Blade group with pinned root

Abstract

A plurality of rotatable turbine blades are formed integral with a shroud and platform and a plurality of arcuate plate root portions which are received by circumferential grooves in a rotor and are fastened to the rotor by three pins extending axially through the root portions and the rotor, the shroud and platform portions having a protrusion on one corner to support the trailing edge of one of the blade portions and a notch in the shroud and the platform on the corner opposite the protrusion whereby the protrusions on one group of blades register with the notch on an adjacent group of blades when the groups of blades are disposed in a circular array on the rotor.

What is claimed is:  
     
       1. A blade group which attaches to a disc disposed on a shaft on an axial flow turbine, said blade group comprising: 
       a shroud; 
       a platform portion;  
       multiple blade portions extending radially outwardly from  between said platform portion and said shroud;  
       multiple root portions extending radially inwardly from said platform portion, said root portions having root end edges;  
       said root portions comprising generally flat spaced-apart arcuate segments disposed normal to the axis of said shaft;  
       said disc having circumferential grooves which receive said root portions;  
       multiple pins extending axially through said root portions and said disc;  
       said platform and said shroud each having a protrusion only on one corner and a notch only on an opposite corner of the same axial side of the blade group so that the protrusions on one blade group fits  fit the notches on an adjacent blade group when a plurality of blade groups are disposed in a circular array on the disc, wherein said protrusion on said platform extends in a direction normal to a radial line and normal to the turbine axis beyond the respective root end edges of all of said root portions and has a slanted surface between the root end edges of said root portions and a top surface of said platform; and  
       a trailing end of one of the blades in each blade group is disposed between the protrusion on the shroud and the protrusion on the platform.  
     
     
       2. A blade group as set forth in  claim 1 , wherein the space between the root portion  portions has an arcuate surface having a radius smaller than the radius of the outer diameter of the disc. 
     
     
       3. A blade group as set forth in  claim 1 , wherein the shroud has an axially disposed step therein. 
     
     
       4. A blade group as set forth in  claim 3 , wherein the step raises on the downstream side of said blade group. 
     
     
       5. A blade group as set forth in  claim 1 , wherein the thickness of said platform portion is generally equal to the thickness of the arcuate root portions. 
     
     
       6. A blade group as set forth in  claim 1 , wherein the root portion comprises three generally flat spaced-apart arcuate segments and the center of mass of the blade portions and the center of mass of the shroud portions are centrally disposed over the middle arcuate root segment. 
     
     
       7. A blade group as set forth in  claim 6 , wherein there are three pins arranged in a triangular relationship. 
     
     
       8. A blade group as set forth in  claim 1 , wherein said pins include outboard pins and a lower pin, and at least said outboard pins extend through each root portion at positions that are substantially equidistant from said edges. 
     
     
       9. A blade group as set forth in  claim 1 , wherein said protrusion on said platform is chamfered from a bottom to a top of said platform portion. 
     
     
       10. A blade group as set forth in  claim 1 , wherein the side edges of all of the root portions are substantially aligned. 
     
     
       11. A blade group which attaches to a disc disposed on a shaft of an axial flow turbine, said blade group comprising: 
       
         a shroud;  
       
       
         a platform portion;  
       
       
         multiple blade portions extending radially outwardly between said platform portion and said shroud;  
       
       
         multiple root portions extending radially inwardly from said platform portion, each root portion having root end edges;  
       
       
         said root portions comprising generally flat space-apart arcuate segments disposed normal to the axis of said shaft, wherein the space between the root portion has a arcuate surface having a radius smaller than the radius of the outer diameter of the disc;  
       
       
         said disc having circumferential grooves which receive said root portions;  
       
       
         a plurality of pins extending axially through said root portions and said disc, wherein at least outboard ones of said pins extend through said root portions at positions that are substantially equidistant from the root end edges;  
       
       
         said platform and said shroud each having a protrusion only on one corner and a notch only on an opposite corner on the same axial side of the blade group so that the protrusions on one blade group fit the notches on an adjacent blade group when a plurality of blade groups are disposed in a circular array on the disc, wherein said protrusion on said platform extends beyond the respective root end edges of all of said root portions in a direction normal to the root end edges of the root portions; and  
       
       
         a trailing end of one of the blades in each blade group is disposed between the protrusion on the shroud and the protrusion on the platform. 
       
     
     
       12. A blade group as set forth in  claim 11 , wherein the shroud has an axially disposed step therein. 
     
     
       13. A blade group as set forth in  claim 12 , wherein the step raises on the downstream side of said blade group. 
     
     
       14. A blade group as set forth in  claim 11 , wherein the thickness of said platform portion is generally equal to the thickness of the arcuate root portions. 
     
     
       15. A blade group as set forth in  claim 11 , wherein the root portion comprises three generally flat spaced-apart arcuate segments and the center of mass of the blade portions and the center of mass of the shroud portions are centrally disposed over the middle arcuate root segment. 
     
     
       16. A blade group as set forth in  claim 15 , wherein there are three pins arranged in a triangular relationship. 
     
     
       17. A blade group as set forth in  claim 11 , wherein said protrusion is chamfered from a bottom to a top of said platform portion. 
     
     
       18. A blade group as set forth in  claim 11 , wherein the side edges of all of the root portions are substantially aligned.