JP4697759B2

JP4697759B2 - Steel pipe cutting control method

Info

Publication number: JP4697759B2
Application number: JP2000309121A
Authority: JP
Inventors: 武夫北岡
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 2000-10-10
Filing date: 2000-10-10
Publication date: 2011-06-08
Anticipated expiration: 2020-10-10
Also published as: JP2002113651A

Description

【０００１】
【産業上の利用分野】
本発明は、溶接管等の管状体を効率よく且つ迅速に切断する際の切断作業を制御する方法に関する。
【０００２】
【従来の技術】
鋼管の切断には、モータからの動力で回転する砥石をスイングさせて鋼管に押し当て切断する装置が使用されている。この切断装置は、概略構成を図１に示すように、機台１の支持部にアーム２の一端を枢支し、アーム２の他端に軸支金具３を介して砥石４を回転可能に設けている。機台１から起立したシリンダ５がアーム２の途中に接続され、シリンダ５の伸縮によってアーム２が揺動する。
切断される鋼管Ｐは、機台１上に送り込まれた後、パイプチャック６で拘束される。次いで、シリンダ５を駆動させ、砥石４を回転させながら上限位置Ｈから出代αを含む下限位置Ｌまで下降させ、鋼管Ｐに押し当てて切断する。
【０００３】
砥石４をスイングさせる方式では、シリンダ５のストロークによって砥石４の可動範囲が決まるため、大口径の鋼管Ｐを対象とする設備構成では砥石４の上限位置Ｈを高くせざるを得ず、切断装置の大型化が避けられない。また、砥石４の移動軌跡が長くなるため、切断開始までに時間がかかる。しかも、アーム２の旋回によって下降した砥石４が鋼管Ｐに接触して鋼管Ｐを切断するため、切断された鋼管Ｐの端面直角度が出にくい。
【０００４】
そこで、本発明者等は、アーム２に代えて砥石４を垂直方向に移動させる昇降機構を採用し、砥石４の高さ方向位置に応じ砥石４の昇降動作及び回転速度を制御する方式を採用した切断装置を特願平１１−８７８９６号で提案した。垂直方向に砥石４を移動させるとき、必要な砥石４の移動距離は切断しようとする鋼管Ｐの外径よりも若干大きく設定するだけでよいため、アーム２を用いたスイング方式のように切断装置が大掛かりになることが避けられ、切断開始までの時間が短縮される。また、昇降ガイドに沿って砥石４が移動するため、枢軸７から砥石４までの距離が長いアーム２を用いたスイング方式に比較して切断端面の管軸に対する直角度は格段に向上する。
【０００５】
【発明が解決しようとする課題】
ところで、駆動系に大きな負荷がかかる大径厚肉管等の鋼管を切断する場合、切込みから切抜けまで砥石４を一定速度で送ると、切込み時の抵抗が大きいため低速になり、切抜けまでに長時間を要する。造管ラインに組み込んだ走間切断機で切断所要時間が長くなると、大径パイプや短尺パイプの切出しではラインスピードの低下を余儀なくされ、生産性が低下する。また、切込み速度を遅くすると、鋼管Ｐの切断面にバリ，焼付き等の欠陥が発生しやすくなる。
【０００６】
【課題を解決するための手段】
本発明は、このような問題を解消すべく案出されたものであり、切断されている鋼管断面の接触部長さに応じて回転砥石の送り速度を制御することにより、切断端面に生じがちなバリ，焼付き等の欠陥発生を防止し、大口径厚肉管であっても短時間切断を可能にすることを目的とする。
【０００７】
