Flush tenon cover for steam turbine blades with advanced sealing

#The present invention relates to steam turbines and more particularly to a steam turbine cover for minimizing or eliminating solid particle erosion of bucket tenons and to improve sealing efficiency.

#In conventional steam turbines, bucket covers are typically attached to the buckets by peening the tenon projecting from the end of the bucket and through an aperture in the bucket cover. This peening operation results in a projecting bulb or knob on the outside diameter of the cover. This raised knob or projection can be eroded by solid particles in the steam path. As a result, the cover may become loose, crack or separate from the buckets. Also, the raised knob or projection, resulting from peening the tenon, substantially prevents the application of one or more labyrinth seal teeth along the outside face of the cover, particularly on units with large differential expansion between the stationary and rotating components.

#In another cover-to-bucket design, the knob or projection of the peened tenon is disposed below the outer surface or outer diameter of the cover. While that configuration enabled the application of sealing teeth configurations to the cover, it is limited to straight tooth or flat surface geometry. Under certain conditions, solid particles may become trapped within the confines of the recess and between the walls defining the recess and the tenon. These trapped particles tend to erode the tenon knob or projection very quickly and have been shown, in certain circumstances, to essentially cut through the tenon.

#FIG. 1 is a fragmentary axial view illustrating a plurality of buckets with an attached cover;

#FIG. 2 is a fragmentary enlarged view illustrating the tenons and openings through the cover prior to assembly;

#FIG. 3 is a fragmentary cross-sectional view illustrating a flush tenon cover/bucket connection;

#Referring now to FIG. 1, there is illustrated a plurality of buckets 10 forming part of a rotating component of a rotor, generally indicated 12, of a steam turbine. Covers 14 are secured to outer tips of the buckets, the covers extending in a circumferential direction. As illustrated in FIGS. 2 and 3, the tips of the buckets 10 have one or more tenons 16 projecting radially outwardly of the tips. Each cover 14 is typically provided in an arcuate circumferentially extending segment for spanning a plurality of buckets, for example, four or five buckets, and has openings 18 for receiving the tenons. The tenons are received in the openings 18 and peened and may be machined to form a flush cover design, as illustrated in FIG. 3.

#In the embodiments of the present invention illustrated in FIGS. 4-11, like parts are designated by like reference numerals, preceded by a numeral identifying that embodiment. Accordingly, in FIG. 4, there is illustrated a bucket 110 having a tenon 116 projecting from a tip thereof for engaging in an opening 118 of a cover 114. The outer surface of the cover at the location of the tenon is machined to remove the projecting portion or mushroom of the tenon to provide a flush cover/tenon configuration. Additionally, the leading edge 122 of the cover 114 is provided with a recess 124 formed by a machining process and which recess extends circumferentially the full length of the segment. It will therefore be appreciated that the recess 124 extends circumferentially around the entire periphery of the rotary component, with the recess 124 in each cover 114 forming a continuation of the recesses 124 of adjoining covers 114.

#Further, the stationary component 126 is provided with a projecting labyrinth tooth 128 which likewise extends the entire circumferential extent about the cover. The tooth 128 is axially located on the stationary component 136 to project into the recess 124 such that its tip lies radially inwardly of the outer surface 130 of cover 114. Consequently, by utilizing a flush tenon/cover design in combination with a recessed leading edge receiving a labyrinth tooth, the flow coefficient across the gap between the stationary component and the cover is changed, affording a reduced pressure drop, which reduces leakage flow, as well as solid particle erosion.