Hot Mill Research Articles

Adaptive fuzzy approach to control the electro-hydraulic servo on the plate width in hot plate mills

An application of an adaptive fuzzy system for compensating the effects induced by the nonlinear and parameter uncertainty existed in the electro-hydraulic servo system is presented. Firstly, the system is divided into two parts, one is known linear part and the other is unknown nonlinear part. A feedback controller is designed for the known part to assure it stable. Secondly a fuzzy basic function is used only to study the upper bound of the unknown part and the output is used as the parameter of compensating controller. Finally an adaptive fuzzy controller and its adaptive parameters are designed based on Lyapunov function to insure the closed system's robustness and the convergence to zero is speeded up. The proposed scheme is implemented and tested on the electro-hydraulic position servo system of vertical roller of hot strip mill. The results show the proposed controller can achieve better performance than conventional PID one.

P-32 Optimal Design on Hot Mill Spindle Assembly under Heavy Duty Load

The top spindle, end coupling and slipper metal are main components of the hot roll process and used for transmission of rotational power with heavy duty load. The top spindle connected with the motor and end coupling connected with the roller are combined with the slipper metal act as a bearing and joint. The contact surface between end coupling and slipper metal is occurred stress concentration, and life cycles of slipper metal is reduced. This study aims to minimize the mechanical problems which might happen in the production process. The derivation of load condition is conducted for hot rolling process under slipper metal combination types and operation situations. The structural analysis is performed by applying mechanical characteristics, combination type, and rotational boundary condition: top spindle, end coupling, slipper metal. Optimal design is performed for contact surface between end coupling and slipper metal. Interference analysis is studied to reduce the stress concentrations. The kinematics simulation is performed by applying the various combination type and dynamic boundary condition of the mill spindle assembly. The interference is not occurred on the top spindle and slipper metal, so actual driving of the hot mill spindle assembly can operate on the normal operation condition.

INDUSTRIAL EXPERIENCES ON APPLICATION OF MULTIVARIATE IMAGE ANALYSIS IN STEELMAKING PROCESSES

Multivariate Image Analysis (MIA) has been developed and applied in process industry primarily for process monitoring and control purposes. This paper discussed some industrial experiences on application of MIA in the steelmaking industry that are illustrated using two case studies: (1) hot mill rolled-in scale defect classification; and (2) real-time monitoring of vacuum degasser ladle eye area. The preliminary results showed that many benefits could be realized through these high-value added applications.

Contact Damage Analysis of Hot Mill Spindle Assembly with Kinematics Simulation

The hot mill spindle assembly is the important component of the hot rolling process and used for transmission of rotational power. The contact surface between end coupling and slipper metal have high stress concentration due to operation interference. The life cycles of slipper metal are reduced by the contact surface damage. In this study, the structural analysis and kinematics simulation are performed by applying the various driving angle and dynamic boundary condition of the mill spindle assembly. This study aims to minimize the contact damage which might happen in the production process.

Tertiary Scale Behaviour during Finishing Hot Rolling of Steel Flat Products

Steel strip surface oxidation during hot mill processing represents an industrial and environmental problem: secondary oxide is removed after roughing, but tertiary oxide scales already start to form before entering the finishing stands. Their properties affect the final steel surface quality and its response to further processing. Controlling the oxide layer growth kinetics and mechanical properties can make pickling easier and improve downstream behaviour. A thin wustite-dominated scale layer (<20 μm) is created under controlled conditions in an original laboratory device adequately positioned in a compression test machine to investigate plane strain compression. A first series of oxidation tests were performed on a ULC steel grade to measure the kinetics of oxide scale growth. The samples were first heated up under a protective atmosphere (nitrogen), before being oxidised in air at different temperatures for various oxidation times. These experiments can be considered fair quantitative and qualitative simulations of scale growth as it occurs in a hot strip mill, insofar as the results thus obtained are in good agreement with the literature. After the oxide growth, plane strain compression (PSC) was performed immediately to simulate the hot rolling process. The oxide layers were characterised before and after compression tests by optical and secondary electron microscopy. As expected, the oxide is seen to deform during compression. The obtained oxide layers exhibit good adhesion to the substrate and homogeneity over the thickness, even after compression.

CONTROL OF LONG PLATE QUALITY: MEASUREMENT SYSTEM AND SIMULATION

Alcoa Kitts Green has identified rolling longer plate as a key step to increase the capacity of hot mills. The two most problematic issues for rolling longer plates are: (1) to identify accurately the availability of power, and (2) to improve the rolled shape quality, e.g., reduce “banana-ing”. Models were developed to calculate the available power and a new tilt control formula was developed to deal with the issue of banana-ing. Trials were successfully completed to test the capability with increased rolling length. A 36% increase in hot mill capacity was achieved.

A NEW HEAT TRANSFER CORRELATION FOR IMPINGING ZONE HEAT TRANSFER ON A HOT STEEL PLATE

Jet impingement heat transfer for a stationary steel plate is investigated to provide a better understanding of the cooling process that occurs in a hot steel mill. Understanding this process will help provide better control in achieving the desired metallurgical properties of the steel. Various effects on heat transfer such as jet diameter, water temperature, nozzle to surface spacing and wall superheat are presented. Correlations presented by other researchers which are used to determine the heat flux within the single phase forced convection and nucleate boiling regimes, were compared with experimental data obtained from the University of British Columbia (UBC) facility for a circular jet. From this, a new heat transfer correlation was developed which can be used to ascertain the heat flux within the single phase forced convection and nucleate boiling regimes. By knowing this heat flux, the desired steel properties can be better accomplished and controlled in the steel mill.On a investigué la transmission de chaleur par impact de jet sur une plaque d’acier stationnaire afin d’obtenir une meilleure compréhension du procédé de refroidissement qui se produit dans une aciérie chaude. Comprendre ce procédé aidera à fournir un meilleur contrôle dans l’obtention des propriétés métallurgiques désirées de l’acier. On présente les effets variés du diamètre du jet, de la température de l’eau, de l’espacement entre la buse et la surface et de la surchauffe de la paroi, sur la transmission de chaleur. On a comparé des corrélations présentées par d’autres chercheurs, qui sont utilisées pour déterminer le flux de chaleur dans les régimes de convection forcée à phase unique et d’ébullition nuclée, aux données expérimentales pour un jet circulaire obtenues dans les installations de l’université de la Colombie Britannique (UBC). À partir de cela, on a développé une nouvelle corrélation de transmission de chaleur que l’on peut utiliser pour identifier le flux de chaleur dans les régimes de convection forcée à phase unique et d’ébullition nuclée. Connaissant ce flux de chaleur, on peut mieux obtenir et contrôler les propriétés désirées de l’acier dans l’aciérie.

Deformation Behavior of a Slab with Width Reduction in a Hot Mill

The deformation of a slab with various width reductions has been investigated using a rigid-plastic finite-element analysis. A commercial finite-element code was used to analyze a dog-bone profile, mean thickness, length of slab, and longitudinal width profile after edging and horizontal rolling. The deformation behavior of a slab in a heavy edger mill was also compared with deformation in a sizing press. It was found that the sizing press followed by horizontal rolling is more efficient in width reduction than deformation by a heavy edger mill followed by horizontal rolling. The finite-element analysis results for the deformation of a slab also show reasonable agreement with measurements from an actual mill test, and from physical modeling experiments.

Simulation of thermal fatigue in hot strip mill work rolls

The surface deterioration of work rolls constitutes a significant constraint on the operation of hot mills, as the duration of rolling campaigns are greatly restricted by the surface condition of the rolls. Work roll changes account for a large proportion of downtime in the operation of hot strip mills, resulting in financial penalties for the mill operators in terms of lost production and roll maintenance.It is generally accepted that thermal fatigue represents one of the main factors influencing work roll wear in the finishing stands of a hot strip mill. In order to assess the thermal fatigue behaviour of typical work roll alloy grades, a series of tests were performed on high‐speed steel (HSS) and high‐carbon high‐chromium steel samples using a stand alone twin‐disc simulation machine under conditions that are comparable to those of hot rolling of steel. The progressive changes in surface condition of the roll samples were monitored and analysed by means of stylus profilometry, optical and scanning electron microscopy. The experimental results were compared with fragments of scrapped work rolls taken from the mill. Tests performed on the HSS samples did not result in appreciable surface degradation of the test sample. On the other hand, examination of the high‐carbon high‐chromium samples after testing revealed thermal crack morphologies and surface defects comparable to those observed in mill roll samples.

Development Of Numerical Methods AndComputer Code For The Mathematical ModellingOf Work Piece Heat Transfer During Processing

A key quality requirement for the production of steel strip is temperature control. During hot rolling, various processes are carried out which improve surface and rolling characteristics but which increase heat extraction from the slab or bar. Moreover, different hot mill configurations at different sites will give rise to different overall thermal behaviour. Temperature control is required to enable the basic properties of the steel strip to be produced. Rather than concentrate on individual sections of the hot strip mill a custom-written thermal finite element model has been developed for Corus to simulate the evolving temperature field in the slab and subsequent thinner bar over the entire hot rolling process. Localised cooling effects caused by hydraulic descale sprays, roll coolant and contact conduction, and local atmospheric conditions have all been included. Heat generation due to adiabatic heating of deformed material and rolling friction has also been combined into the model. Efficient modelling of the temperature effects occurring throughout processing can be used in the optimisation of the process operations. This paper will describe both the practical approach and the numerical methods used to develop the model and examples of simulations of different hot mill configurations will be described.

Influence of roll speed mismatch on strip curvature during the roughing stages of a hot rolling mill

Asymmetrical conditions occurring during the rolling of hot strip can cause strip curvature and can lead to poor product shape, profile, quality and cause reduced productivity. In the most severe of cases, strip with a head-end turning towards the upper work roll may fail to enter the roll gap on its next pass and result in a cobble. In these investigations, finite element techniques have been used to determine the effect of roll speed mismatch on the direction and severity of strip curvature in the roughing stages of a hot mill. A plane strain finite element model has been constructed to simulate the rolling of low carbon steel strip at high temperatures. Five ingoing strip thicknesses were considered, each one representing a particular pass of the reversing rougher at Corus Port Talbot hot mill. Alterations were made to the finite element model's boundary conditions, i.e. roll gap height, to determine how the reduction affects the magnitude of strip curvature. Each model has a 5% roll speed mismatch applied. Results have identified, on selected passes, an optimum reduction range where a straight slab is the predicted outcome. In addition, the results also show the quantified reduction range, where the sensitivity of strip curvature to roll speed mismatch is at a maximum. This is of particular interest, since in many industrial cases the rougher operator utilises roll speed mismatch to counteract the effect of turn down/up caused by other asymmetrical factors, for example temperature differentials or work roll frictional differences.

A machine vision measurement of slab camber in hot strip rolling

A machine vision approach to on-line slab camber measurement in the hot strip steel mill at Port Talbot is described. A digital image of the hot slab is transformed to obtain a plan view and its position is located using greyscale thresholding and binary morphology. The slab centre-line is extracted as an approximate medial axis from its Euclidean distance map and camber is calculated from the curvature of this centre-line. Additional processing stages are included to make the process robust to industrial conditions. The technique is validated through comparison with manual camber measurements made off-line and in this way the curvature accuracy of the final technique is shown to be ±0.9×10−3m−1 at the 95% confidence level.

Mathematical Modeling of Draft Schedule for In-line Rolling of Ultra Thin Strip in the Combined Single-belt Casting/Hot Rolling Process

The single-belt process is a new route to produce steel strips, in which the single-belt caster is directly connected with hot mills. This process should be able to roll strip with thickness 1 mm or below. In hot rolling of the ultra thin strip there are many limitations which are represented by the finishing rolling temperature of the strip, the oxidation of the strip, the overheat of the roll and the maximum rolling speed. In the present paper the possibility of hot rolling ultra thin strip in the single-belt process was investigated. On the basis of mechanical/thermal/metallurgical behavior of the strip a mathematical model of draft schedule was proposed. In terms of different criteria the draft schedule was optimized. The results show that austenitic hot rolling of ultra thin strip in the single-belt process can be carried out like the conventional hot rolling for low carbon steels. With consideration of roll life the maximal roll surface temperature has a large influence on the establishment of the draft schedule for hot rolling of ultra thin strips.

HIGH PRODUCTIVITY IMPROVEMENT IN JFE FUKUYAMA NO.1 HOT STRIP MILL

Productivity improvement technologies we developed at Fukuyama Hot Mills are, high accuracy temperature tracking from entry side of reheating furnaces to finishing mill, automatic reheating furnaces control system, and mill pacing control. Although applied technology is conventional, theoretical model calculation by latest industry computer improves productivity dramatically.

A Study of Modification of M2 Cast High Speed Steel

AbstractM2 cast high speed steel was inoculated by addition of rare earth(RE)‐Al‐N, network eutectic carbides were eliminated, matrix structures were refined and the segregation of tungsten and molybdenum elements were relieved. In the condition that the hardness did not decrease, impact toughness obviously increased. Quenching at 1180 °C and three‐times tempering at 560 °C, the hardness of M2 cast high speed steel kept 65~66HRC, impact toughness reached 21.3J/cm2. Modified M2 cast high speed steel had excellent thermal fatigue resistance and high temperature wear resistance. Roll made in modified M2 cast high speed steel had excellent service effect using in slit rolling mill stand of hot rolling bar mill.

