Patent Publication Number: US-9404377-B2

Title: Turbine blade and non-integral platform with pin attachment

Description:
This application is a continuation of U.S. patent application Ser. No. 13/227,603, filed 8 Sep. 2011. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED DEVELOPMENT 
     Development for this invention was supported in part by Contract No. DE-FC26-05NT42644, awarded by the United States Department of Energy. Accordingly, the United States Government may have certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to means for attaching blades and platforms to a turbine disc, and particularly to attaching platforms that are non-integral with the blades. 
     BACKGROUND OF THE INVENTION 
     A gas turbine blade can be cast of a high-temperature metal alloy in the form of a single crystal per blade to maximize strength. It is difficult and expensive to reliably cast an integral platform in a single-crystal blade casting, due to the complexity of the blade/platform shape and the corresponding complexity and size of the casing mold. Therefore, non-integral platforms have been attached to the turbine disk between blades. 
     For example, U.S. Pat. No. 4,621,979 shows non-integral platforms mounted by a pin and hinge structure. In this patent, a relatively simple blade shape is shown. However, modern turbine blades have a high pitch angle relative to the turbine axis, and high camber and thickness. This geometry requires a platform with a complex asymmetric perimeter, which complicates designing a platform that can be mounted and replaced between the blades. Axial mounting would require a very narrow platform of constant curvature. Radial mounting is difficult regarding sealing around the platform edges, and limiting asymmetric cantilevered centrifugal stress on the platform. 
     The present invention solves these problems. It allows the platforms to be mounted and removed radially, and to be sealed without removing any blades, thus providing fast platform replacement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in the following description in view of the drawings that show: 
         FIG. 1  is a perspective view of a turbine blade and two adjacent platforms mounted on the circumference of a turbine disk. 
         FIG. 2  is a top or radially outer view of  FIG. 1 . 
         FIG. 3  is a sectional view taken along line  3 - 3  of  FIG. 2 . 
         FIG. 4  is an axially front view looking aft at three turbine blades in a disk. The right platform is being mounted by tilted radial insertion. 
         FIG. 5  is a bottom or radially inner view of  FIG. 1 . 
         FIG. 6  is a bottom view of a detached platform. 
         FIG. 7  is a partial perspective view of a blade root, showing a seal wire in a slot. 
         FIG. 8  is a sectional view as in  FIG. 3 , showing an optional damper pin. 
         FIG. 9  shows a seal slot embodiment with an upper wedge portion. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a turbine blade  24  with a suction side  26 , a leading edge  27 , a pressure side  28 , a trailing edge  29 , and a shank  30 . The shank may be formed in the known and illustrated fir tree shape for mounting to a turbine disk  32  by axial insertion into a mating slot  34  as known in the art. Herein, the terms “axial” and “radial” mean with respect to the disk rotation axis. Adjacent non-integral platforms  36 ,  38  are mounted individually to the disk  32  by a respective pin or bolt  40 , for example with a clevis or hinge attachment  42 . 
       FIG. 2  is a top or radially outer view of  FIG. 1 . Each platform  36 ,  38  has rotationally forward edge portions,  44 A (or optionally  44 B) and  45 , and rotationally rearward edge portions  46 ,  47  with respect to the rotation direction  48  of the disk. Each platform may have one or more rotationally rearward edge lap portions  50  that underlie a forward edge portion  45  of the adjacent platform, forming a ship lap that eliminates cantilevered centrifugal bending of the rearward portions  47  of the platforms. A rotationally rearward central edge portion  46  may underlie a shelf  49  on the suction side of the adjacent blade for this same reason. The rotationally forward central edge portion  44 A may follow the camber of the pressure side  28  of the adjacent blade  24 , or it may follow a lesser curvature  44 B. Herein “less curved” means a curve with a larger average radius (i.e. straighter) than another curve. For example the edge  44 B may follow a circular arc between the leading and trailing edges  27 ,  29  of the blade  24 , following a ridge  52  on the pressure side  28  of the blade. 
       FIG. 3  is a sectional view taken along line  3 - 3  of  FIG. 2 , showing the rotationally forward central edge portion  44 B of platform  38  overlying a seal element  51  on the ridge  52  on the pressure side of the blade. This forward central edge portion  44 B does not underlie a shelf on the pressure side of the blade, so as to allow mounting of the platform by tilted radial insertion as later described. Wedge portions  64  on the respective edges  46 ,  44   a  of the platforms  36 ,  38  cause the seal element  51  to wedge against the seal slot under centrifugal force for a tight seal. Cooling channels  53  may be provided in the blade as known. 
       FIG. 4  is an axially front view looking aft at three turbine blades  23 ,  24 ,  25  mounted in a disk  32 . Each blade has a pressure side  26 , a suction side  28 , and a shank  30 . Each shank is mounted to a turbine disk  32  by a fir tree structure. Platform  36  is mounted to the disk between the pressure side  28  of the first turbine blade  23  and the suction side  26  of the second turbine blade  24 . Platform  38  is illustrated in the process of being mounted to the disk between the pressure side  28  of the second turbine blade  24  and the suction side  26  of the third turbine blade  25 . In order to allow radial insertion  57  of the platform  38 , the platform attachment  42  provides room to tilt the platform  38  at an angle  60  during mounting to provide mounting clearance between the rotationally rearward edge portions  50  and the overlapping portions  45  of the adjacent platform (not shown), and to provide clearance between the rearward edge portion  46  and the overlapping suction side shelf  49 , if any, of the adjacent blade  25 . 
       FIG. 5  is a bottom or radially inner view of  FIG. 1 , showing cooling channels  53  in the blade shank  30  and lugs  54  on the platforms  36 ,  38  for the mounting pins or bolts  40 .  FIG. 6  is a bottom view of a detached platform  36 . 
       FIG. 7  is a perspective view of a root portion of a blade, showing a seal wire  51  in a seal slot  58 . The wire and slot may encircle the blade as shown. The wire may be formed of a cobalt alloy, and may have a gap  60  at the trailing edge. The seal slot may be formed in a raised portion of the blade around the blade root. The pressure side ridge  52  is part of this raised portion, on which the seal slot and wire may follow the pressure side camber or a lesser curve as previously described per  FIG. 2 . The seal slot may be bounded in part by the suction side shelf  49 . Clearance  62  between the shelf  49  and the seal element  51  allows insertion of the rearward portion  46  of a platform between them during tilted mounting of the platform as previously described. 
       FIG. 8  is a sectional view as in  FIG. 3 , showing an optional damper pin  56 , which may be a straight or constantly curved pin inserted below the seal element  51  and extending between the leading and trailing edges  27 ,  29 . Such pins may serve as both a seal element and a damper element, and may be round or flattened on one side in various embodiments. 
       FIG. 9  shows a seal slot  58  with an upper wedge portion  65  that cause the seal wire  51  to wedge by centrifugal force against the respective edges  46  and  44 B of adjacent platforms  36 ,  38 . The edges  46  and  44 B may be vertical in this embodiment. 
     Benefits of the invention include strength and low cost due to a simple blade shape and minimal size, since it is cast without an integral platform. It allows replacing individual platforms radially without replacing or even removing a blade. It eliminates cantilevered centrifugal stress on the platform, and provides effective sealing of the platform. Non-integral platforms facilitate engineered surface contouring that reduces boundary layer vortices and thus energy loss, as described for example in U.S. Pat. Nos. 7,134,842 and 7,690,890. 
     While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.