Strip Tension Research Articles

Linear theory for lateral displacements of a metal strip in a tandem cold-rolling mill with asymmetries

Asymmetries in the state of a cold-rolling mill cause lateral displacements of the metal strip, which sometimes result in a major breakdown of the mill. Non-linear model equations, previously employed, are reduced to a linear form via a first-order expansion of the plastic reduction equations, appropriate for small displacements. The continuity equations, normally applied at the entry and exit of a stand, are replaced by simpler equations applied on the neutral line. These simplifications provide explicit formulae for equilibrium lateral displacements, which lead to more general conclusions. Moreover, these formulae do not involve the compliance and reaction of the mill, but relate the displacements to strip conditions and roll-gap asymmetries alone. A strong coupling between the stands and a strong upstream influence are demonstrated. The results agree with that of a non-linear model and with data from a laboratory mill. Increasing entry tension to the first stand, up to moderate levels, has the beneficial effect of reducing the size of the lateral displacements. However, the model predicts that abnormally high strip tension or low friction can lead to divergent displacements, which would crash the mill. The results offer the potential for better control and should be of interest to mill operators.

Manifested flatness predictions in thin strip cold rolling

The paper deals with flatness defects prediction in thin plates which appear during rolling. Their origin is the roll stack thermo-elastic deformation. The combination of the elastic deflection, the thermal crown and the roll grinding crown results in a non-parallel bite. If the transverse roll profile is not an affinity of the incoming strip profile, differential elongation results and induces high stresses in the outgoing strip. The latter combine with the imposed strip tension force, resulting in a net post-bite stress field which may be sufficiently compressive locally to promote buckling. A variety of non-developable shapes may result, generally occurring as waviness, and classified as flatness defects (center waves, wavy edges, quarterbuckles…). The purpose of the present paper is to present a coupled approach, following [1]: a simple buckling criterion is introduced in the FEM model of strip and roll deformation, LAM3/TEC3 [2]. The post-bite stress field is in much better agreement with experiments if this treatment is used, as will be demonstrated.

Robust constrained predictive controllers for hot rolling mills: Disturbance uncertainty case

Looper—tension control among various control problems in hot rolling mills (HRMs) has significance, in particular, because it affects both operational stability of the process and dimensional quality of the products. The control target in this control loop is to maintain looper angle and strip tension simultaneously at their desired values. The most difficult challenge in the controller design arises from the interaction, between strip tension and looper angle, and uncertainty coming from disturbances and a model mismatch. Recently, there has been some research to investigate the potential benefits of model predictive control (MPC) for this control loop. However, most of them used constrained optimization based on nominal models, and this often caused constraint violations for the uncertain case. The purpose of this paper is to develop robust MPC algorithms for the hot rolling mill process, in the presence of disturbance uncertainty, in order to improve the constraint handling performance.

Improved Drive Control for Multi-Stand Cold Rolling Mills

In multi-stand cold rolling mills an accurate synchronization of the mill drives is necessary for a good product quality and for a safe process operation. During the standard commissioning procedure the control performance of each drive is optimized individually. However, in normal operation mode the performance is then not always optimal due to the coupling of the drives by the strip being rolled. Based on a model of the drives and the strip tension force the control performance of the coupled drives is analyzed. A linear observer is proposed to support the standard PI speed controllers. Thus control performance can be improved with a minimum of additional effort. The observer needs only a few parameters and can cover all operating points of a tandem cold rolling mill.

H∞-based PI-observers for web tension estimations in industrial unwinding-winding systems

The system under study is a web handling machine composed of an unwinder, several traction motors, several idlers with or without load cells and a winder. All flexible materials such as textiles, papers, polymers or metals are handled on rollers during their processing. Maintaining strip tension in the entire processing line while increasing web speed is a key factor for achieving good final product quality. Due to sources of disturbance and the high coupling introduced by elastic webs, robust multivariable control strategies such H∞-controllers require the knowledge of web tension in each span of the process. Estimators or observers represent a cost-effective method in order to limit the number of load cells or dancers. After a summary of the main laws used for system modeling, two different approaches to design tension observers in a section of a process line are presented and discussed. The first approach is based on a PI-observer calculated in a H∞ sense thanks to optimization techniques. The second approach uses Kalman filtering theory. Both approaches underline the importance of friction in estimation accuracy and propose alternatives to face this issue. This friction on rollers are generally neglected or assumed to be well-modeled in the literature. The proposed observers are also analyzed and discussed with variations in friction torques and nominal set points of the web velocity and tension. Both observers have the major advantage of being easily understandable for industrial applications and can be rapidly programmable in industrial plant controllers.

