JPH0722802B2 - Hollow tube forging method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a seamless steel pipe by forging a hollow round billet as a raw material.

(Prior Art) Generally, a seamless steel pipe is manufactured by a rolling method as disclosed in, for example, Japanese Patent Publication No. 56-4321, or is manufactured by hot extrusion. Manufactured by.

On the other hand, it is said that the hot extrusion method is suitable for manufacturing a pipe from a material such as alloy steel having low deformability and easily cracked during processing.

On the other hand, in some, after forming a through hole in the center of the hollow round billet that is the material, insert a mandrel into the through hole, and gradually reduce the wall thickness of the material by hot forging The method of doing is also adopted. However, such a method for producing an alloy steel pipe by forging has a low productivity due to a low processing speed, and a large temperature drop of the material causes a large temperature drop. Its application is limited to the manufacture of cross-section, thick-walled tubes.

Although the forging method has low productivity recently, it has a large degree of freedom and is being reconsidered as a means for producing small-quantity and multi-sized pipes. The limits are expanding.

FIG. 3 shows the relationship between the mandrel 1, the material 2 and the mold 3 when manufacturing a steel pipe by forging. The material 2 is successively fed into the mold 3 with the mandrel 1 inserted, and is forged while being rotated in the circumferential direction to reduce the wall thickness to form a steel pipe.

The steel pipe obtained in this way is not said to have excellent surface properties, but the surface properties can be made good by cutting the surface, so if the material temperature can be sufficiently secured at the processing stage. However, there are no major technical problems in steel pipe manufacturing by the forging method.

(Problems to be Solved by the Invention) The present invention is intended to manufacture a thin-walled tube having a size as small as possible by a forging method, for a material having a low deformability such as an alloy steel.

As mentioned above, the hot extrusion method is suitable for producing a tube from a material having a low deformability, but the extruder capacity is limited, and an attempt is made to produce a relatively large size steel tube. Sometimes not applicable.

On the other hand, although the speed of the forging machine has improved, the pipe diameter is 60 to 200 m.
If a tube product with a wall thickness of m and a wall thickness of 5 to 20 mm is to be obtained, it has a large surface area that contributes to heat dissipation compared to its volume because it is a hollow body, and heat is also taken away by the internal mandrel. There are many disadvantages compared to, and the temperature drop of the material is particularly large, which increases the deformation resistance of the material, exceeds the forging functional force, and further processing cannot be performed.

Further, a material such as an alloy steel having a particularly low deformability has a limited processing temperature range, so that a temperature constraint condition also arises. Even with respect to such a problem, it is difficult to secure the temperature particularly in the case of a hollow body as compared with the solid body, and the conventional forging method cannot deal with it.

Therefore, it is important how to prevent the temperature drop of the unforged part and the forged part of the material during the forging process, or to keep it at a predetermined temperature. The present invention has been made as a technical problem.

(Means for Solving Problems) A feature of the present invention is a method in which a hollow round billet is used as a material to reduce its cross-section by forging, and when the material is heated in advance, the material is heated with a heat insulating material. The method is characterized in that heating is performed in a covered state, or after the material is heated or immediately after extraction and after the material is covered with a heat insulating material, hot forging is performed in the forging process with the heat insulating cover attached. It is in the method of forging empty tubes.

Hereinafter, the present invention will be described in detail.

FIG. 1 shows an example of a device for carrying out the present invention.

FIGS. 2 (a) and 2 (b) show a side cross section and a front cross section of the hollow shell covered with a heat insulating material.

In FIGS. 1 and 2, 4 is a hollow shell that is heated while being covered with the heat insulating material 5, or is covered with extraction during heating or immediately after heating. These selections are determined in consideration of the degree of temperature decrease due to the size of the hollow shell and the heating efficiency, but generally, the smaller the wall thickness and the smaller size, the more severe the temperature decrease, and the temperature decrease during the work of the cover cannot be ignored. Therefore, even if the heating efficiency is ignored, it is necessary to cover the heat insulating material in advance.

The heat insulating material 5 is not limited in its material, but is preferably a fibrous refractory material having excellent heat shielding properties from the viewpoint of preventing the temperature drop of the hollow hollow tube as much as possible.

Next, its operation will be described. The hollow shell 4 covered with the heat insulating material 5 extracted from the heating furnace is immediately transferred into the line, and the mandrel 1 whose end is gripped by the manipulator 7 is hollow. It is inserted into the section and then given a circumferential rotation together with the heat insulating material, and is forged by the forging tool 6.

At this time, the heat insulating material is crushed by forging, and a part of the heat insulating material is sandwiched between the die and the material, and acts to prevent heat transfer between the die and the material. Some of the crushed heat insulation material remains adhered to the material surface, and it may also leave indentations on the material surface, but in this process, the forged pipe does not become a product as it is. Permissible.

If the heat insulating material 5 is fixed in its position, the mandrel 1
It is also possible to advance the unforged part to the position of the forging tool 6 by sending out in the axial direction.

As described above, according to the present invention, the seamless pipe is made of a material having a low deformability, such as a high alloy steel, by further suppressing the temperature drop of the material in the forging process without providing special equipment. Can be manufactured.

It should be noted that the present invention also includes inserting a hollow heat insulating material into the inner surface of the hollow tube to prevent heat transfer to the mandrel. Even on the inner surface side, it is effective to prevent lowering of the material temperature before and during forging, but considering the difficulty of the work, it can be applied to both the outer surface, the inner surface and the outer surface depending on the degree of cooling. To be selected.

Example An 80 mmφ × 10 mm t × 10 m (length) stainless steel pipe was forged using a 100 mmφ × 20 mm t × 5 m (length) stainless steel hollow shell as a material.

The heating temperature of the stainless steel hollow shell was set to 1200 ° C., and forging was started 1 minute after extraction, but in the conventional method, heat was lost in the middle of the forging operation.

When forging was carried out according to the embodiment of the present invention shown in FIG. 1, the forging temperature could always be maintained at 1000 ° C. or higher, and it became possible to manufacture.

Also, it is not practical to reheat or forge again because it is not practical to provide a heating device of a length corresponding to the increase in pipe length as the machining progresses (because the lid is closed for heating), and the mandrel cannot be fitted. Therefore, it could not be a practical production method.

(Effect of the invention) By applying the present invention, the diameter of 60 to 200 mm, which could not be manufactured by the rolling method and the hot extrusion method so far,
The production of seamless alloy steel pipes with a wall thickness of 5 to 20 mm has become possible with high efficiency.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of an apparatus for carrying out the present invention, and FIGS. 2 (a) and 2 (b) are side views showing a state in which a hollow shell is covered with a heat insulating material in the present invention. 3A and 3B are a front view and a side cross-sectional view of a conventional apparatus for manufacturing a seamless tube by forging. 1: Mandrel, 2: Material, 3: Mold, 4: Hollow tube, 4 ': Tube after forging, 5: Heat insulating material, 6: Forging tool, 7: Manipulator.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Takeshi Kawakami 2-6-3 Otemachi, Chiyoda-ku, Tokyo Within Nippon Steel Corporation (72) Inventor Shiro Watanabe 3-1, Takami, Hachimanto-ku, Kitakyushu, Fukuoka -1-116 (72) Inventor Yasushi Moriyama 2-10-1 Koume, Hachimansai-ku, Kitakyushu, Fukuoka Prefecture (72) Nobuhiro Tazoe 1 Shin-Nakahara-cho, Isogo-ku, Yokohama, Kanagawa Ishikawajima Harima Heavy Industries Co., Ltd. in the factory

Claims (1)

[Claims] 1. A method of reducing the cross section of a hollow round billet by forging, which comprises heating the material in advance while heating the material while the material is covered with a heat insulating material. Alternatively, a method for forging a hollow tube, which is characterized by performing hot forging with the heat insulating cover attached in the forging process after covering with a heat insulating material immediately after extraction after completion of heating.