CA1149884A - Apparatus for continuous manufacture of butt-welded pipe - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An apparatus for continuous manufacture of butt-welded pipes is constituted by a heating furnace for heating a skelp continuously passed therethrough up to a predetermined temperature less than the butt-welding temperature for the material of the skelp, heaters adjacent the outlet end of the heating furnace and having spaced opposed induction heating coils on opposite sides of the path along which the skelp is passed through said heaters and adjacent the edge portions of the skelp for heating only the edge portions of the skelp discharged from the heating furnace up to the butt-welding temperature. The induction heating coils are such that the electromagnetic coupling between the induction heating coils and the corresponding edge portions of the skelp can be varied to adjust the temperature to which the edge portions are heated. A bending device adjacent the outlet end of the heat-ers bends the skelp into a generally tubular form, and butt-welding rolls adjacent the outlet end of the bending apparatus apply a predetermined pressure to the bent up skelp for butt-welding the edges of the skelp to each other. A cooling device along the path of the pie between pairs of contracting rolls cools the seamed portion of the pipe to the temperature of the remainder of the pipe.

Description

8~34 ; SPECIFICATION~
TITLE OF THE INVENTION
APPARATUS FOR CONTINUOUS MANUFACTURE
OF BUTT-WELDED PIPE
BACKGROUND OF THE INVENTION

This in~ention relates to apparatus for continuous ` manufacturing of bu~t-welded pipes, e.g., butt-welded steel - pipes, by heating a skelp, bending it into a tubular shape, and butt-welding the opposite edges of the skelp to each other.
Generally, butt-welded pipes are manufactured by heating the edges of the skelp by passing the skelp through : a heating furnace at a temperature of 1300C suitabLe for butt-welding (hereinafter called thé butt-welding tempera-ture), bending the skelp into a tubùlar shape on molding rolls, -butt-welding the opposite edges o the skelp to each other by means of butt-welding rolls, and then finishing the pipe by contraction rolling apd other finishing processes. Such a method, however, is disadvantageous in that: the central portion of the skelp is heated as well as both the edg,es as it passes through the heating furnace, although the heating of the central portion is unnecessary and hence wasteful;
both the edges of the skelp, which often are at somewhat different temperatures due to the construction of the heating furnace or differences of the thiokness o the skelp itself, are butt-welded as they come from the furnace and the tempera-ture difference causes a difference in deformation resistance ~ . . . .

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! which in turn makes the upset stress non-uniform; and the re sidual temperature difference between the seamed portion and ' the parent metal portion of the butt-welded pipe causes a de- ' viation in the thickness in the vicinity of the seamed portion during the contraction process.' Heretofore, several remedies have been developed to overcome the above problems, but the results have not been completely effective.'' One method is disclosed in Japanese Patent Publication No. 14092/1~68 and French Patent Application No. 936135. This method has been proposed to facilitate saving of energy, and in it the entire skelp is at first h~ated by passing it through the heating furnace at a temperature of about 1~00C, which is lower than the butt-welding temperature.
Then an inductor for induction heating is used to heat only the opposite edg~s up to the butt-welding temperature, so that ' the central portion of skelp is kept at a lower temperature ' than the butt-welding temperature and in a range suitable for carrying out the bending, contraction rolling, etc., with-` out hinderance, thus achie~ing the desired energy'saving~
Thus, the'equipment for the above prior art method therefore can keep the central portion of s~elp at a lower ' ' temperature than both edges, but that is all that is done.
The temperature of the two edges of the skelp is not adjustable, so that upset stress cannot be made uniform, and thicknass deviation during the contraction rolling process after butt-welding, cannot be kept from increasing. This~is because of the inductor used for heating the'edges of the skelp in the

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above prior art method.
Problems also exist due to the butt-welding rolls which are commonly used. The roll gap between vertically disposed butt-welding rolls has usually been set to be constant. There are, however, variations in the width of the skelp, and the butt-welding rolls are usually slightly eccentric so as to create variations in the pressure applied to the edges of the skelp. The roll gap may be made smaller in an effort to eliminate portions of reduced strength along the seamed portion of the continuous butt-welded pipe, but this causes the problem that bead and thickness variation along the seamed portion increases.
Furthermore, in the above method in which the skelp is bent and the edges of skelp are heated to a higher temperature than the central portion thereof and then butt-welded, because the temperature difference hetween the edges and the central portion of the skelp is prcduced for the purpose of saving thermal energy, the deformation resistance in the central portion is larger than where the entire skelp is heated to the butt-welding temperature, so that the constant roll gap increases the pressure between the butt edges to thereby promote production of the bead along the seamed portion of the finished pipe and increase the thickness variation in the vicinity of the seamed portion, thus causing variations of strength along the seamed portion.

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The present invention has been proposed in order to overcome the above-described problems in the prior art methods and apparatus.
A main object of the invention is to provide an apparatus for continuous manufacture of butt-welded pipe which is capable of restraining the formation of a bead at the seamed portion and thereby reducing thicXness deviation in the vicinity thereo:E, thus reducing variation of strength at the seamed portion and increasing the quality of the pipes.
Another object oE the invention is to provide an apparatus for continuous manufacture of butt-welded pipe which operates with less energy consumption.
Still another object of the invention is to provide an apparatus for continuous manufacture of butt-welded pipe which does not damage the edges of the skelp even when a heater is brought close to the edges of the skelp for conserving energy.
A further object of the invention is to provide an apparatus for continuous manufacture of butt-welded pipe having a heater capable of raising the temperature of the two edges of the skelp to a uniform temperature for improving the quality of the finished product.
A still further object of the invention is to provide an apparatus for continuous manufacture o~ butt-welded pipe which is provided with butt-welding rolls .
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~9~384 capable of controlling the pressure load applied to the skelp so that it coincides with a desired preset value to thereby improve the quality of the finished product.
These and other objects and novel features of the invention will be more apparent from the following description taken together with the accompanying drawings, in which:
Figure 1 is a schematic elevation view, partly in section, of an apparatus for continu-ous manufacture of butt-welded pipe according to the invention, Figure 2 is a perspective view, partly schematic, of a main heater and a control system for energizing it as used in the apparatus shown in Figure 1, Figure 3 is a block diagram of control unit 28, Figure 4 is a diagrammatic flow chart explain-ing the operation by CPU 284;
Figure S is a perspective view, partly schematic, of a sub-heater and a control system for energizing it as used in the apparatus shown in Figure 1, .
Figure 6 is a block diagram of control unit 37, Figure 7 is a diagrammatic flow chart explain-ing the operation by CPU 374, Figure 8 is an elevation view of butt-welding rolls and a control system therefor ~, .

used in the apparatus of Figure 1, Figure 9 is a block diagram of control unit 59, Figure 10 is a diagrammatic flow chart explain-ing the operation by CPU 593, Figure 11 is a graph showing the relation between bead height and upset stress in a continuously butt-welded pipe, Figure 12 is a schematic elevation view, partly in section, of a cooling device and a eontrol system therefor used in the apparatus of Figure 1, Figure 13 is a bloek diagram of control unit 75, Figure 14 is a diagrammatic flow chart explain-ing the operation by CPU 755, Figure 15(a) is a histogram showing the distri-bution of flatness values for a plurality of continuously butt-welded pipes produced by a conventional apparatus, Figure 15(b) is a histogram showing the distri~
bution of flatness values for a plurality of continuously butt-welded pipes -~
produeed by a eonventional apparatus;
Figure 16 is a graph showing the results of measurements and showing the distri-bution of pipe thieknesses for various ways of eontrolling the eooling of the pipe in the apparatus according to the ', '.
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invention;
Figure 17 is a cross-section of a pipe, showing the measuring positions used in measur-ing the values for the graph of Figure 16;
Figure 18 is a perspective view of a modified embodiment of the heater and a control system therefor;
Figure 19 is a partially cut-away perspective view of the heater coil in the heater of Figure 18;
Figure 20 is a diagrammatic sectional view for explaining the function of the heater coil shown in Figure 19; and Figure 21 is a persp~ctive view of a prior art inductor.
DETAILED DESCRIPTIO~ OF THE INVE~TIO~
Figure 21 is a schematic exterior view of such a prior art inductor. The inductor comprises an elongated copper bar 101, a pair of aligned short copper bars 102 and 103 disposed parallel to the copper bar 101 and spaced from the bar lOl a distance slightly greater than the :.
width of a skelp 10, pairs of arcuate-thick copper bands 104 and 104' bridged across the upper and lower surfaces of the front e:nd of copper bar 101 and copper bar 102 and across the upper and lower surfaces of the rear end of copper bar 101 and copper ba~ 103, and a pair of tenminal :: :
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tongues 105 and 106 provided on the opposed ends of copper bars 102 and 103. The inductor thus has the copper bars 101, 102 and 103 extending parallel to the edges El and Er of skelp 10 and opposed to the edge faces of the skelp, and the skelp 10 travels between the thick copper bands 104 at one end of the inductor and between the thick copper bands 104' at the other end. During the travel of the skelp, high frequency current is supplied through terminals 105 and 106 to thereby generate induced currents on the surface of the moving skelp 10 as it cuts the magnetic flux generated around the inductor, thus selec-tively heating the two edges El and Er of the skelp 10.
However, the two edges El and Er of the skelp 10 discharged from the heating furnace and entering the up-stream end of the inductor are not always at the same temperature due to the construction of the heating furnace or variations in the thickness of the skelp itself. Thus, even when the edges of the skelp are heated uniformly by the inductor, the edges will almost always differ in temperature, usually by about 5 to 20C. Furthermore, the path of the skelp moving through the inductor may change slightly due to the natural movements of the skelp, so that the dimensions of the intervals between the copper bars 101, 102 and 103, and the two edges El and Er may vary, which increases the temperature difference between the two edges, so variations in the upset stress increase, resulting in poor quality of the finished . ~

