JP2008280977A - Turbo molecular pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a turbo molecular pump capable of reducing a backflow of gas molecules and improving a discharge function. <P>SOLUTION: A plurality of stages of stationary blades 11 are arranged to surround an outer peripheral face of a rotor 20 having a plurality of stages of rotary blades 21 formed thereon. Each of the stationary blades 11 is held at a predetermined interval by a spacer 13 and is alternately disposed with respect to the rotary blades 21 in the direction of a rotational axis. By providing a means having a labyrinth effect between an outer peripheral side end face of the rotary blades 21 and an inner peripheral face of the spacer 13 opposing thereto, the backflow of the gas molecules is reduced, and the discharge function is improved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a turbo molecular pump.

  The turbo-molecular pump performs evacuation by rotating a rotating blade at a high speed with respect to a fixed blade (see, for example, Patent Document 1). Since the rotating body is supported in a non-contact manner by a magnetic bearing, it is necessary to provide a gap between the rotating body and its peripheral components. Therefore, gaps are also formed between the fixed blade tip and the rotor side surface facing it, and between the rotor blade tip and the spacer side surface facing it. This gap is set in consideration of centrifugal force expansion, thermal expansion, component tolerance, and the like of the rotating body so as to reliably prevent contact between the rotating side and the stationary side.

JP 2005-105846 A

  However, since gas molecules flow backward in the direction opposite to the exhaust direction from the gap, there is a problem that the exhaust performance is reduced by that amount.

The turbo molecular pump according to the first aspect of the present invention is arranged so as to surround the rotor outer peripheral surface and the plurality of stages of rotor blades formed on the outer peripheral surface of the rotor, and alternately in the rotation axis direction with respect to the plurality of rotor blades. A plurality of stages of fixed blades, a spacer ring that maintains a predetermined axial interval between the plurality of stages of fixed blades, an outer peripheral end face of the rotor blade, and an inner periphery of the spacer ring that faces the outer peripheral end face A means having a labyrinth effect is provided between the surface and the surface.
A turbo molecular pump according to a second aspect of the present invention is arranged so as to surround a plurality of stages of rotor blades formed on the outer peripheral surface of the rotor and the rotor outer peripheral surface, and alternately in the rotation axis direction with respect to the plurality of rotor blades. A plurality of stages of fixed blades, a spacer ring that maintains the axial spacing of each of the plurality of stages of fixed blades at a predetermined interval, an inner peripheral end surface of the fixed blade, and an outer periphery of the rotor facing the inner peripheral end surface A means having a labyrinth effect is provided between the surface and the surface.
According to a third aspect of the present invention, in the turbo molecular pump according to the first or second aspect, the means having the labyrinth effect is any one of the inner peripheral side end surface of the fixed blade and the rotor outer peripheral surface facing the inner peripheral side end surface. And a convex portion formed on the other side, and at the time of rotation of the rotor, at least a part of the convex portion enters the concave portion.
According to a fourth aspect of the present invention, in the turbo molecular pump according to the second aspect, the means having the labyrinth effect is a thread groove formed on the inner peripheral side end surface of the fixed blade or the rotor outer peripheral surface facing the inner peripheral side end surface. It is characterized by providing.

  According to the present invention, exhaust performance can be improved by reducing the backflow of gas molecules.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a view showing an embodiment of a turbo molecular pump according to the present invention, and is a cross-sectional view of a pump body 1. The turbo molecular pump includes a pump main body 1 shown in FIG. 1 and a controller (not shown) that supplies power to the pump main body 1 to control rotational driving.

  Inside the casing 3 of the pump body 1, a rotating body composed of a rotor 20 and a shaft 7 that are bolted to each other is provided. The shaft 7 to which the rotor 20 is fixed is supported in a non-contact manner by a pair of upper and lower radial magnetic bearings 31 and 32 and a thrust magnetic bearing 33 provided on the stator column 10 a of the base 10, and is driven to rotate by the motor 6. When the pump is stopped (when magnetic levitation is stopped) or when a power failure occurs, the shaft 7 is supported by protective touch-down bearings 26 and 27.

  The rotor 20 is formed with a plurality of stages of rotating blades 21 and a rotating cylindrical portion 22. On the other hand, on the base 10 side, a plurality of ring-shaped spacers 13 are stacked along the inner peripheral surface of the casing 3, and a plurality of stages of fixed blades 11 are provided so as to be sandwiched between the spacers 13. Furthermore, a fixed cylindrical portion 12 having a spiral groove formed on the inner peripheral surface is provided at the lower portion of the plurality of fixed wings 11. In the turbo molecular pump shown in FIG. 1, the manufacturing method is different between the first to fourth stage stationary blades 11 and the fifth to eighth stage stationary blades 11, and the shapes are also different as described later. .

  In the turbo molecular pump of the present embodiment, a turbine blade portion is configured by a plurality of stages of rotating blades 21 and a plurality of stages of fixed blades 11 arranged alternately in the axial direction. The molecular drag pump unit is configured by the above. The rotating cylindrical portion 22 is provided close to the inner peripheral surface of the fixed cylindrical portion 12, and a spiral groove is formed on the inner peripheral surface of the fixed cylindrical portion 12. In the molecular drag pump unit, the exhaust function by the viscous flow is performed by the spiral groove of the fixed cylindrical unit 12 and the rotating cylindrical unit 22 rotating at high speed.

  The turbo molecular pump in which the turbine blade part and the molecular drag pump part shown in FIG. 1 are combined is called a wide area turbo molecular pump. The gas molecules flowing in from the intake port 14 are knocked down by the turbine blades and are compressed and exhausted toward the downstream side. The compressed gas molecules are further compressed by the molecular drag pump unit and discharged from the exhaust port 15.

  FIG. 2 is a view showing a detailed structure of the tip portions of the rotary blade 21 and the fixed blade 11 shown in FIG. FIG. 2A shows the first-stage rotary blade 21 and the fixed blade 11 from the top, and the second to fourth stages have the same shape. On the other hand, FIG. 2B shows the seventh-stage rotary blade 21 and the fixed blade 11 from the top, and the fifth, sixth, and eighth stages have the same shape.

  As shown in FIGS. 2A and 2B, a concave portion 21 b is formed at the tip of each rotary blade 21 formed in the rotor 20. A convex portion 13a is formed on the inner peripheral surface of the spacer 13 disposed on the outer peripheral side of the tip of the rotary blade 21 so as to face the concave portion 21b. On the other hand, in the case of the fixed wing 11, a recess 11b is formed at the tip on the inner peripheral side. And the convex part 20a is formed in the surface which the recessed part 11b of the rotor 20 opposes over a round.

  FIG. 3A shows a view when the tip of the rotary blade 21 is viewed from the side of the spacer 13 as indicated by an arrow B in FIG. The rotor blades 21 are blades having a predetermined blade angle, and a plurality of rotor blades 21 are arranged at predetermined intervals in the circumferential direction. The convex portion 13a formed on the inner peripheral surface of the spacer 13 is a ring-shaped convex portion, and is formed at a position facing the concave portion 21b of each rotary blade 21 as indicated by a two-dot chain line.

  FIG. 3B is a perspective view showing a part of the fixed wing 11 provided in the first to fourth stages. The fixed wing 11 is a semi-ring shaped plate-like member, and by using a pair of the half ring-shaped fixed wings 11, the ring-shaped fixed wing 11 for one stage is configured. As a method of forming the fixed wing 11, there are generally a method of forming a thin plate material by bending and a method of forming a thick plate material by cutting.

  In the case of the fixed blade 11 shown in FIG. 3B, it is formed by cutting. That is, by forming a plurality of oblique through holes 113 by cutting in a semi-ring-shaped plate material, an inner peripheral rib portion 114, an outer peripheral rib portion 116, and a wing portion 110a connecting them are formed. . A portion remaining between the through hole 113 and the adjacent through hole 113 forms a wing part 110a. On the inner peripheral surface of the inner peripheral rib portion 114, the above-described recess 11b is formed in a semi-ring shape in the circumferential direction.

  As shown in FIG. 2A, the fixed wing 11 is positioned at a predetermined position by sandwiching the outer peripheral rib portion 116 with the spacer 13. At this time, the concave portion 11b formed on the inner peripheral surface of the inner peripheral rib portion 114 faces the convex portion 20a on the outer periphery of the rotor.

  On the other hand, a fixed wing by bending is adopted as the fixed wing 11 arranged below the fifth stage. FIG. 4 is a perspective view showing the fixed wing 11 by bending, and one half of the ring-shaped fixed wing 11 is constituted by using two semi-ring-shaped fixed wings 11. The fixed wing 11 is provided with an inner peripheral rib portion 111 and an outer peripheral rib portion 112, and a plurality of blades 110b are formed between them.

  Although not shown in FIG. 2, each blade 110 b is supported by the outer peripheral rib portion 112 and the inner peripheral rib portion 111 through a narrow support portion. A predetermined blade angle is formed on the blade 110b by bending the blade 110b so as to twist the support portion. As shown in FIG. 2B, when the outer peripheral rib portion 112 is sandwiched between the spacers 13, a part of the inner peripheral rib portion 111 enters the recess 20 b formed on the outer periphery of the rotor 20. In addition, at the time of a stop, the inner peripheral rib part 111 does not need to enter into the recessed part 20b.

  Note that FIG. 2 describes the state in which the rotor 20 is stopped from rotating. In FIG. 2A, between the rotor blade tip and the convex portion 13a and between the fixed blade tip and the convex portion 20a. There is a gap between them. A gap is also formed between the tip of the fixed blade of FIG. 2B and the convex portion 13a.

  FIG. 5A shows a rotor blade 50 of a conventional turbomolecular pump, and FIG. 5B shows a rotor blade 21 according to the present embodiment. When the pump is actually used, the rotor 20 undergoes centrifugal expansion due to rotation. In FIG. 5, the solid line shows the situation at the time of rotation, and the broken line shows the situation at the time of stop.

  In FIG. 5A, when the rotor rotates, the gap between the rotary blade 50 and the spacer 13 is ΔG1, and the gap between the fixed blade 51 and the rotor 20 is ΔG4. The dimensions of the rotary blade 50 and the fixed blade 51 are set so that these gaps ΔG1 and ΔG4 are at least larger than the gap of the magnetic bearing portion.

By the way, if the gap is large, the back flow rate of the gas molecules increases and the exhaust performance is reduced. If the probability that a numerator will pass from the inlet side to the exhaust side is M12, and conversely, the probability that the numerator will pass from the exhaust side to the inlet side is M21, it will be between the inlet side pressure P1 and the outlet side pressure P2. Has a relationship as shown in the following equation (1). Therefore, in terms of exhaust performance, it is preferable to make the gap as small as possible.
P2 / Pl = M12 / M21 (1)

  However, the above-described gaps ΔG1 and ΔG4 are set to be at least larger than the gap of the magnetic bearing portion, and cannot be zero. Therefore, in the present embodiment, as shown in FIG. 5B, the gap between the rotary blade 21 and the spacer 13 and the gap between the fixed blade 11 and the rotor 20 have a labyrinth structure, thereby affecting the influence of the gap. To improve the exhaust performance.

In order to make the structure in which the exhaust port side cannot be seen from the intake port side in the gaps ΔG1 and ΔG2 at the tip of the rotor blade, the following relationship exists between the dimensions ΔG2 and Aout shown in FIG. It only has to be established.
ΔG2 ≦ Aout (2)

The gaps ΔG1 and ΔG2 need to be set larger than the gap of the magnetic bearing portion, and here, the value is ΔG (= ΔG1 = ΔG2). Then, since “Aout = h1 (height of the convex portion 13a)”, Expression (2) becomes Expression (3) below.
h1 = Aout ≧ ΔG (3)

Here, assuming that the radius of the inner periphery of the spacer 13 is Rout, the radius of the rotating blade 21 at the time of stop is rout, and the expansion of the radius at the time of rotation is Δr, Rout and rout are set so that the following expression (4) is satisfied. Set it.
ΔG + Δr = Rout−rout (4)

On the other hand, the tip of the fixed wing 11 may be set in the same manner. That is, the following equation (5) may be established for the gap ΔG4. In this case as well, if ΔG3 = ΔG4 = ΔG is set, “Ain = h2” is obtained, and therefore Equation (5) becomes Equation (6). The gap ΔG3 at the time of stop is set as ΔG + Δr. 2A can be similarly applied to the rotary blade 21 and the fixed blade 11 shown in FIG. 2B.
ΔG4 ≦ Ain (5)
h2 = Ain ≧ ΔG (6)

  FIG. 6 is a view showing a modified example, and (a) shows the first-stage rotary blade 21 and fixed blade 11 from the top, as in (a) of FIG. 2, and (b) shows C It is an arrow view. In the modified example, the thread groove 117 is employed in the labyrinth structure at the tip on the inner peripheral side of the fixed wing 11. That is, the thread groove 117 is formed on the inner peripheral surface of the fixed blade 11 that faces the rotor 20. As shown in FIG. 6B, a plurality of grooves 117a inclined in the oblique direction are formed in the thread groove 117, and the grooves 117a and the protrusions 117b are alternately arranged.

  When the rotor 20 rotates in the R direction with respect to the thread groove 117, an exhaust action similar to that of the molecular drag pump shown in FIG. 1 occurs. Therefore, in addition to the labyrinth effect for preventing backflow, it also has the effect of positively exhausting the gas downstream, so the backflow prevention action is superior to the labyrinth structure shown in FIG. The exhaust action of the thread groove 117 is more effective as it is closer to the exhaust port side. In the case of the modification, the thread groove 117 need only be formed on the fixed blade 11 side, and it is not necessary to form a convex portion on the rotor 20 side. Even if the thread groove 117 is formed on the rotor 20 side, the same effect can be obtained.

  As described above, in the turbo molecular pump of the present embodiment, the tip portions of the rotary blade 21 and the fixed blade 11 have a labyrinth structure, thereby preventing a straight backflow of gas and improving exhaust performance. it can. In addition, since the gap ΔG can be set larger than in the prior art, it is possible to prevent the rotating body from contacting when a disturbance is applied. Further, the exhaust performance can be further improved by using the labyrinth structure as the thread groove 117 as in the modification.

  In the configuration shown in FIG. 2 (a), a concave portion is formed at the tip of the rotary blade 21 and the fixed blade 11, and a convex portion is formed on the spacer 13 and the rotor 20 opposite to them. 21 and the tip of the fixed wing 11 may be formed with a convex portion, and the spacer 13 and the rotor 20 may be formed with a concave portion. Moreover, you may be the structure by which a part of convex part 20a, 13a is inserted in recessed part 11b, 21b at the time of a stop.

  In the above-described embodiment, the hybrid turbo molecular pump has been described as an example, but the present invention can be similarly applied to an all-blade type turbo molecular pump. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

1 is a cross-sectional view showing an embodiment of a turbo molecular pump according to the present invention. It is a figure which shows the labyrinth structure of the rotary blade 21 and the fixed wing | blade 11, (a) shows the 1st stage | paragraph rotary blade 21 and the fixed wing | blade 11 from the top, (b) is the 2nd stage rotation from the bottom. The wing | blade 21 and the fixed wing | blade 11 are shown. (A) is a figure which shows the structure of the outer peripheral part of the rotary blade 21, (b) is a figure which shows the structure of the inner peripheral side of the fixed blade 11. FIG. It is a perspective view which shows the fixed wing | blade 11 by a bending process. It is a figure which compares and shows the time of a rotor rotation, and the time of a stop, (a) shows the rotary blade 50 of the conventional turbomolecular pump, (b) shows the rotary blade 21 by this Embodiment. It is a figure which shows a modification.

Explanation of symbols

  1: pump body, 11, 51: fixed blade, 13: spacer, 13a, 20a, 117b: convex portion, 20: rotor, 21, 50: rotary blade, 21b: concave portion, 22: rotating cylindrical portion, 10: base, 11: fixed wing, 12 fixed cylindrical part, 110a: wing part, 110b: blade, 113: through hole, 111, 114: inner peripheral side rib part, 112, 116: outer peripheral side rib part, 117: screw groove part, 117a: groove

Claims (4)

A plurality of rotor blades formed on the outer peripheral surface of the rotor;
A plurality of fixed blades disposed so as to surround the rotor outer peripheral surface, and alternately disposed in a rotation axis direction with respect to the plurality of rotor blades;
A spacer ring that keeps the axial interval of each of the plurality of fixed blades at a predetermined interval;
A turbo-molecular pump comprising means having a labyrinth effect between an outer peripheral end face of the rotor blade and an inner peripheral face of the spacer ring facing the outer peripheral end face. A plurality of rotor blades formed on the outer peripheral surface of the rotor;
A plurality of fixed blades disposed so as to surround the rotor outer peripheral surface, and alternately disposed in a rotation axis direction with respect to the plurality of rotor blades;
A spacer ring that keeps the axial interval of each of the plurality of fixed blades at a predetermined interval;
A turbo-molecular pump comprising means having a labyrinth effect between an inner peripheral side end surface of the fixed blade and the rotor outer peripheral surface facing the inner peripheral side end surface. The turbo molecular pump according to claim 1 or 2,
The means having the labyrinth effect includes a concave portion formed on one of the inner peripheral side end surface of the fixed wing and the outer peripheral surface of the rotor facing the inner peripheral side end surface, and a convex portion formed on the other side. ,
A turbo-molecular pump characterized in that at least a part of the convex portion enters the concave portion when the rotor rotates. The turbo-molecular pump according to claim 2,
The turbo molecular pump according to claim 1, wherein the unit having the labyrinth effect includes a thread groove formed on an inner peripheral side end surface of the fixed blade or an outer peripheral surface of the rotor facing the inner peripheral side end surface.

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