Rolling Line Research Articles

FEM Modelling of Weld Damage in Continuous Cold Rolling of MIG/MAG Butt-Welded Stainless Steel Strips

Weld line fracture of butt-welded strips in stainless steel continuous rolling has been studied by numerical simulation using ForgeNxT®. The simulation plan includes weld line geometry as well as weld metal constitutive model parameters. The damage criterion used is the non-dimensional Latham & Cockroft function near the singular points of the weld line. Results are confronted to qualitative observations of fracture frequency and fracture initiation loci on the rolling line. Not surprisingly, the protrusion height of the weld line with respect to the strip top surface is found to be a major factor of risk. A second one pertains to the nature of the alloys used: due to the mushroom-like weld line cross-section geometry, damage at the top surface junction of the base metal and the weld metal becomes critical when the weld metal is harder than the base metal. Finally, on the rolling line investigated, prior to rolling properly speaking, the strip goes through a scale-breaking unit followed by acid pickling to eliminate oxides; the multiple, reverse plastic bending applied there contributes significantly to ductile damage, completing the explanation of why the fracture initiation locus is always found to be the same on the rolling line.

Using feed-forward perceptron Artificial Neural Network (ANN) model to determine the rolling force, power and slip of the tandem cold rolling

In this paper, an Artificial Neural Network (ANN) is used to investigate the influence of rolling parameters such as thickness reduction, inter-strand tension, rolling speed and friction on the rolling force, rolling power, and slip of tandem cold rolling. For this reason, the rolling power was derived for 195 various experiments through a series of observation tests. The network is trained and tested using real data collected from a practical tandem rolling line. The best topology of the ANN is determined by Broyden–Fletcher–Goldfarb–Shanno (BFGS) training algorithm and error, and nine neurons in the hidden layer had the best performance. The average of the training, testing, and validating correlation coefficients data sets are mentioned 0.947, 0.924, and 0.943, respectively. The obtained results show MSE value 4.2 × 10−4 for predicting slip. In addition, the effect of friction and angular velocity condition on the cold rolling critical slip phenomena are investigated. The results show that ANNs can accurately predict the cold rolling parameters considered in this study.

Application of Pattern Matching in Heating Furnace – Rough Rolling Process

Hot continuous rolling is a complex industrial process. Aiming at the problems of difficult optimization control, information island between process and strong coupling between parameters in 2250 mm rolling line of a steel plant, a parameter optimization method based on multi-level pattern matching is proposed, which is applied to the heating furnace – rough rolling link to adapt the best operation parameters in the current superior operational pattern library so as to improve the product quality of transfer bar. For the situation that the multi-level matching method cannot find the optimal operation mode, an input-output prediction model based on fuzzy neural network is established and particle swarm optimization algorithm is used until the output optimal operation parameters meet the requirements, and updates the new optimal mode to the superior operational pattern library to complete the expansion of the library. The simulation results show that the minimum relative error between the optimization results and the actual operation parameters is about 0.44%, which proves the feasibility of the pattern matching and evolution strategy, so as to achieve the purpose of improving the quality of hot rolling products and improving the enterprise efficiency.

Predicting of Roll Surface Re-Machining Using Artificial Neural Network

The paper presents a model for predicting the roll wear in the hot rolling process. It includes all indicators from the entire continuous rolling line that best predict the roll wear in the hot rolling process. Data for model development were obtained from annual production on the first rolling stand of the continuous roll mill. The main goal of the research was to determine significant parameters that affect the wear of the roll in the process of hot rolling. It has been found that the amount of rolled material before the re-machining of the roll surface has the greatest impact on the life of the roll contour. Therefore, the amount of material rolled before re-machining of the roll was used to estimate the wear of the roll. An artificial neural network was used to predict this amount of rolled material and was validated using data from one-year production.

