JP3269445B2 - Stripping die - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stripping die used for removing a mandrel bar used as a core metal for a mandrel mill from a hollow shell in a process of producing a seamless steel pipe of a continuous rolling system.

[0002]

2. Description of the Related Art An outline of a process for manufacturing a seamless steel pipe will be described with reference to FIG. The hollow shell 2 which has been fed laterally over the charging table 1 is bitten into the mandrel mill 6 by the mandrel holding device 5 while the mandrel bar 4 is inserted by the mandrel insertion device 3, and is subjected to rolling for adjusting the meat pressure. Is performed. After the end of the rolling, the mandrel bar 4 and the hollow shell 2 are conveyed together, and about 20 to 30 seconds after the end of the rolling, the stripping die 7 arranged on the exit side of the mandrel mill 6. And the mandrel bar 4 is withdrawn from the hollow shell 2.

[0003] With the elapse of the above-mentioned transport time, the inner surface of the hollow shell, which had been about 1000 ° C after the end of rolling, dropped to about 800 ° C before being pulled out by a stripping die, and thermal shrinkage occurred, resulting in a mandrel bar. So that
A large frictional force acts between the surface of the mandrel bar and the inner surface of the hollow shell, and a large force is required to pull out the mandrel bar.

[0004]

The above-mentioned stripping die 7 has an inner diameter suitable for each size of the mandrel bar 4, and as shown in FIG.
Had a right-angled shape. Therefore, when the mandrel bar 4 is pulled out, as shown in FIG. 4A, the mandrel bar 4 comes into contact with the lower part on the entry side at the end 7aa of the inner peripheral surface 7a of the stripping die 7 due to its own weight. However, there is a problem that abrasion occurs over the entire circumference and the entire length of the mandrel bar 4 surface. This abrasion,
The flaws (roughness) and cracks due to abrasion generally occurring have completely different causes, and have been clarified by the investigation of the present inventors.

In addition, the dimensions of the outer diameter of the mandrel bar 4 and the inner diameter of the stripping die 7 cannot be matched, and the mandrel bar 4 used for the stripping die 7 is slightly larger than the regular one. In the case, FIG.
As shown in (1), the stripping die 7 is used in a half-open state, so that the corner of the lower part on the entry side at the end 7aa of the inner peripheral surface 7a of the stripping die 7 stands, and abrasion is more likely to occur.

[0006] The above-mentioned scratches become more remarkable due to a decrease in the surface hardness of the mandrel bar with an increase in the number of times of rolling use. The abrasion reduces the life of the mandrel bar, and the abrasion of the mandrel bar is transferred to the inner surface of the pipe during rolling, leading to a reduction in product quality and an increase in cost due to care for the transfer flaw.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and provides a stripping die which does not generate abrasion extending in a longitudinal direction different from a wear flaw or a crack on a surface of a mandrel bar. It is an object.

[0008]

In order to achieve the above-mentioned object, the stripping die of the present invention has an inner peripheral surface radius of 0.05 ≦ r / d when the inner peripheral surface radius is d. ≦ 0.
It is to be provided with a radius of radius r that satisfies 1.
By doing so, even when the mandrel bar comes into contact with the lower part on the entry side at the end of the inner peripheral surface of the stripping die, occurrence of abrasion can be prevented.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The stripping die of the present invention
When the inner peripheral surface radius is d, 0.05 ≦
It has a radius r that satisfies r / d ≦ 0.1. In the stripping die of the present invention, the radius r of the roundness provided at the end of the inner peripheral surface is 0.05 ≦ r / d ≦ 0.
The reason why it is set to 1 is based on the following reason.

According to the experiment of the present inventor, the width of the flaw in the longitudinal direction of the mandrel bar (hereinafter, simply referred to as “flaw width”) is t.
When the relationship between the flaw width t and the radius r of the roundness provided at the end of the inner peripheral surface is t = r, all the flaw widths t are r / d.
<0.05. The inner peripheral surface end of the stripping die also wears due to friction with the mandrel bar and has roundness. The maximum roundness due to the wear is r / d <0.05. From these results, if the radius r of the roundness provided at the end of the inner peripheral surface from the beginning is set to be 0.05 ≦ r / d with respect to the inner peripheral surface radius d of the stripping die, the abrasion which is a scratch is obtained. Will not occur.

