Patent Application
20070071605
This invention relates generally to steam turbine construction and, more specifically, to integrated nozzle and bucket wheel constructions for a reaction steam turbine.
Current integral-cover reaction nozzle stages are made up of large quantities of individual reaction nozzles that are assembled into a machined stator casting or nozzle carrier. More specifically, individual nozzles are loaded into a dovetail groove and secured within the carrier using individual radial loading pins. Each nozzle tip is machined with a specified tip seal configuration for interaction with the turbine rotor so as to minimize leakage along the hot gas path.
Similarly, current integral-cover reaction bucket stages are also made up of large quantities of individual reaction buckets, assembled into a machined rotor forging using individual radial loading pins. After assembly, the buckets are secured with retention hardware, the bucket tips are machined to the specified tip seal configuration.
The time and cost associated with the manufacture of the stator casting, stator machining, nozzle stock material and nozzle machining, and stator assembly, as well as the rotor forging, rotor machining, bucket stock material, bucket machining and assembly add significant costs overall to the reaction steam path.
In accordance with an exemplary embodiment of this invention, the nozzle and bucket manufacturing/assembly processes are simplified, and the overall cost of the reaction steam path is reduced without impacting the integrity of the overall reaction steam turbine design.
In the exemplary embodiment, a full row of reaction nozzles is machined into a 360° piece of flat stock material. It will be understood that the stock material may be forged, rolled ring or plate stock. The 360° ring is placed into a machining center where the ID, OD, inlet blends, airfoils, airfoil radii, cover shroud sealing configuration, retention features and the balance of the standard nozzle features are machined. Thereafter, the integrated nozzle wheel may or may not be split into two or more arcuate segments in preparation for the final steam path assembly process.
Similarly, a single stage of reaction airfoils may be machined into a 360° piece of flat stock material that also may be forged, rolled ring or plate stock. The bucket seal tip geometry, mating axial face rabbet fits and retention features may also be machined into the integrated bucket wheel.
It is also possible to incorporate into the integrated nozzle and bucket wheels, adjacent stator and rotor surfaces, that are forward and/or aft of the nozzle and/or bucket airfoils, respectively, and utilized to facilitate axial stacking of plural nozzle wheels in an alternating arrangement with respective bucket wheels.
Accordingly, in one aspect, the present invention relates to an integrated bucket wheel for a turbine rotor component comprising a three hundred sixty degree wheel formed from a single piece of stock material, a radially outer portion of the wheel manufactured to include a plurality of buckets, each having an airfoil portion and a radially outer tip shroud portion; and a radially inner portion of the bucket wheel manufactured to include one or more assembly features.
In another aspect, the invention relates to an integrated bucket wheel for a rotor component of a reaction turbine comprising a unitary 360° piece of stock material having a radially outer portion machined to include a plurality of buckets, each having an airfoil portion and a radially outer tip shroud portion; and a radially inner portion machined to include a plurality of tie-rod or bolt holes circumferentially spaced about the radially inner portions.
In still another aspect, the invention relates to a method of making a turbine bucket wheel comprising forming flat stock material into an annular ring; machining a radially outer portion of the annular ring to include a plurality of buckets, each comprising an airfoil portion, and machining a radially inner portion of the annular ring to include assembly features.
The invention will now be described in detail in connection with the drawings identified below.
With initial reference to
In the exemplary embodiment, the wheel 10 is manufactured from a single 360° piece of flat stock material that could be forged, rolled ring or plate stock. The annular ring is thereafter machined to include a plurality of airfoils 16, in a circumferential array at the radially inner portion of the wheel. The radially inner ends of the airfoils 16 are also machined to include an integral cover shroud sealing configuration 18 that determines the ID of the wheel. The remainder of the wheel, specifically the radially outer portion 20, is formed to include assembly bolt or tie-rod holes 22 and any other rim or rabbet configuration to facilitate axial stacking with similar wheels, or with discrete spacer rings therebetween that accommodate the rotating stages on the rotor.
Turning to
The radially inner portion 48 is provided with fastening features which, in the example illustrated, includes a plurality of bolt or tie-rod holes 52 circumferentially spaced about the radially inner portion. The radially outer portion 50 is machined to include a plurality of buckets 54, each including an airfoil portion 56 and an integral shroud or tip cover 58 that extends 360° , over all of the radially outer tips of the air foil portions 56.
As in the case of the turbine nozzle wheel shown in
In addition to the airfoil portion 56 and shroud or tip cover 58, the machining operation may also include finish machining of the wheel OD, ID, inlet blends, airfoil radii and any other standard bucket features.
Adjacent rotor surfaces that are forwarded and aft of the bucket airfoil portions, may also be integrated into the bucket wheel. For example, a single adjacent rotor surface (forward or aft) may be incorporated into the bucket wheel, and may be integral or added on after the air foils have been machined. Alternatively, double adjacent rotor surfaces (forward and aft) may be incorporated into the bucket wheel and may be integral or added on after the airfoils have been machined. Some applications may not require any added adjacent rotor surfaces.
By machining the airfoils in the fashion disclosed hereinabove, the following obstacles associated with current reaction bucket design may be eliminated:
In addition to eliminating the items above, the integrated bucket wheel may also accomplish the following:
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.
This application is a continuation-in-part of application Ser. No. ______ (Attorney Dkt. No. 839-1738), entitled, “INTEGRATED NOZZLE WHEEL FOR REACTION STEAM TURBINE STATIONARY COMPONENTS AND RELATED METHOD,” filed on Sep. 7, 2005.
