Cold Strip Research Articles

An airy function to rapidly predict stresses in wound metal strip having asymmetric thickness profile

With increased demand for thin gage flat metals, control of strip flatness or shape in cold rolling processes has become very important. To improve the flatness quality of cold rolled metal strip and sheet, this work provides a rapid method to predict the transient strains (or stresses) occurring during the rewinding of flat-rolled steels having problematic asymmetric strip thickness profile (or wedge). Flatness control systems, used to monitor and correct the distribution of stress across the width of rolled sheet, are unable to distinguish between stresses induced during rolling, and those caused when rewinding strip containing asymmetric thickness profile. The winding stresses, unless large enough to plastically deform the strip, vanish upon unwinding during subsequent operations such as stamping. Therefore, to help avoid strip flatness defects in thin strip containing wedge, a method is developed to separate the winding stress contribution from the overall stresses that are measured indirectly by flatness control systems. A fourth-order polynomial Airy function is developed to rapidly predict the in-plane stresses based on mandrel wrap number and spatial location on the strip. The Airy function is obtained by applying two-dimensional finite element analysis to study the transient in-plane stresses during rewinding at various numbers of mandrel wraps for a strip containing wedge profile. Three-dimensional finite element analysis is first employed, however, to show justification to a simplified two-dimensional problem described by the plane-stress Airy function. The two-dimensional finite element analysis provides insight as to how the in-plane stresses evolve, and allows determination of coefficients for the Airy function based upon model geometry and displacement boundary conditions. This approach differs from other methods that employ Fourier series to solve the biharmonic equations for an assumed two-dimensional problem. Finally, filtering of the winding stresses from flatness control system input signals is also discussed based on data taken from a rolling mill different to that used for model development.

Online Shape Dynamic Wrapping Angle Compensation Model of Cold Strip

In specific condition, when wrapping angle of cold rolling strip covering surface of shape detecting roll dynamically changes, online radial compression of the shape detecting roll is changed too, and it seriously affects online shape detecting precision of cold strip. Based on the latest intelligent shape meter developed by Yanshan University, using PSO-BP neural network and actual working condition datum, the cold strip online dynamic wrapping angle compensation model is established, and successfully applied in 1250 mm 6-high cold mill, remarkable results are achieved. The error between calculated values and measured values of total tensions is within 3%.

Analysis of Microstructure Effects on Edge Crack of Thin Strip During Cold Rolling

Edge cracks in cold rolling of the thin strip affect the strip quality and productivity significantly. In this study, an experimental and mechanical investigation on microstructures has been carried out to study the edge crack formation during cold rolling of the thin strip. The effects of the feed material microstructures on the edge crack evolution were studied employing optical microscopy and scanning electron microscopy (SEM). Experimental observation indicates that fine grain occurs in hot-rolled microstructure and coarse grain is produced in ferritic rolled microstructure. Different grain sizes affect significantly the formation mechanics of the microcrack, crack initiation, and orientation of crack extension. The grain size and grain boundaries effects on crack retardation are discussed also during edge crack initiation. During the crack growth in coarse grain, most edge crack tips will blunt, which improves the crack toughness by causing less stress concentration. Overall, the fine microstructure shows a good crack initiation resistance, whereas the coarse microstructure has a better resistance to crack propagation. This research provides additional understanding of the mechanism of microstructure influence on edge crack evolution of cold strip rolling, which could be helpful for developing defect-free thin strip.

Numerical and experimental analysis of lubrication in strip cold rolling

In this work an analytical model based on the slab method was built to analyze the lubrication during cold rolling of aluminum strips. Some process variables were studied like the rolling speed, the cross-section reduction, and lubricant viscosity. Numerical results are presented for pressure variation and film thickness at the inlet and work zones. The loads necessary to separate the rolls are also estimated. Some experimental results are shown for the surface roughness of the rolled products. It is shown that analytical results are in good accordance to experimental results, and that rolling pressure, lubricant film thickness and surface roughness are strongly influenced by rolling conditions, especially the lubricant viscosity and the area reduction.

Experimental PIV and interferometric analysis of natural convection in a square enclosure with partially active hot and cold walls

In this paper a PIV and Holographic interferometry measuring campaign on natural convection in a square cavity (side H = 0.05 m) filled with air at atmospheric pressure ( Pr = 0.71) is presented. Two strips (cold and hot) are applied on the vertical sides of the enclosure; tests involve three different configurations, with the hot strip in the middle of one wall, and the cold strip at the bottom, in the middle or at the top of the opposite wall. For each configuration measures are performed with different temperatures of the hot strip. The aim of the paper is to investigate the relation between dynamic and temperature fields and to describe how the flow and the heat transfer inside the cavity are influenced by the temperature of the hot strip and the position of the cold strip. Velocity maps, streamlines maps and interferograms are presented; the average Nusselt number and an expression of Nu(Ra) for each configuration are calculated. Results show that the configuration with the cold strip at the top of the wall produces the fastest dynamic field and the highest Nusselt number.

Precipitation strengthening in high manganese austenitic TWIP steels

At low strains (∊ < 0.25), the precipitation of Ti, Nb, V carbides in austenitic Fe–Mn–C steels which exhibit twinning induced plasticity has no significant effect on work hardening. Strengthening follows the Orowan mechanism and can be described by a simple yield stress offset. However, at higher strains (∊ > 0.3) the work hardening rate decreased slightly. Synchrotron X-ray diffraction analysis suggested that this was due to a reduction in the kinetics of twin formation. The highest strengthening coefficient in cold strips was obtained with Ti additions ≤0.1 wt.% (+1 380 MPa/wt.% Ti) but the effect quickly saturated after an increase of ∼+150 MPa. With Nb additions only modest hardening (+187 MPa/wt.%) could be achieved. The strengthening due to V was >530 MPa/wt.% for V additions ≤ 0.4 wt.% Saturation effects are less critical with V additions and yield stress increases of +375 MPa were demonstrated.

Kinetics of static strain aging after temper rolling of low carbon steel

In this study, static strain aging behaviour of cold rolled steel strips was considered with emphasis on the distribution of residual hydrostatic stress developed during temper rolling. In order to assess residual stress distribution produced by the temper rolling, a three-dimensional model was first employed. Then, samples were rolled at a reduction of 4% under single and double pass rolling programmes and the kinetics of static strain aging phenomenon as well as the required activation energies were then evaluated using hardness and tensile tests on the deformed samples. Considering the predicted residual hydrostatic stress distribution, it was found that tensile hydrostatic stresses promote the kinetics of the static strain aging process and alter the activation energy required for the phenomenon. In addition, it was revealed that different positions of the rolled steel show different aging behaviour owing to non-uniform distribution of residual stresses after temper rolling.

Analysis of friction and surface roughness effects on edge crack evolution of thin strip during cold rolling

Experimental investigation and mechanical analysis have been carried out to study the edge crack formation during cold strip rolling using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The effects of friction and surface roughness on edge crack initiation and growth rate have been discussed. Friction leads to an increase in fracture loads and decreasing the friction coefficient is effective in preventing the microcracks. Surface roughness variation along the strip width contributes to stress distribution and inhibits crack nucleation. The findings reveal that the behaviour of crack evolution is influenced by fracture surface roughness as well as rolling friction.

熱延ダウンコイラへの電気油圧サーボシステムの適用

Many kinds of electro-hydraulic servo systems are applied to rolling mills such as a hot strip mill, a cold strip mill and a seamless tube mill because of quick response, high power and high positioning accuracy. However when applying an electro-hydraulic servo system to a hot strip downcoiler, it was found that the controlled object has low natural frequency and is lightly damped so that stable control is very difficult. Optimal control theory has been recognized as a powerful tool for system synthesis in such a case. This paper first shows that the existing design method of optimal control is effective for designing an electro-hydraulic servo controller, in which the proper weighting matrices in the quadratic performance function can be determined directly from a physical model. A new design method is then proposed by which the state feedback gains can be obtained directly based on the characteristics of the controlled object. The effectiveness of the controller is demonstrated experimentally.

Data Mining and Prediction for the Radial Deformation of Rollers in the Steel Strip Cold Rolling Process

In the steel strip cold rolling process,the radial deformation of roll system will affect the thickness precision of the steel strip,and it is difficult to be detected on line.In allusion to this problem,a method of data mining is put forward Based on the measuring system of auto gauge control(AGC),and by using the collected data such as the exit thickness,downstroke,rolling force and rolling speed,data mining is carried out on the basis of the thickness difference formula,and the roll deformation is computed.Before the data mining,the data are rematched and arranged to solve the problem of thickness difference signal hysteresis caused by the mounting distance of thickness meter.After the date mining,the exponential smoothing is used to smoothen the computed result,and the trends extrapolation is introduced to predict the current radial deformation value of the roll system.Adaptive smooth coefficient algorithm is adopted to further improve the prediction precision.The data mining and prediction methods for radial deformation of roll system are applied to a 4-high mill,a clear and complete deformation process is obtained,which lays the foundation for further research on the axial deformation rule of roll system and the compensation method,thereby improving the thickness control precision.

Study on the Radial Deformation of Rollers Basing on Data Analysis

In the steel strip cold rolling process, the radial deformation of rollers is important for the control precision of AGC system, and difficult to be measured. In allusion to this problem, a method of data analysis is put forward. In this method, the sequence of radial deformation is calculated from acquired data in the rolling process, and the smoothed curve of deforming process is got using wavelet analysis. At last, the analyzed result is used in rollers deform compensating test in 300 cold rolling mill, the effect of compensation show that the deform information analyzed from history data is reasonable, and could used for compensation in the next rolling process.

Nonlinear Self-Adaptive Compensation of Screw down System of Tandem Cold Mill

The Screw Down System (SDS) is a typical hydraulic servo control system. It is the key actuator of cold rolling mill. The dynamic performance of SDS has a significant effect on the accuracy of thickness. Hydraulic servo control system is not always optimal and stable due to highly nonlinear and parameter uncertainties. In this paper, the most important nonlinear relating flow and pressure is analyzed. A nonlinear self-adaptive compensation method is designed. Modeling and simulating the hydraulic servo control system of SDS using this method, the numerical simulation results show that the maximum overshoot and static error of the compensated system are more less than that of without nonlinear compensation. The overshoot of the compensated system is less than 10% when the cold strip is rolling. So the thickness tolerance of the cold strip can be guaranteed easily. This self- adaptive compensation method can be used to other hydraulic servo control systems.

Research on Rolling Model Based on Non-Circular Contact Arc for Cold Strip Temper Rolling

During temper rolling, the reduction is small, the length of contact arc is short, and the elastic deformation of work roll is large. Roll shape is not circular arc, the assumption of circular roll shape is no longer applicable. In this paper, quintic B-spline function is used in interpolation operations with normal pressure distribution so that roll shape can be solved by Gaussian integration. And a rolling model based on non- circular contact arc for cold strip temper rolling is established. The calculated results show good agreement with the actual value. The model can meet manufacturing requirement of the field and receives better control effect of elongation.

Work Roll Thermal Deformation Calculation Model of Cold Rolling Mill

In this article, the factors which have influence on the work roll thermal deformation in cold strip rolling and the heat transferring mechanism are discussed. It is considered that there are three directions, radial, axis and circumference, for heat transferring for work roll thermal deformation. Therefore, it is a three dimensions unstable system for work roll temperature field of cold strip rolling. The plastic deformation work and friction heat are calculated by the divided element and digital integration method. The simplified calculation model is built for the heat transferring along work roll. There are four zones for work roll heat transferring: roll gap zone, air zone, emulsion zone, rolls contact zone. The heat transferring between the zones is decided by the temperature difference. The inter temperature field and thermal deformation of work roll can be calculated by two-dimension finite difference method. The work roll temperature and thermal crown of actual application cold rolling mill are analyzed by the model. By the comparison between calculated values and measured values, the work roll thermal calculation model can meet the accuracy requirement of on-line control.

Vacuum Flat Bed Filter Control System for Cold Strip Rolling Mill

The vacuum flat bed filter is important equipment for the cold strip rolling because the surface quality of cold rolled strip is paid more attention by customer. In the paper, the function, mechanical structure and operation modes of the vacuum flat bed filter for cold strip rolling mill are introduced. The control logic of emulsion liquid level in the filter is discussed. The filter fabric running modes are designed. The control system for vacuum filter is developed based on PCS7 software and S7-400 PLC hardware of SIMENS.

Asymmetric Shape Control Theory and Practice in Cold Strip Mills

In cold rolling process, asymmetric shape defects are still a common problem to strip quality. For the mills with inverse symmetry roll shifting system, different roll wear and thermal contour of top roll system and bottom roll system could cause asymmetric shape defects during shifting operation. In this paper, three dimension finite element simulation models of inverse shifting roll system were established to calculate the parameters and to analyze the effects. Based on the idea in the mill engineering that mill style option depended on the product grade, shifting weakness was evaluated and the opinion of limit shifting was suggested. To improve control effect to asymmetric shape defects in cold rolling, shape control system with asymmetric shape control ability is developed, including asymmetric edge drop control at upstream stands and asymmetric flatness control at last stand. The further improvement of asymmetric shape control theory and practice is the key way to reach the higher precision of shape quality in cold strip mills.

Numerical Simulation of Stamping Right-Hand Front Rail with Hot Strip Steel

The use of hot strip steel instead of part of cold strip steel in making automobile inner board has been considered for cost reduction of materials. To analyse formability of hot strip steel with the thickness of 1.6mm and 2.0mm in making automobile right-hand front rail，a systematic study was made by means of numerical simulation of stamping and stamping experiments in reality.A 3-dimensional finite element model was built to analyse the thinning, major strain, effective strain, effective stress and formability of hot strip steel.The simulative results indicated that two sizes of hot strip steel could deform well. The simulative results were compared with the experimental ones, and good consistency was observed.It is a helpful exploration to apply hot strip steel in making automobile inner board, and to apply numerical simulation of stamping in actual production.

Four-High Cold Rolling Mill for Control of Edge-Drop and Thrust Force

In the paper, control principle and working characters of T－WRS&amp;C（Taper Work Roll Shifting and Crossing）cold rolling mill are analyzed. The working schedule and control parameters are worked out. The mill working modes are determined according to different working conditions. The taper work roll shifting is used for edge drop control and the work roll crossing is used for thrust force control when work rolls shifting. The actual application verifies that the edge drop and thrust force can be controlled effectively during cold strip rolling.

Mathematical Model for Temperature Distributions of Work Roll in Aluminum Strip Cold Rolling

The temperature distribution of the work roll affects the shape and size of final product in aluminum strip cold rolling process. The segmental model is presented to explore the boundaries of the roll. The surface of the work roll is divided into 5 different regions including the outlet roll-strip contact region, the inlet roll-strip contact (bite) region, the roll-spray region, the roll-air region and the roll-roll contact region. Based on the analysis of the roll pressure, the mathematical models of the plastic doformation work and friction heat are proposed to calculate the temperature variation in bite region. The boundaries, including heat convection with lubricant/air and heat conduction with the backup roll, are considered to model the work roll’s temperature distribution.

Significance of blood vessels in optimization of absorbed power and temperature distributions during hyperthermia

This study investigated the significance of blood vessels in the absorbed power and temperature distributions when optimization was employed during hyperthermia. The treated tumor region was simulated using a three-dimensional (3D) tissue model embedded with a countercurrent blood vessel network (Huang et al., 1996). 3D temperature distributions are obtained by solving the conduction equation in the tissues and the convective energy equation with specified Nusselt number in the vessels. 3D absorbed power depositions are obtained by using optimization to reach a uniform temperature of 43 °C for the desired treated region. Results show that the absorbed power deposition for optimization with fine spatial resolution produces a uniform temperature distribution maintained at 43 °C in the desired treated tumor region except for some cold spots and/or small cold strips caused by thermally significant large vessels. The amount of total absorbed power suggests that a region with thermally significant vasculature requires much more power deposited than one without vasculature. In addition, optimization with coarse spatial resolution results in a highly inhomogeneous temperature distribution in the treated region due to the strong cooling effect of blood vessels. Therefore, prior to hyperthermia treatments, thermally significant blood vessels should be identified and handled carefully to effectively reduce their strong cooling effect, particularly those vessels flowing into the treated region.