Patent Application
20060083612
The present invention relates to a cleaning system for removing foreign material from a cooling slot surface of a gas turbine rotor wheel, and particularly to a cleaning system which is applied from the exterior of the rotor wheel for cleaning the cooling surfaces along the cooling slot along the underside of the dovetails.
Rotor wheels, e.g., for gas turbines, typically include a plurality of circumferentially spaced dovetails about the outer periphery of the rotor wheel defining dovetail slots therebetween. The dovetail slots receive corresponding dovetail shaped bases of buckets which carry the plurality of airfoils about the rotor wheel. The buckets or airfoils are often cooled by air entering through a cooling slot in the rotor wheel and through grooves or slots formed in the bases of the buckets. Typically, the cooling slot extends circumferentially 360° through the dovetails and the dovetail slots.
Gas turbine cooling slots are typically inspected via an eddy current testing methods. For acceptable eddy current test results, the areas of inspection must be clean and free of foreign materials, such as dust, rust, scale deposits, oil, grit and the like. There is therefore a need to clean one or more surfaces of the cooling slot without disassembly of the rotor and consequent turbine downtime.
In an example of the invention, there is provided a system for cleaning surfaces of a cooling slot about a gas turbine rotor wheel having a plurality of circumferentially spaced dovetails defining dovetail slots therebetween. The cooling slot extends circumferentially through the dovetails and the dovetail slots. A plurality of blocks are provided and have a shape generally corresponding to and for insertion into at least base portions of the dovetail slots. Each of the blocks has a slot for alignment with the circumferentially extending cooling slots through the adjacent dovetails. An elongated element has at least one abrasive surface for insertion into the circumferentially aligned slots through the blocks and through the dovetails to clean the cooling slot surfaces.
In a further example of the invention, there is provided a method of cleaning surfaces of a cooling air slot about a gas turbine rotor wheel having a plurality of circumferentially spaced dovetails defining dovetail slots therebetween, the cooling air slot extending circumferentially through the dovetails and dovetail slots. The method includes the steps of inserting guides having guide surfaces into adjacent dovetail slots with the guide surfaces generally aligned with the circumferentially extending cooling slot; passing an element having at least one abrasive surface through the circumferentially extending cooling air slot and past the guide surfaces; and displacing the element along the circumferentially extending cooling slot and guide surfaces to abrasively clean the cooling air slot surfaces.
Referring now to the drawings, particularly to
Referring to
In accordance with a preferred embodiment of the present invention, the cleaning system hereof includes a plurality of slot blocks 30, an abrasive belt 32, and a backing member, e.g. a tube 34. Each of the slot blocks 30 has opposite sides generally corresponding to the shape of the base of the dovetail slots 14 together with a rib/groove arrangement, preferably only a single laterally projecting rib 36 being formed along its opposite sides. The slot block 30 has only a limited axial extent, i.e. length, sufficient for insertion generally axially into the dovetail slots 14 from the forward axial face of the rotor wheel to overlie the cooling slot 16, although it will be appreciated that the slot blocks 30 may extend short of, correspond in length to or extend in excess of the length of the dovetail slots 14. The slot block 30 also includes a transverse slot 38 along a base portion thereof intermediate its opposite ends. The radial extent of the slot 38 is such that upon insertion of the slot block 30 into a dovetail slot 14, the base 40 of the slot 38 forms a continuation of the cooling slot surface 22.
The abrasive belt 32 is preferably formed of an abrasive media such as 3M Scotchbright™ cut to a specific width of the cooling slot 16. Other types of abrasive media may be utilized. The backing tube 34 is provided to apply pressure to the abrasive media when the backing tube and abrasive media are disposed in the cooling slot 16. To apply pressure on the backside of the belt to clean the surfaces of the cooling slot, the backing tube 34 preferably comprises a tubular bladder. Particularly, the tubular bladder on tube 44 illustrated in
In
To use the cleaning system hereof, the backing strip 49 is inserted in the gap between the wheel spacer and the cooling slot 16 of the wheel. The slot blocks 30 are then installed, preferably through the forward facing ends of the dovetail slots 14 and form a series or set of blocks 30 which alternate in circumferentially adjacent dovetail slots 14. The blocks are inserted such that their slots 38 align circumferentially with the cooling slot 16. It will be appreciated that by aligning the block slots 38 with the cooling slot 16, a continuous tunnel or arcuate opening about the rim of the rotor wheel is formed. The abrasive media and tube 32 and 34, respectively, are then inserted into the tunnel. The abrasive media 32 also extends through the slots 48 in the feeder blocks at opposite ends of the set of blocks such that the opposite ends project outwardly of the rim of the rotor wheel. The tube 34 extends in the tunnel and through the cooling slot and block slots 38 underlying, e.g., radially inwardly of, the abrasive media 32.
To clean the surfaces 22, 24 and 26, the ends of the abrasive media 32 are moved manually back and forth by grasping the free ends of the media and alternately pulling its opposite ends. With the backing tube bearing against the underside of the media, the abrasive media bears against the surfaces 22, 24 and the radius 26 removing the foreign material as the media moves back and forth in the slot 16. It will be appreciated that the backing tube may be inflatable to provide pressure against the abrasive media, in turn applying pressure against the surfaces to be cleaned. The backing strip 49 provides the reaction surface against which the backing tube pushes against when inflated.
It will be appreciated that by providing end feeder blocks with feeder slots or openings along one side thereof, the edges of the two circumferentially outboard dovetails 12 adjacent the feeder blocks will not contact the edges of those outboard dovetails and will not thereby cause a wearing of those edges. It will also be appreciated that a consumable insert 42 (
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.
