CA1207872A - Method of controlling mill pacing - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
According to the present invention, in a method of controlling a mill pacing in a rolling equipment wherein a plurality of serial rolling mills are provided downstream of a heating furnace in which a plurality of materials are rested on a furnace hearth integrally moving with the materials and can be successively extracted, respective rolling cycle.
times are sought from periods of time between the starts of rolling in respective rolling mills of a subsequent material to be extracted from the heating furnace and the readiness for rolling of the following material in the respective rolling mills, the maximum value of the above-described respecitive rolling cycle times is assumed as an extraction cycle time of the subsequent material to be extracted to thereby presuppose an extraction time of the subsequent material to be extractedfrom the heating furnace, allowable retard periods of time of the materials immediately before the respective rolling mills are predetermined, it is confirmed that the presupposed retard periods of time of the subsequent materials to be extracted immediately before the respective rolling mills are within the aforesaid allowable retard periods of time, and further, it is confirmed that a heating critical cycle time is secured which is sufficient for applying heat of a predetermined value to the subsequent material to be extracted through the latest material to be loaded, whereby the subsequent material is extracted at the aforesaid presupposed extraction time. In consequence, the operating condition of the rolling line as a whole are optimized, so that the productivity can be improved.

Description

1~7~372 SPECIF ICATION
TITLE OF THE INVENTION
_ METHOD OF CONTROLLIHG MILL PACING
BACKCROUND OF THE INYENTION
FIELD OF THE INYENTION
This invention relates to a method of controlling mill pacing uherein an e~traction pitch of a heating furnace is determined while the progress of rolling is controlled in a rolling equipment wherein a plurality o~ serial rolling mills are pro~ided downstream of the heating furnace in which a plurality of materials are rested on a furnace heàrth integrall~ mo~ing the materials and can be successiYel~ egtracted.
DESCRIPTION OF THE PRIOR ART
In a rolling equipment for sea~less steel pipes, shapes and the 10 -like, a multiplicity of ma~erials to be rulled are present in a rolling line consisting of a heating furnace and a plurality of rolling mi31s.
Particularl~, as compared with the pl~e rolling, in the seamless steel pipe rolling, the number of rolling mills under the control is numerous and the number of pipes under the control is numerous, whereby it has been Yery difFicult to shorten a c~cle time. In the aforesaid rclling equipment of the prior art. there ha~e been obser~ed the techniques of controlling the respecti~e rolling mills and the heating furnace, in each o~ the cases of the techniques the operatioDs have relied on the e~periences and the skill of the operations, whereby it has been impnssible to improve the productivity to an ideal e~tremit~.
In addition, as a technique for reference, there is a method o.
controlling a heating furnace described in Patent Kokal (Laid-Open) No.

