Hot Rolling Mill Research Articles

An improved Pareto local search for solving bi-objective scheduling problems in hot rolling mills

Hot rolling scheduling is a complex decision-making optimization problem in the production management of the iron and steel industry. Comprehensively considering temporal and technical constraints of hot rolling production, we formulate a prize-collecting capacitated vehicle routing problem with time windows (PC-CVRPTW) involving special constraints and multiple objectives. Furthermore, this paper develops a Pareto local search (PLS)-based solving algorithm via leveraging problem-specific properties and implements three improvement mechanisms: (1) solution initialization with a greedy strategy; (2) promising solution selection with optimistic hypervolume contribution; (3) hybrid neighborhood exploration integrated variable neighborhood search with constraint programming. To validate the proposed method, computational experiments are conducted on a set of randomly synthetic and realistic industrial instances. The results compared with other variants of PLS and state-of-art algorithms demonstrate that the improved PLS algorithm is effective and can provide promising solutions for bi-objective hot rolling scheduling problems.

Evaluating surface heat flux in planar water-jet cooling of moving hot solid by inversely solving steady-state heat conduction

In steel-manufacturing industries, water-jet quenching of a moving hot solid is commonly used for run-out table cooling in hot rolling mills. Hence, the evaluation of the surface heat flux in the jet-impact region is necessary for precise temperature control. In this study, we developed an evaluation method for surface heat flux in the impact region by inversely solving the steady-state heat-conduction equation, considering the temperature profile on the reverse side of jet impingement. The main advantage was that the heat-flux distribution could be evaluated with a high spatial resolution. The developed method was validated using the exact solution of the heat-conduction equation. The inverse analysis was highly sensitive to the numerical scheme and small errors in the temperature profile on the reverse side. An appropriate numerical scheme and smoothing operation of the temperature profile allowed the reasonable evaluation of surface heat flux on the cooled surface. In addition, the developed method was applied to laboratory-scale cooling experiments to confirm its applicability. The heat-transfer characteristics of planar jet impinging on a moving solid were studied in the conditions that the temperature of the solid with 0.5 mm thickness was 200–600 °C, and its velocity was 1.5, 3.0, and 4.4 m/s. The heat flux in the jet-impact region depended significantly on these parameters.

The relative contributions of TWIP and TRIP to strength in fine grained medium-Mn steels

A medium Mn steel of composition Fe-4.8Mn-2.8Al-1.5Si-0.51C (wt.%) was processed to obtain two different microstructures representing two different approaches in the hot rolling mill, resulting in equiaxed vs. mixed equiaxed and lamellar microstructures. Both were found to exhibit a simultaneous Twinning Induced Plasticity and Transformation Induced Plasticity (TWIP ＋ TRIP) mechanism where deformation twins and α′-martensite formed independently of twinning with strain. Interrupted tensile tests were conducted in order to investigate the differences in deformation structures between the two microstructures. A constitutive model was used to find that, surprisingly, twinning contributed relatively little to the strength of the alloy, chiefly due to the fine initial slip lengths that then gave rise to relatively little opportunity for work hardening by grain subdivision. Nevertheless, with lower high-cost alloying additions than equivalent Dual Phase steels (2–3 wt% Mn) and greater ductility, medium-Mn TWIP ＋ TRIP steels still represent an attractive area for future development.

Interfacial slip verification and slip defect identification in shrink-fitted bimetallic sleeve roll used in hot rolling mill

Shrink-fitted sleeve rolls have several advantages including the ability to reuse shafts by replacing worn sleeves and the ability to apply to next-generation rolls. However, the authors’ previous simulation showed a “non-uniform slip” may appear between the shaft and the shrink-fitted sleeve even under free rolling and when no overall uniform slip condition is satisfied. In this paper, the rolling experiment is conducted by using a miniature rolling mill to verify the slip phenomenon realized by the numerical simulation. To understand the phenomenon, the slip defect formation and the slip growth are investigated by observing the slipped surfaces in detail. It is found that the slip defect starts from the contact of the surface roughness where the width of the defect coincides with the pitch of the machining feed. Eventually, the slip defect is developed by erosion wear and cohesive wear during the rolling and finally forming a large oval-shaped erosion groove at the end of the scratch. Finally, the fatigue strength of the sleeve roll is evaluated by considering the slip defect geometry observed from the experiment.

