JPH11106343A - Displacement type pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a displacement type pump capable of being prevented from seizing by maintaining fine gaps around a rotor within a prescribed region even when being at a high temperature in an expanded state by setting different values on linear expansion coefficients of a housing and the rotor respectively by considering degrees of the thermal expansions of the housing and the rotor. SOLUTION: This displacement type pump having a housing 11, and a rotor for sucking a compressed fluid from a sucking opening 11a of the housing 11 to a rotor room 12, and discharging the fluid from a discharging opening 11b, and installed in the rotor room 12, is regulated so that the housing 11 may have a prescribed thermal expansion coefficient, and the rotor 21 and 22 may have a linear thermal expansion coefficient smaller than that of the housing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive displacement pump suitable for a positive displacement pump, for example, a vacuum pump for evacuating a compressive fluid in which air or another gas is mixed.

[0002]

2. Description of the Related Art Conventionally, positive displacement pumps such as a roots type, a claw type, and a screw type have been widely used as vacuum pumps used for evacuation for obtaining a low-pressure working space. During the evacuation operation of this type of positive displacement pump, the gas transfer chamber whose volume has been reduced at a predetermined compression rate during the transfer to the outlet is continuously connected to the outlet one after another, and the air is exhausted to the atmosphere. You. The heat generated by the adiabatic compression for the exhaust and the loss cycle in which the gas flowing backward from the atmosphere side (discharge port side) into the pump (the subsequent gas transfer chamber side) due to the leakage is returned to the atmosphere side again, etc. The outlet side becomes hot. At this time, the rotor near the outlet has a considerably high temperature and undergoes significant thermal expansion, whereas the housing near the outlet has heat radiation and cooling by forced cooling due to exposure to the atmosphere. Does not undergo significant thermal expansion.

[0003]

Therefore, in the conventional positive displacement pump as described above, when the temperature on the discharge port side increases, the difference in thermal expansion between the rotor section and the housing section increases, and the following problem occurs. Such a problem arises. As shown in FIG. 3, the minute gap ga between the outer peripheral portion of the rotor (rotor) 5 and the inner peripheral surface of the housing 6 and the minute gap (not shown) between a plurality of adjacent rotors are heat. The expansion may be too small, resulting in a seizure of the rotor 5 or a seizure of the bearing 3. Further, the minute gap gb between the end face of the rotor 5 on the discharge port side and the inner wall face of the housing 6 opposed thereto becomes excessively large, and the backflow of air from the atmosphere side to the inside of the pump through the gap increases. This causes a problem that the exhaust performance is reduced.

Further, in order to prevent the above problems from occurring in the actual operation of the pump, the pump must be operated under operating conditions (for example, conditions such as the number of revolutions of the pump) at which the temperature at the pump outlet side does not become excessively high. There was a compelling problem. As a result, for example, in vacuum evacuation of a semiconductor manufacturing apparatus, a specific gas (for example, CVD) exhausted from the low-pressure working space is provided on the outer periphery of the rotor on the suction port side of the pump, which is relatively low in temperature (for example, 100 degrees or less). However, there is a problem that a solid product resulting from a reaction gas in the thin film forming process by the method adheres and maintenance must be frequently performed to remove the solid product.

The present invention has been made in view of the above-mentioned problems to be solved, and keeps a small radial and axial clearance around the rotor within a predetermined range even when the temperature inside the pump rises. Accordingly, an object of the present invention is to provide a positive displacement pump that prevents seizure of a rotor or the like and does not significantly reduce exhaust performance.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a housing having a suction port and a discharge port and having a rotor chamber formed therein, and a compressible fluid from the suction port to the rotor chamber. A rotor rotatably provided in the rotor chamber so as to suck the fluid and discharge the fluid from the discharge port;
Wherein the housing has a predetermined linear expansion coefficient and the rotor has a linear expansion coefficient smaller than the linear expansion coefficient of the housing.