1~7~1~72 127812J79 issued by the Patent Office of Japan. Uowever, this method oP
controlling contemplates that the relat;ons between the elapsed time and the temperature of piercing are sought for the heating furnace and a piecer to thereby control the furnace temperature of the heating furnace, and hence, such a disad~antage has been presented that the conditions of the group of mills in a posterior process following that in the piercer cannot be grasped.
~ h~ present inYentio~ has as its object the pro~ision of a method of controlling a mill pacing in a rolling eyuipment wherein the operating conditions of a rolling line as a whole is optimized to impro~e the productiYit~.
SUMMARY OF THE INVENTION
To achie~e the abo~e-described object, the present invention contemplates that, in a method of controlling a mill pacing in a rollir.g equip~ent wherein a plurality of serial rolling mills are pro~ided downstrea~ of a heatin~ furnace in .~hich a ~lurality of ~aterial~ are rested on a furnace hearth integrally mo~ing with the materials and can be successi~ely ~tracted, respecti~e roll3ng cycle times are.sought from periods of time betNeen the starts of rolling in respectiqe rollin~
mills of a subsequent ~aterial to be e~tracted fro~ the heating furnase and the readiness for roliing of the following ~aterial iD the respecti~e rolling mills~ the maximu~ ~alue of the above-described respecti~e rolling cycle ti~es is assumed as an e~tractiQn cycle time ~f the subsequer ~aterial to be e~tracted to thereby presuppose an e~traction time of the subsequent ~aterial tn be egtractPd from t~e heating furnace, allo~able retard p~riods of time of the materia!s ~2~)'7l 3'72 immediately before the respective rolling mills are predetermined, it is confirmed that the presupposed retard periods of time of the subseq~ent materials to be e~tracted immediately before the respecti~e rolling mills are within the aforesaid allowable retard periods of time, and further, it is confirmed that a heating critical cycle time is secured which is sufficient for applying heat of a predetermined ialue to the subsequent material to be e~tracted through the latest material to be loaded, whereby the subsequent material is e~tracted at the aforesaid presupposed egtraction ti~e.
BRIE~ DESCRIPTION OF THE DRAWING~ `
Fig. 1 is a diagram of control system showing an embodim~t, in which the present invention is applied to a rollin~ equip~ent for seamless steel pipes;
Fig. 2 is a flow chart showing control steps of a calculating means in the abo~e embodi~ent;
Fig. 3 is an e~planatory ~ieu showing the de~inition of a rolling cycle time in the abo~e embodiment;
Fig. 4A is a histogram showing the reiationship between the loss time and the number of materials in the equipment under critical condition of the conventional system; and Fig. 4B is a histogram showing th~ relationship between the loss time and the numbeT of materials in the equip~ent under critical accDrding to the present inYentionO
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INYENTION
Description uill hereunder be given of an e~bodiment o~' the present inYention with reference to the drawings.

, ~2~7~7Z

Fig. 1 is a diagram of control system, sho~ing an embudiment~ in which the present invention is applied to a rollin~ equip~ent for seamless steel pipes. More specifically, this rolling equipment is a Tolling line for seamless steel pipes according to the ~anness0ann-plug mill system, wherein the material~ which has been heated in a heating furnace 11, is pierced and rolled in a piercer 12, rolled for pipe-e~panding and elongating the material in an elongater 13, rolled to a length of a pipe ha~ing a wall thickness substantially equi~alent to tlle product wall thickness in a plug mill 14, the inner and outer sur~aces of the pipe-shaped material are polished by t~o reelers 15 and the wall thickness reduction and pipe-e~panding to a certain e~ter.t are ef~ected, and the material is finished to be a pipe ha~ing an outer diameter of a predeter~;ned value in a sizer 16, thus enabling to pro~ide a ~inal ploduct. In addition, the heating furnace 11 is of a rotary furnace hearth type, in which a plurality of materials are rested on ~urnace hearth integrally movin~ the materials, and can be successiYel~
e~tracted.
In the abo~e rolling equipment9 the heating furnace 11 is controlled by a heatin~ furnace control device 21 and the mills 12 through 16 are ~ontrolled respecti~e rolling mil~ control dev.ices 22 through 26. An actual result of e~traction of the ~aterial obtained i~
the heating furnace control deYiee 21 and actual results of rolling o~
the materials obtained in the respecti~e rolling ~ill control de~ices 22 through 2~ are transmitted to a calculating ~eans 27. As will be described belou, the calculating means 27 deter~ines the optimal e~traction time in the heatin8 ~urnace 11 and makes it possible to ~ 8 ~ 2 transmit the estraction time to the heating furnace control dev;ce 21.
The operation of the calculating ~eans 27 is shown in ~ig. 2.
Hore specificallyl the calculating means 27 calculates and pressupPoses respective rolling cycle times MCT between the starts of rolling in the rPspecti~e rolling mills 12 through 16 of a subsequeDt material to 'oe e~tracted ~rom the heating furnace 11 and the completion of the preparation for rolling of the follo~ing ~aterial on the basis of a rolling schedule. Here, the rolling cycle time MCT is de~ined as a period of time between the time of starting the rnlling and time of completing the preparatio~ for the rolling as indicated by a rolling starting si8nal P, and a following material rollîn~ readiness sig~al P 2 in Fig. 3. Then, after pierced materials of the same lot in material quality, dimensions and the like as the subse~uent Material to be egtraoted ha~e been passed through the ~ills 12 through 16, 1~ respectiYe presuppoosed cycle times NCT are calculated on the basis oP
actual result cycle times MCT collected in the respecti~e rolling ~ill control devioes 22 through 26. ~hereas, before pierced materials oi t~le s~me lot as the subsequent ~ate`rials have riot yet been passed throllgb the mills 12 through 16, the respecti~e presupposed rolling cycle times M~T are calculated on the basis of rolling speeds~ rolling lengths, requircd idle times and the like in the respecti~e mills 12 through 16.
~ore ~pecifically, the aforesaid rolling sycle ti~e ~CT is the truly requ;red rolling cycle time in the rolling mill under the control. The period of time between the completion of preparation for the following

