JP2007278164A - Fastening structure and rotary vacuum pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a device to be exhausted and a rotary vacuum pump from being damaged. <P>SOLUTION: The intake port flange 13a of a turbo-molecular pump 1 is fastened to the flange 16 of a vacuum device with bolts 15. The bolt holes 14 of the intake port flange 13a are elongated ones, and so formed near the peripheral edge of the intake port flange 13a that their longitudinal direction almost match the circumferential tangential direction of the intake port flange 13a. A damping member 30 formed of a foam metal is disposed in the bolt hole 14. If an impact force occurs due to the trouble of the turbo-molecular pump 1, an impact force acting from the intake port flange 13a on the bolts 15 is received by the damping member 30. Since both a shearing stress acting on the bolts 15 and a motion energy transmitted to the device side flange 16 can be reduced, the bolts 15 can be prevented from being broken or the device can be prevented from being damaged. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fastening structure suitable for a rotary vacuum pump such as a turbo molecular pump or a molecular drag pump, and a rotary vacuum pump.

  A turbo molecular pump used for high vacuum evacuation includes a plurality of stages of rotating blades and a plurality of stages of fixed blades arranged alternately. Each of the rotor blades and the stationary blades is composed of a plurality of turbine blades. The rotor blades are formed in a rotor that is driven to rotate by a motor, and the stationary blades are fixed to the base of the pump. Furthermore, in addition to the turbine blades described above, turbomolecular pumps having a drag pump stage are also known. The drag pump stage includes a cylindrical portion formed in the lower portion of the rotor and a thread groove stator disposed in proximity to the cylindrical portion.

  In the turbo molecular pump, the rotor on which the turbine blade and the cylindrical portion are formed rotates at a high speed of tens of thousands of rpm, and there is a possibility that the rotor and the stator side (for example, the thread groove stator) come into contact with each other when an abnormal disturbance acts. In that case, a large impact is applied to the stator side. In addition, a large centrifugal force is constantly acting on a rotor that rotates at high speed, and if the rotor contacts the stator side, or if it is operated continuously under conditions exceeding the design assumptions, the rotor may be destroyed. is there. In such a case, there is a problem that a larger impact is applied to the stator side, and a large shearing force is applied to the bolt that fastens the pump casing to the apparatus main body.

  Therefore, it is known that a bolt formed with a plurality of steps for expanding the bolt hole prevents the bolt from breaking by preventing the shearing force from concentrating on one place (for example, Patent Documents). 1).

JP 2003-148388 A

  However, in the above-mentioned conventional technology, the bolt is in contact with the side surface of the stepped hole and plastically deforms to absorb the impact force. However, because of the stepped hole, the effect of plastic deformation is obtained. There was a disadvantage that it was not sufficiently obtained.

(1) The fastening structure according to the first aspect of the present invention is the fastening structure in which the first member and the second member are fastened by a bolt, and either the first member or the second member via the bolt. A member that absorbs kinetic energy transmitted from one to the other and relieves impact stress acting on the bolt, and includes a buffer member made of a porous metal material.
(2) The invention of claim 2 is the fastening structure according to claim 1, wherein at least one of the first member and the second member is provided with a hole through which a bolt is inserted, , And is arranged between the inner peripheral surface of the hole and the bolt.
(3) The invention according to claim 3 is the fastening structure according to claim 1 or 2, wherein the porous metal material is a foam metal.
(4) A rotary vacuum pump according to a fourth aspect of the present invention is a pump casing formed with an inlet flange that is fastened to an exhaust target device by the fastening structure according to any one of the first to third aspects. And a rotor that is provided with a rotation-side exhaust means and is driven to rotate at high speed in the pump casing, and a fixed-side exhaust means that is provided in the pump casing and cooperates with the rotation-side exhaust means to generate an exhaust action. It is characterized by that.
(5) The rotary vacuum pump according to the invention of claim 5 is provided with a pump casing formed with an inlet flange that is fastened to the exhaust target device, and a rotation side exhaust means, and is driven to rotate at high speed in the pump casing. A fixed-side exhaust means that is provided in the pump casing and cooperates with the rotary-side exhaust means to generate an exhaust action, and is provided between the fixed-side exhaust means and the pump casing. A member that absorbs kinetic energy transmitted to the pump casing from the fixed-side exhaust means when the means is broken, and that relieves impact stress acting on the pump casing, and includes a buffer member made of a porous metal material It is characterized by.

(1) According to the present invention, the buffer member made of a porous metal material absorbs the kinetic energy transmitted from one of the first member and the second member to the other through the bolt, and the bolt. It was constituted so as to relieve the impact stress acting on. Thereby, the breakage of the bolt and the breakage of the first member and the second member can be prevented.
(2) According to the inventions of claims 4 and 5, it is possible to prevent the exhaust target device and the rotary vacuum pump from being damaged.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. 1A and 1B are diagrams showing a schematic configuration of a turbo molecular pump employing a vacuum device fastening structure according to the present invention, wherein FIG. 1A is a sectional view and FIG. 1B is a plan view showing a flange portion. The plan view shows the upper half of the flange. The turbo molecular pump 1 shown in FIG. 1 is a magnetic bearing type pump, and the rotor 2 is supported in a non-contact manner by magnetic bearings 4 a to 4 c provided on the base 3. 4a and 4b are radial magnetic bearings, and 4c is an axial magnetic bearing.

  The base 3 is provided with a motor 6 that rotationally drives the rotor 2, touchdown bearings 7a and 7b, and gap sensors 5a, 5b, and 5c for detecting the floating position of the rotor 2, respectively. Mechanical bearings are used for the touchdown bearings 7a and 7b, and the rotor 2 is supported when the magnetic levitation of the rotor 2 by the magnetic bearings 4a to 4c is turned off.

  The rotor 2 is formed with a plurality of stages of rotating blades 8 in the direction of the rotation axis. Fixed wings 9 are respectively disposed between the rotating wings 8 arranged vertically. These rotor blades 8 and fixed blades 9 constitute a turbine blade stage of the turbo molecular pump 1. Each fixed wing 9 is held by a spacer 10 so as to be sandwiched up and down. The spacer 10 has a function of maintaining a gap between the fixed wings 9 at a predetermined interval as well as a function of holding the fixed wings 9.

  Further, a screw stator 11 constituting a drag pump stage is provided at the rear stage (lower side in the figure) of the fixed blade 9, and the inner peripheral surface of the screw stator 11 faces the cylindrical portion 12 of the rotor 2 at a predetermined interval. The fixed wing 9 held by the rotor 2 and the spacer 10 is housed in a casing 13 in which an inlet flange 13a is formed. As shown in FIG. 1 (b), eight elongated hole holes 14 are formed at equal intervals in the intake port flange 13a. The intake port flange 13a is provided with eight bolts 15 and the flange 16 on the apparatus side. Fixed to. The bolt hole 14 is provided with a buffer member 30 which is a massive member made of a foam metal having many pores. The flange thickness, the bolt size used, and the number of bolts are determined by the standard depending on the diameter of the inlet flange 13a.

  The bolt hole 14 is provided in the vicinity of the peripheral edge of the inlet flange 13a so that the longitudinal direction of the elongated hole substantially coincides with the tangential direction of the circumference of the inlet flange 13a. A buffer member 30 is disposed in the bolt hole 14 in a state of being counterclockwise as shown in FIG. 1B, which is opposite to the rotor rotation direction R. FIG. 2 schematically shows the vicinity of the bolt hole 14 of the inlet flange 13a, and is a schematic diagram showing the AA cross section of FIG. 1 (a). In FIG. 2, the description of the washer is omitted. The left side in FIG. 2 is the counterclockwise direction in FIG. 1B. In the bolt hole 14, the bolt 15 is inserted into a space where the buffer member 30 is not provided (the space on the right side in FIG. 2). The bolt 15 is screwed into a female screw portion 16a provided on the flange 16 on the apparatus side.

