FR2466306A1 - DEVICE FOR THE CONTINUOUS PRODUCTION OF TUBES BY END-TO-END WELDING - Google Patents

Abstract

The invention relates to a device for the manufacture of tubes by close-edge welding of a preheated metal strip 10 1, 2, 3 and bent 4. The marginal edges of the strip 10 are heated with induction coils 2. , 3 arranged on either side of the path of the strip. The temperature is regulated by the electromagnetic coupling of the coils. Application to the continuous manufacture of tubes having a weld bead of reduced thickness, with reduced energy consumption and better quality of the finished product. (CF DRAWING IN BOPI)

Description

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  Device for the continuous manufacture of tubes by welding

end to end.

  The invention relates to a device for the manufacture

  continuous tube welding by said end-to-end or

  or edge to edge, for example, steel tubes

  by welding, by heating a tube strip, in the

  trant to give it a tubular shape, and by welding butt

  end the opposite edges of the tube band to join them together.

  Generally, butt welded tubes are manufactured

  by heating the edges of the tube strip by passing it into a heating furnace at a temperature of

  13000C suitable for end-to-end welding (called

  butt weld joint), by bending the tube strip into a tubular shape on forming cylinders, butt-welding the opposite edges of the tube strip to join them together by means of rollers. butt welding

  end, then finishing the tube by rolling with contrac-

  and other finishing processes. However, such a method is disadvantageous in that the central portion of the tube strip is heated together with the edges

  when it passes through the heating oven, although the

  heating of this central part is not necessary, and consequently causes losses; both edges of

  the tube band, which are often at light temperatures-

  different from the construction of the heating oven.

  or differences in the thickness of the tube strip itself, are welded end to end when they leave the oven and the difference in temperature shows a difference in the resistance to deformation, which has

  as a result of which the repression constraint is not uni-

  form; the residual temperature difference between the welded portion and the adjacent metal portion of the butt welded tube results in a difference in thickness in the vicinity of

  the welded part during the contraction process.

  As a result, several remedies have been developed

  to overcome the problems mentioned above, but the

  The results were not completely satisfactory. One method is described in Japanese Patent No. 14092/1968 and in the

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  French Patent Application No. 936135. This method has been

  in order to promote energy saving and, according to this method, the entire tube strip is first heated, passing it through the heating furnace, to a temperature of about 10,000 ° C, which is below the temperature butt weld. Then, we use an inductor, for a

  induction heating, to heat only the opposite edges

  to the end-to-end welding temperature, so that the central portion of the tube strip is maintained at a temperature lower than the butt welding temperature and yet within a temperature range suitable for bending, rolling with contraction, etc., without

  difficulties, which allows the economy to be

desired energy.

  Thus, the equipment for the implementation of the method

  mentioned earlier allows to maintain the

  the central section of the tube strip at a lower temperature than the two edges, but this is its only result. The

  temperature of the two edges of the tube strip is not

  ble, so that it is not possible to make the discharge stress uniform, and that thickness differences can not be prevented during the rolling process with

  contraction after butt welding. This is due to the

  ductance used to heat the edges of the tube band

  in the earlier method described above. Figure 21

  schematically presents such an inductance. The inductor comprises an elongated copper bar 101, two short aligned copper rods 102 and 103 arranged parallel to the

  copper bar 101 and spaced therefrom a distance of

  significantly greater than the width of a tube strip 10, two

  thick bent copper strips 104 and 104 'passing through

  above the upper and lower surfaces of the front end of the copper bar 101 and the copper bar 102

  and above the upper and lower surfaces of the

  behind the copper bar 101 and the copper bar

  103, and two tabs 105 and 106 serving as terminals and provided on the opposite ends of the copper bars 102 and 103. As a result, the copper bars 101, 102 and 103 of the inductor are parallel to the edges E1 and E1. of the tube strip 10 and opposed to the side faces of the tube strip, and this tube strip 10 moves between the thick copper strips 104 at one end of the inductor and between the thick copper strips 104 'to other end. During movement of the tube strip, a high frequency current is applied through terminals 105 and 106 to generate induced currents on the surface of the moving tube strip as it cuts the magnetic flux. produces around the inductor, which selectively heats

  the two edges El and Er of the tube strip 10.

  However, the two edges El and Er of the tube strip coming out of the heating furnace and entering at the upstream end of the inductor are not always at the same temperature as a result of the construction of the heating furnace. or as a result of variations in the thickness of the tube strip itself. Thus, even when the edges of the tube strip are uniformly heated by the inductor, the

  edges almost always have a different temperature, usually

  from about 5 to 200C. Further, the path of the tube web moving through the inductor may change slightly as a result of the natural movements of the tube strip, so that the dimensions of the intervals between the copper bars 101, 102 and 103, and the two edges El and Er can vary, which increases the temperature difference between the two edges, so that the variations in the discharge stress are greater, which results in a low quality of the finished product. Even if the spaces between the copper bars 101, 102 and 103 and the two edges E1 and E1 of the tube strip 10 are chosen lower to try

  to increase the efficiency of heating, the decrease in

  is limited because of the danger of deformation of the tube strip if the edges El and Er come into contact with the copper bars 101, 102 and 103. Therefore, the efficiency

  must be kept low and the chances of

  to be energy limited. In addition, an inductance of particular dimensions can only process a limited number of different widths of tube strips, so that one must

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  have inductances of different sizes if we want

  treat you with tube strips of different width. In addition, the temperature difference mentioned above between the two edges E1 and E1 of the tube strip 10, when it is removed from the heating furnace, must often be compensated, but the inductance having the constitution described above. above does not allow this compensation. Consequently, the method described above has drawbacks due to

  limitations of the device used for its implementation.

  Problems also arise with regard to

  butt welding cylinders which are commonly used

  tuellement. The gap between butt welding cylinders

  vertically arranged tips is usually constant.

  However, the width of the tube band varies and the cylinders

  The butt welds are usually slightly exceeded so as to vary the pressure applied to the edges of the tube strip. The interval between the rollers

  can be chosen weaker to try to eliminate some

  The resistance of the welded portion of the tube made by continuous butt welding is reduced, but this poses the problem of increasing the variations of the weld bead and the thickness along the welded portion. In addition, in the method described above, wherein the tube strip is bent and the edges of the tube strip are heated to a higher temperature than that of the central portion.

  of this band, then welded end to end, because of the difference

  temperature difference between the edges and the central part of

  the tube strip to save thermal energy, the

  resistance to deformation in the central part is more im-

  only when the entire tube strip is heated to

  the end-to-end welding temperature, so that

  constant valleys between the cylinders increases the pressure between the butt welded edges, which facilitates the formation of the weld bead along the welded portion of the finished pipe and increases the thickness variation in the vicinity of the welded portion; which shows resistance variations on

along the welded part.

  The present invention proposes to eliminate the

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problems mentioned above.

  The invention proposes to provide a device for the continuous manufacture of tubes by butt welding, a device making it possible to reduce the formation of a weld bead at the welded portion and, consequently, to reduce the difference in thickness in its vicinity, which reduces the variation of resistance at the welded portion and

increases the quality of the tubes.

  The present invention further proposes to provide a device for the continuous manufacture of tubes by butt welding, which operates with a power consumption.

weaker.

  The present invention further proposes to provide a device for the continuous manufacture of tubes by butt welding, which does not damage the edges of the tube strip even when a heating element is brought to the close vicinity.

  the edges of the tube strip to conserve energy.

  The present invention further proposes to provide a device for the continuous manufacture of tubes by welding

  end-to-end, having a heating element capable of increasing

  the temperature of both edges of the tube strip to a uniform value to improve the quality of the finished product. The present invention further proposes to provide a device for the continuous manufacture of tubes by butt fusion, which comprises butt welding cylinders capable of controlling the pressure load applied to the

  tube tape, so that it coincides with a pre-

  determined, to improve the quality of the product

finished.

