JPS62261689A - Screw type vacuum pump - Google Patents

Abstract

PURPOSE:To prevent an oil leakage from occurring, by installing a first shaft sealing device being interconnected to a tooth space part or a confined space in a rotor chamber and a second shaft sealing device being interconnected to the atmosphere, between a bearing of each rotor shaft at the suction port side and the rotor chamber. CONSTITUTION:In an interval between a bearing 13 and a rotor chamber 9, a first shaft sealing device 14 being interconnected to a tooth space part 11 and a second shaft sealing device 15 being interconnected to the atmosphere are installed at both sides of a suction port 7 and a discharge port 8 in this order. Inflow of lubricating oil from the bearing 13 part is almost entirely checkable by both first and second atmospheric interconnecting holes 3 and 4, and an air leakage to the rotor chamber 9 from the first atmospheric interconnecting hole 3 is prevented from occurring whereby an ultimate at the suction port 7 is improvable.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a screw-type vacuum pump that uses a screw-type pump body equipped with a pair of male and female screw rotors that mesh with each other, and is particularly suitable for an oil-free type. It is.

(Prior art) Conventionally, as a vacuum pump, for example, a water ring vacuum pump (
Japanese Patent Publication No. 54-37693), a high vacuum pump (Japanese Patent Publication No. 57-59920), and a two-shaft vacuum pump (Japanese Patent Publication No. 59-185889) are known.

Among these, water ring vacuum pumps and high vacuum pumps are
When vacuuming, in order to prevent the temperature of the gas from rising due to the heat generated by compression in the pump, the gas is brought from the suction port to the discharge port in direct contact with water or oil, and in this way, the gas and The equipment is being cooled down.

However, with this type of vacuum pump, water or oil leaks into the suction port, or if the equipment suddenly stops, such as during a power outage, water or oil leaks into the suction port. A backflow situation may also occur. For this reason, these vacuum pumps cannot be used in the semiconductor manufacturing sector, where contamination with impurities is not allowed, or in the food industry, where the generation of odors is particularly disliked (for example, vacuum packaging).

On the other hand, the two-shaft vacuum pump has an oil-free set such as a roots-type mechanical booster (in this specification, it refers to a type that is not used when water and oil are in contact with a gas for vacuuming).

) There is Norano.

However, in this type of vacuum pump, the gap between the rotors must be increased due to the necessity of keeping the rotors in contact with each other. For this reason, even though this vacuum pump can be used in the medium vacuum region (to 3 to I Torr), in the low vacuum region (1 to 760 Torr) gas leakage from between the rotors increases and the gas temperature rises significantly. , not suitable for use in this area.

For this reason, there has been a desire to develop a single-stage, oil-free vacuum pump suitable for use from low to high vacuum ranges.

Therefore, the inventor of the present invention discovered that the main body of an oil-free screw compressor, which is conventionally used mainly for generating high-pressure gas in a region above atmospheric pressure, is different from a vacuum pump in that it sucks in gas and discharges it in a compressed state. Focusing on the common functionality and the ability to reduce gas leakage between the rotors, various attempts were made to use them as vacuum pumps.

As a result, the bearing and shaft sealing parts of the screw rotor in the screw compressor main body are at atmospheric pressure or close to atmospheric pressure, so if this is used as a vacuum pump, the screw rotor shaft will It became clear that the problem was that air was leaking from the shaft seal into the rotor chamber, worsening the ultimate vacuum.

Note that the ultimate vacuum level refers to the highest vacuum level that can be achieved when the vacuum pump is operated with the 7-run section of the suction port completely closed, and is the most important performance point of the vacuum pump.

(Object of the invention) The present invention was made in view of the above-mentioned conventional problems.
The purpose is to provide a screw type vacuum pump with a good ultimate vacuum.

