JPH10291026A - Formation of skelp edge part in forge welded tube production process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of reducing thickening in the skelp width direction due to droop of a skelp edge part/edge forming and reducing an outer face streak and an inner face bead of a forge weld abutting part by an I shaped butting of edges. SOLUTION: In a production process, in which a skelp 1 reheated to 1300-1350 deg.C in a heating furnace 2 is formed by a vertical stand forming roll 3/a horizontal stand forming roll 4 and is made into a tube by forge welding with a forge welding roll 6, by arranging an auxiliary heating device 8 immediately before forming and raising a temp. of the skelp edge part, an edge is formed with pressing an edge of the skelp 1 on a seam guide roll of a horizontal stand forming roll pass. By this method, thickening in the skelp width direction due to droop of a skelp edge part and edge forming, is reduced, an outer face streak and an inner face bead of a forge weld abutting part is reduced by I shaped butting of edges. Further, quality of the forge weld abutting part is significantly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a skeleton edge portion in a process of manufacturing a forged steel pipe.

[0002]

2. Description of the Related Art FIG. 3 shows a method of manufacturing a forged steel pipe by a conventional method. The forged steel pipe is formed by continuously reheating a steel strip 1 as a material from 1300 ° C. to 1350 ° C. in a heating furnace 2 and forming it by a vertical stand forming roll 3 and a horizontal stand forming roll 4. Oxygen is blown from the nozzle 7 of the ding horn 5 to both edges of the skeleton and forged by a forging roll 6. Thereafter, the steel sheet is sequentially drawn with a drawing roll and rolled to continuously produce a forged steel pipe having a predetermined outer diameter and thickness. Skelp for wrought steel pipes is often used with a steel strip sheared by a slitter.

[0003] In this case, the edge portion of the skeleton has sagging, shearing surface, burrs, and the like generated during the shearing process.
Since reheating is performed from 00 ° C. to 1350 ° C., the edge portion further sags, and if it is forged and welded, there is a problem that an outer surface streak is generated at the forged contact portion and the quality is remarkably deteriorated. Here, FIG. 4 shows the shape of the inner and outer surface portions of the abutting portion of the forged steel pipe. (A) is an outer surface streak formed on the outer surface layer portion. (B) is an inner bead formed on the inner surface layer. In addition, the code | symbol H in FIG. 4 shows the width | variety of an external surface streak, d shows the external surface streak depth, and h shows the external surface streak height. JP-A-52-1
In Japanese Patent No. 45363, the thickness of the skeleton edge portion when the skeleton edge is pressed against the finned roll before reheating the skeleton is 2.5% to 7.5% of the thickness of the central portion in the skeleton width direction. An attempt has been made to mold it.

[0004]

The steel strip is sheared by a slitter so as to conform to a predetermined pipe diameter. However, the skelp edge generates sagging, shearing surface, burrs and the like generated during the shearing process. In addition, since the skeleton that has been sheared by the slitter is reheated from 1300 ° C. to 1350 ° C. in a heating furnace, sagging of the edge portion is further increased. An object of the present invention is to provide a method capable of reducing the thickness increase in the skeleton width direction due to the sagging of the skeleton edge portion and the edge molding, and the outer surface streak and the inner surface bead of the forging contact portion by the I-shaped butt of the edge. .

[0005]

SUMMARY OF THE INVENTION In order to reduce the sagging of the skeleton edge portion and the increase in the thickness of the skeleton in the width direction of the skeleton at the time of molding, the present invention relates to a method in which a skeleton re-heated to 1300 ° C. to 1350 ° C. Forming with a stand forming roll and a horizontal stand forming roll, and forging the pipe with a forging roll to form a tube, installing an auxiliary heating device immediately before forming, raising the temperature of the skeleton edge, and forming a horizontal stand forming roll hole type seam guide. A skeleton edge forming method in a process of manufacturing a forged steel pipe, wherein an edge of a skeleton is pressed against a roll to form the edge.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to FIGS. FIG. 1 shows a method for manufacturing a forged steel pipe according to the present invention.
Shown in The steel strip 1 as a material is continuously heated in a heating furnace 2 for 130 minutes.
Reheat from 0 ° C. to 1350 ° C., raise the temperature in the vicinity of the skelp edge by the auxiliary heating device 8, form with the vertical stand forming roll 3 and the horizontal stand forming roll 4, and squelch from the nozzle 7 of the welding horn 5 immediately before forging. Oxygen is sprayed on both edges of the forging roll 6 for forging.

FIG. 2 shows a water level stand forming roll 4 used for forming a skeleton edge. A seam guide roll 10 is provided in the horizontal stand forming roll hole die 9, and the skeleton edge 11 is set so as to be constantly pressed against the seam guide roll 10. The setting method is shown below. The value obtained by subtracting the width of the seam guide roll 10 from the circumference of the horizontal stand forming roll die 9 is defined as the circumference L (mm). The circumference L (mm) at this time is a constant value for each pipe size. In order to press and form the skeleton edge 11 against the seam guide roll 10, the skeleton width W (mm) at the time of molding is set to L (mm) or more.

Further, when the skeleton width W (mm) at the time of molding becomes (L + 20) (mm) or more, the thickness of the skeleton edge portion increases in the skeleton width direction, and the quality of the forged joint portion is remarkably deteriorated. Is (L + 20) or less.
The skeleton width W at the time of molding is defined as W (mm) = (W _O + πt _O ) × 1.0015 (1) from elongation and thermal expansion due to molding. At this time, W _O (mm) is the skeleton width before molding, and t _O (mm) is the thickness of the skeleton. Since the wall thickness at each pipe size is determined, the skeleton width W _O (mm) before molding can be calculated from equation (1). W is (L + 2
0) or less, the edges are thickened in the skeleton width direction since the skeleton width direction is uniformly heated.

Therefore, in order to reduce the increase in the thickness of the edge portion in the width direction of the skeleton, the temperature is increased only in the vicinity of the skeleton edge and a temperature difference is made between the vicinity of the skeleton edge and the vicinity other than the edge. It is easy to mold only the vicinity. Since only the vicinity of the skelp edge is formed, it is important to minimize the heating width of the temperature rise at the edge. As a device used as the auxiliary heating source, for example, there is a high frequency induction heating device. This is because by setting the frequency to be high, the penetration depth of the induced current induced at the skeleton edge is reduced, and the heating width in the skeleton width direction can be reduced.

[0010] Skelp width W during molding for each tube size
Is the skeleton width W before molding such that L ≦ W ≦ L + 20.
Immediately after was only heated near Sukerupuejji unit by setting the _O and auxiliary heater immediately before molding, the horizontal stand molding Russia - Le grooved sheet - Mugaidoro - Sukerupuejji part in forge welding immediately before by pressing the Sukerupuejji Le steel strip Sag when sheared with a slitter, shear surface, burrs, and furthermore, skelp having such an edge shape is reheated from 1300 ° C. to 1350 ° C. in a heating furnace. Can be reduced, and the outer streak and the inner bead of the forged contact portion can be reduced by the I-shaped butting of the edges. From the above, by applying the present invention, a forged steel pipe having a high quality forged portion can be manufactured.

[0011]

EXAMPLES Table 1 shows the shape of the forging contact portion when the method of the present invention is applied to each pipe size of the standard SGP. Table 2 shows the shape of the forging joint in the case of the conventional method for each pipe size of the standard SGP. Comparing the outer streak width, the depth and the inner bead height of the forged joints of the present invention and the conventional method, the shape of the forged joint according to the present invention is clearly superior.

[0012]

[Table 1]

[0013]

[Table 2]

[0014]

According to the present invention, in the process of manufacturing a forged steel pipe in which a skeleton reheated in a heating furnace is continuously hot-formed into a tubular shape, by applying the present invention, sagging of a skeleton edge portion and wall thickness increase in the skeleton width direction by edge forming. Can be reduced, and the outer streak and the inner bead of the forged contact portion can be reduced by the I-shaped butting of the edge. As a result, the quality of the forged joint portion can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for producing a forged steel pipe according to the method of the present invention,

FIG. 2 is a view showing a horizontal stand forming roll provided with a seam guide roll used in the present invention;

FIG. 3 is a diagram showing a conventional method for producing a forged steel pipe;

FIG. 4 is a view showing an outer surface streak and an inner surface bead height of a forging contact portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel strip 2 Heating furnace 3 Vertical stand forming roll 4 Horizontal stand forming roll 5 Welding horn 6 Forging roll 7 Nozzle 8 Auxiliary heating device 9 Horizontal stand forming roll hole 10 Seam guide roll -Le 11 Skelp Edge

Claims (1)

[Claims] 1. In a manufacturing process, a skeleton that is reheated to 1300 to 1350 ° C. in a heating furnace is formed by a vertical stand forming roll and a horizontal stand forming roll, and forged by a forging roll to form a tube, which is immediately before forming. A method for forming a skelp edge in a forged steel pipe manufacturing process, comprising installing a heating device, heating the skelp edge, and pressing the skelp edge against a seam guide roll of a horizontal stand forming roll hole type to form the edge.