JPH05131285A - Manufacture of welded tube - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a method for welding two metal strips by downwardly welding two edges of the two metal strips to be welded, the upper and lower edges being to be welded. With the goal. [Structure] Two steel strips H are formed through a plurality of roll forming stands so that the widthwise cross sections of both steel strips H are semi-circular, and the upper edge portion to be welded has a welded pipe. The upper side welding position Q is irradiated with the laser beam 9 from above in the radial direction, and the lower edge portion to be welded passes between the upper side welding edges and is obliquely above the lower side edge from the lower side welding position Q ′.
A laser beam 9'is irradiated to the upper side and the lower side two edge portions are melted downward.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a welded pipe, and more particularly to a method for producing a thin welded pipe having a wall thickness / outer diameter ratio of 1% or less.

[0002]

2. Description of the Related Art FIG. 1 was proposed by the present inventor (Japanese Patent Application No. 3-25).
No. 761) is a schematic perspective view showing a process of manufacturing a welded pipe by passing two steel strips as raw material metal strips of the welded pipe through a plurality of roll forming stands. The steel strips H, H are erected on their surfaces and fed from the uncoilers 1, 1 to the leveler 2 in parallel with each other, flattened by the leveler 2 and fed to the roll forming machine. The roll forming machine is provided with a pair of rolls for forming each of the steel strips H, H in a coaxial direction with the leveler 2 and the steel strips H, H with the axial direction vertical. And a pair of fin pass rolls 5 and 5 for forming each of the steel strips H and H in the conveying direction of the steel strips H and H. Are installed in series in order.

The steel strips H, H are each conveyed between the breakdown rolls 3, 3 ... And bent so that their inner peripheral surfaces face each other, and the fin passes rolls 5, 5 ,. Is sequentially bent symmetrically so that the cross-section in the width direction becomes a semicircular shape, and becomes an open pipe in which the opposite edges of the steel strips H, H face each other on the upper side and the lower side. afterwards,
Both edges of the steel strip H are heated by a welding machine, a part of which is 7 ", and lateral pressure is applied by the squeeze roll 6,
Alternatively, the opposite edge portions are butt-welded with no lateral pressure.

When high-frequency welding is used as the welding method used in the above-mentioned manufacturing method, it is difficult to evenly press the two welded portions when pressure welding is performed by the squeeze roll after heating the weld end surface. There was a case where the amount of pressurization increased and the welded part became misaligned. As a preventive measure, the present inventor has proposed a method using a fusion welding method (Japanese Patent Application No. 3-276888).
No.).

When the fusion welding method is used, the welding quality is improved as compared with high-frequency welding, but the fusion welding method is said to have a large difference in stability and workability depending on the welding direction. Things are desirable. In the proposed manufacturing method, the welding positions are present at two opposite positions. When the welding machine is symmetrically arranged outside the steel strip, when the edge parts are arranged vertically, the two welding positions are One is facing down and the other is facing up. When the edge portions are arranged on the left and right, both are horizontal welded, and the best fusion welding method cannot be obtained.

[0006]

Therefore, the following method has been used to perform the downward welding on the two edge portions. FIG. 2 is a schematic perspective view showing a process of welding two steel strips by the TIG welding method. Finn Pass Roll 5,5
Steel strips H, H sent to ... are sequentially bent into a circular cross section,
The edge portion is preheated by the preheating high-frequency welding machine 7 ', 7'. Then, the steel strips H, H are melted by the TIG welding machines 7, 7 and a slight lateral pressure is applied by the squeeze roll 6 to weld the edge portions.

FIG. 3 is an enlarged sectional view taken along the line III-III in FIG. 2, where 7T and 7T are welding torches. The upper edge part is welded downward by the welding torch 7T arranged above the weld pipe, and the lower edge part is the welding torch arranged inside the weld pipe.
Welded downward from the inner surface side with 7T. However, in this method, as shown in FIG. 3, the inner diameter of the welded pipe must be larger than the size that allows the welding torch 7T to be arranged vertically downward on the welding surface, and the welding torch 7T exists in the welded pipe. When troubles such as spatter adhesion occurred at the tip of the tube torch 7T, it was necessary to cut the welded pipe and adjust it.

The present invention has been made in view of the above circumstances, and a method of manufacturing a welded pipe capable of obtaining high weld quality by melting and welding two welding positions downward regardless of the inner diameter of the welded pipe. The purpose is to provide.

[0009]

In the method for manufacturing a welded pipe according to the first aspect of the present invention, two metal strips are passed through a plurality of roll forming stands, and the widthwise cross sections of the two metal strips are semicircular. A method of manufacturing a welded pipe, which comprises:
It is characterized in that the upper and lower edge portions of the two metal bands to be welded are respectively irradiated with laser beams from above the both metal bands to perform downward welding. In the method for manufacturing a welded pipe according to the second aspect of the invention, an elliptical laser beam having a major axis in the longitudinal direction of the metal strip is applied to the lower edges of the metal strips to be welded to the lower edges of the metal strips. It is characterized by irradiating obliquely downward and laser welding.

[0010]

In the method of manufacturing a welded pipe of the present invention, laser welding is used. Since the laser welding method transfers energy by light, it propagates in the atmosphere without spreading and without attenuation. When irradiating a laser beam to the edge part of the lower surface of the metal strip to be welded, the laser beam passes through a slight distance between the opposing edge ends on the upper side, and the inner edge of the welded pipe Since the downward welding can be performed from above, the downward welding can be performed at the two edge portions of the upper side and the lower side to be welded. Further, by using an elliptical laser beam having a major axis in the longitudinal direction of the metal strip at the lower edge portion, the laser beam spot can be made smaller, so that the welding quality can be further improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 4 is a schematic perspective view showing a process of welding two steel strips according to the present invention, and FIG.
It is a V line expanded sectional view. In the figure, H and H are two steel strips as raw material metal strips for the welded pipe, and the steel strips H and H are raised from their surfaces and fed from the uncoilers 1 and 1 in parallel to each other, The leveler 2 is flattened and sent to a roll forming machine. The roll forming machine is provided with a pair of rolls for forming each of the steel strips H, H in a coaxial direction with the leveler 2 and the steel strips H, H with the axial direction vertical. And a pair of fin pass rolls 5 and 5 for forming each of the steel strips H and H, and the breakdown rolls 3 in the conveying direction of the steel strips H and H.
3 ..., fin pass rolls 5, 5 ... are installed in series in this order.

The steel strips H, H are respectively conveyed between the breakdown rolls 3, 3 ... And bent so that their inner peripheral surfaces face each other. Is sequentially bent symmetrically so that the cross-section in the width direction becomes a semicircular shape, and becomes an open pipe in which the opposite edges of the steel strips H, H face each other on the upper side and the lower side. Focusing heads 8 ', 8 of the laser welding machine are provided above the open pipes at positions downstream of the fin pass rolls 5, 5 ...

In the focusing head 8 ', the beam axis passes between the upper welding edges, and the upper and lower welding positions Q,
It is fixed toward the lower welding position Q by inclining it to the downstream side in the transport direction with respect to the vertical line connecting Q ′. Further, a focusing head 8 is fixed downstream of this so that the beam axis is in the vertical direction passing through the upper welding position Q. The upper and lower edge portions are welded by the laser beam focused by the focusing heads 8 and 8'and abutted by the squeeze roll 6.

FIG. 6 is an enlarged cross-sectional view of the vicinity of the welded portion in FIG. A final mirror A is installed in the focusing head 8 so that a laser beam emitted from a laser source (not shown) is reflected and passes through the upper welding position Q and is focused at the upper welding position Q. Then, inside the focusing head 8 ', the final mirror A'is focused such that the laser beam emitted from a laser source (not shown) is reflected and passes through the lower welding position Q'. Is installed. The laser beam 9 focused on the upper welding position Q by the final mirror A installed on the focusing head 8 welds the upper edge portion downward.

The final mirror A'installed on the focusing head 8'passes between the upper welding edges, and the laser beam 9'focused at the lower welding position Q'welds the lower edge portion from the inside of the welded pipe downward. To do. Immediately above the upper and lower welding positions, argon gas jet nozzles C, C'for removing plasma of metal vapor generated during welding.
Are installed respectively. Since the jet nozzles C and C'have a very small height compared with a torch for MIG welding or the like, they are not restricted by the inner diameter of the welded pipe. Further, the ejection nozzles C and C'are devices that only eject gas, and there is no risk of spatter adhesion or wire clogging such as torch in MIG welding.

Next, various conditions of the laser beam will be described. Similar to FIG. 6, FIG. 7 is an enlarged cross-sectional view of the vicinity of the welded portion in FIG. 5, and each size is indicated by a symbol. FIG. 8 is a top view of the welded pipe shown in FIG. 7 as seen from above. The condition setting of the laser beam according to the method of the present invention is to prevent the laser beam for welding the lower edge portion from contacting each of the upper edge portions facing each other.

In general, a laser beam is formed by focusing a parallel beam having a diameter of several tens of millimeters on a welding point with a lens or a mirror. Therefore, the output beam diameter of the final mirror A ′ is d, the beam length (distance between the beam output point and the lower welding position) is L,
Welded pipe diameter D, welded pipe wall thickness t, laser beam irradiation angle θ
₁ and P is the intersection of the laser beam and the upper edge of the steel strip H ', the upper welding position of the welded pipe is Q, and the lower welding position is Q', the beam diameter dl at the intersection P is

[0018]

[Equation 1]

Further, as shown in FIG. 8, the shape of the upper edge portion in the vicinity of the welded joint can be regarded as intersecting substantially linearly except in the vicinity of the welding point pole, and the crossing angle of the upper edge portion can be considered. When the the theta _2, the upper edge distance W at the intersection point P of the upper edge portion and the laser beam is W = 2 (D-t) tan θ 1 · tan (θ 2/2) ... (2) where Since the laser beam does not come into contact with the upper edge of the steel strip H ', dl <W ... (3), so from equations (1), (2), and (3)

[0020]

[Equation 2]

Generally, θ ₂ is 2 to 5 ° and d is 50 to 100 mm.
Therefore,

[0022]

[Equation 3]

As is clear from the equation (5), the beam length L> 1200 to 5800 even when the laser beam irradiation angle θ ₁ = 30 °.
mm, and when θ ₁ <30 °, that is, a very large-scale device is obtained by an irradiation method close to vertical, and the spot diameter ρ of the laser beam is ρ = L · λ / (π · d) (6) According to the equation (6), the beam length L increases as it increases, and the degree of spot concentration decreases. Here, λ is the wavelength of the laser light, and π is the circular constant.

FIG. 9 is an enlarged sectional view taken along line IX-IX in FIG. Let elliptic radius in the longitudinal direction of the welded pipe be dL, elliptic radius in the direction orthogonal to this be dS, and ellipticity r = dL / dS.
Equation (5) is

[0025]

[Equation 4]

Therefore, when dL> dS, the L value becomes small. In this case, the spot diameter ρ _L (conveying direction) and the spot diameter ρ _S (orthogonal direction) are the original ρ and

[0027]

[Equation 5]

It can be seen that the relationship of (3) holds and that the degree of concentration of spots improves as the ellipticity r increases. Further, when the beam length L is kept constant, the irradiation angle θ ₁ of the laser beam becomes smaller as the ellipticity r becomes larger, and the welding quality is improved closer to vertical downward welding. However, when the ellipticity r is increased, the size of the mirror A ′ is also required, and therefore the ellipticity r is preferably set to about 2 or 3 in practice.

