JP2001058267A - Welding method for steel and inserting member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding method for steel by which proper welding work can be performed by suppressing an arc blow with simple work, and to provide an inserting member used for this method. SOLUTION: This welding method for steel by arc welding has a degaussing stage in which magnetic field strength in a groove 2 formed between a base material and another base material is reduced in advance, and a welding stage in which arc welding is performed to the groove 2. In the degaussing stage, the inserting member 4 having a ferromagnetic is inserted in the groove 2 near starting point 3 of welding, and the magnetic field strength at the starting point 3 of welding is localy lowered comparing with other magnetic field strength of parts to be welded. In welding stage, the starting point 3 of welding, where the magnetic field strength is reduced, is welded.

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 steel and an insert member used in the method, and more particularly to a technique capable of performing arc welding without being affected by arc blow when welding a groove.

[0002]

2. Description of the Related Art When arc welding is performed on steel materials without considering the effects of arc blowing at all, defects may occur in the welds. This arc blow is guided by Fleming's left-hand rule, and is caused by the interference between the magnetic field formed in the welded portion due to the influence of external magnetic fields such as residual magnetism and geomagnetism in magnetic flaw inspection and the magnetic field created by the welding arc. This is a phenomenon in which an external force acts on the welding arc and its straightness is impaired. The arc blow causes one-side melting of the portion to be welded and an increase in the amount of spatter (metal particles scattered during welding), and also causes welding defects such as blow holes (holes).

[0003] This arc blow is particularly remarkable in butt welding of steel pipes such as gas pipes. In order to make the welding operation difficult, conventionally, the following measures have been taken to suppress the arc blow. Was adopted.

[0004] This method utilizes magnetic hysteresis, and is a method of performing welding after demagnetizing the residual magnetism of a portion to be welded using a demagnetizing device for demagnetizing. Specifically, in the welding operation of a steel pipe such as a gas pipe, as shown in FIG. 6, the captire cord 52 is wound around the welded portion of the steel pipe 50, that is, the butt portion 51 a plurality of times, and both ends of the captire cord 52 are connected. The residual magnetism of the welded portion 51 is demagnetized using a simple demagnetizing device connected to the DC welding machine 53.

More specifically, in the process of supplying the exciting current, the connection between the cap tire cord 52 and the DC welding machine 53 is reconnected each time, and the exciting current having a different polarity is applied to the cap tire cord 52 a plurality of times to thereby form a welded portion. The demagnetization of the residual magnetism prevents arc blow.

In this method, an alternating magnetic field is applied a plurality of times to the magnetic field formed at the welded portion of the steel pipe 50, and the magnetic field strength of the welded portion is gradually weakened before welding. Here, the alternating magnetic field means a magnetic field in which the direction of the magnetic field is reversed after a certain period of time. In the welded portion where the magnetic field strength is reduced, the arc blow is suppressed.

[0007] Another method is to measure the magnetic force of the welded portion and then perform welding using the demagnetizing device while applying a reversing magnetic field having a polarity opposite to that of the magnetic field of the welded portion and having the same strength. is there. That is, a method in which a reversing magnetic field capable of canceling out the magnetic field formed in the welded portion is formed around the welded portion, the magnetic field intensity of the welded portion is apparently reduced, and welding is performed during that time.

[0008]

However, the above-mentioned conventional method has the following problems. Even if the residual magnetism of the portion to be welded is demagnetized by the demagnetizing device, it is only temporary, and after a short time after demagnetization, the portion to be welded is magnetized again by magnetism from the undemagnetized portion. In particular, in the case of a long steel material such as a steel pipe, it is difficult to wind the cap tie cord around the entire steel material, and it is practically difficult to demagnetize the residual magnetism of the entire steel material. Therefore, there was a problem that work efficiency was poor.

When welding is performed while applying a reversing magnetic field having a polarity opposite to that of the magnetic field of the portion to be welded and having the same strength, there are the following problems. Normally, the magnetic field strength of a portion to be welded of a steel material differs from part to part, and precise magnetic force measurement is required to form a reversal magnetic field that cancels out the magnetic field of the part to be welded. In addition, it was necessary to finely control and correct the exciting current flowing through the cap tire cord, and careful work was required. In particular, when the welded product was a steel pipe, the magnetic field strength of the welded portion was significantly varied, and the magnetic field could not be easily offset.

