Strip Rolling Process Research Articles

The Research of 2 Degrees of Freedom Vertical Vibration System Modeling for 4-High Hot Strip Mill Stands

A lumped mass model with two degrees of freedom for the vertical vibration system of four roller hot strip rolling mill stand is proposed, and then the parameters of dynamic model , include the equivalent mass , equivalent stiffness and its natural frequencies, were calculated by MATLAB package. The correctness of the model is verified via field vibration testing and signal analysis in the strip rolling process. Comparative the six degrees freedom model, the two degrees freedom model of our proposed is simplified reasonability and the model accuracy is maintained certainly . The two degrees freedom model is critical for the research of digital simulation of the strip rolling process. The research result have important theoretical and practical significance for the parameter optimization of the AGC system , vertical vibration control, the product quality improvement and the rolling speed increase for the rolling mill system.

Fast Prediction of Temperature by FEM in Hot Strip Rolling

Finite element method (FEM) has been one of the most important numerical simulation tools with the development of computer technology. However, it is only used to simulate and analyze different process offline in many fields because of the longer computational time. The influencing factors of prediction of temperature in the strip rolling by FEM including equations, mesh and storage of matrix was investigated in the paper. The lumped heat capacity matrix was introduced to resolve the oscillation problem and improve precision. Furthermore, the refined elements layer upon layer was discussed to improve solution efficiency and precision. In addition, in order to improve the solution efficiency one dimensional compressed storage method was employed to carry out in the solution of equations. The FEM program code for the solution of temperature was embed in the online rolling control system program successfully. The predictive results are in good agreement with the measured value. The computational time and precision are satisfied in the strip rolling process.

1212 O/Wエマルション圧延における油導入メカニズムの把握(GS-11・16 軸受・潤滑油)

1212 O/Wエマルション圧延における油導入メカニズムの把握(GS-11・16 軸受・潤滑油)

The sticking behavior of an ultra purified ferritic stainless steel during hot strip rolling

During hot rolling of ferritic stainless steels (FSSs), sticking can cause severe surface defects both on work rolls and strips especially for ultra purified FSSs with the total amount of carbon and nitrogen being less than 150ppm. In the present paper, high temperature oxidization behavior of the ultra purified FSSs was characterized. A new experimental method was invented to simulate the sticking behavior of ultra purified 21%Cr FSS, by which specially designed specimens were hot compressed with different processing parameters to simulate hot strip rolling process. The specimens were surface conditioned prior to the simulation test, either by mechanically polishing or by pre-oxidization to form oxide scales with certain thickness. Observation on the cross-section of sticky regions indicated that cracks had been formed by cyclic heating and cooling during hot deformation had been acting as nucleation sites for sticking particles. The results indicated that oxide scale could avoid the direct contact between roll surfaces and rolled materials to help reducing the sticking occurrence. The temperature region for easy sticking occurrence in the ultra purified 21%Cr FSS has been measured to be from 900 to 1100°C, which is enlarged as compared to other plain FSSs. The tendency for sticking occurrence decreased with increasing strain rate and decreasing the hammer or work roll surface roughness.

Application of an Improved Trust-Region Method to Rigid-Plastic Finite Element Analysis in Strip Rolling

Rigid-plastic finite element analysis (RPFEA) is an efficient and practical method to calculate rolling parameters in the strip rolling process. To solve the system of simulations equations involved in the RPFEA, a numerous of numerical methods, including the standard Newton-Raphson method, the modified Newton-Raphson method, and etc., have been proposed by different researchers. However, the computational time of the existed numerical methods can not meet the requirement of the online application. By tracking the computational time consumption for the main components in the standard Newton-Raphson method used in finite element analysis, it was found that linear search of damping factor occupies the most of the computational time. Thus, more efforts should be put on the linear search of damping factor to speed up the solving procedure, so that the online application of RPFEA is possible. In this paper, an improved trust-region method is developed to speed up the solving procedure, in which the Hessian matrix is forced to positive definite so as to improve the condition number of matrix. The numerical experiments are carried out to compare the proposed method with the standard Newton-Raphson method based on the practical data collected from a steel company in China. The numerical results demonstrate that the computational time of the proposed method outperforms that of the standard Newton-Raphson method and can meet the requirement of online application. Meanwhile the computational values of rolling force obtained by the proposed method are in good agreement with experimental values, which verifies the validity and stability of the proposed method.

