JP2000271639A - Plated steel tube and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable brazing through a joining surface having a large area and to improve joining strength, corrosion resistance and air tightness by brazing the high part in the width direction with the bottom part in the width direction of a plated steel strip coiled in a spiral state to the high part of the same via the joining surface having a wide area obtained by superposing the high part in the width direction of the plated steel strip having a difference in level on the bottom part of the same. SOLUTION: A tube wall is composed by coiling in a spiral state a plated steel strip which is provided with a difference in level equivalent to the plate thickness at the central part in the plate width direction, and a cylindrical body P is obtained by superposing a (n+1)th round of high part T in the width direction on a nth round of bottom B part in the width direction. Thus, the joining surface F having a satisfactorily wide area is secured. When flux is coated on the joining surface F, brazing filler metal is coated or filled if necessary and the cylindrical body P is heated at a brazing temperature, since the bottom part B in the width direction is brazed to the high part T in the width direction through the side joining surface F, the steel tube having high-joining strength, excellent corrosion resistance and air tightness is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plated steel pipe having high joining strength, excellent workability, corrosion resistance and airtightness, and a method for producing the same.

[0002]

2. Description of the Related Art Corrosion resistance is required for steel pipes that are exposed to corrosive atmospheres, such as when supplying and discharging corrosive substances and when used in corrosive environments. As a steel pipe with improved corrosion resistance, a steel pipe made of an aluminum-plated steel strip is known. In manufacturing an aluminum-plated steel pipe, a method is employed in which an aluminum-plated steel strip is formed into a cylindrical shape by a roll forming method, and both ends in the width direction of the butted or overlapped parts are welded by TIG welding, high-frequency induction welding, or the like. Further, German Patent No. 854608 discloses a method of manufacturing a spiral tube using a copper-plated steel strip as a raw material. In this method, a flat copper-plated steel strip is spirally wound so as to overlap the width direction ends, formed into a cylindrical shape, a core rod is inserted into the cylindrical body, and the inner surface of the cylindrical body is rolled. After smoothing the outer surface, it is brazed by heating.

[0003]

When welding both ends in the width direction formed into a cylindrical shape, a weld bead is formed at the joint, but the heat input during welding causes the welded portion and the nearby plating layer to disappear. Sometimes. In addition, in order to ensure weldability, in the case of an aluminum-plated steel strip or the like, the aluminum plating layer near the weld may be removed in advance. As a result, the corrosion resistance of the welded portion is liable to be significantly deteriorated as compared with the base material portion not affected by the welding. Corrosion resistance is restored by repairing plating by thermal spraying or the like on the welded portion and the vicinity of the welded portion where the plating layer has disappeared, thinned, deteriorated, etc. However, an extra process is required for repairing the plating, which causes an increase in manufacturing cost. In addition, in the case of a small-diameter pipe, the work of repairing plating itself is difficult, and repair of the inner plating layer is practically impossible.

When a pipe is formed by a brazing method that has a significantly smaller heat input compared to welding, a plated layer also exists on the joint after brazing, so that the joint has the same corrosion resistance as the base metal. Present. However, as shown in FIG. 1, when brazing a mating face F in which the end faces of the steel strip S are simply overlapped in the length direction, the end faces are brazed with a small brazing area. Therefore, the joint strength tends to be insufficient, and the workability of the steel pipe in the subsequent processing step cannot be expected much. The brazing area can be increased by winding the plated steel strip in a spiral shape and forming it into a tubular shape, as introduced in DE 854608. in this case,
Since the steel strips overlap almost entirely, a large brazing area is obtained, and the workability of the obtained steel pipe is improved.

[0005] When the outer and inner surfaces of a tubular body in which a plated steel strip is spirally wound are smoothed by rolling, a defect caused by rolling does not occur in the copper plating layer which is rich in ductility.
However, when an aluminum-plated steel strip is used as a material, the alloy layer at the steel / aluminum-plated layer interface is broken by the strain introduced by the rolling process, and defects such as peeling and cracks are easily generated in the aluminum-plated layer. Become.
In the defect occurrence site, not only does the workability deteriorate, but also the exposed steel base becomes the starting point of corrosion, and the corrosion resistance of the aluminum-plated steel pipe as a whole decreases.

[0006]

SUMMARY OF THE INVENTION The present invention has been devised in order to solve such a problem, and a large-area mating surface is formed by spirally winding a stepped plated steel strip. An object of the present invention is to obtain a plated steel pipe having excellent bonding strength, corrosion resistance, and airtightness, which enables brazing through the steel. The plated steel pipe of the present invention achieves its purpose,
A tube wall is formed by spirally winding a plated steel strip having a step corresponding to the sheet thickness at the center in the sheet width direction to form a tube wall, and a width-direction high portion of the (n + 1) th turn is overlapped on the width-direction bottom of the n-th turn. It is characterized in that the mating surface between the bottom in the direction and the high portion in the width direction is brazed.

If the widthwise end of the plated steel strip is preliminarily processed into an inclined end face corresponding to the step shape, a substantially continuous inner and outer surface can be obtained when the plated steel strip is spirally wound. This plated steel pipe has a step corresponding to the plate thickness at the center in the plate width direction of the plated steel strip, and n +
The plated steel strip is spirally formed into a cylindrical body so that the widthwise high portions of the first round are overlapped with each other, and is formed by brazing the widthwise bottom portion and the widthwise high portion. At the time of brazing, after applying flux to the mating surface,
If necessary, apply or fill a brazing material on the mating surfaces. Alternatively, depending on the type of the plated steel strip, self-brazing using a plated layer as a brazing filler metal can also be employed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a steel pipe material, a plated steel strip such as an aluminum-plated steel strip, a zinc-plated steel strip, a zinc alloy-plated steel strip, and a copper-plated steel strip is used. The plated steel strip S having a flat shape is first processed into a cross-sectional shape (FIG. 2) in which a step H substantially equal to the thickness of the blank is provided at the center in the width direction. The step H is formed by roll forming, press forming, or the like. When the long plated steel strip S is used as a material, the step H is preferably formed by a roll forming method. For example, as shown in FIG. 3, when the plated steel strip S is passed between the upper roll 1u and the lower roll 1d for stepping, a step H following the roll profile is formed on the plated steel strip S.
The width direction bottom portion B and the width direction high portion T on both sides of the step H are:
The flat shape similar to the plated steel strip S before processing is maintained.

The plated steel strip S with the step H is sent to a forming stand in which, for example, three forming rolls 2a, 2b, 2c are arranged as shown in FIG. Plated steel strip S
Is bent toward the forming roll 2a by the forming rolls 2b and 2c, and is wound in a spiral shape surrounding the forming roll 2a. When the feeding direction D of the plated steel strip S is inclined with respect to the axial direction X of the forming rolls 2a, 2b, 2c, the plated steel strip S
Are wound on the n-th and (n + 1) -th turns so as to overlap in the width direction. Although the plated steel strip S is loosely wound around the forming roll 2a, since the width direction high portion T overlaps the width direction bottom portion B, the overlapping state of the tube diameter and the tube wall is stabilized. Alternatively, in the case of using the long forming rolls 2a to 2c, the plated steel strip S can be tightly wound around the forming roll 2a.

More specifically, the width direction bottom portion B (FIG. 2) of the n-th cycle is overlapped with the width direction high portion T (FIG. 2) of the (n + 1) -th cycle so as to overlap between the roll axis direction X and the feed direction D. Feed angle θ
(FIG. 5) is set appropriately. The plated steel strip S wound in a spiral shape is formed to a target size by the bending moment applied by the forming rolls 2b and 2c contacting from the outside. At this time, the forming roll 2 with respect to the forming roll 2a
The pipe diameter is adjusted by the positional relationship between b and 2c. The cylindrical body wound in a spiral shape may be formed by a forming roll 2 if necessary.
The roller is fed in the direction of the roll axis a (rightward in FIG. 5).

When the plated steel strip S having the step H is wound around the roll 2a, a spiral cylindrical body P in which the width direction high portion T of the (n + 1) th turn overlaps the width direction bottom of the nth turn.
Is obtained. Since the tube wall of the tubular body P is composed of the flat bottom portion B in the width direction and the high portion T in the width direction, it is sufficiently flat without the need for rolling separately. Stepping rolls 1u, 1d
(FIG. 3) may be arranged on the upstream side of the forming rolls 2a to 2c. With this arrangement, a plated steel pipe is continuously manufactured from the plated steel strip S of the material. The step generated when the width direction bottom portion B and the width direction high portion T are overlapped can be eliminated or suppressed by the end face processing of the plated steel strip S. For example, if the widthwise end of the plated steel strip S is preliminarily worked on the inclined end face corresponding to the step H, when the width direction bottom B and the width direction high part T are overlapped, as shown in FIG. H and width bottom B
The gap between the inner wall and the widthwise high portion T is reduced, and an inner surface and an outer surface that are substantially continuous in the pipe axis direction can be obtained.

When the width direction bottom portion B and the width direction high portion T are overlapped with each other, compared with a mating surface F (FIG. 1) when the width direction end portions of the steel strip S bent in the width direction are simply overlapped. ,
A mating surface F having a sufficiently large area is secured. In brazing, a flux is applied to the mating surface F of the cylindrical body P, and then a brazing material is applied or filled as necessary. In the plated steel strip S in which the plating layer can be used as a brazing material, the application of the brazing material can be omitted. As a plated steel sheet having a plated layer that can be used as a brazing material, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 9-220.
There is a plated steel sheet and the like introduced in Japanese Patent No. 692.

The flux is applied to the plated steel strip S from the flux coating device 3 (FIG. 5) prior to, for example, feeding the plated steel strip S with the step H to the forming rolls 2a to 2c. Alternatively, the flux is also applied by dipping the plated steel strip S in an aqueous liquid containing the flux and drying the mating surface F. When a brazing material is used, for example, a paste-like brazing material is applied to the plated steel strip S before being sent to the forming rolls 2a to 2c or the plated steel strip S wound in a single state around the forming roll 2a from directly above the forming roll 2a. Is done. Even after being formed into a spiral shape, the brazing material can be filled with a gap between the mating surfaces F by slightly twisting the cylindrical body. Next, when the tubular body P is heated to the brazing temperature, the widthwise bottom portion B and the widthwise high portion T are brazed at the wide mating surface F, so that a plated steel pipe having high joining strength and excellent airtightness and workability. Is obtained. Moreover, the processing to be performed on the plated steel strip S is only a step forming processing and a processing of winding in a spiral shape, and there is no processing step such as rolling which tends to introduce defects in the plated layer. Exhibits excellent corrosion resistance equivalent to the material.

[0014]

EXAMPLE As a material, a hot-dip galvanized steel strip having a width of 80 mm and a thickness of 0.8 mm on which a plating layer of Al-10% by weight Si was formed was used. This hot-dip coated steel strip is a self-brazing plated steel strip introduced in Japanese Patent Application Laid-Open No. 9-220692. A plated steel sheet having a length of 1 m is cut out from the plated steel strip and sent to a roll forming apparatus having an upper roll 1 u and a lower roll 1 d with a roll gap set to 0.8 mm, and a 0.8 mm step H extending in a longitudinal direction is plated. It was attached to the center in the width direction of the steel sheet S. The plated steel sheet S with the step H was sent to a forming apparatus provided with the forming rolls 2a to 2c. When the feed angle θ is set to 75 degrees and the plated steel sheet S is fed into the forming rolls 2a to 2c, the plated steel sheet S is placed in a state where the width direction high portion T of the (n + 1) th turn overlaps the width direction bottom B of the nth turn. Tubular body P wound in a spiral shape
Molded into.

A fluoride-based flux was applied to a joining surface F of a bottom portion B in the width direction and a high portion T in the width direction of the cylindrical body P, and the cylindrical body P was charged into a heating furnace maintained in a nitrogen atmosphere. Tubular body P in heating furnace
Was heated to 600 ° C., and then cooled to room temperature to braze the width direction bottom portion B and the width direction high portion T via the mating surface F. The manufactured plated steel pipe is 170mm long
Thus, both the outer surface and the inner surface of the tube had a substantially flat surface state. The outer diameter of the plated steel pipe is approximately 50 mm at the portion where the width direction bottom portion B and the width direction high portion T overlap to form a tube wall.
Met. A brazing layer without defects is formed between the width-direction bottom B and the width-direction high portion T over the entire area of the mating surface F, and the width-direction bottom B and the width-direction high portion T are firmly bonded, The airtightness of the mating surface F was also excellent. Further, the alloy layer between the plating layer and the base steel had no defects introduced therein, and was maintained in the same healthy state as the material.
For this reason, even when a process such as bending or pipe expansion is performed in a later step, there is no peeling of the plating layer, and the same corrosion resistance as that of the material is maintained. In the above embodiment, the aluminum-plated steel strip is used as a material. However, when a zinc-plated steel strip, a zinc-alloy-plated steel strip, or a copper-plated steel strip is used as a material, the bonding strength, airtightness, workability, and corrosion resistance are similarly determined. An excellent plated steel pipe was obtained.

[0016]

As described above, the plated steel pipe of the present invention has a wide area mating surface obtained by superimposing a widthwise high portion on a widthwise bottom portion of a stepped plated steel strip.
The bottom part in the width direction and the high part in the width direction of the plated steel strip wound in a spiral shape are brazed. Therefore, a plated steel pipe excellent in the strength and airtightness of the brazed portion can be obtained. Moreover,
Since there is no rolling step for introducing defects into the plating layer, the material exhibits the same corrosion resistance and workability as the material. The plated steel pipe thus obtained is used in a wide range of fields, such as transporting corrosive substances and exposing it to a corrosive atmosphere, utilizing its excellent corrosion resistance.

[Brief description of the drawings]

FIG. 1 A conventional plated steel pipe brazed with a mating surface obtained by simply overlapping widthwise ends.

[Figure 2] Stepped plated steel strip

[Fig. 3] Step roll

FIG. 4 is a view of a forming roll for spirally winding a plated steel strip as viewed from the roll axis direction.

FIG. 5 is a view of a forming roll for spirally winding a plated steel strip viewed from a roll radial direction.

FIG. 6 is a partial cross-sectional view of a cylindrical body in which a plated steel strip is spirally wound.

FIG. 7 is a partial cross-sectional view of a cylindrical body obtained by spirally winding a plated steel strip whose end face has been processed.

[Explanation of symbols]

1u: Upper roll for stepping 1d: Lower roll for stepping 2a to 2c: Forming roll S: Plated steel strip (plated steel sheet) H: Step B: Bottom part in width direction T: High part in width direction F: Fitting surface P: Tube X: Roll axis direction D: Feed direction of plated steel strip θ: Feed angle

Continued on the front page (72) Inventor Hiroshi Asada 1 Tsurumachi, Amagasaki-shi, Hyogo F-term in Nisshin Steel Co., Ltd. Technical Research Laboratory (reference) 4E028 DA01 DA03 DA07

Claims (3)

[Claims] 1. A tube wall is formed by spirally winding a plated steel strip having a step corresponding to the sheet thickness at the center in the sheet width direction to form a tube wall. Is a superposed steel plate, and the mating surface of the width direction bottom and the width direction high portion is brazed. 2. The plated steel pipe according to claim 1, wherein an end in a width direction of the plated steel strip is processed into an inclined end face corresponding to a stepped shape. 3. A step corresponding to the sheet thickness is provided at the center of the plated steel strip in the sheet width direction, and the plated steel strip is overlapped with the widthwise high part of the (n + 1) th turn on the widthwise bottom of the nth turn. A method for manufacturing a plated steel pipe, comprising forming a tubular body in a spiral shape and brazing a bottom portion in a width direction and a high portion in a width direction.