JPS62104634A - Double pipe production - Google Patents

Abstract

PURPOSE:To bind both pipes firmly and inexpensively with a simple technique by expanding the inner pipe in a cooling state which is relatively stratified on the outer pipe which is expanded with heating from the outer peripheral part with the rolling of an elastic ring by the movement in the axial direction of an inserting mandrel and by cooling the outer pipe. CONSTITUTION:The inner pipe 2 in a cooling state with a feeding cooling water 10 is relatively stratified to the outer pipe 1 which is expanded by being heated with the high frequency induction heating device 4 located at the outer peripheral part. The inner pipe 2 is closely brought into contact with the outer pipe 1 with its expansion by rolling with the movement in the axial direction of a mandrel 12, the hard rubber elastic ring 11 which is fitted with press-fit to the inner wall of the inner pipe thereof and the inserting rod-like mandrel 12. Thereafter both pipes 1, 2 are firmly bound with cooling the outer pipe 1. Thereafter both pipes 1, 2 are firmly bound with cooling the outer pipe 1. The outer peripheral part heating device 4 and cooling device may be transferred by opposing relatively to the rolling transfer of the elastic ring 11. Thus the double pipe can be manufactured with extremely simple technique.

Description

【発明の詳細な説明】 〈産業上の利用分野〉 開示技術は、配管に用いる耐蝕管や耐摩耗管の二重管を
製造する技術分野に属覆る。DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The disclosed technology belongs to the technical field of manufacturing double pipes such as corrosion-resistant pipes and wear-resistant pipes used for piping.

く要旨の概要〉 而して、この出願の発明は、炭素鋼製外管にステンレス
製内管等のユニット管を相対重層して素管と成し、当該
相対重層の前後いづれかにおいて外管を加熱して増径し
、その状態で内管に対して機械的な拡管を付与し、塑性
変形させ、外管と一体化して外管を弾性変形さけ、両管
一体にして増径し、その後、外管を冷ム［１して縮径さ
せ、両管を°緊結するようにした自緊二重管の製造方法
に関する発明であり、特に、内管の拡管に際し内管の内
部に装着した弾性リングに対しその内側に当接するマン
ドレルを軸方向に移動さけて弾性リングを自転させ、そ
の外周部をして内管を１１ム管させるようにし、更には
、弾性リングの拡管移動に際して内管の拡管されていな
い部分から拡管された部分への冷却液の流過を行うよう
にした二重管の製造方法に係る発明である。Summary of the gist> Therefore, the invention of this application is to form a base pipe by laminating a unit pipe such as a stainless steel inner pipe on a carbon steel outer pipe, and to attach the outer pipe either before or after the relative stacking. The inner tube is heated to increase its diameter, and in that state, the inner tube is mechanically expanded, plastically deformed, integrated with the outer tube to avoid elastic deformation, and both tubes are integrated to increase the diameter. This invention relates to a method of manufacturing a self-contained double pipe in which the outer pipe is cooled to reduce its diameter and both pipes are joined together.In particular, when the inner pipe is expanded, The elastic ring is rotated while avoiding axial movement of the mandrel that abuts on the inside of the elastic ring, and the outer circumference of the elastic ring is made to form an 11 mm tube, and furthermore, when the elastic ring is expanded, the inner tube This invention relates to a method for manufacturing a double-walled pipe in which cooling liquid flows from an unexpanded portion to an expanded portion of the double-walled pipe.

〈従来技術〉 周知の如く、配管はあらゆる産業に利用され、流体輸送
や情報伝達、或は、建築、構造部材や装置の構造部材と
しても広く用いられでいる。<Prior Art> As is well known, piping is used in all kinds of industries, and is widely used for fluid transportation, information transmission, and as a structural member of buildings, structural members, and devices.

而して、配管か単に配管初期の状態のままその数曲を維
持するためには、耐久性が重要であるか、この場合、耐
蝕性や耐摩耗ｉ生が必要であるが、単一の材料によって
これらの条件を全て満足する材１１！ｌか現実には開発
されていないがために、例えば、外管を耐圧、耐熱性に
し、内管を耐蝕、耐摩耗性にする二重管か現実には広く
採用されている。Therefore, durability is important in order to maintain piping or simply maintaining the piping in its initial condition, or in this case, corrosion resistance and wear resistance are necessary, but a single Material 11 that satisfies all of these conditions depending on the material! However, for example, double-pipe tubes, in which the outer tube is pressure and heat resistant and the inner tube is corrosion and abrasion resistant, are widely used, although this has not been developed in practice.