Study on Work Roll Vertical Vibration Under Periodic Spalling of the Oxide Film

The dynamic effect of work-roll oxide-film periodic spalling on vertical vibration in a hot strip rolling mill was studied. Based on dynamic monitoring test analysis, the friction of the work-roll surface under oxide-film periodic spalling is discussed. Using an average rolling pressure formula, the rolling force under the dynamic vertical vibration and the time-varying friction coefficient were found. A two-degrees-of-freedom dynamic system of the hot strip mill was established, considering the roller system symmetry. Based on the multiscale small-parameter perturbation method, the main resonance characteristic of work-roll vertical vibration has been explored. Using the 1780-mm hot strip mill in Chengde Iron and Steel Co., Ltd., the dynamic characteristics of the system are analyzed when oxide-film periodic spalling occurs on the work roll. The results are consistent with the test data, which show the effect of oxide-film spalling on vertical vibration. The simulation results for resonance characteristics show that the vibration of the system can be effectively reduced by increasing the damping and adjusting the stiffness of the system. In rolling production, it is very important to ensure the stability of the oxide film in order to reduce fluctuation. This study provides a reference for the operation and maintenance of a rolling mill in the strip production process.

Coordinated Management of Electrical Energy in a Steelworks and a Wind Farm

This article proposes a coordinated management of electrical energy in a steelworks and a wind farm that are connected to the same distribution network. The suggested solution seeks to improve the efficiency of the hot rolling mill, to reduce greenhouse gas emissions, to minimize the cost of the electrical energy utilized in the manufacture of steel coils, to increase the power system chargeability, and to guarantee power quality. The proposal consists of constituting a virtual plant (comprising the wind farm and the rolling mill) to be managed by a single operator. The approach is mainly focused on the management of the virtual plant reactive power. The algorithm proposed to optimize this reactive power is based on the so-called particle swarm optimization. Three optimization strategies are analyzed: minimization of losses in the distribution network, minimization of the voltage deviation at two of its nodes, and maximization of the displacement factor in both the rolling mill and the wind farm. Energy losses are reduced by up to 20% when adopting the first strategy in comparison to the least efficient case. Voltage variations are kept at less than 1% at both nodes when using the second strategy, whereas deviations between 1% and 5% are obtained when implementing the other two strategies. The study is based on actual measurements and simulation tests.

Development of new composition for sHSS steel used for hot rolling mill rolls at Magnitogorsk Iron and Steel Works

The paper presents the results of the complex scientific and research work directed on development of the new composition of sHSS steel for rolling mill rolls together with Magnito-gorsk Iron and Steel Works (MMK) and Magnitogorsk Mill Rolls Plant (MZPV). The first part includes the review of technical literature in the field of the results of roll steel examination by domestic and foreign researchers, investigation of structure and determination of properties of foreign rolling rolls, which were operated at the MMK hot rolling mill. The minimal level od sHSS steel properties for the working layer of a rolling roll, providing its operation reliability, is also determined. Laboratorial experiments were conducted at the second stage. The formed massif of ex-perimental data was processed using neural net, and as a result, the optimal chemical composition of the roll steel with high wear resistance and hardness was obtained. After processing of the re-sults of the planned experiment, the regression equation was obtained; it describes influence of the alloy chemical composition on wear resistance and hardness coefficients. Optimized composition of the alloy was developed at Magnitogorsk Mill Rolls Plant; it wad resulted in manufacture of the pilot roll sleeve in centrifugal machine. This roll sleeve was subjected to heat treatment according to the standard plant procedure. The final step included laboratorial testing of the pilot roll sleeve which was manufac-tured from steel with optimized chemical composition. It was determined that the developed composition is characterized by wear resistance increased by 27 % in comparison with the re-searched foreign analogue, as well as by similar qualitative parameters of the alloy microstructure.

Rolling of long-length rails with acceleration

The article explains a new temperature-speed mode of rolling long-length rails. Rails up to 50 m long were rolled on linear mills. The production of rails of longer length required the use of larger mass billets and equipment of a new design. At the modern rail-beam rolling mill, the number of stands has increased and some of the stands are combined into a continuous group. Universal rolling stands began to be used not only as calibration stands. Rails with a length of 100 m are rolled from large-mass billets on mills with a continuous reversible group of universal stands. A significant length of the billet leads to the formation of a «temperature wedge» – a decrease in temperature along the length of the rail during rolling in the last stand of the mill. The calculation showed that a decrease in temperature along the rail length can lead to an increase in its height. A similar problem existed in the production of thin sheet metal at continuous broadband hot rolling mill. Rolling the rolled metal in the finishing group of stands with acceleration made it possible to reduce the cooling time of rear section of the rolled metal and warm up the metal due to more intense deformation. The acceleration value is chosen such that at the exit from the finishing group of stands, temperature of the strip is the same along the length of the strip. In this paper, rolling rails with acceleration is proposed. The acceleration value should ensure the same neck temperature along the length of the rail in the mill last stand, which will reduce the height difference along the length of the rolled product. The same rails height along the length will reduce the cost of grinding and accelerate the rail laying, thereby increasing consumer demand and competitiveness of the product.

Quality‐relevant and process‐relevant fault monitoring based on GNPER and the fault quantification index for industrial processes

AbstractTraditional quality‐relevant fault monitoring methods focus on extracting the relationship between the global structural features of the process and quality variables but ignore the local features. At the same time, they lack the quantification of quality‐relevant faults. To solve these problems, a quality‐relevant and process‐relevant fault monitoring method and its fault quantification index based on global neighbourhood preserving embedding regression (GNPER) are proposed. First, by seeking the direction of maximum global variance, the global objective function is applied to neighbourhood preserving embedding algorithm, and the global neighbourhood preserving embedding (GNPE) model is established to fully extract the global and local information of process data. Second, on the basis of GNPE, through the idea of projection regression, the GNPER model is established to obtain mapping relationships among process variables and quality variables, and quality‐relevant subspace and process‐relevant subspace are extracted, the corresponding subspace statistics are established for fault monitoring. Finally, the fault quantification index is established for the faults in the two subspaces, which can provide more meaningful fault monitoring results. A numerical example, the hot rolling mill and the Tennessee Eastman (TE) process, verify the superiority and accuracy of the proposed method.

Development of a finite element model for calculation of the thermal field of coil rolled products in the thermomechanical process

A finite element model has been developed in the Deform-3D software package for calculating the thermal field of low-alloy steel coil rolled products during rolling in the finishing group of stands and cooling on the discharge roller table of the 2000 wide-strip hot rolling mill of PJSC Magnitogorsk Iron and Steel Works (PJSC MMK). The proposed model takes into account heat release during plastic deformation, cooling of the strip due to metal contact with air, heat transfer to the work rolls, cooling of the strip by water supplied in the process of interstand cooling and in the accelerated cooling unit on the discharge roller table. At the same time, the features of cooling by both upper and lower collectors are taken into account. To achieve the required coiling temperature, the possibility of differentiated activation of collectors of the upper and lower sections of the accelerated cooling unit was implemented, which was introduced into the finite element model. Cooling by water jets was updated by dividing the contact of the cooled strip with water into two zones - the area of water impact with the sheet surface and the area of film boiling. As a result of the analysis of the thermal state of the sheet, an assessment was made of the nature of its change depending on the characteristics of each stage of thermomechanical treatment (TMT). The use of the presented model in the development of TMT technological modes makes it possible to evaluate their correctness, as well as to provide the possibility of predicting the structure and properties formed over the thickness of rolled steel in the process of controlled rolling with accelerated cooling.P. P. Poletskov, S. V. Denisov, P. A. Stekanov, E. V. Braichev, and P. G. Adishchev, post-graduate student of the MTa-21-2 group, took part in the work.The work was carried out at the Nosov Magnitogorsk State Technical University with the financial support of the Ministry of Education and Science of Russia as part of the implementation of a comprehensive project to create high-tech production (Agreement with the Ministry of Education and Science of Russia No. 075-11-2021-063 dated 06/25/2021).

