JPS60182394A - Turbomolecular pump - Google Patents

Abstract

PURPOSE:To spread the exhaust-enable range of a pump to the lower vacuum side by forming a spiral groove in the opposite direction to a spiral groove on a screw rotor, onto the inner peripheral surface of the peripheral wall surrounding the screw rotor, and increasing the compression-ratio increasing function for the screw rotor part. CONSTITUTION:On a screw rotor 5, not only a spiral groove 5a formed onto the outer peripheral surface, but a spiral groove 7a in the opposite direction to the spiral groove 5a is formed onto the peripheral wall surrounding the spiral groove 5a, keeping a minute gap, namely onto the inner surface of a spacer 7 fitted onto the inner peripheral surface of an outer frame 6 in the application drawing. Therefore, the spiral grooves 5a and 7a cross each other at each position turning by 180 deg., and the combined body parts 8a, 8b... constituted of the combined spaces of the grooves 5a and 7a are formed at the above-described positions as shown in the figure. These parts 8a, 8b... speedily revolve and lower to an exhaust port B side as the screw rotor 5 revolves at a high speed, and the combined body part pushes-out gas particles very strongly. Therefore, the exhaust speed efficiency is increased in comparison with the conventional.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial application field The present invention provides excellent pumping speed performance even in the low vacuum region.
The present invention relates to a turbomolecular pump that can be obtained.

C) Conventional technology Turbomolecular pumps, as is well known, are designed to mechanically blow out gas molecules to create an ultra-high vacuum.For this purpose, the pump body is rotated at high speed. The rotor has a rotor (rotary blade) having a tilt in the opposite direction, and a stator (rotor blade) having an inclination in the opposite direction, which are usually arranged in multiple stages alternately.

However, since this type of pump has a low compression ratio in its blade group, there is a disadvantage in that the pumping speed performance is significantly reduced in a low vacuum region as an operating characteristic. Specifically, in conventional turbomolecular pumps, the pumping speed deteriorates rapidly from a vacuum level of about 101 to 10-1 Torr, and the pumping speed decreases to 0. I
At around Torr, the pumping speed is almost equal to nothing. For this reason, when operating a turbo molecular pump in a low vacuum region, it is necessary to connect an appropriate auxiliary vacuum pump such as (turbo molecular pump) + (mechanical boost pump) + (rotary pump) to cover its exhaust capacity. It is common to use an exhaust system.

On the other hand, a so-called composite turbo-molecular pump has been developed to alleviate such auxiliary vacuum (Japanese Patent Publication No. 47-33446, etc.).

That is, this compound pump is equipped with a group of impellers in which rotors and stators are arranged alternately on its intake port side, and has a spiral groove on its exhaust port side that guides the exhaust air from the group of impellers. It consists of a series of screw rotors installed on the outer periphery, and the spiral groove guides gas molecules in the circumferential direction while gradually changing the groove depth (gradually making the groove shallower) toward the exhaust port. The compression ratio is increased. Although this device achieves a considerable effect of increasing the compression ratio due to the function of the helical groove, the structure is complicated and the cost is increased by connecting screw rotors and forming elaborate helical grooves on the outer periphery. Compared to the disadvantages of the up-type compressor, it is regrettable that the advantages of the composite structure have not yet been fully utilized in order to achieve a greater effect of increasing the compression ratio.

(c) Purpose The present invention was made based on the above technical background, and basically adopts the configuration of the above-mentioned compound pump, but further adds a spiral groove provided on the outer periphery of the screw rotor. It is an object of the present invention to provide a turbo-molecular pump that can double the compression ratio increasing function of the screw rotor portion by improving the pump, thereby expanding the evacuable range of the pump to a lower vacuum side.

(d) Configuration The present invention aims to achieve such an objective.

In a turbo-molecular pump that rotates the rotor of a group of impellers in which rotors and stators are arranged alternately at high speed to exhaust air, a spiral groove is formed on the outer circumferential surface of the group of impellers, which rotates at high speed together with the rotor, on the exhaust port side of the group of impellers. The screw rotor is characterized in that screw rotors are provided in series, and a helical groove in the opposite direction to the helical groove of the screw rotor is provided on the inner circumferential surface of a peripheral wall surrounding the screw rotor.

(e) Examples Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 illustrates the configuration of the main parts of a turbomolecular pump according to the present invention, and this pump is equipped with a blade wheel group JJ2 consisting of a combination of a rotor 2 and a stator 3 on the intake port A side, and is connected to the impeller group JJ2. A screw rotor 5 is provided on the exhaust port B side. That is, the blade wheel group located at the upper side of the figure has a blade 52a projecting from the outer periphery at a predetermined angle of inclination, and the base end 2b of the blade wheel group is fitted externally to the drive shaft l located at the center. A rotor 2 fixed in multiple stages on the shaft l, and 9R2a of this rotor 2,! l- It has blades 3a with opposite inclination angles and extends its base end 3d from the outer periphery surrounding the rotor 2 to the outer frame 6.
The stator 3 is positioned and fixed by being sandwiched between spacers 4.4 stacked on the inner peripheral surface of the stator 3, and the blades 2a and 3a of the stator 3 are arranged alternately. When such a group of impellers rotates at high speed with the rotor mass 2a being driven by the drive shaft l,
It collides with the gas molecules to give them axial momentum, and the intake port A at one end of the stator blades 3a cooperates with the stator blades 3a.
A flow is forcibly generated from the exhaust port B at the other end,
It has the function of exhausting air.

On the other hand, the screw rotor 5 located in the F direction in the figure is connected to the drive shaft 1 with its upper end adjacent to the lower end of the impeller group. A drive shaft 1 passes through the center of the screw rotor 5, and is fixed to the drive shaft 1 so as to rotate at high speed together with the rotor 2. The outer circumferential surface of the screw rotor 5 is formed with a spiral groove that connects its upper and lower ends and gradually becomes shallower toward the exhaust port B side.
A thread groove) 5a is provided. In addition, this spiral groove 5
The direction a is such that the gas molecules discharged from the impeller group are directed toward the exhaust port B along the grooves with respect to the rotational direction of the drive shaft 1.

Now, in the conventional compound pump, the above-described helical groove 5 is formed only on either the outer peripheral surface of the screw rotor 5 or the inner peripheral surface of the peripheral wall surrounding the screw rotor 5.
I am trying to provide a. In contrast, in the present invention, the spacer 7 is fitted not only to the outer circumferential surface of the screw rotor 5 but also to the circumferential wall surrounding it with a minute gap, and in the illustrated embodiment, to the inner circumferential surface of the outer frame 6. A spiral groove 7a is also provided on the inner circumferential surface. The helical groove 7a is also formed so that its groove depth becomes shallower toward the exhaust port B side, and the direction of the helical groove 7a is opposite to that of the helical groove 5a of the screw rotor 5 that faces it. 5. Therefore, the spiral grooves 5a and 7a are 180 mm deep in the bud.
As shown in the figure, the spaces between the two grooves 5a and 7a intersect at each position where the two grooves turn.
... will be formed.

Next, the operation of this turbomolecular pump will be explained.

The drive shaft 1 is rotationally driven by a motor built in the lower side, and the rotor 2 and the screw rotor 5 on the shaft 1 are rotated at high speed and put into operation. Then, as described above, the gas molecules taken in from the intake port A are forced to pass through the impeller group, and then the helical grooves 5a and 7 on the outer periphery of the screw rotor 5.
It will lead you to a. Here, similar to the conventional compound pump, the screw rotor 5 rotating at high speed imparts momentum to the colliding gas molecules in the circumferential direction along the spiral grooves 5a, compressing them and exhausting them. ) The reverse spiral groove 7a provided facing the spacer 7 serves to double the effect.

That is, the combined portions 8a, 8b, . . . formed by the helical grooves 5a and 7a that intersect with each other form intermittently gas molecule storage portions in the exhaust passage formed by the helical groove 5a. At the same time, a wall surface in the radial direction is created which gives the gas molecules the most effective interlocking thickness in the circumferential direction.
This is because as the screw rotor 5 rotates at a high speed, the screws b--. rotate rapidly and descend toward the exhaust port B side, exerting the function of pushing out one gas molecule very strongly. now,
Spiral grooves 5a and 7a under rotation of the screw rotor 5
To explain the movement of the combined parts 8a, 8b and fist,
As shown in the developed diagram in Figure 2, 1 is located at the intersection of the two.
When the screw rotor 5 rotates, the combined portions 8a, 8b, .
8a-+8a'-+8a", 8b+8b', respectively
→8b”,...Moves downward while changing the Φ and its phase.At this time, the moving speed of each combined part in the axial direction is
Since the spiral grooves 5a and 7a are provided in opposite directions, the movement speed of the groove is twice as high as that in the case where the spiral groove 5a is used alone. Therefore, even if a large compression ratio is given, a sufficiently large exhaust speed can be obtained at the screw rotor 5 portion.

In such a turbo molecular pump, the spiral grooves 5a and 7a provided on the outer periphery of the screw rotor 5, which face each other and intersect with each other, exert a unique synergistic effect as described above, and are different from the conventional composite type pump. In comparison, it can be said that the pumping speed capability has been doubled and the features of the composite structure have been fully utilized. Moreover, compared to a normal turbo-molecular pump, this pump has a large pumping speed capability by extending its pumping speed curve toward the low vacuum side. Specifically, with this configuration, 1
10-I even at a vacuum level of 0-10 Torr
The vacuum level is less than 1 Torr and the same pumping speed is ensured.
0. A certain amount of exhaust speed is maintained even at around I Torr. Therefore, when using this pump, there is no need to connect auxiliary pumps in multiple stages for vacuum support as in the past, and a simple exhaust system can be used. Cost reduction will be achieved. Moreover, even when compared to conventional compound pumps, although the capacity is greatly increased, the structure remains almost the same in complexity.

In the illustrated embodiment, the spiral grooves 5a and 7a are shown to be coarse for convenience, but in practice, they can be formed to have a narrow width and a long groove length. Further, the cross-sectional shape of the groove can be modified in various ways other than the rectangular shape shown in the figure. Further, the spiral grooves 5a and 7a may be oriented in opposite directions, and the direction of the grooves 5a is not limited to that in the above embodiment.

(F) Effect The present invention has the above-mentioned configuration, and although it does not cause much structural complexity compared to conventional compound pumps, it is one step larger than conventional compound pumps. It is possible to provide a pumping speed capability, thereby providing a turbomolecular pump that can exhibit excellent pumping speed in a low vacuum region even when used alone.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of the main part of a pump showing one embodiment of the present invention. FIG. 2 is a developed view for explaining the operation of the spiral groove provided on the outer periphery of the screw rotor. l-φ, adjusting shaft 2φ, φ rotor 3, fist, stator 50 fist 11, rotor 5a, 7a, 1 spiral groove 7... spacer (peripheral wall) agent patent attorney Hiroshi Akazawa LI JuJ.

Claims (1)

[Claims] In a turbo-molecular pump that rotates and exhausts the rotor of a group of impellers in which the rotor and stator are arranged without intersecting each other, the rotor is rotated at high speed to exhaust the rotor. A tarp molecular pump characterized in that a screw rotor provided with a groove is arranged in series, and a helical groove in the opposite direction to the helical groove of the screw rotor is provided on the inner circumferential surface of a peripheral wall surrounding the screw rotor.