Rotary kinetic fluid motors or pumps – Smooth runner surface for working fluid frictional contact
Patent
1995-02-10
1996-11-26
Look, Edward K.
Rotary kinetic fluid motors or pumps
Smooth runner surface for working fluid frictional contact
415177, F04D 1904
Patent
active
055778836
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Vacuum pumps which are operated at high rotor speeds are, for example, turbo vacuum pumps (axial, radial) or molecular pumps, turbomolecular pumps in particular. Molecular pumps, turbomolecular pumps or combinations of these, belong to the class of gas friction pumps. The active pumping surfaces of a molecular pump are formed by the surfaces of a rotor and a starer which face each other, whereby the rotor and/or the stator is equipped with a thread-like structure. Turbomolecular pumps exhibit--much like turbines--rotor and starer blades which form the active pumping surfaces. The active pumping surfaces on the inlet side form the high vacuum (HV) area. The active pumping surfaces close to the ejection side represent the forevacuum (FV) area. In combined gas friction pumps a turbomolecular pump will generally be employed in the HV area whereas a molecular pump will be used in the FV area.
Gas friction pumps of the aforementioned kind are suited for the generation of a high vacuum (from 10.sup.3 mbar and less). They require a backing pump, a rotary vane pump, for example, which is connected to the FV area.
Pumps of the aforementioned kind are being employed more and more for the evacuation of chambers and vessels in which chemical processes such as coating or etching etc. are run. In such applications, relatively large quantities of gas are produced which must be removed by the gas friction pump in order to maintain the required vacuum pressures. Large quantities of gas present a great thermal lead to the active pumping surfaces. Also the drive motor and the rotor bearings--be they rolling bearings or magnetic bearings--contribute to the generation of heat. Also the process gas itself may be warm in the examples given. For these reasons, gas friction pumps employed in connection with chemical processes must be equipped with a cooling system in a manner which is basically known.
SUMMARY OF THE INVENTION
In the applications outlined above, there exists the problem of solids which must be handled by the gas friction pump. The formation and deposition of solids may occur due to chemical reactions between the constituents of the gas which is pumped, by reactions between the gas and the active pumping surfaces and/or by catalytic effects. The deposition of solids leads to the formation of layers, which particularly in the case of a vacuum pumps with very narrow slits soon results in a narrowing of these slits, so that the pumping characteristics of the pump are impaired. Also abrasions, reductions in play etc. will occur, combined with increased wear resulting in a much reduced service life for the pump.
A tandem turbomolecular pump is known from the Journal of Vacuum Science and Technology, No. 3, May 1990, pages 2768-2771. This pump is composed of two turbomolecular pumps arranged above each other. The turbomolecular pump on the high vacuum side is equipped on its forevacuum side with a cooler.
The present invention is based on the task of designing a gas friction pump of the aforementioned kind so that the described problems of solid depositions when operating the pump in connection with chemical process are mostly removed.
This task is solved by equipping the FV side of the pump with a heater so that different operating temperatures for the HV area and the FV area are created in such a way that the temperature of the HV area is lower.
In contrast to the way in which turbomolecular pumps are commonly operated, where the pump is cooled from the FV side, the operating temperature of the pump on the FV side will be higher than the temperature on the HV side. This measure is based on the knowledge that lower temperatures in the HV area will not facilitate the formation of solids owing to the low pressure. It is of significance that the active pumping surfaces in the FV area be warmer than those in the HV area, since the formation of solids is facilitated at increasing pressures and reducing temperatures. As the temperature increases besides the pressure in gas friction pumps designed
REFERENCES:
patent: 4904155 (1990-02-01), Nagaoka et al.
patent: 4926648 (1990-05-01), Okumura et al.
patent: 4929151 (1990-05-01), Long et al.
patent: 5190438 (1993-03-01), Taniyama et al.
Journal of Vacuum Science and Technology, Enosawa, H., "High Throughput Tandem Turbomolecular Pump for Extreme High Vacuum" May (1990).
Patent Abstracts of Japan, vol. 16, No. 458 (M-1315) 24. Sep. 1992 and A, 41 64 188 (Hitachi) Jun. 9, 1992.
Reimer Peter
Schutz Gunter
Szirmay Markus
Lee Michael S.
Leybold Aktiengesellschaft
Look Edward K.
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