JPH11197712A - Rolling method by mandrel mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily draw a seamless steel tube after rolling by a mandrel mill out of a mandrel bar. SOLUTION: In a rolling method by the mandrel mill wherein a mandrel bar 22 is inserted into a tube stock which is obtained by boring a round billet being a stock with a boring machine and the tube stock is rolled by plural grooved roll stands to obtain the seamless steel tube 21, a radius of curvature R1(n+1) of a groove bottom of a groove 24 of the roll stand succeeding the last wall thickness reducing roll stand among the grooved roll stands is set to 1.010-1.025 times the radius of curvature R1n of the groove bottom of the groove 24 of the last wall thickness reducing roll stand, and a clearance angle θof the groove 24 is set to 30-40 degrees to roll the steel tube.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mandrel mill rolling method for rolling a seamless steel pipe by a mandrel mill.

[0002]

2. Description of the Related Art When manufacturing a seamless steel pipe by a mandrel mill rolling method, a billet, which is a material, is heated to a temperature suitable for rolling in a billet heating furnace, and then a through hole penetrating through the billet shaft core by a punching machine. Provided on billet. Then, a mandrel bar is inserted into the base tube provided with the through-hole, and the base tube is rolled by a mandrel mill to have a predetermined inner diameter, but the shell thickness of the shell is larger than the product specification in the intermediate stage. And

[0003] Since a mandrel bar is inserted into the seamless steel pipe at the intermediate stage, the mandrel bar is connected to the bar.
After being pulled out with a stripper, it is reheated by a walking beam type reheating furnace and rolled by a stretch reducer to obtain a seamless steel pipe having both an inner diameter and a shell thickness conforming to the product specifications.

When the mandrel bar is pulled out of a seamless steel pipe at an intermediate stage (hereinafter simply referred to as a seamless steel pipe), the seamless steel pipe is rolled because the seamless steel pipe is shrink-fitted to the mandrel bar. Hole type
If the hole shape of the steel pipe is a circular shape having the same outer diameter as the outer diameter of the seamless steel pipe to be rolled, it is difficult to remove the same. Therefore, as shown in FIG. (Up-down direction) is the hole type 2 of the mandrel bar 22 and the hole type roll 23
4, but in a direction (for example, the left-right direction) perpendicular to the seamless steel pipe 21 is not in contact with the mandrel bar, but is in contact with only the hole 24, that is, an elliptical shape. Designed.

The shape of the hole 24 of the hole roll 23 will be described in detail. As shown in FIG. 2, the direction in which the mandrel bar 22 contacts the seamless steel pipe 21, that is, the groove of the hole 24, The radius of curvature R _1n of the bottom 24 a is a length centered on a point away from the center of the mandrel bar 22 by the distance S, but the portion 2 adjacent to the groove bottom 24 a of the hole 24 is formed.
The radius of curvature R _2n and 4b are a greater length than the radius of curvature R _1n, further the radius of curvature R _3n portion 24c adjacent to the adjacent portion 24b, to the radius of curvature R _1n and R _2n It has a negative value.

For this reason, the seamless steel pipe 21 being rolled has the hole 24 of the hole roll 23 and the mandrel bar in the vertical direction.
22 is rolled, but is not in contact with the mandrel bar 22 in the left-right direction.

In FIG. 2, a line A connecting the center of the radius of curvature R _2n to a boundary point between 24b and 24c and a horizontal axis B
Is referred to as a clearance angle.

However, even with the above-described measures, the high alloy steel has a large thermal expansion coefficient and a large thermal contraction amount of the seamless steel pipe 21, so that the seamless steel pipe 21 is in close contact with the mandrel bar 22. There is a problem that it is difficult to pull out the mandrel bar 22 from the seamless steel pipe 21 because of its ease of deformation and large deformation resistance.

In order to solve such a problem, the technique disclosed in Japanese Patent Application Laid-Open No. 60-46805 discloses a method for forming a proper round in a final stand in which a gap is formed between a mandrel and a rolled material, a so-called round-up stand. In order to make it possible to raise the roll, the deviation of the reaction force with respect to the roll reaction force of the stand determined in advance is detected, and the roll reduction is adjusted during the next material or during rolling in accordance with the deviation. The round-up stand has a caliber having a relief angle of 15 to 30 ° instead of a perfect round caliber.

[0010]

However, the technique disclosed in Japanese Patent Application Laid-Open No. 60-46805 has the following problems.

The outer peripheral length of the seamless steel pipe at the outlet side of the mandrel mill is different between a thin material and a thick material, and the outer peripheral length increases as the material becomes thinner.

Therefore, as the clearance angle θ becomes smaller and becomes closer to a perfect circle, it is impossible to cope with a change in the outer peripheral length.
It may cause a fold flaw. Conversely, if R ₁ is increased to avoid this, for a material with a small perimeter,
The flange side of the former stand cannot be lowered, and the pulling load is not reduced.

The present invention has been made to solve the above-mentioned problems of the prior art. Even when rolling a seamless steel pipe of high alloy steel, a mandrel bar after rolling by a mandrel mill is used. And a method for rolling a mandrel mill capable of easily extracting the same from a seamless steel pipe.

[0014]

SUMMARY OF THE INVENTION A mandrel mill rolling method according to the present invention is characterized in that a mandrel bar is inserted into a raw pipe obtained by piercing a round steel slab as a raw material with a piercing machine, and the raw pipe is inserted into a plurality of holes. In the mandrel mill rolling method of rolling a seamless steel pipe by using a roll stand, the hole-shaped groove of the roll tand after the final thickness reduction roll stand among the hole-shaped roll stands. The radius of curvature R _{1 (n + 1)} at the bottom is 1.010 to 1.025 times the radius of curvature R _{1n at} the bottom of the hole of the final reduced thickness roll stand, and Rolling is performed with a clearance angle θ of 30 to 40 degrees.

The present inventors have proposed a final reduced-roll roller.
Roll stand with no wall thickness reduction after
Roll stall without this thickness reduction
Radius of curvature R at the bottom of the hole_{1 (n + 1)}The final thickness reduction
Radius of curvature R at the bottom of the hole of the roll stand_1nLarger than
By passing through the seamless steel pipe, the seamless steel pipe
Increases ellipticity and makes seamless steel pipe contact with mandrel bar
Range is smaller, so seamless steel pipes can be
-On the premise that it is easy to pull out- _{1 (n + 1)}/
R_1nAnd the relationship between the pulling load.

As a result, as shown in the graph of FIG. 3, the pulling load is such that R _{1 (n + 1)} is 1.010 to 1.025 of R _1n .
Since it was found that the doubled time was the smallest, R
_{1 (n + 1)} is in the range of 1.010 to 1.025 times R _1n .

Further, the relationship between the relief angle θ of the hole and the pull-out load was examined when R _{1 (n + 1)} was in the above range.

As a result, as shown in the graph of FIG. 4, the drawing load is small when the clearance angle θ of the hole shape is 40 degrees or less, but when it exceeds 40 degrees, the ellipticity of the seamless steel pipe advances. It was found that there was a problem in terms of quality, and the pulling load also became large.

However, if the clearance angle θ of the hole is less than 30 degrees, the material is entangled into the hole flange in the case of a thin material, and a breakage flaw is generated in the stretch reducer. , The relief angle θ of the hole is 30-4
0 degrees.

[0020]

EXAMPLE 1 A mandrel was inserted into a perforated rolled 13Cr steel to obtain a roll having the roll specifications shown in Table 1.
A seamless steel pipe was rolled by a mandrel mill of a stand (roll specifications of stands # 1 to # 4 were omitted).

[0021]

[Table 1]

The final thickness reduction stand of this mandrel mill is a # 6 stand, and the groove bottom curvature radius of this stand is
Since R _1n is 72.5 mm, the clearance angle θ is fixed at 40 °, and the radius of curvature R of the groove bottom indicated by R ₁ of the # 7 stand is
_{1 (n + 1)} is varied as shown in Table 2, was examined the relationship between R _{1 (n + 1)} / R ₁ and pulling load. The numerical values of the withdrawal load in the table, R ₁ is 74 mm, theta is the load at 50 ° 1
The ratio was calculated as follows.

[0023]

[Table 2]

As a result, R _{1 (n + 1)} / R ₁ is 1.010-1.
In the range of 025, it was confirmed that the pulling load was the smallest. (Example 2) In the same mandrel mill as in Example 1, the same 13Cr steel as in Example 1 was rolled. In this case, as shown in Table 3, the radius of curvature R of the groove bottom of the # 7 stan is
_{1 (n + 1)} was not changed to 74.0 mm, and the relief angle θ of the hole was changed variously, and the relationship between the relief angle θ and the pulling load was investigated. The calculation by the ratio of the numerical value of the pull-out load in the table of case, R ₁ is 74 mm, when θ is set to 1 the load when the 50 degrees

[0025]

[Table 3]

As a result, it was confirmed that when the clearance angle θ was 40 degrees or less, the pulling load was small. However,
If the clearance angle θ is less than 30 °, a fold flaw may be generated.

[0027]

According to the present invention, in rolling a seamless steel pipe by a mandrel mill, the mandrel bar can be easily pulled out, and a reduction in rolling efficiency and a reduction in yield can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a shape of a seamless steel pipe during rolling.

FIG. 2 is an explanatory diagram showing a detailed shape of a hole of a hole roll.

FIG. 3 is a graph showing the relationship between the ratio of the radius of curvature of the groove bottom hole after the final thickness reduction stand to the radius of curvature of the groove bottom hole of the final thickness reduction stand and the pulling load.

FIG. 4 is a graph showing a relationship between a relief angle of a hole type roll and a pulling load.

Claims (1)

[Claims] 1. A mandrel bar is inserted into a raw tube obtained by piercing a round steel slab as a raw material with a piercing machine, and the raw tube is rolled by a plurality of hole-shaped roll stands to form a seamless steel tube. In the mandrel mill rolling method, the radius of curvature R _{1 ( n + 1)} of the bottom of the hole-shaped groove of the roll tand after the final reduced thickness roll stand among the hole-shaped roll stands is determined by the final the thickness reduction Russia - with a 1.010 to 1.025 times the hole-shaped groove bottom of Le stand curvature radius R _1n, characterized by rolling the relief angle θ of the hole-shaped as 30-40 degrees Mandrel mill rolling method.