JP2002210507A - Method for piercing seamless steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piercing method for a seamless steel tube. SOLUTION: In a method for piercing the seamless steel tube, in this piercing method of the seamless steel tube, by working the tip part of a billet into a taper shape and working the shape of the inlet side of a roll into the same profile angle which is in accord with the tip shape of the billet, bitingness is improved. Moreover, the taper profile angle β of the tip part of the billet and the profile angle α of the inlet side of the roll are respectively taken as 1-4 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for piercing and rolling a seamless steel pipe.

[0002]

2. Description of the Related Art Generally, in the piercing and rolling of a seamless steel pipe, piercing is performed by using a piercer mill of the Mannesmann system. FIG. 2 is a top view of the pierther mill, and FIG. is there. As shown in FIG. 2 or FIG. 3, in the piercer of the Mannesmann system, a billet 4 is pushed by a pusher 7 at the time of piercing, rolled while rotating the billet 4 using a pair of piercer rolls 1, and inserted into the piercer mandrel from the opposite side. The plug 2 at the tip of the hole 3 is used to make a hole at the center of the billet 4 utilizing the Mannesmann effect.
And the billet 4 moves forward while rotating. For this reason, tension and compression force alternately work inside the billet 4, and the central portion of the billet 4 causes fir cracking. Reference numeral 5 denotes a roll shaft, and reference numeral 6 denotes a guide shoe.

[0003]

As described above, the plug 2 inserted in front of the gorge portion 8 with the central portion of the billet 4 being fir-cracked causes the fir-cracked inner surface to be smoothed out. 2 billet along the surface 4
Is extracted and becomes a product. However, at this time, slip may occur between the billet 4 and the piercer roll 1 depending on the interval, shape, and abrasion condition of the rolls. However, if the entrance angle of the roll is increased in order to suppress the slip, the shear stress of the material increases, which adversely affects the inner surface of the product. As described above, when the draft rate is reduced, there is a problem that the material biting property is deteriorated. From the viewpoint of measures against inner surface flaws, it is ideal that the roll shape is as flat as possible. There is a problem that causes.

[0004]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively developed and as a result, the shape of the billet tip is formed into a tapered shape, and the shape of the roll entrance side is also changed. The present invention provides a piercing and rolling method for a seamless steel pipe having an improved biting property by being processed into a shape conforming to the tip shape of the seamless steel pipe. The gist of the invention is as follows: (1) In the method of piercing and rolling a seamless steel pipe, the tip portion of the billet is processed into a tapered shape, and the shape on the entry side of the roll has the same shape and angle that matches the tip shape of the billet. A method for piercing and rolling a seamless steel pipe, characterized by processing to improve biteability. (2) The method for piercing and rolling a seamless steel pipe according to (1), wherein the taper shape angle β of the billet tip and the shape angle α of the roll entry side are each 1 to 4 °.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a billet shape and a piercer roll shape according to the present invention. As shown in FIG. 1, the roll shape is a drum shape, and the gorge part 8 is located at the apex at the center of the roll, and a fixed angle α is set at 1 on the entrance side and the exit side of the billet.
The billet 4 has a tip shape β of 1 to 4 °.
It was processed into a 4 ° taper shape to improve the biting performance.
As described above, the tip shape of the billet 4 is changed so as to have the same angle as the piercer roll shape, thereby increasing the contact area at the time of biting and improving biting performance.

When the angle on the entry side is reduced, the amount of reduction of the billet 4 before passing through the gorge portion 8 is reduced, and the amount of torsion at the gorge portion 8 is also reduced. On the contrary, when the billet 4 is made smaller, the force of the billet 4 biting into the roll becomes weaker and the propulsion force becomes smaller, so that the biting failure often occurs. Therefore, the angle is 1 to
4 °. The results shown in Table 1 were obtained by the occurrence frequency of the biting failure in the state where the piercer roll shape and the billet tip shape were changed. In the evaluation, steel grade: SUJ2, billet:
As a result of rolling 100 billets of φ120 × 2500 mm, product: φ72 × 12 WT, heating temperature: 1130 ° C., ◎: no scratches, good, Δ: slight scratches,
×: A large number of flaws were generated.

[0007]

[Table 1]

As shown in Table 1, as shown in FIG. Nos. 1 to 5 are examples of the present invention. 6 to 11 are comparative examples. No. 6,
In No. 7, since the combination of the shape angle α on the roll entry side and the taper shape angle β of the billet tip is inappropriate, an inner surface flaw was generated. Nos. 8 and 9 are so-called conventional methods in which the taper angle β at the tip of the billet is 0, and in this case, a large number of flaws are generated. No. 10,
In No. 11, since the shape angle α on the roll entry side and the taper shape angle β of the billet tip were outside the conditions of the present invention, flaws occurred in each case. In contrast, in the case of the present invention, good products were obtained without any flaws.

[0009]

As described above, since the contact area between the billet and the roll according to the present invention is increased, there is no biting failure, there is no mis-roll or trouble stop, and the productivity is improved. Further, since there is no biting failure, the angle near the gorge of the roll can be made large, and the shear stress inside the billet is reduced, and the inner surface flaws of the product are reduced, and extremely industrial effects are exhibited.

[Brief description of the drawings]

FIG. 1 is a diagram showing a billet shape and a piercer roll shape according to the present invention.

FIG. 2 is a top view of the piercer mill.

FIG. 3 is a front sectional view of the piercer mill.

[Explanation of symbols]

 Reference Signs List 1 piercer roll 2 plug 3 piercer mandrel 4 billet 5 roll shaft 6 guide shoe 7 pusher 8 gorge part

Claims (2)

[Claims] In the method of piercing and rolling a seamless steel pipe, the tip portion of a billet is processed into a tapered shape, and the shape on the roll entry side is also processed into the same shape angle that matches the tip shape of the billet to improve biting properties. A method for piercing and rolling a seamless steel pipe. 2. A taper shape angle β of a billet tip portion.
2. The method for piercing and rolling a seamless steel pipe according to claim 1, wherein the shape angle α on the roll entry side is 1 to 4 °.