  The present invention will be better understood by reading

  following detailed description and examination

  appended drawings which represent, by way of example not

  limiting, an embodiment of the invention.

  FIG. 1 is a diagrammatic elevational view,

  partially in section, a device for the manufacture in tube content by butt welding, according to the invention Figure 2 is a perspective view, partially

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  schematic, of a main heating element and a system

  order to feed it when used in the dis-

  positive shown in Figure 1; Fig. 3 is a block diagram of a control unit;

  Figure 4 is a flowchart explaining the function

  under the control of Central Unit 284; Fig. 5 is a partially schematic perspective view of an auxiliary heating element and a control system for powering it when used in the device shown in Fig. 1; Fig. 6 is a block diagram of the control unit 37

  Figure 7 is a flowchart explaining the function of

  under the control of the Central Unit 374; FIG. 8 is an elevational view of the cylinders of

  butt welding and a control system of these cylinders

  dres, used in the device of Figure 1; Fig. 9 is a block diagram of the control unit 59;

  Figure 10 is a flowchart explaining the function

  under the control of Central Unit 593; the figure there is a graph representing the relation

  between the height of the weld seam and the stress of

  flow in a pipe welded end to end continuously;

  FIG. 12 is a diagrammatic elevational view,

  partly in section, of a cooling device and

  of a control system for it, used in the

  Figure 1; Fig. 13 is a block diagram of the control unit 75;

  Figure 14 is a flowchart explaining the function of

  under the control of Central Unit 755; Fig. 15 (a) is a bar graph showing the distribution of flattening values for several butt welded tubes continuously with a device according to the invention; Figure 15 (b) is a histogram representing the

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  distribution of flattening values for several butt welded tubes continuously with a conventional device;

  Figure 16 is a graph showing the results of

  measurement states and showing the distribution of the tube thicknesses according to different modes of cooling control of the tube in the device according to the invention; FIG. 17 is a cross-sectional view of a

  tube, representing the measuring positions used for measuring

  set the values for the graph in Figure 16; Fig. 18 is a perspective view of a variant of the heating element and the control system used therefor; Fig. 19 is a perspective view, partially broken away, of the heating coil of the heating element of Fig. 18; FIG. 20 is a schematic cross-sectional view

  explain the operation of the heating coil

shown in Figure 19; and

  FIG. 21 is a perspective view of an inductance

this used in the prior art.

  First, let's give a general description

  of the construction of a device for the manufacture in con-

  end-to-end welding tubes according to the invention, with reference to FIG. 1. In FIG. 1, reference numeral 10 designates the tube strip. The tube strip 10 is pulled from a reel or similar device (not shown) and

  the whole tube strip is heated to a temperature

  lower than the temperature-butt welding, 1150 to 12000C and, preferably, around 12000C, passing it through a heating furnace 1. Then the tube strip passes through a

  main heating element 2 and an auxiliary element 3.

  The main heating element 2 only heats both edges

  El and Er, that is to say a marginal portion of predetermined width

  finished, preferably about 10 mm, to a temperature equal to or close to the butt welding temperature, and the auxiliary heating element 3 adjusts the temperatures of the

  edges El and Er until they become equal and cor-

  respond to the end-to-end welding temperature. Then,

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  the tube strip passes between bending rolls 4 and is bent so as to obtain a 0-shaped cross-section, then the opposite edges El and Er are welded end-to-end by butt welding rolls 5 to tube band in the form of a tube. Immediately after,

  welded portion of the continuous butt welded pipe is cooled

  die by a cooling device 71 disposed between

  contraction cylinders 60, upstream of the cooling device

  dissement, and a group of contraction cylinders 6 downstream

  of the cooling device so that any differences

  this temperature between the welded part and the metal part

  that remaining is reduced or eliminated. Then the tube passes through

  is the group of contraction cylinders 6 and is cut to the *

  desired length. The cut tubes 100 are completely re-

  cooled by a cooling device 72 and are finished by finishing means such as a calibration device

9 or a similar device.

  Each component of the device according to the invention

will be described in detail below.

  The heating oven 1 itself is well known and

  wears an upper preheating zone there to preheat

  the tube strip 10, a return drum 12 at the level of the

  exit end of the zone 11, and the direction change rollers 13 at the inlet end. The tube strip moves in the direction of the arrow to arrive in the preheating zone 11 and passes around the return drum 12 and the rollers 13 of direction change and

  is sent into the heating zone 15 via an inlet 14.

  In the heating zone 15, the tube strip is heated by

  a gas burner, or similar device, when

  poured this heating zone 15, then is evacuated by a

  16. It is then guided successively in the

  heating element 1 and in the heating element

  3. When the tube strip 10 comes out of the heating furnace, its temperature is lower than the butt welding temperature which is about 13000C, i.e.

  that it is equal to about 11800C in the central part

  trale and at about 12000C at the two edges El and Er.

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  Such a temperature distribution along the direction

  cross-section of the tube strip 10 is not limited to these values.

  their; these temperatures may be higher or lower. If the temperature of the central portion of the tube strip 10 exceeds the lower limit of the temperature range,

  for which the tube strip can be subjected without

  blemish to a bending and contraction by the cylinders of

  bending 4 and the cylinders of group 6, because the

  Central section of the tube strip 10 is slightly heated

  when it passes through the main heating element 2 and the

  In an auxiliary heating system 3, the temperature at the central portion of the tube strip 10 approaches the upper limit of the temperature range suitable for bending and contraction, and the energy saving is reduced. On the contrary, if the temperature of the central portion of the tube strip is too low, this increases the load imposed on the main heating element 2, to bring the temperature of the central part to the desired value, as far as o this results in an increase in the consumption of electrical energy and the need to provide a heating element 2 of significant dimensions, which does not bring the benefits

  desired from the point of view of energy saving. As a result

  Therefore, it is desirable to control the heating oven 1 so that when the tube strip 10 comes out of the oven, its central portion has a temperature which corresponds to the limit.

  lower than the correct range of temperatures for the

  contraction, or at least one tempera-

  less than the above lower limit by a value such that heating to the desired temperature can be effected by the main heating element 2 and

the auxiliary heating element 3.

  In Figure 2, which represents the heating element

  2, references 21 and 22 refer to the following coils:

  lower and lower for induction heating. The coils 21 and 22 comprise rectangular cores 211 and 221 and bodies 212 and 222 fixed in grooves 211a and 221a respectively formed in the lower surface of the core 211 and in the upper surface of the core 221.

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  mounting bracket 23 supports the coils 21 and 22 so

  that they are located opposite each other by being

  vertically to provide a space through which the tube strip 10 can pass between the coils. The coil bodies are arranged so that rectilinear portions 212E and 222E of the cores are respectively above and below the left edge E1 of the tube strip, and that the rectilinear portions 212r and 222r of the cores are respectively at above and below the right edge Er of the

  tubing, the core parts also extending

  in the same direction as the edges of the tube strip 10.

  The cores 211 and 221 consist of silicon steel plates joined to each other, and the surfaces of

  these cores opposite the coil bodies 212 and 222 are

  thermal insulators (not shown), for example ceramic plates. The groove 21la is formed in the

  bottom surface of the core 211, and the groove 221a is

  The grooves have a rectangular shape, the long sides being parallel to the long sides of the respective cores 211 and 221. The coil bodies 212 and 222 consist of long rectangle shaped copper strips. and are hollow to circulate a coolant therein. The strips are wound in layers inside the grooves 211a and 221a and are insulated from each other with a varnish. The coil bodies 212 and 222 fit into the grooves 211b and 221b, and the ends extend out of the coils, through

  through bores 211b and 221b extending laterally

  typically through nuclei 211 and 221, respectively.

  The feed system for the bobbin bodies 212

  and 222 is constituted by an available power source 24

  commercially available, a frequency converter 25, a

  current regulator 26 and a capacitor 27 improving the power factor, the individual electric currents at the desired frequency and the current value set by the frequency converter 25 and the current regulator 26 being applied to the respective coil bodies 212 and 222 via the capacitor 27 improving the power factor h1 2466306.

  Reference 28 designates a control unit for

  the current flowing in the coil bodies 212 and

  222. The control unit 28 is connected to a temperature detector.

  spreading over the entire width of the tube strip 10

  upstream of the coils 21 and 22 with respect to the direction of

  placement of this tube strip 10. The temperature distribution

  following the width of the tube strip 10, detected by the

  temperature detector 29, is applied to the control unit

  of 28, and this determines the current value necessary to increase the temperature at the edges E1 and E1 so that it reaches the butt welding temperature during the time when the tube strip 10 passes through the coils 21 and 22, and control signals corresponding to this current value are applied to the current regulator 26 so that it supplies the individual supply circuits with coils of equal or different current values for

  the respective coil bodies 212 and 222.

  Figure 3 is a block diagram of the communication unit

  28, which comprises a thermal converter 281, a con-

  analog / digital converter 282, an input / output device 283, a central unit 284, a digital switch

  285 and digital-to-analog converter 286. The detector of -

  temperature 29 delivers a clock signal 29a, and a temperature signal 29b, which is obtained by a sweep along the width, in synchronism with said clock signal 29a. The cadence signal 29a is applied to the central unit (by

  example iSBC 80/204 manufactured by Intel) 284 through the medium of

  re of the input / output device (eg iSBC 508, 732 manufactured by Intel) 283. The temperature signal 29b is applied to the thermal converter 281 in which it is amplified and its linearity is corrected, and the analog output of this converter 281 is converted to a digital value by the analog / digital converter 282. Said value

  digital system is applied to the central unit 284 via

  of the input / output device 283.

  The digital switch 285, consisting of a

  manual, is used to preset the temperature of

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  butt welding that one wishes to obtain for the edges

  El and Er, and its output signal is applied to the central unit

  tral via the input / output device 283.

  The central unit 284 starts to operate from the

  shown in Figure 4, with interrupts controlled by a timer. First, it reads the temperature signal, specifies Tl and Tr (respective temperature of each of the edges El and Er), and calculates the average value Tea

  temperatures of the two edges El, Er.

Tea = (Tl + Tr) / 2

  The central unit 284 then reads the temperature of

  Ts butt which has been pre-set using the switch

  285, and calculates the difference AT between Ts and Tea.

AT = Ts - Tea

  Then, it calculates the value of current Is which

  makes it possible to obtain AT = 0, and transmits this value Is to the current regulator 26, via the digital converter /

analog 286.

  For the calculation of Is we can use for example

the following equation.

  Is = Is () + A x AT Is: value of Is which was calculated in the previous cycle,

A: proportionality constant.

  The control of the current can naturally be effected

  killed by altering and controlling the frequency of the current that

  crosses the coil bodies 212 and 222.

* The mounting bracket 23 has a vertical bar 231 and upper and lower horizontal arms 232 and 233 which extend horizontally from the vertical bar 231. The coil 21 is fixed on the lower surface of the arm

  232 and the coil 22 is fixed on the upper surface

  lower of the lower arm 233. The coil bodies 212 and 222

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  are located opposite each other in the vertical direction

  The details of the structure of the mounting bracket 23 itself are not shown, but this structure is such that the coils 21 and 22 are turned towards the frame. space they delimit and are spaced from the surfaces of the tube strip 10 a correct distance. Alternatively, to heat the edges E1 and E1 to the end-to-end welding temperature, the coils 21 and / or 22 may be mounted on the support 23 so as to be able to move closer and away from each other. on the other, which allows to move the coils to modify the electromagnetic coupling between the coils and the coils.

  the edges of the tube band, in order to adjust the temperature correctly

  to which the tube strip is heated. In addition, the coil bodies may be arranged facing the lateral edges of the tube strip 10, for example in the same way as the auxiliary heating elements 3 shown in FIG. 5. In addition, the lower arm 233, as shown sure

  FIG. 18 can be mounted so that it can rotate vertically

  wedge around the inner end of the arm 233 to vary the space between the coils 21 and 22 and the edges

  El and Er of the tube strip 10, to adjust the heating.

  Once the tube strip 10 has passed through the main heating element 2, the temperature of its edges E1 and E1 is equal to or close to the butt welding temperature. The

  tube strip is then guided into the heating element

liar 3.

  Figure 5 shows the auxiliary heating element 3 and the supply and control means thereof. The

  references 31 and 32 designate heating coils by means of

  duction. The coils 31 and 32 are mounted on each side of the path of the tube strip 10 and comprise cores 311 and 321 having a U-shaped cross-section in the transverse direction of the tube-to-tube path, and

  coil bodies 312 and 322 consist of long webs

  copper digging horizontally wound. The feed system for the respective bobbin bodies 312 and 322 includes a feed source 34 available in the

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  a frequency converter 34 ', a current regulator 35 and a capacitor 36 improving the power factor to apply distinct currents to the

individual coil 312 and 322.

  A support bar 33 extends transversely with respect to the path of the tube strip, and support rods 331 and 332 descend from the support bar, the

  respective coils being mounted on their lower end

  in such a way that the coil bodies 312 and 322 face the side edges E1 and E1 of the tube strip, the edges E1 and E1 lying between the spaced apart portions

  vertically respective cores 311 and 321.

  The support bar 33 extends horizontally and allows

  pendicularly to the direction of movement of the band at

  tube, and is disposed above the path thereof. A reason

  333 extends along the length of the support bar 33, opening on its lower surface, and houses sliding members 334 and 335 which are supported by flanges extending inwardly from both sides 333. The support rods 331 and 332

  mounted on the lower surfaces of the slide members

  sants. On the extreme faces facing outwards

  sliders 334 and 335 are connected to

  ton and cylinder 336 and 337 which are mounted in turn on

  the lower surface of the support bar 33. The

  outer portions of the piston rods of the piston and cylinder devices are respectively coupled to the sliding members 334 and 335 to move the sliding members closer or apart.

  334 and 335 from each other so as to be able to regulate the

  between the coil bodies 312 and 322 and the edges E1 and

  Er of the tube strip 10, by varying the horizontal distances

zontales hi and hr. -

  A control unit 37 controls the current which circulates

  in the coil bodies 312 and 322, and causes the

  piston and cylinder systems 336 and 337 in response to the

  temperature detection detected by a temperature detector 38 arranged upstream of the coils 31 and 32, with respect to the direction of movement of the tube strip, and extending

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  following the width of the tube web 10. The control unit 37 determines a temperature difference based on the temperature distribution along the width of the tube strip 10, especially the temperature of the edges El and Er, as detected. by the temperature detector 38, and delivers a control signal and applies it to the current regulator 35.

  response, the current regulator changes the value of the

  rants which pass through the respective coil bodies 312 and 322 so as to eliminate the difference in temperature. When the current value is outside the control range

  of the current regulator 35, the device 336 (or 337) with

  and cylinder is driven and it moves the slide organ

  334 (or 335) to roughly adjust the horizontal distances

  zontales hl (or hr) between the coil bodies 312 (or 322) and the edges El (or Er) of the tube strip. Then, the current flowing through the coil bodies 312 and 322 is fine-tuned by the regulator 35 and the two edges E1 and E1 are

  heated to the optimum butt welding temperature

  belonging to the range of butt welding temperatures.

  Figure 6 is a block diagram of the communication unit

  37 which comprises a thermo-converter 371, a conver-

  analog / digital weaver 372, and an input / output device 373 (for example iSBC 508, 732 manufactured by Intel), a central unit 374 (for example iSBC 80/204 manufactured by Intel)

  and digital-to-analog converters 375, 376.

