1359705 (1) 九、發明說明 【發明所屬之技術領域】 ' 本發明是關於抽管加工用插塞及使用該插塞之管製造 • 方法’特別是關於難以產生磨損，可確保使用壽命長之插 * 塞及使用該插塞之管製造方法。 【先前技術】 φ 習知以來’在製造各種用途的管時，有時是以管外徑 '內徑、管壁厚等尺寸精度的提昇，或表面平滑性的提昇 、機械強度的確保爲目的，對管施以抽管加工。 抽管加工，例如第1圖所示，是將後端以心軸Μ支 撐的插塞1’插入管Ρ的內面，然後將管Ρ朝第1圖箭頭 符號所示方向抽拔來進行加工。插塞1，是以可位於模2 及管Ρ之同心圓位置的狀態插入在管Ρ的內面。此時，管 Ρ沿著模2圓錐面狀的斜部22和插塞1 ’圓錐面狀的斜部 φ 12’逐漸變形，同時被導入模2圓柱面狀的直部21和插塞 1 ’圓柱面狀的直部1 1 ’之間。接著，加工形成爲以相向的 各直部2 1所區隔形成的模2開口部的直徑爲外徑，插塞 - 1’的直部11’直徑爲內徑的管Ρ。 .習知於一般的插塞1’，斜部12’和直部11’是直接連 接著。換句話說，如第1(b)圖所示，對插塞 Γ軸方向 成傾斜的斜部12’和平行於插塞軸方向的直部11’的連接 處是形成以S點爲彎折的折線形狀。接著，習知的插塞 1’，爲了要提高耐磨損性，一般是於表面施有塗層。 -5- (2) (2)1359705 但是，若降低插塞的原單位，則對於管P的抽管加工 是以能夠重覆使用的未施有表面塗層的插塞1’爲佳。經 本發明人檢討後的結果，得知若將上述習知的插塞1’在 表面不施有塗層的狀況下重覆使用在管P的抽管加工時， 特別是在斜部12’和直部11’的折線形狀連接處附近容易 產生磨損。該已磨損的插塞1’若未加以保養就使用在管P 的抽管加工時，會導致抽管加工後的管P其尺寸（內徑） 精度變差，恐怕會在管p和插塞1’之間產生燒結。若要 讓插塞1’的使用壽命多少能加長些時，也可對已磨損的 插塞1’加以切削硏磨，以再利用的方式使用在尺寸較小 之管p的抽管加工。然而，上述的再利用方式是需要切削 硏磨的時間，所以會降低管P的生產效率。因此，期望能 開發出一種難以產生磨損可長期間使用（使用壽命長）在 同一尺寸管P之抽管加工的插塞。 另一方面，斜部和直部爲不直接連接的插塞，例如專 利文獻1及專利文獻2所記載的插塞。更加具體說明時， 專利文獻1所記載的插塞，斜部（於專利文獻1稱爲引入 部）和直部（於專利文獻1稱爲軸承部）是由縮頸部（V 字構槽）形成連接著（參照專利文獻1第2圖等）。此外 ，專利文獻2所記載的插塞，如專利文獻2第1圖等所示 ，斜部和直部（於專利文獻2稱爲完成部）是由凹部形成 連接著》 〔專利文獻1〕日本特開平9-225522號公報 〔專利文獻2〕日本特開20 03-112218號公報 (3) (3)1359705 【發明內容】 然而，專利文獻1所記載的插塞，只不過是以確保作 用在插塞之朝抽拔方向的力和作用朝該抽拔方向反向的力 之平衡爲目的（參照專利文獻1之0004段落等），在斜 部和直部之間設有縮頸部而已。於專利文獻1，並未揭示 或暗示該縮頸部對上述插塞磨損的影響如何。 此外，專利文獻2所記載的插塞，只不過是以去除內 削時產生的切入紋路使抽管加工後的內圍面具高平滑度爲 目的（參照專利文獻2之0006段落等），在斜部和直部 之間以指定的位置關係設有凹部而已。於專利文獻2，並 未揭示或暗示該凹部對上述插塞磨損的影響如何》 本發明是爲解決上述習知技術問題而爲的發明，以提 供一種難以產生磨損可確保使用壽命長的插塞及使用該插 塞之管製造方法爲課題。 爲解決上述課題，本發明是提供一種抽管加工用插塞 ，其特徵爲，包括圓柱面狀的直部，和圓錐面狀的斜部， 及可使上述直部和上述斜部形成連接的曲面部，上述曲面 部是於包括上述抽管加工用插塞中心軸的剖面，具有曲率 中心位於上述直部及上述斜部之外方的指定曲率半徑，g 與上述直部成連接之連接點附近的傾斜是和上述直部的胃 斜大致爲相同的同時，與上述斜部成連接之連接點附近$ 傾斜是和上述斜部的傾斜大致相同。 本發明相關的抽管加工用插塞，並非如習知般將直$ (4) (4)1359705 和斜部直接連接，而是由具有指定曲率半徑的曲面部形成 連接。接著，上述曲面部和直部成連接的連接點附近的傾 斜是和直部的傾斜大致相同的同時，上述曲面部和斜部成 連接的連接點附近的傾斜是和斜部的傾斜大致相同。換句 話說，直部和曲面部的連接處，及斜部和曲面部的連接處 ’都不是形成爲折線形狀，直部、曲面部分及斜部是平順 連接著。因此，爲了進行抽管加工而將插塞插入至管的內 面時，和管形成不接觸的未接觸區域是比習知的插塞還少 ’如下述，來自於管其作用的擠壓就會分散（作用在未接 觸區域附近的最大擠壓降低）。如此一來，在未接觸區域 附近的插塞其磨損難以產生，因此能夠確保插塞長的使用 壽命。 於此，曲面部的曲率半徑若太小，則會近似於直部和 斜部成直接連接的習知插塞（習知插塞是相當於曲面部曲 率半徑爲0的插塞），導致上述擠壓分散的效果貧乏。另 一方面，曲面部的曲率半徑若太大，則插塞難以固定在特 定的位置（軸方向的位置），除此之外，恐怕還會導致抽 管加工後的管尺寸（內徑）精度變差。 基於以上觀點，上述曲率半徑最好是2mm以上20mm 以下爲佳。 此外’本發明亦提供一種以包括使用上述抽管加工用 插塞插入要抽管加工的管內面進行抽管加工之作業爲特徵 的管製造方法。 (5) 1359705 【實施方式】 〔發明之最佳實施形態〕 以下，適宜參照附圖的同時，針對本發明之一實施形 態加以說明。 •第2圖爲表示本發明之一實施形態相關抽管加工用插 ‘ 塞的槪略構成軸方向剖面圖，第2(a)圖爲表示使用抽 管加工用插塞進行抽管加工狀態時的全體圖，第2(b) ^ 圖爲表示第2(a)圖虛線圈選部份的放大圖。 如第2圖所示，本實施形態相關的插塞i是和習知插 塞相同地’插入在由模2 —邊擠壓一邊抽管加工之管p的 內面’具備有圓柱面狀的直部11和圓錐面狀的斜部12。 , 另一方面，本實施形態相關的插塞1，其和習知插塞 不同之處是在於直部11和斜部12由曲面部13形成連接 著。如第2(b)圖所示，曲面部13是於包括插塞1中心 軸的剖面，具有曲率中心位於直部11及斜部12之外方的 • 指定曲率半徑R。接著’曲面部13其與直部π成連接之 連接點13 1附近的傾斜是和直部i i的傾斜（和插塞1的 軸方向平行）大致相同。即，直部11和曲面部13的連接 處’並非成折線形狀而是成平順連接著。同樣地，曲面部 13與斜部12成連接之連接點132附近的傾斜是和斜部12 的傾斜大致相同。即，斜部丨2和曲面部〗3的連接處，並 非成折線形狀而是成平順連接著。如上述，本實施形態相 關的插塞1，其直部11、斜部12及曲面部13是形成平順 連接著。 -9- (6) (6)1359705 (1) IX. Description of the Invention [Technical Fields of the Invention] The present invention relates to a plug for pipe drawing processing and a pipe manufacturing method using the same, which is particularly difficult to produce wear and tear, and can ensure long service life. Insert the plug and the method of manufacturing the tube using the plug. [Prior Art] φ Since the manufacture of pipes for various applications, the dimensional accuracy of the outer diameter of the pipe, the wall thickness of the pipe, etc., or the improvement of the surface smoothness and the securing of the mechanical strength may be used. , pipe the tube processing. The pipe drawing process, for example, as shown in Fig. 1, is to insert the plug 1' which is supported by the mandrel at the rear end into the inner surface of the pipe, and then draw the pipe to the direction indicated by the arrow symbol in Fig. 1 for processing. . The plug 1 is inserted into the inner surface of the tube in a state in which it can be located at the concentric position of the mold 2 and the tube. At this time, the tube is gradually deformed along the conical portion 22 of the die 2 and the inclined portion φ 12' of the plug 1 'conical surface, and is introduced into the cylindrical portion 21 and the plug 1 ' Between the straight portions of the cylindrical shape 1 1 '. Next, the processing is formed such that the diameter of the opening of the die 2 formed by the opposing straight portions 2 1 is the outer diameter, and the straight portion 11' of the plug - 1' is the inner diameter of the inner tube. It is known that the general plug 1', the inclined portion 12' and the straight portion 11' are directly connected. In other words, as shown in Fig. 1(b), the connection between the inclined portion 12' which is inclined in the direction of the plug x-axis and the straight portion 11' which is parallel to the direction of the plug axis is formed by bending the point S The shape of the broken line. Next, the conventional plug 1' is generally coated on the surface in order to improve the wear resistance. -5- (2) (2) 1359705 However, if the original unit of the plug is lowered, the pipe drawing of the pipe P is preferably a plug 1' which is not coated with a surface coating which can be reused. As a result of review by the present inventors, it has been found that the above-described conventional plug 1' is repeatedly used in the pipe drawing process of the pipe P without applying a coating on the surface, particularly in the inclined portion 12' and Wear is likely to occur near the fold line shape of the straight portion 11'. If the worn plug 1' is used for pipe drawing of the pipe P without maintenance, the accuracy of the size (inner diameter) of the pipe P after the pipe drawing process may be deteriorated, and it may be in the pipe p and the plug. Sintering occurs between 1'. In order to increase the service life of the plug 1', the worn plug 1' can also be cut and honed, and the pipe processing of the smaller-sized pipe p can be used in a reuse manner. However, the above-mentioned recycling method requires a time for cutting honing, so that the production efficiency of the pipe P is lowered. Therefore, it has been desired to develop a plug which is difficult to produce wear and can be used for a long period of time (long service life) in the same size pipe P. On the other hand, the inclined portion and the straight