Patent Application
20060198743
1. Field of the Invention
The present invention relates to a rotary pump device for transporting a very highly-purity active liquid for use in a process of fabricating semiconductor devices, liquid crystals, etc., and more particularly to a pump device which is capable of preventing metal ions and other fine particles from being produced by isolating an active liquid, such as ultrapure water or the like, and a metallic part of a pump mechanism from each other.
2. Description of the Related Art
For achieving a high level of integration of semiconductor devices, it is necessary to increase the purity of various liquids used in the fabrication process and, in particular, to achieve extremely lower content of impurities in those liquids. With regard to ultrapure water that is used in a cleaning process for semiconductor fabrication, the content of fine particles having a size of 0.1 micron poses a problem and greatly affects the yield of products. Particularly, it was a challenging task for pumps for transporting ultrapure water to prevent fine particles from being produced by the wear of rotary sliding components. The task has been achieved by the inventor of the present application as disclosed in Japanese patent No. 1807169, U.S. Pat. No. 5131806, or Japanese laid-open patent publication No. H3-26897.
As the level of integration of semiconductor devices and the performance of liquid crystals further increase, however, the concentration of metal ions, which remain in ultrapure water, poses a large problem. Today, the content of metal ions is required to be 1 PPT (Part Per Trillion) or less. Metal ions are caused to occur when ultrapure water dissolves a metal in liquid-contacting regions of devices including pumps, pipes, valves, etc. in a wet process. It is understood that ultrapure water of highest purity having a resistance of 18.20 MΩ or higher tends to elute highly active ions of metal or the like.
In order to solve the above disadvantage, it has been customary to apply a surface treatment, such as a lining or coating of tetrafluororesin, to regions of devices, such as pumps, that are brought into contact with ultrapure water. However, it is generally difficult to apply a surface treatment, such as a lining of tetrafluororesin, to rotary sliding components and seals of pumps. Even if very chemically stable, highly hard SiC (silicon carbide) is used for rotary sliding components and seals of pumps, it cannot fully prevent ultrapure water from dissolving the metal. At present, it has been attempted to use functional ultrapure water containing a small amount of ozone (O3) or hydrogen fluoride (HF). Use of functional ultrapure water, however, is problematic in that metal and ceramics are exposed to a chemical attack, causing the liquid-contacting regions in rotary sliding components of pumps, i.e., bearings and seals, to suffer erosion due to elution of metal and ceramics.
A pump device according to the present invention has an impeller rotatable in a pump space, a rotational shaft interconnecting a rotational drive source and the impeller, a rotational shaft casing having a bearing assembly and/or a seal assembly, a first blocking flow mechanism, having a discharge section for discharging a portion of a main delivery liquid introduced from the pump space as a first blocking flow, for preventing a second blocking flow containing fine particles produced by the bearing assembly and/or the seal assembly from being entrained into the main delivery liquid, and a second blocking flow mechanism for combining the second blocking flow with the first blocking flow and discharging the second blocking flow from the discharge section while preventing the first blocking flow from being introduced.
In a preferred aspect of the present invention, the first blocking flow mechanism has a first blocking flow passage defined between the rotational shaft and an inner circumferential surface of the rotational shaft casing, and the second blocking flow mechanism has a second blocking flow passage defined between the rotational shaft and an inner circumferential surface of the rotational shaft casing, the first blocking flow passage and the second blocking flow passage being disposed in respective positioned on both sides of the discharge section, the second blocking flow passage being supplied with an inactive liquid as the second blocking flow from a second blocking flow supply port which is open into the second blocking flow passage.
Preferably, the discharge section comprises a blocking disk mounted on the rotational shaft and a disk chamber defined in the rotational shaft casing and housing the blocking disk therein. Further preferably, a labyrinth is provided in the disk chamber between an inner circumferential surface of the disk chamber and the blocking disk.
The second blocking flow preferably has a higher liquid pressure than the first blocking flow at the second blocking flow supply port.
The second blocking flow passage is preferably filled at all times with the inactive liquid supplied from the second blocking flow supply port.
The first blocking flow is preferably discharged from the discharge section at a rate higher than the second blocking flow, the rate of the second blocking flow being at least 1.5 when the rate of the first blocking flow is 1.
A pump device according to an embodiment of the present invention has regions, other than rotary sliding components, such as a bearing assembly and a seal assembly in a rotational shaft casing, which are brought into contact with a main delivery liquid (ultrapure water) and which have surfaces treated for erosion resistance by a lining of tetrafluororesin or the like. In a first blocking flow mechanism, a first blocking flow as a portion of a main delivery liquid (ultrapure water) flowing from a pump space into the rotational shaft casing is discharged out of the rotational shaft casing through a first blocking flow passage defined between a rotational shaft and an inner circumferential surface of the rotational shaft casing, a discharge section contiguous to the first blocking flow passage and disposed in the rotational shaft casing closely to an impeller, and a discharge passage communicated with the discharge section. Therefore, a second blocking flow containing fine particles produced from the rotary sliding components, such as the bearing assembly and the seal assembly, as they are worn is blocked by the first blocking flow against entry from the rotational shaft casing into the pump space.
Specifically, in a second blocking flow mechanism, an inactive liquid, such as ordinary tap water, which exhibits an excellent lubricity to ultrapure water, flows as the second blocking flow from a supply source into the rotational shaft casing, and then flows through a second blocking flow passage defined between the rotational shaft and an inner circumferential surface of the rotational shaft into the discharge section of the first blocking flow mechanism. Therefore, the first blocking flow is prevented from entering into the rotary sliding components, such as the bearing assembly and the seal assembly. In the rotational shaft casing, the inactive liquid (water) delivered as the second blocking flow into the rotational shaft casing flows along the rotational shaft away from the first blocking flow mechanism, i.e., toward the rotary sliding components, such as the bearing assembly and the seal assembly. Since a terminal end of the rotational shaft casing, i.e., the end thereof close to a rotational drive source, is sealed by a seal mechanism, the inactive liquid (water) fills the rotational shaft casing including the rotary sliding components, such as the bearing assembly and the seal assembly, isolating the first blocking flow (ultrapure water) and the rotary sliding components from each other.
The pressure of the second blocking flow of the inactive liquid at a second blocking flow supply port is higher than the pressure of the first blocking flow. However, the rate of the second blocking flow may be lower than the rate of the first blocking flow at all times, primarily at a level for allowing the second blocking flow to operate as lubricating oil and exhibit a cooling effect. Since the rate of the second blocking flow after it has flowed into the rotational shaft casing is much lower than the rate of the first blocking flow, the pressure of the second blocking flow is gradually lowered toward the pressure of the first blocking flow, and becomes equal to the pressure of the first blocking flow when the second blocking flow is discharged in combination with the first blocking flow. Consequently, the second blocking flow does not flow toward and into the pump space on the impeller side.
The inactive liquid (water), which forms the second blocking flow, is supplied by a diaphragm that is actuatable pneumatically, hydraulically or electrically, or a metering pump comprising a plunger pump that is actuatable by an air cylinder. Tap water having a suitable pressure may also be used as the inactive liquid. If necessary, a supply passage interconnecting the supply source and the rotational shaft casing may have a pressure regulating valve, a flow regulating valve, an on-off valve, and the like.
Embodiments of the present invention will be described in detail below with reference to the drawings.
As shown in
The rotational shaft casing 4 has a disk chamber 5a defined therein by an inner circumferential surface thereof and positioned between the impeller 2 and the bearing assembly B. A blocking disk 5b mounted on the rotational shaft 3 is rotatably housed in the disk chamber 5a. The disk chamber 5a and the blocking disk 5b, housed in the disk chamber 5a and made of fluororesin, make up a discharge section 5 of a first blocking flow mechanism. The disk chamber 5a communicates with a discharge passage 5c having flow rate regulating mechanisms 5e, 5f. In this embodiment, a labyrinth 5d is provided between the inner circumferential surface of the disk chamber 5a and the blocking disk 5b. However, as shown in
The first blocking flow mechanism is constructed of a first blocking flow passage 6 which is defined as a gap between the portion of the rotational shaft 3 extending from the pump space 1 to the disk chamber 5a and the inner circumferential surface of the rotational shaft casing 4, the discharge section 5, and the discharge passage 5c. The first blocking flow mechanism causes a branched flow of ultrapure water as the main delivery liquid to flow from the pump space 1 successively through the first blocking flow passage 6, the discharge section 5, and the discharge passage 5c, preventing a liquid containing fine particles (a second blocking flow) from entering from the bearing assembly B and the mechanical seal assembly S into the pump space 1.
The pump device also has a supply source T of an inactive liquid (water), a metering pump P, a second blocking flow supply port 7 that is open at the inner circumferential surface of the rotational shaft casing 4 between the bearing assembly B and the mechanical seal assembly S, and a second blocking flow passage 8 which is defined as a gap between the portion of the rotational shaft 3 extending from the bearing assembly B to the disk chamber 5a and the inner circumferential surface of the rotational shaft casing 4. The supply source T, the metering pump P, the second blocking flow supply port 7, and the second blocking flow passage 8 make up a second blocking flow mechanism. If the pump space 1 is regarded as a front end, then the second blocking flow supply port 7 of the second blocking flow mechanism is positioned behind the blocking disk 5b disposed at a terminal end of the first blocking flow mechanism. An inactive liquid (water) supplied from the supply source T flows as a second blocking flow successively through the bearing assembly B, the second blocking flow passage 8, the discharge section 5, and the discharge passage 5c, preventing the first blocking flow (ultrapure water) coming from the discharge section 5 of the first blocking flow mechanism from entering into the bearing assembly B.
As described above, the second blocking flow is combined with the first blocking flow in the discharge section 5 of the first blocking flow mechanism, and flows out from the discharge passage 5c. In this embodiment, the discharge section 5 is made up of the disk chamber 5a and the blocking disk 5b, and the labyrinth 5d is provided in the disk chamber 5a, making it difficult for the blocking blows to combine with each other and allowing the blocking flows to flow as centrifugal flows due to the rotation of the blocking disk 5b out from the discharge passage 5c. The first blocking flow is thus fully prevented from entering into the bearing assembly B.
The inactive liquid, which forms the second blocking flow, maybe ordinary tap water, and is supplied under a higher pressure and at a lower rate than the first blocking flow to the second blocking flow passage 8 by the metering pump P. Since the second blocking flow flows under a high pressure and at a low rate, it is equalized in pressure to the first blocking flow in the discharge section 5, and discharged out of the pump device through the flow rate regulating mechanisms 5e, 5f provided in the discharge passage 5c. The ratio of the flow rates of the first and second blocking flows, which are combined with each other, may be 1.5:1, or 50:1 or 100:1 in some cases. The direction of the blocking flows is determined by the flow rate of the first blocking flow as a main flow. The second blocking flow supplied to the pump device can maintain a large discharge rate.
If the pump device is inactivated for a long time, fine particles including metal ions produced from metal and ceramics of liquid-contacting regions brought into contact with the delivery liquid are entrained into the ultrapure water as the delivery liquid. Therefore, for achieving the ultrahigh purity of ultrapure water, whose metal ion concentration is required to be 1 PPT or less, immediately after the pump device has started to operate, it is necessary to clean the contaminated interior of the pump device with a large amount of flushing ultrapure water at the time the pump device starts to operate. However, the flushing process is responsible for an excessive increase in the running cost of the pump device.
According to this embodiment, after the pump device has ceased to operate, the second blocking flow mechanism is immediately inactivated to stop the second blocking flow containing fine particles of metal and ceramics. At the same time, the main pump is operated again to circulate the first blocking flow at a rate, which is 1/10 or less of the ordinary rate, for thereby reliably preventing fine particles including eluted ions of metal and ceramics from entering into the pump space 1. Since the second blocking flow mechanism is filled with the second blocking flow, the first blocking flow does not enter into the bearing assembly B. The second blocking flow mechanism may be operated continuously or intermittently at a rate which is ½ of the ordinary rate. In this embodiment shown in
When a small amount of blocking flow is thus passed intermittently or continuously, ions of metal or the like, which are produced when the pump device is inactivated, are prevented from being spread into the entire pump device due to Brownian movement, thereby keeping a highly pure environment in the pump device.
According to the present invention, with the above-described arrangement and operation, fine particles produced in the rotary sliding regions of the rotary pump are efficiently discharged at a low cost, the main delivery liquid is effectively prevented from entering into the rotary sliding regions, and fine particles, such as metal ions or the like, are prevented from being produced due to contact between the main delivery liquid, such as ultrapure water or the like, and the rotary sliding regions of the pump device.
The present invention has been described above as having an outside-type mechanical seal having a fixed ring disposed in a pump chamber and a rotary ring and a spring disposed outside of the pump chamber. However, the present invention is also applicable to an inside-type mechanical seal mechanism having a rotary ring and a spring disposed in a pump chamber.
The present invention is also applicable to a grand packing mechanism or a lip seal mechanism which is a rotary sliding seal mechanism other than the mechanical seal.
As described above, a pump device according to the present invention for transporting ultrapure water or the like has a pump space, an impeller rotatable in the pump space, a rotational shaft interconnecting a rotational drive source and the impeller, and a rotational shaft casing having a bearing assembly and a seal assembly. The pump device has regions brought into contact with a main delivery liquid and treated for erosion resistance by a lining of tetrafluororesin or the like. The pump device also has a first blocking flow mechanism for preventing worn fine particles produced from rotary sliding components, such as the bearing assembly and the seal assembly, brought into contact with a second blocking flow, from being entrained into the delivery liquid, and a second blocking flow mechanism for preventing a main delivery liquid from entering from the pump space into regions, not treated for erosion resistance, of the rotary sliding components.
The first blocking flow mechanism comprises a first blocking flow passage defined by the rotational shaft and an inner circumferential surface of the rotational shaft casing, a discharge section disposed in the rotational shaft casing closely to the impeller, for discharging a first blocking flow introduced as the main delivery liquid from the pump space into the rotational shaft casing, from the first blocking flow passage, and a discharge passage communicated with the discharge section.
The second blocking flow mechanism comprises a supply source for supplying a inactive liquid, having a lubricity, as the second blocking flow, a second blocking flow passage for delivering the second blocking flow into the rotational shaft casing having the bearing assembly and the seal assembly positioned therein, the second blocking flow passage being defined by the rotational shaft and the inner circumferential surface of the rotational shaft casing, a second blocking flow supply port defined in the rotational shaft casing between an end of the rotational shaft closely to the rotary sliding components and the discharge passage, for combining the second blocking flow through the second blocking flow passage with the first blocking flow and discharging the second blocking flow from the discharge passage of the first blocking flow mechanism, and a supply passage disposed between the supply source and the second blocking flow supply port.
In the above pump device, the discharge section of the first blocking flow mechanism comprises a blocking disk mounted on the rotational shaft in an area where the opposite flows meet each other, and a disk chamber defined in the rotational shaft casing and housing the blocking disk therein.
A labyrinth is preferably provided in the disk chamber for preventing the first blocking flow and the second blocking flow from flowing into the second blocking flow passage and the first blocking flow passage, respectively.
The regions not treated for erosion resistance in the rotational shaft casing is preferably filled at all times with the second blocking flow of the inactive liquid flowing in from the second blocking flow supply port, for isolation from the main delivery liquid having a strong chemical attack tendency which is introduced from the first blocking flow passage.
