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.
Another bucket/cover design includes the integral formation of the bucket and cover. While this design incorporates the necessary sealing options, i.e., application of one or more labyrinth seal teeth, and also minimizes or eliminates the concern for solid particle erosion, the integral bucket/cover combination is costly to manufacture and complex. Accordingly, there has arisen a need for a bucket/tenon/cover design that both eliminates or minimizes solid particle erosion, as well as affords sealing efficiencies without complexity or excessive costs.
In accordance with a preferred embodiment of the present invention, there is provided in a steam turbine, a plurality of buckets mounted on a rotating component, e.g., a rotor, and a plurality of covers mounted on the tips of the buckets, the buckets having tenons peened to secure the buckets to the covers. At least one recess is preferably formed in the outer cover surface to form a profiled surface and at least one tooth projects either radially outwardly from the profiled surface or radially inwardly from the registering stationary component. In a preferred embodiment hereof, the profiled surface includes at least one recess defined at least in part by the tenon. In another preferred embodiment, the profiled surface includes a tooth projecting from the outer surface of the cover toward the stationary component and including at least part of the tenon. It will be appreciated that the recess or the tooth each formed, at least in part, by the tenon extend in a circumferential direction about the cover. To form this preferred configuration, the outer surface of the cover is machined such that the tenon forms part of the recess or the labyrinth tooth, as applicable.
In a preferred embodiment according to the present invention, there is provided in a steam turbine having a plurality of buckets rotatable about an axis and a stationary component surrounding the buckets, a seal between the buckets and the stationary component, comprising a cover mounted on a radial outer end of at least one bucket and having an opening, one bucket having a tenon projecting from the outer end of one bucket and extending into the cover opening, an outer surface of the cover and an outer end surface of the tenon forming a profiled surface in opposition to the stationary component with contiguous surfaces of the tenon end and the cover lying flush with one another, the profiled surface including at least one of a recess formed in the profiled surface and a tooth projecting radially outwardly of the profiled surface.
In a further preferred embodiment according to the present invention, there is provided in a steam turbine having a plurality of buckets rotatable about an axis and a stationary component surrounding said buckets, a seal between the buckets and the stationary component, comprising a plurality of covers mounted on radial outer ends of the buckets arranged in an annular array thereof with one or more buckets being secured to each cover, each cover having at least one opening and each bucket having a tenon projecting from the outer end thereof into the opening, an outer surface of each cover and an outer end face of each tenon forming a profiled surface in opposition to the stationary component with contiguous surfaces of the tenon end faces and the outer cover surface lying flush with one another.
In a further preferred embodiment according to the present invention, there is provided in a steam turbine having a plurality of buckets rotatable about an axis and a stationary component surrounding the buckets, a seal between the buckets and the stationary component, comprising a plurality of covers mounted on radial outer ends of the buckets arranged in an annular array thereof with one or more buckets being secured to each cover, each cover having at least one opening and each bucket having a tenon projecting from the outer end thereof into the opening, an outer surface of each cover and an outer end face of each tenon forming a profiled surface in opposition to the stationary component with contiguous surfaces of the tenon end faces and the outer cover surface lying flush with one another, the profiled surface including at least one recess, the profiled surface including a tooth projecting radially outwardly thereof.