portion are plugs which are not directly connected, and are, for example, those described in Patent Document 1 and Patent Document 2. More specifically, the plug described in Patent Document 1 has a tapered portion (referred to as an introduction portion in Patent Document 1) and a straight portion (referred to as a bearing portion in Patent Document 1) by a constricted portion (V-shaped groove). The connection is formed (refer to the second drawing of Patent Document 1, etc.). In the plug described in Patent Document 2, as shown in Fig. 1 of the patent document 2, the inclined portion and the straight portion (referred to as a completed portion in Patent Document 2) are connected by a concave portion. [Patent Document 1] Japan Japanese Laid-Open Patent Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. For the purpose of balancing the force in the drawing direction of the plug and the force in the opposite direction to the drawing direction (refer to paragraph 0004 of Patent Document 1, etc.), a neck portion is provided between the inclined portion and the straight portion. Patent Document 1 does not disclose or suggest how the constricted neck affects the plug wear. In addition, the plug described in the patent document 2 is only for the purpose of removing the cut-in pattern generated during the internal cutting to improve the smoothness of the inner peripheral mask after the pipe drawing process (see paragraph 0006 of Patent Document 2). A recess is provided between the portion and the straight portion in a specified positional relationship. Patent Document 2 does not disclose or suggest how the recess affects the above-mentioned plug wear. The present invention is an invention for solving the above-mentioned problems of the prior art, and provides a plug which is difficult to generate wear and which ensures a long service life. And a method of manufacturing a tube using the plug is a problem. In order to solve the above problems, the present invention provides a plug for pipe drawing processing, comprising: a straight portion having a cylindrical shape, and a tapered portion having a conical shape, and a line connecting the straight portion and the inclined portion. In the curved surface portion, the curved surface portion is a cross section including the center axis of the plug for processing the pipe, and has a specified curvature radius at which the center of curvature is located outside the straight portion and the inclined portion, and a connection point where the g is connected to the straight portion The inclination in the vicinity is substantially the same as the inclination of the stomach in the straight portion, and the inclination of the vicinity of the connection point to which the oblique portion is connected is substantially the same as the inclination of the inclined portion. The plug for pipe drawing according to the present invention does not directly connect the straight $(4)(4)1359705 and the inclined portion as is conventionally known, but is formed by a curved portion having a specified radius of curvature. Next, the inclination in the vicinity of the connection