JP3328110B2 - ERW pipe welding method and impeder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding an electric resistance welded pipe and an impeder, and more particularly, to an outer diameter of 50.8 mm or less and a ratio (t / D) of a thickness t to an outer diameter D of 10 or less. % And more particularly to a welding method and an impeder for an ERW pipe which is effective to be applied to manufacture a small-diameter thick ERW pipe having a diameter of not less than%.

[0002]

2. Description of the Related Art An electric seam in which a metal strip is bent into an open pipe shape in which both edges in the width direction are opposed to each other, and both edges are intensively heated and melted by Joule heat generated by a high-frequency current to perform abutment welding. In the pipe welding method, in order to increase the degree of concentration of the high-frequency current to both edges and improve welding efficiency, usually, an impedance is inserted and arranged in a metal strip bent into an open pipe shape. I have.

FIG. 4 is a schematic view showing an example of a conventional electric resistance welded pipe welding apparatus. In the figure, reference numeral 1 denotes a high-frequency power supply for generating a high-frequency current. A work coil 2 for inducing an induced current to flow is connected. The work coil 2 is disposed so as to surround a metal band 3 bent into an open pipe shape as a material to be welded. An impeder 4 is arranged inside the metal strip 3 on which the work coil 2 is arranged.
The impedance 4 includes a hollow or solid cylindrical impedance core 5 made of a magnetic material, and an impedance case 6 forming an impedance cooling water passage for protecting and cooling the impedance core 5. The inside of the metal band 3 bent into an open pipe shape by using a mandrel 7 also serving as a supply pipe of the above is inserted and arranged so as not to contact the metal band 3.

In FIG. 4, reference numeral 8 denotes a squeeze roll.
The two edge portions 3a, 3a, which are locally melt-heated intensively by the work coil 2 and the impeder 4, are pressure-welded and welded, and the metal strip 3 is conveyed in the outline arrow direction.

When an electric resistance welded pipe is manufactured by the welding apparatus having the above-described configuration, the work coil 2 is supplied from the high frequency power supply 1.
A high-frequency current flows through the metal band 3 to induce and generate an induced current in the metal strip 3 bent into an open pipe shape. This induced current melts and heats both edges 3a, 3a of the metal strip 3 bent into an open pipe shape, and then the squeeze roll 8
By pressure butting. In this case, the induced current is concentrated on the outer peripheral surface of the metal strip 3 bent into an open pipe shape, and a part of the induced current circulates on the inner peripheral surface to become a reactive current. However, since the impedance of the inner peripheral surface of the metal band 3 is increased by the presence of the impedance 4, the reactive current is reduced, and the induced current concentrates on both edges 3a, 3a.

The following three performances are required as the impedance 4, and these performances are almost determined by the characteristics of the impedance core 5. High permeability and high saturation magnetic flux density. In order to prevent heat generation, it must have a large specific resistivity, low iron loss, and easy to cool. The change in magnetic properties is small and the Curie temperature is high even if the temperature rises due to heat generation.

As the impedance core 5 that satisfies the above-mentioned various characteristics, ferrite, which is an oxide magnetic material, is generally used in many cases. Further, there has been proposed an impeder in which a foil or a wire of a magnetic material such as silicon steel or an amorphous metal alloy (amorphous alloy) having higher performance than ferrite is laminated or bundled and formed into a predetermined cross-sectional shape (for example, And JP-A-2-104479).

[0008] Further, many devices have been proposed to improve the performance of the impedance in terms of structure. For example, using a non-metallic fiber reinforced resin mandrel to increase the filling rate of the impeder core (Japanese Utility Model Application Laid-Open No. 59-135)
No. 884), and an impeder in which spiral fins are provided on the outer periphery of an impedance core body to enhance cooling (Japanese Utility Model Application Laid-Open No. 62-96984).

[0009]

By the way, for example, when the outer diameter is 50.8 mm or less, the ratio of the thickness t to the outer diameter D (t /
In a small-diameter thick-walled pipe having D) of 10% or more, the cross-sectional area of the space inside the pipe becomes extremely small. In this case, the filling rate of the impedance core 5 decreases with a decrease in the cross-sectional area of the inner space of the pipe, the magnetic load per unit volume on the impedance core 5 increases, the calorific value increases, and the temperature of the impedance core 5 itself decreases. It is easy to rise.

FIG. 5 shows Mn- used for the impida core.
FIG. 3 is a diagram showing an example of temperature dependence of saturation magnetic flux density in Zn-based ferrites. Although there is a difference between ferrites A, B, and C having different component ratios, all ferrites have a magnetic property with a rise in temperature. Characteristics deteriorate,
This leads to a decrease in welding efficiency.

As measures to prevent the magnetic characteristics from being lowered due to the temperature rise due to the heat generation, other than the above-mentioned conventional techniques, for example, the temperature of the impeder cooling water for cooling the impeder core 5 is lowered, or the supply pressure of the impeder cooling water is reduced. A certain effect can be obtained by increasing the cooling capacity of the impedance core 5 by increasing the height. However, the effects obtained by these countermeasures are still insufficient and high-efficiency welding cannot be performed. In addition, a special energy is required to lower the temperature of the impeder cooling water or to supply the pressurized water in order to increase the cooling capacity of the impeder core 5. However, there is a drawback that a decrease in the filling rate cannot be avoided.

Therefore, the development of a more efficient welding method,
There has been a demand for the development of an impeder that can suppress the decrease in the filling rate as much as possible and can save energy to prevent a rise in temperature.

SUMMARY OF THE INVENTION An object of the present invention has been made in view of the above circumstances, and a welding method capable of more efficient welding, and an impeder capable of suppressing a decrease in the filling rate as much as possible and achieving energy saving. Is to provide.

[0014]

Means for Solving the Problems The inventors have conducted a detailed investigation on the heat generation characteristics of the impedance core and found the following.

FIG. 6 is a schematic view showing a cross section including the work coil 2. In the prior art, the impedance core 5 is not rotated during welding. In this case, the magnetic flux when the metal strip 3 bent into an open pipe shape is induction-heated by the work coil 2 is uniform in the circumferential direction of the metal strip 3 bent into the open pipe which is the material to be welded. Instead, the magnetic band 3 preferentially flows on the sides near both edges 3a, 3a, and the magnetic flux flowing through the bottom 3b, which is the center in the width direction, is small.

For this reason, both edge portions 3 through which a large amount of magnetic flux flows
6A and 6B, the amount of heat generated in the portion of the impedance core 5 opposite to the impedance 3a is locally increased, and the temperature distribution in the circumferential direction of the impedance core 5 is represented by the isothermal temperature schematically indicated by a bold line in the impedance core 5 in FIG. It looks like a line. As a result, the temperature rise of the portion of the impedance core 5 which is most important for concentrating the high-frequency current on both edges 3a, 3a of the metal band 3 bent into the open pipe becomes the highest, and the magnetic characteristics ( (Permeability) is reduced, and the improvement in welding efficiency is restricted.

However, the impeder core 5 is rotated around its axis so as to oppose both edges 3a, 3a of the metal strip 3 bent into an open pipe shape.
When the portion is constantly changed, the amount of heat generated in the circumferential direction of the impedance core 5 becomes uniform, the temperature distribution in the circumferential direction becomes uniform, the temperature rise temperature decreases, and the magnetism of the impedance core 5 accompanying the temperature rise increases. It has been found that deterioration in characteristics can be reduced.

In this case, if a groove is formed on the outer surface of the impedance core 5 itself to increase the cooling capacity, the volume of the impedance core 5 decreases, the filling rate decreases, and the effect is offset. However, when the impeller core 5 is rotated by attaching a rotor impeller rotated by the impeder cooling water to one or both of the front and rear in the axial direction of the impedance core 5, the volume of the impedance core 5 can be sufficiently increased, It was also found that the rate can be increased and energy saving can be achieved.

The present invention has been made based on the above findings, and has the following (1) and (2) methods for welding an ERW pipe and an impeder.

(1) The metal strip is passed through a forming roll group composed of a plurality of stands, and both edges in the width direction are sequentially bent into an open pipe shape facing each other, and then both edges are subjected to high-frequency induction heating means. In a method for welding an electric resistance welded pipe, which is melt-heated and then subjected to abutment welding with a squeeze roll, welding is performed while rotating an impedance core disposed in the bent open pipe-shaped metal strip. How to weld a sewing pipe.

(2) While the impedance core body is rotatably provided in the impedance case, the impedance cooling water supplied into the impedance case is supplied to one or both of the front and rear end faces in the axial direction of the impedance core body. Impeder characterized by fixedly mounted rotating wings that rotate as power.

In the above method (1), when the rotation of the impedance core is neglected, if the energy saving required for the rotation is neglected, the impedance core is mounted inside the impedance case in a non-rotating manner, and the impedance case is opened. It goes without saying that a mandrel serving also as a supply pipe for the impeder cooling water inserted and supported in the pipe-shaped metal strip may be driven to rotate.

