JPS6336086A - Multi-stage screw type vacuum pump - Google Patents

Abstract

PURPOSE:To make a multi-stage screw type vacuum pump compact by arranging multi-stage screws in a tandem form on a pair of driving and driven shafts for gearing with each other in each stage and equalizing a net supply gas quantity in each stage. CONSTITUTION:A driving shaft 17 is supported on bearings 27 and 28, and has a primary stage rotor 21 of large outer diameter and a secondary stage rotor 22 of small outer diameter. A driven shaft 18 is supported on bearings 29 and 30, and has a primary stage rotor 23 and a secondary stage rotor 24. The primary rotors 21 and 23 are engaged with each other in a primary stage casing 31, the secondary stage rotors 22 and 24 gear with each other in a secondary stage casing 32 and the delivery side of the primary stage casing 31 is connected to the suction side of the secondary stage casing 32, thereby constituting a two-stage vacuum pump. In this case, when a ratio of outer diameter to bottom diameter is changed for the rotors 21, 23, 22 and 24 in each stage, a net supply gas quantity in each stage can be made equal and two-stage compression becomes possible without any drop in efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-stage screw vacuum pump in which a plurality of stages of screw portions are provided on each of one main drive shaft and one drive shaft.

[Prior art and problems]

Vacuum technology has made remarkable progress in recent years, and its application fields include semiconductors,
It has spread to vapor deposition, electronics industry, metals, chemicals, pharmaceuticals, atomic crab industry, etc.

There are many types of vacuum pumps that create a vacuum, including water ring type, oil rotary type, roots type, screw type, reciprocating type,
There are many types, including a complete ejector, oil diffusion type, physical adsorption type, and chemical adsorption type.

However, wet pumps such as water ring pumps and oil rotary pumps (where water or oil is injected into the pump) are gradually being phased out in industrial fields such as semiconductor, food, chemical, and pharmaceutical industries, where impurities should not be mixed in. Dry type (no water or oil is injected into the pump) vacuum pumps gradually began to be used.

For positive displacement dry vacuum pumps, 400 T o rr
(-0.5kg r/colG) or less, it is difficult to achieve this with one stage, and usually the number of stages of the vacuum pump is increased to prevent rotor seizure. Currently, the heat generation of vacuum pumps is suppressed as much as possible by lowering the pressure ratio.

However, as the number of stages of the vacuum pump increases, the number of attached parts and accessories such as motors also increase, resulting in an increase in cost, and furthermore, the pump requires a large floor area.

Regarding the Roots type, miniaturized versions of multi-stage vacuum pumps are already available on the market.

As shown in Fig. 3, a conventional single-stage roots-type vacuum pump has a gourd-shaped rotor 2 at the end of a shaft 1 which receives rotational driving force from a motor output shaft through a coupling, and a pilot gear at the end. 3, and a rotor of the same shape that meshes with the rotor 2 and a gear with the same number of teeth that meshes with the pilot gear 3 are similarly fixed to the driven shaft (not shown) arranged parallel to the shaft 1 to form a rotating part. The outer periphery, left side and right side of the pair of rotors are sealed with a casing 4, a side case (A) 5 and a side case (B) 6, and the gas sucked from the suction lower by the rotation of the pair of rotors is sealed. This is a vacuum pump that discharges water to the discharge port 8.

Reference numeral 9 is a gear case that covers the pilot gear 3, etc.
Reference numeral 10 is a bearing that supports the shirt I-1.

Conventionally, when the Roots type vacuum pump configured as described above is made into two stages, two pumps are arranged facing each other with the motor 11 at the center, as shown in FIG.

The flow of the sucked gas is discharged from the suction lower of the first stage pump A to the discharge port 8, and is further cooled to remove the heat of compression via the intercooler 12, and is then transferred to the suction port 1 of the second stage pump B.
3 and is discharged to the discharge port 14.

In such a facing type, since the shafts of both pumps can be driven by one motor, the number of devices can be reduced by only one motor.

Therefore, recently, a multi-stage Roots type vacuum pump as shown in FIG. 5 has become popular.

That is, a first-stage rotor 2A, a second-stage rotor 2B, and a third-stage rotor 2C are arranged on a single shaft 1, and a sealing partition is provided between the rotors 2A, 2B, and 2C. be.

The gas to be sucked is the first stage suction port 9, the first stage discharge port 1O2, the second stage suction port 13, the second stage discharge port 14, and the third stage suction port 15.
The liquid is then discharged to the third stage discharge port 16.

Therefore, by arranging rotors with widths divided geometrically corresponding to the pressure ratio on the two main and slave shafts 1, it is possible to easily consolidate multiple stages of rotors, and parts This resulted in a reduction in the number of points and the required floor space.

However, screw-type vacuum pumps, which are more efficient than roots-type vacuum pumps, have not yet been made compact.

The present invention provides a compact multistage screw vacuum pump in which multiple stages of rotors are integrated into a screw pump with excellent characteristics.

[Means for solving problems]

Multiple stages of screws are arranged in tandem on a pair of driving and driven shafts, each meshing with each other, and the dimensions and shape of the screws in each stage are adjusted so that the net amount of gas supplied to each stage is the same. It is to determine.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

A conceptual diagram of a two-stage vacuum pump is shown in Figure 6.

The suction pressure, suction side temperature (absolute), air volume and pressure ratio of the first stage pump A are Ps, TsQs and γ1, respectively.
Then, the gas discharged from the first stage pump A passes through the intercooler 12, and the intermediate pressure, intermediate temperature, intermediate air volume and pressure ratio of the second stage pump B at the inlet of the second stage pump B are P m , T m ) Ignoring Qyu, γ2, and pressure loss, the following relational expression % formula % In other words, the suction temperature of the first stage is T, and the pressure ratio is T.

If the air volume of the first stage pump is Q, then the temperature of the second stage is T. The air volume of the second stage pump when the pressure ratio is T2 must be expressed by equation (2).

Therefore, the theoretical air volume of the first stage and the second stage is naturally different, Q3 f:QII, and the rotor specifications are also not the same.

As is well known, in conventional methods, screw rotors cannot be meshed on the same axis if the rotors are different.

However, the screw rotors can be meshed if the following relational expression is satisfied.

Dad + Db+ = Daz + Dbz= 2
H--f3) Here, Da+i first stage rotor outer diameter D
The rotor bottom diameter of the first stage of the device Do; the rotor outer diameter of the second stage Db□; the rotor bottom diameter of the second stage. Also, from equation (2), the following equation holds true.

However, η7□; Volumetric efficiency of the second stage vacuum pump V2
;Second stage theoretical air volume η, ;First stage vacuum pump volumetric efficiency V; ;1st
Theoretical air volume of each stage γ, ; Pressure ratio T of the first stage, ; Intermediate gas temperature (absolute temperature) If the above equations (3) and (4) 2 are satisfied, screws with different air volumes can be installed on the same axis. It becomes possible to mesh the .

Also, in a screw pump with two or more stages, 2 is (i
-1), the relational expression for the first stage screw can be obtained.

The present invention was made by deriving such a relational expression, and the rotor of the present invention is shown in FIG.

A main driving shaft 17 receiving rotational driving force from a motor and a driven wheel 18 parallel to the main driving shaft 17 each have gears 19 and 20 meshing with each other at their ends.

Further, the first stage screw 21 and the second stage screw 22 on the main driving shaft 17 mesh with the first stage screw 23 and the second stage screw 24 on the driven wheel 18, respectively.

In order to mesh, the sum of the first stage rotor outer diameter D□ and bottom diameter Dbl must be equal to the sum of the second stage rotor outer diameter D3□ and bottom diameter Dbz, as shown in equation (3). It won't be, but
As shown in equation (4), the air volumes of the first and second stage screw pumps are not the same.

However, by focusing on the fact that increasing the outer diameter of the rotor and decreasing the bottom diameter will increase the air volume, and that increasing the screw lead will increase the air volume, Dad > Daz (therefore, D b + < D bz ), and PI > p2, however, P,; first stage screw paste P2 ; second
By using the lead of the stage screw, the air volume of the first stage screw pump can be increased.

The above measures apply not only to the relationship between the first stage and the second stage, but also to the screw pump transitioning to the third stage.

Figure 2 shows a pump with the above measures implemented.

Reference numeral 25 is a motor that rotationally drives the main drive shaft 17 via a coupling 26.

The driving shaft 17 is supported by bearings 27 and 28, and includes a first stage rotor 21 with a large outer diameter and a second stage rotor 2 with a small outer diameter.
It has 2.

A fixed gear 19 fixed to the end of the main drive shaft 17 is connected to the main drive shaft 1.
It meshes with an adjustment gear 20 fixed to the end of a driven shaft 18 disposed parallel to the shaft 7 .

The driven shaft 18 has a first stage rotor 23 and a second stage rotor 24, and is supported by bearings 29 and 30.

The first stage rotors 21 and 23 having a large outer diameter are accommodated in the first stage rotors 21 and 23.
The discharge side of the stage casing 31 is connected to the suction side of a second stage casing 32 that accommodates the second stage rotors 22 and 24 having a small outer diameter.

Reference numerals 33 and 34 are a suction boat and a discharge boat provided in the first stage casing 31, respectively.

Further, reference numeral 35 is a suction boat provided in the second stage casing 32.

A second stage discharge boat 3 is provided on the discharge side of the second stage casing 32.
6 and connected to the motor frame 37 is attached.

A first stage side case 40 having a gear case 39 assembled thereto is coupled to the suction side of the first stage casing 31 .

A shaft seal 41 is installed in the side case 40 to prevent air from being sucked in.
is provided.

In the multi-stage screw vacuum pump configured as described above, the main shaft 17 and the driven shaft 18 are rotated by the drive of the motor 25, and the gas sucked from the first stage suction boat 33 is transferred to the first stage. It is fed to the discharge boat 34, once discharged outside the casing, and passed through a cooler (not shown) to the second
is fed into the stage suction port.

Discharge boat 36 along second stage screw 22.24
The gas sent to is exhausted outside the vacuum pump.

〔effect〕

The present invention has a screw in each stage on a pair of driving and driven shafts, and by changing the shape and dimensions of the screws, different air volumes can be delivered while the screws are engaged, resulting in excellent pump efficiency. It has become possible to obtain a compact pump with fewer component parts and a smaller installation area without sacrificing the product.

[Brief explanation of drawings]

1 and 2 show embodiments of the present invention, and FIG.
An explanatory diagram of a stepped screw type rotor, Fig. 2 is a longitudinal cross-sectional view of a two-stage screw type vacuum pump, Fig. 3 is a longitudinal cross-sectional view of a conventional single-stage roots type vacuum pump, and Fig. 4 is a conventional opposed FIG. 5 is a longitudinal cross-sectional view of a conventional multi-stage roots-type vacuum pump, and FIG. 6 is an explanatory diagram of the two-stage roots-type vacuum pump. 17... Main shaft, 18... Driven wheel, 21.23...
1st stage screw, 22. 24... 2nd stage screw, 19... Fixed gear, 20... Adjustment gear, 31...
・First stage casing, 32...Second stage casing, 3
3... 1st stage suction boat, 34... 1st stage discharge port, 35... 2nd stage suction boat, 36... 2nd stage discharge boat, 37... motor frame, 38...・Second
Stage side case, 39... Gear case, 40... 1st stage side case. Patent applicant: Taiko Kikai Kogyo Co., Ltd. Figure 3 Figure 5

Claims (1)

[Claims] A multi-stage screw type vacuum pump characterized in that multiple stages of screws are disposed in tandem on a pair of driving and driven shafts, each stage meshing with each other.