この場合、外管と内管は一体化されて密接に接合されて
いることが素管を一体化するために強く望まれ、これに
対辺するに、例えば、クラツド鋼二重管や自緊二重管等
が用いられるようになってきている。In this case, it is strongly desired that the outer pipe and the inner pipe be integrated and closely joined in order to integrate the raw pipes. Heavy pipes, etc. are now being used.

〈発明が解決しようとする問題点〉 而して、クラツド鋼二重管の製造に際しては外管と内管
の接合面が゛悄密ｈｕ工で仕上げられていなければなら
ず、したかつて、その前段階での加工工程が復鉗でおる
難点が必るうえに、コスト高となる不利点がある。<Problem to be solved by the invention> Therefore, when manufacturing clad steel double pipes, the joint surface of the outer pipe and the inner pipe must be finished with a hard finish. In addition to the disadvantage that the previous processing step is a re-protrusion process, it also has the disadvantage of high costs.

一方、自緊二重管には焼きばめ法や液圧拡管法か必って
前者では温度管理が極めて煩瑣であるという欠点がおり
、後者では充分な嵌合代が得られないという欠点があっ
た。On the other hand, self-tightening double-pipe tubes are manufactured using either the shrink fit method or the hydraulic expansion method.The former method has the disadvantage that temperature control is extremely complicated, and the latter method has the disadvantage that sufficient fitting allowance cannot be obtained. there were.

これに対処するに、出１領大の開発した特公昭５６−４
６４５１号公報ｌこ代表されるような所謂熱拡管法が研
究開発されて大きな嵌合代を得られる優れた二重管が得
られるようになってきた。To deal with this, the special public service developed by De1 Ryōdai in 1986-4
Research and development of the so-called thermal tube expansion method, as exemplified by Publication No. 6451, has made it possible to obtain excellent double-walled tubes with a large fitting margin.

ざりなから、該種熱拡管法で二重管を製造するに際して
は高圧の拡管液が多量に要る等の不都合があり、内管の
両端部に対する正確なシールが必要であるという不具合
もあった。Therefore, when manufacturing double-walled pipes using the thermal expansion method, there are disadvantages such as the need for a large amount of high-pressure pipe expansion fluid, and the need for accurate sealing at both ends of the inner pipe. Ta.

又、ｊｑられる二重管の軸方向の圧縮残留応力を付与す
るために、内管の端部の収縮を許容しなければならず、
上記高圧シールがこのためにより正確に必要であるとい
うことによって装置か複雑でコスト高になり兼ねないと
いう不都合さもあった。In addition, in order to apply compressive residual stress in the axial direction of the double pipe to
There is also the disadvantage that the high-pressure seals are required to be more precise for this purpose, which can make the device complex and costly.

この出願の発明の目的は上述従来技術に基づく二重管製
造の問題点を解決すべき技術的課題とし、出願人が開発
した熱拡管法の良さを充分に生かしなからら拡管の液圧
を必要とぜず、又、冷却液のシールも何ら厳密には必要
とせず、充分な嵌合代か背られるようにして各種産業に
おける配管技術利用分野に益するトラれた二重管製造方
法を提供せんとするしのである。The purpose of the invention of this application is to solve the problems of manufacturing double pipes based on the above-mentioned prior art as a technical problem, and to improve the hydraulic pressure of pipe expansion by fully utilizing the advantages of the thermal pipe expansion method developed by the applicant. We have developed a method for manufacturing double-pipe pipes that does not require any strict sealing of the coolant, but has a sufficient fit, and is beneficial to the field of piping technology application in various industries. This is what I want to offer.

