Abstract:
A card seal with an annular arrangement of leaf elements, where each leaf element has a T shape with an upper ear section and a leaf section extending from the ear section. the leaf elements each include a first raised portion and a second raised portion that form a cross, the raised portions allowing for air to pass to bend ends on the leaf sections to form a floating air seal and to limit leakage flow across the leaf elements from one side to the opposite side.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit to U.S. Provisional Patent Application 61/225,456 filed on Jul. 14, 2009 and entitled FLOATING CARD SEAL. 
    
    
     FEDERAL RESEARCH STATEMENT 
     None. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a rotary machine, and more specifically to a method and an apparatus for sealing a rotary machine. 
     2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98 
     In an industrial gas turbine engine, rotary seals are required to provide a seal between a rotating part (the rotor) and a stationary part (the stator) of the engine and prevent a hot gas flow from passing through to temperature sensitive areas and to prevent leakage of the hot gas in order to increase the efficiency of the engine. Labyrinth seals or brush seals have been widely used in these engines but have limitations. Brush seals will wear relatively easily due to a constant rubbing of the brush ends on the rotating surface that forms the seal surface. Brush seals make good low rotation speed seals. The labyrinth or lab seals provide good sealing at higher rotational speeds without rubbing, but provide high leakages at lower rotational speeds because of a gap formed between the ends of the lab seal teeth or fingers and the stationary part of the casing or housing that forms the seal interface for the brush lab seal. In some cases, the lab seals are designed to rub against a honeycomb structure to provide an even lower leakage flow across the lab seal. 
     Prior art card seals include an annular arrangement of leaf plates that are stacked on top of one another, where one end of each leaf plate is secured to the seal casing while the opposite end rides on and over a rotating surface such as a rotor shaft in which the seal is to be formed. The card seals are made such that the leaf plates can have a slight pivot about the top end that is secured to the seal casing, the slight pivoting allowing for play during operation of the card seal. The prior art leaf plates are flat surfaces and form a small controlled air gap between adjacent leaf plates. Card seals are like a combination of labyrinth seals and brush seals combined into one seal. Because an upstream side of the card seal is at a higher pressure than the downstream side, the pressure differential can force leakage through the leaf plates because of any gap formed between adjacent leaf plates. When all of the gaps for all of the annular arrangement of leaf plates are counted, a large leakage flow is formed across the card seal. 
     U.S. Pat. No. 6,736,597 B2 issued to Uehara et al. on May 18, 2004 and entitled AXIS SEAL MECHANISM AND TURBINE and U.S. Pat. No. 6,874,788 B2 issued to Kono on Apr. 5, 2005 and entitled STRIP BUSH SEAL discloses prior art card seals in which the leaf elements are just plane flat pieces stacked one on top of another to form a full 360 degree annular arrangement of leafs around a shaft. Because the leaf elements are flat, any small space formed between adjacent leaf elements will provide for a direct fluid leakage path from one side of the leaf elements to the opposite side. 
     BRIEF SUMMARY OF THE INVENTION 
     A floating card seal made up of a number of leaf elements that have raised section for passage of a fluid such as air that will provide for a floating leaf element to form a floating card seal. The raised portions also form an obstruction to fluid leakage across the card seal where fluid would pass through adjacent leaf elements. The leaf elements of the card seal includes ends that are bent to form a floating seal forming surface so that the leaf elements will float above the surface instead of making contact therewith. 
     The leaf elements are T-shaped with a top end of the T being secured to a stationary casing of the card seal and the leaf element extending down from the T end toward the surface that the card seal rides over. In one embodiment, all of the leaf elements have the same shape and form. In another embodiment, two different shaped leaf elements are stacked in an alternating manner so that raised portions on the leaf elements do not directly line up but alternate from one leaf element to the next leaf element. 
     In another embodiment of the present invention, a process for treating the tip ends of the leaf elements for surface enhancement to reduce wear in a hard rub of the leaf section tip ends. A sand blaster is used to project etched glass beads coated with a dry lubricant to force the dry lubricant into the surface of the tip ends. This process is used on all of the leaf elements that form the annular arrangement of leaf elements that form the floating card seal. Any wear of the dry lubricant releases more dry lubricant. The dimples with impede the leakage. 
     In another embodiment, a process for testing card seal to quantify an air ride liftoff of the floating card seals of the present invention is disclosed. The process includes placing one of the leaf elements onto a turntable rotor such that the leaf element is fixed and the rotor rotates over the leaf element tip end floating surface. With the leaf element riding on the smooth surface of the turntable rotor, a laser directs a laser beam against a surface of the floating tip end of the leaf element that reflects the laser beam toward a photo pickup that will measure the angle θ in order to determine when a liftoff of the leaf element over the turntable rotor has occurred. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  shows a cross section side view of a stack of card seals of a first embodiment of the present invention. 
         FIG. 2  shows a front view of the card seals of  FIG. 1  of the present invention. 
         FIG. 3  shows an isometric view of two of the card seals of the first embodiment of the present invention. 
         FIG. 4  shows a side view of one of the card seals of the first embodiment of the present invention. 
         FIG. 5  shows a cross section side view of two of the card seals stacked together of the first embodiment of the present invention. 
         FIG. 6  shows a front view of the stack of card seals of the  FIG. 5  card seal arrangement. 
         FIG. 7  shows a top view of one of the card seals of the first embodiment of the present invention. 
         FIG. 8  shows a cross section side view of a stack of card seals of a second embodiment of the present invention. 
         FIG. 9  shows an enlarged view of the  FIG. 8  card seal arrangement. 
         FIG. 10  shows an orientation of the stack of card seals with respect to the seal surface of the rotor of the second embodiment of the present invention. 
         FIG. 11  shows a stack of 6 card seals of the second embodiment of the present invention. 
         FIGS. 12 and 13  show isometric views of the two card seal arrangements for the second embodiment of the present invention. 
         FIGS. 14 and 15  show isometric views of two of the card seals of the second embodiment with surface enhancement to reduce wear during hard rubbing of the seal tips. 
         FIG. 16  shows a cross section side view of a leaf element of the card seal with a wear enhancement coating. 
         FIGS. 17-19  show a process to quantify air ride liftoff of the card seals of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is an axial seal for a large turbo-machine, such as an industrial gas turbine engine, in which an axial seal is needed between a rotating part and a stationary part of the turbo-machine. The axial seal is intended to be an improvement in the type of seals that normally use brush seals or labyrinth seals to provide a seal against leakage of a hot gas flow through the turbo-machine. The turbo-machine of the present invention is a large frame heavy duty industrial gas turbine engine. However, the present invention is not limited to IGT engines, but could be used in an aero engine or even a steam turbine or a compressor in which the prior art labyrinth seals or brush seals are used. 
       FIG. 3  shows a view of two of the leaf elements  11  that, when stacked up, for a card seal of the present invention. Each leaf element  11  includes an ear section  12  and a leaf section  13  that extends from a middle of the ear section  12 . The leaf element  11  forms a cross and includes flow channels  15  and  16  in both the leaf section  13  and the ear section  12 . The flow channels are punched formed sections formed in the middle of these sections that form not flat surfaces on the flat ear and leaf sections  12  and  13 . The leaf elements  11  are punch and die stamped to form the finished element  11 . Also formed on the end of the leaf section  13  is a floating seal forming surface  14  that is bent upward from the flat surface of the leaf section  13  and includes a rounded out section in the middle and substantially aligned with the bended section of the leaf section  13 . 
     The floating card seal of the present invention is formed by stacking a number of the leaf elements  11  one on top of each other in a complete annular arrangement around the rotating part in which the seal is formed.  FIG. 1  shows a side view of three of the leaf elements  11  stacked on top of each other and extending from the stator  21  and in which the ends  14  of the leaf elements  13  ride over a smooth surface  23  of the rotor  22 .  FIG. 2  shows a front view of the card seal arrangement of  FIG. 1  in which the ear section  12  of the leaf element  11  is secured in annular grooves that are formed in the stator  21  to hold the number of leaf elements  11  that form the complete seal. The leaf section  13  extends from a middle of the ear section  12  and rides on the smooth surface  23  of the rotor  22 . Rounded sections  15  are seen in  FIG. 2  that are formed by the bended sections of the leaf and ear sections. The bent ends  14  of each leaf section forms an air riding surface for the leaf elements  11  so that the surfaces of the leaf element  11  and the rotor smooth surface  23  do not rub during operation of the floating card seal of the present invention. The raised channels  15  and  16  form flow channels for the fluid used to produce the air ride if needed. 
     Normal rotation of the leaf elements over the smooth surface of the rotor should be enough to produce the air riding or floating effect. However, to enhance the air riding effect, a compressible fluid such as air can be supplied through the flow channels  15  and  16  formed between adjacent leaf elements  11  to enhance or produce the air riding effect or floating effect of the floating card seal assembly. The flow channel forming surfaces of the leaf elements  11  also form parasitic leakage blocking members of the leaf elements to prevent leakage across the sides of the stacked leaf elements that form the card seal. 
       FIG. 4  shows a single leaf element  11  with a flow channel formed by the raised portion  16  in the ear section  12 .  FIG. 5  shows two leaf elements  11  stacked on top of each other and  FIG. 6  shows a front view of the stacked leaf elements  11  with the raised portions forming the flow channel  15  down the middle of the leaf section  13 .  FIG. 7  shows a top view of the leaf element  11  with the ear section  12  and the leaf section  13  with the locations of the raised portions  15  and  16  in both of the leaf and ear sections that form the flow paths for the fluid that enhances or forms the floating air riding capability of the floating card seal assembly. The slanted end  14  of the leaf section  13  is shown that forms the air riding surface. 
     The ear sections  12  of the leaf elements  11  can also be used to tune the spring by changing the ear  12  lengths or width together with the length of the leaf section  13  of the leaf element  11 . 
     In the first embodiment of the floating card seal shown in  FIGS. 1 through 3 , the individual leaf elements  11  that form the seal are the same leaf elements. Each leaf element can be formed by a punch and die stamp.  FIG. 8  shows a side view of the leaf elements  11  of the floating card seal extending out from the stator  21  with the leaf elements  11  being angled at around 5 degrees from the rotational axis of the stator  21 . In this embodiment, the leaf elements are around 0.7 inches in length with a spacing between adjacent tip ends  14  of around 0.06 inches. The leaf elements have a radius of around 28 inches measured from the tip ends  14 . Adjacent leaf elements  11 , when stacked on top of each other, form a gap of around 0.0014 inches based on a 28-inch seal radius with leaf elements  11  of around 0.005 inches in thickness.  FIG. 9  shows this arrangement and  FIG. 10  shows a stack of leaf elements  11  with a 5 degree slant from an axis of the stator  21 . 
       FIGS. 10 and 11  show a second embodiment of the floating card seal of the present invention in which the leaf elements that form a stack of the floating card seals is formed from two different leaf elements stacked in an alternating series.  FIG. 12  shows a first leaf elements  32  with two raised portions  33  symmetric to a long axis of the leaf element  32  and  FIG. 13  shows a second leaf element  31  with one raised portion  34  symmetric to the long axis of the second leaf element  31 . The raised portions  33  and  34  function as the same in the first and earlier embodiment, which is to provide for a flow channel for addition fluid used to produce the air riding effect and to block any parasitic leakage across adjacent leaf elements  31  and  32 . 
       FIG. 11  shows a cross section view of a stack of six of the leaf elements used in the second embodiment of the floating card seal of the present invention. The first leaf elements  31  are alternating with the second leaf elements  32  so that the raised portion  34  forms a flow channel along a middle of the long axis of the leaf section and the two raised portions  33  form two flow channels on both sides of the flow channel formed by the single raised portion  34 . These raised portions  33  and  34  also form abutment surfaces between adjacent leaf elements  31  and  32  to block parasitic leakage across the card seal. 
     The leaf elements  31  and  32  of the second embodiment are stacked alternating to form a complete annular arrangement of leaf elements around the stator so that the leaf section ends form an air riding surface over the smooth surface of the rotor as in the above first embodiment. The leaf section ends can also include the slanted end surfaces of the first embodiment.  FIG. 12  shows the second leaf element  32  and  FIG. 13  shows the first leaf element  31 . 
       FIGS. 14-16  show a process for treating the tip ends of the leaf elements for surface enhancement to reduce wear in a hard rub of the leaf section tip ends. A sand blaster  41  is used to project etched glass beads coated with a dry lubricant (such as graphite, moly-disulfide, etc.) to force the dry lubricant into the surface  36  of the tip ends. This process is used on all of the leaf elements that form the annular arrangement of leaf elements that form the floating card seal.  FIG. 16  shows a cross section view through one leaf element with surfaces dimples in the leaf element containing the dry lubricant represented in this figure by the thin outer layer on top of the leaf element surface with the dimples. Any wear of the dry lubricant releases more dry lubricant. The dimples with impede the leakage. 
       FIGS. 17-19  show a process to quantify an air ride liftoff of the floating card seals of the present invention. The process includes placing one of the leaf elements ( 11 ,  31  or  32 ) onto a turntable rotor  51  such that the leaf element is fixed and the rotor rotates over the leaf element tip end floating surface  14 . With the leaf element  11  riding on the smooth surface of the turntable rotor  51 , a laser  52  directs a laser beam against a surface of the floating tip end  14  of the leaf element  11  that reflects the laser beam toward a photo pickup  53  that will measure the angle θ in order to determine when a liftoff of the leaf element  11  over the turntable rotor  51  has occurred.  FIG. 18  shows applying a positive and a negative charge to the turntable rotor  51  and the leaf element  11  is order to also detect for a liftoff. When the leaf element makes contact with the surface of the turntable rotor  52 , the electric circuit is closed. When a liftoff occurs, the circuit is open. This open and closed circuit can also be used to detect for a liftoff of the leaf element form the rotating surface.