Strip Processing Line Research Articles

Distribution of the Strip Tensions with Slip Control in Strip Processing Lines

The control of tension in processing lines for metal strips tackles several problems. The process of achieving high tension driven by a multi-motor drive system, where the motors are mechanically coupled by a strip, is affected by the maximal torque of each drive, by friction between the strip and the surface of the tension roll, and by the wrap angle. The friction itself and the wrap angle are described by the eµα factor, which can be also calculated as the ratio of tensions in the strip in the previous section and subsequent section of the multi-motor drive. In this paper, an algorithm for the proper distribution of tensions in the strip for a multi-motor drive system of a continuous processing line is revealed. The algorithm ensures the tension distribution among particular drives of the tension leveler while respecting the physical limits of the drives and also preserving the desired conditions of a constant ratio between the input and output tensions for all drives in the leveler. The algorithm also prevents overloading of the drives. Finally, the algorithm was implemented in a control system of a strip processing line, and the obtained results correspond with the simulations. This, in turn, confirms the correctness of the algorithm design.

Lyapunov Based Reference Model of Tension Control in a Continuous Strip Processing Line with Multi-Motor Drive

The article describes design and experimental verification of a new control structure with reference model for a multi-motor drive of a continuous technological line in which the motors are mutually mechanically coupled through processed material. Its principle consists in creating an additional information by introducing a new suitable state variable into the system. This helps to achieve a zero steady-state control deviation of the tension in the strip. Afterwards, the tension controller is designed to ensure asymptotic stability of the extended system by applying the second Lyapunov method. The realized experimental measurements performed on a continuous line laboratory model confirm the advantages and correctness of the proposed control structure: it is simple, stable, robust against changes of parameters, invariant to operating disturbances and ensures a high-quality dynamics of the controlled system prescribed by the reference model. To demonstrate effectiveness of the design, the performance of the controller was compared with properties of a standard Proportional Integral Derivative/Proportional Integral (PID/PI) controller designed in frequency domain.

Design of an one-sided transverse flux induction coil by using a numerical optimization algorithm

The transverse flux heating (TFH) concept offers very high electrical efficiency in combination with unique technological flexibility. Numerous advantages make this method beyond competition to be applied in e.g. continuous strip production and processing lines. However, all potential advantages of TFH can be realized in practice only by optimal design of the inductor shape and optimal control of the heaters, using numerical modelling and optimization techniques. The paper describes a successive approach to optimal design of a single layer induction coil, which will be used for onesided TFH of moving thin steel strip with constant width. The peculiarity of the design refers to the very slow movement speed of the strip and the target temperature, which is set below Curie.

Implementing an online bond quality inspection system for cold roll bonded Al/Al-Sn/Al/steel strips using guided wave EMATs

A prototype on-line bond inspection system for Al/Al-Sn/Al/steel strips is introduced to detect bond defects that occur in the cold roll bonding (CRB) process of strips. The transmitting and receiving ElectroMagnetic Acoustic Transducer (EMAT) probes inspect 100% material volume whilst the strip is processed continuously. The inspection signals are processed in real-time and are stored for post-processing. Serial production strips with good bond as well as with defects along the bond line were inspected for rigorous testing of the prototype machine. The inspection results were statistically analysed to determine an alarm threshold for serial inspection. The most important results are that the guided waves are sensitive enough for practical non-destructive testing (NDT) to detect all bond defects with only 0.5% false alarm rate, which nowadays can only be detected with a destructive peel-off test. The detection of all kinds of bond defects would lead to unreasonable levels of scrap due to false alarms. The application of this prototype EMAT inspection system to an industrial strip processing line shows that on-line detection of significant defects in CRBed Al/AlSn/Al/steel strips in a harsh serial production environment is possible. Design improvements are proposed to address the issues that occurred during inspection trials to design a more robust mechanical machine for the industrialisation of an EMAT inspection system.

Thermal Treatment of Aviation Aluminum Alloys in Strip Processing Lines

For many years now the use of aluminum as a light weight construction material in the aviation and automotive industry is on the rise. Without the innovative aluminum materials the strategies of constructing in light-weight design cannot be implemented. Last but not least this trend is driven by official requirements directing the reduction of greenhouse gas emissions. Aluminum is used both for structural components as well as for external body parts. Aluminum products for these industries have to undergo a production process which includes homogenizing of the ingots, hot rolling and cold rolling. Subsequent to the cold rolling process, the aluminum sheets have to undergo a heat treatment process to regain formability as well as the required material strength. The material properties required by the aviation and automotive industry are achieved in the annealing furnace and downstream cooling equipment. Equal and well-aimed heating and cooling along the length and across the width provide the strips with the metallurgical properties with regard to hardness and grain size. Hence the annealing furnace and the downstream cooling equipment are the decisive process components and critical for the high quality of the end material. First the material is heated up to a temperature above 500 °C for the solution heat treatment process. The following process step foresees cooling down the material to ambient temperature. Especially 6xxx automotive-alloys as well as 2xxx and 7xxx aerospace-alloys require high cooling rates. Eventually, the material gets heated up again for a certain time to apply an artificial aging process. In floatation heat treatment furnaces the strip is guided sinusoidal and contactless by floatation nozzles through the furnace. The strip is heated up and kept at the required strip temperatures in time, so the aluminum-alloy obtains their structure. The cooling process with high cooling rates is executed as a combination of water and air cooling. A mathematical model calculates the necessary settings for the annealing and cooling process under consideration of the mechanical properties. Paper and presentation will introduce the furnace technology for aluminum strips. Especially, the heat treatment facilities for heat and chemical treatment lines will be presented. It will especially emphasize on heat treatment cycles, the materials and the applications.

A strategy for the controlled setting of flatness and residual stress distribution in sheet metals via roller levelling

Abstract High-efficient, fully-automated strip processing lines rely on homogeneous conditions of the incoming metal strip. Roller levelling machines are therefore placed in the initial stage of sheet processing lines to ensure both the strip flatness and a desired residual stress distribution. Even though a sheet metal appears perfectly flat, the residual stress distribution may be disadvantageous and lead to flatness defects in the downstream production. Furthermore, the material properties of the metal strip may change along its length and make an adaption of the leveller’s setting necessary. To link both target values of sheet flatness and residual stress distribution, a numerical model of a seven-roll leveller is used to determine roll positions resulting in a flat sheet and a defined residual stress distribution. Thus, correlations between the initial sheet properties, the machine settings and the final sheet properties can be derived. Additionally, the influence of changing material parameters is shown. All results will finally be used to provide a reference for a feed-forward process control based on a force measurement in the first load triangle of a roller leveller. In order to validate the numerical results, experiments on a down-sized roller leveller are conducted which show that the changes of the forces in each load triangle correspond to the numerical results when changing both the initial sheet state and the intermesh. Thus, the general potential of changing the residual stress distribution via roller levelling can be investigated using numerical calculations.

Strip lateral position control using electromagnets in continuous processing line

In continuous metal strip processing lines, such as pickling, annealing and surface treatment lines, lateral instability of strips is a common problem. Strip lateral movement has a bad influence on productivity of the processing lines. A simple and effective device to control a lateral position of a strip is required because conventional preventions such as a steering roll and crown roll are not effective. In this study, a method of controlling a strip lateral position using electromagnets was investigated. First, theoretical equations were derived to predict capability to control a strip. Next, the derived theory was verified compared with lab experiments. The results obtained can be summarized as follows: (1) The theoretical equations of velocity of lateral movement are derived from inclination when the strip is attracted by electromagnet(s). The inclination is calculable from geometric relation. (2) It is found that the theoretical equations are valid by lab experiments in the conditions of changing attracting displacement and line speed. Controlling lateral movement using electromagnets is possible, and the control capability can be estimated by the derived theory. (3) The velocity of lateral movement in the case of attracting the half of strip width is three times as fast in the case of attracting the edge of the strip.

