JPH0329996B2 - - Google Patents

Description

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

(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. 59-1989) have been used. 185889) is publicly known.

Among these, water-ring type vacuum pumps and high-vacuum pumps use a suction port to prevent the gas from rising in temperature due to the heat generated by compression in the pump when drawing a vacuum. In this way, the device is cooled together with the gas.

However, according to this type of vacuum pump,
If the smell of water or oil leaks into the suction port, or if the device suddenly stops, such as during a power outage, water or oil may flow back to the suction port. 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 (for example, vacuum packaging), where the generation of odors is particularly disliked.

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

However, in this type of vacuum pump, the gap between the rotors must be increased due to the need to maintain the rotors in a non-contact manner. For this reason, even though this vacuum pump can be used in the medium vacuum region (10 ^-3 ° to 1 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 in low to high vacuum ranges.

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

As a result, the bearing and shaft sealing parts of the screw rotor in the main body of the screw compressor are at atmospheric pressure or close to atmospheric pressure, so if this is used as a vacuum pump, there will be It has become clear that air leaks from the shaft seal of the screw rotor shaft to the suction port of the rotor chamber, resulting in poor ultimate vacuum.

The ultimate degree of vacuum refers to the highest degree of vacuum that can be achieved when the vacuum pump is operated with the flange of the suction port completely closed, and is the most important performance point of the vacuum pump.

(Object of the Invention) The present invention has been made in view of the above-mentioned conventional problems, and its object is to provide a screw type vacuum pump with a good ultimate vacuum degree.

(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 pair of male and female screw rotors that mesh with each other are rotatably housed in a rotor chamber, and a space below atmospheric pressure that 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. A first shaft sealing means communicated with the atmosphere and a second shaft sealing means communicated with the atmosphere were provided in this order from the rotor chamber side.

(Example) Next, an example 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, which is formed by providing a first communicating portion 3 in a casing 2 of an oil-free pump body (hereinafter referred to as the body) 1. FIG. That is, the casing 2 of the main body 1 has a water-cooling jacket 4, and a rotor with one side opening at the suction port 5 provided at the top (double-dashed line) and the other opening at the discharge port 6 provided at the bottom (dotted line). It has a chamber 7, and a pair of male and female screw rotors 8 that mesh with each other are rotatably housed in the rotor chamber 7. By rotating and changing the position of each tooth groove part 9 of this screw rotor 8, the state is open to the suction port 5, the gas trapped state is blocked from the suction port 5 and the discharge port 6, and the state is opened to the discharge port 6. The three states are sequentially repeated, and a gas suction space, a compression (confinement) space, and a discharge space are created corresponding to each state.

In addition, the rotor shaft 11 of the screw rotor 8 is supported by a bearing 12 that is forcibly lubricated, and a tooth groove portion 9 is provided between each bearing 12 on the suction port 5 side and the rotor chamber 7 as described below from the rotor chamber 7 side. A first shaft sealing means 13 communicating with the atmosphere and a second shaft sealing means 14 communicating with the atmosphere are provided in this order. In this embodiment, the first shaft sealing means 13 has a structure in which two seal rings 13a are arranged in parallel, while the second shaft sealing means 14 has a structure that moves toward the bearing 12 side as the screw rotor 8 rotates. A threaded labyrinth seal is used.

Further, two seal rings 13a are similarly provided adjacent to the rotor chamber 7 of the first shaft sealing means 13.
A third shaft sealing means 15 of the type using is provided, and the third shaft sealing means 15 is provided in two stages from the rotor chamber 7 side between each bearing 12 on the discharge port 6 side and the rotor chamber 7, A fourth shaft sealing means 16 using a labyrinth seal similar to the second shaft sealing means is provided in this order.

The labyrinth portions of the second and fourth shaft sealing means 14 and 16 push the lubricating oil toward the bearing 12 side as the screw rotor 8 rotates, and prevent it from flowing into the rotor chamber 7 side.

However, especially on the suction port 5 side, the second shaft sealing means 14
There is a possibility that the lubricating oil cannot be sufficiently removed only by the labyrinth portion except when the screw rotor 8 is rotating at high speed. Therefore, a second communication part 17 is provided at the second shaft sealing means 14 to communicate it with the atmosphere, and the lubricating oil that has flowed from the bearing 12 toward the rotor chamber 7 is transferred to the second communication part 17. This prevents lubricating oil from flowing further into the rotor chamber 7 side even when the screw rotor 8 is not rotating at high speed.

