CA1086105A - Method of rolling metal workpiece and mill therefor - Google Patents

Abstract

ABSTRACT
A method of rolling metal workpiece in a rolling mill consisting of rolling stands or pinch rolls, and more than one high reduction rolling stand disposed successively. The roll gap of the workrolls of the rolling stand at the rear side is set so that the corresponding contact angle ?? (?? = tan -1 (cos .alpha. x tan ?) wherein a denotes contact angle between the workrolls in the bottom of the rolls groove and the workpiece, and .alpha. denotes inclined angle of the groove) is bigger than tan -1 µ (µ denotes a frictlon coefficient between the workpiece and the workrolls at the biting time) and also is smaller than tan -1 µ' (µ' denotes a friction coefficient between the workpiece and the workrolls when the workplece is completely bitten between the workrolls and the rolling is in progress). The workpiece is fed to the rolling stand of the rear side by the rolling stand or the pinch roll of the front side; and compression stress (below the yield stress at the rolling time) is produced in that part of the workpiece which is located between the rolling stand or pinch roll at the front side and the rolling stand by the feeding of the workpiece, to assist biting the workpiece between the workrolls of the rolling stand of the rear side. The peripheral speed of the rolls of the workrolls/and or the pinch roll is adjusted after the tip portion of the workpiece is completely bitten between the workrolls of the rolling stand of the rear side while the workrolls remain with the previously set roll gap, and rolling is continued in the condition where the stress of the direction along the rolling line between the rolling stand or pinch roll of the front side is removed. The workpiece can thus be rolled with the high reduction of area which cannot be achieved by conventional regular rolling mills.

Description

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This invention relates to a method of rolling billet, bar, and rod metal workpieces and a mill for this proccss~ and particularly rela~es to a method of hot rolling of metal workpieces and apparatus therefor which is capable of rolling plate, billet, bar and rod stably with large reduction of area or rate of elongation per pass.
In conventional rolling, where the reduction of area per pass is within the range 20 - 30%, in order to determine a maximum level of the reduc-tion of areaJ a contact angle ~ between a workpiece and workroll must be con-sidered. In any condition of rolling rate and roll workpiece and the like, in order to achieve stable rolling, the contact angle ~ must be in relation of tan 1 ~ ~where ~ denotes the coefficient of fric~ion upon biting of the workpiece between the workrolls), and it is common practice to determine a maximum level of proper reduction of area in the range of such contact angle ~.
On the other hand, assuming the coefficient of friction in the steady rolling condition after the biting is completed is ~', the following relation is well known.
tan 1 ~- > tan~l ~
From this relation, in the steady state rolling condition, rolling with a , ; contact angle which is large as compared with the contact angle at the time of the biting, namely, i.e. rolling with the high reduction of area in the ;. .
~; range of ~ _ tan 1 ~ is possible.
In a known method of rolling a metal workpiece with high reduction of area, the workrolls are supported so that the rolls do not shift in the . . .
advancing direction of the workpiece, and the gap between the workrolls is so , adjusted as to maintain the contact angle ~ in the relation of ~ > tan 1 ~.
;t -Rolling is performed while the workpiece is continuously pushed between the r, rolls having the specified gap, the pushing force being of a magnitude causing a neutral point of the rolling to exist in the plane where the workrolls and the workpiece contact.

However, this method requires a pushing device, such as a large ".
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scale pusher for pushing the workpicce continuously and stcadily through its entire length between the workrolls, and thercfore, has the drawbac~ that con-tinuous rolling with high reduction of area per pass over a plurality of stands is extremely difficult. As the pushing device, a master-slave pusher system can be employed. In this device in the initial stand, the workpiece is pushed in by the master pusher, and in the next stand, the wor~piece is pushed in that pass through the initial stand. However, in this device, in order to push the workpiece through the workrolls continuously, pushing through more than two passes is practically impossible, and accordingly, there is a limit to the effect of making the rolling mill more compact by employing high reduc-tion rolling.
In another method the workpiece is pushed into the roll gap by the pinch rolls or the rolling mill itself, and in this method, the foregoing problems arising from the use of the pusher apparatus can be eliminated. How-ever, instead, when the pushing force becomes zero between the pinch rolls and the rolling mill or between the rolling mills, the workpiece is rolled under .' non-stable conditions. Because of this phenomon, there is a danger of defec-.~ . .
` tive biting and also, greater fluctuations in the width dimensions occur, giv-, . :
ing adverse effect ~ith respect to the rolling operation, yield and product quality. In order to solve these problems, rolling may be performed by connect-Ir,, ing the preceding and succeeding workpieces by means of welding, but for this '!~' operation, a separate installation becomes necessary, greatly complicating, matters related to technical and installation aspects. Also, the pushing force applied to the workpiece influences the deformation of the workpiece ~, between the workrolls, and as the result, spreading in the width direction over the entire length of the workpiece is increased which gives a rise to the deterioration of deformation efficiency.
; As an e~ampIe of another method of rolling a workpiece with high reduction of area, where the contact angle ~ becomes ~ > tan 1 ~, refercnce is made to United States patent No. 3,553,997. This rolling method is employed . .

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for performing in-line reduction in continuous casting wherein a tront end of the wor~piece is made to pass between the workrolls to ~ ccrtain e:ctent by opening the gap of the workrolls sufficiently, and the workpiece is gripped by the workrolls. The roll gap is then made smaller to perform the rolling with a large contact angle. In this rolling method, it is possible to roll the workpiece with high reduction of area, but the tip portion of the work-piece becomes off gauge, lowering the yield. This method has o~her problems, such as that the roll gap has to be changed for every piece of the workpiece, and the rolling installations become complicated and large size. Furthermore, in this rolling method, the cross-section of the tip portion of the workpiece is bigger than the cross section of the latter part, and also it changes abruptly so that a dynamic movable guide is required at the incoming side of the rolling stand of next stage, and the rolling speed has to be changed according to the change of cross section, requiring a complicated control mechanism. Also, in this rolling method, when used for groove rolling, the enlarged front end portion of the workpiece does not fit the groove,~so that rolling of billet, bar, and rod is almost impossible.
Heretofore, to assist biting of the workpiece, a method of cutting -~ the tip of the workpiece in wedge form or a method of push mg the workpiece between the workrolls by causing the following cold or hot workpiece to collide with the one to be rolled can be enumerated. However, these methods are em-ployed in conventional rolling wherein the contact angle 3 is in the relation of ~ < tan 1 ~ Moreover, in these methods, there are too many problems with respect to yield, maintenance of installation and stability of operation and the like, and therefore these are not practical methods.
An object of this invention is to solve the foregoing problems in ,~ the rolling with high reduction of area, and to provide a rolling method cap-able of rolling plate, billet, bar or rod made of metal workpiece with high operating efficiency.
The invention provides a method of rolling a meta~ workpiece in a -- 3 - ~