It is preferable that the impedance of the above (2) is supported by a cantilever through a thrust bearing made of a non-magnetic material on the anti-mandrel mounting side of the impedance case. In this case, the outer diameter of the impedance core can be adjusted. The filling rate can be increased as much as possible. In addition, the impider core expands and contracts due to high frequency magnetism and changes in volume. Therefore, there is a danger of breakage if the expansion and contraction are held so as to be completely restrained. In particular, ferrite whose material is low in strength is very likely to be broken. It does not break because it expands and contracts in the direction.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The same parts as those in the related art are denoted by the same reference numerals, and detailed description will be omitted.

FIG. 1 is a partial longitudinal sectional view showing an example of an impedance 40 according to the present invention. In the figure, reference numeral 5 denotes an impedance core. The impeder core 5 is a cylindrical body made of ferrite, silicon steel or amorphous metal, and one end in the axial direction is cantilevered in a cylindrical impeder case 6 made of a nonmagnetic material such as glass epoxy. It is decorated. On the other end, a hollow mandrel 7
A rotating blade 11 that is rotated by the impeder cooling water 9 supplied into the impeder case 6 through the shaft is fixedly mounted coaxially. In addition, 6a in the figure is a discharge hole of the impeder cooling water.

Here, it is preferable that the rotary blade 11 has a blade shape as used in an axial flow pump, but is not limited to this. In addition, when the cantilever support 10 of the impedance core 5 with respect to the impedance case 6 is preferably provided with a thrust bearing 12 for smooth rotation. Further, the rotor blade 11 and the thrust bearing 12 are preferably made of a non-magnetic material such as glass epoxy, ceramics or the like, similarly to the above-described impedance case 6, since a large amount of high-frequency magnetic flux also flows into these portions. In consideration of the above, it is most preferable to use a high-strength ceramic such as silicon nitride.

When the impeller 40 constructed as described above is used in place of the impeder 4 constituting the conventional electric resistance welded pipe welding apparatus shown in FIG.
The impeller cooling water 9 supplied through the rotor rotates the impeller 11, and the impeller core 5 constantly rotates with the rotation of the impeller 11, so that the circumferential temperature distribution of the impeller core 5 becomes uniform and The temperature is suppressed to be low, and the decrease in the magnetic permeability of the impedance core 5 due to the temperature rise is small, and the welding efficiency is improved. In addition, since the outer diameter of the impeder core 5 can be increased by making the outer diameter of the impeder case 6 closer to the inner diameter of the impeder case 6, the filling rate can be increased. Furthermore, since the rotation of the impedance core 5 is performed only by the supply of the impedance cooling water 9, energy saving can be achieved.

The direction of rotation of the impeder core 5 is not particularly limited, and the impeder core 5 may be rotated in either the left or right direction. Further, the rotating blade 11 may be provided on the cantilever support 10 side, but in this case, it is needless to say that the rotating direction must be the same. Further, the impeder 40 shown in FIG. 1 may be rotated by 180 ° and inserted and arranged in the metal body 3 to discharge the impeder cooling water 9 downstream (to the right in FIG. 4) in the welding progress direction. Good.

The effect of uniformizing the temperature in the circumferential direction and the effect of suppressing the temperature rise due to the rotation of the impeder core 5 can be obtained more reliably as the rotation speed is higher, but it is sufficient if the rotation speed is 30 rpm or more. However, if the speed is too high, the rotor 11
While the life of the shaft support 10 and the thrust bearing 12 is shortened, the supply pressure of the impeller cooling water 9 needs to be increased, and energy saving cannot be achieved.
pm or less. In this case, the supply pressure of the impeder cooling water 9 is equal to the normal industrial water pressure (0.4
Mpa) is sufficient.

The impeder 40 shown in FIG. 1 is the most preferable example which can be applied to a small-diameter and thick-walled pipe having a small cross-sectional area in the pipe to increase the outer diameter of the impeder core, in other words, the filling rate thereof. For a large-diameter thin-walled pipe having a large area, an impedance 41 as shown in FIG. 2 may be used. That is, the annular bearing 13 formed with a plurality of concave notches 13a forming a plurality of concave cutouts 13a in the circumferential direction between the inner surface of the impeder case 6 and the inner surface of the impeder case 6 is arranged at both ends of the impeder core 5 to be supported at both ends. Is also good. In this case, if the impeder core 5 is made of ferrite, it may be damaged by expansion and contraction as described above. Therefore, it is desirable that the annular bearing 13 is externally fitted via a suitable non-magnetic elastic material.

It is to be noted that silicon steel or amorphous thin plates are laminated via an insulating foil plate to form an impeder core 5 having a predetermined shape.
In this case, it is necessary to stack thin plates having a fan-shaped cross section radially around the rotation axis or to stack disk-shaped thin plates in the axial direction of the rotation axis. this is,
When the lamination direction is laminated in the radial direction perpendicular to the rotation axis direction, there is anisotropy in the magnetic characteristics. When this is rotated, the lamination direction changes with respect to the high-frequency induction magnetic flux, and the magnetic characteristics are changed. The reason for this is that the magnetic characteristics do not fluctuate with the rotation of the core when the layers are stacked as described above.

However, when disk-shaped thin plates are laminated in the axial direction of the rotation axis, the impedance core 5 itself generates heat and magnetic properties are deteriorated, which is not preferable. That is, the high-frequency induction magnetic flux at the position where the impedance core 5 is disposed has a larger axial magnetic flux than the circumferential magnetic flux, and the resistance to the eddy current generated by the axial magnetic flux is small. Flows in each of the thin plates, and the thin plates generate heat, thereby deteriorating the magnetic characteristics. On the other hand, when the thin plates having a fan-shaped cross section are laminated radially around the rotation axis, such a situation does not occur. Therefore, it is most preferable to laminate radially.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The conventional welding method using an impeder in which the impeder core is non-rotating and the method of the present invention using an impeder in which the impeding core is rotatable are used to manufacture the same ERW pipe under the conditions shown in Table 1. The heat input (kV · A) required for normal welding at the speed was examined. The result is shown in FIG.

The work coil has a downstream end (right side in FIG. 4) at a position 110 mm away from the center of the squeeze roll, and the impeder core has a downstream end (same as above) at a position 30 mm away from the center of the squeeze roll. Respectively. In the method of the present invention, the impeder core was rotated at 30 rpm. Further, the joining point between the two end faces of the metal band at this time was a position separated by 30 ± 3 mm from the center of the squeeze roll to the upstream side.

[0035]

[Table 1]

As is apparent from the results shown in FIG. 3, in the case of the method of the present invention, the required heat input at the same welding speed can be reduced by about 25% as compared with the conventional method. In other words, the welding speed when welding with the same heat input is about 25% faster, and highly efficient welding can be performed.

[0037]

According to the present invention, it is possible to reduce the decrease in magnetic properties due to the heat generated by the impedance core during high-frequency welding, and to improve the welding efficiency of the ERW steel pipe.

[Brief description of the drawings]

FIG. 1 is a partial longitudinal sectional view showing an example of an impeder of the present invention.

FIG. 2 is a partial vertical sectional view showing another example of the impeder of the present invention.

FIG. 3 is a view showing a result of an example.

FIG. 4 is a schematic view showing an example of a conventional ERW pipe welding apparatus.

FIG. 5 is a diagram illustrating an example of temperature dependence of saturation magnetic flux density (magnetic permeability) of Mn—Zn-based ferrite used for an impedance core.

FIG. 6 is a diagram illustrating a temperature distribution of an impedance core in a conventional impedance.

[Explanation of symbols]

1: High frequency power supply, 2: Work coil, 3: Metal band, 3a: Edge part, 3b: Bottom part, 4: Conventional impedance, 5: Impeder core,
6: impedance case, 6a: discharge hole,
7: Mandrel, 8: Squeeze roll,
9: Impeder cooling water, 9a: Impeder cooling water passage, 10: Cantilever shaft support, 11: Rotor blade, 12: Thrust bearing, 13: Annular bearing, 13a: Concave cutout, 40: Impeder of the present invention, 4
1: Impeder of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-237668 (JP, A) JP-A-8-187580 (JP, A) JP-A-2-114184 (JP, U) (58) Survey Field (Int. Cl. ⁷ , DB name) B23K 13/00

Claims (2)

(57) [Claims] 1. A metal strip is passed through a forming roll group composed of a plurality of stands, and both edges in the width direction are sequentially bent into an open pipe shape facing each other, and then both edges are melted by using a high-frequency induction heating means. A method for welding an electric resistance welded pipe, which is heated and then subjected to an abutment welding by a squeeze roll, wherein the welding is performed while rotating an impedance core disposed in the bent open pipe-shaped metal strip. Pipe welding method. 2. An impeller core body is rotatably provided in an impedance case, and an impeller cooling water supplied into the impedance case is provided on one or both end faces of the impedance body in the front and rear directions in the axial direction. An impeder characterized by fixedly mounted rotating rotors.