WO2021172144A1

WO2021172144A1 - Vacuum pump and vacuum pump constituent component

Info

Publication number: WO2021172144A1
Application number: PCT/JP2021/006004
Authority: WO
Inventors: 健吾三枝; 陽太川口
Original assignee: エドワーズ株式会社
Priority date: 2020-02-26
Filing date: 2021-02-17
Publication date: 2021-09-02
Also published as: JP2021134697A; JP7377130B2

Abstract

[Problem]To provide a vacuum pump with which heat can be dissipated at a small purge gas flow rate. [Solution]Exhaust gas is made to flow from an upstream side to a downstream side on the outside of a rotor 28 by rotation of the rotor 28, and a purge gas flows through a gap 43. A threaded groove part 45 that faces the gap 43 and guides the purge gas is formed in a stator column 26. The threaded groove part 45 has a first threaded groove section, which is located on the upstream side of the flow path of the purge gas, and guides the purge gas in the direction of the upstream side of the flow path of the purge gas, and a second threaded groove section, which is located on the downstream side of the flow path of the purge gas, and guides the purge gas in the direction of the downstream side of the flow path of the purge gas, and a first area, which is the area occupied by the first threaded groove section, is larger than a second area, which is the area occupied by the second threaded groove section.

Description

Vacuum pumps and vacuum pump components

The present invention relates to a vacuum pump such as a turbo molecular pump and its components.

Generally, as a type of vacuum pump, a turbo molecular pump 110 as shown in FIG. 6 is known. In this turbo molecular pump 110, the rotor blades (rotary blades) 120 are rotated by energizing the motor in the pump body, and the gas molecules of the gas (process gas) entering from the intake port of the pump are directed in the direction of the arrow EG. The gas is exhausted by flipping it off.

In FIG. 6, the direction of the process gas flow (vacuum exhaust flow) is indicated by the broken line arrow EG. Actually, the process gas flows from the upper side to the lower side (intake side to exhaust side) in the drawing while being compressed by the rotor blade 120 and the stator blade 119.

Further, in the turbo molecular pump 110, the temperature of the bearing portion, the rotor blade 120, the parts supporting the rotor blade (rotor cylindrical portion 123, etc.) and the like rises during high-speed rotation, resulting in a high temperature. Therefore, as shown by the arrow PG in FIG. 6, the purge gas is flowed through the bearing portion and the gap 143 between the stator column 126 and the rotor cylindrical portion 123.

As this purge gas, a gas having high thermal conductivity (for example, nitrogen (N2) gas) is used. Then, heat is dissipated by heat conduction by flowing the purge gas, and cooling of the portion facing the gap 143 is promoted.

Japanese Patent No. 4156830

By the way, in the cooling method using the purge gas as described above, the cooling effect can be enhanced by using a large amount of the purge gas. However, the use of a large amount of purge gas increases the cost for operating the turbo molecular pump 101. Therefore, in order to reduce the cost, it is desirable to dissipate heat with a smaller flow rate of purge gas.

An object of the present invention is to provide a vacuum pump capable of dissipating heat with a small flow rate of purge gas, and a vacuum pump component.

(1) In order to achieve the above object, the present invention uses a stator and
A rotor that rotates with a gap between the stator and the rotor is provided.
In a vacuum pump that flows exhaust gas from the upstream side to the downstream side on the outside of the rotor by the rotation of the rotor.
Purge gas is flowed through the gap,
At least one of the stator and the rotor is formed with a screw groove portion facing the gap and guiding the purge gas as the rotor rotates.
The thread groove portion is
A first thread groove portion located on the upstream side of the flow path of the purge gas and guiding the purge gas toward the upstream side of the flow path of the purge gas.
It has a second thread groove portion that is located on the downstream side of the flow path of the purge gas and guides the purge gas toward the downstream side of the flow path of the purge gas.
The vacuum pump is characterized in that the first range occupied by the first threaded groove portion is larger than the second range occupied by the second threaded groove portion.
(2) Further, in order to achieve the above object, another invention is characterized in that the size of the first range is a size that changes the flow of the purge gas from an intermediate flow to a viscous flow (1). ) Is in the vacuum pump.
(3) Further, in order to achieve the above object, in another invention, the size of the second range satisfies the relationship of (reverse flow rate of the exhaust gas) <(transportation amount of the second thread groove portion). The vacuum pump according to (1) or (2).
(4) Further, in order to achieve the above object, another invention is characterized in that the size of the first range is twice or more the size of the second range (1) to (1). It is in the vacuum pump according to any one of 3).
(5) Further, in order to achieve the above object, another invention is characterized in that the exhaust gas passage is provided on the outside of the rotor and the gap is provided on the inside of the rotor (1) to (1). It is in the vacuum pump according to any one of 4).
(6) Further, in order to achieve the above object, another invention of the present invention includes a stator and the like.
It is one of the rotors that rotate with a gap between them and the stator.
The rotation of the rotor causes the exhaust gas to flow from the upstream side to the downstream side on the outside of the rotor.
In a vacuum pump component provided in a vacuum pump in which purge gas flows through the gap,
A screw groove portion that faces the gap and guides the purge gas as the rotor rotates is formed.
The thread groove portion is
A first thread groove portion located on the upstream side of the flow path of the purge gas and guiding the purge gas toward the upstream side of the flow path of the purge gas.
It has a second thread groove portion that is located on the downstream side of the flow path of the purge gas and guides the purge gas toward the downstream side of the flow path of the purge gas.
The vacuum pump component is characterized in that the first range occupied by the first threaded groove portion is larger than the second range occupied by the second threaded groove portion.
(7) Further, in order to achieve the above object, another invention is characterized in that the size of the first range is a size that changes the flow of the purge gas from an intermediate flow to a viscous flow (6). ) In the vacuum pump components.
(8) Further, in order to achieve the above object, in another invention, the size of the second range satisfies the relationship of (reverse flow rate of the exhaust gas) <(transportation amount of the second thread groove portion). The vacuum pump component according to (6) or (7).
(9) Further, in order to achieve the above object, another invention is characterized in that the size of the first range is twice or more the size of the second range (6) to (6). It is in the vacuum pump component according to any one of 8).
(10) The item according to any one of (6) to (9), wherein the vacuum pump has an exhaust gas passage on the outside of the rotor and the gap on the inside of the rotor. Located in the vacuum pump components.

