JPH04362294A - Screw type vacuum pump - Google Patents

Abstract

PURPOSE:To reduce the necessary power in the stationary operation after reaching an aimed degree of vacuum by forming a large and a small diameter part which correspond to each other on the inner peripheral surface of a stator which constituted a pump element and the outer peripheral surface of a rotor and forming a screw groove on the large diameter part or small. CONSTITUTION:Inside a casing which has a suction port and an exhaust port and is not shown on the figure, a pump element 2 which consists of a stator 21 and a rotor 22 which revolve to the stator 21 is accommodated. In this case, the rotor 22 is formed to a multistage form from a large diameter rotor part 22a whose suction port side has the larger diameter and at least one small diameter rotor part 22b whose exhaust port side has the smaller diameter. While, on the inner periphery of the stator 21, the large and small diameter inner peripheral surfaces 21a and 21b are formed oppositely to the outer peripheral surfaces of the large and small diameter rotor parts 22a and 33b, A screw groove 24 is formed at one between the outer peripheral surfaces of the large and small diameter rotor parts 22a and 22b and the large and small diameter inner peripheral surfaces 21a and 21b.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw-type vacuum pump used in semiconductor manufacturing equipment and the like.

0002

BACKGROUND OF THE INVENTION Conventionally, screw-type vacuum pumps are already known, as shown in, for example, Japanese Utility Model Application Publication No. 118392/1983. As shown in FIG. 6, this conventional screw-type vacuum pump has an intake port A connected to a semiconductor manufacturing room, etc. at the top, and a cylindrical cylinder at the upper part of the casing C, which has an exhaust port B in the middle part. A pump element M consisting of a shaped stator S and a cylindrical rotor E having a thread groove e on the outer circumferential surface opposite to the inner circumferential surface of the stator S is installed inside the casing C. By connecting the rotor E to the drive shaft I of the motor G disposed in the rotor E and rotating the rotor E at high speed, air flows from the air intake port A into the gas flow path J between the outer circumferential surface of the rotor E and the inner circumferential surface of the stator S. The gas from the exhaust port B
The semiconductor manufacturing chamber and the like are maintained in a vacuum by evacuation.

0003

[Problems to be Solved by the Invention] In the vacuum pump as described above, the rotor E has the task of discharging the gas from the intake port A side to the exhaust port B to reach a target degree of vacuum; After reaching the target degree of vacuum, the job of maintaining the degree of vacuum is to prevent the gas on the side of the exhaust port B from flowing back to the side of the gas flow path J during steady operation. That is, after the target degree of vacuum is reached, the flow rate in the gas flow path J is almost gone, so there is no work required to create a vacuum, but since the pressure is at atmospheric pressure at the exhaust port B, Work is required to prevent the atmosphere on the side of the exhaust port B from flowing back into the gas flow path J and to maintain the target degree of vacuum.

However, as shown in FIG. 6, the rotor E in the conventional screw-type vacuum pump described above is formed into a right cylindrical shape with the same diameter, and a thread groove e is provided on the outer peripheral surface of the rotor E. Therefore, the circumferential length of the rotor E at both ends in the axial direction is the same, and there is almost no difference in area between the opening area of the gas flow path J to the intake port A and the opening area of the gas flow path J to the exhaust port B. It is. Therefore, the amount of backflow of the atmosphere flowing back from the exhaust port B to the gas flow path J increases, so that after reaching a predetermined degree of vacuum, it takes a large amount of air to prevent the backflow of the atmosphere and maintain the target degree of vacuum. The amount of work required is the same, and the rotor E
Since it will be necessary to rotate the motor at high speed, the required power during steady operation will increase. In addition, since the rotor E, which is formed into a right cylindrical shape with the same diameter, has almost no difference in pressure receiving area between the end surface on the intake port A side and the end surface on the exhaust port B side, the rotor E is subjected to a large axial force F, That is, F=A0 (
P2 - P1) will act. In addition, A0 is the cross-sectional area of rotor E, P1 is the pressure on the intake port A side, and P2
is the pressure on the exhaust port B side. Therefore, an excessive load will be applied to the bearing K that supports the drive shaft H connected to the rotor E, so if a magnetic bearing is used, the electromagnet will be large and it will be difficult to perform magnetic control. However, when ball bearings are used, there is a problem that the durability of the bearings is deteriorated.

