JP7244554B2

JP7244554B2 - screw pump

Info

Publication number: JP7244554B2
Application number: JP2021017797A
Authority: JP
Inventors: 敏生鈴木; 正樹西山; 建治橋本; 智成田中
Original assignee: Ulvac Inc
Current assignee: Ulvac Inc
Priority date: 2021-02-05
Filing date: 2021-02-05
Publication date: 2023-03-22
Anticipated expiration: 2041-02-05
Also published as: JP2022120715A; CN114856997A

Description

本発明は、スクリューポンプに関する。 The present invention relates to screw pumps .

真空処理装置の真空チャンバなどを真空排気する真空ポンプとして、容積移送型のスクリュー（真空）ポンプが一般に知られている（例えば、特許文献１参照）。このものは、ねじれ方向が逆方向で所定ピッチの螺旋歯を夫々有する一対のスクリューロータと、これら一対のスクリューロータを非接触で互いに噛み合わせた状態で且つ各螺旋歯の歯先の面との間に隙間を存して格納するケーシングとを備える。真空排気に際しては、各スクリューロータをそれらの回転軸回りで夫々逆方向に同期回転させ、一対のスクリューロータの螺旋歯で区画される容積を移動させる。これにより、ケーシングの軸方向一端より真空チャンバ内の気体（被移送物）を吸引し、この吸引されたものをケーシングと各スクリューロータとの間に軸方向に沿って形成される複数の作動空間に閉じ込めて圧縮しながら移送して、ケーシングの軸方向他端より吐出する。このとき、気体の逆流量が可及的に抑制されるように、使用環境に応じた熱膨張や加工精度等を考慮して、ケーシング内面と各螺旋歯の歯先の面との間の隙間や、非接触で互いに噛み合う各螺旋歯の歯先の面相互の隙間が設定される。 As a vacuum pump for evacuating a vacuum chamber of a vacuum processing apparatus, a positive displacement screw (vacuum) pump is generally known (see, for example, Patent Document 1). This rotor consists of a pair of screw rotors having helical teeth with opposite twist directions and a predetermined pitch, and the tip surfaces of the helical teeth in a state in which the pair of screw rotors are meshed with each other in a non-contact manner. and a casing for storing with a gap therebetween. When evacuating, the screw rotors are synchronously rotated about their rotation axes in opposite directions to move the volume defined by the helical teeth of the pair of screw rotors. As a result, the gas (object to be transferred) in the vacuum chamber is sucked from one end of the casing in the axial direction, and the sucked matter is placed in a plurality of working spaces formed along the axial direction between the casing and each screw rotor. It is confined in the casing, transferred while being compressed, and discharged from the other end in the axial direction of the casing. At this time, the gap between the inner surface of the casing and the surface of the tip of each spiral tooth should be considered in consideration of thermal expansion and processing accuracy according to the usage environment so that the back flow of gas is suppressed as much as possible. Alternatively, a gap is set between surfaces of the tips of the spiral teeth that mesh with each other in a non-contact manner.

ここで、真空雰囲気の真空チャンバ内にて各種のプロセスを実施していると、真空チャンバ内で、その壁面（防着板の壁面）から剥離した成膜物や、その真空チャンバ内の気中にて反応生成物といった固体（微細な粉状）の異物が発生し、この異物がスクリューポンプのケーシング内に進入する場合がある。そして、ケーシング内に進入した異物のサイズや進入した異物の量によっては、ケーシングの内面と各螺旋歯の歯先の面との間の隙間に侵入した結果、その異物が詰まることがある。このように侵入した異物は、スクリューロータの回転に伴って、ケーシングの内面や各螺旋歯の歯先の面を転がりながら下流側（軸方向他端側）へとやがて送られるが、このときの状態（詰まり度合）に応じてスクリューロータの回転軸を回転駆動するモータトルクの増大を招き、状態によっては、モータの最大トルクを超過させ、スクリューポンプの異常停止を招く。また、ケーシング内面や各螺旋歯の歯先の面を摩損させて、気体の逆流量増加に伴うスクリューポンプの排気性能の劣化を招くことがあり、これでは、継続的に当該条件下で排気性能を保つ運転が期待できず、スクリューポンプとして支障をきたす虞がある。 Here, when various processes are carried out in a vacuum chamber in a vacuum atmosphere, film-formed substances peeled off from the wall surface (wall surface of the anti-adhesion plate) in the vacuum chamber and air in the vacuum chamber A solid (fine powder) foreign matter such as a reaction product is generated at , and this foreign matter may enter the casing of the screw pump. Depending on the size and amount of the foreign matter that has entered the casing, the foreign matter may clog the space between the inner surface of the casing and the tip of each helical tooth. As the screw rotor rotates, the foreign matter that has entered in this way rolls on the inner surface of the casing and the surface of the tip of each helical tooth and is eventually sent downstream (the other end in the axial direction). Depending on the state (degree of clogging), the torque of the motor for rotationally driving the rotating shaft of the screw rotor may increase, and depending on the state, the maximum torque of the motor may be exceeded, resulting in abnormal stoppage of the screw pump. In addition, the inner surface of the casing and the tip surface of each helical tooth may be worn away, which may lead to deterioration of the exhaust performance of the screw pump due to an increase in the backflow of gas. Therefore, the screw pump cannot be expected to operate while maintaining

そこで、気体を吸引するケーシングの軸方向一端より上流側に、例えば、真空チャンバとスクリューポンプとを接続する排気管に上記異物の進入を阻止するトラップを設けることが一般に知られている（例えば、特許文献２参照）。然し、上記隙間に詰まるサイズの異物を捕捉できるようにトラップを構成すると、排気コンダクタンスが大きくなって排気速度の低下を招くという問題がある。この場合、例えば、所定容積の真空チャンバ内を所定圧力まで真空排気するのに多大な時間を要する。また、スクリューポンプのケーシング内で、例えば、プロセスに使用されるガスの析出により異物が発生し、これが上記隙間に詰まるような場合があるが、このような場合には上記従来例の方法では何らの対応もできない。 Therefore, it is generally known to provide a trap that prevents the foreign matter from entering, for example, an exhaust pipe that connects a vacuum chamber and a screw pump upstream from one axial end of a casing that sucks gas (for example, See Patent Document 2). However, if the trap is configured so as to trap the foreign matter of a size that clogs the gap, there is a problem that the exhaust conductance increases and the exhaust speed decreases. In this case, for example, it takes a long time to evacuate a vacuum chamber of a predetermined volume to a predetermined pressure. In addition, in the casing of the screw pump, for example, foreign matter may be generated due to precipitation of gas used in the process, and this may clog the gap. I can't even respond to.

特開平８－１８９４８５号公報JP-A-8-189485 特開２０００－５３２５０号公報JP-A-2000-53250

本発明は、以上の点に鑑み、ケーシングの内面と各螺旋歯の歯先の面との間の隙間に侵入した異物の影響を受けずに、常時、正常な運転が可能なスクリューポンプ及びこのスクリューポンプに好適に利用可能なスクリューロータを提供することをその課題とするものである。 In view of the above points, the present invention provides a screw pump that can always operate normally without being affected by foreign matter that has entered the gap between the inner surface of the casing and the tip surface of each helical tooth. An object of the present invention is to provide a screw rotor that can be suitably used for a screw pump.

上記課題を解決するために、ねじれ方向が逆方向で所定ピッチの螺旋歯を夫々有する一対のスクリューロータと、これら一対のスクリューロータを非接触で互いに噛み合わせた状態で且つ各螺旋歯の歯先の面との間に隙間を存して格納するケーシングとを備え、各スクリューロータをそれらの回転軸回りで夫々逆方向に同期回転させ、ケーシングの軸方向一端より吸引し、この吸引されたものをケーシングと各スクリューロータとの間に軸方向に沿って形成される複数の作動空間に閉じ込めて圧縮しながらケーシングの軸方向他端より吐出する本発明のスクリューポンプは、各螺旋歯の歯先の面に、ケーシングの内面と各螺旋歯の歯先の面との間の隙間に侵入した異物が退避する窪み部を歯先の面の軸方向範囲内に収まる螺旋に沿って連続または不連続で形成して当該窪み部に退避した異物が各スクリューロータの回転に伴って直接または各螺旋歯の歯先の面との間の隙間を経て窪み部の終端まで移送されるようにし、前記窪み部の始端が前記各螺旋歯の吸引端から離間した位置に、及び、前記窪み部の終端が前記各螺旋歯の吐出端から離間した位置に夫々設定されることを特徴とする。この場合、前記ケーシングに前記異物を排出する排出口が設けられ、前記排出口が重力加速度方向からみて最下流側に位置することが好ましい。 In order to solve the above-mentioned problems, a pair of screw rotors having helical teeth with opposite twist directions and a predetermined pitch, and a tooth tip of each helical tooth in a state in which the pair of screw rotors are meshed with each other in a non-contact manner. The screw rotors are synchronously rotated in opposite directions around their rotation axes, sucked from one axial end of the casing, and this sucked is confined in a plurality of working spaces formed along the axial direction between the casing and each screw rotor, and is discharged from the other end of the casing in the axial direction while being compressed. on the surface of the spiral tooth, continuous or discontinuous along the spiral that fits within the axial range of the tooth tip surface, in which foreign matter that has entered the gap between the inner surface of the casing and the tooth tip surface of each spiral tooth retreats The foreign matter that is formed in the recess and evacuated in the recess is transported to the end of the recess directly or through the gap between the tip surface of each spiral tooth as the screw rotor rotates, and the recess The starting end of the portion is set at a position separated from the suction end of each spiral tooth, and the terminal end of the recessed portion is set at a position separated from the discharge end of each spiral tooth. In this case, it is preferable that the casing is provided with a discharge port for discharging the foreign matter, and the discharge port is positioned on the most downstream side when viewed from the direction of gravitational acceleration.

