JP4660967B2

JP4660967B2 - Turbo molecular pump

Info

Publication number: JP4660967B2
Application number: JP2001152365A
Authority: JP
Inventors: 慎吾筒井
Original assignee: Shimadzu Corp
Current assignee: Shimadzu Corp
Priority date: 2001-05-22
Filing date: 2001-05-22
Publication date: 2011-03-30
Anticipated expiration: 2021-05-22
Also published as: JP2002349472A

Description

【０００１】
【発明の属する技術分野】
本発明は、モータにて回転軸と一体の回転体に付設され回転駆動される回転翼と、この回転翼に対向してケーシングに固定設置された固定翼との組み合わせからなるターボ機構を複数段備え、このターボ機構の作動によって前記ケーシングの吸気口側より排気口側へ排気を行うターボ分子ポンプに関する。
【０００２】
【従来の技術】
ターボ分子ポンプは、回転翼と固定翼との組み合わせからなるターボ機構の作動により排気を行うもので、その構成は図３に示すとおりである。このターボ分子ポンプは、たとえばアルミニウム合金製の固定部１Ｆとケーシング１を主体として構成される固定側と、この固定部１Ｆの中央上方の保持枠１Ｍに軸受ＳＢを介して回転自在に支持され、モータＭにて回転駆動される回転軸５とこの回転軸５に一体的に結合された回転体２を主体として構成される回転側よりなっている。そして、この回転体２の外周には回転翼２Ｂが突出した形で付設されている。他方、ケーシング１の内周には、積層形にリング状のスペーサ１Ｓが設置され、この各スペーサ１Ｓ間に基端が保持され、かつ内方に突設された固定翼１Ｂが設けられている。この回転翼２Ｂと固定翼１Ｂとの組み合わせにより、ターボ機構Ｔが構成される。そして、このターボ機構Ｔの作動、すなわち回転翼２Ｂ側の高速回転によって、吸気口３から吸入したガス分子をこのターボ機構Ｔによって叩き飛ばし、排気口４に向かって圧縮排気するのである。
【０００３】
さらに、この回転体２の排気口４側の端部には、回転円筒部２Ｄが延設されていて、この回転円筒部２Ｄがケーシング１に固設された固定円筒部１Ｄの内周面に近接対応している。さらに、この固定円筒部１Ｄには、２点鎖線で示すように、内周面にねじ溝１Ｎが刻設されている。そして、このねじ溝１Ｎと回転円筒部２Ｄとの協働により、粘性流による排気機能が行われるモレキュラードラッグポンプすなわちねじ溝ポンプが構成されている。このように、ターボ機構によるポンプとモレキュラードラッグポンプとを結合させたターボ分子ポンプをハイブリッド形ターボ分子ポンプと称している。Ｂは排気口４を排気管（図示していない）に接続するためのベントである。
【０００４】
なお、回転体２も高速回転に耐えるために、アルミニウム合金などの金属材料で製作されている。また、図示例の場合、回転体２と一体の回転軸５は、上下一対配設されたラジアル用およびスラスト用の軸受ＳＢによって、保持枠１Ｍに対して支持される。
【０００５】
ところで、モータＭは回転軸５と保持枠１Ｍとの間で構成された高周波形のモータで、具体的には図３に示すように、回転軸５には回転子巻線が付設され、他方保持枠１Ｍの側の内周面には電機子巻線が設置され、この両者の組み合わせによって構成されている。この高周波形のモータＭによって、回転体２は毎分２００００〜１０００００回転で回転駆動される。
【０００６】
【発明が解決しようとする課題】
このようなターボ分子ポンプにおいては、回転体２を構成する材料に欠陥があったり、あるいは腐蝕性ガスの排気等で回転体２の材料が徐々に腐蝕を受け使用を重ねるうちに強度が低下して高速回転による遠心力にて回転体２が破壊する場合がある。高速回転する回転体２が遠心破壊を起したときは、回転体２は分裂し半径方向に飛散し、固定円筒部１Ｄなどの固定側に衝突し衝撃力となる。このとき固定円筒部１Ｄが薄く強度が不足していると大きく変形し、ケーシング１に衝突してしまう。結果としてポンプ外部に衝撃を与えることになる。一方、固定円筒部１Ｄが厚くて回転体２が破壊しても変形しない場合には、衝撃が吸収されずポンプ外部に衝撃力を直接的に伝達してしまうことになる。この衝撃力は複合ポンプから外部の装置へと伝達される。この外部への伝達は各種装置、機器の損傷を招き耐久性を低下させることになる。
本発明はこのような課題を解決するターボ分子ポンプを提供せんとするものである。
【０００７】
【課題を解決するための手段】
本発明が提供するターボ分子ポンプは、上記課題を解決するために、複数段のターボ機構を有するターボ分子ポンプにおいて、回転体を包囲する固定側の固定円筒部を２重の円筒部材からなる分割体として構成するとともに、内側の円筒部材の肉厚を前記ねじ溝ポンプのねじの深さに対応して一様な厚さとしたものである。さらに本発明は２重の円筒部材における内側部材の肉厚を固定円筒部が２重の円筒部材で構成するとともに、内側の円筒部材の肉厚を、前記回転体が破壊したときに生起する衝撃力にて内側の円筒部材の内側表面全体が受ける内圧がトレス力の降伏条件式にて導出される内側の円筒部材の降伏する内圧より小さくなるよう設定するものである。したがって、固定円筒部が受ける衝撃が緩わらげられる。
【０００８】
【発明の実施の形態】
以下、本発明を図面に示す実施例にしたがって説明する。
本発明が第１に提供するターボ分子ポンプの構成は図１に示される。図１は本発明のターボ分子ポンプにおける要部を拡大して示す断面図で、図３と同一の符号で示される構成、部品は図３と同様であり、詳細な説明は省略する。
本発明は、固定円筒部を内側の円筒部材１ＤＮと外側の円筒部材１ＤＳによる２重の部材で構成し、これらを有機的に組み合わせた点に特徴を有する。すなわち、内側の円筒部材１ＤＮには上端部（吸気口側端部）に、フランジ部１ＤＦが形成されていて、このフランジ部１ＤＦが外側の円筒部材１ＤＳの上端部に形成された環状の凹部１ＤＫに嵌合され、両者が互いに固着されている。この嵌合固着によって内側の円筒部材１ＤＮは外側の円筒部材１ＤＳに対して位置決めされ固定保持される。
【０００９】
この内側の円筒部材１ＤＮと外側の円筒部材１ＤＳは、このフランジ部１ＤＦの環状の凹部１ＤＫへの嵌合により簡略にてかつ正確に嵌合される。しかもこの保持の仕方はいわゆる一端側で保持する片持式であって、保持が簡略であるとともに他方端が自由端となり、回転体２の破壊時における衝撃力を吸収するに有益である。
さらにこのフランジ部１ＤＦはその降伏する力を充分小さく設定されている。具体的には、このフランジ部１ＤＦは充分に肉厚が薄く形成されている。したがって、内側の円筒部材１ＤＮの膨張を許容するようになっている。
【００１０】
本発明が第２に提供するターボ分子ポンプは、２重に分割された内側の円筒部材１ＤＮと外側の円筒部材１ＤＳのうち、内側の円筒部材１ＤＮの肉厚をねじ溝１Ｎの深さに対応して一様の厚さにした点を特徴としている。すなわち、具体的にはねじ溝１Ｎの溝底の傾斜面と並行な斜面を有する形状になるような形とする。図１に示す実施例においては、円筒部材１ＤＮの外周を長手方向に３段階に分け、各段階においては同径として下方になるに従ってねじ溝１Ｎに対応し小径にして、全体的にはねじ溝１Ｎの深さに対応する一様な厚さとなっている。
【００１１】
このような形状は円筒部材１ＤＮの加工を容易にするためであるが、最も基本的にはテーパ状の円筒部材とするのが望ましい。ただ、この形状では加工が図示例に比して困難で熟練を要する。図示例以外の変形例としては、階段を３段以上の多段、たとえば４段、あるいは６段などにして各段同径とする形とすることもできる。
このような形状にすることによって、内側の円筒部材１ＤＮは回転体２の破壊の衝撃力によって変形するものの、一様な厚さのため局所的な変形を防止できる。
【００１２】
さらに本発明は、上記内側の円筒部材１ＤＮを一様な厚さとすることに加えて、この円筒部材１ＤＮの肉厚を降伏条件式から導出される厚さとした点に特徴を有するものである。
すなわち、回転体２が破壊したときに生起する衝撃力にて、円筒部材１ＤＮの内側表面全体が受ける内圧を実内圧とするとき、この実内圧をトレス力の降伏条件式にて導出される円筒部材１ＤＮの降伏する内圧（理論内圧）より小さくなるように円筒部材１ＤＮの肉厚を設定することである。ここで衝撃力について図２に示される原理図に従い明らかにするとつぎのとおりである。
【００１３】
図２において、各符号はつぎの内容である。
Ｍ＝回転体２が破壊したときの破片の質量
Ｒ＝回転体２の破片が破壊前に回転したときの半径
ＲＧ＝内側の円筒部材１ＤＮの内径
ＲＩ＝回転体２の内径
Ｒ０＝回転体２の外径
θ＝角度
ω＝回転体２の回転における角速度
ＲＨ＝回転体２の軸方向長さ
今、破壊が生起し、回転体２の破片が円筒部材１ＤＮに衝突したとすると、その衝突時間、厳密には衝突開始から衝突終了までの時間をｔとすると、回転体２が内側の円筒部材１ＤＮに与える衝撃力はつぎの式にて求められる。