According to the above invention, it is possible to provide a vacuum pump capable of dissipating heat with a small flow rate of purge gas, and a vacuum pump component.

It is a vertical cross section in which the flow of process gas and the flow of purge gas are simplified and added to the turbo molecular pump according to the best embodiment of the present invention. It is explanatory drawing which shows by expanding the thread groove part. (A) is an explanatory diagram schematically showing the flow of various gases in the gap facing the first thread groove portion, (b) is an explanatory view schematically showing the first thread groove portion expanded, and (c) is (c). It is a graph which shows typically the flow rate characteristic of various gases which concerns on a). (A) is a graph schematically showing the difference in flow rate characteristics depending on the type of gas, and (b) is a graph schematically showing the difference in flow rate characteristics depending on the shape of the thread groove. It is a graph which shows typically the flow rate characteristic of FIG. 3C from another viewpoint. It is explanatory drawing which simplifies the flow of process gas and the flow of purge gas in a conventional turbo molecular pump.

Hereinafter, the vacuum pump according to the best embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a turbo molecular pump 10 as a vacuum pump according to the present embodiment longitudinally. The turbo molecular pump 10 is connected to a vacuum chamber (not shown) of a target device (exhaust target device) such as a semiconductor manufacturing device, an electron microscope, a mass spectrometer, or the like.

The turbo molecular pump 10 integrally includes a cylindrical pump body 11 and a box-shaped electrical case (not shown). Of these, the pump main body 11 has an intake unit 12 connected to the upper side of FIG. 1 with the intake port facing the target device side, and an exhaust unit 13 connected to the auxiliary pump or the like on the lower side. The turbo molecular pump 10 can be used not only in the vertical posture as shown in FIG. 1 but also in an inverted posture, a horizontal posture, and an inclined posture.

The electrical case (not shown) houses a power supply circuit unit for supplying electric power to the pump body 11 and a control circuit unit for controlling the pump body 11. Is omitted.

The pump main body 11 includes a main body casing 14 as a casing that is a substantially cylindrical housing. The main body casing 14 is configured by connecting the intake side casing 14a located at the upper part in FIG. 1 and the exhaust side casing 14b located at the lower side in FIG. 1 in series in the axial direction. Here, the intake side casing 14a may be referred to as, for example, a casing, and the exhaust side casing 14b may be referred to as, for example, a base or the like.

The intake side casing 14a constitutes the intake side portion of the main body casing 14, and the exhaust side casing 14b constitutes the exhaust side portion of the main body casing 14. The intake side casing 14a and the exhaust side casing 14b are overlapped in the radial direction (left-right direction in FIG. 1). Further, the intake side casing 14a has an inner peripheral surface at one end in the axial direction (lower end in FIG. 1) facing the outer peripheral surface at the upper end 29 of the exhaust side casing 14b. The intake side casing 14a and the exhaust side casing 14b are hermetically coupled to each other by a plurality of casing bolts 14c (hexagon socket head bolts) with the O-ring 36 accommodated in the groove portion interposed therebetween. Here, FIG. 1 shows only a part of the plurality of casing bolts 14c.

An exhaust mechanism unit 15 and a rotary drive unit (hereinafter referred to as a "motor") 16 are provided in the main body casing 14 configured in this way. Of these, the exhaust mechanism portion 15 is a composite type composed of a turbo molecular pump mechanism portion 17 as a pump mechanism portion and a thread groove pump mechanism portion 18 as a thread groove exhaust mechanism portion.

The turbo molecular pump mechanism unit 17 and the thread groove pump mechanism unit 18 are arranged so as to be continuous in the axial direction of the pump main body 11, and in FIG. 1, the turbo molecular pump mechanism unit 17 is arranged on the upper side in FIG. , The thread groove pump mechanism portion 18 is arranged on the lower side in FIG. Hereinafter, the basic structures of the turbo molecular pump mechanism portion 17 and the thread groove pump mechanism portion 18 will be schematically described.

The turbo molecular pump mechanism 17 arranged on the upper side in FIG. 1 transfers exhaust gas (process gas, cleaning gas, etc.) by a large number of turbine blades, has a predetermined inclination or curved surface, and radiates. It includes a fixed blade (hereinafter referred to as a "stator blade") 19 and a rotary blade (hereinafter referred to as a "rotor blade") 20 formed. In the turbo molecular pump mechanism portion 17, the stator blades 19 and the rotor blades 20 are arranged so as to be alternately arranged in about ten stages.

The stator blade 19 is integrally provided in the main body casing 14, and the rotor blade 20 is inserted between the upper and lower stator blades 19. The rotor blade 20 is integrated with the tubular rotor 28, and the rotor 28 is concentrically fixed to the rotor shaft (also referred to as “rotor shaft” or the like) 21 so as to cover the outside of the rotor shaft 21.

The rotor 28 is fixed to the rotor shaft 21 by using a plurality of rotor fixing bolts 22 (only two are shown) on one end side (upper end side in FIG. 1) of the rotor shaft 21 in the axial direction. ..

The rotor shaft 21 is supported by a hollow stator column 26 as a stator via a magnetic bearing (described later). The stator column 26 is coaxially bolted to the exhaust side casing 14b described above to support the motor 16 and the rotor shaft 21.

The rotor shaft 21 is processed into a stepped columnar shape, and reaches from the turbo molecular pump mechanism portion 17 to the lower thread groove pump mechanism portion 18. Further, a motor 16 is arranged at the center of the rotor shaft 21 in the axial direction. The motor 16 will be described later.

The thread groove pump mechanism portion 18 includes a rotor cylindrical portion 23 and a screw stator 24.
The screw stator 24 is also called a "soto screw" or the like, and aluminum is used as the material of the screw stator 24. An exhaust port 25 for connecting to the exhaust pipe is arranged at the rear stage of the thread groove pump mechanism portion 18, and the inside of the exhaust port 25 and the screw groove pump mechanism portion 18 are spatially connected.

Further, in the turbo molecular pump 10, purge gas (protective gas) is supplied to the gap between the rotor 28 and the stator column 26. This purge gas is used for protecting the bearing portion described later and the rotor blade 20 described above, and is used for preventing corrosion due to the process gas, cooling the rotor blade 20, and the like.

In order to supply this purge gas, in this embodiment, a purge gas introduction pipe 41 is attached to a predetermined portion of the exhaust side casing 14b. The purge gas introduction pipe 41 extends linearly in the radial direction of the exhaust side casing 14b to form a purge gas flow path 42.

Further, as will be described later, the purge gas flows through the gap 43 between the stator column 26 and the rotor cylindrical portion 23, and in FIG. 1, a screw groove portion 45 is formed on the lower side of the gap 43. .. The details of the threaded groove portion 45 will be described later, but in the present embodiment, the threaded groove portion 45 is formed by processing a spiral groove having a predetermined shape along the outer peripheral surface of the stator column 26. There is.

The above-mentioned motor 16 has a rotor fixed to the outer circumference of the rotor shaft 21 (reference numeral omitted) and a stator (reference numeral omitted) arranged so as to surround the rotor. The power supply for operating the motor 16 is performed by the power supply circuit unit and the control circuit unit housed in the above-mentioned electrical case (not shown).

Here, in the pump body 11 of the turbo molecular pump 10, aluminum alloy or stainless steel is adopted as the material of the main parts. For example, the material of the exhaust side casing 14b, the stator blade 19, the rotor 28, and the like is an aluminum alloy. Further, the material of the rotor shaft 21 and the rotor fixing bolt 22 is stainless steel. Further, in FIG. 1, the description of the hatching showing the cross section of the component in the pump main body 11 is omitted in order to avoid complicating the drawing.

A magnetic bearing, which is a non-contact type bearing by magnetic levitation, is used to support the rotor shaft 21. The magnetic bearings include two sets of radial magnetic bearings (radial magnetic bearings) 30 arranged above and below the motor 16 and one set of axial magnetic bearings (axial magnetic bearings) 31 arranged below the rotor shaft 21. And are used.

Of these, each radial magnetic bearing 30 is composed of a radial electromagnet target 30A formed on the rotor shaft 21, a plurality of (for example, two) radial electromagnets 30B facing the target, a radial direction displacement sensor 30C, and the like. The radial displacement sensor 30C detects the radial displacement of the rotor shaft 21. Then, the exciting current of the radial electromagnet 30B is controlled based on the output of the radial direction displacement sensor 30C, and the rotor shaft 21 is levitated and supported so that it can rotate around the axial center at a predetermined position in the radial direction.

The axial magnetic bearing 31 is slightly separated from the disk-shaped armature disk 31A attached to the lower end side of the rotor shaft 21, the axial electromagnet 31B facing up and down with the armature disk 31A in between, and the lower end surface of the rotor shaft 21. It is composed of an axial displacement sensor 31C or the like installed at a vertical position. The axial displacement sensor 31C detects the axial displacement of the rotor shaft 21. Then, based on the output of the axial displacement sensor 31C, the exciting currents of the upper and lower axial electromagnets 31B are controlled, and the rotor shaft 21 is levitated and supported so that it can rotate around the axial center at a predetermined position in the axial direction. Twice

By using these radial magnetic bearings 30 and axial magnetic bearings 31, the rotor shaft 21 (and rotor blades 20) does not wear when rotating at high speed, has a long life, and does not require lubricating oil. Has been realized. Further, in the present embodiment, by using the radial direction displacement sensor 30C and the axial direction displacement sensor 31C, only the rotation direction (θz) around the axial direction (Z direction) of the rotor shaft 21 is freed, and the other 5 Position control is performed in the axial directions of X, Y, Z, θx, and θy.

Further, around the upper part and the lower part of the rotor shaft 21, radial protection bearings (also referred to as "protection bearings", "touchdown (T / D) bearings", "backup bearings", etc.) 32 at predetermined intervals. , 33 are arranged. These

protective bearings

32 and 33 do not significantly change the position and orientation of the rotor shaft 21 even in the unlikely event of a trouble in the electrical system or intrusion into the atmosphere, and the rotor blade 20 and its peripheral portions. Is not damaged.

When the turbo molecular pump 10 having such a structure is operated, the motor 16 described above is driven and the rotor blade 20 rotates. As the rotor blade 20 rotates, the process gas is sucked from the intake unit 12 shown on the upper side in FIG. 1, and the gas molecules collide with the stator blade 19 and the rotor blade 20 toward the screw groove pump mechanism unit 18. The gas is transferred. Further, the gas is compressed in the thread groove pump mechanism unit 18, the compressed gas enters the exhaust port 25 from the exhaust unit 13, and is discharged from the pump main body 11 through the exhaust port 25.

The rotor shaft 21, the rotor blade 20 that rotates integrally with the rotor shaft 21, the rotor cylindrical portion 23, the rotor (reference numeral omitted) of the motor 16, and the like are, for example, the "rotor portion" or the "rotating portion". , Etc. can be collectively referred to.

In FIG. 1, the direction of the process gas flow (vacuum exhaust flow) is indicated by the broken line arrow EG. Actually, the process gas flows from the upper side to the lower side (from the intake side to the exhaust side) in the drawing while being compressed by the rotor blade 20 and the stator blade 19.

Further, in FIG. 1, the flow of the purge gas is shown by the solid arrow PG. The purge gas is supplied to the purge gas flow path 42 described above from the outside of the exhaust side casing 14b via a purge gas cylinder, a flow rate controller (valve device), or the like. Then, the purge gas introduced into the purge gas flow path 42 directs the bearing portion and the motor portion from the lower side to the upper side (exhaust side to the intake side) in the drawing along the axial direction (rotational axis direction of the rotating part). Flows.

Further, the purge gas flows through the protective bearing 32 and through the gap (space) between the stator column 26 and the rotor cylindrical portion 23. Further, the purge gas flows toward the lower side in the drawing, passes through the thread groove portion 45, and reaches the exhaust portion 13. Although not shown, the purge gas is discharged to the outside of the main body casing 14 through the exhaust port 25 in the same manner as the process gas (arrow EG).

Here, in addition to the gap 43 between the stator column 26 and the rotor cylindrical portion 23, there is also a space between the stator blade 19 and the rotor blade 20, for example. And it is also possible to call such a space a "gap". However, in the present embodiment, a gap (a gap intended for the flow of process gas) formed on the outside of the rotor 28, such as a space between the stator blade 19 and the rotor blade 20, is referred to as a “passage”. And. This is to clearly distinguish between the gap (passage) intended for the flow of process gas and the above-mentioned gap 43 (gap intended for flow of purge gas) formed inside the rotor 28.

In addition, it is possible to adopt various general purge gas cylinders and flow rate controllers as described above. Further, as the purge gas, various general purging gases can be adopted. For example, as the purge gas, hydrogen (H2) gas, helium (He) gas, nitrogen (N2) gas, argon (Ar) gas and the like can be exemplified.

A screw groove portion 45 is provided in the flow path of the purge gas (indicated by the arrow PG in FIG. 1) as described above. As shown in FIG. 2, the threaded groove portion 45 is configured by combining two threaded groove portions, a first threaded groove portion 51A and a second threaded groove portion 51B. Here, FIG. 2 schematically shows the configuration of the thread groove portion 45 in a plane.

That is, FIG. 2 schematically shows a cylindrical portion of the stator column 26 (another portion provided with a screw groove portion 45) that is schematically developed and flattened in a rectangular frame. Further, in FIG. 2, the direction of rotation of the rotor 28 is indicated by an arrow C. The upper part of FIG. 2 corresponds to the upstream side (the side of the intake portion 12 and the upper side of FIG. 1) in the axial direction of the rotating portion, and the lower part corresponds to the downstream side (exhaust portion 13) of the rotating portion in the axial direction. Side, lower side of FIG. 1).

Further, the thread groove portion 45 has a first thread groove portion 51A on the upstream side and a second thread groove portion 51B on the downstream side. Of these, the first screw groove portion 51A has a screw groove 52A formed continuously so as to rise to the left in the developed view of FIG. Further, the second screw groove portion 51B has a screw groove 52B formed continuously so as to be downward to the left in the developed view of FIG.

Of these, the thread groove 52A of the first thread groove portion 51A may be continuous as a single thread (one) from the start point side end portion indicated by reference numeral 53A in FIG. 2 to the end point side end portion 54A. , Multiple threads (plural) may be present. Then, as the rotor 28 rotates (arrow C), the screw groove 52A spirals purge gas from the start point side end portion 53A to the end point side end portion 54A, as shown by arrow D (only a part of which is indicated by a reference numeral). It is possible to guide you to.

On the other hand, the other second thread groove portion 51B is formed in the opposite direction to the first thread groove portion 51A. Further, the second thread groove portion 51B is formed so as to be substantially line-symmetrically downward to the left with the first thread groove portion 51A in the developed view of FIG.

The screw groove 52B may be continuous as one (one) thread groove from the start point side end portion indicated by reference numeral 53B in FIG. 2 to the end point side end portion 54B, or may have a plurality of threads (plural lines). Threaded grooves may be present. Then, the screw groove 52B can guide the purge gas from the start point side end portion 53B to the end point side end portion 54B as shown by an arrow E (only a part of which is indicated by a reference numeral) in FIG.

Here, in FIG. 2, the linear raised portions (convex portions) that partition the

screw grooves

52A and 52B (recessed portions) are hatched to clarify the illustration. The hatched portion in FIG. 2 does not show a cross section.

