JP5115627B2 - Turbo molecular pump - Google Patents

Description

  The present invention relates to a turbo molecular pump.

  Conventionally, there is known a turbo molecular pump in which a turbine blade portion is constituted by a plurality of stages of rotating blades and fixed blades, and a molecular drag pump portion is constituted by a rotating cylinder and a fixed cylinder (for example, Patent Documents). 1). In the turbo molecular pump described in Patent Document 1, the depth of the thread groove provided in the fixed cylinder is increased on the suction side.

JP 2000-516321 (particularly FIG. 1)

  By the way, in this kind of turbo molecular pump, in order to maintain an appropriate axial clearance between the rotor blades and the stationary blades, spacers are provided at the support portions of the respective stationary blades, and the spacers and the stationary blades are laminated. The body is formed. In such a configuration, since the base member is generally arranged separately around the laminate and the fixed cylinder, the laminate and the fixed cylinder are supported separately from the case member, and between the laminate and the fixed cylinder. A discontinuity of the gas passage occurs. As a result, even if the depth of the thread groove of the fixed cylinder is increased on the suction side as described in Patent Document 1, smooth flow is prevented between the laminate and the fixed cylinder, and the exhaust efficiency is reduced.

A turbo molecular pump according to the present invention includes a rotating body in which a plurality of stages of rotating blades are formed in the axial direction and a rotating cylindrical portion is provided on the exhaust side, a plurality of stages of fixed blades and spacers arranged around the rotating blades, Between the fixed cylinder and the fixed blade at the exhaust-side final stage. A final-stage spacer is provided, and the axial end surface of the fixed cylinder is provided in contact with the end surface of the final-stage spacer, and the diameter of the valley bottom of the spiral groove at this contact portion is disposed immediately upstream of the fixed cylinder. It is formed larger than the outer diameter of the rotor blade at the exhaust side final stage or the outer diameter of the blade portion of the fixed blade at the exhaust side final stage.
The diameter of the valley bottom of the spiral groove in the contact portion can be formed substantially equal to the inner diameter of the final stage spacer.
The last stage spacer is preferably sandwiched between the fixed cylinder and the stationary blade on the exhaust side last stage.
The first case member covering the periphery of the laminate, the second case member covering the periphery of the fixed cylinder, the first case member and the second case member are fastened, and the intake side of the first case member It is good also as what has a fastening device which pinches | interposes a laminated body and a fixed cylinder between an axial direction edge part and the suction side axial direction edge part of a 2nd case member.
The groove bottom surface on the intake side of the spiral groove is preferably formed in a taper shape in the axial direction so that the angle formed with the axis is 45 ° or less.
A plurality of spiral grooves can be formed in the circumferential direction, and the number of spiral grooves can be increased on the intake side than on the exhaust side.
The outer diameter of the rotor blade at the exhaust-side final stage may be made smaller than the outer diameter of the rotor blade at the upstream side, and the inner diameter of the final-stage spacer may be made smaller than the inner diameter of the spacer at the upstream side.

  According to the present invention, since the gas passage is continuously provided from the laminated body to the fixed cylinder, the gas flow becomes smooth and the exhaust efficiency can be improved.

The figure which shows the whole structure of the turbo-molecular pump which concerns on embodiment of this invention. The principal part enlarged view of FIG. The perspective view of the fixed cylinder of FIG. The figure which shows the comparative example of FIG. The figure explaining operation | movement of this invention. The figure which shows the modification of FIG.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
FIG. 1 is a cross-sectional view schematically showing an overall configuration of a turbo molecular pump according to an embodiment of the present invention. This turbo molecular pump is, for example, a vacuum pump used in a semiconductor manufacturing apparatus. For convenience of explanation, the vertical direction of the turbo molecular pump is defined below as shown in the figure.

  A turbo molecular pump T shown in FIG. 1 includes a base 1, a substantially cylindrical casing 2 disposed on the upper surface of the base 1, and a rotor housed in the base 1 and the casing 2 and rotatably supported by the base 1. 3. The upper end flange portion 2a of the casing 2 is fastened by a bolt to a flange of a vacuum chamber on the semiconductor manufacturing apparatus side (not shown). The lower end surface of the casing 2 is fastened with bolts 42 to the upper surface of the base 1 via an O-ring 41.

  A plurality of stages of rotary blades 31 are formed on the outer peripheral portion of the rotor 3 at intervals in the vertical direction. Between the rotating blades 31 of each stage, the fixed blades 21 are alternately inserted from the outer peripheral side. The fixed wings 21 of each stage are stacked via spacers 22, and a stacked body 23 is formed by the fixed wings 21 and the spacers 22. The spacer 22 has a substantially ring shape, and the fixed wing 21 is formed on a wing portion composed of a plurality of wing bodies extending in the radial direction of the rotor 3 and an outer peripheral portion of the wing portion, and is sandwiched by the spacer 22. And a half crack shape divided into two in the circumferential direction.

  A rotating cylindrical portion 32 is provided below the rotor blade 31 of the rotor 3. The rotating blade 31 is partially formed on the circumferential surface of the rotor 3, while the rotating cylindrical portion 32 is provided over the entire circumference. For this reason, in order to obtain sufficient strength of the rotor 3, the diameter of the rotating cylindrical portion 32 is smaller than the outer diameter of the rotating blade 31. A fixed cylinder 24 is disposed around the rotating cylinder portion 32, and a spiral groove 25 is formed on the inner peripheral surface of the fixed cylinder 24. The rotary blade 31 and the fixed blade 21 described above constitute a turbine blade portion, and the rotary cylinder portion 32 and the fixed cylinder 24 constitute a molecular drag pump portion.

  The rotor 3 is supported in a non-contact manner by a pair of upper and lower radial magnetic bearings 51 and a thrust magnetic bearing 52 and is driven to rotate by a motor 53. The motor 53 is constituted by a DC brushless motor, for example. That is, a permanent magnet is built in the rotating shaft 33 of the rotor 3, and a motor stator for forming a rotating magnetic field is disposed around the rotating shaft 33. The base 1 is provided with an emergency mechanical bearing 54, and the rotating shaft 33 is supported by the mecha bearing 54 when an abnormality occurs in the magnetic bearings 51 and 52.

  In such a turbo molecular pump, when the rotor 3 is rotated at a high speed by driving the motor 53, gas molecules are sucked from the intake port 11. The sucked gas molecules are compressed through the gas passages of the turbine blade part and the molecular drag pump part, respectively, and are exhausted from the exhaust port 12. Due to the flow of gas molecules, the intake port 11 side (upstream side) is in a high vacuum state.

  In this case, the turbine blade part mainly performs exhaust by molecular flow, and the molecular drag pump part mainly performs exhaust by viscous flow. That is, since the pressure increases on the exhaust side (downstream side) of the turbine blade, intermolecular collisions occur frequently, and the rotating blade 31 that rotates at high speed creates a macro flow field toward the exhaust side and the outer peripheral side. Transition to the current. Note that exhaust is performed by an intermediate flow in which a molecular flow and a viscous flow are mixed from the exhaust side of the turbine blade portion to the intake side of the molecular drag pump portion.

  In such a turbo molecular pump, the configuration of the gas passage changes from the turbine blade portion to the molecular drag pump portion, and thus a flow loss is likely to occur. Therefore, the present embodiment is configured as follows in order to reduce the flow loss.

  FIG. 2 is an enlarged view of a main part of FIG. As shown in FIG. 2, a flange surface 13 is formed on the upper surface of the base 1, and a flange surface 14 is formed on the inner diameter side via a peripheral wall 15. A flange portion 27 is provided at the upper end portion of the fixed cylinder 24, and the outer peripheral surface of the flange portion 27 expands to the outer diameter side. The flange portion 27 of the fixed cylinder 24 is fitted to the peripheral wall 15 of the base 1, and the end surface of the flange portion 27 is in contact with the flange surface 14 of the base 1. The flange surface 13 is a flange surface for fastening the bolt 41, and the bottom surface of the casing 2 faces the flange surface 13.

  A lowermost spacer 22 (lowermost spacer 221) is disposed above the fixed cylinder 24, and the upper surface of the fixed cylinder 24 and the lower surface of the lowermost spacer 221 are in contact with each other. The lower end of the lowermost spacer 221 is fitted to the outer peripheral surface of the flange portion of the fixed cylinder 24, and the lowermost spacer 221 is positioned with respect to the base 1 via the fixed cylinder 24. A fixed blade 21 (lowermost fixed blade 211) is disposed above the lowermost spacer 221, and a spacer 22 (222) is further disposed above the lowermost spacer 221, and the upper surface of the lowermost spacer 221 and the bottom surface of the lowermost fixed blade 211, The upper surface of the lowermost fixed blade 21 and the bottom surface of the spacer 222 are in contact with each other.