【００１４】
すなわち上式（１）に示すように、回転体２の破片が円筒部材１ＤＮに与える力Ｆ０は運動量保存の法則より（１）式で示される形となる。
したがって、円筒部材１ＤＮにおける角度θの半径方向の力ＦＲ０は（２）式で求められる。この（２）式に（１）式を代入すると（３）式が求められる。この（３）式は回転体２の破片１個のみについてであり、これを回転体２全体において衝突が起こるとすると、上記（３）式を半径Ｒの円周長さ２πＲ分だけ拡張すると（４）式のとおりとなる。
つぎにこの（４）式を半径Ｒ方向にＲＩからＲ０まで加算すると（５）式が得られる。このときθは半径Ｒの関数となるので（６）式が得られる。
【００１５】
つぎに（５）式に上記（４）式、（６）式を代入すると（７）式が得られる。そして更にこの（７）式を回転体２の軸方向の長さＲＨ分だけ拡張すると最終的には（８）式が得られる。
この（８）式におけるＦＲ３がすなわち回転体２が内側の円筒部材１ＤＮに与える衝撃力なのである。この衝撃力は下記の式で示す形の式として表現できる。この式におけるＦがすなわち全体の衝撃力である。

この式からも明らかなように、この衝撃力Ｆは回転体２の半径Ｒが大きくなるほど大きく、円筒部材１ＤＮの内径ＲＧが大きくなるほど小さくなる。
【００１６】
さて、このような衝撃力Ｆが作用することから、この円筒部材１ＤＮの厚さを所定の大きさに設定しなければならない。すなわち、この衝撃力Ｆが円筒部材１ＤＮの内周面全域に作用するわけであるから、この作用による圧力は衝撃力Ｆを円周面面積で除算した圧力（実圧力）となる。この実圧力により大きな内圧力に耐えうる円筒部材１ＤＮであれば、回転体２の破壊によっても破壊するおそれはないということになる。
【００１７】
ところで、円筒部材１ＤＮが降伏する内圧力は理論上「トレス力の降伏条件」式にて求めることができる。この「トレス力の降伏条件」はつぎの式に示すとおりである。

すなわち、上式において
ＰＥ＝円筒部材１ＤＮの降伏する内圧
δｓ＝円筒部材１ＤＮの降伏応力
ＲＮＡ＝円筒部材１ＤＮの内径
ＲＯＴ＝円筒部材１ＤＮの外径
を示している。Ｋは円筒部材１ＤＮの内外径比をあらわしている。ここでδｓは円筒部材１ＤＮの材質によって定まる値であり、したがって円筒部材１ＤＮの内径ＲＮＡ、外径ＲＯＴを設定する場合、その設定による結果の内圧ＰＥが上記した実圧力Ｆより大きくなるように内径ＲＮＡ、外径ＲＯＴを設定すればよいということになる。
【００１８】
本発明はこのような形で理論上求められる肉厚を有する内側の円筒部材１ＤＮを有することを特徴としている。したがって、回転体２の破壊による衝撃力や塑性変形する肉厚を計算によって求めることができ、また吸収したい衝撃力をも求めることができる。このことからポンプ外部の機器、装置への衝撃を適性に減少させることが可能となる。
【００１９】
本発明が提供するターボ分子ポンプは以上詳述したとおりであるが、上記ならびに図示例に限定されるものではなく、種々の変形実施例を包含するものである。
まず、内側の円筒部材１ＤＮを外側の円筒部材１ＤＳに対して固定保持する方法であるが、円筒部材１ＤＮの下方端、すなわち排気口側の端部を外側の円筒部材１ＤＳに対して片持ち形で保持させることも可能である。
図示例では回転円筒部２Ｄが回転軸の上端より傘のように吊設された構成のターボ分子ポンプが示されているが、この回転円筒部を上方向けに架設する形とすることもできる。この場合、回転円筒部としての２重の円筒部材はターボ分子ポンプの上方に設置することになる。さらには上下両方向に架設し断面がＨ形となる回転体とすることもできる。回転体２を磁気軸受にて支持するターボ分子ポンプにも本発明は適用可能である。
本発明は、これらすべての変形実施例を包含する
【００２０】
【発明の効果】
本発明が提供するターボ分子ポンプは以上詳述したとおりであるから、ポンプ全体を大形化することなく、そして回転体が破壊した場合、その衝撃力を減少することができる。したがって、ポンプ破壊時における衝撃に対して大形の対策をとる必要もなく、小型化にしてかつ経済的なポンプを提供できる。
【図面の簡単な説明】
【図１】本発明によるターボ分子ポンプの構成の要部を示す縦断面図である。
【図２】本発明によるターボ分子ポンプにおける原理を説明するための図である。
【図３】従来におけるターボ分子ポンプの構成を示す図である。
【符号の説明】
１…ケーシング
１Ｂ…固定翼
１Ｄ…固定円筒部
１ＤＮ…内側の円筒部材
１ＤＳ…外側の円筒部材
１ＤＦ…フランジ部
１ＤＫ…環状の凹部
１Ｓ…スペーサ
２…回転体
２Ｂ…回転翼
２Ｄ…回転円筒部
３…吸気口
４…排気口
５…回転軸
Ｔ…ターボ機構[0001]
BACKGROUND OF THE INVENTION
The present invention provides a turbo mechanism comprising a combination of a rotating blade attached to a rotating body integral with a rotating shaft by a motor and driven to rotate, and a fixed blade fixedly installed on a casing facing the rotating blade. The present invention relates to a turbo molecular pump that performs exhaust from the intake port side to the exhaust port side of the casing by the operation of the turbo mechanism.
[0002]
[Prior art]
The turbo molecular pump performs exhaust by the operation of a turbo mechanism composed of a combination of rotor blades and fixed blades, and the configuration thereof is as shown in FIG. This turbo molecular pump is rotatably supported via a bearing SB on a fixed side mainly composed of, for example, an aluminum alloy fixed part 1F and a casing 1, and a holding frame 1M above the center of the fixed part 1F. The rotating shaft 5 is composed of a rotating shaft 5 that is rotationally driven by a motor M and a rotating body 2 that is integrally coupled to the rotating shaft 5. And the rotary blade 2B is attached to the outer periphery of this rotary body 2 in the form which protruded. On the other hand, on the inner periphery of the casing 1, a ring-shaped spacer 1 </ b> S is installed in a laminated form, and a fixed wing 1 </ b> B is provided that has a proximal end held between the spacers 1 </ b> S and protrudes inward. . A turbo mechanism T is configured by a combination of the rotary blade 2B and the fixed blade 1B. Then, by the operation of the turbo mechanism T, that is, the high speed rotation on the rotary blade 2B side, the gas molecules sucked from the intake port 3 are beaten by the turbo mechanism T and compressed and exhausted toward the exhaust port 4.
[0003]
Further, a rotating cylindrical portion 2D extends from the end of the rotating body 2 on the exhaust port 4 side, and the rotating cylindrical portion 2D is formed on the inner peripheral surface of the fixed cylindrical portion 1D fixed to the casing 1. Proximity support. Further, as shown by a two-dot chain line, a thread groove 1N is formed on the inner peripheral surface of the fixed cylindrical portion 1D. A molecular drag pump, that is, a thread groove pump, that performs an exhaust function by a viscous flow is configured by cooperation of the thread groove 1N and the rotating cylindrical portion 2D. In this way, a turbo molecular pump in which a turbo mechanism pump and a molecular drag pump are combined is referred to as a hybrid turbo molecular pump. B is a vent for connecting the exhaust port 4 to an exhaust pipe (not shown).
[0004]
The rotating body 2 is also made of a metal material such as an aluminum alloy in order to withstand high-speed rotation. In the illustrated example, the rotating shaft 5 integrated with the rotating body 2 is supported with respect to the holding frame 1M by radial and thrust bearings SB arranged in a pair.
[0005]
By the way, the motor M is a high-frequency motor formed between the rotating shaft 5 and the holding frame 1M. Specifically, as shown in FIG. 3, the rotating shaft 5 is provided with a rotor winding, An armature winding is installed on the inner peripheral surface on the holding frame 1M side, and is configured by a combination of both. By this high-frequency motor M, the rotating body 2 is rotationally driven at 20000 to 100,000 rotations per minute.
[0006]
[Problems to be solved by the invention]
In such a turbo molecular pump, the material constituting the rotating body 2 has a defect, or the material of the rotating body 2 is gradually corroded by exhaust of corrosive gas or the like, and the strength decreases as the use continues. In some cases, the rotating body 2 may be broken by centrifugal force due to high-speed rotation. When the rotating body 2 that rotates at a high speed causes a centrifugal fracture, the rotating body 2 is split and scattered in the radial direction, and collides with a fixed side such as the fixed cylindrical portion 1D to generate an impact force. At this time, if the fixed cylindrical portion 1D is thin and insufficient in strength, it is greatly deformed and collides with the casing 1. As a result, an impact is given to the outside of the pump. On the other hand, when the fixed cylindrical portion 1D is thick and does not deform even when the rotating body 2 is broken, the impact is not absorbed and the impact force is directly transmitted to the outside of the pump. This impact force is transmitted from the composite pump to an external device. This transmission to the outside causes damage to various devices and equipment, and decreases durability.
The present invention is intended to provide a turbo molecular pump that solves such problems.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, a turbo molecular pump provided by the present invention is a turbo molecular pump having a multi-stage turbo mechanism, in which a fixed cylindrical portion on a fixed side surrounding a rotating body is divided into double cylindrical members. In addition to being configured as a body, the inner cylindrical member has a uniform thickness corresponding to the screw depth of the thread groove pump. Further, according to the present invention, the thickness of the inner member in the double cylindrical member is constituted by the double cylindrical member having the fixed cylindrical portion, and the wall thickness of the inner cylindrical member is generated when the rotating body breaks. The internal pressure received by the entire inner surface of the inner cylindrical member due to the force is set to be smaller than the inner pressure of the inner cylindrical member yielded by the yield condition expression of the tress force. Therefore, the impact received by the fixed cylindrical portion is relaxed.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described according to embodiments shown in the drawings.
The structure of a turbo molecular pump provided by the present invention is shown in FIG. FIG. 1 is an enlarged cross-sectional view showing a main part of the turbo molecular pump of the present invention. The components and components indicated by the same reference numerals as those in FIG. 3 are the same as those in FIG.
The present invention is characterized in that the fixed cylindrical portion is composed of a double member composed of an inner cylindrical member 1DN and an outer cylindrical member 1DS, and these are organically combined. That is, the inner cylindrical member 1DN is formed with a flange 1DF at the upper end (inlet side end), and the flange 1DF is an annular recess 1DK formed at the upper end of the outer cylindrical member 1DS. And are fixed to each other. By this fitting and fixing, the inner cylindrical member 1DN is positioned and fixedly held with respect to the outer cylindrical member 1DS.
[0009]
The inner cylindrical member 1DN and the outer cylindrical member 1DS are simply and accurately fitted by fitting the flange portion 1DF to the annular recess 1DK. Moreover, this holding method is a so-called cantilever type that is held at one end side, and is simple in holding, and the other end is a free end, which is useful for absorbing impact force when the rotating body 2 is broken.
Further, the flange portion 1DF is set to have a sufficiently small yielding force. Specifically, the flange portion 1DF is sufficiently thin. Accordingly, the inner cylindrical member 1DN is allowed to expand.
[0010]
The turbo molecular pump provided by the present invention secondly corresponds to the depth of the thread groove 1N with respect to the thickness of the inner cylindrical member 1DN of the inner cylindrical member 1DN and the outer cylindrical member 1DS which are divided into two. It is characterized by a uniform thickness. Specifically, the shape is such that it has a shape having an inclined surface parallel to the inclined surface of the groove bottom of the thread groove 1N. In the embodiment shown in FIG. 1, the outer periphery of the cylindrical member 1DN is divided into three stages in the longitudinal direction, and in each stage, the diameter becomes the same as that of the screw groove 1N and becomes smaller as it goes downward. It has a uniform thickness corresponding to a depth of 1N.
[0011]
Although such a shape is for facilitating the processing of the cylindrical member 1DN, it is most preferable to use a tapered cylindrical member. However, with this shape, processing is more difficult and requires skill than the illustrated example. As a modified example other than the illustrated example, the stairs may be multi-stages having three or more steps, for example, four steps, six steps, or the like so that each step has the same diameter.
By adopting such a shape, the inner cylindrical member 1DN is deformed by the impact force of destruction of the rotating body 2, but it is possible to prevent local deformation because of the uniform thickness.
[0012]
Furthermore, the present invention is characterized in that, in addition to the inner cylindrical member 1DN having a uniform thickness, the thickness of the cylindrical member 1DN is a thickness derived from the yield condition equation.
That is, when the internal pressure received by the entire inner surface of the cylindrical member 1DN by the impact force generated when the rotating body 2 breaks is the actual internal pressure, this actual internal pressure is derived from the yield condition expression of the tress force. The thickness of the cylindrical member 1DN is set to be smaller than the internal pressure (theoretical internal pressure) at which the member 1DN yields. Here, the impact force is clarified according to the principle diagram shown in FIG. 2 as follows.
[0013]
In FIG. 2, each symbol has the following contents.
M = Mass of fragments when the rotating body 2 breaks R = Radius when the fragments of the rotating body 2 rotate before breaking RG = Inner diameter RI of the inner cylindrical member 1DN = Inner diameter R0 of the rotating body 2 = Rotating body 2 Outer diameter θ = angle ω = angular velocity RH in rotation of the rotating body 2 = axial length of the rotating body 2 Now, assuming that a fracture occurs and a piece of the rotating body 2 collides with the cylindrical member 1DN, the collision time Strictly speaking, assuming that the time from the start of the collision to the end of the collision is t, the impact force that the rotating body 2 applies to the inner cylindrical member 1DN is obtained by the following equation.

[0014]
That is, as shown in the above equation (1), the force F0 applied to the cylindrical member 1DN by the fragments of the rotating body 2 takes the form represented by the equation (1) from the law of conservation of momentum.
Therefore, the force FR0 in the radial direction of the angle θ in the cylindrical member 1DN is obtained by the equation (2). Substituting equation (1) into equation (2) yields equation (3). This equation (3) is for only one piece of the rotator 2, and if this occurs in the entire rotator 2, the above equation (3) is expanded by the circumferential length 2πR of the radius R ( 4) As shown in the equation.
Next, when this equation (4) is added in the radius R direction from RI to R0, equation (5) is obtained. At this time, θ is a function of the radius R, so that equation (6) is obtained.
[0015]
Next, when the above equations (4) and (6) are substituted into equation (5), equation (7) is obtained. Further, when the equation (7) is further expanded by the length RH in the axial direction of the rotating body 2, the equation (8) is finally obtained.
FR3 in the equation (8) is the impact force that the rotating body 2 gives to the inner cylindrical member 1DN. This impact force can be expressed as an expression of the form shown by the following expression. F in this equation is the total impact force.

As is apparent from this equation, the impact force F increases as the radius R of the rotating body 2 increases, and decreases as the inner diameter RG of the cylindrical member 1DN increases.
[0016]
Now, since such an impact force F acts, the thickness of this cylindrical member 1DN must be set to a predetermined size. That is, since the impact force F acts on the entire inner peripheral surface of the cylindrical member 1DN, the pressure resulting from this action is a pressure (actual pressure) obtained by dividing the impact force F by the circumferential surface area. If the cylindrical member 1DN can withstand a large internal pressure due to the actual pressure, there is no possibility of destruction even if the rotating body 2 is destroyed.
[0017]
By the way, the internal pressure at which the cylindrical member 1DN yields can theoretically be obtained by the expression “yield condition of the tress force”. This “torsion force yield condition” is as shown in the following equation.