point where the curved surface portion and the straight portion are connected is substantially the same as the inclination of the straight portion, and the inclination in the vicinity of the connection point where the curved surface portion and the oblique portion are connected is substantially the same as the inclination of the inclined portion. In other words, the joint between the straight portion and the curved portion, and the joint between the inclined portion and the curved portion are not formed into a polygonal shape, and the straight portion, the curved portion, and the inclined portion are smoothly connected. Therefore, when the plug is inserted into the inner surface of the tube for the pipe drawing process, the uncontacted area which is not in contact with the tube is less than the conventional plug 'as follows, the squeeze from the action of the tube Will disperse (the maximum squeeze in the vicinity of the untouched area is reduced). As a result, the plug near the uncontacted area is less likely to be worn, so that the long life of the plug can be ensured. Here, if the radius of curvature of the curved surface portion is too small, a conventional plug that is directly connected to the straight portion and the inclined portion is formed (the conventional plug is a plug having a curvature radius of 0 corresponding to the curved portion), resulting in the above. The effect of extrusion dispersion is poor. On the other hand, if the radius of curvature of the curved surface portion is too large, the plug is difficult to be fixed at a specific position (position in the axial direction), and in addition, the tube size (inner diameter) accuracy after the pipe drawing process may be caused. Getting worse. From the above viewpoints, the radius of curvature is preferably 2 mm or more and 20 mm or less. Further, the present invention also provides a pipe manufacturing method characterized by comprising an operation of performing pipe drawing processing by inserting the inner surface of a pipe to be piped by using the above-mentioned pipe drawing processing plug. (5) 1359705 [Embodiment] BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 2 is a cross-sectional view showing the axial direction of the plug for the pipe drawing process according to the embodiment of the present invention, and Fig. 2(a) is a view showing the state of the pipe drawing process using the plug for pipe drawing processing. The overall map, the second (b) ^ figure is an enlarged view showing the selected portion of the dotted circle of the second (a). As shown in Fig. 2, the plug i according to the present embodiment is inserted into the inner surface of the pipe p which is piped by the die 2 and has a cylindrical surface like the conventional plug. The straight portion 11 and the conical portion 12 are tapered. On the other hand, the plug 1 according to the present embodiment is different from the conventional plug in that the straight portion 11 and the inclined portion 12 are connected by the curved portion 13. As shown in Fig. 2(b), the curved surface portion 13 is a cross section including the central axis