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ONLINE ISSN: 1883-2954
PRINT ISSN: 0021-1575

Tetsu-to-Hagané Vol. 67 (1981), No. 15

  • Improvement in Rolling Yield at Blooming Mills

    pp. 2261-2269

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    Readers Who Read This Article Also Read

    1. Recent Progress of the Product Yield in Wire Rod and Bar Mills Tetsu-to-Hagané Vol.67(1981), No.15
    2. Development of Control Techniques for Mixing Small Coke at Bell-less Top Blast Furnace Tetsu-to-Hagané Vol.102(2016), No.11
    3. Yield Improvement Techniques in Plate Rolling Tetsu-to-Hagané Vol.67(1981), No.15
  • Yield Improvement Techniques in Plate Rolling

    pp. 2270-2284

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    [in Japanese]
  • The Recent Yield of Hot Strip Mill in Japan

    pp. 2285-2288

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    Readers Who Read This Article Also Read

    1. Technique to Decrease Crop Loss in Hot Strip Mill Tetsu-to-Hagané Vol.67(1981), No.15
    2. A New Method of Slab Rolling for Prevention of Growth of Crops Tetsu-to-Hagané Vol.67(1981), No.15
    3. Reduction of Crop Loss on Slab Rolling Tetsu-to-Hagané Vol.67(1981), No.15
  • Recent Progress of the Product Yield in Wire Rod and Bar Mills

    pp. 2289-2295

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    Readers Who Read This Article Also Read

    1. Improvement in Rolling Yield at Blooming Mills Tetsu-to-Hagané Vol.67(1981), No.15
    2. Development of Control Techniques for Mixing Small Coke at Bell-less Top Blast Furnace Tetsu-to-Hagané Vol.102(2016), No.11
    3. Yield Improvement Techniques in Plate Rolling Tetsu-to-Hagané Vol.67(1981), No.15
  • Automatic Measurement and Controls on Rolling Processes of Seamless Pipes

    pp. 2296-2302

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  • Off-gauge Reduction and Improvement of Thickness Accuracy in Cold Rolling

    pp. 2303-2315

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  • Computer Control of Hot Strip Mill

    pp. 2316-2326

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  • Study on Characteristics of Cold Tandem Mills

    pp. 2327-2336

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  • Finite Element Analysis of Nonsteady State Deformation in Flat Rolling

    pp. 2337-2342

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  • The Improvement Techniques of Slabbing Yield from a Capped Steel Ingot

    pp. 2343-2349

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    Based on extensive utilization of traditional improvement techniques of slabbing yield and several newly-developed improvement ones, a record-breaking yield of 96.8% has been achieved for capped steel ingots in Nagoya Works, Nippon Steel Corp.
    The new techniques are as follows:
    1) Determination of optimum ingot profile to maximize yield such as cross-section dimensions, ingot top-corner profile and top capped figure.
    2) Introduction of special rolling precesses of ingot such as one-way rolling and reverse one-way rolling.
    3) Development of defect free capped steel ingot making method with bottom pouring technique and defect minimization rolling method.
    4) Development of multi-step well type bottom plate to minimize slab crop.
    It has been actually proved that these new techniques give a great yield improvement and the cost for adequately compensated by the effects.
  • A New Method of Slab Rolling for Prevention of Growth of Crops

    pp. 2350-2355

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    We have developed new slabbing methods to reduce the crop losses remarkably. The new methods were devised after investigating the basic deformation behavior at both ends of the slab during slab rolling.
    In particular there are two methods, namely, "Bite Back Rolling method" and "Ultra High Reduction Slabbing method", and both are effective in minimizing the crop losses. As a result of applying the two methods to an actual mill at our works, Kawasaki Steel Corp., a slab yield of 96% after conditioning of capped steel was attained by the Bite Back Rolling method, and the slab rolling yield of capped steel increased by 4%. A slab rolling yield of 97.5% for AISI 430 was attained by the Ultra High Reduction Slabbing method.
    x