本発明の切断制御方法は、その目的を達成するため、回転砥石を垂直方向に昇降させて鋼管を切断する際、鋼管の管軸を通る回転砥石の移動軌跡に沿って次の各位置Ｐ₀〜Ｐ₇を設定し、回転砥石の最下点がＰ₀−Ｐ₁の間にあるとき回転砥石の送り速度を上昇させ、最下点がＰ₁−Ｐ₂の間にあるとき回転砥石を一定の第１設定値Ｆ₁で送り、最下点がＰ₂−Ｐ₃の間にあるとき回転砥石の送り速度を上昇させ、最下点がＰ₃−Ｐ₄の間にあるとき回転砥石を一定の第２設定値Ｆ₂で送り、最下点がＰ₄−Ｐ₅の間にあるとき回転砥石の送り速度を下げ、最下点がＰ₅−Ｐ₆の間にあるとき回転砥石を一定の第３設定値Ｆ₃で送り、最下点がＰ₆−Ｐ₇にあるとき回転砥石の送り速度を下げ、最下点が位置Ｐ₇に達した時点で回転砥石を逆転させて最下点を位置Ｐ₀に上昇させることを特徴とする。
【０００８】
Ｐ₀：待機代を含み鋼管外周上の最高位置Ｐ₁から回転砥石の最下点までの高さ位置
Ｐ₁：回転砥石の最下点が最初に接触する鋼管外周上の最高位置
Ｐ₂：最高位置Ｐ₁に対応する鋼管内周上の位置（鋼管に接触する回転砥石の接触長さが減少し始める位置）
Ｐ₃：鋼管に接触する回転砥石の接触長さが減少からほぼ一定になる位置
Ｐ₄：鋼管に接触する回転砥石の接触長さが増加し始める位置
Ｐ₅：鋼管内周上の最低位置
Ｐ₆：鋼管外周上の最低位置
Ｐ₇：出代を含む最下点の最低到達位置
ここで、Ｐ ₃ からＰ ₄ の間は鋼管に接触する回転砥石の接触長さの変動幅が３０％以下とする
【０００９】
【作用】
回転砥石１０を用いて鋼管Ｐを切断するとき、鋼管Ｐに対する回転砥石１０の位置関係に応じて回転砥石１０の接触長さが変わる。接触長さは、上昇位置Ｐ₀から下降した回転砥石１０の最下点ｂが鋼管Ｐ外周上の最も高い位置Ｐ₁に接触した後、回転砥石１０の下降に伴って徐々に長くなる（図２）。なお、上昇位置Ｐ₀は前回切断された鋼管Ｐの径を基にして今回送られてくる鋼管Ｐの径Ｄに適した高さ位置に設定され、切断開始前の状態では上昇位置Ｐ₀よりも高い位置に回転砥石１０の初期位置が設定される。
【００１０】
位置Ｐ₁から回転砥石１０が下降するとき、鋼管Ｐ及び回転砥石１０がほぼ接線方向に接触するため、接触長さは一途に増加する。回転砥石１０の最下点ｂが鋼管Ｐ外周上の位置Ｐ₁に対応する内側の位置Ｐ₂を抜けた後では、最下点ｂを含む回転砥石１０の周縁が鋼管Ｐに接触せず、且つ鋼管Ｐの接線と回転砥石１０の接線との間の角度が大きくなるため、接触長さが減少する。
接触長さの減少傾向は、位置Ｐ₂の若干下方にある位置Ｐ₃まで続き、位置Ｐ₃から接触長さがほぼ一定になる。位置Ｐ₃以降、鋼管Ｐの管壁がほぼ厚み方向に切断される。回転砥石１０が更に下降すると、鋼管Ｐの接線と回転砥石１０の接線との間の角度が小さくなり、位置Ｐ₄から接触長さが増加し始める。
【００１１】
位置Ｐ₃及び位置Ｐ₄は、鋼管Ｐ及び回転砥石１０の径に応じて幾何学的及び過去の実績から算出される。ただし、鋼管Ｐの断面に接触する回転砥石１０の接触長さは、Ｐ₃−Ｐ₄の間で完全に一定化するものではなく、鋼管Ｐの肉厚方向に対する回転砥石１０の接線方向の角度によって若干変わる。そこで、本発明においては、接着長さの変動幅が３０％以下の範囲に収まることをもって位置Ｐ₃，Ｐ₄を設定する。
【００１２】
位置Ｐ₄以降、回転砥石１０の周縁が鋼管Ｐに接触していない最下点ｂ周辺部分が短くなるため、鋼管Ｐに対する回転砥石１０の接触長さが増加する。最下点ｂ周辺部分が短くなることに起因する接触長さの増加は、最下点ｂが鋼管Ｐ外周上にある最下部に対応する内側の位置Ｐ₅に接触するまで継続する。接触長さは、最下点ｂが位置Ｐ₅に接触した後では、最下点ｂが鋼管Ｐ外周上の最低位置Ｐ₆を通過するまで一途に減少する。回転砥石１０は、出代αを取り込んだ最下位置Ｐ₇まで下降する。
【００１３】
切断中の鋼管Ｐに接触する回転砥石１０の接触長さは、このように鋼管Ｐと回転砥石１０との位置関係に応じて変わる。接触長さの変化によって、回転砥石１０を回転・降下させる駆動系に加わる負荷も変動する。
そこで、鋼管Ｐと回転砥石１０との位置関係を基準として駆動系のモータ回転数を制御し、接触長さｌに応じて回転砥石１０の送り速度を調整することにより、大口径厚肉管であっても短時間切断を可能にしている。接触長さｌの変化は、昇降する回転砥石１０の高さ位置ｈと鋼管Ｐの外径Ｄ，肉厚ｔから算出されるが、回転砥石１０を駆動するモータに加わる負荷の変動から求めることも可能である。
