Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
1998-08-04
2001-07-03
Yuen, Henry C. (Department: 3747)
Pumps
Motor driven
Electric or magnetic motor
C417S279000
Reexamination Certificate
active
06254362
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vacuum pump with a dust collecting function for use when a vessel for a process, in which various processes of productions by reaction or melting and crystallization processes are carried out under a reduced pressure atmosphere evacuated by a vacuum pump, is used. The process may be a process of epitaxial growth for producing monocrystalline film of silicon, in which an amount of dust is produced when the reaction process or a melting and crystallization process take place and the produced dust flows into the vacuum pump together with the existing gas.
2. Description of the Related Arts In general, the process of productions by reaction and the melting and crystallization processes in a vessel for processing under a reduced pressure are carried out in vacuum. Therefore, the specific gravity of the gas which flows into a vacuum pump is very small. When the gas, together with the dust, flows into the vacuum pump, the gas flows appropriately but has less ability to convey the dust, and therefore a greater portion of the dust is accumulated in the vacuum pump. In prior arts, the increased amount of the accumulated dust prevents the satisfactory running of the vacuum pump to cause difficulty in continuing the running of the vacuum pump so that frequent operations to remove the dust in the vacuum pump are needed.
Also, there is a problem that, if the sizes of grains of the dust which flows together with the gas into the vacuum pump are large, the internal structures of the vacuum pump, such as rotors, collect the grains of the dust to which can lead to a failure or a stoppage of the vacuum pump.
To prevent dust from flowing into the vacuum pump attempts have been made to separate the dust by providing filters or the like between the vacuum pump and the dust producing device. There is a problem, however, in that the dust causes blocking of the through-paths in the filter which are then greatly reduced. The effective evacuation performance of the vacuum pump for the process of production by reaction and the melting and crystallization in the vessel for processing prevent the reaction process and the melting and crystallization in the vessel for processing from continuing.
It is possible to provide a dust separator for separating dust utilizing the flow of gas, such as a cyclone type separator, between the vacuum pump and the vessel for processing. However, in this case, to reduce the loss of the pressure by the cyclone type separator, if the cross-sectional area of the gas flow in the separator is increased, no sufficient gas flow velocity is obtained so that the satisfactory separation of the dust cannot be realized in the cyclone type separator. Since the process is carried out under high degree of vacuum in the vessel for processing, the amount of the flow of the gas entering into the vessel, coming out from the vessel and being sent to the vacuum pump is relatively small. Therefore, the ability of the vacuum pump to transfer the dust to discharge the dust is low, and accordingly the dust tends to be accumulated in the vacuum pump to lead to a stoppage of the vacuum pump.
Since the dust is discharged together with the gas from the vacuum pump, a large amount of dust flows into the exhaust gas processing system. Therefore, there is a problem that the exhaust gas processing system is quickly contaminated and this prevents the functioning of the system.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above described problems by providing an appropriate vacuum pump with a dust collecting function.
According to the present invention, there is provided a vacuum pump with a dust collecting function comprising: a vessel for processing which can be decompressed by a vacuum pump; suction piping connected to said processing vessel; a vacuum pump operatively connected to said suction piping; vacuum pump piping adapted to constitute a main exhaust operation path including the vacuum pump for exhausting gas and an auxiliary dust collecting circulation path including the vacuum pump for collecting dust; gas discharge piping; and a dust separator connected directly to the vacuum pump in the main exhaust operation path; wherein, during the exhaust period, the auxiliary dust collecting circulation path is shut to allow exhaust through the main exhaust operating path to be carried out, and, during the period in which the decompression by the vacuum pump is not necessary, the auxiliary dust collecting circulation path is formed to constitute a circulation path together with the main exhaust operation path to carry out the dust.
The dust separator may be is connected directly to the vacuum pump in the main exhaust operation path.
A shut-off valve for opening and closing the auxiliary dust collecting path may be inserted in the auxiliary dust collecting path.
A gas diffusing liquid chamber may be inserted in the gas discharge piping.
In a vacuum pump with a dust collecting function according to the present invention, decompression of a vacuum pump is carried out, and, during the reaction process or the melting and crystallization in the processing vessel, the shut-off valve in the auxiliary dust collecting path is closed, and the gas exhausted from the processing vessel flows together with the dust into the vacuum pump. The gas is exhausted by the vacuum pump, and the exhaust gas as is discharged from the vacuum pump through the exhaust piping which leads to the exhaust gas processing system or the discharge outlet. Since the processing in the processing vessel is carried out under a high degree of vacuum and therefore the specific gravity of the gas exhausted from the processing vessel is very small, the vacuum pump is not able to satisfactorily convey the dust from the vacuum pump and, accordingly, the dust is progressively accumulated in the vacuum pump. After that, when the process of productions by reaction or the melting and crystallization process in the processing vessel is completed when decompression by the vacuum pump is no longer necessary, the shut-off valve in the auxiliary dust collecting path is opened. Upon opening the shut-off valve, the suction piping and the exhaust piping of the vacuum vessel communicate with each other, and a large amount of gas which is exhausted from the vacuum pump circulates through the auxiliary dust collecting path, the dust separator, the shut-off valve, and the vacuum pump. Since the loss of pressure due to the circulation of the gas is small and the difference between the suction pressure and the discharge pressure is small, the flow rate of the circulating gas is approximate to the flow rate corresponding to the maximum exhaust rate. Therefore, the flow rate of the circulating gas is great and the specific gravity of the gas is far greater than that under the high degree of vacuum, which produces a very high capability of conveying out the dust. The dust accumulated in the vacuum pump is appropriately conveyed out to a dust separator, such as a cyclone type dust separator. The dust is separated and collected at high efficiency in the dust separator. Since the dust accumulated in the vacuum pump is discharged, the subsequent reaction process or the melting and crystallization in the processing vessel can be satisfactorily carried out.
A check valve may be provided in the exhaust piping which passes the gas exhausted from the vacuum pump to the exhaust outlet at a location downstream of the diverging point of the auxiliary dust collecting path and the exhaust piping. Also, a sealed liquid chamber having the structure to diffuse the gas into a liquid may be provided downstream of the check valve. In such arrangements, the gas containing the dust exhausted from the vacuum flows from the exhaust piping through the check valve into the sealed liquid chamber. In the liquid chamber the gas is diffused into the liquid, the dust contained in the gas is caught by the liquid due to the viscosity thereof, and only the gas flows through the exhaust p
Higuchi Tsutomu
Kambe Shigeharu
Gimie Mahmoud
Merchant & Gould P.C.
Unozawa-Gumi Iron Works, Ltd.
Yuen Henry C.
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