(Structure of the Invention) In order to achieve the above object, the present invention includes a casing having a rotor chamber opened to a suction port on one side and a discharge port on the other side, and a rotor shaft supported by a forced lubrication type bearing. A closed space in the rotor chamber that is provided with a pair of male and female screw rotors that are rotatably stored in the chamber and that mesh with each other, and that is located between at least the bearing of each rotor shaft on the suction port side and the rotor chamber, and that does not communicate with the suction port. A plurality of first shaft sealing means communicated with the tooth groove portion, and a second shaft sealing means communicated with the atmosphere.
and the second shaft sealing means of the stage are provided in this order from the rotor chamber side.

(Example) Next, one embodiment of the present invention will be described with reference to the drawings.

1 and 2 show a screw type vacuum pump according to the present invention, in which a first atmospheric communication hole 3 is provided in a casing 2 of a pump body l.
．． It is formed by providing a second atmosphere communication hole 4 and a confined space communication part 5. That is, the casing 2 of the pump body l
What is the rotor chamber 9, one of which is open to the suction lower (double-dashed line) provided at the top and the other to the discharge port 8 (dashed line) provided at the bottom? A pair of screw rotors 10 are rotatably housed. Each tooth groove portion 11 of this screw rotor lO rotates and changes its position, so that it is opened to the suction lower, the gas trapped state is blocked from the suction lower and the discharge port 8, and the state is opened to the discharge port 8. The three states are repeated sequentially, and the gas suction space and compression (confinement) are
The space becomes the discharge space.

Furthermore, if the rotor shaft I2 of each screw rotor IO is supported by a forced lubrication type bearing 13, the bearing! 3 and the rotor chamber 9, a first sealing means 14 communicated with the tooth groove It from the side of the rotor chamber 9, and a second shaft sealing means 5 communicated with the atmosphere, as described below. Two stages are provided in this order on the suction lower side and the discharge port 8 side. In this embodiment, the first shaft sealing means 14 and the second shaft sealing means 15 on the rotor chamber side have a structure in which two seal rings 14a are arranged in parallel, while the remaining second shaft sealing means! 5 uses a labyrinth seal formed with a thread that advances toward the bearing 13 as the screw rotor lO rotates.

The labyrinth portion of the second shaft sealing means 15 on the bearing 13 side pushes out the lubricating oil toward the bearing 13 as the screw rotor lO rotates, and prevents it from flowing into the rotor chamber 9 side.

However, this second shaft sealing means! If the labyrinth portion 5 is used alone, the lubricating oil may not be sufficiently removed except when the screw rotor lO is rotating at high speed.

Therefore, a first atmosphere communication hole 3 and a second atmosphere communication hole 4 are provided to communicate each of the second shaft sealing means 15 provided in two stages with the atmosphere, so that the lubricating oil can flow even when the screw rotor IO is not rotating at high speed. This reliably prevents any further flow into the rotor chamber 9 side. That is, by keeping the part of the second shaft sealing means 15 on the bearing 13 side at a high pressure state approximately equal to atmospheric pressure, the rotor chamber is In addition to making it difficult for lubricating oil to flow into the 9 side, as shown by arrows A and B in FIG.
Due to the flow of air from the air to the second atmosphere communication hole 4, even if lubricating oil flows from the gap, the second atmosphere communication hole 4
The lubricating oil is discharged from the rotor chamber 9 to the outside, thereby thoroughly preventing the lubricating oil from proceeding any further toward the rotor chamber 9 side.

Furthermore, a confined space communication section 5 is provided which allows a part of the first shaft sealing means 14 that is closer to the bearing 13 to communicate with the tooth groove section 11 which is a higher pressure confined space that does not communicate with the suction port 6. be.

That is, the part of the second shaft sealing means 14 is the same as that of the first shaft sealing means 14. Since the rotor chamber 9 side of the single-shaft sealing means 14 is in a vacuum region, the pressure is set to atmospheric pressure through the second atmosphere communication hole 3.4, and the rotor chamber 9 side of the single-shaft sealing means 14 is in a vacuum region, so that the First shaft sealing means 1 provided
A pressure gradient that decreases from the bearing 13 side toward the rotor chamber 9 side occurs in the portion 4. Therefore, we have set up multiple stages! The high-pressure part of the shaft sealing means 14 is the tooth groove part, which is in a closed state with even higher pressure! (1) The lower pressure area is sucked in stages from the tooth groove part 11 which is in the confinement state with lower pressure, and the rotor chamber 9 which is in the vacuum region is drawn from the first atmosphere communication hole 3 which is at atmospheric pressure. The first shaft sealing means 14 effectively blocks air that tends to leak toward the shaft.

