JP4093015B2

JP4093015B2 - Method for forming welded steel pipe joint and its manufacturing apparatus

Info

Publication number: JP4093015B2
Application number: JP2002314584A
Authority: JP
Inventors: 寿雄大西; 康二菅野
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2002-10-29
Filing date: 2002-10-29
Publication date: 2008-05-28
Anticipated expiration: 2022-10-29
Also published as: JP2004148337A

Description

【０００１】
【発明の属する技術分野】
本発明は、溶接鋼管の接合部成形方法及びその製造装置に係わり、詳しくは、連続移動する鋼帯の幅方向両端側を曲げ加工し、両端部を突き合わせて円形断面の空筒にした所謂「オープン管」の両端部の接合状態を良好にするための鋼帯両端部の成形技術に関する。
【０００２】
【従来の技術】
溶接鋼管は、図２に示す製造工程において、まず長尺の鋼板又は鋼帯１の幅方向両端側を曲げ加工し、両端部を突き合わせて円形断面の空筒にした所謂「オープン管」２とし、その後突き合わせた該両端部（接合部ともいう）を接合して製造される。その接合には、電気抵抗溶接（電縫）、鍛接、圧接、電弧溶接等、種々の手段が用いられている。
【０００３】
ところで、このような溶接鋼管のうち所謂電縫鋼管を製造するに際しては、前記接合部を誘導コイル３で融点以上に加熱するため、その直後にスクイズロール４で該接合部を衝合する時に、溶融した鋼が管の内外面に流出し、図３（ａ）に示すような余盛（ビード）５と称する不要部分が形成される。そのため、電縫鋼管の製造では、接合後にこれらビード５をバイト６で切削除去しているのが現状である。
【０００４】
また、接合を鍛接、圧接等の所謂「固相接合」で行う溶接鋼管の製造では、図３（ｂ）に示すように、接合部の温度、スクイズロール４の接合部への当接の有無、管円周方向への絞り程度に起因して、該接合部７の管内外に管体肉厚の５％以上の盛り上がり（増肉８）を生じることがある。この増肉８は、管内外に配置したロール（図示せず）で圧延して平滑化しているのが現状である。
【０００５】
しかしながら、特に溶接鋼管の管内に生じるビード５や増肉８については、該ビードや増肉の程度が大きく、その研削や圧延が不足すると、図３（ｃ）にハッチで示すように、平滑化が不十分な状態になる。これでは、溶接鋼管として肉厚偏差（Δｔ＝ｔ₁-ｔ₂）が大きく、品質不良で製品にならない。ここで、ｔ₁は所定の肉厚、ｔ₂は増肉部分の厚みである。また、そのような増肉等があると、その部分は以降に鋼管をさらにダイスで引き抜き縮径する際に、ダイス等を損傷する原因になる。
【０００６】
そのため、かかる接合部の内面増肉を抑制し、平滑化を図る技術が本出願人より提案されている。それは、『帯鋼を成形ロールにより連続的に成形して所謂「オープン管」とし、該オープン管の両エッジ部を誘導加熱により融点未満の温度域に加熱したのち、スクイズロールで衝合圧接する鋼管の製造方法において、前記オープン管両エッジ部の内面側となるエッジ端を、帯鋼の段階で予成形するものであり、この予成形を、エッジャーロールや機械切削による面取り加工で行う』という技術である（例えば、特許文献１参照）。
【０００７】
この技術によれば、図４（ａ）及び（ｂ）に示すように、予成形する部分の形状を断面視でテーパー状あるいはラウンド状として増肉を抑制することが期待される。
【０００８】
