JPH03168388A - Vacuum pump - Google Patents

Abstract

PURPOSE:To accommodate a vacuum pump to usage in a wide-range from a medium vacuum area to a high vacuum area by making the screw angle of a deep groove located on an suction port side large and the screw angle of a shallow groove located on an exhaust port side small. CONSTITUTION:The inlet portion of a screw groove 4 located on a suction port 2 side is formed as a deep groove 41 which has the depth 1/3 or more the size of a rotary inner cylinder 5, and a space between the deep groove 41 and a shallow groove 42 on an exhaust port 3 side in the screw groove 4 is formed in such a shape as groove depth along a continuous curve. The screw angle of the deep groove 41 is made large and the screw angle of the shallow groove 42 is made small, to complete continuous angle-variation connection between the deep groove 41 and the shallow groove 42. In this way, as the screw angle of the screw groove at the inlet portion located on the suction port 2 side is made large, shift to large exhaust flow and large exhaust speed can be achieved. Also, the screw angle of the screw groove at an outlet portion located on the exhaust portion 3 side is made small and these inlet and outlet are connected to each other with continuous groove depth and screw angle, so that it is possible to ensure high compression ratio and exhaust performance in a medium vacuum area.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention comprises a threaded pump element having a rotating inner cylinder and a stationary outer cylinder forming a threaded structure on one side,
This invention relates to a vacuum pump suitable for evacuation in a medium to high vacuum range of around Torr.

(Prior Art) As has been known for a long time from Japanese Patent Publication No. 47-3344Et, etc., this type of thread groove type pump element is
Because it has excellent exhaust characteristics in the medium vacuum region, which is called the viscous region and the slip region of about 1.2 to 3.5 orr. It's being used. Also, Jiko Sho 8
As is known from Japanese Patent No. 0-9439, etc., a thread groove type pump element alone has recently been put into practical use as a pump for evacuating a medium vacuum region.

(Problem to be Solved by the Invention) However, all of the above conventional devices are intended for exhaust in a medium vacuum region, and the depth of the thread groove is different between the inlet on the intake side and the outlet on the exhaust side. Although it has a slight inclination, it is extremely shallow in depth, and the screw angle is approximately 15" to 206", and is formed at the same angle from the intake side to the exhaust side. When used, there is a problem that the exhaust flow rate is overwhelmingly insufficient, the exhaust speed is inferior, and a large compression ratio cannot be secured between the inlet and outlet of the screw structure, making it practically unusable.

In the present invention, by devising the thread depth and thread angle based on various experimental considerations, it is possible to achieve high air flow speed and ensure a high compression ratio in a high vacuum region, and The purpose of the present invention is to provide a vacuum pump that can ensure evacuation performance in a medium vacuum region comparable to that of conventional vacuum pumps and is suitable for use in a wide range from medium vacuum regions to high vacuum regions.

(Means for Solving the Problem) Therefore, in the present invention, in order to achieve the above object, a rotating inner cylinder (5) and a stationary outer cylinder (6) are provided between the intake port (2) and the exhaust port (3). ) and a threaded pump element (7) with a threaded groove (4) formed on one side,
The entrance portion of the threaded groove (4) located on the side of the intake port (2) is formed to have a depth of about 1/3 or more of the diameter of the rotating inner cylinder (5). Then, the depth i
:2? (4 1) and the shallow groove (42) on the exhaust port (3) side of the screw mechanism (4) is formed into a groove depth shape that follows the continuous curve, and the depth T + 1 yen.
Increase the thread angle of (4 1) and make the shallow '779
By reducing the thread angle of (4 2), these deep grooves (4
1) and & ? I decided to connect it with i'1 ¥ (42) by continuously changing the angle.

(Function) Thoroughly tighten the thread of the inlet located on the intake port (2) side to a depth of m (
4 1), by increasing the screw angle, it is possible to achieve a large exhaust flow rate and therefore a large exhaust speed, and the screw reservoir at the outlet located on the exhaust port (3) side has been made shallow m (
4) As for 2), the screw angle is small, and by 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. becomes possible.

(Example) The pump shown in FIG.
) is formed on the outer circumferential surface of the inner cylinder (5). Extremely small gap of about 2■ (δ)
A threaded pump element (7) is provided with a stationary outer cylinder (6) having an inner circumferential surface adjacent to the rotating inner cylinder (5).
) to the drive shaft (9) of the motor (8), for example 3
Due to high-speed rotation of approximately 10,000 revolutions per minute, the intake loft flange (1
1) is designed to evacuate the semiconductor wafer chamber, etc. attached to the device.

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

In the above configuration, the depth and screw angle of the screw +WC4) are set as follows.

First, in order to increase the exhaust flow rate, that is, to increase the exhaust speed, the inlet portion of the threaded hole (4) located on the side of the intake port (2) is adjusted to approximately one third of the diameter of the rotating inner cylinder (5). It is formed in a depth (41) having a depth greater than or equal to the depth. This is because in a high vacuum region called the molecular region, gas molecules are not subjected to the action of colliding with each other and being evacuated as in the viscous region up to the medium vacuum region, but are This is because it is considered that the gas is stochastically exhausted, so it is necessary to ensure a sufficient opening area on the inlet side for molecules to jump into. It is thought that the larger the full depth at the inlet, the higher the rate of infiltration of gas molecules and the greater the exhaust flow rate, but in reality, mainly from the point of view of mechanical strength, there is no upper limit. The depth should be about 1/2 or less, and the deep groove (
The groove depth of 4 1) is one third of the diameter of the rotating inner cylinder (5).
Set it to about 1/2.

Furthermore, in order to achieve this large exhaust flow rate, it is more preferable that the screw H
The width of the screw thread (40) other than I (4) shall be minimized to the extent that it is not affected by leakage in each structure and is allowed for strength, and as shown in Figure 2, Saw:
I cap ratio (ε=groove width A/(groove width A tenth width D)) is 0.8~
0.95} Set to 2 degrees.

This is mainly to increase the opening area at the inlet, and as shown in Figure 5, υ1 air velocity is equal to this groove width ratio (ε).
The larger the value, the higher the value. In FIG. 5 to FIG. 7, the exhaust speed on the vertical axis is marked on a scale at equal intervals, and the compression ratio on the vertical axis is marked on a logarithmic scale.

Furthermore, as with the above-mentioned mountain width, as a preferable example for increasing the exhaust flow rate, the number of threads (N) is determined by selecting a portion where the pumping speed is high in the characteristic fill line for the number of threads shown in FIG. As shown in Figure 2.3, it should be as low as about 4.

Then, the screw angle (θ1) at the depth m (4 1) is set in the range of θ1 = α = 35@~50'' by selecting the part where the pumping speed is high rather than the compression ratio, as shown in Fig. 7. The model shown in Fig. 7 is data when the thread angle is the same from the inlet to the outlet.

Next, in order to ensure a high compression ratio and exhaust performance in a medium vacuum region, the screws on the exit side near the exhaust port (3) are set as follows.

That is, as shown in Fig. 7, in order to ensure a high compression ratio, the screw angle (θ2) must be set at 356 to 50 on the inlet side.
' is set large, but it is set small at 10' to 15°. Furthermore, in order to ensure IJ gas performance in the medium vacuum region, the depth d}+t of the rotary inner cylinder (5) is adjusted as usual according to the well-known viscous screw structure pump theory in the medium vacuum region. 3~ of the gap (δ) between and the stationary outer cylinder (6)
It is formed into a shallow i+M (4 2 ) with a depth of about 10 times.

In addition, in order to suppress the heat generation during exhaust to the medium vacuum region, the intermediate portion connecting the full depth and thread angle set at the inlet and outlet, respectively, as described above, is designed to avoid sudden changes in shape and achieve smooth compression. Because it is necessary to make
As shown in Fig. 1, the full depth in the middle is formed by a curve (L) that connects the full bottom in the vertical direction, for example, in a shape along a quadratic curve, and the thread angle in the middle is As shown in Figure 4, the angle changes continuously along the thread.

The actual machining of the above screw thread (4) is performed by cutting using an end mill or the like while keeping the thread width constant. By the way, if the thread width is kept constant and the thread angle is changed in this way, the planar iN width ratio (ε) on the exit side will be 0.4 to 0, as shown in Figure 3. 6, which automatically contributes to improving the compression ratio on the outlet side, as shown in FIG.

When we evaluated the performance of the pump with the above configuration, we found that, as shown in Figures 8 and 9, the model to which the present invention was applied was fully satisfied in the medium to high vacuum range. Models with constant depth■ and models with constant screw angle■
Compared to (2), the intake pressure, that is, the attained f (airness and exhaust speed are both excellent).

(Effects of the Invention) As described above, according to the present invention, it is possible to increase the pumping speed and secure a high compression ratio in the high vacuum region, and also to ensure the air efficiency in the medium vacuum region. It is possible to effectively perform evacuation over a wide range from the vacuum region to the high vacuum region.

In addition, the pump of the present invention does not have moving blades like a turbo-molecular pump, so it is easy to process, and is resistant to foreign matter contamination and air entry, and the blades act as resistance, especially in medium vacuum regions. As a result, heat generation can also be reduced.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of the vacuum pump of the present invention, Fig. 2 is a top view of the rotating inner cylinder, Fig. 3 is a bottom view of the inner cylinder, and Fig. 4 is a screw i.
Developed diagram of IIS, Figure 5 is a characteristic diagram showing the influence of thread width, Figure 6 is a characteristic diagram showing the influence of thread number, Figure 7 is a characteristic diagram showing the influence of thread angle, and Figure 8 is a characteristic diagram showing the influence of thread thread number. FIG. 9 is an exhaust characteristic diagram for evaluating the performance, and FIG. 9 is a compression characteristic diagram for evaluating the same performance. (2)...Intake port (3)...Exhaust port (4)...Thread groove (5)...Rotating inner cylinder (6)...Stationary outer cylinder (7) ...Screw iR type pump element (4 1) ... Deep groove (42) ... Shallow groove Fig. 1 13 l6 15 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Groove width (ε No-thread thread soft《N》1 Figure 7

Claims (1)

[Claims] 1) A rotating inner cylinder (
5) and a stationary outer cylinder (6), the vacuum pump is provided with a thread groove type pump element (7) having a thread groove (4) formed on one side, the screw located on the side of the intake port (2). groove(
4), the inlet portion of the rotating inner cylinder (5) is approximately one third of the diameter
A deep groove (41) having a depth of
1) and the shallow groove (42) on the exhaust port (3) side of the thread groove (4) is formed into a groove depth shape that follows a continuous curve, and the thread angle of the deep groove (41) is A vacuum pump characterized in that the thread angle of the shallow groove (42) is made small, and the deep groove (41) and the shallow groove (42) are connected by continuously changing the angle.