JPH1076372A - Device for preheating open tube edge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an open tube edge preheating device which enables the solid phase pressure-welding tube manufacture to be realized that dispenses with bead machining, that secures high productivity, and that produces a steel tube superior in seam and surface quality. SOLUTION: This device is so structured that it is arranged in the upstream of a main heating device such as a work coil for heating an open tube 1 at a joint to a joining temperature; that it is provided with a U-shaped inductor 17 in the form of winding an induction coil 11 on the two poles 13, 13a of a U-shaped magnetic core, and with a high frequency power source for supplying a high frequency current to the induction coil 11; that the two poles of the U-shaped magnetic core is made to face the slit 10 of the open tube 1 so that the width of each pole 13, 13a may cover at least the slit 10 from outside the open tube 1; and that the poles and the slit 10 are aligned in the center of the width.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for preheating an open pipe edge portion, and more particularly, to an apparatus for preheating an edge portion of an open pipe which is a steel pipe formed by abutting both ends.

[0002]

2. Description of the Related Art Welded steel pipes are formed by forming a steel plate or a steel strip into a tube and welding the seams thereof, and are made by various manufacturing methods from a small diameter to a large diameter.
Examples include electric resistance welding (electric resistance welding), forge welding, and electric arc welding. For small to medium diameter steel pipes, an electric resistance welding method (electric resistance welded steel pipe, electric resistance welded pipe) utilizing high frequency induction heating is mainly used. In this method, a steel strip is continuously supplied, formed into a tubular shape with a forming roll to form an open pipe, and then the end faces of both edges of the open pipe are heated by high-frequency induction heating to a temperature equal to or higher than the melting point of the steel. (See, for example, the third edition of the Iron and Steel Handbook, Vol. III (2), 1056-10).
92).

In the above-described method of manufacturing an electric resistance welded tube utilizing high frequency induction heating, since the end surfaces of both edges of the open tube are heated to the melting point of the steel or higher, the molten steel flows under the influence of electromagnetic force, and the generated oxidation occurs. An object is caught in the abutment weld and welding defects such as penetrators or molten steel scatter (flash)
There is a problem that is easy to occur. For this issue,
For example, Japanese Patent Application Laid-Open No. 2-299782 proposes a method for manufacturing an electric resistance welded steel pipe having two heating devices. That is,
The temperature of both edges of the open pipe is heated to the Curie point or higher by the first heating device, the temperature is further raised to the melting point by the second heating device, and the both edges are impact-welded with a squeeze roll to produce a steel pipe. I do. In addition, Japanese Patent Application Laid-Open No. 2-29983 discloses the first
A current having a frequency of 45 to 250 kHz is passed by the heating device, and both edges are preheated. The second heating device is further heated to a temperature equal to or higher than the melting point, and both edges are impact-welded with a squeeze roll to produce a steel pipe. A sewing tube manufacturing device has been proposed.

However, in these ERW pipe manufacturing techniques, although a sound weld is obtained, since both edges are heated to the melting point of steel or more, the molten steel is applied to the inner and outer surfaces of the pipe at the time of impact welding. It is discharged and a bead is formed. Therefore, it is necessary to remove the weld bead on the inner and outer surfaces of the pipe after the impact welding, and most of the bead is removed by cutting with a bead cutting tool.

[0005] For this reason, in this method, loss of material and time occurs due to adjustment of the cutting amount of the bead cutting tool. Since the bead cutting tool is a consumable, it needs to be changed every 3000-4000m bead cutting length, depending on the pipe forming speed. Therefore, it is necessary to change the bite for 3-5 minutes every hour. Forced to stop the line.