たとえば、直径ｄ＝５０ｍｍの回転砥石１０で肉厚ｔ＝２ｍｍ，外径Ｄ＝４０ｍｍの鋼管Ｐを切断する場合、接触長さｌは、回転砥石１０の高さ位置ｈに応じて図３に示すように変化する。そこで、最高送り速度をＶ_maxとするとき、Ｖ＝Ｖ_max／ｌとして送り速度Ｖを設定する。
【００１４】
【実施の形態】
本発明では、たとえば図４に示す構成の切断装置が採用される。この切断装置では、回転砥石１０を垂直方向にピッチ送りするボールスクリュー１１を、昇降駆動機構の昇降モータ１２に動力的に連結している。回転砥石１０は、昇降ベース１５に搭載されている砥石回転用モータ１６からタイミングベルト１７を介して伝達される動力によって回転する。
ボールスクリュー１１の回転数は、エンコーダ１３で検出され、回転砥石１０の高さを表す情報として制御回路１４に出力される。制御回路１４には切断しようとする鋼管Ｐの外径Ｄ及び肉厚ｔが予め入力されており、エンコーダ１３から入力された回転砥石１０の高さ情報に応じて負荷を演算する。演算結果は、制御信号として昇降モータ１２及び砥石回転用モータ１６に出力され、昇降モータ１２及び砥石回転用モータ１６の回転数，電流等が制御される。
【００１５】
鋼管Ｐの切断に当たって回転砥石１０を駆動すると、Ｐ₀−Ｐ₁までの間は駆動系に負荷がかからないため、駆動系のモータ回転数、換言すると回転砥石１０の送り速度を自由に設定できる。Ｐ₀−Ｐ₁の距離ｄ₁は、上昇位置Ｐ₀の高さ及び鋼管Ｐの外径から定まる待機代βであり、たとえば特開平１１−８７８９６号で採用しているように前回切断の結果から求められる。
回転砥石１０の最下点ｂが鋼管Ｐ外周上の位置Ｐ₁に接触すると、回転砥石１０の駆動系に負荷が加わり始める。そこで、回転砥石１０の送り速度を第１設定値Ｆ₁に一定維持する（図５）。この状態は、最下点ｂが位置Ｐ₂に達するまで継続される。Ｐ₁−Ｐ₂の距離ｄ₂は、切断されている鋼管Ｐの肉厚ｔに等しい。
最下点ｂが位置Ｐ₂を通過した後では接触長さが減少する傾向（図２）にあるので、回転砥石１０の送り速度を上昇させる。Ｐ₂−Ｐ₃の距離ｄ₃は、鋼管Ｐ及び回転砥石１０の径に応じて定まる値である。
【００１６】
鋼管Ｐの切断が進行して最下点ｂが位置Ｐ₃に達すると、接触長さがほぼ一定の低い値になる。この状態では回転砥石１０の送り速度を比較的高い第２設定値Ｆ₂に一定維持する。第２設定値Ｆ₂は、昇降モータ１２の能力に応じた最大値に設定することが好ましい。第２設定値Ｆ₂での回転砥石１０の送りは、最下点ｂが位置Ｐ₄に到達するまで継続される。Ｐ₃−Ｐ₄の距離ｄ₄は、鋼管Ｐ及び回転砥石１０の径に応じて定まる値である。
接触長さが長くなる位置Ｐ₄から最下点ｂが位置Ｐ₅に達する時点まで、回転砥石１０の送り速度を低下させる。Ｐ₄−Ｐ₅の距離ｄ₅も、鋼管Ｐ及び回転砥石１０の径に応じて定まる値である。
【００１７】
最下点ｂが位置Ｐ₅に達した時点から最下位置Ｐ₆を通過するまで、回転砥石１０の能力に応じて比較的低い第３設定値Ｆ₃で回転砥石１０を送り、鋼管Ｐの下部を切断する。Ｐ₅−Ｐ₆の距離ｄ₆は、鋼管Ｐの肉厚ｔに相当する値である。
鋼管Ｐの最下位置Ｐ₆を最下点ｂが通過した後、回転砥石１０の送り速度を下げ、最下点ｂを下降位置Ｐ₇まで下げる。Ｐ₅−Ｐ₆の距離ｄ₇は、鋼管Ｐを確実に切断するために予め設定している出代α（図２）に当たる。最下点ｂが下降位置Ｐ７に達した時点で回転砥石１０を逆方向に送り、最下点ｂを上昇位置Ｐ₀に復帰させ、次回の切断に待機させる。
制御回路１４では、図６に示すフローに従って回転砥石１０の最下点ｂから昇降モータ１２の回転数及び昇降モータ１２に送る電流を制御し、以上に説明したように鋼管Ｐと回転砥石１０との位置関係に応じた最適条件で鋼管Ｐを切断する。
【００１８】
【実施例】
図４の設備構成をもつ切断装置に外径８６０ｍｍの回転砥石１０を取り付け、外径２１０ｍｍ，肉厚６．０ｍｍのステンレス鋼製溶接鋼管を切断した。この条件下では、待機代β＝１０ｍｍ，出代α＝１５ｍｍに設定するとき、鋼管Ｐと回転砥石１０との位置関係を表す各位置Ｐ₀〜Ｐ₆は、Ｐ₇（基準点）からの高さとして次表のように算出される。回転砥石１０の送り速度は、鋼管Ｐとの位置関係に応じて次表のように制御した。