As described above, the demagnetization work is complicated in the conventional method, and the effect is not sufficient. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a welding method for a steel material capable of effectively suppressing arc blow with a simple operation and performing an appropriate welding operation, and an insertion member used for the method. And

[0011]

According to the present invention, there is provided a method for welding steel by arc welding, wherein the magnetic field strength of a groove formed between a base material and a base material is reduced in advance. And a welding step of performing arc welding on the groove.In the degaussing step, an insertion member having ferromagnetism is inserted into the groove near the welding start point to reduce the magnetic field strength at the welding start point. In the above welding step, the magnetic field strength is locally reduced as compared with the magnetic field strength of the other welded parts, and the welding starting point where the magnetic field strength is reduced is used as a method of welding steel.

The main components of the present invention will be described below. (Arc welding) An arc is generated between a metal or a carbon electrode and a metal, and welding is performed using the heat. (Groove) A groove is a space formed between the end faces of the base material facing each other and is a welded part. The groove may be V-shaped, I-shaped, U-shaped, X-shaped, Y-shaped, or any other conventionally used shape. (Base material) An object to be welded, such as steel, including not only steel pipes but also steel plates and round bars. The shape is not particularly limited as long as the portion to be welded is groove-welded.

(Insertion member) A ferromagnetic substance such as iron, cobalt, nickel, or a compound thereof, or a ferromagnetic substance including these, for example, a ferromagnetic layer formed on the surface is suitable. It is desirable that the insertion member has a shape capable of contacting each of the facing groove surfaces. In addition, at least a part thereof has a substantially triangular prism-shaped appearance having two planes that intersect at substantially the same angle with the corresponding groove, and the two surfaces are in surface contact with each of the facing groove surfaces. Is preferred.

By inserting the insertion member into the groove, it is sufficient that the insertion member comes into contact with the groove or the clearance of the groove becomes small. In short, it is only necessary that the magnetic permeability of the groove is larger than the case where nothing is inserted, so that the insertion member may be arranged in contact with the groove surface, or may be slightly floated from the groove surface. It is possible. In addition, it is necessary to arrange the insertion member so that the clearance between the insertion member and the groove surface is sufficiently smaller than the root interval of the groove (a portion where the clearance of the groove becomes minimum).

(Welding start point) The welding start point is a portion where welding is first started on a portion to be welded having a predetermined length.
The insertion member can be inserted into the portion to be welded, and the vicinity of the insertion member can be set as the welding start point. Here, the welding is preferably main welding such as clamp welding, but may be tack welding.

According to the method of the present invention, when a ferromagnetic insertion member is inserted into a groove, the magnetic permeability of the portion to be inserted into which the insertion member is inserted is higher than the magnetic permeability of the other portions to be welded. As described above, the magnetic flux density near the insertion member becomes locally sparse and the magnetic field strength decreases. In this way, by changing the traveling direction of the magnetic force lines running linearly on the groove, a portion where the magnetic flux density becomes low and the magnetic field intensity decreases is provided in the groove, and the portion where the magnetic field intensity decreases is welded. In other words, by inserting an insertion member having a high magnetic permeability into the groove, magnetic lines of force running linearly from one groove surface to the other groove surface are guided to the insertion member, and the magnetic flux density is sparse in the groove. Is formed. Therefore, welding can be performed at the groove where the magnetic flux density is low without being affected by arc blow.

Further, the degaussing step and the welding step may be repeated a plurality of times on the portion to be welded to weld the entire portion to be welded. In other words, this is a welding method in which a plurality of welding start points having a low magnetic field strength are provided in the welded portion, and the plurality of welding start points are welded to weld the entire welded portion. In this case, a plurality of insertion members may be prepared in advance, and the plurality of insertion members may be inserted into the portion to be welded to provide a plurality of welding start points at once. Further, as for the welding at the plurality of welding start points, welding may be performed simultaneously at a plurality of locations, in addition to sequentially welding each one.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a welding method and an insertion member according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a butt-welded portion of a steel pipe adopting the welding method of the present invention, and FIG. 2 is a diagram showing an insertion member inserted into a groove. FIGS. 3 and 4 are magnetic field lines distribution diagrams near the groove. FIG. 5 is a view showing an insertion member having another shape.

First, the working steps relating to the welding method of the present invention will be schematically described. In the present embodiment, the work to be welded is a steel pipe 1 and the work to be welded is a V-shaped groove 2. The work process is divided into a degaussing process for previously reducing the magnetic field strength of the groove 2 and a welding process for performing arc welding of the groove 2. In the degaussing step, the insertion member 4 having ferromagnetism is inserted into the groove 2 near the welding start point 3 to locally lower the magnetic field strength at the welding start point 3 as compared with the magnetic field strength of the other grooves 2, In the welding step, welding is performed at the welding start point 3 where the magnetic field strength has decreased. In the present embodiment, a description will be given of a method in which a plurality of insertion members 4 are inserted into the groove 2 in advance, and the groove 2 located between the insertion members 4 is clamp-welded.

(Demagnetization Step) The insertion member 4 inserted into the V-shaped groove 2 in the demagnetization step is inserted into the groove 2 located on both sides of the welding start point 3 as shown in FIG. That is, the groove 2 located between the insertion members 4 is the welding start point 3. The interval T between the insertion member 4 and the insertion member 4 is determined by an empirical rule in consideration of the magnetic field strength of the groove 2, and is set to about 50 mm to 200 mm in butt welding of a steel pipe having an outer diameter of 750 mm. .

The insertion member 4 is made of metal and has a substantially triangular prism shape as shown in FIG. More specifically, it is processed into a triangular prism having two planes 5 intersecting at the same angle with the groove angle θ of the corresponding groove 2. When welding steel pipes having an outer diameter of 750 mm, the length is 50 mm.
It was about 200 mm.

Further, the insertion member 4 includes a groove surface 6 of the V-shaped groove 2.
Are arranged in surface contact with the respective slopes 7 formed on the surface. That is, the groove surfaces 6 of the steel pipes 1 facing each other come into contact with each other through the insertion member 4, and the magnetic force lines X that pass the welding start point 3 linearly as shown in FIG. Starting point 3 which is guided by the insertion member 4 having high magnetic permeability
Is transmitted from one steel pipe 1 to the other steel pipe 1 without passing through. Therefore, the magnetic flux density at the welding start point 3 located in the vicinity of the insertion member 4 is lower than the magnetic flux density of the other grooves 2, and the magnetic field strength is clampable.

(Welding step) In the welding step, clamp welding is performed at the welding start point 3 where the magnetic field strength is locally reduced.
The welding operation itself is the same as the conventional method.

In the welding step, the welding start point 3 which is demagnetized in the above-described degaussing step and whose magnetic field strength is lower than the magnetic field strength of the other groove 2 is immediately clamp-welded while suppressing the influence of arc blow. can do.

In the actual steel pipe work, a plurality of insertion members 4 are inserted into a plurality of positions of the groove 2 at intervals, and thereafter, the opening between the adjacent insertion members 4 is inserted. The tip 2 is arc welded. For your reference,
The vicinity of the insertion member 4 subjected to the clamp welding in the welding step has the same effect as the state where the insertion member 4 is inserted. That is, the lines of magnetic force existing near the welded portion concentrate on the welded portion having high magnetic permeability, so that the magnetic flux density near the welded portion decreases and the magnetic field strength decreases. Therefore, the magnetic field strength of the groove 2 to be welded gradually decreases, and eventually, there is no need to insert the insertion member 4.

As described above, since the influence of the arc blow can be easily prevented without using the demagnetizing device, an appropriate arc welding can be performed on the groove 2. Although the insertion member 4 used in the present embodiment has an appearance of a substantially triangular prism, an insertion member 4 having a U-shaped cross section can be used for a U-shaped groove 8 as shown in FIG. . As described above, the cross-sectional shape of the insertion member 4 is preferably similar to the cross-sectional shape of the corresponding groove 2, and may be selected according to the shape of the groove 2 to be welded.