Pareto multi-objective optimization of tandem cold rolling settings for reductions and inter stand tensions using NSGA-II

In this paper, multi-objective optimization of tandem cold rolling settings for reductions and inter-stand tensions using NSGA-II and Pareto-optimal front are investigated. In this multi-objective optimization, the total power consumption and uniform power distribution are suggested as objective functions, and reduction thicknesses in each stand and inter stand tensions were selected as problem decision variables. Analytical formulations are introduced to determine the rolling forces and power based on the Stone approach. Then, the main variables of the optimization problem, objective functions, linear and nonlinear constraints, are defined. Moreover, some empirical constraints are introduced regarding the practical limitations of cold rolling equipment and the mechanical properties of the material. At first, considering the conditions of a practical tandem rolling line, single-objective optimization is performed separately, and finally, NSGA-II was used for multi-objective optimization. Compared to the initial setting of the rolling line, the obtained single objective schedules have better performance. Moreover, the multi-objective results based on the Pareto-optimal front are investigated, and an optimized setting for rolling schedule has been suggested. Using this proposed schedule the total power consumption is reduced by more than 11% comparing to the initial setting and more uniform power distribution has been obtained in rolling stands. The normalized reductions calculated from this investigation are compared with numerical and experimental results found in the literature and the similarity was observed in the pattern of thickness reduction distribution.

Assessment of the Impact of Wear of the Working Surface of Rolls on the Reduction of Energy and Environmental Demand for the Production of Flat Products: Methodological Approach.

An important element in the correct operation of the rolling mill is appropriate planning of the condition of the rolls because this factor constitutes a limiting element in the production process. In this work, with the aim of indicating the method of proper use of production tools–metallurgical rollers during their operation in a Polish rolling mill, the wear and tear of particular kinds of rollers built in the whole rolling set was determined. For this purpose, data were collected at the strip mill from grinding processes, production reports and roll files, while our statistical analysis, laboratory calculations and measurements were used. These data were used to perform computer calculations on the service life of metallurgical rollers installed in the rolling line. Wear mechanisms were identified in industrial practice. The characteristic features of roller wear were investigated using non-destructive tests, including eddy currents. The laboratory tests reproduced the wear mechanisms in very hot rolling rolls. The statistical method for determining the service life of working rolls indicated that their reconstruction is determined both by natural physical phenomena and inappropriate use in about 30% of cases, mainly in the F5 and F6 cages of the finishing unit. Calculations indicated the possibility of replacing the working rolls made of high chromium cast iron Hi-Cr with those made of HSS in the F5 and F6 cages, which will contribute to an increase in the durability of the rolls, a reduction in production costs and a decrease in the number of roll rebuildings. The service life of HSS rolls is 14,000–20,000 Mg of rolled material per 1 mm of wear on its surface in the radial direction, compared to 2000 Mg for rolls made of high chromium cast iron Hi-Cr. The constructed model may be a source of information for further analyses and decision-making processes supporting the management of metallurgical enterprises. On the basis of the constructed model, it was shown that the analyzed projects, depending on their type and technical specification, will bring measurable economic benefits in the form of reduced annual energy consumption and environmental benefits in the form of reduced carbon dioxide emissions into the atmosphere. The constructed model of the roll consumption, verified in the real conditions of the rolling mills, will contribute to the fulfillment of energy and emission obligations with the EU.

Requirements for the mass and heating of blanks selection in automated ring-rolling complexes

The conditions for choosing a billet mass for the manufacture of an ring part on an automated ring-rolling complex, the features of heating the billets in the conditions of an automated line and heat treatment of manufactured parts are considered. The expediency of differentiated assignment of tolerances for the rings’ sizes after ring rolling, depending on their type, conditions of subsequent mechanical treatment and operation, is substantiated. Attention is focused on the need to design a ring-rolling technology with control of the billet parameters not only during the cutting, heating and pressing operations, but also before the ring-rolling operation, especially when using reheating. To evaluate the technological temperature state of the ring blanks at different stages of manufacturing in an automated line, it is offered to use the billet’s “conventional temperature”, which is determined in the 2nd zone from the middle of the billet. The use of single gas heating of billets in rotary-hearth furnaces in the manufacture of annular billet on an automated line is justified. The problems of the automated ring rolling line and the heat treatment complex synchronization are determined. It is shown that the clock capacity of the automated ring rolling line significantly exceeds the clock capacity of the planned heat treatment complex. It is concluded that it is necessary to develop software for their synchronous operation.The proposed recommendations are intended for the development of technological support for an automated ring-rolling complex at OJSC “PAK Plant” as part of “BELAZ-HOLDING”.

