JPS62168987A - Screw type vacuum pump - Google Patents

Abstract

PURPOSE:To prevent the leakage of a gas from the shaft seal means of a first stage suction port by positioning the suction port of each stage of pump body on the other pump body side, while connecting the discharge port of a first stage pump body to the suction port of a second stage pump body. CONSTITUTION:The suction port 8 of each of pumps 1, 2 is positioned on the other pump body side, placing a first stage suction port 8 on the left side in the figure on the right side while a second stage suction port 8 on the right side in the figure on the left side, while a first stage discharge port 9 is connected to the second stage suction port 8 by means of a pipe 10. And, the first stage suction port 8 is connected to a place to be sucked by vacuum, e.g., a vacuum tank, and a gas which is sucked here is sent out to a second stage discharge port 9 via the first stage discharge port 9 and the second stage suction port 8 to make the inside of the tank vacuum. By this structure, the quantity of gas leaking from the shaft seal means 7 of the first stage suction port 8 which greatly affects the degree of vacuum of the vacuum tank can be reduced, improving the ultimate vacuum at the first stage suction port.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a screw type vacuum pump using a screw rotor.

(Prior Art) Conventionally, various types of vacuum pumps have been used, such as water ring vacuum pumps, oil rotary vacuum pumps, Roots vacuum pumps, and the like.

However, in a water ring type or oil rotary vacuum pump, since the device and the suction gas are cooled with water or oil, molecules of this water or oil tend to leak to the suction side of the device. In particular, if equipment suddenly stops, such as during a power outage, water or oil may flow back into the suction side. These pumps are not suitable for the food industry sector.

Roots-type vacuum pumps are also used in the medium vacuum region (10-' to I
Torr), it operates effectively in the low vacuum region (1 to
Even if the gas is evacuated (760 Torr), gas leakage from between the rotors will increase and the gas temperature will rise significantly, so it is not suitable for use in this area.

Therefore, as shown in FIG. 2, the inventors of the present invention have attempted various uses of screw-type vacuum pumps as vacuum pumps suitable for use in a wide range of vacuum regions.

This screw type vacuum pump basically has the same structure as a screw type compressor, and has the same function in that it sucks in gas and discharges gas at a higher pressure than the sucked gas. That is, this pump has a pair of male and female screw rotors (hereinafter referred to as rotors) 4 that are engaged with each other and can be rotated through bearings 5 on both sides in a casing 3 that has a suction port 8 on one side and a discharge port 9 on the other side. The rotor 4 is supported by a shaft sealing means 7 between both bearings 5 and the rotor 4 as appropriate.

The suction port 8 side is connected to a vacuum point (not shown), gas is sucked in from here, and this gas is discharged from the discharge port 9, thereby forming a vacuum area on the suction port 8 side. .

(Problems to be Solved by the Invention) The part of the shaft sealing means 7 of the vacuum pump shown in FIG. 2 on the side far from the rotor 4 is generally at atmospheric pressure (760 Torr), and in reality 7 and the shaft of the rotor 4, it is impossible to eliminate the gap between the shaft sealing means 7 and the rotor 4 from the atmosphere side, in particular, from the atmosphere side to the vacuum area suction port 8 (approximately Gas leaks to the 10 Torr) side.

Unlike in the case of a compressor, in the case of a vacuum pump, the pressure at the suction port 8 is very low compared to atmospheric pressure, so the pressure difference between the bearing side of the shaft sealing means 7 and the inside of the suction port 8 is very large. This makes it easy for gas leakage to occur, and furthermore, the expansion rate of the gas leaking into the suction port 8 becomes extremely large. For this reason, with the vacuum pump shown in Figure 2, it is not possible to obtain a very high degree of ultimate vacuum, and the vacuum pump in a single stage is approximately 10 Torr. Even in the case of two stages in which only the suction port 8 is connected, the limit is about I Torr, and there is a problem that it cannot reach the medium vacuum region.

For example, if the suction pressure is 10 Torr in the case of a single stage,
Since the discharge pressure (atmospheric pressure) is 760 Torr, even if the total amount of leaked gas is 512/a+in, it expands from atmospheric pressure to suction pressure, so the total amount of gas at the suction port is 5 x (760 Torr). /I0)=38012/min.

Therefore, this causes a decrease in the displacement amount and a decrease in the ultimate degree of vacuum.

The present invention has been made in view of the problems of the conventional art.
The purpose is to provide a screw-type vacuum pump that makes it possible to improve the ultimate degree of vacuum.

(Structure of the Invention) In order to solve the above-mentioned problems, the present invention provides a pair of male and female screw rotors that mesh with each other in a casing having a suction port on one side and a discharge port on the other side, and appropriate shaft sealing means on both sides of the screw rotors. The casings of both bodies are integrated, and the male and female rotors of the two stages are installed coaxially and rotatably. The suction port was located on the other pump main body side, and the discharge port of the first pump main body and the suction port of the second pump main body were formed in communication with each other.

(Example) Next, an example of the present invention will be explained according to the drawings. Fig. 1 shows a screw type vacuum pump according to the present invention.
The screw-type vacuum pump shown in Fig. 2 is a pump body 1.2 that has substantially the same structure except for the bearing 5, which is directly connected to each other, and corresponding parts are given the same numbers. The explanation will be omitted.

That is, the present screw type vacuum pump includes a pump main body 1.2 provided in two stages that share a casing 3, and each rotor 4 has a shaft 6 rotatably supported by bearings 5 at both ends.
The shaft sealing means 7 is provided between the two rotors 4 and is formed so as to rotate together.

In addition, the suction port 8 of the pump body 1.2 is located on the other pump body side, the first stage suction port 8 on the left side in FIG. 1 is on the right side, and the second stage suction port 8 on the right side is located on the right side. The first stage discharge port 9 and the second stage suction port 8 are communicated with each other through a pipe 10 along with a pipe arranged on the left side.

Then, the suction port 8 of the first stage is connected to a place to be evacuated, for example, a vacuum tank, and the gas sucked from here is transferred to the first stage.
The inside of the tank is evacuated by sending the liquid from the discharge port 9 of the first stage to the second stage discharge port 9 via the second stage suction port 8.

With this configuration, the first stage suction port 8 has a large influence on the degree of vacuum of the vacuum tank, and hence the vacuum degree of the first stage suction port 8, and the pumping speed.
This is to reduce the amount of gas leaking from the shaft sealing means 7 side.

That is, the second-stage suction port 8 is at an intermediate pressure between the first-stage suction port 8 in the vacuum region and the second-stage discharge port 9 in the atmospheric pressure state. Binocular port 8.8
The first stage This is to improve the degree of vacuum achieved at the suction port 8.

For example, if you just connect two vacuum pumps as shown in Figure 2,
Therefore, by simply using the numerical values of the above conventional example in which the first-stage discharge port and the second-stage suction port are connected, the first-stage suction port 8 is 1 Torrs. 20 Torr at the intermediate stage between the outlet 9 and the second stage suction port 8
, the second stage discharge port 9 is set to atmospheric pressure (760 Torr). Even if the amount of gas leaking from the intermediate shaft sealing means 7 is the same as above, 5 fJ/min, the expansion i1 = 5 x (20/ ] ) = 10 H/
min, which is considerably smaller than the above calculation result.

Furthermore, since gas leakage from the shaft sealing means 7 is actually reduced, the degree of vacuum achieved at the suction port 8 of the first stage and the exhaust speed are improved.

By the way, in addition to the above-mentioned gas leakage, the cause of the decrease in the ultimate vacuum degree at the suction port 8 of the first stage is that from the gap in the end surface of the rotor 4 on the discharge port 9 side of the same pump body 1,
There is gas leakage from the tooth groove space of the rotor 4 that communicates with the suction port 8. That is, as the rotor 4 rotates, the pump main body l sucks gas into the tooth groove portion of the rotor 4 that is open to the suction port 8 in a first state, and in a second state, the gas is sucked into the tooth groove portion of the rotor 4 on the suction port 8 side. By closing at the end face of the rotor chamber, the gas is trapped in the tooth groove. Then, in a third state, the discharge port 9 side of the tooth groove is closed with the end face of the rotor chamber, and the seal line formed along the ridgeline of the tooth on the suction port 8 side among the teeth on both sides of the tooth groove is closed to the rotor 4. Gas compression is performed by moving toward the discharge port 9 side with the rotation of. Then, as a fourth state, compressed gas is discharged to the discharge port 9 by opening the end surface (axial boat) and the radial wall surface (radial boat) of the rotor chamber on the discharge port 9 side of the tooth groove portion.

Further, as the tooth groove rotates, its discharge port 9 side is closed by the end face of the rotor chamber, and its suction port 8 side is communicated with the suction port 8 to be in the first state, and the same state as described above is repeated thereafter.