  The spacers 22 and the fixed wings 21 are alternately stacked until reaching the uppermost spacer 223 (FIG. 1), so that a stacked body 23 is formed as a whole. The spacer 22 regulates the position of the fixed wing 21 in the axial direction and is fitted to the outer peripheral surface of the lower fixed wing 21 to regulate the position of the fixed wing 21 in the circumferential direction. Wings 21 are positioned with respect to the base 1. Each spacer 22 is formed with a predetermined thickness so that the clearance between the fixed blade 21 and the rotary blade 31 has an appropriate value.

  Between the lowermost fixed blade 211 and the fixed cylinder 24, the rotary blade 31 (lowermost rotary blade 311) is disposed. The outer diameter of the lowermost rotor blade 311 is smaller than the outer diameter of the upper rotor blade 31, and the inner diameter of the lowermost spacer 221 is correspondingly smaller than the inner diameter of the upper spacer 22. ing.

  FIG. 3 is a perspective view showing the configuration of the spiral groove 25 of the fixed cylinder 24. A plurality of spiral grooves 25 are provided at equal intervals in the circumferential direction. The depth of each spiral groove 25 increases toward the intake side, and the groove bottom surface 26 of the fixed cylinder 24 has a tapered shape as shown in FIG. 2, and the inclination of the groove bottom surface 26 is on the intake side (intake portion 26a). It is steeper than the exhaust side. An angle α (FIG. 1) formed by the groove bottom surface 26 on the intake side and the axis is, for example, 45 ° or less.

  As shown in FIG. 2, the position of the groove bottom surface 26 at the intake side end of the fixed cylinder 24 and the position of the inner peripheral surface of the lowermost spacer 221 connected to this substantially coincide. That is, the diameter D0 (FIG. 3) of the bottom of the suction side end of the fixed cylinder 24 is substantially equal to the inner diameter D1 (FIG. 2) of the lowermost spacer 221. As a result, a gas passage is smoothly and continuously formed from the inner peripheral surface of the lowermost spacer 221 to the groove bottom surface 26 of the fixed cylinder 24.

  Next, an assembly procedure of the pump body T of the turbo molecular pump according to the present embodiment will be described. When assembling the pump body T shown in FIG. 1, first, the rotor 3 is rotatably supported on the base 1 via the magnetic bearings 51 and 52, and the fixed cylinder 24 is fitted inside the peripheral wall 15 of the base 1. Then, the flange portion 27 of the fixed cylinder 24 is brought into contact with the flange surface 14 of the base 1. As a result, the fixed cylinder 24 is positioned with respect to the base 1.

  Next, ring-shaped spacers 22 and half-cracked fixed blades 21 are alternately stacked on the upper surface of the fixed cylinder 24. The fixed blades 21 are stacked by being inserted between the rotating blades 31 of each stage from the outer side in the circumferential direction. At this time, the outer peripheral surface of each fixed blade 21 is fitted into the spacer 22. Thereby, each fixed wing | blade 21 can be positioned with respect to the base 1 through the spacer 22 and the fixed cylinder 24, respectively.

  When the spacer 22 has been laminated to the uppermost stage, the casing 2 is covered from above the uppermost spacer 223, and the flange surface 13 of the base 1 and the bottom surface of the casing 2 are fastened with bolts 42 via the O-ring 41. The O-ring 41 is crushed by the fastening force of the bolt 42 and the flange surface 13 is sealed. At this time, the upper end surface of the uppermost spacer 223 comes into contact with the step 2 b at the upper end of the casing 2. As a result, the laminate 23 and the fixed cylinder 24 are sandwiched between the upper end portion (step portion 2 b) of the casing 2 and the upper end portion (flange surface 14) of the base 1 by fastening the bolts 42.

  In the turbo molecular pump assembled in this way, the upper end surface of the fixed cylinder 24 is in contact with the lower end surface of the lowermost spacer 221, and the diameter D0 of the valley on the intake side of the fixed cylinder 24 is the inner diameter of the lowermost spacer 221. It is almost equal to D1. For this reason, the gas molecules flowing in from the intake port 1a due to the rotation of the rotor 3 smoothly flow from the turbine blade portion to the molecular drag pump portion as shown by the arrows in FIG. To do.

  FIG. 4 is a diagram showing a comparative example of the present embodiment. In this example, the flange portion 27 of the fixed cylinder 24 is fastened to the flange surface 14 of the base 1 with bolts (not shown), and the flange surface 151 is provided on the peripheral wall 15 of the base 1 to support the spacer 22 from the flange surface 151. ing. In this case, the fixed cylinder 24 and the laminated body 23 are separately supported from the base 1, and the upper end surface of the fixed cylinder 24 and the lowermost spacer 221 are not in contact with each other. As a result, the gas passage becomes discontinuous from the stacked body 23 (lowermost spacer 221) to the fixed cylinder 24, the smooth flow of molecules is hindered as shown by the arrows in FIG. 4, and the exhaust efficiency is lowered.

