JPH0784878B2 - Screw groove type vacuum pump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Industrial Application The present invention relates to a thread groove type vacuum pump suitable for use in thin film formation in the manufacture of ICs and semiconductors.

(2) Conventional Technology Conventionally, in a thread groove type vacuum pump, its performance depends largely on the gap between the stator and the rotor, and it is known that the smaller the gap, the higher the exhaust speed and the back pressure resistance performance. However, due to the relationship between the circularity of the outer diameter of the rotor and the coaxiality of the rotating shaft in terms of working accuracy and the expansion of the rotor diameter during rotation, the gap between the stator and the rotor should be relatively small. Wide (0.5m during operation
accidents due to contact were prevented.

(3) Problems to be Solved by the Invention However, in recent years, with the development of thin film application industries such as manufacturing of ICs and semiconductors, it has been desired to improve the performance of screw groove type vacuum pumps. Particularly, there has been a demand for a vacuum pump capable of expanding the capability in a wide range from low vacuum to high vacuum at a high pumping speed and compressing to atmospheric pressure only with this pump.

However, as mentioned above, due to the gap between the stator and the rotor, which is essential for performance improvement, the rotor that can be compressed from high vacuum to atmospheric pressure has no choice but to miniaturize the rotor. There wasn't.

Therefore, the present invention intends to provide a thread groove type vacuum pump capable of increasing the diameter of the rotor, compressing it to the atmospheric pressure, and generating a high pumping speed.

(4) Means for Solving the Problems In order to achieve the above-mentioned points, the present invention has a thread groove on either the inner peripheral surface of the stator or the outer peripheral surface of the rotor, and has a small gap. In a thread groove type vacuum pump in which the rotor rotates within the stator, the inner peripheral surface layer of the stator is formed of a soft material, and the rotor is centrifugally operated in the first operation after assembly. It is characterized in that it is formed in advance so as to expand and substantially contact the stator.

(5) Action During initial operation, the inner circumference of the stator made of a soft material is scraped off by the outer circumference of the rotor that expands due to centrifugal force, and then the operating state is minimized with the gap between the inner circumference of the stator and the outer circumference of the rotor. Thus, a large pumping speed can be obtained while maintaining the characteristic that it can be compressed to atmospheric pressure.

(6) Embodiment One embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, a rotor (1) has a columnar shape, and a screw thread (1a) having a cylindrical or trapezoidal cross section with an inclination angle on its outer periphery.
And a thread groove (1b) is formed. The rotor (1) is supported by a bearing (not shown) so that it can rotate at high speed, and is made of a lightweight and rigid metal such as an aluminum alloy. The stator (2) is cylindrical and is supported coaxially with the rotor (1), and has a screw thread (1) of the rotor (1).
There is a small gap (3) between the outer periphery of a),
At least the inner peripheral surface layer is formed of a soft material, for example, a fluororesin such as polytetrafluoroethylene resin.

Generally, the thread groove type vacuum pump is originally called a molecular drag pump and is mainly intended to be used in the free molecular flow region by utilizing the viscosity of gas.
By reducing the inclination angle of the thread groove (1b) formed on the outer peripheral surface of the rotor (1) provided to rotate with a gap (3) in the stator (2), the rotor (1 ) Of the peripheral speed along the thread groove (1b) is made as large as possible, and at the same time, the gap (3) between the thread (1a) of the rotor (1) and the stator (2) is made as small as possible, and the screw The design is made on the basis of obtaining a high compression ratio by increasing the width of the mountain (1a) and reducing the leakage flow rate through the gap (3). For the gap (3), for example, Holbeck Japanese Patent Laid-Open No. 49-1283
According to JP-B No. 06, the gap is 0.04 mm, and according to JP-B No. 47-33446 concerning the axial flow molecular pump with a thread groove by Sawada, the gap is as small as 0.1 mm. That is, to obtain a high vacuum, an extremely small gap of 0.1 mm to 0.04 mm or less (3)
Need.