The above is a change in state over time as the rotor 4 rotates for one tooth space, whereas the discharge port 9 of the rotor 4
On the side end face, cross sections of the tooth groove portions in the first to fourth states are always generated at each rotation angle of the rotor 4, that is, at each location. Among the different states that are formed in different places at any given moment, especially the first one! The cross section of the state of
Seven quarters I, 1 The median 1- is the fourth state in which the pump body 1 has the highest pressure because it is impossible to eliminate the gap between the rotor 4 and the wall surface (including the end surface) of the rotor chamber. Direct gas leakage occurs from the part in the first state where the pressure is lowest. For this reason, this has a large effect on the decrease in the degree of vacuum at the suction port 8, and prevents an improvement in the ultimate degree of vacuum.

This phenomenon occurs because the end face of the tooth groove portion on the discharge port 9 side is closed with the end face of the rotor chamber in the first state. In other words, it is caused by the short length of the rotor 4. It becomes.

When the rotor 4 is short, the tooth space in the first state is formed by the wall surface of the rotor 4 and the teeth of the two adjacent rotors 4, but if the rotor 4 is lengthened to a certain extent, the tooth space between the male and female rotors becomes smaller. They go around each rotor 4 once and come into communication again on the discharge port 9 side. In this state, the surface of the tooth groove in the first state on the discharge port 9 side is no longer formed by the wall surface of the rotor chamber, but is formed only by the teeth of the rotor 4.

Therefore, by increasing the length of the rotor 4, especially the rotor 4 of the first stage, as described above, the gas can be directly transferred from the discharge port 9 in the high pressure state of the first stage to the suction port 8 where the degree of vacuum should be increased. can be prevented from leaking.

Furthermore, considering the case where both adjacent tooth grooves are not communicating with the discharge port 9, the tooth groove on the discharge port 9 side is under a somewhat higher pressure state. As mentioned above, rotor 4
Since the gap between the space and the rotor chamber wall surface cannot be eliminated, gas may leak from the tooth groove on the adjacent discharge port 9 side to the suction port 8 side. The pressure is not as high as in the pressure part), but since it is adjacent to the suction port 8, the pressure is only slightly high, and the influence of gas leakage is small.

In this way, in the above embodiment, by increasing the length of the rotor 4 in the first stage, gas leakage from the end surface of the rotor chamber on the discharge port 9 side can be prevented, and the shaft sealing means can be prevented from leaking. Together with the prevention of gas leakage, the ultimate degree of vacuum can be further improved.

Note that the two-stage rotor 4 provided coaxially and integrally rotatably in the above embodiment may be formed from the same material as the shaft 6, or may be formed from a different material. That is, one shaft 6 and two rotors 4 may be fitted and fixed, or one round bar may be turned to form the shaft 6 and both rotors 4. It is not limited to.

(Effects of the Invention) As is clear from the above description, according to the present invention, a pair of male and female screw rotors that mesh with each other are provided in a casing having a suction port on one side and a discharge port on the other side. The pump body, which is rotatably housed with a sealing means, is provided in two stages, and the casings of both bodies are integrated.
The male and female rotors of the stages are coaxially arranged so that they can rotate together, and the suction port of the pump main body of each stage is located on the side of the other pump main body, and the discharge port of the first stage pump main body and the second stage pump main body are arranged. The suction ports are connected to each other.

For this reason, the pressure on the rear stage side of the shaft sealing means in the intermediate portion is lowered, so the amount of gas leaking from this shaft sealing means to the suction port side of the first stage in the vacuum area is reduced, and the amount of gas leaking is reduced. The expansion rate of gas becomes smaller. As a result, the exhaust from the first stage suction port is promoted, and a high ultimate vacuum degree can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a screw type vacuum pump according to the present invention, and FIG. 2 is a schematic sectional view of a conventional screw type vacuum pump. 1.2...Pump body, 3...Casing, 4...
・Rotor (screw rotor), 7... Shaft sealing means, end ・
- Suction port, 9...discharge port, 10...pipe. Patent applicant: Kobe Steel, Ltd. Agent: Patent attorney: Aohaku Ao and two others Figure 1: Evening figure

Claims (1)

[Claims] (1) A pair of male and female screw rotors that mesh with each other are placed inside a casing that has a suction port on one side and a discharge port on the other side.
The pump body is rotatably housed with appropriate shaft sealing means arranged on both sides, and the casings of both bodies are integrated, and the male and female rotors of the two stages are coaxially rotatable. , a screw type characterized in that the suction port of the pump main body of each stage is located on the side of the other pump main body, and the discharge port of the first stage pump main body is communicated with the suction port of the second stage pump main body. Vacuum pump.