  In the present embodiment, since the taper angle α of the groove bottom surface 26 on the intake side of the fixed cylinder 24 is 45 ° or less, the exhaust efficiency can be improved even when the molecular flow on the intake side of the fixed cylinder 24 is taken into consideration. That is, in the case of the molecular flow, as shown in FIG. 5, the molecules flowing into the spiral groove 25 collide with the groove bottom surface 26 and are reflected. Since the reflection direction at this time is determined by the cosine theorem, when the taper angle α is large, the molecular weight flowing back to the turbine blade increases. In this regard, when the taper angle α is set to 45 ° or less, most of the molecules are reflected toward the rotating cylindrical portion 32, so that backflow is suppressed and exhaust efficiency is improved.

According to the above embodiment, the following effects can be obtained.
(1) The axial end surface of the fixed cylinder 24 is provided in contact with the end surface of the lowermost spacer 221, and the diameter D0 of the valley bottom of the spiral groove 25 at this contact portion is substantially equal to the inner diameter D1 of the lowermost spacer 221. Thereby, since the gas passage is continuously provided from the laminate 23 to the fixed cylinder 24, the gas flow from the turbine blade portion to the molecular drag pump portion becomes smooth, and the exhaust efficiency is improved.
(2) Since the lowermost spacer 221 is sandwiched between the fixed cylinder 24 and the lowermost fixed blade 211, the fixed cylinder 24 and the lowermost spacer 221 are in close contact with each other, and the flow loss is small. Further, it is not necessary to separately provide a support portion for the lowermost spacer 221 on the base 1, and the configuration can be simplified.
(3) By fastening the base 1 and the casing 2 with the bolts 42, the laminate 23 and the fixed cylinder 24 are placed between the upper end portion (step portion 2 b) of the casing 2 and the upper end portion (flange surface 14) of the base 1. Because it is sandwiched, assembly is easy.

(4) Since the taper angle α of the groove bottom surface 26 on the intake side of the fixed cylinder 24 is set to 45 ° or less, the backflow of the molecules flowing into the spiral groove 25 to the turbine blade can be suppressed, and the exhaust of the molecular flow region is performed. Efficiency can be improved.
(5) Since the taper angle α of the groove bottom surface 26 is increased at the intake portion 26a, the depth of the spiral groove 25 becomes deeper on the intake side. As a result, conductance increases and it is easy to incorporate molecular flow.
(6) The outer diameter of the lowermost rotor blade 311 is made smaller than the outer diameter of the upper rotor blade 31, and the inner diameter of the lowermost spacer 221 is made smaller than the inner diameter of the upper spacer 22. As a result, the difference in outer diameter between the lowermost rotating blade 311 and the rotating cylindrical portion 32 is reduced, so that the groove 25 can be prevented from becoming too deep. As a result, the molecules flowing in from the rotor blade 31 side are easily reflected from the fixed cylinder 24 to the rotor cylinder 32, and the backflow to the turbine blade section can be suppressed.

  The depth of the spiral groove 25 may be set as appropriate in consideration of the gas flow rate and pressure. For example, when the flow rate is large or the pressure is high, the viscous flow is dominant. Therefore, the helical groove 25 may be shallowed to give priority to gas compressibility. When the flow rate is small or when the pressure is low, the influence of the molecular flow is large, so the spiral groove 25 may be deepened to increase the conductance. In the present embodiment, the taper angle α of the groove bottom surface 26 of the spiral groove 25 is changed in two stages, but the configuration of the spiral groove 25 is not limited to this.

  In the above embodiment, the spiral grooves 25 are provided at equal intervals in the circumferential direction on the inner peripheral surface of the fixed cylinder 24 (FIG. 5), but the number of spiral grooves 25 may be different on the intake side and the exhaust side. . An example is shown in FIG. FIG. 6 is an example in which the number of spiral grooves 25 is increased only by the intake portion 26a (FIG. 2). The spiral grooves 251 and 252 adjacent in the circumferential direction are joined together to form the spiral groove 253, and the spiral groove on the intake side. The number (25) of 25 is twice the number (6) of spiral grooves 25 on the exhaust side. As a result, the groove width of the intake portion 26a is narrowed to prevent backflow of molecules, and it is possible to prevent the groove width from becoming too narrow on the exhaust side, so that an optimal groove design is possible.

  In the above embodiment, the diameter D0 of the valley bottom of the spiral groove 25 is made substantially equal to the inner diameter D1 of the lowermost spacer 221 as the final spacer, but D0 is at least the lowermost stage disposed on the upstream side of the fixed cylinder 24. As long as it is larger than the outer diameter of the rotary blade 311, D0 and D1 may not be equal. Although the rotary blade 311 is disposed immediately upstream of the fixed cylinder 24, the fixed blade 211 may be disposed. In this case, D0 may be made larger than the outer diameter of the blade portion of the lowermost fixed blade 211. .

  The lowermost spacer 221 is sandwiched between the lowermost stationary blade 211 and the fixed cylinder 24. However, if the axial end surface of the fixed cylinder 24 and the end surface of the lowermost spacer 221 are provided in contact with each other, the lowermost spacer You may support 221 and the fixed cylinder 24 separately. The taper angle α of the intake portion 26a is set to 45 ° or less. However, when the viscous flow is dominant, the taper angle α may be larger than 45 °.

  The configuration of the casing 2 as the first case member and the configuration of the base 1 as the second case member are not limited to those described above. Although the base 1 and the casing 2 are fastened by the bolts 42, any fastening device may be used. Although the outer diameter of the lowermost fixed blade 311 is made smaller than the outer diameter of the fixed blade 31 thereabove, the configuration of the fixed blade is not limited to this.

  The configuration of the turbo molecular pump to which the present invention is applied is not limited to that shown in FIG. A plurality of stages of rotor blades 31 are formed in the axial direction, the rotor 3 is a rotating body provided with a rotating cylindrical portion 34 on the exhaust side, and a plurality of stages of fixed blades 21 and spacers 22 arranged around the rotor blades 31. It is also applicable to other turbo molecular pumps including a laminate 23 formed by laminating and a fixed cylinder 24 which is disposed around the rotary cylinder portion 32 and has a spiral groove 25 formed on the inner peripheral surface thereof. That is, the present invention is not limited to the turbo molecular pump of the embodiment as long as the features and functions of the present invention can be realized.

Claims (7)

A rotating body in which a plurality of rotating blades are formed in the axial direction and a rotating cylindrical portion is provided on the exhaust side;
A laminate formed by laminating a plurality of stages of fixed blades and spacers arranged around the rotor blades;
A fixed cylinder that is disposed around the rotating cylindrical portion and has a spiral groove formed on an inner peripheral surface thereof;
A final stage spacer is disposed between the fixed cylinder and the fixed blade of the final stage on the exhaust side,
The axial end surface of the fixed cylinder is provided in contact with the end surface of the final stage spacer, and the diameter of the valley bottom of the spiral groove at the contact portion is the exhaust side final stage disposed immediately upstream of the fixed cylinder. The turbo molecular pump is formed to be larger than the outer diameter of the rotor blade or the outer diameter of the blade portion of the stationary blade at the final stage of the exhaust side. The turbo-molecular pump according to claim 1,
Furthermore, the diameter of the valley bottom of the spiral groove in the contact portion is a turbo molecular pump formed to be substantially equal to the inner diameter of the final stage spacer. The turbo molecular pump according to claim 1 or 2,
The last stage spacer is a turbo molecular pump that is sandwiched between the fixed cylinder and the fixed blade of the last stage on the exhaust side. The turbomolecular pump according to claim 3,
A first case member covering the periphery of the laminate;
A second case member covering the periphery of the fixed cylinder;
Fastening the first case member and the second case member between the intake side axial end of the first case member and the intake side axial end of the second case member A turbo-molecular pump having a laminate and a fastening device for sandwiching the fixed cylinder. The turbo molecular pump according to any one of claims 1 to 4,
A turbo molecular pump in which a groove bottom surface on the intake side of the spiral groove is formed in a taper shape in the axial direction so that an angle formed with an axis is 45 ° or less. The turbomolecular pump according to any one of claims 1 to 5,
A plurality of the spiral grooves are formed in the circumferential direction, and the number of spiral grooves on the intake side is larger than the number of spiral grooves on the exhaust side. The turbo molecular pump according to any one of claims 1 to 6,
The turbo molecular pump in which the outer diameter of the rotor blade at the exhaust-side final stage is smaller than the outer diameter of the upstream rotor blade, and the inner diameter of the final-stage spacer is smaller than the inner diameter of the upstream spacer.

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