That is, in the above equation, PE = internal pressure δs at which the cylindrical member 1DN yields = yield stress RNA of the cylindrical member 1DN = inner diameter ROT of the cylindrical member 1DN = outer diameter of the cylindrical member 1DN. K represents the inner / outer diameter ratio of the cylindrical member 1DN. Here, δs is a value determined by the material of the cylindrical member 1DN. Therefore, when the inner diameter RNA and the outer diameter ROT of the cylindrical member 1DN are set, the inner pressure PE resulting from the setting is larger than the actual pressure F described above. This means that RNA and outer diameter ROT should be set.
[0018]
The present invention is characterized by having an inner cylindrical member 1DN having a wall thickness theoretically required in such a form. Therefore, the impact force due to the fracture of the rotating body 2 and the thickness of plastic deformation can be obtained by calculation, and the impact force desired to be absorbed can also be obtained. This makes it possible to appropriately reduce the impact on the equipment and devices outside the pump.
[0019]
The turbo molecular pump provided by the present invention is as described in detail above, but is not limited to the above and illustrated examples, and includes various modified embodiments.
First, the inner cylindrical member 1DN is fixedly held to the outer cylindrical member 1DS. The lower end of the cylindrical member 1DN, that is, the end on the exhaust port side is cantilevered with respect to the outer cylindrical member 1DS. It is also possible to hold it.
In the illustrated example, a turbo molecular pump having a configuration in which the rotating cylindrical portion 2D is suspended like an umbrella from the upper end of the rotating shaft is shown. However, the rotating cylindrical portion may be constructed so as to extend upward. In this case, the double cylindrical member as the rotating cylindrical portion is installed above the turbo molecular pump. Furthermore, it can also be set as the rotary body constructed in the up-down both directions, and a cross section becomes H shape. The present invention is also applicable to a turbo molecular pump that supports the rotating body 2 with a magnetic bearing.
The present invention encompasses all these variations.
【The invention's effect】
Since the turbo molecular pump provided by the present invention is as described in detail above, it is possible to reduce the impact force without enlarging the whole pump and when the rotating body breaks down. Therefore, it is not necessary to take a large measure against an impact when the pump is broken, and a compact and economical pump can be provided.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a main part of a configuration of a turbo molecular pump according to the present invention.
FIG. 2 is a diagram for explaining the principle of a turbo molecular pump according to the present invention.
FIG. 3 is a diagram showing a configuration of a conventional turbo molecular pump.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Casing 1B ... Fixed wing | blade 1D ... Fixed cylindrical part 1DN ... Inner cylindrical member 1DS ... Outer cylindrical member 1DF ... Flange part 1DK ... Ring-shaped recessed part 1S ... Spacer 2 ... Rotating body 2B ... Rotating wing 2D ... Rotating cylindrical part 3 ... Inlet 4 ... Exhaust 5 ... Rotating shaft T ... Turbo mechanism

Claims

A turbo mechanism comprising a combination of fixed blades and rotary blades installed on the inner periphery of the casing has a plurality of stages, and a rotary shaft integrated with the rotary body provided with the rotary blades has a fixed shaft integrated with the casing. A pump that is rotatably supported through a bearing, and that rotates the rotation shaft by a motor to exhaust molecules from the intake port of the casing to the exhaust port. In the turbo molecular pump provided with a fixed cylindrical portion on the mouth side, and provided with a thread groove pump mechanism in cooperation with the thread groove engraved on the inner peripheral surface of the fixed cylindrical portion and the outer peripheral surface of the rotating body, The fixed cylindrical portion is configured as a divided body composed of double cylindrical members, and the inner cylindrical member has a uniform thickness corresponding to the screw depth of the thread groove pump. The Turbo-molecular pump.

A turbo mechanism comprising a combination of fixed blades and rotary blades installed on the inner periphery of the casing has a plurality of stages, and a rotary shaft integrated with the rotary body provided with the rotary blades has a fixed shaft integrated with the casing. A pump that is rotatably supported through a bearing, and that rotates the rotation shaft by a motor to exhaust molecules from the intake port of the casing to the exhaust port. In the turbo molecular pump provided with a fixed cylindrical portion on the mouth side, and provided with a thread groove pump mechanism in cooperation with the thread groove engraved on the inner peripheral surface of the fixed cylindrical portion and the outer peripheral surface of the rotating body, The fixed cylindrical portion is configured as a split body composed of double cylindrical members, and the inner cylindrical member is fixed to the casing only by the inlet side end or the exhaust side end of the cylindrical member. Turbomolecular pump according to claim 1, characterized in that so as to lifting.

A turbo mechanism comprising a combination of fixed blades and rotary blades installed on the inner periphery of the casing has a plurality of stages, and a rotary shaft integrated with the rotary body provided with the rotary blades has a fixed shaft integrated with the casing. A pump that is rotatably supported through a bearing, and that rotates the rotation shaft by a motor to exhaust molecules from the intake port of the casing to the exhaust port. In the turbo molecular pump provided with a fixed cylindrical portion on the mouth side, and provided with a thread groove pump mechanism in cooperation with the thread groove engraved on the inner peripheral surface of the fixed cylindrical portion and the outer peripheral surface of the rotating body, The fixed cylindrical portion is configured as a split body composed of double cylindrical members, and a thin flange portion is formed at the intake port side end or exhaust port side end of the inner cylindrical member. Turbomolecular pump according to claim 1, wherein the serial and the respective cylindrical member attached to one another.

A turbo mechanism comprising a combination of fixed blades and rotary blades installed on the inner periphery of the casing has a plurality of stages, and a rotary shaft integrated with the rotary body provided with the rotary blades has a fixed shaft integrated with the casing. A pump that is rotatably supported through a bearing, and that rotates the rotation shaft by a motor to exhaust molecules from the intake port of the casing to the exhaust port. In the turbo molecular pump provided with a fixed cylindrical portion on the mouth side, and provided with a thread groove pump mechanism in cooperation with the thread groove engraved on the inner peripheral surface of the fixed cylindrical portion and the outer peripheral surface of the rotating body, The fixed cylindrical portion is constituted by a double cylindrical member, and the internal pressure that the entire inner surface of the inner cylindrical member receives the thickness of the inner cylindrical member due to the impact force generated when the rotating body breaks. Turbomolecular pump according to claim 1, characterized in that it is set to be smaller than the yield to the internal pressure of the inner cylindrical member to be derived by Torres force of the yield condition.