In particular, in high-speed pipe forming in which the pipe forming speed exceeds 100 m / min, the life of the bead cutting tool is short and the frequency of replacement is high. There was a problem that bead cutting became a bottleneck and high-speed pipe making was not possible, resulting in low productivity. On the other hand, there is a method for producing a forged steel pipe having extremely high productivity for a relatively small diameter steel pipe. In this method, a continuously supplied steel strip is heated to about 1300 ° C in a heating furnace, and then formed into a tubular shape with a forming roll to form an open pipe. After performing the scale-off of
Oxygen is blown to the end face by a welding horn, the end face is heated to about 1400 ° C by the heat of oxidation, and then the end faces of both edges are abutted by a forging roll to produce a solid-phase welded steel pipe ( For example, 3rd Edition Iron and Steel Handbook, Vol. III (2), pp. 1056-1092).

However, in this method for producing a forged steel pipe, the scale-off of the end face is not perfect, so that the scale is caught in the forged joint portion, and the strength of the seam portion is considerably inferior to that of the base material portion. For this reason, in the flattening test, the flattened height ratio h / D = 2t / D (t: plate thickness) can be achieved with an ERW steel pipe, while the flattened height ratio h / D is inferior to about 0.5 with a forged steel pipe. It will be.

[0008] Since the steel strip is heated to a high temperature, scale is formed on the pipe surface, and the surface skin is poor. Although the pipe-making speed is as fast as 300 m / min or more and the productivity is high, there is a problem that seam quality and surface skin are poor, and products requiring strength reliability and surface quality such as JIS STK cannot be manufactured. . To solve the above problem advantageously,
It is preferable to use the solid-state pressure welding tube method invented by the present inventors. This is an unconventional tube-forming method in which the end of an open tube is induction-heated and pressed to a proper solid-state pressure welding temperature range (1300 ° C to 1500 ° C) lower than the melting point. Unlike conventional welded pipes, steel pipes manufactured by this solid-state pressure welding method do not require bead cutting, so high-speed pipe forming is possible and productivity is high. No deterioration of seam quality and surface skin.

However, the induction heating apparatus and the resistance heating apparatus used in the conventional production of welded pipes have the following drawbacks, and have problems in applying them to the solid-state pressure welding pipe method. FIGS. 7A and 7B are perspective views showing the concepts of a general induction heating device and a general resistance heating device, respectively.
In FIG. 7, 1 is an open pipe, 2 is a steel pipe, 3 is an edge, 3a is an end face of an edge, 4 is a joint point, 5 is a seam, 6
Denotes a work coil, 16 and 16A denote contact tips, 7 denotes a junction current path, and 8 denotes a direction of material passing. In this figure, a common squeeze roll that forms the joining point 4 by abutting opposing edge end surfaces 3a and a common high-frequency power supply that applies a high-frequency voltage to both the work coil 6 or the contact chips 16 and 16A are shown in FIG. Illustration is omitted. Note that the arrow in the junction current path 7 indicates the direction of the current at a certain point in time, and of course, this direction is alternately reversed with time.

Hereinafter, a heating method using a high-frequency current will be described as a typical example of the conventional induction heating apparatus shown in FIG. This device has a simple structure in which a multi-turn coil called a work coil 6 is arranged near the upstream side of the junction 4 so that the open tube 1 passes through the coil. However, the induction current tends to concentrate at the corners of the edge end surface 3a due to the high frequency skin effect and the like.
In particular, when forming a thick-walled pipe at a high speed, the temperature difference between the corner portion and the flat portion of the edge portion end surface 3a becomes excessive, and the corner portion and the flat portion simultaneously reach the appropriate solid-state pressure welding temperature range at the joint 4 at the joining point 4. Can not.

The non-uniform temperature of the edge portion 3 has been regarded as a problem from a different viewpoint even in a conventional welded pipe. As a countermeasure, a preheating coil is provided upstream of the work coil 6 to heat the edge portion 3 in advance. In addition, it is known that the temperature difference between the corner portion and the flat portion of the edge portion end surface 3a due to the rapid heating in the work coil 6 is reduced (see Japanese Patent Laid-Open No. 2-2997).
No. 82, Japanese Patent Application Laid-Open No. 2-29983).

