JP2012041857A - Turbo-molecular pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce breakdown torque when a rotor rotating at high speed is broken due to abnormal conditions.SOLUTION: The rotor shaft 5 has the fitting shaft 5a at the upper end thereof and the opening 4a for fitting passing through in a thickness direction is formed in the center of the rotor 4. The rotor 4 has not a part overlapping the fitting shaft 5a of the rotor 5 in an axial direction in the center, the rotor 4 and the fitting shaft 5a of the rotor shaft 5 are secured only by fitting by cooling or fitting by heating/cooling. The mass of the rotor 4 is reduced by the degree not having a bolt fastening part, thereby the breakdown torque can be reduced.

Description

  The present invention relates to a turbo molecular pump, for example.

A turbo molecular pump that obtains a high vacuum or an ultra-high vacuum rotates a rotor and a rotor shaft at high speed in a case member, and transfers gas molecules from an intake port side to an exhaust port side by a rotor blade and a stator blade. The rotor and the rotor shaft are, for example, 20,000 to 40,000 r. p. Since it is rotated at a high speed of m, a strong fixing structure is adopted.
In general, the rotor and the rotor shaft are superposed in the axial direction in a state where the shaft centers coincide with each other, and are fastened by a plurality of bolts.
A structure in which an opening that penetrates in the axial direction is provided at the center of the rotor, a penetration shaft that penetrates the opening of the rotor is provided in the upper part in the axial direction of the rotor shaft, and the rotor and the penetration shaft are fixed by shrink fitting Is also known (see, for example, Patent Document 1, paragraph [0040]). Also in this structure, a portion that overlaps in the axial direction is provided on the rotor and the rotor shaft, and these portions are fastened with bolts.

JP 2007-239464 A

In the turbo molecular pump described in the above-mentioned prior document, the rotor has a superposed portion for fastening to the rotor shaft with a bolt, and the mass is increased accordingly. The turbo molecular pump needs to ensure safety to the outside of the case member even if the rotor breaks down during operation.
Since the breaking torque of the rotor is proportional to the mass of the rotor, in the structure having the overlapping portion for fastening the bolt, the mass increases accordingly. Further, in the structure by bolt tightening, when the bolt is tightened, the mounting position is displaced due to the tolerance of the bolt outer diameter and the drill hole, so that an unbalance occurs when the rotor rotates.

  A turbo molecular pump according to the present invention is a turbo molecular pump that rotates a rotor shaft in a case member and a rotor fixed to the rotor shaft at a high speed to transfer gas molecules from the suction port side to the exhaust port side. Has a fitting shaft portion having a predetermined thickness in the axial direction at the upper end portion in the axial direction, and the rotor has a fitting opening for fitting into the fitting shaft portion of the rotor shaft. The shaft fitting shaft portion does not have a portion that overlaps in the axial direction, and the rotor shaft fitting shaft portion is fitted into the fitting opening of the rotor, and the rotor and the rotor shaft Is fixed by cold fitting or baking / cold fitting.

According to this invention, since the rotor does not have the overlapping portion for fastening the bolt, the rotor mass can be reduced correspondingly, and the breaking strength of the rotor can be reduced.
Moreover, since it is fixed by cold fitting or baking / cold fitting and not bolt fastening, it is possible to eliminate rotor imbalance caused by deviation at the time of bolt fastening.

Sectional drawing which shows Embodiment 1 of the turbo-molecular pump which concerns on this invention. Sectional drawing which shows Embodiment 2 of the turbo-molecular pump which concerns on this invention. Sectional drawing of the rotor axis | shaft cut | disconnected by the III-III line in FIG. Sectional drawing of the center part vicinity of the rotor cut | disconnected by the III-III line | wire in FIG.

(Embodiment 1)
The first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a magnetic bearing type turbo molecular pump. The turbo molecular pump 1 includes a case member 11 including an upper case 12 and a base 13. The upper case 12 and the base 13 are in close contact with each other via a seal member 42 and are sealed from the outside.

  A rotor shaft 5 is disposed on the central axis of the case member 11. On the rotor shaft 5, the rotor 4 attached coaxially with the rotor shaft 5 is disposed. As will be described in detail later, the rotor shaft 5 and the rotor 4 are firmly fixed by an interference fit so that the shaft center does not shift due to centrifugal force during high-speed rotation. The rotor shaft 5 is supported in a non-contact manner by a radial magnetic bearing 31 (two locations) and a thrust magnetic bearing 32 (upper and lower pair). The flying position of the rotor shaft 5 is detected by radial displacement sensors 33a and 33b and an axial displacement sensor 33c. The rotor shaft 5 magnetically levitated by the magnetic bearings 31 and 32 is rotated at a high speed by a motor 35.

