Gauge meter model has been developed to establish plate thickness control with high accuracy in plate mill. First, stretch of mill housing has been predicted using measured mill stretch, and roll deformation model has been newly formulated by considering contact length between top and bottom work rolls in roll kissed rolling. Second, roll deformation model during plate rolling has been derived in case that pressure distributions expressed by polynomial of 4 degree work between rolled plate and work roll as well as between back up roll and work roll. Furthermore, highly accurate and flexible prediction model of thermal profile of work roll has been newly constructed by solving two dimensional heat transfer equation with the method of perturbation on thermal conductivity. Prediction model of roll wear profile model has been also reconstructed on the basis of measured rolls' wear. Gauge meter model has been applied to plate mill in Kakogawa Works, and consequently the accuracy of plate thickness has improved about 15% in comparison with the former model.
Newly developed plate shape control system, using attached shape meter, was put in service in Mizushima Works, Kawasaki Steel Corp. This system consists of (1)Sensors ; attached shape meter, multi head γ ray thickness meter (crown meter) (2)Actuator ; oil pressure type work roll bending device and (3)Models : shape prediction model, plate crown prediction model. The closed loop, comprising attached shape meter and work roll bending system based on the shape prediction model, characterizes this system. Introduction of this system, enables the improvement of flatness and plate crown accuracy, which meets ever upgrading customer's demand and also yields improvement and chance free rolling. This report describes the following terms ; (1)Specification of shape meter and work roll bending device. (2)Algorithm of shape control system. (3)Results.
This paper describes a new approach of pass schedule design for hot strip rolling. Recently theoretical optimization techniques have been applied to obtain the optimum schedule instead of the usual power curve. In this method, the pass scheduling is treated as a single objective programming problem. There are plural objectives in the pass design, which are to satisfy the thickness specification and the temperature specification, to attain the high productivity, and so on. The conflict of the objectives is not considered and the conflict can not be modified. In order to solve these problems, the pass schedule is formulated as a multi-objective programming problem in which the objectives are thickness, temperature, flatness, productivity (rolling time) and cost (rolling energy). A multi-objective optimization technique is applied to obtain the Pareto optimum solution. The interactive fuzzy satisficing method is employed to reflect the pass designers preference and modify the conflicts. Through the numerical simulation, it is confirmed that the interactive fuzzy satisficing for multi-objective programming problem can generate the reasonable pass schedule which has a small amount of scatter in the grade for each objective, compared with the usual approach.
Draft-schedule in hot strip mill is made by the computer automatically with theoretical model. But in some cases, especially in case of material with high deforming resistance or thin gage material, supplemental operater's manual operation is needed to cope with the higher level problem, such as the transversal movement in the direction of strip width or the strip shape fluctuation between the stands. So we introduced the expert system in the finishing mill set-up system at No.2 hot strip mill in NKK Fukuyama Works to ensure the fully automatic computing at the last stage. In this system, we summarized the operator's know-how to avoid the above mentioned higher level problem in two major control items. One is the planning to vary the load distribution over the stands in one cycle, and the other is the restriction of main motor current distribution over the stands and roll gap difference between the neighboring stands. In a feasibility test, the prototype system was 90% applicable to the real process, and we have developed the real-time guidance system.
A set-up technology of the hot strip mill has been newly developed to control the head-end gauge with high accuracy. This technology consists of the rolling load model, which has the equations of rolling temperature, deformation resistance and friction coefficient, and the roll gap model. The equation of deformation resistances expresses the influences of phase transformation and strain accumulation besides the basic deformation hardening, which are derived from the results of hot compression tests of eighteen kinds of steels with typical chemical compositions. Using this equation, the friction coefficients in actual rolling are calculated from measured rolling loads, and the equation of the friction coefficient is expressed as a function of several rolling conditions. Moreover, in order to compensate errors of the rolling load model, the adaptive control by groups of material kinds and sizes is combined with the conventional time-series adaptive control not to interfere with each other. The roll gap model takes into consideration the change of elastic deformation of rolls with roll profiles. These models are applied to the hot strip mill at Kakogawa Works, and the gauge accuracy at the head-end can be remarkably improved over all kinds of steel strips with any size.
