US2974924A - Turbine bucket retaining means and sealing assembly - Google Patents

Description

March 14, 1961 A. w. RANKIN ETAL 2,974,924

TURBINE BUCKET RETAINING MEANS AND SEALING ASSEMBLY Filed Dec. 5, 1956 INVENTORS ANDREW W. RANKIN EVERETT E. ZWICKY JR. ARTHUR W.WHEELER JR.

THEIR ATTORNEY TURBINE BUCKET RETAINING NIEAN'S AND SEALING ASSEMBLY Andrew W. Rankin, Schenectady, Everett E. Zwicky, Jr., Latham, and Arthur W. Wheeler, Jr., Schenectady, N.Y., assignors to General Electric Company, a corporation of New York Filed Dec. 5, 1956, Ser. No. 626,417

4 Claims. (Cl. 25339) This invention relates to elastic fluid turbines comprising a rotor disposed in a turbine casing and having at least one turbine wheel in which the buckets and/or bucket fastening means must be retained against axial movement, and a diaphragm secured in the turbine casing to conduct elastic fluid to the turbine wheel. More particularly, it relates to an improved bucket fastening means and steam sealing assembly in which axial movement of the bucket and/or its fastening means is prevented and the sealing assembly is replaceable, if desired, without replacing the bucket.

The steam thrust, vibration forces, thermal transients, etc., acting on turbine buckets can impose substantial axal forces thereon which necessitates the use of means for preventing axial movement of the turbine buckets or their fastening means if either or both are free to move in an axial direction. Also, the spaces between the bucket wheels and adjacent diaphragms should be substantially sealed off to prevent leakage of motive fluid out of the main flow path which, if permitted, reduces turbine efliciency.

Accordingly, it is the main object of this invention to provide an improved bucket fastening construction incorporating means for preventing axial movement of the turbine buckets and/or bucket fastening means relative to the bucket wheel, and for restricting leakage through the space between the bucket wheels and adjacent diaphragms.

A further object is to provide a sealing means between 'the bucket wheels and adjacent diaphragms which can be readily removed and replaced if desired.

Other objects and advantages will become apparent from the Specification and claims and from the accompanying drawing which illustrates various aspects and embodiments of the invention, in which:

Fig. 1 is a partial sectional view of an elastic fluid turbine of a type which may advantageously employ the invention;

Fig. 2 is an exploded perspective view of a turbine wheel incorporating the invention; and

Fig. 3 is a perspective view disclosing a modification of the invention.

Generally stated, the invention is practiced by providing an improved type of bucket fastening in which axial movement of the bucket cannot occur together with. a readily replaceable combination retaining and sealing member which prevents axial movement of the bucket fastening means and substantially seals the space between the bucket wheel and adjacent diaphragm to prevent leakage of motive fluid out of the main flow path. Also, if a bucket fastening is used which by itself cannot prevent axial movement of the bucket, the combination retaining and sealing member will perform this function.

Referring now to Fig. i, there is illustrated a first stage nozzle ring 1 having a plurality of circumferentially spaced partitions in for directing motive fluid to a first stage turbine wheel 2, a stationary diaphragm 3 for directing motive fluid to a second stage turbine wheel 4, and a atent C ice diaphragm 5 for directing motive fluid to a third stage bucket wheel (not shown). Secured to the circumferences of the bucket wheels 2, 4, which may be formed integral with a rotor shaft (not shown), are a plurality of circumferentially spaced buckets 6 surrounded by shrouds 6a. Diaphragms 3, 5 are supported in casing 7 and are in the form of segmented annular disk members containing a plurality of circumferentially spaced blades 3a, 5a respectively forming nozzle passages.

