JP5626150B2 - Drawing method of metal pipe - Google Patents

Description

  The present invention, when cold drawing a metal tube using a die and a plug, keeps the core axis and the drawing axis aligned with each other until the drawing process is completed using a special jig. The present invention relates to a drawing method that suppresses whirling and bending, suppresses the deterioration of uneven thickness of a drawn metal tube, and prevents the occurrence of bending.

Unless otherwise stated, the definitions of terms in this specification are as follows.
“Metal pipe”: Not limited to the high Ni alloy pipe used in the examples described later, but also includes a carbon steel pipe, an alloy steel pipe, and a stainless steel pipe.
“Swinging”: Undrawn parts are pulled out while swinging on the die insertion side due to uneven thickness of the tube and strength variation in the drawing process. A phenomenon in which uneven thickness worsens.
“Deterioration of uneven thickness”: refers to the deterioration amount (%) of the uneven thickness ratio [(maximum thickness−minimum thickness) / {(maximum thickness + minimum thickness) / 2}} × 100] associated with the drawing process. It is shown by the following formula (1).
Uneven thickness deterioration = Pull-out pipe thickness change rate (%)-Raw tube thickness change rate (%) (1)

  FIG. 1 is a vertical partial cross-sectional view for explaining the behavior in which straightness deteriorates due to the bending of a raw tube by a conventional drawing method, where (a) shows the initial stage state of drawing and (b) shows drawing. The state of the final stage of is shown.

  In general, when the metal tube 1b using the die 4 and the plug 2 is cold-drawn, the processed portion of the element tube 1a is dies due to the uneven thickness of the element tube 1a, the strength variation in the circumferential direction, or the weight of the element tube 1a. Curved from 4 as the starting point, straightness deteriorates during the drawing process. Due to this, there is a problem that uneven thickness deterioration and bending occur in the processed metal tube 1b.

  At this time, the higher the degree of drawing is, the larger the raw pipe 1a swings on the entrance side of the die 4 and the worsening of the metal pipe thickness and bending occur. In particular, in the final stage of the drawing process as shown in FIG.

  Further, as the uneven thickness deteriorates due to the swinging of the raw tube, the metal tube 1b becomes longer in the thin portion than in the thick portion, so that a difference occurs in the length to the rear end of the metal tube 1b. Since the rear end portion of the long metal tube 1b warps to the outer surface side, the bending after the drawing process becomes large, and an extra round-down is necessary to obtain a product satisfying the straightness, which deteriorates the product yield. There is also a problem.

  Conventionally, various studies have been made in order to obtain a product with little uneven thickness and excellent straightness. For example, Patent Documents 1 to 3 are disclosed as conventional techniques.

Figure 2 is a longitudinal partial cross-sectional view illustrating a modification method for preventing the pipe described in Patent Document 1, (a) shows the state before the blank tube 1a the rear end passes through the inner surface support 5 _2, (b ) shows a state after the blank tube 1a trailing edge has passed the inner surface support 5 _2.

As shown in FIG. 2 (a), in Patent Document 1, in the drawing process of a steel pipe, the pipe 2 is arranged in the vicinity of the plug 2 of the mandrel 3 to be inserted into the inner surface of the raw pipe 1a and at the substantially central position of the processed part. There is disclosed a method for preventing deformation of a tube, characterized by detachably attaching inner surface supports 5 ₁ and 5 ₂ (auxiliary rings) whose outer peripheries that are loosely inscribed in a spherical shape are detachably attached. According to the method of Patent Document 1, bending during drawing can be removed, and product quality can be improved.

In the method of Patent Document 1, as shown in FIG. 2 (b), the rear end of the blank tube 1a passes through the inner surface support 5 ₂ mounted on the pull-out direction of the center position of the mandrel 3, blank tube 1a shake In particular, there is a problem that the straightness of the rear end of the pipe drawn out at the final stage of processing deteriorates and the uneven thickness deteriorates.