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rolling mill consis~ing of a first rolling stand, ~nd a plurali~ high reduc-tion rolling stands disposed successively to said ~irst stand, the improved method comprising: setting a roll gap of the workrolls o~ the first lligh reduction rolling stand following said first rolling stand so that the equiva-lent contact angle ~9 ~ = tan 1 ~cos x tan ~) wherein ~ denotes contact angle between the workrolls in the bottom of the roll groove and the workpiece, and ~ denotes the inclined angle of the groove) is bigger than tan ~ ~where ~ denotes the coefficient of friction between the workpiece and the workrolls at the biting time) and ~e also is smaller than tan 1 ~- ~where ~' denotes the coefficient of friction between the workpiece and the workrolls when the work-piece is completely bitten between the workrolls and rolling is in progress);
feadin~ the workpiece to said first high reduction rolling stand by means of said first rolling stand; producing compression stress in the rolling direc-tion which is below the yield stress at the rolling time, in that portion of the workpiece which is located between said first rolling stand and said first high reduction rolling stand by feeding the workpiece and biting the workpiece . , .
'~ between the workrolls of said first high reduction rolling stand; and adjust-~, ing the peripheral speed of the rolls of said first rolling stand after the ; tip portion of the workpiece i5 completely bitten be*ween the workrolls of ... . .
said first high reduction rolling stand ~while said workrolls remain with the previously set roll gap) to reduce said compression stress while continuing ~ -the rolling whereby the workpiece can be rolled with high reduction of area.
From another aspect, the invention provides a train of rolling mills for rolling a metal workpiece with high elongation comprising: a first rolling - .: . . :
stand wherein the roll gap is set so that the contact angle ~ between the rol-ling rolls and workpiece satisfies ~ < tan 1 ~ (wherein ~ is the coefficient of friction between the rolling rolls and workpiece); a plurality of high reduction rolling stands wherein the roll gap is set so that the contact angle 3 becomes at least ~ > tan 1 ~, high reduction rolling stands being disposed successively to the rear of the first rolling stand; a speed detecting device ~, .
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for detecting the peripheral speed of the rolls of the first high reduction rolling stand; a device for detecting completion of biting of the tip portion of the workpiece in the first high reduction rolling stand; a device for con-trolling the peripheral speed of the rolls of the first rolling stand on the basis of th~ signal from the speed detecting device so that a compressive stress of above 1% and below 100% of the yield stress of the workpiece is generated on the workpiece as it is bitten into the incoming side of the first high-reduction rolling stand; and controlling the peripheral speed of the rolls of the first rolling stand or first high reduction rolling stand in response to the signal from the biting completion detecting device so that stress is not generated on the workpiece at the incoming side of the first high reduction rolling stand after the workpiece is bitten into therein; an arithmetic operation processing device for storing the sliding limit curve in the relationship of the corresponding contact angle and the rolling speed in i . .
the first high-reduction rolling stand and comparing the speed signal from the a sl~pP'~
speed detec~ing device and thc-clL~u~ qimit speed and producing a speed cor-rection amount as an output; and a device for controlling the peripheral speed , of the rolls of the first high-reduction rolling stand in response to the and ; biting completion signal~the speed correction amount signal. With the aid of the invention it becomes possible to decrease the diameter of the workrolls . .~: . .
~-- and reduce the number of units of the rolling stands, whereby rolling mills can be made more compact. The method makes possible the rolling of workpieces - with the high reduction of area by adding simple devices to existing rolling mills.
Figure 1 is a graph showing the relationship between the pushing ` force and corr;esponding contact angle;
- Figure 2 is a diagram to illustrate the corresponding contact angle, Figure 2a showing the inclined angle of the groove, and Figure 2b showing the contact angle between the bottom of the groove of the roll;
Figure 3 is a graph showing schematically the rolling load changes ... .