The present invention was invented in view of the above problems, and its purpose is to reduce the power required during steady operation after reaching the target degree of vacuum, and to reduce the axial force acting on the rotor. The advantage is that it can be made small and also allows for high vacuum.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a stator 21 in a casing 1 having an intake port 4 and an exhaust port 5, and a rotor 22 rotatable with respect to the stator 21. In the screw type vacuum pump, the rotor 22 has a large diameter rotor part 22a having a large diameter on the side of the intake port 4, and at least one small diameter rotor part 22a having a small diameter on the side of the exhaust port 5. Part 22
b, and the stator 21 is provided with a large-diameter inner circumferential surface 21a and a small-diameter inner circumferential surface 21b facing the outer circumferential surfaces of the respective rotor parts 22a and 22b of the rotor 22 on the inner periphery of the stator 21. The outer peripheral surface of each rotor portion 22a, 22b,
A thread groove 24 is provided on one of the inner peripheral surfaces 21a and 21b.

The large diameter rotor portion 22a and the small diameter rotor portion 22b of the rotor 22 may be formed integrally,
Alternatively, the large-diameter rotor portion 22a and the small-diameter rotor portion 22b may be formed separately, and the thread grooves 24 may be provided on the outer peripheral surfaces of each of the rotor portions 22a, 22b.

[0008] Furthermore, the large diameter inner circumferential surface 21 of the stator 21
The a section and the small diameter inner circumferential surface 21b section can be formed integrally, or the large diameter inner circumferential surface 21a section and the small diameter inner circumferential surface 21
It is also possible to form the screw groove 24 separately from the b portion and provide the thread groove 24 on each inner circumferential surface 21a, 21b.

Further, it is preferable that the thread groove 24 has a groove depth H1, a groove pitch H2, and a helical angle H3 that are large on the large diameter side and small on the small diameter side.

0010

[Operation] When vacuuming is performed by rotating the rotor 22 at high speed, the gas in a chamber such as a semiconductor manufacturing chamber that communicates with the intake port 4 is transferred to the gas flow between the large-diameter rotor portion 22a and the large-diameter inner peripheral surface 21a. Through the path, the small diameter rotor portion 22b and the small diameter inner peripheral surface 21b
The rotor 22 is formed in multiple stages including a large diameter rotor part 22a and a small diameter rotor part 22b.
Since the circumferential lengths at both axial ends of the gas flow path are different, and the opening area of the gas flow path toward the exhaust port 5 side is made smaller than the opening area toward the intake port 4 side, the target degree of vacuum can be achieved. After reaching , the amount of atmospheric air flowing back from the exhaust port 5 into the gas flow path can be reduced. Therefore, after the target degree of vacuum is reached, the amount of work required to prevent the atmospheric backflow and maintain the target degree of vacuum can be reduced, and the power required during steady operation can be reduced accordingly.

In other words, as shown in FIG. 5, in a pump using rotors of different sizes but similar in shape, the power required to rotate the large diameter rotor is L1, and the power required to rotate the small diameter rotor is L1. If the power required for is known to be proportional to the cube of the ratio of the rotor rotational speed N1 and N2, and the differential pressure between the gas inlet pressure and outlet pressure of the large-diameter rotor is expressed as △P1
The differential pressure between the gas inlet pressure and outlet pressure of the small diameter rotor is △P.
2, △P2 /△P1 is proportional to the square of the ratio of rotor outer diameters D1 and D2 and the square of the ratio of rotor rotational speeds N1 and N2, as shown in Equation 2. It has been known. In Equation 1, the gas outlet pressure of the large-diameter rotor is P1, and the gas outlet pressure of the small-diameter rotor is P2.