Heat Transfer Coefficient Prediction by FEM in the Hot Strip Rolling

It is necessary to know the heat transfer intensity for predicting temperature distribution in the hot strip rolling process. The HTC (heat transfer coefficient) was usually obtained by the experiments and mathematical model. In this paper the HTC prediction was discussed based on the measured or target temperature by the proposed finite element method (FEM). The temperature evolution and HTC in the hot strip rolling process according to a certain plant were analyzed by the iteration calculation. The result shows that the HTC between strip and work roll was much more than the value in the air cooling and water cooling process. Furthermore, the HTC value is lower in the air cooling process compared with that of water cooling. The maximum and minimum value of HTC were about 1.5×105 (W/m2.K) and 80(W/m2.K) respectively. The temperature in the rough rolling according to the predicted HTC has been solved and the calculated results have a good agreement to the meausred value. Therefore, the research could be used to control the temperature distribution accurately and optimize the parameters.

A Holistic Framework for Multiple Response Optimization of Hot Strip Rolling Process

The hot strip rolling (HSR) process typically depends on setting of its various process parameters. Controlling these parameters to obtain optimal response is always a critical and difficult task for researchers and practitioners. The complexity of the problem is compounded for multiple response (multiobjective) situations. This article critically reviews the various approaches proposed for modelling and optimization of HSR process in single and multiple response situations. Based on the research scope, a holistic framework for modelling and optimization of HSR process is proposed in this article. The proposed framework is expected to facilitate the researchers and industry practitioners to select the appropriate approach and its intrinsic technique(s) for any typical HSR optimization problem.

Hot Strip Rolling State Analysis Based on Geodesic Distance Spectral Clustering

In the hot strip rolling production process, mechanical properties are detected offline. The process data is used for clustering analysis to acquire the state in advance. During the mechanical properties detection, the outliers in the same steel grade are regarded as the focal points. Spectral clustering is one of the advanced methods, where the Euclidean distance as the common similarity measure, can only extract the features of the spherically distribution data and can not express the complex distribution data. In this paper geodesic distance is introduced to spectral clustering, which is used to do the production state clustering. The Tennessee Eastman and hot strip rolling process data are used for model validation, as a result the proposed method has better performance on clustering, compared with the Euclidean distance.

Effects of rolling parameters on temperature distribution in the hot rolling of aluminum strips

A model for the study of hot strip rolling of aluminum alloys is proposed, and the approach is based on thermo-mechanical analysis using the Finite-Element Method (FEM). To assess the rolling behavior of materials during a pass, finite element program Abaqus/Explicit has been employed and the hot rolling process was modeled in three dimensions. The appropriate models for heat transfer mechanisms are considered and the temperature distribution along the rolled strip and the temperature variation during hot strip rolling process is predicted. The effects of various process parameters such as rolling speed, amount of thickness reduction, initial thickness of the strip and interface heat transfer coefficient are considered. To verify the validity of the model and predicted results, a multi-pass hot rolling program is used and a comparison is carried out between the predicted results by model with plant-recorded results.

The Optimal Design for the Production of Hot Rolled Strip with “Tight Oxide Scale” by Using Multi-objective Optimization

Recently, customers are demanding for hot rolled strip products to have tight oxide scales on the surfaces. Therefore, high finishing rolling temperature, low coiling temperature and fast finishing rolling speed have to be used to obtain tight oxide scale, which is different from conventional controlled rolling. In order to ensure the mechanical properties at the same time, a framework consisting of the Bayesian neural network and multi-objective particle swarm optimization has been established to determine the optimal hot strip rolling parameters. Due to excellent generalization ability, the Bayesian neural network was employed to develop the model for the prediction of mechanical properties of hot rolled automotive beam steels. The accuracy between the measured and predicted values was within ±30 MPa and ±4% for strength and elongation, respectively, providing a reliable model for the optimal process design. By applying multi-objective particle swarm optimization, the optimized hot rolling process was obtained for the production of hot rolled automotive beam steel with “Tight Oxide Scale”. Industrial trials have been carried out, which showed good agreement with the optimized hot strip rolling processes. It has been theoretically and practically proven that the optimal process design framework can effectively locate the optimal processing window for hot strip rolling.