FIG. 3 is a vertical partial cross-sectional view illustrating a drawing method of a metal tube described in Patent Document 2. In Patent Document 2, among the inner surface supports 5 ₁ and 5 ₂ (guide members) mounted on the mandrel 3 so that the axis of the raw tube 1a coincides with the drawing axis, the inner surface support 5 near the entry side of the die 4 is used. drawing method of the metal tube, characterized in that the _first length to 3 times the length of the outer diameter of the blank tube 1a is disclosed.

In drawing method of Patent Document 2, since the contact area between the blank tube 1a and the inner surface support 5 ₁ is large, the processing defects of blank tube 1a inner surface problems. That is, as described in Patent Document 2, in order not to cause the machining scratches on the blank tube 1a inner surface if the inner surface support 5 ₁ made of hard resin, the friction between the blank tube 1a inner surfaces support 5 ₁ surface Hard resin wear debris is generated. When this abrasion waste is pressed down by the inner surface of the raw tube 1a and the plug 2, wrinkles are generated on the inner surface of the raw tube 1a.

On the other hand, in the drawing method of Patent Document 2, if the inner surface support 5 ₁ made of steel, the lubrication shortage, scratches caused on the inner surface support 5 ₁ is printed on the blank tube 1a inner surface, the blank tube 1a inner surface there is a problem that seizure on the inner surface support 5 ₁ and the plug 2. Furthermore, in the drawing process, since a longer inner surface support 5 ₁ has a problem of reducing the insertion of the mandrel into the blank tube 1a inner surface.

  FIG. 4 is a vertical partial cross-sectional view illustrating the pipe material drawing apparatus described in Patent Document 3. In Patent Document 3, a guide rail 21 is installed in parallel with the central axis of the mandrel 3 and the die 4, and a holding mechanism 23 provided on a carriage 22 that is guided by the guide rail 21 and travels is provided on the inner end of the raw tube 1 a. The pipe drawing apparatus is disclosed in which the carriage 22 travels with the rear end of the raw tube 1a by frictional force generated by the holding mechanism 23 holding the inner surface end of the raw tube 1a. Has been.

  The processing apparatus of Patent Document 3 has a problem that, on the work surface, the mandrel 3 needs to be easily replaced in order to correspond to the insertion of the raw tube 1a and the size of the plug 2. Furthermore, in terms of the structure, first, since only the inner surface end portion of the raw tube 1a is held, the central portion of the raw tube 1a bends due to its own weight, and secondly, the carriage 22 moves linearly along the guide rail 21. The third problem is that the pulling machine having the guide tube cannot be used when the base tube is curved. Third, the carriage 22 contacts the guide tube and cannot be used. Fourth, the holding claw slips with the lubricating oil. . In addition, since the apparatus becomes complicated, there is an economic problem that capital investment increases.

JP-A-49-86255 JP-A-9-52114 JP-A 63-115611

  The present invention has been made to solve the above-described problems in the prior art, and suppresses the swinging and bending of the elemental tube due to the drawing process, suppressing the deterioration of the uneven thickness of the drawn metal pipe, and An object of the present invention is to provide a drawing method for preventing the occurrence of bending.

  In order to solve the above-mentioned problems, the present inventors have studied a method for suppressing the whirling and bending of the elementary tube accompanying the drawing process over the entire length of the elementary tube using an inner surface support. As a result, the drawing process is performed with the axis of the pipe and the drawing (tool) axis aligned with each other over the entire length of the pipe, and the drawing is performed using an internal support that can move along the drawing direction. In the final stage, the focus was placed on positioning the inner surface support in the vicinity of the rear end of the blank tube.

  Specifically, by using an inner surface support that can move along the drawing direction, the inner tube can always be held on the inner surface by the inner surface support. Furthermore, by positioning the inner surface support in the vicinity of the rear end of the blank tube at the final stage of the drawing process, the rear end of the blank tube is not swung around on the entry side of the machining die.

  In this way, since the core axis and the drawing axis can be kept in alignment until the drawing process is completed, it is possible to suppress swinging and bending of the pipe, and deterioration of the thickness of the drawn metal pipe And bending can be prevented.

  The present invention has been completed on the basis of the above findings, and the gist of the following (1) to (3) is a method of drawing a metal tube.

(1) A mandrel equipped with an inner surface supporter that supports the inner tube from the inner surface is inserted into the inner tube, and the axial center of the raw tube is aligned with the extraction shaft over the entire length of the raw tube. In a drawing method of a metal tube that performs drawing using a plug and a plug, the two or more inner surface supports are attached to the mandrel so as to be movable along the drawing direction,
When the length of the raw pipe in the drawing direction from the die to the rear end of the raw pipe is L ₀ , at least one of the inner surface support members is disposed within a range of 1/2 L _{0 to} L ₀ from the die. ,
Furthermore, when the distance from the die in the pulling direction of the inner surface support tool arranged closest to the die among the inner surface support tools arranged at 1/2 L _{0 to} L ₀ is L ₁ , the arranged inner surface A metal tube drawing method characterized in that at least one of the inner surface support tools different from the support tools is placed in a range of 1 / 3L ₁ to 2 / 3L ₁ at a distance from the die to perform the drawing process. is there.

(2) In the method for pulling out the metal tube of (1), it is preferable that a stopper member is provided at the rear end of the raw tube as a mechanism for preventing the inner surface support from coming out from the rear end of the raw tube.

(3) In the method for pulling out a metal tube according to the above (1) and (2), the inner surface support is formed so that the outer diameter of the closest part to the inner surface of the raw tube is 1 to 10 mm smaller than the inner diameter of the raw tube. Is desirable.
In the present invention, the “closest portion outer diameter” means an outer diameter at a portion where the inner surface support is closest to the inner surface of the raw tube.

  According to the metal tube drawing method of the present invention, it is possible to suppress the whirling and bending of the element tube accompanying the drawing process, and it is possible to obtain a metal tube that is less deteriorated in thickness and excellent in straightness. Thereby, even a honing type cylinder material that requires high dimensional accuracy can be manufactured with a high yield.

It is a longitudinal fragmentary sectional view explaining the deterioration of straightness and the bending behavior of an element pipe by the conventional drawing method, (a) is the state of the initial stage of drawing, (b) is the final stage of drawing. Indicates the state. A longitudinal partial cross-sectional view illustrating a modification method for preventing the pipe described in Patent Document 1, (a) is a state before the mother tube rear end passes through the inner surface support 5 _2, (b) after base pipe end showing a state after passing through the inner surface support 5 _2. It is a vertical fragmentary sectional view explaining the drawing method of the metal pipe of patent document 2. It is a vertical fragmentary sectional view explaining the pipe material drawing apparatus described in patent document 3. It is a figure explaining the arrangement | positioning condition of the inner surface support tool prescribed | regulated by this invention. It is a longitudinal fragmentary sectional view explaining the behavior form which the inner surface supporter of the present invention exhibits in the process of drawing, (a) is an initial stage of drawing, (b) is an intermediate stage of drawing, (c ) Shows the final stage of drawing.

It is a cross-sectional view which shows the cross-sectional shape of the inner surface support tool used by this invention, (a)-(c) has illustrated the shape which can be employ | adopted. It is a vertical fragmentary sectional view explaining the installation situation of the stopper member provided in a blank tube, (a) shows an installation form, and (b) shows an installation form which improved (a). It is a cross-sectional view showing a mechanism for preventing the stopper member from rotating on the mandrel when the drawing process is completed. It is a vertical fragmentary sectional view explaining the installation situation of the inner surface support tool and stopper member of the comparative example in an example. It is a longitudinal fragmentary sectional view explaining the installation situation of the inner surface support tool and stopper member of the example of the present invention in an example. It is a figure which shows the uneven thickness deterioration in the comparative example of an Example, and the example of this invention.

  In the drawing method of the present invention, a mandrel equipped with an inner surface supporter for supporting the blank tube from the inner surface is inserted into the blank tube so that the axis of the blank tube and the draw shaft center are aligned over the entire length of the blank tube. It is premised on a drawing method of a metal tube that is held and is drawn using a die and a plug.

