Hot Strip Rolling Mill Research Articles

Modelling surface thermal damage to hot mill rolls

Surface thermal damage to hot mill work roll materials was investigated using twin-disc high-temperature laboratory test rig under conditions that are relevant to those of the early stands of a hot strip rolling mill. Two typical roll grades were tested: high speed tool steel and high-carbon high-chromium steel. Mill data were scaled down to suit the test sample dimensions and used to calculate the thermal cycle, contact times and contact pressure. A coupled thermomechanical model based on the finite element method was developed to predict the temperature distribution within the core and at the surface of the roll test samples. The predictions of the model showed good agreement with the temperatures measured using embedded thermocouples at several depths in the sub-surface of the roll test sample. After high temperature testing, the test samples were sectioned and prepared by conventional metallography for microscopic analysis. The thermally induced surface damage in the test samples were found to exhibit similar features to those observed in actual mill work rolls during service, especially the high-carbon-high-chromium steel, which showed a greater extent of surface thermal damage than the high speed tool steel test samples. Based on the results, it is concluded that the new test rig was proven capable of producing thermal damage in a consistent and reproducible manner and, thus, it can be regarded as a valuable off-line test resource to assist in further understanding the work roll surface deterioration phenomena.

Hybrid Hot Strip Rolling Force Prediction using a Bayesian Trained Artificial Neural Network and Analytical Models

The authors discuss the combination of an Artificial Neural Network (ANN) with analytical models to improve the performance of the prediction model of finishing rolling force in hot strip rolling mill process. The suggested model was implemented using Bayesian Evidence based training algorithm. It was found that the Bayesian Evidence based approach provided a superior and smoother fit to the real rolling mill data. Completely independent set of real rolling data were used to evaluate the capacity of the fitted ANN model to predict the unseen regions of data. As a result, test rolls obtained by the suggested hybrid model have shown high prediction quality comparatively to the usual empirical prediction models.

A Multivariable and Multi-Objective Approach for the Control of Hot-Strip Mills

The control of a hot strip rolling mill is quite a complex problem due to the presence of many simultaneous control tasks. This is the main motivation that spurred the major steel corporations to adopt more sophisticated control techniques based on multi-variable concepts. The main drawback of most multi-variable approaches is the lack of transparency of the resulting controller that, consequently, can turn out hard to tune on site. In this paper we solve the tuning problem by adopting a multi-objective control approach that allows explicitly taking into account the existence of actuator limitations and nonlinear dynamics. Furthermore, the application of the proposed control technique to a narrow hot strip mill is here described.

PRESSURE DISTRIBUTION AND DAMAGES OF OIL-FILM BEARING SLEEVE DURING THE PROCESS OF INTERFERENCE FIT

According to the sleeve damage of oil-film bearing in 1580 PC hot strip rolling mill, during the process of setup, disassembly and usage, mechanic model on sleeve assembly by boundary element method (BEM), together with boundary conditions, is established. The deformation and load properties of oil-film bearing by interference fit between sleeve and rollneck in rolling mill are quantitatively analyzed by BEM for 3D elastic and plastic contact problems. The energetic parameters of different load models are set to simulate the setup and assembly processes. The influences of contact pressure and deformation on sleeve and rollneck, under partial loads on oil-film bearing, are discussed as well. Consequently, different expanding pressure, stress and strain varying distribution laws, under axial thrust load during setup and assembly process, are obtained. The fundamental reason that results in sleeve damage is found. Detailed improvement measures on damage depreciation are brought forward. Finally, reasonable experiments on two sample testing rolling mill, which are equipped with oil-film bearing, prove the validity of analytical results, and reasons that result in bearing damage are deduced from above analysis.

Control Scheme Using Forward Slip for a Multi-stand Hot Strip Rolling Mill

Forward slip is an important parameter often used in rolling-speed control models for tandem hot strip rolling mills. In a hot strip mill, on-line measurement of strip speed is inherently very difficult. Therefore, for the set-up of the finishing mill, a forward slip model is used to calculate the strip speed from roll circumferential velocity at each mill stand. Due to its complexity, most previous researches have used semi-empirical methods in determining values for the forward slip. Although these investigations may be useful in process design and control, they do not have a theoretical basis. In the present study, a better forward slip model has been developed, which provides for a better set-up and more precise control of the mill. Factors such as neutral point, friction coefficient, width spread, shape of deformation zone in the roll bite are incorporated into the model. Implementation of the new forward slip model for the control of a 7-stand hot strip tandem rolling mill shows significant improvement in roll speed set-up accuracy.