2~ material and the start of rolling is a loss time l~ing idle for the rolling mill under the control. Therefore, it is desirable that the 12~3~872 loss ti~es be eli~inated in all of the rolling mills, howe~er, the loss times in all of the rolling mills cannot be eliminated because the rolling cycle times MCT are different from one rolling mill to anoth~r Then~ if the loss time is eliminated in the roll;ng ~ill (equipment under critical condition) ha~ing the largest rolling cycle time MGT, tllen it becomes possible to impro~e the producti~ity to the ut~ost uIl~er given conditions. In other words, this means that the subsequent material should be e~tracted fro~ the heating furnace 11 by the rollin~
cycle time of one of the mills 12 through 16, ~hich has the largest 10 rolling cycle time MCT. In consequence, the calculating ~eans 27 adds the largest Yalue of the rolling cycle times MCT relating to the aforesaid subsequent material to `oe e~tracted, i.e. an assumed e~traction c~cle time to the latest actual result e~traction time o~ the heating furnace 11 transi~itted ~ro~ the heating furnace control device 21, to thereby assume an e~traction time of the subsequent material to be e~tracted.
Here, if the assuoed e~traction cgcle time determined from the respecti7e rolling cycle times MCT as described abo~e is too short, the~
the loss times in the respecti~e mills 12 through 18 are decreased, howeYer, there occur so~e cases where Daterials are retarded i~mediateiy before the mills 12 through 16, thus leading to deteriorated product quality and considerably worn rolling tools such as reduction rolls due ~o louered temperature of the material. Therefore, the calculating means ~7 pre~iously deter~ines alloffable retard periods of time for the materials im~ediately before the ~iils 12 through 16, con~ir~s that the presupposed retard periods of time of the suhsequent ~aterials to be ~Z~7~372 e~tracted immediately before the mills 12 through 16 are ~ithin the range of the aforesaid allo~able retard periods of time, and when the presupposed retard periods of ti~e are beyond the range of the allo~able retard periods o~ time, the calculating means 27 perfor~s again the calculation and presupposition of respecti~e rolling c~cle times MCT and the pro~isional calculation of e~traction ti~e.
More specifically, the aforesaid allo~able retard periods of tine will be determined in the follo~ing manner. To cite a seamless steel pipe for e~a~ple, a theoretical radiation calculation for~ula ~the relationship o~ the loNered ~alue of the temperature of a pipe ~aterial with the elapsed time) on the di~ensions (outer diameter and ~all thickness~ of the pipe materials in the respective mills 12 throttgh 16 is sought, while, the relationships between the temperature of the ~ipe material and defects on the inner surface of the pipe material and lS between the te~perature of the piPe material and wear ~f the rollin~
tools, etc. are sought on the basis of the actual results, and it i~
determined within what retard period of ti~e at the largest the rollin~
can be started in order to roll the pipe material within the ra~ge of suitable temperature.
Furthermore, the calculation of the presupposed retard periods nf time immediate]g before the mills 12 through 16 and the confîr~ation of that the presupposed retard periods of time are Nithin th~ range of tne allowable retar~ period of ti~e are carried out in the followillg ~anner Namely, if a presupposed rolling cycle ti~e ~CT of a ~aterial No. i counted from the latest ~aterial ~1) to be started for rolling in a rnlling mill No. ~ is made to be ~CT~(i), a target e~traction time of the subsequent material (n) to be e2tracted from the heating furnace 11 is made to be Tn and an actual result time when the latest material to be started for rolling in the rolling mill No. ~ is e~tracted from th0 heating furnace 11 is made to be Tl , then a presupposed retard period of time hg of the subsequent material to be e~tracted im~ediatel7 before the rol]ing mi~l No. ~ is sought thrnugh the follouing equation.
hg = ~ MCT~ Tn - Tl 3 -- ~ l~
i~ 1 Subsequently, an allnwable retard period of time in the rolling mill No. ~ is ~ade tc be r~ and a difference f~ between rg and the presupposed retard period of time h2 is sought through the follo~ing equation.
n f~ = ~ MCT~ Tn - T, ) - rg ( 2?
i = l Further~ calculation is made through the following equation for tne rolling mills from No. 1 to the final one ~No. m~. And, if F ~ 0, the~
it is iudged that e~traction càn be made, and, if ~ > 0, then it ïs judged that e~traction cannot be made.
F = MAX( fl ~ fg -- f~ - ( 3) As described abo~e, when the subseque~t ~aterials to be e~tracted are con~eyed to the mills 12 through 1~, the oaleulating ~eans 27 calculates and presupposes the periods of time for a~aiting the rnlling immediately before the ~ills 12 through 16~ i e~ retard periods of ti~e.