If the roundness r at the end of the inner peripheral surface of the stripping die is too large, a high-temperature hollow shell enters between the stripping die and the mandrel bar, causing poor pulling. The radius r of the roundness is required to have a relationship of r / d ≦ 0.1 as a result of experiments with various sizes in relation to the radius d of the inner peripheral surface of the stripping die.

According to the stripping die of the present invention, even when the mandrel bar comes into contact with the lower portion on the entry side of the inner peripheral surface end of the stripping die, it is provided at the inner peripheral surface end of the stripping die. Due to the roundness, the occurrence of scratches can be effectively prevented.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a stripping die according to the present invention will be described with reference to an embodiment shown in FIG. FIG. 1 is a view showing one side of a stripping die of the present invention, (a) is a front view,
(B) is a side view.

In FIG. 1, reference numeral 11 denotes a stripping die according to the present invention, wherein the radius of the inner peripheral surface 11a is d.
At the end 11aa of the inner peripheral surface 11a, 0.05 ≦ r / d ≦
It is rounded with a radius r that satisfies 0.1.

The stripping die 11 of the present invention has the shape described above.
75 and 180 mm) and the outer diameter is 198
mm, a wall thickness of 6.5 mm and a length of 28,700 mm were inserted into a hollow shell having an outer diameter of 179 mm and a length of 27000.
Table 1 shows the results when the mandrel bar of mm was pulled out. Table 1 below also shows the results of the comparative example in which the roundness r of the end 11aa is out of the range of the present invention and the result in the case of using the conventional example in which the end is right-angled.

[0016]

[Table 1]

From the above Table 1, it can be seen that, when the stripping die of the present invention is used, abrasions occur not only when the mandrel bar is adapted in size but also when the mandrel bar is slightly larger in size. Many mandrel bars could be pulled out without any.

On the other hand, in the case of the comparative example in which the roundness of the end is out of the range of the present invention, when the present invention is applied to a mandrel bar of a suitable size, abrasion does not occur much, but the number of times of stripping per mandrel bar Decreased. Also,
When applied to a slightly larger mandrel bar,
In addition to the reduction in the number of times of stripping per mandrel bar, abrasion occurred, poor pull-out, or pull-out failed.

In the case of the conventional example having a right-angled end, both the mandrel bar of a suitable size and the mandrel bar of a slightly larger size gave worse results than the comparative example.

[0020]

As described above, when the stripping die of the present invention is used, the life of the mandrel bar does not decrease due to the abrasion, and the life of the mandrel bar can be extended, and the steel pipe can be used. The inner surface quality is improved, and the manufacturing cost can be rationalized.

[Brief description of the drawings]

FIG. 1 is a view showing one side of a stripping die of the present invention, wherein (a) is a front view and (b) is a side view.

FIG. 2 is a schematic plan view of a seamless steel pipe manufacturing process.

FIG. 3 is a diagram showing a conventional stripping die.
(A) is a front view, (b) is an AA view of (a).

FIGS. 4A and 4B are diagrams showing a state in which a mandrel bar is pulled out when a conventional stripping die is used. FIG. 4A shows a case where the size of the mandrel bar is appropriate, and FIG. 4B shows a case where the size of the mandrel bar is large. is there.

[Explanation of symbols]

 Reference Signs List 11 stripping die 11a inner peripheral surface 11aa end d radius of inner peripheral surface 11a r radius of roundness of end 11aa

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-11-123410 (JP, A) JP-A-3-114605 (JP, A) JP-A-62-124004 (JP, A) JP-A-58-124 74206 (JP, A) JP-A-56-122605 (JP, A) JP-A 61-17204 (JP, U) JP-A 60-71403 (JP, U) JP-A 59-16703 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B21B 25/00 B21C 45/00

Claims (1)

(57) [Claims] An inner peripheral surface having a radius d satisfying 0.05 ≦ r / d ≦ 0.1 at an end of an inner peripheral surface, where d is an inner peripheral surface radius. Ripping die.