Next, the results of laser welding using the above-described apparatus under the following conditions are shown in Table 1 in comparison with those by MIG welding. Test material: Outer diameter 101.6mm, wall thickness 0.8mm, material API standard line pipe X-65 equivalent material Welding speed: 1m / min Laser beam diameter d: 50mm Upper edge angle θ ₂ : 3 ° Beam length L: 2000 mm

[0030]

[Table 1]

As shown in Table 1, in the conventional method of arranging the welding machine symmetrically on the outside of the welded pipe and performing MIG welding and laser welding, the welding quality of the upper side is good, but there are defects on the lower side. The results of welding the lower edge portion with the laser beam irradiation angle θ ₁ = 30 ° by the method of the present invention are high, and the result is that the upper welding quality is good and the lower edge has a small hole (porosity). Was slightly recognized. In addition, the downward welding of the lower edge of the MIG welding method could not be measured because the welding torch could not be inserted into the welded pipe. Further, the results of observing the welding quality on the lower side by changing the ellipticity r and the irradiation angle θ ₁ of the laser beam under the same conditions as described above by the method of the present invention are shown in Table 2.
Shown in.

[0032]

[Table 2]

As shown in Table 2, as the ellipticity r is increased or the irradiation angle θ ₁ is decreased, that is, the vertical downward direction is approached, the welding quality on the lower surface side becomes better. still,
In the embodiment of the present invention, the laser beam is focused directly on the lower welding position of the welded pipe through the upper edge portion of the welded pipe, but it is possible to adjust the laser beam inside the welded pipe or between the laser beam emitting position and the lower welding position. It doesn't matter if the optical system is inserted.

[0034]

As described above, in the method for manufacturing a welded pipe of the present invention, since the two welding positions of the upper side and the lower side can be melt-welded downward regardless of the inner diameter of the welded pipe, high welding is possible. You can get quality. Further, the present invention has excellent effects such as further improving the welding quality by making the laser beam with which the lower edge portion of the metal band is irradiated into an elliptical shape having a long system in the longitudinal direction of the metal band. ..

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a process of manufacturing a welded pipe from two metal strips by a conventional method.

FIG. 2 is a schematic perspective view showing a state in which two edge portions are melt-welded downward by a conventional method.

FIG. 3 is an enlarged sectional view taken along line III-III in FIG.

FIG. 4 is a schematic perspective view showing a state in which two edge portions are melt-welded downward according to the present invention.

5 is an enlarged sectional view taken along line VV of FIG.

FIG. 6 is an enlarged cross-sectional view of the vicinity of the welded portion in FIG.

7 is an explanatory view showing respective sizes by symbols in the enlarged cross-sectional view of FIG.

8 is a top view of the welded pipe shown in FIG. 7 as seen from above.

9 is an enlarged sectional view taken along line IX-IX in FIG.

[Explanation of symbols]

7 TIG welding machine 7'High frequency preheating welding machine 7 "High frequency welding machine 8,8 'Laser welding machine (focusing head only) 9,9' Laser beam A, A'Final mirror C, C'Spout nozzle D Outside welding tube Diameter H Steel strip L Beam length of bottom welding laser P P Intersection of laser beam and edge of welded pipe upper surface Q Welded point of welded pipe upper surface R Welded point of welded pipe lower surface W Edge distance at intersection P d Output beam diameter dL Elliptic radius (conveying direction) dS Elliptic radius (vertical direction) r Ellipticity θ ₁ Laser beam irradiation angle θ ₂ Top edge crossing angle

Claims (2)

[Claims] 1. Two metal strips are formed through a plurality of roll forming stands so that the widthwise cross sections of both metal strips are semi-circular, and the corresponding edges of both metal strips are positioned above and below. A method of manufacturing a welded pipe in which two metal strips are opposed to each other on the lower side and are welded to each other. A method for manufacturing a welded pipe, which comprises performing downward welding. 2. An oval-shaped laser beam having a major axis in the longitudinal direction of the metal strips is radiated obliquely downward to the lower edges of both metal strips to be welded. The method for manufacturing a welded pipe according to claim 1, wherein laser welding is performed.