New integer programming models for slab stack shuffling problems

In the steel industry, a slab yard is a buffer that receives the slabs from the continuous casting and sends them to the hot rolling mill based on the hot rolling schedule. When a hot rolling schedule is released, several slabs are available for each rolling item, stored in different stacks in the yard. If the required slab is not on top of the stack, its above slabs must be first shuffled. The main problem is the slab stack shuffling problem related to selecting an appropriate slab for each rolling item to minimize the total number of shuffles. The present study considers two different variants of the slab stack shuffling problem based on the situation of the slab yard. A new integer programming model is proposed for each variant. Based on the properties of the problem, a theoretical analysis is derived to accelerate the models’ execution procedures. Then, the proposed models are applied to various numerical instances. Based on the results, optimal solutions can be obtained for practical scale problems in less than a few minutes. Finally, a real case study was conducted on a slab yard of a steel production company. Experimental results show that the proposed model for the classic problem version can reduce the total number of shuffles by 22.7%, on average.

열간압연 코일러 시스템의 코일 장력에 대한 최적 서보 제어

This paper designs an optimal servo controller for the coiler system in hot rolling mill in order to suppress the tension fluctuation of the tail-end part after a steel plate leaves the final stand of hot rolling mill. The state space model of the coiler system is firstly modeled. Next, the optimal servo controller combined with a disturbance observer is designed using the inverse LQ optimal control method and the full state observer algorithm. Finally, it is shown by a computer simulation that the proposed control system is very effective to control tension fluctuations between the pinch roll and the mandrel under disturbances.

Multi-Level Stacked Regression for predicting electricity consumption of Hot Rolling Mill

Predicting electrical power consumption is essential in many industries. This paper presents a method to predict total electrical power consumption in a certain period of Hot Rolling Mill (HRM) in steel mills. We adequately pre-processed operation data, including work schedule, work result, and power measurement. In addition, based on domain knowledge, we derived several useful variables relevant to power consumption. To predict power consumption, we developed a Multi-Level Stacked Regression model that combines the strengths of multiple prediction models. Real-world applications have dataset shift characteristics in which the covariance between features or distribution of the features changes over time due to frequent changes in the working environment. To verify the generalization accuracy of our model, we trained and tested our model for various training/test splits and compared it with several comparative models. Our model showed the best accuracy in all training/test splits. We verified whether the predictive model reflects the real-world environment well by analyzing the actual physical meaning of the essential features used in the predictive model.

Using the "minimum risk" method in the technical diagnosis of metallurgical equipment