of the plug 1, and has a specified curvature radius R which is located outside the straight portion 11 and the inclined portion 12. Next, the inclination of the vicinity of the connection point 13 1 where the curved surface portion 13 is connected to the straight portion π is substantially the same as the inclination of the straight portion i i (parallel to the axial direction of the plug 1). That is, the joints ' between the straight portion 11 and the curved surface portion 13 are not in a broken line shape but are connected in a smooth manner. Similarly, the inclination in the vicinity of the connection point 132 where the curved surface portion 13 and the inclined portion 12 are connected is substantially the same as the inclination of the inclined portion 12. That is, the joint between the inclined portion 丨2 and the curved surface portion 〖3 is not connected to the fold line shape but is smoothly connected. As described above, in the plug 1 according to the present embodiment, the straight portion 11, the inclined portion 12, and the curved surface portion 13 are formed to be smoothly connected. -9- (6) (6)
1359705 本實施形態相關的插塞1，因具有上述構 管P的抽管加工時和管P不接觸的未接觸區域 塞還少。其結果，來自於管P作用的擠壓就會 在未接觸區域附近的最大擠壓降低）。以下，針 以具體說明。 第3圖是表示分別使用曲面部13的曲率半 的插塞及曲率半徑R = 〇mm的插塞（相當於習知 對同一規格的管P抽管加工時之來自於管P其 經數値解析算出的結果一例圖表。第3圖的橫軸 直部11的延長線和斜部12的延長線成交叉的點 (=〇mm )的軸方向位置（mm)，縱軸是表示經 算出後的擠壓（MPa )。另，對於數値解析是採 法（二元軸對稱彈塑性變形FEM )。 如第3圖所示，習知的插塞是在基準點SB 在斜部和直部的折線形狀連接處附近，擠壓急遽 原因是連接處爲折線形狀，因此產生和管P不接 觸區域。即，於上述未接觸區域因未獲得來自於 壓作用，所以反之使作用在鄰接於未接觸區域的 性變大。 另一方面，如第3圖所示，本實施形態相關 (第3圖所示例爲R= l〇mm)，其基準點S附近 壓降低。這是因爲直部11、曲面部13及斜部： 平順的關係，所以管P的抽管加工時該插塞和管 的未接觸區域比習知插塞還少的原故。即，由於 ，所以在 比習知插 散（作用 對該點加 [R= 10mm 插塞）， 用的擠壓 是表示以 S爲基準 數値解析 用有限元 近，即， 變大。其 觸的未接 管P的擠 擠壓急遽 的插塞1 的最大擠 2連接成 P不接觸 未接觸區 -10- (7) 1359705 域較少，使來自管P作用的擠壓分散在接觸區域的 因此作用在未接觸區域其鄰接區域的擠壓就降低。 從以上所說明的數値解析結果得知，本實施形態 的插塞1，因直部11、曲面部13及斜部12成平順連 ，所以管P的抽管加工時該插塞和管P不接觸的未接 域就會比習知插塞還少，使來自管P作用的擠壓形成 (作用在未接觸區域附近的最大擠壓降低）。如此一 在未接觸區域附近的插塞1的磨擦就難以產生，能夠 插塞使用壽命長。 不過，曲面部1 3的曲率半徑R若太小，則會近 直部11和斜部13成直接連接的習知插塞（習知插塞 當於曲面部13其曲率半徑爲0的插塞），導致上述 分散的效果貧乏。因此，曲率半徑R最好是2mm以 佳。 另一方面，曲面部13的曲率半徑R若太大，則 難以固定在特定的位置（軸方向的位置），除此之外 怕還會導致抽管加工後的管P其尺寸（內徑）精度變 因此，曲率半徑R最好是2 0mm以下爲佳。 以下，是針對本實施形態相關的插塞1及習知的 ，就實際使用壽命評估後的結果加以說明。 分別使用不同曲率半徑R的複數插塞，進行了下 驗：對管外徑38.1mm、管壁厚3.8mm的管進行抽管 ，將其加工成管外徑22.5 5mm、管壁厚2.65mm。接 對抽管加工後的管其尺寸是否偏離公差，或以管和插 果， 相關 接著 觸區 分散 來， 確保 似於 是相 擠壓 上爲 插塞 ，恐 差。 f -t*- 插塞 述試 加工 著， 塞之 -11 - (8) 1359705 間產生燒結爲止的管總抽拔長度進行了使用壽命的評估。 表1，是表示上述試驗結果。 〔表1〕 曲率半徑R 使用壽命（總抽拔長度） 0mm 7211m 2 mm 9330m 5 mm 9250m 1 0mm 9945m 20mm 9863m 3 0 mm 8811m1359705 The plug 1 according to the present embodiment has less plugs in the non-contact area where the pipe P is not in contact with the pipe P. As a result, the extrusion from the action of the tube P reduces the maximum extrusion near the uncontacted area). The following is a detailed description. Fig. 3 is a view showing a plug having a curvature half of the curved surface portion 13 and a plug having a radius of curvature R = 〇 mm (corresponding to the conventional method for pipe P from the same specification. An example of the result of the analysis is the graph. The extension of the horizontal straight portion 11 and the extension of the oblique portion 12 in Fig. 3 are in the axial direction (mm) of the point (=〇mm) where the extension line intersects, and the vertical axis indicates that after the calculation Extrusion (MPa). In addition, the analysis of the number of enthalpy is the mining method (binary axisymmetric elastoplastic deformation FEM). As shown in Fig. 3, the conventional plug is at the reference point SB at the oblique portion and the straight portion. The vicinity of the connection of the broken line shape, the reason for the sudden squeezing is that the joint is in the shape of a broken line, so that a region that does not contact the tube P is generated. That is, since the uncontacted region is not obtained from the pressure, the opposite is caused to be adjacent to the On the other hand, as shown in Fig. 3, in the present embodiment (R = l〇mm in the example shown in Fig. 3), the pressure in the vicinity of the reference point S is lowered. This is because the straight portion 11 The curved surface portion 13 and the inclined portion: a smooth relationship, so the plug and the tube are processed during the pipe drawing of the pipe P The untouched area is less than the conventional plug. That is, because of the fact, it is inserted more than the conventional one (the action is added to the point [R = 10mm plug), and the squeeze is used to indicate the reference number S.値 用 用 , , , , , 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値 値When the extrusion from the tube P is dispersed in the contact region, the pressing of the adjacent region in the uncontacted region is lowered. From the results of the numerical analysis described above, the plug 1 of the present embodiment is straight. The portion 11, the curved surface portion 13 and the inclined portion 12 are smoothly connected, so that the unconnected region where the plug and the tube P are not in contact during the pipe drawing processing of the pipe P is less than the conventional plug, so that the action from the pipe P is performed. Extrusion formation (maximum extrusion reduction in the vicinity of the uncontacted area). Such a friction of the plug 1 in the vicinity of the uncontacted area is difficult to produce, and the plug can be used for a long service life. However, the radius of curvature of the curved portion 13 If R is too small, the conventional straight insertion of the straight portion 11 and the inclined portion 13 is directly connected. (The conventional plug is a plug whose curvature radius is 0 in the curved surface portion 13.) The effect of the above dispersion is poor. Therefore, the radius of curvature R is preferably 2 mm. On the other hand, the radius of curvature R of the curved surface portion 13 If it is too large, it is difficult to fix it at a specific position (position in the axial direction), and in addition, it may cause the accuracy of the size (inner diameter) of the pipe P after the pipe drawing process. Therefore, the radius of curvature R is preferably 2 The following is a description of the results of the evaluation of the actual service life for the plug 1 according to the present embodiment