JPH073422A - Method for repairing machined weld bead zone of al-plated electric resistance welded tube - Google Patents

Abstract

PURPOSE:To improve the adhesion of a thermally sprayed metal to a machined zone and improve the corrosion resistance and heat resistance welded tube by regulating the temp. of a machine weld bead zone to a specific value or above and thermally spraying an Al alloy continuously. CONSTITUTION:An aluminum plated steel strip is passed through a tubemaking machine and successively formed into tubular shape by means of forming roll, and the resulting abutting zone is electric resistance-welded. Subsequently, a weld bead is machine, and, while the temp. of this machined zone is >=250 deg.C, an Al alloy is thermally sprayed continuously by means of a low pressure arc thermal spraying method by using an Al alloy wire. By this method, the corrosion resistance and heat resistance of a resistance welded tube, prepared by using an Al-coated plated steel strip as a stock, can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a thermal spray having good adhesion when a coating metal is continuously sprayed onto a weld bead cutting portion of a galvanized electric resistance welded pipe manufactured using an Al-plated steel strip as a raw material. The present invention relates to a method for repairing a weld bead cutting portion of an electric resistance welded pipe that can form a repair layer.

[0002]

2. Description of the Related Art Since an Al-plated steel pipe is excellent in corrosion resistance, weather resistance and heat resistance, it is widely used as a building material, automobile parts, electric equipment material and the like. These galvanized steel pipes were previously manufactured by subjecting steel pipes made by welding or drawing to hot dip plating. However, recently, except for some applications, from the viewpoint of manufacturing cost reduction, a steel strip pre-plated with Al is used as a raw material, and this is sequentially bent in the width direction by a forming roll group, and both end edges of the steel strip are bent. A mainstream method is to manufacture an electric resistance welded pipe by butt-joining the butt joints to form a tubular shape and welding the butt joints by electric resistance welding.

However, in this method, the plating layer in the vicinity of the weld bead is destroyed by the heat during electric resistance welding, so that the original corrosion resistance and heat resistance are impaired at that portion. The weld bead itself forming a part of the surface of the plated electric resistance welded pipe does not originally have a plated layer having such characteristics.

Therefore, as a method of imparting characteristics such as corrosion resistance and heat resistance to a weld bead that does not conventionally have such characteristics and the vicinity thereof, the weld bead is cut and removed after electric resistance welding, that is, the weld bead cutting portion. In addition, a method of spraying a spraying metal wire made of a coating metal by gas flame spraying is practiced. According to this method, a metal wire for thermal spraying is melted and injected into a combustion flame of oxygen and combustible gas (acetylene gas, propane gas, etc.). However, this gas flame spraying method has a limit to the melting amount of the metal wire for thermal spraying per unit time, and when the target sprayed object is running, one spraying gun is equivalent to the surrounding plating layer. Spraying to a film thickness is difficult.
Therefore, there is a problem that performances such as corrosion resistance and heat resistance are significantly inferior to those of the plated layer of the material.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, has good adhesion to the material of the thermal spray repair layer formed on the weld bead cutting portion, and has performances such as corrosion resistance and heat resistance. It is an object of the present invention to provide an excellent method for repairing a bead cutting portion of a galvanized electric resistance welded pipe.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive research to solve the above-mentioned problems, the inventors of the present invention have found that the bead cutting portion of a galvanized electric resistance welded pipe manufactured from an Al-plated steel strip is not repaired by the gas flame spraying method. We focused on arc spraying as a spraying method. This arc spraying method has an advantage that a spraying metal wire is used as an electrode and the spraying amount of the spraying metal wire can be increased or decreased depending on the feeding speed. For example, when performing arc spraying, a reduced pressure arc spraying method (JP-A-61-1674) is used.
No. 72), and the applicant of the present invention has disclosed the method disclosed in Japanese Patent Laid-Open No. 4-20089.
As disclosed in No. 8, if the spraying voltage and the feed rate per hour of the metal wire for spraying are set to appropriate conditions, it will continue to the bead cutting part of the galvanized electric resistance welded pipe, which is the object to be sprayed at high speed. It has been found that it is possible to form a sprayed layer having an arbitrary thickness.

However, in the spray repair of the weld bead cutting portion sprayed by arc spraying, a plated electric resistance welded tube which causes poor adhesion was generated. This is because the manufacturing process differs depending on various conditions such as the thickness of the plated steel strip to be piped, the type of steel, the pipe diameter, etc., and even when the same steel pipe is manufactured, the manufacturing conditions are not always constant due to variations in welding conditions. It can be judged as a reason. Then, as a result of further intensive investigation to improve the adhesiveness and stability of the sprayed repair layer, the temperature of the weld bead cutting part has a great influence on the adhesion between the sprayed repair layer and the base steel. It was clarified that the thermal spraying should be performed while the temperature of the bead cutting portion is 250 ° C. or higher, and the present invention was completed.

That is, according to the present invention, an aluminum-plated steel strip is run, and while sequentially forming a tubular shape by a group of forming rolls, both edges are butted and electric resistance welding is performed, and then a welding bead is cut to spray the cut portion. When repairing the weld bead cutting portion by spraying a metal wire, a reduced pressure internal arc spraying method is used for spraying the metal wire for spraying, and Al-M is used as the metal wire for spraying.
The present invention has been completed by clarifying that it is sufficient to set a sprayed metal of Al alloy wires such as n, Al-Si, and Al-Mg, and to continuously spray the bead cutting portion at 250 ° C. or higher. did.

The method for repairing the weld bead cutting portion of the Al-plated electric resistance welded pipe according to the present invention will be described in detail below. The basic steps of continuously producing a galvanized electric resistance welded pipe using an Al-plated steel strip as a raw material by the method of the present invention are as follows. That is, while moving the plated steel strip horizontally, it is formed into a tubular shape sequentially from the forming roll group of the pipe making machine, and the welded beads are formed by the electric resistance welding at the squeeze roll positions of the abutting portions of both ends of the plated steel strip. The welding bead just after the electric resistance welding is welded with a bite while it is still hot while supporting and passing the electric resistance welded pipe welded and sewn in this way with a support roll so that it does not vibrate horizontally and vertically. The process of cutting the bead, and the temperature of the bead cutting part is 25
From the process of continuously spraying the sprayed metal on the weld bead cutting part with a spray gun inside the vacuum while connected to the arc sprayer inside the vacuum while it is 0 ° C or higher, then cooling and finally straightening with a straightening roll. Become.

In such a process, the feature of the present invention resides in, as described above, that the temperature of the weld bead cutting portion is 250 ° C. or higher and the thermal spray repair is performed by the reduced pressure arc spraying method. . Usually such a spray is
As a pretreatment, it is generally performed after roughening the surface by blasting with shots or grit. However, it is not practical to blast the weld bead cutting portion that continuously travels like a galvanized electric resistance welded pipe because it deteriorates workability in the manufacturing process and increases cost. Therefore, we investigated how the adhesion of the droplets of the metal for thermal spray repair sprayed to the weld bead cutting part changes depending on the temperature after cutting the weld bead. Table 1 shows the results of an investigation of the influence of the temperature of the thermal spray base material on the adhesion of the thermal spray layer.

[0011]

[Table 1]

The experimental results shown in Table 1 indicate that the outer diameter of the Al-plated steel strip having a thickness of 1.2 mm and coated with Al is 25.4 mm.
This is a survey of plated ERW pipes manufactured in
In this Table 1, the adhesion evaluation of the sprayed layer was performed by applying a radius of 5 to the plated ERW pipe that had been sprayed and repaired with the sprayed repaired layer being the outside.
This is the result of judging the adhesion of the thermal spray repair layer according to the following criteria when a 0.8 mm bending process was performed, a cellophane tape was attached to the surface of the thermal spray repair layer, and the cellophane tape was peeled off. ○: No peeling △: Partial peeling ×: Almost peeling

From the results shown in Table 1, in order to obtain a repair layer having stable and good adhesion, it must be carried out while the temperature of the sprayed base metal, that is, the temperature of the weld bead cutting portion is 250 ° C. or higher. I understood. It is considered that this is because when the temperature of the weld bead cutting portion is increased, a metallic reaction easily occurs with the droplets sprayed by the thermal spraying, so that the adhesion is improved. However, the distance from bead cut to thermal spray should be as short as possible.
This is because if the distance is long, the exposure time to the atmosphere becomes long, the oxidation progresses, and the adhesiveness decreases.

[Action]

As described above, by performing the thermal spray repair while the temperature of the weld bead cutting portion is higher than a predetermined value, a stable thermal spray repair layer having good adhesion of the sprayed metal to the weld bead cutting portion and being stable. You can get it. As a method for stably spray-repairing the weld bead cutting portion by the arc-spraying method under reduced pressure, the present inventor et al.
It is preferable to use the method disclosed in No. 98.

Hereinafter, the method of the present invention will be described more specifically by way of examples.

【Example】

Example 1 Hot-dip Al-plated steel strip having a plate thickness of 1.2 mm [amount of coating 6
0 g / m ² (single side)] through a pipe forming machine equipped with a reduced pressure arc spray device and a reduced pressure arc spray gun. After forming a tubular shape, welding the butt portion, cutting the weld bead, and setting the Al-1% Mn alloy wire with a wire diameter of 1.1 mm to both electrodes as a metal wire for spraying on the weld bead cutting part and spraying Then, a plated electric resistance welded pipe having an outer diameter of 25.4 mm was manufactured. At this time, the pipe forming speed of the line was 150 m / min, the feed speed of the metal wire for thermal spraying was 18 m / min, and the distance between the welding bead cutting portion and the arc spray gun in the reduced pressure was 50 mm. Also,
In order to determine the thermal spray repair position after cutting the weld bead, the weld bead cut portion was measured with a radiation thermometer, and spraying was performed at a temperature of the cut portion of 250 to 300 ° C. As a result,
The resulting sprayed layer on the weld bead cutting portion has an adhesion amount of 30 g.
/ M ² showed good adhesion as in the case of the investigation result in Table 1.

Example 2 A plated electric resistance welded tube was manufactured under the same conditions as in Example 1 except that Al-10% Si alloy wire was used as the metal wire for thermal spraying in both electrodes. As a result, the sprayed layer on the weld bead cutting portion showed a good adhesion as in Example 1 with an adhesion amount of about 30 g / m ² .

Example 3 A plated electric resistance welded pipe was manufactured under the same conditions as in Example 1 except that Al-5% Mg alloy wire was used as a thermal spraying metal wire for both electrodes. As a result, the sprayed layer on the weld bead cutting portion showed a good adhesion as in Example 1 with an adhesion amount of about 30 g / m ² .

[0018]

As described in detail above, according to the method for repairing the weld bead cutting portion of the galvanized electric resistance welded pipe according to the present invention,
When repairing the weld bead cutting part in the process of manufacturing an electric resistance welded pipe made of a coated steel strip coated with Al, the reduced pressure arc spraying method is used for spraying the metal wire for spraying, and the temperature of the weld bead cutting part is still 250. By continuously performing Al alloy spraying on the weld bead cutting portion while the temperature is higher than or equal to ℃,
Since the performance such as corrosion resistance and heat resistance of the electric resistance welded pipe made of the plated steel strip coated with Al can be improved, it is expected that the quality of the products of these electric resistance welded pipes will be stabilized and the application thereof will be expanded, The effect of the present invention is very large.

Claims (1)

[Claims] 1. An Al-plated steel strip is run, and while sequentially forming a tubular shape by a forming roll group, both edges are abutted to each other to perform electric resistance welding and then a welding bead is cut, and a depressurized arc is formed in the welding bead cutting portion. When repairing the weld bead cutting portion by spraying the metal wire for thermal spraying using the thermal spraying method, the welding bead cutting portion is 2 by using the Al alloy wire as the metal wire for thermal spraying.
A method for repairing a weld bead cutting portion, which comprises continuously spraying an Al alloy while the temperature is 50 ° C. or higher.