Modernization of screw rolling technology in a multi-roll mill

Analysis of the screw rolling process showed that change in axial speed of the roll along the length of the roll groove of cross rolling mill does not correspond to the required character of change in the speed of deformed billet. The process proceeds under intense axial compression, as a result of which a significant part of the metal crimped in the contact zone is displaced into the inter-roll area. It is shown that direction of the axial force in the corresponding zone of the roll groove depends on the value of inclination angle of the considered roll section generatrix to the rolling axis. The proposed modernization of screw rolling technology makes it possible to carry out deformation of the billet under the influence of intra-focal axial tension. The task is accomplished by rolls calibration when at the beginning there is a ridge section of the roll on which the axial force is directed against rolling direction; and behind it, a pulling one, on which the direction of the axial force coincides with rolling direction. Such a scheme of the axial forces action in the zone of intensive billet reduction creates the most favorable conditions for the metal flow in axial direction. A technical solution is proposed for the implementation of the stage of the billet gripping by rolls, and description of this stage and the process stationary phase is given. The cardinal change in the billet deformation condition after modernization makes it possible to reduce the power load on the work rolls, increase their efficiency and reduce energy costs during rolling. This will ensure the rolling of a solid billet in a roughing mill with a higher stretch, create the preconditions for expanding the size and grade assortment when obtaining rods in radial-displacement rolling mills and at production of pipes in rolling lines with the Assel mill. The range of finished products can be significantly expanded due to the production of thin-walled highprecision pipes.

Digital twin for combined casting and rolling line control

Digital twin for combined casting and rolling line control

A finite-element-aided ultrasonic method for measuring central oil-film thickness in a roller-raceway tribo-pair

Roller bearings support heavy loads by riding on an ultra-thin oil film (between the roller and raceway), the thickness of which is critical as it reflects the lubrication performance. Ultrasonic interfacial reflection, which facilitates the non-destructive measurement of oil-film thickness, has been widely studied. However, insufficient spatial resolution around the rolling line contact zone remains a barrier despite the use of miniature piezoelectric transducers. In this study, a finite-element-aided method is utilized to simulate wave propagation through a three-layered structure of roller-oil-raceway under elastohydrodynamic lubrication (EHL) with nonlinear characteristics of the i) deformed curvature of the cylindrical roller and ii) nonuniform distribution of the fluid bulk modulus along the circumference of the oil layer being considered. A load and speed-dependent look-up table is then developed to establish an accurate relationship between the overall reflection coefficient (directly measured by an embedded ultrasonic transducer) and objective variable of the central oil-film thickness. The proposed finite-element-aided method is verified experimentally in a roller-raceway test rig with the ultrasonically measured oil-film thickness corresponding to the values calculated using the EHL theory.

Development of an Automatic Elastic Torque Control System Based on a Two-Mass Electric Drive Coordinate Observer

Development of control system based on digital twins of physical processes is a promising area of research in the rolling industry. Closed-loop control systems are developed to control the coordinates of two-mass electromechanical systems in order to limit the dynamic loads on the equipment of main rolling lines. These control systems are based on observers (digital shadows) that indirectly detect (reconstruct) the roll speed and the elastic torque of the shaft (spindle) in real time. Notably, observers are required to work fast in order to reconstruct transients attributable to shock (impact) loads. Literature review shows that the known observers, which use complex algorithms to compute coordinates, do not respond fast enough. The paper analyzes the kinematic diagram of Mill 5000, a plate rolling mill. It presents oscillograms that prove that the elastic torque does oscillate as the rolls grip the strip dynamically. The authors hereof have developed an observer that reconstructs the coordinates of the uncontrolled mass (the shaft) and the spindle torque from the parameters of the controlled mass, namely the torque and speed of the motor. The paper further rationalizes an approach that consists of simulating the processes on a model to further directly configure them on the object. The authors analyze the transients of the reconstructed two-mass system coordinates, which are associated with the rolls gripping the strip. The paper compares data against oscillograms recorded on the mill itself. The accuracy is satisfactory. The proposed observer has been used to developed a three-loop automatic speed control system for the uncontrolled mass. Controller configurations are substantiated. The paper shows coordinates obtained by simulation modeling as functions of time. It further presents experiments run on Mill 5000; the conclusions are that the amplitude and oscillations of the elastic torque drop significantly. The paper concludes with recommendations on industrial adoption of the observer and the novel electric drive coordinate control system. Study presented herein substantiates and implements a concept of developing algorithms that solve specific problems and are readily implementable on the existing equipment without need for additional computing devices. The contribution of the paper consists of stating and solving the problem of developing and testing an automatic elastic torque control system for the shaft of a heavy-duty rolling mill. This system has been implemented in the form of algorithms that run in the software of the existing industrial controllers (PLCs). It is simple and performs well. It does not need additional sensors or computers to be implemented, nor does it rely on complex computational algorithms. Such algorithms are based on computational tables that require a priori data on numerous process parameters. In our literature review, we have not come across any industrial implementation of such algorithms on hot-rolling mills.

