JPH1043802A - Press roll piercing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a press roll piercing method capable of making the service life of a plug long in a press roll piercing method. SOLUTION: In the case of piercing an angle billet 4 with the press roll piercing method manufacturing a hollow stock from the angle steel billet, piercing is executed after the surface of the plug 3 is previously covered with a wooden cap 5, or an iron oxide is embeded into a vacant hole and piercing is executed after working the vacant hole in the end of the angle steel billet 4. When the iron oxide is embeded and piercing is executed, an angle of intersection between the surface of the vacant hole and the surface of the plug 3 in the tube axial direction is preferably specified to be 30 degrees or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a press roll perforation method for producing a seamless steel pipe from a square steel slab using a plug and a roll.

[0002]

2. Description of the Related Art Various stainless seamless steel pipes manufactured by a hot extrusion method represented by the Eugene Sejournet method have recently been rolled by a mandrel mill method and a plug mill method which have higher productivity than the hot extrusion method. Manufactured by law.

[0003] As one of the rolling methods, a press roll punching method is well known. In the press roll punching method, as shown in FIG. 1, a pair of rolling rolls 2 having a circular die 1 and a plug 3 fixed to the center of the circular die 1 are punched while pressing a square steel piece 4 from the front. It is a thing.
-56645).

[0004] plug used in a press roll piercing machine, 3% Cr-1% Ni-based low alloy steel material is used, to ensure the thermal insulation, Fe ₃ O ₄ on the surface layer by heat treatment, F
A process for forming an oxide scale such as eO is performed.

In order to extend the life of the plug, Japanese Patent Laid-Open No. Sho 60-3 discloses a method of specifying the shape of the plug so that the metal flow near the plug of the material to be rolled does not damage the tip of the plug.
No. 7204. When carbon steel is pierced by this method, the life of the plug is 600 or more and there is no problem.

[0006]

However, even if such improvements are made, if stainless steel, which has a higher deformation resistance than carbon steel and hardly generates oxide scale on its surface, is pressed with a press roll, the plug will melt earlier. Damage, and as a result, seizure flaws occur on the inner surface of the tube. For example, SUS420J1
The life of a plug when drilling steel or SUS304 is several.

The inventor of the present invention has investigated the causes of seizure and erosion of the conventional plug material when austenitic stainless steel was punched by press rolls. As a result, the oxide scale previously formed on the plug was consumed during the press roll drilling. It was found that the plug and the material to be pierced came into metal-to-metal contact, seizing and melting. From this result, it was found that there is a limit in maintaining the heat insulating effect and the lubricating effect of the oxide scale layer formed in advance on the plug over a long period of time.

Accordingly, the present invention provides a press roll punching method that can extend the life of a plug in the press roll punching method.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a press roll drilling method for producing a hollow material from a square billet. In the case of drilling a square billet, the surface of a plug is covered with a wood cap before drilling. Alternatively, after a hole is formed at the tip of a steel slab, iron oxide is embedded in the hole and drilling is performed.

In the case where a hole is formed at the tip of a billet and then iron oxide is buried in the hole and the hole is drilled, the angle formed between the surface of the hole and the plug surface in the pipe axis direction should be 30 degrees or less. Piercing.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When a cap is put on a plug,
What is required for the material of the cap is that it does not cause seizure with the material to be pierced, and that there is no material that would interfere with the subsequent rolling mill. Further, in order to reduce the heat input to the plug, a material having a low thermal conductivity is desirable. From this perspective,
Wood is the most suitable material for the cap to be placed on the plug.

During drilling with a press roll punch, the surface of the wooden cap 5 covering the plug 3 is in an oxygen-deficient state because the entire surface of the wooden cap 5 covers the plug 3 as shown in FIG.
Wood is difficult to burn easily and is present during press roll perforation. In addition, although it is gradually carbonized, a good inner surface can be obtained because the carbide acts as a lubricant. After the plug is pulled out, air enters the pipe inner surface, so that the remaining wood does not burn and does not adversely affect the subsequent rolling mill.

