Abstract:
A system and method for securing a blade within a disk so as to eliminate the need for permanently deforming materials associated with the blade disk is disclosed. A recess is formed generally within each slot used to secure a blade within the disk. A retaining insert is positioned within the recess and a wedge insert is positioned within a slot of the retaining insert, such that a pressure is applied to the retaining insert thereby deflecting the retaining insert into a pre-set radial position to prevent axial movement of the blade within the slot of the disk.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     TECHNICAL FIELD 
     The present invention generally relates to a rotating blade and disk of a gas turbine engine and more specifically to a system and method of securing the blade to the disk. 
     BACKGROUND OF THE INVENTION 
     Blades of a gas turbine engine have an airfoil and are held within a rotating disk by an attachment. The disk rotates at a high rate of speed or revolutions per minute in order to compress a fluid passing through, such as air. For example, an axial compressor typically comprises a plurality of stages, where each stage includes a set of stationary compressor vanes which direct a flow of air into a rotating disk of compressor blades, where each stage of the compressor decreases in diameter, causing the pressure and temperature of the air to increase. 
     Axial compressors having multiple stages are commonly used in gas turbine engines for increasing the pressure and temperature of air to a pre-determined level at which point a fuel can be mixed with the air and the mixture ignited. The hot combustion gases then pass through a turbine to provide either a propulsive output or mechanical output. 
     Despite operating in a relatively low temperature environment, compressor blades still require routine inspection and maintenance, which typically requires removal from the disk. However, prior art blade retention mechanisms, typically utilize staking or rolling of material from the disk over material of the compressor blade in order to prevent the blade from sliding within the disk slot. Staking is defined as the process of plastically deforming material using a tool similar to nail punch. While this process accomplishes the purpose of retaining the blade within the slot, in order to remove the blades, the rolled material must also be removed, leaving behind the holes and divots shown in  FIGS. 2 and 3 . After multiple times staking or rolling the disk material, the disk itself must be repaired or replaced. Other ways of securing blades in place include staking material of a replaceable staking insert as discussed in U.S. Published Patent Application 2009/0077795. 
     SUMMARY 
     In accordance with the present invention, there is provided a novel and improved system and method for securing a blade within a disk so as to eliminate the need for permanently deforming materials associated with the blade disk. 
     The present invention is directed towards a system and method for securing a compressor blade within a disk. In a first embodiment, a rotating assembly is provided comprising a disk having a plurality of slots with each slot having a retaining recess. A plurality of blades is positioned within the slots of the disk. A retaining insert is positioned within a portion of the slot and secures a blade within the slot by bending upward after assembly due to a load applied by a wedge insert, and remain locked in a pre-set radial position relative to blade root. 
     In an alternate embodiment of the present invention, a retaining mechanism is provided for securing a blade to a rotor disk. The retaining mechanism comprises a retaining recess positioned within the rotor disk and a retaining insert sized to fit within the recess. An angled wedge insert is positioned within a slot of the retaining insert so as to displace and secure in radial position a portion of the retaining insert. 
     In yet another embodiment of the present invention, a method of retaining a blade within a rotor disk is disclosed. The method comprises placing a retaining insert into a retaining recess of the rotor disk, depressing an upper portion of a retaining insert, inserting a blade into a slot of a rotor disk and placing a wedge insert into a slot of the retaining recess so as to exert a force in a radially outward direction on an upper portion of the retaining insert so as to locate the upper portion of the retaining insert in a preset radial location preventing the removal of the blade from the slot of the rotor disk. 
     Additional advantages and features of the present invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. The instant invention will now be described with particular reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The present invention is described in detail below with reference to the attached drawing figures, wherein: 
         FIG. 1  is a cross section view of a portion of an axial compressor in which the present invention is capable of operating; 
         FIG. 2  is a perspective view of a portion of a compressor utilizing a prior art means of securing the compressor blades to the rotor disk; 
         FIG. 3  depicts an end view of a slot of the rotor disk in accordance with the prior art; 
         FIG. 4  is an end view of a portion of a rotor disk assembly in accordance with an embodiment of the present invention; 
         FIG. 5  is an exploded view taken in cross section depicting an embodiment of the present invention; 
         FIG. 6  is a perspective view taken in cross section depicting an embodiment of the present invention in which the blade is installed in the rotor disk; 
         FIG. 7  is a flow chart identifying a method of securing a blade within a slot of a rotor disk. 
     
    
    
     DETAILED DESCRIPTION 
     The subject matter of the present invention is described with specificity herein to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventors have contemplated that the claimed subject matter might also be embodied in other ways, to include different components, combinations of components, steps, or combinations of steps similar to the ones described in this document, in conjunction with other present or future technologies. 
     Referring initially to  FIG. 1 , a portion of an axial compressor  100  is shown in cross section. The engine in which the compressor  100  operates includes a centerline axis A-A about which the compressor blades and turbine blades rotate. As discussed above, a gas turbine engine draws air into compressor  100  through an inlet  102  and the air passes through a plurality of stages of stationary vanes  104  and rotating blades  106 . The pressure and temperature of the air increases as the air is further compressed into a smaller volume as the air passes through the compressor and towards a combustion system (not shown). 
     Referring now to  FIGS. 4-6 , an embodiment of the present invention is depicted. Referring initially to  FIG. 4 , the present invention is shown in an end view. A portion of a rotating disk assembly is shown comprising a rotor disk  400 , a plurality of slots  402  positioned about the circumference of rotor disk  400 . Within each slot  402  is a retaining recess  404 . The retaining recess  404  extends from a face  406  of the disk  400  a depth into the disk  400 . Located within each slot  402  of the disk  400  is a blade  408 . The rotating disk assembly also comprises a plurality of retaining inserts  410  positioned within each of the retaining recesses  404 . 
     Referring now to  FIGS. 5 and 6 , each of the retaining inserts  410  also has a slot  412  located therein. The slot  412  divides the retaining insert  410  into an upper portion  414  and a lower portion  416 . The slot  412  extends across an entire width of the retaining insert  410 , as shown in  FIG. 4 . The rotor disk assembly also comprises a plurality of wedge inserts  418 , where each wedge insert  418  is positioned within a slot  412 . The wedge insert  418  is of generally triangular cross section, but this is only an exemplary wedge insert. As one of ordinary skill in the art understands, embodiments of the wedge insert  418  are not limited to the sides of the wedge being flat or parallel. Other embodiments of the wedge insert  418  can be utilized, including gradually curving faces of the wedge. The wedge insert  418  is positioned and sized such that when the wedge insert  418  is placed in the slot  412 , the wedge insert  418  pushes the upper portion  414  of the retaining insert  410  radially outward and locks the upper portion  414  radially in position so that it contacts a portion of the attachment region of blade  408 , as shown in  FIG. 6 . The wedge insert  418  has a locking feature  422 , which engages locking step  424  and retains wedge insert  418  axially in position relative to retaining insert  410  after assembly. As discussed above, and depicted in  FIGS. 2 and 3 , one of the shortcomings of the prior art is the rolling or staking of disk material required to secure the blade in the disk slot. An additional shortcoming of the prior art is that the magnitude of deformation caused by the staking is highly variable depending on the skill of the installer. The present invention, as depicted in  FIGS. 4-6  provides for a retaining mechanism to a blade  408  without deforming the rotor disk  400 . The retaining insert  410  provides retention block  420  to secure the blade within the slot  402 . 
     The retention block  420  extends from the upper portion  414  of the retaining insert  410 . The retention block  420  is configured to contact a surface of the blade  408  so as to prevent axial movement of the blade  408  within the slot  402 . In an embodiment of the invention, the retention block  420  has a generally triangular cross sectional shape. This is but one embodiment and the shape of the retention block  420  can vary depending on the size and shape of the blade attachment and slot in the disk. For example, the retention block  420  depicted in  FIG. 6  does not extend the width of the retaining insert  410 . The size of the retention block  420  could be increased so as to span the width of the retaining insert  410 . When it is desired to remove the blade  408  from the slot  402  of the disk  400 , the retention block  420  can be ground off so the blade  408  can be removed from the slot  402 , or the wedge insert  418  can be removed from the slot  412  of the retaining insert  410 . 
     The retaining insert  410  has a slot  412 , as discussed above. For an embodiment of the present invention, the slot  412  has a keyhole cross sectional shape as shown in  FIG. 5 . The keyhole cross sectional shape allows for the upper portion  414  to flex and move relative to the lower portion  416  without creating a concentration of plastic strain that could result in a crack within the retaining insert  410 . Because of the movement between the upper and lower portions, it is necessary for the end of the slot  412  to be rounded so that when the upper portion  414  moves relative to the lower portion any stresses at the end of the slot  412  are dissipated. The convex corner of the slot  412  forms a locking step  424 . When the wedge insert  418  is fully inserted into slot  412 , the wedge locking feature  422  engages the locking step  424  to prevent unintended removal of the wedge insert  418  from the slot  412 . 
     The retaining insert  410  and wedge insert  418  can be fabricated from a steel alloy such as AISI  4340 . This alloy is acceptable to use for fabricating the retaining insert  410  and wedge insert  418  because it provides excellent corrosion resistance properties and wear capability. The retaining inserts  410  are solution annealed while the wedge insert  418  is tempered to a high hardness. This allows the wedge insert  418  to maintain maximum elasticity so as to eliminate plastic deformation when the wedge is inserted into the retaining insert  410 . This is but one embodiment of the materials that may be used for fabricating the retaining insert  410  and wedge insert  418 . 
     While it is possible to apply a wear reduction coating to the surface of the slot  412  of the retaining insert  410  or the wedge insert  418 , because of the hardening and solution annealing processes outlined above, the additional step of applying a coating is not believed to be necessary. 
     Referring to  FIG. 7 , a method  700  is provided for retaining a blade within a rotor disk. In a step  702 , a retaining insert  410  is placed within a retaining recess  404  of the rotor disk. Once the retaining recess is placed within the rotor recess  404 , in a step  704 , the upper portion  414  is depressed to provide clearance between the blade  408  and the retention block  420 . Once the path of the blade  408  is clear, in a step  706 , the blade  408  is inserted into the slot  402  of the rotor disk  400 . Then, in a step  708 , a wedge insert  418  is placed in the slot  412  of the retaining insert  410 . The wedge insert, when placed in the slot of the retaining insert, applies a force to the upper portion  414  of the retaining insert and locks it radially in place, which either applies a force to the blade and/or places a retention block of the retaining insert into contact with the blade. The upper portion of the retaining insert bends upward due to a force applied by the wedge insert and generally returns to its designed position relative to the bottom of blade  408 , as shown in  FIG. 5 . 
     The present invention can be applied to both newly manufactured disks and blades as well as part of an overhaul to existing hardware. For incorporation as part an overhaul, disk material within the slot  402  can be removed to form the recess  404 . 
     The present invention has been described in relation to particular embodiments, which are intended in all respects to be illustrative rather than restrictive. Alternative embodiments will become apparent to those of ordinary skill in the art to which the present invention pertains without departing from its scope. 
     From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects set forth above, together with other advantages which are obvious and inherent to the system and method. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and within the scope of the claims.