Abstract:
The knife edge air seal ring of a gas turbine is modified to receive a replacement or second seal ring portion having a wire brush seal. The replacement or wire brush air seal ring is mounted with the existing knife edge air seal mounting ring at a location so that the existing mounting ring may be used, while providing adequate strength and structural support for installation of the second, wire brush seal ring. The replacement seal ring may be provided with knife edge seals as well, if desired.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to turbine air seal rings. 
     2 Description of the Prior Art 
     Turbine blades of a gas turbine have employed a multiplicity of blades mounted around the peripheral portion of a rotatable disk. The disk rotated within an enclosed duct of a gas turbine under the drive forces of gases which have a high pressure and a high temperature. Air seals are required between the ducts and the circumferential rings formed by mating shrouds of the turbine disc to seal the gases in the turbines. The knife edge components which form the turbine air seals are relatively thin, typically on the order of 0.018 to 0.020 inches thick, and are typically formed from nickel based super alloys. 
     High temperature gases which pass over the turbine air seals cause the turbine air seals to wear or corrode. The thermal effects of combustion gas contaminants, the thermal stresses imposed by the cyclic nature of the operation of the turbine and the frictional engagement of the rotating disc against the stationary turbine outer air seal are some of the factors which cause damage to the air seals over time. A principal manifestation of the damage is an increase in the clearance gap between the seals and the disc. The increase in the clearance gap decreases the turbine efficiencies due to the power loss from escaping gases. In addition, turbine components which are heated by the escaping hot gases tend to deteriorate. A significant segment of turbine technology is directed to the repair of turbine air seals and the maintenance of air seal integrity. 
     Recently, one of the major turbine vendors, Westinghouse, has begun providing an air seal ring which uses wire brushes for sealing purposes. The wire brush air seals are provided in air brush rings. The wire brush air seals mounted in such rings have been asserted to increase cooling and efficiency. However, existing knife edge seal rings were not adapted to receive the new wire brush modifications. If an existing air seal ring was modified to receive the new wire brush ring, too much material from the existing ring had to be removed. There was inadequate structural support for the brush ring. Therefore, the existing ring had to be scrapped and a new replacement air seal purchased. The new replacement air seal was specifically sized to receive the wire brush ring with adequate support. However, the new replacement air seal was costly, and scrapping the entire prior existing ring to install a new ring fitted with the wire brush was wasteful and inefficient. 
     Other conventional turbine air seal repair technology involved machining of portions of the corroded damaged knife edge portions and the application of a weld build-up oft he worn seal edges. The weldment was then remachined to the original specifications of the turbine component. However, considerable design and tooling efforts were frequently expended in controlling the distortion inherent in the welding process which caused some weld metal shrinkage and part distortion. Additional tooling was frequently provided to correct distortion where shrinkage otherwise could not be controlled. The design and tooling requirements for controlling distortion could often result in a repair process which was not cost effective in comparison with the cost of new replacement parts. 
     U.S. Pat. Nos. 4,285,108; 4,028,788; 3,771,978 and 4,924,581 dealt with techniques for removal and replacement of damaged areas of conventional knife edge seals. Typically new knife edge seals were installed in place of the damaged ones. However, this did not provide the increased cooling and efficiency of the wire brush seals. 
     SUMMARY OF THE INVENTION 
     The present invention relates to turbine air seal replacement rings, such as those used in gas turbines in power generation, electrical power plants or other electrical energy production facilities. A method for repairing or updating turbine air seal rings is also provided. The replacement air seal rings of the present invention provide a first seal ring portion having an annular groove formed therein, a second seal ring portion having a wire brush seal formed thereon and a mounting ring fitted into the annular groove of the first seal ring portion and being capable of receiving the second seal ring portion therein. The first seal ring portion may also have a plurality of knife edge seals formed thereon. The present invention also provides an adapter for repairing or converting a turbine air seal for use with a replacement seal ring. The adapter has a mounting ring for connecting a replacement wire brush seal ring to a knife edge seal ring of a gas turbine. 
     The gas turbine seal ring of the present invention provides a first seal ring portion having an inner wall from which a plurality of knife edge seals extend inwardly. The seals may be of any suitable number and dimension, as determined by the specific application for which the seal ring is used. An annular groove, channel or seat is formed in the first seal ring portion, the channel being capable of receiving a mounting ring therein. Typically, the annular groove is formed by milling or cutting material from a first seal ring portion of an existing seal ring. 
     The mounting ring provides an increased inner diameter to the air seal ring, thereby allowing installation of the new or improved second seal ring portion. The mounting ring is formed having an outer diameter or surface substantially conforming to the inner diameter or surface of the annular groove formed in the first seal ring portion. The mounting ring further has a generally rectangular cross sectional shape and may have at least one knife edge seal formed on an inner surface and extending inwardly therefrom. A cylindrical slot or seat is formed in the mounting ring, outwardly from the inner surface thereof. The slot partially defines an inner lip or edge of sufficient thickness to support and retain the second seal ring portion. 
     The second seal ring portion is securely fitted or mounted in the cylindrical channel formed in the mounting ring. A wire brush seal extends inwardly from the inner surface of the second seal ring portion, the wire brush seal being comprised of a plurality of relatively small bristle elements. 