Further, a first communication portion 3 is formed at the location of the first shaft sealing means 13 , and the first shaft sealing means 13 is a gas-contained space that does not communicate with the suction port 5 in the rotor chamber 7 . It is communicated with the groove portion 9. Note that the lower the pressure in this tooth groove portion 9, the better, so the portion immediately after closing is preferable.

Furthermore, this first communication portion 3 is connected to the first shaft sealing means 1.
A connection that connects the first through hole 18 that allows the seal ring No. 3 to communicate with the outside of the casing 2 and the second through hole 19 that allows the space immediately after gas confinement to communicate with the outside of the casing 2, and the first and second through holes 18 and 19. The first shaft sealing means 13 is kept at as low a pressure as possible by evacuating the space immediately after confinement which has the lowest pressure among the spaces cut off from the suction port 5.

By doing this, the suction port 5
The pressure difference between the first shaft sealing means 13 and the first shaft sealing means 13 is reduced to prevent air from leaking from the first shaft sealing means 13 to the suction port 5 side. Furthermore, even if lubricating oil were to leak from the labyrinth portion, it would be discharged through the gas confinement space that is cut off from the suction port 5 through the first communication portion 3, so that the lubricant oil would be discharged from the suction port 5 side. It will not leak.

The function of these first communicating portions 3 utilizes the unique feature of the screw type in that it always operates while separately forming three spaces: a gas suction space, a confinement space, and a discharge space, as described above.

In Fig. 3, the horizontal axis represents the position x in the rotor axis direction (the right direction is positive) when the end surface on the side of the discharge port 6 of the rotor chamber 7 is the origin, and the vertical axis represents the degree of vacuum, that is, the pressure. , represents the pressure change along the rotor axis direction from the rotor shaft 11 part on the suction port 5 side to the suction port 5, the inside of the rotor chamber 7, and the discharge port 6, and l ₁ is the second
Through-hole 19, _l2 indicates the end surface of the rotor chamber 7 on the suction port 5 side, _l3 indicates the first through-hole 18, _l4 indicates each position of the second communication part 17, and Pi indicates the position of the second through-hole 19. Indicates pressure.

In FIG. 3, the dashed line indicates that only the first through hole 18 is provided instead of the first communication portion 3, and the first shaft sealing means 1 is
The seal ring 13a section of No. 3 is also kept at approximately atmospheric pressure to prevent the lubricating oil from leaking to the rotor chamber 7 side even if the lubricating oil leaks from the labyrinth side. leak 2
This figure shows the pressure state when heavy protection is applied.

Therefore, when comparing the dashed-dotted line portion (former) and the solid line portion (latter) in Fig. 3, we find that x= Pressure at l ₃ and x at suction port 5 =
The pressure at l ₂ , that is, the differential pressure from the ultimate vacuum level P ₀ , is expressed as ΔP ₁ in the former case, and becomes ΔP ₁ = atmospheric pressure - ultimate vacuum level P ₀ , whereas in the latter case, it is also expressed as ΔP ₂ . Expressed as ΔP ₂ = Pi - ultimate vacuum degree P ₀ .

Here, since Pi is naturally smaller than atmospheric pressure (Pi<
(atmospheric pressure), ΔP ₂ < ΔP ₁ is guaranteed.

Therefore, the leakage of air from the first shaft sealing means 13 to the rotor chamber 7 is reduced correspondingly to the reduction in the differential pressure.

In the above embodiment, the first communication section 3 communicates with the space immediately after gas confinement in the rotor chamber 7, but the present invention is not limited to this, and the first communication section 3 communicates with the space immediately after the gas is trapped in the rotor chamber 7. It is only necessary to form the means 13 so that it can be evacuated to below atmospheric pressure. For example, in addition to the above embodiments, the first through hole 17 may be connected to another vacuum pump via piping, and the vacuum pump can be used to evacuate the part. It may be formed into

Furthermore, the first shaft sealing means 13 is not limited to one stage, and if two or more stages are provided, the first shaft sealing means 13 closer to the bearing 12 is placed in a state where the higher pressure gas in the rotor chamber 7 is trapped. The suction port Gas leakage to 5 can be effectively reduced.

