JPH0924408A - Method for controlling elongation rolling of steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate defective drawing of a mandrel bar after rolling and generation of bulging flaws or faulty drawing of a tube at the time of executing thinning rolling of both end parts of a hollow tube stock with a mandrel mill. SOLUTION: When the curvature in the relief parts from the groove to the flange parts of a grooved roll 26 in the stand of an elongation mill for executing screw-down location control so as to thin thickness in the tip and rear end parts of the tube is expressed by R3 and the depth of groove bottom from the groove bottom part 26D to a flange part 26B by DK, the roll gap G of the flange part 26B is controlled in the range of -0.67G/DK+0.4<=R3/DK-G/DK +0.8 over the entire length between the tip of rolling and the rear end of rolling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when producing a seamless steel pipe from a hollow shell through a drawing and rolling machine and a drawing and rolling machine, prevents a defective shape of the tube at the tip and rear ends of the drawing and rolling machine. In addition, the present invention relates to a method for controlling the stretching and rolling of a steel pipe that suppresses the thickening of the front and rear ends in a drawing rolling mill.

[0002]

2. Description of the Related Art Generally, a mandrel mill method, a plug mill method, or a Eugene Sejournet method, an Erhart push bench method, or another hot extrusion method is used to manufacture a seamless steel pipe. For small diameter size, there are many mandrel mill rolling methods that are more excellent in productivity and dimensional accuracy.

First, a general seamless steel pipe manufacturing process by the mandrel mill rolling method will be described with reference to FIG.

The manufacturing equipment includes a heating furnace 1, a piercing and rolling mill (Mannesmann piercer) 2, and a drawing and rolling mill (mandrel mill).
3, a reheating furnace 4 and a reduction rolling machine (stretch reducer) 5. A continuous casting machine 6 for hollow tube production may be used instead of the heating furnace 1 and the piercing and rolling machine 2.

In the heating furnace 1, a predetermined temperature (generally 11
The material billet 7 heated to 00 ° C to 1300 ° C is
A hollow shell 7A is obtained by piercing and rolling with a plug 9 between the piercer rolls 8 of the piercing and rolling machine 2.

Next, in the hollow shell 7A, a mandrel bar 10 having a surface coated with a lubricant for hot rolling is inserted in the drawing and rolling mill 3, and a plurality of mandrel mill rolls (hole type rolls) 11 are provided. The thickness of the reducer element pipe 1
It is set to 2.

The reducer element tube 12 is reheated in the reheating furnace 4 and then subjected to drawing rolling in the drawing rolling mill 5 to determine its outer diameter or to reduce the outer diameter to a small diameter.

In this final drawing rolling mill 5, tension between stands is applied to control the metal flow in the longitudinal direction, but tension between stands cannot be applied to the front and rear ends of the reducer element tube 12. Unsteady rolling,
For example, as shown in FIG. 5, the wall thickness of the front and rear end portions becomes thicker than that of a steady portion (intermediate portion) to which tension between stands is applied.

If the wall thickness at the front and rear ends is out of the wall thickness tolerance required for the product, it is cut as a crop, which is a major cause of lowering the product yield.

As a measure against this, in the drawing rolling machine before the reduction rolling, as shown in FIG. 6, the wall thickness of the front and rear end portions of the reducer element tube 12 is thinned as compared with the steady portion. Various rolling methods have been proposed.

[0011] For example, in the hydraulic pressure reduction control method for a mandrel mill disclosed in Japanese Patent Publication No. 51-43825, in two specific stands of the mandrel mill,
A hydraulic pressure reduction mechanism, which has a quick response compared to the conventional roll reduction device using a motor, is installed, and the hydraulic pressure reduction mechanism controls the thickness of the pipe tip rear end so as to offset the thickening that occurs in the drawing and rolling mill in the next process. I try to make it thin.

However, the above Japanese Examined Patent Publication No. 51-4382.
In the hydraulic reduction control method disclosed in Japanese Patent Laid-Open No. 5 publication, the material called out bulging into the gap between the flanges of the hole-shaped rolls is largely caused by the reduction of the hole-shaped rolls at the front and rear ends of the hollow shell in the drawing rolling mill. Therefore, there is a problem in that the reducer element tube is defective in shape. When this bulging portion becomes large, there is a problem that the roll surface pressure in the drawing rolling machine increases, causing the material to seize, causing a surface flaw, or causing a metal flow defect.

On the other hand, for example, Japanese Patent Publication No. 3-7700
In Japanese Patent Publication No. 3, the bulging deformation is suppressed by reducing the gap between the hole-shaped rolls at the time of rolling both ends of the hollow shell and controlling the roll rotation speed so as to apply additional tension to the hollow shell in the longitudinal direction. A method for continuous drawing and rolling of tubes is disclosed.

[0014]

However, in the tube continuous drawing and rolling method disclosed in the above Japanese Patent Publication No. 3-77003, when the responsiveness of the motor for rotating the hole-type roll is slow, especially the roll gap is reduced. When the wall thickness reduction amount is made small, the response delay of the motor controlling the roll rotation speed makes it impossible to apply a desired additional tension in the longitudinal direction to the end of the hollow shell.

Therefore, it is impossible to completely prevent the bulging deformation of the thinned and rolled portions at both ends of the hollow shell, and there arises a problem that quality defects such as inner and outer surface flaws of the pipe and metal flow defects occur. .

On the other hand, in consideration of the response delay of the motor, if the rolling-down control is performed in advance so as to apply an excessive load tension in the longitudinal direction, the bulging deformation at both ends of the pipe can be prevented, but the inside of the pipe can be prevented. There is a problem that the circumference becomes too small, the tube comes into close contact with the mandrel bar, and stripping error occurs that makes it impossible to pull out the mandrel bar from the finishing rolling stock tube (reducer stock tube) after rolling. .

The present invention has been made in view of the above problems, and in the case of carrying out thinning rolling for thinning the front and rear ends of the steel pipe at the time of stretch rolling, a motor for controlling the rotation speed of the roll is used. Even when the response is slow, it prevents bulging deformation of the pipe end of the rolled stock pipe and close contact between the rolled stock pipe and the mandrel bar, and quality defects such as inner and outer surface flaws of the pipe, metal flow defects, etc. An object of the present invention is to provide a method for controlling the stretching and rolling of a steel pipe, which can reduce stripping mistakes and improve the yield.

[0018]

As a result of repeated studies by the inventor of the present invention, the present invention has revealed a gap in a flange portion of a hole-type roll and a curvature of a clearance portion from a roll-hole-type groove to a flange portion. The reason for this is that it is possible to prevent bulging deformation at both tube ends of the raw material pipe to be rolled and close contact between the raw material pipe to be rolled and the mandrel bar by keeping the relationship with the roll hole depth constant. .

The inventor first found a condition for preventing bulging deformation and adhesion between the rolled raw pipe and the mandrel bar at the front and rear ends of the rolled raw pipe to be thinned and rolled. It was found that in rolling, bulging deformation and close contact with the mandrel bar may occur in the longitudinal middle portion of the material tube to be rolled that is not subjected to thinning rolling.

As a result of further studies, the following conditions have been found that can prevent bulging deformation and close contact with the mandrel bar over the entire length of the material tube to be rolled.

That is, when a hollow shell having a mandrel bar inserted therein is stretch-rolled by a continuous stretch-rolling machine composed of a plurality of stands each having a hole-type roll, the tube in a draw-rolling machine in a subsequent step is used. In the method for controlling the stretching and rolling of the pipe, which controls the rolling position to reduce the wall thickness of the front and rear ends of the pipe in advance in the stretching rolling machine in order to suppress the thickening of the front and rear ends, the rolling position control is performed. When the curvature of the relief portion from the groove of the hole-type roll in the stand of the stretch rolling mill to be performed to the flange portion is R3 and the groove bottom depth from the groove bottom portion to the flange portion is DK, the roll gap G of the flange portion is , -0.67G / DK + 0.4≤R3 / DK≤-G / DK from the rolling tip to the rolling trailing edge
This is a method for controlling the stretching and rolling of a steel pipe, which is characterized by controlling the range within +0.8.

That is, as shown in FIG. 1, since the steel pipe is stretch-rolled in the optimum range in which neither of the bulging occurrence region and the stripping error occurrence region occurs,
It is possible to eliminate defective drawing of the mandrel bar after rolling, occurrence of bulging defects, and the like.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of a more specific embodiment of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 2, the example of this embodiment is a draw rolling machine 20 composed of a plurality of stages of hole type rolls of first to eighth stands 20A to 20H, and a hollow shell 22
When the mandrel bar 24 is inserted into and stretch-rolled, when thinning the front and rear ends of the hollow shell 22 with the fifth stand 20E and the sixth stand 20F, under the following conditions,
The control device 30 controls the rolling position of the hole type roll 26.

As shown in FIG. 3, the stretching rolling is carried out from the groove 26A of the groove in the hole roll 26 to the flange portion 26.
When the curvature R3 of the relief portion 26C reaching the B and the groove bottom depth DK from the groove bottom portion 26D to the flange portion 26B are set to be −0. 67 G / DK + 0.4 ≦ R3DK ≦ −G / DK + 0.8 (1) Control is performed within the range of the condition.

Reference numeral R1 in FIG. 3 indicates the radius of curvature of the groove bottom portion 26D, R2 indicates the radius of curvature of the shoulder portion 26E, and B0 indicates the wrapping angle.

The fifth and sixth stands 20E, 20
Bulge width measuring devices 32E and 32F are provided on the output side of F, and the bulge width is measured by the bulge width measuring devices 32E and 32F. The bulge width measuring device 32
E and 32F are preferably optical measuring devices capable of non-contact width measurement of high temperature materials. However, the bulge width measuring device is for confirming the result of the stretching and rolling control of the present invention,
Since it is not an essential requirement for implementing the present invention, it is not always necessary to provide it.

The fifth and third stands 20E, 20F
Then, the rolling control is carried out as follows by using the hydraulic pressure reducing devices each having excellent responsiveness to the rolling position control.

Predicting or empirically grasping the degree of thickening formed at the front and rear ends of the finish pipe finish-rolled by the stretch reducer, and before and after the finish-rolling raw pipe that cancels the thick-walled portion. Calculate the wall thickness distribution in the longitudinal direction theoretically or empirically, and use this wall thickness distribution as a target value so that the front and rear ends are thinner than the central portion in the longitudinal direction of the finishing rolling pipe. The position of reduction of the hole type roll 26 is controlled.

More specifically, initially, the roll gap G of the fifth and sixth stands 20E, 20F is set so as to obtain a target wall thickness corresponding to the most distal end of the finish rolling stock pipe. , The tip of the hollow shell 22 is bitten into the fifth stand 20E, and then the roll gap G of the fifth stand 20E is expanded so as to follow the pattern of the roll gap predetermined with respect to the tip portion. .

At the same time as the hollow shell 22 advances and the portion where the wall thickness is to be thinned passes through the fifth stand 20E, at the same time, the roll gap G becomes the roll gap at the central portion in the longitudinal direction of the shell. The same applies to the sixth stand 20F.

Next, at the same time that the portion corresponding to the rolling start portion of the rear end of the finish rolling stock pipe reaches the fifth stand 20E, at the same time, the roll gap G of the fifth stand 20E changes the longitudinal direction of the stock pipe up to that point. From the roll gap with respect to the central portion, it starts to close along the pattern of roll gaps defined for the rear end of the hollow shell 22.

The rear end of the hollow shell 22 is the fifth stand 20.
When trailing through E, the roll gap G of the fifth stand 20E is set to a roll gap that achieves the target wall thickness corresponding to the rearmost end of the tube. The same applies to the sixth stand 20F.

The control pattern of the roll gap as described above has the hole shape of the hole roll 26 to be used and the hollow shell 2
2 dimensions, rolling speed, etc. are taken into consideration.

When the above rolling control is performed within the range of the condition of the above formula (1), it is possible to avoid the pulling-out failure of the mandrel bar and the occurrence of bulging defects over the entire length of the material pipe to be rolled.

According to an experiment conducted by the present inventor, the mandrel mill having the roll arrangement and the control pattern as described above was used to transfer the hole type rolls having the respective sizes shown in Table 1 to the fifth and sixth stands 20E and 20F. Built-in, outer diameter 1
A carbon steel hollow shell having a wall thickness of 0 to 120 mm and a wall thickness of 13.5 mm is used, using a mandrel bar having a diameter of 64 to 85 mm, an outer diameter of 80 to 100 mm, and a wall thickness of 6.0 m at the center in the longitudinal direction.
m, the thickness of the front and rear end part is 3.0 to 5.0 mm, and the thickness is straight from the front and rear end part to be equal to the thickness of the central part in the longitudinal direction of the raw pipe at a position 1 m from the front and rear end part. As a result of rolling the finishing rolling pipe so as to change the value, as shown in the column of basil width in Table 1, bulging occurs in the upper region of the optimum range shown in FIG. 1 and strike occurs in the lower region. It was confirmed that ripping mistakes occurred.

That is, when the bulge width measured by the bulge width measuring devices 32E and 32F is less than the lower limit value, the inner peripheral length of the material tube to be rolled becomes too small and stripping error occurs, and the bulge width exceeds the upper limit value. It was confirmed that the material pipe to be rolled out protruded from the hole type roll flange portion to generate bulging defects.

[0038]

[Table 1]

[0039]

EFFECTS OF THE INVENTION Since the present invention is configured as described above, when the hollow shell containing the mandrel bar is stretch-rolled by the stretch-rolling machine, both ends of the hollow shell are thinned and rolled. In this case, it is possible to prevent the pulling-out failure of the mandrel bar after rolling and the occurrence of bulging defects.

[Brief description of drawings]

FIG. 1 is a diagram showing a result of drawing and rolling a steel pipe under the conditions according to the present invention and a result of drawing and rolling under other conditions.

FIG. 2 is a schematic plan view showing a drawing and rolling mill for carrying out the method of the present invention.

FIG. 3 is a sectional view showing a hole-type roll in a drawing and rolling mill for carrying out the method of the present invention.

FIG. 4 is a process diagram showing a manufacturing process of a seamless steel pipe.

FIG. 5 is a diagram showing the wall thickness distribution at the front and rear ends of the finish rolling stock pipe.

FIG. 6 is a schematic cross-sectional view showing a raw tube for finish rolling in which front and rear end thinning control is performed.

[Explanation of symbols]

 20 ... Stretching and rolling mill 20E ... Fifth stand 20F ... Sixth stand 22 ... Hollow shell 24 ... Mandrel bar 26 ... Hole roll 26A ... Groove 26B ... Flange portion 26C ... Escape portion 26D ... Groove bottom portion 30 ... Control device 32E, 32F ... Bulge width measuring device G ... Roll gap

Claims (1)

[Claims] 1. A pipe in a draw-rolling machine in a post-process when a hollow shell having a mandrel bar inserted therein is stretch-rolled by a continuous stretch-rolling machine composed of a plurality of stands each having a hole-type roll. In the method for controlling the stretching and rolling of the pipe, which controls the rolling position to reduce the wall thickness of the front and rear ends of the pipe in advance in the stretching rolling machine in order to suppress the thickening of the front and rear ends, the rolling position control is performed. When the curvature of the clearance portion from the groove of the hole-type roll to the flange portion in the stand of the stretch rolling mill to be carried out is R3 and the groove bottom depth from the groove bottom portion to the flange portion is DK, the roll gap G of the flange portion is
Is −0.67 G / DK + 0.4 ≦ R3 / DK ≦ −G / DK from the rolling front end to the rolling rear end.
A method for controlling the stretching and rolling of a steel pipe, which is characterized by controlling within a range of +0.8.