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Axial entry dovetails on buckets are installed axially into generally complementary-shaped female dovetails about the rim of the turbine wheel. The buckets include bucket covers having an interference fit such that upon installation, the buckets tend to rotate, which causes radial inward displacement of the buckets. To eliminate the bucket rotation and radial displacement, the male dovetails mount an anti-rotation key for reception in a generally complementary-shaped recess at the base of the female dovetail. The anti-rotation key in the slot eliminates rotation and radial displacement of the bucket, maintaining the buckets on radii and enables the bucket covers to be machined to proper diameters.
DETAILED DESCRIPTION OF THE INVENTION
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings, particularly to FIG. 1, there is illustrated a portion of a turbine wheel having a plurality of dovetail-shaped slots , i.e., female dovetails, spaced circumferentially one from the other about the peripheral margin of wheel . Also illustrated are a plurality of buckets each having a radially inwardly extending male dovetail generally complementary in shape to the female dovetail-shaped slot . The female and male dovetails and , respectively, are aligned in an axial direction of the turbine such that the buckets can be installed on the wheel by displacing the bucket dovetails into the female dovetail-shaped slots in the axial direction as illustrated in FIG. . Thus, the buckets will form an array of buckets about the rim of the wheel. In FIG. 1, there is illustrated a Cartesian coordinate system designated A, T and R, representing axial, tangential and radial directions vis-à-vis the turbine wheel and buckets .
The buckets also include bucket covers . The circumferentially facing margins or edges of each bucket cover has a generally Z-shaped configuration when viewed in a radial inward direction, as illustrated in FIG. . The edges thus have intermediate edges which are at a steep angle in the direction of rotation of the rotor of the turbine, i.e., form an acute angle α with a tangent along the bucket cover. Consequently, upon axial insertion of each bucket in sequence about the rotor, the steep angle intermediate edge of the bucket being inserted abuts the steep angle edge of the installed adjacent bucket. As explained above, the tight-fitting arrangement of the bucket covers causes an interference between the adjoining edges , tending to rotate the bucket being installed generally about a radial axis upon installation. The tendency of the buckets to twist or rotate about this generally radial axis, as illustrated by the arrows in FIG. 3, is transmitted through the blade of the bucket to the male dovetail .
Referring more particularly to FIG. 2, the male dovetail includes a plurality of laterally oppositely directed hooks , three hooks on the male dovetail being illustrated. Fillets are provided between the hooks . The male dovetail necks down in a radial inward direction, terminating in a radial inward base portion . The female dovetail slots are generally complementary in shape to the male dovetail and each includes hooks having crush surfaces underlying the hooks in a radial inward direction. As explained previously, the sequential axial insertion of the buckets causes edges of the covers to interfere with one another, tending to rotate or torque the buckets upon further axial insertion. That tendency to rotate or torque the bucket causes the hooks to ride along the opposite crush surfaces , in turn causing a radial inward movement of the bucket relative to the wheel. The radial inward movement causes a change in diametrical dimension across the covers of the assembled buckets and wheel which causes difficulty in machining the covers to the proper diameter. Consequently and in accordance with a preferred embodiment of the present invention, the male and female dovetails are provided with complementary keys and recesses, respectively, to prevent rotation and, hence, movement in a radial direction.
To accomplish the foregoing, the male dovetail includes a radial inward projection or key extending along the base of the dovetail and formed integrally with the male dovetail . In a corresponding manner, the base of the female slot is provided with a radially inwardly directed recess . While the key and recess may extend from one end face of each bucket and wheel toward the opposite end faces thereof, terminating short of such opposite end faces, it is preferable that the keys and recesses are coextensive in length and extend between opposite end faces of the buckets and wheel, respectively. With tight tolerances between the side walls of the keys and recesses , for example, a tolerance of 0.002 inches, it will be appreciated, that any tendency of the bucket dovetail to rotate in the female slot is eliminated by engagement of the side walls of the lug with the side walls of the recess. That is, the flat parallel axial extending side wall surfaces of each bucket dovetail engages with tight tolerances the flat parallel axial extending side wall surfaces of each wheel slot to preclude rotation of the bucket generally about a radius of the wheel passing through the bucket. As illustrated, the radial inner faces of the keys are spaced from the bottoms of the recesses . However, the interaction of the sides of the keys and the recesses eliminates any rotation of the bucket and, hence, also eliminates any movement of the buckets in radial directions and offline from their radii.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary perspective view of a portion of a wheel and a plurality of buckets forming part of a turbine and illustrating axial entry dovetail connections between the buckets and wheel;
FIG. 2 is a fragmentary enlarged end face elevational view of the male dovetail of a bucket in a female dovetail slot of the wheel;
FIG. 3 is a radial inward view illustrating the configuration of the bucket covers in assembly; and
FIG. 4 is a fragmentary view similar to FIG. 1 illustrating the male dovetail portion of a bucket aligned for axial insertion into the female dovetail slot of the wheel.
1. A rotor wheel assembly comprising: a rotor wheel having a plurality of circumferentially spaced, axial entry, female dovetail-shaped slots about a margin of the wheel, each of said female slots having a plurality of hooks extending axially along opposite sides thereof and projecting toward one another; a plurality of buckets, each having an axial entry male-shaped dovetail generally complementary to said female dovetail-shaped slot for reception in said female dovetail-shaped slot, each said male dovetail having a plurality of hooks extending axially alone opposite sides thereof and extending away from one another; each said slot including a base defining a recess radially inwardly of radially innermost hooks of the female dovetail shared slot and opening through at least one end face of the wheel and radially outwardly; each said male-shaped dovetail having a key projecting radially inwardly from a base of said male-shaped dovetail at a location radially inwardly of radially innermost hooks carried thereby and received in said recess, said key and walls defining said recess in said base slot being cooperable to preclude rotation of said bucket generally about a radius of the wheel passing through the bucket.
2. An assembly according to claim 1 wherein said keys are formed integrally with said male-shaped dovetails.
3. An assembly according to claim 1 wherein said side walls of said recesses and side walls of said keys extend linearly in an axial direction.
4. An assembly according to claim 1 wherein each said recess extends between opposite end faces of the wheel.
5. An assembly according to claim 4 wherein said key extends between opposite end faces of each bucket dovetail.
6. An assembly according to claim 5 wherein said recess extends between opposite end faces of the wheel.
7. An assembly according to claim 1 wherein said side walls of said recesses and side walls of said keys extending linearly in an axial direction, each said recess extending between opposite end faces of the wheel and each said key extending between opposite end faces of the bucket dovetail.
8. An assembly according to claim 1 including a cover on each said bucket having circumferentially spaced edges having a generally Z-shaped configuration.
9. A rotor wheel assembly comprising: a rotor wheel having a plurality of circumferentially spaced, axial entry, female dovetail-shaped slots about a margin of the wheel; a plurality of buckets, each having an axial entry male-shaped dovetail generally complementary to said female dovetail-shaped slot for reception in said female dovetail-shaped slot; each said slot including axially extending opposite side walls having flat parallel surfaces opening through at least one end face of the wheel; each said male-shaped dovetail having axially extending opposite side walls having flat parallel surfaces, the flat surfaces of said male-shaped dovetail and the flat surfaces in said slot being cooperable to preclude rotation of said bucket generally about a radius of the wheel passing through the bucket.
10. An assembly according to claim 9 wherein said flat surfaces of said buckets extend axially between opposite end faces of the buckets.
11. An assembly according to claim 9 wherein said flat surfaces of said wheel slot extend between opposite end faces of each wheel.
12. An assembly according to claim 11 wherein said flat surfaces of said buckets extend axially between opposite end faces of the buckets.
13. An assembly according to claim 9 including a cover on each said bucket having circumferentially spaced edges having a generally Z-shaped configuration.
14. An assembly according to claim 9 wherein said axially extending flat side wall surfaces of each said male-shaped dovetail form a radial inwardly projecting key formed integrally with each said male-shaped dovetail and received within a recess formed by the flat parallel surfaces of said female dovetail-shaped slot.
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