ところが、かかる予成形を、実際の鋼管製造のライン上を１００ｍ/ｍｉｎという高速で走行する鋼帯１に対して、図示していないミーリング装置（例えば、フライス盤）による切削やグラインダーによる研削で行うと、鋼帯の振動で切削あるいは研削部分に所謂「ビビリ」が生じ、所望形状を安定して得ることが難しい。また、使用冶具の交換を頻繁に行う必要があり、定期的なラインの停止頻度も高いという問題がある。一方、ロールを用いて面取りすると、上記のような問題は発生しなかった。しかしながら、図５（ａ）及び（ｂ）に示すように、鋼帯１の表裏面をロールで圧下すると、鋼帯１の端面に肉がはみ出し、そこに肉の盛り上がり（以下、別の増肉部分１２という）を生じた。この状態で両端部の突合せが適切に行うことができないので、前記技術のさらなる改良が望まれる。
【０００９】
【特許文献１】
特開平１０−２７７６３９号公報（第３、右欄の３０行〜５０行）
【００１０】
【発明が解決しようとする課題】
本発明は、かかる事情に鑑み、連続移動する鋼帯の幅方向両端側を曲げ加工し、両端部を突き合わせて円形断面の空筒にした所謂「オープン管」を成形するに際し、該オープン管の内面接合部のどこにも肉の盛り上がりを形成させない溶接鋼管の接合部成形方法及び該溶接鋼管の製造装置を提供することを目的としている。
【００１１】
【課題を解決するための手段】
発明者は、上記目的を達成するため、前記特許文献１に記載した技術の改良に鋭意努力し、その成果を本発明に具現化した。
【００１２】
すなわち、本発明は、鋼帯の幅方向両端側を曲げ加工し、両端部を突き合わせて円形断面の空筒に成形し、その突き合わされた両端部を互いに接合して溶接鋼管を製造するに際して、前記曲げ加工前の鋼帯両端部の鋼帯の幅方向両端から ( ０．５〜１０ ) ×板厚 ( ｔ ) ｍｍの範囲の一定領域（Ｌ）における肉厚が、断面視で端部を最小としたテーパー状になるように、両端面の部分圧下量（ｈ）を（０．１〜０．５）×板厚（ｔ）ｍｍとして、該一定領域（Ｌ）をロールで部分圧下すると共に、該部分圧下で両端面側に生じる増肉部分をエッジミラーで研削除去することを特徴とする溶接鋼管の接合部成形方法である。この場合、前記テーパの水平面に対してなす角度が２〜２０°であると一層良い。
【００１３】
また、本発明は、連続移動する鋼帯の幅方向両端側を曲げ加工し、両端部を突き合わせて円形断面の空筒にする一群の成形機からなる成形装置と、突き合わされた両端部を互いに接合して管体とする接合装置とを備えた溶接鋼管の製造装置において、前記成形機の上流側に,前記鋼帯の幅方向両端部の一定領域を部分圧下する左右一対の上下ロールと、その圧下で両端面に生じる増肉部分を研削するエッジミラーとを順次配設してなり、前記上下ロールのうちの上ロールが、両端の径が異なり水平からの斜角度θが２〜２０°であるテーパを有するテーパロール、あるいは、軸の水平からの斜角度θを２〜２０°にさせた円筒状ロールであることを特徴とする溶接鋼管の製造装置である。
【００１４】
本発明によれば、連続移動する鋼帯の幅方向両端側を曲げ加工し、両端部を突き合わせて円形断面の空筒にした所謂「オープン管」を成形しても、該オープン管の内面接合部のどこにも肉の盛り上がりを形成しないようになる。その結果、溶接鋼管の内面品質が向上し、製品歩留りが従来より高まるばかりでなく、溶接鋼管が円滑、且つ安定して製造できるようになる。
【００１５】
【発明の実施の形態】
以下、発明をなすに至った経緯をまじえ、本発明の実施の形態を説明する。
【００１６】
まず、発明者は、鋼帯の幅方向両端側を曲げ加工し、両端部を突き合わせて円形断面の空筒に成形した所謂「オープン管」において、その突き合わされた両端部を曲げ加工する前に、成形によって該オープン管の内面側になる鋼帯表（上）面の両端部の一定領域を面取りする。このこと自体は、前記特許文献１記載の技術と同じである。また、その面取りは、鋼帯端部の肉厚が最小で幅方向の中心よりに向けて厚くなる所謂「テーパー状」になるようにする。つまり、鋼帯の端部から幅方向へ向かう一定領域を製品鋼管の肉厚より薄くするのである。なお、この場合、「テーパ状」とは必ずしも一定角度で傾斜していなくても良い。
