Abstract:
A seal is provided between a pair of members by a flexible seal element fixed to one member and having a turned edge. The seal element overlies a contact surface of the other member to effect the seal, the seal element spanning a gap between the members and being pressed into the contact surface by a high pressure region on the same side of the gap as the sealing element. In other forms, a second sealing element is employed in conjunction with a spline seal forming a tortuous sealing path between the members.

Description:
[0001] This invention was made with Government support under Contract No. DE-FC21-95MC31176 awarded by the Department of Energy. The Government has certain rights in this invention. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to seals for sealing adjacent components in a gas turbine and particularly relates to an overlapping interference seal for minimizing fluid flow through a gap between adjacent components and methods of assembly.  
           [0003]    Many and various types of seals have been applied between adjacent components to seal the components to one another or to minimize the flow between opposite sides of the seal. For example, spline seals are employed to prevent or minimize leakage through the gap between adjacent shroud segments of a gas turbine. It will be appreciated that a plurality of such shroud segments are arranged in an annular array thereof about the rotor axis of a gas turbine. Both of the inner and outer side walls of the shrouds form a gap between high and low pressure regions which either must be sealed or at least leakage flow minimized. Such spline seal systems utilize long narrow flat seals loosely assembled in opposing slots of two adjacent side walls of the shrouds. The pressure differential forces the spline seal against a sealing surface along each of the shroud slots. The slots and spline seal serve to create two labyrinth paths, impeding leakage flow through the gap. While such spline seals have been satisfactory, they are characterized by high temperatures, variable pressure gradients and excessive life requirements. Thus, there is a need for a seal between components in a gas turbine having improved sealing characteristics.  
         BRIEF SUMMARY OF THE INVENTION  
         [0004]    In accordance with a preferred embodiment of the present invention, there is provided an overlapping interference seal for sealing a gap between a pair of adjacent gas turbine components. The seal is rugged and robust and can tolerate finite amounts of relative motion, misalignment and manufacturing tolerances. To accomplish the foregoing, and in a first embodiment hereof, there is provided a pair of gas turbine components, for example, shrouds, disposed in side-by-side relation one with the other with a gap therebetween. The components generally have planar surfaces along the edges of the components adjacent the gap. A seal element is disposed between the components and has seal surfaces engaging the planar surfaces of the components. The seal element is secured to one of the components and overlies a planar sealing surface along the opposite component, enabling relative sliding movement therebetween. Because the seal element is formed of a thin material, the high pressure on one side of the seal element forces the element into contact and sealing engagement along the planar surface of the other component to effect the seal. In this embodiment, the seal element includes an upturned elongated leading edge. With the proximal edge of the seal secured to one of the components, the assembly of the seal is facilitated by displacing the components toward one another. In this manner, the leading upturned edge of the seal element engages along the opposing surface of the component, enabling a smooth engagement of the sealing element with the planar surface. The sealing element may be employed separately from or in combination with a spline seal. The spline seal may be disposed in slots along the adjoining edges of the components, with the sealing element overlying the spline seal.  
           [0005]    In another form of the present invention, a pair of sealing elements are provided. One sealing element is fixed to one of the components and has an elongated leading edge, while the other sealing element is fixed to the other component. A recess is formed in the components for receiving a spline seal. The recess may directly underlie the sealing elements or comprise registering slots along opposing side edges of the components to receive the spline seal. One of the edges of the recesses is preferably chamfered to facilitate assembly of the seal, as described below. In final assembly, the one sealing element overlies the other sealing element, forming a seal between their contacting surfaces. The underlying sealing element may also overlie and contact a portion of the spline seal between the components. Alternatively, the spline seal may be spaced from the sealing elements and have chamfered surfaces along opposite edges thereof to facilitate assembly of the seal.  
           [0006]    The present invention also embraces a method of forming the seal. For example, the adjacent components are placed in lateral registration with one another. As the components are relatively advanced toward one another, the leading edge of the sealing element facilitates initial engagement between the sealing element and the other component. Continued displacement causes the sealing surface to engage along the planar surface. Where two sealing elements are employed, the spline seal is first inserted into the recess, e.g., slot. In one form, the spline seal is inserted between a component and one of the sealing elements and is releasably retained, e.g., clamped between the component and element. Consequently, with a chamfer on the other component and a leading edge on the other sealing element, the components may be displaced toward one another with the sealing element and spline engaging between the first sealing element and the component with the chamfer. Alternatively, the spline seals may have chamfers along opposite edges to facilitate their insertion into the recess, e.g., slots, upon relative displacement of the components toward one another.  
           [0007]    In a preferred embodiment according to the present invention, there is provided in a gas turbine, a seal between high and low pressure regions, comprising a pair of members spaced from one another and movable toward and away from one another, each member having a generally planar surface, a seal element between the members and having sealing surfaces engaging the planar surfaces, respectively, the seal element being secured to one of the members, one of the sealing surfaces of the seal element being in slidable engagement with the planar surface of another of the members and the seal element having a leading edge overlying another member and extending away from another member.  
           [0008]    In a further preferred embodiment according to the present invention, there is provided in a gas turbine, a seal between high and low pressure regions, comprising first and second members spaced from one another and movable toward and away from one another, each member having a generally planar surface, first and second seal elements carried by the first and second members, respectively, the seal elements having respective sealing surfaces in slidable engagement with one another, one of the seal elements having a leading edge overlying another of the sealing elements and extending away from another sealing element, each member having an elongated recess in opposition to an elongated recess along an opposing member, an elongated spline seal engaged in the recesses and having sealing surfaces therealong engaging seal faces along the recesses of the members, the spline seal extending between the members and lying on one side of the seal element.  
           [0009]    In a further preferred embodiment according to the present invention, there is provided in a gas turbine having first and second members spaced from one another and movable toward and away from one another, a seal including at least one sealing element between the members, the sealing element being fixed to the first member and extending therefrom to overlie a planar sealing surface along the second member, a method of assembling the seal, comprising the steps of forming a leading edge on one sealing element along a distal edge thereof extending to one side of a plane containing the sealing element and displacing at least one of the members toward another member such that the leading edge guides the one sealing element along the second member to engage a sealing surface carried by the one sealing element along an opposite side of the plane containing the sealing element against the planar sealing surface of the second member to form a seal between the members.  
           [0010]    In a further preferred embodiment according to the present invention, there is provided in a gas turbine having first and second members spaced from one another and movable toward and away from one another, a seal between the members including first and second sealing elements carried by the first and second members, respectively, a method of assembling the seal comprising the steps of forming a leading edge on the first sealing element along a distal edge thereof extending to one side of a plane containing the first sealing element and displacing at least one of the members toward another of the members such that the leading edge guides the first sealing element along the second sealing element to engage a sealing surface carried by the first sealing element along an opposite side of the plane against a sealing surface carried by the second sealing element. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective view of a nozzle stage segment for a stage of a gas turbine in which intersegment seals are employed;  
         [0012]    [0012]FIG. 2 is an enlarged fragmentary cross-sectional view of a conventional spline seal between adjacent segments; and  
         [0013]    FIGS.  3 - 7  are respective fragmentary cross-sectional views of various overlapping interference-type seals between components in accordance with embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    Referring to the drawings, particularly to FIG. 1, there is illustrated a nozzle stage segment, generally designated  10 , forming part of an annular array of segments about the rotational axis of a gas turbine, not shown. Each nozzle segment  10  comprises an outer band portion  12 , an inner band portion  14  and one or more vanes  16  extending between the outer and inner band portions  12  and  14 , respectively. In the annular array of nozzle segments, it will be appreciated that the side walls or edges of the outer and inner band portions lie directly adjacent side walls or edges of adjacent nozzle segments whereby the vanes  16  and the outer and inner bands form a complete annular array of nozzle segments about the rotor axis.  
         [0015]    As finally assembled, the nozzle segments are arranged in an annular array thereof, with a gap  30  between the adjacent segments. As illustrated in FIG. 2, spline seals  36  are typically provided to reduce the flow leakage between high and low pressure regions on opposite sides of the outer band portions, represented, respectively, by high pressure region  32  and low pressure region  34 . A spline seal  36  is disposed in slots  38  along adjacent side walls of the nozzle segments for reducing the flow leakage across the seal and through the gap. It will be appreciated that the foregoing description of a seal between adjacent nozzle segments of a gas turbine is exemplary of a seal for preventing leakage between any pair of components of a gas turbine in which a seal is provided for sealing between high and low pressure regions on opposite sides of the seal. Therefore, the foregoing and following references to seals between adjacent nozzle segments are considered exemplary.  
         [0016]    Referring now to FIG. 3, there is illustrated a pair of members  40 ,  42  spaced one from the other and defining a gap  44  therebetween. The members  40 ,  42  may comprise any two components of a gas turbine, e.g., the outer shroud portions, which have a gap therebetween and which components are movable toward and away from one another during turbine operation. Typically, the members  40 ,  42  lie on opposite sides of high and low pressure regions  46  and  48 , respectively, and require sealing between the components and across the gap. To accomplish this, a flexible seal element  50 , preferably formed of metal, extends between the components  40 ,  42  and seals gap  44 . Seal element  50  is secured to one of the members  42 , for example, by welding, and includes a cantilevered portion  52  which extends beyond the edge of member  42  and beyond the width of the gap. The members  40 ,  42  are preferably recessed along their opposite surfaces, for example, at  54  and  56 , to receive the overlying seal element  50 . The seal element  50  includes a leading edge  58  turned in a direction away from the underlying member  40 . Preferably, the turned edge  58  forms a radius. The surfaces of the recesses  54  and  56  form planar contact surfaces against respective sealing surfaces  55  and  57  of the seal element  56  bear for sealing the gap  44  between the two members  40  and  42 .  
         [0017]    It will be appreciated that the seal illustrated in FIG. 3 may be readily assembled. For example, in the event the seal is used to seal outer band portions of the shrouds to one another, the member  42 , to which the seal element  50  is fixed, may be displaced toward the member  40 . The leading edge  58  engages the member  40  and ensures that the seal element  50 , when displaced toward member  40 , engages the contact sealing surface  54  of the recess. Consequently, the seal illustrated in FIG. 3 affords easy assembly, as well as an effective seal, enabling the high pressure on one side of the seal to flex or deform the seal element  50  into sealing engagement with the members  40  and  42 .  
         [0018]    Referring to FIG. 4, wherein like parts are designated by like reference numerals, preceded by the prefix  1 , the recesses  154  and  156  carry a spline seal  60 . The spline seal is an elongated flat strip  60 , preferably formed of metal, which seats on the sealing surfaces of the recesses  154  and  156 . For reasons discussed below, member  142  includes a chamfer  62  along a leading edge thereof. As in the previous embodiment, a seal element  150  extends from and is fixed to member  142 , element  150  being cantilevered at  152  to extend across the gap  144  between the members  140  and  142 . Instead of directly engaging member  140 , seal element  150  engages another seal element  64  fixed on member  140 . Seal element  64  projects from and overlies recess  154 . Both seal elements  150  and  64  are formed of thin, flexible sheet, preferably metal, materials.  
         [0019]    It will be appreciated that the seal thus formed has multiple sealing surfaces, i.e., between the spline  60  and the contact surfaces of the members  140 ,  142 , respectively; between spline  60  and seal element  64 ; and between the seal elements  64  and  150 . Moreover, the seal illustrated in FIG. 4 is easily assembled. By disposing the spline seal  60  in the recess  154  formed by member  140  and overlying seal element  64 , the spline seal  60  is captured in the position illustrated in FIG. 4 prior to assembly. By relatively displacing the members  140  and  142  toward one another, the chamfer  62  enables the spline seal  60  to ride over the edge of member  142  onto the planar contact surface  156  of member  142 . Similarly, the turned leading edge  158  of seal element  150  facilitates engagement of seal element  150  over seal element  64 .  
         [0020]    Referring now to FIG. 5, wherein like reference numerals are applied to like parts preceded by the prefix  2 , the seal element  250  seals with the contact surfaces in recesses  254  and  256 , sealing the members  240  and  242  to one another across the gap  244  spanned by cantilevered portion  252 . In addition, a spline seal  260  is disposed in registering slots  70  and  72  formed along the edges of members  240 ,  242 . The slots  70  and  72  open through the edge faces and register one with the other. Consequently, a tortuous sealing path is provided, first by the engagement of the seal element  252  along the contact surfaces of the recesses  254  and  256  and, secondly, by the contact between the edges of the spline  260  and the slot faces of the members  240  and  242 . by the engagement of the seal element  252  along the contact surfaces of the recesses  254  and  256 . Additionally, the embodiment of FIG. 5 is readily assembled. By locating the spline seal  260  in the slot  72  and relatively displacing the members  240 ,  242  toward one another, the spline seal is captured in the slots  70  and  72 . Additionally, the leading edge  258  of the seal element  250  facilitates engagement of the seal surface of seal element  250  along the contact surface of the recess  254 .  
         [0021]    Referring now to the embodiment hereof illustrated in FIG. 6, wherein like reference numerals are applied to like parts, preceded by the prefix  3 , the members  340  and  342  are provided with recesses  354  and  356  forming sealing contact surfaces. A spline seal  360  is disposed along the contact surfaces. The seal element  350  is fixed to the member  342 , for example, by a weld  80 , while the seal element  364  is similarly fixed to the member  340  by a weld  82 . The seal element  364 , however, forms a continuation of the perforated impingement plate, such as plate  22  illustrated in FIG. 2. The perforated plate  364  extends over the contact surface  354  of the member  340 , as well as an edge portion of the spline seal  360 . Note also the chamfer  362  formed along the edge of member  342 .  
         [0022]    It will be appreciated that a tortuous seal is similarly formed in the embodiment hereof illustrated in FIG. 6 between the spline seal  360  and the contact surfaces of the recesses  354  and  356 ; the spline seal  360  and the seal element  364 ; and the engagement of the seal element  364  and the cantilevered portion  352  of seal element  350  one with the other. Additionally, the seal of FIG. 6 is easily assembled. With the spline seal  360  captured in the recess  354  between member  340  and seal element  364 , the members  340 ,  342  may be relatively displaced toward one another, as indicated by the arrows. The chamfer  362  facilitates the sliding engagement of the edge of spline seal  360  along the contact surface of member  342 . Similarly, the leading or turned edge  358  of seal element  350  facilitates engagement of seal element  352  over seal element  364 .  
         [0023]    Referring now to the final embodiment hereof, illustrated in FIG. 7, wherein like parts have like reference numerals, preceded by the prefix  4 , the edges of the members  440  and  442  have recesses or slots  470  and  472  which receive the margins of a spline seal  460 . In this form, however, the spline seal has chamfers  90  formed along its opposite edges to facilitate assembly. The seal elements  450  and  464  engage one another along sealing surfaces. The seal thus has a tortuous sealing passage which minimizes leakage, the sealing surfaces including the engagement of the spline seal  460  along the contact surfaces of slots  470 ,  472 , and the engagement of the seal elements  450  and  464  with one another. As in the preceding embodiments, the seal of FIG. 7 is readily assembled by disposing the spline seal  460  in one slot  472  and relatively displacing the members  440 ,  442  toward one another. The turned edge  458  on seal element  450  facilitates the engagement of seal element  450  along the sealing surface of seal element  464 .  
         [0024]    In all of these embodiments, it will be appreciated that the flexibility of the seal elements and their location along the high pressure side of the seal enables the seal elements to press firmly in sealing contact against the underlying contact surfaces, whether it is the corresponding sealing element or a contact surface of a member. Additionally, the arrangement facilitates assembly of the seals.  
         [0025]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.