Modelling of the Temperature Distribution of Coiled Hot Strip Products

It has always been of greatest importance to control the temperature distribution in the products throughout the hot strip rolling process including the final coiling operation. A computational model of the latter has been developed and validated, which is presented in this paper. Furthermore, the influences of the different parameters on the transient thermal distribution are evaluated. The formulated model as accounts for two-dimensional heat conduction is assuming axi-symmetric conditions. Temperature dependent properties are accounted for results in a nonlinear heat conduction problem that is solved by use of the Finite Element Method (FEM). The calculations have been validated by two full scale measurement campaigns and show a good agreement with measurements.

A Useful Control Model for Tandem Hot Metal Strip Rolling

The tandem hot metal strip rolling process is a highly complex nonlinear system that presents a difficult control challenge. This challenge is exacerbated by the hostile hot metal rolling environment, which precludes the location of sensors to measure variables that are important for control. In addition, the controller must have a structure that offers simplicity of tuning during commissioning by personnel who usually are unfamiliar with advanced process control techniques. Based on our previous work using a state-dependent Riccati equation technique for control of the tandem cold metal rolling process, it is considered that a similar method might also be useful for control of tandem hot strip rolling. For the hot rolling process, the development of a process model in a form that is suitable for control development is a significant and challenging task. This paper describes our work to expand on an initial portion of this model to develop a comprehensive nonlinear model of this process. Based on simulation results, it is determined that the complete model has the potential to be useful in the development of a viable nonlinear control method for significant improvement in the control of the tandem hot rolling process.

Modeling of 3D Lateral Flow during the Process of Strip Rolling

The three dimensional deformation of strip during flat rolling is always a key issue, the lateral flow of metal on the strip edge will determines the quality of final product. In this paper, a theoretical analysis focus on the lateral flow of strip edge is discussed. Lateral Flow Factor and Relative Lateral Flow Factor are developed originally to analyze the lateral flow of strip and edge drop. For special process condition mentioned in paper, value of lateral flow factor is about 0.07.

Friction Model for Strip Rolling

To improve the accuracy and speed of finite element calculation, a new friction model was proposed, in which a layer of thin friction element between the roller and workpiece was introduced to consider the contact friction. This model was used in the three-dimensional elastic-plastic finite element model of strip rolling process. Taking the geometrical size and physical characteristics of intermediate medium between roller and workpiece into consideration, the stiffness of the friction element was corrected by two factors, i. e., the thickness of friction element and β factor. Without any assumption about the value and direction of friction force and neutral point position, the rolling process was simulated by using this model. The results obtained by this model were compared with the experimental results and the feasibility of the model was verified.

Effect of Nb Content on Hot Flow Stress, Dynamic Recrystallization and Strain Accumulation Behaviors in Low Carbon Bainitic Steel

Compressive deformation behaviors of low carbon steels with different Nb contents were investigated in the temperature range 900oC to 1100oC and strain rates from 0.05s-1 to 2s-1 by single pass deformation. Multi-pass compressive deformation processes were also carried out to examine strain accumulation under different Nb contents. In single pass deformations, dynamic recrystallization (DRX) can be observed in the case of low strain rate and high temperature, and the higher Nb steel exhibits higher deformation activation energy (Qdef) and critical strain value (εc) for the onset of DRX. However during multi-pass compression process (interval time of 3-4s), the higher Nb steel has larger strain accumulation between passes, so it is easier for high Nb steel that DRX happens during hot strip rolling process, which starts at relative high rolling temperature.