~ Zc~78 7~

When the retard periods of time are ~ithin the range of allowable vallles for all of the rolling mills, it is judged that e~traction can be ~ade, and when the retard period of time e~ceeds the allowable retard period of ti~e in an~ one of the rolling mills, it is judged that e~traction sannot be made.
However, when the subsequent ~aterial is e~tracted froQ the heating furnace 11 as described aboYe, if the egtractio~ cy~le t;me is short, then such a case oocurs in the heating furnace 11 that the material is not satisfactorily and uniformly heated~ thus causi~g undesirable influence to the product qualit~. Then, the calculating means 27 calculates a heating critical cycle time HCT sufficient for appl~ing heat of a predeter~ined ~alue to the respective ~aterials including the subsequent ~aterial to be e~tracted and the latest material to be e~tracted, ~hich are present in the heating furnace 119 on the basis of the rolling schedule~ Nore specifically, the calculatiDg ~eans 27 calculates the heating critical c~cle time su~ficient for applying heat of the predeter~ined ~alue tD the respecti~e ~aterials being present in the heating furnace 11 through the following equation.
HC~ - MAXtCTI - CTm --CTn) -- ( 4 The CTm abo~e is sought through the equation (5) ~hich will ~e shown belo~.
CTm = f(Dm, Lm) -- ( 5) where CT~ is a furnace neck e~traction s~cle time to a ~aterial of lot No~ m in luoking from the side of e~traction, Dm a diaEeter of the ~aterial of lot No. m, and Lm a lengt~ of the ~aterial of lot No. m.