FIGS. 8A and 8B are perspective views showing the concept of the structure of a conventional preheating coil. FIG. 8A shows a horizontal turn type, FIG. 8B shows a vertical turn type, and FIG. The preheating coil 7A is a preheating current path, and the same members as those in FIG. In this figure, a common squeeze roll that forms the joining point 4 by abutting opposing edge end surfaces 3a and a common high-frequency power supply that applies a high-frequency voltage to both the work coil 6 or the contact chips 16 and 16A are shown in FIG. Illustration is omitted. The preheating current path 7A
The arrow in the middle indicates the direction of the current at a certain point in time, and this direction is alternately reversed with time as in the case of the junction current 7.

However, the horizontal turn type shown in FIG.
Since the induced current is densely distributed and heated not only in the edge 3a but also in a region slightly away from the edge 3a, the heating efficiency is very poor, and the vertical turn type shown in FIG. Since the induced current is more densely distributed on the outer surface closer to the use coil 9, the temperature difference in the edge portion end surface 3a becomes larger,
The saddle type (c) has a disadvantage that the heating efficiency is very poor because the preheating current path 7A induced as shown in the figure is long.

Due to these disadvantages, even if the edge portion 3 of the open tube 1 is heated using a conventional preheating coil,
The averaging of the temperature difference between the corner portion and the flat portion of the edge portion end surface 3a at the start of the heating by the work coil 6 becomes insufficient, and the entire edge portion end surface 3a at the joining point 4 is brought to the appropriate solid-state pressure welding temperature region. It is difficult. The same problem caused by non-uniform heating is important not only in the production of solid-phase welded steel pipes, but also in the production of ERW pipes. In thick-walled pipes such as line pipes, the current tends to concentrate at the corners of the edge end face 3a due to the skin effect of high-frequency current, etc., so the corners are preferentially melted and the center of the flat part is sufficiently melted A phenomenon such as so-called cold welding occurs. This tendency increases as the wall thickness increases, and it is difficult to sufficiently cope with the conventional composite heating method using a preheating coil.

[0015]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides a solid-state pressure welding capable of producing a steel pipe which can ensure high productivity without bead cutting, and has excellent seam quality and surface texture. An object of the present invention is to provide an open pipe edge portion preheating device that can realize not only a pipe forming method but also a high-speed and high-quality pipe forming method of an electric resistance welded pipe.

[0016]

According to a first aspect of the present invention, an induction coil is disposed upstream of a heating device for heating an open tube to a joining temperature at a joining point, and has two poles of a U-shaped magnetic core. A U-shaped inductor of the form and a high-frequency power supply for supplying a high-frequency current to the induction coil, and the two poles of the U-shaped magnetic core are externally provided to the slit portion of the open tube so that the width of each pole covers at least the slit portion. An open tube edge preheating device characterized by being exposed.

The term "U-shaped magnetic core" is a concept including not only a literally U-shaped magnetic core, but also a U-shaped or horseshoe-shaped magnetic core composed of two poles and a connecting portion connecting them. The U-shaped inductor has a U-shaped magnetic core with a 100mm gap between the two poles.
Preferably and / or variable, and
The distance between the pole and the slit is preferably 80 mm or less, and the width W [mm] of the pole is determined by the gap g [m
[m] and the frequency f [kHz] of the high-frequency current are preferably selected so as to satisfy the following expression (1).

(Wg) / 2 ≧ 10 × f ^−1/2 (1) According to a second aspect of the present invention, in the first aspect of the present invention, the outer circumference of the open pipe is provided in a section where the U-shaped inductor is provided. The gist of the present invention is that a guide roll for restraining is provided, and a slit portion guide roll for restraining the slit portion is provided in the same section. It is desirable that the guide roll that restrains the outer periphery is nonmagnetic.

The section in which the U-shaped inductor is disposed is not only a section in which the U-shaped inductor itself extends, but also a section between the U-shaped inductor and the preceding and following equipment (forming roll, main heating device, etc.). Section is included. The third invention is the first invention
Alternatively, in the second aspect of the present invention, the gist is that an impedance is inserted into an open pipe in a section where the U-shaped inductor is provided.