  A rotor disk 38 is attached to the lower surface of the rotor shaft 5 via a mechanical bearing 34. A mechanical bearing 36 is provided on the upper side of the rotor shaft 5. The mechanical bearings 34 and 36 are emergency mechanical bearings, and the rotor shaft 5 is supported by the mechanical bearings 34 and 36 when the magnetic bearing is not operating.

The rotor 4 has a two-stage structure of an upper side and a lower side, and a plurality of stages of rotor blades 7 are provided on the upper side. The lower part from the lowermost rotor blade 7 is the lower side which is the rotor cylindrical part 9.
On the upper side of the rotor 4, the rotor blades 7 and the stator blades 6 are alternately stacked in the axial direction of the pump with ring-shaped spacers 21 therebetween. On the inner surface of the upper case 12, the spacers 21 and the stator blades 6 are alternately stacked on the upper surface of the base 13, and the upper case 12 is fixed to the base 13. The stator blade 6 is positioned between the case 12 and the stator blade 6.

  On the outer peripheral side of the rotor cylindrical portion 9 of the rotor 4, a ring-shaped screw stator 8 is fixed to the base 13 with bolts 41. The screw stator 8 has a spiral protrusion 8a, and a screw groove 8b is formed between the spiral protrusions 8a. A gap is provided between the outer peripheral surface of the rotor cylindrical portion 9 of the rotor 4 and the inner peripheral surface of the screw stator 8 so that gas molecules can be transferred downward from above when the rotor 4 rotates at high speed. .

  The base 13 is provided with an exhaust port 45, and a back pump is connected to the exhaust port 45. The rotor 4 is magnetically levitated, and in this state, the motor 35 is driven to rotate at high speed, whereby the gas molecules on the intake port 15 side are exhausted to the exhaust port 45 side.

  The turbo molecular pump 1 is a composite type turbo molecular pump having a blade exhaust part 2 in an internal space of an upper case 12 and a thread groove exhaust part 3 in an internal space of a base 13. The blade exhaust part 2 is composed of a plurality of stages of rotor blades 7 and a plurality of stages of stator blades 6, and the thread groove exhaust part 3 is composed of a rotor cylindrical part 9 and a screw stator 8.

  The flange 17 is attached to a flange of an exhaust system of a vacuum chamber (not shown) by a fastening member (not shown). When the rotor 4 is rotationally driven by the motor 35, gas molecules in the vacuum chamber flow from the intake port 15. The gas molecules flowing in from the intake port 15 are blown off downstream in the blade exhaust part 2. Although not shown, the rotor blades 7 and the stator blades 6 are oppositely inclined in the direction of the blades, and the inclination angle is changed from the front side, which is the high vacuum side, to the downstream side, which is the downstream side. Is formed to change at an angle that is difficult to reverse. The gas molecules are compressed in the blade exhaust part 2 and transferred to the screw groove exhaust part 3 below in the figure.

  In the thread groove exhaust portion 3, when the rotor cylindrical portion 9 rotates at a high speed with respect to the screw stator 8, an exhaust function by a viscous flow is generated, and the gas transferred from the blade exhaust portion 2 to the thread groove exhaust portion 3 is compressed. It is transferred to the exhaust port 45 and evacuated. In the present embodiment, the screw groove exhaust portion 3 having a screw groove configuration is used. However, a portion that exhibits an exhaust function by viscous flow, including configurations other than the screw groove configuration, may be referred to as a drag pump portion.

Details of the fixing structure of the rotor 4 and the rotor shaft 5 will be described.
The rotor 4 is made of, for example, an aluminum-based metal such as aluminum or an aluminum alloy. A cylindrical fitting opening 4 a penetrating in the thickness direction is formed at the center of the rotor 4. The rotor shaft 5 is formed in a cylindrical shape, and is made of, for example, steel such as chromium molybdenum steel (SCM). The rotor 4 and the rotor shaft 5 are fixed so that their axes are coaxial, and a cylindrical fitting shaft portion 5 a having a large diameter is formed at the upper end portion in the axial direction of the rotor shaft 5. . The fitting shaft portion 5a has a predetermined thickness in the axial direction, and the fitting shaft portion 5a is formed thicker than the thickness of the central portion of the rotor 4 where the fitting opening 4a is formed. Has been.

  The fitting shaft portion 5a of the rotor 4 and the rotor shaft 5 is fixed only by interference fitting, and no portion overlapping in the axial direction is formed on any member. That is, the inner peripheral side surface of the fitting opening 4a of the rotor 4 is in pressure contact with the outer peripheral surface of the fitting shaft portion 5a of the rotor shaft 5 throughout the thickness direction, and has a portion through which the bolt is inserted. Not done. Further, the outer peripheral surface of the fitting shaft portion 5a of the rotor shaft 5 is formed in parallel with the axial direction over the entire thickness, and does not have a portion through which a bolt is inserted.

Here, the linear expansion coefficient of aluminum which is the material of the rotor 4 is 23.4E-06. The material of the rotor shaft 5, for example, the linear expansion coefficient of the SCM 425 is 12.0E-06.
That is, the linear expansion coefficient of the rotor 4 is larger than that of the rotor shaft 5. This means that when the temperatures of the rotor 4 and the rotor shaft 5 rise to the same temperature, the inner peripheral side surface of the fitting opening 4 a of the rotor 4 is displaced more outward than the outer peripheral surface of the rotor shaft 5. Means that.
For this reason, if the rotor 4 and the rotor shaft 5 are fixed by shrinkage fitting, the fixing force is reduced when the temperature rises. Therefore, other fixing structures such as bolt fastening are required.

Therefore, in this embodiment, the rotor 4 and the fitting shaft portion 5a of the rotor shaft 5 are fixed by cold fitting or baking / cooling fitting.
In the case of cold fitting, for example, the rotor shaft 5 including the fitting shaft portion 5a is cooled to about −100 ° C., and in this state, the rotor shaft 5 is fitted into the fitting opening 4a. In this case, the outer diameter dimension of the fitting shaft portion 5a and the dimension of the fitting opening portion 4a of the rotor 4 are a size that fits tightly in a state where the fitting shaft portion 5a is cooled, that is, an interference fit dimension. Set to.
In the case of baking and cold fitting, for example, the rotor 4 is heated to about 100 ° C., the rotor shaft 5 including the fitting shaft portion 5a is cooled to about −100 ° C., and the fitting shaft portion 5a is moved to the rotor 4 in this state. Is fitted into the fitting opening 4a. In this case, the outer diameter size of the fitting shaft portion 5a and the size of the fitting opening portion 4a of the rotor 4 are tightly fitted while the fitting shaft portion 5a is cooled and the rotor 4 is heated. The dimensions are set to the interference fit dimensions.

  By doing so, a pressure contact force acts on the fitting shaft portion 5a of the rotor 4 and the rotor shaft 5 and is firmly fixed at normal temperature. And even if the temperature of the rotor 4 rises, the firm fixation between the rotor 4 and the fitting shaft portion 5a of the rotor shaft 5 is maintained.

According to the said embodiment, there exist the following effects.
(1) Since bolt fastening is not required for fixing the rotor 4 and the rotor shaft 5, it is not necessary to provide a portion overlapping the rotor shaft 5 in the rotor 4. For this reason, the mass of the rotor 4 can be reduced correspondingly, and the rotor breaking torque can be reduced.
(2) Since it is not bolt fastening, there is no occurrence of displacement at the time of bolt fastening caused by the tolerance between a drill hole provided in one of the fitting shaft portions 5a of the rotor 4 or the rotor shaft 5 and the bolt outer diameter. For this reason, the unbalance of the rotor resulting from the shift | offset | difference at the time of bolt fastening can be eliminated.
(3) Since no bolts are used, the number of parts can be reduced, and the assembly time can be shortened, so that the cost can be reduced.

  In the above embodiment, the outer diameter of the fitting shaft portion 5 of the rotor shaft 5 is larger than that of the other portions. The diameter of the fitting shaft portion 5a may be the same as or smaller than that of the other portions. Further, the materials of the rotor 4 and the rotor shaft 5 are not limited to the materials described above. Although the thickness of the fitting shaft portion 5 of the rotor shaft 5 in the axial direction is thicker than the thickness of the central portion of the rotor 4, it can be equal to or less than the thickness of the central portion of the rotor 4.

(Embodiment 2)
2 to 4 show a second embodiment of the turbo-molecular pump 1 according to the present invention, FIG. 2 is a side view of the rotor 4 ′ and the rotor shaft 5 ′, and FIG. 3 is a III-III line in FIG. 4 is a cross-sectional view of the rotor shaft 5 ′ taken along line III-III in FIG.
In the second embodiment, as shown in FIG. 3, the rotor shaft 5 ′ is formed with a protruding portion 5b protruding from the outer peripheral surface of the fitting shaft portion 5a ′ in a direction perpendicular to the axial direction. A pair of protrusions 5b are formed symmetrically with respect to the center line of the shaft.

On the other hand, a recess 4b having a shape corresponding to the protrusion 5b of the fitting shaft portion 5a ′ is formed on the inner peripheral surface of the fitting opening 4a ′ in the rotor 4 ′.
Also in the second embodiment, the rotor shaft 4 ′ and the fitting shaft portion 5a ′ of the rotor shaft 5 ′ are fixed by cold fitting or baking / cooling fitting. In this case, the interference fitting dimension including the protrusion 5b of the fitting shaft portion 5 and the recess 4b of the rotor 4 is set.

Therefore, in the case of the second embodiment, the same effect as that of the first embodiment can be obtained.
Further, even when a large load is suddenly applied to the rotor 4 or the rotor blade 7, the protrusion 4 b of the fitting shaft 5 and the recess 4 b of the rotor 4 prevent the rotor 4 ′ and the rotor shaft 5 ′ from loosening. Can be prevented. That is, it has a strong holding force against an external force acting around the outer circumferences of the rotor 4 ′ and the rotor shaft 5 ′.

  In addition, in the said embodiment, although the turbo molecular pump 1 has the thread groove part 8b, it is also applicable to the turbo molecular pump which does not have the thread groove part 8b.

  Moreover, although the magnetic bearing type turbo molecular pump has been described as an embodiment, the present invention is not limited to the magnetic bearing type and can be applied. In addition, the present invention can be applied in various modifications within the scope of the invention. In short, the rotor shaft and the rotor fixed to the rotor shaft are rotated at high speed in the case member, and suction is performed. In a turbo molecular pump that transfers gas molecules from the mouth side to the exhaust port side, the rotor shaft has a fitting shaft portion having a predetermined thickness in the axial direction at the upper end portion in the axial direction, and the rotor is There is a fitting opening that fits into the fitting shaft, and each of the rotor and the fitting shaft of the rotor shaft does not have a portion that overlaps in the axial direction. Any fitting shaft portion of the rotor shaft may be fitted, and the rotor and the rotor shaft may be fixed by cold fitting or baking / cold fitting.

DESCRIPTION OF SYMBOLS 1 Turbo molecular pump 2 Blade exhaust part 3 Thread groove exhaust part 4, 4 'Rotor 4a, 4a' Opening part for fitting 4b Recessed part 5, 5 'Rotor shaft 5a, 5a' Fitting shaft part 5b Protrusion part 6 Stator blade 7 Rotor Blade 8 Screw stator 8a Spiral protrusion 8b Screw groove 9 Rotor cylindrical portion 11 Case member 12 Upper case 13 Base 15 Inlet 21 Spacer 45 Exhaust port

Claims (5)

In the turbo molecular pump that rotates the rotor shaft in the case member and the rotor fixed to the rotor shaft at high speed and transfers gas molecules from the suction port side to the exhaust port side,
The rotor shaft has a fitting shaft portion having a predetermined thickness in the axial direction at an upper end portion in the axial direction, and the rotor has a fitting opening for fitting into the fitting shaft portion of the rotor shaft. In addition, each of the rotor and the fitting shaft portion of the rotor shaft does not have a portion that overlaps in the axial direction, and the fitting shaft portion of the rotor shaft is provided in the fitting opening of the rotor. A turbo-molecular pump, which is fitted, and the rotor and the rotor shaft are fixed by cold fitting or baking / cooling fitting.   2. The turbo molecular pump according to claim 1, wherein the rotor is formed of a material having a larger linear expansion coefficient than a fitting shaft portion of the rotor shaft.   3. The turbo molecular pump according to claim 1, wherein at least a part of the fitting shaft portion of the rotor shaft has a dimension in a direction orthogonal to the axial direction larger than other portions of the rotor portion. Turbo molecular pump.   3. The turbo molecular pump according to claim 1, wherein the fitting shaft portion of the rotor shaft has a larger dimension in a direction orthogonal to the axial direction over the entire circumference than other portions of the rotor shaft. Turbo molecular pump. 5. The turbo molecular pump according to claim 1, wherein the fitting shaft portion of the rotor shaft has a protruding portion protruding in a direction perpendicular to the axial direction on a circumferential side portion, and the fitting of the rotor is performed. The turbo-molecular pump, wherein the joint opening has a recess corresponding to the protrusion of the fitting shaft of the rotor shaft.

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