  Like the CPU 284, the CPU 374 reads the

  timing signal 38a and the temperature signal 38b that

  1 to the current controller 35 and the control valves 336v and 337v which are respectively in the pneumatic circuits of the piston and cylinder devices 336 and 337. The central unit 284 begins a cycle such as that shown in Figure 7 with interruption by the synchronization circuit. First of all she reads the temperature signal,

  determines Tl and Tr, and compares them. Then, it calculates the increase

  LTl temperature (at the edge El), LTr (at

  edge level Er) to eliminate the gap between Tl and Tr.

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  When Tl> Tr; at T1 = O ATr = Tl - Tr When Tl <Tr; AT1 = Tr - Tl ATr = O Then, the central unit 284 calculates the current values Isl and Isr which must be applied respectively

  to the coils 31 and 32. For this calculation it is possible, for example, to use

  read the following equations: Isl = Isl () + B x aT Isr = Isr + C x ATr

  Isl (), Isr (): Values of Isl and Isr which were respectively

  calculated in the previous cycle,

  B, C: Constants of proportionality.

  In the next phase, Isl and Isr are compared to Is max, which is the maximum value of the range that can be regulated by the current regulator. When Isl (Isr) <Is max, the values of Isl and Isr

  are transmitted to the current regulator 35. In the case of

  In the process, the CPU determines the positions of the edges E1 and E1 using the values of the temperature signal 38b, for example, and calculates Si (or Sr) and transmits it to the solenoid of the control valve 336v (or 337v). Sl (or Sr) is a

  time interval during which the solenoid will have to be

  mented, and corresponds to the length hi (or hr) which must be

adjusted.

  Thus, the horizontal distances hi and hr are modified

  to change the intensity of the electromagnetic coupling between the coil 31 and the edge E1, and between the coil 32 and the edge Er, which makes it possible to control separately the heating and

  the temperature of the respective edges.

  In a variant, only the horizontal distances

  hi and hr can be set to equalize the temperatures

  edges of El and Er. Similarly, we can delete one or

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  the other of the devices 336 and 337 piston and cylinder and one of the length hl or hr can be fixed while the other is variable. In addition, the main heating element 2 can be omitted and only the auxiliary heating element 3 or the heating element shown in FIG.

  to heat the El and Er edges at the same temperature

haitée.

  In addition, another temperature detector can be placed.

  said tide (not shown) downstream of the auxiliary heating element 3, for measuring the temperature of the tube strip 10 after it has been heated by the auxiliary heating element 3, in order to detect any temperature difference between the El and Er edges. To eliminate any difference in temperature, it is possible to provide a feedback circuit on

  the control unit to adjust the locations of the bobbin

  31 and 32, which increases the accuracy of the

  temperature for the edges El and Er.

  The tube strip 10, whose two edges E1 and E1 are heated to the correct end-to-end welding temperature, is then sent, as shown in FIG. 1, between bending rolls 4 to bend the edges downwards relative to each other. at the central part, which gives the tube strip a 0-shaped cross section. Then, the tube strip is passed between the butt welding cylinders 5

  for butt welding the El and Er edges to form a tube.

  As shown in FIG. 8, the butt welding cylinders 5 are constituted by working rolls 51

  and 52 having calibration grooves having approximately

  the same semi-circular profile, and comprising both

  ends of the edges that have the appropriate width. Au-

  above the work roll 51 and below the work roll 52 are support cylinders 53 and 54 supported respectively on the edges of the rolls of

  job. The ends of the shaft of the support cylinder

  54 are mounted so as to be rotatable in a support 561 provided on a frame 56. The ends of the upper support cylinder shaft 53 are mounted so as to

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  being able to turn in a support 551, in which a device for adjusting the pressure load can enter and exit,

  and this upper support cylinder can move vertically-

  on a short distance. The pressure load adjusting device 55 is controlled by an oil pressure control valve 57 to move vertically, so that the pressure exerted by the working rolls 51 and 52 on the tube strip for the bending into a tubular shape can be adjusted, allowing the opposite edges El and Er to be butt welded together with a desired pressure for welding. The pressure exerted by the working cylinders 51 and

  52 on the outer periphery of the tube strip 10, other-

  In other words, the pressure load is detected by a load cell 58 provided at the bearings of the support cylinder shaft 53 mounted on the support 551. There is provided a control unit 59 which is connected to the load cell. 58 and which adjusts the oil pressure control valve 57 in response to the pressure load adjusting device 55. The pressure load detected by the load cell 58 and applied to the controller 59, is compared with the load of

  pre-set pressure preference so as to place correct-

  butt the El and Er edges. The opening of the valve

  57 to control the oil pressure to eliminate any dif-

  The difference between the sensed load and the predetermined load is calculated, and the oil pressure control valve 57 receives a control signal to increase or decrease.

  the pressure load. The reference pressure load applied

  The working rolls 51 and 52 of the tube strip 10 are located within a pressure range which ensures correct welding of the edges E1 and E1 and furthermore the value is selected so that be uniform and that any increase in thickness around the welded part, namely the height of the weld bead, is reduced in a

to stay in a constant range.

  FIG. 9 is a block diagram of the control unit 59 comprising an analog / digital converter 591, an input / output device 592 (for example iSBC, 508, 732 manufactured by Intel), a central unit 593 (by example

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  iSBC 80/204 manufactured by Intel) and a digital switch 594. The unit 593 starts a duty cycle as

  the one shown in Figure 10 with interruption by the cir-

  cooks out of sync. First, it reads the pressure load PA which is detected by the load cell 58, via the analog-to-digital converter 591 and the input / output device 592, and reads the reference pressure load. predicted Ps from the digital switch 594. It calculates the difference AP between Ps and PA 'AP = Ps - P Then the difference AP is compared with the value

zero.

  When AP> O, the CPU 593 calculates the time AT1, and when aP <O, it calculates the time AT2, using the following equations, and transmits them to the control valve 57.

AT = D AP + E

AT2 = F AP + G

D, E, F, G: constants.

  When AP> O, the control valve 57 is open

  to apply oil to the fuel control device 55

  pressure, and when AP <O, the control valve 57 is opened to reduce the oil pressure in the adjusting device 55. AT1 and AT2 are the opening times of the valve

  57 that are necessary to obtain AP = 0.

  We will now explain why the pressure load controlled by the butt welding cylinders

  5 limits the height of the weld seam and the increase

  thickness around the welded part.

  FIG. 11 shows the results of experiments carried out to obtain the relation between the height of the weld bead and the backflow stress, experiments in

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  a 320 mm wide and 3.2 mm thick tube strip was first heated so that the two edges, over a width of 10 mm, were at a temperature higher than that of the part The tube was bent and welded end to end with a discharge of mm, which made it possible to obtain a continuous butt welded pipe with a diameter of 101.9 mm. The graph represents the discharge stress (kg / cm 2) on the ordinate and the height of the weld bead (mm) at the welded portion on the abscissa. The marks 0, o, A and x on the graph represent the relationship between the discharge stress and

  the height of the weld seam which corresponds to different

  these temperature between the edges and the central part of 50, 150 and 3000C, when the temperature of the central part

  is 13000C and the edge temperatures are respectively

  1250, 1200, 1150 and 10000C. The solid line curve represents the relationship between the discharge stress and the height of the weld seam when the two edges are at a temperature of 13000C and the central portion is at a temperature of 10000C. As seen in the graph, more

  the temperature difference between the edges and the central part

  the higher the discharge stress and the height of the weld seam are important for a

  given tube, and when the temperature difference is con-

  aunt, the height of the weld seam increases almost

  tionally to the increase of the discharge stress.

  In addition, the dashed line represents the lower limit

  pressure stress required to ensure adequate resistance of the butt weld at the

the welded part.

