Seal for a joint or juncture – Seal between relatively movable parts – Brush seal
Reexamination Certificate
2000-04-24
2001-10-30
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Brush seal
C277S347000
Reexamination Certificate
active
06308958
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to brush seals for rotary machines, such as steam and gas turbines, and, more particularly, is concerned with an arrangement and method for radially positioning a turbine brush seal.
Rotary machines, such as steam and gas turbines, used for power generation and mechanical drive applications are generally large machines having multiple turbine stages. In turbines, high pressure fluid flowing through the turbine stages must pass through a series of stationary and rotary components, and seals typically are used between the stationary and rotating components to minimize leakage of the fluid. The efficiency of the turbine is dependent on the ability of the seals to prevent fluid leakage.
Traditionally, one type of seal that is used to control fluid leakage in turbines is a labyrinth seal which has sharp rigid teeth. While the labyrinth seal has proven to be quite reliable, its performance degrades over time. This occurs as a result of transient events in which the stationary and rotating components move radially relative to and thus interfere with one another causing rubbing on the teeth of the labyrinth seal so as to enlarge the clearance between the stationary and rotating components and allow an increase of leakage.
Another type of seal that is used in combination with the labyrinth seal to improve leakage control is a brush seal. The brush seal is generally less prone to leakage than the labyrinth seal because the brush seal has seal bristles that can flex and thus better accommodate the relative radial movement between the stationary and rotating components. The brush seal also generally conforms better to surface non-uniformities than does the labyrinth seal. Such combination brush and labyrinth seal arrangements are disclosed in U.S. Pat. No. 5,749,584 to Skinner et al. assigned to General Electric Company, the assignee of the present invention, and U.K. Pat. Application No. 2,301,635 to Hemsley et al assigned to GEC Alsthom Limited.
A problem exists, however, with some combination brush and labyrinth seal arrangements. Accurate radial positioning of the brush seal relative to the rotor must be achieved in order to gain optimum performance while not adversely affecting rotordynamics. In the current method of assembly, a slot is provided in the labyrinth seal to receive the brush seal. The cross-sectional size of the slot is larger than the cross-sectional size of the portion of the brush seal that is received in the slot to facilitate the ease of mounting of the brush seal to the labyrinth seal. The larger cross-sectional size of the slot results in there being sufficient radial clearance between the brush seal and labyrinth seal to allow the brush seal to “float” radially within the slot, making it difficult to accurately align the brush seal to the rotor. The current method may allow the seal radial position to vary by several thousandths of an inch over its arc length. These variations may reduce the desired seal performance.
Consequently, a need exists for an innovation which will provide an effective solution to the aforementioned problem without introducing any new problems in place thereof.
BRIEF SUMMARY OF THE INVENTION
The present invention provides an arrangement and method for radially positioning a turbine brush seal designed to satisfy the aforementioned need. The arrangement and method of the present invention utilize a shim of a desired thickness to locate a brush seal at a desired position relative to a rotor of a turbine and one or more fasteners, such as set screws, to hold the brush seal at such position against the shim. The use of the shim allows for radial adjustment of the brush seal position. The current method of assembly of the brush seal to the labyrinth seal is generally retained but without allowing the brush seal to “float” radially within the slot of the labyrinth seal. Instead, once the brush seal and the shim are inserted into the slot of the labyrinth seal, the fasteners are tightened to hold the brush seal against the shim and thus at the desired radial position relative to the labyrinth seal as determined by the thickness of the shim. These seemingly simple added elements of the arrangement and step of the method permit the achievement of total control circumferentially and radially of the position of the brush seal relative to the labyrinth seal.
In one embodiment of the present invention, an arrangement and method are provided for radially positioning a turbine brush seal relative to a main seal, such as a labyrinth seal, and a turbine rotor. The arrangement and method employ a main seal segment and a brush seal segment. The main seal segment has a slot open toward the rotor and defining an interior ledge facing away from the rotor. The brush seal segment has an exterior shoulder facing toward the rotor and a portion smaller in size cross-sectionally than the slot so as to allow insertion of the brush seal segment into the slot where the exterior shoulder of the brush seal segment overlies the interior ledge of the main seal segment and the brush seal segment can move radially relative to the main seal segment and rotor and the exterior shoulder of the brush seal segment can move toward and away from the interior ledge of the main seal segment. The arrangement and method also employ means for establishing a minimum spacing between the interior ledge of the main seal segment and the exterior shoulder of the brush seal segment. The arrangement and method further employ means for forcing the brush seal segment toward the rotor such that the exterior shoulder of the brush seal segment is brought toward the interior ledge of the main seal segment so as to place and hold the exterior shoulder of the brush seal segment at the established minimum spacing relative to the interior ledge of the main seal segment and thereby prevent radial floating of the brush seal segment relative to the main seal segment and rotor.
The main seal segment has an arcuate shape for placing the main seal segment about the rotor, an outer periphery facing away from the rotor, an inner periphery spaced radially inwardly from the outer periphery and facing toward the rotor, and a slot defined in the main seal segment between the outer and inner peripheries thereof. The slot has a radial portion open at the inner periphery and extending away from the rotor toward the outer periphery and an axial portion spaced from the outer and inner peripheries and merging in a transverse relationship from a side of the radial portion along the rotor so as to define the interior ledge in the main seal segment facing away from the rotor. The brush seal segment has an arcuate shape for conforming to the arcuate-shaped main seal segment, a radial section, and an axial section connected to and merging in a transverse relationship from a side of the radial section so as to define the exterior shoulder on the brush seal segment facing toward the rotor such that the radial and axial sections of the brush seal segment conform in shape to the radial and axial portions of the slot of the main seal segment as to slidably fit therein with the brush seal segment being movable radially relative to the main seal segment and the rotor and with the exterior shoulder of the brush seal segment overlying and being movable toward and away from the interior ledge of the main seal segment. The means for establishing the minimum spacing includes a shim which is disposed between the interior ledge of the main seal segment and the exterior shoulder of the brush seal segment and has a thickness which establishes the minimum spacing between the interior ledge of the main seal segment and the exterior shoulder of the brush seal segment. The shim is comprised of a substantially rigid material such that the thickness of the shim is maintained when pressure is applied to the shim. The means for forcing the brush seal segment toward the rotor includes at least two threaded holes extending through the main seal segment to the slot at spaced apart locat
Turnquist Norman Arnold
Wolfe Christopher Edward
Cabou Christian G.
General Electric Company
Ingraham Donald S.
Knight Anthony
Peavey Enoch
LandOfFree
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