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with elapse of time;
Figure ~ is a graph showing the rel~tionship between the rolling speed and corresponding contact ~ngle;
Figure S is a schematic drawing of one e~ample of rolling mill for working the method of this invention;
Figure 6 is an elevation showing e~amples of the guide rolls em-ployed in the mill of Figure 5;
Figure 7 is a diagram of the groove arrangement oE a diamond system;
Figure ~ is a diagram of the groove arrangement of a box system and an oval system;
Figure 9 is a diagram showing a conventional train of rolling mills, Figures 9 a - c showing a train of billet mills and Figure 9 d - e showing a train of rod rough continuous mills;
Figure 10 is a diagram showing an example of a train of rolling ~ mills according to this invention, Figure lOa showing a train of billet mills, ; Figure lOb showing a train of bar mills, and Figure 10 c showing a train ~f rod rough continuous mills;
Figure 11 is a block diagram of a control device in the train of , .
rolling mills according to this invention;
Figure 12 is a diagram showing the definition of the groove; and Figure 13 is a diagram showing an e~ample of the groove employed in the rolling of the bar or rod.
Figure 1 shows the relationship between the force pushing the work-piece between the workrolls and the contact angle of the workrolls against the workpiece. In the graph, the pressing force is represented by ~/k which is -~
the ratio of the compression stress generated in the workpiece at the pushing time to the yield stress k of the workpiece at tlle rolling time. The contact angle is represented by the corresponding contact angle ~e which takes account of the inclined angle of the groove of the workroll.
. , , ~ 30 As shown in Figure 2a, an angle formed by the working surface(3~of :- :
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~v~ s the groove (2) of the ~Yor~rolls ~1) with the line _ parallel to t~le roll a~is is shown as ~, and as shown in Figure 'b, the contact ~ngle at the di~meter Do (is the bottom of the groove of the roll) is shown as ~, the corresponding contact angle a~ is represented as follo-~s.
~e = tan 1 ~cos x tan ~) In the case of an oval groove, the oval groove is approximated by an angular groove and the inclined angle of the angular groove is assumed as the inclined angle of the oval groove. The area of the substituted angular cross-section and the longer diagonal line are equal to the area of the cross-section of the oval groove and the long axis thereof, and in the case of the rolling by the flat roll, since a - 0, cos ~ = 1, and when this equivalent contact angle ~e is used, both groove rolling and flat rolling can be inclusively represented.
The curve I shown in Figure 1 is the line showing the corresponding contact angle of the limit of biting the workpiece in the rolls. The point A
represents the corresponding contact angle of the limit of biting the workpiece between the workrolls without the pushing force, and the si7e is, as described .~. _1 .
;~ in the ~oregoing, ~e = tan ~ ~. The curve II is the line showing the limit of } rolling the workpiace in the steady state condition after biting the workpiece - between the workrolls, namely, the limit of generating slip between the work-piece and the workrolls. For example, it shows that if the pushing force b is given, rolling with high reduction of area wherein the maximum corresponding contact angle is D can be possible.
The curve II shows that after the workpiece is bitten into the work-`,~ rolls, steady state rolling can be performed with a pushing force b'. Also, the point B shows the corresponding contact angle of the limit of steady state rolling of the workpiece without a pushing force, after the workpiece has been .
~ bitten into the workrolls, and the magnitude is, as described in the foregoing, v" ~

, The range wherein the equivalent contact angle ~ is from O to A
;- 30 is a range where the workpiece is bitten into by the workrolls when the pushing . . .
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force is zero, and rolling with conventional ordinary reduction of area deter-mines the rolling condition, based on the equivalent contact angle within this range. Also, the r~nge of s - C is a range wherein the workpiece can be bitten with a pushing force within the yield stress of the workpiece, and after com-pletion of the biting, the pushing force is applied continuously whereby rol-ling is performed, and the foregoing high reduction rolling method belongs to this range. Furthermore, assuming that the pressing force ~/k) is 1.0, biting can be effected with the equivalent contact angle of the point C. At this time, the minimum required pressing force for continuing steady rolling is the pushing force c represented by the intersection of the line perpendicular to the abcissa from the point B' on the curve II with the abcissa. When the pressing force exceeds 1.0, the workpiece at the time of the biting is subject-ed to a pressing force above its yield stress, and is deformed just before the rolling mill so that the range of the equivalent con~act angle greater than ` the point C is such a range. In this range, for example, the high reduction ; extrusion method is employed for rolling a heated workpiece housed in a con-tainer while pushing it into the forming aperture portion by the pushing ap-plied by the pushing device.
The rolling method of this invention is such that the contact angle lies in the range A - B shown in Figure 1, and the size of the equivalent con-tact angle is not comparable to those of the high reduction rolling method and the high reduction extrusion method, but exceeds the reduction of area achieved by conventional methods. In the high reduction extrusion method, continuous rolling in more than 2 passes is practically impossible, and even in high re- -duction rolling continuous rolling of substantially up to 2 passes is a limit as described in the foregoing, and as compared with that method, the rolling method of this invention has the merit that it is capable of rolling the work-piece continuously in more than 2 passes.
- In general, in the rolling of billet, bar and rod, normally the ~ 30 total elongation from the starting material to the produc~ is 400 - 500 %
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which is frequently used, and also thore is the ~ollol~ing relation~hip bet-~een the to~al elongation ~ total and the elongation for each I~ass ~i.
~ total = ~o, ~1 ~2 ....... ~n The important technical problem to be solved is the magnitude of elongation for each pass, or how to continue plural rollings at high rates of elongation. The gist of this invention resides in this point.
The pushing force employed in this rolling method of this invention is basically in the range of O - a in Figurc 1, and in this case the range of reduction of area that can be achieved in the range A - B in terms of the equivalent contact angle as described in the foregoing, namely, tan 1 ~ < ~ <
tan~l ~'.
Accordingly, when the workpiece is bitten into by the workrolls, the ; corresponding contact angle B can be achieved by applying the pressing force a.
Also, in this invention, after the biting of the workpiece by the workrolls is completed, even when the stress of the direction of the rolling line is not generated on the workpiece, rolling is continued. ~Yhen the tip portion of the workpiece reaches the roll center line m (Figure 2b) over the entire cross section biting of the workpiece is completed, but if only a local ~ portion of the tip of the workpiece ~for example the crop portion) reaches the - 20 roll center line (m), the biting of the workplece is not completed.
Figure 3 shows the change of the rolling load during rolling, the point e showing biting start, that is the start of contact between the wor~-piece and the workrolls, the point f showing completion of biting, the point g showing the point wllere stress ~i.e. pressing force) in the direction along the rolling line is no longer applied to the workpiece, the point h showing the start of release of the workpiece, and the point i showing completion of release, respectively. In Figure 3, the portion between the point e and the point _ represents non-stable rolling where the rolling load fluctuates great-,. ly, and in the portion between the point g and the point _ the rolling load has a substantially constant fixed value F, so that in this section rolling is ,.'.:
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, performed under ste~dy-state conditioning.
After rolling reaches the steady-s-tate condition, cven if thc push-ing force becomes zero, the equivalent contact angle in Figure 1 is in the ;
range beloN the curve II, and therefore no slip between the workpiece and the workrolls occurs.
: The condition of the point f can be detected by a load cell, not metal detector and the like. The point g shifts according to the adjustment `~ of the peripheral speed of the rolls, but, for example, the follo~ing method of timing can be used. The rolling average load F for steady-state rolling is known from past rolling performance. After the workpiece is bitten into the .~
workrolls, the rolling load A rises, and when it reaches 0.8 F, a timer is operated and after the elapse of a predetermined time, the peripheral speed of ~ -the roll is adjusted to eliminate stress of the rolling direction of the work-piece.
As described in the foregoing, the magnitude of the pressing force is basically in the range of 0 - a in Figure 1. Howe~er, in order to obt~in i a stable pushing force, the magnitude of the pushing force is desirable such ` that the compression stress generated in the workpiece by the pressing force is above 1%. The magnitude of the pressing force may be selected to be above the point a to assure biting of the workpiece. In order to prevent the stress ~
generated on the workpiece before it is bitten by the rolls f~om exceeding the ~ -.~. .: . .
~ yield stress so that plastic deformation occurs, it is necessary that the com-;~ pression stress generated on the workpiece is below the yield stress of the :., - workpiece at the rolling time, namely, a/k in Figure 1 is below 1Ø. .
~- As described in the foregoing, after completion of biting of the : - .
`~ workpiece, the steady-state rolling is performed, but the peripheral speed of . .......................................................................... .
the rolls is selected so as not to generate slip between the workrolls ~set with a roll gap wherein the corresponding contact angle ~e is tan ~ < ~ <
`: -1 tan ~') and the workpiece. As shown in Figure 4, betwecn the rolling speed .,.; ;~ ~
Vm and the equivalent contact angle ~e a close relationship can be obtained.
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os The result of Figure 4 is obtained on hot steel workpiece.
The curve III of Figure 4 arises from the results of various experi-ments, and where the pushing force is made ~ero, it shows the curve of a limit of generation of the slip between the workpiece in the steady state rolling ~ condition and the workrolls. The upper region K of the curve III is a region ; where continuous rolling is difficult due to the generation of the slip. The curve IV shows the result of experiment conducted by the inventiors on the case of hot rolling employing workrolls whose roll surface skin is rough, and it shows the curve of the limit o biting where the pushing force is zero. The region L above the curve IV represents the region where biting is difficult unless the pushing force is applied, and the region M below the curve IV is a region where the biting is possible without applying the pushing force.
This curve IV perfectly coincides with the result disclosed by W. Tafel ~literature "Stahl und Eisen'r 1921). The curve V is a curve showing the equiv-alent contact angle of the maximum level employed in the present hot rolling, and it can be said that a great margin is given to the contact angle. The curve VI causes no problem from the point of slip but in the region N above the curve VI, due to the falling or buckling of the workpiece, scars or flaws ; occur and represents the limit curve that has practically no significance.
Figure 4, the rolling speed adopted in this invention is the speed corresponding to the region enclosed by the curves III, IV and VI. In this speed rangel in the steady-state rolling condition, as will be understood from the foregoing~ no slip occurs between the workpiece and the workrolls. When ; the rolling speed such as the actual billet mill and rod rough rolling train is made to correspond to the rolling speed shown in Figure 4, it becomes a range of roughly below 2.5 M/S. Namely, in Figure 4, the rolling speed range adopted in this invention matches perfectly with the actual rolling installa-tion for billet, bar and rod. Inversely speaking, the rolling method of this invention shows its effectiveness particularly in the rough rolling of billet, - 30 bar and rod. Furthermore, at the high speed side, the curves III and IV
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approac}- with eacll o~her, alld no substantial significant ~ fcrence is jecn between the curves. This rolling speed is generall~ ' - 5 ~ S.
In the following, a concrete method of rolling by the prescnt inven-tion will be described.
Figure S sholYs an e~ample of the rolling mill for working the me~hod of this invention. The roll gap of the workrolls 6 of the first stand 5 is - set to be similar to that of the ordinary stand, namely, the contact angle ~e becomes ~ ~ tan 1 ~, but the roll gap of the workrolls 6a and 6b of the second and third stands Sa, Sb are previously set so that the corresponding contact ~ngle ~e becomes tan 1 ~ tan 1 ~ "
The workpiece M is supplied to the first stand 5 by ordinary means, namely, roller tables,but since the roll gap is previously set as described in the foregoing, the workpiece M is bitten by the workrolls G of the first stand S without depending on any particular means. The workpiece M passing through the first stand 5 reaches the second stand 5a being guided by a buck-ling preventing device 16. Until the tip of the workpiece M reaches the second stand 5a, no stress in the direction of rolling is generated on the workpiece M. However, when the top of the workpiece M reaches the second stand 5a, since the roll gap of the workrol}s 6a of the second stand 5a is set previous-, . .
.`~ 20 ly, the workpiece M is not immediately bitten into the workrolls 6a, and com-. ~
pression stress in the direction of rolling is generated in that portion of . .
workpiece M disposed between the first stand 5 and the second stand 5a. In " ?
this condition, as the workpiece M is continuously discharged from the first stand 5, the compression stress in the workpiece ~ gradually increases and ^ finally, exceeds the value shown by the curve I of Figure 1, and the workpiece M is bitten into by the workrolls 6a of the second stand 5a.
' The condition where the workpiece M is completely bitten in the workrolls 6a of the second stand 5 (the point f of the rolling load curve shown in Figure 3) can be detected by means of a load cell ~a, and the detect-ing signal is transmitted to a tension detecting signal amplifier lla. ~oad '' .. . .