A Study on Ball-Race Contact in Angular Contact Ball Bearing during Rotation

Angular contact ball bearings (ACBBs) are widely used in rotating machinery due to their heavy load-carrying capacity and excellent accuracy in high-speed operation. However, employing an ACBB requires a careful analysis because the characteristics of the ACBB significantly depend on the operating condition. The ball-race contact condition of an ACBB is one of the most important factors that can change its properties. This study deals with the ball-race contact behavior concerning several important parameters, such as rotational speed, unloaded contact angle, and external loading. Between the ball and race under loading, an elliptical contact area is formed, in which pure rolling lines may exist. In the region other than the pure rolling lines, sliding dominates due to differential slippage in the elliptical contact area. We investigated the behavior of ball-race contact in terms of the pure rolling lines. A computational procedure was presented to determine the pure rolling lines. Through simulations, it was found that rotational speed, unloaded contact angle, axial preload, and radial load significantly affected the number and locations of pure rolling lines. The presented results are useful for investigating and estimating the sliding friction torque for ACBBs.

Задачи технологического обеспечения автоматизированного кольцераскатного комплекса

The physical foundations and advantages of ring rolling are described. The materials science and technological processes of manufacture of products with its use are generalized. An analysis of the equipment of an automated ring rolling line was carried out, which showed that it is a complex and expensive technical solution. Moreover, the organization of the line with maximum load and efficiency is not included in the supplier’s tasks. The requirements for the maximum load of the line and its efficient operation have been determined. It is shown that the use of the experience of creating automated production of railway wheels when creating an automated production of ring blanks is impossible due to the need to ensure the production of rings of different structural shapes from different steel grades with different temperature ranges of plastic deformation and with different (from a hundred to several thousands) annual production programs. This requires the use of a different ratio of the radial and axial forces of the ring rolling, different technological equipment, taking into account different stiffness of the rings and their tendency to deformations during processing, transportation and cooling, a special development of mechanization means for readjustments. It is impossible to work out in advance all the technological options for the production of rings of different standard sizes on an automated line. In this regard, for the effective work of the complex, it is necessary to develop technological support and software for the manufacturing processes of each ring, to provide for the possibility of adjusting technological processes directly on the automated line with the participation of operators. On this basis, the tasks of technological support for the operation of the automated ring rolling complex at the OJSC “BELAZ” were formulated.

A new dust removal technology used in hot rolling mills: Atomized spray with higher dedusting efficiency

In order to effectively remove the oxide scale dusts in the hot rolling strip steel, this study focuses on the principle of atomized spray and use it to develop a new dust removal technology used in the hot rolling mills. Through establishing a mathematic model of particle collision, 4 critical factors most affecting the dedusting efficiency are analysed: the diameter of nozzles, the diameter of water droplets, the diameter of dust particles, and the spray pressure. For further discovering the principles of the movements and concentration changes of the dust particles, a numerical model is established based on the gap space between the hot rolling mills. 2 scenarios of running the atomized dedusting or not are simulated to compute the dedusting efficiency so that the dedusting effect of the atomized spray can be confirmed for the hot rolling. The case study on the 1580 mm hot rolling line in WISCO plant demonstrates a successful dedusting efficiency of 93.50% on the R2 rough rolling mill. The spray pressure of 0.5 MPa and the nozzle diameter of 1.4 mm are appropriate to generating the proper water droplets with the diameter of 71.1 μm in order to capture the dust particles with the mean diameter of 27 μm. The study on the principles and simulations of the atomized spray facilitates more efficient dust removal for cleaner hot rolling mills.