Bucket wheel 2 is separated from nozzle ring 1 and diaphragm 3 by axial clearances 8, 9 respectively, and bucket wheel 4 is separated from diaphragms 3, 5 by axial clearances 10, 11 respectively. These clearances must necessarily be provided to permit the rotor and associated bucket wheels to freely rotate relative to the diaphragms. However, it is also important from the standpoint of both thermal and aerodynamic efiiciency, that provision be made to keep the leakage out of the main flow path to a minimum. To accomplish this, the bucket wheels 2, 4 are provided with segmental ring members 12 defining circumferential flanges 12a, 1211 which are arranged to form close axial and radial clearances with the adjacent nozzle ring 1 and diaphragms 3, 5, respectively. The specific details of ring members 12 and their relationship to their respective bucket Wheels are illustrated in Pig. 2 and the description thereof will be noted hereinafter. It remains to. note that the distance between diaphragm 3 and bucket wheel 2 is substantial, and the clearance space 9 therebetween is sufl'iciently sealed by circumferential flange portion 3b of diaphragm 3. Therefore, ring 12 located on the downstream side of bucket wheel 2 is not in a position to seal the space between the bucket wheel 2 and diaphragm 3 and thus does not define any circumferential sealing flanges. However,

rings 12 with sealing flanges 12a, 12b are provided on both sides of bucket wheel 2 to substantially seal ofl clearance spaces 10, 11.

Referring now to Fig. 2, there is illustrated, by way of example, turbine wheel 4 comprising a rim portion 4a provided with a circumferential row of evenly spaced V- or chevron-shaped grooves 4b. Located in each of these grooves 4b are radially inserted buckets 6 which have a blade portion 6d and a chevron-shaped base portion 61) that fits in grooves 4b. The main advantage of a chevron-shaped bucket is that it is possible to locate the dovetail directly under the vane section and the total weight that must be carried by the means retaining the bucket against radial displacement is significantly reduced. Locating the V-shaped base portion 617 directly under the generally crescent-shaped vane 6d substantially eliminates the heavy solid bucket base portion between the vane and the dovetail normally required to properly distribute the centrifugal forces on the vane through the dove-tail when portions of the bucket overhang the base. Buckets 6 are secured to the wheel 4 against radial displacement by pins 13 located in keyways formed by cooperating recesses 40, 6c in the wheel rim 4a and bucket base 617 respectively. Pins 13 need not have a circular cross-section, but may beyany shape of key which will prevent radial displacement, e.g. having a square crosssection. Pins 13 are located on both sides of the bucket base 612 and extend longitudinally along each leg of the chevron-shaped groove 4b. The upper portion of buckets 6 have integral shroud portions 6a which cooperate with adjacent shrouds to prevent the leakage of motive fluid beyond the outer tips of blades 6d. However, integral shrouds are not needed, since the invention may be used also with separate shrouds pinned or peened to the blades 6d, or with shroudless buckets.

in an axial flow turbine, the buckets are subjected to large axial forces resulting from the steam flow vibrational forces, thermal transients, etc. In the chevron dovetail, these forces are transmitted to the wheel either directly or through the pins 13. These forces acting on the pins 13 tend to cause them to move axially out of therecesses 4c, '60. It will be. obvious that if pins 13 project. from the sides of the wheel rim, they will eventually contact adjacent stationary parts and cause substantial damage to the turbine. To prevent the pins-13 from moving axially, we utilize in accordance with our invention the segmentalretainingirings 12 (see Fig. 2), which as already disclosed may also have portions adapted to function to seal the axial spaces between the bucket wheels and adjacent diaphragm's. I