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Cl 5 cells 9 and 10 are provided on the ~ir-~t stand 5 and load cclls 9a ancl lOa are provided on the second stand 5a, and the tension in the workpiece ~I between -;
the first stand 5 and the second stand 5a ~i.e. the stress in the dircction of : .
the rolling a minus value indicating compression stress) is detected by the load cells 10 and 9a. The tension detectinv signal is amplified by the ten-sion detecting signal amplifier lla, and is transmitted to a tension control device 12. The output signal from the tension control device 12 is compared with the output signal from a comparator 13a at a comparator 13. The speed of rotating ~he drive motor 7 is detected by a tachometer generator 15, and the signal is applied toge~her with the signal from the comparator 13 to an auto-matic speed control device 14. The automatic speed control device 14 controls the rotating speed of the drive motor 7 so that tension is not applied to the workpiece M disposed between the first stand 5 and the second stand 5a.
; The workpiece M delivered from the second stand 5a is bitten in the third stand 5b, and in case of continued the rolling tension control of the ~ work~ieceM between both the stands is similarly effected by controlling the ; rotating speed of the drive motor 7a by devices such as the tension detecting ~ signal amplifier llb, tension control device 12a, tachometer generator 15a and -, the like on the basis of signals from the load cells 8b, lOa and 9b. Figure ,~ 20 5 shows only up to the third stand 5b, but where further rolling stands are successively disposed, the tension of the workpiece ~I disposed between the third stand 5b and the next stand is controlled by controlling the speed of the drive motor 7b by the devices such as load cell lOb, control devices 12b, l~b, ` comparator 13b and tachometer generator 15b and the like similar to these de-scribed to the foregoing. These controls are known to those skilled in the art. The rotating speed of the workrolls may also be ad~usted by the manual operation on the basis of the detected tension so that the tenslon is made zero.
hen the workpiece ~l is made to bite into the workrolls 6a of the second stand Sa, the peripheral speed of the workrolls 6a is set slightly lower ;''' ~ - 13 -' ' ;- , . .:

~08~ 5 than that of the first stand 5. OÇ course~ e~en if thc peri~her.ll spceds of the workrolls of both the stands are set identical, as de~cribed in tlle fore-going, the tip of the workpiece ~l is not immediately bitten into the workrolls 6a of the second stand 5a, and as the compression stress is generated, and finally it is bitten into them. However, in the former case, the rate of increment of the compression stress is great so that the workpiece is bitten into the workrolls faster than it is supposed to be bitren,which is not desirable from the standpoint of the rolling operation. In either case, when the work-piece is bitten into the workrolls, temporarily between both the stands, a fixed condition of mass flow is established. A1SQ~ w]len the peripheral speeds of the workrolls 6 and 6a are made to be equal to the peripheral speed for steady state conditions or made to be a value similar thereto, correction of the speeds of the workrolls 6 and 6a after the completion of the biting is done with a minimum degree.
The buckling preventing device 16 is provided with a plurality of pairs of rotatable guide rolls 17, these guide rolls 17 extending before the ~orkrolls 6a and 6b in the transfer direction of the workpiece M. As the work- -~
piece M is guided by the guide rolls 17, no buckling occurs just before the .
stands 5a and 5b, and the workpiece M is also properly guided between the workrolls 6a and 6b. The shape of the guide rolls 17 is preferably similar ` to the cross sectional shape of the path formed by the guide rolls 17 and the cross sectional shape of the workpiece M as shown in Figure 6b, but the cross sectional shapes may be different as shown in Figure 6c, as long as the buck-ling preventing and guiding functions are maintained.
In a rolling stand applying high reduction of area, the correct i corresponding contact angle ae at the lower side is normally selected with a certain margin as compared with that of the point B shown in Figure 1. The reason for this is that it is necessary to apply the pushing force even though it is instant in the stand immediately at the lower s~ream except for the ~- 30 final stand, and also the generation of the trouble due to the sudden disturb-." ~, ,.
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anc0 ~uring the rolling can be avoided.
Furthermore) instead of the first stand 5, the pinch rolls may be used to bite the workpiece M into the second stand 5a. Also, instead of - detecting the completion of biting of the workpiece M by means of the load cells 8a and 8b, detection may be performed by employing the well known hot metal detector.
In the case of the grooved rolling rolls, the groove is formed on the rolls by a lathe, but grooving by the diamond - diamond system or diamond-square system as shown in Figure 7 is advantageous from the standpoint of the operation and obtaining a quality product or of achieving the high elonga~ion desired. Besides, the box- box system or oval- square system as shown in Fig-ure 8 may achieve the high elongation desired but there are dangers of fall down of the workpiece or generation of wrinkles or flaws in the groove, and requiring advanced operation technology of accompanied by considerable diffi-culties. Where the final cross sectional shape is square, as for a billet, ,: ~
, the square groove with normal reduction rate employed in the conventional rolling may be disposed behind the diamond groove, and also, for round steel bar, the square groove and round groove of normal reduction rate employed in the conventional rolling may be disposed behind the diamond groove.
As will be obvious from the foregoing detailed description, high ."
:~ reduction continuous rolling can be performed in a manner similar to continu-:
ous rolling with conventional normal reduction of area, without applying the tension or compression forces to the workpiece, in the range where trouble in in rolling operation is totally absent. This means elimination of rolling under non-stable conditions, and is advantageous from the point of securing the dimensional accuracy and high yield. Also, since rolling can be performed continuously with high reduction of area exceeding conventional standards, it is extremely advantageous from the standpoint of improving the total elonga-tion.
- 30 Rolling with high reduction of area can be made possible by decreas-. .

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ing the equivalent contact angle by using relatively large diameter workrolls.
However, in this case, the installation becomes unnecessarily~big and it i5 not practical.
In this invention, rolling can be performed with the high reduction of area by a compact rolling installation having high efficiency which has the required small diameter of workrolls.
The following compares the method of this invention and the conven-tional method, for installations rolling a product 100 mm square from a 230 mm square steel starting material, Table 1 shows the comparison of the diameters of the workrolls of the rolling apparatus train for rolling the product.
Table 1 _Method of this Conventional Rolling speed Stand No. invention method . ..
Roll dia. Corresponding Roll dia. Corresponding (M/S) ~MM)contact angle (MM) angle ~degrees) (degree) l 59630.0 988 20.0 0.45

2 65138.0 1678 20.0 0.70

3 69736.0 1599 20.0 1.12

4 60830.6 1187 20.0 1.66 44620.0 446 20.0 2.00 i~ .
In this Table, the diameter of the rolls in the method of this in-vention is determined by the curve III of Figure 4, and the diameter of the rolls of the conventional method is determined by the curve V.
The No. 5 stand of this invention performs rolling with the conven-tional reduction of area. As will be obvious from Table 1, in the method of this invention, the diameter of the rolls is extremely small as compared with ! those of the conventional method.
- 20 In the conventional method, the large diameter workrolls described above are not actually used, and it being common practice that the diameter of , . .

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~l~8~ 5 the rolls is kept belo~ 800 mm and to compensate the number of stands is in-creased to 7 - 8 units.
In the foregoing, the description relates to the case where the workpiece is steel, but it is obvious that the operation and effect of this invention can be applied to materials other than steel for example, aluminum alloy or copper alloy.
Next, the continuous rolling mill for working the method of this invention will be described in comparison with a conventional mill.
In Figure 9, layouts of the train of conventional rolling mills are shown. In the drawing, sym~ol 21 denotes a hea~ing furnace, and M denotes a rolled workpiece, and 23 denotes a breakdown mill. In Figure 9a, 9b, and 9c ; in order to obtain a total reduction of area of about 85%J 6 - 8 units of continuous billet mills 24, 24a are required, and to obtain a similar total reduction of area in Figure 9d, 9e, almost the same number of units of rough rod rolling mills 25, 25a are required. Symbols 26, 26a show the mills after the intermediate mills.
By contrast, Figure 10 shows the train of a rolling mill for working the method of this invention. In Figure lOa, b, c, examples of the layout for manufacturing billet, round bar or rod from ingot, bloom or continuous cast bloom is shown.
~ The rolled workpiece M heated to a predetermined temperature in the : furnace 21 is removed by an extracting device ~not shown) and delivered to the pinch roll 27. The pinch roll is adjusted to provide a sufficient and neces-sary pressing force to provide rolling with high reduction in area in the following roll stands. The workpiece M is made to pass through a rolling mill 29 having a normal reduction of area of about 10% to 30% which allows the bit-: ing of the rolled workpiece easily without an auxiliary pressing force to enter the train of high elongation rolling mill having high reduction of area.
Thus the device for carrying the rolled workpiece to the first roll-ing mill and abutting the workpiece against the rolls or the roller table or .

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simple pinc~l rolls frcquently cmplovcd in thc normal rollin~l m~y be provided.
The number of units in the train of high elongation rolling mills having high reduction of area is determined by the e~fective outgoing side ma~imum speed of the group of rolling mills having similar total reduction of area from the starting material to the product,that is,it is determined in an effective speed range of the present high elongation rolling method shown in Figure 4. The rolled wor~piece is then made to pass through primarily the group of rolling mills 29. ~lore than one unit of shaping rolling mills having extremely low reduction of area is included in this group for the purpose of achieving the desired shape and dimension. The rolling mills in group 29 have a normal reduction of area of about 10 - 30%, whereby the workpiece is finish-ed in the product shape.
In actual rolling, the workpiece is formed into the final product through a shearing machine or cooling device ~not shown).
Figure 11, symbols 31, 61 show rolling stands of ~1 ' tan 1 ~ and symbols 41 and 51 show rolling stands of tan 1 ~ < ~2 ~ tan 1 ~ " - -The final stand 51 rclling with the contact angle 32 is made as the pivot stand, the speed of revolution which is the reference speed set within the range L shown in Figure 4. The reason for this is that the limit of roll-ing with the contact angle ~1 as shown in Figure 4 is subject to restriction by the rolling speed, and therefore, a method of controlling the rolling speed ;~ of the rolling mills tdisposed before and after) by monitoring the maximum , rolling speed of the final stand 51 ~which has the highest rolling speed) is preferable.
The controlling method is shown in Figure 11 using the non-tension and non-compression control system of the current memory system as the example.
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In the drawing, symbols 32, 42, 52, 62 are respectively current value detecting devices, symbols 33, 43, 53, 63 being current memories, 34, 44, 54, 64 are speed control devices,45, 55 are rolling speed monitoring devices, 46, 56 are signals for giving the limited rolling speed range, 48, 58 are pilot generators ... "

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and ~9, 59 are l~o~ ~etal ~letectors.
The rolled l~or~piece ~l is bitten by thc rolling stand 31, and at this moment, the constant current value excluding the impact portion is detect-ed by the current value detecting device 32, and is stored in a memory device 33. The rolled workpiece is then bitten by the rolling stand 41 after recei~-ing the au~iliary pressin~ force from the rolling stand 31. At this time, between the rolling stand 31 and rolling stand 41, the compression force is generated temporarily and the current of the drive motor of the rolling stand 31 increases, but upon completion of the biting, it reaches a fixed current value, and then this value is detected and is compared with the previously stored current value to control the roll speed in the rolling stand 31 by means of the control device 34, whereby the non-tension and non-compression force condition is generated. In this case, the confirmation of the completion of the biting is performed by the hot metal detectors 41, 51 , and it is pos-sible to start the control by using their signals. Should problems such as defective ~iting, occur, it is possible to use the signals as the counter-measure of the preceding process.
The wor~piece M is then bitten by the rolling stand 51, by being .~ .
subjected to the auxiliary pushing force of the biting from the rolling stand 41, and co~trol between the rolling stands 51 and 41 is performed in an en-tirely similar manner to the control between the rolling stands 31 and 41.
HoweveT, before entering the control of the rolling stands 41 and 51, it is advantageous to complete the control between the rolling stands 31 and 41.
Naturally, during the control of the rolling stands 41 and 51, the speed in the rolling stand 31 is changed by the successive control when the , -speed in the rolling stand 41 is changed.
. The workpiece is next bitten into the rolling stand 61, but in this -- case, since the rolling machine has a contact angle ~l ~ tan 1 ~, the auxiliary pushing force for biting becomes unnecessary and the control of the non-tension r~
~ 30 and non-compression in steady rolling is performed as in the foregoing descrip-.
:''' , ' ' ~ 516~5 tion. ~lowever, in this case, the rolling stand 51 is the pivot stancl, jo control o~ the unbalance speed of the rcvolution is compens~te~ by controlling the speed of revolution o~ the wor~rolls of rolling stand 61.
Similar control is applied to the succeeding stands. The rolling speed of the pivot stand 51 is constantly monitored by the rolling speed monitoring device 55, and is compared witll the speed standard value 56 de~er-mined from the relationship of the rolling speed Vm and the equivalent contact angle ~e in Figure 4, and is controlled ~ithin the range. In this case7 for example, in case the control of the rolling speed of the rolling stand 51 is required, a method of changing the entire line speed is adopted.
As described in the foregoing, the example of the current memory ;~ system has been described, but in the operating condition where the uniform heatlng is sufficiently performed in a conventional walking beam heating - furnace, the-foregoing controlling method is sufficiently effective. However, when control is performed in a condition where skid marks occur, or the uni-form heating condition is extremely poor, a known current memory load correct-ing system wherein the load value in addition to the current value is employed -` to use the ratio, or a system of completing the control between the rolling stands 31 as of 41 in case the control is performed between the rolling stands 41 and 51 as described in the foregoing is the most preferable. It is not essential to adhere to the systems, and in the condition where the workpiece is bitten in a plurality of stands of more than 2 units, it is possible to ., I , .
employ a kno~n full length control system wherein the control is effected on .~. . .
the entire length. Alternatively, a known control method wherein the tension generated between the stands is directly detected and then is reduced to zero may be used.
Figure lOa shows a layout of the case where the billet of 120 ~ is made from 300 ~ continuously cast bloom, and an example of the billet mill in case the total elongation 6.25 (hereinafter the elongation is used for de-scription since it means S4% when converted to the reduction of area) is . .
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., ,~ -~ 05 required. In this case, the number of units of the total rolling mills is 4 - 5 stands~ and although the manufacturing is possible, the examp]e is shown. The elongation distribution among rolling stands is as per the follow-ing Table 2.
Table 2 shows that the light elongation is taken in ~he first stand, and the rolling mill is of far more compact type as compared with conventional mills, and the primary emphasis is placed on biting of the workpiece into the second stand.
Table 2 Stand No. 1 No. 2 No. 3 No. 4 No. 5 Total _ Elongation1.10 1.85 1.85 1.50 1.11 6.25 _ _ .
Groove DS D D DS S ___ , Remarks: The symbol of the groove shows the following shapes ~as shown in Figure 12).
D: diamond, DS: diamond resembling square S: square In the No. 2 - No. 3 stands, a high elongation greatly exceeding the conventional level is performed. In the No. 4 stand, although a high elongation is performed, in order to obtain a workpiece resembling the final cross sectional shape of the square, a diamond groove whose groove ratio of axis resembling 1.0 is employed. Accordingly, in the final No. 5 stand, only small elongation is required, and dimensional fluctuation due to the fluctua-tion of spread in the rolled workpiece at the outlet of the No. 4 stand is wholly absorbed, and as the result, the product of high dimensional accuracy ;~ is high and extremely good shape can be manufactured. Moreover, the rolling !, .
mill of the No. 5 stand can be of compact si~e. This layout provides an ex--- tremely compact billet mill when considered as the rolling mill group, and since the No. 1 stand and No. 5 stand can be of very compact si~e, substantial-ly, the entire elongation can be obtained with 3 units of the stands.

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36~5 Although the rolling speed Call be selcctcd in relation to the scale of the mills, in the mills of 50,000/~ont~l to 'OO,OQ0/m~nth \iith normal rolling operation factor, the rolling speed can be sufficiently within the range of the effective rolling speed shown in Figure 4 and can be freely selectcd.
Table 3 shot~s that the elongation of the No. 1 stand and ~ stand is set at the conventional rolling level, and the high elongation is confined to the No. 2 and No. 3 stands, and the dimensional accuracy is slightly in-ferior to that of the Table 2, and also the No. 1 and No. 4 stand are of the conventional mill scale. However, as the whole, a set of 4 stands is suffi-cient to perform the operation, and this is a layout with much merit such as simplification of the mill line length and installation.
Table 3 Stand No. 1 No. 2 No. 3 No. 4 Total ., . .,, Blongation 1.26 1.95 1.95 1.30 6.25 Groove D D D S _ __ ..
~ Remarks: Symbols of the groove are the same with the Table 1. - -- By way of comparison in a group of rolling mills according to the conventional method, in order to manufacture the product from 300 ~ to 200 ~, ~` about 8 passes are needed, requiring a combination mill of 1 unit of break- ~ -down mill and 4 units of continuous mills, or continuous mills of 7 to 8 stands, so that it is the common practice that the conventional mill group requires an extremely large installation as compared with the method of the :....................................................................... . .
present invention.

` Next, a layout of the case where the round bar shown in Figure lOb , .
is manufactured will be described referring to Figure lOb. A workpiece having the square cross section is formed from bloom by employing the process shown in Figure lOa, and then at least 2 units of rolling mills having normal reduc-,. . .
tion of area are disposed in the succeeding process ~hereby the manufacture :.
of the round bar is made possible.

- However, the required si~e of the round bar in general is variable .
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., r by several mm and ranges o~er inan- ~inds, and therefore depending on the range of the si~e, it becomes necessary to increase the number o~ ~olling stands.
~ lso, for round bar ~hose cross section resembles the cross section of the starting material, there is no need to effect excessively high elonga-tion, and in this case, in the process of Figure 10a, the groove for manufac-ture of the round bar is incorporated whereby manufacturing can be effected.
For the manufacture of round bar, as the groove in the latter half, oval and round are necessary. There are two types shown in Figure 13a, b and either one may be adopted, provided that, with respect to effecting high .; 10 elongation with l pass, it becomes disadvantageous as compared with the above-mentioned diamond, square and groove.
Rolling will be described with respect to the case of the rolling line of bar and rod in Figure lOc.
In the bar and rod rolling line, as will be obvious from the example of the normal 125 ~ ~o 5.5c~, the total elongation required is extremely large, such as about 500. Accordingly, the number of units of the high elongatio~
rolling mills of the train of rolling stands in this case will be controlled by the size of the rolled workpiece and the maximum high rolling speed.
i Namely, as representative examples of the bar and rod, example .- 20 applied to the roughing mill train are: 20 mm bar steel from 200 mm square, .~ and 5.5 mm round rod from 120 mm square, manufactured with a finishing speed : of 20 M/Sec (1200 M/Min), 60 ~I/Sec ~3600 M/hlin) respectively, are shown in i ~
Table 4 and Table 5.
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~ Table 4 -- i ~ Starting Rolling stands :}~ material , _ _ _ No. 1 ,No. Z No- 3 ¦NO- 4 ¦ No- 5 ¦---- Final ;. Size 200 ~182.5) j(l36 1~ ¦~101.4) ~75.6) j~56.4) ~

~ Elongation ___ 1.20 ¦ 1.80 ~ 0 1.80 1.80 l.10,:, I _ --~
~- Speed 0.16 0.19 0.34 0.61 1.10 1.98 _ 20 ` at outlet .
Bracketed numerals represent the corresponding size converted to square - cross-section.

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Table 5 Starting Rolling stands material No. 1 No. 2 No. 3 No. 4i No. 5 No. 6 __ Final _ _ , Size (MM) 120 ' '~109.5) ~81.6) ~60.8) (45.3) ~33.8) ~25.6) ___ 5.5 _ Elongation ___ 1.20 1.80 1.80 1.80 1.80 1.80 1.10 __ _ _ _ .
Speed 0.10 0.12 0.21 0.38 0.69 1.25 2.24 60 at outlet _ _ _ _ _ Bracketed numerals represen~ the corresponding size converted to square cross-section.
Table 4 shows an example of tha bar steel rolling line, wherein the rolling mills of high elongation are disposed at No. 2 - No. 5 stands. The reason for disposing the rolling mills taking high elongation up to No. 5 stand is that the rolling speed after the No. 5 stand will exceed the effective roll-ing speed range shown in Figure 4. Accordingly, in the stand after the No. 6 stand, conventional rolling in the range of the equivalent contact angle to be controlled by the curve IV is performed.
Also, Table 5 shows an example of a rod rolling~ine, wherein the rolling mills effecting high elongation are disposed at No. 2 - No. 6 stands.
In this case too, at the stand after the No. 7 stand, the rolling speed will exceed the effective rolling speed range shown in Figure 4.
In the Table 4, the stands effecting the high elongation of 1.8 are 4 units, and in the Table 5, there are 5 units, and the total elongation with the train of the roughing rolling stands is 1.2 x 1.84 = 12.6 in Table 4, and in the Table 5, it reaches 1.2 x 1.85 = 22.7.
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,r~ In the train of the conventional rolling mills whose elongation .~.:;
.; level per pass is 1.25, 11 - 14 units of stands would be necessary to achieve .;
20 the same elongations. On the contrary, in this invention, the number of unitsof the stands of the train of the roughening rolling mills is 5 - 6 units, and therefore, 6 - 8 units of the stands are eliminated, which effect is remarkable.Accordingly, this is an excellent layout making possible large scale j reduction of the expenses related ~o the installation, including the shortening .~., - 2~ -;., .;

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of the rolling line.
Of course, in the foregoing embodiments, the rolling efficiency, compacting the rolling mills are taken into consideration, and rolling with the maximum contact angle as shown in Figure 4 is employed as the basic prin-ciple, and although the diameter of the rolls is relatively made smaller, and the whole installation has high efficiency as described in the foregoing.

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Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of rolling a metal workpiece in a rolling mill consisting of a first rolling stand, and a plurality high reduction rolling stands dis-posed successively to said first stand, the improved method comprising:
setting a roll gap of the workrolls of the first high reduction rolling stand following said first rolling stand so that the equivalent contact angle ??
(?? = tan -1 (cos .alpha. x tan ?) wherein ? denotes contact angle between the work-rolls in the bottom of the roll groove and the workpiece, and .alpha. denotes the inclined angle of the groove) is bigger than tan -1 µ (where µ denotes the co-efficient of friction between the workpiece and the workrolls at the biting time) and ?? also is smaller than tan -1, µ' (where µ' denotes the coefficient of friction between the workpiece and the workrolls when the workpiece is completely bitten between the workrolls and rolling is in progress); feeding the workpiece to said first high reduction rolling stand by means of said first rolling stand; producing compression stress in the rolling direction which is below the yield stress at the rolling time, in that portion of the workpiece which is located between said first rolling stand and said first high reduc-tion rolling stand by feeding the workpiece and biting the workpiece between the workrolls of said first high reduction rolling stand; and adjusting the peripheral speed of the rolls of said first rolling stand after the tip por-tion of the workpiece is completely bitten between the workrolls of said first high reduction rolling stand (while said workrolls remain with the previously set roll gap) to reduce said compression stress while continuing the rolling;
whereby the workpiece can be rolled with high reduction of area.

2. A method as defined in the claim 1 wherein the magnitude of the com-pression stress generated on the workpiece is above 1% of the yield stress of the workpiece.

3. A method as defined in the claim 1 or claim 2 wherein the peripheral speed of said workrolls is below 2.5 M/S.

4. A train of rolling mills for rolling a metal workpiece with high elongation comprising: a first rolling stand wherein the roll gap is set so that the contact angle ? between the rolling rolls and workpiece satisfies ? < tan -1 µ (where µ is the coefficient of friction between the rolling rolls and workpiece); a plurality of high reduction rolling stands wherein the roll gap is set so that the contact angle ? becomes at least ? ? tan -1 µ, high reduction rolling stands being disposed successively to the rear of the first rolling stand; a speed detecting device for detecting the peripheral speed of the rolls of the first high reduction rolling stand; a device for detecting completion of biting of the tip portion of the workpiece in the first high reduction rolling stand; a device for controlling the peripheral speed of the rolls of the first rolling stand on the basis of the signal from the speed detecting device so that a compressive stress of above l% and below 100% of the yield stress of workpiece is generated on the workpiece as it is bitten into the incoming side of the first high reduction rolling stand; and control-ling the peripheral speed of the rolls of the first rolling stand or first high reduction rolling stand in response to the signal from the biting comple-tion detecting device so that stress is not generated on the workpiece at the incoming side of the first high reduction rolling stand after the workpiece is bitten into therein; an arithmetic operation processing device for storing 2 slipping limit curve in the relationship of the corresponding contact angle and the rolling speed in the first high-reduction rolling stand and comparing the speed signal from the speed detecting device and the sliding limit speed and producing a speed correction amount as an output; and a device for controlling the peripheral speed of the rolls of the first high-reduction rolling stand in response to the biting completion signal and the speed correction amount signal.