As shown in FIG. 2, the start point side end 53A of the screw groove 52A in the first thread groove 51A and the start point side end 53B of the screw groove 52B in the second thread groove 51B are spatially connected. Then, the purge gas that flows through the gap 43 between the stator column 26 and the rotor cylindrical portion 23 (the overall flow indicated by the arrow PG in FIG. 1) and flows into the thread groove portion 45 is upstream by the first thread groove portion 51A. The flow returned to the side (reverse direction) (indicated by arrow D in FIGS. 1 and 2) and the flow sent to the downstream side (forward direction) by the second thread groove 51B (indicated by arrow E in FIGS. 1 and 2). ) And occur.

The overall gas flow in the thread groove portion 45 (indicated by the arrow PG in FIG. 1) is formed by a purge gas, a process gas mixed in the gap 43, or the like. The process gas mixed in the gap 43 becomes a mixed gas with the purge gas (hereinafter, simply referred to as "gas").

The purge gas also has a function of pushing back the process gas that enters the gap 43 (a function of preventing the backflow of the process gas). That is, it can be said that the backflow of the process gas into the gap 43 is prevented by the pressure difference between the pressure of the purge gas itself and the E portion of FIG. 1 and the flow generated by the second thread groove portion 51B.

Further, in the developed view of FIG. 2, reference numeral A indicates a range in which the first thread groove portion 51A is formed, and reference numeral B indicates a range in which the second thread groove portion 51B is formed. .. Hereinafter, the range in which the first thread groove portion 51A is formed is referred to as a “first range” and is designated by a reference numeral “A”. Further, the range in which the second thread groove portion 51B is formed is referred to as a "second range" and is designated by a reference numeral "B".

Since FIG. 2 is a developed view, the above-mentioned first range A and second range B directly cover the entire length of the thread groove 52A of the first thread groove portion 51A and the total length of the thread groove 52B of the second thread groove portion 51B. It is not something to represent. However, in the present embodiment, since the first thread groove portion 51A and the second thread groove portion 51B are formed line-symmetrically with substantially the same groove width, the magnitude relationship between the first range A and the second range B is that both screws are used. It almost corresponds to the magnitude relationship of the length (total length) of the

grooves

52A and 52B. Therefore, in the present embodiment, the first range A and the second range B are used as one of the indexes representing the characteristics related to the length of the first thread groove portion 51A and the second thread groove portion 51B.

The characteristics of the first thread groove portion 51A and the second thread groove portion 51B can be expressed by using the actual total length of each of the

thread grooves

52A and 52B without being limited to this. Further, it is also possible to form the first thread groove portion 51A and the second thread groove portion 51B non-axisymmetrically, and in this case as well, the characteristics can be determined based on the actual total length of each of the

thread grooves

52A and 52B. It is possible.

Further, in the present embodiment, in order to simplify the description, conditions relating to elements such as the width and depth of the

thread grooves

52A and 52B, the cross-sectional shape, the flow path area (cross-sectional area), and the volume per unit length are set. It is the same. However, the present invention is not limited to this, and for example, factors such as the width and depth of the

thread grooves

52A and 52B, the cross-sectional shape, the flow path area (cross-sectional area), the inclination angle of the screw, and the volume per unit length. It is also possible to make at least one of them different.

Next, the change in the flow of the purge gas due to the provision of the thread groove portion 45 will be described. As a whole, the purge gas exerts the function of a dynamic seal (dynamic seal) that prevents the process gas (arrow EG in FIG. 1) from flowing back toward the gap 43. In addition to this, in the present embodiment, the flow rate of the purge gas used can be reduced by providing the thread groove portion 45 having the first thread groove portion 51A.

Here, regarding the above-mentioned gas (mixed gas) and purge gas, the upstream side is the high pressure side and the downstream side is the low pressure side. In the present embodiment, the pressure on the high pressure side of the gas (mixed gas) is represented by P2, and the pressure on the low pressure side is represented by P1.

FIGS. 3 (a) and 3 (b) show the first thread groove portion 51A in a more simplified manner. Of these figures, FIG. 3A shows the gas (arrow F) flowing downward in the gap 43 (particularly the portion facing the first thread groove 51A) between the stator column 26 and the rotor cylindrical portion 23. , It is schematically shown that the gas flowing upward (arrow G) can be generated.

Of these, the arrow F indicates the direction of the flow generated by the pressure difference (P2-P1) between the pressure P2 on the high pressure side and the pressure P1 on the low pressure side. Further, the arrow G represents the direction of the flow generated when the rotor rotates.

Subsequently, FIG. 3B shows the first thread groove portion 51A in an expanded manner. Further, in FIG. 3B, the upper side of the figure is the high pressure side (P2) and the lower side is the low pressure side (P1) with reference to the gas (arrow F) flowing downward. Then, the gas flow (arrow G) in the first thread groove portion 51A is generated by the rotation of the rotor 28 as shown by the arrow C.

Further, FIG. 3 (c) shows the flow rate of the downward gas (arrow F) with respect to the pressure difference (horizontal axis, P2-P1) on the high pressure side and the low pressure side for the models shown in FIGS. 3 (a) and 3 (b). (Reference H) and the tendency of the flow rate (reference numeral I) of the upward gas (arrow G) generated when the rotor rotates are shown.

Of these, the pressure difference (P2-P1) on the horizontal axis increases as the number of rotations in the rotating parts of the motor 16, rotor 28, etc. increases. Further, as the pressure difference (P2-P1) increases, the downward gas flow (corresponding to the arrow F in FIG. 2) increases as shown by the straight line H in the figure. Here, at the origin O according to the graph of FIG. 3C, the rotating portions such as the motor 16 and the rotor 28 are in a state of rated rotation.

Further, the curve indicated by reference numeral I in FIG. 3C is the flow rate of the gas flowing upward as described above (corresponding to the arrow G in FIG. 3A). As described above, the upward gas flow rate represents the flow rate of the first thread groove portion 51A from the low pressure side (here, the lower side of FIG. 2) to the high pressure side (here, the upper side of FIG. 2). There is.

When this upward flow is explained using the pressures P2 and P1 related to the downward gas described above, it can be said that this flow is the gas flowing in the direction from P1 to P2. Then, it can be said that the flow rate of this gas (curve I) indicates the transport capacity of the upward flow (directions from P1 to P2) in the first thread groove portion 51A.

The flow rate of the curve I in FIG. 3C shows a state of being substantially constant (flow rate R) until the pressure difference (P2-P1) of the downward flow increases to a certain magnitude (FIG. 3C). Horizontal portion with reference numeral I1).

The curve I showing the flow rate of the upward flow intersects the straight line H with a predetermined pressure difference, but at this intersection Q, the flow rates of each other match (balance). This intersection Q can be referred to as a "balance point at a purge flow rate of 0 (zero)" or the like.

Further, the curve I exceeds the intersection Q with the straight line H in a substantially constant (horizontal) state, and drops sharply when the pressure difference (P2-P1) reaches a certain size. A reference numeral I2 is attached to this rapidly descending portion. That is, in the state where the gas flows upward (the portion of reference numeral I1), the effect of the thread groove portion is almost the same when the pressure difference (P2-P1) passes through the straight line H and then the pressure difference (P2-P1) increases to some extent. It will not appear.

Therefore, in order to reduce the supply amount of purge gas and maintain the P2 pressure required for heat conduction, the turbo molecular pump 10 is in the pressure difference (P2-P1) range in which the gas amount indicated by the curve I does not drop sharply. It is necessary to use.

Further, good heat conduction is performed by selecting the purge gas and designing the thread groove portion 45 so that the range of the pressure difference in which the horizontal portion (reference numeral I1 portion) of the curve I continues is as large as possible. It becomes possible.

With respect to the flow rate characteristic (curve I) when such a thread groove portion 45 (particularly the first thread groove portion 51A) is provided, the threads J and K in FIG. The pressure difference and the purge gas flow rate required for sufficient heat conduction when the thread groove portion 51A and the second thread groove portion 51B) are not provided.

On the other hand, when the thread groove portion 45 is provided, in order to achieve the pressure difference J required for heat conduction (the flow rate of the purge gas of K is passed through the gap 43), there is an upward R flow rate due to the first thread groove portion 51A. Therefore, the purge gas amount of T may be added (K = R + T).

Therefore, the amount of purge gas can be reduced by providing the screw groove portion 45 as in the present embodiment. As a whole, heat conduction can be promoted with a small amount of purge gas, and sufficient heat conduction can be performed while reducing the amount of purge gas. Further, as a whole, a small amount of purge gas makes it possible to prevent the intrusion of process gas.

FIG. 5 is a graph of this from a viewpoint different from that of FIG. 3 (c). H'in the figure is the amount that flows due to the pressure difference, and corresponds to the straight line H in FIG. 3 (c). Further, Q'in the figure is a balance point when the purge gas flow rate = 0, and corresponds to Q in the graph of FIG. 3 (c).

Further, the curve I'in FIG. 5 is the amount (transportation capacity of the screw groove) that the screw groove flows during rotation, and corresponds to the curve I in FIG. 3 (c). That is, FIG. 5 shows the curve I of FIG. 3 (c) turned to the fourth quadrant. Then, the curve L obtained by adding the curve H'and the curve I'is the net purge gas flow rate flowing through the gap of FIG. 3 (a). Further, J', K', and T'in FIG. 5 correspond to J, K, and T in FIG. 3 (c). Then, according to the example of FIG. 5, the amount obtained by subtracting the amount of T'from the amount of K'is the amount of purge gas reduction during rotor rotation.

If the threaded groove 45 is not provided with the first threaded groove 51A and is composed of only the second threaded groove 51B, only downward gas (arrow F) is generated with respect to the purge gas. .. Then, the second thread groove portion 51B functions to lower the pressure P2 on the high pressure side described above. Therefore, when the thread groove portion 45 is composed of only the second thread groove portion 51B, it is necessary to supply a larger amount of purge gas in order to sufficiently increase P2.

As described above, the flow rate of the purge gas can be reduced by providing the thread groove portion 45, but the straight line H related to the downward gas (arrow F) and the curve I related to the upward gas (arrow G) described above can be reduced. The mode changes depending on the type of various gases.

For example, when a gas having a relatively large molecular weight is used as the purge gas, the slope of the straight line HH becomes relatively small as shown in FIG. 4A in the flow generated by the pressure difference. However, when a gas having a relatively small molecular weight is used, the slope of the straight line HL becomes relatively large.

In other words, when the molecular weight is large, the viscosity of many types of gas generally increases, and the flow velocity of the gas slows down. Therefore, the increase in the flow rate with respect to the increase in the pressure difference (P2-P1) becomes small, and as shown in FIG. 4A, the gradient of the straight line HH indicating the amount of gas becomes small.

On the other hand, when a gas having a small molecular weight is used, the viscosity of many types of gas is generally low, and the flow velocity of the gas is high. Therefore, the increase in the flow rate with respect to the increase in the pressure difference (P2-P1) becomes large, and as shown in FIG. 4A, the gradient of the straight line HL indicating the amount of gas is larger than the above-mentioned straight line HH. Become. That is, when a gas having a small molecular weight is used, the gas flow rate increases with a small pressure difference (P2-P1) as compared with the case where the molecular weight is large.

Further, the upward (arrow G) flow generated in the first thread groove portion 51A when the rotor rotates has a curve IH as shown in FIG. 4A when a gas having a relatively large molecular weight is used as the purge gas. The position of the portion (the portion of the symbol IH2) in which the horizontal portion (the portion of the symbol IH1) becomes long and sharply decreases does not appear until the pressure difference (P2-P1) becomes relatively large. That is, for many types of purge gas, since the viscosity of the gas becomes high, it is easy to maintain the upward flow of the purge gas even if the pressure difference (P2-P1) increases.

On the other hand, when a gas having a relatively small molecular weight is used as the purge gas, the horizontal portion (the portion of the symbol IL1) on the curve IL becomes shorter, and the position of the portion (the portion of the symbol IL2) that sharply decreases becomes It appears in a situation where the pressure difference (P2-P1) is relatively small. That is, for many types of purge gas, the viscosity of the gas becomes low, so that when the pressure difference (P2-P1) increases, it becomes difficult to maintain the upward flow of the purge gas.

From these facts, the upward flow rate of the first thread groove 51A is not reduced by a small pressure difference (P2-P1) with respect to the molecular weight of the gas that causes a downward flow due to the pressure difference (P2-P1). , It is desirable to select the type of purge gas.

Further, regarding the aspect of the curve I (FIG. 3 (c)) relating to the purge gas, the shape of the thread groove in the thread groove portion 45 (particularly the shape and length of the screw groove 52A in the first thread groove portion 51A) also determines FIG. Changes appear as shown in b).

For example, when the length of the screw groove 52A in the first screw groove portion 51A is relatively long, the horizontal portion (the portion of reference numeral I1) is on the side where the pressure difference (P2-P1) is large, as shown by the broken line. The descending portion (the portion of reference numeral I2) also moves to the side where the pressure difference (P2-P1) is large. That is, by lengthening the screw groove 52A, even if the pressure difference (P2-P1) becomes large and the amount of gas downward (arrow F in FIG. 2) increases, the necessary purge gas can be secured more reliably, which is good. It is possible to carry out heat conduction.

Further, as also shown in FIG. 4B, by reducing the depth of the screw groove 52A and the inclination angle (screw angle) of the screw, the flow rate is reduced, but the descending portion (the portion of reference numeral I2) is formed. It moves to the side where the pressure difference (P2-P1) becomes large. Therefore, even if the pressure difference (P2-P1) increases, the upward flow of the purge gas can be ensured. Then, it is possible to maintain the upward flow of the purge gas against a large pressure difference while reducing the flow rate of the purge gas.

Here, the inclination angle (screw angle) of the screw may be expressed as an upward angle with respect to the horizontal direction (diameter direction of the stator column 26), for example, as shown by adding a reference numeral θ to FIG. 3 (b). It is possible.

Further, based on the characteristics of the thread groove portion 45 as described above, the amount of purge gas transported in the entire thread groove portion 45 and the amount of purge gas transported in each of the first thread groove portion 51A and the second thread groove portion 51B should be considered. Can be done.

For example, when trying to increase the amount of upward transportation (downward in the second threaded groove 51B) in the first threaded groove 51A (or the second threaded groove 51B), the first threaded groove 51A (or the first threaded groove 51A (or downward in the second threaded groove 51B) depends on the type of purge gas. Alternatively, it is conceivable to design the structure of the second thread groove portion 51B) or select a purge gas having characteristics that facilitate the flow. In designing these structures and selecting purge gas, it is important to optimize factors such as the mean free path of gas molecules, the cross-sectional area of the gas flow path, and the length of the gas flow path. ..

Then, in order to optimize these elements, for example, the above-mentioned first range A in which the first thread groove portion 51A is formed is made larger than the above-mentioned second range B in which the second thread groove portion 51B is formed. Is possible.

In the present embodiment, as described above, since the first thread groove portion 51A and the second thread groove portion 51B are formed line-symmetrically, the width, depth, cross-sectional shape, and cross-sectional shape of the

respective screw grooves

52A and 52B are formed. Factors such as the flow path area (cross-sectional area) are almost the same. Further, the inclination angles of the screws differ only in positive and negative values with the boundary between the first thread groove portion 51A and the second thread groove portion 51B in between, and the magnitudes (absolute values) of the angles are almost the same.

Therefore, regarding making the first range A larger than the second range B as described above, for example, the transport capacity of the first thread groove portion 51A is made larger than the transport capacity of the second thread groove portion 51B. It can be said that it is a thing.

Further, the specific relationship between the size of the first range A related to the first threaded groove portion 51A and the size of the second range B related to the second threaded groove portion 51B cannot always be freely determined, and is required. It is limited to some extent by factors such as the ability of heat conduction to be performed and the size of the stator column 26. Therefore, it is necessary to provide the first range A and the second range B in a limited area with an appropriate magnitude relationship.

And, as an optimum magnitude relationship, for example, it can be exemplified that the first range A: the second range B is determined within the range of about 1: 1 to 10: 1. In particular, according to the findings of the inventors, the function of the first thread groove portion 51A can be more clearly exhibited by setting the first range A to twice or more (2: 1 or more) of the second range B.

Further, the action of the flow and heat conduction of the purge gas as described here occurs better when the flow of the purge gas is an intermediate flow or a viscous flow than in the case of a molecular flow. It is a thing. Therefore, it is desirable to determine the type of purge gas and the structure of the first thread groove portion 51A (and the second thread groove portion 51B) so that the flow of the purge gas becomes an intermediate flow or a viscous flow.

Further, as described above, the second thread groove portion 51B also functions to prevent the process gas from flowing back. Therefore, for example, by designing the second thread groove portion 51B so as to satisfy the relationship of (reverse flow rate of the process gas) <(transportation amount of the second thread groove portion 51B), the sealing function of the process gas is more reliable. It becomes possible to.

Further, the purge gas is compressed in the screw groove portion 45 by reducing the cross-sectional area of the screw groove 52A (thread groove 52B) by forming the first screw groove portion 51A (and the second screw groove portion 51B) shallowly (purge gas). It is possible to increase its own pressure).

Further, since the flow rate of the purge gas can be reduced, it becomes possible to adopt a more expensive gas (for example, helium (He) gas).

According to the turbo molecular pump 10 as described above, the threaded groove portion 45 is provided, and the threaded groove portion 45 is further configured by a combination of the first threaded groove portion 51A and the second threaded groove portion 51B having a reverse screw relationship with each other. Therefore, it is possible to reduce the flow rate of the purge gas. As a result, the cost of purging gas can be reduced.

Further, the thread groove portion 45 of the present embodiment corresponds to a difference in the type of purge gas by changing the formation range of the first thread groove portion 51A and the length of the screw groove (L: here, the first range A). It is something that can be done. Therefore, by appropriately selecting factors such as the formation range of the first thread groove portion 51A, the length of the thread groove (L: here, the first range A), the type of process gas, and the type of purge gas, the optimum conditions can be obtained. Heat conduction is possible.

The present invention is not limited to the present embodiment, and can be variously modified without departing from the gist. For example, the shape of the gas flow path (screw

groove

52A, 52B) in the screw groove portion 45 is not limited to a rectangle (FIG. 3A), but may be a semicircular shape, a triangular shape, or a polygonal shape of a pentagon or more. It may be. Further, the thread groove portion 45 can be formed not only on the outer peripheral surface of the stator column but also on the inner peripheral surface of the rotor 28. Further, the present invention is applicable not only to turbo molecular pumps but also to other types of vacuum pumps.

10 Turbo molecular pump (vacuum pump)
26 Stator column (stator, vacuum pump components)
28 Rotor (vacuum pump component)
43 Gap (Purge gas flow path)
45 Thread groove 51A 1st thread groove 51B 2nd thread groove A 1st range B 2nd range

Claims

With the stator
A rotor that rotates with a gap between the stator and the rotor is provided.
In a vacuum pump that flows exhaust gas from the upstream side to the downstream side on the outside of the rotor by the rotation of the rotor.
Purge gas is flowed through the gap,
At least one of the stator and the rotor is formed with a screw groove portion facing the gap and guiding the purge gas as the rotor rotates.
The threaded groove is
A first thread groove portion located on the upstream side of the flow path of the purge gas and guiding the purge gas toward the upstream side of the flow path of the purge gas.
It has a second thread groove portion that is located on the downstream side of the flow path of the purge gas and guides the purge gas toward the downstream side of the flow path of the purge gas.
A vacuum pump characterized in that the first range occupied by the first threaded groove portion is larger than the second range occupied by the second threaded groove portion.
The vacuum pump according to claim 1, wherein the size of the first range is a size that changes the flow of the purge gas from an intermediate flow to a viscous flow.
The vacuum pump according to claim 1 or 2, wherein the size of the second range satisfies the relationship of (reverse flow rate of the exhaust gas) <(transportation amount of the second screw groove portion).
The vacuum pump according to any one of claims 1 to 3, wherein the size of the first range is at least twice the size of the second range.
The vacuum pump according to any one of claims 1 to 4, wherein the exhaust gas passage is provided on the outside of the rotor and the gap is provided on the inside of the rotor.
With the stator
It is one of the rotors that rotate with a gap between them and the stator.
The rotation of the rotor causes the exhaust gas to flow from the upstream side to the downstream side on the outside of the rotor.
In a vacuum pump component provided in a vacuum pump in which purge gas flows through the gap,
A screw groove portion that faces the gap and guides the purge gas as the rotor rotates is formed.
The thread groove portion is
A first thread groove portion located on the upstream side of the flow path of the purge gas and guiding the purge gas toward the upstream side of the flow path of the purge gas.
It has a second thread groove portion that is located on the downstream side of the flow path of the purge gas and guides the purge gas toward the downstream side of the flow path of the purge gas.
A vacuum pump component characterized in that the first range occupied by the first threaded groove portion is larger than the second range occupied by the second threaded groove portion.
The vacuum pump component according to claim 6, wherein the size of the first range is a size that changes the flow of the purge gas from an intermediate flow to a viscous flow.
The vacuum pump component according to claim 6 or 7, wherein the size of the second range satisfies the relationship of (reverse flow rate of the exhaust gas) <(transportation amount of the second screw groove portion).
The vacuum pump component according to any one of claims 6 to 8, wherein the size of the first range is at least twice the size of the second range.
The vacuum pump component according to any one of claims 6 to 9, wherein the vacuum pump is provided with an exhaust gas passage on the outside of the rotor and the gap on the inside of the rotor.