Abstract:
A method and apparatus for repairing damaged fins in a labyrinth seal, the seal without the use of welding or metallurgical bonding. The method comprises the steps of removing a section of the shaft containing the damaged fins, and providing a sleeve with replacement fins.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to repair of a labyrinth seal and a replacement component for use therein. 
       BACKGROUND OF THE ART 
       [0002]    The invention relates to repair of a labyrinth seal, particularly in a fan rotor in gas turbine engines wherein the seal is formed on a shaft that rotates in relation to another moving or stationary runner surface. 
         [0003]    The air seal comprises the fan rotor with labyrinth seal fins, which rotates, and a concentric shaft known as the seal runner which is stationary. Frequently, a bearing contained in a bearing compartment supports the motion of the two shafts. The bearing compartment contains oil lubricant which must be contained within the compartment. The oil must be confined to the bearing chamber by using a seal. In this instance the oil is retained in the bearing chamber by using an air pressurized labyrinth seal. 
         [0004]    A labyrinth seal is useful in sealing an air-oil interface in gas turbine engines. If the seal fins are damaged or incorrectly manufactured, however, the sealing of the bearing compartment may be jeopardized and result in oil leakage. If the oil leakage is excessive, the fan rotor will have to be replaced and scrapped. This is expensive and wasteful. Alternatively, the seal may be repaired by removing and replacing only the damaged fins. Challenges in repairing the damaged fins include the limited line of sight access of the fins within the fan rotor, the structural integrity of the fan rotor and the precision of the labyrinth seal dimensions. 
         [0005]    Existing repair methods use weld repair build-up and subsequent re-machining of the fins to the required dimensions, however this approach presents several drawbacks. Accordingly, there is room for improvement. 
       SUMMARY OF THE INVENTION 
       [0006]    One aspect of the present invention is a method for replacing at least one damaged fin in a labyrinth seal comprising the steps of: removing a section of the labyrinth seal containing the damaged fin, thus forming a recess; providing a sleeve with at least one replacement fin; and fitting the sleeve into the recess, the sleeve being attached to the labyrinth seal by way of an interference fit with the labyrinth seal. 
         [0007]    Another aspect of the present invention is a sleeve for replacing at least one damaged fin of a labyrinth seal, the damaged fin being on a section removed from the labyrinth seal, thus forming a recess, the sleeve comprising at least one replacement fin, wherein the sleeve fits into the recess and is attached by way of an interference fit. 
         [0008]    Another aspect of the present invention is a turbine engine having a labyrinth seal, the labyrinth seal having a plurality of fins, wherein the labyrinth seal comprises a sleeve attached by way of an interference fit, and at least one of the plurality of fins is formed on the sleeve. 
         [0009]    Features that distinguish the present invention from the background art will be apparent from review of the disclosure, drawings and description of the invention presented herein. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In order that the invention may be readily understood, one embodiment of the invention is illustrated by way of example in the accompanying drawings. 
           [0011]      FIG. 1  shows an axial cross-section through a turbo-fan gas turbine engine. 
           [0012]      FIG. 2  is cross-section showing a section of a fan rotor with a labyrinth seal. 
           [0013]      FIG. 3  is a close-up cross-section of the labyrinth seal in the fan rotor, showing a damaged section that is to be removed. 
           [0014]      FIG. 4  is a sleeve containing replacement fins in accordance with one embodiment of the invention. 
       
    
    
       [0015]    Further details of the invention and its advantages will be apparent from the detailed description included below. 
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0016]      FIG. 1  shows an axial cross-section through a turbo-fan gas turbine engine. It will be understood however that the invention is equally applicable to any type of engine with a combustor and turbine section such as a turbo-shaft, a turbo-prop, or auxiliary power units. Air intake into the engine passes over fan blades  1  in a fan case  2  and is then split into an outer annular flow through the bypass duct  3  and an inner flow through the low-pressure axial compressor  4  and high-pressure centrifugal compressor  5 . Compressed air exits the compressor  5  through a diffuser  6  and is contained within a plenum  7  that surrounds the combustor  8 . Fuel is supplied to the combustor  8  through fuel tubes  9  which is mixed with air from the plenum  7  when sprayed through nozzles into the combustor  8  as a fuel air mixture that is ignited. A portion of the compressed air within the plenum  7  is admitted into the combustor  8  through orifices in the side walls to create a cooling air curtain along the combustor walls or is used for cooling to eventually mix with the hot gases from the combustor and pass over the nozzle guide vane  10  and turbines  11  before exiting the tail of the engine as exhaust. 
         [0017]      FIG. 2  shows an axial cross-section through a turbo-fan gas turbine engine. It will be understood however that the invention is equally applicable to any type of turbine, such as a steam turbine, or any rotary engine requiring repair to labyrinth seals. 
         [0018]    A fan rotor in the gas turbine engine comprises an inner shaft  12  and a concentric outer stationary shell  13 . Bearings  14  in an enclosed bearing compartment  15  supports the rotation of the inner shaft  12  relative to the shell  13 . Integral with the inner shaft  12  is a labyrinth seal  16 , with a plurality of fins  17  in close proximity to a seal runner  18  on the bearing compartment. When the fan rotor is in operation, air pressure from the inside of the shaft  12  flows through radial holes in the shaft and flows through the radial gap in the air seal thus preventing the oil from escaping. 
         [0019]    In  FIG. 3 , the labyrinth seal  16  with fins  19  is shown in greater detail. Repair of the damaged fins  19  is carried out by first removing a section from the inner shaft  12  containing the damaged fins  19 , to form a recess  20  as indicated. In addition to removing damaged fins  19 , other neighbouring fins may be removed, to facilitate the step of machining or removing fins  19  to form a recess  20 . Preferably, the removed section forms a recess  20  that is relatively shallow to minimize material removed and avoid weakening the inner shaft  12 . This may be done by machining or grinding off the section to avoid heat damage which may be caused by other removal methods. The removed section may contain only the damaged fins  19 , other undamaged fins  17 , or all fins on the labyrinth seal  16  depending on the needs of the application. 
         [0020]    Shown in  FIG. 4  is a sleeve  21  containing replacement fins  22 . Preferably, the replacement fins  22  are equal in number and arrangement to the removed fins. The sleeve  21  is designed to form a tight interference fit between the interior of the sleeve  21  and the exterior of the recess  20  formed by removing the section as described above. Because the replacement fins  22  are already machined on the prefabricated sleeve  21 , the problems associated with limited access space and need for precise dimensions are overcome. 
         [0021]    The sleeve  21  is then fitted into the inner shaft  12  by interference fitting techniques known in the art. One preferred method of interference fitting is to heat up the sleeve  21  to achieve an expansion of the sleeve diameter, and to cool down the inner shaft  12  to achieve a shrinkage of the shaft diameter. The expanded sleeve  21  is fitted over the shrunken inner shaft  12  and both are allowed to return to room temperature. This causes the sleeve  21  and the inner shaft  12  to engage each other in a tight fit. Other interference fitting techniques are possible, such as press fitting with a hydraulic ram or clamping. As shown in  FIG. 3 , the sleeve  21  may have a radial flange  23  to limit the motion of the sleeve  21  relative to the recess  20  and ensure a positive axial engagement. As a result, the sleeve  21  is held in place by friction and interference, and no welding or metallurgical bonding is required. 
         [0022]    The use of an interference fit instead of an interlocking fit between the inner shaft  12  and the sleeve  21  allows for simpler machining operations. This is not only quicker and less expensive, but also reduces possible wear to the parts. Additionally, the removed section can be shallow so that the strength of the inner shaft  12  is not significantly reduced. 
         [0023]    Although the above description relates to a specific preferred embodiment as presently contemplated by the inventor, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described herein.