According to a fourth aspect of the present invention, in any one of the first to third aspects of the present invention, a non-magnetic material is disposed between both poles of the U-shaped magnetic core.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION

<First Invention> FIG. 1 is a perspective view showing the concept of the first invention. In FIG. 1, 10 is a slit portion, 11 is an induction coil, 12 is a U-shaped magnetic core, 13 and 13a are poles, 14 is a line of magnetic force, 17
Is a U-shaped inductor. The same members as those in FIG. 8 are denoted by the same reference numerals, and description thereof will be omitted. Further, the present heating device and the high-frequency power supply for supplying electricity to the induction coil 11 arranged downstream along the passing direction 8 are not shown.

As the heating device, a local heating device such as a laser beam device, an electron beam device, and a plasma beam device can be used in addition to the induction heating device and the resistance heating device shown in FIG. As shown in FIG.
The U-shaped inductor 17 is formed by winding an induction coil 11 around two poles 13 and 13a of a magnetic core 12, and the two poles 13 and 13a are arranged from the outside of the open tube 1 to the slit portion 10 of the open tube 1 with a width center approximately. It was arranged along with it. In FIG. 1, W is the width of the pole, g is the gap between the slits, h is the distance between the poles and the slit, S is the distance between the poles, and L is the length of the pole.

As a result, the lines of magnetic force 14 running in the space between the one pole 13 of the U-shaped inductor 17 and the other pole 13a are changed from the one pole 13 of the U-shaped magnetic core 12 to the slit portion 10 to the inside of the open tube 1 to the slit portion 10
By following the path of the other pole 13a of the U-shaped magnetic core 12, it can be concentrated and evenly distributed near the opposing end surfaces 3a of the open tube 1 and the current density induced there increases. As a result, the induction heating efficiency is improved several hundred times as compared with the case where the conventional preheating coil having no magnetic core shown in FIG. 8 is used, and the temperature difference between the corner portion and the flat portion is reduced by both edges. The edge end face 3a can be quickly preheated to an appropriate temperature while maintaining the edge end face 3a at the same small size.

It should be noted that the way of winding the induction coil 11 around the poles 13 and 13a is, of course, opposite to each other so that the magnetic flux circulates. In the first aspect of the present invention, if the distance S between the two poles 13 and 13a of the U-shaped magnetic core 12 is smaller than 100 mm, the opposite directions induced in the edge portion 3 by the lines of magnetic force 14 entering and exiting the poles 13 and 13a. Induced current (eddy current)
However, since S interferes with each other and lowers the heating efficiency, S is preferably set to 100 mm or more. Further, since the degree of the interference varies depending on the frequency, the tube diameter, and the like, the U-shaped magnetic core 12 is provided with the two poles 13 and 13a so that the heating efficiency can be adjusted to the maximum pole interval.
Are preferably configured to be slidable in the direction of the tube. In addition, the more preferable range of S is 200 mm or more. Although the upper limit of S is not particularly set, it is appropriate to set the upper limit to about 1000 mm or less from the viewpoint of the arrangement space.

The poles 13 and 13a and the slit portion
If the distance h from the gap 10 exceeds 80 mm, the degree of concentration of the lines of magnetic force 14 on the end surface 3a tends to decrease. Therefore, it is preferable to dispose the U-shaped inductor 17 so that h is 80 mm or less. In addition, a more preferable range of h is 50 mm or less.
There is no particular lower limit for h.
It is sufficient that the slits 10 do not contact the slits 13 and 13a.