く問題点を解決するための手段・作用〉上述目的に沿い
先述持直請求の範囲を要旨とするこの出願の発明の）育
成（は、前述問題点を解決するために、加熱して増径し
た外管と冷却して縮径した内管とを可及的に両者の間隙
を小さくして相対重層する等して素管に成し、該素管の
内管の一方端に硬質ゴム製であって内部に液体を密封し
たような弾性リングを内管の内部内面に接触させると共
に、その内周にマンドレルを仲通し、該マンドレルを軸
方向に引き（ムくように移動することにより、弾性リン
グを内管の内部にて転動させ、内管に対し強引」す的に
挺域的に拡管させて塑性変形させ、外管と一体化し、外
管は弾性変形して拡管され、その間、内管の拡管されな
い部分から拡管された部分へ冷却液を弾性リングのリン
グ状溝等を介して流過させるようにして、更に、拡管後
の外管を冷却して縮径させ、素管の外管と内管を大きな
嵌合代を介して緊結するようにして自緊二重管を得るよ
うにした技術的手段を講じたものである。In order to solve the above-mentioned problems, the invention of the present application, which is summarized in the above-mentioned claims, is developed (means and operation for solving the above-mentioned problems). The outer tube that has been cooled and the inner tube that has been cooled and reduced in diameter are layered relative to each other with as small a gap as possible to form a blank tube, and one end of the inner tube of the blank tube is made of hard rubber. An elastic ring with a liquid sealed inside is brought into contact with the inner surface of the inner tube, and a mandrel is passed through the inner circumference of the ring, and the mandrel is pulled in the axial direction. The elastic ring is rolled inside the inner tube, and the inner tube is forcibly expanded and plastically deformed, becoming integrated with the outer tube, and the outer tube is elastically deformed and expanded. , the cooling liquid is allowed to flow from the unexpanded part of the inner pipe to the expanded part through the ring-shaped groove of the elastic ring, and the expanded outer pipe is further cooled and reduced in diameter to form the base pipe. A technical measure has been taken to obtain a self-tightening double pipe by tightly connecting the outer pipe and inner pipe of the pipe with a large fitting margin.

〈実施例〉 次に、この出願の発明の実施例を図面に従って説明すれ
ば以下の通りである。<Example> Next, an example of the invention of this application will be described below with reference to the drawings.

図示実施例は耐蝕二重管の製造態様でおり、第１〜３図
に示す実施例においては所定の長さのユニット管として
の炭素鋼製の外管１に対し当該外管１の長さよりも設定
長さ長い同じく同じユニット管としてのステンレス製の
内管２を相対重層させる。The illustrated embodiment is a manufacturing mode of a corrosion-resistant double pipe, and in the embodiment shown in Figs. Also, the stainless steel inner tubes 2, which are the same unit tubes and have a longer set length, are layered relatively.

尚、この場合、予め外管１を加熱増径させておき、内管
２を冷却縮径させておくことにより両者の間隙を可及的
に小さい状態で相対重層し、後工程での嵌合代を充分大
きくするよ°うにしておく。In this case, the diameter of the outer tube 1 is increased by heating in advance, and the diameter of the inner tube 2 is decreased by cooling, so that the gap between the two is kept as small as possible so that they overlap each other, and the fitting is performed in the subsequent process. Make sure to make the amount large enough.

このようにして得られた素＠３を第２図に示す様に、例
えば、高周波誘導加熱装置４の内部にセットし、内管２
の一端側に単なるシール装置５を介して冷却水６のタン
ク７からポンプ８、バルブ９を介して通路１０により冷
却水６を内管２の内部に供給しておく。As shown in FIG. 2, the element @3 thus obtained is set inside a high frequency induction heating device 4,
Cooling water 6 is supplied into the inner tube 2 from a tank 7 through a pump 8 and a valve 9 through a passage 10 through a simple sealing device 5 at one end of the tube.

そして、内管２の他方端部に第３図に示す様に、断面円
形の硬質ゴムより成る弾性リング１１を嵌着させて棒状
のマンドレル１２の他端部を挿通し、マンドレル１２、
及び、内管２に弾性リング１１か当接するようにしてあ
く。Then, as shown in FIG. 3, an elastic ring 11 made of hard rubber and having a circular cross section is fitted onto the other end of the inner tube 2, and the other end of the rod-shaped mandrel 12 is inserted therethrough.
And, the elastic ring 11 is made to come into contact with the inner tube 2.

尚、この場合、マンドレル１２の初期姿勢では大径部と
小径部をテーパ部で接続させ、当該小径のテーパ部に弾
性１ソングが外装されるようにしてあく。In this case, in the initial posture of the mandrel 12, the large diameter part and the small diameter part are connected at the tapered part, and the small diameter tapered part is covered with an elastic song.

このようなセット状態でマンドレル１２を軸方向に移動
させていくと、当該テーパ部を乗り越えた弾性リング１
１は強制的に増径されてマンドレル１２の軸方向移動の
摩擦により転動じて内管２の内面に当接し、これを強制
的に拡管して塑性変形し、外管１と一体化して７ＪＯ熱
状態にある外管１をも拡管し、弾性的に変形させていく
。When the mandrel 12 is moved in the axial direction in this set state, the elastic ring 1 that has overcome the tapered part
1 is forcibly increased in diameter, rolled by the friction of the axial movement of the mandrel 12, and comes into contact with the inner surface of the inner tube 2, which is forcibly expanded and plastically deformed, and integrated with the outer tube 1 to form 7JO. The outer tube 1 in a heated state is also expanded and deformed elastically.

そして、経時的にこの状態を維持することによりマンド
レル１２の軸方向移動で弾性リング１１は転動して内管
２の他端側から一端側に移動し、上述の如く、内管２を
塑性変形拡管し、外管１については弾性変形して一体的
に拡管していく。By maintaining this state over time, the elastic ring 11 rolls as the mandrel 12 moves in the axial direction and moves from the other end of the inner tube 2 to the one end, thereby causing the inner tube 2 to become plastic as described above. The outer tube 1 is elastically deformed and expanded integrally.

そして、マンドレル１２、及び、弾性リング１１が拡管
を終わって内管２の一端側から取り出されると、誘導加
熱装置４を停止して加熱を終了させ、外管２は自然冷却
されて縮管し、その弾性戻り差により塑性変形した内管
２に対し大きな１■合代で緊結されていく。Then, when the mandrel 12 and the elastic ring 11 have finished expanding and are taken out from one end of the inner tube 2, the induction heating device 4 is stopped to finish heating, and the outer tube 2 is naturally cooled and contracted. , due to the difference in elastic return, the inner tube 2, which has been plastically deformed, is tightened with a large joint width.

この場合、内管２側から見ると、予め、及び、拡管プロ
セスで冷却されているために、自然昇温加熱されるため
に増径し、したかって、内管２の加熱増径と外管１の冷
却縮管により大きな嵌合代が得られる。In this case, when viewed from the inner tube 2 side, since it has been cooled in advance and during the tube expansion process, the diameter increases due to natural temperature rise and heating, and therefore, the inner tube 2 is heated and the outer tube diameter increases. A large fitting allowance can be obtained by the cooling contraction tube of No. 1.

尚、当該実施例においては弾性リング１１は内部に液を
密封されていない断面充密型の硬質ゴムリングにしても
良い。In this embodiment, the elastic ring 11 may be a hard rubber ring with a filled cross section and whose interior is not sealed with liquid.

次に、第４〜６図に示す実施例においては、予め相対重
層した素管３の内管２の内側に第５．６図に示す周方向
に所定等間隔でリング状のノツチ１４を形成させた弾性
リング１１′をマンドレル１２と内管２の内面に当接さ
せてセットし、該弾性リング１１．′の軸方向移動速度
に合致する速度で移動するリング状の高周波誘導開発装
置４′　と同速度で移動する冷却液シトワー装買１３を
レットして上述態様同様に拡管作用を行わせるようにす
る態様であり、当該実施例では内管２の拡管のなされて
いない部分に供給された冷却水は弾性リング１１′　の
ノツチ１４．１４・・・を介して弾性リング１１′の軸
方向移動に無関係に拡管されない部分に対して冷却水が
流過し、拡管５の内管２に対しても冷却作用を与えて大
きな嵌合代が得られることか出来るようにされ、したが
って、弾性リング１１′の内管２１／））ら取り外され
た後、強制加熱装置４′　と強制冷却装置１３の通過後
に自然冷却される外管１と自然加熱される内管２どの結
果的な嵌合代をより大きくしてより強固な自緊二重管を
得ることが出来るようにされている。Next, in the embodiment shown in FIGS. 4 to 6, ring-shaped notches 14 are formed at predetermined equal intervals in the circumferential direction as shown in FIG. The elastic ring 11' is set in contact with the inner surface of the mandrel 12 and the inner tube 2, and the elastic ring 11. The ring-shaped high-frequency induction development device 4', which moves at a speed that matches the axial movement speed of In this embodiment, the cooling water supplied to the unexpanded portion of the inner pipe 2 is unrelated to the axial movement of the elastic ring 11' through the notches 14, 14, etc. of the elastic ring 11'. Cooling water flows through the portion that is not expanded, and it also gives a cooling effect to the inner tube 2 of the expanded tube 5, making it possible to obtain a large fitting margin. After being removed from the inner tube 21/)), the outer tube 1 is naturally cooled after passing through the forced heating device 4' and the forced cooling device 13, and the inner tube 2 is naturally heated. This makes it possible to obtain a stronger self-contained double pipe.

