JPH09192728A - Manufacturing equipment for butt welded steel tube having high quality of butt weld part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture tubes reduced in scale inclusion by providing a high frequency wave induction heating coil heating the edge part of tubular skelp between a forming roll and a butt welding roll and providing a nozzle blowing an oxygen inert gas just before butt welding. SOLUTION: The high frequency wave induction heating coil 8 is provided between the forming roll 3, 4 and the butt welding roll 6 in order to easily melt and blow away scale attached to the edge part. Scale inclusion is eliminated by completely removing molten scales from the butt weld surface with the oxygen inert gas blown just after that. Since reheating is possible just before butt welding by providing the high frequency wave induction heating coil 8, the temp. heating skelps in a heating furnace 2 is set in a low level, thereby reducing its manufacturing cost. By this way, scale inclusion in the butt weld part is reduced and steel tubes having an excellent quality are manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forged steel pipe manufacturing facility having a high-strength and high-quality forged welded portion.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional process for manufacturing a forged steel pipe. As shown in this figure, the forged steel pipe is made of steel strip 1
Is continuously heated in a heating furnace 2 to 1200 ° C to 1300 ° C and is molded by the molding rolls 3 and 4, the nozzle of the welding horn 5 immediately before forging is used to raise the temperature to an appropriate forging temperature and blow off the scale of the forging surface. Blow oxygen from 7 to the edge and forge welding. After that, it is successively drawn by a drawing roll and rolled to continuously produce a forged steel pipe having a predetermined outer diameter and thickness. About half of the oxygen blowing is to raise the temperature of the steel strip to a proper temperature and blow off the scale adhering to the forged surface. At this time, if the amount of oxygen blown is increased, the effect of blowing off the scale becomes greater, but the oxidation reaction proceeds and the amount of scale produced also increases.

On the other hand, if the amount of oxygen blown is reduced, the effect of blowing off the scale is reduced and the effect of raising the temperature of the steel strip is reduced. In this way, it is difficult to control the amount of oxygen blown for heating to an appropriate temperature and the amount of oxygen blown for blowing off the scale. If the scale of the forged part is not completely removed and it is directly bitten into the forged part, the strength of the forged part is significantly reduced. Therefore, in order to improve the quality of the forged portion of the forged steel pipe, Japanese Patent Application Laid-Open No. 50-545
There is a method of manufacturing a steel pipe as described in Japanese Patent No. 62, in which an edge is heated by injecting a mixed gas of oxygen and acetylene immediately before forging, and the scale is scattered to continuously forge. However, since a mixed gas of oxygen and acetylene is blown just before forging, it is difficult to instantly raise the temperature of the steel strip to an appropriate temperature, and there is a problem that the scale of the forged portion cannot be completely removed.

[0004]

Generally, in a method for manufacturing a forged steel pipe, after hot forming a steel strip heated in a heating furnace into a tubular shape, oxygen is blown just before forging, but this oxygen blowing adheres to the edge. There are two purposes: to remove the scale that is present, to heat the edge due to the heat of oxidation, and to blow away the scale generated at that time. However, it is very difficult to remove the scale attached before the oxygen is blown, which causes a problem that the scale is caught in the forged portion.
The present invention solves these problems, reduces the scale bite in the forged portion, and provides a manufacturing facility for obtaining a steel pipe having excellent properties in the forged portion.

[0005]

Means for Solving the Problems The gist of the present invention is to manufacture a forged steel pipe in which a steel strip heated in a heating furnace is hot-formed into a tubular shape and then forged, and a tubular skelp is formed between the forming roll and the forging roll. It is a device that reheats the edge part with a high frequency induction heating coil and blows oxygen inert gas immediately before forging.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail with reference to FIG. Generally, in the method of manufacturing a forged steel pipe, oxygen is blown just before forging, but the scale attached before the blowing of oxygen is very difficult to remove, and therefore the problem of scale biting in the forged portion occurs. Oxygen blowing immediately before forging has a function of instantly causing an exothermic reaction with the base iron to raise the temperature of the base iron, thereby melting the scale on the surface and blowing the melted scale away. However, when the heating temperature of the base iron is low or when the scale is thickly attached to the entire edge portion, the exothermic reaction between oxygen and the base iron does not occur and the scale remains on the forged surface. In order to easily blow off the scale attached to the forged surface, it is important to melt the scale and reduce the viscosity.

For this reason, a high-frequency induction heating coil 8 is installed between the forming rolls 3 and 4 and the forging roll 6 in order to melt the scale adhering to the edge portion, lower the viscosity and make it easier to blow off from the edge portion. . The high-frequency induction heating coil 8 reheats the edge portion to completely melt the scale on the edge portion. Immediately thereafter, the molten scale can be completely removed from the forged welded surface by spraying with an oxygen-inert gas, and scale entrapment at the forged welded portion is completely eliminated. Further, since the high-frequency induction heating coil is installed and reheating can be performed immediately before forging, the heating temperature of the skelp in the heating furnace can be set low and the manufacturing cost can be reduced. From the above, according to the apparatus of the present invention, it is possible to reduce the scale bite in the forged portion and obtain a steel pipe having excellent characteristics in the forged portion.

[0008]

[Examples] Table 1 shows the results of the practical tests and the occupancy ratio of foreign matters in the forged portion in the manufacturing process of the conventional method shown in FIG. Table 2 shows the results of the practical tests and the occupancy ratio of the foreign matter in the forged portion in the manufacturing process of the method of the present invention shown in FIG. Flatness ratios shown in Table 1 and Table 2,
The methods for calculating the expansion ratio and occupancy ratio of foreign matter in the forged portion are shown in the following formulas. Flatness = (1-H / D) x 100 (%) D: Outer diameter of plain tube H: Flatness height Expansion ratio = D '/ D D: Outer diameter of plain tube D': Outer diameter of expanded tube Occupancy rate of foreign matter in forged portion = L / t x 100 L: Length of all foreign matter in forged portion, t: Pipe wall thickness

[0009]

[Table 1]

[0010]

[Table 2]

[0011]

As described above, with the apparatus according to the present invention, it is possible to reduce the scale bite in the forged portion of the forged steel pipe and obtain a steel pipe having excellent forged portion characteristics, which is extremely excellent in industry. It has a great effect.

[Brief description of the drawings]

FIG. 1 is a plan view showing a method for manufacturing a forged steel pipe according to the present invention,

FIG. 2 is a plan view showing a process for manufacturing a forged steel pipe according to a conventional method.

[Explanation of symbols]

 1 Steel strip 2 Heating furnace 3 Forming roll 4 Forming roll 5 Welding horn 6 Forging roll 7 Nozzle 8 High frequency induction heating coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Daigo Sumimoto 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Kimitsu Steel Co., Ltd.

Claims (1)

[Claims] 1. High-frequency induction heating for heating an edge portion of a tubular skelp in the middle of a forming roll and a forging roll in the production of a forged steel pipe in which a steel strip heated in a heating furnace is hot-formed into a tubular shape and then forged. Equipment for manufacturing forged steel pipes with high-quality forged parts, which is equipped with a coil and a nozzle for blowing oxygen inert gas immediately before forging.