    Readers Who Read This Article Also Read

    1. Technique to Decrease Crop Loss in Hot Strip Mill Tetsu-to-Hagané Vol.67(1981), No.15
    2. The Recent Yield of Hot Strip Mill in Japan Tetsu-to-Hagané Vol.67(1981), No.15
    3. Reduction of Crop Loss on Slab Rolling Tetsu-to-Hagané Vol.67(1981), No.15
  • Calculation Model for Pass Schedules of Slabbing Mills

    pp. 2356-2364

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    Mathematical models which are necessary to construct the pass schedule of slabbing mills are proposed.The results of this research are summarized as follows;
    (1) The equations are introduced by which the rolling force and rolling torque in the horizontal and vertical slabbing mills and the edging mill of hot strip mill are predicted.
    (2) The calculation method of the thickness reduction to give the predetermined rolling force or rolling torque without iteration is introduced.
    (3) The pass schedule appropriate either for high yield or high production is selectable according to the situation in the present system.
    (4) The adaptive calculation method to adjust deformation resistance of rolled material using the ratio of z (=actual rolling force/calculated rolling force) is developed.
    These models have been applied to the slabbing mill computer control system of the Kashima Steel Works, Sumitomo Metal Ind., Ltd. and the results are satisfactory.
  • A Mathematical Model of Crop Loss and Its Applications to Minimizing Crop Loss in Slabbing and Blooming

    pp. 2365-2374

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    To formulate an optimum condition for minimizing crop loss in slabbing and blooming, the crop calculation program has been constructed on the basis of the model tests for plasticine and hot steel. In slabbing, it is shown that the influence of each factor of ingot size, ingot end profile, and rolling schedule upon crop loss formation changes in different ways according to the choice of their combination by use of the crop calculation program. The optimum rolling condition also depends upon the production mix of slabs.
    The crop calculation program is applicable to minimize crop loss in blooming, as well. It is shown that most of crop loss is formed in the earlier stage of rolling schedule before the groove rolling pass, and that the influence of reduction at each pass on the change of crop loss decreases in proportion to the increase of pass number.
  • Reduction of Crop Loss on Slab Rolling

    pp. 2375-2384

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    For the improvement of the yield in making a slab from an ingot, it is important to decrease crop loss. Studies have been carried out to reduce crop loss, mainly by using plastcine as model rolling material, and the results are summarized as follows:
    (1) A high-lift mill has an advantage over a universal mill. A high-lift universal mill is the best type of slabbing mills when productivity is taken into account in addition to the yield of product.
    (2) Crcp loss can be drastically reduced by making the bottom shape of a flat bottom ingot to compensate overlap and fish-tail obtained by rolling it.
    (3) A new rolling method has been developed for reduction of crop loss, on the basis of the fact that overlap and fish-tail are smaller at the front end than the tail end of rolling. In this method the rolling end is sufficiently rolled at the preceding pass to avoid rolling at tail end at the earlier stage of passes.
    x

    Readers Who Read This Article Also Read

    1. The Recent Yield of Hot Strip Mill in Japan Tetsu-to-Hagané Vol.67(1981), No.15
    2. A New Method of Slab Rolling for Prevention of Growth of Crops Tetsu-to-Hagané Vol.67(1981), No.15
    3. Technique to Decrease Crop Loss in Hot Strip Mill Tetsu-to-Hagané Vol.67(1981), No.15
  • Effect of Rolling Conditions on Annihilation Process of Loose Structure in Large Slab Ingot

    pp. 2385-2394

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    The effect of rolling condition on the annihilation process of loose structure in large slab ingot was investigated to clarify the possibility of getting sound heavy steel plate by rolling. The most important parameters for annihilating the loose structure were found to be reduction ratio, rolling shape factor, and deformation resistance ratio. The following formulae were derived to predict the rolling conditions required for annihilating loose structure.
    a=∑n1=1ψi(Δh/Ho)i≥1,
    ψ=(Δb/bo)/(Δh/Ho)=3[1-0.14/1d/hm·exp{-4·(1d/hm)0.77·Pav/koc}]
    where a : Critical closing hole index ψ : Rate of closing hole
    Δh : Reduction 1d/hm : Rolling shape factor
    Ho : Initial thickness koc : Deformation resistance at the center of thickness
    Pav : Average of hydrostatic stress
    Δb : Reduction of hole diameter bo : Initial hole diameter
  • Development of a New Rolling Method Using Edger Rolls to Get High Yield at Plate Mill