TiN/NbC Compound Particle Formation during Thin Slab Direct Rolling of HSLA Steel

Compound two‐phase particles were found in thin slab direct rolled Ti‐added Nb high strength low alloy (HSLA) steel after the rough rolling stage of an in‐line strip processing line. The compound two‐phase particles are composed of a cuboid Ti‐rich (TixNb1−x)N (0.73≥x > 0.60) core and an Nb‐rich cap‐shaped epitaxial deposit of (TixNb1−x)C (0.35≥x > 0.06) or NbC formed on the {100}‐type faces of the cuboid (TixNb1−x)N (0.73≥x > 0.60) core. At the interface between the cuboid core and the cap‐shaped deposit, the Ti/(Nb + Ti) atomic ratio was found to increase gradually from a low value of Ti/(Nb + Ti) ≈ 0, on the cap‐side of the particles, to a high value of Ti/(Nb + Ti) ≈ 0.7, on the cuboid core side of the precipitate. The fact that compound TiN/NbC two‐phase particles are present in the matrix indicates that NbC has a greater thermodynamic stability, i.e. a lower solubility, in the presence of TiN precipitates. A kinetic precipitation model is proposed to explain this effect. The model is based on the formation of geometrically necessary dislocation (GND) around TiN precipitates. A high TiN volume fraction leads to a high density of GND and a high density of heterogeneous nucleation sites for NbC. Consequently, the solute Nb content is lowered and the strain accumulation due to the suppression of the inter‐pass recrystallization is limited. This results in the high softening ratio observed in multi‐hit compression test.

Large Deflection Strip Model for Strip Running Simulation

Strips are produced in steel, plastic and paper making industries and the strip is a primitive structure. Lateral movement problems cause low productivity in continuous strip processing lines. Now most these problems are solved experimentally only. Development of realistic, robust and speedy simulation methods for these problems is required. In this paper, we propose a large deflection strip model to simulate the running strip on rolls. The new model is a basic one, which is defined on approximated curvilinear coordinate systems along the strip deflection and includes in-plane bending. We confirmed that numerical simulation results from the new method correspond with conventional results from the large deflection plate model.

Computational analysis of the curvature distribution and power losses of metal strip in tension levellers

Tension levelling is employed in strip processing lines to minimise residual stresses resp. to improve the strip flatness by inducing small elasto-plastic deformations. To improve the design of such machines, precise calculation models are essential to reliably predict tension losses due to plastic dissipation, power requirements of the driven bridle rolls (located upstream and downstream), reaction forces on levelling rolls as well as strains and stresses in the strip. FEM (Finite Element Method) simulations of the tension levelling process (based on Updated Lagrangian concepts) yield high computational costs due to the necessity of very fine meshes as well as due to the severely non-linear characteristics of contact, material and geometry. In an evaluation process of hierarchical models (models with different modeling levels), the reliability of both 3D and 2D modelling concepts (based on continuum and structural elements) was proved by extensive analyses as well as consistency checks against measurement data from an industrial tension leveller. To exploit the potential of computational cost savings, a customised modelling approach based on the principle of virtual work has been elaborated, which yields a drastic reduction of degrees of freedom compared to simulations by utilising commercial FEM-packages.

Development of Pinch Rolls to Control Strip Wandering in Strip Processing Lines.

In strip processing lines, it is important to restrain strip wandering which obstructs operational reliability and makes productivity decline. To improve the stability of the strip conveyance at the existing facilities in addition to the new facilities, a compact guiding apparatus was able to be introduced easily and was valid. In this report, the structure of the unique bent roll covered with a rubber sleeve, which has a wandering restraint function, was examined and the effect was clarified using an experimental apparatus. A rubber sleeve that needs durability to endure expansion and contraction by rotation of the bent roll was also examined. Production machine size rolls were newly developed and evaluated as pinch rolls in processing lines. Under the general condition to set pinch forces identically on both sides of the roll, this roll always has the ability to restrain strip wandering. When putting deviation of pinch forces on both sides, the ability of the wandering correction was increased. It was proposed that the wandering correction system, which controls the pinch force using the output of width sensor, was useful in the processing line. It was also possible to use these pinch rolls as the wandering correction apparatus at the place where it is difficult to use a general guiding apparatus because there is no restriction of line tension.

Dynamics and control of accumulators in continuous strip processing lines

Accumulators in a strip processing line are primarily used to allow for rewind or unwind core change while the process continues at a constant velocity. Accumulators facilitate continuous operation of the process line and thus constitute an important element of a continuous strip processing line. This paper studies the coupled dynamics of the accumulator carriage motion, rollers, and web spans. Suggestions are made in an effort to integrate the tension dynamics of individual spans in an accumulator. An average dynamic model that integrates the dynamic models of individual spans in the accumulator is derived. This aggregation of the dynamics can facilitate control design for the accumulator carriage. Hydraulic system modeling associated with the accumulator is studied. Aspects of the hydraulic system such as drop due to friction in long pipes and dominant damped resonant frequency of the hydraulic system are discussed. A compact state-space model of the dynamic model of the accumulator is obtained from the average span tension dynamics, carriage dynamics, and pressure dynamics. Some experiments conducted on an ALCOA Corporation continuous process line are discussed.

A new tension controller for continuous strip processing line

The strip tension as well as the line speed should be controlled tightly for the quality of products and productivity of the continuous strip processing line. In this paper, a new tension control algorithm with tension observer is proposed using observed tension as a regulator feedback. The tension observer as based on the torque balance of a roller stand, including the acceleration torque. Using this estimated tension, a new tension controller can be constructed with faster dynamic response in case of line speed acceleration or deceleration. The proposed scheme needs no additional hardware because the inputs of observer, current and speed, are already being monitored by the motor drive system. As this scheme directly controls torque current of the motor, better control performance can be obtained even without the tension transducer. Through the simulations and experiments with the laboratory setup, the performance of conventional schemes and the proposed one are compared. The results show the effectiveness of the proposed tension controller.

Robust observer-based control of an aluminum strip processing line

Robust observer-based control of an aluminum strip processing line

Design of optimal machine-control systems

A method is described for the design of optimal linear servomechanisms. The system to be controlled is assumed to be linear, time invariant and multivariable. The cost function to be minimised is quadratic and is measured over an infinite time interval. Expressions are given to enable the optimal controllers for both open-loop and closed-loop systems to be calculated. A result is obtained that allows the cost function weighting terms to be related to the optimal-compensated system pole positions, and hence to the system transient response. The relationship can be used when choosing the weighting constants. The design procedure is illustrated in the design of a controller for a strip processing line for which the tension in the strip and the speed of the drives is to be controlled. A new method of spectral factorisation is also introduced. This can only be used on a restricted-class matrices having a degree of symmetry; however, it is much easier to use than previous methods.

Tension controls in strip processing lines

AbstractThe problem of tension control in metal-strip processing lines is discussed. A tensioncontrolled zone is considered and the relationships between tension change and motor-speed changes are developed. The effects of placing a number of undriven rolls within the controlled zone are discussed and the associated tension-change state equations and transfer functions are derived. Relationships are developed between the order of the system (or the system gain) and the number offree rolls. The steady state and dynamic accuracy of tension controls are discussed and relationships are produced to allow the calculation of tension-loop gain and static- and dynamic-tension errors. The difficulties associated with the definition of tension-loop gain are also described. This quantity is shown to be dependent on the gain of the tension-error amplifier and the drive-system speed regulation.