  On the other hand, for a given temperature of the tube strip, the discharge stress is mainly related to the pressure load at the butt welding rolls. The height of the weld bead and the increase in thickness around the welded portion both vary depending on the temperature at both the edges of the tube strip and the discharge stress. In summary, when the temperature of the edges of the tube strip is regulated

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  Precisely upstream of the butt welding cylinders, as is the case with the device according to the invention, the pressure load at the end of the welding cylinders

  end can be adjusted to obtain the constraint of

  desired flow and the desired weld seam height in the relationship shown in FIG. 11, which desirably reduces the height of the weld seam.

  welding and the increase in thickness around the

  being supplied. Another effect is the reduction of variations in

  the resistance of the welded part of the tube.

  Referring again to FIG. 1, the tube 100 welded end to end by the cylinders 5 passes through contraction cylinders 60 and a group of contraction cylinders 6, and

  the welded part is cooled by means of a

  cooling 71 disposed between the contraction cylinder 60

  and the first contraction cylinder 61 of group 6, and

  facing the welded part of the tube 100.

  The cooling device 71 comprises a number of

  number of spray holes 712 in the upper surface of a hollow box 711 located in front of the part

  welded tube 100, the box 711 having, in the direction

  displacement of the pipe 100, a length that allows it to perform the desired cooling. With reference

  FIG. 12 shows the cooling device

  71 and the downstream cooling device 72 and

  which will be described in more detail below. A pump 74 is

  linked to the cooling device 71 via a control valve 73, so that water can be

  supplied selectively by the pump 74 and sent to the

  The control unit 75 for controlling the control valve 73 is connected to temperature detectors 761 and 762 respectively facing the welded portion of the tube 100, and of the remaining metal part of the tube, an upstream of the cooling device 71 relative to the

  direction of movement of the tube 100, and a generator of

  pulses 77 is connected to the contraction cylinder 60. The control unit 75 calculates, from the temperature of the part

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  welded and the temperature of the remaining metal portion, which are detected by the detectors 761 and 762, the speed of movement of the tube 100 which is detected by the pulse generator 77, and the outer diameter and the thickness of the tube 100 which are provided by a data input device 78, the amount of water required to reduce the temperature of the welded portion to a value equal to that of the remaining portion of the tube. Then, the control unit 75 delivers a

  signal to the control valve 73 which then delivers the quantity

  calculated water quantity which must be sprayed on the

from the tube 100.

  Figure 13 is a block diagram of the communication unit

  75, comprising thermo-converters 751, 752, a con-

  753 analog / digital converter, an input device

  output 754 (as above), a CPU 755 (as hereinafter

  above), a counter 756 and a digital / analogue converter

  757. The counter 756 counts the impulses which are

  supplied by the pulse generator 77.

  As shown in Figure 14, the central unit

  755 reads Tsm (weld temperature) and Trm (temperature)

  the remaining metal portion) provided respectively by the temperature detectors 761 and 762, and reads Cu (count value of the counter 756). Then, the CPU 755 calculates the difference ATm between Tsm and Trm, according to the following equation ATm = Tsm - Trm and calculates the velocity VA of the tube 100 according to the equation VA = K1 (Cu - Cu ( -) Cu (): value of Cu that was read in the previous cycle

K1: proportionality constant.

  Next, the amount of water W to be sprayed by the cooling device 71 is calculated from the following equation:

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  W = W + K2 × LTm W0: amount of constant water which is determined by the dimensions of the tube 100, K2: variable dependent on VA.

  The central unit 755 transmits the value of W to re-

  the control valve 73, via the conver-

  digital / analog weaver 757, after a certain delay which corresponds to the distance between the detectors 761, 762 and the cooling device 71 and which is determined from

  said distance and said speed VA.

  Alternatively, the cooling device 71 may be positioned just downstream of the butt welding cylinders 5 or between the rolls of the group 6. For example, a butt welded pipe 100 having an outside diameter of 60.5 mm and a thickness of 3.8 mm and which moves at a speed of 85 m / min and whose temperature is about 1320 ° C at the welded portion and about 11800C at the remaining metal part, receives water at 200C and a pressure of more than 5 kg / cm2 with a flow rate of about 150 1 / min, to cool the welded part to the temperature of the part

remaining metal.

  The tube 100 is subjected to the action of the cylinder of

  pull 60 and the group 6 of contraction cylinders to be finished, and is sent to the hot saw 8 which cuts it into sections of desired axial length, this hot saw 8 being a conventional saw. The cut tube 100 then passes through the other cooling device 72 and is cooled there

  quickly to around 9000C. The cooling device

  72 comprises a cylinder 721 whose wall comprises a

  number of radially oriented spray orifices

  inwardly of the cylinder 721, and an outer cylinder 722 coaxial with the inner cylinder, the inner cylinders

  and outside 721 and 722 being united at their

  downstream by an end plate, and the inner cylinder 721 diverging outwardly at the upstream end

  and being welded to the inner periphery of the outer cylinder

  722. The outer cylinder 722 is connected to an orifice of

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  discharge of the pump 74 for the cooling device

  71 through a control valve 77, whereby the water from the pump 74 is sprayed radially inwards through the spray ports into the inner cylinder 721. The cut tube 100 is rapidly cooled to about 900 ° C as it passes through the inner cylinder

  721, of the cooling device 72, passes through the device

  calibrating 9 to be sent to other devices

finishing (not shown).

  In the device according to the invention, having the constitution described above, the tube strip 10 is heated

  at 12000C, which is a lower temperature than

  end-to-end welding during its passage through the

  heating 1, then passes through the main heating element 2.

  The temperature detector 29 attached to the control unit 28 for the main heating element 2 detects the temperature distribution along the width of the tube strip 10, just after it leaves the heating furnace 11, and applies this information to the control unit 28. The control unit 28, based on the temperature distribution, detects the difference between the temperatures of the two edges E1 and E1 and the preset end-to-end welding temperature, and determines

  the current values needed to increase the temperature

  respective edges El and Er up to the temperature of

  butt welding. The current regulator 26 receives signals from

  control rods from the control unit 28, and applies separate appropriate currents to the coil bodies 212 and 222 to bring the edges E1 and E1 to the end-to-end welding temperature. Therefore, the edges El and Er are heated from about 12000C, at which temperature they

  at the time of leaving the heating oven,

  at approximately 13000C, butt welding temperature, then

  the tube strip is introduced into the heating element

  hlaire 3. The temperature of the edges El and Er is detected by the temperature detector 38 provided just upstream of the element

  auxiliary heater 3, and if both edges are heated

  that at the butt welding temperature and that there is no

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  With the difference in temperature, the control unit 37 does not supply the coil bodies 312 and 322 of the coils 31 and 32, and the tube strip 10 can simply pass through the auxiliary heating element without being heated again. When a temperature difference between the edges is detected, the control unit 37 calculates the value of the currents for the coil bodies.

  312 and 322 which is necessary to eliminate the difference

  and produces appropriate control signals. If the current value supplied by the control unit 37 exceeds the capacity of the current regulator 35, the piston and cylinder devices 336 and / or 337 receive the necessary signal.

  to move the support rods 331 and / or 332 perpendicularly

  1 to the direction of movement of the tube strip 10, which adjusts the horizontal spacing between the coil bodies 312 and 321 and the edges E1 and E1, and the current values are again set by the control unit 37 and the current regulator 35. As a result, the temperature of the edges El and Er is set to the same butt welding temperature.

  The tube strip 10 leaving the heating element

  3 passes between the bending cylinders 4, the edges El and Er being uniformly heated to a temperature of

  predetermined butt welding, and the tube strip is

  to take a shape having a cross section in

  0, then passes between the cylinders 5 butt welding.