A MPC for Start-up Phase Tension and Looper Control in Hot Strip Finishing Mills Using Continuation Approach

Abstract TThis paper gives a design method for a model predictive control (MPC) approach based on a unified performance index throughout the start-up phase tension and looper control which consists of the non-contact and contact modes in order to suppress the deviation of the strip tension while the looper contacts with the strip as quickly as possible. We will formulate the control problem by using a MPC for a piecewise affine (PWA) system with the terminal condition and an unknown terminal time. However, in order to realize the feedback control using a receding horizon strategy, we have to solve nonlinear equations in an on-line manner as precisely as possible. Therefore, the paper gives a method using a continuation method for solving the nonlinear equations efficiently. The efficiency of the proposed method is shown through numerical simulations.

Modelling and simulation of MIMO non-linear systems web winding system of a reversible rolling mill

This work treats the modelling and the simulation of the non-linear dynamic behaviour of a web winding process during traction and by consideration the variations of the radius and inertia rollers. We designate by a winding process any system applying the cycles of unwinding, transport, treatment and winding to various flat products. This system knows several constraints such as the thermal effects caused by the frictions, and the mechanical effects provoked by metal elongation, that generates dysfunctions due to the influence of the process conditions. Our study is relative to the modelling and the identification of the parameters of a Web Winding System (WWS) of a reversible mill. Modelling is based on the general laws of physics laws using the strip elasticity, frictions between strip and rolls and the flow of strip between two rolls. Our goal is the determination of the strip tension in movement and the strip velocity in order to synthesise the coupling between variables. Because of the important variation of the radius and inertia of the rolls, the system dynamics change considerably during the winding/unwinding process. Thus, the stability and performances of system are studied on different range of radius variation. The modelling conditions are specified and a mathematical model is presented. Numerical results are exposed and discussed.

SVR을 이용한 Looperless 열연 공정에서의 스텐드간 장력 추정

This paper proposes a novel tension estimation of interstand strip in looperless hot rolling process using SVR(Support Vector Regression). The quality of hot coil which is final product of hot rolling process is substantially decided by tension control of finishing rolling in hot rolling process. The fluctuation of the strip tension in conventional hot rolling process is controlled by the strip tension measured by an inter-stand looper. However, the looper can cause a motor trip and tension hunting in hot rolling process, therefore, alternative method is essential to replace it. In this paper, the mathematical modeling of tension mechanism is implemented to estimate the tension using the proposed SVR algorithm without looper in hot rolling process. The simulation results show a reliable estimation performance and a possibility of tension control using SVR technique.

Fracture Toughness Calculation by Movable Cellular Automata Method

Fracture toughness calculation by Movable Cellular Automata (MCA) method is demonstrated in this study in order to verify the validity of application of MCA method to the fracture problems. Two different geometries: edge-cracked strip and center cracked plate tension specimen have been considered to simulate numerically, which make place in real experiments. Soda-Lime silica glass for brittle material, AISI 1040 Steel and Aluminum Alloy 2024 for ductile materials were used, respectively. Fulfillment of basic principles of fracture mechanics has been checked. In MCA method, special fracture criterion is used to describe the process of crack propagation and critical stress and displacement was obtained, which are used as input data for evaluating the fracture toughness. In comparisons with table data, the results showed the sufficient agreement, which states the facility of the MCA method in application to the fracture problems.

Hybrid FEM/HTA analysis of friction contact in elastic and elastoplastic plane stress problems

The Hopfield–Tank neural network evolutionary equations (called for short HTA – HT Analog) were modified for the analysis of friction contact interface. The modified HTA was used for modeling a function in the hybrid program FEM/HTA and applied to the analysis of two numerical examples. The first example, taken from [Mistakidis ES, Panagiotopoulos PG. Numerical treatment of the nonmonotone (zig-zag) friction and adhesive contact problems with debounding: approximation by monotone subproblems. Comput Struct 1993;(47):33–46], is related to the analysis of nonmonotone (zig-zag) contact of elastic strips. The second example concerns the tension of elastoplastic strip with a rigid bolt inserted into a circular hole of the strip. The example generalizes the analysis performed in [Pabisek E. Neural analysis of elastoplastic plane stress problem with unilateral constraints. Comput Assis Mech Eng Sci, in press], considering Coulomb’s friction contact in the bolt–hole inference.

Looper and tension control in hot rolling mills: A survey

Looper and tension control is important in hot strip mills because they affect the strip quality as well as strip threading. Moreover, the most difficult challenge in controller design and control performance arises from the interaction between looper angle and strip tension. Disturbances from several sources cause a deterioration in control performance, and thus a major role of the control algorithm is effective disturbance rejection. Many authors have proposed and applied a variety of control schemes to this control problem, but nevertheless, the increasingly strict market demand for strip quality requires further improvements in this control area. Hence, this paper critically surveys the strengths and weaknesses of several existing academic and industrial approaches and explores the potential for development in this area.

