JPS61223295A - Vacuum pump with oil-free screw - Google Patents

Abstract

PURPOSE:To achieve high vacuum condition with one stage pump by forming a region in which both ends of an operating chamber is closed by the meshing of rotors in a screw type vacuum pump. CONSTITUTION:An operating chamber 65 is filled with gas sucked from an intake port 63 as a rotor is rotated. Further, as the rotor is rotated, the gas charged in operating chambers 67, 70 moves axially with a constant volume since both ends of the operating chamber are sealed with meshing portions 68, 72 of the rotor. When ends of operating chambers 72, 73 contact a discharge side end plate 10, the volume of the gas begins to decrease and soon is discharged from a discharge port. Since two portions between the intake port 63 and discharge port are enclosed by the meshing of the rotors, the gas can be compressed with high compression ratio irrespective of the intake side pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a screw vacuum pump, and more particularly to a non-lubricated screw vacuum pump suitable for low to medium vacuum ranges from atmospheric pressure to 10-' Torr level.

[Background of the invention]

To manufacture semiconductors, wafers are stored in a vacuum container, but to create a vacuum inside the container, a vacuum pump is used while supplying an inert gas such as N2 gas into the container. Aspirate and remove impurities in the container (O* -CO*, etc.)
is removed to create a vacuum state of several Torr to 10-' Torr level.

Vacuum pumps used in these semiconductor manufacturing processes include oil rotary pumps and Roots-type mechanical booster pumps.

However, these pumps have the following drawbacks.

In oil rotary pumps, the lubricating oil used comes into contact with various gases used in the semiconductor manufacturing process (e.g., arsenic, gallium, salt, etc., Poly-Si, etc.), resulting in a very short lifespan as a lubricating oil. There was a drawback that it became In addition, there is the problem that oil molecules back diffuse into the semiconductor manufacturing container, which is unfavorable for the semiconductor manufacturing process.
T. Since the operating pressure range for impi**'tea is narrow, there is a drawback in that several types of pumps must be switched and used until a predetermined pressure is reached.

Furthermore, it is not possible to pump air from atmospheric pressure to the 10-'Torr level with a single vacuum pump, and there has been a demand for the development of a vacuum pump that is non-lubricated and can cover the above pressure range with a single vacuum pump. .

Related to the present invention are the following:
There is a publication No. 17559.

[Purpose of the invention]

In view of the problems in the previous term, the purpose of the present invention is to
The object of the present invention is to provide a vacuum pump capable of achieving a medium-level vacuum with a single stage and without lubrication.

[Summary of the Invention] In FIGS. 1 and 2, reference numerals 2 and 4 indicate a pair of male and female rotors that are arranged in mesh with each other in the casing 1, and the shaft portions of the respective rotors 2 and 4 are connected to radial bearings 5 and thrust bearings. Synchronous gears 9 and 10 are provided on the shafts of the six rotors 2 and 4 supported by bearings 6 (6A, 6B), so that both rotors 2 and 4 rotate in synchronization, and the casing Gas is compressed by both rotors 2 and 4 from a suction port 11 formed at the upper end of the casing 1 and discharged to a discharge port 12 formed at the lower end of the casing 1.
The inside of a vacuum container (not shown) which is in communication with 1 is kept in a vacuum state. Lubricating oil is supplied to the radial bearing 5, thrust bearing 6, and synchronous gears 9 and 10.
In order to prevent these lubricating oils from entering the casing in which both rotors 2 and 4 are housed, a shaft sealing device 16, 17 consisting of a carbon ring seal 14 and a screw seal 15 is provided on the shaft support of the rotor. .

