US20100284796A1

US20100284796A1 - Pump

Info

Publication number: US20100284796A1
Application number: US12/811,235
Authority: US
Inventors: Kimihiko Mitsuda; Yasuharu Yamamoto
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 2008-03-14
Filing date: 2009-01-16
Publication date: 2010-11-11
Also published as: TWI416014B; JP2009221938A; JP5291363B2; WO2009113324A1; KR20100115362A; CN101960149A; TW201000771A

Abstract

In a pump, a main shaft (16) is rotatably supported by ball bearings (14, 15) in a casing (13) having a suction opening (11) and a discharge opening (12), an impeller (1) is connected to an end of the main shaft (16), and a canned motor (18) rotatably drives the impeller (17) through the main shaft (16). A front shroud (44) is provided at the front side in the axial center direction of the impeller (17), and a rear shroud (45) is provided at the rear side in the axial center direction. A predetermined gap (47) facing the axial direction is formed between the casing (13) and the front shroud (44), and sealing units (48, 49) facing the radial direction are provided between the casing (13) and the front shroud (44). This allows for extended life of the pump.

Description

TECHNICAL FIELD

The present invention relates to a pump, for example, for carrying supercritical carbon dioxide (CO₂) fluid or liquid carbon dioxide (CO₂).

BACKGROUND ART

For example, a pump for carrying supercritical CO₂fluid or liquid CO₂is a circulation pump for cleaning semiconductors. In recent years, with the increased integration of semiconductor devices, there has emerged a demand to reduce the line width on a wafer, and relative to the mainstream of 0.18 micrometers at present, it is predicted that the line width will be equal to or less than 0.10 micrometers in future. However, in the conventional method for cleaning semiconductors using liquid such as extra pure water, a phenomenon may occur in which the resist on the wafer is collapsed (resist collapse), while being dried, by the capillary force caused by the interfacial tension between vapor and liquid.
To eliminate such a disadvantage, a semiconductor cleaning device that uses supercritical liquid instead of the conventional liquid such as extra pure water has been developed. The supercritical fluid has a high permeability compared with liquid and is capable of penetrating into any fine structures. Because an interface does not exist between vapor and liquid, the capillary force does not act while the wafer is being dried.
Carbon dioxide (CO₂) is mainly used as the supercritical fluid. Compared with the other liquid solvents, carbon dioxide has relatively mild conditions, in other words, the supercritical density is 468 kg/m³at the supercritical temperature of 31.2 centigrade and at the supercritical pressure of 7.38 megapascals. Because the supercritical fluid is vapor at normal temperature and pressure, the supercritical fluid is gasified by returning to normal temperature and pressure. Accordingly, an object to be cleaned and a contaminated object can be easily separated. In this manner, because an object to be cleaned need not be dried after cleaning and similar processes, it is possible to simplify the cleaning process and reduce costs.
In the semiconductor cleaning device using such supercritical CO₂fluid, the pressure of the supercritical CO₂fluid is usually increased to approximately 20 megapascals. Accordingly, as a circulation pump for cleaning wafers by circulating the supercritical CO₂fluid, a so-called sealless canned motor pump type is used to withstand high pressure. A ball bearing is used as a bearing, and the ball bearing is placed in pumped liquid (supercritical CO₂fluid) used as a cleaning agent for semiconductors.
The ball bearing receives the radial load and the thrust load applied to the rotor. The preload load is controlled by a bearing preload spring mounted on a bearing at the end of the shaft, opposite from the side with an impeller, thereby preventing what is termed as revolution skidding (side skidding) of the ball bearing. The rigidity (spring constant) of the ball bearing in the radial direction is controlled by the bearing preload load, and the natural frequency of the rotor is also adjusted by the bearing preload load.
Patent Document 1 described below discloses such a pump.
[Patent Document 1] Japanese Patent Application Laid-open No. 2007-231958

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

In the conventional pump described above, the ball bearing is used in a supercritical CO₂fluid (or fluid CO₂) with low viscosity. Accordingly, lubrication by the pumped liquid cannot be expected. Consequently, abrasion occurs at the ball bearing, thereby moving the main shaft and the impeller in the rotation axis direction. The impeller increases the pressure of fluid suctioned in from a suction opening by the rotation, and discharges the fluid from a discharge opening. To prevent reverse flow of fluid from the discharge opening to the suction opening, an extremely narrow gap is formed between the casing and the impeller in the axial direction. However, if the main shaft and the impeller move in the rotation axis direction due to abrasion at the ball bearing, interference occurs between the impeller and the casing. As a result, the life of the pump may be reduced.
The present invention has been devised in view of the circumstances above, and an object of the present invention is to provide a pump with an extended life.

Means for Solving Problem

According to an aspect of the present invention, a pump includes: a casing having a suction opening and a discharge opening; a main shaft rotatably supported by a ball bearing in the casing; an impeller connected to an end of the main shaft; and a canned motor capable of rotatably driving the impeller through the main shaft, the pump increasing pressure of fluid suctioned in from the suction opening by rotation of the impeller and discharging the fluid from the discharge opening. A front shroud is provided at a front side in an axial center direction of the impeller, and a rear shroud is provided at a rear side in the axial center direction of the impeller, a predetermined gap facing an axial direction is formed between the casing and the front shroud, and a sealing unit facing a radial direction and being provided between the casing and the front shroud.
Advantageously, in the pump, the sealing unit is arranged in plurality in the axial center direction of the impeller.
Advantageously, in the pump, the casing includes a fluid outlet from the impeller communicated with the discharge opening through a diffuser and a volute chamber, and the diffuser contains a throttle portion.
Advantageously, in the pump, a shape of the throttle portion is set corresponding to a fluid outlet angle at an outlet of the diffuser, and to a passage area ratio between the outlet of the diffuser and the volute chamber.
Advantageously, the pump further includes a preload spring that applies a preload to the ball bearing, wherein the preload spring is formed by stacking a plurality of corrugated plates in a ring shape.
Advantageously, in the pump, the impeller is capable of carrying supercritical CO₂fluid or liquid CO₂through rotational driving, and the pump is used as a circulation pump for cleaning a semiconductor.

Effect of the Invention

In the pump of the first aspect of the present invention, the main shaft is rotatably supported by the ball bearing in the casing having the suction opening and the discharge opening, the impeller is connected to an end of the main shaft, and the canned motor rotatably drives the impeller through the main shaft. The front shroud is provided at the front side in the axial center direction of the impeller, and the rear shroud is provided at the rear side in the axial center direction. A predetermined gap facing the axial direction is formed between the casing and the front shroud, and a sealing unit facing the radial direction is provided between the casing and the front shroud. Accordingly, reverse flow of fluid from the discharge opening to the suction opening is prevented by the sealing unit, and even if the main shaft and the impeller move in the rotation axis direction due to abrasion of the ball bearing, the impeller and the casing do not interfere with each other because the predetermined gap is formed between the impeller and the casing. This allows for extended life of the pump.
In the pump of the second aspect of the present invention, the sealing unit is arranged in plurality in the axial center direction of the impeller. Accordingly, leakage of fluid from the area between the impeller and the casing is reduced by the sealing units. Consequently, it is possible to appropriately prevent the reverse flow of fluid from the discharge opening to the suction opening.
In the pump of the third aspect of the present invention, the fluid outlet from the impeller is communicated with the discharge opening through the diffuser and the volute chamber, and the diffuser contains the throttle portion. By increasing the fluid outlet angle at the outlet of the diffuser, the loss from the outlet of the diffuser to the inlet of the volute chamber can be reduced. Accordingly, interference can be prevented by allowing the impeller to move.
In the pump of the fourth aspect of the present invention, the shape of the throttle portion is set corresponding to the fluid outlet angle at the outlet of the diffuser, and the passage area ratio between the outlet of the diffuser and the volute chamber. Accordingly, diffuser effect, in other words, conversion from the speed energy (dynamic pressure) of fluid to pressure energy (static pressure) can be sufficiently obtained, by appropriately setting the shape of the throttle portion, and reducing the total speed of the radial speed and the circumferential speed of fluid that flows from the outlet of the diffuser to the volute chamber. Consequently, it is possible to improve the pump efficiency.
In the pump of the fifth aspect of the present invention, the preload spring for applying a preload to the ball bearing is provided, and the preload spring is formed by stacking a plurality of corrugated plates in a ring shape. Because the preload is applied to the ball bearing by the preload spring, it is possible to prevent the revolution skidding of the ball bearing, thereby enabling extended life of the ball bearing. Because the preload spring is formed by stacking the corrugated plates, the load variation due to the variation of crushing margin of the spring can be reduced. Consequently, it is possible to apply an appropriate preload to the ball bearing.
The pump of the sixth aspect of the present invention is capable of carrying supercritical CO₂fluid or liquid CO₂by rotatably driving the impeller, and the pump is used as a circulation pump for cleaning semiconductors. Because an object to be cleaned need not be dried after cleaning, it is possible to simplify the cleaning process and reduce costs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a circulation pump for a semiconductor cleaning device as a pump according to an embodiment of the present invention.

FIG. 2 is an enlarged view of an essential part of the circulation pump for the semiconductor cleaning device of the present embodiment.

EXPLANATIONS OF LETTERS OR NUMERALS

11 suction opening
12 discharge opening
13 casing
14, 15 ball bearing
16 main shaft
17 impeller
18 canned motor
31 preload spring
44 front shroud
45 rear shroud
46 impeller blade
47 predetermined gap
48, 49 sealing unit
51 diffuser
52 volute chamber

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Exemplary embodiments of a pump according to the present invention will be described below in greater detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments.

Embodiment

FIG. 1 is a sectional view of a circulation pump for a semiconductor cleaning device as a pump according to an embodiment of the present invention. FIG. 2 is an enlarged view of an essential part of the circulation pump for the semiconductor cleaning device of the present embodiment.
The circulation pump for the semiconductor cleaning device of the present embodiment, as illustrated in FIGS. 1 and 2, includes a casing 13 having a suction opening 11 and a discharge opening 12, a main shaft 16 rotatably supported by ball bearings 14 and 15 in the casing 13, an impeller 17 connected to an end of the main shaft 16, and a canned motor 18 capable of rotatably driving the impeller 17 through the main shaft 16. The circulation pump for the semiconductor cleaning device increases the pressure of fluid suctioned in from the suction opening 11 by the rotation of the impeller 17, and discharges the fluid from the discharge opening 12.
In the casing 13, a discharge-suction side casing 21 and a purge side casing 22 formed in ring shapes are arranged interposing an outer casing 23 formed in a cylindrical shape therebetween, and are connected by a connection bolt 24. A manifold 25 is fixed outside the suction-discharge side casing 21, and connected by a connection bolt 26. At the manifold 25, the suction opening 11 for pumped liquid is formed on the line extended from the axial center of the main shaft 16, and the discharge opening 12 is formed at the outer peripheral side of the suction opening 11.
The ball bearings 14 and 15 are angular ball bearings, are provided in the discharge-suction side casing 21 and the purge side casing 22, and rotatably support the main shaft 16. The impeller 17 is fitted to an end of the main shaft 16, and fixed by a connection bolt 27.
In the present embodiment, inner and outer rings and balls of the ball bearings 14 and 15 are made of a ceramic material (such as silicon nitride (Si₃N₄), alumina (Al₂O₃), and silicon carbide (SiC)), to improve abrasion resistance and corrosion resistance, and to reduce the centrifugal load on the ball bearings during high-speed rotation. In this manner, by using full ceramics for the bearings, the abrasion resistance against particles carried in from the exterior is also improved. A cage is designed so as to reduce drag loss (rotational resistance). In this manner, it is possible to prevent the revolution skidding and reduce the preload load (thrust bearing load), thereby enabling extended life of the ball bearings 14 and 15. In view of securing corrosion resistance against a cleaning agent, abrasion resistance, and strength for high-speed rotation, a poly-ether-ether-ketone (PEEK) material is used, as a material for the cage. Stainless steel and fiber composite may also be used, instead of the PEEK material.
The canned motor 18 includes a stator 28 fixed to the inner periphery of the outer casing 23, and a rotor 29 provided at the outer periphery of the main shaft 16 so as to face the stator 28.
At the purge side casing 22, a purge opening 30 for discharging a part of the pumped liquid being suctioned in is formed on the line extended from the axial center of the main shaft 16. A preload spring 31 is held between the purge side casing 22 and the angular ball bearing 15. The preload spring 31 is a corrugated plate spring in a ring shape stacked in plurality, placed near the other end of the main shaft 16. The preload spring 31 applies a preload to the ball bearing 15 in the axial direction, as a constant pressure spring system.
Accordingly, if a current is passed through the canned motor 18, the rotor 29 rotates about the stator 28, and the main shaft 16 rotates with the rotor 29. The impeller 17 also rotates in conjunction with the rotation. Accordingly, the pumped liquid is suctioned in from the suction opening 11, and the pressure of the pumped liquid is increased by the centrifugal force of the impeller 17. The pumped liquid is then guided to the side of the discharge opening 12, and discharged to the exterior. A part of the pumped liquid being suctioned in from the suction opening 11 passes through the ball bearings 14 and 15, and the canned motor 18, and discharged from the purge opening 30 as a purge flow, after cooling the ball bearings 14 and 15, and the canned motor 18.
In a circulation pump formed in this manner, in the present embodiment, the impeller 17 is a closed type, and the main shaft 16 and the impeller 17 are movable relative to the casing 13 in the axial center direction, as much as a predetermined amount. The casing 13 and the impeller 17 are also sealed in the radial direction.
A housing hole 41 communicated with the suction opening 11 is formed at the center of the suction-discharge side casing 21 of the casing 13, and an outer ring 42 and an outer ring 43 are fixed at the inner peripheral surface of the housing hole 41. The impeller 17 is provided between a front shroud 44 formed in a ring shape provided at the front side in the axial center direction, and a rear shroud 45 formed in a disk shape provided at the rear side in the axial center direction. The impeller 17 has a plurality of impeller blades 46 provided at an equal interval in the circumferential direction.
In this case, the front shroud 44 includes a disk portion 44 a horizontally placed in the radial direction of the impeller 17, and a cylinder portion 44 b horizontally placed in the axis direction. A predetermined gap 47 is formed between an end of the outer ring 43 (casing 13) and a front surface of the disk portion 44 a at the front shroud 44, facing the axial direction. Sealing units 48 and 49 are provided between the inner periphery of the outer ring 43 (casing 13) and the outer periphery of the cylinder portion 44 b at the front shroud 44, facing the radial direction. The sealing units 48 and 49 are shifted in the radial direction of the impeller 17, and are arranged in line in the axial center direction of the impeller 17. The sealing units 48 and 49 are preferably provided in plurality, and three or more sealing units may be provided instead of two.
At the casing 13, a fluid outlet 17 a from the impeller 17 is communicated with the discharge opening 12, through a diffuser 51, a volute chamber 52, and a communication passage 53. In other words, the fluid outlet 17 a from the impeller 17 is formed at a joint portion of the suction-discharge side casing 21 and the manifold 25, and the diffuser 51 is communicated with the fluid outlet 17 a. The diffuser 51 converts the speed energy (dynamic pressure) of fluid to pressure energy (static pressure).
The volute chamber 52 is formed at the joint portion of the suction-discharge side casing 21 and the manifold 25 in a spiral form, and one end of the volute chamber 52 is communicated with the diffuser 51 and the other end is communicated with the communication passage 53.
The diffuser 51 has a throttle portion. In other words, in the diffuser 51, the throttle portion is formed by narrowing (reducing) the size of a flow passage width W₂(flow passage area) of an outlet portion to the side of the volute chamber 52, than a flow passage width W₁of an inlet portion at the side of the fluid outlet 17 a from the impeller 17. In other words, by making the size of the inlet portion of the diffuser 51 larger than that of the outlet portion, the impeller 17 is capable of moving in the axial center direction by the predetermined gap 47. Accordingly, it is possible to appropriately guide the pressure fluid to the diffuser 51.
The shape of the throttle portion in the diffuser 51, in other words, the inclination angle, is set corresponding to a fluid outlet angle α from the outlet portion of the diffuser 51, and to an area ratio Y between the passage area of the outlet portion at the diffuser 51 and the area of the volute chamber 52. The fluid that flows into the volute chamber 52 from the diffuser 51 has the fluid outlet angle α relative to the tangent of the diffuser 51, and the speed V is divided into the circumferential speed Vθ and the radial speed Vm. The area ratio Y of the volute chamber 52 is a ratio (Y=Ad/Av) between a passage area Ad at the outlet portion of the diffuser 51 and an area Av at the volute chamber 52.
In general, in view of the friction loss from the outlet portion of the diffuser 51 to the inlet portion of the volute chamber 52, and the loss caused by the speed difference between the discharge speed of the diffuser 51 and the inflow speed of the volute chamber 52, the maximum efficiency of the pump can be obtained by setting the fluid outlet angle α to approximately 15 degrees. The loss at the blade of the volute chamber 52 occurs if the difference between the mounting angle of the blade of the volute chamber 52 and the fluid outlet angle is excessively large. Because the blade of the volute chamber 52 is thick, it is difficult to set the mounting angle of the blade of the volute chamber 52 to a few degrees (small angle).
As a result, in the present embodiment, the loss is reduced by providing the throttle portion in the diffuser 51, and increasing the fluid outlet angle α at the outlet portion of the diffuser 51. By increasing the width of the inlet portion at the diffuser 51, the impeller 17 is movable in the axial direction. In this case, the radial speed Vm is increased by narrowing the diffuser 51, but the circumferential speed Vθ is reduced due to the law of conservation of angular momentum (free vortex flow). Accordingly, the throttle portion is narrowed to a degree that the total speed of the radial speed Vm and the circumferential speed Vθ is reduced.
Accordingly, if the impeller 17 is rotated, the pumped liquid is suctioned in from the suction opening 11, and the pressure of the pumped liquid is increased by the centrifugal force of the impeller 17. Because the pumped liquid whose pressure is increased passes through the diffuser 51 from the fluid outlet 17 a, the speed energy of the fluid is converted into the pressure energy. The pumped liquid then flows into the volute chamber 52, and is discharged to the exterior from the discharge opening 12 through the communication passage 53. At this time, the casing 13 and the impeller 17 are sealed by the sealing units 48 and 49 in the radial direction. Consequently, the pumped liquid whose pressure is increased by the impeller 17 appropriately flows to the diffuser 51 from the fluid outlet 17 a, without leaking to the suction opening 11.
Even if the main shaft 16 and the impeller 17 move in the axial center direction by the predetermined gap 47, the positional relationship between the outer ring 43 and the front shroud 44 does not change because of the sealing units 48 and 49. Accordingly, the pumped liquid appropriately flows to the diffuser 51, without leaking to the suction opening 11.
In this manner, in the pump of the present embodiment, the main shaft 16 is rotatably supported by the ball bearings 14 and 15 in the casing 13 that has the suction opening 11 and the discharge opening 12, the impeller 17 is connected to an end of the main shaft 16, and the canned motor 18 rotatably drives the impeller 17 through the main shaft 16. The front shroud 44 is provided at the front side of the impeller 17 in the axial center direction, and the rear shroud 45 is provided at the rear side in the axial center direction. The predetermined gap 47 is formed between the casing 13 and the front shroud 44 facing the axial direction, and the sealing units 48 and 49 are provided between the casing 13 and the front shroud 44 facing the radial direction.
Accordingly, the sealing units 48 and 49 prevent the reverse flow of fluid from the discharge opening 12 to the suction opening 11, and even if the main shaft 16 and the impeller 17 move in the rotation axis direction due to abrasion of the ball bearings 14 and 15, and the like, the impeller 17 and the casing 13 do not interfere with each other because the predetermined gap 47 is formed between the impeller 17 and the casing 13. This allows for extended life of the pump.
In the pump of the present embodiment, the sealing units 48 and 49 are arranged in plurality in the axial center direction of the impeller 17. Accordingly, the leakage of fluid from the area between the impeller 17 and the casing 13 is reduced by the sealing units 48 and 49. Consequently, it is possible to appropriately prevent the reverse flow of fluid from the discharge opening 12 to the suction opening 11.
In the pump of the present embodiment, the fluid outlet 17 a from the impeller 17 is communicated with the discharge opening 12 through the diffuser 51 and the volute chamber 52, and the diffuser 51 has a throttle portion. Accordingly, the total speed of the circumferential speed and the radial speed of the fluid that flows into the diffuser 51 from the fluid outlet 17 a of the impeller 17 is reduced, thereby appropriately converting the speed energy (dynamic pressure) of fluid to the pressure energy (static pressure) at the diffuser 51.
At this time, the diffuser 51 has the throttle portion, and it is possible to reduce the loss, by increasing the fluid outlet angle α at the outlet portion of the diffuser 51. It is also possible to reduce the loss at the diffuser inlet of the impeller outlet due to the movement of the impeller 17 in the axial direction, by increasing the width at the inlet portion of the diffuser 51.
The shape of the throttle portion at the diffuser 51 is set corresponding to the fluid outlet angle from the outlet portion of the diffuser 51, and the passage area ratio between the outlet portion of the diffuser 51 and the inlet portion of the volute chamber 52. Accordingly, by appropriately setting the shape of the throttle portion, the speed in the radial direction of the diffuser 51 is increased, but the speed in the circumferential direction is reduced, thereby reducing the total speed. As a result, it is possible to appropriately convert the speed energy of fluid to the pressure energy by reducing the speed at the diffuser 51. It is also possible to improve the pump efficiency, by appropriately setting the speed of the fluid at the volute chamber 52.
In the pump of the present embodiment, the preload spring 31 for applying a preload to the ball bearings 14 and 15 is provided, and the preload spring 31 is formed by stacking the corrugated plates in a ring shape. Accordingly, because the preload is applied to the ball bearings 14 and 15 by the preload spring 31, the revolution skidding of the ball bearings 14 and 15 can be prevented, thereby enabling extended life of the ball bearings 14 and 15. Because the preload spring 31 is formed by stacking the corrugated plates, the load variation due to the variation of crushing margin of the spring is reduced. Consequently, it is possible to apply an appropriate preload to the bearings 14 and 15.
The pump of the present embodiment is capable of carrying supercritical CO₂fluid or liquid CO₂by rotatably driving the impeller 17, and the pump is used as the circulation pump for cleaning semiconductors. Accordingly, an object to be cleaned need not be dried after cleaning, and it is possible to simplify the cleaning process and reduce costs.
In the embodiment described above, the pump of the present invention is explained as the circulation pump for the semiconductor cleaning device. However, the pump of the present invention may be applied to a general centrifugal pump.

INDUSTRIAL APPLICABILITY

In the pump according to the present invention, a predetermined gap facing the axial direction is formed between the casing and the front shroud, and the sealing units facing the radial direction are provided between the casing and the front shroud. Accordingly, the pump according to the present invention is capable of preventing leakage of fluid and abrasion of components, thereby enabling extended pump life, and is applicable to any pump.

Claims

1. A pump comprising:

a casing having a suction opening and a discharge opening;

a main shaft rotatably supported by a ball bearing in the casing;

an impeller connected to an end of the main shaft; and

a canned motor capable of rotatably driving the impeller through the main shaft,

the pump increasing pressure of fluid suctioned in from the suction opening by rotation of the impeller and discharging the fluid from the discharge opening, wherein

a front shroud is provided at a front side in an axial center direction of the impeller, and a rear shroud is provided at a rear side in the axial center direction of the impeller;

a predetermined gap facing an axial direction is formed between the casing and the front shroud; and

a sealing unit facing a radial direction and being provided between the casing and the front shroud.

2. The pump according to claim 1, wherein the sealing unit is arranged in plurality in the axial center direction of the impeller.

3. The pump according to claim 1, wherein the casing includes a fluid outlet from the impeller communicated with the discharge opening through a diffuser and a volute chamber, and the diffuser contains a throttle portion.

4. The pump according to claim 3, wherein a shape of the throttle portion is set corresponding to a fluid outlet angle at an outlet of the diffuser, and to a passage area ratio between the outlet of the diffuser and the volute chamber.

5. The pump according to claim 1, further comprising a preload spring that applies a preload to the ball bearing, wherein the preload spring is formed by stacking a plurality of corrugated plates in a ring shape.

6. The pump according to claim 1, wherein the impeller is capable of carrying supercritical CO₂fluid or liquid CO₂through rotational driving, and the pump is used as a circulation pump for cleaning a semiconductor.