0012

[Math 1]

[0013]

[Math 2]

Since the power L required to rotate the rotor is proportional to the gas pressure P, the fifth power of the rotor outer diameter D, and the third power of the rotor rotational speed N, the power L is In order to reduce the rotor speed, it is better to reduce the rotor outer diameter D, which varies by a value to the fifth power, than by reducing the rotor rotational speed N, which varies by a square value.
Moreover, the rotor 22 is made multi-stage, and the small diameter rotor portion 22
By providing b on the exhaust port 5 side, the amount of backflow of the atmosphere after reaching the target degree of vacuum is also small.
Even if the power is reduced, there is no reduction in vacuum capacity.

Furthermore, since the small diameter rotor portion 22b of the rotor 22 formed in multiple stages is provided on the exhaust port 5 side, the pressure receiving area of the end face on the exhaust port 5 side can be made smaller than the pressure receiving area on the intake port 4 side. Therefore, the axial force acting on the rotor 22 can be reduced, and the load on the bearing supporting the drive shaft connected to the rotor 22 can be reduced accordingly.

Furthermore, since the rotor 22 formed in multiple stages has its small-diameter rotor portion 22b provided on the exhaust port 5 side, the differential pressure between the gas inlet pressure and outlet pressure of the large-diameter rotor portion 22a can be reduced by △.
P1 and the pressure difference between the gas inlet pressure and the outlet pressure of the small diameter rotor portion 22b is ΔP2.As is clear from Equation 2 above, by reducing the outer diameter D2 of the small diameter rotor portion 22b, ΔP2 is /ΔP1 can be made small and a high vacuum can be achieved.

[0017] Also, the large diameter rotor portion 22a of the rotor 22
By integrally forming the small diameter rotor portion 22b,
The center runout in each rotor portion 22a, 22b can be easily reduced. Similarly, by integrally forming the large-diameter inner circumferential surface 21a and the small-diameter inner circumferential surface 21b of the stator 21, it is possible to easily center the inner circumferential surfaces 21a and 21b.

Furthermore, the large diameter rotor portion 22 of the rotor 22
By forming the small diameter rotor portion 22b separately and providing the thread groove 24 on the outer peripheral surface of each rotor portion 22a, 22b, it is easy to process the thread groove 24 of each rotor portion 22a, 22b. That is how much the cost can be reduced. Similarly, the large diameter inner peripheral surface 21 of the stator 21
By forming the part a and the small diameter inner circumferential surface 21b separately and providing the thread grooves 24 on each inner circumferential surface 21a, 21b, it is easy to process the thread grooves 24 on each inner circumferential surface 21a, 21b. Yes, and the cost can be reduced accordingly.

Furthermore, the thread groove 24 has a groove depth H1, a groove pitch H2, and a helical angle H3 that are large on the large diameter side and small on the small diameter side, thereby reducing the differential pressure per unit length. can be made larger, making it possible to create an even higher vacuum.

[0020]

[Example] The vacuum pump shown in FIGS. 1 and 2 has a partition wall 1
A pump element 2 consisting of a cylindrical stator 21 and a rotor 22 that is rotatable with respect to the stator 21 is housed inside the upper part of the casing 1 which is divided into upper and lower parts via a, and a motor is installed inside the lower part of the casing 1. 3 is arranged, and the drive shaft 31 of this motor 3 is coupled to the rotor 22 through the partition wall 1a. Further, an intake port 4 connected to a semiconductor manufacturing room or the like is provided at the upper end of the casing 1, and an exhaust port 5 opened to the outside is provided in the partition wall 1a to rotate the rotor 22 at high speed. The gas flowing into the gas flow path 23 between the rotor 22 and the stator 21 from the intake port 4 is discharged to the exhaust port 5 while increasing the pressure, thereby evacuating the semiconductor manufacturing room etc. I try to keep it in a vacuum.

[0021] As shown in FIG. 1, the rotor 22 has a large-diameter rotor portion 22a whose diameter is larger on the side of the intake port 4.
and three small-diameter rotor parts 22b, 22b, 22b whose diameters are gradually reduced on the exhaust port 5 side. a large-diameter inner circumferential surface 21a facing each other with a slight interval therebetween, and each of the small-diameter rotor portions 22b, 22.
Three small-diameter inner circumferential surfaces 21b, 21b, 21b facing the outer circumferential surfaces of the rotor parts 22a, 22b with a slight interval are provided in stages, and a threaded groove 24 is formed on the outer circumferential surface of each of the rotor parts 22a, 22b.
was established.

As shown in FIG. 2, the thread groove 24 preferably has a groove depth H1, a groove pitch H2, and a helical angle H3 that are different between the rotor parts 22a and 22b. That is, in the large diameter rotor portion 22a, the groove depth H1
, groove pitch H2, and helical angle H3 are increased to increase the discharge flow rate, and in the minimum diameter rotor portion 22b, the groove depth H1, groove pitch H2, and helical angle H3 are increased. It is preferable to make the diameter smaller than that of the small diameter rotor portion 22b so that the differential pressure per unit length can be increased. Note that the thread groove 24 has the groove depth H1,
Either one or both of the groove pitch H2 and the helical angle H3 may be made different between the rotor parts 22a and 22b as described above.

Furthermore, the gas flow path 23 between the large-diameter rotor portion 22a and the large-diameter inner peripheral surface 21a, and each small-diameter rotor portion 22
b and the gas flow paths 23 between each small-diameter inner circumferential surface 21b are in communication with each other via a predetermined vertical gap N. These vertical gaps N are preferably set to 1 mm or more in order to ensure the discharge flow rate and to avoid contact between the rotor 22 and the stator 21 due to the difference in thermal expansion between the drive shaft 31 and the rotor 22 and the stator 21. .

[0024] The rotor 22 also includes each rotor portion 22a.
, 22b are integrally formed or formed separately and connected to each rotor part 22a, 22b or to the drive shaft 31 so as to be integrally rotatable.

In FIG. 1, 6 is an upper radial magnetic bearing, 7 is a lower radial magnetic bearing, 8 is a thrust magnetic bearing, 9 is an upper touchdown bearing, 10 is a lower touchdown bearing, and 11 is the pump element 2. Cooling piping 12 is a cooling piping that cools the motor 3.

In the screw-type vacuum pump constructed as described above, the rotor 22 rotates at a high speed of, for example, about tens of thousands of times per minute by the drive of the motor 3, and the rotor 22 generates a gas flow from the intake port 4. The gas flowing into the passage 23 is discharged to the exhaust port 5, where the atmospheric pressure (76
0T0 rr) and is discharged to the outside from the exhaust port 5 at this atmospheric pressure. After the intake port 4 side reaches the target degree of vacuum, the gas flow path 2
3, the amount of work required to create a vacuum becomes very small. However, since the pressure is at atmospheric pressure at the exhaust port 5, the rotor 22 is continuously rotated to remove the atmosphere from the gas flow. It is necessary to prevent backflow into channel 23 and maintain the target vacuum level.

The rotor 22 is formed in multiple stages including a large diameter rotor portion 22a and three small diameter rotor portions 22b, and the outer diameter D2 of the rotor 22 on the exhaust port 5 side is set to the intake port 4.
Since it is formed to have a smaller diameter than the side outer diameter D1 and the opening area of the gas flow path 23 to the exhaust port 5 is smaller than the opening area to the intake port 4, after reaching the target degree of vacuum, This makes it possible to reduce the amount of atmospheric air flowing back from the exhaust port 5 into the gas flow path 23. Therefore, after the target degree of vacuum is reached, the amount of work required to prevent atmospheric backflow can be reduced, and the power required during steady operation can be reduced accordingly. In other words, D2 in Equation 1 becomes small, (D2 /D1)5 becomes small, and the power L
2/L1 can be reduced. Therefore, since the amount of heat generated by the motor 3 can be reduced, the motor 3 can be made smaller, and the amount of cooling water used to suppress heat generation in the motor 3 can be reduced, and running costs can be reduced. Furthermore, since the rotor 22 is formed in multiple stages as described above to reduce the backflow of the atmosphere, the target degree of vacuum can be maintained even if the power for driving the rotor 22 is reduced. , the vacuum capacity will not go down.

Furthermore, by providing the small diameter rotor portion 22b of the rotor 22 formed in multiple stages on the exhaust port 5 side, the pressure receiving area of the end surface on the side of the exhaust port 5 can be made smaller than the pressure receiving area of the end surface on the side of the intake port 4. Therefore, the axial force acting on the rotor 22 can be reduced, and the load on the bearings 6 to 8 that support the drive shaft 31 connected to the rotor 22 can be reduced accordingly, and the electromagnets of the bearings 6 to 8 can be made smaller. At the same time, magnetic control can be made easier.

[0029] Also, the outer diameter D2 of the small diameter rotor portion 22b
By reducing △P2 /△P in the above equation 2
Since 1 can be made small, a high vacuum can be created.

In the embodiment described above, the rotor 22
Although three small-diameter rotor parts 22b are provided in the above, the number of small-diameter rotor parts 22b may be one or two;
There may be four or more.

Further, in the above embodiment, the thread grooves 24 were provided on the outer peripheral surface of each of the rotor parts 22a and 22b of the rotor 22, but in addition, as shown in FIG.
1a, 21b may be provided with the thread groove 24, and each rotor portion 22a of the rotor 22 may be provided with the thread groove 24, although not shown.
, 22b outer peripheral surface, and each inner peripheral surface 21a of the stator 21.
, 21b may be provided with the thread groove 24 to increase the differential pressure per unit length. Furthermore, the stator 21
When providing the thread groove 24 on each inner circumferential surface 21a, 21b,
The inner circumferential surfaces 21a and 21b are formed integrally or separately. Furthermore, when the thread grooves 24 are provided on the outer peripheral surface of each of the rotor parts 22a and 22b of the rotor 22, each small diameter inner peripheral surface 2 of the stator 21 as shown in FIG.
1b may be provided with a plurality of circumferential grooves 25 at predetermined intervals in the axial direction to increase the differential pressure per unit length. 2
1a and 21b, each rotor portion 22a and 22b of the rotor 22 is provided with the thread groove 24, as in FIG.
A plurality of circumferential grooves may be provided at predetermined intervals in the axial direction on the outer circumferential surface of the tube to increase the differential pressure per unit length.

Further, although FIG. 1 shows a vacuum pump in which the drive shaft 31 of the motor 3 is supported by magnetic bearings 6 to 8, other vacuum pumps in which the drive shaft 31 is supported by ball bearings, for example, may be used. Good too.

[0033]

As described above, the present invention provides a rotor 22 rotatable with respect to a stator 21, with a large diameter rotor portion 22a having a large diameter on the intake port 4 side, and at least one small diameter rotor portion 22a having a small diameter on the exhaust port 5 side. A large-diameter inner circumferential surface 21a is formed in multiple stages by a large-diameter inner circumferential surface 21a on the inner circumference of the stator 21, and faces the outer circumferential surface of each rotor section 22a, 22b of the rotor 22.
and a small diameter inner circumferential surface 21b, each of the rotor portions 22a,
A screw groove 24 is provided on one of the outer peripheral surface of the rotor 22b and the inner peripheral surfaces 21a and 21b, so that the rotor 22 and the stator 2
Since the opening area of the gas flow path between the exhaust port 5 and the exhaust port 5 can be made smaller than the opening area of the gas flow path toward the intake port 4, after reaching the target degree of vacuum, the This makes it possible to reduce the amount of air flowing back into the gas flow path. Therefore, after the target degree of vacuum is reached, the amount of work required to prevent the atmospheric backflow and maintain the target degree of vacuum can be reduced, and the power required during steady operation can be reduced accordingly. By reducing the required power, the amount of heat generated by the motor that drives the rotor 22 can be reduced, making it possible to downsize the motor, reducing initial costs, and reducing the voltage applied to the motor. At the same time, since the amount of cooling water used to suppress heat generated by the motor etc. can be reduced, running costs can be reduced.

Moreover, since the small diameter rotor portion 22b of the rotor 22 formed in multiple stages is provided on the exhaust port 5 side, the pressure receiving area of the end surface on the side of the exhaust port 5 can be made smaller than the pressure receiving area of the end surface on the side of the intake port 4. Therefore, the axial force acting on the rotor 22 can be reduced, and the load on the bearing supporting the drive shaft connected to the rotor 22 can be reduced accordingly. Therefore, when a magnetic bearing is used, the electromagnet can be made smaller and magnetic control can be made easier, and when a ball bearing is used, the durability of the bearing can be increased.

Furthermore, while reducing the required power and reducing the axial force as described above, by reducing the outer diameter D2 of the small diameter rotor portion 22b, △P2/△P1 in Equation 2 can be reduced. This makes high vacuum possible.

Furthermore, each rotor portion 22a of the rotor 22,
22b is formed integrally, each rotor part 22a, 22b
It is possible to easily reduce the center runout in the
If each rotor part 22a, 22b is formed separately and the thread groove 24 is provided on the outer peripheral surface of each rotor part 22a, 22b, it is easy to process the thread groove 24 of each rotor part 22a, 22b. That is how much the cost can be reduced.

Similarly, each inner peripheral surface 21 of the stator 21
If the a and 21b parts are integrally formed, each inner peripheral surface 21a and 2
It is possible to easily center the part 1b, and
If the inner circumferential surfaces 21a and 21b are formed separately and the thread grooves 24 are provided on each of the inner circumferential surfaces 21a and 21b, it is easy to process the thread grooves 24 on the inner circumferential surfaces 21a and 21b. , the cost can be reduced accordingly.

Furthermore, the thread groove 24 has a groove depth H1, a groove pitch H2, and a helical angle H3 that are large on the large diameter side and small on the small diameter side, thereby reducing the differential pressure per unit length. can be made larger, making it possible to create an even higher vacuum.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a vacuum pump of the present invention.

FIG. 2 is a partial sectional view of only the essential parts.

FIG. 3 is a partial cross-sectional view of only essential parts showing another embodiment.

FIG. 4 is a partial cross-sectional view of only the main parts showing another embodiment.

FIG. 5 is an explanatory diagram for explaining Formulas 1 and 2.

FIG. 6 is a sectional view of a conventional example.

[Explanation of symbols]

1 Casing 2 Pump element 21 Stator 21a Large diameter inner circumferential surface 21b Small diameter inner circumferential surface 22 Rotor 22a Large diameter rotor part 22b Small diameter rotor part 24 Thread groove 4 Intake port 5 Exhaust port

Claims (6)

[Claims] 1. A screw-type vacuum pump comprising a pump element 2 consisting of a stator 21 and a rotor 22 rotatable relative to the stator 21 inside a casing 1 having an intake port 4 and an exhaust port 5. , the rotor 22 has a large diameter rotor part 22a with a large diameter on the side of the intake port 4, and at least one small diameter rotor part 22b with a small diameter on the side of the exhaust port 5.
The stator 21 is formed in multiple stages, and a large diameter inner circumferential surface 21a and a small diameter inner circumferential surface 21b are provided on the inner periphery of the stator 21, and are opposed to the outer circumferential surfaces of the respective rotor parts 22a and 22b of the rotor 22. A screw-type vacuum pump characterized in that a thread groove 24 is provided on one of the outer circumferential surface of the rotor portions 22a and 22b and the respective inner circumferential surfaces 21a and 21b. 2. The screw-type vacuum pump according to claim 1, wherein the large diameter rotor portion 22a and the small diameter rotor portion 22b of the rotor 22 are integrally formed. 3. A large-diameter rotor portion 22a and a small-diameter rotor portion 22b of the rotor 22 are formed separately and connected to be rotatable together, and a threaded groove 24 is provided on the outer peripheral surface of each of these rotor portions 22a, 22b. A screw-type vacuum pump according to claim 1, further comprising: a screw type vacuum pump. 4. The screw-type vacuum pump according to claim 1, wherein the large-diameter inner circumferential surface 21a and the small-diameter inner circumferential surface 21b of the stator 21 are integrally formed. 5. The large-diameter inner circumferential surface 21a and the small-diameter inner circumferential surface 21b of the stator 21 are formed separately, and each inner circumferential surface 21a
, 21b are provided with a thread groove (24). 6. The threaded vacuum pump according to claim 1, wherein the threaded groove 24 has a groove depth H1, a groove pitch H2, and a helical angle H3 that are larger on the larger diameter side and smaller on the smaller diameter side. .