JPS59174203A - Manufacture of seamless metallic pipe - Google Patents

Abstract

PURPOSE:To reduce remarkably the generation of specks such as pits or eruption by forming a center hole which satisfies a prescribed condition at the center of the rear-end surface of a billet before piercing, in a Mannesmann pipe manufacturing method. CONSTITUTION:In a Mannesmann pipe manufacturing method, a center hole 15 of circular conical-shape is formed in a hot state at the center of the rear-end surface 13a of a billet 13. And the hole 15 is formed into a continuously circular conical-shape from the rear-end surface 13a of the hole 15. Further, the hole 15 is formed so that the diameter (d) of its bottom surface is 30mm.- a plug diameter and the circular conical angle theta is 40-100 deg.. In this method, the generation of earing 3 is prevented and the generation of pits and eruption are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a seamless metal pipe using the Mannesmann pipe manufacturing method, in which a center hole is formed in the rear end face of a billet before drilling.

[Technical background of the invention and its problems]

When manufacturing seamless steel pipes using the Mannesmann pipe manufacturing method,
When drilling a heated round steel billet with a piercer, at the end of the drilling process, as shown in FIG.
may occur.

Note that 4 is a roll and 5 is a core metal.

This lug falls off into the piercer or during the rolling and polishing process mentioned above, is scooped into the inner surface of the subsequent tube and adheres to the stamped sheet, and also to the rolls and guides, resulting in This can cause bit flaws on the inner and outer surfaces.

As a countermeasure against this problem, a method is known in which a center hole is formed at the rear end of the billet, as described in Japanese Patent Publication No. 45-31753. It is true that this method is extremely effective in preventing the occurrence of bit defects, but according to the inventor's numerous basic experiments and actual operational experience, the effect of preventing the occurrence of bit defects is still not necessarily sufficient. As described later,
It was found that there was room for improvement in the shape of the hole.

[Purpose of the invention]

The present invention was developed in view of the above-mentioned circumstances, and its main purpose is to provide a method for manufacturing a seamless metal pipe in which the incidence of pit defects is extremely low.

[Summary of the invention]

The method of the present invention that achieves this object is a Mannesmann pipe manufacturing method in which a conical center hole that satisfies the following conditions (a) to (C) is formed in the center of the rear end surface of the billet in a hot state,
Then, the hole is drilled. (a) The center hole has a continuous conical shape from the rear end of the billet. (b) The bottom diameter d of the center hole is 30 mm≦d≦
Plug diameter, (c) Cone angle θ is 40°≦θ≦100°.

[Specific Examples of the Invention] In the present invention, a center hole is formed by a press method in a hot state before drilling, for example, after leaving a heating furnace and before reaching a piercer.

An example is shown in FIGS. 2 and 3. That is, after extraction from the heating furnace and before drilling, a pair of upper and lower dies 11. , 12
While restraining the heated billet 13, a punch 14 attached to the tip of a hydraulic cylinder (not shown) is pressed on the rear end surface 13a to form a center hole 15.

Here, it is important that the center hole 15 has a shape as shown in FIG. First, the center hole 15 is located at the rear end surface 1.
It has a continuous conical shape starting from 3a. If, as described in the above-mentioned publication and as shown in Figure 6,
If the center hole 15' has a parallel portion 15'a, the parallel portion 15'a collapses onto the inner surface of the tube at the end of the drilling stage, and
A scab (inner scab) occurs on the inner surface.

Second, the bottom diameter d of the center hole needs to be set to satisfy the following relationship: 30 l≦d≦plug diameter.

If d is less than 30+++m, bit flaws will occur, which is the same as when there is no center hole. Furthermore, if d exceeds the diameter of the plug, the rolling reaction force cannot be taken at the final stage of drilling, and the plug cannot be pulled out.

Third, the cone angle θ,· should be 40°≦θ≦100°. Conventionally, cold billets had a tip angle of 120°.
Either they were lathed using a drill and finished in the shape shown in Figure 6, or they were scarfed to make a center hole with a large opening angle.

In contrast, in the present invention, the hole is made to be sharper than the conventional center hole. As shown in Examples below, when θ exceeds 100°, external bit flaws are likely to occur. If θ is less than 40°, although the incidence of bit defects on the outer surface is low, it is undesirable because it causes center scab defects (inner surface scuff defects).Particularly preferred is 50°≦θ≦70°.

As mentioned earlier, conventionally it is customary to make a center hole on the rear end face of the billet by cold processing, but in the case of lathe processing,
It is practically difficult to form the center hole into the shape according to the present invention, and the processing ability is insufficient compared to the pipe manufacturing ability, and on the other hand, if scarf ink is used, the eccentricity of the hole In addition to the problem of uneven shape, slag generated during scarf inking adheres to the billet and has to be removed because it does not adversely affect quality, which increases processing costs.

In any case, the conventional method has a poor yield.

Therefore, in the present invention, the center hole is hot-processed, and the equipment shown in FIG. 7 can be used for this purpose.

20 is a rotary heating furnace, and the heated billet 13 extracted from this furnace is conveyed to a predetermined position by a group of conveying rollers 21, and then transferred to the first skid table 22, and then transferred to the first skid table 22. Between the top table 23 and the top centering machine 24, the chucking die 2
A center hole is drilled at the tip of the billet 13 fixed to the billet 5. Thereafter, the billet 13 passes through the first exit side skid table 23, the transport roller group 26, the second person side skid table 27 in order, and then passes through the second exit side skid table 28.
At a position between , the bottom centering machine 29 equipped with a punch 14 punches the center hole described above in the rear end surface while being restrained by the dies 11 and 12. After perforation, the billet passes through the second exit side skid table 28, is provided to the first piercer 30, and is perforated while being pushed by the zosher 31.

Note that for centering, the rear end may be drilled first, and the tip may be drilled later.

〔Example〕

A large number of pipes were manufactured from a billet of 187 mm diameter by changing the shape of the rear end center hole and the processing method.1. When the outer pit flaw occurrence rate and the outer bit flaw scrap rate were investigated, the results shown in Table 1 were obtained. All other processing conditions were the same.

This result also shows that the method of the present invention is highly effective in preventing pit defects and blemish defects.

〔Effect of the invention〕

In summary, according to the present invention, it is possible to reliably reduce the occurrence of inner/outer pit flaws and middle curvature flaws.

Explanatory drawings, FIG. 2 is a front view of an example of processing a center hole, FIG. 3 is a side view thereof, FIG. 4 is a partially sectional front view showing a center hole shape according to the present invention, and FIG. 5 is a front view of an example of processing a center hole. FIG. 6 is a partially cutaway front view showing an example of a conventional center hole shape, and FIG. 7 is a schematic plan view of an example of pipe manufacturing equipment.

13... Billet, 13a... Rear end surface, 14...
Punch, 15... Center hole, θ... Cone angle, d.
...Bottom diameter.

1st part Figure 2 Figure 4 ρ-----A Otsu 4η ,,)-4 Figure 3 ”3G

Claims (1)

[Claims] (1) In the Mannesmann pipe manufacturing method, a conical center hole that satisfies the following conditions (a) to (c) is formed in the center of the rear end surface of the billet in a hot state, and then the hole is drilled (a).
) The center hole has a continuous conical shape from the rear end surface of the billet, (b) The bottom diameter d of the center hole is 30 mm≦d≦plug diameter, (c) The cone angle θ is 40°≦θ ≦100°. A method for producing a seamless metal pipe.