Dynamics of exit section of automatic mill of pipe rolling line

Nonuniformity of pipe wall thickness is one of significant indices, determining quality of hot-rolled seamless pipes. One of the reasons of increased nonuniformity arising is dynamics of exit section mechanisms of pipe rolling line (PRL). Results of study of mandrel holding mechanism dynamics of PRL presented. Dynamic models of exit section, accounting parameters of technological process and inertia of a rolled hollow billet elaborated, which enabled to determine the character of dynamic processes at the exit section of PRL automatic mill. Differential equations of exit section elements motion at the exit section of PRL automatic mill were made up. The solution of the differential equations system was obtained in a numerical form by application of Runge‒Kutta method for correspondent dynamic models of exit section based on the example of calculations for ТПА-350 automatic mill. The pattern of dynamic processes arising at the exit section was specified at realization of the whole technological process of a hollow billet rolling at automatic mill, taking into consideration alternative action from the side of deformation center and mass of the rolled hollow billet. It was shown, that the specified solution of the task for three advanced dynamic models of mechanical system considerably differs from those of the known mathematical models. It was established, that the dynamics of the mandrel holding mechanism of ТПА-350 automatic mill equivalently form the mechanism of finished pipes geometry forming. Analysis of dynamic models of the mill exit section enabled to select the necessary technological and dynamic parameters of the mechanical system, to determine stable modes of hollow billets rolling at the ТПА-350 automatic mill. Results of the study of dynamics of exit section ТПА-350 automatic mill presented. A scheme of modernization of the exit section ТПА-350 automatic mill proposed, which enables to realize rational modes of operation accounting level of mechanical system dynamics and to control quality (geometric parameters) of the rolled pipes.

Strip Crown Prediction in Hot Rolling Process Using Random Forest

This paper established a model based on an ensemble method to predict strip crown using 230,000 coils of data obtained from a hot rolling line. Before modeling, a specific method was proposed to reduce noise and remove outliers, and a new dataset of 5657 samples was generated. Parameter tuning considering mean squared error (MSE) was carried out to establish three machine learning models including support vector machine (SVC), regression tree (RT), and random forest (RF). Determination coefficient (R2), mean absolute error (MAE) and root mean squared error (RMSE) were used as indicators to evaluate the prediction of models. Results showed that the RF had the best performance with the highest R2 of 0.707, as well as the lowest RMSE of 5.66 μm. Moreover, an additional method that repeated the three models 100 times was developed, and box plots were used to visualize the distribution of R2, MAE and RMSE. RF can correct for decision trees to reduce overfitting to their training set, improving the generalization, and in this paper, the trained RF which had stable performance is considered as the most recommended model. After that, for RF, rankings of rolling process variable were validated to make a comparison with the existing physical understanding.

Rarely Occurring Defects on Tinplates

This paper deals with rarely occurring defect on the surface of the tinplates produced in the conditions of U. S. Steel Košice, s.r.o. at the cleaning section of the continuous annealing line (CAL), which was caused by burnt. Random occurrence of such surface imperfections was observed within the short period of time (two months) for various continuous annealed tinplate grades, i.e. TH415, TH435 or TH550 with the thickness of the materials in the interval of 0.172 – 0.240 mm. Surface defects caused by burnt (thermal attack) manifested in different ways. Their appearance on the sheet surface was spot with regular or irregular circle shape, as well as line with the length of up to 2 mm oriented not directly in the rolling direction. By observing of the imperfections in scanning electron microscope (SEM) it was found that the surface of the steel substrate was always compact in the defective areas with clearly visible rolling lines. Foreign material, EDS analysis of which revealed that its chemical composition was on the basis of Fe and Cr, was deposited on the surface of the base material. The appearance of the foreign material shape indicated that it was in the liquid state at the time of incidence on the steel substrate surface. Metallographic analysis from the longitudinal metallographic sections through the defective areas revealed that the substrate under the spot defect with regular circle shape had thermally influenced microstructure. Similar manifestations of the microstructure influence were observed for the line defects. In the case of the spot defect with irregular shape, the microstructure of the material was not influenced, what indicated that the particle of liquid metal was solidified at the time of incidence on the plate surface. After revising technical conditions of the cleaning section of CAL, this type of imperfection was suppressed.