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product. Even though the spaces between the copper bars 101, 102 and 103, and the two edges El and Er of the skelp 10 are made smaller to try to increase the heating efficiency, the amount the space can be reduced is limited because of the danger of deforming the skelp if the edges El and Er contact the copper bars 101, 102 and 103. Hence, the heating efficiency must remain rather low and the opportunity for energy saving is limited. Moreover, an inductor of a particular size can handle only a limited number of different widths of skelp, so that inductors of various sizes must be avail~
able if many different widths of skelp are to be handled.
Further, the aforesaid temperature difference between the two edges El and Er of the skelp 10 when it is discharged from the heating furnace must often be compensated for, but the inductor having the above-described construction is unable to carry out such compensation. Hence, the above-described method has disadvantages due to the limitations in the apparatus used to carry it out.
A general description of the construction of an apparatus for continuous manufacture of butt-welded pipe according to the invention will be given with reference to Fig. 1. In Fig. 1, reference numeral 10 designates the skelp. The skelp 10 is withdrawn from an uncoiler or the like (not shown) and the entire skelp is t :~ ~

heated up to a temperature lower than the butt-welding temperature, 1150 to 1200C, and preferably about 1200C, by being passed through a heating furnace 1.

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, ~ Thereafter, the skelp is passed through a main heater 2 and a t sub-heater 3. The main h.eater 2 h.eats only the two edges El and Er, i.e. an edge porti~n:of ~ p;redetermined width, preferably about 10 mm,to a temperature at or near the butt-welding tem-perature, and the sub-heater.3 adjusts the temperature of the edges El and Er until they are equa}. and are at the butt-welding temperature. Next, the skelp is passed between bending rolls

4 and is bent in an O-like cross~sectional shape and the opposed edges.El and Er are butt-welded by butt-welding rolls 10 5 to form the skelp into a pipe. Immediately thereafter, the seamed portion of the continuously butt-welded.pipe is cooled by a cooling device 71 disposed between contraction rolls 60 upstream of the cooling device and a group of contraction rolls 6 downstream.of the cooling-device, so that any.tempera- .
15 . ture difference between the seame~ portion and remaining metal is reduced or eliminated. The pipe, thereater, passes through the group of contraction rolls 6 and is cut to the desired length. The thus cut pipes 100 are completely cooled .
by a cooling device 72 and are finished by a finishing méans such as a sizer 9 or the lik.e.
~ - Each component of the apparatus of the invention will be described in detail in the following description.
The heating furnace 1 itself is well-known and com-; ~ prises an upper preheating zone ll for preheating the skelp 25. 10, a return drum 12 at the exi.t end of zone 11, and turnaround . rolls 13 at the entrance end. Skèlp 10 is moved`in the ;~ direction of the arrow into the prehèating zone 11 and passes : : .
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!, around the return drum 12 and the turnaround rolls 13 and is directed into the heating zone 15 through an inlet 14. In the heating zone 15, the skelp is heated by a gas burner or the li~e as it moves through'heating zone 15, and it is discharged ~rom the heating zone 15 through'an outlet 16. It is then guided sequentially through the main,heater 1 and the sub~
heater 3. When it is discharged fxom the heating furnace, the temperature of the skelp 10 is lower than the butt-welding temperature of about 1300~C, i.e. it is about 1180C at the central portion and about 120pC at the two edges El and Er.
Such distribution of the temperature transversely of the skelp 10 is not limited to these values; they may be higher or lower ; than these values. If the temperature of the central portion of the skelp 10 exceeds the lower~limit of the temperature range within which'the temperatures are proper for the skelp to be bent and contracted without hinderance by the bending , rolls 4 and the rolls~of the contraction roll group 6, because the central portion of'skelp 10 is heated so~ewhat , as it passes through the main heater 2 and sub-heater ~, the temperature at the central portion of skelp 10 will approach the upper limit o~ the range of temperatures proper for bend-ing and contraction rolling, and energy savings will be reduced.
On the contrary, if the temperature of the central portion of the skelp is too low, this will increase the load on main heater 2, to bring the temperature of the ce~tral portion up ' to the desired levels to the extent that an increase in elec-tric power consumption and the necessity to provide a large ;' ~: ,. . , :
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f scale main heater 2 will result, which will not produca the desired economical advantages. Hen~_e, it is desirable to control the heating furnace 1 so that the s]celp 10, when it is discharge~
from the furnace, has the central portion heated up to the lower limit of the proper range of temperatures for bending and contraction rolling, or at least to a temperature lower than the above lower limit by an amount such that heating to the desired temperature can be carried out by the main heater 2 and sub-heater 3.
In Fig. 2, which shows the main heater 2, reference numerals 21 and 22 designate upper and lower coils for induc-tion heating. The coils 21 and 22 have rectangular cores 211 and 221 and coil bodies 212 and 222 fixed in grooves 211a and 221a in the lower surface of core 211 and in the upper surface 15 of core 221, respectively. A mounting frame 23 supports the coils 21 and 22 in vertically spaced opposed relationship to provide a space through which the skelp 10 can pass between the coils. ~he coil bodies are positioned with straight core portions 212~ and 222Q aboYe and below the position of ~e left edge El of the skelp and the straight core portions 212r and 222r above and below the position of the righ~ edge Er of the skelp, the core portions also extending in tha same direc-tion as the edges of the skelp 10. Cores 211 and 221 are formed of laminated silicon steel plates adhered to each other, 25 and the surfaces ~lereof opposed to the coil bodies 212 and 222 are provided with heat insulators (not shown), è.g. ceramic pla~es. The groove 211a is formed in the lower surface of ~