【００１７】
そして、面取りも、特許文献１に記載されているように、上下ロール１１で両端部を部分圧下することにした（図６（ａ）参照）。ミーリング装置やグラインダーによる方法では、高速走行している鋼帯の振動で切削あるいは研削部分に所謂「ビビリ」が生じ、所望形状を安定して得ることが難しいからである。ただし、本発明では、図８に示すように、ロールで圧下する前記一定領域（Ｌ）を、鋼帯の幅方向両端から（０．５〜１０）×板厚（ｔ）ｍｍの範囲で、且つ両端面の部分圧下量（ｈ）を（０．１〜０．５）×板厚（ｔ）ｍｍでに限定する。ここで、Ｌが０．５ｔｍｍ未満では、図８に示すように盛り上がり部１６が生じ、また１０ｔｍｍを超えても効果は変わらない。さらに、ｈが、０．１ｔｍｍ未満であると効果がなく、０．５ｔｍｍ超えても効果は変わらない。このように本発明では、面取りする領域を両端部より１０ｔｍｍ以下で且つ部分圧下距離（ｈ）も一定範囲に抑えるようにしたが、それでも、図５にハッチで示すように、鋼帯１の表面をロールで圧下すると、鋼帯１の端面側に肉がはみ出し、そこに別の増肉部分１２を生じてしまう。この状態では、両端部の突合せが適切に行うことができない。そこで、本発明では、ロールでの部分圧下で両端面側に生じるこの別の増肉部分１２を，図６（ｂ）に示すように、エッジミラー１３で研削除去することにしたのである。
【００１８】
なお、ロールによる面取りは、図８から明らかなように、水平面に対して角度（θ）で傾斜させて行われるが、本発明では、その角度は２〜２０°である。より好ましくは、３〜１０°である。
【００１９】
また、この本発明を実施する具体的な装置としては、図１にフローを示すように、連続移動する鋼帯の幅方向両端側を曲げ加工し、両端部を突き合わせて円形断面の空筒にする一群の成形機９からなる成形装置と、突き合わされた両端部を互いに接合して管体とする接合装置１０とを備えた溶接鋼管の製造装置において、前記成形機９の上流側に、前記鋼帯１の幅方向両端部の一定領域を部分圧下する左右一対の上下ロール１１と、その圧下で両端面に生じる前記別の増肉部分１２を研削するエッジミラー１３とを順次配設すれば良い。この場合、面取りを行うのは、前記上下ロール１１のうちの上ロールであるので、該上ロール１１ａに、両端の径が異なるテーパロールあるいは軸を水平から傾斜させた円筒状ロールを利用することになる。ロールの材質は、本発明では特に限定せず、鋼帯の圧延に通常採用されるものであれば良い。また、下ロールも鋼帯の圧延に通常採用されるもので十分である。さらに、両端面に生じる増肉部分を研削するエッジミラー１３は、軸を垂直にして使用する。
【００２０】
【実施例】
板厚（ｔ）が４．５ｍｍ、鋼種（規格）がＳＴＫＭ１５Ａのコイル状鋼帯を、図１に示した製造工程を用いて溶接鋼管を製造した。まず、コイル状の鋼帯１をアンコイラー１４で巻き戻してから１００ｍ/ｍｉｎで移動させ、一群の成形機９からなる成形装置で幅方向の両端側を曲げ成形し、外径が７６．３ｍｍφのオープン管２とする。その際、本発明に係る溶接鋼管の接合部成形方法を適用し、圧延機の前に配設した上下ロール１１で鋼帯１の両端部を部分圧下した。圧下した量は、図４に示すように、Ｔ１＝１．５ｍｍ，Ｔ２＝１０．０ｍｍである。そして、この圧下で生じた端面の増肉部分（長さで約１ｍｍ）をエッジミラー１３で研削除去した。そして、誘導コイル３で１２５０℃に加熱後、スクイズロール４で衝合して溶接鋼管を得た。
【００２１】
この本発明の実施成績は、得られた溶接鋼管の接合部を図７（ａ）及び（ｂ）に示すように垂直（０度）あるいは横（９０度）にして扁平になるよう押し潰し、割れが発生した時の外径と押し潰し開始前の初期径（Ｄ）との比で評価した。つまり、突合せた接合部の形状が良好であるほど、押し潰し抵抗が大きくなるからである。