Numerical Study of the Process of Hot Helical Rolling of Hollow Billets with a Small-Diameter Bottom

The paper presents the results of numerical simulation and experimental studies of the process of helical rolling of billets having a small-diameter bottom. An improved technology for producing small-diameter billets without the need for subsequent machining of the inner surface is proposed. Pilot-scale piercing and calibration of the billets was performed using an automated helical rolling line.

Finite Element Analysis of the Deformation Behavior of the Up and Down Roll Differential Diameter Rolling for Medium Plate

In order to realize the rolling technology with different reduction of upper and lower surface in the production of medium and heavy plate, a rolling technology with the same rolling line speed and different diameter of upper and lower rolls was adopted in a factory, and good results were achieved. This technology is different from the previous large roll diameter difference rolling and differential speed rolling. Large roll diameter difference rolling is an asynchronous rolling technology, which uses the difference of upper and lower roll diameter to cause the different linear speed of rolling, so as to achieve the purpose of upper and lower pressure rolling. It is mainly used in the production of section steel, and belongs to the asymmetric rolling condition. Under the condition of asymmetric rolling with unequal roll diameter, a three-dimensional large deformation and asymmetric rolling FEM model is established by using the finite element software. The stress and deformation behavior of the deformation area of the steel plate are analyzed. The fiber length changes along the longitudinal direction at different thickness positions and the shape change of steel plate in the rolling process are obtained. The results show that when the diameter of the upper roll is larger than that of the lower roll, the Mises equivalent stress, equivalent plastic strain and the change of the length of the longitudinal fiber in the deformation area are approximate distributed symmetrically along the center of the two sides, the center value of steel plate is small, and the upper and lower surface values are large; the equivalent stress of the lower surface is larger than the upper surface, and the minimum change of the fiber length appears about 1/3 of the thickness from the lower surface. Under the condition of asymmetric up and down rolling, the head of steel plate tends to down-bending. The maximum distance of the steel plate head buckle ∆y is 0.185 m, the bending radius is 6.519m and the bending curvature is 0.153.

Study of the dynamics of ТПА 350 automatic mill working stand elements

To form a necessary geometry of a hollow billet to be rolled at a pipe rolling line, stable dynamics of the base equipment of the automatic mill working stand has a practical meaning. Among the forces, acting on its parts and elements, significant by value short-time dynamic loads are the least studied phenomena. These dynamic loads arise during transient interaction of the hollow billet, rollers, mandrel and other mill parts at the forced grip of the hollow billet. Basing of the calculation scheme and dynamic model of the mechanical system of the ТПА 350 automatic mill working stand was accomplished. A mathematical model of dynamics of the system “hollow billet (pipe) – working stand” within accepted calculation scheme and dynamic model of the mechanical system elaborated. Influence of technological load of the rolled hollow billet variation in time was accounted, as well as variation of the mechanical system mass, and rigidity of the ТПА 350 automatic mill working stand. Differential equations of oscillation movement for four-mass model of forked sub-systems of the automatic mill working stand were made up, results of their digital calculation quoted. Dynamic displacement of the stand elements in the inter-roller gap obtained, which enabled to estimate the results of amplitude and frequency characteristics of the branches of the mill rollers setting. It was defined by calculation, that the maximum amplitude of the forced oscillations of elements of the ТПА 350 automatic mill working stand within the inter-roller gap does not exceed 2 mm. It is much higher than the accepted value of adjusting parameters of the deformation center of the ТПА 350 automatic mill. A scheme of comprehensive modernization of the rollers setting in the ТПА 350 automatic mill working stand was proposed. It was shown, that increase of rigidity of rollers setting in the ТПА 350 automatic mill working stand enables to stabilize the amplitude of forced oscillations of the working stand elements within the inter-rollers gap and considerably decrease the induced nonuniform hollow billet wall thickness and increase quality of the rolled pipes at ТПА 350.