In such a configuration, when the inside of the pump becomes high in temperature due to adiabatic compression or loss cycle for exhaust, and the rotor having a small linear expansion coefficient thermally expands by a predetermined amount, the housing is cooled to a lower temperature than the rotor side by heat radiation or the like. However, since the coefficient of linear expansion is larger than that of the rotor, thermal expansion close to that of the rotor occurs. Therefore, the minute gap between the rotor and the housing is kept within a predetermined range from a low temperature range to a high temperature range. Further, since the distance between the rotor shafts is slightly increased due to the thermal expansion of the housing and the thermal expansion of each rotor is suppressed to a small value, the reduction of the gap between the rotors (meshing gap) due to the thermal expansion is also suppressed. Further, in the rotor bearing portion in an operating state in which the discharge port side of the pump is at a considerably high temperature, the thermal expansion in the bearing portion of the rotor is small, and the diameter expansion due to the thermal expansion in the shaft hole side is promoted. The application of a heavy load is reduced. Therefore, seizure of the rotor and the bearing can be prevented, and the exhaust performance is not significantly reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 are views showing one embodiment of a positive displacement pump according to the present invention, and show an example in which the present invention is applied to a screw type vacuum pump. 1 and 2, reference numeral 11 denotes a pump housing having a rotor chamber 12 formed therein.
Has an inlet 11a and an outlet 11b (FIG. 2).
reference). Reference numerals 21 and 22 denote minute gaps (for example, about 50 μm) in the rotor chamber 12 of the pump housing 11.
And male and female screw rotors rotatably housed. Among the screw rotors 21 and 22, the male screw rotor 21 is formed in a male screw shape and the female screw rotor 22 is formed in a female screw shape in a reverse screw direction to the rotor 21, and these screw rotors 21 and 22 are formed inside the pump housing 11. They are arranged adjacent to each other in parallel with a small gap (for example, about 50 μm), and are driven in mutually opposite directions by a driving means described later.

Between the pump housing 11 and the rotors 21 and 22 in the rotor chamber 12, there are formed a plurality of spiral working chambers 25 and 26 (gas transfer chambers) partitioned by portions close to the rotors 21 and 22. Operating chambers 25 and 26
Has a predetermined volume corresponding to the lead length in each transfer section of the screw rotors 21 and 22. When the rotors 21 and 22 rotate, the working chambers 25 and 26 increase the volume to a predetermined value in the transfer section on the suction side communicating with the suction port 11a to perform a suction action, and the suction chamber 11 In the intermediate transfer section not communicating with the discharge port 11b, the transfer is performed at a predetermined volume, and in the transfer section on the discharge side communicating with the discharge port 11b, the volume is reduced to a minimum to generate a discharge pressure of about atmospheric pressure or more. It works. By changing the lead lengths of the screw rotors 21 and 22 and the cross-sectional areas of the screw grooves, the working chambers 25 and 2 are changed.
6 may gradually decrease (in multiple stages) in the intermediate transfer section. In this case, it is possible to eliminate the need for a mechanical booster pump by improving the exhaust performance, and the effect of applying the present invention is particularly large.

Further, the screw rotors 21 and 22 are formed integrally with rotor shafts 31 and 32 (rotation center axes) which are rotation center axes thereof.
One end portions 31a and 32 protruding from both axial ends of the first and second axial directions.
a and the other end portions 31b and 32b. 41, 4
Reference numeral 2 denotes a first bearing interposed between one end portions 31a and 32a of the rotor shafts 31 and 32 and shaft hole portions 13a and 14a of the pump housing 11, respectively. These are second bearings interposed between the other end portions 31b and 32b and the shaft holes 13b and 14b of the pump housing 11, respectively. These first and second bearings 4
1 to 44 connect the rotors 21 and 22 to the pump housing 11.
It has the function of supporting it rotatably. Further, the first bearing devices 41 and 42 are arranged such that the rotors 21 and 22 with respect to the pump housing 11
The second bearings 43 and 44 have the function of restricting the axial displacement of the rotors 21 and 22 with respect to the pump housing 11 (specifically, the first bearing devices 41 and 42). The rotor shafts 31, 32 whose axial displacements of the one end portions 31a, 32a are regulated by 42 expand in accordance with thermal expansion, and the other end portions 31b, 32b are displaced.

Reference numeral 50 denotes a driving means for driving the screw rotors 21 and 22, and an electric motor 51 connected to the rotor shaft 31 of the male screw rotor 21 and the same number of teeth fixed to the rotor shafts 31 and 32 and meshing with each other. And transmission gears 52 and 53 which are timing gears. The pump housing 11 is formed of a material having a predetermined coefficient of linear expansion, for example, an aluminum alloy or stainless steel.
Reference numerals 1 and 22 are made of a material having a linear expansion coefficient smaller than that of the pump housing 11, for example, invar or low-carbon alloy steel. Here, the linear expansion coefficient is set so that the linear expansion coefficients of the screw rotors 21 and 22 are at least 20 times smaller than the linear expansion coefficient of the pump housing 11.
% Is subtracted, and more preferably,
From the coefficient of linear expansion of the pump housing 11, 30% to 5
A material having a linear expansion coefficient of a value reduced by 0% is selected. In addition, the bearing devices 41 and 42 include the screw rotors 21 and
It is preferable to have a coefficient of linear expansion that is not less than the coefficient of linear expansion of 2 and not more than the coefficient of linear expansion of the pump housing 11.

In the above configuration, when the male screw rotor 21 is driven by the electric motor 51 of the driving means 50, the female screw rotor 2 is driven via the transmission gears 52 and 53.
2 is driven in synchronization with the male screw rotor 21 in the opposite direction, and a plurality of helical working chambers 25 and 26 partitioned by adjacent portions of both rotors 21 and 22 are connected to the suction side communicating with the suction port 11a. In the transfer section, the volume is increased to a predetermined value to perform the suction action, and the suction port 11a is also connected to the discharge port 11b.
In the intermediate transfer section which does not communicate with the discharge port 11b, the transfer is performed at a predetermined volume or while gradually decreasing the volume. In the transfer section on the discharge side communicating with the discharge port 11b, the volume is reduced to a minimum to perform the discharge operation.

In this operation state, on the discharge port 11b side, the working chambers 25 and 26 are successively connected to the discharge port 11b and exhausted to the atmosphere. However, heat generated by adiabatic compression for the exhaust, The pump housing 1 from the atmosphere side (the working chambers 25 and 26 side communicating with the discharge port 11b) due to leakage.
The temperature of the outlet 11b becomes high due to a loss cycle or the like in which the gas entering the inside 1 (the subsequent working chamber) is returned to the atmosphere again. Further, during operation, most of the working chambers 25 and 26 are in a negative pressure state to perform an adiabatic operation. Therefore, even though the pump housing 11 capable of releasing heat to the outside air is relatively low in temperature, the screw rotor 21 is relatively low. , 22 are maintained in a high temperature state because heat is hardly transmitted to the pump housing 11 side.

At this time, the screw rotors 21 and 22 and the rotor shaft 3 are located on the discharge port 11b side of the pump housing 11.
The temperatures of the first and second bearing devices 41 and 42 become considerably high, and each of them undergoes thermal expansion according to the temperature rise as shown by the phantom line in FIG. On the other hand, the pump housing 11
Although the temperature does not rise as much as these due to heat radiation or the like, since the linear expansion coefficient is larger than the screw rotors 21 and 22 and the rotor shafts 31 and 32 at a predetermined ratio, the inner peripheral surface of the pump housing 11 is 2
Thermal expansion to an extent corresponding to the outer diameter increase due to thermal expansion of 2,
The radial gap g2 between the pump housing 11 and the screw rotors 21, 22 is kept within a predetermined range.