Static and Metadynamic Recrystallization of Interstitial Free Steels during Hot Deformation

A rapid method was used to identify kinetics of the recrystallization for two IF (Interstitial Free) steels which have different phosphorous and boron contents. The static and metadynamic softening behaviour of the materials for a range of strain rates and temperatures were quantified. The critical strain for initiation of strain independent softening was estimated for the IF steels in respect to the time for 50 percent softening after deformation. The results showed that the strain for the initiation of strain independent softening (often referred to as metadynamic recrystallization) varies with the Zener Hollomon parameter. Classic static recrystallization was observed at strains below the strain independent softening for all processing conditions and the strain rate had a strong effect on the time for strain independent softening. Results also revealed that static and metadynamic recrystallization was delayed owing to the phosphorous and boron alloying elements. Hence, the large strain at above no-recrystallization temperature may be required for the early stage of Finishing Stands Unit (FSU) in hot strip rolling mills to initiate austenite grain refinement of phosphorous and boron added IF steels.

A Multivariable and Multi-Objective Approach for the Control of Hot-Strip Mills

The control of a hot strip rolling mill is a quite complex problem due to the presence of many simultaneous control tasks. This is the main motivation that spurred the major steel corporations to adopt more sophisticated techniques based on multivariable concepts. The main drawback of most multivariable approaches is the lack of transparency of the resulting controller that, consequently, can turn out hard to tune on site. In this paper we solve the tuning problem by adopting a multi-objective control approach that allows explicitly taking into account the existence of actuator limitations and nonlinear dynamics.

Visual predictive maintenance tool based on SOM projection techniques

This paper presents a portable condition monitoring system named MAPREX which was developed as result of the cooperation between the University of Oviedo and Aceralia inside of a research project funded by the ECSC - Steel RTD Program. The system integrates powerful monitoring and data visualization techniques based on the Self Organizing Map (SOM) algorithm. In this paper is described in detail the system architecture and performances, visualization techniques implemented and an example displaying real data from a 6,000 kW DC motor of a hot strip mill rolling stand.

圧延圧接方式による熱間シートバー接合技術の検討

圧延圧接方式による熱間シートバー接合技術の検討

Modelling and a genetic algorithm solution for the slab stack shuffling problem when implementing steel rolling schedules

Iron and steel production is a multistage process. A slab yard serves as a storage buffer between the continuous casting stage and the steel rolling mill. Slabs from continuous casting are stacked in the yard to await rolling. When implementing the rolling production schedule, slabs need to be picked up from the slab yard one by one according to the scheduled rolling sequence, heated in the heating furnace and then rolled. There are usually a number of suitable candidate slabs in the yard satisfying the requirement for each rolling item. In general, these candidate slabs are not at the most convenient positions in the stacks. To pick up a required slab, the slabs above it need to be shuffled. To save slab-handling cost and prevent the handling cranes from becoming a bottleneck, slabs for a rolling schedule must be selected from among the candidate slabs so that the total number of slabs shuffled is minimized. The paper studies the slab stack-shuffling problem using the hot strip rolling mill in Shanghai Baoshan Iron and Steel Complex as an application background. We first formulate the problem using an integer-programming model and then develop a modified genetic algorithm to solve it. Genetic codes and genetic operators are specially designed to ensure the feasibility of solutions and to speed up the solution process. The algorithm is implemented and compared with the existing algorithm that the mill has been using. Experiments on randomly generated problems show that the proposed new method reduces the number of slab shuffles by 11.19% on average.

An effective heuristic algorithm to minimise stack shuffles in selecting steel slabs from the slab yard for heating and rolling

Steel production is a multi-stage process. A slab yard serves as a buffer between the continuous casting stage and the steel rolling stage. Steel slabs are stored in stacks in the yard. Shuffling is needed when picking up a slab for heating and rolling, if it is not in the top position of a stack. This paper studies the problem of selecting appropriate slabs in the yard for a given rolling schedule so as to minimise the total shuffling cost. The study uses the hot strip rolling mill in Shanghai Baoshan Iron and Steel Complex as an application background. We propose a new heuristic algorithm to solve the problem. This is a two-phase algorithm that first generates an initial feasible solution and then improves it using local search. The new algorithm is compared with the algorithm in use on randomly generated test problems and on real data. Experimental results show that the proposed algorithm yields significant better solutions. The average improvement over the old algorithm is 15%.

Inferential control for rolling mills

A robust inferential controller is developed for hot strip rolling mill tension control. Tension cannot be measured, therefore a nonlinear model is used to infer the tension from the looper angle. The model uses constant physical parameters while the actual physical system will be uncertain, therefore quantitative feedback theory is used to design a tension controller, which will provide robust performance despite uncertainty from both the physical system and the inference model or soft sensor.

Robust inferential control for hot strip mills

An robust inferential controller is developed for hot strip rolling mill tension control. Since tension cannot be measured a non-linear model is used to infer the tension from the looper angle. Since the model uses constant physical parameters and the actual physical system will be uncertain then Quantitative Feedback Theory is used to design a tension controller which will provide robust performance despite physical system uncertainty and uncertainty in the inference model or soft sensor.

Evaluation of hot strip mill backup roll cladding

A new cladding material based on the Fe–Cr–Mo–V–C alloy system, suitable for submerged arc welding, has been designed for the refurbishment of forged and cast backup rolls used in the finishing stands of hot strip rolling mills. The work undertaken includes mechanical analysis, mechanical testing, and microstructural characterisation. The mechanical analysis indicated the nature and level of stresses operating near the surface of rolls; mechanical testing allowed material performance to be anticipated. An optimal post-weld heat treatment procedure, which maximises strength while minimising material strain hardening, was subsequently chosen. The microstructure of the candidate cladding material is a mixture of lower bainite and martensite, containing a very fine distribution of molybdenum carbides. In situresults have shown that welded rolls outperform traditional rolls, as the amount of steel rolled per millimetre of cladding material is 40% higher than with forged rolls and double that obtained with cast rolls.

A time-encoded signal-processing approach to fault classification of an electrohydraulic pressure control system and its application to a hot steel strip rolling mill

A technique is presented whereby time domain signals may be classified in terms of four shape parameters. These parameters are processed to create a condition indicator, its variation being used to identify system faults. In this study, the leakage flowrate and a faulty servo-valve are identified on a pressure control system and a comparison is made with a conventional fast Fourier transform approach and a commercial software package, time-encoded signal processing and recognition. A new code, CARCODE, is then applied to 28 servo-valve-controlled work roll bending circuits on a seven-stand hot steel strip rolling mill and a simple graphics presentation is developed to aid real-time condition monitoring.

CARCODE for Time Encoded Signal Processing and fault trending of the Work Roll Bending hydraulic control systems on a 7-stand Hot Steel Strip Rolling Mill

CARCODE for Time Encoded Signal Processing and fault trending of the Work Roll Bending hydraulic control systems on a 7-stand Hot Steel Strip Rolling Mill

Analysis of the fatigue failure of tee pieces forming part of a header in a descaling system in a hot strip rolling mill : Watson, J.F., Rance, J.M. and Anderson, H.J. Int. J. Pressure Vessels Piping (1996) 68 (1), 121–126

Analysis of the fatigue failure of tee pieces forming part of a header in a descaling system in a hot strip rolling mill : Watson, J.F., Rance, J.M. and Anderson, H.J. Int. J. Pressure Vessels Piping (1996) 68 (1), 121–126

Analysis of the fatigue failure of tee pieces forming part of a header in a descaling system in a hot strip rolling mill

Several fatigue failures occurred in tee pieces forming part of a header which supplies high pressure water for descaling steel slabs. The failures were in the form of through cracks which were initiated at the inside of the tee radius. Analysis of the stresses in the tee piece indicated a significant local stress intensification at the tee radius. This stress intensification is not taken into account in the standard design codes, however, the analysis indicates that it should be a main parameter in designing tee pieces for pressurised applications. The reason for the failures was shown to be due to the cyclic nature of the loading resulting in a fatigue failure. A failure model has been established which interfaces fatigue crack initiation with crack propagation. The model gave a predicted life which agreed well with the actual life of the tee pieces.

Disturbance Attenuation in a Hot Strip Rolling Mill via Feedforward Adaptive Control

A control scheme for the attenuation of input disturbances in the finishing mill (FM) train of a hot steel strip rolling mill is considered. The scheme has been successfully commissioned on an operational mill, with proven performance benefits, illustrated herein. It operates during thread of the mill train: mill references for unthreaded stands are refined based on information derived from the threaded stands. By this means, both thickness and flatness performance on the leading end of the strip may be improved, though the latter requires flatness control actuators such as roll bending or sideshifting. In the absence of flatness actuators, the scheme can be configured so that gauge performance is improved without sacrificing flatness performance.

Stabilization System for the Bar Temperature in the Roughing Train of the Strip Mill

The paper is concerned with the stabilization of the bar temperature in the roughing train of the hot strip rolling mill consisting of two reverse stands, i.e. “duo” and “quarto”. The controlling effort is variation of the reduction mode in the roughing train stands. A concept of the two-channel (“rough” and “fine”) control is discussed.The “rough” control channel functions by indirect measurement of the rolled metal temperature as a function of the main drive armature current in the “duo” stand with the adaptive adjustment of the coefficients as a function of the deviation of the measured bar temperature from the specified one. The reductions redistribution in the “quarto” stand using a fine “control channel is based on the direct measurement of the metal before and after the “quarto” stand using an adaptive model which takes care of the main rolling parameters.