~07~72 Further, when the subsequent material is e~tracted at the assu~ed e~traction time, the calculating means 27 judges whether or not the aforesaid heating critical cycle time HCT is secured between the subsequent material to be extracted and its preceding material to be e~tracted. When it is judged that the heating critical cycle time H~l' can be secured, the calculating means 27 trans~its the aforesaid assu~ed e~tractîon time to the heating furnace control de~ice 21 as the opti~al e~traction ti~e for the subsequent ~aterial to be extracted. When it is judged that the afoTesaid heatin~ critical cycle time HCT is not secured, the calculating ~eans 27 repeats the calculation and presupposition of the respecti~e rolling cycle times ~CT, assu~tion of the extraction time, confirmation of that the presupposed retard period of time is within the allowable retard period of time and confir~atio of that the heating critical cycle ti~e can be secured.
In addition. the rolling start signal necessary for determining the rolling c~cle times MCT ~n the mills 12 through 16 and the subsequent material rolling readiness signal are deter~ined as sho~n in Table 1.
Figs~ 4A and ~B are histogra~s showing the relationship bet~een the loss time and the nu~ber of materials H in the equip~ent under critical condition in the operating system according to the prior art and in the operating system according to the present invention, respectiYel~, when the ~aterials each haYing a diioeter of 230 mm and a length of 1,535 ~ are loaded into the h~ating furnace in t~o rows ~d rolled into steel pipes eash ha~ing an outer dia~eter of 273.8 m~, a wall thickness of 6.35 m~ and a length of 11,705 m~. As apparent fro~

Table 1 . . ~
DeYices Signals Timing of generatin signals _ Rolling start When a pusher starts ad~ancing Piercer 12 . Subsequent material When the subsequent ~aterial rolling readiness is completed in set-up -- _ Rolling start When the pusher starts advancing Elongater 13 Subsequent material When the subsequent ~aterial rolling readiness is completed in set-up , ...
Rolling start When one pass rolling pusher Plug mill starts ad~ancing Subsequent material When the subsequent ~aterial i3 . rolling readiness ~ompleted in set-up _ _._ . Rolling start When a table roller on input . side of rolling mill starts ~eelers normal rotation . Subsequent material When the subsequent ~aterial rolling readiness is ou~pleted in set-up _ . .
RolliDg start When the table roller on input side of rolling mill starts Sizer normal rotation . Subsequent material When the subsequent ~aterial is rolling readiness campleted in set-up _ _ .. ., _ __ ... ..

~igs. 4A and 4R~ an average loss time in the operating syste~ accordir.
to the prior art is 1.08 sec., whereas an a~erage loss time in the operating system accordingto the Present in~entioD is 0.33 sec., thus remarkably impro~ing the nroductivity according to the present inYention.
The present invention is applicable not only to the production line for seamless steel pipes in accordance Nith the Manness~ann-plug mill system but also to the rolling equipment ~or sea~less steel pipes according to the Mandrel ~ill s~ste~, Assel mill syste~ and the like.
Further, the present in~ention is applicable to the rolling equip0ent for rolling bar steel, wire steel and the like. ~urther~ore, the present invention is applicable irrespectiYe of the number of rolling mills, and on the contrar~, the larger the number of rDlling ~ills is~
the greater the e~fects can be attained.

Claims

WHAT IS CLAIMED IS:

1 A method of controlling a mill pacing in a rolling equipment where in a plurality of serial rolling mills are provided downstream of a heating furnace in which a plurality of materials are rested on a furnace hearth integrally moving with the materials and can be successively extracted, characterized in that respective rolling cycle times are sought from periods of time between the starts of rolling in respective rolling mills of a subsequent material to be extracted from said heating furnace and the readiness for rolling of the following material in the respective rolling mills, the maximum value of said respective rolling cycle times is assumed as an extraction cycle time of the subsequent material to be extracted to thereby presuppose an extraction time of the subsequent material to be extracted from said heating furnace, allowable retard periods of time of the materials immediately before the respective rolling mills are predetermined, it is confirmed that the presupposed retard periods of time of the subsequent materials to be extracted immediately before the respective roiling mills are within said allowable retard periods of time, and further, it is confirmed that a heating critical cycle time is secured which is sufficient for applying heat of a predetermined value to the subsequent material to be extracted or the latest material to be loaded, whereby the subsequent material is extracted at said presupposed extraction time.