Roll performance – technical overview and future outlook

An overview is given of roll developments and experience in the context of hot mills and flat rolled products. After 30 years of slow change, there are now strong productivity and quality incentives driving developments in roll technology. International developments are noted, in particular the acceptance that high speed steel (HSS) rolls must be used to meet current surface finish requirements. The most significant need at present is for an improvement of late stand work rolls.

Development of hot rolling practices for lithographic sheet using a thermo-mechanical and microstructural model of a reversing hot finishing mill

Commercial purity AA1050 alloy, which is used for lithographic sheet, is mostly hot rolled using a conventional hot-line consisting of a reversing hot breakdown mill and a tandem hot finishing mill (HFM). The production of lithographic sheet using an alternative hot-line with a single stand (reversing) HFM which requires less capital cost is examined. A model of the single stand HFM (with front and rear coilers) was developed to predict the thermo-mechanical histories and the Zener–Hollomon parameter. Microstructural relationships were incorporated into the model to evaluate the effects of different rolling conditions and thermo-mechanical histories on the recrystallisation behaviour. The model was validated with experimental results and then used to develop suitable hot rolling practices for lithographic sheet. Simulations of hot rolling showed that process conditions could be altered to minimize partial recrystallisation and to promote a more homogeneous microstructure. Favourable rolling practices can be readily determined, thereby reducing the need for expensive and often ad hoc plant trials.

Effect of Pass Schedule on Cross-Sectional Shapes of Circular Seamless Pipes Reshaped into Square Shapes by Hot Roll Sizing Mill

A heavy gauge square steel pipe is manufactured by a hot roll sizing process, in view of difficulty in manufacturing such a pipe with sharp corners by cold roll forming. In this paper, the effect of pass schedule on a cross-sectional shape is discussed by referring to experimental measurements, and results calculated by the rigid-plastic finite element method. The experiment was carried out at the last step of the sizing process for seamless pipes. The comers of a product become sharper as the magnitude of total reduction increases. In the case of a two-roll type roller, the comer near the roll flange becomes sharper than the comer near the groove bottom. The hollow depth at the sides is small when the incremental reduction at each sizing stand is high at the early reshaping stage with a large bending curvature ((D 0 /2)/R i , R i : bending radius, Do: initial external diameter of a circular seamless pipe) and low at the late reshaping stage with a small bending curvature.

Modelación matemática de la evolución de la temperatura en la banda laminada en caliente

The goal of this work is to construct a mathematical model to describe the strip temperature evolution at a continuous finishing hot rolling mill. The model predicts in a satisfactory way the strip temperature, with a finishing one (exit of stand 6) with a deviation of + 6.5 °C for a mean temperature drop of 150 °C at the continuous finishing hot mill and a mean error of 43 %. It also predicts a coiler temperature with a difference of + 9.2 °C for a mean temperature drop of 240 °C in the cooling table and a mean error of 3.8%

The rolling sliding wear response of conventionally processed and spray formed high speed steel at ambient and elevated temperature

The effect of spray forming on the wear properties of a 1.2C–3.4W–8.9Cr–4.3V–2.7Mo high speed steel is described. The microstructure, fracture behaviour and wear response of the spray cast materials are compared with those of conventionally cast material of the same composition. Spray forming resulted in a substantial reduction in microstructural scale for both grain size and carbide size. In addition, large primary and interconnected eutectic carbides observed in the conventionally cast material were replaced by a more uniform distribution of discrete globular carbides in the spray cast material. This refinement is shown to give rise to an increase in the resistance to fracture. Wear testing was undertaken in the rolling/sliding configuration (8% slippage) at 300 N against an M2 tool steel counterface in the temperature range 20–650 °C. The wear rate of the conventional material was significantly higher than that of the spray cast material at all temperatures. Both adhesive and oxidative wear mechanisms were observed, with the latter becoming more prominent as the test temperature increased. Surface degradation occurred preferentially at the carbide/matrix interface for both materials, but was particularly prominent in the Fe/M 2C–M 6C eutectic regions and at large primary VC carbides in the conventionally cast material, resulting in higher rates of material loss in these regions. The improvement in wear resistance observed for the spray formed material can be directly attributed to the refinement of both primary and eutectic carbide phases and the elimination of microsegregation. The laboratory observations are compared to a worn surface of a spun cast hot mill work roll of nominally the same composition following a normal campaign in the roughing stands of a hot rolling mill. This showed that the wear mechanisms in the field were reproduced in the laboratory. The relationship between process parameters microstructure and wear mechanisms is discussed.