Backup Roll Research Articles

A Comprehensive Model to Compute Roll Gap Profile for a Rolling Mill Including Bearing and Mill Housing Deflections

Abstract Obtaining the desired strip profile is of paramount importance in cold rolling. The final strip profile depends on several parameters of the plants including crown and taper profiles and segmented backup roll positions. This paper aims to present a newly developed combined finite element–analytical model of the rolling mill able to model not only the roll cluster but also the mill housing and backup bearings deformations. This makes the proposed model especially suitable to simulate cluster-type rolling mills. The model exploits a modified elastic foundation formulation for a precise computation of the contact forces between rolls, taking into account rolls’ crown and taper. A reduced stiffness matrix approach is implemented for accurate mill housing modeling. A full 3D finite element model of the rolling mill and experimental data are used for the validation of the presented model. By exploiting the validated model, the paper shows that the deformation of supporting bearings and mill housing plays a crucial role in the strip profile calculation and should be included in any cluster-type roll mill model.

An integrated approach to analysis and assessment of condition parameters of the surface layer of backup roll bodies of a continuous broad-strip hot rolling mill

An integrated approach to analysis and assessment of condition parameters of the surface layer of backup roll bodies of a continuous broad-strip hot rolling mill

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.

Microstructure and Hardness Characteristics of Swing-Arc SAW Hardfacing Layers.

Hot-rolled backup rolls are widely used in steel rolling and usually need to be repaired by arc hardfacing after becoming worn. However, a corrugated-groove defect commonly occurs on the roll surface due to the uneven hardness distribution in the hardfacing layers, affecting the proper usage of the roll. Accordingly, a new swing-arc submerged arc welding (SA-SAW) process is proposed to attempt to solve this drawback. The microstructure and hardness are then investigated experimentally for both SAW and SA-SAW hardfacing layers. It is revealed that a self-tempering effect occurs in the welding pass bottom and the welding pass side neighboring the former pass for both processes, refining the grain in the two areas. In all the zones, including the self-tempering zone (STZ), heat-affected zone (HAZ), and not-heat-affected zone in the welding pass, both SAW and SA-SAW passes crystallize in a type of columnar grain, where the grains are the finest in STZ and the coarsest in HAZ. In addition, the arc swing improves the microstructure homogeneity of the hardfacing layers by obviously lowering the tempering degree in HAZ while promoting the even distribution of the arc heat. Accordingly, the hardness of the SA-SAW bead overall increases and distributes more uniformly with a maximum difference of < 80 HV0.5 along the horizontal direction of the bead. This hardness difference in SA-SAW is accordingly decreased by ~38.5% compared to that of the SAW bead, further indicating the practicability of the new process.

The effect of highly elongated micro-contacts on rolling contact stress field

This study presents a boundary element model to analyze contact pressure distribution and the subsurface stress field in rough rolling elements. The methodology is demonstrated by the stress field of the backup roll and work roll in the cold/temper rolling process and characterized by a parallel orientation of roughness lay with rolling direction, resulting in a cluster of highly elongated elliptical micro-contacts. The numerical outcomes revealed that the amplitude of in-plane and out-of-plane shear stress components are strongly dependent on the ellipticity of the micro-contacts. Comparison with experimental results shows that the crack plane is oriented transversal to the rolling direction and the crack initiation location corresponds to the location where the shear stress components are maximum.

Numerical simulation study on integral induction heating of backup roll

A finite element model (FEM) of the electromagnetic-thermal coupling is developed to study the integral induction heating of the backup roll. The method of calling different B–H curves of the material at different temperature moments is proposed to consider the change of the relative permeability of the backup roll in the temperature rise process. The magneto-thermal two-way coupling simulation of backup rolls was carried out in ANSYS with consideration of the heating power or current change, and the field test verifies the result. The influence of critical heating process parameters, such as the effective heating length of the coil, the chamfer radial, and the diameter of the backup roll on the temperature distribution, is studied. The results reflect that the length of the induction coil above the roll on one side should be controlled between 100 mm and 200 mm. Temperature near the end of the backup roll increases significantly when the length of one side of the coil exceeds 200 mm. The coils with the same diameter can heat the rolls with different diameters. The diameter difference between the coil to the roll should control around 200 mm to ensure uniformity of temperature distribution along the axial direction. The current value needs to be increased to confirm that the temperature near the end of the roll meets the requirement when the diameter difference between the coil and the roll exceeds 200 mm. The results provide a possibility for pre-evaluating the rationality of induction heating processes in production.

