Vacuum pump

Abstract

Provided is a vacuum pump in which no finish processing has to be carried out after shaping of a cylindrical rotor even in use of a cylindrical rotor obtained by shaping a fiber-reinforced plastic material into a cylindrical shape. The vacuum pump has a turbo-molecular pump section and a thread groove pump section. The upper end section of a cylindrical rotor, which is obtained by shaping a fiber-reinforced plastic material into a cylindrical shape, of the thread groove pump section, is joined to the lower end section of a rotor of the turbo-molecular pump section. A joining portion of the rotor of the turbo-molecular pump section and the cylindrical rotor of the thread groove pump section is disposed upstream of an exhaust passage. As a result, finish processing does not have to be carried out after shaping of the cylindrical rotor. If finish processing is performed after shaping of the cylindrical rotor a resin may be coated onto a rugged portion of the cylindrical rotor, or fibers may be helically wound at a winding angle not greater than 45 degrees.

Claims

1. A vacuum pump having a rotor such that a cylindrical rotor formed in a substantially cylindrical shape out of a fiber-reinforced composite material is joined to a rotor of another material and forming a cylindrical pump section and removal processing is applied to at least a part of an outer periphery of the cylindrical rotor, wherein said cylindrical rotor is formed as a multilayer structure that includes hoop layers in which fibers are oriented in less than 45 degrees with respect to a circumferential direction, and wherein said removal processing is not applied at least at a joining portion of said cylindrical rotor so as to prevent shredding fibers in the layer that constitutes an outermost layer, from among said hoop layers.

2. The vacuum pump according to claim 1, wherein in said cylindrical rotor that is formed in such a manner that said hoop layers constitute an outermost layer.

3. The vacuum pump according to claim 2, wherein said joining portion is provided upstream of an exhaust passage of said cylindrical pump section.

4. The vacuum pump according to claim 1, wherein said joining portion is provided upstream of an exhaust passage of said cylindrical pump section.

5. A vacuum pump having a rotor such that a cylindrical rotor formed in a substantially cylindrical shape out of a fiber-reinforced composite material is joined to a rotor of another material and forming a cylindrical pump section, wherein said cylindrical rotor is formed as a multilayer structure that includes hoop layers in which fibers are oriented in less than 45 degrees with respect to a circumferential direction, a protective countermeasure is provided at an outer periphery of an outermost layer, from among said hoop layers, so as to prevent shredding fibers in the layer that constitutes said outermost layer at least at a joining portion of said cylindrical rotor, and said protective countermeasure is a resin layer further provided outside of said hoop layers so as to reduce irregularities in the surface of said cylindrical rotor.

6. The vacuum pump according to claim 5, wherein after said resin layer is provided, the resin layer is subjected to removal processing within a thickness range of the resin layer.

7. The vacuum pump according to claim 6, wherein said resin layer is formed by cast article.

8. The vacuum pump according to claim 7, wherein said joining portion is provided upstream of an exhaust passage of said cylindrical pump section.

9. The vacuum pump according to claim 6, wherein said joining portion is provided upstream of an exhaust passage of said cylindrical pump section.

10. The vacuum pump according to claim 5, wherein said resin layer is formed by cast article.

11. The vacuum pump according to claim 10, wherein said joining portion is provided upstream of an exhaust passage of said cylindrical pump section.

12. The vacuum pump according to claim 5, wherein said joining portion is provided upstream of an exhaust passage of said cylindrical pump section.

13. A vacuum pump having a rotor such that a cylindrical rotor formed in a substantially cylindrical shape out of a fiber-reinforced composite material is joined to a rotor of another material and forming a cylindrical pump section, wherein said cylindrical rotor is formed as a multilayer structure that includes hoop layers in which fibers are oriented in less than 45 degrees with respect to a circumferential direction, a protective countermeasure is provided at an outer periphery of an outermost layer, from among said hoop layers, so as to prevent shredding fibers in the layer that constitutes said outermost layer at least at a joining portion of said cylindrical rotor, and said protective countermeasure is a helical layer provided outside of said hoop layers, the helical layer has fibers oriented in 45 degrees or more with respect to the circumferential direction.

14. The vacuum pump according to claim 13, wherein after said helical layer is provided, fibers wound in the helical layer and resin around the fibers are subjected to removal processing within a thickness range of the helical layer.

15. The vacuum pump according to claim 14, wherein said joining portion is provided upstream of an exhaust passage of said cylindrical pump section.

16. The vacuum pump according to claim 13, wherein said joining portion is provided upstream of an exhaust passage of said cylindrical pump section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a vertical cross-sectional diagram of a vacuum pump in an embodiment of the present invention;

(2) FIG. 2 is an explanatory diagram illustrating an embodiment of finish processing of a cylindrical rotor in a composite vacuum pump of the present invention illustrated in FIG. 1; and

(3) FIG. 3 is an explanatory diagram illustrating another embodiment of finish processing of a cylindrical rotor in a composite vacuum pump of the present invention illustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) The object of preventing low-load damage to a cylindrical rotor, even when using a cylindrical rotor obtained by shaping a fiber-reinforced plastic material to a cylindrical shape, is attained by providing a vacuum pump having rotors such that a cylindrical rotor formed to a substantially cylindrical shape out of a fiber-reinforced composite material is joined to a rotor of another material, and forming a thread groove pump, wherein the cylindrical rotor is formed as a multilayer structure that comprises hoop layers in which fibers are aligned by less than 45 degrees with respect to a circumferential direction, and a protective countermeasure is provided at an outer periphery of an outermost layer, from among the hoop layers so as to prevent shredding fibers in the layer that constitutes the outermost layer, at least at a joining portion of the cylindrical rotor.

(5) Embodiments

(6) Preferred embodiments of the vacuum pump of the present invention are explained below with reference to FIG. 1 to FIG. 3. FIG. 1 is a vertical cross-sectional diagram of a vacuum pump according to the present invention.

(7) In FIG. 1, a vacuum pump 10 comprises a chassis 13 that has an intake port 11 and an exhaust port 12. Inside the chassis 13 there is provided a turbo-molecular pump section 14 at the top, and a cylindrical thread groove pump section 15 below the turbo-molecular pump section 14; and there is formed an exhaust passage 24 that passes through the interior of the turbo-molecular pump section 14 and the thread groove pump section 15 and that communicates the intake port 11 with the exhaust port 12.

(8) More specifically, the exhaust passage 24 elicits communication between a gap formed between the inner peripheral face of the chassis 13 and the outer peripheral face of a below-described rotor 17 that opposes the turbo-molecular pump section 14, and a gap between the inner peripheral face of a stator 23 at the outer peripheral face of a below-described cylindrical rotor 21 of the thread groove pump section 15. Also, the exhaust passage 24 is formed so as to elicit communication between the intake port 11 and the upper end side of the gap on the turbo-molecular pump section 14 side, and communication between the exhaust port 12 and the lower end side of the gap on the thread groove pump section 15 side.

(9) The turbo-molecular pump section 14 results from combining multiple rotor blades 18, 18 . . . projecting from the outer peripheral face of the rotor 17, made of an a aluminum alloy and fixed to a rotating shaft 16, with multiple stator blades 19, 19 . . . that project from the inner peripheral face of the chassis 13.

(10) The thread groove pump section 15 comprises: the cylindrical rotor 21 that is press-fitted and fixed, for instance using an adhesive or the like, to a joint 20a, i.e. to the outer periphery of a flange-like annular section 20 that is protrudingly provided at the outer peripheral face of the lower end section of the rotor 17 in the turbo-molecular pump section 14; and the stator 23, which opposes the cylindrical rotor 21, with a small gap between the outer periphery of the cylindrical rotor 21 and the stator 23, and in which there is disposed a thread groove 22 that is formed by the abovementioned small gap and a part of the exhaust passage 24. The depth of the thread groove 22 is set so as to grow shallower in the downward direction. The stator 23 is fixed to an inner face of the chassis 13. The lower end of the thread groove 22 communicates with the exhaust port 12 at the furthest downstream side of the exhaust passage 24. The rotor 17 of the turbo-molecular pump section 14 and the joint 20a of the cylindrical rotor 21 of the thread groove pump section 15 are disposed upstream of the exhaust passage 24.