An advanced gauge control technology has been developed for a hot strip finishing mill. A linear numerical model which is able to discribe the rolling phenomena, the gauge control system and the looper control system was derived for integrating the following control system. First, a looper angular velocity feedback control for the unstationary parts of the strip was developed in order to compensate for the strip tension fluctuation and the material mass flow fluctuation caused by the quick adjustments of screw down positions. The looper angular velocity is estimated by a minimal order state observer and the feedback gain is determined according to the pole assignment method. Second, a new gauge and strip tension control which is a multivariable control based on the optimal regulator theory was developed for the stationary parts of the strip. The purpose of the control is to minimize the finishing mill exit thickness deviation by means of improving the response of the automatic gauge control without unstabilizing the strip rolling. The superiority of these new controls to the conventional controls was proved by the simulation and experimental results.
Advanced mathematical models for predicting sheet profile in hot rolling have been developed. One of the models is a 3-dimensional FEM model, which is named as "CORMILL (Computational Rolling Mill) System", based on the combination of the 3-dimensional rigid-plastic FEM for sheet deformation and the 3-dimensional elastic FEM for work roll deformation. Another is a matrix calculation method which is applicable to sheet profile control in production mills. Numerical analysis of sheet profile and lateral spread is compared with mesurements in 4-Hi experimental hot rolling. As a result, it has become clear that CORMILL System can give us accurate estimation of sheet profile and lateral spread and that the matrix model improved in estimation of rolling force near the sheet edge will have the same accuracy as CORMILL System.
Recently, for thickness gauge of cold strip, higher accuracy is required by customers than ever. To supply high quality strip, we have developed a New AGC system, and have applied it to No.1 Cold Tandem Mill at Kawasaki steel's Mizushima Works in 1990. To decide revamping items, each item is evaluated using dynamic simulater. This revamping is composed of three functions as below. : (1)All stands back up roll roller type bearings as a substitute for oil film type bearings (mogoil bearings) (2)The new AGC controller (high-response AGC and non-interference fuzzy control) (3)The new sensors (strip speed meter of Laser Doppler Type) By this improvement, the thickness accuracy of strip is remarkably improved. The thickness accuracy is within 0.3% in the steady rolling and within 1.6% of finished thickness for a 0.8mm strip thickness in the unsteady rolling.
In cold rolling, sectional profile must be able to be controlled within the limited region where edge drop grows by rolling. The characteristics of profile control are qualified by the experiments in an experimental mill and a real tandem mill installing a work-roll-shift device with tapered work rolls. Studying stress and strain conditions near width edge in a roll gap introduces some infomations concerning to edge drop formation. And the printing ratio of work roll profile, the ratio between change of work roll profile and change of strip profile is introduced as theoretical equations. By this expression, the tendencies of change of edge drop by the change of rolling conditions and work roll shift coditions are able to be estimated. Further the plasticity curve involving the effect of tension feed back near width edge is expressed, and simulations of control of edge drop are performed by introducing the curve into the roll deformation model. By those studies, it is clarified that the range where the plane stress condition affects is a key factor for formation and control of edge drop.
A demand of quality improvement for flatness and edge-drop has been recently increasing in cold rolling of steel strip. The accurate control systems of strip shape and edge-drop have been developed for the new tandem cold rolling mill in Yawata Works, which has 5 stands of 6 Hi-UC·WR shift mill. The control system of strip shape consists of the initial set-up for roll benders, intermediate roll shifts of all stands, a feedback control for roll benders and roll levelling of No.5 stand by using signals of the shape meter which is installed at the exit of No.5 stand. The control system of edge-drop consists of the initial set-up for work roll shifts of No.14 stands and the feedforward control for work roll shifts of No.14 stands by using signals of the crown meter which is installed at the entry of No.1 stand. Application of these control systems to the new tandem cold mill shows the good controllability of flatness and edge-drop in cold rolling of steel strip. The strip flatness is within ±0.7% of inclination in an overall length of strip, and the accuracy of edge-drop is 1.2μm in average and within ±3μm in an overall length of strip.