     The adapter of the present invention provides a mounting ring for fitting into an annular groove in a knife edge seal ring and a replacement seal ring having a wire brush seal extending inwardly from an inner surface thereof. Depending on the specific application in which the adapter will be used, the mounting ring may have at least one or a plurality of knife edge seals extending inwardly from an inner surface. A cylindrical lip portion may be provided in the mounting ring for providing a support rim or shoulder for supporting and retaining the replacement seal ring, the lip extending between an inner surface and an annular slot or seat of the mounting ring. 
     The method of the present invention provides for first cutting or milling an annular groove or channel in the interior surface of the air seal ring. The milling process involves removing only a relatively small portion of material from the seal ring, sufficient to allow attachment of the mounting ring. The mounting ring is then fitted or installed into the groove and further then secured or attached to the air seal ring, thereby creating a modified or improved air seal ring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of an end portion of an arcuate segment of a conventional knife edge seal ring of a gas turbine. 
     FIG. 2 is an isometric view of an end portion of an arcuate segment of a wire brush seal ring. 
     FIG. 3 is an isometric view of the seal ring structure of FIG. 1 modified according to the present invention. 
     FIG. 4 is an isometric view of an end portion of a mounting ring adapter according to the present invention. 
     FIG. 5 is an isometric view of an end portion of a seal ring for a gas turbine according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, an air seal ring  10  of the conventional type having a plurality of inwardly extending knife edge seals  12  formed on a cylindrical inner wall  14  is shown. The air seal ring  10  is of the type used in gas turbines such as the Model W501D5 gas turbine units sold by Westinghouse Electric Corporation. The knife edges  12  seal, as is conventional, between ducts and mating shrouds of turbine disc on a rotor in the gas turbine. The air seal ring  10  is one of a series of such air seal rings in the gas turbine to confine the high pressure, high temperature gases to a desired flow pattern to impart drive force to the turbine rotor. The general direction of air flow through the turbine is indicated at  16 , and the knife edges serve as mentioned to confine the air flow of such gases in a desired flow path. During the service life of the gas turbine, the knife edges  12 , particularly those at an area  18  and closest to the incoming direction of general air flow tend to suffer wear, typically in the form of gaps or spacing between the knife edge seals  12  and the turbine blades, for reasons discussed above. 
     The air seal ring  10  shown in FIG. 1 is an arcuate segment of the conventional type known to those in the art which extends arcuately as indicated by an arrow  19 . The amount of such extent is considerable, usually 180° and only a portion of the air seal ring  10  is shown. The air seal ring portion  10  is a component of circumferential ring formed by assembling together two segments like that shown in FIG.  1 . The air seal ring is of a typical construction and has a mounting flange  20  formed extending radially outwardly from a shoulder or body portion  22 . Further, the mounting flange  20  has a connector lug or pin  24  extending outwardly therefrom. A connector socket  26  is also formed in the mounting flange  20 . The pin  24  and connector socket  26  are adapted to engage and fit with corresponding sockets and lugs, respectively, of the next adjacent arcuate segment in the circumferential air seal ring formed. 
     As is also conventional, the air seal ring portion  10  has a lower arcuately extending rim or shoulder  28  extending below the body portion  22  outwardly from the knife edges  12 . The shoulder  28  has a threaded connector socket  30  formed in it for receipt of a connector, such as a bolt or the like, to assembly the air seal ring portion  10  with other such seal ring portions to form the circumferential seal ring of knife edges  12 . The seal ring  10  is conventional and other structural features shown not necessary for an understanding of the present invention are not described. 
     FIG. 2 in the drawings shows a wire brush air seal ring W of the type recently introduced by Westinghouse Electric Corporation. One particular model of such an air seal ring is that available from Westinghouse Electric Corporation as a Row  3  air seal for a 501D5 turbine. The wire brush seal ring W is shown, as is the case with air seal ring  10  of FIG. 1 in an end view of an arcuate segment extending arcuately, as indicated by an arrow  32 . The typical arcuate extent of the seal ring W is comparable to that of the seal ring  10  and thus only a portion is shown. The wire brush seal ring W has an inwardly extending wire brush seal segment  34  formed of multiple, closely packed metal wires, which at their inner ends individually contact with rotor structure and seal therewith in the gas turbine. The multiple contacts with the rotor structure by the inwardly extending wire brush seal segments  34  are said to afford increased efficiency and cooling over that provided by the individual knife edge seal rings of the type shown in FIG.  1 . The brush seal segments  34  are mounted in a lower segment  36  of a mounting ring  38  which also includes an intermediate body portion  40  and an upper connector rim  42 . The mounting body  40  for brush seal segment  34  has dimensions and size determined by structural integrity considerations based on rotational speed and other factors. These dimensions cannot be reduced below a specified or established minimum. Thus, for a particular gas turbine seal ring, the upper connector rim  42  has specified dimensions which cannot safely be reduced. 