and the conventional one. The complex plugs of different curvature radii R are respectively used for the test: The tube with an outer diameter of 38.1 mm and a wall thickness of 3.8 mm was piped and processed into a tube outer diameter of 22.5 5 mm and a tube wall thickness of 2.65 mm. Whether the size of the tube after the pipe drawing process is out of tolerance, or the tube and the insert are separated, and then the contact zone is dispersed to ensure that the phase is squeezed as a plug. f -t*- Plug The test is performed. The total extraction length of the tube between the -11 - (8) and 1359705 is evaluated for the service life. Table 1 shows the results of the above test. [Table 1] Curvature radius R Service life (total drawing length) 0mm 7211m 2 mm 9330m 5 mm 9250m 1 0mm 9945m 20mm 9863m 3 0 mm 8811m
如表1所示，相較於習知的插塞（R = 0 )，本實施形 態的插塞1 ( R = 2、5、10、20、30)是能夠確保使用壽命 長。特別是使用曲率半徑R = 2〜20mm範圍的插塞時’能 夠較習知插塞更爲大幅延長使用壽命。 【圖式簡單說明】 第1圖爲表示習知抽管加工用插塞的槪略構成軸方向 剖面圖，第1(a)圖爲表示使用抽管加工用插塞進行抽 管加工狀態時的全體圖，第1(b)圖爲表示第1(a)圖 虛線圈選部份的放大圖。 第2圖爲表示本發明之一實施形態相關抽管加工用插 塞的槪略構成軸方向剖面圖，第2(a)圖爲表示使用抽 管加工用插塞進行抽管加工狀態時的全體圖，第2(b) 圖爲表示第2(a)圖虛線圈選部份的放大圖。 -12- (9) 1359705 第3圖爲表示來自於管其作用在插塞上的擠壓經數値 解析算出後的結果一例圖表。 【主要元件符號說明】 1 :插塞 1’ ：插塞（習知） 1 1 :直部As shown in Table 1, the plug 1 of the present embodiment (R = 2, 5, 10, 20, 30) is capable of ensuring a long service life as compared with the conventional plug (R = 0). In particular, when a plug having a radius of curvature R = 2 to 20 mm is used, it is possible to extend the service life more significantly than conventional plugs. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view showing a schematic configuration of a plug for a conventional pipe drawing process, and Fig. 1(a) is a view showing a state in which a pipe drawing process is performed using a plug for pipe drawing. In the entire figure, Fig. 1(b) is an enlarged view showing a selected portion of the dotted circle of Fig. 1(a). Fig. 2 is a cross-sectional view showing the axial direction of the plug for processing the pipe according to the embodiment of the present invention, and Fig. 2(a) is a view showing the entire state of the pipe drawing process using the plug for pipe drawing. Fig. 2(b) is an enlarged view showing the selected portion of the dotted circle of Fig. 2(a). -12- (9) 1359705 Fig. 3 is a graph showing an example of the results obtained by analyzing the number of squeezings from the tube acting on the plug. [Description of main component symbols] 1 : Plug 1' : Plug (known) 1 1 : Straight
1 1 ’ ：直部（習知） 1 2 :斜部 1 2 ’ ：斜部（習知） 13 :曲面部 131:曲面部和直部11的連接點 132:曲面部和斜部12的連接點 2 :模 2 1 :模的直部 22 :模的斜部 Μ :心軸 Ρ :管 R :曲率半徑 S :點（斜部1 2 ’和直部1 1 ’的連接處） -13-1 1 ': straight portion (conventional) 1 2 : oblique portion 1 2 ': oblique portion (conventional) 13 : curved surface portion 131: connection point 132 between curved surface portion and straight portion 11 : connection of curved surface portion and oblique portion 12 Point 2: modulo 2 1 : straight portion 22 of the mold: oblique portion of the mold 心 : mandrel Ρ : tube R : radius of curvature S : point (join at the oblique portion 1 2 ' and the straight portion 1 1 ') -13-