With regards to the hot-rolling of parallel flange section (ex. H-beam, Channel), the authors have succeeded a new size-free-rolling method with highly accurate dimensions. This rolling method is characterized by using adjustable width horizontal rolls of universal stands and web-height reduction rolling. The universal horizontal roll width can be changed within 20 seconds and the web-height of the parallel flange sections can be reduced by max. 32mm in the mill line. As the result, it becomes possible to roll the parallel flange sections with constant outer-depth and highly accurate dimensions. These rolling technology has been applied for new H-beams in the Large Shape Mill of the Kashima Steel Works.
In conventional H-shapes, the inner dimensions are fixed because the roll dimensions cannot be varied during rolling.However, from the viewpoint of economy and on-site productivity in construction work, rolled H-shapes with fixed outer dimensions(web depth, flange width)have been strongly required. Newly developed hot rolling techniques make it possible to produce such H-shapes with quality equal to that of welded H-shapes. Using an experimental model mill, it was found that a web width reducing method using a universal mill can produce a constant web depth with different flange thicknesses. At the same time, it is possible to prevent web buckling, web off-center, and nonunifomity of the web thickness, which have been the main problems in web width reduction. It was also found through model rolling experiments that grooveless edger rolling is effective in controlling the flange width. Using these techniques, it is possible to manufacture H-shapes with substantially more accurate fixed outer dimensions than those produced by conventional rolling.
H-beams are manufactured by multiple reverse rolling through universal mill and edger. In this process, complexity of relationship among rolling parameters makes it difficult to get H-beams with closed tolerance. The objectives of this study are to clear the effect of each rolling parameter on dimensions and develop the method for controlling dimensions with accuracy. In this study, the influence coefficients method available for making effects of many parameters clear quantitatively was used to attain the objectives. Firstly, fundamental equations are made up based on mathematical model of rolling and characteristics of mills such as mill spring. Secondly, dimensional variation caused by change in rolling conditions was investigated by analysis using fundamental equations and the relation between dimensions and rolling parameters was clarified. Thirdly, the rule for controlling dimensions was established by applying influence coefficients method to calculate the modified roll gaps for getting H-beams with higher accuracy. Finally, the application of this method for practical operation verified its validity for rolling H-beams with closed tolerance. Especially, the universal mill with the function for moving upper horizontal roll in the axial direction results in the remarkable improvement for decreasing the deviation among wall thicknesses at four flange parts.
This paper describes the latest performance of bar rolling employing the high rigid two-roll sizing mill. This technology is comprising of three stands 2-roll sizing mill with roll parting adjustment mechanism, dedicated roll turning lathe and roll scheduling software system. The sizing mill offers not only the precision tolerance and free size availability for customers but also the improvement of mill utilization and operation cost at bar mill. 2-roll sizing mill for bar-in-coil and wire rod has also started the operation.
Three-dimensional deformation of tubes in stretch reducing milll is simulated both by rigid-plastic finite-element method and by rolling experiments with a single three-roll stand. The mechanism responsible for circumferential wall thickness variation, so-called polygonization of the tube bore is clarified: (1) The wall is thinned at the groove root and is thickened at the flange after a single-pass rolling. (2) The degree of polygonization increases as the t/D ratio, the reduction in diameter and the ovality of the roll groove increase. It decreases as the front or/and back tension increases. The position of the neutral line which is closely related to the stress-strain distribution in the tube has a great influence on the degree of polygonization. (3) The finite element analysis on the polygon formation appeared in a multi-pass rolling reveals that the circumferential position of the thickest wall lies between the groove root and the flange side. The degree of polygonization after each pass is also calculated. The rolling conditions such as the reduction in diameter, the ovality of the roll groove and the magnitude of inter-stand tension are optimized to suppress the polygon formation. This leads to the expansion of the product range of thick-walled tubes of which the t/D ratio exceeds 30% in a small-diameter seamless tube mill.