Abstract:
A fixture assembly and inspection method by which the internal diameter and/or concentricity of a segmented annular seal can be readily inspected and optionally measured prior to final installation. The fixture assembly has at least two fixture segments supported on a base, by which an annular fixture housing is defined having an outer rim and a groove with a cross-sectional shape corresponding to a cross-sectional shape of the annular seal. The fixture assembly further includes a device or apparatus for assessing at least one dimensional characteristic of the annular seal when installed in the groove of the fixture housing and as the assessing device/apparatus travels along the interior circumference of the fixture housing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to annular seals, such as dynamic seals of the type used in turbomachinery. More particularly, this invention relates to a fixture and inspection method by which dimensional characteristics of an annular seal can be ascertained prior to installation. 
         [0002]    Labyrinth-type packings and brush seals are widely used in steam turbines and in aircraft and industrial gas turbines to provide dynamic seals between rotating and static turbine components, such as the rotor and diaphragm inner web of a steam turbine. Traditional labyrinth packing comprises a series of teeth that project radially inward from the inner circumference of a static component and toward but out of contact with the adjacent rotary component, thereby defining a series of partial barriers that create a tortuous axial flow path immediately adjacent the surface of the rotary component. Brush seals comprise fibers or bristles that, similar to the teeth of a labyrinth packing, project radially inward from the inner circumference of a static component toward a rotary component. In contrast to labyrinth packings, brush seals are normally intended to be in rubbing contact with the adjacent circumferential surface of the rotary component, creating a substantially continuous barrier to flow around the circumference of the rotary component. In this regard, brush seals provide a more effective barrier to secondary flow losses, i.e., provide better sealing performance, as compared to labyrinth packings, and therefore have the potential for significantly improving section performance. However, because their sealing performance relies on rubbing contact, the conformance of a brush seal to its design dimensions and tolerances, particularly its internal diameter and concentricity, is important. 
         [0003]    Brush seals have been developed that are manufactured as a full-annular structure and then cut to create multiple arcuate segments that can be later reassembled during installation to reestablish the original annular seal structure. In a particular example, a brush seal formed of high strength polymer (e.g., KEVLAR®) is sectioned along its diameter to create two semicircular (180-degree) arcuate segments. The flexible nature of the polymeric material along with residual stresses (in the back structure supporting the bristles) that are redistributed during cutting causes each segment to have altered inner diameter (ID) dimensions. As a result, dimensional inspection of the seal in its “free” (uninstalled) state is difficult and leads to an increased risk of seals that do not conform with design dimensions and tolerances. Though the seal can be inspected after its segments are reassembled during final installation, such an approach can be impractical because of the limited space of typical turbine installations and the difficulty with which such an inspection can be performed in the field. 
         [0004]    In view of the above, it would be desirable to verify the dimensional characteristics of a segmented brush seal (as well as other annular seals) without the requirement to install the seal prior to inspection. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a fixture assembly and inspection method by which the internal diameter and/or concentricity of a segmented annular seal can be readily inspected and optionally measured prior to final installation. 
         [0006]    According to a first aspect of the invention, the fixture assembly comprises a base and at least two fixture segments supported on the base. When assembled, the fixture segments define an annular fixture housing having an outer rim and a groove adjacent the outer rim and defined in an interior circumference of the fixture housing. The groove has a cross-sectional shape corresponding to a cross-sectional shape of the annular seal. The fixture assembly further comprises means for assessing at least one dimensional characteristic of the annular seal when installed in the groove of the fixture housing and as the assessing means is moved along the interior circumference of the fixture housing. 
         [0007]    According to a second aspect of the invention, the inspection method comprises assembling at least two fixture segments on a base to define an annular fixture housing having an outer rim and a groove adjacent the outer rim, defined in an interior circumference of the fixture housing, and having a cross-sectional shape corresponding to a cross-sectional shape of the annular seal. After installing the multiple arcuate segments in the groove of the fixture housing so as to assemble the annular seal therein, at least one dimensional characteristic of the annular seal is assessed by causing an inspection device to move along the interior circumference of the fixture housing. 
         [0008]    From the above, it can be appreciated that an advantage of the present invention is that a relatively uncomplicated, split fixture housing is employed that enables a flexible, multi-segment annular seal, such as a polymeric brush seal of a turbomachine, to be dimensionally inspected relative to one or more critical data while the seal is in a simulated installed condition. Another advantage is that the fixture assembly can be portable, permitting the inspection method to be performed in the field. The fixture assembly and inspection method can be employed to quantitatively and/or qualitatively ensure the concentricity of the inner diameter of the seal and/or compliance with maximum and minimum diametrical dimensions of the seal. 
         [0009]    Other objects and advantages of this invention will be better appreciated from the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  represents a cross-sectional view of a seal assembly for a turbomachine and containing a brush seal assembly of a type that can be inspected in accordance with the present invention. 
           [0011]      FIG. 2  represents a perspective view of a fixture assembly in accordance with a first embodiment of this invention. 
           [0012]      FIG. 3  is an exploded view of the fixture assembly of  FIG. 2 . 
           [0013]      FIG. 4  is a cross-sectional view of the fixture assembly of  FIG. 2 . 
           [0014]      FIG. 5  represents a perspective view of a fixture assembly in accordance with a second embodiment of this invention. 
           [0015]      FIG. 6  is a cross-sectional view of the fixture assembly of  FIG. 5 . 
           [0016]      FIG. 7  is a perspective view of an inspection block of the fixture assembly of  FIG. 5 . 
           [0017]      FIGS. 8 and 9  are cross-sectional and perspective views, respectively, of inspection blocks in accordance with alternative embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]      FIG. 1  is a cross-sectional view through an annular seal assembly  10  of a type that can be inspected with fixture assemblies and methods of this invention. The seal assembly  10  is representative of seals used in steam turbines between axially adjacent stages of such turbines to minimize leakage between a rotor to which buckets are mounted and a casing that surrounds the rotor and from which nozzle partitions are supported. As is well known by those skilled in the art, various turbine configurations and applications are possible and within the scope of this invention. As such, the particular type of installation intended for the seal assembly  10  will not be discussed in any detail. 
         [0019]    As represented, the seal assembly  10  comprises a housing  13  that contains a brush seal assembly  12  situated within a groove  15  between a pair of teeth  14 , the latter being of the type associated with labyrinth-type packings. It should be understood that the seal assembly  10  of  FIG. 1  is merely intended to be exemplary of the type of annular seal that can be inspected in accordance with this invention, and that other annular seal types and configurations are also within the scope of the invention. When the seal assembly  10  is installed in its intended turbomachine, the brush seal assembly  12  is axially positioned between the teeth  14  relative to the axis of the turbomachine. As such, the labyrinth teeth  14  serve as backup seals to the brush seal assembly  12 , and are therefore preferred but optional components of the seal assembly  10 . Consistent with brush seals of the types used in turbomachinery, the brush seal assembly  12  represented in  FIG. 1  is adapted to continuously maintain a prescribed gap or pre-determined contact with the surface with which it is intended to seal, e.g., the rotor of a turbomachine, thereby effecting a better seal than possible with a labyrinth packing. For this reason, the brush seal assembly  12  is represented as comprising bristles  16  that, when the seal assembly  10  is installed in a turbomachine, project radially inward for rubbing contact with the rotor. As known in the art, the brush seal bristles  16  and the labyrinth teeth  14  may be formed of a variety of materials, with KEVLAR® and other high-temperature, high-strength polymeric materials being notable examples for the brush seal assembly  12  and its bristles  16  if used in advanced technology turbomachinery, while ductile metals are preferred for the teeth  14  and the housing  13  surrounding and supporting the brush seal assembly  12 . Other materials that could foreseeably be used in the seal assembly  10  include carbon fiber materials. 
         [0020]    Seal assemblies of the type represented in  FIG. 1  are typically installed in a groove of a stationary structure of a turbomachine, such as a diaphragm inner web of a steam or gas turbine. When installed in this manner, the outer circumferential surface  18  of the seal assembly  10  is received in the groove so that the teeth  14  and bristles  16  extend radially inward toward the rotor of the turbine. Because the sealing performance of the seal assembly  10  relies largely on maintaining a prescribed gap or pre-determined rubbing contact between the bristles  16  and the rotor, the bristles  16  establish a critical inner diameter (ID) and concentricity of the seal assembly  10 . 
         [0021]      FIGS. 2 through 4  depict a fixture assembly  20  adapted for assessing the inner diameter and/or concentricity of the brush seal assembly  12  of the seal assembly  10  in accordance with a first embodiment of the invention. As represented in  FIGS. 2 through 4 , the fixture assembly  20  comprises a pair of fixture segments  21  that, when assembled and secured to a base  30 , form a fixture housing  22  having an annular shape. The fixture segments  21  and fixture base  30  can be fabricated from a wide variety of materials, and various fastening techniques can be employed to secure the fixture segments  21  to the fixture base  30  so as to provide sufficient strength and rigidity to house the brush seal assembly  12  and support the equipment used to assess the brush seal assembly  12 . As evident from  FIG. 4 , the fixture housing  22  includes a groove  24  located in its interior circumference  26  near an outer rim  28  of the fixture housing  22 . The fixture groove  24  is configured and sized to coincide with the diameter, width, and depth of the groove  15  of the seal assembly  10  in which the brush seal assembly  12  will be housed when installed on its intended turbomachine. Furthermore, the rim  28  of the fixture housing  22  is preferably shaped and sized to simulate the upper tooth  14  of the seal assembly  10  in  FIG. 1 . 
         [0022]    In  FIGS. 2 and 3 , the brush seal assembly  12  is shown as being installed in the groove  24  for inspection by an armature assembly  32 . The armature assembly  32  is represented as including a bar  34  pivotally mounted to the fixture base  30  so that at least one of its opposing ends will pass adjacent the groove  24  of the fixture housing  22  and the brush seal assembly  12  when installed in the groove  24 . The bar  34  is depicted as having a bore  36  preferably located midway along its length, and a bushing  38  within the bore  36  that receives a pin  40  secured to the fixture base  30  and by which the bar  34  is rotatably supported above the base  30 . A clamp  42  secures the bar  34  to the pin  40  to ensure that the bar  34  rotates within a plane perpendicular to the pin  40  and parallel to a plane containing the fixture groove  24  and therefore the brush seal assembly  12  installed in the fixture groove  24 . 
         [0023]    A micrometer  44  is shown in  FIGS. 2 and 3  as being mounted with a holder  46  to one end of the bar  34 , so that the micrometer  44  is oriented and positioned to measure the inner diameter (ID) of the brush seal assembly  12  as established by its bristles  16 . The micrometer  44  can be of any suitable type, such as a dial indicator, comparator, non-contacting measurement device, etc., capable of providing an indication of variations in the ID of the seal assembly  10  as the bar  34  is rotated on its axis of rotation established by the bushing  38  and pin  40 . Measurement indications of the micrometer  44  can be provided electronically or visually, such as with a dial. As the bar  34  is rotated on the pin  40 , the output of the micrometer  44  can be used to obtain precise quantitative dimensions of the inner diameter of the brush seal assembly  12 , or provide a qualitative assessment of conformance (“go-no go”) to the minimum and maximum ID dimensions permitted for the assembly  12 . 
         [0024]      FIGS. 5 and 6  depict a fixture assembly  50  adapted for assessing the inner diameter and/or concentricity of the brush seal assembly  12  in accordance with a second embodiment of the invention. Similar to the fixture assembly  20  of  FIGS. 2 through 4 , the fixture assembly  50  is represented as comprising a pair of fixture segments  51  that, when assembled and secured to a base  60 , yield a annular fixture housing  52 . Also consistent with the previous fixture assembly  20 , the fixture housing  52  can be seen in  FIG. 6  to have an internal groove  54  located in its interior circumference  56  near an outer rim  58  of the housing  52 , and configured and sized to coincide with the diameter, width, and depth of the groove  15  that houses the brush seal assembly  10  within the seal assembly  10  of  FIG. 1 . Furthermore, the rim  58  of the fixture housing  52  can be shaped and sized to simulate the upper tooth  14  of the seal assembly  10  in  FIG. 1 . In contrast to the embodiment of  FIGS. 2 through 4 , the fixture assembly  50  of  FIGS. 5 and 6  is equipped with an inspection block  62  intended to qualitatively assess the brush seal assembly  12  installed in the groove  54  on the basis of conformance (“go-no go”) to the minimum and maximum ID dimensions permitted for the seal assembly  12 . 
         [0025]    The inspection block  62  is represented in  FIGS. 5 and 6  as being supported from the rim  58  of the fixture housing  52  by a pair of rollers  64  rotatably mounted to the block  62  so that a contoured surface  66  of the block  62  abuts the inner circumference of the rim  58  and a rib  74  axially spaced below the rim  58 . For this reason, the contoured surface  66  preferably has a radius of curvature approximately equal to that of the interior circumference of the rim  58  and rib  74 . As seen in  FIG. 7 , a pair of bores  76  are present in the contoured surface  66  by which the rollers  64  can be rotatably mounted with shafts (not shown). As also seen in  FIG. 7 , a channel  68  is defined in the contoured surface  66  beneath the bores  76 . The position of the channel  68  relative to the rollers  64  is such that the channel  68  is axially aligned with the brush seal bristles  16  of the brush seal assembly  12  installed in the fixture groove  54 , and the width of the channel  68  is sized to accommodate the width of the bristles  16 . By precisely sizing the radial depth of the fixture groove  54  relative to the inner circumferences of the rim  58  and rib  74  of the fixture housing  52 , as the inspection block  62  travels around the housing  52  with the contoured surface  66  abutting the rim  58  and rib  74 , the channel  68  will pass a precise predetermined distance from the bottom of the groove  54  and have a precise position relative to the brush seal assembly  12  installed in the groove  54 . 
         [0026]    The depth of the channel  68  is sized to enable the block  62  to assess the inner diameter and concentricity of the seal assembly  12  (established by the bristles  16 ) in one of several ways. For example, the depth of the channel  68  can be sized to coincide with the minimum ID of the brush seal assembly  12 , such that by moving the block  62  (e.g., by hand) along the circumference of the fixture housing  52 , an out-of-tolerance ID condition can be ascertained by detecting rubbing contact between the bristles  16  and the bottom of the channel  68 . Detection of rubbing contacts can be facilitated by placing a contact-sensitive material  70  in the bottom of the groove  68 , as depicted in  FIG. 8 , to assist in detecting if the bristles  16  have contacted the groove  68 . The material  70  may be a pressure-sensitive adhesive tape whose adhesion to the groove  68  following inspection will indicate if and to what extent the bristles  16  made interference contact with the bottom of the groove  68 . Another alternative for the material  70  is a powder such as chalk applied to the bottom of the groove  68 , by which a brush seal assembly  12  with an undersized ID can be detected by visually inspecting its bristles  16  to see if any powder has been transferred to the bristles  16 . A second inspection block  62  whose channel  68  has a depth sized to coincide with the maximum ID of the seal assembly  10  is then used to determine an out-of-tolerance maximum ID condition by the absence of rubbing contact between the bristles  16  and the bottom of the channel  68 . 
         [0027]      FIG. 9  depicts an alternative configuration for the groove  68 , in which a step  72  is present to define two different depths corresponding to the minimum and maximum allowable ID&#39;s for the brush seal assembly  12 . As shown in  FIG. 9 , two staggered sets of bores  76  are provided in which the two rollers  64  can be selectively mounted to axially align one of the channel depths with the brush seal bristles  16  of the brush seal assembly  12  installed in the fixture groove  54 . With this approach, a single inspection block  62  is able to simultaneously detect out-of-tolerance minimum and maximum ID conditions. This approach can also make use of the contact-sensitive material  70  of  FIG. 8 . 
         [0028]    While the invention has been described in terms of a particular embodiment, it is apparent that other forms could be adopted by one skilled in the art. For example, while the fixture housings of the invention are shown and described as comprising two fixture segments, the housings could be divided into any number of segments. Furthermore, though the invention has been described in reference to a brush seal for a turbomachine, the invention can find application for use with other types of annular-shaped seals. Therefore, the scope of the invention is to be limited only by the following claims.