JPH06513A - Perforation method for inner surface flaw prevention of seamless pipe - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent internal flaws when drilling seamless pipes. [Composition] The material is bited at the specified biting limit x,
At the same time as the biting, the roll entrance face angle α is increased. That is, the roll interval is opened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a perforating method for preventing inner surface defects of a seamless pipe.

[0002]

2. Description of the Related Art In the production of a seamless pipe, first, a hollow shell is made from a hot solid billet, and the hollow shell is expanded to a predetermined size by a mandrel mill or the like. When making this hollow shell, a two-roll type inclined rolling mill as shown in FIGS. 2 and 3 is generally used. In the figure, 1 is a material, 2 is an inclined roll arranged oppositely, the roll axis 11 and the pass line 10 are symmetrically arranged so as to form an angle β, and the roll inlet face angle α The taper roll has a (projection angle with respect to the pass line). 3 is a guide roller arranged between these inclined rolls 2 and 4 is a plug for punching the material 1.

The material 1 is rolled and perforated by the Mannesmann effect between the plug 4 and the inclined roll 2, and the hollow shell 1
a is formed.

Internal flaws may occur during the perforation. It is known that the occurrence rate of internal defects correlates with the biteability of the material.

As a parameter for determining the inner surface quality of the hollow shell, generally, the value of the plug tip rolling reduction is used as an index.
From the plug tip reduction ratio, the indentation limit, which represents the indentability of the material, is derived as in the following equation. x = (2Stan α + H) / D × 100 (%) (1) However, x: Material entrainment limit (%) α: Roll entrance face angle H: Roll interval (mm) D: Material diameter (mm)

According to the conventional perforation method, from the formula (1), the perforation limit x is defined by the roll entrance surface angle α and the perforation is performed. For example, (a) if α ≦ 9 °, 92% ≦ x <93% (b) if 9 ° <α ≦ 10 °, 92.5% ≦ x <9
3.5% (c) If 10 ° <α ≦ 11 °, 93% ≦ x <94% (d) If 11 ° <α ≦ 12.5 °, 93.5% ≦ x
<95.5%

[0007]

When the roll entrance face angle α and the biting limit x are punched as described above, the inner surface flaw occurrence rate, that is, the defective rate is as follows. In the case of (a), the defective rate is 5%, in the case of (b), the defective rate is 3.5%, in the case of (c), the defective rate is 5%, and the defective rate is 4%. It is 100.

One of the factors causing such a defective rate is that the roll inlet face angle is fixed during rolling because the embeddability of the material is emphasized. Since the material is perforated by the Mannesmann effect once it is bitten in, it is considered that it is not always necessary to fix the roll inlet face angle as long as the Mannesmann effect is exhibited well.

From this point of view, it is an object of the present invention to provide a seamless pipe inner surface flaw preventing perforation method capable of reducing the occurrence rate of inner surface defects.

[0010]

SUMMARY OF THE INVENTION According to the present invention, by increasing the roll inlet face angle at the same time as the material biting and rolling within a biting limit derived from the plug tip draft, the rate of occurrence of inner surface defects can be improved. It was possible to reduce. That is, in the present invention, rolling is performed under the following conditions, but the roll entrance face angle is increased at the same time when the material is bited. When α ≦ 10 °, x ≦ 92.7% ... When 10 ° <α ≦ 12.5 °, x ≦ 93.8% ...

[0011]

When rolling under the above conditions, if the roll inlet face angle is kept fixed, the above (a) to
Although the defect rate is as shown in (d), in the present invention, since the roll entrance face angle is increased at the same time as the material is bited, an excessive rolling reduction force does not act on the flow of the material, so that the inner surface flaw can be reduced.

In the present invention, the roll inlet face angle is raised by opening the roll interval with, for example, a load-on signal of an inclined roll as shown in FIG.

[0013]

EXAMPLE As an example, rolling was carried out at α = 9.5 ° during biting, α = 12 ° during rolling, and x = 93.2% (n
= 200 lines), the results are as follows. Defect failure 0, inner defect rate 3 (1.5%), which is a decrease of 2% compared to the conventional method.

[0014]

As described above, according to the present invention, the inner surface flaw can be reduced by enlarging the roll inlet surface angle at the same time as the material is bitten.

[Brief description of drawings]

FIG. 1 is a diagram showing a timing of increasing a roll entrance face angle in the present invention.

FIG. 2 is a plan view of a conventional two-roll type inclined rolling mill.

FIG. 3 is a side view of the tilt rolling mill.

[Explanation of symbols]

 1 Material 2 Inclined roll 3 Guide roller 4 Plug

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Suzuki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (1)

[Claims] 1. A method for perforating a seamless pipe, characterized in that the roll inlet face angle is increased simultaneously with the biting of the material within the range of the biting limit derived from the plug tip reduction ratio, and rolling is performed. Method for perforating inner surface flaws.