In this way, the first. Bearing 1 through the second atmospheric communication hole 3.4
In addition to almost completely blocking the inflow of lubricating oil from the three parts,
The first shaft sealing means 14 communicated with the confined space communication part 5 in stages prevents air from leaking from the first atmosphere communication hole 3 to the rotor chamber 9, thereby improving the degree of vacuum achieved at the suction lower. There is.

In addition, on the end face of the rotor chamber 9 on the discharge port 8 side, not only the discharge space but also the end face of the tooth groove part which is in the state of the suction space immediately after changing from discharge to suction are generated, so not only the end face on the suction lower side , the gap at the end face portion on the discharge port 8 side is in a vacuum state. As a result, the first. Second shaft sealing means 14
．． Similarly to the suction lower side, lubricating oil and air tend to head towards the rotor chamber 9 side and leak to the suction lower side. Therefore, in this embodiment, the confined space communication section 5 is provided not only on the suction lower side but also on the discharge port 8 side to thoroughly prevent leakage of lubricating oil and air into the rotor chamber 9.

As mentioned above, the suction and gradual suction of leaked air by the confined space communication section 5 operates while separately forming three spaces: the gas suction space, the confined space, and the discharge space. This is because the unique feature of the screw type, that the pressure in the tooth groove portion 11, which is a confined space, is different is used.

Next, in FIG. 3, the horizontal axis shows the position X in the rotor axis direction (the right direction is positive) when the origin is at the discharge port 8 side of the rotor chamber 7, and the vertical axis shows the degree of vacuum, that is, the pressure. from the rotor shaft 12 part on the suction lower side and the rotor chamber 9 from the suction lower side.
It shows the pressure change inside and along the rotor axial direction towards the discharge port 8. In the figure, Q, (1, indicates the through hole 5aS12+ on the high pressure side and low pressure side of the confined space communication section 5.
is the end face of the rotor chamber 9 on the suction lower side, Q, (1, is the through hole on the first shaft sealing means 14 side of the confined space communication portion 5 that communicates with the through hole 5a on the low pressure side and high pressure side in the suction lower ,1
2@, 12. is the first. The second atmospheric communication hole C, , C is a through hole corresponding to the above C, , C, on the discharge port 8 side, Q
l. indicates each position of the first atmospheric communication hole. Also, P
+, Pg indicate the pressure at the tooth groove corresponding to the above positions C, , C, and the positions C, , C and C, communicating with this
, 12, is equal to the pressure at the first shaft sealing means 14.

As is clear from the figure, the atmospheric pressure! As the position of atmospheric communication hole 3 progresses from X=('II to X=(!S, (!4), the degree of vacuum is gradually increased,
The differential pressure between ゜34 and ゜ is small. The amount of air leaking into the rotor chamber, which lowers the ultimate vacuum, is approximately proportional to the above differential pressure, so by effectively reducing the differential pressure in this way, the ultimate vacuum can be improved. be. Also, the bearing 13 on the discharge port 8 side. 1st. The pressure change along the rotor axis direction in the second shaft sealing means 14 and 15 is also similar to the above, and the air leaking to the suction lower through the gap at the end surface of the rotor chamber 9 on the discharge port 8 side is reduced. be.

In addition, in the above embodiment, the confined space communication part 5 from the suction lower side and the confined space communication part 5 on the discharge port 8 side are merged to communicate with the tooth groove part 11, but The present invention is not limited to this, and as shown by arrows X and Y indicated by dashed lines in FIG.
Of the second shaft sealing means 14 on the side, the one on the rotor chamber 9 side may be communicated with the position indicated by the arrow X, and the one on the bearing 13 side may be communicated with the position indicated by the arrow Y.

