Abstract:
The positions of brush seal segments are positively adjusted relative to a housing carrying the brush seal segments and the opposing sealing component by employing members formed of thermally responsive material. The members are heated by heating elements receiving controlled power. By increasing or decreasing the power provided to the heating elements, the members are expanded or contracted to move the brush seal segments toward or away from the opposing sealing component.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to brush seals and more particularly to apparatus and methods for positively adjusting clearance between a brush seal and an opposing component against which the brush seal bears to form the seal. 
     Brush seals are commonly used to minimize leakage through a gap between parts or components which are to be sealed to one another. For example, brush seals are commonly used in rotating machinery such as steam and gas turbines used for power generation. Typically, the brush seals minimize leakage between regions at different pressures on opposite sides of the seal. As a specific example, a steam turbine may employ a brush seal for minimizing leakage of steam between a stationary component and a rotating component such as a rotor. 
     While brush seals are discussed herein in a preferred embodiment with respect to sealing between stationary and rotating components, it will also be appreciated that brush seals can be applied to seal components which are non-rotating and may be irregularly shaped. For example, a brush seal may be used to seal between a combustor transition piece and a sealing cap of a first stage nozzle in a gas turbine. In a typical application of a brush seal between stationary and rotating components, however, the brush seal comprises a plurality of arcuate segments, each segment conventionally including a pair of plates with a plurality of brush bristles disposed between the plates. The plates and proximal ends of the brush bristles between the plates are typically welded to one another, forming a completed brush seal segment. Opposite ends of the bristles project from between the plates, terminating in free ends or tips engaging and forming a seal with the other component, typically the rotating component. The arcuate brush seal segments are typically disposed in a groove of the stationary component and may have a spring between the component and the segment biasing the segment for movement between the opposing sealing components, e.g., for movement toward the rotating member. 
     It has been found, however, that because of stack-up tolerances and machine-to-machine variations, it is very difficult to achieve accurate clearance control, even with brush bristles biased by a spring toward the opposing sealing component. Also, it is common that for the same machine, the sealing clearance may be different from the bottom half to the upper half of the machine. For example, gravity affects the brush seal segments in the semi-circular upper and lower casings of a steam turbine tending to engage and disengage, respectively, the bristle tips relative to the rotor. These operating clearance variations result in performance changes in different applications. Additionally, brush seal leakage performance also tends to degrade with time and progressive bristle wear. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with a preferred embodiment of the invention, an adjustable clearance brush seal is provided wherein the sealing clearance between the parts or components being sealed may be positively controlled, particularly during operation of the associated machine, and from locations external to the machine. For example, the brush seal may be provided in arcuate brush seal segments disposed in a groove of a stationary component with the bristles in opposition to, and engaging, the rotating component. The seal clearance between the bristles and the opposing component can be positively controlled. The seal clearance is the degree of interference between the brush bristles and the opposing sealing component, as well as any gap between the tips of the bristles and the associated sealing component, e.g., where it may be desired to maintain a gap permitting flow between opposite sides of the seal. To accomplish the foregoing, a member or members formed of a thermally expansible or contractible material are disposed in controlling relation to the brush seal in the component carrying the brush seal to control the location of the brush seal vis-a-vis the seal component engaged by the bristle tips. For example, each member may comprise one or more pins or sleeves carried by the stationary component and disposed in the groove between the stationary component and the brush seal to extend in a generally radial direction. Upon application of heat to the thermal material of the members, the members tend to elongate, displacing the brush seal segment radially toward the opposing seal component. Conversely, when the temperature of the members is lowered, any interference between the opposing seal component and the bristles of the brush seal tend to displace the brush seal segment in an opposite direction toward the component in which the brush seal is mounted. Consequently, the opposite ends of the members need not be secured to either the component or the brush seal. Alternatively, one or both ends of the members may be secured, for example, by welding, to the component mounting the brush seal and to the brush seal per se, whereby positive control of the brush seal can be effected to move the brush seal in opposite directions responsive to the differential heat applied to the members. 
     More particularly, and as noted previously, the members may comprise pins or hollow sleeves having heating elements about the pins or within the sleeves. The heating elements preferably comprise electrically actuated elements which can be controlled through suitable circuitry employing, for example, a rheostat. By adjusting the rheostat to control the magnitude of the heat supplied to the members, the members can be differentially expanded or contracted. A still further alternative may comprise a circumferentially extending member, e.g., a band, having a heating element contained within the band or about the band for expanding or contracting the band and, hence, displacing the brush seal segment toward or away from its opposing seal component. 
     The members are formed of materials having a high thermal coefficient of expansion and the electric heating elements may be embedded in or about the materials. By increasing or decreasing the power supplied to the heating elements, the pins or bands expand or contract, respectively, moving the seal segments toward or away from the opposing seal component, respectively. Consequently, the user may adjust the power setting to achieve the desired clearance. This also can be accomplished externally of the machine and while the machine is in operation. A particular advantage of the invention resides in elimination of a need for tight tolerances for the seal and its mounting, thereby easing machining constraints and reducing costs. 
     In a preferred embodiment of the invention, apparatus for adjusting a seal between two components includes a brush seal carried by one of the components for disposition between the two components and having a plurality of bristles projecting from the brush seal, with free ends of the bristles terminating in bristle tips in engagement with the other of the components forming a seal between the components. The brush seal is mounted for movement relative to one component and toward and away from the other component. A member disposed between the one component and the brush seal is responsive to heat either applied thereto or removed, by expanding or contracting, respectively, thereby displacing the brush seal relative to the one component toward or away from the other component, respectively. 
     In a further preferred embodiment, a rotary machine includes a rotatable component and a component fixed against rotation, the components being disposed about an axis, and a seal between the components comprising an arcuate brush seal segment carried by one of the components, including a plurality of bristles projecting from the one component and having free ends terminating in bristle tips in engagement with the other of the components, forming a seal between the components. The brush seal segment is mounted for movement relative to the one component and toward and away from the other component. A member is carried by the one component for displacing the brush seal segment relative to the other component and is formed of a material thermally responsive to heat applied differentially thereto by expanding or contracting and thus moving the brush seal relative to the one component, thereby adjusting the sealing clearance between the brush seal segment and the other component. 
     In a still further preferred embodiment of the invention there is provided in a seal between adjacent components including a brush seal carried by one of the components for movement relative to the one component toward and away from a second one of the components, the brush seal having a plurality of projecting bristles terminating in bristle tips in engagement with the second one of the components, a method of positively controlling the brush seal position relative to the one component comprising the steps of disposing a member between the brush seal and the one component which is formed of a thermally responsive material; and applying heat at different temperatures to the member of thermally responsive material to expand or contract the member and thereby move the brush seal relative to the one component and toward or away from the second component. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary cross-sectional view of a brush seal between stationary and rotating components according to the prior art; 
     FIG. 2 is a perspective view of the brush seal illustrated in FIG. 1; 
     FIG. 3 is a fragmentary cross-sectional view illustrating a positive adjustable clearance brush seal according to a preferred embodiment of the invention and disposed between two components to be sealed; 
     FIG. 4 is a perspective view similar to FIG. 2 illustrating a thermally responsive material in conjunction with a brush seal for positive clearance control according to a preferred embodiment of the invention; 
     FIG. 5 is a view similar to FIG. 3 illustrating a further preferred embodiment of the invention; 
     FIG. 6 is a view similar to FIG. 3 illustrating a still further preferred embodiment of the invention; and 
     FIG. 7 is a view similar to FIG. 3 illustrating a further preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1, illustrates a brush seal,  10 , in accordance with the prior art, for sealing between a first component, e.g., a stationary component  12 , and a second, rotatable component  14 . Brush seal  10  comprises a plurality of arcuate segments  16 , each having a pair of backing plates  18  and  20  enclosing therebetween a plurality of bristles  22 . The bristles are secured at their proximal ends to the backing plates, for example, by welds  24 . The bristles extend from their proximal ends between backing plates  18  and  20  to project freely therefrom, terminating in bristle tips in engagement with a surface of rotatable component  14 . The bristles generally extend radially of the rotatable component and are offset from radii of that component generally in the direction of rotation. The bristles are formed of metal or may be formed of other material, such as ceramics. As shown in FIG. 2, one of the backing plates  23  extends to a lesser radial extent than the opposite backing plate  26 . In the typical prior art brush seal configurations illustrated in FIGS. 1 and 2, the brush seal segment is disposed in a groove within stationary component  12  at a fixed radial location with the bristle tips engaging the sealing surface of rotatable component  14 . Alternatively, the seal segment may be disposed in a groove within the stationary component and displaced under spring pressure toward or away from the rotating component. However, in both instances, the position of the brush seal is not achieved by positive control at the position or location of the brush seal segment. 
     In a preferred embodiment of the invention illustrated in FIGS. 3 and 4, each segment of a brush seal  30  comprises a pair of backing plates  32  and  34 , with bristles  36  disposed therebetween. As in the prior art, the bristles are secured at their roximal ends between the backing plates by suitable means, for example, a weld  38 . The bristles extend from the weld between the backing plates, terminating in bristle tips  37  in engagement with the surface to be sealed. contracts in the longitudinal direction of the long axis of the sleeve, which axis is oriented in a radial direction. For example, sleeve  41  may contain a heating element  44  connected in an electrical circuit including a power source  46  and a controller for adjusting the magnitude of the power supplied to heating element  44 . The controller, for example, may comprise a rheostat  48 . Alternatively, other types of controls can be us ed for controlling the power supplied to heating element  44  and hence the magnitude of the heat applied to sleeve  41 . Moreover, while the heat applied to sleeve  41  is shown provided by an electrical heating element, other sources of heat may be used to expand o r contract the sleeve. For example, a fluid thermal medium, such as steam, may flow through or about the sleeve to expand the sleeve. A lower temperature fluid medium may also be used, such as a refrigerant, to contract the sleeve. 
     While the embodiment of FIG. 3 illustrates heating element  44  residing within sleeve  41 , member  39  may comprise a solid element, such as a pin  47  having heating element  44  disposed about the pin, as illustrated in FIG.  5 . Other elements of the preferred embodiment hereof illustrated in FIG. 5 are denoted by like reference numerals as in the preceding embodiment. 
     By increasing or decreasing power supplied to the heating element , e.g. by adjusting rheostat  48 , member  39  (or  47 ) is expanded or contracted, respectively, moving or displacing the seal segments in response thereto. For example, by increasing the power supplied to heating element  44  within sleeve  41  of FIG. 3, the sleeve is expanded in its axial direction and hence displaces the brush seal segment in a radial direction toward rotatable component  14 . If the ends of the members are not secured to stationary component  12  or to the segments of brush seal  30 , decreasing the power supplied to heating element  44  still positively controls the position of the brush seal segments because the engagement of rotatable component  14  with the bristle tips tends to displace the brush seal segments radially outwardly. Moreover, one or both ends of the members (e.g. sleeves  41  of FIG. 3 or pins  47  of FIG. 5) can be positively secured to the stationary component and/or the brush seal. In either instance, positive control over the location of the brush seal segments relative to the stationary component mounting the brush seal segments is achieved by increasing or decreasing power supplied to thermally expansible and contractible pins  47 . 
     In another form of a preferred embodiment of the invention illustrated in FIG. 6, heating elements  50  may be disposed within a circumferentially extending member, e.g. a heating band  52 , formed of a thermally responsive material. The heating band preferably resides in a space between brush seal segment  54  and the base of groove  56  in the stationary component. Thus, band  52  extends circumferentially between the brush seal segments and the base of groove  56 , and may extend the entire circumferential length of the segments, or for only part of their length, or a plurality of band segments, separated from one another, may be provided along the circumference of the segments. Upon actuation of the heating elements within band  52 , the increase or decrease of power supplied to the heating elements will respectively expand or contract band  52  in a radial direction to displace brush seal segments  54  in groove  56 , thereby positively adjusting the clearance between the bristle tips and the surface of the rotatable component. One or both of the radially opposite faces of the heating bands may be secured to the stationary component and the power supplied to band  52  can be adjusted externally of the machine as in the preceding embodiment. 
     In FIG. 7, a pair of bands  60 , similar to band  52  shown in FIG. 6, are located between hook portions  62  of the brush seal segment and hooks  64  of groove  40 . Heating elements  66  are disposed within bands  60  and each band, like bands  52  of FIG. 6, may extend in part or completely around the entire brush seal segment circumferentially. Consequently, upon increasing or decreasing power supplied to electrical elements  66 , bands  52 , formed of thermally expansible and contractible material, will expand or contract radially, respectively, causing the brush seal segments to move in a radial direction. The radially opposed faces of bands  60  may be secured to hooks  64  and hook portions  62 , respectively. Alternatively, springs (not shown) may be disposed circumferentially about groove  40  to bias the segments for movement radially inwardly, the radial extent of bands  60  controlling the position of the brush seal segments against the bias of the spring. 
     It will be appreciated that the pins or bands need not be secured to either the stationary component or the brush seal in order to positively control the movement of the brush seal. For example, when the pin of FIG. 5 or the band of FIG. 6 is expanded, the brush seal is displaced radially inwardly. Upon decreasing the power supplied to the heating element, the pin or band contracts in a radial direction, providing a gap in which the interference between the rotating component and bristles forces the brush seal segment to move in a radially outward direction. The pins or bands, however, can be fixed at one end or along one face, respectively, to the stationary component or to the brush seal segment, or they can be fixed to both the stationary component and the brush seal segment at opposite ends or along opposite faces, respectively. With both ends or both faces fixed, the brush seal segment follows both the expanding and contracting movement of the pins or bands without external assist. 
     While only certain preferred features of the invention have been illustrated and described, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention