JP2011152576A - Method of manufacturing small-diameter thin-walled tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a small diameter thin-walled tube having no internal stripe flaws in a method of manufacturing a small-diameter thin-walled seamless steel tube by drawing a tube stock which is made by hot tube-making. <P>SOLUTION: In the method of manufacturing a seamless steel tube, the small-diameter thin-walled thickness tube is drawn by using a tapered die 1 including a taper-shaped approach part 1a and a bearing part 1b by which a drawing outside diameter is determined as a working die, and a plug 2 which is inserted into the inside of a tube 3 to be drawn while the diameter is reduced with the tapered die. In the method of manufacturing the small-diameter thin-walled thickness tube, a tapered die 1 having both the angles α of 15-20° of the approach part 1a is used. In this method of manufacturing the small-diameter thin-walled thickness tube, it is preferable to use a semi-floating plug 2 provided with a finishing part 2b for controlling the finished inside diameter of the tube and the tapered part 2a provided successively to the finishing part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a small-diameter, thin-walled seamless steel pipe by drawing a raw pipe that has been hot-formed. More particularly, the present invention relates to a method for manufacturing a small diameter thin walled tube that does not have internal streaks.

Unless otherwise stated, the definitions of terms in this specification are as follows.
“Small-diameter thin-walled pipe”: A seamless steel pipe obtained by drawing a base pipe obtained by hot-rolling into a predetermined size by drawing, and the ratio of thickness / outer diameter (T / D) after drawing is 5 to 15%, an outer diameter of 20 to 30 mm, and a wall thickness of 1.0 to 3.5 mm.

  A seamless steel pipe that is cold-finished is made by forming a solid steel slab into a hollow base pipe by hot pipe making by Mannesmann pipe manufacturing method or Eugene pipe manufacturing method, and then drawing the base pipe cold. Manufactured. In the Mannesmann tube method, Mannesmann is drilled in a steel slab, and a constant diameter or reduced diameter rolling is performed with a sizer or a reducer to form a raw pipe. The obtained tube is subjected to cold drawing. The main purposes of cold drawing are to improve the dimensional accuracy of the outer diameter, inner diameter, and wall thickness, to ensure mechanical strength, and to improve the inner surface smoothness. That is, the reduction of wrinkles on the inner surface of the steel pipe is one of the major purposes of the cold drawing process.

  Seamless steel pipes finished by drawing have applications such as for plant piping and machine structures, and are sometimes used in automobiles as steel pipes for automobiles. In the use of an air bag, the seamless steel pipe is used as a pressure vessel and is used in a state in which a high-pressure gas is sealed. Therefore, wrinkles on the inner surface of the seamless pipe are not preferable.

  Therefore, when a streak is formed on the inner surface of the raw tube obtained by hot pipe making (hereinafter, also simply referred to as “inner surface scissors”), the streak is reduced on the inner surface by drawing or Need to be removed.

  Moreover, since the pressure vessel of an airbag is calculated | required that it is small and lightweight, a small diameter thin wall pipe is used for the steel pipe for airbags.

By the way, in the case of reducing / removing the internal streak due to the drawing process, the effect of removing the internal streak is larger as the thickness processing degree expressed by the following equation (1) is larger.
TD = (T′−T) / T ′ × 100 (1)
However, the thickness processing degree is TD (%), the thickness of the steel pipe before drawing is T ′ (mm), and the thickness of the steel pipe after drawing is T (mm).

  FIG. 1 is a schematic diagram showing a drawing process using a taper die and a semi-floating plug. In the figure, a taper die 1, a plug 2 inserted into an inner surface of a blank pipe (steel pipe before drawing), and a blank pipe 3 to be drawn are shown, and the blank pipe moves in a direction indicated by a black arrow. Thus, it is drawn. The taper die 1 guides the pipe material to the die exit side, so that the taper-shaped approach portion 1a in which the inner diameter of the die on the entry side is reduced, the bearing portion 1b having a constant inner diameter and determining the processing shape of the pipe material, And a side relief portion 1c. The shape of the approach portion 1a of the taper die is defined by both angles α (°).

  The semi-floating plug 2 is fixed at a processing position by a support rod 2c held at a fixed end (not shown), and has a taper portion 2a for preventing displacement of the plug as the raw pipe is thickened, and a finished inner diameter of the pipe. And a finishing portion 2b to be defined. The shape of the tapered portion of the semi-floating plastic is defined by both angles β (°).

  In the drawing process using the taper die 1 and the semi-floating plug 2, the tube 3 is reduced in diameter in accordance with the contact with the taper die approach portion 1a, and then further contacted with the taper portion 2a of the semi-floating plug to be thickened. Is done. Thereafter, the blank tube 3 is thickened by a tapered die bearing portion 1b and a semi-floating plug finishing portion 2b to be finished into a seamless steel pipe having a predetermined outer diameter and inner diameter.

  A frictional force acts on the semi-floating plug 2 in the drawing direction as the raw pipe is processed during the drawing process. Further, when the raw pipe is thickly processed by the tapered portion 2a and the tapered die approach portion 1a, a reaction force acts on the semi-floating plug 2 in the direction indicated by the white arrow in FIG.

  The semi-floating plug 2 is fixed at the machining position by the support bar 2c. However, if the component of the reaction force in the pulling direction is small, the support bar 2c is elastically deformed by the frictional force, and the floating plug is displaced from the machining position. It causes drawing defects such as generation and breakage of the tube. For this reason, in order to stably perform the drawing process, it is preferable that the component in the drawing direction of the reaction force is equal to the frictional force, and the support bar 2c suppresses elastic deformation.

Conventionally, various proposals have been made regarding a drawing process using a taper die and a semi-floating plug. For example, Patent Document 1 proposes a drawing method that can stabilize the plug position. In the drawing method proposed in Patent Document 1, both angles (die both angles) α (°) of the approach portion of the die and both angles (plug both angles) β (°) of the taper portion of the plug are the following (2) and (3 ) Satisfying the equation, the pulling direction component of the reaction force described above and the frictional force are balanced, so that the position of the plug can be prevented from shifting in the drawing direction, and the seizure of the blank tube to the die and the breakage of the blank tube Can be prevented.
15 ≦ α ≦ 30 (2)
α-10 ≦ β ≦ α-3 (3)

  When the drawing method proposed in Patent Document 1 is used for manufacturing a small-diameter and thin-walled seamless steel pipe, the small-diameter thin-walled pipe obtained may have an internal stripe depending on the angle of the die even if the above equation (2) is satisfied. May remain.

  As described above, the removal effect of the inner surface streak is higher as the wall thickness processing degree is larger. Therefore, in order to prevent the inner streak from remaining, it is conceivable to increase the thickness of the raw tube. If the thickness ratio between the thickness and the steel pipe wall thickness after drawing is too large, vibrations and breakage of the raw pipe occur during drawing, and stable drawing cannot be performed. For this reason, in the drawing process of a small-diameter thin wall tube, the thickness of the raw tube cannot be increased so much.

  Patent Document 2 relates to the reduction of inner surface streaks in a thick-walled seamless steel pipe having a thickness / outer diameter (T / D) ratio of 20% or more, and is an oil-lubricated or chemical-coating-lubricated base pipe Has been proposed for drawing under the processing conditions that satisfy the conditional expression defined by the thickness processing degree and the die angle.

  Since the object of the drawing method proposed in Patent Document 2 is a thick-walled steel pipe, the thickness ratio before and after the drawing process does not increase so much even if the thickness of the raw pipe is increased. If the conditional expression is satisfied, good results can be obtained. However, in the case of a small-diameter thin-walled tube, as described above, since the thickness of the raw tube cannot be increased so much, even if the conditional expression described in Patent Document 2 is satisfied, depending on the die angle, inner surface streaks may remain. .

JP 2006-272396 A JP 2002-361319 A

  As described above, by using a conventionally proposed drawing method to produce a small-diameter, thin-walled seamless steel pipe by drawing a hot-formed blank, even if the previously proposed conditions are satisfied, Depending on the angle, there is a problem that the inner surface streaks formed by hot pipe making cannot be removed. This invention is made | formed in view of such a condition, and it aims at providing the manufacturing method of a small diameter thin wall tube which does not leave an internal surface fistula.

In order to solve the above-mentioned problem, the pipe tube is drawn only with a taper die without using a plug, and a drawing test by “empty drawing” is performed, and the influence of both angles of the approach part of the taper die on the wall thickness of the pipe. confirmed. In this test, the relationship between the thickness / outer diameter (T / D) ratio and the rate of increase in wall thickness when the angle α of the approach portion was 20 °, 25 °, and 30 ° was investigated. Here, the thickness increase rate TW (%) can be calculated by the following equation (4), where T '(mm) is the thickness of the blank tube and T (mm) is the thickness after drawing by empty drawing.
TW = (T−T ′) / T ′ × 100 (4)

The test conditions in this test were as follows.
Base tube specifications: wall thickness / outer diameter = 7% to 9%
Material Cr-Mo steel (C 0.1-0.2%,
Cr 0.5-0.7%,
Mo 0.3-0.4% contained)
Drawing tube specifications: wall thickness / outer diameter = 8% to 10%

  FIG. 2 is a diagram showing the relationship between the thickness / outer diameter (T / D) ratio (%) and the thickness increase rate TW (%) when a small-diameter thin tube is obtained by emptying only with a taper die. . From this figure, it can be confirmed that the thickness increase rate TW (%) is a positive value. From this test, it was found that the wall thickness was increased (thickened) by pulling out the small-diameter thin-walled tube using a taper die (empty drawing). Moreover, it turned out that the wall-thickening rate TW (%) increases by making both angles (alpha) of an approach part small.

The present inventors have obtained the following findings (a) to (c) based on the above test results.
(A) When a drawing process using a die and a plug is performed on a small-diameter thin wall pipe, the thickness of the pipe to be processed is once increased (increased) in the approach portion of the taper die, and then in the bearing portion (facing The thickness is reduced (thinned) by being sandwiched and pulled out by the finished part of the plug, resulting in the final processed thickness (target thickness).

(B) Moreover, if both angles of the approach part of a taper die | dye are made small, the amount of thickness increase in this approach part will increase (thickness will become thicker).

(C) Therefore, even if the thickness of the steel pipe (base pipe) before drawing and the thickness of the steel pipe after drawing are constant, by reducing both angles of the approach portion of the taper die, Because the thickness of the steel pipe is once increased, the substantial thickness workability can be increased. Therefore, it seems to be able to enhance the effect of removing internal muscles.

  The present invention has been completed on the basis of the above findings and the results of the confirmation test described below, and the summary thereof is the following (1) to (3) manufacturing method of a small-diameter thin-walled tube:

(1) A taper die having a tapered approach portion and a bearing portion for determining a drawing outer diameter as a processing die;
A method for producing a seamless steel pipe by drawing a small-diameter thin wall pipe using a plug inserted into an inner surface of a pipe that is drawn while being reduced in diameter by the taper die,
A method for producing a small-diameter thin-walled tube, wherein a taper die having both angles of 15 to 20 ° is used in the approach portion.

(2) The small-diameter thin-walled tube according to (1) above, wherein the plug to be used is a semi-floating plug having a finished portion that defines a finished inner diameter of the tube and a tapered portion that is connected to the finished portion. Production method.

(3) The method for producing a small-diameter thin tube according to (1) or (2) above, wherein the small-diameter thin-walled tube obtained does not have inner surface streaks.

The method for producing a small-diameter thin-walled tube of the present invention has the following remarkable effects.
(1) By drawing using a taper die and a plug, a small-diameter thin tube with excellent inner surface quality can be obtained by reducing inner surface streaks that occur during hot pipe manufacturing without increasing the thickness of the tube. Obtainable.

It is a schematic diagram which shows the drawing process using a taper die and a semi-floating plug. It is a figure which shows the relationship between ratio (%) of thickness / outer diameter (T / D), and thickness increase rate TW (%) when a small diameter thin tube is obtained by emptying only with a taper die. This is a photograph of the inner surface properties of the pipe that was cut in the middle of the drawing process, and the pipe was cut, and (a) in the figure shows a comparative example in which both angles of the approach portion of the taper die are 25 °. (B) shows an example of the present invention in which both angles are 20 °. It is a figure which shows the thickness ratio and inner surface reinforcement depth ratio in each position of the drawing direction of a pipe about the thing which stopped the drawing process of the pipe in the middle process, and cut the pipe. (B) shows the depth ratio of the inner surface reinforcement at each position.

  Below, the manufacturing method of the small diameter thin wall pipe | tube of this invention is demonstrated.

  The steel pipe used as the object of the present invention is a small diameter thin wall pipe. Here, the small-diameter thin-walled pipe is a seamless steel pipe obtained by finishing a raw pipe obtained by hot pipe making into a predetermined dimension by drawing, and the thickness / outer diameter (T / D) after drawing. The ratio is 5 to 15%, the outer diameter is 20 to 30 mm, and the wall thickness is 1.0 to 3.5 mm.

  When the ratio of thickness / outer diameter (T / D) after drawing is 15% or the thickness exceeds 3.5 mm, the internal stripes can be reduced by the conventional drawing, and the small diameter thin wall of the present invention There is no need to use a tube manufacturing method. On the other hand, if the thickness / outer diameter (T / D) ratio after drawing is 5% or the thickness is less than 1.0 mm, sufficient strength as a pressure vessel for an airbag cannot be ensured. The outer diameter after the drawing is set to 20 to 30 mm is based on the use of the steel pipe for airbag.

  Small-diameter thin-walled pipes are made of various steel types such as Cr-Mo steel and carbon steel. It tends to remain. Therefore, it is preferable to use the method for producing a small-diameter thin tube of the present invention for drawing a small-diameter thin tube made of Cr-Mo steel.

  The method for producing a small-diameter thin-walled tube according to the present invention includes a taper die having a tapered approach portion as a working die and a bearing portion for determining a drawing outer diameter, and is drawn while being reduced in diameter by the taper die. A method of manufacturing a seamless steel pipe in which a small-diameter thin-wall pipe is drawn using a plug inserted into the inner surface of the pipe, wherein a taper die having both angles of 15 to 20 ° is used.

  In the method for manufacturing a small diameter thin tube of the present invention, both angles of the approach portion of the taper die are set to 15 to 20 °. From the results shown in FIG. 2, it can be seen that in the emptying of the small-diameter thin-walled tube, the thickness increase rate TW (%) increases when both angles of the approach portion are reduced. For this reason, in the drawing process using a plug, by reducing both angles of the approach part, it is possible to increase the thickness of the raw pipe (drawn pipe) at the approach part. Can increase the degree. That is, even if the thickness of the steel pipe (raw pipe) before drawing and the thickness of the steel pipe after drawing are constant (in other words, the thickness of the pipe is not increased), the approach portion In this case, since the thickness once increases, the thickness processing degree can be substantially secured in the processing at the bearing portion, and the inner surface streak of the obtained seamless steel pipe can be reduced.

  If both angles of the approach part of the taper die exceed 20 °, the thickness increase rate TW due to the taper die will decrease, so it is not possible to secure the wall thickness processing in the bearing part, and the obtained seamless steel pipe has no internal reinforcement. Remains. On the other hand, if both angles of the approach portion are less than 15 °, the contact distance between the approach portion and the raw pipe increases, and therefore vibration due to poor lubrication is likely to occur. In this case, the inner surface quality of the obtained seamless steel pipe deteriorates.

  In the method for manufacturing a small-diameter thin-walled tube of the present invention, various plugs such as a cylindrical plug, a semi-floating plug, and a floating plug can be used as the plug, but a semi-floating plug is preferably used. By using a semi-floating plug as the plug, the plug can be stably disposed at the processing position, and drawing defects can be suppressed.

In the method for manufacturing a small-diameter thin-walled tube of the present invention, when using a semi-floating plug, it is preferable that both angles of the tapered portion satisfy the following expression (3).
α-10 ≦ β ≦ α-3 (3)
Here, both angles α (°) of the approach portion of the taper die are defined as both angles β (°) of the taper portion of the plug.

  When the difference between both angles α of the approach portion and both angles β of the tapered portion is larger than 10 °, that is, when β <α−10, the reaction force acting on the plug during the drawing process decreases the component in the drawing direction. To do. For this reason, since the position of the plug is shifted in the drawing direction with the drawing of the raw tube, a drawing defect may occur. On the other hand, when the difference between both angles α of the approach portion and both angles β of the tapered portion is smaller than 3 °, that is, when β> α-3, the rear end of the tapered portion bites into the inner surface of the raw tube. Since the position of the plug is shifted in the drawing direction, a drawing failure is likely to occur.

  As described above, the small-diameter thin-walled tube used for the air bag is used in a state in which high-pressure gas is sealed, and therefore, internal streaks are not preferable. In the method for manufacturing a small-diameter thin-walled tube of the present invention, it is possible to substantially secure the thickness processing degree without increasing the thickness of the raw tube so much. The inner surface streak can be removed.

  A test for obtaining a small-diameter thin-walled tube was performed by drawing a hot-tubed raw tube by the method for producing a small-diameter thin-walled tube of the present invention, and the effect of the present invention was verified.

[Test method]
Using the taper die and the semi-floating plug shown in FIG. 1, the base pipe was subjected to a drawing process to obtain a drawn pipe. The conditions are as follows.
Specifications of the raw tube: outer diameter 31.80mm, wall thickness 2.90mm,
Material Cr-Mo steel (C 0.1-0.2%,
Cr 0.5-0.7%,
Mo 0.3-0.4% contained)
Drawing tube specifications: outer diameter 25.05mm, wall thickness 2.02mm

  Both angles of the approach portion of the taper die were 15 ° in the present invention example 1, 20 ° in the present invention example 2, and 25 ° in the comparative example 1. Further, both angles of the tapered portion of the floating plug were 10 ° in the present invention example 1, 15 ° in the present invention example 2, and 20 ° in the comparative example 1.

[Evaluation index]
In both the inventive examples and the comparative examples, the inner surface properties of the drawn pipes were confirmed visually. Furthermore, in Invention Example 2 and Comparative Example 1, the pipe drawing process was stopped in the middle of the process, and after the pipe was cut, the thickness of the pipe and the depth of the inner surface streak were measured at a plurality of positions in the drawing direction. The wall thickness ratio and the depth ratio of the internal muscles were calculated. Here, the thickness ratio refers to a value represented by T / T ′, where T is the measured thickness of the tube and T ′ is the thickness of the raw tube. Further, the depth ratio of the inner surface streak is a value represented by A / A ′, where A is the measured depth of the inner surface streak and A ′ is the depth of the inner surface streak of the raw tube. That means.

[Test results]
When the inner surface of the drawn pipe was visually confirmed, no inner surface streak was observed in Invention Example 1 and Invention Example 2. On the other hand, in Comparative Example 1, the depth of the inner surface streak was reduced, but the inner surface streak remained.

  FIG. 3 is a photograph of the inner surface properties of the pipe that was cut in the middle of the drawing process, and the pipe was cut, and FIG. 3A is a comparative example in which both angles of the tapered die approach portion are 25 °. FIG. 4B shows an example of the present invention in which both angles are 20 °. In the drawing, a cut surface 3a of the drawn tube and a tube inner surface 3b are shown, and a contact start position 3d with the approach portion of the taper die and a contact start position 3e with the finish portion of the floating plug are shown by white dotted lines. . In the figure, the portion surrounded by the white imaginary line is the inner surface streak.