     Turning again to FIG. 1, a phantom line  44  depicts the border of a cross-sectional area of the air seal ring  10  which would need to be removed to accommodate the connector rim  42  of the mounting body  40  for the brush seal segment  34 . As can be seen, only a very thin wall portion  46  between an inner border  44   a  of the phantom line  44  and an inner wall  14  where knife edge seals  12  are formed. This wall portion  46  afforded inadequate strength and support, and it was thought necessary therefore to scrap or discard the existing air seal ring  10  and purchase an entire new air seal ring, especially designed and structurally adapted for fitting of the wire brush seal ring W. As has been set forth above, this approach was expensive and could be considered wasteful and uneconomic. 
     FIG. 3 shows the initial structural element of an air seal ring A according to the present invention. The initial structural element of FIG. 3 is formed by modifying the knife edge air seal ring  10  shown in FIG. 1, and accordingly like structure FIG.  1  and FIG. 3 bears like reference numerals. A number of existing knife edge seals  12  of the knife edge seal  10  of FIG. 1 remain extending inwardly from an inner upper surface  10   a  of the first seal ring portion  10  in the structure shown in FIG. 3, as can be seen. An annular groove, channel or seat  50  is cut or milled into the shoulder or body portion  22  using any suitable process, the channel  50  being formed adjacent an upper surface  52  and a rear or outer surface  54  in the body portion  22 . A lower surface  56  is formed in the rim or shoulder  28  below the annular groove  50 . The formation of channel  50  typically includes the removal of a number of knife edge seals  12  in the area  14 . However, these knife edge seals are typically the ones more likely to be damaged or worn during service use. Thus, the present invention enables these potentially damaged or worn knife edge seals to be replaced while also accommodating the additional sealing function of the wire brush seal W of FIG.  2 . 
     In order to mount the wire brush seal W (FIG. 2) to the knife edge seal ring  10 , (FIG. 3) and form the air seal ring A of the present invention, a mounting ring  60  (FIG. 4) is provided. The mounting ring  60  is cylindrical and has a generally rectangular cross-sectional shape. The mounting ring  60  is formed to fit within the annular channel  50  formed in the knife edge seal ring  10  of FIG.  3 . The mounting ring  60  is typically formed of a comparable material, for example a super alloy known as 2{fraction ( 1 / 4 )} chrome 1 moly, to that of the mounting body  50  and seal ring. The mounting ring  60  has dimensions in conformance with those of the channel  50 . The mounting ring  60  may be attached to the body  22  of seal ring  10  by any suitable connecting mechanisms, but is preferably attached using a suitable number of circumferentially spaced, countersunk screws or bolts. These connectors extend upwardly through ports in the ring  60  into tapped sockets in the body portion  22  above channel  50 . The mounting ring  60  has an outer surface  62  conforming to fit against the outer surface  54  formed against channel  52 . The mounting ring  60  also includes a lower surface  64  adapted to fit against, and preferably of like dimensions to, the lower surface  56  in the shoulder  28 . The mounting ring  60  also includes an upper surface  66  extending inwardly from surface  62 . The upper surface  66  is adapted to fit against upper surface  52  formed in body portion  22  and extends inwardly to an inner surface  68  which is oriented in a plane parallel to the inner surface  10   a  of the first seal portion  10 . 
     The mounting ring  60  preferably has an annular slot or seat  70  formed extending upwardly above the surface  64 . The slot  70  is of dimensions capable of receiving the connector rim  42  of the brush seal segment  34 . However, with the present invention, the mounting ring  60  has an inner lip portion  72  extending inwardly (FIG. 5) beyond an inner diameter of the surface  10   a  of the first seal ring portion  10 . In this manner, the lip portion  72  forms a support shoulder for the mounting ring  60 . The thickness of the support shoulder by lip portion  72  is selected to meet the structural requirements for the particular seal ring and is not limited to the reduced area  46  shown in FIG.  1 . 
     The mounting ring  60  when fitted (FIG. 5) in the annular groove  70  in the first seal ring portion  10  extends inwardly at lip  72  a greater distance than the inner wall  10   a  of the first seal ring portion  10 , providing additional support and strength. The lip  72  so formed affords sufficient material and thickness to support and retain the mounting body  40  of brush seal segment  34  of the wire brush seal W in place during service use. The mounting body  40  may be attached to the mounting ring  60  in a like manner to the attachment of ring  60  to seal ring  10  described above. It is to be noted that the mounting ring  60  preferably has one or more knife edge seal members  74  disposed extending inwardly from the inner surface  68 . Preferably, the mounting ring  40  has a number of knife edge seals  74  formed on the mounting ring  60  to correspond to the number of knife edge seals removed when the annular channel  50  was formed. This permits addition of the wire brush seal W without reduction in the number of knife edge seals. 
     After the mounting ring  60  is secured to the first seal ring portion  10  and the wire brush mounting ring  40  attached, the improved and more efficient air seal ring A (FIG. 5) of the present invention is formed. The air seal ring A may have number of knife edge seals as the original air seal ring  10  of FIG.  1 . In addition, the air seal ring A has an improved wire brush seal segment  34  capable of providing a more efficient seal. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, and components, as well as in the details of the illustrated construction may be made without departing from the spirit of the invention.