【００２２】
この扁平試験の結果を、本発明に係る接合部成形方法を採用しない従来の方法で製造した溶接鋼管の場合と比較し、表１に一括して示す。
【００２３】
【表１】

【００２４】
表１より、従来法では、接合部位置を０度及び９０度にしたいずれの場合も、初期径（Ｄ）を２０〜５０％に扁平化した時点で割れが発生したのに対して、本発明では、上下の肉が密着しても割れが発生しないことが明らかである。また、成形後のオープン管の突合せ部分を肉眼で観察したが、図５にハッチで示したような別の増肉部分１２はほとんど認められなかった。さらに、製品の不良率が従来より半減した。
【００２５】
【発明の効果】
以上述べたように、本発明により、連続移動する鋼帯の幅方向両端側を曲げ加工し、両端部を突き合わせて円形断面の空筒にした所謂「オープン管」を成形しても、該オープン管の内面接合部のどこにも肉の盛り上がりを形成しないようになる。その結果、溶接鋼管の内面品質が向上し、製品歩留りが従来より高まるばかりでなく、溶接鋼管が円滑、且つ安定して製造できるようになる。
【図面の簡単な説明】
【図１】本発明に係る溶接鋼管の製造装置を示すフロー図である。
【図２】従来の電縫鋼管の製造装置を示すフロー図である。
【図３】溶接鋼管の接合部を示す図であり、（ａ）は電縫によるビードの発生状況を、（ｂ）は圧接等による肉の盛り上がりを、（ｃ）は前記ビードや肉の盛り上がり量が大きい場合の切削後の状態を表している。
【図４】鋼帯の両端部を面取りした場合の理想的状態を示す図であり、（ａ）は、面取りした部分が断面視でテーパ状、（ｂ）はラウンド状の場合である。
【図５】ロールで鋼帯両端部を面取りした際に、その端面に別の増肉部分が生じることを指摘した図であり、（ａ）は、面取りした部分が断面視でテーパ状、（ｂ）はラウンド状の場合である。
【図６】本発明に係る鋼帯両端部の面取りを説明する図であり、（ａ）は、上下ロールによる所謂「テーパ状」の部分圧下状況を、（ｂ）エッジ・ミラーによる端面の研削状況を示す。
【図７】溶接鋼管の接合部を評価する試験方法を説明する図であり、（ａ）は、接合線を垂直にした０度扁平試験（内面引っ張り）を、（ｂ）は接合線を水平にした９０度扁平試験（外面引っ張り）を行う時の接合部の位置を示している。
【図８】鋼帯両端部の面取り量を説明する図である。
【符号の説明】
１鋼帯（長尺の鋼板）
２オープン管
３誘導コイル
４スクイズロール
５ビード
６バイト
７接合部
８増肉
９一群の圧延機
１０接合装置
１１上下ロール
１１ａ上ロール
１１ｂ下ロール
１２別の増肉部分
１３エッジミラー
１４アンコイラー
１５押し潰す方向を示す矢印
１６盛り上がり部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a welded steel pipe joint forming method and a manufacturing apparatus therefor, and more specifically, a so-called “cylinder having a circular cross section is formed by bending both ends in the width direction of a continuously moving steel strip and butting both ends. The present invention relates to a technology for forming both ends of a steel strip to improve the joining state of both ends of an “open pipe”.