【００１９】

【００２０】
このように回転砥石１０の送り速度を制御しながら鋼管Ｐを切断したとき、切断所要時間は０．１５分／本であった。また、切断端面にバリ，焼付き等の欠陥発生がなり良好な切断端面をもつ鋼管製品が得られた。これに対し、欠陥発生を避けるために一定した送り速度（０．６ｍ／分）で回転砥石１０を送りながら鋼管Ｐを切断した場合、切断所要時間が０．４０分／本であった。この対比から明らかなように、本発明に従って回転砥石１０の送り速度を制御することにより、切断時間の短縮が図られ、生産性が向上することが判る。
【００２１】
【発明の効果】
以上に説明したように、本発明は、鋼管と回転砥石との位置関係に応じて変わる接触長さを基準として回転砥石の送り速度を制御し、且つ駆動系の能力を最大限に発揮させ、バリ，焼付き等の欠陥を発生させることなく鋼管を短時間で切断している。この方法によるとき切断所要時間が短縮されるため、たとえば走間切断に適用した場合、レール長さを長く或いはラインスピードを遅くする必要なく生産性を向上させることができる。
【図面の簡単な説明】
【図１】従来の鋼管切断装置を示す概略図
【図２】鋼管と回転砥石との位置関係に応じて切断長さが変わることを示す説明図
【図３】砥石の高さ位置に応じて砥石の接触長さが変わることを示したグラフ
【図４】本発明に従った制御を実施するための設備構成を示す概略図
【図５】切断長さに応じて回転砥石１０の送り速度を制御したこをと示すグラフ
【図６】本発明に従った制御を示すフロー図
【符号の説明】
１０：回転砥石１１：ボールスクリュー１２：昇降モータ１３：エンコーダ１４：制御回路１５：昇降ベース１６：砥石回転用モータ
１７：タイミングベルト
Ｐ₀：待機代を含み鋼管外周上の最高点から回転砥石の最下点までの高さ位置
Ｐ₁：回転砥石の最下点が最初に接触する鋼管外周上の最高位置
Ｐ₂：最高位置Ｐ₁に対応する鋼管内周上の位置
Ｐ₃：鋼管に接触する回転砥石の接触長さが減少し始める位置
Ｐ₄：鋼管に接触する回転砥石の接触長さが増加し始める位置
Ｐ₅：鋼管内周上の最低位置
Ｐ₆：鋼管外周上の最低位置
Ｐ₇：出代を含む最下点の最低到達位置
Ｆ₁：第１設定値Ｆ₂：第２設定値Ｆ₃：第３設定値[0001]
[Industrial application fields]
The present invention relates to a method for controlling a cutting operation when cutting a tubular body such as a welded pipe efficiently and quickly.
[0002]
[Prior art]
For cutting a steel pipe, a device is used that swings a grindstone rotated by power from a motor and presses and cuts the steel pipe against the steel pipe. As shown in FIG. 1, the cutting device is configured such that one end of an arm 2 is pivotally supported on a support portion of a machine base 1, and a grindstone 4 is rotatable on the other end of the arm 2 via a pivotal support 3. Provided. A cylinder 5 erected from the machine base 1 is connected to the middle of the arm 2, and the arm 2 swings due to the expansion and contraction of the cylinder 5.
