Abstract:
Nozzles for a turbine have dovetail-shaped bases for reception in corresponding dovetail-shaped grooves in the carrier halves of a turbine. The nozzles at each of the horizontal joint faces of each carrier half have notches formed along their bases including an abutment face. Key slots are formed in the horizontal joint faces and receive keys bearing against the abutment faces. The keys are peened or screwed into the carrier half at the horizontal joint faces. Radial loading pins engage the end nozzle bases to bias the end nozzles radially inwardly without interfering with the keys retaining the nozzles in the grooves.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to apparatus for retaining nozzles stacked one against the other in a groove of a carrier of a turbine and particularly relates to a turbine nozzle retention apparatus for retaining the nozzles in carrier grooves at the horizontal joint faces between upper and lower carrier halves which does not interfere with radially loading the nozzles. 
     In turbines, for example, steam turbines, there is provided a carrier for the axially spaced, circumferential arrays of nozzles. The carrier typically includes carrier halves which extend arcuately 180° and are secured to one another at a horizontal joint face to form a 360° array of nozzles at each axial stage position. While various techniques have been employed to retain the nozzles within the grooves of the carrier, typically the nozzles comprise an airfoil having a radial outer dovetail-shaped base for reception in a generally correspondingly dovetail-shaped groove in the carrier. Generally, the opposite side faces of each base of the nozzles are angled relative to the axis of the turbine enabling the base to accommodate the angularity of the airfoil. When the nozzles are installed in each carrier half groove, the nozzle bases are stacked one against the other within the grooves forming a semi-circular array of nozzles. The end nozzle at each horizontal joint face, prior to securing the carrier halves to one another, projects outwardly of the joint face. Radial loading pins are also provided for each nozzle. Each pin is disposed between the base of the nozzle and the base of the groove biasing the nozzle radially inwardly. A clearance between adjacent end nozzles across the horizontal joint of the upper and lower carrier halves is necessary when the carrier halves are secured to one another. Accordingly, there is a need for a retaining device at the horizontal joint face for retaining the nozzles within the carrier half groove and which does not interfere with the radial loading of the nozzles. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In accordance with a preferred embodiment of the present invention, there is provided a turbine nozzle retention apparatus for retaining nozzles at the joint interface of each carrier half that does not interfere with but works in conjunction with the radial loading device, e.g., the radial loading pins. For example, each carrier half has a plurality of axially spaced grooves having semi-circular configurations about the carrier half. Each groove has a dovetail configuration. Nozzles having a correspondingly dovetail-shaped radially outer base are inserted into the carrier groove and stacked one against the other to form an arcuate array of nozzles. At each joint interface where a clearance between adjacent nozzles of the upper and lower carrier halves is required, each end nozzle projects beyond its associated joint face. 
     To retain the end nozzle in the horizontal joint face while accommodating a radial loading pin, the nozzle base of each end nozzle includes a notch formed along its radial outward face and which notch includes an abutment face extending in an axial direction. A key slot is formed in each carrier half at each joint face and lies in alignment with the notch and the abutment face. An elongated key is disposed in the notch in engagement against the abutment face of the nozzle base. A radial loading pin is disposed in a recess in the outermost wall of the carrier groove and engages the portion of the nozzle base which is not notched to provide the radial inward bias to the end nozzle. The key is secured to the carrier half and in the key slot at the joint face, for example, by peening between the joint face and the key. Alternatively, the key may be retained in the key slot by one or more screws having heads recessed below the joint interface. The key therefore prevents circumferential movement of the nozzle from the carrier groove while the radial loading pin biases the nozzle radially inwardly. It will be appreciated that the end nozzle and retainer key of the present invention is provided at at least one of two horizontal joint faces for each groove of each carrier half. Preferably, all four horizontal joint faces of the two carrier halves forming each annular groove of the carrier are provided with the nozzle retention apparatus hereof. 
     In a preferred embodiment according to the present invention, there is provided nozzle retention apparatus for a turbine comprising a generally semi-cylindrical nozzle carrier half for extending about an axis of the turbine and having an arcuate, radially inwardly opening, shaped groove terminating at opposite ends in respective joint faces, a plurality of nozzles for the turbine, each nozzle including an airfoil and an outer base having a shape generally corresponding to the shape of the groove and received in the groove, a key slot in one of the horizontal joint faces at one end of the groove, one of the nozzles in the groove of the carrier half at the one horizontal joint face extending circumferentially beyond the joint face and having a notch formed in the base thereof extending inwardly of the one joint face and a key in the key slot secured to the carrier half and engaging in the notch of the one nozzle to retain the nozzles in the carrier half groove. 
     In a further preferred embodiment according to the present invention, there is provided nozzle retention apparatus for a turbine comprising a generally semi-cylindrical nozzle carrier half for extending about an axis of the turbine and having an arcuate, radially inwardly opening dovetail-shaped groove terminating at opposite ends in respective joint faces, a plurality of nozzles for the turbine, each nozzle including an airfoil and an outer base having a dovetail shape generally corresponding to the dovetail shape of the groove and received in the dovetail-shaped groove, a key slot in one of the horizontal joint faces at one end of the groove, one of the nozzles in the groove of the carrier half at the one horizontal joint face having a notch formed in the base inwardly of the one joint face, a key in the key slot secured to the carrier half and engaging in the notch of the one nozzle to retain the nozzles in the carrier half groove and a pin engaging the one nozzle to bias the one nozzle in a radial inward direction and extending between the key and a radially inwardly facing surface along a base of the groove. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary perspective view of a carrier illustrating axially spaced carrier grooves for a turbine and illustrated with the nozzles stacked in the grooves; 
     FIG. 2 is a perspective view of a representative nozzle disposed within the carrier grooves between end nozzles at the joint interfaces; 
     FIG. 3 is a perspective view of an end nozzle and a key for retaining the nozzle at a carrier joint face; 
     FIG. 4 is a view similar to FIG. 3 illustrating the nozzle at the horizontal joint face with a radial loading pin inserted; 
     FIG. 5 is an enlarged fragmentary view at the joint face illustrating the key in the key slot peened to the carrier shell; and 
     FIG. 6 is a view similar to FIG. 5 illustrating retention of the key in the slot by screws. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, particularly to FIG. 1, there is illustrated a carrier, generally designated  10 , for the nozzles  12  of a turbine, for example, a steam turbine. The carrier  10  includes upper and lower carrier halves  14  and  15 , respectively, which are joined one with the other along a horizontal joint face  16 . As illustrated, nozzles  12  are arranged in an annular array thereof at axially spaced locations along the carrier  10 . Each array of nozzles  12  includes a plurality of discrete nozzles  12  stacked one against the other. When a rotor, not shown, is disposed within the lower carrier half and the carrier halves  14  and  15  are secured one to the other at the joint interface  16 , the nozzles  12 , together with airfoils or buckets on the rotor, form multiple stages of a turbine. 
     As illustrated in FIG. 2, each nozzle includes an airfoil  17  including an inner band  18  and a base  20  having a dovetail configuration. Each base  20  has opposite sides parallel to one another and, when disposed in the carrier grooves, the opposite sides are angled relative to the axis of rotation of the turbine. In the illustrated form of the dovetail-shaped base of each nozzle, there is provided a pair of flanges  22  and  24  projecting in both axially upstream and downstream directions defining recesses  26  therebetween. The upper and lower carrier sections  14  and  15 , respectively, are provided with generally correspondingly-shaped grooves  27  as the bases of the nozzles  12 . The radial outward base of each groove also has a radial outward annular recess  30  (FIG.  4 ). 
     Typically, the nozzles  12  are stacked in the grooves one against the other in each of the upper and lower carrier halves  14  and  15 , respectively. By setting a first or end nozzle at one of the horizontal joint faces, the remaining nozzles of the carrier section may be inserted by locating the dovetail-shaped bases  20  of succeeding nozzles in the opposite end of the groove  27  and sliding the nozzles into abutment one with the other until the groove  27  is entirely filled. As the nozzles are inserted, radial biasing pins  32  are inserted into the carrier groove from the opposite end of groove  27 . The pins  32  engage between the radial outer base of the groove  27  and the radial outer faces of the bases  20  of the nozzles  12  to bias the nozzles  12  radially inwardly. The pins  32  have a flat face on one side for engaging the nozzle base  20  and are inserted from the opposite end of the carrier groove  27  from the nozzles being inserted into the groove. Once the nozzles are stacked in the groove, the final or end nozzle  13  (FIG. 3) for each carrier section at the horizontal joint face  16  is specifically configured for securement at the horizontal joint, as well as to avoid interference with and facilitate radial loading of the end nozzle  13  in a radial inward direction. 
     Preferably, end nozzles  13 , as described herein, are provided at each of the opposite ends of each groove  27  of a carrier half. It will be appreciated, however, that such end nozzle  13  and the following described retention apparatus may be provided only at one end of each groove of each carrier half with the opposite end being otherwise secured. To accomplish the foregoing, and referring to FIG. 3, the end nozzles  13  for each of the carrier halves  14  and  15  are provided with a notch  34  along the radial outer face of the base  20  of the nozzle  12 . The notch  34  includes an abutment face  36  which is formed generally parallel to the axis of rotation of the turbine. Thus, the notch  34  is essentially wedge-shaped as illustrated. When the end nozzles  13  are disposed in the grooves  27  at the joint faces, the abutment faces  36  lie below the horizontal joint faces  16  and a portion of each nozzle base  20  projects above the correspondingly horizontal joint face  16 . The end nozzle  13  at the opposite end of each carrier groove  27  preferably has a similar arrangement with, however, the notch and the abutment face being formed on the opposite side of the end nozzle. That is, left and right hand end nozzles  13  are provided with the notches  34  and abutment faces  36  formed on respective opposite sides of their bases. 
     Prior to assembly of the nozzles  12  and  13  into the carrier shell grooves  27 , a key slot  38  is formed in the horizontal joint face  16 , preferably at the end of each groove. The key slot  38  extends in an axial direction forward and aft of the extent of the nozzle bases  20 . Key slot  38  has a depth from the horizontal joint face  16  at least equal to the depth of the abutment face  36  from the joint faces when the end nozzle  13  is located at the horizontal joint face. As illustrated in FIG. 4, a key  40  is disposed in the key slot  38 . The key  40  comprises an elongated rectilinear locking element which seats in the key slot  38  and bears against the abutment face  36  of the end nozzle base  20 . 
     As illustrated in FIG. 5, key  40  is secured in the key slot  38 , for example, by peening  41  adjacent opposite ends of the key  40 . That is, the metal of the key  40  and portions of the adjoining joint face  16  is deformed to interfere with one another and thereby secure the key in the key slot with the key butting the abutment face  36 , retaining the stacked nozzles  12  and  13  in the carrier half from displacement from the grooves. The key  40  may also be secured in the key slot  38  and to the carrier half by means other than peening. For example, and as illustrated in FIG. 6, the key  40  may have bore holes for receiving screws  44  threadedly received in the base of the key slot  38  and in the carrier half. 
     To radially load each end nozzle  13 , the final radial load pin  32  is disposed between the base of the groove and bears against the base of the end nozzle  13  to bias the end nozzle radially inwardly, similarly as the other stacked nozzles in the carrier groove. Thus, the radial loading pin  32  at the end joint interface does not interfere with the key  40  and key slot  38  arrangement securing the nozzles in the carrier grooves. 
     It will be appreciated that the key  40  and radial pins  32  as well as the means for securing the key in the slot and preventing displacement of the nozzles from the grooves in a circumferential direction are all flush with or slightly recessed below the joint face  16 . This is significant in order to secure the joint faces of the upper and lower carrier halves to one another with appropriate sealing, not shown, and with the appropriate clearance between the adjoining end nozzles at each of the joint faces. 
     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.