The difficult operating conditions of metallurgical equipment due to dynamic loads require special attention when designing components in the field of reliability and fail-free operation. In order to increase the reliability and durability of the spindle drive unit of the rolling stand of the hot rolling mill "1680", it is proposed to switch from "oil mist" type lubrication systems to "oil-air" type systems for bronze liners and bearings of the balancing mechanism. The oil-air lubrication principle has undeniable advantages in terms of component lubrication, flow distribution, and provides a volumetric flow of oil by injecting air into each bearing of the equipment, guaranteeing an accurate volume at each lubrication point, regardless of bearing back pressure, atmospheric pressure, temperature and oil viscosity . In order to optimize decision-making when designing new components and parts of metallurgical equipment, the vector of making reliable design decisions is increasingly shifting towards mathematical modeling of production processes and situations that arise during the performance of technological operations. It has been established that in order to determine the permissible value of the content of wear products in the form of metal shavings, one can use the general theory of recognition, which is an important section of technical cybernetics and deals with the recognition of images of any nature, namely, the "minimal risk" method. Recognition algorithms are partly based on diagnostic models that establish a connection between the state of a technical system and diagnostic signals coming from these systems. The performed calculations make it possible to accurately establish the limiting values of iron-containing impurities in the working fluid of the "oil-air" lubrication system and indicate that if the limit value x0 = 11 is exceeded, that is, if the content of iron-containing impurities in the working fluid is more than 11 g per 100 cm3, the object should be stopped for inspection and the working fluid should be cleaned by filtration. The possibility of determining the permissible value of the content of wear products in the form of metal shavings in "oil-air" lubrication systems using the general theory of recognition, namely the "minimal risks" method, which simplifies the process of setting the date of its cleaning by filtration, without burdening it with especially cumbersome formulas and calculations.

IMPROVING THE DRIVE OF THE ROLLING MILL 2000 AT PJSC SEVERSTAL

The purpose of the scientific work is to modernize the gear cage of the hot rolling mill 2000 at PJSC Severstal, which will increase the service life of the drive as a whole. The method of drive modernization consists in the modernization of the gear cage, namely, the replacement of the chevron engagement with an increased class of manufacturing accuracy and contact strength of gears, with the same dimensions of the foundations. As a result of the calculations performed, it was found: an increase in service life due to the material, the average service life of the chevron engagement made of steel grade 12KHN3A is 8.2 years, the possibility of reducing the width of the gear engagement. When calculating the contact strength, the calculated value was 872.9 MPa, which did not exceed the permissible 1209.6 MPa. The bending load capacity also showed an estimated value of 116.8 MPa, not exceeding the permissible 458.1 MPa. The designed gear engagement, where the module, the number of teeth and the width of the gear ring were changed, has fatigue endurance.

Novel design concept for shrink-fitted bimetallic sleeve roll in hot rolling mill

Novel design concept for shrink-fitted bimetallic sleeve roll in hot rolling mill

ДИАГНОСТИРОВАНИЕ ЭЛЕКТРОПРИВОДА ОТВОДЯЩЕГО РОЛЬГАНГА ТЯНУЩИХ РОЛИКОВ ШИРОКОПОЛОСНОГО СТАНА ГОРЯЧЕЙ ПРОКАТКИ

Abstract. The purpose of the study is to develop an automated system for technical diagnostics of the state and regu-lation of the electric drive of the rollers of the collector roller table at a wide hot rolling mill based on change in the load currents of the rollers electric motors. The system allows the quality of finished rolled products and the produc-tivity of the mill to be enhanced due to the timely detection of faulty equipment and its rapid replacement based on the results of diagnostics. The following methods of diagnostics of the electric drive of the diverting roller table and its possible malfunctions which can negatively affect the quality of the finished rolled products were analyzed: experimental identification of the relation of the forms of change in the load currents of the electric motors of the rollers with specific types of malfunctions; determination of diagnostic signs of malfunctions in the values of change in the load currents of the electric motors of the rollers; creation of a mathematical model for calculating the forces of strip transportation; develop-ment of methods and algorithms for technical diagnostics of the electric drive of the collector roller table based on charac-teristics of change in the load currents of the electric motors of the rollers; development of a generalized algorithm for the operation of the automated technical diagnostics system; experimental evaluation of the effectiveness of the proposed methods and algorithms for diagnostics on the operating mill. Analytical methods of solving algebraic and differential equations and systems were used in the study. As a result of the research, the technical effectiveness of the methods and algorithms developed to diagnose the eccentricity of the roller barrel of the diverting roller table, malfunctioning of the brush-collector device of the roller electric motor, the destruction of the couplings in the roller electric drive line, malfunc-tioning of the bearing units in the roller electric drive line or the roller sides, the correct alignment of the roller relative to the technological plane of the diverting roller was experimentally confirmed. The diagnostic methods and algorithms de-veloped can be used to create diagnostic systems for electric drives of diverting roller table at operating mills during their reconstruction, as well as at newly built mills. The system thus developed was installed at the industrial plant's 2000 hot rolling mill.