  The load cell 58 located on the landing of one of the cylinders

  The butt welding machine 5 detects the pressure load of the cylinder 5 relative to the outer periphery of the curved tube web 10, and applies it to the control unit 59, and the detected pressure load is compared with the predetermined desired pressure load, and a control signal is

  then returned by the control unit 59 to the control valve

  the load 57 mandates to actuate the pressure control device 55 so as to match the pressure load at the

  butt welding cylinders 5 with the load of pres-

  predetermined resolution. Thus the tube strip 10 is subjected to the correct pressure from the butt welding cylinders 5, and the opposite edges El and Er are butt welded at a constant pressure. Butt welding of the edges El and

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  Er at a constant pressure keeps the backflow at a

* minimum value, which means that the increase

  Thickness at and around the weld bead, which is due to butt welding, is kept to a minimum. Equal temperatures and uniform deformation resistance at the edges El and Er also help to achieve this result, which avoids external deformation, for example variations in the outside diameter of the tube 100, and variations in resistance at the level of the party

welded.

  Once the tube 100 has left the cylinders 5 of

  end-to-end welding, its temperature at the level of the

  This temperature is detected by the temperature detector 761, and the temperature of the remaining metal portion is detected by the detector 762, and the results are applied to the control unit 75. The control unit 75 compares the temperatures of the two parts. and calculates the amount of water required to reduce the temperature of the welded portion to a value equal to the temperature of the remaining metal portion,

  the basis of the temperature difference, the speed of

  placement of the tube 100, provided by the pulse generator 77, and the outside diameter and the thickness of the tube 100, which are provided by the data input device 78. The control valve 73 receives a control signal from

  of the control unit 75 to deliver the amount of water required to

  which must be sprayed on the welded part. Thus, once the tube has left the butt welding cylinders, the temperature of the welded portion is reduced to a value which is equal to or close to the temperature of the remaining metal portion, and then this tube passes through the group 6 of contraction cylinders to be dilated. As a result, even when the tube is subjected to contraction and expansion by the group 6 of cylinders as it passes through, the thickness of the welded portion and the portion that is located

around does not increase.

  We will now describe the advantages of the device

according to the invention.

  Table 1 gives the results of comparative tests,

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  and indicates the percentage of production of defective weld seams (ratio of the number of tubes with defective weld seams to the total number of tubes manufactured) in the manufacture of tubes of the same dimensions by changing the temperature difference between the edges and the central part

  of the tube strip, using the device according to the invention

  and a conventional device in which the entire tube strip is brought to a temperature equal to the temperature of

  butt welding in the heating furnace.

TABLE 1

  As can be seen from Table 1, the device according to the invention considerably reduces, compared to a conventional device, the percentage of cords production.

  defective weld for all temperature differences

  ture. It will be understood that the percentage corresponding to

  tif is even weaker than the difference in temperature

is important.

  Figures 15 (a) and 15 (b) are histograms

  sensing the distribution of flattening values obtained from a flattening test for the resistance at the welded portion of butt welded tubes continuously at

  means of the device according to the invention and by means of the

  classic tif. Fig. 15 (a) shows the results for the device according to the invention, and Fig. 15 (b) shows the results for the conventional device. For the test, the continuous butt welded pipe is placed horizontally so that the welded part faces towards the side, and

  vertical load is applied to the tube. When a deterioration

  In the welded part, the height of the tube

  is generally flattened is divided by its mean outside diameter Difference of Device according to temperature device the classical invention

500C 0.31% 0.63%

1000C 0.47% 1.36%

2000C 0.78% 5.73%

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  and the quotient gives the value of flattening. In Figs. (A) and (b), this value is plotted on the abscissa, and the number of tubes having a flattening value within a given range is shown on the ordinate. The number N of samples in this test was equal to 54, for both the device according to the invention and for the device

  classic. The average value X is 0.201 for the tubes

  with the device according to the invention, and 0.213 for tibes made with the conventional device. The standard deviation is 0.044 for tubes made with the following device

  the invention and 0,043 for tubes manufactured with the

classic tif.

  As can be seen from the histograms of the figures

  (a) and 15 (b), the flattening value, ie the

  The end-to-end weld of a continuous butt welded pipe using the device according to the invention is almost the same as that of tubes made by a conventional device.

  Figure 16 is a graph showing the results of

  comparative test reports for the thickness distribution at

  level of the circumference of a tube welded end to end in con-

  tinu in which the welded part is cooled according to the

  and for other cases where it has not been cooled in this way. The ordinates represent the thickness (mm), and

  the abscissae represent the locations of the thickness measurements.

  around the circumference of the tube. On the graph the curve in solid lines represents the values for a tube in which the welded part has been cooled with a quantity

  of water corresponding to its temperature, using the

  According to the invention, the dotted curve represents values without cooling of the welded portion, and the curve

  in phantom lines represents the values obtained with a cooling

  draining the welded part by simply spraying a constant amount of water. The positions in which the thickness of the sample has been measured are represented on the

  Figure 17 on which the welded portion is at point g.

  As can be seen from the graph of FIG. 16, when the device according to the invention is used for

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  adjust the cooling of the welded part, the tube has

  a substantially uniform thickness throughout its periphery.

  On the contrary, when simply spraying a constant amount of water on the welded portion, the thickness increases at this welded portion. When the welded part is not re-

  cold, we obtain a rather significant increase in thickness

  especially at the level of the inner periphery,

  significant variation in thickness across the entire

tube.

  We will now describe a variant of the heating element according to the invention, which can be used to

  the main heating element or for the heating element

  in the device described above, or which can replace

the two heating elements.

  This heating element and its control system are shown in Fig. 18, and the corresponding heating coils are shown in Fig. 19. The element

  2 'is usable as a primary heating element.

  and as auxiliary heating element. The tube strip 10 exiting the heating furnace passes between coils

  91 and 92 arranged opposite each other and spaced vertically

  calmly, then moves towards the cylinders of

  4 and end-to-end welding cylinders.

  As shown in Fig. 19, the induction heating coils 91 and 92 comprise cores 911 and 921 and coil bodies 912 and 922 housed in grooves

  911a and 921a respectively in the lower surface

  re of the 911 core and in the top surface of the 921 core.

  The respective rings 911 and 921 are constituted by

  of silicon steel in the form of strips which are

  to form recesses corresponding to the grooves

  911a and 921a, the silicon steel plates being superimposed

  and having a rectangular shape, seen in plan. The plates are joined by strips (not shown) or the like and are provided on the surfaces opposite the tube strip with thermal insulators to prevent damage to the coil bodies 912 and 922. The grooves 911a and 921a have a general rectangular shape and their

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  sides are respectively parallel to the four sides of the cores 911 and 921. The coil bodies 912 and 922 are of rectangular shape and are formed by long hollow copper strips which are arranged in layers along the grooves 911a and 921a and which are isolated from each other by varnish. The ends 912a and 922a of the respective coil bodies 912 and 922 leave the coils via bores 911b and 921b respectively formed in the cores 911 and 921. The coil bodies 912 and 922 are traversed by a current of

given frequency.

  Referring to Figure 18, the mounting bracket 93 for the coils has a vertical bar 931 and arms

  932 and 933 which are united at the

  above and below the 931 bar and which are parallel

  between them so as to give the support a form of C, seen from the front. The spool 91 is fixed to the lower surface of the upper arm 932, and the spool body 912 is attached to the lower surface of the spool 91. The spool 92 is attached to the upper surface of the lower arm 933, and the spool body

  coil 922 is attached to the upper surface of the coil 92.

  The long sides 912e and 912r of the coil body 912 and 922 and 922r of the coil body 922 are aligned with the edges E1 and

Er of the tube strip 10.

  Suspension rods 94 are mounted on the upper surface of the arm 932 and extend vertically upwardly therefrom, and wheels 941 are journalled on the upper ends of the rods 94 and roll on a rail 942. mounting bracket 93 is suspended on the rail 942 which extends horizontally and transversely to the

  direction of movement of the tube strip 10, and can be

  positioned in a direction perpendicular to the direction of movement of the tube strip 10 to position the vertical bar 931 laterally with respect to the edges E1 and

  10, and to maintain the reels 91 and 92 respectively.

  in front of the upper and lower surfaces of the

tube band 10.

  A motor 943 is disposed on the upper surface of the upper arm 932, and its output shaft is coupled by

31 2466306

  via a chain, to a toothed wheel 944 mounted coaxially with a wheel 941. The motor 943 can rotate in

  both directions to move the mounting bracket 93

  pendicularly to the direction of movement of the tube strip 10, so as to be able to adjust the distances h1, h2, h3 and h4 between the edges El and Er and the long sides 9121, 912r,

  9221 and 922r of the coils, as shown in FIG.

  The lower arm 933 is pivotally mounted on the end

  lower end of the vertical bar 931, on a horizontal shaft

  zontal 933a fixed on the base of the arm 933, and can move vertically around the shaft 933a. The horizontal shaft 933a has at one end a pinion 933b which meshes with a pinion 933c which meshes in turn with a pinion mounted on

  the output shaft of a motor 945 mounted on the lower end

  vertical bar 931, so that when the

  motor 945 rotates in one direction or the other, it pivots

  the lower arm 933 around the 933a shaft, as shown

  is shown in phantom in Figure 20, which varies the vertical distances v and v between the edges El and Er of

1 2

  the tube strip 10 and the surfaces of the long sides 9221 and

922r of the coil body 921.

  Reference 95 designates a drive control for motors 943 and 945. At drive control 95, having a microcomputer system similar to control units 28 and 37, respectively, temperature detectors 961 and 96r are connected by via a generator 97 of temperature difference signals, and temperature detectors 981 and 98r, via a feedback circuit 99. The detectors 961 and 96r are arranged in front of the edges El and Er of the tube strip 10, upstream of the coils 91 and 92. The temperatures detected at the edges E1 and E1 are applied to the signal generator 97 of

  temperature difference, and the difference between the temperatures

  edges is detected and applied to the control of

  95. The drive control 95 delivers signals

  motor drives 943 and 945 for driving the motor 943 to move the mounting bracket 93 along the width of the tube strip 10 along the rail 942,

32 2466306

  and to drive the 945 engine so that it rotates

  vertically the lower arm 933 around the lower end

  931, in order to adjust the horizontal distances

  the h1, h2, h3 and h4 between the parts 9121, 912r, 9221 and 922r of the coil bodies 912 and 922 and the edges E1 and E1 of the tube strip 10, and the vertical distance v and v2 between the parts 9221 and 922r and the edges El and Er, so as to cancel the difference between the temperatures at the edges El and Er. The temperature detectors 981 and 98r arranged downstream of the coils 91 and 92 detect the temperature of the edges E1 and

  Er once the tube strip 10 has been heated by the bobbin

  91 and 92, and these temperatures are returned to the control unit 95, via the feedback circuit 99. The control unit delivers no signal when the temperature difference between the edges is zero but when there is a difference in temperature, it provides the motors 943 and 945 with drive signals to adjust the horizontal and / or vertical distances h1 and h2, v1 and v2,

  to cancel the temperature difference.

  The detectors 981 and 98r, which detect the temperature of the edges of the tube strip to correct the positions of the

  coils 91 and 92, can also be used to determine

  if the edges have been heated or not

desired butt welding.

  The adjustment ratio of the displacement of the support of

  floor 93 to the pivoting movement of the lower arm 933 is not

  limited to a particular value, but the setting may be

  for example by roughly adjusting the displacement of the mounting bracket 93 along the width of the tube strip 10, and finely adjusting the vertical pivoting movement of the lower arm 933, or by moving the mounting bracket 93

  in response to the temperature difference detected by the

  961 and 96r and rotating the lower arm

  933 to compensate for the setting in response to the temperatures de-

  sensed by detectors 981 and 98r.

  When a high frequency current, having a frequency

  predetermined quency, flows in the coil bodies 912 and 922, a magnetic flux is produced in the tube strip 10

-33 2466306

  to induce a current, especially in the edges El and Er

  to heat them. A change in the horizontal distance

  The vertical flow between the edges E1 and E1 and the coil bodies 912 and 922 varies the magnetic flux which flows in the tube strip 10. As a result, the induced current produced in the tube strip 10 changes and the energy that

  El and Er edge heating also changes. The heating element

  fant 2 'thus modifies the horizontal distances h1 and h4 and

  the vertical distances v1 and v2 so as to modify the

  electromagnetic range between the coils 91 and 92 and the tube strip 12, so as to equalize the temperatures of the

El and Er edges.

  In one variant, one of the coils 91 or 92 may be

  stationary, and the other can be mobile in the horizontal direction

  tale or can rotate in the vertical direction.

  As can clearly be seen from the above, in the device according to the invention, the tube strip, once it has been heated in the heating oven, is heated only at its edges to the butt welding temperature, by induction heating, and the central portion of the tube strip is maintained at a temperature

  low. As a result, energy savings are achieved

  siderable. In addition, the temperatures of the edges of the tube strip are set simply and reliably to be equal, so that when the two edges are welded end to end, the resistance to deformation is equalized and, as a result of the control constant pressure load applied to the tube strip in butt welding cylinders,

  edges are welded end to end with a constraint of

  uniformly, so that the value of the repression is uni-

  shape, which results in a lower height of the weld seam, a smaller variation-in thickness and outside diameter of the tube, and a smaller increase in

  the thickness in the vicinity of the welded part.

  In addition, just before the contraction or in the middle of the contraction, the butt welded part of the tube is cooled to the temperature of the rest of the tube, so that there is no increase in temperature. thickness at the level of

  the welded part of the tube during the rolling with

  tion. In addition, the strength of the welded portion is improved.

  relative to the welded portion of a tube made using a conventional device that heats the entire tube strip to the welding temperature in the heating furnace. Therefore, the device according to the invention provides a considerable improvement in the continuous manufacture

butt welded tubes.

  Of course, the invention is in no way limited to the embodiment of the example described and shown, it is capable of numerous variants accessible to humans.

  of art, according to the intended applications and without

  ter for that of the scope of the invention.

Claims (23)

  1. Device for the continuous manufacture of butt welded tubes, characterized in that it comprises a heating furnace for bringing to a predetermined temperature a tube strip which passes through it continuously; heating means comprising at least one heating element comprising induction heating coils located opposite one another   the other at a distance from each side of the journey   before which the tube strip passes through said heating means   ge, and in the vicinity of the marginal portions of the tube strip, to heat only the marginal portions of this tube strip from the heating furnace to the butt welding temperature, and means connected to at least one of the induction heating coils for varying the electromagnetic coupling between said induction heating coil and the corresponding marginal portion of the tube strip to adjust the temperature at which the corresponding marginal portion is heated; bending means located in the vicinity of the outlet end of the heating means and intended to bend the tube strip to give it a generally tubular shape; and butt welding cylinders disposed adjacent the exit end of the bending means for applying a predetermined pressure to the bent tube web to butt weld the edges thereof. tube tape.   2. Device according to claim 1, characterized   in that the means for varying the electronic coupling   are connected to the two heating coils by means of   duction. 3. Device according to claim 2, characterized   in that the induction heating coils are constituted by   killed by two inductive heating coils arranged opposite each other at a certain distance above and   below the path of the tube strip, said coils have   of a generally rectangular shape and their long sides being substantially aligned with the marginal parts of the   tube band crossing the gap between these coils.   4. Device according to claim 3, characterized 36 2466306-   in that the coils have a fixed position with respect to the path of movement of the tube strip, and in that said means for varying the electromagnetic coupling are constituted by means which vary the current applied to said coils. 5. Device according to claim 4, characterized in that the means for varying the current comprise temperature detection means located in the vicinity of the   of the tube strip to detect at least the temperatures   the marginal portions of the tube strip, means connected to said temperature detecting means for determining, at   From the temperatures detected, the difference between the temperatures   temperatures of the marginal parts of the tube band and the temperature   desired end-to-end welding temperature, and means of   current regulation connected to said determining means and said coils for applying a current thereto, for heating the marginal portions of the tube strip to the   desired end-to-end welding temperature.   6. Device according to claim 3, characterized in that one of said coils is mounted so as to be able to   move transversely to the direction of movement   of the tube strip between the coils to vary   induced current in the tube strip according to the posi-   the moving coil with respect to this tube strip, and that the means for varying the electromagnetic coupling   comprise means for moving said coil.   7. Device according to claim 6, characterized in that said means for moving the coil comprise temperature detection means in the vicinity of the path of the tube strip, for detecting at least the temperatures of the marginal portions of the tube strip, related means   the temperature detection means for determining, in particular   the temperatures detected, the difference between the temperatures   of the marginal parts of the tube strip and the temperature   desired butt welding structure, and means of   placement connected to said determining means and to said   coil to move this coil to vary the neck   induced in the tube strip, to obtain the desired temperature. 8. Device according to Claim 6, characterized   in that said means for moving said coil comprises   temperature sensing means located in the vicinity of the tube-to-tube path for detecting at least the temperatures of the marginal portions of the tube strip, means for detecting   connected to said temperature detecting means for determining   from the detected temperatures, the difference between the temperatures of the marginal portions of the tube strip, these means being connected to the displacement means for moving the coil to vary the induced current in the strip to   tube so as to cancel said difference.   9. Device according to claim 3, characterized in that one of said coils is mounted so as to be able to move perpendicular to the direction of movement of the tube strip between said coils, to vary the induced current in the tube strip depending on the position of the voice coil relative to the tube strip, and that the   means for varying the electromagnetic coupling   means for moving said coil.   10. Device according to claim 9, characterized in that the means for moving the coil comprise temperature sensing means in the vicinity of the path of the   tube to detect at least the temperatures of the   marginal portions of the tube strip, means connected to the temperature detection means for determining, from   detected temperatures, the difference between the temperatures   the marginal portions of the tube strip and the desired butt welding temperature, and moving means connected to said determining means and said coil for moving said coil to vary the induced current.   in the tube strip, to obtain the desired temperature.   11. Device according to claim 9, characterized in that the means for moving said coil comprise   temperature sensing means in the vicinity of the work   jet of the tube strip for detecting at least the temperatures of the marginal portions of the tube strip, means connected to said temperature detection means for determining, at 38 2466306   From the temperatures detected, the difference between the temperatures   temperatures of the marginal portions of the tube strip, said means being connected to the displacement means for moving the coil to vary the induced current in the tube strip so as to cancel said difference. Device according to Claim 3, characterized   in that one of the coils is mounted so that it can move   transversely to the direction of travel of the tube web between said coils for varying the induced current in the tube strip according to the position of the voice coil relative to the tube strip, and   the other coil is mounted so that it can move   perpendicularly to the direction of movement of the tube strip between said coils to vary the induced current in the tube strip according to the position of the voice coil relative to the tube strip, and that the means for varying the electromagnetic coupling   means for moving said coils.   Device according to Claim 12, characterized in that the means for moving the coils comprise   temperature sensing means in the vicinity of the work   jet of the tube strip for detecting at least the temperature of the marginal portions of the tube strip, means connected to said temperature detecting means for determining, at   From the temperatures detected, the difference between the temperatures   temperatures of the marginal parts of the tube band and the temperature   desired butt welding temperature, and displacement means connected to said determining means and said coils for moving said coils to vary the   induced current in the tube strip, to obtain the temperature desired form.   14. Device according to claim 12, characterized in that said means for moving the coils comprise temperature detection means located in the vicinity of the path of the tube strip to detect at least the temperature of the marginal portions of the tube strip, means connected to said temperature detecting means for determining, from the detected temperatures, the difference between the temperatures of the marginal portions of the tube strip, said means also being connected to the displacement means for   move said coils to vary the current   in the tube strip to cancel said difference.   15. Device according to claim 12, characterized in that the means for moving the coils comprise   temperature sensing means in the vicinity of the work   jet of the tube strip for detecting at least the temperature of the marginal portions of the tube strip, means connected to said temperature detecting means for determining, at   From the temperature detected, the difference between the   temperatures of the marginal parts of the tube band and the temperature   desired butt welding temperature, means of   cement connected to said determining means and to one of said coils for moving said coil to vary the induced current in the tube strip to obtain the desired temperature, second temperature sensing means located in the vicinity of the path of the tube strip for detecting at least the temperature of the marginal portions of the tube strip, second means connected to the second detection means   temperature to determine, from the temperatures de-   tected, the difference between the temperatures of the   of the tube strip, and second means of moving   connected to the second means and the second coil for moving said second coil to vary the current   induced in the tube strip to cancel said difference.   16. Device according to claim 2, characterized in that the induction heating means comprise two induction heating coils disposed opposite each other at a distance so as to face the opposite sides of the strip. tube, said coils having   a U-shaped cross-section and partially surrounding   the path of the marginal parts of the tube strip.   17. Device according to claim 16, characterized in that said coils are mounted so as to move transversely relative to the direction of movement of the   the tube strip between the coils, in order to vary the   induced in the tube strip according to the position 2466306   of coils relative to this tube strip, and that the means for varying the electromagnetic coupling comprise means connected to said coils for moving these and   means for varying the current applied to said coils.   18. Device according to claim 17, characterized   in that the means for varying the electromagnetic coupling   also include temperature detection means   located in the vicinity of the path of the tube strip for detecting   at least the temperature of the marginal parts of the band   tube means connected to said temperature detecting means   to determine, from the detected temperatures, the difference between the temperatures of the marginal portions of the tube strip, said determining means being connected   said means for varying the current so as to   the coils when the means varying the current can not vary it sufficiently to heat   the marginal parts of the tube strip up to the temperature re desired.   19. Device according to Claim 1, characterized   in that it furthermore comprises a plurality of contraction cylinders   located in the vicinity of the exit of the butt welding cylinders, and cooling means associated with said   contraction cylinders for sending a cooling agent   towards the butt welded pipe in order to cool the   welded tube to the temperature of the rest of the tube.   20. Apparatus according to claim 19, characterized in that said cooling means are located in front of   the first cylinders of contraction compared to the direc-   displacement of the welded tube.   21. Device according to claim 19, characterized in that said cooling means are situated after   at least one of the contraction cylinders with respect to   rection of the displacement of the welded tube.   22. Apparatus according to claim 19, characterized in that said cooling means comprise detection means located in front of the cooling means for detecting the temperature of the welded part of the tube and the temperature of the remaining part of the tube, means for 41 - 2466306   supplying a coolant to the welded portion of the tube, valve means connected to said coolant directing means for controlling coolant flow to said coolant directing means, cooling means velocity detection for detecting the velocity of the tube as it exits the butt welding cylinders, and control means connected to the valve means and to which said temperature detecting means and said detecting means are connected.   speed, and which include means for receiving information   the outer diameter and thickness of the tube and to determine the amount of coolant   necessary to cool the welded part of the tube of the   the temperature at which it exits the butt welding cylinders to the temperature of the remaining portion of the tube, and controlling the duration during which the valve means is open to allow only the necessary amount of coolant to be supplied towards the welded part of the tube.   Device according to Claim 1, characterized   in that it further comprises means for changing the posi-   welding cylinders to adjust the pressure   applied to the tube strip, detection means in   contact with said butt welding cylinders for de-   sensing the pressure that is applied by the rolls to the tube web, and control means connected to said pressure adjusting means and said detecting means for controlling the pressure to a predetermined value.