Furthermore, in the above embodiment, the first,
Although the second shaft sealing means 13 and 14 are shown, the present invention is not limited to this. In addition, as shown in FIG. The first and second shaft sealing means 13 and 14 may be provided by forming the communication part 3 and the second communication part 17. On the end surface of the rotor chamber 7 on the side of the discharge port 6, in addition to the gas discharge space, the end surface of the tooth groove immediately after changing from the gas discharge space to the suction space is always visible. Needless to say, the tooth groove portion which serves as the suction space is in a vacuum state, and therefore the gap between the rotor chamber 7 on the side of the discharge port 6 and the screw rotor 8 is in a vacuum state. Therefore, on the discharge port 6 side as well as on the suction port 5 side, lubricating oil and air tend to leak from the shaft sealing means to the suction port 5 through the above-mentioned gap and the tooth groove portion that becomes the suction space. . First and second shaft sealing means 13 on the side of the discharge port 6,
14 prevents the occurrence of such a phenomenon and effectively contributes to improving the ultimate vacuum degree.

Note that in FIG. 4, parts common to those in FIG. 1 are given the same numbers (the same applies hereinafter). Moreover, FIG. 5 shows the state of pressure conversion in the screw type vacuum pump shown in FIG. 4, and is a diagram corresponding to the above-mentioned FIG. 3.

In addition, the second shaft sealing means 14 is not limited to one stage, but may be provided in two stages, for example, as shown in FIG. 6. In this case, the lubricating oil trying to proceed from the bearing 12 side to the rotor chamber 7 side is moved from the second communication portion 17 on the bearing 12 side to the
Lubricating oil can be discharged to the outside of the machine more effectively than in the case of stages.

In this case, the two-stage second shaft sealing means 14 may be provided only on the suction port 5 side, and the present invention provides first and second shaft sealing means 13 and 1 symmetrically on both sides of the female and male rotors.
4, but the first communicating portion 3 may be provided only on either the female or male rotor.

In the embodiments shown in FIGS. 4 and 6, if it is necessary to cool the inside of the rotor chamber, the casing 2 may be of a type having a water cooling jacket as appropriate.

(Effects of the Invention) As is clear from the above description, according to the present invention, the rotor shaft is supported by a casing having a rotor chamber with one side opened to the suction port and the other side opened to the discharge port, and a forced lubrication type bearing. A pair of male and female screw rotors are supported and rotatably housed in the rotor chamber and mesh with each other, and at least atmospheric pressure is provided between the bearings of each rotor shaft on the suction port side and the rotor chamber, which does not communicate with the suction port. A first shaft sealing means communicating with the following space and a second shaft sealing means communicating with the atmosphere are provided in this order from the rotor chamber side.

Therefore, the differential pressure between the first shaft sealing means and the suction port is reduced, reducing air leakage to the suction port, and also preventing lubricating oil supplied to the bearing from leaking to the suction port. This makes it possible to achieve a good ultimate vacuum and prevent contamination of the rotor chamber by lubricating oil. As a result, even if it is an oil-free type, it is possible to vacuum a wide range in a single stage.

[Brief explanation of drawings]

1 is a cross-sectional view of a screw-type vacuum pump according to a first embodiment of the present invention, FIG. 2 is an enlarged view of part a in FIG. 1, and FIG. 3 is a rotor axial direction in the vacuum pump shown in FIG. 1. 4 is a cross-sectional view of the screw type vacuum pump according to the second embodiment of the present invention, and FIG. 5 is a diagram showing the state of pressure change in the vacuum pump shown in FIG. 4. The figure shown,
FIG. 6 is a cross-sectional view according to a third embodiment of the present invention. 1... Main body (pump main body), 2... Casing,
3...First communication part, 5...Suction port, 6...Discharge port, 7...Rotor chamber, 8...Screw rotor, 1
2...Bearing, 13...First shaft sealing means, 14...Second shaft sealing means, 16...Second communication portion.

Claims (1)

[Claims] 1. A casing having a rotor chamber with one side open to the suction port and the other side open to the discharge port, and a casing that supports a rotor shaft by a forced lubrication type bearing and is rotatably housed in the rotor chamber. a pair of male and female screw rotors that mesh with each other, and a first shaft sealing means that communicates with a space below atmospheric pressure that does not communicate with the suction port, at least between the bearing of each rotor shaft on the suction port side and the rotor chamber; , and a second shaft sealing means communicated with the atmosphere, in this order from the rotor chamber side. 2. The screw type vacuum pump according to claim 1, wherein the space below atmospheric pressure is a space immediately after gas confinement in the rotor chamber. 3. A plurality of stages of the first shaft sealing means are provided, and the first shaft sealing means, in which the first communication portion is closer to the bearing, is communicated with the tooth groove portion, which is a higher pressure gas confined space in the rotor chamber. A screw type vacuum pump according to claim 1, characterized in that: