JPH0692799B2 - Vacuum pump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (INDUSTRIAL FIELD) The present invention includes a thread groove-type pump element having a rotational inner cylinder and stationary outer cylinder forming a thread groove on one, 10~10- ⁸ Torr
The present invention relates to a vacuum pump suitable for exhausting in a medium to high vacuum range.

(Prior Art) As has been known for a long time in Japanese Patent Publication No. 47-33446, this kind of thread groove type pump element is excellent in a slip flow region of about 1 Torr to a medium vacuum region called a viscous flow region. Since it has an exhaust characteristic, it is used in a downstream stage of a turbo molecular pump having a moving blade and a stationary blade, and is widely used as a so-called composite type vacuum pump. Also, as is known from Japanese Utility Model Publication No. 60-9439, the screw groove type pump element has recently been put into practical use as a pump for exhausting a medium vacuum region.

(Problems to be Solved by the Invention) However, all of the above-mentioned conventional devices are intended for exhaust in a medium vacuum region, and the thread groove depths thereof are different between the intake side inlet part and the exhaust side outlet part. Even though it has some inclination, it has an extremely shallow depth, and its screw angle is formed at the same angle from the intake side to the exhaust side at an angle of about 15 ° to 20 °. When used in, the exhaust flow rate is overwhelmingly inferior, the exhaust speed is inferior, and a large compression ratio cannot be secured between the inlet and outlet of the screw groove, which is a problem that cannot be practically used.

In the present invention, by devising the depth and screw angle of the thread groove based on various experimental considerations, it is possible to increase the pumping speed in a high vacuum region and to secure a high compression ratio. It is an object of the present invention to provide a vacuum pump suitable for use in a wide range from a medium vacuum region to a high vacuum region, which can ensure the exhaust performance in a vacuum region as well as the conventional one.

(Means for Solving the Problem) Therefore, in the present invention, in order to achieve the above object, the rotating inner cylinder (5) and the stationary outer cylinder (6) are provided between the intake port (2) and the exhaust port (3). And a thread groove type pump element (7) having a thread groove (4) formed on one side,
The inlet portion of the screw groove (4) located on the intake port (2) side is formed in a deep groove (41) having a depth of about one third or more of the diameter of the rotating inner cylinder (5). A groove depth shape along a continuous curve is formed between the deep groove (41) and the shallow groove (42) on the exhaust port (3) side of the screw groove (4), and the deep groove (41) is formed. ) Has a larger screw angle, and the shallow groove (42)
The screw angle of these is made small, and these deep groove (41) and shallow groove (42)
We decided to connect between and by a continuous angle change.

(Function) The thread groove of the inlet located on the intake port (2) side is replaced with the deep groove (41).
As a result, by increasing the screw angle, it is possible to increase the exhaust flow rate and thus the exhaust speed. Also, the screw groove at the outlet located on the exhaust port (3) side is the shallow groove (42). By making the angle small and connecting these inlets and outlets with continuous groove depth and screw angle, it is possible to secure a high compression ratio and exhaust performance in the medium vacuum region.

(Embodiment) The pump shown in FIG. 1 has a rotating inner cylinder (5) in which a screw groove (4) is formed on an outer peripheral portion between an intake port (2) provided in an upper part and an exhaust port (3) provided in a lower part. ) And a stationary outer cylinder (6) having an inner peripheral surface (6) adjacent to the outer peripheral surface of the inner cylinder (5) with a very small gap (δ) of about 0.1 to 0.2 mm during rotation. (7) is provided and the rotating inner cylinder (5) is provided.
Is connected to the drive shaft (9) of the motor (8), and the intake port flange (11) is rotated by high speed rotation of about 30,000 rpm, for example.
The vacuum is applied to the semiconductor wafer chamber or the like attached to the.

In the embodiment shown in FIG. 1, the thread groove (4) is formed on the rotating inner cylinder (5), but it may be formed on the stationary outer cylinder (6) side as conventionally known. Of course. or,
In the figure, (13) is a sump of lubricating oil for supplying the upper and lower bearings (14) and (15), and (16) is an oil pickup.

In the above structure, the depth and the screw angle of the screw groove (4) are set as follows.

First, in order to increase the exhaust flow rate, that is, increase the exhaust speed, the inlet portion of the screw groove (4) located on the intake port (2) side is set to approximately one third of the diameter of the rotating inner cylinder (5). The deep groove (41) having the above depth is formed. This is because in the high vacuum region called the molecular flow region, the gas molecules are not subjected to the action of being exhausted while colliding with each other as in the viscous flow region up to the medium vacuum region, but in the same geometry as the turbo molecular pump. Since it is considered that the gas is stochastically exhausted, it is necessary to secure a sufficient opening area for molecules to jump in on the inlet side. It is considered that the larger the groove depth at the inlet, the higher the probability that gas molecules will jump in, and the larger the exhaust flow rate can be. However, in practice, the upper limit is 2 mainly from the viewpoint of mechanical strength. 1/4 or less, deep groove (4
The groove depth of 1) is set to about 1/3 to 1/2 of the diameter of the rotating inner cylinder (5).

Further, in order to increase the exhaust flow rate, it is more preferable that the width of the screw threads (40) other than the screw groove (4) be within a range that is not affected by leakage between the grooves and is allowable in terms of strength. As a minimum, as shown in FIG. 2, the groove width ratio (ε = groove width A / (groove width A + mountain width D)) seen in a plane is set to about 0.8 to 0.95. This is mainly to increase the opening area at the inlet portion, and as shown in FIG. 5, the exhaust speed becomes higher as the groove width ratio (ε) becomes larger. In addition, in FIG. 5 and FIG. 7, the exhaust speed on the vertical axis is divided into equal intervals.
The compression ratio on the vertical axis is plotted on a logarithmic scale.

Further, like the above-mentioned mountain width, as a preferable example for increasing the exhaust flow rate, the number of screw threads (N) is the characteristic curve for the number of screw threads shown in FIG. As shown in Figures 2 and 3, reduce it to about 4.

Then, as shown in FIG. 7, the screw angle (θ1) of the deep groove (41) is set in the range of θ1 = α = 35 ° to 50 ° by selecting a portion having a high exhaust speed instead of the compression ratio. . The model of FIG. 7 is the data when the screw angle is the same from the inlet to the outlet.

Next, in order to secure a high compression ratio and an exhaust performance in the medium vacuum region, the screw on the outlet side near the exhaust port (3) is set as follows.

That is, as shown in FIG. 7, in order to secure a high compression ratio, the screw angle (θ2) is set large at 35 ° to 50 ° on the inlet side, whereas it is set at 10 ° to 15 °. And set it smaller. Further, in order to secure the exhaust performance in the medium vacuum region, the groove depth of the rotary inner cylinder (5) and the stationary outer cylinder are changed according to the well-known theory of the viscous screw groove pump in the medium vacuum region. It is formed in a shallow groove (42) having a depth of about 3 to 10 times the gap (δ) with (6).

As described above, the middle part connecting the groove depth and the screw angle set at the inlet and outlet, respectively, is mainly used to suppress heat generation during exhaust to a medium vacuum region, so avoiding a sharp shape change and smooth compression. Need to be done,
As shown in FIG. 1, the groove depth in the middle is formed such that a curve (L) connecting the groove bottoms in the vertical direction follows a quadratic curve, and the screw angle in the middle is As shown in FIG. 4, the angle is continuously changed along the thread groove.

The actual processing of the thread groove (4) described above is performed by cutting with an end mill or the like while keeping the thread width constant. By the way, if the screw width is made constant and the angle of the screw angle is changed in this way, the planar groove width ratio (ε) on the outlet side becomes about 0.4 to 0.6 as shown in FIG. As shown in FIG. 5, it is possible to automatically contribute to the improvement of the compression ratio on the outlet side.

In this way, when the performance of the pump having the above configuration is evaluated, as shown in FIG. 8 and FIG. 9, the model to which the present invention is applied extends from the medium vacuum region to the high vacuum region. Both the intake pressure, that is, the ultimate vacuum and the exhaust speed are superior to the model with a constant value and the model with a constant screw angle.

(Effects of the Invention) As described above, according to the present invention, it is possible to increase the pumping speed in a high vacuum range and to secure a high compression ratio, and also to secure the exhaust performance in a medium vacuum range. It is possible to satisfactorily evacuate in a wide range from to the high vacuum region.

Further, in the pump of the present invention, since it does not have a moving blade like a turbo molecular pump, it is easy to process, and it is resistant to impacts such as foreign matter mixing and atmospheric rushing, and the blade becomes resistant especially in a medium vacuum region. Therefore, the heat generation can be reduced.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a vacuum pump of the present invention, FIG. 2 is a top view of a rotating inner cylinder, FIG. 3 is a bottom view of the same inner cylinder, FIG. 4 is a development view of a thread groove, and FIG. Characteristic diagram showing the influence of mountain width, No. 6
Fig. 7 is a characteristic diagram showing the influence of the number of screw threads, Fig. 7 is a characteristic diagram showing the influence of the screw angle, Fig. 8 is an exhaust characteristic diagram for evaluating the performance,
FIG. 9 is a compression characteristic diagram for evaluating the same performance. (2) …… Intake port (3) …… Exhaust port (4) …… Screw groove (5) …… Rotating inner cylinder (6) …… Stationary outer cylinder (7) …… Screw groove type pump element (41) …… Deep groove (42) …… Shallow groove

Front page continued (72) Inventor Takao Matsumoto 3-12 Chikko Shinmachi, Sakai City, Osaka Prefecture Daikin Industries, Ltd. Sakai Plant's seaside factory

Claims (1)

[Claims] 1. A thread groove type in which a rotating inner cylinder (5) and a stationary outer cylinder (6) are provided between an intake port (2) and an exhaust port (3), and a thread groove (4) is formed on one side. In a vacuum pump provided with a pump element (7), the inlet portion of the screw groove (4) located on the intake port (2) side has a diameter equal to or more than about one-third of the diameter of the rotating inner cylinder (5). To form a deep groove (41) having a depth of, and along the continuous curve between the deep groove (41) and the shallow groove (42) of the screw groove (4) on the exhaust port (3) side. In addition to forming the groove depth shape, the deep groove (41) has a large screw angle and the shallow groove (42) has a small screw angle to continuously connect the deep groove (41) and the shallow groove (42). A vacuum pump that is connected by changing the angle.