JPH10277636A - Manufacture of butt-welded tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove the scale in a non-contact manner with a skelp by blowing the high-speed combustion flame against a butt-welded seam surface to heat a butt-welded part before butt-welding a heated skelp, and removing the scale at the butt-welded part, and to realize the excellent operability by increasing the heat source for heating immediately before the skelp. SOLUTION: A skelp 2 heated by a heating furnace 1 is bent in a tubular shape by rolls 3, 4. A surface 7 to be butt-welded is irradiated with the high- speed combustion flame 6 formed by a high-speed combustion flame generating device 5 to perform the butt-welding by a butt-welding roll 8. The combustion flame is increased in number according to the increase in the butt-welding speed and the drop in the skelp temperature. The scale is removed by the high- speed combustion flame 6 through the shearing force of the high-speed combustion flame 6. When the speed of the high-speed combustion flame 6 is >=800 m/sec., the scale can be completely removed. When the temperature of the combustion flame is about 1200-1400 deg.C, the sagging of the edge of the butt- welded part is reduced, and the expansion ratio can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a forged pipe used for a water pipe, a building pipe, and the like.

[0002]

2. Description of the Related Art Forging welding is performed by blowing oxygen to a heated skeleton to about 1350 ° C. to oxidize the ground iron, melting the surface scale by the reaction heat, and blowing the molten scale by the blowing force of oxygen. In this method, the scale-removed surfaces are pressed and diffusion-bonded to each other.

[0003] However, in this method, scale removal is incomplete, and scale remains at the forged joint portion, which causes a reduction in strength and expandability of the forged joint portion. In order to solve this problem, it is the same as the prior art in that oxygen is sprayed. However, a technique for improving the quality of the forging joint portion by controlling the spraying method and the temperature of the skelp is disclosed in Japanese Patent Publication No. 1339219. Kaihei 8-132133, JP-A-7
-2047334. In addition, development of skelp components suitable for forging, temperature conditions, oxygen blowing pressure,
Optimization of the upset amount and the like is also disclosed in
And Japanese Patent Laid-Open No. 7-278748.

[0004] Among these, temperature control is mainly performed, and skelp heating is mainly performed in a heating furnace.
In addition, in order to minimize the temperature rise inside the heating furnace and to suppress the fuel consumption rate, a method of heating only the skeleton around the forged portion immediately before forged welding has been developed. As the heating source, a method using a plasma arc is Japanese Patent No. 1298628, a method using high-frequency induction heating is Japanese Patent No. 1398957 or Japanese Patent No. 1588719, a method using a heating burner is Japanese Patent Application Laid-Open No. 58-199824, and a method using a laser is Japanese Patent Application Laid-Open No. 7
-32034 and JP-A-7-32035.

[0005] Further, for descaling, the pressure of oxygen blowing is basically used. Thus, the scale becomes molten and is removed by the oxygen blowing pressure. Here, in the case of melting, dripping of the edge is likely to occur at the forged contact portion. For this reason, a technique for forge welding in an unmelted scale has been developed. For example, a method using air blow has been developed in JP-A-1-118313, and a method using mechanical cutting tool has been developed in JP-A-61-26985.

Up to this point, there has been described a conventional technique relating to forging. In the present invention, in order to solve the problems of the prior art described below, a high-speed combustion flame used for thermal spraying or the like (for example, a dissertation, Proceedings of the 7th).
International Thermal Spr
ay Conference 20-24 July
1994, Boston, Massachusett.
The technique of spraying s) immediately before forging after the heating furnace was diverted.

[0007]

By the conventional oxygen spraying method, the control of the temperature, and the optimization of the forging conditions (temperature, pressure, upset amount, etc.), the characteristics of the forging joint are surely improved. The removal is hardly complete, and the characteristics of the forged joint are insufficient compared to the base metal.

[0008] The method using a plasma arc, which is a heating method immediately before forge welding of a skelp, has difficulty in continuous operation due to the presence of electrodes, and has a problem in wind resistance. Further, in the laser method, the size of the heat source is small, and it is difficult to cope with the rolling of the tube.

Regarding scale removal, air blow is insufficient and the temperature is low, so that the blow causes a decrease in the temperature of the forged joint. In the case of a cutting tool, the contact type is difficult to control, and the temperature of the forged surface is lowered.

Therefore, in the present invention, the skeleton is not contacted,
It is an object of the present invention to provide a method for producing a high-strength forged pipe having a large heat source capable of removing scale and heating immediately before skelping, and having excellent continuous operability.

[0011]

The gist of the present invention is that when forging a heated skeleton, before forging, a high-speed combustion flame is sprayed on the forged seam surface to raise the temperature of the forged portion and to increase the forged portion. And a method for manufacturing a forged pipe. Further, when the temperature of the high-speed combustion flame is 13
50 ° C. or higher, the speed is 800 m / sec or higher, and the temperature at the exit side of the heating furnace of the skelp is 1200 ° C.
The temperature is 1400 ° C. or lower.

[0012]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a high-speed combustion flame used for thermal spraying or the like is used as a method for removing a heating source and scale as a method capable of continuous operation and having a large cross section of a heat source (about 15 mm). It is characterized by having. In particular, the temperature of the oxygen gas at the time of the conventional oxygen spraying is room temperature, the speed is at most 100 m / sec, or the temperature at the time of plasma arc heating is 10000 ° C., the speed is at most 300 m / sec, and the laser heating is There is no speed (in the case of plasma arcs and lasers, these are simply used as heating sources, not for scale removal).

FIG. 1 shows the present invention. The skeleton 2 heated in the heating furnace 1 (the skeleton is a coiled plate in front of the heating furnace) is bent into a pipe shape by a roll of 3 or 4 to form a high-speed combustion flame 6 from a 5 high-speed combustion flame generator. Then, the forged surface 7 is irradiated and forged by a forged roll 8. At this time, it is desirable to increase the number of combustion flames by increasing the forging speed and lowering the skelp temperature.

The scale removal by the high-speed combustion flame depends on the shear force of the combustion flame, and the shear force depends on the speed of the combustion flame. If the speed of the combustion flame is less than 800 m / sec, the scale cannot be completely removed. Therefore, the speed is set to 800 m / sec or more. Further, when a high-speed combustion flame is sprayed on the forged surface, if the temperature of the combustion flame is lower than 1200 ° C., the skeleton is cooled and cannot be forged, so the temperature is set to 1400 ° C. or higher.

[0015] Regarding the temperature of the skelp, in order to enable scale removal and forge welding, if the temperature at the exit side of the heating furnace is less than 1200 ° C, forge welding cannot be performed.
If the temperature exceeds 00 ° C., dripping of the edge of the forged portion becomes large, so the temperature of the high-speed combustion flame of the skelp needs to be 1200 ° C. or more and 1400 ° C. or less.

[0016]

【Example】

(Example 1) Conventional oxygen spraying method, plasma arc auxiliary heating method, laser heating method, the characteristics of the forged portion of the present invention method, continuous operability, rolling of anti-skelp, temperature of skelp and overall evaluation result were performed. Table 1 shows the results.
Shown in Table 2 shows the irradiation conditions of the high-speed combustion flame at this time. Compared with the conventional method, the heating temperature of the skelp can be lowered and the characteristics of the forged portion are improved.

[0017]

[Table 1]

[0018]

[Table 2]

(Example 2) Table 3 shows the characteristics of the forged portion when the temperature and speed conditions of the high-speed combustion flame were changed.

[0020]

[Table 3]

(Embodiment 3) Table 4 shows the characteristics of the forged portion when the skeleton temperature immediately before blowing the high-speed combustion flame is changed in the present invention.

[0022]

[Table 4]

[0023]

As described above, it is possible to manufacture high quality forged pipes for water pipes and architectural pipes, increase the expansion rate, reduce the edge drooping at the forged surfaces, and improve the joint characteristics and the end pipe. Increased productivity of multi-layer pipes.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the method of the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiro Ohara 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Masao Fuji 20-1 Shintomi, Futtsu-shi, Chiba New Japan (72) Inventor Shinya Sakamoto 1 Kimitsu, Kimitsu City, Chiba Prefecture Nippon Steel Corporation Kimitsu Works (72) Inventor Daigo Sumimoto 1 Kimitsu, Kimitsu City, Chiba Prefecture Nippon Steel Corporation Inside Kimitsu Works (72) Inventor Yoshio Terada 1 Kimitsu, Kimitsu City, Chiba Prefecture Nippon Steel Corporation Kimitsu Works

Claims (3)

[Claims] When a heated skeleton is forged and welded, a high-speed combustion flame is sprayed on a forged seam surface immediately before forged welding to raise the temperature of the forged weld and remove scale of the forged weld. Production method. 2. A temperature of 1400 ° C. or more and a speed of 800 m
2. The method for manufacturing a forged pipe according to claim 1, wherein the forged part is pressure-welded and diffusion-bonded using a high-speed combustion flame of not less than / sec. 3. The method according to claim 1, wherein the temperature of the skelp before spraying the high-speed combustion flame is 1200 ° C. or higher and 1400 ° C. or lower.