Patent Publication Number: US-8974188-B2

Title: Blade clip

Description:
BACKGROUND 
     This invention relates generally to blades in a gas turbine engine, and specifically to clips to connect a blade root to a rotor disk. 
     A blade in a gas turbine engine has a root, which connects to the rotor disk, and a tip opposite the root. The thickness of the blade greatly changes over a short length at the root. The root enables the airfoil to withstand typical operational loads from rotation and bending and loads from foreign object strikes. The root typically slides into a slot in a rotor disk to hold the airfoil in place while the rotor disk is spinning. 
     SUMMARY 
     A clip to connect a blade to a rotor disk includes a locking mechanism shaped to engage a complementary slot extending into the bottom surface of the blade root in a spanwise direction; a support connected to the locking mechanism extending the length of the bottom surface of the root in the chordwise direction; and first and second arms extending radially inward converging in the axial direction so that the arms are closer at their distal ends to engage the rotor disk. 
     A method of locking a blade to a rotor disk with slots includes sliding a locking mechanism of a clip into a complementary slot extending from the bottom surface of blade root in the spanwise direction until a support of the clip sits directly below the bottom surface of the blade root; sliding the clip and blade root axially into a slot in the rotor disk; and bending a first arm on the clip radially inward to engage a concave surface on the rotor disk. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a connection between a blade, a clip and a disk. 
         FIG. 1B  shows a cross-sectional view of the connection between the blade, the clip and the disk of  FIG. 1A . 
         FIG. 1C  shows an exploded perspective view of the clip and the blade of  FIG. 1A . 
         FIG. 2A  shows a perspective view of a second embodiment of a clip with a root. 
         FIG. 2B  shows a cross-sectional view of  FIG. 2A . 
         FIG. 3  shows a view of a clip connected to a root and with an arm axial for connecting to a disk. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  shows a connection between blade  32  and disk  34  in a gas turbine engine,  FIG. 1B  shows a cross-sectional view of the connection between blade  32  and disk  34 , and  FIG. 2C  shows an exploded perspective view of clip  54  and blade  32 .  FIGS. 1A-1C  include blade  32  with airfoil  36 , leading edge  38  and trailing edge  40  in a chordwise direction, firtree root  44  opposite a tip (not shown) in a spanwise direction, pressure side  46  and suction side directly opposing pressure side  46  (not shown) and clip  54 . Firtree root  44  includes bottom surface  50  and locking mechanism slot  52 . Disc  34  includes firtree slots  56  and web  57  with concave surface  59 . Firtree root  44  is inserted in slot  56  in disc  34 . Clip  54  includes locking mechanism  58  with head  60  (with flat upper surface  68  and rounded sides  70 ) and neck  62 , support  64 , shoulders  65  and arms  66  with convex inner surface  67 . Dimensions shown include length of root L R  and length of slot L S . While only blade  34  is illustrated, it is to be understood that in operation, a disk  34  would include a plurality of slots  56 , and a blade that is substantially similar to blade  32  would be inserted into each slot  56  in disc  34 , and a clip  54  would connect each blade  32  to disk  34 . 
     Firtree root  44  of blade  32  and slot  56  in disc  34  are shaped so that root  44  slides into slot  56  (i.e., the shapes are complementary). Disc  34  spins, rotating blade  32 . Root  44  retains blade  32 , resisting the centrifugal load when disk  34  is spinning during engine operation. 
     Clip  54  engages root  44  through locking mechanism  58  and slot  52 . In one embodiment, length of slot L S  can be about ⅓ of the length of root L R . Head  60  of locking mechanism is larger in the chordwise direction than neck  62  to secure clip  54  to root  44  and to give more contact area between clip  54  and root  44  for load transfer. In the embodiment shown, head  60  includes a flat upper surface  68  with rounded sides  70 . Clip  54  engages rotor disk  34  through arms  66  bending radially inward toward each other so that convex inner surfaces  67  of arms  66  engage concave surface  59  of web  57  on forward and aft sides of disk  34 . Support  64  of clip  54  supports bottom surface to distribute loads from root  44  to disk  34  and to keep blade  32  from shifting on disk  34 . Clip  54  is generally one integral part and can be made of titanium (including alloys), aluminum (including alloys) or other materials depending on engine requirements. 
     Clip  54  with locking mechanism  58 , support  64  arms  66  secures blade  32  to disk  34 , helping to reduce stress on root  44  and prevent shifting on disk  34 . Past systems either didn&#39;t include a clip when connecting blade to disk, or used a small clip with short radial arms and a small pin with radial sides. Clip  54  with locking mechanism  58  that includes head  60  which is larger than neck  62  and engages a slot extending into the bottom surface of root  44 , provides a large interface contact area between clip  54  and blade  32  (upper surface  68  and sides  70 ), distributing loads through the thickness of root  44 . By extending radially inwards to engage concave surface  67  on disk  34 , arms  66  provide a secure connection between blade  32  and disk  34 , connecting with a tight fit to disk  34  to transfer part of the centrifugal load to disk  34 . 
       FIG. 2A  shows a perspective view of another embodiment of clip  54 ′ with root  44 ′, and  FIG. 2B  shows a cross-sectional view of  FIG. 2A .  FIGS. 2A-2B  include blade  32 ′ with leading edge  38 ′, trailing edge  40 ′, firtree root  44 ′, and clip  54 ′ with locking mechanism  58 ′. Locking mechanism  58 ′ includes head  60 ′ and neck  62 ′, support  64 ′ and arms  66 ′. Firtree root  44 ′ includes bottom surface  50 ′ and locking mechanism slot  52 ′. Dimensions shown include length of root L R , length of head L H  and length of neck L N . In this embodiment, L H  is about ⅕ of L R , and L N  is about ⅙ of L R . Other embodiments can have different ratios. 
     In the embodiment shown in  FIGS. 2A-2B , locking mechanism  58 ′ has a bulbous shaped cross-section, with head  60 ′ having a generally oval or round shape. Locking mechanism  58 ′ provides a secure connection between clip  54 ′ and root  44 ′ and provides a substantial amount of mass in head  60  to shear some of the load transferring to disk  34 ′, thereby minimizing stresses in root  44 ′. Support  64 ′ and arms  66 ′ are substantially the same as respective support arms  64 ,  66  shown in  FIGS. 1A-1C . 
       FIG. 3  shows a cross-sectional view of clip  54  connected to root  44  and with an arm  66  axial for connecting blade  32  to a disk (not shown). Blade  32  includes firtree root  44  (with bottom surface  50  and locking mechanism slot  52 ) that is coupled to clip  54  (with locking mechanism  58  with head  60  and neck  62 , support  64 , shoulders  65  and arms  66  with convex inner surfaces  67 ). In this embodiment, one arm  66  is bent axially (i.e., towards the longitudinal axis of blade  32 ) for insertion of blade  32  into slot  56  (see  FIG. 1A ) of disk  34 . 
     Blade  32  with clip  54  slides axially into slot  56  ( FIG. 1A ) in disk  34 . Arm  66  can then be bent around disk  34  when connecting blade  32  to disk  34  ( FIG. 1A ). Alternatively, both arms  66  can start out axial and then both be bent when blade  32  with clip  54  is inserted into slot  56  ( FIG. 1A ). In other embodiments, arms  66  can start out somewhat pre-bent and then bent further, when engaging concave surface  67  of disk  34  ( FIG. 1A ). 
     In summary, clip  54 ,  54 ′ with locking mechanism  58 ,  58 ′, support  64 ,  64 ′ and arm  66 ,  66 ′, helps to transfer centrifugal load and secure blade  32 ,  32 ′ to disk  34 ,  34 ′. Locking mechanism  58 ,  58 ′ with head  60 ,  60 ′ and support that is greater in length in the chordwise direction than neck  62 ,  62 ′ and support  64 ,  64 ′ help to minimize stress in root  44 ,  44 ′ by providing a greater contact area to transfer loads to disk  34 . Arms  66 ,  66 ′ with convex surfaces  67 ,  67 ′ wrap radially inwards, converging in the axial direction so that the arms are closer at their distal ends than at shoulders  65 ,  65 ′ to secure clip  54 ,  54 ′to concave surfaces  59  of disk  34 , minimizing or preventing shifting of blade  32 ,  32 ′ when in operation. By distributing centrifugal force loads through the thickness of root  44 ,  44 ′ and transferring part of the loads to disk  34 , and providing a stronger connection to minimize or prevent blade shifting, clip  54 ,  54 ′ improves blade  32  performance and durability, thereby improving overall life of blade  32 . 
     While clip  54 ,  54 ′ is shown to connect a blade with a firtree root  44  to a disk  32 , other types of blades with other types of roots could be used. Additionally, the embodiments shown are for example purposes only, and clip  54  could be sized differently according to system requirements. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.