Further, in the above embodiment, the first shaft sealing means 14 is provided on the suction lower side and the discharge port 8 side, but the present invention is not limited to this, and as shown in FIG. The first shaft sealing means 14 may be provided only on the side.

Note that the pressure state in the vacuum pump shown in FIG.
As shown in the figure. In the drawings, the same reference numerals are given to the same parts as in FIGS. 1 to 3 (the same applies hereinafter).

Further, in the above embodiment, the first shaft sealing means 14 closer to the bearing 13 was communicated with the higher pressure tooth groove portion, but the present invention is not limited to this.
Each of the first shaft sealing means may be communicated with the same tooth groove portion (however, it is still in the closed state).

In addition, the present invention provides first and second rotors symmetrically on both sides of the male and female rotors.
The shaft sealing means 14 and 15 are not limited to those provided, and the confined space communication portion 5 may be provided only on one of the male and female rotors, and furthermore, in the case of an oil-free set, it may be provided with a shaft sealing means 14, 15 for cooling the inside of the rotor chamber 9. , a water cooling jacket may be provided on the outside of the casing 2.

(Effects of the Invention) As is clear from the above description, according to the present invention, the rotor shaft is supported by a casing that forms a rotor chamber with one side opening at the suction port and the other side opening at the discharge port, and a forced lubrication type bearing. and a pair of male and female screw rotors that mesh with each other and are rotatably housed in the rotor chamber, and at least between the bearing of each rotor shaft on the suction port side and the rotor chamber,
A plurality of first shaft sealing means communicated with tooth grooves between confinement chambers in the rotor chamber that do not communicate with the suction port, and two stages of second shaft sealing means communicated with the atmosphere are installed on the side of the rotor chamber. It is then formed in this order.

For this reason, the first step is to prevent oil leakage from the bearing portion to the rotor chamber.
Assuming that the second atmosphere communication hole can prevent oil from contaminating the rotor chamber, the pressure difference between the rotor chamber side portion of the first shaft sealing means and the suction port becomes small, and the suction port Air leakage can be reduced. As a result, the ultimate degree of vacuum can be improved, and a wide range of vacuum can be drawn using a single-stage, oil-free compressor body.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a screw type vacuum pump according to the first embodiment of the present invention, Fig. 2 is an enlarged view of part a in Fig. 1, and Fig. 3 is a view of the screw compressor main body relative to the position in the rotor axial direction. Figure 1 is a cross-sectional view of the screw type vacuum pump according to the second embodiment, and Figure 5 is a diagram showing the pressure change in the screw type vacuum pump shown in Figure 4. be. l...Pump body, 2...Casing, 3...First atmosphere communication hole, 4...Second atmosphere communication hole, 5...Confined space communication part, 7...Suction port, 9...Rotor chamber, 1
0...Screw rotor, 11...Tooth groove portion, 13...
- Bearing, 14...first shaft sealing means, 15...second shaft sealing means. Patent applicant Kobe Steel Co., Ltd. Representative Patent attorney Two idiots mentioned above 4th t1! Figure 5

Claims (2)

[Claims] (1) A casing with a rotor chamber with one side open to the suction port and the other side open to the discharge port, and a pair of male and female screw rotors that engage with each other and are rotatably housed in the rotor chamber, supporting the rotor shaft by forced lubrication type bearings. and a plurality of first shaft seals, which are connected to a tooth groove portion, which is a confined space in the rotor chamber, which does not communicate with the suction port, between at least the bearing of each rotor shaft on the suction port side and the rotor chamber. and a two-stage second shaft sealing means communicated with the atmosphere in this order from the rotor chamber side. (2) The first shaft sealing means is arranged in a plurality of stages, and the first shaft sealing means closer to the bearing is formed so as to communicate with the higher pressure tooth groove portion. Screw-type vacuum pump described in section.