  In Comparative Example 1, using a taper die with both angles of the approach portion being 25 °, it was confirmed from FIG. On the other hand, in Example 2 of the present invention, it was confirmed from the drawing (b) that no streak was present on the inner surface 3b after drawing using a taper die with both angles of the approach portion being 20 °.

  FIG. 4 is a diagram showing the wall thickness ratio and the inner surface muscle depth ratio at each position in the drawing direction of the pipe with respect to what the pipe drawing process is stopped in the middle of the process as in FIG. The figure (a) shows the thickness ratio in each position, and the figure (b) shows the depth ratio of the inner surface reinforcement at each position. The horizontal axis of the figure (a) and (b) shows the distance from the contact position of the plug to the measurement position, the taper die approach part side is negative (-), the taper die escape part side is positive (+) To express.

  From FIG. 5A, the wall thickness ratio before the bearing portion is greater in the present invention example 2 in which both angles of the approach portion are 20 ° than in Comparative Example 1 in which both angles of the approach portion of the taper die are 25 °. It was confirmed that it was large, that is, the wall thickness was increased more in the approach part. Therefore, it was confirmed that the substantial thickness processing degree in the bearing portion was increased.

  Moreover, from the same figure (b), in Comparative Example 1 in which both angles of the approach portion are 25 °, the depth of the inner surface streak is reduced by the drawing process, but the inner surface streak remains after the drawing process. Was confirmed. On the other hand, in Example 2 of the present invention in which both angles of the approach portion were 20 °, it was confirmed that the inner surface streak was removed after the drawing process.

  From these, by the manufacturing method of the small-diameter thin wall tube of the present invention, the amount of increase in the raw tube is increased in the approach part, and in the subsequent wall thickness processing, the wall thickness processing degree is increased according to the increase in the wall thickness increase in the approach part. As a result, it was clarified that the inner surface streaks of the drawn tube can be reduced and the inner surface quality of the obtained tube can be improved.

The method for producing a small-diameter thin-walled tube of the present invention has the following remarkable effects.
(1) By drawing using a taper die and a plug, a small-diameter thin tube with excellent inner surface quality can be obtained by reducing inner surface streaks that occur during hot pipe manufacturing without increasing the thickness of the tube. Obtainable.
(2) When the obtained small-diameter thin-walled tube is applied to a pressure vessel that constitutes an airbag, it has excellent resistance to bursting because it has no inner surface streaks.
Therefore, according to the manufacturing method of the present invention, it is possible to provide a small-diameter thin-walled tube suitable for a pressure vessel used for an automobile airbag.

1. Taper dies, 1a. Approach section, 1b. Bearing part,
1c. 1. escape part, Semi-floating plug, 2a. Taper,
2b. Finishing part, 2c. 2. a support rod; Element tube, 3a. Raw tube cut surface,
3b. Inner surface of the tube 3c. Inner muscle,
3d. Contact start position with taper die,
3e. Contact start position with floating plug,
α. Both angles of approach part, β. Both corners of taper

Claims (3)

A taper die having a tapered approach portion and a bearing portion for determining a drawing outer diameter as a processing die;
A method for producing a seamless steel pipe by drawing a small-diameter thin wall pipe using a plug inserted into an inner surface of a pipe that is drawn while being reduced in diameter by the taper die,
A method for producing a small-diameter thin-walled tube, wherein a taper die having both angles of 15 to 20 ° is used in the approach portion.   2. The method for producing a small-diameter thin-walled tube according to claim 1, wherein the plug to be used is a semi-floating plug having a finish portion that defines a finish inner diameter of the tube and a tapered portion that is connected to the finish portion.   The method for producing a small-diameter thin-walled tube according to claim 1 or 2, wherein the obtained small-diameter thin-walled tube does not have an inner surface fistula.

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