On the other hand, in terms of performance in terms of manufacturing process and elongation of the rotor (1) due to centrifugal force generated during high speed operation, and thermal expansion of the rotor (1) generated when compressing and exhausting a high temperature gas or a large amount of gas. It is difficult to satisfy the required gap (3).

Therefore, the present invention has a large gap (3) at the time of high-speed operation and provides a screw groove type vacuum pump with a large exhaust speed that does not pose a problem such as contact during operation or causes no problem at all when contacting. The outer diameter of the rotor () during high-speed rotation is preliminarily calculated using the diameter rotor (1), and the inner diameter of the stator (2) is manufactured according to the dimension.

For example, when a rotor (1) having an outer diameter of 200 mm is rotated at 24,000 rpm, the outer diameter of the rotor (1) is extended by 0.5 mm. Therefore, the inner diameter of the stator (2) is 200.4 mm to 200.5 mm. By doing so, from the above calculation, the outer diameter of the rotor (1) becomes 200.5 mm in the initial operation, which is equivalent to the inner diameter of the stator (2) or scraped by 0.1 mm. The shavings of the soft material on the inner circumference of the stator generated at this time are accumulated in the lower portion of the pump. If necessary, the shavings may be removed by removing the stator after the end of the initial operation.

Therefore, in the present invention, at least the inner surface layer of the stator (2) is made of a fluororesin having heat resistance and made of a soft material, and the inner diameter of the stator (2) is the outer diameter of the rotor (1). Diameter (for example, the inner diameter of the stator is 0.4 mm compared to the outer diameter of the rotor)
~ 0.5mm larger) and assemble.

If the pump thus assembled is initially operated at the rated speed or a slightly higher speed, the gap (3) between the rotor (1) and the stator (2) is extremely small, for example, for the reason described above.
It is possible to obtain 0.01 mm to 0.02 mm.

Further, FIG. 2 shows another embodiment in which the stator (2) is provided with a thread groove and is formed of a soft material.

Also, Fig. 3 shows the gap of the thread groove type vacuum pump with a rotor diameter of 200 mm and a rotation speed of 24,000 rpm, which is necessary to compress nitrogen gas with a flow rate of 10 Torr / s from 1 Torr to atmospheric pressure (760 Torr). From the graph of FIG. 3, the smaller the gap (δ) is, the smaller the axial length (L) is. It becomes clear that it contributes to the improvement of the discharge performance of the vacuum pump.

Even if the stator and the rotor come into contact with each other due to usage conditions that deviate from the design conditions, there is no problem because the outer circumference of the rotor cuts the inner circumference of the stator as described above.

(7) Effects of the Invention As described above, according to the present invention, in the screw groove type vacuum pump, the stator is made of a soft material, the inner diameter of the stator and the outer diameter of the rotor are approximated, and the inner diameter of the stator is cut by the initial operation. Since the gap is minimized in the loose state, a large exhaust velocity can be generated while maintaining the feature that it can be compressed to atmospheric pressure, and only the circularity of the rotor outer diameter and the coaxiality with the rotation axis are accurate. As long as the property is secured, it has the effect of facilitating the manufacture without requiring specially precise processing in other parts.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a pump according to the present invention, FIG. 2 is a sectional view of an essential part of another embodiment, and FIG. 3 is a relationship between a gap between a rotor and a stator of a pump and an axial length. It is a graph shown. (1) …… Rotor (3) …… Stator (4) …… Gap

Claims (2)

[Claims] 1. A screw groove type vacuum pump having a screw groove on either one of the inner peripheral surface of the stator or the outer peripheral surface of the rotor, wherein the rotor rotates in the stator with a small gap,
While forming the inner peripheral surface layer of the stator with a soft material,
A screw groove type vacuum pump, characterized in that the rotor is preliminarily formed in a size such that the rotor expands by centrifugal force and substantially contacts the stator in the first operation after assembly. 2. The thread groove type vacuum pump according to claim 1, wherein the soft material is a fluororesin.