(Test Example) Next, a test example for confirming a decrease in magnetic force by the method of the present invention will be described. Test object The test was performed on a steel pipe having an outer diameter of 750 mm used for an actual gas pipe. Test Method The value of the residual magnetism by the method using the conventional demagnetizer and the value by the method using the insertion member 4 of the present invention were measured and compared. The values of the remanence were measured before and after the demagnetization treatment. In this case, before the demagnetization treatment, the magnetic field strength in a state where nothing was applied to the groove was measured. In the first demagnetization treatment, the magnetic field intensity was measured after the excitation current was applied once to the groove. The second time of the demagnetization treatment was to measure the magnetic field intensity after applying the exciting current twice. When the insertion member was inserted, the insertion member was inserted into the groove subjected to the second demagnetization treatment, and the magnetic field strength was measured. In addition, the measurement performed the magnetic force of the groove | channel 2 used as a to-be-welded part over the perimeter of the steel pipe 1. FIG. Test results The results are shown in Table 1.

[0028]

[Table 1] In Table 1, the measurement position of the groove 2 located in the circumferential direction of the steel pipe,
As shown in FIG. 6, it is represented by the time axis H (clockwise 1
H, 2H, 3H ... 12H), and the unit of magnetic force is G
(Gaussian). As can be seen from Table 1,
In the demagnetization process using the conventional demagnetization apparatus, the magnetic force is not significantly reduced. However, according to the method of the present invention, when the insertion member 4 is inserted, the magnetic force is reduced to approximately half over the entire circumference of the steel pipe 1. I have.

[0029]

As described above, according to the present invention, an idea is adopted in which the insertion member is inserted into the groove to locally reduce the magnetic field strength at the welding start point as compared with the magnetic field strength of other welded parts. By doing so, it is possible to provide a method for welding steel materials that can perform arc welding with a simple operation and perform an appropriate welding operation.

Further, it is possible to provide the insertion member 4 which can easily prevent the arc blow only by being inserted into the groove.

[Brief description of the drawings]

FIG. 1 is a view showing butt welding of steel materials to which a welding method of the present invention is applied.

FIG. 2 is a view showing an insertion member according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating a magnetic field line distribution near a groove where an insertion member is not inserted.

FIG. 4 is a diagram illustrating a magnetic field line distribution near a groove where an insertion member according to an embodiment of the present invention is inserted.

FIG. 5 is a view showing an insertion member having another shape according to the embodiment of the present invention.

FIG. 6 is a diagram showing the magnetic force measurement points of the steel pipe related to Table 1.

FIG. 7 is a diagram showing a conventional demagnetization method.

[Explanation of symbols]

 Reference Signs List 1 steel pipe 2 groove (welded portion) 3 welding start point 4 insertion member 5 plane of insertion member 6 groove surface 7 slope 8 U-shaped groove θ groove angle X magnetic field line 50 steel pipe 51 butted portion (welded portion) 52 Captire cord 53 DC welding machine

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yasuo Unemoto 88, Ono-cho, Tsurumi-ku, Yokohama-shi, Kanagawa Japan F-term (reference) 4E001 AA03 CA01 LD20 4E082 EA01 HA03 HA04

Claims (4)

[Claims] 1. A method for welding steel material by arc welding, comprising: a demagnetization step of previously reducing the magnetic field strength of a groove formed between a base material and a base material; In the degaussing step, a ferromagnetic insertion member is inserted into a groove near the welding start point, and the magnetic field strength at the welding start point is locally compared with the magnetic field strength of the other welded parts. A method for welding steel materials, wherein the welding is performed at the welding start point where the magnetic field strength is reduced in the welding step. 2. The method for welding steel material according to claim 1, wherein the degaussing step and the welding step are repeated a plurality of times with respect to the welded portion to weld the entire welded portion. 3. An insert member used in the method for welding steel material according to claim 1, wherein the insert member has a shape that comes into contact with each of the facing groove faces. 4. At least a part of the insertion member has a substantially triangular prism shape having two planes which intersect at substantially the same angle with a corresponding groove angle, and the two surfaces face each other. The insertion member according to claim 3, wherein each of the surfaces is in surface contact.