The pole width W [mm] satisfies the following equation (1), more preferably the following equation (1A), with respect to the gap g [mm] of the slit portion and the frequency f [kHz] of the high-frequency current. It is preferable to select (Wg) / 2 ≧ 10 × f− ¹ / 2 (1) ( ^Wg ) ^{/2≧17.4×f−1/2} (1A) Equations (1) and (1A) Indicates the half of the width of the facing section between the edge portion 3 of the open tube 1 and the pole. On the other hand, according to the inventor's intensive studies, the uniformity of the heating of the edge portion end face 3a is shown. The lower limit of the appropriate range of the facing section width from the viewpoint strongly depends on the penetration depth δ [mm] of the induced current, and among the factors limiting the penetration depth δ [mm], the temperature dependence It has been found that the expression can be well represented by using the frequency f [kHz] of the high frequency current which is not available to the ^-1/2 power.

That is, from the formulas (1) and (1A), W may be a value that satisfies the following formula (2), preferably (2A). W ≧ 20 × f− ^{1 / 2} + g (2) W ≧ 34.8 × f− ^{1 / 2} + g (2A) The open tube edge is effectively used by effectively using the magnetic flux induced by the high-frequency current. In order to heat the portion, it is preferable that W be suppressed to 1.25 times or less the diameter of the open pipe.

The preferred range for the length L of the pole is
Although it depends on the frequency f and the number n of turns of the induction coil, selecting from the range shown in Table 1 is advantageous in terms of heating efficiency.

[0029]

[Table 1]

However, if the frequency f exceeds 10 kHz, eddy currents are concentrated at the corners of the end face of the edge portion, and the corner portion is preferentially heated and the temperature difference in the end face becomes excessive. Is performed at a frequency of 10 kHz or less,
It is desirable to make the temperature within the end face uniform. Further, the number of turns n of the induction coil per pole can be increased by one turn depending on the equipment scale, and there is no particular upper limit, but it is preferable to select from the range in Table 1. <Second Present Invention> FIG. 2 is a perspective view showing the concept of the second present invention. In the same figure, 18 is a squeeze roll, 19 is a guide roll, 20 is a slit part guide roll, and 21 is a slide part, and the same or corresponding parts as those shown in FIGS. And the description is omitted. The high-frequency power supply is not shown.

As shown in the drawing, the second invention is different from the first invention in that the outer periphery of the open pipe 1 is restrained at a key point in a section where the U-shaped inductor 17 is provided (including short sections before and after). A guide roll 19 is provided, and slit guide rolls 20 and 20a for restraining the slit 10 in the same section are provided. Guide roll 19, slit part guide roll 20,
It is more preferable to deploy 20a simultaneously as shown in this figure.

In accordance with the above-mentioned preferred requirements (variable pole spacing) according to the first aspect of the present invention, the U-shaped magnetic core 12 has two poles 13 and 13a.
Is provided with a slide portion 21 for changing the interval S between the two.
FIG. 3 is a cross-sectional view illustrating various types of restriction of the guide roll according to the second embodiment of the present invention. The same or corresponding parts as those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted. FIG. 2A shows two guide rolls 19 (of course, the roll profile is processed along the pipe circumference) from both sides.
(B), three from both sides and below, (c) three from both shoulders and below, (d) four from four sides, one open tube
Is arranged so as to be rotatably abutted on the outer periphery of the horn. The guide roll 19 may employ various arrangements other than those shown here, such as a flat roll that restricts the guide roll 19 from multiple directions. Thus, the guide roll 19 is U
It is sufficient to dispose a plurality of inductors per section in an arbitrary arrangement form at various points in the arrangement section of the inductor.

When these guide rolls 19 are electromagnetically induced by a U-shaped inductor, they cause a disturbance to a preheating current in addition to their own heat deterioration, so that they are made of a non-magnetic material such as stainless steel or ceramics. It is desirable to use one. FIG. 4 is a cross-sectional view exemplifying a restrained form of the slit portion guide roll according to the second embodiment of the present invention. Reference numerals 20, 20a denote slit portion guide rolls, and the same or corresponding parts as those in FIG. And description thereof is omitted. The upper slit guide roll 20a is the slit 1
A roll having a convex portion that fits into and restricts the roll is particularly called a finned roll.