However, since the lubricating oil in the shaft sealing device 17 faces the atmosphere at the end of the rotor shaft, it is equal to atmospheric pressure, but the lubricating oil on the rotor shaft is lower due to the atmospheric pressure at the shaft portion on the suction port ll side. A differential pressure is generated between the shaft sealing device 117 and the shaft sealing device 117 alone cannot reliably prevent lubricating oil from entering the casing. The problems of the conventional technology have not yet been fully solved, such as air entering from the inside and reducing efficiency. - Figure 3 shows a screw fluid machine in which the male rotor 20° and the female rotor 21 are engaged. This figure shows a model developed in the circumferential direction of the rotor in which the male rotor has 5 teeth and the female rotor has 6 teeth, but if the male rotor has 2 or more teeth, It is also effective for combinations of the number of teeth where the number of teeth on the female rotor is always one more.

A casing 22 covering the rotor has a large opening at one axial end as a gas suction port 23, and a discharge port 24 on the opposite side. In areas other than these two ports, the casing 22 covers the rotors 20 and 21 with a small gap, and the rotor and the casing form a V-shaped working chamber.

When the rotors rotate, the meshing parts of both rotors move from the suction port 23 to the discharge port 24, but at this time, the working chambers 25 and 26 have the maximum volume,
For 5, the volume decreases, that is, 0, which is just before the start of compression.
While the working chamber 26 moves its volume to the position of the working chamber 25, there is no compression effect.

It is only transported.

In addition, in FIG. 1, each working chamber communicating with the suction port 23 increases its volume as the rotor rotates, and performs a gas suction action.

In FIG. 3, the working chamber 27 is discharging gas through the discharge port 24, and the pressure here is equal to the discharge pressure, and the gas from the 0 working chamber 27, which has the highest pressure among the working chambers, is being discharged. Leakage occurs through the outer periphery of the rotor and the gap between the rotor end face and the casing into the adjacent working chamber 28, and through the meshing part K of both rotors into the working chamber of the female rotor at 26° and into the working chamber of the male rotor. There is something that leaks to 25.

For a screw compressor, the winding angle of the male rotor is.

Since the angle is usually 360° or less, the working chambers 25 and 26 are in direct communication with the suction port, and the quality of the sealing effect at the meshing portion of the rotor greatly influences the performance of the compressor.

Regarding the rotor outer circumference, a sealing effect can be expected due to several screw ridges between the discharge port and the suction port, so gas leakage from there is relatively small.

Therefore, in order to prevent the working chambers 29 and 30 from directly leaking into the suction port, the rollers may be lengthened to the solid line portion in the third WI.

This will be explained again using FIG. 5W.

FIG. 5 is a diagram of a sealing loop formed by the meshing portions of the male and female rotors, the casing, and the rotor helix portion. Here, att-a is the helix of the leading lobe tip, a.

-a, the seal line of the trailing lobe chip; the respective symbols below are as shown in Table 11 and Table 2 below.

Table 1. Female rotor sea link loop configuration arrow 3 b,
-b, -bl. Lotus, -b4-b, part 01 in the Z direction.

-Tallid, H2 parallel movement honor 4 b, -b, lotus, -b, (H, -H, /Z,)
Table 2. Parallel movement in the Z direction. Configuration Homare I Bl of male rotary sea link loop
B, -B111 is a male rotor lead for a4-a, part of -a2 in the Z direction! (, parallel movement *2B, .-61, is a, -a4 (H, +H, /ZM
) in two directions. Also, in Table 19 Table 2, plane A, plane B, and plane 0.

Side D shows the following.

Surface A: Front surface in the direction of travel of the lobe that precedes the groove. Surface B: Back surface in the direction of travel of the lobe that precedes the groove. Surface 0: Front surface in the direction of travel of the lobe that follows the groove. Front surface: Back surface in the direction of travel of the lobe that follows the groove. Therefore, the sealing loop for groove 26 in Fig. 3 is expressed in Fig. 5, and 23 in Fig. 5 is the suction end face, and the situation where ← a4 and b4 are in contact is expressed in Fig. 3. It is that you are.

Lines 29, 30, 31, and 32 in FIG. 3 are indicated by the same numbers in FIG. 5, respectively. In Figure 5, a1~a@tt
) t to b6 cannot be sufficiently expressed in FIG. 3 because it is a developed view in the circumferential direction.

In FIG. 5, the number of teeth on the male rotor is 1 second less than the number of teeth on the female rotor, so that b and al. coincide, so that the sealing loops of the male and female rotors form one sealed working chamber.

Next, the method for determining the length of L will be described in more detail.

Figure 6 shows a male rotor with 5 teeth. Although the female rotor is expressed in the case where the number of teeth is 6, other combinations of the number of teeth are also possible.

In this case, L is the tooth groove formed by the two meshing parts of the rotor between the tooth groove 10- (where the tooth is completely ejected) and the tooth groove 23 before the tooth groove 1 oz- (1 oz-g). This is shown in Fig. 6.

In the figure, a4#b4 is the length L when it is in contact with the discharge end surface and in contact with the first suction end surface.

1. As is clear from the description, the situation in Fig. 7 is as follows.

This means that it is long enough to accommodate seven complete grooves.

If we convert this into a formula for the total winding angle, in the case of a 5-6 tooth profile, we get: 5 In other words, the winding angle of the male rotor is 504 @. This is made into a film and the number of male teeth is increased to 2 or more. Is it the full winding angle of the male rotor? Yo is as follows.

L described above is the longest. Based on the same design concept, the shortest distance is determined as follows.

In FIG. 7, when the rotor further rotates and the required volume ratio is reached, the xox- (mutual) groove portions communicate with the discharge port to initiate the discharge process.

FIG. 7 is a developed view when the groove 101-■ starts discharging.

In this case, it will be shorter by Q2-m than the longest length. Convert this to a winding angle and let this amount be α.

Therefore, if we further generalize the total winding angle T of the male rotor.

2゜ Here, α is less than the winding angle of one groove.

That is, 2 degrees.By the way, when the compression ratio is increased, the discharge port becomes an axial port, that is, it is formed only on the discharge end face.The argument that the discharge port is 0 or more is developed for the case where the compression ratio is large. However, if the compression ratio is made small, this is no longer the case. This case will now be explained.

For example, we will discuss the case where the compression ratio is set to 1. In this case, as shown in Fig. 5, the discharge process starts at the same time as 81°tbs reaches the discharge end surface. .

If we consider this as a developed diagram, it will look like Figure 9. In FIG. 9, the groove (■)-102 is the groove immediately before the start of discharge. In other words, in this case, the length after -102 and 1 is L. Glue in the shaded area! In the case of the figure 0, the groove ■-101, which is one before the groove 102, is connected to the helix of the leading rotor of Di, D2, i.e., 0-102. Alongside, there is a radial port.

If Ll is found in the figure, it will be as follows. by the way.

In Fig. 5, the total winding angle ψ of the male rotor for the entire length of the sealing loop is □ 2°, of which γ is allal in Fig. 5. This is equivalent to .

? The length corresponding to , is L2. Ll is exactly one tooth shorter than L2. This is the angle obtained by subtracting one tooth from the winding angle tp of the male rotor. Let this be β, β=360″10γ This is the maximum value of β, and if the compression ratio is made larger than 1, β will be in the following range.

0〈β≦360°+γ Putting all the above together, l) Compression ratio range from 1 to 0 where radial ports disappear 0〈β≦360°+γ 2) Compression ratio Z at which radial ports disappear.

3) Further increase the compression ratio and use only axial ports Z.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 9 and 10.

The male rotor 39 and the female rotor 40 are rotatably supported by bearings 45.46.degree. 47.48 in the main casing 41 and the suction casing 42, respectively. A timing gear 49.50 is attached to the #l end of the rotor, and the gap between the male and female rotors is adjusted so that they do not come into contact with each other. Bearing 4
Lubrication of 5 and 46 is done by splash lubrication, and the suction cover 4
The lubricating oil 56 accumulated in the inside 3 is splashed by the timing gear. On the other hand, a disk 51 is attached to the male rotor shaft to lubricate the bearings 47 and 48, and the disk 51 splashes the lubricating oil 57 inside the discharge cover 44. Shaft seals 52, 53
, 54 and 55 prevent lubricating oil from the bearings and timing gear from entering the working chamber. Rotor discharge side working chamber 6
6 and the inside of the discharge cover 44, so the differential pressure acting on the shaft seals 54 and 55 on the discharge side is relatively small. If the inside of the shaft seal 43 is opened to the atmosphere, the differential pressure acting on the suction side shaft seals 52 and 53 increases, making sealing difficult. Therefore, the inside of the suction cover 43 is connected to the exhaust pressure pipe 5.
9 and 60 communicate with the low-pressure differential chamber 67 to lower the pressure inside the suction cover 43 and reduce the differential pressure acting on the shaft seals 52 and 53, thereby enhancing the sealing effect. Since the inside of the suction cover 43 is filled with oil droplets, a droplet separation chamber 58 is provided in the suction cover to prevent this oil from entering the working chamber through the exhaust pressure pipe 59 and 60. An oil trap 61 is attached.

In addition, even if oil enters the working chamber through the exhaust pressure pipe,
In order to prevent this oil from flowing back to the suction port 63 side, the exhaust pressure port 62 of the main casing 41 is connected to the working chamber 67 of the rotor.
is opened from the suction port 63 at a position after it is completely closed. After the working chamber 67 of the male rotor 39 passes through the suction port 63 and before communicating with the discharge port 64, the working chamber 67 engages with the female rotor 40 at two positions 68.
Similarly, the working chamber 70 of the female rotor has two engagement portions 71.69 with the male rotor.

As the rotor rotates, gas is sucked into the working chamber formed by the rotor tooth space and the casing through the suction port 63, and is discharged from the discharge port 1-64.

The working chambers 67, 70 move gas while keeping their volume constant as the rotor rotates, and the working chambers 72, 70 are located at the position where the rotor rotates. '73 reduces the volume of the rotor as it rotates, compressing the gas internally. For this reason, the temperature of the gas increases on the discharge side, so cooling jackets 74a to 74e are provided on the discharge side of the main casing 41, and cooling water is passed through the jackets to cool the casing and the compressed gas.

〔Effect of the invention〕

As described in detail above, according to the present invention, from atmospheric pressure to
It is possible to provide a vacuum pump that can achieve a medium vacuum of about 0-'Torr level with a single stage pump.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional plan view of a non-lubricated screw compressor suitable for a vacuum pump, and FIG. 2 is a longitudinal sectional view thereof. Figures 3 to 8 are the outline of the present invention, and Figure 10 is Figure 9@A.
-A cross section. 20... Male rotor model, 21... Female rotor model, 22... Casing model, 39... Male rotor, 40... Female rotor, 41... Main casing,
42...Suction casing, 45.46...Deep groove ball bearing, 47°48...Cylindrical roller bearing, 49.50...
・Timing gear, 52, 53, 54. 55...Shaft seal, final) 63...Suction port, 64...Discharge port 6t. Agent Patent Attorney Katsune Ogawa −′! 41 days deaf 1 Yang 5. . ), t. ,. Cb) LL Rogue Bodhisattva 6 Medication 7

Claims (1)

[Claims] A pump casing in which a suction port and a discharge port are formed, a pair of rotors that mesh with each other and are arranged in the former pump casing so that both ends are journalled and rotate in synchronization, and each rotor has a shaft support. The number of teeth of the pair of rotors is one fewer than that of the male rotor than that of the female rotor, and the rotor length is such that the male rotor has a full winding. The range in terms of angle is (number of male rotor teeth Z_m+1) ÷ Z_m x 360
Centered on °, between (Z_m+1) ÷ Z_m x 360° - α and (Z_m+1) ÷ Z_m x 360° + 360° + γ, where α is the compression ratio and γ is the length of the part of the lobe tip helix. An oil-free screw vacuum pump characterized by: