JPH01237384A - vacuum pump equipment - Google Patents

Abstract

PURPOSE:To increase the speed of discharge and reduce pressure increased so as to improve the performance of a pump by respectively disposing a volume type compressor pump with a pair of screw rotors and a molecular type pump with rotors having screw grooves on discharge and suction sides, respectively. CONSTITUTION:An operation chamber 6 is formed with a pair of screw rotors 4a, 4b with respect to a discharge casing 1. A flow passage 7 is formed with a pair of rotors 5a, 5b having screw grooves with respect to a casing on a suction side. The rotors 4a, 4b and the rotors 5a, 5b are respectively fitted monolithically to rotor shafts 10a, 10b. Both ends of the respective shaft 10a, 10b, on the other hand, are supported by rolling bearings 11a, 11b, 12a, 12b, respectively. Further, the rotors 4a, 4b are meshed with each other through timing gears 13a, 13b fitted at the ends of the rotor shafts 10a, 10b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vacuum pump device, and particularly to an oil-free vacuum pump device suitable for obtaining a clean vacuum in, for example, semiconductor manufacturing equipment. It is.

[Conventional technology]

As a vacuum pump that can exhaust from atmospheric pressure to 10' Torr level, for example,
A screw vacuum pump described in the above publication is known.

A feature of this screw vacuum pump is that the working chamber formed by a pair of male and female screw rotors and a casing has two or three sealed parts between the suction port and the discharge port. It has a working chamber for the transfer stroke, which is unnecessary in the compressor. In this vacuum pump, each working chamber sequentially performs a suction stroke, a transfer stroke, a compression stroke, and a discharge stroke as the rotor rotates.

[Problem to be solved by the invention]

In the above conventional technology, in order to improve the performance of the vacuum pump, that is, the ultimate pressure, the winding angle of the rotor is adjusted to 200 mm.
It was significantly larger than ~300 degrees.

FIG. 7 is a diagram showing the relationship between the rotor winding angle and the ultimate pressure of a conventional screw vacuum pump.

That is, Fig. 7 shows an example of the relationship between the rotor winding angle (degrees) and the ultimate pressure (Torr) of a screw vacuum pump pumping to the atmosphere. Requires a rotor winding angle of at least 100 degrees. As shown in the figure, increasing the winding angle of the rotor is sufficient to increase the ultimate pressure, but increasing the winding angle of the rotor significantly reduces the pumping speed of the vacuum pump.

The theoretical pumping speed of a screw vacuum pump can be simply expressed as the product of the tooth groove area in a cross section perpendicular to the axis, the groove length (lead), and the rotor rotation speed.

Therefore, a rotor with a large rotor winding angle has a short lead, which causes a problem in that the exhaust speed decreases.

The present invention was made to solve the problems of the prior art described above, and improves pump performance by significantly increasing the pumping speed when the suction pressure is 10-2 to 10-8 Torr and lowering the ultimate pressure. To provide vacuum pump equipment that can
That is the purpose.

[Means to solve the problem]

In order to achieve the above object, the configuration of a vacuum pump device according to the present invention is a vacuum pump device in which a screw pump element and a thread groove pump element are provided in a casing having an inlet on one side and a discharge port on the other side. The screw pump element is disposed on the discharge side and the thread groove pump element is disposed on the suction side, and the screw pump element is a positive displacement compression pump comprising a pair of male and female screw rotors that engage with each other, and The grooved pump element is a molecular pump comprising a threaded rotor.

More specifically, a threaded rotor is arranged on at least one rotating shaft of a pair of male and female screw rotors.

As an additional note, the above purpose is to place the screw pump element, which performs compression by changing the volume of the working chamber formed by a pair of male and female screw rotors and the casing, on the discharge side, and the thread groove pump element, which does not change volume, on the suction side. This is achieved by providing them coaxially.

[Effect]

The operation of the above technical means will be described below.

A screw pump element consisting of a pair of screw rotors provided on the discharge side performs the same function as the screw vacuum pump described in JP-A-60-216089. That is, by suctioning, transferring, compressing, and discharging gas, an ultimate pressure of 10-2 to 10-8 Torr can be obtained with a single screw pump element.

On the other hand, a threaded pump element consisting of a threaded rotor on the suction side has almost no pumping action when the suction pressure is at a high level, but when it becomes a molecular flow, the so-called molecular drag effect occurs, so it operates as a pump.

FIG. 8 is a pumping speed diagram comparing the pump of the prior art and the pump of the present invention.

That is, in FIG. 8, the horizontal axis shows the suction pressure (Torr) and the vertical axis shows the pumping speed, and the pumping speed curve of the vacuum pump device of the present invention is shown as a solid line, and the pumping speed curve of the conventional screw vacuum pump is shown as a broken line. , a comparison of the two.

In conventional screw vacuum pumps, the pumping speed tends to decrease as the ultimate suction pressure approaches 10-8 Torr, but with the vacuum pump device of the present invention, the suction pressure is 10-2 to 1.0" ``When the pressure is Torr, the pumping speed is maximum.

In general, thread groove pump (molecular pump) when there is no leakage
The pumping speed of is expressed by the following formula.

S=-・bh-u-n Here, S: pump pumping speed b: groove width, h: Groove depth U: Speed in the groove direction of the threaded rotor n: Number of grooves That is, the thread specifications of the screw rotor (b.

By selecting one of the thread specifications of the thread groove rotor to be larger than those of h, n, and u), the pumping speed in the molecular region can be increased.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 6.

1 is a longitudinal cross-sectional view of a vacuum pump device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line B-B in FIG. The arrow sectional view, Fig. 4, is C in Fig. 1.
-C arrow sectional view, FIG. 5 is an enlarged external view of the screw rotor and the threaded rotor of FIG. 1.

In the figure, 1 is a discharge side casing, 2 is a suction side casing, and 3 is an end cover, which constitute the casing.

4a and 4b are screw rotors, and a pair of male and female screw rotors 4a and 4b that engage with each other form a working chamber 6 between them and the discharge side casing 1, and constitute a screw pump element.

5a and 5b are threaded rotors, which are attached to the suction side casing 2.
A flow path 7 is formed between the two and constitutes a threaded groove pump element.

The discharge side casing 1 has a discharge port 8 communicating with the working chamber 6.
The suction side casing 2 has a suction port 9 that communicates with the flow path 7 .

Screw rotors 4a, 4b and thread groove rotors 5a, 5b
are fitted integrally with the rotor shafts 10a and 10b, respectively, and both ends of the rotor shafts 10a and 10b are supported by rolling bearings 11a+11bH12a*12b, respectively. Further, the screw rotors 4a and 4b are engaged with each other with a minute gap maintained by timing gears 13a and 13b fitted to the shaft ends of the rotor shafts 10a and 10b.

14a, 14b, 15a, and 15b are shaft sealing devices.

As shown in FIGS. 4 and 5, the pair of male and female screw rotors 4a and 4b have the same specifications except for the twisting direction, and are formed of one or more screws with a winding angle of 1080 degrees (3 turns). ing.

The threaded rotors 5a and 5b also have the same specifications except for the twisting direction, as shown in FIGS. 3 and 5. The threaded rotors 5a and 5b are formed with four threads and have a winding angle of 225 degrees. In addition, a threaded rotor 5a,
The groove depth of the screw rotor 5b is sufficiently larger than that of the screw rotors 4a and 4b, and the width ratio of the ridge portion to the groove portion is 1:3. Therefore, the threaded rotors 5a, 5b
There is no gas compression due to meshing.

The operation of the vacuum pump device configured in this way will be described next.

When one of the rotor shafts 10a, 10b (drive side) is driven by an external drive mechanism (not shown), the screw rotor 4a, the threaded rotor 5a, and the screw rotor 4b, the threaded rotor 5b are opposite to each other. Rotate in the direction. Therefore, as the rotor rotates, gas is sucked in through the suction port 9, passes through the flow path 7, the working chamber 6, and is discharged from the discharge port 8.

In a viscous region where the pressure at the suction port 9 is from atmospheric pressure to I Torr, the threaded rotors 5a, 5b do not have a pumping action, but only act as a flow path. The pump action is performed by the screw rotor 4a whose maximum pumping speed is smaller;
Perform only with 4b. Therefore, the exhaust speed is determined by the screw specifications of the screw rotors 4a, 4b.

When the pressure at the inlet 9 goes from an intermediate flow below I Torr to a further molecular flow, the threaded rotor 5a.

Since the compression action occurs due to the molecular drag effect of 5b, the exhaust speed is the same as that of the threaded rotor 5a.

It will be determined by the screw specifications of 5b.

According to this embodiment, as shown in FIG.
The pumping speed at 0-2 to 10'' Torr can be significantly improved, and the ultimate pressure can also be lowered by nearly an order of magnitude compared to the conventional method, which has the effect of improving vacuum pump performance.

Next, FIG. 6 is a longitudinal sectional view of a vacuum pump device according to another embodiment of the present invention. In the figure, parts with the same reference numerals as in FIG. 1 are equivalent parts, so their explanation will be omitted.

The embodiment shown in FIG. 6 differs from the previous embodiment shown in FIG. 1 in that a threaded port is provided only on one side of the rotor shaft.

That is, a screw rotor 4a is provided on the discharge side of the rotor shaft 10a, a threaded rotor 5a is provided on the suction side, a screw rotor 4b is provided on the discharge side of the rotor shaft 10b, and there is no threaded rotor on the suction side. . A surrounding wall 2a of the suction side casing 2 is provided opposite the threaded rotor 5a to form a flow path 7'.

According to the embodiment shown in FIG. 6, the same effects as those described in the previous embodiment can be expected. In other words, if a threaded rotor is placed on at least one of the rotating shafts of the pair of screw rotors, when the pressure at the suction port 9 reaches a molecular region, a pumping action occurs as the threaded rotor rotates. The vacuum pump performance of the vacuum pump device can be improved.

〔Effect of the invention〕

As described above, according to the present invention, the suction pressure is 1O-
Significantly increase the pumping speed at 2 to 10-” Torr,
It is possible to provide a vacuum pump device that can lower the ultimate pressure and improve pump performance.

[Brief explanation of the drawing]

1 is a longitudinal sectional view of a vacuum pump device according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line AA in FIG. 1, and FIG. 3 is a sectional view taken along the line BB in FIG. 1. The arrow sectional view, Fig. 4, is C in Fig. 1.
-C arrow sectional view, FIG. 5 is an enlarged external view of the screw rotor and threaded rotor of FIG. 1, and FIG. 6 is a longitudinal sectional view of a vacuum pump device according to another embodiment of the present invention. , FIG. 7 is a diagram showing the relationship between rotor winding angle and ultimate pressure of a conventional screw vacuum pump, and FIG. 8 is a pumping speed diagram comparing the conventional pump and the pump of the present invention. . 1... Discharge side casing, 2... Suction side casing, 4a, 4b... Screw rotor 5a, 5b.
...Threaded rotor, 6...Working chamber, 7,7'...
・Flow path, 8...Discharge port, 9...Suction port, 10a, 1
0b...low 3rd figure 4th figure Kaya SI! ]

Claims (1)

[Claims] 1. A vacuum pump device comprising a screw pump element and a thread groove pump element in a casing having a suction port on one side and a discharge port on the other side, the screw pump element being placed on the discharge side. , disposing the threaded groove pump element on the suction side;
A vacuum pump characterized in that the screw pump element is a positive displacement compression pump comprising a pair of male and female screw rotors that engage with each other, and the thread groove pump element is a molecular pump comprising a threaded rotor. Device. 2. A vacuum pump device according to claim 1, characterized in that a threaded rotor is disposed on at least one rotating shaft of a pair of male and female screw rotors.