Optimization of Short Stroke Control Preset for Automatic Width Control of Hot Rolling Mill

Automatic width control is a key issue in hot strip rolling process. The edge rolling has been widely used in the roughing stand of hot strip mill to control the width of the slab. However, the edge rolling and consequent horizontal rolling will cause a significant width change in the head part and tail part of the slab, which have to be trimmed before the finishing stands. Based on the width reduction deformation curve of the head and tail along the longitudinal direction of slab, the short stroke control (SSC) technology has been developed to overcome this problem. The finite element method has been used to simulate the unsteady edge rolling process. Three short stroke control curves have been compared in order to obtain the best width control result. The optimized short stroke control curve has been applied to the automatic width control system of industrial hot rolling mill, and good performance is obtained.

Vibration of Moving Strip With Distributed Stress in Rolling Process

Taking the moving strip between two stands of some tandem rolling mill in rolling process as a subject for investigation, according to the Poisson-Kirchhoff sheet theory, the vibration model of the moving strip in rolling process was established. Model of distributed stress was built based on rolling theory. And then, vibration model of moving strip with distributed stress was established. The partial differential equation was discretized by Galerkin truncation. The natural frequency and stability of the moving strip were investigated and simulation in time domain was made by numerical method. Taking the moving strip between the second stand and third stand of some tandem mill as a subject for investigation, distributions of stress, natural frequencies and stability of moving strip were determined under six different rolling conditions which are “uniform distribution of stress”, “flat roll flat”, “flat roll convex”, “flat roll concave”, “convex roll flat” and “concave roll flat”. At last, three-dimensional dynamic simulation was made and the moving law of the strip was determined. This model can be used to study the stability of moving strip, depress the shape wave of strip and develop new rolling technology from the aspect of dynamics.

Prediction of thermal stresses and temperature field in work rolls during hot strip rolling process

In this work, a combined finite element analysis and upper bound technique is employed to assess temperature field and thermal stress distribution within the work rolls during continuous hot strip rolling process. Two-dimensional finite element analysis is utilised to simultaneously predict temperature fields within the rolling metal and the work roll as well as thermal stresses in the work rolls. In order to calculate the velocity field and the rate of heat of deformation, an upper bound solution is coupled with the employed finite element analysis. The utilised model makes it possible to estimate the effects of different parameters such as idling revolutions and initial temperature on thermal stresses within the work rolls. The predictions are compared with the experimental data as well as the published results and reasonable agreement is observed.

Analysis of Strip Temperature in Hot Rolling Process by Finite Element Method

The program was developed by finite element method to calculate the temperature distribution in hot strip rolling process. The heat transfer coefficients of air cooling, water cooling and thermal resistance between work roll and strip were analyzed. A new heat generation rate model was proposed according to the influence of source current density, work frequency, air gap and distance to edge on induction heating by finite element method (FEM). The heat generation rate was considered in the thermal analysis to predict the temperature distribution in the induction heating. The influence of induction heating on the strip temperature was investigated for different slab thicknesses. The temperature difference became more and more obvious with the increase of thickness. The strip could be heated quickly by the induction heating both in surface and center because of the thermal conductivity and skin effect. The heat loss of radiation has important influence on the surface temperature. The surface temperature could be heated quickly by high frequency when the strip is thicker.

An integrated model for prediction of thermo-mechanical behaviour of metal and work-rolls during hot strip rolling process

In this paper an integrated model has been developed that is capable of considering the effects of process parameters on the thermo-mechanical behaviour of the work-roll and the strip during hot rolling operations. The commercially finite element package ABAQUS is utilized to solve the governing equations, while an elasto-viscoplastic material behaviour is utilized in the model. The model may be employed in single-pass as well as multi-pass rolling layouts. Various aspects of the hot rolling process are predicted including temperature field and thermo-mechanical stresses within the work-roll as well as temperature, strain, and residual stresses distributions within the strip. To assess the accuracy of the model, predicted results have been compared with experimental data and good agreement has been observed.