(11) A rotor 26a of a high-frequency motor 26, such as an induction motor or the like that is provided in a motor chassis 25, is fixed to an intermediate section of the rotating shaft 16. The rotating shaft 16 is supported on a magnetic bearing, and is provided with upper and lower protective bearings 27, 27.

(12) The cylindrical rotor 21 is obtained by shaping a FRP material to a cylindrical shape. The cylindrical rotor 21 is a composite layer that results from combining, for instance, hoop layers, in which fibers are aligned in the circumferential direction, so as to share forces in both the circumferential direction and the axial direction, with a helical layer, in which fibers are aligned in an angle of 45 degrees or more with respect to the circumferential direction.

(13) A resin material is sprayed onto a site, at an upper end section corresponding to the joint 20a, of the rotor 17 of the turbo-molecular pump section 14 and of the cylindrical rotor 21 in the thread groove pump section 15, i e. at the outermost layer portion of the upper end section of the cylindrical shape rotor 21, so that the interior of the recesses in the surface is filled up with the resin material and is rendered smooth thereby.

(14) The operation of the vacuum pump illustrated in FIG. 1 is explained next. Gas that flows in through the intake port 11, as a result of driving by the high-frequency motor 26, is in a molecular flow state or in an intermediate flow state close to a molecular flow state. The rotor blades 18, 18 . . . that rotate in the turbo-molecular pump section 14 and the stator blades 19, 19 . . . that project from the chassis 13 impart a downward momentum to the gas molecules, and the high-speed rotation of the rotor blades 18, 18 . . . causes the gas to be compressed and to move downstream.

(15) The compressed and moving gas is guided, in the thread groove pump section 15, by the rotating cylindrical rotor 21, and by the thread groove 22 that becomes shallower downstream along the stator 23 that is formed having a small gap with respect to the cylindrical rotor 21. The gas flows through the interior of the exhaust passage 24 while being compressed up to a viscous flow state, and is discharged out of the exhaust port 12.

(16) If the cylindrical rotor 21 has not been subjected to a predetermined finish processing in a case where the cylindrical rotor 21 is formed through shaping of a FRP material to a cylindrical shape, then the gap between the cylindrical rotor 21 and the opposing stator 23 must be increased on account of the rugged state of the surface of the cylindrical rotor 21. In the vacuum pump 10 of the present embodiment, however, the joint 20a between the rotor 17 of the turbo-molecular pump section 14 and the cylindrical rotor 21 of the thread groove pump section 15 is disposed upstream of the exhaust passage 24, where the pressure is lower than on the exhaust port 12 side, at which the influence of a wider gap is smaller. Therefore, gas is discharged through the exhaust port 12 without incurring a significantly lower discharge rate or compression ratio, even if there is a large gap between the cylindrical rotor 21 and the opposing stator 23.

(17) In the vacuum pump 10 of the present embodiment, therefore, at least the portion of the joint 20a, which is acted upon by a load, in the cylindrical rotor 21 that is obtained by shaping a FRP material to a cylindrical shape, need not be subjected to finish processing after shaping of the cylindrical rotor 21. Accordingly, it becomes possible to solve the conventional problems of shredding the meandering fibers in the vicinity of the surface layer of the cylindrical rotor 21, caused finish processing, and occurrence of partial peeling, fraying and resulting damage of the fiber structure of the FRP material at times of high load (load weight). Moreover, the manufacturing process of the vacuum pump is made simpler, and hence manufacturing costs can be reduced.

(18) Herein, a predetermined degree of precision can be secured by providing a processing allowance 28 in the outermost layer at the upper end section of the cylindrical rotor 21 corresponding to at least the joint 20a, and, after shaping of the cylindrical rotor 21, by carrying out finish processing only at the portion of the processing allowance 28, within the thickness range of the outermost layer of the processing allowance 28. Drops in discharge rate and compression ratio can be expected to be further reduced thereby.

(19) FIG. 2 is an explanatory diagram illustrating an embodiment of finish processing of a cylindrical rotor in the composite vacuum pump of the present invention illustrated in FIG. 1. For instance, a portion 21a of the outermost layer of the cylindrical rotor 21, as illustrated in FIG. 2, can be cut, within the thickness range of the outermost layer, in a case where the entire cylindrical rotor 21 undergoes finish processing after shaping of the cylindrical rotor 21.

(20) FIG. 3 is an explanatory diagram illustrating another embodiment of finish processing of a cylindrical rotor in the composite vacuum pump of the present invention illustrated in FIG. 1. In a case where the entire cylindrical rotor 21 undergoes finish processing after shaping of the cylindrical rotor 21, finish processing may be performed, for instance, by coating a resin material 30 into recessed portions 29 of the outermost layer of the cylindrical rotor 21, as illustrated in FIG. 3, within the thickness range of the outermost layer.

(21) In the vacuum pump of the present invention, thus, two methods may be carried out, one method in which the joint 20a at the outer periphery of the cylindrical rotor 21 comprising FRP is not subjected to finish processing, and a method in which the joint 20a is subjected to finish processing. In the former case, where the joint 20a at the outer periphery of the cylindrical rotor 21 undergoes no finish processing, the FRP surface is ordinarily rugged, and therefore the gap (clearance) between the component (i.e. the flange-like annular section 20 of the rotor 17) that opposes the outer periphery of the cylindrical rotor 21 (FRP) must be made wider. In the embodiment of the present invention, however, the joint 20a is disposed upstream of the exhaust passage 24; as a result, FRP can be used even if the surface thereof is significantly rugged through not having been subjected to finish processing. That is, because the influence of clearance widening is small at a site of low pressure upstream of the exhaust passage 24, even if the clearance with respect to an opposing component is large.

(22) In the latter case, where the joint 20a of the outer periphery of the cylindrical rotor 21 comprising FRP is subjected to finish processing, a processing allowance is provided on the outermost layer of the joint 20a, and the finish processing is carried out within the range of the processing allowance of the outermost layer. Herein, the finish processing of the processing allowance is carried out in accordance with a method that involves coating a resin material, clamping the FRP in a semicircular mold or the like and injecting a resin material, or winding helical fibers of FRP at a winding angle no greater than 45 degrees.

(23) An explanation follows next on the reason why finish processing of the fiber-reinforced plastic material (FRP) needs to be performed in a case where the joint 20a is not provided upstream of the exhaust passage 24. The evacuation performance of the thread groove pump section 15 in which FRP is used as the cylindrical rotor 21 is influenced, to a high degree, by the clearance between the rotating blades (rotor blades 18) and the chassis 13 of the thread groove pump section 15. Therefore, the clearance must be maintained as small as possible.

(24) On the other hand, surface ruggedness occurs on account of winding unevenness upon shaping of FRP through fiber winding. Also, the fiber winding density fluctuates depending on the degree of tension applied during fiber winding. The finished dimensions exhibit therefore large variability. In consequence, the clearance cannot be made smaller unless the surface of the cylindrical rotor 21 is subjected to finish processing. That is, the irregularities on the surface of the FRP must be reduced as much as possible through finish processing of the outer periphery of the FRP.

(25) The reason why a substantial load acts on the FRP is explained next. The cylindrical rotor 21 is supported by the magnetic bearing in a contact-less manner, and hence heat dissipation in the rotating blades (rotor blades 18) is poor. Accordingly, the FRP is pushed wide on account of the thermal expansion of the aluminum alloy that is press-fitted on the inward side. A substantial load acts on the FRP as a result.

(26) As a characterizing feature of the manner in which the above inconvenience is eliminated, the FRP is wound in a state where waviness is imparted along the irregularities of the surface. As a result, the fibers split at the ridges of the undulated portions during the finish processing. No load acts on the split fibers upon pushing wide of the FRP on account of the thermal expansion of the aluminum alloy. In consequence, a shear force acts on the cylindrical rotor 21. If the strength limit of the resin material that binds the fibers together is exceeded at this time, cracks appear on the resin, and fraying occurs. In ordinary applications, the occurrence of fraying is not a problem. In the case of a high-speed rotating body, however, fraying is problematic in that the centrifugal force at the frayed portion causes the cracks in the resin to propagate faster, so that entire fibers peel off. In the present embodiment, therefore, the above problem is solved by taking protective countermeasures to prevent shredding fibers that are acted upon by a load in the circumferential direction.

(27) The surface treatment method of the FRP is explained next in further detail. A resin layer may be provided in the surface, by spraying, brush-coating, casting or the like, in a case where no finish processing is carried out in the surface treatment of the FRP, as described above. In the latter case, where a resin layer is provided on the surface of the FRP, finish processing is performed within the thickness range of the resin layer. A further finish processing need not be carried out if the resin layer is formed on the surface using a mold, since shape and dimensional precision, among others, is secured in that case.

(28) In another surface treatment method of the FRP, a layer resulting from winding fibers helically, within a range of ±45 degrees with respect to the axial direction of the cylindrical rotor 21, may be provided on the surface of the FRP. In this case, winding of the fibers within and range of ±45 degrees with respect to the axial direction of the cylindrical rotor 21 allows reducing the shear force that is generated upon pushing wide of the press-fit section on account of thermal expansion. In this case as well, the finish processing is performed within the thickness range of the layer in which the fibers are wound. The FRP press-fit section is disposed upstream of the exhaust passage 24. The influence of a widening of the clearance with respect to the fixed section can be reduced at such a site where pressure is low.

(29) In summary, in a vacuum pump having the rotor 17 such that the cylindrical rotor 21 formed out of FRP to a substantially cylindrical shape by FRP is joined to the joint 20a of the flange-like annular section 20 of another material, and the cylindrical rotor 21 makes up a thread groove pump 15, the cylindrical rotor 21 is formed as a multilayer structure having a hoop layers in which fibers are aligned by less than 45 degrees with respect to the circumferential direction, and a protective countermeasure is provided, at the outer periphery of the outermost layer, so that fibers in the outermost layer from among the hoop layers are not shredded, at the joint 20a of the cylindrical rotor 21.

(30) Herein, a resin layer is provided outside of the hoop layers so as to reduce irregularities in the surface of the cylindrical rotor 21, at least at the portion at which the cylindrical rotor 21 is joined to the joint 20a. Once the resin layer has been provided, the resin layer is subjected to removal processing within the thickness range of the resin layer. The resin layer can be formed beforehand by resin casting.

(31) Also, a helical layer in which fibers are aligned at an angle of 45 degrees or more with respect to the circumferential direction may be provided outside of the hoop layers, at the portion where the cylindrical rotor 21 of FRP is joined to the joint 20a. Once the helical layer has been provided, the fibers wound in the helical layer, and the resin around the fibers, may be subjected to removal processing within the thickness range of the helical layer.

(32) Alternatively, the range of removal of the outer periphery of the cylindrical rotor 21, which is formed in such a manner that a hoop layers is the outermost layer, may be set to at least a part of a portion of the cylindrical rotor 21 other than the joint 20a. Finish processing of the outer periphery of the cylindrical rotor 21 need not be carried out if the joint 20a is provided upstream of the exhaust passage 24 in the thread groove pump section 15.

(33) Specific embodiments of the present invention have been explained above, but the present invention is not limited to those embodiments, and may accommodate various improvements without departing from the spirit and scope of the invention. Such improvements are encompassed, as a matter of course, by the present invention.

(34) Other than in vacuum pumps, as described above, the present invention can also be used in various devices that utilize a cylindrical rotor obtained by shaping an FRP material to a cylindrical shape.

EXPLANATION OF REFERENCES

(35) 10 Vacuum Pump 11 Intake Port 12 Exhaust Port 13 Chassis 14 Turbo-Molecular Pump Section 15 Thread Groove Pump Section 16 Rotating Shaft 17 Rotor 18 Rotor Blades 19 Stator Blades 20 Flange-Like Annular Section 20a Joint 21 Cylindrical Rotor 21a A Portion of the Outermost Layer 22 Thread Groove 23 Stator 24 Exhaust Passage 25 Motor Chassis 26 High-Frequency Motor 26a Rotor 27 Protective Bearings 28 Processing Allowance 29 Recessed Portions of the Outermost Layer 30 Resin Material