JPH10277608A - Method for drawing metallic tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drawing method of a metallic tube by which a round tube whose angular rate is <=1% is easily obtained by rolling with a stretch reducer whose elliptic rate is in the ordinary range (0-12%). SOLUTION: By selecting the diameter reducing rate (y) (%/std.) per stand at each stand, phase angle (x) (deg.) and stretch coefficient Z so that the relation of the formula: y<=Y(Z)-1.4 In(x) (Where, the coefficient Y(Z) is corresponded to the range [0, 0.3), [0.3, 0.4), [0.4, 0.5), [0.5, 0.6), [0.6, 1) of the Z and taken as Y(Z)=13.7, 14.2, 14.7, 15.2, 15.7.) is satisfied and drawing is executed, preferably, at 400-800 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drawing and rolling a metal tube, and more particularly to a method for drawing and rolling a metal tube capable of reducing the squareness of the inner surface of the tube.

[0002]

2. Description of the Related Art A draw rolling mill called a stretch reducer is often used for draw rolling to finish a metal tube having a small diameter to a product outer diameter with high efficiency. This rolling mill is a two-roll type, and in recent years, a three-roll type caliber roll stand is usually arranged in tandem with 20 or more stands, and the outer diameter and thickness of the hollow tube are increased while applying tension between stands. Finished to predetermined dimensions, depending on the outer diameter and thickness of the product
The major feature is that the number of stands to be used and the tension between stands can be adjusted to finish the product from a raw tube (base tube) having the same outer diameter to various product dimensions with high efficiency.

In a stretch reducer, considering the symmetry, the phase difference (phase angle) of the center of the caliber bottom between adjacent stands is 90 ° for a two-roll type and 60 ° for a three-roll type (FIG. 2). It is common to set to (see). However, when the wall thickness of the pipe is large and the reduction of the outer diameter is large, as shown in FIG.
It is known that a square (b) square is generated in the two-roll system. Such squareness may interfere with the internal thread cutting of the pipe. FIG. 4 shows the definition of the squareness ratio that quantitatively describes the squareness.

It has been empirically known as a countermeasure to prevent such squareness that the outer diameter reduction amount is reduced, the stand-to-stand tension is increased, and the shape of the caliber is rounded. Furthermore, Japanese Patent Publication No. 3-78161 proposes to roll the ellipticity O _v = (B−H) / H of the roll caliber shape defined in FIG. 5 as a negative value (B <H). This is to achieve uniform thickness in the circumferential direction by tightly rolling the flange portion, which is conventionally easy to increase the thickness, and allowing the meat to escape to the caliber portion.

In Japanese Patent Application Laid-Open No. 61-216806, the phase difference (phase angle) between stands is 180 ° / N and 90 ° / N.
It has been proposed to perform rolling in a rolling pattern in which (N is the number of rolls per stand = 2, 3). This is achieved by appropriately adding a phase difference (45 ° for two rolls and 30 ° for three rolls) that is half of the conventional phase difference (90 ° for two rolls and 60 ° for three rolls) to the rolling pattern. The number of corners of the tension is doubled (octagonal for two rolls, dodecagonal for three rolls) to reduce the thickness difference in the circumferential direction. In connection with this, the rolling mill for the forged pipe line was installed at 20st
d. (abbreviation of stand) was increased to 27std., and the phase (phase angle) of the squeezing roll was changed from 60 ° to 15 ° (CA)
MP-ISIJ vol8 (1995), p.1222). According to this, it is considered that the squared shape becomes twenty-four-sided and further approaches a circle.

[0006]

As described above, factors affecting the squaring phenomenon in the stretch reducer rolling are the diameter reduction ratio (outer diameter reduction ratio), the roll ellipticity, the tension between the stands, and the phase angle. Although it is known that there is a certain tendency and the tendency of the correlation between them and the squareness is also known to some extent individually, the squareness is within an allowable range (eg, squareness ratio ≦ 1%).
From the viewpoint of selecting the optimal drawing and rolling conditions that fall within the range, there is no technology that can easily select such optimal drawing and rolling conditions in consideration of the above factors.

Therefore, in order to reduce the angularity in the stretch reducer rolling, for example, when the phase angle of any stand is changed, how to change the other three factors is examined by a small number of trials each time. At present, it is necessary to decide by rolling, and this test rolling hinders productivity, and there is also a problem that it is not always possible to grasp the optimum conditions with a limited number of test rolling. It was difficult to finish the inner surface shape without average squareness.

In the present invention, therefore, the ellipticity is in the normal range (0
~ 12%) by stretch reducer rolling, squareness ratio 1%
An object of the present invention is to propose a method of reducing and rolling a metal tube in which the following circular tube can be easily obtained.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a method for drawing and rolling a metal tube using a stretch reducer in which the roll ellipticity of each stand is 0 to 12%. y (% / std.), phase angle x (d
eg.) and a stretch coefficient Z are selected so as to satisfy the relationship of the following equation (1) and then the reduction rolling is performed.

Note that y ≦ Y (Z) −1.4 ln (x) (1) where the coefficient Y (Z) is in the Z range [0, 0.3), [0.3, 0.
4), [0.4, 0.5), [0.5, 0.6), [0.6,1)
(Z) = 13.7, 14.2, 14.7, 15.2, 15.7. Further, in the present invention, it is preferable that the rolling is performed in a temperature range of 400 to 800 ° C.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the stretch coefficient Z is a value obtained by dividing the arithmetic mean of the front tension and the rear tension of the stand by the deformation resistance of the tube. Further, the description format of the range of Z, "[lower limit, upper limit)" means that this range includes the lower limit and does not include the upper limit. The present inventors used a three-roll type stretch reducer equipped with a normal ellipticity caliber roll and used an outer diameter of 62 to 146 mm φ and a wall thickness of 2 to 6 mm.
Outer diameter: 21.7 ~ 114.3mm φ, wall thickness:
We analyzed the results of many drawing rolling operations to produce product pipes with a pipe wall thickness of ± 20% and repeated several model rolling experiments using a model mill of a three-roll type stretch reducer. Diameter reduction per hit y
(% / Std.), The phase angle x (deg.), And the stretch coefficient Z satisfy the above-mentioned formula (1), it is extremely low that the angulation rate of the product pipe is 1% or less irrespective of the temperature of the reduction rolling. Important findings were obtained.

According to the present invention employing the above configuration based on such knowledge, it is possible to easily select the rolling conditions for reducing the squaring ratio to 1% or less, and to obtain a metal having an extremely small squaring inner surface shape. Tubes can be produced with high efficiency by stretch reducer rolling. On the other hand, if rolling is performed at a temperature lower than 400 ° C., the rolling load increases,
A brittle zone of steel exists around 0 to 400 ° C., which is not preferable. Further, it is not preferable to perform the rolling at a temperature higher than 800 ° C., because the surface skin of the product tube is deteriorated due to the bite of the scale. Therefore, the present invention is preferably applied to reduction rolling in a temperature range of 400 to 800 ° C. In order to perform such warm reduction rolling, a heating furnace such as a heating furnace or a high-frequency induction heating device may be provided on the stretch reducer entrance side to heat the raw tube before the reduction reduction to a desired temperature.

[0013]

FIG. 1 is a graph showing the relationship among x, y, and Z according to equation (1). With reference to this figure, the embodiment of the present invention will be described by taking as an example the case where the stretching coefficient Z is selected from the desired phase angle x when the diameter reduction ratio per stand y = 10% / std. From FIG. 1, if x ≦ 15 °, a product pipe having a squaring ratio of 1% or less can be obtained regardless of Z. In this case, Z can be freely selected within the thickness controllable range. 15 °
If ≦ x ≦ 60 °, the squaring ratio is 1% in the small Z region.
May be exceeded. Therefore, when x is within this range, a straight line having a level of y = 10% / std. Or more is adopted among the straight lines drawn in the figure according to each range of Z, and Z is taken from the range corresponding to the straight line. Is selected. Also, x> 60 °
Then, no matter how Z is selected, it is difficult to obtain a product pipe having a squaring ratio of 1% or less, so x or y is reviewed.

As described above, according to the present invention, it is possible to easily select the rolling conditions for reducing the squaring ratio to 1% or less without repeating the test rolling. A 3-roll stretch reducer with 14 stands, equipped with a caliber roll with an ellipticity of 0 to 12%. The outer diameter of the tube is 62 to 146 mm, and the wall thickness of the tube is 2 to 6.
The present invention was carried out in a pipe production line in which a steel pipe having a diameter of 21.7 to 114.3 mm was squeezed and rolled into a product pipe having a tube thickness of ± 20%. A heating furnace is arranged on the inlet side of the stretch reducer, and the raw tube is heated to about 650 to 900 ° C and the drawing rolling temperature is set to 400 to
The temperature was controlled at 800 ° C.

Table 1 shows examples of the reduction rolling schedule satisfying the present invention in comparison with the conventional example.

[0016]

[Table 1]

From Table 1, it can be seen that the squaring ratio exceeds 1% in the conventional example, but is suppressed to 1% or less in the embodiment. As a result, a remarkable effect was obtained in that the ratio of product pipes having a squaring ratio exceeding 1% was reduced by about 97% as compared with the conventional case.

[0018]

As described above, according to the present invention,
An excellent effect that a metal tube having an inner surface shape with a squareness of 1% or less can be easily obtained by stretch reducer rolling having an ellipticity in a normal range.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship among x, y, and Z according to equation (1).

2 (a) is a front view and FIG. 2 (b) is a side view showing a phase angle between stands exemplified for a three-roll type stretch reducer.

FIG. 3 is a cross-sectional view showing a squaring of the inner surface of a pipe by stretch reducer rolling.

FIG. 4 is a definition diagram of an angular tension ratio.

FIG. 5 is a definition diagram of an ellipticity of a roll caliber shape.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Motoaki Itaya 1-1-1, Kawasaki-cho, Handa-city, Aichi Prefecture Inside the Chita Works, Kawasaki Steel (72) Inventor Akira Ito 1-1-1, Kawasaki-cho, Handa-city, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Yuji Hashimoto 1-1-1, Kawasakicho, Handa City, Aichi Prefecture Kawasaki Steel Corporation Chita Works (72) Inventor Taro Kanayama 1-1-1, Kawasakicho, Handa City, Aichi Prefecture Kawasaki Steel Corporation Chita Works

Claims (2)

[Claims] 1. The roll ellipticity of each stand is 0 to 12%
In the method of drawing and rolling a metal tube using a stretch reducer, the diameter reduction ratio y (% / std.), Phase angle x (deg.), And stretch coefficient Z per stand in each stand are calculated by the following formula ( A reduction rolling method for a metal tube, wherein the reduction is performed by selecting so as to satisfy the relationship 1). Note that y ≦ Y (Z) −1.4 ln (x) (1) where the coefficient Y (Z) is in the Z range [0, 0.3), [0.3, 0.
4), [0.4, 0.5), [0.5, 0.6), [0.6, 1)
(Z) = 13.7, 14.2, 14.7, 15.2, 15.7. 2. The method according to claim 1, wherein the reduction is performed in a temperature range of 400 to 800 ° C.