  FIG. 3 is a diagram for explaining the operation of the buffer member 30, and is a schematic diagram showing a cross section taken along the line AA of FIG. In the bolt 15, a region H <b> 1 is screwed into the female screw portion 16 a of the device side flange 16 from the tip of the shaft, and this region H <b> 1 is restrained by the device side flange 16. On the other hand, the region H2 that is not screwed into the apparatus side flange 16 is in an unconstrained state.

  When the rotor and the stator side come into contact for some reason, or when the rotor is damaged, an impact force acts on the base 3 and the casing 13 in the rotor rotation direction R. This impact force generates a torque T that rotates the intake port flange 13a, and the intake port flange 13a rotates and moves with respect to the apparatus side flange 16 so as to shift to the right side in the figure. By this rotational movement, the end face 30 a on the right side of the buffer member 30 is in contact with the shaft of the bolt 15.

  Since the impact force acting on the base 3 and the casing 13 is very large, the intake port flange 13a moves to the right side even after the buffer member 30 and the shaft of the bolt 15 come into contact with each other, and the buffer member 30 is moved in the right direction in the figure. Compress and deform. Due to the deformation of the buffer member 30, the impact energy applied to the base 3 and the casing 13 is absorbed, and the impact stress transmitted to the bolt 15 is relaxed.

  When an impact force is transmitted through the buffer member 30, the shaft of the bolt 15 is deformed so as to be bent to the right side. Therefore, the distance between the axis of the bolt 15 in the region H2 and the left end surface of the bolt hole 14 in the drawing differs in the vertical direction in the drawing. However, since the buffer member 30 is compressed and deformed in the right direction in the drawing in accordance with the inclination of the shaft of the bolt 15, the buffer member 30 comes into contact with the shaft of the bolt 15 in a wide range of the right end face 30a in the drawing. . Thereby, the working area of the impact stress transmitted to the bolt 15 is expanded.

  As described above, in the present embodiment, the buffer member 30 made of foam metal is disposed in the bolt hole 14. As a result, even if an abnormal state occurs in the turbo molecular pump and an impact force acts on the base 3 or the casing 13, the shearing stress applied to the bolt 15 and the motion transmitted to the flange 16 on the apparatus side by the buffer member 30. Both energy can be reduced. As a result, it is possible to prevent the bolt 15 from breaking and the deformation and damage on the apparatus side.

  4A and 4B show a standard flange structure as a comparative example, in which FIG. 4A shows a fastening state before the impact force acts, and FIG. 4B shows a case where the impact force acts. Bolt holes 24 are provided in the intake flange 13a. As for the axis | shaft of the volt | bolt 15, the part of the area | region H1 is restrained by the apparatus side flange 16, and the area | region H2 is an unconstrained state.

  A torque T that rotates the inlet flange 13a due to the impact force is generated, and the inlet flange 13a rotates and moves with respect to the apparatus side flange 16 so as to shift to the right side in the figure. By this rotational movement, the region H2 of the bolt 15 comes into contact with the side surface of the bolt hole 24 as shown in FIG. As a result, the region H2 is constrained by the intake flange 13a, and the shear stress is concentrated on the boundary portion 15a between the region H1 and the region H2. Although the inlet flange 13a is fixed to the apparatus side flange 16 by a plurality of bolts 15, the state as shown in FIG. Therefore, a state occurs in which shear stress concentrates only on the bolt 15 first in the state as shown in FIG. 4B and breaks instantaneously.

  On the other hand, in this embodiment, since the buffer member 30 is deformed, the position error of each bolt hole 14 is absorbed, so that the torque T can be received by all the bolts 15 used for fastening. . Therefore, the strength of all the bolts 15 used for fastening can be used effectively, and the bolts 15 can be prevented from breaking.

The absorption of impact energy and the reduction of impact stress by the buffer member 30 will be described below. The absorption of impact energy will be described with reference to the simple model shown in FIG. In FIG. 5, 100 is an impact absorbing mechanism that absorbs impact energy, 110 is a support portion that supports the impact absorbing mechanism 100, and 120 is a collision object that collides with the impact absorbing mechanism 100. The length of the impact absorbing mechanism 100 in the direction in which the impact energy acts is L, the Young's modulus is E, the cross-sectional area perpendicular to the direction in which the impact energy acts is A, and the amount of deformation due to the collision of the impact object 120 is Δ Let L be. The mass of the collision object 120 is M, and the initial speed before the collision is V ₀ .

_Assuming that the kinetic energy acting on the shock absorbing mechanism 100 is E _m0 , the strain energy of the shock absorbing mechanism 100 is E _e, and the strain of the shock absorbing mechanism 100 is ε = ΔL / L, the following equations (1), (2 ) Holds.
E _m0 = 1/2 × MV ₀ ² (1)
E _e = 1/2 × Eε ² AL (2)

_Assuming that the kinetic energy acting on the support 110 is E _m1 , the following equation (3) is established from the energy conservation law.
E _m1 = E _m0 −E _e (3)
In order to reduce the kinetic energy E _m1 acting on the support portion 110, the kinetic energy absorbed by the shock absorbing mechanism 100, that is, the strain energy E _e may be increased.

However, if the impact stress acting when the impact absorbing mechanism 100 is deformed is large, the stress acting on the support portion 110 also becomes large. Therefore, the reduction of impact stress will be examined with reference to the simplified model shown in FIG. When the impact stress is σ, the impulse I given to the impact absorbing mechanism 100 during the elapsed time Δt from the start of the collision of the colliding object 120 is expressed by the following equation (4).
I = −σAΔt (4)

The density of the shock absorbing mechanism 100 is ρ, and the stress propagation speed is C. Assuming that the coefficient of restitution between the collision object 120 and the shock absorbing mechanism 100 is 1, the section CΔt of the shock absorbing mechanism 100 becomes the speed V ₀ after Δt from the initial speed. The momentum change ΔP of the shock absorbing mechanism 100 at this time is expressed by the following equation (5).
ΔP = ρACΔtV ₀ (5)
Since the impulse I given to the shock absorbing mechanism 100 and the momentum change ΔP of the shock absorbing mechanism 100 are equal, the following equation (6) is derived from the above equations (4) and (5).
σ = −ρCV ₀ (6)

The stress propagation speed C can be obtained from the physical property value of the material as shown in the following formula (7).
C = (E / ρ) ^0.5 (7)
From the above equations (6) and (7), the following equation (8) is derived.
σ = −V ₀ (ρE) ^0.5 (8)

From Hook's law, the strain ε is expressed by the following equation (9).
ε = −σ / E (9)
From the above equations (2), (8), and (9), the kinetic energy (strain energy) E _e absorbed by the shock absorbing mechanism 100 is expressed by the following equation (10).
E _e = 1/2 × Eε ² AL
= EAL / 2 × (V ₀ ρ ^0.5 / E ^0.5 ) ^{2
_{= ALρV 0 2/2 ··· (}} 10)

From the above, it is desirable to design the impact absorbing mechanism 100 so that the impact stress σ expressed by the above equation (8) is reduced. It is desirable to design the shock absorbing mechanism 100 so that the kinetic energy (hereinafter simply referred to as absorbed energy) E _e absorbed by the shock absorbing mechanism 100 represented by the above equation (10) becomes large. Therefore, it is desirable to design the shock absorbing mechanism 100 as follows.
(1) Increase the cross-sectional area A or length L of the shock absorbing mechanism 100 (2) Use a material with a small Young's modulus E (3) Adjust the density ρ to an optimum value

  When this desirable design of the shock absorbing mechanism 100 is applied to the buffer member 30 of the present embodiment, the following is obtained. Regarding (1) described above, since the size of the bolt hole 14 into which the buffer member 30 is inserted is limited, the above-described cross-sectional area A is secured by increasing the contact area between the buffer member 30 and the bolt 15. It is desirable to disperse impact stress. As described above, when the buffer member 30 is compressed, it is compressed and deformed in the right direction in the drawing in accordance with the inclination of the shaft of the bolt 15. Therefore, since the buffer member 30 contacts the shaft of the bolt 15 in a wide range of the right end face 30a in the drawing, the above-described cross-sectional area A can be secured.