  The metal pipe targeted by the present invention is not limited to the high Ni alloy pipe used in the examples described later, and includes a carbon steel pipe, an alloy steel pipe, a stainless steel pipe, and the like. Any of the exemplified pipes may cause the raw pipe to swing or bend in the drawing process depending on the pipe properties and processing conditions.

[Arrangement and shape of internal support]
In the drawing method of the present invention, in order to secure the above premise from the start to the completion of the drawing process, two or more of the inner surface supports are attached to the mandrel so as to be movable along the drawing direction. When the length of the raw tube in the drawing direction to the rear end of the raw tube is L ₀ , at least one of the inner surface supports is disposed within a range of 1/2 L _{0 to} L ₀ from the die, and When the distance from the die in the pulling-out direction of the inner surface support disposed closest to the die among the inner surface supports disposed at 1/2 L _{0 to} L ₀ is L ₁ , the disposed inner surface support At least one of the inner support members different from the above is arranged in the range of 1 / 3L ₁ to 2 / 3L ₁ at a distance from the die, and the drawing process is performed.

FIG. 5 is a diagram illustrating an arrangement state of the inner surface support defined in the present invention. In the same figure, it shows about the case where there are two inner surface supports. The inner surface support 5 ₂ is arranged so that the distance from the die can be moved within a range of 1 / 2L _{0 to} L ₀ when the length of the pipe in the drawing direction from the die to the rear end of the pipe is L _0. .

With this configuration, the inner surface support 5 _2, the distance from the die to the drawing processing to completion are placed in the range of 1 / 2L ₀ ~L _0, in the final stage of the drawing processing, the inner surface the support 5 ₂ can be positioned in the vicinity of the base pipe rear end, the rear end of the blank tube can be eliminated that the whirling in the inlet side of the processing die.

On the other hand, when the distance from the die in the pulling direction of the inner surface support tool arranged closest to the die among the inner surface support tools arranged at 1/2 L _{0 to} L ₀ is L ₁ , the inner surface support tool 5 ₁ is movably disposed so that the distance from the die is between 1 / 3L _{1 and} 2 / 3L ₁ .

Inner surface support 5 _1, intermediate position from the die to the inner surface support 5 _2, i.e. since the disposed range distance of 1 / 3L ₁ to 2 / 3L ₁ from the die, bending of the central portion due to the weight of the base pipe Thus, the core axis and the drawing axis can be held in a matched state until the drawing process is completed.

  FIGS. 6A and 6B are vertical partial cross-sectional views for explaining the behavioral form exhibited by the inner surface support tool of the present invention in the process of drawing, wherein FIG. 6A is an initial stage of drawing, and FIG. 6B is an intermediate stage of drawing. (C) shows the final stage of drawing.

As shown in FIGS. 6 (a) and 6 (b), from the initial stage to the intermediate stage of the drawing process, the inner surface supports 5 ₁ and 5 ₂ are arranged in the range defined by the present invention, while being arranged with respect to the raw tube 1a. It will approach the rear end of the raw tube 1a relatively. That is, blank tube 1a is moved in the drawing direction at a constant speed, the inner surface support 5 ₁ and 5 ₂ are not moved, or is moved dragged slightly withdrawing direction on the inner surface of the blank tube 1a of blank tube 1a drawing It gradually approaches the rear end of the raw tube 1a without exceeding the speed.

As shown in FIG. 6 (c), in the final stage of the drawing process, by the inner surface support 5 ₂ approaching the rear end direction relatively blank tube 1a, the inner surface support 5 ₂ blank tube 1a rear It can be located in the vicinity of. As a result, it is possible to suppress swinging of the raw tube at the final stage of processing, and to prevent uneven thickness deterioration and bending.

As shown in FIG. 6 (a) ~ (c) , toward the final stage from the initial stage of the drawing process, the inner surface support 5 ₁ arranged in the range distance of ₁ / 3L 1 to 2 / 3L ₁ from the die 4 Since the inner surface of the element tube 1a is supported while moving in the rear end direction relative to the element tube 1a, the axis of the element tube and the extraction axis coincide with each other over the entire length of the element tube. It can be kept in a state of being allowed to enter.

On the other hand, since the inner surface support 5 ₂ is disposed within a range of 1/2 L _{0 to} L ₀ from the die 4, it is possible to prevent the back end of the raw tube 1a from swinging. Therefore, drawing method of the present invention, the behavior of inner surface support 5 ₁ and the inner surface support 5 ₂ together, it is possible to obtain a metal tube uneven thickness deterioration excellent less straightness.

  Although FIG. 5 and FIG. 6 describe the case of using two inner surface supports, the drawing method of the present invention is not limited to this, and the same effect can be obtained even when three or more are used. be able to. In the drawing method of the present invention, the appropriate number of the inner surface support tools depends on factors such as the length of the raw pipe to be drawn, and therefore the upper limit is not specified.

  FIG. 7 is a cross-sectional view showing a cross-sectional shape of an inner surface support used in the present invention, and (a) to (c) illustrate shapes that can be employed. The inner surface support used in the present invention is not limited to the exemplified cross-sectional shape, and may be any cross-sectional shape that can support the inner surface of the raw tube.

  As shown in FIG. 7, the inner surface support 5 has a ring shape, is attached to the mandrel 3, and can move along the pulling direction by providing a clearance between the mandrel 3 and the inner surface support 5. Become. The inner diameter of the inner surface support 5 is desirably 1 mm or less with respect to the mandrel 3 to be mounted. Thereby, the inner tube 3 can be supported from the inner surface without the inner surface support 3 being shaken during the drawing process.

The closest part of the inner surface support 5 to the inner surface of the raw pipe 1a can be chamfered, and the outer diameter of the closest part to the inner surface of the raw pipe is 1 to 10 mm, more preferably 1 to 10 mm. It is desirable to mold 5 mm smaller. Thus, contact with the inner surface of the raw tube can be effectively eliminated.
Furthermore, it is desirable that the inner surface support 5 of the present invention is subjected to R chamfering on both end faces opposed to the pulling direction in order to ensure insertion into the mandrel 3.

  For the inner surface support of the present invention, it is desirable to select a material that does not easily deform and does not cause wrinkles on the inner surface of the raw tube. For example, hard resin, plastic, tool steel, and the like can be mentioned. Among them, it is desirable to select tool steel having a wear resistance of about HRC50 (JIS G 0202 hardness). Tool steel is not easily deformed and does not generate large wear debris, so that no flaws are generated on the inner surface of the pipe.

  The thickness (length in the drawing direction) of the inner surface support of the present invention is not particularly specified, but the thickness does not affect the holding performance of the inner surface of the raw tube, preventing wrinkles, handling properties and economy. From the viewpoint of safety, it is desirable to set it to 100 mm or less. The lower limit of the thickness may be a dimension that allows the inner surface support to support the inner surface of the raw tube.

[Installation of stopper members]
The drawing method of the present invention has a configuration in which the inner surface support is positioned in the vicinity of the rear end of the blank tube in the final stage of the drawing process, but a stopper is used to prevent the inner surface support from coming out of the rear end of the blank tube. The member can be attached to the mandrel and provided at the rear end of the blank tube.

  It is desirable that the stopper member has a mechanism that can be freely attached and detached at the rear end of the raw tube and that does not fall off from the mandrel after the drawing process is completed. If it is difficult to attach or detach the tube from the rear end, the productivity will be reduced. If the mechanism is to be removed after the drawing is completed, the stopper member will be scattered due to the shock coming off the tube end, which is dangerous.

  FIGS. 8A and 8B are vertical partial cross-sectional views for explaining the installation state of the stopper member provided at the rear end of the raw pipe, where FIG. 8A shows an installation form, and FIG. 8B shows an installation form obtained by improving (a). The stopper member 6 has a ring shape, and a form in which a groove is cut in the end surface of the stopper member in accordance with the diameter of the raw tube 1a is preferable.

  8A, the stopper member 6 is mounted on the mandrel 3 in advance, and when the mandrel 3 is inserted into the element tube 1a, the rear end of the element tube 1a is fitted into the groove 61 of the stopper member 6, and is screwed. The stopper member fixing tool 62 is used for fixing. Thereby, the stopper member 6 can move following the rear end of the raw tube 1a in the drawing process. The stopper member fixture 62 is not limited to a screw type, and a mechanism such as a hydraulic chuck can also be used.

  In the installation mode shown in FIG. 8B, when the raw tube 1a is supported from below by using the guide roll 7 or the like and the raw tube 1 is guided, the lower portion of the stopper member 6 does not contact the guide roll 7 or the like. This is an improved installation form. Even in this case, since the rear end of the raw tube 1a is sufficiently fitted into the groove 61 of the stopper member 6 and is fixed by the stopper member fixture 62, the stopper member 6 has a sufficient function. It can be demonstrated.

  In the case where the stopper member 6 is provided, in the final stage of the drawing process, the stopper member 6 can position the inner surface support 5 in the vicinity of the rear end of the blank tube until the drawing process is completed. As the drawing process is completed, the pulling force of the raw tube 1 is superior to the pressing force of the stopper member fixture 62 against the raw tube 1. Therefore, the rear end of the raw tube 1 is the groove 61 on the end surface of the stopper 6 in the drawing direction. Pulled out from.

  FIG. 9 is a cross-sectional view showing a mechanism for preventing the stopper member from rotating on the mandrel when the drawing process is completed. If the stopper member 6 rotates on the mandrel 3 after the drawing process is completed, the work for mounting the element pipe 1a used for the next drawing process becomes complicated.

  In order to prevent the rotation of the stopper member upon completion of the drawing process, the mandrel groove 31 is provided in the mandrel 3 and the stopper member convex portion 61 is provided in the stopper member 6 so that these can be fitted.

  In order to confirm the effect of the metal pipe drawing method of the present invention, the drawing process was carried out by changing the arrangement of the inner surface support, and the thickness deterioration of the obtained metal pipe was evaluated. The evaluation results will be described by classifying them into processing conditions, the arrangement status of the inner surface support, the thickness measurement procedure, and the evaluation results.

1. Machining conditions The tools used for drawing are an R die, a cylindrical plug, and a mandrel that supports it, and their dimensions and materials are as follows.
[R dice]
Bearing part inner diameter: 194mm
Curvature radius of approach part: 90mm
Drawing direction thickness: 75mm
Material: Cemented carbide [Cylindrical plug]
Outer diameter: 175.0mm
Effective length excluding chamfered ends: 80mm
Material: SKD11
[Mandrel]
Outer diameter: 152.4mm

The material of the specimen tube is a 25 mass% Ni-35 mass% Cr alloy, a chemical lubrication coating treatment with oxalate is applied as a pre-processing treatment, an oil lubrication treatment (chlorine) is applied, and a drawing speed of 3 m / min is applied. The drawing process was performed. The processing schedule for drawing is as follows.
Outer diameter before drawing: 223.0mm
Inner diameter before drawing: 195.0mm
Thickness before drawing: 14.00mm
Outer diameter after drawing: 194.2mm
Internal diameter after drawing: 174.9mm
Thickness after drawing: 9.65mm
Cross-sectional reduction rate Rd: 43.5%
However, the cross-sectional reduction rate Rd (%) is represented by (cross-sectional area before drawing−cross-sectional area after drawing) / cross-sectional area before drawing} × 100].

2. Arrangement condition of inner surface support The inner surface support mounted on the mandrel was formed in the shape shown in Fig. 7 (a), was made of tool steel, had a closest outer diameter of 191mm, and was formed 4mm smaller than the inner diameter of the raw tube.
10 and 11 are vertical partial cross-sectional views for explaining the arrangement of the inner surface supporter and the stopper member in the embodiment. FIG. 10 shows the arrangement of Comparative Examples 1 to 5, FIG. 2 shows the arrangement status. Table 1 shows detailed arrangement conditions.

