JPH04314990A - Two-stage screw vacuum pump - Google Patents

Abstract

PURPOSE:To reduce the driving torque by lowering the intermediate pressure below the atmospheric pressure, in a two-stage screw vacuum pump in which the discharge port of a forestage pump and the suction port of a rear stage pump communicate through an intermediate passage. CONSTITUTION:A two-stage screw vacuum pump is equipped with a pair of male and female rotors 7A and 7B which revolve in meshing around parallel shafts, forestage pump 22 consisting of a casing having a suction port and a discharge port and a rear stage pump 24A, and the discharge port 28 of the forestage pump and the suction port 29 of the rear stage pump communicate through an intermediate passage 23. The exhaust speed of the rear stage pump is increased over the exhaust speed of the forestage pump, and the suction fluid volume of the rear stage pump is always increased over the discharge fluid volume of the forestage pump. Accordingly, the intermediate pressure of an intermediate passage is reduced below the atmospheric pressure. Accordingly, the driving torque of a driving machine 25 can be reduced, and the abnormal rise of temperature due to the compression heat can be prevented.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a front stage consisting of a pair of male and female rotors that mesh with each other and rotate around two parallel axes, and a casing that houses these rotors and is equipped with a suction port and a discharge port. The present invention relates to a two-stage screw vacuum pump that includes a pump and a second stage pump, and in which a discharge port of the first stage pump and a suction port of the second stage pump are communicated through an intermediate passage.

0002

2. Description of the Related Art First, a screw vacuum pump will be explained with reference to FIG.

In the figure, a male screw rotor 7 (the female screw rotor is not shown) is mounted on a bearing 5a in the cavity formed by the main casing 1 and the discharge casing 2.
, 5b, and is rotatably supported by the shaft seal 6a.
, 6b from the lubricating oil of the bearings 5a and 5b.

[0004] A timing gear 10 is provided at one end of the male screw rotor 7 to rotate both rotors simultaneously with a small gap between them, and the rotor 7 is rotated at high speed by an electric motor (not shown) via a speed increasing device (not shown). It has become so.

[0005]The gas sucked in through the suction port 8a passes through the suction port 8b and is sucked into the tooth space formed by both rotors, undergoes a compression process, and is discharged from the discharge port 9a via the discharge port 9b. It looks like this.

In FIG. 4, a vacuum container 21 is connected to a pre-stage suction port 27 of a pre-stage pump 22.
The front stage discharge port 28 is connected to the rear stage pump 2 by the intermediate passage 23.
It is connected to the rear stage suction port 29 of No. 4.

On the other hand, a speed increasing gear 26 is provided on the output shaft of the driving machine 25, and the speed increasing gear 26 is connected to both pumps A1,
It is linked to the male rotors 7A and 7B of A2.

The gas inside the vacuum container 21 is discharged from the rear discharge port 30 via the front pump 22, the intermediate passage 23, and the rear pump 24, and the inside of the vacuum container 21 is maintained at a high degree of vacuum. There is.

In such a two-stage screw vacuum pump, the suction pressure of the front-stage pump 22 during steady operation is:
The pressure in the intermediate passage 23 (this is the back pressure of the front pump 22 and the suction pressure of the rear pump 24) is about 1 to 20 torr, and the pressure in the intermediate passage 23 is about 1 to 20 torr, The discharge pressure is atmospheric pressure. Therefore, the volume of gas sucked into the front stage pump 22 is
Then, it will be compressed to 1/100 or less. Therefore, the front pump 22, which sucks dilute gas with low suction pressure, has a high pumping speed so that it can take in more gas, while the rear pump 24 only needs to pump out a small amount of gas. In order to reduce the overall size, the front pump 22
The pumping speed is set to be 15 to 70% of that of the previous one.

Therefore, when starting the front and rear stage pumps 22 and 24 from atmospheric pressure with one drive unit 25, the amount of gas discharged by the rear stage pump 24 is smaller than the amount of gas discharged from the front stage pump 22 into the intermediate passage 23. Since the amount is small, the pressure in the intermediate passage 23 rises above atmospheric pressure, and the front and rear pumps 22,
24, the driving torque increases significantly. Moreover, the compression heat generated at that time causes an abnormal temperature rise, which may cause damage to each member. This is the front and rear stage pump 22,
The same holds true even if 24 are driven by separate drive machines.

[0011]

On the other hand, when both pumps 22 and 24 are driven by separate drive machines, first of all,
The rear pump 24 is started, and after the suction pressure and back pressure of the front pump 22 have fallen below a predetermined pressure, the front pump 24 is started.
2 has been adopted.

When both pumps 22 and 24 are driven by one drive unit 25, in order to start both pumps 22 and 24 at different timings, for example, an electromagnetic clutch or the like is used as a power transmission means for the front pump 22. The electromagnetic clutch is connected at the appropriate timing. Therefore, the structure is complicated, the cost is high, and the size is large.

Further, an on-off valve is provided which opens when the intermediate pressure in the intermediate passage 23 becomes high by drawing atmospheric pressure.
A technique is known in which the atmosphere of No. 3 is released to the atmosphere or discharged into the discharge pipe of the rear pump 24 (Japanese Utility Model Publication No. 2-7268, Publication No. 2-29259). However, in this known technique, since the discharge destination is at atmospheric pressure, the pressure in the intermediate passage 23 cannot be lowered to below atmospheric pressure, and therefore the effect of reducing the driving torque is not sufficient.

The present invention has been made in view of the above-mentioned problems, and is designed to suppress the rise in intermediate pressure and reduce drive torque.
The purpose is to provide a stage screw vacuum pump.

[0015]

[Means for Solving the Problems] A two-stage screw vacuum pump of the present invention includes a pair of male and female rotors that mesh with each other and rotate around two parallel axes, and a suction port and a discharge port that house these rotors. In a two-stage screw vacuum pump, the exhaust speed of the rear pump is equal to that of the front pump. It is configured to be faster than the pumping speed.

[0016] In carrying out the present invention, a pre-stage pump is provided which comprises a pair of male and female rotors that mesh with each other and rotate around two parallel axes, and a casing that houses these rotors and is equipped with a suction port and a discharge port. A two-stage screw vacuum pump is provided with a second-stage pump, and the discharge port of the first-stage pump and the suction port of the second-stage pump are communicated through an intermediate passage, and the rotor size of the second-stage pump is formed to be larger than the rotor size of the first-stage pump. I can do it.

[0017] Furthermore, a front-stage pump and a rear-stage pump are comprised of a pair of male and female rotors that mesh with each other and rotate around two parallel axes, and a casing that houses these rotors and has a suction port and a discharge port. a two-stage screw vacuum pump in which the discharge port of the front stage pump and the suction port of the rear stage pump are connected through an intermediate passage; can be formed.

[0018]

[Operation] The two-stage screw vacuum pump constructed as described above is constructed so that the pumping speed of the rear stage pump is faster than the pumping speed of the front stage pump. Therefore, the suction fluid volume of the rear stage pump is always larger than the discharge fluid volume of the front stage pump. Therefore, even if atmospheric air is sucked in during startup or steady operation, the pressure in the intermediate passage can be kept below atmospheric pressure. As a result, driving torque is reduced and abnormal temperature rise due to compression heat is prevented.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

In these drawings, parts corresponding to those in FIG. 4 are designated by the same reference numerals and redundant explanation will be omitted.

In FIG. 1, the male rotor 7b (female rotor is not shown) of the rear stage pump 24A is connected to the front stage pump 24A.
It is formed to have a larger diameter than the second male rotor 7A (the female rotor is not shown).

Therefore, the suction fluid volume of the rear stage pump 24A is always larger than the suction fluid volume of the front stage pump 22. Therefore, even if atmospheric air is inhaled during startup or steady operation,
The pressure in the intermediate passage 23 is suppressed to below atmospheric pressure. As a result, the driving torque of the driving machine 25 is reduced, and
Abnormal temperature rise due to compression heat is prevented.

FIG. 2 shows another embodiment of the present invention, in which the speed increasing ratio of the rear stage pump 24 of the speed increasing gear 26A is set larger than the speed increasing ratio of the front stage pump 22. That is, the number of teeth of driven gear b is smaller than the number of teeth of driven gear a. Therefore, the rotation speed of the rear stage pump 24 is higher than the rotation speed of the front stage pump 22, and the same effects as described above can be obtained.

[0024]

Effects of the Invention Since the present invention is configured as described above, the pumping speed of the rear stage pump is made faster than the pumping speed of the front stage pump, so that the suction fluid volume of the rear stage pump is lower than the discharge fluid volume of the front stage pump. By always increasing
It is possible to suppress the pressure in the intermediate passage below atmospheric pressure and reduce the driving torque, thereby preventing abnormal temperature rise due to heat of compression.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the present invention.

FIG. 3 is a side sectional view showing a screw vacuum pump.

FIG. 4 is a configuration diagram showing a two-stage screw vacuum pump.

[Explanation of symbols]

7A, 7B, 7b...male rotor 21...Vacuum container 22...Pre-stage pump 23...middle passage 24, 24A...Late stage pump 25...Driver 26, 26A... Speed-up gear 27...Previous suction port 28...Pre-stage discharge port 29...Late stage suction port 30...Late stage discharge port

Claims (1)

[Claims] Claim 1: A front-stage pump and a rear-stage pump are comprised of a pair of male and female rotors that mesh with each other and rotate around two parallel axes, and a casing that houses these rotors and is equipped with a suction port and a discharge port. A two-stage screw vacuum pump in which the discharge port of the front-stage pump and the suction port of the rear-stage pump are connected through an intermediate passage, characterized in that the exhaust speed of the rear-stage pump is faster than the exhaust speed of the front-stage pump. A two-stage screw vacuum pump.