Note that the lower slit portion guide roll 20 is used for a reaction force against the finned roll 20a.
Although only books are illustrated, a plurality of books may be provided in the pipe circumferential direction. According to the second aspect of the present invention employing the above-described configuration, the open pipe 1 can pass through the section in which the U-shaped inductor is provided without deviation, and the temperature control accuracy of the edge portion preheating is further improved. <Third Present Invention> FIG. 5 is a sectional view showing the concept of the third present invention. As shown in the drawing, the third invention is characterized in that in the first or second invention, the impeder 15 is inserted into the open pipe 1 in the section where the U-shaped inductor 17 is provided. Thereby, the degree of concentration of the lines of magnetic force on the edge portion 3 is further increased, and the induction heating efficiency is further improved. It is preferable to use a ferromagnetic material such as ferrite as the impedance 15. <Fourth Invention> FIG. 6 is a partially cutaway perspective view showing the concept of the fourth invention. As shown in the drawing, the fourth invention is characterized in that in any one of the first to third inventions, a non-magnetic material 22 is additionally arranged between the poles 13 and 13a of the U-shaped magnetic core 12. As a result, the poles 13 and 13a and the slit 10
When the distance between the two is large, it is possible to preferably prevent the magnetic flux from unnecessarily looping in the external space of the open tube 1, and the induction heating efficiency is further improved. As the non-magnetic material 22, a non-metallic material, austenitic stainless steel, or the like may be used.

As described above in detail, according to the first to third aspects of the present invention, the edge portion of the open pipe is heated by the main heating device such as a work coil to raise the entire end surface to the appropriate solid-state pressure welding temperature range. It is possible to properly adjust the edge surface temperature distribution at the start of heating to increase the temperature, and for the first time, it is possible to secure high productivity without the need for bead cutting, and to provide a steel pipe with excellent seam quality and surface skin. A solid-state pressure welding tube method that can be manufactured becomes feasible. In addition, even when a conventional electric resistance welded steel pipe is manufactured, a steel pipe of excellent quality can be manufactured without causing welding defects such as cold welding and generation of a penetrator.

[0036]

[Example] In a continuous pipe-making line in which both edges of an open pipe are abutted and pressed into a steel pipe, an open pipe formed from a strip and entirely heated to an initial pipe temperature of 600 ° C is 140 m / min.
The edge is preheated at the line position where the gap between both end faces of the edge (gap of the slit part g) is 10 mm, and both edge end faces are further induction-heated to the pressure contact temperature downstream of the line, and the joint is pressed and pressed. When manufacturing a steel pipe for machine structure (equivalent to STKM11A) having a thickness of 6 mm and an outer diameter of 130 mm, the edge portion was preheated by using the apparatus of the present invention in the form of FIG. Also, under the same pipe-making conditions as in the example, the edge portion was preheated by using preheating coils without magnetic cores shown in FIGS. 7 (a: horizontal turn type), (b: vertical turn type), and (c: saddle type). Conventional examples A, B, and C were used.

Table 2 shows the specifications and induction conditions of the apparatus and the average temperature of the end face after preheating (abbreviated as T _PH ) obtained by measuring the end face of the edge portion immediately after preheating with a radiation thermometer. Table 2
, N is the number of coil turns (in the embodiment, the value per pole; conventional example C is not applicable for saddle type), S is the distance between the two poles of the U-shaped core, L is the pole length, and W is The width of the pole, h is the distance between the slit and the pole, f is the frequency, I _HF is the current value, IP
Is the presence or absence of an impeder.

[0038]

[Table 2]

As is clear from the comparison of T _PH in Table 2, according to the present invention, it is possible to preheat the edge portion of the open pipe much more efficiently than in the prior art.

[0040]

According to the present invention, the end face temperature distribution at the start of heating for heating the entire end face of the edge portion of the open pipe with the main heating device such as a work coil to raise the temperature to the appropriate solid phase pressure welding temperature range. Can be adjusted appropriately, and for the first time, it is possible to realize a solid-state pressure welding method that can secure high productivity without the need for bead cutting and can produce steel pipe with excellent seam quality and surface skin. It has a remarkable effect.

Further, if the present invention is applied to ordinary ERW pipe production, productivity and quality can be remarkably improved, and a remarkable effect can be obtained particularly in the production of thick-walled pipes.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the concept of the first invention.

FIG. 2 is a perspective view showing the concept of the second invention.

FIG. 3 is a cross-sectional view illustrating various constrained forms of a guide roll according to a second invention.

FIG. 4 is a cross-sectional view illustrating a restraining form of a slit portion guide roll according to a second invention.

FIG. 5 is a sectional view showing the concept of the third invention.

FIG. 6 is a partially cutaway perspective view showing a fourth concept of the present invention.

FIG. 7 is a perspective view showing the concept of a general induction heating device or resistance heating device.

8A and 8B are perspective views showing the concept of the structure of a conventional preheating coil, wherein FIG. 8A shows a horizontal turn type, FIG. 7B shows a vertical turn type, and FIG. 7C shows a saddle type.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Open pipe 2 Steel pipe 3 Edge part 3a Edge part end face 4 Joining point 5 Seam part 6 Work coil 7 Joining current path 7A Preheating current path 8 Direction of passing material 9 Preheating coil 10 Slit part 11 Induction coil 12 U-shaped magnetic core 13, 13a pole 14 magnetic field line 15 impeder 16, 16A contact chip 17 U-shaped inductor 18 squeeze roll 19 guide roll 20 slit guide roll (for reaction force) 20a slit guide roll (finned roll) 21 slide 22 non-magnetic material

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiaki Amagasa 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Chiba Works of Kawasaki Steel Corporation (72) Inventor Motoaki Itaya 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Toshio Onishi 1-1-1, Kawasakicho, Handa City, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Yuji Hashimoto 1-1-1, Kawasakicho, Handa City, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Nobuki Tanaka 1-1-1, Kawasaki-cho, Handa City, Aichi Prefecture Kawasaki Steel Corporation Chita Works

Claims (10)

[Claims] 1. A U-shaped inductor which is disposed upstream of a heating device for heating an open tube to a joining temperature at a joining point and has an induction coil wound around two poles of a U-shaped magnetic core; A high-frequency power supply for supplying a current, wherein two poles of a U-shaped magnetic core are made to face a slit portion of the open tube from the outside of the open tube so that the width of each pole covers at least the slit portion. Edge preheating device. 2. The open tube edge preheating device according to claim 1, wherein the distance between the two poles of the U-shaped core is 100 mm or more. 3. The open tube edge preheating apparatus according to claim 1, wherein the distance between the two poles of the U-shaped magnetic core is variable. 4. The open pipe edge preheating apparatus according to claim 1, wherein a distance between the pole and the slit portion is 80 mm or less. 5. The width W [mm] of the pole is expressed by the following equation with respect to the gap g [mm] of the slit portion and the frequency f [kHz] of the high-frequency current.
The open pipe edge portion preheating device according to any one of claims 1 to 4, which satisfies the relationship of (1). (W−g) / 2 ≧ 10 × f− ¹ / 2 (1) 6. A guide roll for restraining an outer periphery of an open pipe in a section in which a U-shaped inductor is provided.
5. The open-tube edge preheating device according to any one of 5. 7. The open pipe edge preheating apparatus according to claim 1, further comprising a slit portion guide roll for restricting the slit portion in a section where the U-shaped inductor is provided. 8. The open pipe edge preheating apparatus according to claim 6, wherein the guide roll is non-magnetic. 9. The open tube edge preheating apparatus according to claim 1, wherein an impedance is further inserted into the open tube in the section where the U-shaped inductor is provided. 10. The open tube edge preheating device according to claim 1, wherein a nonmagnetic material is further disposed between both poles of the U-shaped magnetic core.