FIELD OF THE INVENTION
This invention relates to the retention of aerodynamic blades around the circumference of a turbomachine disk, and particularly to the retention of blade root or dovetails in respective dovetail slots around the circumference of a rotating disk of a turbine or axial compressor.
BACKGROUND OF THE INVENTION
Axial compressors and the hot gas path of turbines or turbomachines have one or more rotating disks or wheels, each holding a circular array of aerodynamic blades that extend radially from the disk or wheel circumference. The blades may be mounted in respective dovetail slots in the disk or wheel circumference in a conventional retention configuration as shown in FIG. 1. Clearance in the slot may be eliminated by deforming portions 32 of the disk or wheel to create an interference fit with the blade root. This deformation is called “staking”. Operational vibrations can wear the displaced material 38, loosening the fit and reducing blade stability.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained in the following description in view of the drawings that show:
FIG. 1 is a front view of a blade mounted in a dovetail slot in a turbomachine disk or wheel.
FIG. 2 is a perspective view of a blade, platform, and root with spacers in a second conventional retention configuration.
FIG. 3 is a front view of a blade with a root with partly chamfered front and back ends showing aspects of embodiments of the invention.
FIG. 4 is a front view of a blade as in FIG. 3 mounted in a dovetail slot.
FIG. 5 is a perspective view of a blade as in FIG. 2 mounted in a dovetail slot with spacers in accordance with aspects of the invention.
FIG. 6 is a front view of a blade root with a bottom spacer mounted in a dovetail slot.
FIG. 7 is a bottom perspective view of a root bottom spacer with end chamfers.
FIG. 8 is a front view of a turbomachine disk or wheel holding a circular array of blades in a retention arrangement showing aspects of an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a blade retention configuration 20A in which a blade 22 has a dovetail root 24 that is slidably mounted in a dovetail slot 26 in the circumference 28 of a turbomachine disk or wheel 29. As is known in the art, dovetail slot 26 extends between a forward and aft position on disk or wheel 29. Clearance 30 in the slot 26 is eliminated by mechanically deforming portions 32 of the disk to create an interference fit 33 that presses the blade root 24 radially outwardly 34 with respect to the disk axis, which presses the blade root against centrifugal retention surfaces 36 of the slot 26. The deformation process is called “staking”. Operational vibrations can cause wear in the material 38 displaced by staking, thus reducing blade stability. In exemplary embodiments of the invention, blade 22 may be one or more compressor blades mounted within respective slots of one or more compressor wheels 29 used within an industrial gas turbine, for example. Embodiments of the invention may be utilized in alternate turbines and are not limited to compressor blade and wheel combinations.
FIG. 2 is a perspective view of a blade 22, platform 23, and root 24. Spacers 40A, 40B may bracket the respective front (forward) and back (aft) ends of the root 24 in the slot 26 of FIG. 1 to retain the root axially in the slot. Staking 32 as in FIG. 1 may be used on the disk 29 adjacent such spacers.
FIG. 3 is a front view of a blade 22C and root 24C showing aspects of embodiments of the invention. The root has a chamfer 42A, which may be offset circumferentially 46. For example, the chamfer 42A may cover only a left or right portion of the front bottom edge 44 the root. Alternately, the chamfer may cover the whole front bottom edge 44 of the root. A second chamfer 42B may cover part or all of the back bottom edge 45 of the root. The first and second chamfers 42A, 42B may be offset circumferentially to opposite sides of the root as shown. For example, the front chamfer 42A may be limited to the left half of the root, and the back chamfer 42B may be limited to the right half of the root as shown, or vice versa. Alternately, the two chamfers may be circumferentially offset to the same side (not shown).
FIG. 4 is a front view of a blade 22C with a partly chamfered root 24C as in FIG. 3 mounted in a dovetail slot 26C in a turbomachine disk 29 in a retention configuration 20C. Staking depressions 32A, 32B may be limited to only a circumferentially 46 left or right side of the root as shown. The chamfers 42A, 42B create a ramp effect providing a mechanical advantage that increases the radially outward 34 force on the root caused by the distorted portions 38. The chamfers also block sliding of the root axially (in a direction of the disk axis).
The surface of a chamfer 42A, 42B may be non-circumferential, meaning it is non-parallel to the disk circumference 28 as shown. For example, it may be at least 10 degrees or at least 15 degrees away from perpendicular to a radial line 47 through a center of the root 24C. Such an angled surface blocks the shifting of the root circumferentially 46 leftward for 42A and rightward for 42B. The bottom of the slot 26C may be concave and the bottom of the root 24C may be convex as shown. The chamfers 42A, 42B may be planar as shown, or in alternate embodiments of the invention they may follow the curvature of the root.
The chamfers 42A, 42B may be approximately 45-degree chamfers relative to the bottom and end surfaces of the root 24C. Alternately, each chamfer 42A, 42B may form an angle of about 30 degrees relative to the bottom of the root 24C in an axial direction, or it may form an angle of between about 25-35 degrees in some embodiments. Such an angle increases the mechanical advantage of the deformation on the root 24C in the radial 34 force direction when the deformed portion impinges on the surface of chamfer 42A, 42B.
FIG. 5 is a perspective view of a blade 22D on a platform 23 with a root (not visible) mounted in a dovetail slot 26C in the circumference 28 of a disk 29. Spacers 40C, 40D bracket the front and back ends of the platform and the root in the slot 26C. An offset chamfer 42A may be provided on the front spacer 40C. A second offset chamfer 42B may be provided on the back spacer 40D as previously described for the back end 45 of the root 24C in FIG. 3. Together the root and spacers form a root apparatus or root arrangement that is mounted in the dovetail slot 26C in a retention arrangement 20D.
FIG. 6 is a front view of a blade 22E with a platform 23, a root 24E, and a bottom spacer 50 under the root 24E that acts as a shim between the root 24E and the slot 26E. Together the root 24E and spacer 50 form a root apparatus or root arrangement that is mounted in the dovetail slot 26E in a turbomachine disk 29 via a retention configuration 20E. Staking depressions 32A, 32B may be limited to only a left or right side of the root bottom spacer 50 as shown. The spacer 50 may have a bottom front edge 52 with a first chamfer 42C. The chamfer may be circumferentially offset as shown. The bottom of the spacer 50 may be convex as shown. A second chamfer 42D may be provided in the bottom back edge 53 of the spacer 50. The first and second chamfers may be offset in opposite circumferential directions. For example, the first chamfer 42C may be limited to the left half of the spacer 50 and the second chamfer 42D may be limited to the right half of the spacer 50. Alternately, not shown, the chamfers may cover most or all of the respective edges 52, 53.
FIG. 7 is a bottom perspective view of exemplary geometry of a root bottom spacer 50 as in FIG. 6, with a first chamfer 42C in the front bottom edge 52, a second chamfer 42D in the back bottom edge 53, and a convex bottom surface 54. Similar chamfer and bottom surface geometry may apply to an embodiment of the blade root as in FIG. 3 when a spacer is not used.
FIG. 8 is a front view of a turbomachine disk 29 with an axis 56 and a circular array of blades 22C mounted in retention arrangements 20C as in FIG. 4.
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.
Patent Application
20160305259