Fatigue failure risk evaluation of bimetallic rolls in four‐high hot rolling mills

AbstractIn hot rolling mills, bimetallic rolls are used because of the excellent hardness and wear resistance by applying high‐speed steel (HSS) and ductile casting iron (DCI). Because most of the previous studies focused on surface spalling, almost no study is available for internal fatigue failure based on the stress during the rolling. In this study, therefore, a three‐dimensional finite element method is applied to investigate the rolling stress of the work roll in the four‐high rolling mill. A suitable chamfer geometry in the backup roll is discussed as well as the standard wear profile by considering those effects on the fatigue. Then, to evaluate the fatigue risk under compressive mean stress, the fatigue limit lines in the stress amplitude versus mean stress diagram are newly discussed. With the aid of previous experience in industries, the fatigue fracture risk is discussed by focusing on three critical points inside the work roll.

Effect of titanium addition on sub-structural characteristics of low carbon copper bearing steel in hot rolling

<abstract> <p>The low carbon copper-bearing steel exhibits high toughness and better weldability. In the present investigation, 0.05C–1.52Cu–1.45Mn stainless steel and its titanium added counterpart which is 0.05C–0.05Ti–1.52Cu–1.45Mn stainless steel were subjected to hot rolling. The hot rolling test followed by quenching to retain the microstructure was done using a hot-rolling mill. The rolling was done at two different temperatures of 800 ℃ and 850 ℃. The characterization of microstructure was done using electron back scattered diffraction and transmission electron microscopy analysis. The 0.05C–1.52Cu–1.45Mn stainless steel when subjected to hot rolling at a lower temperature envisaged a deformed microstructure rather transformed one. However, the same steel at a higher temperature envisages a transformed microstructure. There was no variation in hardness was observed. However, the addition of 0.05 wt% of titanium in 0.05C–1.52Cu–1.45Mn stainless steel influenced the softening and the microstructure showed some recrystallization; the hardness was decreased with the increasing rolling temperature because the solubility of titanium in the austenite phase increased with temperature which leads to suppression austenitic grain/sub-grain growth and hardness. The mean sub-grain size for 0.05C–1.52Cu–1.45Mn stainless steel was 2.75 µm. However, the addition of titanium leads to a decrease in the mean sub-grain size. A marginally larger mean sub-grain size was observed when 0.05C–0.05Ti–1.52Cu–1.45Mn stainless steel was rolled at a higher temperature. A comparatively finer precipitate of copper, titanium and oxy-silicates of Ferrous/Manganese in order of nanometer was formed during rolling at a higher temperature.</p> </abstract>

Evaluation of a NMPC Flowrate Controller for a Hot Rolling Finishing Mill for Steel Bars

In this work, the material flowrate control of a hot rolling finishing mill for steel bars is evaluated in simulation. First, a reduced model for control purpose is developed and described. This model uses nonlinear equations from the rolling theory and leads to the nonlinear control structure. The simulations are tested on a hot rolling mill simulator that implements a more detailed process behavior and is outside of the scope of this work. For controlling this plant, a Nonlinear Model Predictive Control (NMPC) is tested in various conditions. It is compared as a benchmark with a classical Linear Quadratic Regulator with integral action (LQI). The controller is implemented with help of CasADi and the control problem is solved by a SQP solver. The NMPC uses an underlying EKF as disturbance observer to handle the reference tracking problem.