Abstract:
An apparatus for treating a dovetail in a dynamoelectric machine is provided. The apparatus includes a housing, at least two pads for treating, cleaning or polishing a dovetail surface, at least a pair of guide wheels for aligning the apparatus within the dovetail, and at least one motor connected to the pads. The motor is operatively configured to rotate the pads. The dovetail surface is treated, cleaned or polished by sliding the apparatus along the dovetail and activating the motor to rotate the pads.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to a method and apparatus for cleaning dovetails. More specifically, the subject matter disclosed herein relates to a method and apparatus for cleaning dovetails in a dynamoelectric machine. 
         [0002]    Conventional dynamoelectric machines, such as generators used with gas and steam turbines, typically employ forged rotors of magnetic material into which radial slots are machined for receiving the conductive turns of field windings that are interconnected such as to produce a desired magnetic flux pattern. Typically, included in such conventional rotor slots are creepage blocks at both the top and bottom ends of the slot as well as coil slot wedges for resisting the radially outward forces exerted on the windings when the rotor is operational. Dovetails are typically located at the top of the radial slots, and may be used in conjunction with slides, wedges and ripple springs that aid in retaining the windings within the radial slots. 
         [0003]    The slot wedges, which are generally dovetail shaped, are used to maintain the copper coils or windings in place while the rotor is spinning at, for example, 3600 revolutions per minute. During the lifetime of the rotor one or more re-winding operations may be needed. This process entails removing the windings from the radial slots and either repairing, refurbishing or replacing the windings. The dovetail slots at the top of the radial slots also may need to be cleaned or polished, as the material from the slides, wedges and/or ripple springs can adhere to the surfaces of the dovetail. In addition, negative sequence events (e.g., arcs) can cause fretting. One known method for cleaning the dovetail surfaces requires a worker to manually clean or polish the dovetail. However, this process is labor intensive, time consuming and costly. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to an aspect of the present invention, an apparatus for treating a dovetail in a dynamoelectric machine is provided. The apparatus includes a housing, at least two pads for treating, cleaning or polishing a dovetail surface, at least a pair of guide wheels for aligning the apparatus within the dovetail, and at least one motor operatively connected to the pads. The motor is configured to rotate the pads. The dovetail surface is treated by sliding the apparatus along the dovetail and activating the motor to rotate the pads. 
         [0005]    According to another aspect of the present invention, a method of treating, cleaning or polishing a dovetail in a dynamoelectric machine is provided. The method includes the steps of providing a powered tool having a plurality of abrasive pads, inserting at least a portion of the powered tool into the dovetail, activating the tool to begin rotation of the abrasive pads, and moving the powered tool along the dovetail to treat the dovetail. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These and other features of the invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
           [0007]      FIG. 1  illustrates a three-dimensional perspective view of a portion of a generator rotor; 
           [0008]      FIG. 2  illustrates a simplified and partial, cross-sectional view of the rotor of  FIG. 1 ; 
           [0009]      FIG. 3  illustrates a cross-sectional view of a winding in a radial slot; 
           [0010]      FIG. 4  illustrates a cross-sectional view of a tool used for cleaning and/or polishing the dovetail in a radial slot, according to an aspect of the present invention; 
           [0011]      FIG. 5  illustrates a bottom view of a tool used for cleaning and/or polishing the dovetail in a radial slot, according to an aspect of the present invention; 
           [0012]      FIG. 6  illustrates a perspective view of a tool used for cleaning and/or polishing the dovetail in a radial slot, according to an aspect of the present invention; 
           [0013]      FIG. 7  illustrates the tool of  FIGS. 5-6  positioned in a dovetail of a radial slot, according to an aspect of the present invention; 
           [0014]      FIG. 8  illustrates a cleaning pad and its construction, according to an aspect of the present invention. 
       
    
    
       [0015]    It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 1  shows a three-dimensional perspective view of a portion of a rotor  100 . Rotor  100  may include a spindle  110  and groups of coils (or windings)  120  disposed about spindle  110 . Each group of coils  120  may include a plurality of ducts  130 . Further, rotor  100  may include a plurality of subslots  140  disposed about spindle  100 . Each subslot  140  may extend between spindle  110  and group of coils  120  and may be in fluid communication with group of coils  120 . 
         [0017]      FIG. 2  illustrates a partial, cross-sectional view of rotor  100 . Of particular significance here are the axially oriented coil slots  210  arranged circumferentially about the mid-section of the rotor, that are used for holding the copper field windings or coils  120 . The radially outward portion of each slot  210  contains two opposing dovetails  220 . 
         [0018]    With further reference to  FIG. 3 , the coil slots  210  are each radially directed and typically contain, in a radially outward sequence, insulated copper coils  120 , a creepage block  310 , and a plurality of axially aligned slot wedges  320 . The wedges  320  have a generally dovetail shape in cross section, and are located and arranged so as to maintain the copper coils  120  and creepage block  310  in place while the rotor is spinning. The slot wedges  320  may also contain ventilation holes  330  (one shown), which are in general alignment with ventilation channels  340  (one shown), which pass through the copper conductors or coils, as well as through the creepage block  310 . 
         [0019]      FIG. 4  illustrates a side view of an apparatus  400  that can be used to treat, such as clean or polish, opposing dovetails  220  in a radial slot  210 , according to an aspect of the present invention. The apparatus  400  can be positioned on top of slot  210  and slid along a portion or the entire length of the slot, and cleaning pads can be activated to clean the opposing dovetail surfaces. 
         [0020]    The apparatus  400  includes two or more cleaning pads  410 , which may be formed of an abrasive material. The pads  410  can be formed of steel wool, woven or non-woven polyester fiber or web, woven or non-woven nylon fiber or web, combinations thereof or any other suitable abrasive material, and may be built up of several circular shaped pads having different diameters. Various abrasive particles (e.g., silicon carbide, limestone, etc.) may also be bonded to the material of pads  410 . In addition, any material may be added to the pads or dovetail surface to facilitate treating. (e.g., polishing or rubbing compound, cleaning solutions, etc.) Using a plurality of circular shaped pads stacked one upon the other, allows the pad to be designed to have a similar shape to the dovetail surface. The pads  410  can be fit over a rotating shaft connected to motor  415 . The motors  415  can be pneumatically (e.g., compressed air, etc.), electrically or battery powered. 
         [0021]    Guide wheels  420  are located at the base of the unit and aid in centering the unit in the dovetail  220 . The guide wheels may be fabricated of rubber or steel and are mounted on shafts connected to a pivotable shaft  422  connected to bracket  424 . The pads  410  are also connected to a pivotable shaft and bracket (not shown in  FIG. 4 ). The apparatus is provided with an enclosure  430  having transparent sides  432  and transparent bottom  434 . The transparent bottom and sides permits an operator to monitor the cleaning process. Activation lever  440  can be used to activate the rotation of pads  410 . Alternatively, a switch, button or any other suitable activation device can be substituted for lever  440 . One or more connectors  450  may be located near the top of the unit for connection of air supply and exhaust hoses. Alternatively, electrical plugs or connections may be provided to connect an electrical power supply. One or more handles  460  may also be provided to facilitate transport and use of the apparatus  400 . 
         [0022]      FIG. 5  is a bottom view of the apparatus  400 . The pads  410  are connected to a lever  510 . The lever can be moved back and forth along slide  512  and between stops  514 . Operation of the lever  510  causes the pads  410  to pivot about point  515 . As is shown in  FIG. 5 , the pads  410  are shown near the retracted position. This retracted position enables the pads to be easily placed into dovetail  220 . After the pads are positioned in dovetail  220 , the lever  510  can be moved to rotate the pads  410  in a counter-clockwise direction around pivot point  515  until they contact the surfaces of dovetail  220 . 
         [0023]    The guide wheels  420  can be arranged in pairs (as shown) and are connected to lever  520  via bracket  526 . Four pairs of guide wheels are shown, however, more or fewer guide wheels may be used as desired in the specific application. The guide wheels are shown near their retracted position, but may be pivoted about pivot points  525  by operation of lever  520 . The lever  520  can be moved back and forth along slide  522  and between stops  524 . The retracted position enables the guide wheels  420  to be easily placed into dovetail  220 . After the guide wheels are positioned in dovetail  220 , the lever  520  can be moved to rotate the guide wheels  420  in a counter-clockwise direction around pivot point  525  until they contact the surfaces of dovetail  220 . 
         [0024]      FIG. 6  illustrates a perspective view of the tool or apparatus  400 . The housing of the apparatus may include end wall cover  610 , tapered cover  612  and top cover  614 . These covers may be formed of metal, plastic or any suitable material and may be opaque or transparent. Transparent covers may aid in allowing a worker to monitor the cleaning process. The handles  460  can be attached to tapered cover  612  and/or to end wall cover  610 , top cover  614  or sides  432 . 
         [0025]      FIG. 7  illustrates the apparatus  400  positioned so that the pads  410  and guide wheels  420  are within dovetail  220  of radial slot  210 . During insertion of pads  410 , the pads  410  and guide wheels can be retracted to enable ease of insertion. Once the pads have reached the dovetail, the pads and guide wheels can be deployed by moving levers  510  and  520 , respectively. The guide wheels center the apparatus within the dovetail and help to maintain alignment of the apparatus during a cleaning process. The pads  410  are formed of a resilient material and at least partially conform to the shape of dovetail  220 . 
         [0026]    The motors  415  can be energized by activation of switch or lever  440 , thereby beginning rotation of pads  410 . The rotating pads “scrub” or polish the surface of dovetail  220  and clean off any residual material deposited by creepage block  310  and/or slot wedges  320 . 
         [0027]      FIG. 8  illustrates the construction of one of the abrasive pads  410 , according to one aspect of the present invention. The dovetail  220 , may have a variety of shapes, including but not limited to generally “S” shaped, generally “C” shaped, or any other shape that may be used to aid in retaining the windings or coils in a dynamoelectric machine. The dovetail  220 , as shown in  FIG. 3  may be viewed as having an “S” shape, and the shape of the pad  410  can be constructed to have a similar shape or profile. 
         [0028]    Abrasive material is typically available in sheets. The pads  410  can be formed of a stack of cylindrical “punches” of material having a central hole. For example, a plurality of cylindrical discs  801 - 806  may be punched out of a sheet of abrasive material. A central hole  810  may also be formed in the discs. Each disc can have a diameter that is chosen to conform to the shape of dovetail  220 . As shown in  FIG. 8 , discs  801 - 802  have a smaller diameter, discs  803  and  804  have increasing diameters, and discs  805 - 806  have the largest diameters. In this manner, a plurality of discs may be fabricated and stacked together to form a pad having a shape or profile conforming to the shape of the dovetail to be cleaned. The pads  801 - 806  can be stacked together with or without adhesive to bind them together. The hole  810  is provided to fit over a shaft or spindle of motor  415 . The pads can also be designed to be easily replaceable during use. The pads may be machined from semi to rigid material, and these materials may be impregnated with abrasive material, grit or fiber. This type of material can be machined to the dovetail geometry. 
         [0029]    A method for cleaning, polishing or treating a dovetail, according to one aspect of the present invention will now be described. The method may include the steps of providing a powered tool having a plurality of abrasive pads and/or guide wheels, inserting at least a portion of the powered tool into a radial slot, activating the tool to begin rotation of the abrasive pads, and moving the powered tool along the slot to clean the dovetail. The inserting step may also include the step of manipulating the abrasive pads and guide wheels into a retracted position, followed by inserting the abrasive pads and guide wheels into the radial slot, and manipulating the abrasive pads and guide wheels into a deployed position so that they contact the surface of the dovetail. One or more levers may be used to manipulate the abrasive pads and guide wheels into and between the retracted and deployed positions. 
         [0030]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.