本発明によれば、例えば、真空チャンバ内の真空排気中に、固体（微細な粉状）の異物がケーシング内に進入し、ケーシングの内面と各螺旋歯の歯先の面との間の隙間に侵入して異物が詰まったとしても、この異物をスクリューロータの回転に伴って速やかに各螺旋歯の歯先の面に形成した窪み部内に落ち込ませて退避させることができる。このことは、例えば、ケーシング内でのプロセスガスの析出により発生した異物が上記隙間に詰まった場合も同様である。このため、ケーシングの内面と各螺旋歯の歯先の面との間の隙間に異物が詰まった状態が可及的速やかに解消されることで、モータトルクの増大や、ケーシング内面や各螺旋歯の歯先の面の摩損といった不具合の発生が可及的に抑制される。その結果、凹溝状の窪み部を歯先の面の軸方向範囲内に収まる螺旋に沿って形成したことで（言い換えると、軸方向で互いに隣接する作動空間を、窪み部を介して直接連通させないことで）、排気性能の低下を確実に抑制しながら、上記隙間に侵入した異物の影響を受けずに、常時、正常な運転が可能になる。その上、上記従来例のように、上記隙間に詰まるサイズの異物を捕捉できるようにトラップを必要としないため、排気速度の低下を招くといった不具合も生じない。 According to the present invention, for example, during the evacuation of the vacuum chamber, solid (fine powder) foreign matter enters the casing and causes the gap between the inner surface of the casing and the tip surface of each helical tooth. Even if foreign matter enters into the screw rotor and becomes clogged, the foreign matter can be quickly dropped into the recess formed on the tip surface of each helical tooth and evacuated as the screw rotor rotates. This is also the case when, for example, the gap is clogged with foreign matter generated by deposition of process gas within the casing. For this reason, the state in which the foreign matter is clogged in the gap between the inner surface of the casing and the surface of the tip of each helical tooth is eliminated as quickly as possible, thereby increasing the motor torque and preventing the inner surface of the casing and each helical tooth from The occurrence of defects such as abrasion of the tooth tip surface of the tooth is suppressed as much as possible. As a result, by forming the concave groove-shaped depression along the spiral within the axial range of the tooth tip surface (in other words, the working spaces adjacent to each other in the axial direction are directly communicated via the depression). Therefore, it is possible to always operate normally without being affected by the foreign matter that has entered the gap while reliably suppressing the deterioration of the exhaust performance. Moreover, unlike the above-described conventional example, no trap is required for trapping the foreign matter of a size that clogs the gap, so that the problem of reducing the exhaust speed does not occur.

本発明においては、前記窪み部が形成される前記螺旋は、前記歯先の面の軸方向幅に応じて、軸方向に間隔を存した複数のもので構成されることが好ましい。これにより、ケーシングの内面と各螺旋歯の歯先の面との間の隙間に侵入して詰まった異物を可及的速やかに窪み部内へと退避させることができ、有利である。 In the present invention, it is preferable that the spiral on which the recessed portion is formed is composed of a plurality of spirals spaced apart in the axial direction according to the axial width of the surface of the tooth tip. As a result, it is possible to quickly retract the foreign matter that has entered and clogged the gap between the inner surface of the casing and the tip surface of each helical tooth into the recess, which is advantageous.

ここで、各螺旋歯の歯先の面に窪み部を形成した場合、ケーシング内面と各螺旋歯の歯先の面との間の隙間が局所的に大きくなって気体の逆流量が増加し、排気性能が低下する虞がある。本発明においては、前記窪み部の始端が前記各螺旋歯の吸引端から離間した位置に、及び、前記窪み部の終端が前記各螺旋歯の吐出端から離間した位置に夫々設定されることが好ましく、また、前記各螺旋歯の歯先の面の単位面積に対する、前記窪み部の開口面の単位面積の比が０．１～０．６の範囲に設定されることが好ましい。 Here, when a recessed portion is formed on the tip surface of each helical tooth, the gap between the inner surface of the casing and the tip surface of each helical tooth becomes locally large, resulting in an increase in backflow of gas. There is a possibility that the exhaust performance may deteriorate. In the present invention, the starting end of the recessed portion is set at a position separated from the suction end of each spiral tooth, and the terminal end of the recessed portion is set at a position separated from the discharge end of each spiral tooth. Preferably, the ratio of the unit area of the opening surface of the recess to the unit area of the tip surface of each spiral tooth is set in the range of 0.1 to 0.6.

ところで、窪み部内に退避させた異物をケーシング外に速やかに排出しようとする場合、前記窪み部は、前記各螺旋歯の歯先エッジ部の稜線に平行な螺旋に沿ってのびる凹溝状のものを含むように構成することが考えられるが、これでは、窪み部の開口面の単位面積を上記のように設定していても気体の逆流量が増加してしまう虞がある。そこで、前記ケーシングの軸方向一端側に位置する前記窪み部の壁面と歯先の面とがなす角度が３０度～９０度の範囲に設定されることが好ましい。これによれば、逆流する気体が窪み部の壁面と歯先の面との角部に衝突して渦を巻くような還流が発生することで、気体の逆流を抑制することができる。なお、凹溝状の窪み部は、例えば、エンドミルを用いた切削加工により形成することが考えられ、このときの加工性を考慮すると、前記ケーシングの軸方向一端側に位置する前記窪み部の壁面と歯先の面とがなす角度と、前記ケーシングの軸方向他端側に位置する前記窪み部の壁面と歯先の面とがなす角度との和が９０度以下に設定されることが好ましい。 By the way, when it is intended to quickly discharge the foreign matter that has been evacuated into the recessed portion to the outside of the casing, the recessed portion has the shape of a concave groove extending along a spiral parallel to the ridge line of the tooth tip edge portion of each of the spiral teeth. However, in this case, even if the unit area of the opening surface of the recess is set as described above, there is a risk that the backflow of gas will increase. Therefore, it is preferable that the angle formed between the wall surface of the recess located at one end in the axial direction of the casing and the surface of the tooth tip is set within a range of 30 degrees to 90 degrees. According to this, the backflowing gas collides with the corner between the wall surface of the recess and the surface of the tooth tip to generate a swirling return flow, thereby suppressing the backflow of the gas. It should be noted that, for example, it is conceivable to form the concave groove-shaped hollow portion by cutting using an end mill. It is preferable that the sum of the angle formed by the tooth tip surface and the angle formed by the wall surface of the recess portion located on the other end side in the axial direction of the casing and the tooth tip surface is set to 90 degrees or less. .

また、各螺旋歯の歯先の面に窪み部を形成した場合、非接触で互いに噛み合う各螺旋歯の歯先の面相互の隙間も局所的に大きくなって気体の逆流量が増加し、排気性能が低下してしまう虞がある。本発明においては、前記一対のスクリューロータの各回転軸に突部が夫々形成され、両スクリューロータの相対回転時に一方のスクリューロータの回転軸に形成した突部が他方のスクリューロータの歯先の面に形成した窪み部内に進入する構成を採用してもよい。 In addition, when a recessed portion is formed on the surface of the tip of each spiral tooth, the gap between the surfaces of the tip of each spiral tooth that meshes with each other in a non-contact manner is also locally increased, resulting in an increase in the backflow of the gas and exhaust gas. There is a possibility that the performance will be degraded. In the present invention, projections are formed on the respective rotating shafts of the pair of screw rotors, and when the two screw rotors rotate relative to each other, the projections formed on the rotating shaft of one of the screw rotors are formed on the tips of the teeth of the other screw rotor. It is also possible to employ a configuration in which it enters into a recess formed in the surface.

真空チャンバに接続される本発明の実施形態のスクリューポンプを示す概略図。Schematic diagram showing a screw pump of an embodiment of the invention connected to a vacuum chamber. 図１に示すスクリューポンプの構造を示す断面図。Sectional drawing which shows the structure of the screw pump shown in FIG. 図２に示す一対のスクリューロータの断面図。Sectional drawing of a pair of screw rotor shown in FIG. スクリューロータの斜視図。The perspective view of a screw rotor. （ａ）及び（ｂ）は、窪み部の変形例を示す模式平面図。(a) And (b) is a schematic plan view which shows the modification of a hollow part. スクリューロータの変形例を示す断面図。Sectional drawing which shows the modification of a screw rotor. （ａ）及び（ｂ）は、本実施形態のスクリューポンプの排気性能を確認する実験結果のグラフ。(a) and (b) are graphs of experimental results for confirming the exhaust performance of the screw pump of the present embodiment.

以下、図面を参照して、真空処理装置の真空チャンバを真空排気するものを例に本発明のスクリューポンプ及びこのスクリューポンプに好適に使用可能なスクリューロータの実施形態を説明する。以下においては、上、下、左、右といった方向を示す用語は、図２に示すスクリューポンプＳＰの姿勢を基準として説明する。 Embodiments of the screw pump of the present invention and a screw rotor that can be suitably used for this screw pump will be described below with reference to the drawings, taking as an example an apparatus for evacuating a vacuum chamber of a vacuum processing apparatus. Hereinafter, terms indicating directions such as up, down, left, and right will be explained based on the attitude of the screw pump SP shown in FIG.

図１を参照して、Ｖｃは、シリコンウエハやガラス基板等の被処理物に対して成膜処理やエッチング処理といった各種のプロセスが実施される真空チャンバである。真空チャンバＶｃには、その内部を所定圧力まで真空排気するために、排気管Ｐｅを介して真空ポンプユニットＰｕが接続されている。真空ポンプユニットＰｕは、メカニカルブースターポンプなどのメインポンプＰｍと、メインポンプＰｍの背圧側の補助ポンプＰａとで構成される。そして、補助ポンプＰａとして、本実施形態のスクリューポンプＳＰが用いられる。 Referring to FIG. 1, Vc is a vacuum chamber in which various processes such as film formation and etching are performed on objects to be processed such as silicon wafers and glass substrates. A vacuum pump unit Pu is connected to the vacuum chamber Vc through an exhaust pipe Pe to evacuate the inside thereof to a predetermined pressure. The vacuum pump unit Pu is composed of a main pump Pm such as a mechanical booster pump, and an auxiliary pump Pa on the back pressure side of the main pump Pm. As the auxiliary pump Pa, the screw pump SP of this embodiment is used.

図２～図４を参照して、スクリューポンプＳＰは、左右一対のスクリューロータ１_１，１_２とケーシング２とを備える。各スクリューロータ１_１，１_２は、回転軸１１ａ，１１ｂと、回転軸１１ａ，１１ｂに形成した螺旋歯１２ａ，１２ｂとを有する。各スクリューロータ１_１，１_２の各螺旋歯１２ａ，１２ｂは、捩れ方向が互いに逆方向として一対として構成される以外、同一の形態を有する一条のものである。特に図示して説明しないが、螺旋歯１２ａ，１２ｂの軸直角断面形状は、その歯底の面を構成する、スクリューロータ１_１，１_２の回転中心を中心とする第１円弧と、その歯先の面を構成する、スクリューロータ１_１，１_２の回転中心を中心とする第２円弧と、第１円弧と第２円弧とを夫々結ぶ、エピトロコイド曲線、外サイクロイド曲線やインボリュート曲線などから適宜選択される第１曲線と第２曲線とで創成されるものである。本実施形態では、各螺旋歯１２ａ，１２ｂが、不等ピッチ部（不等リード部）１２１と、等ピッチ部１２２とで構成される。不等ピッチ部１２１は、各螺旋歯１２ａの吸入端１２１ａ，１２１ｂから軸方向下方に向う所定範囲にて、歯先の面１３ａ，１３ｂの軸方向幅（上下方向幅）Ｗ１ａ，Ｗ１ｂと、ピッチＰ１ａ，Ｐ１ｂとを次第に小さくして形成され、等ピッチ部１２２は、不等ピッチ部１２１の後端から各螺旋歯１２ａ，１２ｂの吐出端１２２ａ，１２２ｂまでの範囲にて、歯先の面１３ａ，１３ｂの軸方向幅Ｗ１ｃと、ピッチＰ１ｃとが不等ピッチ部１２１より小さい同等のものとして形成されている。なお、各スクリューロータ１_１，１_２の各螺旋歯１２ａ，１２ｂとしては、公知ものが利用できるため、これ以上の詳細な説明は省略する。 2 to 4, the screw pump SP includes a pair of left and right screw rotors 1 ₁ and 1 ₂ and a casing 2. As shown in FIG. Each screw rotor 1 ₁ , 1 ₂ has a rotating shaft 11a, 11b and spiral teeth 12a, 12b formed on the rotating shaft 11a, 11b. Each of the helical teeth 12a, 12b of each of the screw rotors 1 ₁ , 1 ₂ is a single thread having the same form, except that they are configured as a pair with twist directions opposite to each other. Although not shown and described, the cross-sectional shapes of the spiral teeth 12a and 12b at right angles to the axes are composed of first circular arcs centered on the rotation centers of the screw rotors ₁₁ and ₁₂ , which constitute the tooth bottom surfaces, and From the epitrochoid curve, the epicycloid curve, the involute curve, etc., which connect the second arc centered on the rotation center of the screw rotors 1 ₁ and 1 ₂ and the first arc and the second arc, respectively, which constitute the above surface It is created by appropriately selected first and second curves. In this embodiment, each of the helical teeth 12 a and 12 b is composed of a nonuniform pitch portion (nonuniform lead portion) 121 and a uniform pitch portion 122 . The unequal pitch portion 121 has axial widths (vertical widths) W1a and W1b of the tip surfaces 13a and 13b and pitch The uniform pitch portion 122 is formed by gradually decreasing P1a and P1b. , 13b in the axial direction and the pitch P1c are equal to or smaller than the uneven pitch portion 121. As shown in FIG. As the helical teeth 12a and 12b of the screw rotors ₁₁ and ₁₂ , well-known ones can be used, so further detailed description will be omitted.

ケーシング２は、螺旋歯１２ａ，１２ｂが形成された各スクリューロータ１_１，１_２の部分を格納する筒状のケーシング部本体２１を備え、ケーシング部本体２１の上部開口及び下部開口は上カバー２２及び下カバー２３で夫々閉塞されている。上カバー２２（または上カバー２２近傍のケーシング部本体２１を含んだ箇所）には吸引口２４が設けられ、吸引口２４にメインポンプＰｍからの排気管Ｐｅが接続されている。下カバー２３には吐出口２５が設けられると共に、後述する異物を排出する排出口２６が設けられ、排出口２６から排出された異物は、ケーシング本体部に２１外に設けられる図示省略の回収容器で回収されるようにしている。なお、排出口２６の位置は、スクリューポンプＳＰの設置姿勢（重力加速度方向）に応じて適宜設定することができる。 The casing 2 includes a cylindrical casing main body 21 that houses portions of the respective screw rotors 1 ₁ and 1 ₂ having helical teeth 12 a and 12 b. and a lower cover 23, respectively. A suction port 24 is provided in the upper cover 22 (or a portion including the casing body 21 in the vicinity of the upper cover 22), and an exhaust pipe Pe from the main pump Pm is connected to the suction port 24. FIG. A discharge port 25 is provided in the lower cover 23, and a discharge port 26 for discharging foreign substances, which will be described later, is provided. It is made to be collected by In addition, the position of the discharge port 26 can be appropriately set according to the installation attitude (gravitational acceleration direction) of the screw pump SP.

ケーシング部本体２１には、上下方向に貫通して、後述の各軸受及びギアにより、各螺旋歯１２ａ，１２ｂを非接触で互いに噛み合わせた状態で格納できる、互いに結合した一対の円筒状内壁（ケーシング２の内面）２１ａが形成されている。そして、一方の（図２中、左側）スクリューロータ１_１の第１の螺旋歯１２ａと、隙間Ｇｐ１を存して、他方の（図２中、右側）スクリューロータ１_２の第２の螺旋歯１２ｂとを非接触で噛み合わせた状態で、円筒状内壁２１ａにより区画される空間に、第１及び第２の各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂとケーシング２の内面２１ａとの間に隙間Ｇｐ２を存して格納される。これにより、一方のスクリューロータ１_１の第１の螺旋歯１２ａとケーシング部本体２１との間、他方のスクリューロータ１_２の第２の螺旋歯１２ｂとケーシング部本体２１との間に上下方向に複数の作動室Ｓ１ａ～Ｓ６ｂが形成される。隙間Ｇｐ１，Ｇｐ２は、気体の逆流量が可及的に抑制されるように、例えば、０．０５ｍｍに設定される。なお、各作動室Ｓ１ａ～Ｓ６ｂの回転軸方向の区画は、上記第１円弧と第２円弧とを夫々結ぶ曲線よって創生された図示省略の面の隙間にて構成され、この区画が作動空間となる。この回転軸方向の区画は螺旋（ピッチ）に依存して確定されるため、図中の隣接する各作動室Ｓ１ａ～Ｓ６ｂは一部連通した容積として、作動空間となる構成としてもよい。 The casing main body 21 has a pair of mutually coupled cylindrical inner walls ( An inner surface 21a of the casing 2 is formed. The first helical tooth 12a of one (left side in FIG. ₂ ) screw rotor 11 and the second helical tooth 12a of the other (right side in FIG. ₂ ) screw rotor 12 with a gap Gp1. In the space defined by the cylindrical inner wall 21a, the tip surfaces 13a and 13b of the first and second spiral teeth 12a and 12b and the inner surface 21a of the casing 2 are placed in a space defined by the cylindrical inner wall 21a. are stored with a gap Gp2 between them. As a result, between the first helical tooth 12a of _one screw rotor 11 and the casing body 21, and between the _second helical tooth 12b of the other screw rotor 12 and the casing body 21, vertical A plurality of working chambers S1a to S6b are formed. The gaps Gp1 and Gp2 are set to 0.05 mm, for example, so that the backflow of gas is suppressed as much as possible. The partitions of the working chambers S1a to S6b in the direction of the rotation axis are formed by gaps between surfaces (not shown) created by curves connecting the first and second arcs, respectively, and these partitions are working spaces. becomes. Since the sections in the direction of the rotation axis are determined depending on the spiral (pitch), each of the adjacent working chambers S1a to S6b in the figure may be configured to be working spaces by partially communicating volumes.

上カバー２２及び下カバー２３には、軸受３ａ，３ｂと軸受４ａ，４ｂとが夫々設けられ、各スクリューロータ１_１，１_２の回転軸１１ａ，１１ｂの両端が夫々支承される。下カバー２３の下側には補助ケーシング部２７が取り付けられている。そして、補助ケーシング部２７内に延出した回転軸１１ａ，１１ｂの下端部には、互いに噛合うギア５ａ，５ｂが夫々外嵌され、一方の回転軸１１ａの下端が補助ケーシング部２７内に設けた駆動モータ６に連結されている。駆動モータ６を回転駆動すると、各スクリューロータ１_１，１_２が回転軸１１ａ，１１ｂ回りで夫々逆方向に同期回転される。これにより、真空チャンバＶｃ内の気体が吸引口２４より吸引され、吸引したものがケーシング部本体２１とスクリューロータ１_１，１_２との間に上下方向に沿って形成される複数の作動室Ｓ１ａ～Ｓ６ｂまたは作動空間に閉じ込めて圧縮しながら移送して、吐出口２６より吐出される。 Bearings 3a, 3b and bearings 4a, 4b are provided on the upper cover 22 and the lower cover 23, respectively, and both ends of the rotating shafts _11a , _11b of the screw rotors 11, 12 are respectively supported. An auxiliary casing portion 27 is attached to the lower side of the lower cover 23 . Gears 5a and 5b that mesh with each other are fitted to the lower ends of the rotary shafts 11a and 11b extending into the auxiliary casing portion 27, and the lower end of one of the rotary shafts 11a is provided inside the auxiliary casing portion 27. The drive motor 6 is connected to the When the drive motor 6 is rotationally driven, the screw rotors 1 ₁ and 1 ₂ are synchronously rotated in opposite directions about the rotary shafts 11a and 11b, respectively. As a result, the gas in the vacuum chamber Vc is sucked from the suction port 24, and the sucked gas is a plurality of working chambers S1a formed along the vertical direction between the casing body 21 and the screw rotors ₁₁ , ₁₂ . ∼ S6b or confined in the working space, transported while being compressed, and discharged from the discharge port 26.

ところで、真空チャンバＶｃの真空排気中に、例えば、真空チャンバＶｃ内で発生した異物が吸引口２４からケーシング部本体２１内に進入して上記隙間Ｇｐ２に侵入したり、堆積が進行することで詰まることがある。ここで、「詰まる」とは、隙間Ｇｐ２に介在する異物の接触面（歯先の面１３ａ，１３ｂおよび円筒状内壁２１ａ）部位の面圧、及び、この反力となる、各軸受３ａ，３ｂ，４ａ，４ｂに生じる面圧が上昇する現象を示す。各面圧の上昇は垂直荷重の上昇であり、摩擦力の増大を生じさせる。このため、モータトルクの増大や、ケーシング内面２１ａや第１及び第２の各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂの摩損の発生が可及的に抑制されるように構成しておく必要がある。そこで、本実施形態では、第１及び第２の各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂに、上記隙間Ｇｐ２に侵入した異物が退避する第１の窪み部１４ａ，１４ｂと第２の窪み部１４ｃ，１４ｄとを夫々形成することとした。なお、各窪み部１４ａ～１４ｄは、異物からみて受ける面圧を減ずる領域であることから、異物を高い面圧領域から低面圧領域へと誘引する効果を奏するといえる。 By the way, during evacuation of the vacuum chamber Vc, for example, foreign matter generated in the vacuum chamber Vc enters the casing main body 21 from the suction port 24 and enters the gap Gp2, or clogs due to progress of accumulation. Sometimes. Here, "clogging" refers to the surface pressure of the contact surfaces (top surfaces 13a and 13b and cylindrical inner wall 21a) of foreign matter intervening in the gap Gp2 and the reaction force of the bearings 3a and 3b. , 4a and 4b increase in surface pressure. Each increase in surface pressure is an increase in normal load and causes an increase in frictional force. For this reason, it is constructed so as to suppress as much as possible the increase in the motor torque and the occurrence of abrasion of the casing inner surface 21a and the tip surfaces 13a and 13b of the first and second spiral teeth 12a and 12b. need to leave Therefore, in the present embodiment, first recesses 14a, 14b and second recesses 14a, 14b for retreating foreign matter that has entered the gap Gp2 are formed on the tip surfaces 13a, 13b of the first and second spiral teeth 12a, 12b. recesses 14c and 14d are formed respectively. Since each of the recesses 14a to 14d is a region that reduces the contact pressure received from the foreign matter, it can be said that there is an effect of inducing the foreign matter from the high contact pressure region to the low contact pressure region.

具体的には、不等ピッチ部１２１に形成される第１の窪み部１４ａ，１４ｂは、歯先の面１３ａ，１３ｂの稜線Ｌ１，Ｌ２に平行状に沿い、且つ、互いの間隔比率を変えずに３本の螺旋Ｌｓに沿い、不等ピッチ部１２１の後端まで連続して夫々のびる凹溝状のもので構成される。等ピッチ部１２２に形成される第２の窪み部１４ｃ，１４ｄは、上記同様、歯先の面１３ａ，１３ｂの稜線Ｌ１，Ｌ２と平行な１本の螺旋Ｌｓに沿って連続してのびる凹溝状のもので構成される。第１及び第２の各窪み部１４ａ～１４ｄの歯たけ方向の深さｄ１と、軸方向幅Ｗ２は、図３中に拡大して示すように、上記隙間Ｇｐ２と同等以上に設定される。この場合、図４中に拡大して示すように、異物を第１及び第２の各窪み部１４ａ～１４ｄ内に速やかに退避させる目的と、隣接する作動空間における大気圧力側作動空間から気体の逆流量の増加を抑制する目的を両立させるため、第１及び第２の各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂの単位面積に対し、各窪み部１４ａ～１４ｄの開口面（ハッチングを付した部分）の総面積が０．１～０．６の範囲に設定される。これに応じて、不等ピッチ部１２１及び等ピッチ部１２２に形成する凹溝状の窪み部１４ａ～１４ｄの軸方向幅Ｗ２または第１及び第２の各窪み部１４ａ～１４ｄの本数（軸方向幅Ｗ２の分割数）が適宜決定される。 Specifically, the first recessed portions 14a and 14b formed in the uneven pitch portion 121 are parallel to the ridgelines L1 and L2 of the tooth tip surfaces 13a and 13b, and the spacing ratio between them is changed. It is composed of concave grooves extending continuously to the rear end of the uneven pitch portion 121 along the three spirals Ls. The second depressions 14c and 14d formed in the equal pitch portion 122 are grooves continuously extending along one spiral Ls parallel to the ridgelines L1 and L2 of the tip surfaces 13a and 13b in the same manner as described above. It consists of The depth d1 in the tooth depth direction and the axial width W2 of each of the first and second recessed portions 14a to 14d are set equal to or greater than the gap Gp2, as shown in an enlarged view in FIG. In this case, as shown in an enlarged view in FIG. 4, the object is to quickly evacuate the foreign matter into the first and second depressions 14a to 14d, and to release the gas from the adjacent working space on the atmospheric pressure side. In order to achieve both the purpose of suppressing an increase in backflow, opening surfaces (hatching) of the recesses 14a to 14d are shown with respect to the unit area of the tip surfaces 13a and 13b of the first and second spiral teeth 12a and 12b. ) is set in the range of 0.1 to 0.6. Correspondingly, the axial width W2 of the concave groove-shaped depressions 14a to 14d formed in the uneven pitch portion 121 and the equal pitch portion 122 or the number of the first and second depressions 14a to 14d (axial The number of divisions of the width W2) is appropriately determined.

なお、上記螺旋Ｌｓは、歯先の面１３ａ，１３ｂの稜線Ｌ１，Ｌ２を除いた軸方向幅（軸方向範囲）Ｗｒ１、Ｗｒ２，Ｗｒ３（図４参照）内に収まっていれば、稜線Ｌ１，Ｌ２に対して必ずしも平行である必要はない。螺旋Ｌｓの目的は異物の排出促進であるため、例えば、異物を回転軸方向（排出口２６方向）へ移動させる運動を付与することが望ましく、具体的には、稜線Ｌ１，Ｌ２に比べ、螺旋Ｌｓを排出口２６方向へと傾ける（螺旋のピッチを伸ばす）構成を用いることは好ましいといえる。更に、本発明における各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂの単位面積の１単位は、最大で作動空間の区画単位で示される範囲の歯先の面１３ａ，１３ｂの面積で示され、最小で作動空間の区画単位の１／８（π／４ｒａｄ）に相当する範囲の歯先の面１３ａ，１３ｂの面積または後述する不連続な窪み部の１周期に相当する範囲の歯先の面１３ａ，１３ｂの面積として示される。 If the spiral Ls is within axial widths (axial ranges) Wr1, Wr2, Wr3 (see FIG. 4) excluding the ridgelines L1, L2 of the tooth tip surfaces 13a, 13b, the ridgelines L1, It is not necessarily parallel to L2. Since the purpose of the spiral Ls is to promote the discharge of foreign matter, it is desirable to impart motion to move the foreign matter in the direction of the rotation axis (direction of the discharge port 26). It can be said that it is preferable to use a configuration in which Ls is inclined toward the discharge port 26 (extending the pitch of the spiral). Further, one unit of the unit area of the tip surfaces 13a and 13b of each spiral tooth 12a and 12b in the present invention is indicated by the area of the tip surfaces 13a and 13b in the range indicated by the division unit of the working space at the maximum. , and the area of the tip surfaces 13a and 13b in a range corresponding to at least 1/8 (π/4 rad) of the division unit of the working space or the tip in a range corresponding to one period of discontinuous recesses described later. is shown as the area of the faces 13a, 13b of the .

また、不等ピッチ部１２１における第１の窪み部１４ａ，１４ｂの始端１４０ａは、凹溝状の第１の窪み部１４ａ，１４ｂ（例えば、図３における、壁面１４１ａ、壁面１４１ｂ、窪み部１４ｂの底面、円筒状内壁２１ａの４面で区画される雰囲気空間）が吸引口２５に連通しないように、第１及び第２の各螺旋歯１２ａ，１２ｂの吸引端１２１ａ，１２１ｂから離間した位置に設定される。他方、等ピッチ部１２２における第２の窪み部１４ｃ，１４ｄの始端は、いずれかの不等ピッチ部１２１の第１の窪み部１４ａ，１４ｂの後端（窪み部の雰囲気空間を連通）させることができるが、第１の窪み部１４ａ，１４ｂの後端と縁切りして不連続とすることもできる。好ましくは、等ピッチ部１２２に設けられる第２の窪み部１４ｃ，１４ｄを、同一形状を保った状態で不等ピッチ部１２１まで連続させ、等ピッチ部１２２から不等ピッチ部１２１の歯先の面１３ａ，１３ｂの軸方向幅の増加に応じた窪み部を不連続的に追加する構成とする。不連続的に追加される窪み部を、連続する窪み部を挟むように構成すれば、螺旋歯１２ａ，１２ｂの所定ピッチに全域に対して各窪み部が平行状態を保てる面で更に好ましい。このように構成することで窪み部の加工時間（切削時間）を短くすることができ、スクリューロータ１_１，１_２の製造面で効果を奏する。 In addition, the starting ends 140a of the first recessed portions 14a and 14b in the uneven pitch portion 121 are groove-shaped first recessed portions 14a and 14b (for example, in FIG. At a position spaced apart from the suction ends 121a and 121b of the first and second spiral teeth 12a and 12b so that the atmosphere space defined by the four surfaces of the bottom surface and the cylindrical inner wall 21a does not communicate with the suction port 25. be done. On the other hand, the starting ends of the second recessed portions 14c and 14d in the uniform pitch portion 122 should be the rear ends of the first recessed portions 14a and 14b of one of the uneven pitch portions 121 (communicating the atmospheric space of the recessed portion). However, it is also possible to cut off the edges from the rear ends of the first recessed portions 14a and 14b so as to be discontinuous. Preferably, the second recessed portions 14c and 14d provided in the uniform pitch portion 122 are continued to the uneven pitch portion 121 while maintaining the same shape, and the tooth tip of the uniform pitch portion 122 to the uneven pitch portion 121 is extended. A configuration is adopted in which recesses are discontinuously added according to the increase in the axial width of the surfaces 13a and 13b. If the discontinuously added depressions are configured to sandwich the continuous depressions, it is more preferable in that each depression can be kept parallel to the entire range of the predetermined pitch of the spiral teeth 12a and 12b. By configuring in this way, the processing time (cutting time) of the recessed portion can be shortened, which is effective in manufacturing the screw rotors 1 ₁ and 1 ₂ .

更に、等ピッチ部１２２における第２の窪み部１４ｃ，１４ｄの後端（終端）１４０ｂは、凹溝状の第２の窪み部１４ｃ，１４ｄが吐出口２５に連通しないように、第１及び第２の各螺旋歯１２ａ，１２ｂの吐出端１２２ａ，１２２ｂから離間した位置に設定される。また、第１及び第２の各窪み部１４ａ～１４ｄのケーシング２上端側（低圧側）に位置する壁面１４１ａと歯先の面１３ａ，１３ｂとがなす角度θ１は、３０度～９０度の範囲内に設定され、角度θ１と、第１及び第２の各窪み部１４ａ～１４ｄのケーシング２下端側（高圧側）に位置する壁面１４１ｂと歯先の面１３ａ，１３ｂとがなす角度θ２との和（θ１＋θ２）は、９０度以下に設定される。このような角度で窪み部１４ａ～１４ｄを形成することで、ケーシング２の内面と各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂとの間の隙間に異物が侵入し、その隙間や、特に角部１４２にて面圧を発生させたとしても、角部１４２の変形が抑止される効果が得られる。加えて、窪み部の底面側より開口（軸方向幅Ｗ２）側が広い形状とされていることにより、切削粉の排出が用意になるために加工時間（切削時間）を短くすることができ、スクリューロータ１_１，１_２の製造面で効果を奏する。 Furthermore, the rear ends (terminating ends) 140b of the second recessed portions 14c and 14d in the equal pitch portion 122 are arranged at the first and the second recessed portions 14c and 14d so that the groove-shaped second recessed portions 14c and 14d do not communicate with the discharge port 25. 2 are set at positions separated from the discharge ends 122a, 122b of the respective spiral teeth 12a, 12b. Further, the angle θ1 formed between the wall surface 141a of each of the first and second recessed portions 14a to 14d located on the upper end side (low pressure side) of the casing 2 and the tooth tip surfaces 13a and 13b is in the range of 30 degrees to 90 degrees. between the angle θ1 and the angle θ2 between the wall surface 141b located on the lower end side (high pressure side) of the casing 2 of each of the first and second recesses 14a to 14d and the tooth top surfaces 13a and 13b. The sum (θ1+θ2) is set to 90 degrees or less. By forming the depressions 14a to 14d at such an angle, foreign matter enters the gaps between the inner surface of the casing 2 and the tip surfaces 13a and 13b of the spiral teeth 12a and 12b, causing the gaps and In particular, even if surface pressure is generated at the corners 142, the effect of suppressing deformation of the corners 142 is obtained. In addition, since the opening (axial width W2) side of the recessed portion is wider than the bottom side of the recessed portion, it is possible to easily discharge the cutting powder, so that the machining time (cutting time) can be shortened. This is effective in manufacturing the rotors 1 ₁ and 1 ₂ .

以上の実施形態によれば、真空チャンバＶｃ内の真空排気中に、固体（微細な粉状）の異物がケーシング２内に進入して、ケーシング２の内面２１ａと第１及び第２の各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂとの間の隙間Ｇｐ２に異物が侵入して詰まったとしても、この異物は、スクリューロータ１_１，１_２の回転に伴って、上記のようにして不等ピッチ部１２１、等ピッチ部１２２に適宜形成された第１及び第２の各窪み部１４ａ～１４ｄ内に速やかに退避できる（このことは、例えば、ケーシング２内でのプロセスガスの析出により発生した異物が上記隙間Ｇｐ２に詰まった場合も同様である）。そして、第１及び第２の各窪み部１４ａ～１４ｄ内に退避した異物は、スクリューロータ１_１，１_２の回転に伴って直接または、不等ピッチ部１２１と等ピッチ部１２２との境界に位置する第１及び第２の各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂとの間の隙間Ｇｐ２を更に経て、第２の窪み部１４ｃ，１４ｄの終端まで移送され、排出口２６から回収容器に回収される。このため、ケーシング２の内面２１ａと第１及び第２の各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂとの間の隙間Ｇｐ２に異物が詰まった状態、即ち、異物に起因する面圧上昇並びに摩擦力の上昇が可及的に解消されることで、モータトルクの増大や、ケーシング２の内面２１ａや第１及び第２の各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂの摩損といった不具合の発生が可及的に抑制される。これにより、凹溝状の第１及び第２の各窪み部１４ａ～１４ｄを歯先の面１３ａ，１３ｂの軸方向範囲Ｗｒ１，Ｗｒ２，Ｗｒ３内に収まる螺旋Ｌｓに沿って形成したことで（言い換えると、軸方向で互いに隣接する作動空間を第１及び第２の各窪み部１４ａ～１４ｄにより直接連通させないことで）、排気性能の低下を確実に抑制しながら、上記隙間Ｇｐ２に侵入した異物の影響を受けずに、常時、正常な運転が可能になる。その上、上記従来例のように、上記隙間Ｇｐ２に詰まるサイズの異物を捕捉できるようにトラップを必要としないため、排気速度の低下を招くといった不具合も生じない。 According to the above-described embodiment, during evacuation of the vacuum chamber Vc, solid (fine powder) foreign matter enters the casing 2 and causes the inner surface 21a of the casing 2 and the first and second spirals to collapse. Even if foreign matter enters and clogs the gap Gp2 between the tooth tip surfaces 13a and 13b of the teeth 12a and 12b, the foreign matter will move as described above as the screw rotors ₁₁ and ₁₂ rotate. can be quickly retracted into the first and second depressions 14a to 14d appropriately formed in the uneven pitch portion 121 and the uniform pitch portion 122 (this means, for example, that deposition of process gas in the casing 2 The same applies to the case where the gap Gp2 is clogged with foreign matter generated by the above). As the screw rotors 1 ₁ and 1 2 rotate, the foreign matter that has retreated into the first and second depressions 14 a to ₁₄ d is directly or at the boundary between the uneven pitch portion 121 and the uniform pitch portion 122 . Further through the gap Gp2 between the tip surfaces 13a and 13b of the first and second helical teeth 12a and 12b located, it is transferred to the ends of the second recessed portions 14c and 14d, and from the discharge port 26. Collected in a collection container. Therefore, the gap Gp2 between the inner surface 21a of the casing 2 and the tip surfaces 13a and 13b of the first and second spiral teeth 12a and 12b is clogged with foreign matter, that is, the surface pressure caused by the foreign matter By eliminating the rise and the rise of the frictional force as much as possible, the motor torque is increased, and the inner surface 21a of the casing 2 and the tip surfaces 13a and 13b of the first and second spiral teeth 12a and 12b are reduced. The occurrence of defects such as wear and tear is suppressed as much as possible. As a result, the groove-shaped first and second depressions 14a to 14d are formed along the spiral Ls within the axial ranges Wr1, Wr2, and Wr3 of the tooth tip surfaces 13a and 13b (in other words, and by not allowing the working spaces adjacent to each other in the axial direction to directly communicate with each other by the first and second recessed portions 14a to 14d), while reliably suppressing the deterioration of the exhaust performance, the foreign matter that has entered the gap Gp2 can be removed. Normal operation is always possible without being affected. In addition, unlike the conventional example, no trap is required to trap the foreign matter of a size that clogs the gap Gp2, so that the problem of lowering the exhaust speed does not occur.

また、第１及び第２の各窪み部１４ａ～１４ｄのケーシング２の軸方向一端側（上端側）に位置する壁面１４１ａと歯先の面１３ａ，１３ｂとがなす角度θ１を３０度～９０度の範囲に設定したことで、逆流する気体が窪み部１４ａ～１４ｄの壁面１４１ａと歯先の面１３ａ，１３ｂとの角部１４２に衝突して渦を巻くような還流が発生して気体の逆流を抑制することができ、しかも、角度θ１と、各窪み部１４ａ～１４ｄの軸方向他端側（下端側）に位置する壁面１４１ｂと歯先の面１３ａ，１３ｂとがなす角度θ２との和（θ１＋θ２）を９０度以下に設定したことで、凹溝状の窪み部１４ａ～１４ｄを例えばエンドミルを用いた切削加工により加工性よく形成することができる。なお、エンドミルを用いた切削加工において、軸心の振れ等や切削粉等の影響等により、角度θ２との和（θ１＋θ２）が９０度をやや超過する加工法が用いられる場合もあるが、これらも、本発明の９０度とする技術思想に含まれる。 Further, the angle θ1 between the top surface 13a and 13b and the wall surface 141a of each of the first and second recessed portions 14a to 14d located on the one axial end side (upper end side) of the casing 2 is 30 to 90 degrees. , the backflowing gas collides with the wall surfaces 141a of the recessed portions 14a to 14d and the corners 142 of the tooth top surfaces 13a and 13b to generate a swirling backflow, thereby causing the backflow of the gas. In addition, the sum of the angle θ1 and the angle θ2 formed by the wall surface 141b located on the other axial end side (lower end side) of each of the recessed portions 14a to 14d and the tooth tip surfaces 13a and 13b By setting (θ1+θ2) to 90 degrees or less, the recessed portions 14a to 14d having groove shapes can be formed with good workability, for example, by cutting using an end mill. In cutting using an end mill, there are cases where the sum of the angle θ2 (θ1 + θ2) slightly exceeds 90 degrees due to the influence of axial runout, cutting dust, etc., but these is also included in the technical concept of 90 degrees of the present invention.

次に、第１及び第２の各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂに第１及び第２の各窪み部１４ａ～１４ｄを夫々形成した上記実施形態のスクリューポンプＳＰの排気性能を歯先の面に窪み部を形成していない従来品との比較で確認した。この場合、発明品のスクリューポンプＳＰでは、第１及び第２の各螺旋歯１２ａ，１２ｂの歯先の面１３ａ，１３ｂとの間の隙間Ｇｐ２を０．１３ｍｍ、不等ピッチ部１２１に形成される３本の第１の窪み部１４ａ，１４ｂの幅を４ｍｍ（歯先の面１３ａ，１３ｂの単位面積に対する各窪み部１４ａ，１４ｂの開口面の単位面積が約０．４）、等ピッチ部１２２における１本の第２の窪み部１４ｃ，１４ｄの幅を４ｍｍ（歯先の面１３ａ，１３ｂの単位面積に対する各窪み部１４ｃ，１４ｄの開口面の単位面積が約０．４）、各窪み部１４ａ～１４ｄの深さｄ１を０．５ｍｍ、角度θ１を３０度とした。図７（ａ）は、吸引口２４の圧力に対する排気速度の変化を示す。図中、実線が発明品、点線が従来品であり、排気速度比に置き換えたものを図７（ｂ）に示す。これによれば、１０Ｐａ～１００００Ｐａの範囲において、発明品は、従来品の９０％以上の排気速度を保つことができたことが確認された。 Next, the exhaust performance of the screw pump SP of the above-described embodiment in which the first and second recesses 14a to 14d are formed on the tip surfaces 13a and 13b of the first and second spiral teeth 12a and 12b, respectively. was confirmed by comparison with the conventional product that does not have a recess on the tooth tip surface. In this case, in the screw pump SP of the present invention, the gap Gp2 between the tip surfaces 13a and 13b of the first and second spiral teeth 12a and 12b is 0.13 mm, and the uneven pitch portion 121 is formed. The width of the three first recesses 14a, 14b is 4 mm (the unit area of the opening surface of each recess 14a, 14b with respect to the unit area of the tooth top surface 13a, 13b is about 0.4), and the equal pitch part The width of one second recessed portion 14c, 14d in 122 is 4 mm (the unit area of the opening surface of each recessed portion 14c, 14d with respect to the unit area of the tip surface 13a, 13b is about 0.4), and each recessed portion The depth d1 of the portions 14a to 14d was 0.5 mm, and the angle θ1 was 30 degrees. FIG. 7(a) shows changes in the exhaust speed with respect to the pressure of the suction port 24. FIG. In the figure, the solid line is the product of the present invention and the dotted line is the conventional product. According to this, it was confirmed that in the range of 10 Pa to 10000 Pa, the inventive product was able to maintain an exhaust speed that was 90% or more of that of the conventional product.