Each ring 12has an axially extending leg portion 12 from which extends a dovetail'IZd disposed in a circumferential grove for securing the ring segments against radial movement relative to 'bucket wheel 4. The grooves 4d are formed in the wheel-rim portion 4a on both sides of the wheel adjacent the bottom of the axially extending grooves 412. A radially extending portion 122 of the ring 12 is located adjacent the wheel surface 42 and extends thereacross to prevent longitudinal displacement of pins 13. The circumferentialflanges 12a, 12b are defined by the leg portions 12a, 12 respectively. The rings 12 consist of arcuate segments 12c, which as disclosed span one bucket but can of course be made to span more than one bucket if desired, as dictated by manufacturing convenience. Whil'e segments 12c serve antenna:

but is free to move axially. As in Fig. 2, the pins 16 have a circular cross-section but other key cross-sections would perform equally as well. To prevent axial movement of the pins 16 and bucket 14, the combination sealing and retaining segments 12c are located in recesses 15d defined by the rim portion 15a and thus functions to prevent axial movement of 'both the bucket 15" and pins 16,-. and to substantially eliminate leakage intothe spaces between the bucket wheeel and adjacent diaphragms.

Thus, it will be seen that the invention provides an improved form of bucket fastening with a combination sealing and retaining means for preventing axial movement of the bucket fastening means relative to the wheel,

adequately to prevent axial'dis'plaern'ent of pins i3, the

ends of the pins may also be peened to further lock them relative to the wheel rim do. It remains to note that a portion of the wheel rim is removed to form a notch opening 4;. This openingisfilled by arcuate segment 17 which is secured against radial movement by pins 18 located in keywaysffliz, 1-2; in the segmentsd'l E20, respectively. 7 v i v I Thus,- thesegmented rings 12 function to prevent both .axial movement of pins- 13' and leakage of motive fluid out of the main flow path. In addition, our novel consive wear makes replacement of the seal members necesary. This construction eliminates the necessity of having to replace the entire bucket or extensively repair the bucket bases or wheel when buckets or a wheel having integral sealing strips are used.

The bucket wheel is assembled in the following manner. The buckets 6 are inserted radially intothe grooves 4b and then keyed to the rim portion 4a by pins 13 to prevent radial displacement of the buckets. The pins 13 may then be fixed in place by peening at the ends, if desired. The segments 120 are then inserted'radially into the circumferential recess 4d through the notch opening d and moved to the left or right along the rim portion 4a ofwheel member 4. After all segments 120 are located on the wheel member the notch opening is closed by arcuate segment 17 which isthen locked against radial movement by driving in pins 13. While the chevronshaped buckets 6 illustrated in Fig. l are inserted radially and maintained in place by pins 13 extending along the 7 legs of the bucket in a longitudinal direction, the invention may not be limited to such a construction. Another modification disclosed in Fig. 3 illustrates a bucket wheel containing bucket 14 having an axially extending base portion 144 located in axially extending grooves 15b defined by rim portion 15a of disk member in this modification, the bucket is prevented from moving radially relative to the wheel member'ls by the axially extending pins 36 located in cooperating'recess 14c, 15c

and serves the additional function of restricting leakage of motive fluid into the space between the diaphragm and bucket wheel. Furthermore, it permits ready replacement of the retaining and sealing means in the event of excessive wear or necessity to replace damaged buckets. 'While only two embodiments of the invention have been described in detail herein, it will be obvious to those skilled in the art t' at many changes and substitutions of equivalents might be made; and it is desired to cover by the appended'olaims all such modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire'to secure by Letters Patent in the United States is: I

1. in a turbomachine having a casing containing a rotor with at least one Wheel rim portion and at least one diaphragm supported in the casing adjacent the wheel rim portion and axially spacedtherefrom to form a sub stantial clearance space therewith, the combination of a wheel rim portion defining a circumferential row of axially extending chevron-shaped grooves, a plurality of buckets each having a base portion or" substantially the configuration of said grooves, cooperating key means interengaging between the bucket and Wheel rim portions, said key means constituting the sole means to prevent radial displacement of the buckets, and at least one segmented ring member separably connected to the wheel rim at one side of said buckets, the connection of said ring member to said rim including means to removably key each of the segments of said ring member against radial movement relative to said rim, said segmented ring having a first annular portion abutting the exterior ends of said cooperating key means to prevent relative axial displacement thereof and a second annular portion projecting from the wheel rim towards the adjacent diaphragm to restrict. leakage of fluid through said clearance space.

' 2. In an elastic fluid turbine having a casing containing a rotor with at least one bucket wheel. and at least one nozzle diaphragm member supported in the casing ad jacent the bucket wheel and axially spaced therefrom to form a substantial clearance space therewith, the combination ofabucket wheel rim portion defining a circumferential row of axially extending grooves and a circumferentiallyextending dovetail grove on at least one side of said axially extending grooves, a circumferential row of buckets each having a base with a-portion disposed in at least one of ,said grooves, cooperating key means disposedbetween the buckets and wheel rim portion, said key means constituting the sole, means for preventing radial displacement of the buckets, and at least one segmented ring member defining a coniugate dovetail disposed in said circumferentially extending dovetail groove, the ring member defining a first-flange portion abutting the ends of said buckets and cooperatingkey means to.

prevent axial displacement of said buckets and cooperating key means, the ring member defining also a second annular portion projecting from the wheel rim towards an adjacent diaphragm portion to restrict leakage of fluid through said clearance space.

3. In a turbomachine having a casing containing a rotor with at least one ,bucket wheel and at least one nozzle diaphragm member supported in the casing adjacent the bucket wheel and axially spaced therefrom to form a substantial clearance space therewith, the combination of a wheel rim portion defining a circumferential row of substantially axially extending grooves, a circumferential row of buckets each having a base with a portion disposed in at least one of said grooves, cooperating key means disposed between the buckets and wheel rim portion constituting the sole means to prevent radial displacement of the bucket bases relative to the rim, and a segmented ring member separably connected to said rim portion on at least one side of said buckets, the connection of said ring member to said rim portion including means to removably key each of the segments of said ring member against radial movement relative to said rim portion, the segments of said ring each having a first flange portion abutting the exterior ends of said key means to prevent axial displacement thereof and a second arcuate portion projecting from the wheel rim toward an adjacent diaphragm portionto restrict leakage of fluid through said clearance space.

4. In a turbomachine having a casing containing a rotor with at least one wheel rim portion and at least one diaphragm supported in the casing on at least one side of the wheel rim portion and axially spaced therefrom to form a substantial clearance space therebetween, the combination of a wheel rim portion defining a circumferential row of axially extending chevron-shaped grooves, a circumferential row of buckets each having a base with a portion disposed in at least one of said grooves, pins located in cooperating grooves defined by the wheel rim and bucket bases, said pins constituting the sole means to prevent radial displacement of the buckets, and at least one segmented ring member separably connected to the wheel rim on at least one side of the buckets, the connection of said ring member to said rim including means to removably key each of the segments of said ring member against radial movement relative to said rim, said segmented ring having a first flange portion abutting the exterior ends of said pins to prevent axial displacement thereof and a second annular portion projecting from the wheel rim towards an adjacent diaphragm portion to restrict leakage of fluid through said clearance space.

References Cited in the file of this patent UNITED STATES PATENTS 784,431 Rambal Mar. 7, 1905 961,328 Wait June 14, 1910 1,050,187 Westinghouse Jan. 14, 1913 2,279,258 Allen Apr. 7, 1942 2,651,494 Persson Sept. 8, 1953 2,658,718 Walker Nov. 10, 1953 2,755,063 Wilkinson July 17, 1956 FOREIGN PATENTS 59,398 France Jan. 6, 1954 250,728 Switzerland July 1, 1948 618,011 Great Britain Feb. 15, 1949 662,517 Great Britain Dec. 5, 1951 701,263 Great Britain Dec. 23, 1953 742,476 Great Britain Dec. 30, 1955 986,022 France Mar. 21, 1951 1,103,348 France May 18, 1955 OTHER REFERENCES Publication: Flight, volume 56, page 168, August 11, 1949.

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