Seal for a joint or juncture – Seal between relatively movable parts – Relatively rotatable radially extending sealing face member
Reexamination Certificate
2001-01-16
2003-06-17
Sandy, Robert J. (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Relatively rotatable radially extending sealing face member
C277S412000
Reexamination Certificate
active
06578849
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a sealing configuration for sealing off a first region from a second region through which a fluid can flow and which can be kept at different pressures. A differential pressure can be produced between the two regions by the different pressures. The invention relates in particular to a sealing configuration that can be used for sealing in rotary machines, such as electrical rotary machines and thermal fluid-flow machines.
A device for non-contact sealing between spaces of different pressure, in particular for a fluid-flow machine in which shaft leadthroughs between spaces of different pressure have to be provided with suitable seals, is described in European Patent Application No. 0 611 905 A1. The specified device is formed of a labyrinth seal in which step-shaped labyrinth gaps are formed between a rotating part and a stationary part. Sealing tips are disposed in the labyrinth gaps on each of the rotating part and the stationary part, as a result of which a high degree of swirling of a medium flowing through is said to be achieved. The sealing tips between the stationary part and the rotating part are disposed as close to one another as possible, so that there is only a slight radial gap. The sealing tips extend radially in such a way that sealing tips of two adjacent steps overlap. A group of sealing tips can be caulked in place in a corresponding groove through the use of a caulking wire.
Various seals for a turbine stage of a steam turbine are specified in an article entitled “MaBnahmen zur Modernisierung und Lebensdauerverlängerung an Dampfturbinenkomponenten” [Measures for Modernizing and Prolonging the Life of Steam Turbine Components] by D. Bergmann, M. Jansen and H. Oeynhausen, in VGB Kraftwerkstechnik 71, 1991, No. 2, pages 116 to 112.
FIG. 13
of the article shows relative leakage-steam flows between a guide blade and a turbine rotor. In that case, recesses are made in the guide blade in some embodiments. The lowest relative leakage-steam flow rates are achieved for labyrinth seals in which sealing tips are disposed on the turbine rotor and on the guide blades in an alternate manner in the axial direction. Efficiency losses of a steam turbine plant can be reduced by an improvement in gap sealing between the turbine rotor and the guide blade.
Austrian Patent No. 362 639 shows a non-contact seal between a part rotating in a space to be sealed off and a stationary part. A ring-shaped sealing body surrounds a shaft leading out of a casing. A pressure medium is stored under a pressure T
1
in the casing. The sealing body is pressed by the pressure of the pressure medium in the direction of a sealing surface of the shaft. A gap remains between the sealing surface and the sealing body due to pressure chambers. The height of the gap is firmly preset by choke points which reduce the pressure Tl to a lower pressure in the pressure chambers. An end-wall section of the sealing body, which is opposite the sealing surface, is positioned in such a way that possible tilting of the sealing body is automatically compensated for by a tilt-point displacement.
German Published, Non-Prosecuted Patent Application DE 35 33 829 A1 shows a sealing device with a gas-lubricated mechanical surface seal. Two sealing rings lying opposite one another form a sealing gap through which a gaseous medium flows. A gas lubricating film is obtained at a very specific pressure, and that gas lubricating film keeps the two sealing rings at a distance apart at a defined gap width. During a pressure reduction, one of the sealing rings is pushed back into an open position by a spring force.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a sealing configuration, in particular for a rotary machine, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which is used for sealing off two regions through which a fluid can flow that are at different pressure levels in order to reduce a leakage flow from one region into the other region, as may be necessary, for example, in thermal fluid-flow machines or electrical rotary machines.
With the foregoing and other objects in view there is provided, in accordance with the invention, a sealing configuration, comprising first and second regions for conducting a fluid flow and/or being filled with a fluid. The regions are to be sealed-off relative to one another and kept at different pressures forming a differential pressure. An opposing surface and a deformation region are provided. A sealing surface is connected to the deformation region and spaced apart from the opposing surface by a sealing gap. The sealing gap has a height to be set by a deformation of the deformation region as a result of a force exerted by the differential pressure.
The invention is based on the concept that, in pressure-carrying machines, such as fluid-flow machines, in particular steam turbines, different pressure levels of the working medium, for example steam or gas, are to be sealed off from one another, or the working medium is to be sealed off from the ambient medium. In the case of known seals between stationary and rotating parts, non-contact seals are mainly used, in particular in steam turbines, due to the high circumferential velocities and the nature of the sealing task. If there are pressure differences, the non-contact seals have an unavoidable leakage mass flow, which leads to losses in output or efficiency of the pressure-carrying machine. The leakage mass flow is substantially determined by the clearances in the seal, e.g. tip-to-tip seals or a labyrinth seal, and by gap widths in seals without tips. In known seals, those clearances are to be constructed in such a way that the loading cases occurring in the machine can be controlled without damage, i.e. without grazing. For example, that applies during normal operation, cold or hot start, when passing a critical speed, during operation of turning gear, and in the event of plant malfunctions. That is because, in the event of grazing, the clearance would be bridged and the rotating component would touch the stationary component. In order to avoid that in every operating or malfunction situation of the machine, the clearances as a rule are dimensioned too generously for the actual operation, that is when there are stringent tightness requirements. On the contrary, for the dimensioning of the clearance, transient processes and the passing of a critical speed as well as the compensation for any production tolerances in size, form and position are decisive. In addition, a reduction in the clearance in known seals in a steam turbine, at high steam pressures and in the case of slim turbine rotors, could lead to gap excitation, which in turn influences the dynamic behavior and may lead to self-excited vibrations. Furthermore, the leakage mass flows which occur in the current seals through the seals of the blade stages in a steam turbine in cylinder type of construction during the re-entry to the blading space cause disturbances in the inflow to the following blade row, e.g. due to incorrect incident flows.
If the differential pressure changes, the height of the sealing gap is changed by a differential-pressure-controlled sealing configuration so that, in particular when the differential pressure is increasing, the height of the sealing gap, i.e. the clearance, is reduced and a considerable sealing effect is thereby produced. The sealing in that case is effected by an interaction of the sealing surface with the opposing surface, which in particular is axial. A considerable sealing effect is achieved in the process by the functioning mode of the deformation region, which undergoes a deformation, in particular an axial elongation, toward the sealing surface when the differential pressure is applied to the sealing configuration. Furthermore, the change in the spacing between the sealing surface and the opposing surface forms a sealing region through the use of which an i
Sandy Robert J.
Schwing Karlena D
Siemens Aktiengesellschaft
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