JPH03111690A - Vacuum pump - Google Patents

Abstract

PURPOSE:To reduce energy loss, and to achieve smooth gas exhaust by forming screw parts in multiple stages on a screw rotor, and by providing a relief valve on an inter-stage position of the screw rotor of a casing, while a gas introducing port on a screw rotor position on the exhaust side. CONSTITUTION:Screw rotors 7, 8, 9 are coaxially installed along shaft at a certain interval, and a screw part of a screw rotor is formed in each stage so as to form the transfer capacity of the screw rotor on the exhaust side smaller than that on the suction side. On the outer surface of a casing 2 on the side of each gap, relief valves 10, 11 are mounted, so as to prevent the pressure of the gas exceeding which gas is in the gap between the respective screw rotors 7, 8, 9. A gas introduction port 12 is connected to the side surface of the casing 2 on the position of the third stage screw rotor, through which the gas in a form of air pressure is supplied in the casing 2 in the vicinity of the third screw rotor 9, and a certain flow of gas stream is formed in the casing 2 and is discharged from an exhaust port 4 at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vacuum pump, and particularly to a vacuum pump with a small transfer volume on the exhaust side.

[Conventional technology]

Generally, in the field of semiconductor manufacturing, oil rotary pumps are used as roughing vacuum pumps for vapor deposition equipment and sputtering equipment. This oil rotary pump has a casing sealed with lubricating oil, and can provide a vacuum environment relatively easily. However, with this oil rotary pump, the lubricating oil may back diffuse into the exhaust chamber or the oil may deteriorate depending on the type of gas being exhausted, which poses problems in terms of equipment maintenance and product quality.

In order to solve these problems, a vacuum pump using a positive displacement screw pump that does not use operating lubricating oil has been proposed. In this type of vacuum pump, a transfer space is formed by a threaded portion of a screw rotor, and a fixed volume of gas within this transfer space is transferred from an intake side to an exhaust side by rotation of the screw.

According to this vacuum pump, the use of lubricating oil is limited to the bearings, and since the sealing is sufficient, the lubricating oil will not diffuse back into the vacuum container. When this vacuum pump is used as a roughing pump,
When the intake port side is in a vacuum state and the exhaust port is in an atmospheric pressure state, the transfer space of the screw rotor will transfer vacuum, and the work energy for gas transfer will theoretically be zero.

[Problem to be solved by the invention]

However, in the above-mentioned vacuum pump, when the vacuum in the transfer space is released near the exhaust port, the atmosphere suddenly flows into the transfer space and collides with the screw rotor. For this reason, vibrations and collision sounds are generated in the transfer space on the exhaust side due to the inflow of air and collisions.

Then, there is a problem in that a large amount of energy is consumed to push out this atmosphere, and the pump efficiency is significantly reduced.

Further, the pressure of the gas exhausted by the operation of this vacuum pump at the intake port is 100 Pa or less, and the volume of the gas exhausted is only 1/1000 or less of the volume of the gas flowing in from the exhaust port. Therefore, even if the gas is released near the exhaust port, it is not discharged outside the casing and is kept in an adiabatic compressed state inside. As a result, the gas is heated within the casing, the temperature of the casing also rises, thermal expansion occurs, and the gap between the casing and the screw rotor becomes distorted.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a vacuum pump that solves the problems of the conventional technology described above, reduces energy loss during operation, and enables smooth evacuation of gas even in a vacuum state. be.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a screw rotor that is arranged in multiple stages coaxially with a rotating shaft and has a threaded portion so that the transfer volume on the exhaust side is smaller than that on the intake side; It is characterized by comprising a relief valve provided in the casing at the position between the stages of the screw rotors arranged in multiple stages, and a gas inlet port provided on the side surface of the casing at the position of the screw rotor on the exhaust side.

[For production]

According to the present invention, the screw rotors are arranged in multiple stages on the rotating shaft, and the threaded portion of the screw rotor at each stage is formed so that the transfer volume of the screw rotor on the exhaust side is smaller than that on the intake side. , the exhaust volume is small, and even if the intake side is in a vacuum state, the energy loss consumed to push out the popularity can be reduced. In addition, a relief valve is provided in the casing between the stages of the screw rotor arranged in multiple stages, and a gas inlet is connected to the side of the casing at the screw rotor position on the exhaust side, so gas can be smoothly transferred from atmospheric pressure to vacuum state. The casing can be vented outside.

〔Example〕

An embodiment of the vacuum pump according to the present invention will be described below with reference to the drawings.

In the drawings, reference numeral 1 indicates a support stand, and a casing 2 is fixed onto the support stand 1. The casing 2 has a substantially cocoon-shaped cylindrical planar shape with bilateral symmetry, and an air intake port 3 is formed in the center of the upper plate 2a of the casing 2. This inlet port 3 is communicated with a container (not shown) to be evacuated via piping. on the other hand,
An exhaust port 4 is formed at the lower end of the casing 2.

Also, inside this casing 2 there are two rotating shafts 5.5.
extends vertically through the support base 1 to the vicinity of the upper plate 2a. The rotating shaft 5.5 can be rotated synchronously in opposite directions below the support base 1 by meshing with two timing gears 6.6. This timing gear 6.6 is driven by a drive motor (not shown). And each of the rotating shafts 5.5 has
Three-stage screw rotors 7, 8, whose screws are in opposite directions and mesh with each other and can rotate synchronously in opposite directions. 9 are coaxially attached.

In this embodiment, the thread of the first stage screw rotor 7 on the intake port side is formed with ten square threads.

A second stage screw rotor 8 is installed below the first stage screw rotor 7 with a gap in the axial direction. A first relief valve 10 is attached to the outer surface of the casing 2 on the side of this gap. This first relief valve 10 is used when the gas discharged from the first stage screw rotor 7 cannot flow into the second stage screw rotor 8, which has a small transfer capacity.
It plays a role in preventing gas pressure from becoming excessive.

The screw of the second stage screw rotor 8 is formed of a single square thread, and a third stage screw rotor 9 is installed below the second stage screw rotor 8 with a gap in the axial direction. . A second relief valve 11 is attached to the outer surface of the casing 2 on the side of this gap. This second relief valve 11 serves to prevent the pressure of the gas in the gap between the second stage screw rotor 8 and the third stage screw rotor 9 from becoming excessive. The thread of the third stage screw rotor 9 is formed of a single square thread with a thread pitch smaller than that of the second stage screw rotor 8. In this embodiment, the transfer volume formed in the threaded portion of the third stage screw rotor 9 is set to be approximately 1/10 of the transfer volume formed in the threaded portion of the first stage screw rotor 7. There is. Therefore, even if the vacuum in the transfer space is released near the exhaust port in this state, the amount of air that rapidly flows into the transfer space will be greatly reduced, and the energy loss for pushing out this air will be minimal. .

Further, a gas inlet 12 is connected to the side surface of the casing 2 at the position of the third stage screw rotor 9. A needle valve 13 is installed on the piping side of the gas inlet 12. Gas at atmospheric pressure is supplied to the casing 2 near the third stage screw rotor 9 through the gas inlet 12, and is supplied to the exhaust port 4 while forming a constant gas flow within the casing 2. is being discharged from. Therefore, even if the vacuum in the transfer space is released near the exhaust port, the atmosphere will not flow back from the exhaust port, and a portion of this gas flow will flow into the transfer space. Therefore, air does not remain in the casing, and an adiabatic compression state can be avoided.

Note that the number of stages of the screw rotor, the number of threads of the screw, etc. are not limited to those in this embodiment, and preferable values can be set depending on the pump capacity, etc.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, screw rotors are arranged in multiple stages on the rotating shaft, and each stage is arranged such that the transfer volume of the screw rotor on the exhaust side is smaller than that on the intake side. The threaded part of the screw rotor is formed, a relief valve is provided protruding from the casing between the stages of the screw rotor arranged in multiple stages, and the gas inlet is connected to the side of the casing at the screw rotor position on the exhaust side, so that the pump can be operated easily. This has the effect of reducing energy loss during operation, significantly improving the operating efficiency of the pump, and allowing gas to be smoothly evacuated from an atmospheric pressure state to a vacuum state.

[Brief explanation of drawings]

The drawing is a cross-sectional view showing an embodiment of a vacuum pump according to the present invention. 2... Casing, 3... Intake port, 4... Exhaust port, 5... Rotating shaft, 7.8.9... Screw rotor,
10゜11...Relief valve, 12...Gas inlet.

Claims (1)

[Claims] 1. Two rotating shafts are provided in parallel within the casing, and screw rotors that mesh with each other and rotate synchronously in opposite directions are fixed on the rotating shafts, and In a vacuum pump that forms a transfer space and transfers gas flowing in from the intake port toward the exhaust port by rotation of a screw rotor, the vacuum pump is arranged at intervals in the axial direction on the rotating shaft and is located on the exhaust side. A screw rotor is provided in a casing located between multiple sets of screw rotors having threaded portions so that the transfer volume is smaller than the transfer volume on the intake side, and each stage of the screw rotors arranged in multiple stages. A vacuum pump characterized by comprising a relief valve and a gas inlet port provided on the side of the casing at the screw rotor position on the exhaust side. 2. The vacuum pump according to claim 1, wherein the plurality of sets of screw rotors are configured to have a small transfer volume by changing the number of screw threads. 3. The vacuum pump according to claim 1, wherein the plurality of sets of screw rotors are configured to have a small transfer volume by changing the screw pitch.