    pp. 2395-2404

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    The effect of the edging on the plate profile has been studied by a 1/10 model of plasticine. The plate profile was improved by the adoption of combination of longitudinal and cross directional edging. At Plate Mill in Nagoya Works, the optimum system of longitudinal and cross directional edging was accomplished by studying experimentally the change of plate profile through edging and flat rolling. The proper rectangular plate profile has been made by making, firstly, the plate profile concave type by cross directional edging before broadside rolling and secondly by edging in longitudinal direction after the broadside rolling. The aimed value of rolling width was decided by considering the width change at finishing stage. The yield of plate mill has been improved by 3% using this system.
  • Improvement of the Yield by Edging Method in Plate Rolling

    pp. 2405-2411

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    It is important to improve the plane view patterns of plates, in order to increase the yield of steel plates. For this purpose, edging method is examined by a laboratory test using lead plates, so that optimum edging condition is established, and the results are applied to actual plate rolling.
    The results are as follows:
    (1) By the edging method, plane view patterns are improved with the yield increase of about 2%.
    (2) The edging method is more effective when both top-bottom edging and side edging are carried out.
    (3) The edging method is also effective to diminish the side overlap of heavy plates.
  • Development of New Plan View Pattern Control in Plate Rolling

    pp. 2412-2418

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    Recently, the techniques to improve material yield in plate rolling have been rapidly progressed. Among them the progress of the plan view pattern control rolling, represented by MAS (Mizushima Automatic Plan View Pattern Control System) rolling and others, is remarkable. The authors have developed another plan view pattern control rolling, which can be easily applied to existing mills.
    The new method is characterized by the inclination of the upper roll during broadside rolling, which is effective to modify the convex side crop shape.
    On the other hand, in order to modify the convex end crop shape edger rolling has been used, but it generates the convex side crop shape.
    Then it is effective to use edger rolling together with our new rolling to modify both the convex end crop shape and the convex side crop shape.
    This plan view pattern control system is easily applicable and can improve material yield by 11.5%. Satisfactory results are being obtained by its application to the plate mill at Chiba Works of Kawasaki Steel Corporation.
  • Development of the Plan View Pattern Control System in Plate Rolling

    pp. 2419-2425

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    In plate rolling, it has been sought for many years to make plates rectangular as correct as possible, as one of the methods to improve the yield. MAS rolling (Mizushima Automatic Plan View Pattern Control System) has been developed as a completely new method to make the plan view pattern into a rectangular shape. To improve the controlling accuracy of the MAS rolling system, the following techniques also have been developed.
    (1) Plan View pattern prediction models which also calculates the width gain in the MAS rolling.
    (2) Application of AG (Absolute Gauge)-AGC (Automatic Gauge Control) to the thickness profile control of the MAS rolling.
    This report also describes the different width rolling as an application.
  • Instrument for Detecting Plate Shape and System for Analyzing Optimum Slab Size for Plate

    pp. 2426-2432

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    For the improvement of plate product yield, a new unique system which contains high level technology for sizing and cutting plates and appropriate slab size design has been developed. The characteristic features of the system are as follows:
    (1) PSG (Plate Shape Gauge) has been developed and can measure a plate upon completion of rolling and provide that data to the computer accurately indicating the plate's top view profile.
    (2) The automation of optimum sizing, optimum cutting and inspection of plate has been realized using the recognized plate pattern image along with finishing data for the plate.
    (3) The system for analyzing optimum slab size for plate with various data such as data obtained by PSG has been developed.
    This system has been carried out at the plate mill in Wakayama Steel Works since 1977 and has brought about the improvement of product yield of 2.2% as a direct effect plus substantial labor savings.
  • Accurate Rolling Techniques in Plate Rolling

    pp. 2433-2442

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    Intensive efforts have been taken to improve yield ratio and quality of products in plate rolling. It concerns with mainly production of flat and rectangular plates by application of accurate rolling techniques. In this paper, fundamental study of crown or shape, camber, and plane view of plate is carried out by experiments and numerical simulations. Following rolling techniques have been developed respectively:
    (1) A pressure control of work roll bender by chamfered back-up roll,
    (2) An automatic transverse leveling adjustment system at interpass (ATLAS) by hydraulic screwdown,
    (3) Dog bone rolling method (DBR) by high speed and long stroke hydraulic screwdown.
    At present, these techniques have been applied at a plate mill in Fukuyama works and it is confirmed that yield ratio is improved.
  • Optimal Size Control in Plate Rolling

    pp. 2443-2451

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    This report describes plate thickness control and plate width control whose accuracy directly influences product yield. Concerning thickness control, it is necessary to increase the accuracy of gagemeter model for absolute mode AGC (Automatic Gage Control). Therefore, the authors developed a new roll bending model for operation. This model was obtained by correcting the solution of simply supported beam with the quadratic function of plate width by considering work roll balance force. Concerning width control, the authors developed a new method for calculating the thickness after broadside rolling, which was based upon the slab volume calculated in actual slab weight without scale losses in the reheating furnace.
    These techniques greatly improved the accuracy of plate thickness and width. Consequently, ordered product yield can constantly be maintained at a high level of 94.5% (C. C. slab).
  • New Seamless Pipe Rolling Technology for Higher Dimensional Accuracy

    pp. 2452-2458

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    It is a recent tendency that higher accuracy in dimensions of seamless pipe has been more frequently requested as the application becomes more critical.
    Technology which has enabled to obtain higher dimensional accuracy in a mass production line of seamless pipe is described here on each process from bloom reheating to sizing. The technologies involve the individual method for prevention of eccentricity at Mannesmann Piercer and Press Roll Piercer, reduction of eccentricity at Elongator, improvement of wall thickness accuracy at Plug Mill, Mandrel Mill and Semi-floating Mandrel Mill, improvement of outer-diameter accuracy at Sizer and prevention of hexagon at Stretch Reducer. Some of actual dimensional accuracy data achieved with the PRP-Plug Mill which has been installed recently in Japan are also shown.
  • Reduction of the Polygonization in Continuous Butt-weld Pipe Rolling

    pp. 2459-2462

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    This paper describes the method for eliminating the polygonization of thick-wall steel tube in a reducing mill.
    (1)Roll-r.p.m. pattern which realizes the stretch pattern corresponding with O.D. reduction distribution in reducing stands.
    (2)Roll caliber which satisfies such a condition that the sum of O. D. reduction in two adjacent stands is constant at arbitrary point on tubular circumference.
    These two made it possible to produce the steel tube which has no polygonization even in thickwall size (for example, butt-welded pipe of 48.6φ×8.5t or 60.5φ×8.5t) and to increase the rolling yield.
  • Improvement in Cold Shear Yield of Bar Mill by Computer Control System

    pp. 2463-2469

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    The rate of crop loss in bar production is greater than those of other products.
    The reason is that bars devided in rolling line are sheared again simultaneously to specific lengths.Furthermore, this loss depends on the quality demanded and facilities of shearing as well as billet weight and bar size. Therefore improvement of equipment such as shear mechanism or measuring instrument is as important as sophistication of software to increase the yield.
    As a result of computer simulation for Nippon Steel's new bar mill, in 1973, Dynamic Programming was found effective for minimizing crop loss and improving productivity. These results were used for modification of equipment plan under construction. In actual bar mill erected in 1974, the highly functional shearing machine and basic "Shearing schedule" were installed as a part of the total computer control system. After integral improvement of software and instruments in two stages, the yield has reached above 97.6%.
    Additional approaches would become necessary in the next step such as systematization including decision of optimum billet length and introduction of Dynamic Programming to online system.
  • Improvement of Yield at No. 8 Rod Mill in Kakogawa Works, Kobe Steel, Ltd.

    pp. 2470-2476

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    In 1980, we have improved the yield ratio up to 99.0% in No. 8 wire rod mill, Kakogawa Works, Kobe Steel, Ltd.
    Generally, the yield ratio yaries with types of mill, including steel grade, rod size and coil weight. From this point of view, No. 8 wire rod mill has a lot of advantages.
    In addition, we continued to make efforts to reduce yield loss such as scale loss, crop loss and cobbles. The yield ratio of 99.0% was accomplished by the accumulation of the above J. K. activities.
  • Spread Characteristics and Its Mathematical Models in Rod Rolling

    pp. 2477-2482

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    In order to develop a simple general formula for calculating the spread in rod rolling, the hot rolling of steel by square-oval, round-oval, square-diamond, and diamond-diamond passes has experimentally been studied. The profile of stress-free side surface of rolled rods and the various geometrical factors related with spread ratio have been investigated.
    The profile of stress-free side surface differs for the four types of passes; in the square-oval pass, it is assumed to be a straight line; in the round-oval pass, two circular arcs with a radius larger than that of initial rods; in the square-diamond pass, the angle of side surface is similar before and after rolling; in the diamond-diamond pass, its angle after rolling is slightly smaller than before rolling. The calculated and measured values of the maximum projected width of contact are compared and a close agreement is obtained between them.
    For all of these four passes, the spread ratio can be expressed by a single formula as follows:
    Spread ratio=B1-B0/B0Ldm/B0+0.5·H0·FH/F0
    where B0, B1 : Width of material before and after rolling
    H0 : Height of material before rolling
    Ldm : Mean projected arc of contact
    FH/F0 : Fractional reduction of area before rolling
    α : Coefficient (=0.83).
    This is a general, simple and sufficient accurate formula.
  • Development of Rolling Technique for Large H-shapes from Continuously Cast Slabs

    pp. 2483-2492

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    A new rolling technique has been developed at Mizushima Works for producing large H-shapes from CC slabs. While H-shapes up to 500mm in web depth and 350mm in flange width are rolled from CC beam blanks and blooms, larger H-shapes had to resort to ingot-bloomed beam blanks, at the sacrifice of product yield and quality. The new technique has proved satisfactory in rolling these larger H-shapes using CC slabs by one-heat rolling on the wide flange beam mill.
    The key point of the new rolling method consists in deforming a slab into the dogbone profile by a heavy edge-rolling of a slab under a newly designed caliber with belly and a partial web rolling of the dogbone. With the following features, the new rolling process can be applied to CC stock to produce any dimensions of the existing H-shapes by one-heat rolling.
    1) A 7-15 percent improvement in a raw steel to product yield, depending on H-shape dimensions.
    2) Marked improvement in surface quality and internal soundness.
    3) Energy saving by eliminating the ingot-making and blooming steps.
  • Rolling of Large Universal Beams from Continuous Casting Slabs

    pp. 2493-2501

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    In the Large Shape Mill at Kashima Steel Works, new rolling methods are developed and all universal beams (max;H900×300mm) are produced from continous casting slabs with 300mm in thickness.
    (1) Slab edging methord
    The characteristics of this rolling method consists of a strong edging reduction of slabs to make a dog-bone shape and a following forming reduction to make a beam blank through the forming groove and sizing groove in the break-down mill. By this method, large universal beams (max;H700×300mm, H400×400mm) are produced directly from continous casting slabs by hot-charge.
    (2) Universal blanking method
    Beam blanks for H900×300mm and H800×300mm are rolled previously from continous casting slabs by a universal mill. In this methods, the flange thickness of the workpiece is reduced highly and the flange width spreads much larger than the original slab thickness. The resultant beam blanks are rolled to universal beams after reheating.
  • Technique to Decrease Crop Loss in Hot Strip Mill

    pp. 2502-2508

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    Techniques to decrease crop loss in hot strip mill become important under introducing high width reduction process, which makes better relation between continuous casting plant and hot strip mill.
    By plasticine medel rolling experiment, it is observed how the crop grows under the rolling condition at roughing train in hot strip mill. Forming top end and bottom end of slab into a certain shape before rolling is effective to decrease crop growth at both ends of slab. The reasons of that effect are,
    (1) to lower the width reduction by edging rolling at slab end,
    (2) to cancel the crop growth after edging rolling.
    Results of experiment with plasticine on pre-forming by parallel edging press machine have shown that it is necessary to determine the optimum pre-forming condition (the width reduction and the contact length between slab and press) according to the total width reduction. One method to control the crop length is explained.
    It has been confirmed by actual mill test at Mizushima hot strip mill that pre-forming by edging press is effective in hot rolling of steel and control of the crop length is possible.
    x

    Readers Who Read This Article Also Read

    1. The Recent Yield of Hot Strip Mill in Japan Tetsu-to-Hagané Vol.67(1981), No.15
    2. A New Method of Slab Rolling for Prevention of Growth of Crops Tetsu-to-Hagané Vol.67(1981), No.15
    3. Reduction of Crop Loss on Slab Rolling Tetsu-to-Hagané Vol.67(1981), No.15
  • Edger Set-up Model at Roughing Train in Hot Strip Mill

    pp. 2509-2515

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    Width change in roughing train of a hot strip mill is investigated. Formulas by which width spread in vertical and horizontal rolling is predicted are derived according to a regression analysis using measured values on a production mill.
    A new mathematical model for edger set-up is developed using above mentioned formulas. A feature of the new model is that it is practicable to adjust the roll opening at each edger depending on a given distribution pattern of width reduction at each stand.
    The new set-up model has been applied to Kashima Steel Works, Sumitomo Metal Ind., Ltd. since March 1979. Compared with the accuracy obtained by the conventional set-up method, width accuracy has been much improved by the present new model.
  • Width Behavior of Head and Tail of Slabs at Edge Rolling in Hot Strip Mills

    pp. 2516-2525

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    Deformation of slab in vertical rolling has been simulated in laboratory scale mills to investigate width deviation. Rolling load and torque formula have been derived by dimensional analysis technique. The error of formulas is within ±10 percent. The limit of slab buckling at heavy width reduction has been formulated. The shape of localized deformation at the edge of slab has been modeled. The width spread of edge-rolled slab after thickness reduction has been investigated on the basis of Siebel's formula. These deformation formulas have been extended to that of head and tail end of slab where unsteady deformation is predominant. Finally, resultant width shortage pattern has been quantitatively predicted by applying principle of superposition. The validity of the model has been checked at a hot strip mill.
    On the basis of these fundamental equations, an optimum edge rolling schedule has been derived to minimize width shortage at the head and tail end of coils. This optimum schedule requires allowable heavy width reduction from the last pass to the upper stream in edger stands. Better yield has been achieved through application of this schedule at hot strip mills.
    x

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    1. Direct Width Control Systems Based on Width Prediction Models in Hot Strip Mill ISIJ International Vol.47(2007), No.1
    2. Novel Method to Spread the Width of Strip ISIJ International Vol.42(2002), No.9
  • Study on Drum-type Differential Speed Crop Shears in Hot Strip Rolling Mills

    pp. 2526-2531

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    Recently it is required to improve the cutting performance of crop shears in hot strip mills. This paper shows the development of a new drum-type crop shear which is characterized by the differential speed cutting mechanism. The effect of this mechanism is proved by shearing tests of heated steel (at a temperature ranging between 800°C and 1 100°C) using an about 1/2 scale test machine. It is confirmed that this shearing method has such advantages as stated below, compared with the conventional drum-type crop shear, and can improve the cutting performance as expected.
    (1) Shearing surface has less "curl deformation" and "burr"
    (2) Thrust force, which is the cause of interior shearing, is effectively reduced to an amount between a half and a quarter, and the critical clearance can become twice as large as on the conventional drum-type crop shear.
  • Methods of Reducing Off Gauge Lengths in Cold Rolling

    pp. 2532-2541

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    The causes of off gauge at the top and tail end of strip cold rolled on a tandem mill have been clarified theoretically and experimentally. Some counter-measures for reducing the length of off gauge have been adopted at the No. 3 cold tandem mill in Kimitsu Works of Nippon Steel Corp.,
    (1) The off gauge at the top of strip is caused by reducing the rolling speed when the top edge of the strip is threaded through each stand by the off set of the rolling speed and by the decreasing in front slip. As the counter measures taken for these phenomena, current delay compensation and minor speed control by digital computer are efficient in reducing off gauge at the top of strip.
    (2) The off gauge at the bottom of strip is caused by the rapid increasing of strip thickness at the i stand which is caused by the loss in back tension immediately after the tail end of strip leaves the i-1 stand. The counter-measure developed, reducing the back tension by narrowing the roll gap of the i stand before the tail end of the strip leaves the i-1 stand, is efficient in reducing off gauge at the bottom of strip.
    The off gauge length of strip has been reduced by almost 50% by the adoption of these counter-measures.
  • A Mathematical Model on Strip Profile and Shape in Cold Tandem Rolling

    pp. 2542-2550

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    A mathematical model by which the transverse thickness profile and the shape of finished strip in a cold tandem rolling are predicted is developed by taking account of lateral metal flow and the distribution of the front tension. Calculated profiles are in good agreement with measured profiles obtained by rolling experiments in a production tandem mill. Calculated shapes are found to be similar to observed shapes obtained by rolling experiments in a experimental mill and also the production mill except for the case of center buckle.
  • Dynamic Optimization of AGC Gain during Acceleration and Desceleration of Cold Strip Rolling

    pp. 2551-2557

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    Bode diagram technique was used to design the appropriate gain of Automatic Gauge Control (AGC) system in cold rolling. Study was focused on non-stationary rolling conditions such as acceleration and desceleration periods.
    Transfer time of strip between rolling stand and thickness meter depends on the rolling speed. In acceleration and desceleration periods, the rolling speed varies greatly. Therefore, the gauge control system has variable time lag in acceleration and desceleration periods. This leads to the instability of total gauge control and yields off gauges in strip thickness. Accordingly, for finer thickness control, there is a need to regulate control gain at optimal value during acceleration and desceleration periods.
    Under such circumstances, an investigation has been made on optimal control gain using Bode diagram technique. Firstly, the gain margins of the gauge control system have been calculated for various rolling speeds. It is revealed that the gain margin varies greatly in acceleration and desceleration periods. For finer thickness control, it is necessary to maintain gain margin at a constant level for all rolling periods. Under this consideration, the optimal gain which depends on rolling speed is calculated. And the gain compensation curve is obtained, which represents the relation between calculated gain and rolling speed. This compensation curve is plotted for various strip sizes and steel grades.
    The electrical circuit design, based on these compensation curves, has been developed and applied to cold strip mills at Kakogawa Works. The applied results are successful and off gauge length of the strip is remarkably reduced both in acceleration and desceleration periods.
  • Automatic Gage Control for Sendzimir Mills

    pp. 2558-2563

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    Recently, severe demands for the accurate thickness of cold rolled strip have required the appearance of a new type Automatic Gage Control (AGC) system for Sendzimir mills. AGC systems which meet the requirements have been completed in Hanshin Works, Kawasaki Steel Corp. They are baced on the principle of mass flow constant.
    Characteristics in this AGC system are as follows ;
    1 AGC is baced on the principle of mass flow constant.
    2 System has two modes and they are alternatively used in rolling passes.
    3 To improve response extremly in screw down, the electrical-hydraulic servo system is adopted.
    The following accuracy for the strip thickness has been brought about on cold rolling for silicon steel with this AGC system ; more than 98.5% of overall length of a coil falls within thickness deviation 5 μms.
  • Development of Newly Designed Oil Film Bearing and Improvement of Gauge Accuracy

    pp. 2564-2570

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    Thickness accuracy has markedly been improved by the application of large mill modulus, but this causes eccentric behavior of backup roll in a mill using oil film bearing, leading to thickness fluctuation in the rolling direction. It has been found that the eccentric behavior of the rolls is caused by the deformation of the sleeve generated at the groove of the key connecting the sleeve and the tapered roll neck, and the resultant fluctuation in oil film thickness.
    A theoretical analysis has been made on this phenomenon assuming the journal as an elastic body, and newly designed oil film bearing (keyless bearing) has been developed, which has no key groove at the tapered roll neck.. As a result, gauge fluctuation has been minimized and a considerable advantage obtained.

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