JP2514523B2 - Mandrel bar manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a mandrel bar by cold drawing using a used or unused mandrel bar or rolled round bar as a material to be processed.

[0002]

2. Description of the Related Art Conventionally, for downsizing a mandrel bar, complicated work has been carried out, which involves a number of steps such as straightening, rough turning, finish turning, grinding and straightening. Further, even when a mandrel bar is newly manufactured, a rolled round bar which is a raw material is subjected to rough turning (peel), finish turning and grinding.

The surface of the mandrel bar directly contacts the inner surface of the material to be rolled, and is therefore an important factor for determining the properties of the inner surface of the product. When turning with a lathe, etc., in principle, there will be blades (bites) due to the feed pitch of the material to be turned and the feed pitch of the blades, and this blade will cause a significant reduction in rolling performance, especially when using a mandrel bar after maintenance. Has become. Therefore,
In order to reduce or eliminate the cutting edge due to turning, steps such as finishing turning and grinding are added to finish the surface roughness of the mandrel bar to 20S or less.

[0004]

By the way, in the size reduction by the above-mentioned turning work, since the outer diameter is basically reduced by cutting, a machining allowance of at least about 2 mm is necessary for the outer diameter of the mandrel. There is a problem that the bar intensity is deteriorated. A normal mandrel bar has a length of about 10 to 30 m, and since a device used for maintenance uses a dedicated long lathe and a long grinder, there is a problem that the equipment cost becomes enormous.

The present invention solves the above-mentioned problems and, regardless of the conventional method by turning, can shorten the working time, improve the basic unit of the mandrel bar, have a good finishing accuracy, and a cold drawing process with a low equipment cost. An object of the present invention is to provide a method for manufacturing a mandrel bar according to.

[0006]

In order to achieve the above-mentioned object, the present invention is characterized in that the material to be processed of the mandrel bar is subjected to cold drawing for forming and surface finishing. The manufacturing method is as follows.

The material to be processed for the mandrel bar of the present invention includes a used or unused mandrel bar or a rolled round bar. Here, the used mandrel bar is a mandrel bar that has been worn during rolling and has become unusable due to surface properties, etc., but it can still be used from the viewpoint of quality, but for the time being The following working dimensions, which include a mandrel bar prepared for rolling smaller sizes due to reasons such as no rolling plans, are from the size of 111 mm to the diameter of 106. Use a size of 5 mm. The dimensional difference between them is usually 4 to 5 mm in diameter difference, but in reality, the diameter difference may be 2 mm. Cold drawing for size reduction depends on the capacity of the processing machine,
Since the diameter of the mandrel bar can be machined to about 0.5 to 5 mm, the mandrel bar which has already been used can usually be machined once to be machined to the next used size. The surface roughness of the cold drawn mandrel bar is 20 S or less,
The surface roughness does not require special finishing. The cold drawn mandrel bar can be heat-treated as necessary. Next, a mandrel bar that has not been used as a material to be processed for a mandrel bar is a mandrel bar that has been newly manufactured regardless of the manufacturing method. Therefore, in addition to the mandrel bar whose size is reduced without being subjected to rolling in the initial size, a new mandrel bar downsized by the method of the present invention is included. Further, the rolled round bar as the material to be processed of the mandrel bar is usually as rolled, but it means that the rolled round bar is roughly turned (peeled).

[0008]

According to the present invention, by subjecting the material to be processed of the mandrel bar to cold drawing, the mandrel bar can be formed into the following dimensions and the surface finish can be achieved to the surface roughness required for the mandrel bar. it can.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a mandrel bar, and 1a is a grip portion of the mandrel bar 1 which is gripped by a retainer device or a stripper chuck device. The grip portion 1a of the mandrel bar 1 is inserted into the die 2 of the cold working machine and attached to the chuck 3 of the cold working machine. The chuck 3 is retracted, and the mandrel bar 1 is cold drawn by a die 2 to have a smaller diameter.

Using a mandrel bar having a diameter of 106.5 mm and a length of 12 m, a diameter of 120 mm and a wall thickness of 4.1 mm
From the hollow shell of 34.0mm in diameter, 3.4mm in wall thickness
The seamless steel pipe of No. 2 was rolled by 200 tons. Then the diameter 12
From a 0 mm hollow shell with a wall thickness of 5.1 mm, a diameter of 34.
In order to roll a seamless steel pipe having a thickness of 0 mm and a thickness of 4.5 mm, the mandrel bar was cold drawn to reduce the diameter to 104.5 mm by one-time drawing. The inner diameter of the die of the cold drawing machine is 104.5 mm. As a result, the mandrel bar after being processed has a dimensional accuracy comparable to that of the conventional turning method and a surface roughness of 20.
It was S or less, and the straightness could be maintained.

An unused mandrel bar having a diameter of 106.5 mm and a length of 12 m and a diameter of 110 mm and a length of 12 m.
By subjecting the rolled round bar of (1) to cold drawing in the same manner, a mandrel bar having a diameter of 104.5 mm was obtained, and similarly good results were obtained in terms of surface roughness and the like.

[0012]

The present invention is configured as described above.
The following effects can be achieved. (1) It is possible to replace the conventional rough turning, finishing turning, and grinding processes with a cold drawing process, and the passing process can be simplified. (2) The surface roughness of the mandrel bar after cold drawing is 20 S or less, and no separate finishing process is required. (3) The cold drawing process has a shorter processing time than the processes such as turning and grinding, and the maintenance time of the mandrel bar can be relatively shortened. (Comparing the size reduction time of the mandrel bar alone is 1/10 or less.) (4) Cold drawing is plastic working, and the outer diameter is 1 mm.
The following size reductions are possible, and the mandrel bar unit consumption is relatively improved. (5) A dedicated long lathe and long grinder for maintenance of the mandrel bar are unnecessary, and the size of the mandrel bar can be reduced even with the existing cold drawing equipment for steel pipes.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a cold drawing process of the present invention.

[Explanation of symbols]

 1 Mandrel bar 1a Gripping part 2 Dice 3 Chuck

Claims (1)

(57) [Claims] 1. A method for manufacturing a mandrel bar, which comprises subjecting a material to be processed of the mandrel bar to cold drawing to perform forming and surface finishing.