The lower limit of the thickness of the wooden cap 5 is set to 2 mm or more because it is difficult to manufacture the wooden cap 5 if it is less than 2 mm and there is a possibility that the cap 5 may be broken at the start of drilling. The upper limit is set to a thickness such that the tip of the wooden cap 5 is located on the exit side from the contact start point of the material to be pierced 4 and the roll 2 when attached to the plug 3 as shown in FIG. Within this range, the thickness of the wooden cap 5 may be determined according to the length of the material 4 to be perforated. That is, the thickness of the wooden cap 5 may be reduced when the length of the perforated material 4 is short, and may be increased when the length of the perforated material 4 is long.

Next, when the oxide scale is supplied during the punching of the press roll, the feature of the punching of the press roll is utilized.
Iron oxide is supplied to the tip of the material to be perforated.

In the case of rolling by an inclined rolling mill, since there is a portion where the material to be rolled does not come into contact with a plug which is an inner tool in the circumferential direction, iron oxide is buried in a hole formed at the tip of the material to be rolled and rolled. However, since the iron oxide flows through the portion where the material to be rolled and the plug do not come into contact with each other and flows to the rolling-out side, the iron oxide does not remain until the end of rolling, and the effect is small.

However, in the case of piercing with a press roll piercing machine, the plug and the material to be pierced are in full contact with each other.
As shown in FIG. 2, the iron oxide buried in the hole 6 formed at the tip of the material 4 to be pierced does not easily flow to the exit side, but remains until the end of piercing, and its effect can be exhibited.

[0017] Iron oxide is _{FeO, Fe 3 O 4, Fe} 2 may be any of O _3, but industrially easily obtained inexpensive Fe ₂ O ₃
It is appropriate to use

As shown in FIG. 2, the diameter of the hole 6 formed at the tip of the material 4 to be pierced is determined by the size of the plug in order to prevent the iron oxide embedded therein from easily flowing out of the drilling machine. It should be smaller than the diameter.

As a method of supplying the iron oxide, the iron oxide may be directly buried in the pores. However, in order to prevent the iron oxide buried in the pores from dropping out of the pores, the iron oxide is supplied at 1100 ° C. (press roll punching temperature). It is desirable that the iron oxide be wrapped with aluminum foil or the like that melts and act as a lubricant, and that it be preformed into the shape of a hole be buried in the hole.

The method of forming a hole at the tip of the material to be pierced includes a method of processing with a drill or the like before heating and a method of pressing with a punch after heating and before drilling, but is not particularly limited. .

Further, since a streak-like flaw sometimes occurred on the inner surface of the steel pipe after the drilling, in order to investigate the cause,
An interim rolling stop experiment was performed with a press roll punching machine, and the rolled material being punched was cut in half, and the inner surface was examined. as a result,
As shown in FIG. 3, an annular metal piece 7 peeled off from the material to be pierced 4 adheres to the front surface of the plug 3, and the inner surface of the material to be pierced slides on the annular metal piece 7, resulting in streak-like defects. Was generated.

Therefore, in order to investigate the cause of the generation of the annular metal piece 7, the shape of the hole 6 and the shape of the plug 3 were changed, and a rolling stop experiment was performed by a press roll punching machine. When the angle θ formed between the inner surface of the hole and the plug surface in the pipe axis direction shown in (1) becomes larger, the flow of the perforated material 4 to the rear of the plug is hindered and stays on the front surface of the plug to form the annular metal piece 7. . When the angle θ between the inner surface of the hole and the plug surface in the tube axis direction and the incidence rate of the annular metal piece 7 were investigated, as shown in FIG. Was found to be able to be prevented.

The length of the hole in the tube axis direction is as follows. The lubricant 8 embedded in the holes forms a shape like a dead metal during the drilling as shown in FIG. 3 and is captured on the front surface of the plug. Lubricant caught on front of plug 8
Is at most 0.4 times the plug diameter. Therefore, the length of the hole to be formed in the material 4 to be pierced is
0.4 to 1.0 times the diameter of the plug 3 is sufficient.

[0024]

【Example】

(1) Example 1 Press roll perforation was performed using JIS standard SUS420J1 steel. A square slab having a side length of 80 mm and a length of 650 mm was heated to 1250 ° C., and then pierced and rolled into a hollow shell having an outer diameter of 93 mm and a wall thickness of 23.75 mm using a press roll piercing machine.

The piercing and rolling described above was performed using a plug with a 5 mm thick wood cap (the method of the present invention) and a plug with no cap (the conventional method).

Table 1 shows the results.

[0027]

[Table 1] As is evident from Table 1, in the case of the conventional method in which the press roll was drilled without covering the wood with the plug, seizure was caused by piercing and rolling 1 to 3 times, and erosion occurred. In the case of the present invention in which rolling is performed, even after piercing and rolling 20 times or more, only roughening occurs at a transition portion (shoulder) where the diameter decreases from the base portion where the diameter of the plug is constant.

(2) Example 2 JIS standard SUS having a side length of 80 mm and a length of 650 mm
Press roll perforation was performed using a square piece of 420J1 steel. At that time, a square steel slab having holes shown in FIG. 2 machined by a drill at the tip and a square steel slab not machined were used.

A square slab having a hole formed at its tip is 1250
After heating to ° C, Fe ₂ O ₃ was wrapped in aluminum foil and formed into a hole, and the hole was buried in the hole. The hollow element having an outer diameter of 93 mm and a wall thickness of 23.75 mm was then pressed using a press roll punch. The tube was pierced and rolled. Similarly, square billets without holes are also
After heating to 1250 ° C, the hollow shell of the above size was pierced by a press roll piercing machine.

Table 2 shows the results.

[0031]

[Table 2] As is clear from Table 2, when piercing and rolling was performed using a square steel slab in which iron oxide was not embedded at the tip, seizure was caused by piercing and rolling one to three times and melting was caused. After processing, in the case of the present invention in which press roll punching was performed using a square slab in which iron oxide was embedded, even after piercing and rolling 30 times or more,
The roughening only occurs at the transition (shoulder) where the diameter decreases from the base where the diameter of the plug is constant.

(3) Example 3 JIS standard SUS having a side length of 80 mm and a length of 650 mm
Drilling was performed using a square piece of 420J1 steel. After the square billet was heated to 1250 ° C, Fe ₂ O ₃ was wrapped in aluminum foil and formed into a hole, and the hole was buried in the hole, and then the outer diameter was 93 mm and the wall thickness was 23 using a press roll punch. .75
The sample was pierced and rolled into a hollow shell having a diameter of 1 mm. The inner surface of the perforated steel pipe was observed, and the presence or absence of streak-like flaws was investigated. Table 3 shows the results.

[0033]

[Table 3] As is clear from Table 3, streak-like flaws were generated in Comparative Examples not applicable to the present invention, but no streak-like flaws were generated in the method of the present invention.

[0034]

According to the present invention, the life of the plug in press roll piercing and rolling can be greatly extended, the frequency of equipment downtime for plug replacement can be reduced, productivity can be increased, and the tool unit consumption can be reduced. It has a great industrial effect.

Further, the perforation can be performed without causing streak-like flaws on the inner surface after the perforation.

[Brief description of the drawings]

FIG. 1A is an explanatory view of a contact start position between a roll and a material to be rolled in press roll perforation, and FIG.
It is sectional drawing which follows an X-ray.

FIG. 2 (a) is a front view of a hole processed into a square steel slab according to the present invention, and FIG. 2 (b) is a longitudinal sectional view.

FIG. 3 is an explanatory diagram of an annular peeling piece.

FIG. 4 is a definition diagram of an angle θ formed between an inner surface of a hole and a surface of a plug in a tube axis direction.

FIG. 5 is a graph showing the relationship between the angle θ formed between the inner surface of the hole and the plug surface in the tube axis direction and the incidence of annular metal pieces.

[Explanation of symbols]

 Reference Signs List 1 circular hole type 2 roll 3 plug 4 square steel piece (perforated material) 5 wooden cap 6 hole 7 circular metal piece 8 lubricant (iron oxide)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koichi Furusho 1-1 Niwahata-cho, Tobata-ku, Kitakyushu-shi Nippon Steel Corporation Inside Yawata Works

Claims (3)

[Claims] 1. A press roll drilling method comprising: in a step of drilling a seamless steel pipe for drilling a square steel piece by a press roll drilling method, previously covering a plug with a wood cap and then drilling. . 2. In the step of piercing a seamless steel pipe for piercing a square steel slab by a press roll piercing method, a hole is machined at a tip of the steel slab, and iron oxide is buried in the hole to perform piercing. Press roll perforation method. 3. The press roll perforating method according to claim 2, wherein the angle between the surface of the hole and the surface of the plug in the pipe axis direction is set to 30 ° or less, and the perforation is performed.