3. Uneven thickness measurement procedure and evaluation results The thickness deviation rate (%) of the raw tube and the drawn tube is determined from the results obtained by measuring the circumferential thickness over the entire length in the axial length direction using an ultrasonic thickness measuring device. [(Maximum thickness−minimum thickness) / {(maximum thickness + minimum thickness) / 2}} × 100].

The evaluation part was set to 1 m of the rear end of the drawn pipe, and the thickness deviation rate in the corresponding raw pipe part was compared, and the deterioration of the thickness deviation was determined by the following equation (1).
Uneven thickness deterioration = Pull-out pipe thickness change rate (%)-Raw tube thickness change rate (%) (1)

  FIG. 12 is a diagram showing deterioration in uneven thickness in the comparative example of the example and the example of the present invention. In Comparative Examples 1 to 5, the deterioration of uneven thickness varied from over 2% to about 10%. On the other hand, it turns out that the invention examples 1 and 2 which satisfy the conditions prescribed | regulated by this invention were able to suppress the uneven thickness deterioration to about 1%. Further, by comparing the comparative example 5 with the inventive example 1, the superiority of using a plurality of inner surface supports could be confirmed.

  In addition, by providing the stopper member as in the present invention examples 1 and 2, the inner surface support is pushed by the stopper member located at the rear end of the blank tube in the final stage of the drawing process, so that the rear end portion of the blank tube Then, the drawing process is performed while supporting the rear end portion of the blank tube. Finally, the inner surface support comes into contact with the plug and stops, and the stopper member is dropped from the blank tube, and the drawing process is completed.

  Thus, according to Examples 1 and 2 of the present invention, since the drawing is performed while the inner surface support member supports the rear end portion of the blank tube until the final stage of the drawing process, the uneven thickness deterioration is small and the straightness is low. An excellent drawn product can be obtained. For this reason, it is possible to manufacture material pipe products such as those for honing type cylinders that require high dimensional accuracy, for example, that the thickness deviation is less than ± 0.4 mm, at a low yield. It was confirmed that it could be supplied.

  According to the metal tube drawing method of the present invention, it is possible to suppress the whirling and bending of the element tube accompanying the drawing process, and it is possible to obtain a metal tube that is less deteriorated in thickness and excellent in straightness. Accordingly, even a honing type cylinder material that requires high dimensional accuracy can be manufactured with a high yield, and thus can be widely applied. .

1a: Elementary tube, 1b: Metal tube,
2: plug, 3: mandrel, 31: mandrel groove,
4: Dice, 5,5 _1, 5 _2, 5 _3, 5 _4: inner surface support,
6: Stopper member,
61: Stopper member groove, 62: Stopper member fixture,
63: stopper member convex portion,
7: Guide roll

Claims (2)

Insert a mandrel equipped with an inner surface supporter that supports the inner tube from the inner surface into the inner tube and keep the axis of the tube and the drawing axis aligned with each other over the entire length of the tube. In the drawing method of metal pipes that are drawn using
Attach to the mandrel movably along the pulling direction using two or more inner surface supports,
When the length of the raw pipe in the drawing direction from the die to the rear end of the raw pipe is L ₀ , at least one of the inner surface support members is disposed within a range of 1/2 L _{0 to} L ₀ from the die. ,
Furthermore, when the distance from the die in the pulling direction of the inner surface support tool arranged closest to the die among the inner surface support tools arranged at 1/2 L _{0 to} L ₀ is L ₁ , the arranged inner surface Disposing at least one of the inner surface support members different from the support member in a range of 1 / 3L ₁ to 2 / 3L ₁ from the die ;
As a mechanism for preventing the inner surface support from coming out of the rear end of the raw tube, a stopper member is provided at the rear end of the raw tube,
In order to prevent rotation of the stopper member upon completion of the drawing process, a groove is provided in the mandrel, and a convex part is provided in the stopper member, and the groove and the convex part are fitted and the drawing process is performed. A method for drawing a metal tube. The method of drawing a metal tube according to claim 1, wherein the inner surface support tool is formed such that the outer diameter of the closest part to the inner surface of the element tube is smaller by 1 to 10 mm than the inner diameter of the element tube.

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