以上、本発明の実施形態について説明したが、本発明の技術思想の範囲を逸脱しない限り、種々の変形が可能である。上記実施形態では、第１及び第２の各窪み部１４ａ～１４ｄとして、不等ピッチ部１２１、等ピッチ部１２２にて夫々、螺旋Ｌｓに沿ってのびる凹溝状のものを連続して形成したものを例に説明したが、これに限定されるものではない。例えば、図５（ａ）に示すように、第１及び第２の各窪み部１４ｅを歯先の面１３ａ，１３ｂにおいて矩形の輪郭を持つ凹部とし、このような凹部１４ｅの複数個が、歯先の面１３ａ，１３ｂの軸方向範囲Ｗｒに収まる螺旋Ｌｓに沿って間隔を置いて不連続で形成されていてもよい。これにより、渦を巻くような還流をより発生させて気体の逆流を抑制することができる。この場合、特に図示して説明しないが、凹溝状の第１及び第２の各窪み部１４ａ～１４ｄ内に所定間隔で詰め物を充填して凹部１４ｅの複数個が不連続で形成されるようにしてもよい。また、図５（ｂ）に示すように、凹部１４ｅと、スリット状の凹部１４ｆとを螺旋Ｌｓに沿って不連続で形成（例えば交互に形成）してもよい。 Although the embodiments of the present invention have been described above, various modifications are possible without departing from the scope of the technical idea of the present invention. In the above-described embodiment, as the first and second recesses 14a to 14d, the unequal pitch portion 121 and the equal pitch portion 122 are formed continuously in the form of concave grooves extending along the spiral Ls. Although the description has been made using the example, the present invention is not limited to this. For example, as shown in FIG. 5A, each of the first and second recessed portions 14e is a recessed portion having a rectangular outline on the tooth tip surfaces 13a and 13b, and a plurality of such recessed portions 14e are formed on the tooth tip. They may be discontinuously formed at intervals along the spiral Ls within the axial range Wr of the surfaces 13a and 13b. As a result, it is possible to generate more vortex-like reflux and suppress backflow of the gas. In this case, although not shown and described in particular, the first and second groove-shaped recesses 14a to 14d are filled with filling material at predetermined intervals so that a plurality of recesses 14e are formed discontinuously. can be In addition, as shown in FIG. 5B, recesses 14e and slit-shaped recesses 14f may be discontinuously formed (for example, alternately formed) along the spiral Ls.

ところで、上記実施形態のように、歯先の面１３ａ，１３ｂに第１及び第２の各窪み部１４ａ～１４ｄを形成すると、両スクリューロータ１_１，１_２間の隙間Ｇｐ１が局所的に大きくなり、これに伴い、気体の逆流量が増加し、排気性能が低下する虞がある。なお、実験により、隙間Ｇｐ１および図示しない面の隙間である回転軸方向の第１円弧と第２円弧とを夫々結ぶ曲線よって創生された面間の隙間は、隙間を貫通する距離が短いことから、異物を詰まらせる確率が低く、この部位のついての凹部等の窪み部は不要という知見が得られている。また、変形例に係るスクリューロータ１０_１，１０_２では、図６に示すように、一対のスクリューロータ１_１，１_２の螺旋歯１２ａ，１２ｂのない各回転軸１１ａ，１１ｂの部分には、螺旋Ｌｓに沿ってのびる突条（突部）１５ａ，１５ｂが夫々形成され、両スクリューロータ１_１，１_２の相対回転時に、一方のスクリューロータ１_１（１_２）の回転軸１１ａ（１１ｂ）の部分に形成した突条１５ａ，１５ｂが他方のスクリューロータ１_２（１_１）の歯先の面１３ｂ（１３ａ）に形成した第１及び第２の各窪み部１４ｂ（１４ａ）、１４ｄ（１４ｃ）内に連続して進入するようにしている。これによれば、気体の逆流量を抑制でき、排気性能の低下を抑制することができる。突部１５ａ，１５ｂの形状は、第１及び第２の各窪み部１４ａ～１４ｄの形状に応じて適宜設定される。 By the way, if the first and second depressions 14a to 14d are formed on the tooth tip surfaces 13a and 13b as in the above embodiment, the gap Gp1 between the two screw rotors 1 ₁ and 1 ₂ becomes locally large. As a result, there is a risk that the back flow rate of the gas will increase and the exhaust performance will deteriorate. Experiments have shown that the gap Gp1 and the gap between the surfaces (not shown) created by curves connecting the first and second arcs in the rotation axis direction have a short distance through which the gap passes. Therefore, it has been found that the probability of clogging with foreign matter is low, and that a recessed portion such as a concave portion for this portion is unnecessary. Further, in _the screw rotors 10 ₁ and 10 ₂ according to the modified example, as _shown in FIG. Ridges (protrusions) 15a and 15b extending along the spiral Ls are respectively formed, and when the two screw rotors 1 ₁ and 1 ₂ rotate relative to each other, the rotating shaft 11a (11b) of one of the screw rotors 1 ₁ (1 ₂ ) The ridges 15a, 15b formed on the other screw rotor 1 ₂ (1 ₁ ) form first and second depressions 14b (14a), 14d (14c ) in a continuous manner. According to this, it is possible to suppress the backflow of the gas, and to suppress the deterioration of the exhaust performance. The shapes of the protrusions 15a and 15b are appropriately set according to the shapes of the first and second recesses 14a to 14d.

また、上記実施形態では、第１及び第２の各螺旋歯１２ａ，１２ｂが、不等ピッチ部１２１と等ピッチ部１２２とを持つ一条のもので構成される場合を例に説明したが、これに限定されるものではなく、不等ピッチ部または等ピッチ部のみで構成されたものや、複数条で構成されたものにも本発明は適用することができる。更に、上記実施形態では、真空チャンバＶｃ内を真空排気するために用いられるスクリューポンプＳＰ及びスクリューロータ１_１，１_２を例に説明したが、これに限定されず、粉体移送用真空置換タンク内を真空排気する場合にも本発明を適用することができる。また、上記実施形態では、下カバー２３に排出口２６を形成したものを例に説明したが、スクリューポンプＳＰの設置姿勢、即ち、重力加速度方向からみて最下面を含むように構成されていてもよい。これにより、異物の移動について重力による移動障壁が存在せず、その結果、ケーシング２及び下カバー２３より容易に排出可能な構成となる。また、歯先の面１３ａ，１３ｂとのなす角度θ１を９０度とした方形状の溝として窪み部を構成すれば、より異物を退避させることが可能となる。なお、各螺旋歯１２ａ，１２ｂの、歯先の面１３ａ，１３ｂの稜線（Ｌ１，Ｌ２部）形成されている角部は、軸方向の気密に寄与しているため、その近傍に窪み部を設けることは避けることが好ましい。つまり、窪み部が一つの螺旋で示されるように校正されている場合は、稜線（Ｌ１，Ｌ２部）から見て中央にその螺旋を設けることが好ましい。また、各螺旋歯の断面視で鋭角側の稜線（Ｌ１，Ｌ２部）が特に気密に寄与していることから、螺旋は中央より鈍角側に設けることがより好ましい。 In the above embodiment, the first and second helical teeth 12a and 12b are each composed of a single tooth having a nonuniform pitch portion 121 and a uniform pitch portion 122, but this is not the case. However, the present invention can also be applied to a structure composed only of uneven pitch portions or uniform pitch portions, or a structure composed of a plurality of threads. Furthermore, in the above embodiment, the screw pump SP and the screw rotors 1 ₁ and 1 ₂ used for evacuating the vacuum chamber Vc have been described as an example, but the present invention is not limited to this, and the powder transfer vacuum replacement tank The present invention can also be applied when the inside is evacuated. In the above-described embodiment, the lower cover 23 is provided with the discharge port 26. However, the screw pump SP may be configured to include the lowermost surface when viewed from the installation posture of the screw pump SP, that is, the gravitational acceleration direction. good. As a result, there is no gravitational obstacle to movement of the foreign matter, and as a result, the foreign matter can be easily discharged from the casing 2 and the lower cover 23 . Further, if the concave portion is formed as a rectangular groove having an angle θ1 formed with the tip surfaces 13a and 13b of 90 degrees, it becomes possible to further evacuate the foreign matter. The corners formed by the ridgelines (L1, L2 portions) of the tip surfaces 13a, 13b of the spiral teeth 12a, 12b contribute to airtightness in the axial direction. It is preferable to avoid providing them. In other words, if the recessed portion is calibrated so as to be indicated by one spiral, it is preferable to provide the spiral in the center when viewed from the ridgeline (L1, L2 portions). In addition, since the ridge lines (L1, L2) on the acute angle side in the cross-sectional view of each spiral tooth particularly contribute to airtightness, it is more preferable to provide the spiral on the obtuse angle side of the center.