尚、この出願の発明の実施態様は上述各実施例に限るも
のでないことは勿論でおり、例えば、第７．８図に示す
様な弾性リング１１′　において、弾性リング１１″の
周方向長さを大きくすることか出来ても、その部分断面
が拡大して拡管作用か阻害されないようにピアノ線１５
によるスパイラル状の４Ｊブリングを巻装せざるように
することか出来るようにする等種々の態様か採用可能で
おる。The embodiments of the invention of this application are, of course, not limited to the above-mentioned embodiments. For example, in an elastic ring 11' as shown in Fig. 7.8, the circumferential length of the elastic ring 11'' is Even if it is possible to increase the size of the piano wire 15, the partial cross section will expand and the tube expansion effect will not be hindered.
It is possible to adopt various modes such as not having to wrap the spiral 4J bling or allowing it to be wound.

又、耐蝕二重管、耐摩耗二重管以外の二重管にも適用出
来ることも可能である。It is also possible to apply the present invention to double pipes other than corrosion-resistant double pipes and wear-resistant double pipes.

〈発明の効果〉 以上、この出願の発明によれば、基本的に耐圧、耐熱性
の外管と耐蝕、耐摩耗斗の内管とを充分な嵌合代をもっ
て緊結することか出来る効果かおるうえに、液圧拡管等
の製造方法と異なり、高圧の拡管液か要らＪ、したかっ
て、勤カコスｊ〜も支くなり、高圧拡管液に対する＠密
なシールか不要であるために、製造工程は勿論、製造装
置ら簡単になり、コストダウンを図れることか出来ると
いう効果かあるうえに、短い時間で出来るという優れた
効果か奏される。<Effects of the Invention> As described above, according to the invention of this application, basically the pressure-resistant and heat-resistant outer tube and the corrosion-resistant and wear-resistant inner tube can be tightly connected with sufficient fitting allowance. In addition, unlike manufacturing methods such as hydraulic pipe expansion, high-pressure pipe expansion liquid is not required, which also helps with labor costs, and there is no need for a tight seal against high-pressure pipe expansion liquid, so the manufacturing process is Of course, the manufacturing equipment becomes simpler and costs can be reduced, and it also has the excellent effect of being able to be completed in a short time.

又、内管の両端に対する厳密なシールが不要であるため
に、内管の両端の収縮が充分に許容され、したかつて、
製造後の二重管の引張り残沼応力か形成されず、応力腐
食割れが生じないという効果が奏される。In addition, since strict sealing at both ends of the inner tube is not required, contraction of both ends of the inner tube is sufficiently allowed.
The effect is that no residual tensile stress is formed in the double pipe after manufacture, and stress corrosion cracking does not occur.

又、マンドレルによる弾性リングの転動により内管の外
管に対する拡管と外管の拡管も併せて行えることか出来
るために、弾性リングの拡管力も少くて済みなから、軸
方内金ての領域に拡管が行えるという効果か奏される。In addition, since the rolling of the elastic ring by the mandrel allows expansion of the inner tube to the outer tube and the expansion of the outer tube at the same time, the expansion force of the elastic ring is also small, which reduces the area of the axial inner metal. The effect is that tube expansion can be performed.

そして、弾性リングはそのサイズを交換するだけで各種
サイズの二重管か製造出来、設計にも自由度か与えられ
るという優れた効果か秦される。Moreover, the elastic ring can be used to manufacture double-walled pipes of various sizes simply by exchanging its size, and it has the excellent effect of providing flexibility in design.