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core 211 and sroove 221a is formed in the upper surface of core 221, and the grooves are rectangular in shape with the longer sides parallel to the longer sides of the respective cores 211 and 221. The coil bodies 212 and 222 are long strips of copper extending in a rectangular pattern and are hollow to permit - ~ cooling liquid to flow therethrough. The strips are wound in layers within the grooves 211a and 221a and insulated from each other with varnish. The coil bodies 212 and 222 fit into grooves 211a and 221a and the ends extend to the exterior of the coils throu~h bores 211b and 221b extending lat~rally through the cores 211 and 221,respectively.-The power supply system for the coil bodies 212 and 222 comprises a commercial power source 24, a frequency con-verter 25, a current regulator 26 and a power-factor improving condenser 27, individual electrlc~currents at a desired fre-quency and current value set by;the frequency converter 25 and current regulator 26 being fed through the power-factor improving condensor 27 to the respective coil bodies 212 and 222. - ~
Reference numeral 28 designates a control unit for controlling the current flowing through the coil bodies 212 and 222. The control unit 28 is connected with a temperature sen~or extending across the width of the s~elp 10 upstream of the coils 21 and 22 with respect to the direction of movement of the skelp 10. The temperature distribution widthwise of the skelp 10 as detected by the temperature sensor 29 is fed into the control unit 28, and the control unit 28 determines a :
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' ~ ~, ' '' ' , current value necessary for raising the temperature at both the edges El and ~r up to the butt~weldi~g temperature durin~ ths time the skelp 10 is passed between the co~.ls 21 and 22, and control signals corresponding to thi~
current valu~ are fed to the current regulat~r 26 to cause the current regulator to feed individual co~l energiz~ng circuitg which are o~ equal or di~ferant vAlue~ ko the respactive coil bodies 212 and 222.
Fig. 3 is a block diagram of the control u~it 28, which is composed of thermo-converter 281, A/D
(analog/digital) convertar 282, process I/0 (input/
output) device 283, CPU (central processing unit) 284, digital switch 285 and D/A (digital/analog) convexter 286. ~he temperature sensor 29 generates timing signal 29a, and temperatuxe signal 29b which is obtai~ed byaa widthwisa scan sy~chronizing with said timing sig~al 29a, ~ha timing signal 29a is fed to CPU (~or example9 iSBC 80/20~ mada b~ IN~EL) 284 through the proce8s I/0 device (for examp~e,l~BC 508, 732 made by IN~EL) ~: 20 283~ TemParatura signal 29b is fed to thermo-convarter 281, wherein tha signal is amplified and correctsd linearity thereof, and the a~alog output of the co~verter 281 i8 convertad to digital data by A/D
convarter 282J Said digital data is ~ed to CP~ 284 through ~rocess I~'0 device 283. .-.
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8~4 Digital switch 285, composed o~ thumb wheel switch,:.is used ~or pre~etting the butt-welding temperature which should be aimed as a temperature ~t - the edges El and Er, and the output i~ fed to CP~
throug~ process I~0 device 283.
CPU 28~ begins an operation as shown in ~ig. ~ with timer interruption. ~t first it read~ in - temperature signal, speci~ies 2l and ~ (tamper~turs of each edge El and Er~ respectively), a~d calculate~
the average value ~ea of tha temperatures o~ both edges El, Er.

2ea ~ (2l ~ ~r)~2 ', CP.~ 284, next, re~ds in the but~-welding temperature 2s being preset by digital witch 285, A 15 ~nd calcu~ate the dif~erence ~ between ~8 and ~ea.

~ = 2s - ~ea "'"'''. ' ' After that, it calculates the current valuo Is which ena~les ~ ~ 0, and transmits the data of Is to the current regulator 26 through D/A converter 286. For the calculation of Is, followinæ ~quatlon can be used, for ex~mple.

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9 ~8 Is = I~ )~ A

the value of Is that..~as calculated i~
preceding cycla A : proportional co~st~t ~he control of the curre~t can of course be carried out b~,changing and controlling tho fre~ua~cy of cuxrent flowing through coil bodie~ 212 and 222.
~he mounting frame 23 comprise~ a vertical b~r 231 ; and uppPr and lower hori~ontal arms 232 and 233 extendin~
horizontally from the vertical bar 231. The coil 21 i~ ~ixed to the lower surface of the upper arm 232 and the coil 22 i8 ~ixed to the upper surface of the lower arm 233. ~he coil bodie~ 212 and 222 are opposed to.each other in the ~ertical direction and face the space through which the skelp 10 pa~ses.
~he details of the ~tructure of the mountinæ frame 23 it,sel~
are not sho~n, but the structure i5 such a~ to cause coils 21 - and 22 to face the space therebetween and be spaced from the surface~ of the ske}p 10 at proper distances. Alternati~e1y~
for heating the edge~ El and Er up to the butt-welding temperatures, the coils 21 and/or 22 may be mounted on the ' ~ frame 23 to move toward and awa~ from ~ach other, whereby the coils c~ be moYed to change the.electromagnetic connection .
between the coil~ and the edges of the skelp; for properl~
ad~usting the temperature to which skelp ~8 heated., Moreover~ ;
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bodies may be disposed opposite the side edge faces of theskelp 10, for example, similar to l:he sub-heaters 3 shown in - Fig. ~. Furthermore, the lower arm 233, as shown in Fig. 1~, may be mounted so as to be vertically rotated around the inner end of the arm 233 to thereby change the space between the - coils 21 and 22 a~d the edges El and Er of the skelp 10, for adjusting the heating thereof.
The skelp 10, after passing through the main heater 2, has the edges El and Er heated up to or near the butt-weld-ing temperature. The skelp is then guided into the sub-heater 3.
Fig. ~ shows the sub-heater 3 and the drive means ; and control system therefor. Reference numerals 31 and 32 designate induction heating coils. -The coils 31 and 32 are mounted on opposite sides of the path of the skelp lD and comprise cores 311 and 321 having U,-shape cross-section transverse to the path of the skelp and coil bodies 312 and 322 constituted by horizontally'wound long strips of hollow copper respectively. The power supply system for the r,espéc-tive coil bodies 312 and 322 comprises a commercial power source 34, a frequency converter 341, and a current regulator 35 and a power-factor improving condenser 36 for supplying ' separate currents'to the individual coil bodies 312 and 322. ' A support beam 33 extends transversely of the path of the skelp and support rods 331 and 332 depend f,rom the support beam and have the respective coils mounted on the lower ends with the coil bodies 312 and 322 facing the side edye ' ~ 7 ~ , ~

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sur~ace~ of the skelp edges El ~nd Er, with the ed~33 El and Er between the vertically spaced opposed portions of the re-~pective core~ 311 and 321.
The support beam 33 extends horizontall~ and perpen-dicularly to the direction o~ move}nent of the skelp 10 and i8 positioned abova the path thsreof. A guide groove ~33 extends lengthwise of the support beam 33 and opens out of the lower surface thereo~ and houses sliders 334 and 335 which ~re aup-ported by flanges extendi~g inwardly from both side~ of the gu~de groove 333. The support rods 331 and 332 are mounted on the lower surfaces of the sliders. ~o the outwardly faclng end faces of the sliders 334 and 335 are connected pi~ton-cylinder devices 336 and 337 which.in turn are mou~ted o~ the lower surface of support beam 33. The outer end~ of the pi8-15 ton rod~ of the pisto~-cylinder de~vices are oonnected to the sliders 334 and 335 respective?y, for moving the sliders 334 and 335 toward or away from each other, ~o that the Rpaces between the coil bodies 312 and 322 and tha edges El and ~r of the .~kelp 10 can b~ ad~usted b~ changing the horizo~tal distances hl and hr.
. A controI unit 37 controls current ~low through the coil bodies 312 and 322, drives the piston-cylinder devices 336 and 337 in response to the temperatures distribution sen~ed by a temperature s~sor 38 positione~ upstream o~ the coils ~1 and 32 relative to the direction of movement of the skelp and extendinæ acros~ the width of tha skelp 10. ~he control unit 3? determines a temperature dif~erence , -18- .

, on the basis of the temperature distributio~ across the ~kelp 10, especiall~ the temperature of the edges El and Er9 as detected by the temperature sensor 38, and generates a control - signal and feeds it into the current regulator 35O In respon~e thereto, the current regulator changes the value3 cf the - currents flowing to the respective coil~bod~e~ 312 and 322 so as to elliminate the temperature difference. When said current value exceedR the control range of the current regulator 35~
the piston-cylinder device 336 (or 337) i9 drived and it moves the slider 334 (or 335) to roughly set.the horizontal distances hl (or hr) between the coil bodies 312 (or 322) and the edge3 El (or ~r) o~ skelp 10. ~hereafter, the current which ~l~ws through the coil bodies 312 and 32~ is fi~ely.~d~.u~ted.~y`bhe ragulator 35 and both the edges El and Er are heated to the optimum butt-welding temperaturè;within the range o~ butt-welding temperatures.
~ig. 6 is a block diagram of the control unit 37, which iq composed of thermo-converter 371, A/D converter 372 proce3s I/0 device 373 (for example, ~B9 508~ 732 made by O I~EL), CP~ 374 (for e~ample, ~BC 80/204 made by.IN~E~) and D/A converters 375, 376.
Like CPU 284, CPU 374 reads in the timing 3ig~al 38a and temperatu~e ~ignal 38b which the temperature 3ensor 38 generates, and it faeds control signalQ~;~o ~he:curr~t regulator 35 and the control valves ~36v &` 337v which are located in the air circuits o~ piston-c~linder.deYice8 336 `~ 337 respecti~ely.

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CPU 284 begins an operation a~ ~hown in ~i~. 7 with timer interruption. At first; it reads in temperature signal, ~pecifies Tl and Tr, and c:ompares them. After that, it calculates a temperature to be raiqed a~l (at the ed~e El), ~Tr (at the edge Er) for elimi~ating th~ deviatio~ of ~l and Tr~
When ~ r ;
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a ~1 = Tr - ~1 Ir = 0 ~hen, CPU 284 calculates the currevt values IB1 and Iqr which should be ~upplyed for the coil~ 31 and 32 respectively~ At thi~ calculatio~, following equations c~ be used, for example.
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IB1, IS~ ~ R 7 Isr = Isr~ C x ~r :
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Isl( )9 Isr~o the values of Isl and Isr that 20 . were calculated in preceding cycle re~pecti~ely B , C : proportional co~stant ~' ' " ' ..

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', : . . ' ' Bf34 In the next step, Isl and Isr is compared with Is max, which is the maximum value of the controllable range of the current regulator.
When Isl (Isr) C Is ma~, the data of Isl and Isr are transmitted to the current regulator 3S. On the contrary, it decides the pos:itions of edges El and Er by the use of the pattern of temperature signal 38b, for example, and calculates Sl (or Sr) and transmits it to the solenoid of the control valve 336v (or 337v). Sl (or Sr) is a time during which said solenoid should be magnetized, and corresponds to the length hl (or hr) to be adjusted.
Thus, the horizontal distances hl and hr are changed to change the strength of the electromagnetic connection between the coil 31 and the edge El and between the coil 32 and the edge Er, thereby enabling the heating and temperature of the respective edges to be separately controlled.
Alternatively, only adjustment of the horizontal distances hl and hr can be carried out to make the temperature of both the edges El and Er the same. Also, one or the other .. . .

of the piston-cylinder devices 336 and 337 may be omltted and one of the lengths hl or hr can be fixed and the other made variable.
Furthermore, the main heat:er 2 may be omitted and only the sub-heater 3 or the heater shown in Fig. q~ used for heating the edges El and Er to the clesired equal temperature.
Still further, a further temperature sensor (not shown) can be placed downstream from the sub-heater 3 for measuring the temperature of the skelp 10 after it has been heated by the sub-heater 3 to detect any temperature difference between edgss El and Er. In order to eliminate any such temperature difference, a feed-back circuit to the control ; unit may be provided for adjusting the locations of coils 31 and 32 to thereby increase accuracy of the temperature control for the edges El and Er. ` -The skelp 10 with both edges El and Er heated to theproper butt-welding temperature is then, as shown in Fig. 1, passed through bending rolls 4 or bending the edges downwardly relative to the central portion, thus forming the skelp ~nto an O-like cross-sectional shape. Then, the skelp is passed through the butt-weiding rolls 5 for butt-welding the edges El and Er to each other to form a pipe. As shown in Fig. ~, ~; the butt-welding rolls 5 are constitured by work rolls 51 and 52 which have caliber grooves of approximately the same -semicircular profile and have flanges at both ends which have the proper width. Above the work roll 51 and below the work roll 52 are back-up rolls 53 and 54 abutting the flanges of the .
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f work rolls respectively. The lower back-up roll 54 has the ends of the shaft rotatably supported irn a support frame 561 on a stand 56. The upper back-up roll 53 has the ends of the shaft rotatably supported in a frame 551, into and out of which a

5 pressure-load adjusting device 55 is movable, and is vertically - movable a small distance. The pressure-load adjusting device 55 is controlled by an oil-pressure control valve 57 for being vertically moved, so that the rolling pressure o~ the work rolls 51 and 52 on the skelp 10 for bending i t into a 10 tubular shape can be adjusted to thereby make it possible to butt-weld the opposed edges E1 and Er at a desired pressure for welding. The rolling pressure of work rolls 51 and 52 on the outer periphery of skelp 10, in other- words, the pressure-load, is detected by a load cell 58 provided at the bearings for the 15 shaft of back-up roll 53 carried by the support frame 551.
A control unit 59 is provided which is connected to the load cell 58 and adjusts the oil-pressure control valve 57 in response to the pressure-load adj~sting device 55. The pressure-load detected by the load cell 58, when fed into the c~ntrol 20 59, is compared with the preset reference pressure-load for properly abutting the edges El and Er. Opening of the - oil-pressure control valve 57 for eliminating any difference between the detected and predetermined loads i5 calculated, and the oil-pressure control valve 57 is supplied with a control 25 signal for increasing or decreasing thP pressure-load. The reference pressure-load supplied to the skeip io by work rolls 51 and 52 is within a range of pressures which insure proper ~ i , , ' ' -~3~
, ` . : ; `:

welding of the edges El and Er, and moreover the value i8 selected so that the amount of upset i9 uniform and any thick-ness increase around the seamed portion9 or the bead height, - is reduced so that it is kept within a constant range.
Fig. 9 is a block diagram o~ the contrdl;~unlt!;99, which is composed of A/D converter 591, process I/0 device 592 (for example iSBC 508, 732 made by INTEE), CPU 5g3 (~or example, iSBC 80/204 made by IN~EL) and digital switch 594 CPU 593 begins an operation as shown in Figa 10 with timer interruption. At first, it reads i~ pressure load PA, which is detected b~ the load c~ll 58~ through A/D converter 591 and proces~ I/0 device 592, and reads in the preset reference pre~sure-load Ps from the digital switch 594. It calculates the diiference ~P between P~ and P~.
15~p = ~S - PA
- Aft~r that, the di~fe~ence ~P i8 compared with zero.
When ~P > 0, CPU 593.calculate~ the time ~
and when ~P ~ 0, it calculates the time D~ by the ~ollowing ? equation~, and transmits them to the control Yalve 57.
~T~ D aP ~ E
F ~P + G
D, E, F, G :,con~tants 25,When ~P ~ 0, the control valve 57 is opend to : supply oil to the pressure-load ad~usting ~evice 55, an~

. ~ , : , 1 ~: !

88~L
~ .. ... . .... . . . .. . . . ..... . . ..

when oP ~ 0, the control valve 57 is ope~d to releas~ the oil pressure in the ~djusting device 55O ~ ~1 and ~ are nece~sary times to open the control ~alYe 57 in order to m~ke ~P ~ 0.
~he reason why the pressure-load controlled by the butt-we~ding rolls 5 limits the height of the bead and the thick~e~s increase around the seamed portion, will ~ow bo explained.
~ig~ 11 shows the results of experiments rarried out for obtaining the relation between the height o~ the bead a~d upset ~tress, in which a skelp 320 mm wide and 3.2 mm thick ; was first heated so that both edge portions 10 mm wide wer~
; heated to a higher temperature than the ce~tral portion, and the skelp waa bent and butt-welded with an amou~t Or upset o~
10 mm, whereb~ a continuously butt_welded pipe having a~ out~
side diameter o~ 101.9 mm was produced from the butt-welding rolls. ~he graph shows the upset stresq (kg/cm~ along the ordinate and the height o~ the bead (mm) at the seamed portlo~
along the abscissa. Marks 0. D, ~ and X in the graph, repre-3ent the rela~ion between the upset stress and the bead heightcorrespondin~ to temperature differen~e between the edge por-tion3 and the central portio~ o$ 50, 100, 150, and 300-C when the temperaturs ol the central portion was 1300'C and the tem-perature~ of the edge portions were 1250, 1200, 1150,~nd 1000 C~
~he solid line shows relation between the upset stre~ and the bead height when both edges were at a temperature of 1300 a ~-~ a~d the central portion was at 1000UCo As see~ from the graph, .
~ ~ .
' ~' ~; ~ '. ' ' 8~4 ~ the ~reater the temperature difference between the edges and I the central portion, the larger the upset stress and bead height for a given skelp, and when the temperature difference is constant, the bead height becomes larger nearly in propor-tion to the increase in the upset stress. In addition, thedot-dash line shows the lower limit of upset stress necessary for ensuring adequate stxength of the butt-welding at the seamed portion.
On the other hand, for a given temperature of th~
skelp, the upset stress is princlpally related to the pressure load at the butt-welding rolls. Both the height o bead and increase in thickness around the seamed portion change in ; association with each other due to the temperature at both edges of the skelp and the upset stress. In brief, where the temperature of the edges of the skelp~upstream of the butt-welding rolls is closely controlled, as,by the apparatus of the invention, the pressure load at the butt-welding rolls ~an be controlled to achieve a desired upset stress and bead height va`lue according to the relation jshown in Fig.11~, thereby making possible desirable reduction of bead height and thickness increase around the seamed portion. A further effect is to ` reduce variations in the strength of the seamed portion of the pipe.
- Referring again to Fig. 1, the pipe 100 butt-welded by rolls 5 passes through contraction rolls 60 and a group of contraction rolls 6 and has the seamed portion cooled by means of a cooling-device 71 disposed between the contraction roll "~ ', , - ' .

.
.
. . , ' ~ : , : . , .

88~ i - t ~' 60 and the foremost contraction roll 61 in the roll group 6 and facing the seamed portion of pipe 100.
The cooling device 71 has a number of spray orifices - 712 in the upper surface of a hollow box 711 opposed to the S seamed portion of pipe 100, the b.ox 711 having a length in the ~ direction of movement of the pipe 100 for achieving the desired amount of cooling~ Referring to ~ig.12, there are shown the cooling device il and the cooling device 72 downstream ~here-from and described more fully hereinafter. A pump 7~ is con-nected to the cooling device 71 by way of a control valve . 73, so that water can be selectively supplied from the pump74 and directed against the seamed portion through the spray . orifice 712. A control unit 75 for controlling the control va:lve 73 is connected-with temperature sensors 761 and 762 15 . facing the seamed portion of the-pip~ 140 and the remaining metal portion of the pipe at a position upstream relative to the moving direction of pipe 100 of the cooling .
device 71 and a pulse generator 77 is connected to the con-traction rolls 60. The control unit 75 calculates from,the temperature of the seamed portion and the temperature of the remaining metal as detected by the sensors 7Çl and 762, the speed of movement of the pipe 100 detected by the pulse gen-- erator 77, and the outer diameter and thickness of pipe 100 supplied from a data input device 78 the amount of water necessary for reducing the temperature of the s~amed portion down to a temperat~re e~ual to that of the remaining metal portion of the pipe. Then the control unit 75 supplies a -2~- .

. ', . ~' ., , ' '.
' ',, ~ ' -: ~ ' , ' ~9~
_ _ _ _ .. . , . . . , .... , . .. . . . . _ . ......... . . _ . ~ _ . . ..

signal to the control valve 73 to cause the valve to open to supply the calculated ~mount of water to be isprayed onto the seamPd portion of pipe 100.
Fig. 13 is a block diagram of tha control unit 75, which is composed of thermo-converters 751, 752, A/D converter ~ 753, process I/0 device 754 (ditto), CPU 755 (ditto), counter 756 and D/A converter. ~ha cou~ter 756 eo~nts the pulses fed b~ the pulse generator 77.
As shown in ~ig~ 14t CPU 755 read~ in ~8m (temperature of the ~eamed portion) and ~rm (that of the remaining metal portion) from the temperature sensors 761 i~nd 762 respe~tivelg, and reads in Cu (ths count up value of the counter 756)~ ~hen, CPU 755 calculates the difference ~Tm bstween ~sm ~nd Trm by following equation, ~m S Tsm - Trm and calculates the jspeed VA 0~ the PiPe 100 bY rO110Wing equation, for example.
VA - K~ (CU - CU' ') . Cu~ : the value of Cu that wài3 read i~ at the preceding cycle K, : proportional constant After that, the amount of water W, which should be prayed from the cooling device 71, is calculated by the followin~ equation.
W = WO + K~ ~ ~ I!m :
: Wo : constant amount of water whic~ ii3 docided b~
- . the~dimension~i of pipe 100 vi~riable value depen~in~ on VA
. ' 1 ` . . -28- :
; , ~ , 1 l 8~3~

CPU 755 transmits the data of W for ad~u~ing the control valve 73 through D/A converter 757 after certain delay time, which corresponds to the di~tance between the sensor3 761, ~ 762 and the cooling device 71 and dLecidad from the distance and ~id ~peed V~.
~ Alternatively, the cooling device 71 may be positioned just downstream of the butt-welding rolls 5 or intermediate the rolls of the roll group 6. ~or example, a butt-welded pipe 100 having an outb~r diamater of 60.5 mm and a thickness of 3.8 mm and moving at a speed of 85 m/min. and having a tempera-ture of about 1320C at the seamed portion a~d about 1180C at the remaining metal portion, is sprayed with water at 20'G and at a pressure of more than 5 ~g/cm2` at; a rate of about 150 ¢/min.
to cool the seamed portion to the temperature of the remaining, metal portion.
~he pipe 100 i~ moved through ths contraction roll 60 and the contraction roll group 6 for being finished and i~
- dolivered to the rotary hot saw 8 for bein~ cut therewith ~nto desired axial length~, the rotary hot saw 8 bein~ a convehtional saw. ~he cut pipe 100 i~ then passed ~hrough the other cooling device 72-a~d is abruptly quenched therei~ do~n to about 900'C. ~, : ~he cooling device 72 comprises an inner cylinder 721 havi~g .
in its wall a number o~ spray orifices oriented radially inwardly of ¢ylinder 721, and an o~ter cyIinder 722 coaxial therewith, the inner cylinder 721 and outer cylinder 722 bsing connected at the downstream ends thereof ~y an end plate, the inner cylinder 721 diverging outwardly ~t the upstream end - and being welded to~the inner periphery o~ the outer cylinder : 722. ~he outer cylinder 722 i~ connected to the discharge .
: ~ -29~

, -;

port of the pump 74 for the cooling device 71 through a ~ontrol valve 79, whereby water from the pump 74 is sprayed radially inwardly through spray orifices in the inner cylinder 721.
The cut pipe 100 is quenched down to about gO0C
during its passage through the inner cylinder 721 of the cooling - device 72, and passes through the si.zer 9 for deliYery to other finishing apparatus (not shown).
In the apparatus of the invention, constructed as described above, the skelp 10 is heated to 1200C, which is lower than the butt-welding temperature, during its passage through the heating furnace l and then passes through the main heater 2. The ~emperature sensor 29 attached to control ; unit 28 for the main~heater 2 detects temperature distribu-tion across the widthj of the skelp 10 just after it is dis-charged from the heating funcace l a~d s~pplies this infor-mation to the control unit 28. ~he control unit 28, on the basis of the tempera~ure distribution, detects the difference ; between the temperatures of ~he two edges El and Er and the preset butt-welding temperature and determinescurrent values necessary for raising the temperature of the respective edges El and Er to the butt-welding temperature. The current regu- -.
~: lator 26 receives control signals from the control unit 28 .
and provides separate appropriate currents to the coil bodies 212 and 222 fox heating the edges El and Er to the butt-welding temperature. Hence, the edges El and Er are heated from about 1200C, the temperature at the time of being discharged . from the heating furnace, to about 130QC,;the butt-weldlng ., ~ . . .
~ 3~ :

8~3~

f temperature, and then the skelp is introduced into the sub-heater 3. The temperature of the edges El and Er is detected by the temperature sensor 38 provided just upstream of the sub-heater 3, and if both the edges are heated up to the butt-welding temperature and there is no temperature'difference, the control unit 37 does not energize the coil hodies 312 and 322 in coils 31 and 32, and the sXelp 10 simply passes through the sub-heater without being further heated. When a temperature difference between the edges is detected, the control unit 37 calculates the value of the currents for the respective coil bodies 312 and 322 which are required to eliminate the difference and generates appropriate control signals. If the current value ; obtained from the control unit 37 exceeds the capacity o the current regulator 35, the piston-cylinder devices 336 and/or 337 are supplied with the necessary signal to move the support r4ds 331 and/or 332 perpendicularly to ~he direction of move-ment of the skelp 10, thereby adjusting horizontal space between the coil bodies 312 and 322 and the edges El and Er, and also ~-' the current values are further adjusted by the control ~nit 37 and the current regulator 35. As a result, the temperature of the edges El and Er is adjusted to the same butt-welding - , temperature. ' ' ;~ The skelp 10 which leaves the sub-heater 3 passes -through the bending rolls 4 with the edges El and Er heated uniformly to the predetermined butt-welding te~perature, and the ~' skelp is bent into an O-like cross-sectional shape and then passes through'the butt-welding rolls 5. The load cell 58 at , :: . . . ~ . - .

- -;' the bearing of one butt-welding roll 5 detects the pressure ~
,r load of butt-welding roll 5 with respect to the outer periphery of ~he bent skelp 10, and supplies it to the control unit 59, and the detected pressure load is compared with the predeter-mined desired pressure load, and control signal is then sentfrom the control unit 59 to the control valve 57 to actuate the pressure load adjusting device 55 for making the pressure load at the butt-welding rolls 5 coincide with the predeter-mined pressure load. Thus the skelp 10 is subjPcted to the proper pressure from the butt-welding rolls 5 and the opposite edges ~1 and Er are butt-welded at a constant pressure. The butt-welding of edges El and Er at a constant pressure keeps the amount of upset ~to a minimum and in turn keeps the thick-ness increase at thelbead portion and t~ereabout caused by, lS butt-welding to a minimum. The equal temperature and uniform deformation resistanpe at the edg,es El a,nd Er also assist in ~chieving the result, whereby external deformation, such as variations in the outer diameter of the pipe lOO! and varia- , , tions in the strength at the seamed portion are prevent~d.
After leavin~ the butt-welding rolls 5, the tempera-ture of the pipe 100 at the seamed portion is detected by the-, temperature sensor 761 and the temperature of the remaining metal portion is detected by the sensor 762 and the results are fed into the control unit 75. Th~ control unit 75 compares temperatures of both portions and calculates ,the amount of water necessary to reduce the temperature of thè seamed portion down to-that o~ the'remainin~ metal portion on the basis of , ~ .
c-- . .

~, --, ,,;

88~
.

! the temperature of difference, the speed of movement of the -~ pipe 100 as supplied from the pulsle generator 77, and the outer diameter and thickness of the pipe 100 as suppliad from the data input device 78. The control valve 73 is supplied with a con-S trol signal from the control unit 75 or supplying the amountof water necessary for spraying the seamed portion. Thus, the pipe, after leaving the butt-welding rolls 5, has the tem-perature of the seamed portion reduced to the temperature of the remaining metal portion or thereabout, and then passes through the contracting roll group 6 to be extended. As a result, even when the pipe is subjected to contraction and extension by the roll group 6 while passing therethrough, the thickness of the seamed portion and the portion thexeabout is not increased. - , The advantajges of the apparatus of the invention will now be described.
Table 1 shows data from comparative test results, and shows ~he defec~ive bead production percen~age (the ratio of the number of pipes having defective beads to the to~al num ber of pipes produced) when producing pipes of the same size while changing the temperature difference between the edges and the central portion of skelp by use of the apparatus of the inven~ion and conventional apparatus in which the temperature of the entire skelp is raised to the butt-welding temperature within the heating furnace.

' ' .' :
;

389~
.

TABLE l . .. ~ ... ~
Temperature Apparatus of Conventional Difference the Inventi~n _ Apparatus 50C 0.31% ~ 0.63 5` 100C 0.47% l.36 200C 0.78~ 5~73~

As seen from Table l, the apparatus of the present invention considerably reduces the defective bead production per centage for all the temperature differences as compared with the conventional apparatus. It is understandable that the percentage for the apparatus is much less the larger the temperature differ-ence. ` `:

~ .
Figs.1~a) and1~(b) are histograms, in which distribu-tion of flatness values resulting from a flatness test for strength at the seamed portion of continuously butt-welded pipes produced by the apparatus of the invention and the conventional apparatus are shown. Fig.1~(a) shows the results for the invention and Fig~1~(b) the results for the conventional- appara-tus. In the test, the continuously butt-welded pipe is laid horizontal with the seamed portion facing laterally, and thè
pipe has a vert~cal load imposed on it. h77hen damage occurs in the seamed portion, tha height of the partially flattened pipe is divided by average outer diameter thereof and ~he quotient is the flatness value. In Figs.15(a) and ~b), this value is shown on the abscissa, and the number of pipes having the .

; ~34 :
.; ' ~

1..................................................................... _ .

88~ , ~ flatness value in a given range is shown on the ordinate. The ;~ number N of specimens in this test was 54, both for the appara~
tus of the invantion and the conventional apparatus. The average value X is 0.201 for the pipes produced on the apparatus accord-ing to the invention, and 0.213 fox the pipes produced on the - conventional apparatus. The standard deviation is 0.044 for pipes produced on apparatus according to the invention and 0.043 for pipes produced on the conventional apparatus.
As seen from the histograms in Figs. 1~a) and1~b), - lO the flatness value, in other words, the butt-welding strength, of continuously butt-welded pipe produced by the apparatus of the invention is almost the same as that for pipes produced by the conventional~apparatus.
Fig.16 is a graph showing comparative test results for thickness distribu;tion at each circumferential p~rt of a c,ontinuously butt-welded pipe where the seamed portion is~ .
cooled according to the invention and for other cases where it is not so cooled. The ordi~ate shows thickness (mm), and the abscissa shows locations of thickness measurements circum-.-- .
ferentially of the pipe. The solid line in the graph repre-sents the values for a pipe in which the seamed portion was cooled with an amount of water corresponding to the temperature thereof by use of the apparatus according to the in~ention, the broken line represents values where there has been no cooling of the seamed portion, and the one-dot-dash line represents the values where cooling of the seamed por~ion was simply by spraying a constant amount of water. The positions at which . . .. .
..
5~
.
,^ , . , ' - ~;

i584 .

f the thickness of the specimen was measured are as shown in Fig.1~, in which the seamed portion is at g.
As seen from the graph of Fig.1~j when the apparatus of the invention was used for controlling the cooling of the seamed portion, the pipe has a substantially uniform thickness throughout the periphery thereof. On the contrary, when the seamed portion was merely sprayed by a constant amount of water, thickness increase occurred at the seamed portion~ When there was no cooling of the seamed portion, a rather large 19 thickness increase was found to occur especially at the inner periphery, and also ~a large variation in thickness occured throughout the periphery of pipe.
A modifieq embodiment of the heater according ~o the invention will be described whlch can be used for the main -heater or the sub-heater in the above-described apparatus, or can replace both the heaters.
~ The above heater and a control system therefor is shown in Fig. ~8 and the heating coils therefor are shown in : Fig. ~. The heater 2l is usable as both the main heater and the sub-heater. The skelp 10 discharged from the heating furnace passes between vertically spaced opposed coils 91 and t 92 and then travels ~oward the bending rolls 4 and butt-weld-ing rolls 5. -Induction heating coils 91 and 92, as shown in Fig.
25 1~, comprise cores 911 and 921 and coil bodies 912 and 922 fitted into grooves 911a and 921a formed in.the lower surface of core 911 and the upper surface of core 921, respectively. The .

. ~
'. ,' ~ .
,, . . ... .: :
- . . :: : :
;. : ~.. :: .-, :
.: ~ . . . .
.

respective cores 911 and 921 are constituted by strip-shaped ~ silicon steel plates punched to form recesses corresponding - to the grooves 911a and 921a, the silicon steel plates being laminated having a rectangular shape when viewed in plan. The plates are bound by bands (not illustrated) or the like and provided on~the surfaces opposed to the s~elp with heat insula-tors for preventing damage to the coil bodies 912 and 922. The grooves 911a and 921a are generally rectangular and the parts are parallel to the four sides of the cores 911 and 921, re-spectively. The coil bodies 912 and 922 are rectangular in shape and are formed by lon~ hollow copper bands is wound in layers along the grooves 911a and 921a and insulated from each other by varnish. The ends 912a and 92i2a of the respective coil-bodies 912 and 922 extend out of the coils through bores 911b and 921b in the cores 911 and 921, respectively. The coil bodies 912 and 922 have current ofta given frequency 10w-ing therethrough. l - `
Referringjto Fig. ~, the mountin~ frame 93 for the coils co~prises a vextical bar 931 and ùpper and lower arms 932 and 933 connected to the upper and lower ends of bar 931 and extending parallel to each other so as to give the frame a C-like shape when viewed from the front. The coil 91 is fixed to the lower surface of upper arm 932 and has the coil body 912 at the lower surface of coil 91. The coil 92 is -fixed to the upper surface of lower arm 933 and has the coil body 922 at the upper surface of coil 92. The longer portions 912Q and 912r of the coil body 912 and 922Q and 922~ at the .
;37--`.
:. ' ' ' . : ' '''~ ': ' .: - .

884 - i f coil body 922 are aligned with the edges El and Er of skelp lo .
' Suspension rods 94 are mounted on the upper surface of arm 932 and extend vertically upward therefrom, and wheels 941 are journalled on the upp,er ends of rods 94 and run on a rail 942. The mounting frame 93 is suspended from the rail 942 which extends horizon*ally and transversely to the direc-~ion of movemant of skelp 10, and is movable in a direc~ion perpendicular to the direction of movement of the skelp 10 for positioning the vertical bar 931 laterally of edge El and skelp 10 and for keeping the coils 91 and 92 opposed to the upper and lower surfaces of skelp 10, respectively. A motor 943 is positioned on~the upper surface of upper arm 932 and the output shaft thereof is coupledlthrough a chain with a sprocket 944 coaxially mounted on one wh~eel 941O The motor 943 rotates in opposite directions to moye the mounting fra!me ' :
93 perpçndicularly to the dixection of movement of the skelp 10, so that the distances hl, h2, h3 and h4 between the edges El and Er and ~he longer coil portions 912Q, gl2r, 922Q-and 922r, as shown in Fig. ~3, can be adjusted. The lower arm 933 is pivoted to the lower end of ver~ical bar 931 on a horizon-tal shaft 933a fixed to the base of arm 933 and is movable '' ' vertically around the shaft 933a. The horizontal shaft 933d has a gear 933b on one axial end meshing with a a gear 933c 25 - which in turn meshes with a gear on the output shaft of a motor 945 mounted on the lower end of vertical bar 931, so that when the motor 945 ro~ates one way or the other i~ swings the lower : ~ ' . . ', ' ~ ' ' ' . , . - . ~ . .

, ' ' . .' ' ' , arm 933 around the shaft 933a, as illustrated by the broken lines in Fig. 20, thereby changing vertical distances vl and v2 between the edges El and Er of skelp 10 and the surfaces of the longer portions 922~ and 922r of coil body 921.
Reference numeral 95 designates a drive control for the motors 943 and 945. The drive control 95, compris-ing a microcomputer system like said control units 28 and 37, has temperature sensors 96~ and 96r connected thereto through a temperature difference signal generator 97 and has temperature sensors 98~ and 98r connected thereto through a feedback circuit 99. The sensors 96~ and 96r are disposed opposite the edges El and Er of skelp 10 upstream of the coils 91 and 92. The temperatures detected at the edges El and Er are fed into the temperature difference signal generator 97 and the difference between the temperatures of the edges is detected and is fed into the drive control 95. The drive control 95 provides drive signals to the motors 943 and 945 for driving the motor 943 so as to move the mounting frame 93 across the skelp 10 along the rail 942 and for driving the motor 945 to swing the lower arm 933 vertically around the bottom of bar 931 to thereby adjust the size of the horizontal distances hl, h2, h3 and h4 between the portions 912~, 912r, 922~ and 922r of the coil bodies 912 and 922 and the edges El and Er of the skelp 10 and the vertical distance vl and .... ~ , ~.

.. : , , - ~ - --' ~. .: ~ ' ' .

8~L

V2 between the portions 922~ and 922r and the edges El and Er so as to eliminate the difference between the temperatures at the edges F.l and Er. The temperature sensors 98~ and 98r disposed downstream from the coil 91 and 92 detect the temperatures of the edges .:~

- . . ~ -' ' :' ' . : ' . :
.: : : ..
.

~98B4 El and Er after the skelp 10 has been heated by the coils 91 and 92, and these temperatures are fed back to the control unit 95 through the feedback circuit 99. The control unit 95 gener-ates no signal when the temperature difference between the S edges is zero, but when a temperature difference exists, it supplies the motors 943 and 945 with drive'signals for adjust-ing the horizontal and/or vertical distances hl and h2, vl and V2 to eliminate the temperature difference.
The sensors;98Q and 98r, which detect the temperature' of the edges of the skelp for correction of the positions of the coils 91 and 92, may also be used to determine whether or not the edges have been heated to the desired butt-welding ` temper~ture.
The ratio of the adjustment o movement of the mount-ing frame 93 and the swinging mot~.on'of t,he lower arm 933, is not limited to any particular ~alue, b~t the adjustment j ;' may be carried out, for example, by rough adjustment of the movement of the mounting frame 9i across the width',of the ' skelp 10 and fine adjustment of the vertically swinging ~ower arm 933, or by moving the mounting frame 93 in response to the temperature difference detected by the sensors 96Q and 96r and swinging the lower arm 933 for compensating adjustment '~ -'in response to th~e temperatures detected by the sensors 98Q
- and 98r.
25, When high frequency current at the predetermined frequency flows in the coil bodies 912 and 922, magnetic flux is generated in the skelp,10 to induce a flow of induced ' ~` ` ' ' ' ` ' ' ~ ' ,' ' ' ' ; ' , ' ' '. ' .

: ~ ' ' ' '' ' :
. . .
.
.: .. , , ~9~3~34 current in the skelp 10, and especially in the edges El and Er~
to thereby heat them. A change of the hori20ntal or vertical distance between the edges El and Er and the coil bodies 912 and 922 causes the magnetic flux flowing in the skelp 10 to change. As a result, the induced current generated in the skelp 10 changes and the energy by which the edges El and Er are heated also changes. The heater 2' thus changes the hori-zontal distances hl and h4 and vertical distances Yl and v2 so as to change electromagnetic relation of the coils 91 and 92 with the skelp 10 for making the temperature of the edges El and Er equal.
Alternatively, one of the coils 91 and 92 may of ; course be fixed and the other may be horlzontally movable or vertically swingable. - - - ~
- As clearly understood from the~aforesaid description,' in the apparatus according to the invention, the skelp, after ~eing heated in the heating furnace, futher has only the edges thereof heated up to the butt-wçlding temperature '` by induction heating, and the'central portion of the skélp is kept at- a low temperature. Hence, considerable saving of energy is achieved. ~Moreover, temperatures of the edges of ' the skelp are adjusted easily and reliably so that they are ' equal, so that the 'two edges, when they are butt-welded, the deformation resistance is equalized and due to the constant control of the pressure load applied to the s~elp by the butt-'welding rolls, the edges are butt-welded under uniform upset-ting stress, so that the amount of upset is uniform, resulting .

': ' ' ~ ~ ' -`

:; - ' `

~ in a reduced height of the bead, less variation in the thick~ess - ,) and outer diameter of the pipe thickness, and a reduced amount of increase in the thic~ness in th~e vicinity of seamed portion.
Furthermore, just prior to contraction rolling or midway thereof, the butt-welded portion of the pipe is cooled ~ down to the temperature of the remainder of the pipe so that no thickness increase occurs at the seamed portion o~ the pipe during contraction rolling. Moreover, the strength o~
the seamed portion is improved as compared with the seamed portion of the pipe manufactured by conventional apparatus which heats the who~e skelp to the welding temperature in the heating furnace. Hence, tha apparatus of the invention con-; ~ siderably improves the continuous manufacturing of butt-welded pipes.
Because many widely different embodiments of this invention may be made without departing!from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments described, but rather ;
is limited only as defined in the appended claims. ~ ' `~ ! .
- ' , ~ ' . . .

, ,; - .
.: ' ; - . ' '', ' ~
.

~ `

' .~

Claims (23)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus for continuous manufacture of butt-welded pipes, comprising:
a heating furnace for heating a skelp continuously passed therethrough up to a predetermined temperature;
a heater means having at least one heater with spaced opposed induction heating coil means on opposite sides of the path along which the skelp is passed through said heater means and adjacent the edge portions of the skelp for heating only the edge portions of the skelp discharged from said heating fur-nace up to the butt-welding temperature, and having means con-nected to at least one of said induction heating coil means for varying the electromagnetic coupling between said one in-duction heating coil means and the corresponding edge portion of the skelp for adjusting the temperature to which the corre-sponding edge portion is heated;
bending means adjacent the outlet end of said heater means for bending the skelp into a generally tubular form;
and butt-welding rolls adjacent the outlet end of said bending means for applying a predetermined pressure to the bent up skelp for butt-welding the edges of the skelp to each other.

2. An apparatus as claimed in claim 1, in which means for varying the electromagnetic coupling is connected to both of said induction heating coil means.

3. An apparatus as claimed in claim 2, in which said induction heating coil means comprises a pair of induction heating coils positioned in spaced opposed relation above and below the path of the skelp, said coils having a generally rectangular shape and having the longer sides substantially aligned with the edge portions of the skelp passing through the space between said coils.

4. An apparatus as claimed in claim 3, in which said coils are fixed in position relative to the path of movement of the skelp, and said means for varying the electromagnetic coupling comprise means for varying current supplied to said coils.

5. An apparatus as claimed in claim 4, in which said means for varying the current comprise a temperature sensing means adjacent the path of the skelp for sensing at least the temperatures of the edge portions of the skelp, means connec-ted to said temperature sensing means for determining from the temperatures sensed the difference of the temperatures of the edge portions of the skelp and the desired butt-welding temperature, and current regulating means connected to said determining means and to said coils for supplying currents to said coils for heating the edge portions of the skelp to the desired butt-welding temperatures.

6. An apparatus as claimed in claim 3 in which one of said coils is mounted for movement transversely of the direc-tion of movement of the skelp between said coils for varying the current induced in the skelp depending on the position of the movable coil relative to the skelp, and said means for varying the electromagnetic coupling comprises means for moving said one coil.

7. An apparatus as claimed in claim 6 in which said means for moving said one coil comprise a temperature sensing means adjacent the path of the skelp for sensing at least the temperatures of the edge portions of the skelp, means connected to said temperature sensing means for determining from the temperatures sensed the difference of the temperatures of the edge portions of the skelp and the desired butt-welding temperature, and moving means connected to said determining means to said one coil for moving said one coil for varying the current induced in the skelp to produce the desired temperature.

8. An apparatus as claimed in claim 6 in which said means for moving said one coil comprise a temperature sensing means adjacent the path of the skelp for sensing at least the temperatures of the edge portions of the skelp, means connected to said temperature sensing means for determining from the temperatures sensed the difference between the temperatures of the edge portions of the skelp, and said means being connected to said moving means for moving said one coil for varying the current induced in the skelp to eliminate said difference.

9. An apparatus as claimed in claim 3 in which one of said coils is mounted for movement perpendicular to the direc-tion of movement of the skelp between said coils for varying the current induced in the skelp depending on the position of the movable coil relative to the skelp, and said means for varying the electromagnetic coupling comprises means for mov-ing said one coil.

10. An apparatus as claimed in claim 9 in which said means for moving said one coil comprise a temperature sensing means adjacent the path of the skelp for sensing at least the temperature of the edge portions of the skelp, means connected to said temperature sensing means for determining from the temperatures sensed the difference of the temperatures of the edge portions of the skelp and the desired butt-welding temperature, and moving means connected to said determining means and to said one coil for moving said one coil for varying the current induced in the skelp to product the desired temperature.

11. An apparatus as claimed is claim 9 in which said means for moving said one coil comprise a temperature sensing means adjacent the path of the skelp for sensing at least the temperature of the edge portions of the skelp, means connected to said temperature sensing means for determining from the temperatures sensed the defference between the temperatures of the edge portions of the skelp t and said means also being connected to said moving means for moving said one coil for varying the current induced in the skelp to eliminate said difference.

12. An apparatus as claimed in claim 3 in which one of said coils is mounted for movement transversely of the direc-tion of movement of the skelp between said coils for varying the current induced in the skelp depending on the position of the movable coil relative to the skelp, and the other of said coils is mounted perpendicular to the direction of movement of the skelp between said coils for varying the current induced in the skelp depending of the position of the movable coil relative to the skelp, and said means for varying the electromagnetic coupling comprises means for moving said coils.

13. An apparatus as claimed in claim 12 in which said means for moving coils comprises a temperature sensing means adjacent the path of the skelp for sensing at least the temperature of the edge portions of the skelp, means connected to said temperature sensing means for determining from the temperatures sensed the difference of the temperatures of the edge portions of the skelp and the desired butt-welding temperature, and moving means connected to said determining means and to said coils for moving said coils for varying the current induced in the skelp to produce the desired temperature.

14. An apparatus as claimed in claim 12 in which said means for moving said coils comprise a temperature sensing means adjacent the path of the skelp for sensing at least the temperature of the edge portions of the skelp, means connected to said temperature sensing means for determining from the temperatures sensed the difference between the temperatures of the edge portions of the skelp " and said means also being connected to said moving means for moving said coils for varying the current induced in the skelp to eliminate said difference.

15. An apparatus as claimed in claim 12 in which said means for moving said coils comprises a temperature sensing means adjacent the path of the skelp for sensing at least the temperature of the edge portions of the skelp, means connected to said temperature sensing means for determining from the temperature sensed the difference of the temperatures of the edge portions of the skelp and the desired butt-welding temperature, moving means connected to said determining means and to one of said coils for moving said one coil for varying the current induced in the skelp to produce the desired temperature, a further temperature sensing means adjacent the path of the skelp for sensing at least the temperature of the edge portions of the skelp, further means connected to said further temperature sensing means for determining from the temperatures sensed the difference between the temperatures of the edge portions of the skelp, further moving means connected to said further means and to the other of said coils for moving said other coil for varying the current induced in the skelp to eliminate said difference.

16. An apparatus as claimed in claim 2 in which said induction heating coil means comprises a pair of induction heating coils positioned in spaced opposed relation so as to face the opposite side edges of the skelp, said coils having a generally U-shaped cross-section and partially surrounding the path of the edge portions of the skelp.

17. An apparatus as claimed in claim 16 in which said coils are mounted for movement transvarsely of the direction of movement of the skelp between the coils for varying the current induced in the skelp depending on the position of the coil relative to the skelp, and said means for varying the electromagnetic coupling comprises means connected to said coils for moving said coils and means for varying the current supplied to said coils.

18. An apparatus as claimed in claim 17 in which said means for varying the electromagnetic coupling further comprises a temperature sensing means adjacent the path of the skelp for sensing at least the temperature of the edge portions of the skelp, means connected to said temperature sensing means for determining from the temperatures sensed the difference between the tempera-tures of the edge portions of the skelp, said determining means being connected to said current varying means for varying the current means for moving the coils when the current varying means cannot vary the current sufficiently to heat the edge portions of the skelp to the desired temperature.

19. An apparatus as claimed in claim 1 further compris-ing a plurality of contracting rolls adjacent the outlet of said butt-welding rolls, and a cooling means associated with said contracting rolls for directing a cooling medium against the butt-welded pipe for cooling the seamed portion of the pipe to the temperature of the remainder of the pipe<

20. An apparatus as Claimed in claim 19 in which said cooling means is ahead of the first contracting rolls relative to the direction of movement of the welded pipe.

21. An apparatus as claimed in claim 19 in which said cooling means is after at least one of said contracting rolls relative to the direction of movement of the welded pipe.

22. An apparatus as claimed in claim 19 in which said cooling means comprises temperature sensing means ahead of said cooling means for sensing the temperature of the seamed portion of the pipe and the temperature of the remaining por-tion of the pipe, means for directing cooling medium against the seamed portion of the pipe, valve means connected to said cooling medium directing means for controlling the flow of cooling medium to said cooling medium directing means, velocity sensing means for sensing the velocity of the pipe as it comes from said butt-weldinq rolls, and control means connected to said valve means and to which said temperature sensing means and said velocity sensing means is connected and having means for receiving information as to the outside diameter and thickness of the pipe and for determining the amount of cooling medium needed to cool the seamed portion of the pipe from the temperature as it comes from the butt-welding rolls to the temperature of the remaining portion of the pipe and controlling the time said valve is open to permit only the necessary amount of cooling medium to be directed against the seamed portion of the pipe.

23. An apparatus as claimed in claim 1 further compris-ing means for changing the positions of said butt-welding rolls for adjusting the pressure applied to the skelp, sensor means engaged by said butt-welding rolls for sensing the pressure which the rolls apply to the skelp, and control means connected to said pressure adjusting means and to said sensor for controlling the pressure to a predetermined Pressure.