Patent Grant
7517195
The present application relates generally to turbines and more particularly relates to a turbine bucket closure group.
Steam turbine airfoils or buckets are positioned around a turbine wheel at regular intervals. The buckets are assembled by inserting them one at a time axially into an opening on the wheel surface and then sliding the buckets circumferentially about the wheel. The buckets are attached by complimentary male and female dovetails. In order to close the assembly, however, the last blade must be restrained by means other than a dovetail. This last bucket, the closure bucket, generally is pinned to the wheel or affixed to its adjacent neighbors by keys.
The curved nature of the round skirt buckets, however, does not lend themselves to the use of keys in the solid portion of the skirt, i.e., the dovetail, so as to restrain the closure bucket from centrifugal forces. Axially positioned keys also are undesirable because the engagement with the adjacent buckets is very small so as to limit shear strength. Further, keys placed at an angle to the machine axis may be undesirable because the curved nature of the round skirt creates an irregular shear plane that does not intersect the center of the key at its thickest part. This may force the use of a closure block fixed to the wheel using pins. A closure block generally is a bucket without an airfoil. By removing the airfoil, the mass and centrifugal load is reduced, thereby lowering stress on the wheel pins to an acceptable level. Because the closure block has no airfoil, however, there is an opening in the steam path with detrimental effects on performance.
There is a desire therefore for an improved closure bucket that can support an airfoil without undue stress. Such a bucket should increase overall system performance.
The present application thus describes a closure bucket group for mounting on a dovetail of a turbine wheel. The closure bucket group may include a leading bucket with a leading bucket rear side, a closure bucket with a closure bucket front side and a closure bucket rear side, and a trailing bucket with a trailing bucket front side. The leading bucket rear side and the closure bucket front side define a first enclosed keyway and the closure bucket rear side and the trailing bucket front side define a second enclosed keyway. A number of keys may be positioned within the first enclosed keyway and the second enclosed keyway so as to support the closure bucket.
The leading bucket and the trailing bucket may include a pair of hooks for mating with the dovetail. The rear side of the leading bucket may include a leading bucket flat axial portion and a pair of leading bucket keyways that lie at an angle to the wheel axis along a pair of outer flat portions. The front side of the closure bucket may include a closure bucket front flat axial portion and a pair of closure bucket front keyways that lie at an angle to the wheel axis along a pair of outer flat portions. The rear side of the closure bucket may include a closure bucket rear flat axial portion and a pair of closure bucket rear keyways that lie at an angle to the wheel axis along a pair of outer flat portions. The closure bucket may include an airfoil. The front side of the trailing bucket may include a trailing bucket flat axial portion and a pair of trailing bucket keyways that lie at an angle to the wheel axis along a pair of outer flat portions. The first enclosed keyway may include a pair of first enclosed keyways and the second enclosed keyway may include a pair of second enclosed keyways
The present application further describes a closure bucket group for mounting on a dovetail of a turbine wheel. The closure bucket group may include a leading bucket with a pair of leading hooks so as to mate with the dovetail, a closure bucket, and a trailing bucket with pair of trailing hooks so as to mate with the dovetail. The leading bucket and the closure bucket may define a pair of first enclosed keyways and the closure bucket and the trailing bucket may define a pair of second enclosed keyways. A number of keys may be positioned within the first enclosed keyways and the second enclosed keyways so as to support the closure bucket.
The closure bucket may include an airfoil. The leading bucket nests with the closure bucket and the trailing bucket nests with the closure bucket.
These and other features of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description of the embodiments when taken in conjunction with the drawings and the appended claims.
Referring now to the drawings, in which like numerals refer to like elements throughout the several views,
Referring again to
The enclosed keyways 390, 400 provide a straight shear plane along the entire length of the keys 410, 420, 430, 440. The closure bucket 120 is thus secured and supported via the keys 410, 420, 430, 440. The centrifugal load of the closure bucket 120 thus is largely transferred to the leading and trailing buckets 110, 130 via the hooks 200, 360.
It should be apparent that the foregoing relates only to the preferred embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.
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| Number | Date | Country | |
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