又、弾性リングによる拡管を行うプロセスにおいて拡管
の行われていない部分から拡管の行われた部分に対する
拡管液の流過により拡管の前俊過程で内管の冷却状態が
保持出来るために、得られた二重管の自然温度による外
管の冷却と内管の加熱かより大きく現れて大きな嵌合代
が得られるという優れた効果か奏される。In addition, in the process of pipe expansion using an elastic ring, the cooling state of the inner pipe can be maintained during the pre-expansion process due to the flow of the pipe expansion liquid from the part where the pipe has not been expanded to the part where the pipe has been expanded. The cooling of the outer tube and the heating of the inner tube due to the natural temperature of the double-walled tube are more pronounced, resulting in an excellent effect in that a large fitting margin can be obtained.

【図面の簡単な説明】[Brief explanation of drawings]

図面はこの出願の発明の詳細な説明図であり、第１図は
１実施例の素管の部分切截斜視図、第２図は同拡管工程
の縦断面図、第３図は第２図に用いられる弾性リングの
部分切截斜視図、第４図は第２図相当他の実施例の′＠
ｌ断面図、第５図は第４図に用いる弾性リングの斜視図
、第６図は第５図の部分断面図、第７図は第５図相当他
の実施例の斜視図、第８図は同断面図である。 １・・・外管、　　２・・・内管、　　３・−・素管、
１２・・・マンドレル、 １１．１１’　、１１’・・・弾性リング出願人　　川
崎重工業、株式会社 −１”１−。 代理人　　冨　１）幸　春２．′−゛１１゜・〕 ３−１−２　　＋Ｃ ’ＶＬ：ζＪ 第１図 ７１！ 第４図The drawings are detailed explanatory diagrams of the invention of this application, in which FIG. 1 is a partially cutaway perspective view of the raw pipe of one embodiment, FIG. 2 is a longitudinal cross-sectional view of the same pipe expansion process, and FIG. 3 is FIG. FIG. 4 is a partially cutaway perspective view of an elastic ring used for
5 is a perspective view of the elastic ring used in FIG. 4, FIG. 6 is a partial sectional view of FIG. 5, FIG. 7 is a perspective view of another embodiment equivalent to FIG. 5, and FIG. is the same sectional view. 1... Outer tube, 2... Inner tube, 3... Base tube,
12... Mandrel, 11.11', 11'... Elastic ring Applicant: Kawasaki Heavy Industries, Ltd. -1"1-. Agent: Tomi 1) Yukiharu 2.'-゛11゜・] 3-1 -2 +C 'VL:ζJ Figure 1 71! Figure 4

Claims (2)

【特許請求の範囲】[Claims] （１）外管と内管を相対重層した素管の外管を加熱増径
し次いで内管を強制拡管して内外管一体化増径しその外
管の冷却を経て両管を緊結するようにした二重管製造方
法において、上記内管の拡管をマンドレルの軸方向移動
による弾性リングの転動によって冷却状態の内管に対し
て行うようにしたことを特徴とする二重管の製造方法。(1) The diameter of the outer tube of the base tube in which the outer tube and the inner tube are layered relative to each other is increased by heating, then the inner tube is forcibly expanded to increase the diameter of the inner and outer tubes, and after the outer tube is cooled, both tubes are tied together. A method for manufacturing a double-layered tube according to the present invention, characterized in that the expansion of the inner tube is performed on the cooled inner tube by rolling an elastic ring due to axial movement of a mandrel. . （２）外管と内管を相対重層した素管の外管を加熱増径
し次いで内管を強制拡管して内外管一体化増径しその外
管の冷却を経て両管を緊結するようにした二重管製造方
法において、上記内管の加熱をマンドレルの軸方向移動
による弾性リングの転動によって冷却状態の内管に対し
て行うと共に内管の拡管前の部分から拡管後の部分に該
弾性リングを介して冷却液を通過するようにしたことを
特徴とする二重管製造方法。(2) The diameter of the outer tube of the base tube in which the outer tube and the inner tube are layered relative to each other is increased by heating, then the inner tube is forcibly expanded to increase the diameter of the inner and outer tubes, and after the outer tube is cooled, both tubes are tied together. In the method for manufacturing double-walled pipes, the heating of the inner pipe is performed on the cooled inner pipe by the rolling of an elastic ring caused by the axial movement of the mandrel, and the heating is performed on the inner pipe in a cooled state from the part before expansion to the part after expansion. A method for manufacturing a double tube, characterized in that a cooling liquid is passed through the elastic ring.