About (2) and (3) mentioned above, it depends on the physical property value of the material used for the buffer member 30. The density ρ is desirably a small value from the viewpoint of the impact stress σ, and the density ρ is desirably a large value from the viewpoint of the absorbed energy E _e . Therefore, it is conceivable to increase the absorbed energy E _e by selecting the material so as to increase the density ρ while keeping the impact stress σ within the range where the bolt 15 does not break. That is, it is desirable to maximize the density ρ within a range that satisfies the following expression (11).
σ = −V ₀ (ρE) ^0.5 <(breaking stress of bolt 15) / (safety factor) (11)

Since the buffer member 30 is a member made of foam metal as described above, the density ρ of the buffer member 30 can be changed in a pseudo manner by adjusting the porosity of the foam metal used for the buffer member 30. The density ρ of the buffer member 30 is obtained by multiplying the density of the foam metal material by the porosity of the foam metal. Accordingly, the Young's modulus E and the density ρ of the buffer member 30 can be set to desirable values by appropriately changing the material and porosity of the foam metal used for the buffer member 30, so that the impact stress σ and the absorbed energy E _e can be set. Thus, the buffer member 30 having desirable characteristics can be obtained. By using this buffer member 30, both the shear stress applied to the bolt 15 and the kinetic energy transmitted to the flange 16 on the apparatus side can be effectively reduced.

The turbo molecular pump employing the fastening structure described above has the following operational effects.
(1) An impact force acting on the bolt 15 from the intake port flange 13a is configured to be received by the buffer member 30. Thereby, since both the shear stress applied to the bolt 15 and the kinetic energy transmitted to the apparatus-side flange 16 can be reduced with a simple configuration, the breakage of the bolt 15 and the apparatus-side damage can be prevented.

(2) The buffer member 30 is arranged in the bolt hole 14 of the intake port flange 13a. Thereby, since the bolt hole 14 of the inlet flange 13a is processed into a long hole and the buffer member 30 only needs to be disposed in the bolt hole 14, the cost increase is small, and the present invention can be easily applied. Further, the present invention can be applied to existing turbo molecular pumps at a small cost.

(3) Since the buffer member 30 is configured using the foam metal, the pseudo density ρ of the buffer member 30 can be easily changed by changing the porosity. Thereby, by using the buffer member 30 with the porosity appropriately selected, both the shear stress applied to the bolt 15 and the kinetic energy transmitted to the flange 16 on the apparatus side can be effectively alleviated. Further, since the buffer member 30 has a simple structure of a massive foam metal, it is highly reliable for reducing the shear stress applied to the bolt 15 and the kinetic energy transmitted to the flange 16 on the apparatus side, and the cost can be reduced.

(4) Since the buffer member 30 is compressed and deformed in accordance with the inclination of the shaft of the bolt 15, the buffer member 30 comes into contact with the shaft of the bolt 15 in a wide range of the end surface 30a. Accordingly, the working area of the impact stress transmitted from the buffer member 30 to the bolt 15 can be secured and the impact stress can be dispersed, and the absorbed energy E _e can be increased. Can be effectively prevented.

(5) Since the absorbed energy E _e and the impact stress σ can be controlled by appropriately selecting the material and porosity of the foam metal used for the buffer member 30, the design of the buffer member 30 is easy. Further, since the buffer member 30 can be appropriately designed according to the turbo molecular pump or vacuum device to be applied, the application range is wide.

---- Modified example ---
(1) Although foam metal is used for the buffer member 30 in the above description, the present invention is not limited to this. For example, various porous metal materials such as a porous metal material obtained by sintering powdered or granular metal without foaming in the manufacturing process may be used for the buffer member 30.

(2) In the above description, the buffer member 30 is provided in the bolt hole 14 of the inlet flange 13a. However, the present invention is not limited to this. For example, a long hole may be provided in the flange 16 on the apparatus side, the buffer member 30 may be disposed, and the bolt 15 may be screwed into the intake port flange 13a.

(3) In the above description, the buffer member 30 is disposed at the fastening portion between the inlet flange 13 a and the apparatus-side flange 16, whereby the shear stress applied to the bolt 15 is transmitted to the apparatus-side flange 16. Although it is configured to relax kinetic energy, the present invention is not limited to this. For example, in order to alleviate the impact force acting on the base 3 and the casing 13 due to contact between the rotor and the stator or damage to the rotor, as shown in FIG. The buffer members 40 and 50 made of foam metal may be provided between the screw stator 11 and the base 3.

(4) In the above description, the turbo molecular pump 1 and the vacuum apparatus are directly connected, but the present invention is not limited to this. For example, as shown in FIG. 8, when a rotary vacuum pump 103 such as a turbo molecular pump 1 or a molecular drag pump is mounted in a vacuum chamber, it is fixed via a valve such as a gate valve or a control valve. There are many. The valve 101 is fixed to the vacuum chamber 100 via a pipe 102. Even in such a configuration, in order to suppress the impact on the apparatus side flange 16, that is, the vacuum chamber 100, a fastening structure similar to that described above may be adopted in each fastening part of the valve 101 and the pipe 102. Good. That is, the buffer member 30 may be disposed by processing the bolt hole 14 of the inlet flange 13a and the bolt holes 14 of the flanges 102a and 102b of the pipe 102 into long holes in the same manner as described above. Thereby, there exists an effect similar to embodiment mentioned above.
(5) You may combine each embodiment and modification which were mentioned above, respectively.

  In the above embodiment and its modifications, for example, the pump casing corresponds to the casing 13, and the fixed exhaust means corresponds to the fixed blade 9 and the screw stator 11. The above description is merely an example, and when interpreting the invention, there is no limitation or restriction on the correspondence between the items described in the above embodiment and the items described in the claims.

It is a figure which shows schematic structure of the turbo-molecular pump which employ | adopted the fastening structure of the vacuum apparatus by this invention, (a) is sectional drawing, (b) is a top view which shows a flange part. It is the figure which showed typically the vicinity of the bolt hole 14 of the inlet flange 13a. It is a figure explaining the effect | action of the buffer member. It is the figure which showed the standard flange structure, (a) shows the fastening state before an impact force acts, (b) is a figure which shows the case where an impact force acts. It is a figure which shows the simple model for demonstrating absorption of impact energy. It is a figure which shows the simple model for examining reduction of impact stress. It is a figure which shows a modification. It is a figure which shows a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Turbo molecular pump 2 Rotor 8 Rotary blade 9 Fixed blade 10 Spacer 11 Screw stator 12 Cylindrical part 13 Casing 13a Inlet flange 14 Bolt hole 15 Bolt 16 Apparatus side flange 30,40,50 Buffer member

Claims (5)

In the fastening structure that fastens the first member and the second member with bolts,
A member that absorbs kinetic energy transmitted from one of the first member and the second member to the other through the bolt and relieves impact stress acting on the bolt, and is porous. A fastening structure comprising a buffer member made of a porous metal material. The fastening structure according to claim 1,
At least one of the first member and the second member is provided with a hole through which the bolt is inserted,
The said buffer member is arrange | positioned between the internal peripheral surface of the said hole, and the said volt | bolt, The fastening structure characterized by the above-mentioned. In the fastening structure according to claim 1 or 2,
The fastening structure is characterized in that the porous metal material is a foam metal. A pump casing formed with an inlet flange that is fastened to the exhaust target device by the fastening structure according to any one of claims 1 to 3;
A rotor provided with a rotation-side exhaust means and driven to rotate at high speed in the pump casing;
A rotary vacuum pump comprising: a fixed-side exhaust means provided in the pump casing and generating an exhaust action in cooperation with the rotary-side exhaust means. A pump casing formed with an inlet flange that is fastened to the exhaust target device;
A rotor provided with a rotation-side exhaust means and driven to rotate at high speed in the pump casing;
A fixed-side exhaust means provided in the pump casing and generating an exhaust action in cooperation with the rotary-side exhaust means;
Provided between the fixed-side exhaust means and the pump casing to absorb kinetic energy transmitted from the fixed-side exhaust means to the pump casing when the rotary-side exhaust means is damaged; A rotary vacuum pump, comprising a buffer member made of a porous metal material, which is a member that relieves impact stress that acts.

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