GB2146073A

GB2146073A - Turbomolecular pumps

Info

Publication number: GB2146073A
Application number: GB08419569A
Authority: GB
Inventors: Tadao Ishizawa
Original assignee: Seiko Seiki KK
Current assignee: Seiko Seiki KK
Priority date: 1983-08-16
Filing date: 1984-08-01
Publication date: 1985-04-11
Also published as: FR2550829B1; JPS6034594U; GB8419569D0; JPS6332393Y2; DE3429137C2; GB2146073B; DE3429137A1; FR2550829A1

Abstract

The pump comprises a rotor which is rotatably mounted within a vertically extending housing (2) which has a fluid inlet at its upper end (2d) the lower end of the rotor housing (2) being closed by a base member (3) having a side wall (3a) provided with a fluid outlet (4) for connection to an auxiliary pump, the base member (3) having a bottom wall (3b) through which extends at least one opening which connects the interior of the rotor housing (2) to the exterior thereof, the base member (3) being provided with screw holes for connecting the base member (3) to a cover (36) or to the inlet of a second turbomolecular pump. <IMAGE>

Description

SPECIFICATION Pump The present invention relates to a pump and, although the invention is not so restricted, it relates more particularly to a vertical type turbo-molecular pump having means permitting a series connection either to another turbo-molecular pump or to other vacuum apparatus.

Turbo-molecular pumps are particularly suitable for systems, such as evaporation devices, particle accelerators and electron microscopes, which require a high vacuum or an ultra-high vacuum, which tend to be damaged by pollution caused by hydrocarbon vapors, and which must have high discharge speeds.

Although the invention is primarily directed to any novel integer or step, or combination of integers or steps, as herein described and/or shown in the accompanying drawings, nevertheless according to one particular aspect of the present invention to which however the invention is in no way restricted, there is provided a pump comprising a rotor which is rotatably mounted within a vertically extending rotor housing which has a fluid inlet at its upper end, the lower end of the rotor housing being closed by a base member having a side wall provided with a fluid outlet, the base member having a bottom wall through which extends at least one opening which connects the interior of the rotor housing to the exterior thereof, the base member being provided with connector means for connecting the base member to a cover or to further equipment.

Preferably the pump is a turbo-molecular pump.

The rotor is preferably provided with a plurality of rotor vanes which alternate with stators fixed to the interior of the rotor housing.

The connector means are preferably arranged radially outwardly of the said opening or openings and may comprise an annular array of angularly spaced apart screw holes.

There are preferably a plurality of angularly spaced apart openings.

Preferably, the cross-sectional area, or the total cross-sectional area, of the said at least one opening is greater than that of the said fluid outlet.

Preferably each said opening extends axially of the rotor housing.

The side wall of the base member may be provided with an electrical connector which is connected to any electric motor for driving the rotor.

The said cover may be sealed to the said bottom wall by way of a sealing member.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figure 1 is an elevation of a two-stage pump assembly comprising two interconnected vertical turbo-molecular pumps, Figure 2 is a longitudinal section through one embodiment of a vertical turbo-molecular pump according to the present invention; Figure 3 is a view looking in the direction of the arrow A of Figure 2, and Figures 4(A) and (B) illustrate examples of assemblies of turbo-molecular pumps according to the present invention.

In Figure 1 there is shown a previously suggested vertical turbo-molecular pump which is formed basically of a rotor housing 2, whose upper or fluid inlet end is connected by a flange 2b to the lower end of a vacuum chamber 1, and a base member 3 which is hermetically secured to the lower end of the rotor housing 2. Within the rotor housing 2 there are a plurality of stator stages (not shown) and a rotor (not shown). The latter is provided with a plurality of rotor vanes (not shown) arranged so that they alternate with the stators, the upper end of the rotor being rotatably mounted in the rotor housing 2. The base of the rotor is rotatably supported within the base member 3.A discharge pipe 4, which constitutes a fluid outlet from the rotor housing 2, and an electrical connector 5, which is connected to a motor (not shown) for driving the rotor, are provided on opposite sides respectively of the base member 3.

In normal use, the discharge pipe 4 side of the vertical turbo-molecular pump thus constructed is connected to an auxiliary oil-sealed rotary vacuum pump (not shown) or the like by a suction hose (not shown) to provide an auxiliary discharge.

In such a vertical turbo-molecular pump, the diffusion of oil from the auxiliary pump can be prevented and an ultra-high vacuum can be obtained by connecting two stages of such vertical turbomolecular pumps to each other, as shown in Figure 1.

With previously suggested vertical turbomolecular pumps, however, the discharge pipes 4 or other discharge members thereof are designed only from the point of view of this connection to an auxiliary pump, although the suction-side opening, for the connection of the suction side of the turbomolecular pump to the vacuum chamber, has a large area. Accordingly, when turbo-moleclar pumps are connected to each other as described above, they can only be connected by means of the discharge pipe 4 of one of them, as shown in Figure 1.

More specifically, one end of an elbow 6 is attached to the outer end of the discharge pipe 4 of one of the turbo-molecular pumps, and the other end of the elbow 6 is connected to the inlet end of the other turbo-molecular pump. Since such a connection cannot provide sufficient rigidity to support the lower turbo-molecular pump, pump support means have been proposed, such as the provision of a support bracket 7, to bear the weight of the lower turbo-molecular pump.

However, the diameter of the discharge pipe 4 is not large enough, especially for the purpose of connecting two vertical turbo-molecular pumps to each other. In other words, the conductance (i.e. the ease of passage) of a gas through the discharge pipe 4 is reduced, and thus the gas which has passed through the upper orfirst-stage turbo-molecular pump encounters a large resistance to flow in the discharge pipe 4 and elbow 6 before it reaches the lower or second-stage turbo-molecular pump. This means that the efficiency of the assembly shown in Figure 1 is very low. In addition, the support of the second-stageturbo-molecular pump is unstable.

Vibrations, etc., are easily propagated in a structure in which such a connection is used between the pumps and such vibrations tend to damage equipment, such as an electron microscope in particular, which is readily affected thereby.

In Figures 2 and 3 there is therefore shown one embodiment of a vertical turbo-molecular pump according to the present invention which is designed to enable the direct stacking of turbo-molecular pumps, orthe direct stacking of one pump and of another vacuum apparatus.

In the description of Figures 2 and 3 components and members identical to those of the apparatus of Figure 1 are referred to by the same reference numerais.

In the vertical turbo-molecular pump shown in Figures 2 and 3, a vertically extending rotor housing 2 comprises a hollow cylindrical member 2a; a flange member 2b which is adapted to be connected to a vacuum chamber (not shown), the flange member 2b being secured to the top of the hollow cylindrical member 2a and being adapted to connect an upper or fluid inlet opening 2d of the latter which may be connected to suction and thus to the vacuum chamber; and a flange member or base part 2c positioned below the hollow cylindrical member 2a, the flange member 2c being hermetically sealed to the outer periphery of the upper edge of a base member 3 and being supported by the latter. Several stator stages 10 are provided internally of and are attached to the hollow cylindrical member 2a.The base member 3 closes the lower end of the rotor housing 2 whose upper end is provided with the fluid inlet opening 2d, the base member 3 having a side wall 3a, which is provided with a discharge pipe 4 which constitutes a fluid outlet, and a bottom wall 3b.

A rotor case 20 is arranged within both the rotor housing 2 and the base member 3. Several stages of rotor discs 22 are provided around the periphery of a rotor shaft 21 which is rotatably mounted within the rotor housing 2 and which extends from the upper side of the rotor case 20. Rotor vanes 23, which are provided around the outer periphery of each of the rotor discs 22, are arranged so that they are positioned alternately with the stators 10.

An electric driving motor (not shown) and a mechanism (not shown) for controlling this motor, are also housed in the rotor case 20, the side wall 3a of the base member 3 being provided with an electrical connector 5 which is connected to the said electric motor.

A flange member 24, which is provided at the lower portion of the rotor case 20, is attached to the upper edge of the base member 3 by bolts 22a.

Four angularly spaced apart openings 31 (Figure 2) are formed concentrically in the bottom wall 3b of the base member 3, the openings 31 establishing communication between the interior and the exterior of the base member 3, and thus of the rotor housing 2. If desired, however, one single opening 31 could be provided.

The total cross-sectional area of the openings 31 is made to be considerably iargerthan the internal cross-sectional area of the discharge pipe 4 which is provided to discharge gas sucked in by the rotation of the rotor. In addition, the openings 31 are arranged to extend axially of the rotor housing 2 and are thus formed along the straight line of the passage of the gas, so that the value of the conductance of the gas passing through the openings 31 is large.

A plurality of angularly spaced apart mounting screw holes 34 are formed in an annular array around the peripheral edge of the bottom of the base 3 and thus radially outwardly of the openings 31. A cover member 36 (Figure 2) is attached to the lower surface of the bottom wall 3b of the base member 3, with a sealing member 35 therebetween, by means of bolts 37 each of which is inserted into a screw hole 34 to attach the cover member 36 firmly to the said lower surface, whereby to seal the inner side of the base member 3 hermetically and thus to seal the lower end of the rotor housing 2.

The turbo-molecular pump shown in Figures 2 and 3 may be used as follows. The state shown in Figure 2 is that of the pump in normal use, wherein a normal vacuum is obtained by connecting the discharge pipe 4 to an oil-sealed rotary vacuum pump.

When two stages of turbo-molecular pumps are connected, an arrangement such as that shown in Figure 4 (A) can be used in which the upper suction side of the upper or first-stage turbo-molecular pump is connected to the vacuum chamber 1, and a vacuum pressure gauge 40 is connected to the discharge pipe 4 of this pump. One end of a hollow cylindrical connection member 41 is connected, instead of the cover member 36, to the lower surface of the bottom wall of the base member 3, and the suction-side flange member 2b of the lower or second-stage turbo-molecular pump is connected to the lower surface of the hollow cylindrical member 41,so that the two pumps can be stacked with the member 41 therebetween.

It is also possible in this embodiment to provide a butterfly valve or the like (not shown) within the hollow cylindrical member 41 to close the gas passage when the turbo-molecular pumps are stopped.

Figure 4(B) shows another embodiment which is such thatthe mounting screw holes (not shown in Figure 4 (B) but corresponding to the holes 34) in the base of one of the turbo-molecular pumps are matched with the shape and mounting screw holes of the flange member 2b of the other rotor housing.

In this embodiment, two or more turbo-molecular pumps can be stacked directly without the use of a hollow cylindrical member 41.

In the arrangements shown in Figures 4(A) and 4(B), the parts which are stacked are turbo-molecular pumps. It should be noted, however, that any other auxiliary pump, such as an oil diffusion pump for instance, can be connected to the lower surface of such a turbo-molecular pump. Any other vacuum apparatus can be attached directly to the opening or openings 31 in the base member 3, and the discharge pipe 4 can therefore support a vacuum gauge, or it can be sealed hermetically.

In the vertical turbo-molecular pump of the pre sent invention, as described above, the crosssectional area of a base opening thereof, or the total cross-sectional area of a plurality of such openings, can be made larger than that of a previously suggested pump shown in Figure 1 which is connected to an auxiliary vacuum pump by the discharge pipe projecting from the side thereof. Consequently, the conductance through the base opening or openings is larger than that of connection structure in which the discharge pipe 4 is used, the resistance to the passage of gas is reduced, the piping for connecting this passage is greatly simplified, the rigidity etc., of the pumps when connected is high, and a firm connection can be ensured. In addition, pumps can be combined into units according to the desired degree of vacuum.

Thus the present invention provides a structure which is suitable for the achieving of a far higher degree of vacuum than that of the previously suggested apparatus.

Claims

1. A pump comprising a rotor which is rotatably mounted within a vertically extending rotor housing which has a fluid inlet at its upper end, the lower end of the rotor housing being closed by a base member having a side wall provided with a fluid outlet, the base member having a bottom wall through which extends at least one opening which connects the interior of the rotor housing to the exterior thereof, the base member being provided with connector means for connecting the base member to a cover or to further equipment.

2. A pump as claimed in claim 1 in which the pump is a turbo-molecular pump.

3. A pump as claimed in claim 1 or 2 in which the rotor is provided with a plurality of rotor vanes which alternate with stators fixed to the interior of the rotor housing.

4. A pump as claimed in any preceding claim in which the connector means is arranged radially outwardly of the said opening or openings.

5. A pump as claimed in claim 4 in which the connector means comprise an annular array of angularly spaced apart screw holes.

6. A pump as claimed in any preceding claim in which there are a plurality of angularly spaced apart openings.

7. A pump as claimed in any preceding claim in which the cross-sectional area, or the total crosssectional area, of the said at least one opening is greater than that of the said fluid outlet.

8. A pump as claimed in any preceding claim in which the or each said opening extends axially of the rotor housing.

9. A pump as claimed in any preceding claim in which the side wall of the base member is provided with an electrical connector which is connected to any electric motor for driving the rotor.

10. A pump as claimed in any preceding claim in which the said cover is sealed to the said bottom wall by way of a sealing member.

11. A pump substantially as hereinbefore described with reference to and as shown in Figures 2-4 of the accompanying drawings.

12. Any novel integer or step, or combination of integers or steps, hereinbefore described and/or shown in the accompanying drawings, irrespective of whether the present claim is within the scope of, or relates to the same or a different invention from that of, the preceding claims.

13. A vertical turbo-molecular pump comprising a rotor housing provided with a plurality of stators fixed in stages to the inner peripheral part thereof and an upper opening connected to the suction side thereof; a rotor which is housed rotatably in said housing and is provided, around the periphery thereof, with a plurality of rotor vanes arranged alternately between adjacent of said stators; and a base which is fitted hermetically and integrally to the lower surface of said housing, which supports a base part of said rotor, and which is provided, on a side thereof, with a discharge pipe for discharging gas sucked in by the rotation of said rotor; said vertical turbo-molecular pump having opening means which connects the interior to the exterior of said base, and to a passage of said sucked gas, the opening means being formed on the lower side of said base; a connecting means for connecting said base to a cover or other vacuum apparatus, with a sealing membertherebetween, being formed on the outer lower side of the base around the peripheral edge of said opening means.