Further, since the axial distance between the screw rotors 21 and 22 is slightly increased due to the thermal expansion of the pump housing 11, and the thermal expansion of each of the screw rotors 21 and 22 is suppressed to a small value. A change in the gap (meshing gap) between the portions 21 and 22 can be suppressed to a small value. Further, one end 3 of the rotor shafts 31, 32 by the first bearing devices 41, 42 on the discharge port 11b side.
In the bearing portions 1a and 32a, the thermal expansion of the rotor shafts 31 and 32 having a small linear expansion coefficient is suppressed, and the shaft hole portions 13a and 1 of the pump housing 11 having a large linear expansion coefficient are provided.
Since the diameter expansion of 4a is promoted by thermal expansion, an excessive load does not act on the first bearing devices 41 and 42. When the rotor shafts 31 and 32 extend in the axial direction due to thermal expansion, the other ends 31
b, 32b slide with respect to the second bearings 43, 44, and the first bearing devices 41, 42 and the second bearings 43, 44
44 causes the rotor shafts 31 and 32 to
The first shaft holes 13a and 14a are stably supported on the central axis.

In this state, the screw rotor 2
Since the axial displacement of the rotor shafts 1 and 22 and the rotor shafts 31 and 32 is restricted by the first bearing devices 41 and 42 on the discharge port 11b side, the axial position of the first bearing devices 41 and 42 shown in FIG. From the end faces 21 of the screw rotors 21 and 22
a, L1 to the screw rotor 21,
22 and the linear expansion coefficients of the rotor shafts 31 and 32 and the temperature thereof increase. On the other hand, the pump housing 11 moves from the axially intermediate position of the first bearing devices 41 and 42 shown in FIG.
The distance L2 to the inner wall surface 11c of the pump housing 1
It increases in accordance with the linear expansion coefficient of 1 and its temperature rise. However, the screw rotors 21, 22 and the rotor shaft 31,
Since the thermal expansion of the pump housing 11 is suppressed by a small linear expansion coefficient for its temperature rise, and the linear expansion coefficient of the pump housing 11 whose temperature rise is small due to heat radiation or the like is increased at a predetermined rate. Wall 11
c and the end faces 21a, 22a of the screw rotors 21, 22
Are displaced by the same amount in the same direction so as to keep the axial gap g2 between them within a predetermined range.

Further, in the present embodiment, since the linear expansion coefficients of the screw rotors 21 and 22 are values obtained by subtracting at least 20% of the linear expansion coefficient of the pump housing 11, the screw rotors 21 and 22 Even at the time of high-temperature thermal expansion in which the temperature difference of the pump housing 11 partially becomes several tens to one hundred and several tens degrees or more, the minute gap g1,
g2 can be suppressed, and these can be kept within a predetermined range.

Accordingly, the conventional problem that the seizure of the screw rotor and the bearing occurs is solved, and the exhaust performance is not greatly reduced. Therefore, operation at high speed rotation becomes possible, and exhaust performance can be improved. In addition, by improving the exhaust performance,
It is also possible to eliminate the need for a mechanical booster pump. In addition, the high-temperature operation reduces the adhesion of solid products to the rotor and the like.

The material of the pump housing 11 and the screw rotors 21 and
Material 2 is merely one example and pump housing 1
1 becomes larger than the linear expansion coefficients of the screw rotors 21 and 22, and thermal expansion of the screw rotors 21 and 22 causes outer diameter contact between the screw rotors 21 and 22 and conversely, an excessive gap at low temperatures. Other combinations of materials can be appropriately selected within a range that does not occur.

In the above description, the embodiment of the present invention has been described by taking a vacuum pump as an example. However, the present invention, which is characterized by a combination of a rotor material and a housing material, is not limited to a vacuum pump, but is applied to a compression pump. Can also be applied.

[0021]

EXAMPLE As an example, SUS316L (stainless steel) having a linear expansion coefficient of 16 × 10 ⁻⁶ / ° C. was used as a material of the pump housing 11, and the male and female screw rotors 21, 21 were used.
SCM having a coefficient of linear expansion of 11.6 × 10 ^-6 / ° C.
Using 435 (chromium molybdenum steel), a positive displacement pump having the same structure as that of the above-described embodiment is manufactured. Further, the material of the pump housing and the screw rotor is SUS316L having a linear expansion coefficient of 16 × 10 ⁻⁶ / ° C., respectively. When a positive displacement pump of the comparative example having the same size and the same structure as the example using (stainless steel) was produced, and these comparative tests were performed, the results shown in the following table were obtained.

In each of the following examples and comparative examples, the outer diameter of the male screw rotor 21 is about 160 mm, the outer diameter of the female screw rotor 22 is about 120 mm, and the distance between the screw rotors 21 and 22 is about 110 mm. And the length of the screw rotors 21 and 22 is 240 mm. As is clear from this table, in the comparative example, while the radial gap at the outer diameter portion of the screw rotor end face at the time of high temperature decreases, the axial gap at the screw rotor end face becomes excessive, and further, the thermal expansion of the screw rotor becomes large. As a result, the three-dimensional shape error of the screw increased. As a result, excessive exhaust gas backflow occurred at the end face of the screw rotor near the exhaust port (* 1 in the table), and the outer peripheral portion of the screw rotor contacted the inner peripheral wall surface of the housing, causing seizure (see the table). of 2). On the other hand, in the pump of the embodiment, the gap g1 in the rotor radial direction and the gap g2 in the axial direction at the rotor end face were both kept within the allowable ranges, and the three-dimensional shape error of the screw of the screw rotor was suppressed to a small value. Therefore, the screw pump according to the embodiment of the present invention was able to reliably prevent the seizure of the rotor even at the time of operation at a high temperature, and was able to perform a stable long-term continuous operation.

[0023]

According to the present invention, the linear expansion coefficient of the rotor is made smaller than that of the housing by a predetermined ratio. When a small rotor thermally expands by a predetermined amount, the housing whose temperature becomes lower than that of the rotor due to heat radiation or the like can be thermally expanded to a degree close to the thermal expansion of the rotor. The change in the gap can be suppressed within a predetermined range, and the exhaust performance does not significantly decrease. In addition, when there are a plurality of rotors, the thermal expansion of the housing can slightly reduce the distance between the rotor shafts due to the thermal expansion of the housing while suppressing the thermal expansion of each rotor, and the gap between the outer peripheral surfaces of the rotors can also be kept within a predetermined range. it can. Furthermore, in the bearing part of the rotor,
Even in an operating state where the pump outlet side is at a considerably high temperature, the thermal expansion of the rotor in the bearing portion is reduced and the diameter of the shaft is expanded due to the thermal expansion of the shaft hole side, so that no excessive load acts on the bearing. You can do so. As a result, high-speed rotation can be performed, and the exhaust performance can be improved. In addition, the pump can be used under operating conditions in which the temperature inside the pump rises to a temperature range where solid products such as reaction gas do not easily adhere to the outer periphery of the rotor or the like. The number of maintenance operations for removal can be reduced.

[Brief description of the drawings]

FIG. 1 is a plan sectional view showing one embodiment of a positive displacement pump according to the present invention.

FIG. 2 is an operation explanatory view of the positive displacement pump of one embodiment.

FIG. 3 is an operation explanatory view of a conventional positive displacement pump.

[Explanation of symbols]

 Reference Signs List 11 pump housing 11a suction port 11b discharge port 11c inner wall surface 12 rotor chamber 13a, 14a shaft hole 21, 22 screw rotor (rotor) 21a, 22a end face (rotor axial one end face) 25, 26 working chamber (gas transfer chamber) ) 31, 32 Rotor shaft 31a, 32a One end (end on the discharge port side)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C07J 1/00 C07J 1/00 F04C 18/16 F04C 18/16 R 25/02 25/02 M

Claims (1)

[Claims] 1. A housing having a suction port and a discharge port and having a rotor chamber formed therein, and a compressor fluid sucked into the rotor chamber from the suction port, and the compressor fluid is discharged into the rotor chamber from the discharge port. A rotatable rotor, wherein the housing has a predetermined linear expansion coefficient, and the rotor has a linear expansion coefficient smaller than the linear expansion coefficient of the housing. Positive displacement pump.