Cold-rolled Strip Research Articles

Method for calculation the modes of strips cold rolling on multiple-stand rolling mill ensuring cost reduction of sheet rolling shop production. Report 1

A method for calculating the modes of strips cold rolling on multiple-stand (reversing) rolling mill is considered providing minimum power consumption with maximum process stabilization at high speeds and obtaining the given quality of cold-rolled strips (minimum probability of surface defects, compliance with thickness tolerances and flatness requirements of the used standards). The problem is solved using the conditional optimization method. As an optimization criterion, it is proposed to use the total energy expenditure spent on the rolling process, as conditions – technological and structural limitations on the rolling parameters and conditions of strips stability to breaks and surface defects formation. The decision to develop this innovative method is due to the fact that a large number of existing approaches to calculation and design of rolling modes have visible advantages and disadvantages. In many cases, the researchers are trying to take into account several requirements that ensure stability of rolling process, its quality, the equipment operating conditions, reduction of energy consumption, metal, auxiliary materials and the specified (maximum) mill productivity. However, some of these requirements can be contradictory and the best one will be the mode that with a high degree of probability guarantees the fulfillment, in a certain proportion, of the entire set of requirements. Therefore, such calculation method is the presented in this article. Calculation of the cold rolling regimes was limited to selection and distribution of the crimping along the cages (passages in the reversing mill). Also, the strip strains are selected in the intercellular spaces, on the decoiler and coiler, and in setting the speed wedge in a particular system of constraints imposed on the input and output process variables as a function of the adopted optimality criterion. As it was noted earlier, the problem was solved with the help of the conditional optimization method with specification of the optimization criterion.

Efficient Cold Rolling and Coiling Modes

The tension modes of cold-rolled strip coiling are analyzed. The dependences of the stress-strain state of the coils on the strain degree, temperature, velocity, strip rolls surface roughness during cold strip rolling are considered. Coiling methods provide improvement of production efficiency and the quality of cold-rolled sheet steel by preventing the appearance of such rolling defects as bent fractures and coil shape defects.

A comprehensive mathematical model for an accurate calculation of the oil film thickness of strip cold rolling

The surface quality of cold rolled strip is related to a greater extent on the rolling oil film thickness, and there are many factors that affect the oil film thickness. Considering the various factors comprehensively, an integrated mathematical model is established, such as roughness of rolls and strips, elastohydrodynamic lubrication, friction heat and plastic deformation heat in the rolling zone, viscosity varying with temperature and pressure, etc. A series of equations are developed, such as the Reynolds equation of partial membrane hydrodynamic lubrication based on average flow theory, equation of oil film thickness on rough elastic surface, the thermal interface equations between strip, oil film and roller surface, surface asperity contact pressure equation, lubricant viscosity and density equations, motion equation of the oil film, etc. This model is solved by finite difference method to get the film pressure, oil film thickness, and temperature distribution in the rolling zone. The average rolling pressure, the roll, and strip temperature calculated by the model are very close to the field test results. Comparing the minimum film thickness calculated by the model with the regression formula of other literature test, the error is less than 10%. The minimum oil film thickness is analyzed. It increases with the decrease of the rolling force and is approximately proportional to the rolling speed and lubricant viscosity.

Industrial X-ray Fluorescence Analyzer for Real-Time Thickness Measurements of Aluminium Coatings on Rolled Steel

Aluminium coatings that are formed by physical vapour deposition (PVD) on rolled steel products are more resistant to atmospheric and seawater corrosion than zinc coatings. We developed a coating thickness analyzer (CTA) with an X-ray fluorescence (XRF) measuring head, that is integrated into the PVD pilot line. In this study, to conduct measurements of elements with atomic numbers less than 20 while avoiding the problem of registration of light elements, the measuring head was integrated into a process vacuum chamber to maintain a vacuum during the measurements. To validate the proposed tool, cold-rolled steel strips of different grades are used as substrates, and aluminium was deposited on the surface via PVD in thicknesses ranging from 1 to 20 g/m2. The thin-film thickness measurements during a pre-acceptance test were found to have a relative accuracy of less than 5% and a relative precision of less than 1% – 2%. The proposed CTA can be readily integrated in the factory’s automatic process control system and the real-time measurements in operating and calibration modes, and the status of all spectrometric equipment (X-ray tube, detector etc.) can be transmitted to the upper-level computer. Thus, the process engineer can properly control the deposition process.

Induction heat treatment as a way to control cold-rolled strip transverse profile

Induction heat treatment as a way to control cold-rolled strip transverse profile

Effect of Interstand Tensions on Lubrication Regime in Cold Strip Rolling with O/W Emulsion

Oil‐in‐water are cost saving emulsions. These emulsions are widely used in cold rolling mills due to their beneficial characteristics as lubricants and coolants. In this study, an extension of the Reynolds equation for emulsions has been applied to the mixed-film lubrication of cold strip rolling. This model involves solving equations for emulsion in two inlet and working zones plus plastic deformation of the strip considering interstand tensions. In order to achieve a more realistic model, the strain hardening effect of the strip and elastic deformation of the rolls are taken into account. To evaluate the model, an integrated form of simulation program outputs—that is, rolling force and torque—was verified by experimental data from a real tandem rolling mill. Distributed parameters such as rolling pressure and friction, oil concentration, lubricant film thickness along the roll gap, and forward slip were found and presented for different values of backward and forward tensions, supply oil concentration values, and rolling speeds. Results show that the higher oil concentration leads to more lubricant pressure buildup, a thicker film, and a smaller contact ratio, which consequently reduce friction and total rolling pressure. Interstand tensions have a similar effect on film thickness, but results show that backward tension, which is more efficient than forward tension, has a critical effect on determining the lubricant inlet condition, which improves lubrication for the whole roll bite.

Choosing the materials performance and the form of an indenter for arrangement of texture at the surface of skin mill rolls

The fraction for forming texture of rolls surface of the training mills is investigated in this work. The fraction from various manufacturers has been estimated by comparing the most important characteristics. Metallographic studies of the steel fraction microstructure were carried out on the MEIJI 2700 optical microscope (Japan). Automated processing of measuring results of various shapes indenters microhardness was conducted. Comparing the obtained results with the characteristics declared by the manufacturers was carried out. The rolling roll surface microstructure with which the texture of the cold-rolled strip surface is formed, is investigated in the paper. Roller steel widely used at present as well as the most common methods of rolling roll surface microrelief forming, such as mechanical and electroerosion ones, are discussed in the work. It was established that with the electroerosion method, a more uniform structure with a smoothly changing microrelief was formed on the surface of the roll as compared with the mechanical action of the abrasive. According to the results of the research, recommendations were formulated on the use of the fraction that has the best performance characteristics and which allows one to obtain surface roughness by transferring it to the surface of a cold-rolled strip in accordance with the requirements of consumers.

Cold-rolled magnesium hydride strips decorated with cold-sprayed Ni powders for solid-state-hydrogen storage

The present work reports for the first time application of cold spray coating for doping plastically deformed Mg-strips by different concentrations of fine Ni powders. For present study, Mg rods were cold-rolled for 300 passes and then coated by Ni fine powders, using a cold spray process operated at 150 °C under high argon gas pressure. The Ni powders were pelted into Mg-substrate through the high-velocity jet at a speed of 500 m/s. Under these preparation conditions, Ni powders were plastically deformed at the surface of Mg strips to create numerous pores and cavities, worked as hydrogen diffusion gateway. The as-coated Mg sheets with 3-Ni layers (5.28 wt%) possessed good hydrogenation/dehydrogenation kinetics, implied by a short absorption/desorption time (5.1/11 min) of 6.1 wt% hydrogen at 150 °C/10 bar and 200 °C/200 mbar, respectively. The fabricated solid-state hydrogen storage nanocomposite strips revealed good cyclability of achieving 600 cycles at 200 °C without failure of degradation.

Roller Stress and Strain in a Broad-Strip Cold-Rolling Mill

On the basis of SIMULIA Abaqus finite-element software, the stress and strain in the rollers of a four-high rolling mill may be mathematically described. The convex–concave (CVC) profiling of the rollers and the axial shift of the working rollers are taken into account here. The transverse profile of the cold-rolled strip obtained by simulation is verified experimentally. The influence of the axial shift and hydraulic flexure of the working rollers on the stress–strain state of the working rollers in cold rolling is studied. It is established that the control procedures employed for the 2100 four-stand broad-strip cold-rolling mill at PAO Severstal permit broad regulation of the transverse strip-thickness variation in rolling without significant increase in stress in the working rollers. The proposed model of the roller system is recommended for use in improving the CVC profiling of rollers and assessing roller life in sheet production.

Study on Amplitude and Flatness Characteristics of Elastic Thin Strip under Fluid–Structure Interaction Vibration Excited by Unsteady Airflow

Based on unsteady airflow excitation and elastic thin strip vibration theory, a SI-FLAT flatness meter was taken as the research object, and an amplitude–residual stress simulation analysis model of the cold rolling strip under aerodynamic loads was established by using ANSYS Workbench. First, the influences of fluid–structure interaction on the strip amplitude distribution and the flatness calculation deviation were analyzed. It was found that the analysis with fluid–structure interaction matched the actual measurement of the flatness meter better. Then, the influences of different aerodynamic loads and tensions on the strip midpoint amplitude and the flatness calculation deviation were analyzed. It was found that when alternating aerodynamic loads increased, the strip amplitude increased in the form of a quadratic polynomial. However, when the tensions decreased, the strip amplitude decreased exponentially. The strip dimensions also influenced the amplitude of vibration: The wider and thinner the strip, the larger the amplitude. Finally, the influences of different flatness defects on the strip amplitude distribution and the flatness calculation deviation were analyzed. The deviation was serious on the strip edge, and the fluctuation characteristics of the deviation were opposite to those of the initial flatness defects.

Optimum run parameters in cold strip rolling

The process of strip rolling is analyzed using engineering mechanics and the theory of plasticity, and presented through a closed form procedure. The effect of input running parameters on the process is presented quantitatively by explicit expressions. The presented expressions are simple to implement on any personal computer, and their execution time is fast. The procedure provides the tools for selecting optimal operating conditions and avoids defects that lead to failure. The minimum required friction to prevent roll-strip skidding is determined. Forward slip as a function of friction and the location of the neutral point on the roll was also determined. The results obtained from this study were found to agree reasonably well with those obtained from the literature. One application of the proposed analysis is demonstrated in the optimal design of cold strip rolling. The optimal solution improved the objective function of maximizing the process outcome by 696%.

Hamilton‐based adaptive robust control for the speed and tension system of reversible cold strip rolling mill

SummaryThe adaptive robust control problem for the speed and tension system of reversible cold strip rolling mill is studied based on the Hamilton theory in this paper. First, the dissipative Hamilton model of the rolling mill system's speed and tension outside loop is built through pre‐feedback control, and then, dissipative Hamilton controllers are designed by utilizing the interconnection and damping assignment and the energy shaping method. Second, in order to realize tensiometer‐free control and adaptive robust control for the perturbation parameters and load disturbance, full‐order state observers and adaptive robust controllers are designed for the rolling mill system's speed and tension outside loop by using the “extended system + feedback” method. Third, robust controllers for the rolling mill system's current inside loop are designed based on the cascade control thought, so as to realize the tracking control for the speed and tension of reversible cold strip rolling mill. Theoretical analyses show that the resulting closed‐loop system is stable. Finally, simulation research is carried out on the speed and tension system of a 1422‐mm reversible cold strip rolling mill, and simulation results verify the validity of the proposed control strategy in comparison with the decentralized overlapping control strategy.

State of production sheet steel rolled stock in the world and tendencies of development of cold strip rolling mills

The conditions of production and the most relevant directions of development of technology and equipment of cold rolling mills for the production of thin flat rolled steel are investigated, analyzed and summarized. A comparative analysis of cold rolling technology is carried out, which is implemented in continuous and reversed modes of mill. The technological limitations and criteria for the development of deformation modes on cold rolling strip mills, which allow to expand the assortment towards a smaller thickness, are given. A method for determining the thickness is proposed, and a series of thicknesses of thin (1.5-1.8 mm) hot-rolled break-down are recommended for the production of tinplate of single rolling and thin strips of high quality. The method of calculation schedule drafting on a specific mill is developed. The technique of determination of the smallest thickness of a strip on a concrete mill is presented, taking into account the influence of rigidity of the working cage and features of the force load of the roller node with a decrease in the thickness and width of the strip. The use of the above materials allows to select and justify the optimal variant of cold band rolling technology, as well as to develop rational deformation modes that ensure the implementation of the cold rolling process with maximum efficiency, given the desired range and the required volume of thin cold-rolled sheet steel or tinplate. As a result of taking into account the features of the force interaction of the thin strip with the rolls during cold rolling and the rigidity of the working stands of the mill, the accuracy and reliability of determining the parameters are increased, it opens additional possibilities for expanding the range of cold rolling mills towards smaller thicknesses.

Increasing the chatter instability speed limit in cold strip rolling using wavy layered composite plates as a damper

High rolling speed and high reduction are the optimal conditions for increasing the production in the cold strip rolling process. On the other hand, increasing the rolling speed and the reduction induce chatter phenomenon. This phenomenon reduces the quality of production and causes serious damages to the devices. This research studies the feasibility of using thin wavy-layered composite plates in the role of chatter vibration damper in cold strip rolling mills. For this purpose, the behavior of composite plates subjected to the harmonic displacement was simulated using the finite element method to estimate their damping coefficient. In addition, some experimental studies were conducted to validate the simulation results. Afterward, the rolling process and the rolling mill structure were simulated while the composite plates were connected to the rolling stand. The results show that the connection of the designed wavy-layered composite plates to the rolling mill stand columns can control the chatter vibrations in the whole mill and can significantly increase the critical limit of chattering speed of the rolling process.

Adaptive Nonsingular Terminal Sliding Mode Backstepping Control for the Speed and Tension System of the Reversible Cold Strip Rolling Mill Using Disturbance Observers

In order to weaken the influences of system uncertainties and coupling items on the coordinated tracking control performance of the speed and tension system of the reversible cold strip rolling mill, an adaptive nonsingular terminal sliding mode (ANTSM) backstepping control strategy using disturbance observers is proposed. First, time-varying gain extended state observers (TVGESOs) are constructed to dynamically observe the system's mismatched uncertainties, which weaken the initial peak phenomenon of the traditional extended state observer (ESO), and effectively improve the system's tracking control precision. Next, based on the backstepping control and the second order sliding mode integral filters, adaptive nonsingular terminal sliding mode controllers (ANTSMCs) for the speed and tension system of the reversible cold strip rolling mill are designed, which solve the “differential explosion” problem of conventional backstepping control, and make sliding mode variables converge in finite time. Again, neural network adaptive method is used to approximate the system's matched uncertainties, and the approximation values are introduced into the designed controllers for compensations. Finally, simulation research is carried out on the speed and tension system of a 1422 mm reversible cold strip rolling mill by using actual data, and the results show the validity of the proposed control strategy.

Stability Loss and Defects in Coils of Cold-Rolled Strip

Abstract—Shape defects in coils of cold-rolled strip are analyzed. An algorithm for assessing the stability loss of coils is proposed, on the basis of a fundamentally new approach to calculating the stress–strain state in strip winding on the drum of the cold-rolling mill. Methods are recommended for preventing the following defects of coils of cold-rolled thin steel sheet: sagging, folded structure, mutual slip of the layers, and telescopic distortion.

Influence of profile indicators of hot-rolled strip on transverse thickness difference of cold-rolled silicon steel

In order to evaluate the transverse thickness difference of cold-rolled strips according to the information of hot-rolled strips and scientifically guide the setting of the indicators of the hot-rolled silicon strip, the influence model about the relation of the transverse thickness difference of cold-rolled strip to the profile indicators of hot-rolled strip is established in this paper based on simulation results. The transverse thickness difference of cold-rolled strip predicted based on the influence model have strong correspondences to the measured data. Based on the influence model and the statistical analysis of the measured data, the control criterion of the profile indicators of hot-rolled silicon steel according to the requirements for the transverse thickness difference of cold-rolled strip are finally recommended. The simulation results show that the transverse thickness difference of cold-rolled strip is quadratic nonlinearly related to the wedge and crown of hot-rolled strip. The influence model and statistical data analysis indicate that reducing the edge-drop of hot-rolled strip is beneficial to restrain the transverse thickness difference of cold-rolled strip.

Research on flexible roll profile electromagnetic control technology in precision rolling mill

To obtain a better strip shape control method, this paper proposes roll profile electromagnetic control technology (RPECT) based on induction heating technology and the principle of metal thermal expansion. Using the thermally driven and internal constraint mechanism of the electromagnetic stick, the technology innovatively converts the energy of induction heating into a thermodynamic hybrid power source, which achieves segmented micro-scale flexible roll profile adjustment and enhances the capacity for strip shape control. To research the technology, an electromagnetic control roll (ECR) with five control regions is built based on a ϕ560 × 2180 mm roll, and an electromagnetic-thermal-mechanical coupling model is established. Based on the model, the typical roll profile curves obtained by the ECR are researched, the strategy of increasing the growth rate of the roll crown is analysed, and the applications of RPECT in strip shape control and cold rolling are discussed. Finally, a roll profile electromagnetic control experiment platform is established to verify the model accuracy and feasibility of RPECT. The results show that RPECT can realize flexible roll profile adjustment and that the model has sufficiently high computational accuracy to research the roll profile of multi-segment RPECT.

Plate profile control during ultra-thin strip rolling utilizing work roll edge contact

During ultra-thin strip cold rolling, a phenomenon of work roll edge contact always appears. Very serious work roll edge contact and an edge wave occur when the strip thickness decreases; however, it is difficult to eliminate these problems with traditional control methods. To accurately analyse the influence of the mechanism of work roll edge contact on the strip shape control for ultra-thin strips, a finite-length semi-infinite body model of the roll is established based on the boundary element method. Then, a new work roll edge contact model which is applied to the rolling process of a laboratory twenty-high mill was established. The results show that when very serious work roll edge contact and an edge wave occur, the strip shape defect cannot be eliminated by traversing the first intermediate roll. Therefore, the roll gap is adjusted by utilizing work roll edge contact to improve its profile.

Effect of electropulsing treatment on static recrystallization behavior of cold-rolled magnesium alloy ZK60 with different reductions

Effect of electropulsing treatment (EPT) on recrystallization behavior of cold-rolled Mg alloy ZK60 strips was investigated. It was found that EPT significantly improved nucleation rate and migration ability of grain boundaries, leading to accelerated recrystallization of the deformed metals at relatively low temperature. After the recrystallization induced by EPT, the average grain size of 20% rolling reduction samples decreased from 113 μm to around 10 μm, meanwhile the typical basal-type texture of the cold-rolled sample was weakened. EPT was normally accompanied with a thermal and an athermal effects. The athermal effect played a dominated role in increasing nucleation rate, while the thermal effect promoted grain growth. A fewer recrystallized grains originated along the grain boundaries in the 10% reduction samples, while most of the recrystallization took place inside the twins in the 20% reduction samples.