Seal for a joint or juncture – Seal between relatively movable parts – Brush seal
Utility Patent
1998-08-05
2001-01-02
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Brush seal
C277S926000
Utility Patent
active
06168162
ABSTRACT:
TECHNICAL FIELD
The present invention relates to brush seals for rotary machines such as steam and gas turbines, and particularly relates to self-centering brush seals for sealing between rotary and stationary components.
BACKGROUND OF THE INVENTION
Rotary machines such as steam and gas turbines, used for power generation and mechanical drive applications, are generally large machines consisting of multiple turbine stages. In the turbines, hot high pressure fluid flowing through the turbine stages must pass through a series of stationary and rotating components and seals between the stationary and rotating components are used to control leakage. Seals are also employed in other areas of the turbine than in the hot gas path; e.g., in end packings between the rotating shaft and the stationary components. Turbine efficiency is directly dependent upon the ability of the seals to prevent leakage.
Various types of seals have been employed between rotary and stationary components in turbomachinery, as well as in other machinery. Such seals have included labyrinth-type seals, brush seals, combination labyrinth/brush seals and the like. Brush seals have many advantages and benefits as compared with other types of seals. Brush seals typically are affixed in the stationary component, for example, in a fixed radial position about the rotating component. While such fixed brush seals afford very satisfactory seals for systems that are always concentric, they do not accommodate large relative off-axis motion between the rotary and fixed components, for example, during thermal transients and steady-state running conditions of the turbine. That is, brush seals accommodate only very small radial excursions of a shaft relative to a housing about the shaft. Predicting transient movement precisely by analysis is a very difficult task. Measurement of relative motion between stationary and fixed components can be costly and time-consuming. If the rotary and stationary component centerlines are not concentric during assembly or operation, the seal cannot itself maintain concentricity about the rotary component. The consequences of an incorrectly located fixed brush seal can be severe. For example, the shaft and brush seal backing plate can rub and rotor vibrations can be a consequence of heat generated during the rub. In general, brush seal performance degrades. While the brush seal fence height, i.e., the radial distance between the rotary shaft and the edge of the backing plate, can be increased to reduce the likelihood of a rub, this decreases the pressure capability of the seal.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a self-centering brush seal assembly which enables the brush seal to maintain concentricity with the axis of the rotary component during radial excursions of the rotary component. The present brush seal may be provided in a number of different configurations. In its basic form, the brush seal hereof may comprise an annular backing plate with brush seal bristles extending radially from the backing plate or canted in the direction of rotation for engagement with the rotary component. The brush seal is disposed in a groove in the stationary component which affords a radial clearance between the base of the groove and radial outermost portions of the brush seal. By removing the radial constraints on the brush seal, the seal is allowed to “float” in a radial direction and follow the radial excursions of the rotating shaft without large asymmetric bristle deformations. In this manner, the seal can remain concentric with the axis of rotation of the rotary component.
In another form of the present invention, the self-centering brush seal hereof is provided in a segmented configuration. That is, a plurality of arcuate segments which may comprise the backing plate or upstream and downstream backing plates for the bristles of the brush seal are provided in short segments, for example, segments extending 60° or 90° which, together, make up a substantially closed annular ring about the rotary component. The segments and annular ring formed thereby are disposed in a groove in the stationary component with the required radial clearance, as well as with a spring which biases the segments radially inwardly to maintain engagement of the brush seal bristles with the rotary component. The spring in a preferred form may be a garter spring extending about the periphery of the segments for the full 360°. Alternatively, the radial inward bias may be provided by a plurality of leaf springs, one leaf spring for each segment, bearing between the base of the radial groove and an outer surface of the segment. In a still further form of the present invention, a combined garter/O-ring seal may be provided for disposition in a secondary groove within the groove of the stationary component.
By combining the garter spring and O-ring seal, a pressure balanced segmented brush seal may be provided. This embodiment balances the pressure on the inside and outside diameters of the brush seal by admitting low pressure fluid into the groove downstream of the O-ring seal. It will be appreciated that the bias afforded by the springs in all embodiments hereof must be such that the stiffness of the springs is low in comparison to the stiffness of the bristle pack. The springs not only maintain the seal segments in contact with the shaft but also allow the seal to maintain the designed fence height during relative off-axis motion between the rotary and stationary components.
In a preferred form of the present invention, there is provided a rotary machine comprising a component rotatable about an axis and a component fixed against rotation about the axis, the fixed component having a circumferentially extending groove opening toward the rotatable component, a brush seal disposed in the groove and including a plurality of bristles and a support for the bristles, the bristles being secured to the support and projecting therefrom beyond the support into sealing engagement with the rotatable component and the brush seal and the groove having a radial clearance therebetween enabling the brush seal for radial movement to maintain substantial concentricity and sealing engagement with the rotatable component, notwithstanding deviation of the axis of rotation of the rotatable component relative to the axis of the fixed component.
Accordingly, it is a primary object of the present invention to provide a novel and improved self-centering brush seal assembly for sealing between rotary and stationary components in turbomachinery.
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Dinc Osman Saim
Reluzco George Ernest
Turnquist Norman Arnold
Wolfe Christopher Edward
Woodmansee Donald Ernest
General Electric Co.
Knight Anthony
Nixon & Vanderhye
Patel Vishal
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