C, the yield point is 1060 MPa. In this case, variation in the Ni content and Cequ has little influence on the yield point. The steel consists of bainite (mean grain size 6.9–8.3 μm), with a large dislocation density (1–2) × 1015 m–2 and considerable fragmentation within the grain. On the basis of the new technology, a group of low-temperature steels with yield points of 270–690 MPa and Cequ = 0.32–0.65% is created. The thickness of the steel sheet is up to 130 mm; it may operate at temperatures as low as –60°C. Such steel may be used for atomic icebreakers, other Arctic vessels, and fixed and floating drilling platforms for oil and gas extraction from Russia’s Arctic shelf. This research demonstrates the possibility of creating structural steels with relatively little alloying (up to 20–30%) and with standardized chemical composition.

Roll shape design for foil rolling of a four-high mill

In this paper, a mathematical model for a four-high mill is proposed to analyze the elastic deformation of the backup and work rolls, including their respective axial deflection and surface flatness. The contact pressure between the backup and work rolls and that between the work roll and foil are functions of the roll’s position in the axial direction. In this analytical model, the rolls and foil are divided into many small regions and finite difference or matrix methods are used to derive the deflections of the work and backup rolls as a function of the force density in the foil width direction. A camber shape at the surfaces of the backup and work rolls is designed to counteract the rolls’ elastic deformation and to make the rolled foil as flat as possible. The effects of the selected roll materials upon the rolled thickness distribution are also discussed. A thickness variation within 1 μm can be obtained for a foil of 50-μm thick and 40-mm wide under reduction of 32 % using a WC work roll with a camber radius of 150 m.

3-D rolling processing analysis by Fast Multipole Boundary Element Method

This paper presents the numerical analysis of 3-D rolling processing by a kind of Fast Multipole Boundary Element Method (FM-BEM). The FM-BEM combines the Fast Multipole Method (FMM) and Boundary Element Method (BEM), for which the fundamental formulations and numerical implementations are obtained. Then a node-to-surface frictional contact model is provided and contact constraints are linearized. For the solution system, an improved Generalized Minimal Residual Algorithm (GMRES) is employed as a fast solver. Combined with high performance computing, a cold rolling process of 2030 four-high mill with a width-to-thickness ratio of 1850 is successfully simulated, and comprehensive new rolling information is obtained. Numerical results show that the presented FM-BEM requires less artificial assumptions, and it has higher precision and efficiency as compared to the traditional BEM, Finite Element Method (FEM) and Finite Difference Method (FDM). It is a breakthrough progress in the simulation of rolling engineering, which is of great significance.

Impact Analysis of Roller System Stability for Four-High Mill Horizontal Vibration

In order to study the hot Compact Strip Production (CSP), four-high mill vibration characteristics, and vibration suppression method, the roller system structure stability was analyzed and calculated at first in the paper. And then, the mill stand gap was measured at field and its influence on roll transverse vibration was analyzed. The drum gear coupling effect on the roller system stability and the automatic balance conditions of the coupling transmission torque were studied; the influence of axial force caused by the roller cross on the system stability was analyzed. Finally, the roller transverse friction chatter vibration mechanics model was established; the simulation analysis was carried out with eliminating mill house-bearing clearance and adding floating support for coupling, respectively. And the characteristics of the roller “jump vibration” were studied. We applied copper gaskets to eliminate or reduce mill house-bearing clearance for suppressing the rolling mill vibration on the spot; the test results show that the roller transverse vibration was suppressed after eliminating clearance.

The Evolution of the Surface Morphologies and Microstructures of an Unleveled Hot-Rolled Steel Strip During Cold Rolling After Hydrogen Reduction

The removal of oxide scale from a hot-rolled strip surface can completely eliminate environmental pollution if performed by hydrogen-reduction descaling instead of traditional pickling descaling. However, a large number of cracks appear on the surface of a leveled hot-rolled steel strip after hydrogen reduction. This effect is likely to impede the application of reduction descaling to cold-rolled products. Nevertheless, there are almost no cracks on the surface of an unleveled hot-rolled steel strip if the hot-rolled steel strip is not subjected to repeated bending by the leveler machine. The surface quality of a reduced steel strip will be better than that of a pickled steel strip. To investigate the evolution of the surface morphologies, microstructures, and properties of an unleveled strip steel during cold rolling, unleveled strip steel samples were rolled using a four-high mill after hydrogen reduction and after pickling. The surface morphologies and cross-sectional microstructures of the samples were observed by SEM, and the surface-roughness values were measured using a TR200 profilometer before and after cold-rolling deformation. The evolution of the surface morphologies and cross-sectional microstructures of the sample after cold rolling were analyzed. The results show that the oxide scale formed on the surface turns into a metallic iron layer, and a decarburization layer appears between the metallic iron layer and the steel matrix after hydrogen reduction. Few cracks, besides pores, and bubbles, appeared on the surface of the sample after hydrogen reduction. The pores and bubbles were roll-flattened after five passes of cold rolling. The work hardening degree and mechanical properties of the reduced sample are similar to those of the pickled sample after cold rolling. Compared with the rolled sample after pickling, the surface qualities of the reduced samples are better than those of the pickled samples and better than those of the reduced samples that were subjected to leveling prior to reduction.

Fuzzy Self-Tuning PID Control of the Main Drive System for Four-High Hot Rolling Mill

The main drive system used for four-high mill is usually a double closed-loop DC motor speed regulating system. Generally, the speed controller and current controller are proportional-integral-derivative (PID) controllers. The parameters of these controllers are usually determined by the engineering design method and are constant in the whole process. So the controllers can give good control effect in the rated operating condition. Once disturbance occurs, the control effects are often just passable. In this paper, fuzzy logic is used to adjust the parameters of the speed PID controller to improve the disturbance rejection ability. Simulation results show that the fuzzy tuning PID controller can give better control effect than the regular designed PID control.

Fuzzy Tuning PID Control of the Rolling Mill Main Drive System

The main drive system using for four-high mill is usually a double closed loop DC motor speed regulating system. Generally, the speed controller and current controller are PID controllers, and the parameters of controllers are determined by the engineering design method. Once disturbance occur, the control effects are often just passable. In this paper, fuzzy logic is used to set the parameters of the speed PID controller, so as to improve the disturbance rejection ability. Simulation results show that the fuzzy tuning PID controller can give better control effect than the regular control.

A Control Method for Load Balance between Upper and Lower Roll of Four-High Hot Rolling Mill

In the rolling process, the upper and lower working rolls of the mill usually under different load. In order to keep good product quality, load balance control is necessary. This paper proposes a control method which uses the torque difference between upper and lower roll to compensate the given current of the upper roll motor. Simulation results show that the proposed control method can give good control effect and keep load balance.

Spatial Vibration and Its Numerical Analytical Method of Four-high Rolling Mills

The rolls in contemporary four-high mills cannot be maintained parallel during the rolling process. Therefore, four-high rolling mill vibrations take place in six degree of freedom (DOF) leading to spatial behaviors involving vertical, horizontal, axial, torsional, cross and swinging vibration modes resulting in complex relative motions between the rolls. Two numerical methods, modified Riccati-transfer matrix method (Riccati-TMM) and finite element method (FEM), are presented to analyze a spatial vibration characteristic of two four-high rolling mills with different stability. The natural frequency and mode shape of four-high rolling mills are obtained, and the clearance has a great effect on natural frequency and mode shape. In addition, field testing experiment is also conducted to measure natural frequency by power spectrum analysis of rolling mill vibration. Experimental results basically agree with those calculated by Riccati-TMM and FEM, which means that the Riccati-TMM and the FEM can be used for analysis of spatial vibration of four-high rolling mill. Meanwhile, the spatial vibration shows more compound vibration behaviors and the negative effect of horizontal, vertical, cross and swinging vibration modes are effectively controlled after redesign of rolling mill. These advantages have a great significance for the rolling mill to be operated with a much higher rolling speed and improved yield of products.

Vibration Behavior of Roll System under Nonlinear Constraints of the Hydraulic Cylinder

With four-high plate mill as an example, two nonlinear constraints that are segmented elastic force and friction force of hydraulic screw-down cylinders and bending cylinders in rolling mill roll system vibration are analyzed, the model that nonlinear roll system vibration under the nonlinear constraint action from hydraulic cylinder is established, and amplitude-frequency response of the vibration system is obtained by using average method. The behavior characteristic of roll system under the action of segment elastic force and friction force is studied by analysis of vibration curves under the function produced by two kinds of nonlinear factors. The law of amplitude-frequency characteristics of roll system influenced by two kinds of nonlinear factors respectively is studied by taking different segmented elastic force and friction force. The results show that vibration speed is affected by the magnitude of elastic force, the instability frequency area is wider with increases of segmented elastic force increasing, and the influence on the vibration behavior of the roll system turns damping into nonlinear with friction force increasingly. This conclusion provides a theory reference for roll system vibration control.

Comparative Analysis of the Durability of Solid-Forged and Bimetallic Backup Rolls on Rolling Mills

A method has been developed for evaluating the durability of large solid-forged and bimetallic backup rolls on rolling mills with allowance for the residual stresses from heat treatment. Results are presented from a numerical study performed for a 600/1350 × 1420 four-high mill. The stresses created in the rolling operation are determined by solving a three-dimensional contact problem in the finite-element program ANSYS. The service life of the rolls is determined by calculating their durability in a deterministic formulation. The calculation is performed with the use of the Paris equation to describe the linear section of the kinetic diagram that characterizes fatigue fracture. It is shown that hard-faced bimetallic rolls subjected to carbide-intermetallide hardening last roughly twice as long as solid-forged rolls made of traditional low-alloy roll steels.