ROLL SPEED SET-UP IN HOT STRIP FINISHING ROLLING MILL

Hot strip finishing mill is initially set up with rolling conditions such as roll speed, roll gap, and cooling pattern obtained by a set-up model. To improve the accuracy of initial roll speed setting for a 7–stand finishing mill, an equation for predicting forward slip and a compensation method for initial roll speed setting were proposed and applied for No.1 Hot Strip Mill at Pohang Steel Works, Pohang, Korea. As the results, mass flow was improved and width error for strip head-end part caused by excessive strip tension was decreased largely.

Third-octave-mode chatter in rolling. Part 3: Stability of a multi-stand mill

The stability of a tandem mill is analysed by considering interstand interactions. In this part of the paper the stability of the multistand multimodal chatter model, developed in Part 1 [1], is ascertained. The general model is represented in a simplified form, which highlights only phenomena caused by strip velocity, or equivalently, strip tension variations between stands. This mechanism constitutes one of the most critical sources of self-excitation in the operation of tandem mills and leads to the most detrimental effects associated with third-octave mode chatter. As before, the theoretical analysis of the stability conditions is followed by a simulation study that shows the major dynamic trends in the mill's behaviour.

Electromyographic detection of purinergic activity in Guinea pig detrusor smooth muscle.

We recorded nerve mediated extracellular electrical activity from guinea pig detrusor smooth muscle strips using suction electrodes and determined the electrophysiological origins of this signal and its relationship to contractile activity. Mucosa-free detrusor strips were prepared from male guinea pigs sacrificed under Home Office license, physiologically superfused, attached to a pressure transducer and electrically stimulated (0.1 millisecond pulses). Electrical signals recorded using a bipolar reversible suction electrode were processed and recorded simultaneously with changes in strip tension. The effect of superfusion with alpha, beta-methylene adenosine triphosphate (ATP), atropine, extracellular [CaCl(2)] depletion and pharmacological Ca2+ channel blockade on the electrical and mechanical signals was determined. A biphasic electrical signal was consistently recorded from 37 detrusor strips. The signal was sensitive to graded reduction in [CaCl(2)] of the superfusate and abolished by tetrodotoxin in 7 preparations. The signal was also abolished in 12 preparations by alpha, beta-methylene ATP in association with an attenuated contraction but not significantly reduced in amplitude (p = 0.77) despite a significant reduction in tension with atropine (mean plus or minus SD 74% +/- 14% of control, p <0.001). The signal was attenuated to a mean maximum of 9% +/- 3% of control by pharmacological Ca2+ channel blockade and the remaining signal was abolished by alpha, beta-methylene ATP. The extracellular electrical signal recorded from guinea pig detrusor strips using suction electrodes originates from a purinergic mechanism. Although an atropine sensitive component may be present, the signal does not depend on cholinergic neuromuscular transmission and would not be expected to be generated by normal human detrusor. Provided that the electrophysiological basis of purinergic neurotransmission in guinea pig and human bladders is similar suction electrodes may be a valuable tool with which to evaluate in vitro and clinically by electromyography the pathological purinergic neuromuscular transmission that can be expressed in addition to normal cholinergic mechanisms in detrusor from dysfunctional human bladders.

Inhibitory Effects of Sildenafil Citrate on the Tonus of Isolated Dog Internal Anal Sphincter

Although the exact pathogenesis of anal fissure is not known, hypertonicity of the internal anal sphincter might be involved in its pathogenesis as main event. To gain information about possible usefulness of the novel, smooth-muscle-relaxing drug, sildenafil, in chronic anal fissure, we investigated the effect of sildenafil citrate on acetylcholine-induced contractility of internal anal sphincter isolated from dogs. Internal anal sphincter strips were taken from German shepherd dogs and suspended in a tissue bath filled with Krebs solution at 37 degrees C (pH 7.4) continuously bubbled with 95 percent oxygen and 5 percent carbon dioxide, and isometric contractions were recorded. Contractions were evoked by 10 muM acetylcholine, and the effects of different concentrations of sildenafil citrate (0.1, 0.3, and 1 mM) on the isometric tension of each internal anal sphincter strip were examined. The statistical significance was analyzed by one-way analysis of variance. Pretreatment with sildenafil citrate (0.1 mM) attenuated contractile response to acetylcholine (n = 3), which were significantly weak compared with the maximum contractile response to the acetylcholine alone (610 +/- 110 mg vs. 2,825.17 +/- 416 mg; n = 12; P < 0.05). Sildenafil citrate also significantly inhibited the acetylcholine-induced contractions in a dose-dependent manner when applied after. This experimental in vitro study showed that sildenafil citrate relaxes acetylcholine stimulated contractions of isolated dog internal anal sphincter. This may be of importance for raising the possibility that sildenafil cit-rate may have future potential in the treatment of chronic anal fissure. Further studies are needed for a conclusive decision on possible usefulness of sildenafil citrate in patients with chronic anal fissure.

Computational Intelligence-Based Process Optimization for Tandem Cold Rolling

The requirements for the manufacturers of steel have been increased in many respects in recent years. Harsh competition among manufacturers demands a continuous reduction of production costs and improvement of product quality. The work presented herein describes maximizing rolling mill throughput and minimizing processing costs and crop losses by computational intelligence-based process modeling and optimization. In this article, an intelligent searching mechanism is introduced to optimize the rolling schedule by assessing rolling constraints and the combined cost function of tension, shape, and power distribution. The optimization results have been compared with current rolling practices based on empirical models. It is shown that the proposed model can significantly reduce the power distribution cost, maximize the safe level of strip tension, and obtain good strip shape. The proposed model is generic for complex engineering problem optimization, and is capable of multiple-objective problem solving.

Strip tension control considering the temperature change in Multi-Span systems

The mathematical model for tension behaviors of a moving web by Shin (2000) is extended to the tension model considering the thermal strain due to temperature variation in furnace. The extended model includes the terms that take into account the effect of the change of the Young’s Modulus, the thermal coefficient, and the thermal strain on the variation of strip tension. Computer simulation study proved that the extended tension model could be used to analyze tension behaviors even when the strip goes through temperature variation. By using the extended tension model, a new tension control method is suggested in this paper. The key factors of suggested tension control method include that the thermal strain of strip could be compensated by using the velocity adjustment of the helper-rollers. The computer simulation was carried out to confirm the performance of the suggested tension control method. Simulation results show that the suggested tension control logic not only overcomes the problem of the traditional tension control logic, but also improves the performance of tension control in a furnace of the CAL (Continuous Annealing Line).

A SURVEY OF THE LOOPER-TENSION CONTROL TECHNOLOGY IN HOT ROLLING MILLS

Looper and tension control is important in hot strip mills because it affects the strip quality as well as strip threading. Moreover, the most difficult challange in the controller design and control performance comes from the interaction between looper angle and strip tension. Disturbances from several sources also cause a deterioration in control performance, and thus they should be rejected effectively by proper control algorithms. Up to now, various kinds of control schemes have been proposed and applied to this control problem. Recently nevertheless, strict demand for strip quality by the market has required improved approaches to this control area. This paper investigates strong and weak points of various control algorithms proposed in academia as well as industry. It also explores the potential of future technology in this area.

Full Stand Modeling and Tension Control for the Hot Strip Finishing Mill

We describe a looper controller design for a hot strip finishing mill in steel plants. The main function of the looper system is to balance the mass flow of the strip by accumulating material in the middle of the stands. Another function is to control the strip tension which influences the width of the strip. To ensure strip quality, it is very important to control the tension of the hot strip finishing mill. However, because there is a mutual interaction between the looper angle and the strip tension, it is difficult to control the looper system. Previous researches examined only the operation of a single stand. But it is not sufficient to examine the operation and effect of whole stands because the operation is wholly interdependent. In this paper, we present a full model of the hot strip finishing mill in order to more effectively control strip tension. We propose several control methods for the full-stand hot strip finishing mill, denoted as conventional PI, PI with cross gain, and coefficient diagram method (CDM) PID control. In the real plants, there are some problems by using higher order controllers such as LQ, LQG and H∞. By comparison, the PID controller is very simple and easy to apply to all real plants. To that end, we present our findings on PID controls and their potential use in the hot strip finishing mill.

Characterization of strip vibration at the wiping nozzles

A portable system to measure strip vibration at the nozzles level on continuous galvanizing lines is presented. It consists of three inductive sensors: two sensors are located near the strip edges and the last one is at the centre of the strip. This system has allowed reproducible results, provided the appropriate calibration procedure is used. The device has been successfully implemented on three lines of Arcelor. Considering the effect of strip tension and size, the frequency and amplitude measurements confirm the trends that can be expected from numerical modelling. Amplitude is always increased by the gas cooling power in the tower. Strip tension has a predictable effect on the frequency peaks; however its effect on amplitude is more ambiguous. Other observations have been made concerning the effects of pot roll bearings and roll intermesh.