The steel pipe P to be cut is fed onto the machine base 1 and then restrained by the pipe chuck 6. Next, the cylinder 5 is driven, while the grindstone 4 is rotated, it is lowered from the upper limit position H to the lower limit position L including the allowance α and pressed against the steel pipe P to be cut.
[0003]
In the method of swinging the grindstone 4, the movable range of the grindstone 4 is determined by the stroke of the cylinder 5, and therefore the upper limit position H of the grindstone 4 must be increased in the equipment configuration for the large-diameter steel pipe P, and the cutting device The increase in size is inevitable. Moreover, since the movement locus | trajectory of the grindstone 4 becomes long, it takes time to start cutting. Moreover, since the grindstone 4 lowered by the turning of the arm 2 comes into contact with the steel pipe P and cuts the steel pipe P, the squareness of the end face of the cut steel pipe P is difficult to be obtained.
[0004]
Therefore, the present inventors employ a lifting mechanism that moves the grindstone 4 in the vertical direction instead of the arm 2, and adopts a method that controls the lifting and lowering operation and rotation speed of the grindstone 4 according to the height direction position of the grindstone 4. A cutting apparatus was proposed in Japanese Patent Application No. 11-87896. When the grindstone 4 is moved in the vertical direction, the necessary moving distance of the grindstone 4 only needs to be set slightly larger than the outer diameter of the steel pipe P to be cut, so that the cutting device as in the swing method using the arm 2 is used. Is avoided, and the time to start cutting is shortened. Moreover, since the grindstone 4 moves along the raising / lowering guide, the perpendicularity with respect to the pipe axis of a cutting end surface improves markedly compared with the swing system using the arm 2 with the long distance from the pivot axis 7 to the grindstone 4.
[0005]
[Problems to be solved by the invention]
By the way, when cutting a steel pipe such as a large-diameter thick-walled pipe that requires a large load on the drive system, if the grindstone 4 is sent at a constant speed from the incision to the through-hole, the resistance at the time of the incision is large, resulting in a low speed. Takes a long time. If the time required for cutting is increased with a running cutter incorporated in a pipe making line, the cutting of large-diameter pipes and short pipes will inevitably reduce the line speed, resulting in lower productivity. Moreover, when the cutting speed is slowed, defects such as burrs and seizures are likely to occur on the cut surface of the steel pipe P.
[0006]
[Means for Solving the Problems]
The present invention has been devised to solve such problems, and tends to occur on the cut end face by controlling the feed speed of the rotating grindstone in accordance with the length of the contact portion of the cross section of the steel pipe being cut. The purpose is to prevent the occurrence of defects such as burrs and seizures, and to cut even large-diameter thick-walled pipes in a short time.
[0007]
In order to achieve the object, the cutting control method according to the present invention, when the rotating grindstone is moved up and down in the vertical direction to cut the steel pipe, each of the following positions P ₀ along the trajectory of the rotating grindstone passing through the tube axis of the steel pipe. set to P _7, to increase the feed speed of the grinding wheel when the lowest point of the grinding wheel is between P ₀ -P _1, the grinding wheel when the lowest point is between P ₁ -P ₂ Feeding at a constant first set value F ₁ , the feed speed of the rotating whetstone is increased when the lowest point is between P ₂ -P ₃ , and rotating whetstone when the lowest point is between P ₃ -P ₄ At a constant second set value F ₂ , when the lowest point is between P ₄ -P ₅ , the feed speed of the rotating wheel is reduced, and when the lowest point is between P ₅ -P ₆ the feed at a constant third predetermined value F _3, reduce the feed rate of the grinding wheel when the lowest point is at the P ₆ -P _7, nadir by reversing the grinding wheel when it reaches the position P ₇ Characterized in that raising the bottom point to the position P _0.
[0008]
P ₀ : Height position from the highest position P ₁ on the outer periphery of the steel pipe including the standby allowance to the lowest point of the rotating wheel P ₁ : The highest position P ₂ on the outer periphery of the steel pipe where the lowest point of the rotating wheel first contacts: Position on the inner circumference of the steel pipe corresponding to the highest position P ₁ ( position where the contact length of the rotating grindstone that contacts the steel pipe starts to decrease)
P ₃ : Position at which the contact length of the rotating whetstone that contacts the steel pipe becomes substantially constant from the decrease P ₄ : Position at which the contact length of the rotating whetstone that contacts the steel pipe starts to increase P ₅ : Minimum position P on the inner circumference of the steel pipe ₆ : Minimum position P on the outer periphery of the steel pipe ₇ : Minimum position of the lowest point including the allowance
Here, between P ₃ and P ₄ , the fluctuation range of the contact length of the rotating grindstone that contacts the steel pipe is 30% or less.
[Action]
When the steel pipe P is cut using the rotating grindstone 10, the contact length of the rotating grindstone 10 changes according to the positional relationship of the rotating grindstone 10 with respect to the steel pipe P. The contact length gradually increases as the rotating grindstone 10 descends after the lowest point b of the rotating grindstone 10 lowered from the ascending position P ₀ contacts the highest position P ₁ on the outer periphery of the steel pipe P (see FIG. 2). Incidentally, it raised position P ₀ is set to a height position suitable for the diameter D of the current sent come steel pipe P based on the diameter of the steel pipe P was last disconnected, from the raised position P ₀ in the state before the start of the cutting The initial position of the rotating grindstone 10 is set at a higher position.
[0010]
When the rotating grindstone 10 descends from the position P ₁ , the steel pipe P and the rotating grindstone 10 are contacted substantially in the tangential direction, so the contact length increases all the time. After the lowest point b of the rotating grindstone 10 passes through the inner position P ₂ corresponding to the position P ₁ on the outer periphery of the steel pipe P, the periphery of the rotating grindstone 10 including the lowest point b does not contact the steel pipe P. And since the angle between the tangent of the steel pipe P and the tangent of the rotary grindstone 10 becomes large, a contact length reduces.
Decrease of contact length continues to the position P ₃ in slightly below the position P _2, the contact length is substantially constant from the position P _3. After the position P ₃ , the pipe wall of the steel pipe P is cut substantially in the thickness direction. When the grinding wheel 10 is further lowered, the smaller the angle between the tangent of the grinding wheel 10 and the tangent of the steel pipe P, the contact length starts to increase from the position P _4.
[0011]
The position P ₃ and the position P ₄ are calculated from geometric and past results according to the diameters of the steel pipe P and the rotating grindstone 10. However, the contact length of the rotating grindstone 10 that contacts the cross section of the steel pipe P is not completely constant between P _{3 and} P ₄ , and the angle of the tangential direction of the rotating grindstone 10 with respect to the thickness direction of the steel pipe P It varies slightly depending on. Therefore, in the present invention, the positions P ₃ and P ₄ are set when the variation width of the adhesion length is within a range of 30% or less.
[0012]
After the position P ₄ , the peripheral portion of the lowest point b where the periphery of the rotating grindstone 10 is not in contact with the steel pipe P becomes shorter, so that the contact length of the rotating grindstone 10 with respect to the steel pipe P increases. The increase in the contact length due to the shorter peripheral portion of the lowest point b continues until the lowest point b comes into contact with the inner position P ₅ corresponding to the lowermost part on the outer periphery of the steel pipe P. Contact length, after the lowest point b is brought into contact with the position P ₅ is the lowest point b decreases mindedly until it passes the lowest position P ₆ of the steel pipe P periphery. The rotating grindstone 10 descends to the lowest position P ₇ where the allowance α is taken.
[0013]
Thus, the contact length of the rotating grindstone 10 that contacts the steel pipe P being cut varies depending on the positional relationship between the steel pipe P and the rotating grindstone 10. Due to the change in the contact length, the load applied to the drive system for rotating and lowering the rotating grindstone 10 also varies.
Therefore, by controlling the motor rotation speed of the drive system based on the positional relationship between the steel pipe P and the rotating grindstone 10, and adjusting the feed speed of the rotating grindstone 10 according to the contact length l, Even if it is, it enables cutting for a short time. The change in the contact length l is calculated from the height position h of the rotating grindstone 10 that moves up and down, the outer diameter D of the steel pipe P, and the wall thickness t, but is obtained from the variation in load applied to the motor that drives the rotating grindstone 10. Is also possible.
For example, when cutting a steel pipe P having a wall thickness t = 2 mm and an outer diameter D = 40 mm with the rotary grindstone 10 having a diameter d = 50 mm, the contact length l is as shown in FIG. 3 according to the height position h of the rotary grindstone 10. It changes as shown. Therefore, when the maximum feed speed is V _max , the feed speed V is set as V = V _max / l.
[0014]
Embodiment
In the present invention, for example, a cutting device having the configuration shown in FIG. 4 is employed. In this cutting apparatus, a ball screw 11 that pitch-feeds the rotating grindstone 10 in the vertical direction is dynamically connected to a lifting motor 12 of a lifting drive mechanism. The rotating grindstone 10 is rotated by the power transmitted via the timing belt 17 from the grindstone rotating motor 16 mounted on the lifting base 15.
The rotation speed of the ball screw 11 is detected by the encoder 13 and is output to the control circuit 14 as information indicating the height of the rotating grindstone 10. The control circuit 14 is preliminarily input with the outer diameter D and the wall thickness t of the steel pipe P to be cut, and calculates a load according to the height information of the rotating grindstone 10 input from the encoder 13. The calculation result is output as a control signal to the elevating motor 12 and the grindstone rotating motor 16, and the rotation speed, current, and the like of the elevating motor 12 and the grindstone rotating motor 16 are controlled.
[0015]
When the rotary grindstone 10 is driven to cut the steel pipe P, no load is applied to the drive system from P _{0 to} P _1, so the motor rotation speed of the drive system, in other words, the feed speed of the rotary grindstone 10 can be set freely. P ₀ distance d ₁ -P ₁ is the height and standby allowance determined from the outer diameter of the steel pipe P raised position P ₀ beta, for example, the result of the previous cut as adopted in JP-A-11-87896 It is requested from.
When the lowest point b of the rotating grindstone 10 contacts the position P ₁ on the outer periphery of the steel pipe P, a load is applied to the drive system of the rotating grindstone 10. Therefore, the feed speed of the rotating grindstone 10 is kept constant at the first set value F ₁ (FIG. 5). This state is the lowest point b is continued until the position P _2. The distance d ₂ of P ₁ -P ₂ is equal to the thickness t of the steel pipe P being cut.
Since the contact length tends to decrease after the lowest point b passes through the position P ₂ (FIG. 2), the feed speed of the rotating grindstone 10 is increased. The distance d ₃ of the P ₂ -P ₃ is a value determined according to the diameter of the steel pipe P and the grinding wheel 10.
[0016]
When the cutting of the steel pipe P proceeds and the lowest point b reaches the position P ₃ , the contact length becomes a substantially constant low value. To constant maintaining the feed rate of the grinding wheel 10 relatively high in the second set value F ₂ in this state. The second set value F ₂ is preferably set to a maximum value according to the capacity of the lifting motor 12. The feeding of the rotating grindstone 10 at the second set value F ₂ is continued until the lowest point b reaches the position P ₄ . The distance d ₄ of P ₃ -P ₄ is a value determined according to the diameter of the steel pipe P and the grinding wheel 10.
From the position P ₄ of the contact length is longer to the point where the lowest point b reaches the position P _5, reducing the feed speed of the grinding wheel 10. Distance d ₅ of P ₄ -P ₅ is also a value determined according to the diameter of the steel pipe P and the grinding wheel 10.
[0017]
From the time when the lowest point b reaches the position P ₅ until the lowest point P ₆ is passed, the rotary grindstone 10 is fed at a relatively low third set value F ₃ according to the capability of the rotary grindstone 10, and the steel pipe P Cut the bottom. The distance d ₆ of P ₅ -P ₆ is a value corresponding to the wall thickness t of the steel pipe P.
After the lowest position P ₆ of the steel pipe P is the lowest point b has passed, reduce the feed rate of the grinding wheel 10, lower the lowest point b to the lowered position P _7. The distance d ₇ of P ₅ -P ₆ corresponds to the allowance α (FIG. 2) set in advance for reliably cutting the steel pipe P. Sends a grinding wheel 10 in the opposite direction when the lowest point b has reached the lowered position P7, the lowest point b is returned to the raised position P _0, to wait for the next cutting.
The control circuit 14 controls the number of rotations of the lifting motor 12 and the current sent to the lifting motor 12 from the lowest point b of the rotating wheel 10 according to the flow shown in FIG. 6, and as described above, the steel pipe P and the rotating wheel 10 The steel pipe P is cut under optimum conditions according to the positional relationship.
[0018]
【Example】
A rotating grindstone 10 having an outer diameter of 860 mm was attached to a cutting device having the equipment configuration shown in FIG. 4, and a stainless steel welded steel pipe having an outer diameter of 210 mm and a wall thickness of 6.0 mm was cut. Under this condition, when setting the standby allowance β = 10 mm and the output allowance α = 15 mm, the positions P _{0 to} P ₆ representing the positional relationship between the steel pipe P and the rotating grindstone 10 are from P ₇ (reference point). The height is calculated as shown in the following table. The feed speed of the rotating grindstone 10 was controlled as shown in the following table according to the positional relationship with the steel pipe P.
[0019]

[0020]
Thus, when the steel pipe P was cut while controlling the feed speed of the rotating grindstone 10, the time required for cutting was 0.15 minutes / piece. Moreover, defects such as burrs and seizures were generated on the cut end face, and a steel pipe product having a good cut end face was obtained. On the other hand, when the steel pipe P was cut while feeding the rotating grindstone 10 at a constant feed rate (0.6 m / min) in order to avoid the occurrence of defects, the time required for cutting was 0.40 min / piece. As is clear from this comparison, it can be seen that by controlling the feed speed of the rotating grindstone 10 according to the present invention, the cutting time is shortened and the productivity is improved.
[0021]
【The invention's effect】
As described above, the present invention controls the feed speed of the rotating grindstone based on the contact length that changes according to the positional relationship between the steel pipe and the rotating grindstone, and maximizes the drive system capability. Steel pipes are cut in a short time without generating defects such as burrs and seizures. When this method is used, the time required for cutting is shortened. For example, when applied to cutting between runs, productivity can be improved without having to lengthen the rail length or slow down the line speed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a conventional steel pipe cutting device. FIG. 2 is an explanatory diagram showing that the cutting length changes depending on the positional relationship between the steel pipe and the rotating grindstone. FIG. 3 is a diagram showing the height position of the grindstone. FIG. 4 is a schematic diagram showing the equipment configuration for carrying out the control according to the present invention. FIG. 5 shows the feed speed of the rotating grindstone 10 according to the cutting length. FIG. 6 is a flow chart showing control according to the present invention.
10: revolving whetstone 11: Ball screw 12: elevation motor 13: encoder 14: Control circuit 15: the elevation base 16: grinding wheel rotation motor 17: timing belt P _0: the grinding wheel from the highest point on the steel pipe outer circumference includes a standby allowance Height position P _{1 to} the lowest point: The highest position P ₂ on the outer periphery of the steel pipe where the lowest point of the rotating grindstone first contacts: A position P ₃ on the inner circumference of the steel pipe corresponding to the highest position P ₁ : A contact with the steel pipe Position P ₄ at which the contact length of the rotating grindstone begins to decrease: Position P ₅ at which the contact length of the rotating grindstone that contacts the steel pipe begins to increase: Minimum position P ₆ on the inner circumference of the steel pipe: Minimum position P on the outer circumference of the steel pipe ₇ : Minimum reaching position of the lowest point including the allowance F ₁ : First set value F ₂ : Second set value F ₃ : Third set value

Claims

When cutting the steel pipe by raising and lowering the rotating grindstone in the vertical direction, the following positions P _{0 to} P ₇ are set along the movement trajectory of the lowest point of the rotating grindstone passing through the pipe axis of the steel pipe. When the lower point is between P ₀ -P ₁ , the feeding speed of the rotating grindstone is increased, and when the lowest point is between P ₁ -P ₂ , the rotating grindstone is fed at a constant first set value F ₁ , When the lowest point is between P _{2 and} P ₃ , the feeding speed of the rotating wheel is increased, and when the lowest point is between P _{3 and} P ₄ , the rotating wheel is fed at a constant second set value F ₂ . When the lowest point is between P _{4 and} P ₅ , the feeding speed of the rotating wheel is lowered, and when the lowest point is between P _{5 and} P ₆ , the rotating wheel is fed at a constant third set value F ₃ . When the lowest point is at P ₆ -P ₇ , the feeding speed of the rotating grindstone is lowered, and when the lowest point reaches position P ₇ , the rotating grindstone is reversed to raise the lowest point to the initial position P ₀ . To let Cutting control method for a steel pipe according to symptoms.
P ₀ : Height position from the highest position P ₁ on the outer periphery of the steel pipe including the standby allowance to the lowest point of the rotating wheel P ₁ : The highest position P ₂ on the outer periphery of the steel pipe where the lowest point of the rotating wheel first contacts: Position on the inner circumference of the steel pipe corresponding to the highest position P ₁ ( position where the contact length of the rotating grindstone that contacts the steel pipe starts to decrease)
P ₃ : Position at which the contact length of the rotating whetstone that contacts the steel pipe becomes substantially constant from the decrease P ₄ : Position at which the contact length of the rotating whetstone that contacts the steel pipe starts to increase P ₅ : Minimum position P on the inner circumference of the steel pipe ₆ : Minimum position P on the outer circumference of the steel pipe ₇ : Minimum position to reach the lowest point including the allowance
Here, between P ₃ of P ₄ is the variation width of the contact length of the grinding wheel in contact with the steel pipe is 30% or less