ＳP…スクリューポンプ、１_１，１_２，１０_１，１０_２…スクリューロータ、１１ａ，１１ｂ…回転軸、１２ａ，１２ｂ…螺旋歯、Ｐ１ａ，Ｐ１ｂ，Ｐ１ｃ…ピッチ、１２１ａ，１２１ｂ…吸引端、１２２ａ，１２２ｂ…吐出端、１３ａ，１３ｂ…歯先の面、Ｗｒ１～Ｗｒ３…軸方向幅（軸方向範囲）、１４ａ～１４ｄ…凹溝状の窪み部、１４ｅ…凹部（窪み部），１４ｆ…スリット状の凹部（窪み部）、Ｌｓ…螺旋、１４０ａ…第１の窪み部の始端、１４０ｂ…第２の窪み部の終端、１４１ａ，１４１ｂ…窪み部の壁面、θ１，θ２…角度、１５ａ，１５ｂ…突部、２…ケーシング、２１ａ…円筒状内壁（ケーシングの内面）、Ｓ１ａ～Ｓ６ｂ…作動室。 SP... screw pump, ₁₁ , ₁₂ , ₁₀₁ , ₁₀₂ ... screw rotor, 11a, 11b... rotating shaft, 12a, 12b... helical tooth, P1a, P1b, P1c... pitch, 121a, 121b... suction end, 122a , 122b... discharge end, 13a, 13b... tooth tip surface, Wr1 to Wr3... axial width (axial range), 14a to 14d... concave groove-shaped depression, 14e... concave portion (hollow), 14f... slit concave portion (hollow portion), Ls... spiral, 140a... starting end of the first hollow portion, 140b... end of the second hollow portion, 141a, 141b... wall surface of the hollow portion, θ1, θ2... angles, 15a, 15b ... Projection 2 ... Casing 21a ... Cylindrical inner wall (inner surface of casing) S1a to S6b ... Working chamber.

Claims

ねじれ方向が逆方向で所定ピッチの螺旋歯を夫々有する一対のスクリューロータと、これら一対のスクリューロータを非接触で互いに噛み合わせた状態で且つ各螺旋歯の歯先の面との間に隙間を存して格納するケーシングとを備え、各スクリューロータをそれらの回転軸回りで夫々逆方向に同期回転させ、ケーシングの軸方向一端より吸引し、この吸引されたものをケーシングと各スクリューロータとの間に軸方向に沿って形成される複数の作動空間に閉じ込めて圧縮しながらケーシングの軸方向他端より吐出するスクリューポンプにおいて、
各螺旋歯の歯先の面に、ケーシングの内面と各螺旋歯の歯先の面との間の隙間に侵入した異物が退避する窪み部を歯先の面の軸方向範囲内に収まる螺旋に沿って連続または不連続で形成して当該窪み部に退避した異物が各スクリューロータの回転に伴って直接または各螺旋歯の歯先の面との間の隙間を経て窪み部の終端まで移送されるようにし、
前記窪み部の始端が前記各螺旋歯の吸引端から離間した位置に、及び、前記窪み部の終端が前記各螺旋歯の吐出端から離間した位置に夫々設定されることを特徴とするスクリューポンプ。 A gap is provided between a pair of screw rotors having helical teeth with opposite twist directions and a predetermined pitch, and the tip surfaces of the helical teeth in a state in which the pair of screw rotors are meshed with each other in a non-contact manner. The screw rotors are synchronously rotated in opposite directions about their rotation axes, sucked from one end of the casing in the axial direction, and the sucked material is transferred between the casing and the screw rotors. In a screw pump that discharges from the other axial end of a casing while being confined in a plurality of working spaces formed along the axial direction between and compressed,
On the surface of the tip of each helical tooth, a recess is formed in the spiral that fits within the axial range of the surface of the tip of the tooth. As the screw rotor rotates, the foreign matter formed continuously or discontinuously and retreated to the recess is transferred directly or through the gap between the tip surface of each spiral tooth to the end of the recess. so that
A screw pump, wherein a starting end of the recessed portion is set at a position separated from the suction end of each of the spiral teeth, and a terminal end of the recessed portion is set at a position separated from the discharge end of each of the spiral teeth. .

前記ケーシングに前記異物を排出する排出口が設けられ、前記排出口が重力加速度方向からみて最下流側に位置することを特徴とする請求項１記載のスクリューポンプ。2. A screw pump according to claim 1, wherein said casing is provided with a discharge port for discharging said foreign matter, and said discharge port is positioned on the most downstream side when viewed from the direction of gravitational acceleration.

前記窪み部が形成される前記螺旋は、前記歯先の面の軸方向幅に応じて、軸方向に間隔を存した複数のもので構成されることを特徴とする請求項１または請求項２記載のスクリューポンプ。 Claim 1 or Claim 2 , wherein the spiral on which the recessed portion is formed is composed of a plurality of spirals spaced apart in the axial direction according to the axial width of the surface of the tooth tip. The described screw pump.

前記各螺旋歯の歯先の面の単位面積に対する、前記窪み部の開口面の単位面積の比が０．１～０．６の範囲に設定されることを特徴とする請求項１または請求項２記載のスクリューポンプ。 1 or 2, wherein the ratio of the unit area of the opening surface of the recess to the unit area of the top surface of each spiral tooth is set within a range of 0.1 to 0.6. 2. The screw pump according to claim 2 .

請求項１または請求項２記載のスクリューポンプにおいて、
前記窪み部は、前記各螺旋歯の歯先エッジ部の稜線に平行な螺旋に沿ってのびる凹溝状のものを含み、
前記ケーシングの軸方向一端側に位置する前記窪み部の壁面と歯先の面とがなす角度が３０度～９０度の範囲に設定されることを特徴とするスクリューポンプ。 In the screw pump according to claim 1 or claim 2,
The recess includes a recessed groove extending along a spiral parallel to the ridgeline of the tip edge of each spiral tooth,
A screw pump according to claim 1, wherein an angle between a wall surface of said recess located at one axial end of said casing and a surface of a tooth tip is set within a range of 30 degrees to 90 degrees.

前記ケーシングの軸方向一端側に位置する前記窪み部の壁面と歯先の面とがなす角度と、前記ケーシングの軸方向他端側に位置する前記窪み部の壁面と歯先の面とがなす角度との和が９０度以下に設定されることを特徴とする請求項５記載のスクリューポンプ。 The angle formed between the wall surface of the recess located on one axial end side of the casing and the surface of the tooth tip, and the angle formed between the wall surface of the recess located on the other axial end side of the casing and the surface of the tooth tip. 6. The screw pump according to claim 5, wherein the sum with the angle is set to 90 degrees or less.

前記一対のスクリューロータの各回転軸に突部が夫々形成され、両スクリューロータの相対回転時に一方のスクリューロータの回転軸に形成した突部が他方のスクリューロータの歯先の面に形成した窪み部内に進入するように構成したことを特徴とする請求項５または請求項６記載のスクリューポンプ。 A protrusion is formed on each of the rotating shafts of the pair of screw rotors, and the protrusion formed on the rotating shaft of one screw rotor when the two screw rotors rotate relative to each other forms a depression formed on the tooth tip surface of the other screw rotor. 7. The screw pump according to claim 5 or 6, wherein the screw pump is constructed so as to enter into a portion.