MODELING OF PHASE TURNING PID HOUR OF PERMANENT COOLING OF HIGH-CARBON ALLOYING STEELS

On the basis of the author's analytical model together with finite element models, simulation of phase transformations during continuous cooling of high-carbon alloyed steels, intended for the manufacture of metal products of responsible purpose, in particular for the metallurgical and machine-building industries, was performed. The simulation results are summarized by constructing thermokinetic diagrams of austenite decay in the process of continuous cooling of steels 65Cr3SiMoV, 80Cr3MoV, 80Cr5MoV. The obtained results will be used during the adjustment of industrial modes of heat treatment of metal products of responsible purpose, in particular, back-up rolls of rolling mills. At the next stage of research, it is advisable to construct isothermal and structural diagrams of steels 65Cr3SiMoV, 80Cr3MoV, 80Cr5MoV including the determination of the distribution of structural components according to the depth of the strengthened layer (0–100 mm), which will allow to create scientifically based principles for improving the technology of heat treatment of support rolls rolling mills, which are made of high-carbon alloy steels.

Wear prediction model of hot rolling backup roll based on FEM + ML algorithm

Wear prediction model of hot rolling backup roll based on FEM + ML algorithm

Analysis of Edge Drop on Strip Due to Bending and Elastic Deformation of Back up Rolls in a Four-High Cold Mill

The superficial quality of the strip is a very important issue in steel production. Considering the dimensions, the thickness is one of the most important variables in the production of a strip. In the present study, the elastic curve of Back Up Rolls (BURs) is analyzed, considering them as simply supported beams as well as the effect of rolls on the profile of the strip, specifically in the strip edge producing edge drop. The analysis included theoretical and numerical measurements in the mill. The results showed that there is an instability zone of 76 mm in the strip edge, and this geometry is symmetrical in both ends of the strip. This study not only provides a theoretical basis for the edge drop, but also provides a basis for the understanding of deformation on rolls used in rolling mill processes and their effect on the thickness, profile, shape, and dimensional quality of strips. To reduce the edge drop and significantly improve the surface quality of the strip, it is suggested to complement the simulation by compensating for the elastic curve of BUR, in the process applying bending on Work Roll (WR) combined with the use of positive crowns on it.

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.

Investigation on contact pressure of backup roll with parabolic chamfer curve and intelligent modeling of plate crown in plate rolling process

Investigation on contact pressure of backup roll with parabolic chamfer curve and intelligent modeling of plate crown in plate rolling process

Fatigue-Damage Prediction Model of Backup Roll of Hot Strip Mills and its Applications

Fatigue-Damage Prediction Model of Backup Roll of Hot Strip Mills and its Applications

Influence of microstructure on degradation of cast graphitic high-speed steel

Work rolls used in hot rolling of steel suffer severe wear caused by combinations of adhesion, abrasion, rolling contact fatigue, thermal fatigue, and tribo-chemical corrosive attack. Depending on the specific wear mechanisms, damage of these rolls may include loss of material, surface, and subsurface cracking, as well as impairment of the surface finish. In this work, wear tests were performed using a custom-designed roll test rig which simulates the contact conditions between the work roll, the back-up roll and the hot-rolled steel. To simulate typical conditions occurring in a hot rolling mill, different contact pressures and rolling temperatures were considered. Wear and damage mechanisms were analyzed by optical microscopy and scanning electron microscopy (SEM). A systematic approach was used for correlating wear and microstructure of the roll materials. Therefore, graphitic high-speed steels (G-HSS) with different fractions and types of carbides were investigated. MC and M2C/M6C were identified to influence mainly the wear behavior of G-HSS. Increasing the fraction of these carbides reduced the wear rate but increased the surface roughness. The optimum balance between carbide types, graphite content and metal matrix has been identified as mandatory for achieving high wear performance of work roll materials.

Investigation of surface strain hardening of the barrel of back-up rolls in the finishing group of a broadband hot rolling mill

Investigation of surface strain hardening of the barrel of back-up rolls in the finishing group of a broadband hot rolling mill

Прогнозирование упрочнения бочки опорного валка на основе компьютерного моделирования

Представлены результаты моделирования напряженно-деформированного состояния бочки опорного валка методом конечных элементов в зависимости от интенсивности его работы за кампанию в клети непрерывного стана. Установлена зависимость, позволяющая прогнозировать упрочнение бочки опорного валка от длины прокатанной полосы и средней погонной нагрузки в межвалковом контакте в клети непрерывного стана. Получено соответствие результатов с данными промышленных опытных измерений приращения твердости после прокатки на широкополосном стане горячей прокатки 2000. Предложено использовать полученные результаты в программном инструменте для оперативной обработки информации об эксплуатации опорных валков чистовой группы на участке подготовки валков производства плоского проката листопрокатного цеха № 2 ПАО «Северсталь». The authors present the results of simulating the stress-strain state of the back-up roll barrel by the finite element method depending on the intensity of its work during the campaign in the continuous mill stand. The dependence has been established that makes it possible to predict hardening of the back-up roll barrel due to the length of the rolled strip and the average linear load in the roll-to-roll contact in the stand of a continuous mill. The results are consistent with the data of industrial experimental measurements of the increase in hardness after rolling on a wide-band hot rolling mill 2000. It is proposed to use the obtained results in a software tool for online processing of information on the operation of the back-up rolls of the finishing group at the roll preparation section of the flat-rolled production at sheet-rolling section No. 2 of PJSC Severstal.

Study on the VCRplus Back-Up Roll Contour of 1500 mm CVC Mill

The back-up rolls of hot strip mills wear considerably under the conditions of high temperature and heavy load, which affects the roll service period and the stability of strip profile control. Serious uneven wear, short service periods, and spalling problems occurred on conventional back-up rolls of upstream stand CVC mills in 1500 mm continuous hot rolling production lines. Through finite element simulations, the problems are determined to be caused by the configuration of a flat roll contour of the back-up roll and the CVC roll contour of the work roll, which leads to uneven contact pressure between the rolls. The wear distribution form is ‘anti-CVC’ shape, and there is peak contact pressure between the rolls on both sides of the roll body. In particular, the long-term negative shifting of CVC on site further increases the peak contact pressure between the rolls, resulting in uneven wear and spalling accident. Based on the design technology of VCR back-up roll contours with variable contact lengths, and considering the cooperation between the middle of the back-up roll and the CVC work roll contour, the roll contour of the back-up roll has been improved. The designed VCRplus roll contour was analyzed and evaluated by finite element simulation, including the distribution of contact pressure between rolls, the control effect of bending force, and the transverse stiffness of the roll gap. The simulation results show that the VCRplus roll contour can effectively improve the uneven distribution of contact pressure between the rolls, and effectively improve the control effect of bending force and the transverse stiffness of the roll gap. Industrial tests demonstrate that VCRplus back-up roll contours have the advantages of uniform back-up roll wear, enhanced self-sustaining of the roll contour, and further extension of the back-up roll service life. The roll contour has now stably been put into industrial production, and the rolling capacity during the back-up roll service period has been extended from 150,000,000 kg to 250,000,000 kg.

Development and Practical Implementation of Digital Observer for Elastic Torque of Rolling Mill Electromechanical System

The strategic initiative aimed at building “digital metallurgy” implies the introduction of diagnostic monitoring systems to trace the technical condition of critical production units. This problem is relevant for rolling mills, which provide the output and determine the quality of products of metallurgical companies. Making up monitoring systems requires the development of digital shadows and coordinate observers, the direct measurement of which is either impossible or associated with numerous difficulties. These coordinates include the spindle torque applied by the spring-transmitting torque from the motor to the rolling stand rolls. The development and research are conducted by the example of the electromechanical systems of the horizontal stand at the plate mill 5000. The stand electric drive characteristics are given, and the emergency modes that cause mechanical equipment breakdowns are analyzed that. The relevance of analyzing transient torque processes in emergency modes has been accentuated. The paper points to the shortcomings of the system for elastic torque direct measurement, including low durability due to the harsh operating conditions of precision sensors. It also highlights the need to install the measuring equipment after each spindle. The disadvantage of the previously developed observer is the function of calculating the electric drive speed derivative. This causes a decrease in noise immunity and signal recovery accuracy. The contribution of this paper is building a digital elastic torque observer that has advantages over conventional technical solutions, based on the theoretical and experimental studies. The technique for virtual observer adjustment was developed and tested in the Matlab-Simulink software package. For the first time, a comprehensive analysis was conducted for spindle elastic torques in emergency modes that caused equipment damage. An algorithm was developed for an emergency shutdown of a stand electric drive in the worst-case mode of strip retraction between work and backup rolls, due to the overlap of the strip on the roll. Further, the algorithm was tested experimentally. The criteria for diagnosing pre-emergencies was then justified. An adaptive motor-braking rate controller was developed. The developed observer and emergency braking system are in operation at the mill 5000. Long experimental research proved the efficiency of dynamic load monitoring and the reduction in the number of equipment breakdowns.

Vibrations of tandem cold rolling mill: coupled excitation of rolling force and variable stiffness of fault-free back-up roll bearing

Vibrations of tandem cold rolling mill: coupled excitation of rolling force and variable stiffness of fault-free back-up roll bearing

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.

Analysis and measures of rolling marks on hot galvanizing leveler

Hot-dip galvanized sheet is widely used in industries, such as automobiles, home appliances, electronic appliances and construction, due to its good corrosion resistance, processability, weldability, and paint ability. With the development of the automobile industry, the surface quality requirements of automobile steel are gradually improved. However, The galvanized sheet produced on our GJSS 2# galvanizing line often has rolling marks defects, which seriously affects the quality of products. This paper analyzed the physical and chemical features of the defect sample of roller marks on the sheet. Based on the research and analysis, measures such as adding side guide pulleys on the work roll chocks, high-pressure water spray was added to the lower backup rolls when changing rolls, and water barriers were added to the work roll tracks. The results showed that these measures reduced the occurrence of roll marks.