[0002]
[Prior art]
The welded steel pipe is a so-called “open pipe” 2 in which, in the manufacturing process shown in FIG. 2, first, both ends in the width direction of a long steel plate or steel strip 1 are bent and both ends are butted into a hollow cylinder having a circular cross section. Then, it is manufactured by joining the both end portions (also referred to as a joint portion) which have been butted together. For the joining, various means such as electric resistance welding (electro-sewing), forge welding, pressure welding, and arc welding are used.
[0003]
By the way, when manufacturing a so-called ERW steel pipe among such welded steel pipes, the joint portion is heated to the melting point or more by the induction coil 3, so that when the joint portion is abutted by the squeeze roll 4 immediately after that, The molten steel flows out to the inner and outer surfaces of the pipe, and an unnecessary portion called a bead 5 is formed as shown in FIG. For this reason, in the manufacture of ERW steel pipes, these beads 5 are removed by cutting with a cutting tool 6 after joining.
[0004]
Further, in the manufacture of a welded steel pipe in which joining is performed by so-called “solid phase joining” such as forging and pressure welding, as shown in FIG. 3B, the temperature of the joined portion, the presence or absence of contact of the squeeze roll 4 to the joined portion Due to the degree of squeezing in the pipe circumferential direction, a bulge (thickening 8) of 5% or more of the pipe wall thickness may occur inside and outside the pipe of the joint 7. The thickness increase 8 is currently rolled and smoothed by a roll (not shown) arranged inside and outside the pipe.
[0005]
However, especially for the bead 5 and the thickening 8 generated in the pipe of the welded steel pipe, if the degree of the bead or the thickening is large and the grinding or rolling is insufficient, as shown by hatching in FIG. Is inadequate. In this case, the thickness deviation (Δt = t ₁ -t ₂ ) is large as a welded steel pipe, and the product does not become a product due to poor quality. Here, t ₁ is a predetermined thickness, and t ₂ is the thickness of the increased thickness portion. Further, if there is such a thickening or the like, the portion may cause damage to the die or the like when the steel pipe is further drawn and reduced in diameter thereafter.
[0006]
Therefore, the present applicant has proposed a technique for suppressing the increase in the inner surface thickness of the joint and smoothing it. That is, “strip steel is continuously formed with a forming roll to form a so-called“ open tube ”, and both edge portions of the open tube are heated to a temperature range lower than the melting point by induction heating, and then subjected to abutting pressure welding with a squeeze roll. In the steel pipe manufacturing method, the edge ends that are the inner surface sides of the two edge portions of the open pipe are pre-formed at the stage of the steel strip, and this pre-forming is performed by chamfering by an edger roll or mechanical cutting. (See, for example, Patent Document 1).
[0007]
According to this technique, as shown in FIGS. 4A and 4B, it is expected that the shape of the part to be preformed is tapered or rounded in a cross-sectional view to suppress the increase in thickness.
[0008]
However, when such pre-forming is performed on a steel strip 1 traveling at a high speed of 100 m / min on an actual steel pipe production line by cutting with a milling device (for example, a milling machine) not shown or grinding with a grinder. The so-called “chatter” occurs in the cut or ground portion due to the vibration of the steel strip, and it is difficult to stably obtain a desired shape. In addition, it is necessary to frequently replace the jig used, and there is a problem that the frequency of periodic line stoppage is high. On the other hand, when chamfering was performed using a roll, the above problem did not occur. However, as shown in FIGS. 5 (a) and 5 (b), when the front and back surfaces of the steel strip 1 are squeezed with a roll, meat protrudes from the end surface of the steel strip 1, and the rise of the meat (hereinafter referred to as another thickening) Part 12). In this state, since both ends cannot be properly matched, further improvement of the technique is desired.
[0009]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-277739 (line 3, lines 30 to 50 in the right column)
[0010]
[Problems to be solved by the invention]
In view of such circumstances, the present invention bends both ends in the width direction of a continuously moving steel strip and forms a so-called “open tube” in which both ends are butted into a hollow cylinder having a circular cross section. It is an object of the present invention to provide a method for forming a welded steel pipe joint that does not form a bulge of meat anywhere on the inner surface joint, and a manufacturing apparatus for the welded steel pipe.
[0011]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the inventor diligently improved the technique described in Patent Document 1 and realized the result in the present invention.
[0012]
That is, the present invention bends both ends of the steel strip in the width direction, forms both ends into a hollow cylinder having a circular cross section, and joins the joined ends to each other to produce a welded steel pipe. The thickness in a certain region (L) in the range of ( 0.5 to 10 ) × plate thickness ( t ) mm from both ends in the width direction of the steel strip at both ends of the steel strip before the bending is shown in cross section. The partial reduction (h) at both end faces is set to (0.1 to 0.5) × plate thickness (t) mm so that the constant region (L) is partially reduced with a roll so that the taper is minimized. In addition, the present invention is a method for forming a welded steel pipe joint, characterized in that an increased thickness portion generated on both side faces under the partial pressure is ground and removed by an edge mirror. In this case, even better when the angle formed with respect to the horizontal plane of the previous SL taper is 2 to 20 °.
[0013]
The present invention also includes a forming apparatus comprising a group of forming machines which bend both ends in the width direction of a continuously moving steel strip and abut the end portions into a hollow cylinder having a circular cross section. In a welded steel pipe manufacturing apparatus comprising a joining device that joins to form a tubular body, a pair of left and right upper and lower rolls that partially compresses a constant region at both ends in the width direction of the steel strip on the upstream side of the forming machine, An edge mirror that grinds thickened portions generated on both end faces under the pressure is sequentially disposed , and the upper roll of the upper and lower rolls has a different diameter at both ends and an oblique angle θ from the horizontal of 2 to 20 °. It is the taper roll which has the taper which is, or the cylindrical roll which made the inclination angle (theta) 2 to 20 degrees from the horizontal of an axis | shaft, The manufacturing apparatus of the welded steel pipe characterized by the above-mentioned .
[0014]
According to the present invention, even if both ends in the width direction of a continuously moving steel strip are bent and both ends are abutted to form a so-called “open tube” having a circular cross section, the inner surface of the open tube is joined. The meat swells nowhere in the department. As a result, not only the quality of the inner surface of the welded steel pipe is improved and the product yield is increased as compared with the prior art, but also the welded steel pipe can be manufactured smoothly and stably.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below based on the circumstances leading to the invention.
[0016]
First, the inventor bends both ends of the steel strip in the width direction, and joins both ends to form a hollow cylinder having a circular cross section before bending both ends. Then, a certain region of both ends of the steel strip surface (upper) surface which becomes the inner surface side of the open pipe is formed by chamfering. This itself is the same as the technique described in Patent Document 1. Further, the chamfering is so-called “tapered” that the thickness of the end portion of the steel strip is minimized and becomes thicker from the center in the width direction. That is, the fixed area | region which goes to the width direction from the edge part of a steel strip is made thinner than the thickness of a product steel pipe. In this case, the “tapered shape” does not necessarily have to be inclined at a certain angle.
[0017]
And also as for chamfering, as described in Patent Document 1, both end portions were partially reduced by the upper and lower rolls 11 (see FIG. 6A). Milling The method according to equipment and grinder, cutting or grinding portion by vibration of the steel strip is traveling at high speed occurs so-called "chatter", because it is difficult to obtain stably a desired shape. However, in this invention, as shown in FIG. 8, the said fixed area | region (L) rolled down with a roll is the range of (0.5-10) x board thickness (t) mm from the width direction both ends of a steel strip, And the partial reduction amount (h) of both end faces is limited to (0.1 to 0.5) × plate thickness (t) mm. Here, when L is less than 0.5 tmm, the swelled portion 16 is generated as shown in FIG. 8, and the effect is not changed even if it exceeds 10 tmm. Furthermore, if h is less than 0.1 tmm, there is no effect, and if h exceeds 0.5 tmm, the effect does not change. Thus, in the present invention, the area to be chamfered is 10 tmm or less from both ends and the partial reduction distance (h) is also kept within a certain range. However, as shown by hatching in FIG. When rolling down with a roll, the meat protrudes from the end face side of the steel strip 1, and another thickened portion 12 is produced there. In this state, both ends cannot be properly matched. Therefore, in the present invention, this additional thickened portion 12 generated on both side faces under partial pressure with the roll is ground and removed by the edge mirror 13 as shown in FIG. 6B.
[0018]
As is apparent from FIG. 8, the chamfering by the roll is performed while being inclined at an angle (θ) with respect to the horizontal plane. In the present invention, the angle is 2 to 20 °. More preferably, it is 3 to 10 °.
[0019]
Further, as a specific apparatus for carrying out the present invention, as shown in the flow in FIG. 1, both ends in the width direction of a continuously moving steel strip are bent, and both ends are abutted to form a circular cross-section empty cylinder. In a welded steel pipe manufacturing apparatus comprising a forming apparatus composed of a group of forming machines 9 and a joining apparatus 10 that joins both butted ends together to form a tubular body, on the upstream side of the forming machine 9, If a pair of left and right upper and lower rolls 11 that partially reduce a certain region at both ends in the width direction of the steel strip 1 and an edge mirror 13 that grinds the other thickened portion 12 that occurs on both end faces under the reduction are sequentially disposed. good. In this case, since it is the upper roll of the upper and lower rolls 11 that chamfers, a taper roll having different diameters at both ends or a cylindrical roll having an inclined axis from the horizontal is used for the upper roll 11a. become. The material of a roll is not specifically limited in this invention, What is necessary is just what is normally employ | adopted for rolling of a steel strip. Moreover, what is normally employ | adopted for rolling a steel strip is enough for a lower roll. Furthermore, the edge mirror 13 that grinds the thickened portion generated on both end faces is used with its axis vertical.
[0020]
【Example】
A coiled steel strip having a thickness (t) of 4.5 mm and a steel type (standard) of STKM15A was manufactured using the manufacturing process shown in FIG. First, the coiled steel strip 1 is unwound by the uncoiler 14 and then moved at 100 m / min. The both ends in the width direction are bent and formed by a forming apparatus including a group of forming machines 9, and the outer diameter is 76.3 mmφ. The open tube 2 is used. At that time, the method for forming a welded steel pipe joint according to the present invention was applied, and both ends of the steel strip 1 were partially crushed by the upper and lower rolls 11 disposed in front of the rolling mill. As shown in FIG. 4, the amount of reduction is T1 = 1.5 mm and T2 = 10.0 mm. And the thickened part (about 1 mm in length) of the end surface produced under this pressure was ground and removed by the edge mirror 13. And after heating to 1250 degreeC with the induction coil 3, it collided with the squeeze roll 4, and the welded steel pipe was obtained.
[0021]
As shown in FIGS. 7 (a) and 7 (b), the results of the practice of the present invention are such that the joints are flattened in a vertical (0 degree) or lateral (90 degree) form, Evaluation was based on the ratio between the outer diameter when cracking occurred and the initial diameter (D) before starting crushing. In other words, the better the shape of the joined part, the greater the crushing resistance.
[0022]
The results of this flat test are collectively shown in Table 1 in comparison with the case of a welded steel pipe manufactured by a conventional method that does not employ the joint forming method according to the present invention.
[0023]
[Table 1]

[0024]
According to Table 1, in the conventional method, the crack occurred when the initial diameter (D) was flattened to 20 to 50% in both cases where the joint position was 0 degree and 90 degrees. In the invention, it is clear that cracks do not occur even when the upper and lower meats are in close contact. Further, when the butted portion of the open pipe after molding was observed with the naked eye, another thickened portion 12 as shown by hatching in FIG. 5 was hardly recognized. In addition, the defective rate of products has been halved compared to the past.
[0025]
【The invention's effect】
As described above, according to the present invention, even if both ends in the width direction of a continuously moving steel strip are bent and both ends are butted into a hollow cylinder having a circular cross section, the so-called “open tube” is formed. No bulge of meat is formed anywhere on the inner joint of the tube. As a result, not only the quality of the inner surface of the welded steel pipe is improved and the product yield is increased as compared with the prior art, but also the welded steel pipe can be manufactured smoothly and stably.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a welded steel pipe manufacturing apparatus according to the present invention.
FIG. 2 is a flow diagram showing a conventional ERW steel pipe manufacturing apparatus.
FIGS. 3A and 3B are diagrams showing a welded steel pipe joint, wherein FIG. 3A shows a bead generation state due to electric sewing, FIG. 3B shows a rise of meat due to pressure welding, and FIG. 3C shows a rise of the bead and meat. The state after cutting when the amount is large is shown.
4A and 4B are diagrams showing an ideal state when both ends of a steel strip are chamfered. FIG. 4A shows a case where the chamfered portion is tapered in a sectional view, and FIG. 4B shows a round shape.
FIG. 5 is a diagram indicating that when the steel strip is chamfered at both ends, another thickened portion is generated on the end surface, and (a) shows that the chamfered portion is tapered in a sectional view; b) is a round case.
6A and 6B are diagrams for explaining chamfering at both ends of a steel strip according to the present invention, in which FIG. 6A shows a so-called “tapered” partial reduction state by upper and lower rolls, and FIG. 6B shows end face grinding by an edge mirror. Indicates the situation.
FIGS. 7A and 7B are diagrams for explaining a test method for evaluating a joint portion of a welded steel pipe, wherein FIG. 7A is a 0-degree flattening test (internal tension) with the joint line made vertical, and FIG. The position of the joint when the 90-degree flatness test (external tension) is performed is shown.
FIG. 8 is a diagram for explaining a chamfering amount at both ends of a steel strip.
[Explanation of symbols]
1 Steel strip (long steel plate)
2 Open tube 3 Inductive coil 4 Squeeze roll 5 Bead 6 Bite 7 Joining part 8 Thickening 9 Group of rolling mills 10 Joining device 11 Upper and lower rolls

11a Upper roll

11b Lower roll 12 Another thickening part 13 Edge mirror 14 Uncoiler 15 Crush Directional arrow 16 Swell

Claims

Bending both ends of the steel strip in the width direction, butting both ends together to form a hollow cylinder with a circular cross section, when manufacturing the welded steel pipe by joining the butted ends together
The thickness in a certain region (L) in the range of ( 0.5 to 10 ) × plate thickness ( t ) mm from both ends in the width direction of the steel strip at both ends of the steel strip before the bending is shown in cross section. The partial reduction (h) at both end faces is set to (0.1 to 0.5) × plate thickness (t) mm so that the constant region (L) is partially reduced with a roll so that the taper is minimized. In addition, a method for forming a welded steel pipe joined portion, characterized in that an increased thickness portion generated on both side faces under the partial pressure is ground and removed by an edge mirror.

2. The method for forming a welded steel pipe joint according to claim 1, wherein an angle formed with respect to a horizontal plane of the taper is 2 to 20 [deg.].

Bending both ends in the width direction of the continuously moving steel strip, and forming a group of forming machines that make both ends meet but a circular cross-section cylinder, and the joined ends are joined to each other A welded steel pipe manufacturing apparatus comprising:
On the upstream side of the molding machine, a pair of left and right upper and lower rolls that partially reduce a certain region at both ends in the width direction of the steel strip, and an edge mirror that grinds the increased thickness portion that occurs on both end faces under the reduction are sequentially disposed. And
The upper roll of the upper and lower rolls is a taper roll having a taper in which the diameters at both ends are different and the horizontal oblique angle θ is 2 to 20 °, or the oblique angle θ from the horizontal of the shaft is 2 to 20 °. An apparatus for manufacturing a welded steel pipe, characterized in that the apparatus is a cylindrical roll .