US2858102A

US2858102A - Turbomachine wheels and methods of making the same

Info

Publication number: US2858102A
Application number: US454175A
Authority: US
Inventors: David J Bloomberg
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1954-09-03
Filing date: 1954-09-03
Publication date: 1958-10-28
Anticipated expiration: 1975-10-28

Description

Oct. 28, 1958 D. J. BLOOMBERG TURBOMACHINE WHEELS AND METHODS OF MAKING THE SAME Filed Sept. 5. 1954 2 Sheets-Sheet 1 m w 5) W ml M x %////7// L\ MM 1 M 03W -& W

4 l u flifflflflflflfll% y lllffllliffllll/rllyl/ I! United States Patent @fiice 2,858,102 Patented Oct. 28, 1958 TURBOMACIUNE WHEELS AND METHODS OF MAKING THE SAME David J. Bloornberg, Newton, Mass., assignor to General Electric Company, a corporation of New York Application September 3, 1954, Serial No. 454,175

3 Claims. (Cl. 253-3915) The present invention relates to turbomachine wheels and methods of making the same.

It is a general object of the present invention to provide a turbomachine wheel including a disk and a plurality of circumferentially spaced-apart and radially outwardly extending buckets carried by the periphery of the disk, and comprising an improved and simplified arrangement for rigidly securing the buckets to the disk and for rigidly securing together the individual elements of each bucket and for achieving etfective circulation of cooling air through the individual elements of each bucket.

Another object of the invention is to provide in a turbomachine wheel of the character noted, a bucket construction of improved and simplified arrangement, wherein the component elements thereof are formed of materials especially selected to fulfill the individual operating requirements thereof with respect to stresses, temperatures and related factors.

Another object of the invention is to provide a turbomachine wheel bucket construction including an inner post formed of high-stress material especially selected to withstand the loads imposed thereon due to centrifugal force, gas bending forces, misalignment forces, and the like, and an outer shell formed of temperature-resistant material especially selected to withstand the high temperature of the working gas medium, and embodying an improved arrangement for providing a rigid connection between the inner post and the outer shell.

Another object of the invention is to provide a turbomachine wheel bucket construction of the character described, that comprises an improved arrangement for providing a rigid connection between the inner post and the outer shell, and that consists essentially of first and second interference partsrespectively formed integrally with the outer surface of the inner post and the inner surface of the outer shell and cooperating with each other to provide an interference fit therebetween, and accommodating thepassage through ducts formed therein of cooling air between the inner and outer ends of the bucket.

Another object of the invention is to provide a turbomachine Wheel bucket construction of the character described, wherein the interference parts mentioned are disposed on both the leading side and the trailing side of the inner post so that cooling air is conducted through the bucket both immediately behind the leading wall of the outer shell and immediately ahead of the trailing wall of the outer shell in order effectively to cool the outer shell and effectively to insulate the inner post from the high temperature of the outer shell.

A further object of the invention is to provide an improved method of making a turbomachine Wheel including a metal disk and a plurality of circumferentially spaced-apart and radially outwardly extending buckets carried by the periphery of the disk, wherein each. of the buckets includes a metal inner post and a metal Outer shell; whereby the method involves an exceedingly simple first casting step for producing the outer shells in situ upon the respective outer surfaces of the inner posts, and an exceedingly simple second casting step for producing the disk in situ fusing in place the inner ends of the inner posts of the buckets.

A further object of the invention is to provide a method of making a turbomachine wheel bucket including a metal inner post and a metal outer shell, and involving a first simple casting step in which the inner post is cast with integral first interference parts on the outer surface thereof, and a second simple casting step in which the outer shell is cast in situ about the inner post with integral second interference parts on the inner surface thereof and cooperating with the first interference parts on the outer surface of the inner post to provide an interference fit therebetween and a resulting rigid connection between the inner post and the outer shell.

A still further object of the invention is to provide a method of making a turbomachine wheel bucket of the character described, wherein first notches are formed in the first interference parts mentioned incident to the casting thereof and second notches are formed in the second interference parts mentioned incident to the casting thereof which notches cooperate to provide ducts through the bucket between the outer surface of the inner post and the inner surface of the outer shell and accommodating the passage of cooling air therethrough.

Further features of the invention pertain to the particular arrangement of the elements of the turbomachine wheel and of the steps of the method of making the same, whereby the above-outlined and additional operating features thereof are attained. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which: I

Figure 1 is a fragmentary side elevational view, partly broken away and partly in section, of a turbomachine wheel embodying the present invention, and that may be made in accordance with the method of the present invention;

Fig. 2 is a substantially vertical sectional view of the turbomachine wheel, taken in the direction of the arrows along the line 2-2 in Fig. 1;

Fig. 3 is an enlarged vertical sectional view of one of the buckets carried on the periphery of the disk of the turbomachine wheel shown in Figs. 1 and 2;

Fig. 4 is an enlarged horizontal sectional view of the bucket, taken in the direction of the arrows along the line 44 in Fig. 3;

Fig. 5 is another enlarged horizontal sectional view of the bucket, taken in the direction of the arrows along the line 5-5 in Fig. 3; and

Fig. 6 is a plan view of only the extreme outer end of the bucket shell, taken in the direction of the several arrows 6 in Fig. 3.

Referring now to Figs. 1 and 2 of the drawings, the turbomachine wheel 10 there illustrated, and embodying the features of the present invention, may comprise the first-stage wheel in a plural stage gas turbine unit including a rotatable operating shaft 11. The wheel 10 comprises an annular disk 12 provided with an inner hub 13 that is rigidly secured to the operating shaft 11 for rotation therewith; and the periphery of the disk 12 carries a plurality of circumferentially spaced-apart and radially outwardly extending composite buckets 14, described more fully hereinafter. Also the wheel 10 comprises a pair of annular members 15 disposed on opposite sides of the disk 12 and carried by the opposite ends of the hub 13 and spaced laterally from the respective faces of the disk 12 to provide a pair of annular chambers 16 therebetween extending radially from the hub 13 to the

flange portions

33 and 34 of the buckets 14. A number of circumferentially spaced-apart openings 17 are formed in each of the members 15 adjacent to the hub 13 in order to accommodate the passage of cooling air from the exterior into the corresponding one of the chambers 16; and in order further to assist in the circulation of cooling air into the openings 17, each of the members 15 carries an outwardly projecting annular ring 18 disposed radially outwardly with respect to the openings 17 and surrounding the operating shaft 11.

The composite buckets 14 are substantially identical; and each bucket 14 essentially comprises a radially extending inner post 19 and a surrounding radially extendingv outer shell 20, the inner end of the inner post 19 being fused into and forming a part of the adjacent portion of the periphery of the disk 12, and the outer end of the inner post 19 being rigidly secured to the intermediate portion of the outer shell 20. As best shown in Figs. 3 to 6, inclusive, the outer surface of the outer shell 20 is provided with a typical configuration defining the usual gasfoil, the leading and trailing walls of the outer shell 20 being respectively indicated at 21 and 22; whereby the wheel is rotated in the counterclockwise direction, as viewed in Fig. 1, when the working gas medium passes through the buckets 14. The junction between the

walls

21 and 22 at the front of the outer shell 20 comprises a rounded section, as indicated at 23; while the junction between the

walls

21 and 22 at the rear of the outer shell 20 comprises an elongated tail, as indicated at 24. Of course, the outer shell 20 is hollow, having an open outer end, and the

walls

21 and 22 have a minimum thickness consistent with the required strength thereof; and in order to conserve material, a cavity 25 is formed in the outer end of the inner post 19.

As best shown in Figs. 3 and 5, the outer shell 20 is supported intermediate the ends thereof upon the outer end of the inner post 19 by a rigid connection therebetween, whereby the inner end of the outer shell 20 projects radially inwardly toward the periphery of the disk 12 and in surrounding relation with respect to the adjacent portion of the inner post 19, providing a continuous space 26 therebetween, while the outer end of the outer shell 20 projects radially outwardly beyond the outer end of the inner post 19. The rigid connection mentioned between the inner post 19 and the outer shell 20 is formed by an interference fit consisting of a first series of radially spaced-apart teeth 27- formed integrally with the outer end of the inner post 19 and projecting circumferentially outwardly therefrom, and a second series of radially spaced-apart teeth 28 formed integrally with the intermediate portion of the outer shell 20 and projecting circumferentially inwardly therefrom; the first series of teeth 27 being provided on the outer surface of the inner post 19, and the second series of teeth 28 being provided on the inner surface of the outer shell 20, and the two series of

teeth

27 and 28 being disposed in interfitting relation. The interfitting

teeth

27 and 28 are dis posed both immediately behind the leading wall 21 of the outer shell 20 and immediately ahead of the trailing wall 22 of the outer shell 20; and first and second series of spaced-

apart ducts

29 and 30 are formed by cooperating notches in the first and second sets of teeth 27' and 28, the first set of ducts 29 being disposed immediately behind the leading wall 21 of the outer shell 20 and communicating between the leading portion of the space 26 and the space 31 defined in the hollow outer end of the outer shell 20, and the second set of ducts 30 being disposed immediately ahead of the trailing wall 22 of the outer shell 20 and communicating between the trailing portion of the space 26 and the space 31.

The extreme lower end of the outer shell 20 terminates in an outwardly directed flange 32 including a portion 33 extending forwardly and a portion 34 extending rearwardly, each of the

flange portions

33 and 34 being arranged in spaced relation radially outwardly of the root of the inner post 19, and consequently in this relationship with respect to the periphery of the disk 12. As best shown in Fig. l, the leading flange portion 33 carried by the outer shell 20 of each bucket 14 cooperates with the trailing flange portion 34 carried by the outer shell 20 of the adjacent bucket 14 to provide a substantially continuous circumferentially extending bridge therebetween defining a corresponding arcuate space 35 therebelow adjacent to the periphery 42 of the disk 12 and commonly communicating between the leading and trailing portions of the two spaces 26 provided in the two adjacent buckets 14. Also leading and trailing

grooves

37 and 38 are respectively formed in the leading and trailing portions of the root of each inner post 19, whereby the

adjacent grooves

37 and 38 provided in the roots of adjacent inner posts 19 define a laterally extending cooling air outlet passage 39 communicating between the annular chambers 16 adjacent to the periphery of the disk 12 and also communicating with the space 35. Finally, a series of forwardly directed ribs 40 and a series of rearwardly directed ribs 41 are carried below the

respective flange portions

33 and 34 provided on the inner end of the outer shell 20 and arranged in engagement with the root portion of the associated inner post 19, and consequently in this relationship with respect to the periphery 42 of the disk 12.

In view of the foregoing description of the construction and arrangement of the wheel 10, it will be understood that when the operating shaft 11 is rotated at high speed the cooling air that is drawn through the inlet passages 17 into the chambers 16 proceeds radially therethrough and thence into the opposite ends of the circumferentially spaced-apart and laterally extending outlet passages 39 disposed adjacent to the periphery of the disk 12. The cooling air in each outlet passage 39 proceeds into the adjacent space 35 and thence into the leading and trailing portions of the two spaces 26 provided in the adjacent leading and trailing buckets 14. From the leading portion of the space 26 in each bucket 14, the cooling air proceeds through the set of ducts 29 into the space 31; and from the trailing portion of the space 26 in each bucket 14, the cooling air proceeds through the set of ducts 30 into the space 31; and ultimately the cooling air is discharged from the space 31 radially outwardly through the outer open end of the outer shell 20 of each bucket 14. Thus, it will be understood that the two streams of cooling air proceeding through each bucket 14, not only effectively cools the respective leading and

trailing walls

21 and 22 of the outer shell 20 thereof, but it also serves efiectively to insulate the inner post 19 from the high temperature of the outer shell 20.

In the construction of the wheel 10, the disk 12 is formed of a suitable cast metal having a relatively high strength with respect to tension stresses in order to withstand the centrifugal load thereon resulting from highspeed rotation thereof; each of the inner posts 19 is formed of a suitable cast metal having a very high strength with respect to tension and torsion stresses in order to withstand the centrifugal force, the gas bending forces and any misalignment forces to which it is subjected; while each of the outer shells 20 is formed of a suitable cast metal that is exceedingly resistant to very high temperatures (at least 1500 F.), and that has considerable strength at such high temperatures, with respect to tension, compression and torsion stresses in order to withstand the corresponding effects thereon produced both by centrifugal force and by the high-temperature gas medium in contact therewith. In this connection, it will be appreciated that when the wheel 10 is rotated at high speed, the inner end of each outer shell 20 is also subjected to compression forces; the outer end of each outer shell 20 is also subjected to tension forces; each inner post 19 is subjected fundamentally to tension and torsion forces; and the interfitting

teeth

27 and 28 respectively carried by each inner post19 and by each outer shell 20 are subjected fundamentally to shearing forces. As a constructional example, when the wheel comprise sthe first-stage wheel of a 600 H. P. gas turbine unit, the diameter thereof between the outer extremities of oppositely directed buckets 14 may be approximately 18", each of the buckes 14 may have a radial length of the outer shell 20 thereof of approximately 1%, the leading and trailing walls 21 and 22of each outer shell 20 may have a thickness of about hi and the other dimensions are related to those set forth in accordance with: standard design considerations. Moreover, the disk 12 and the members may be cast of a suitable lowcarbon steel, such, for example, as that sold by Allegheny Ludlum under the designation A-286"; each of the inner posts 19 may be cast of a suitable chromesteel, such, for example, as the commercially available 12% chrome-steel alloy; while each of the outer shells may be cast of a suitable special alloy, such, for example, as that sold as X-40. Really, only the alloy of the outer shells 20 comprises a strategic material; and the composition of the alloy X 40 is essentially as follows:

In making the turbo machine wheel 10, the plurality of composite buckets 14 are first produced; and in fabricating each of the buckets 14, both the inner post 19 and the associated outer shell 20 is formed employing respective precision investment casting steps (the lost wax technique). More particularly, a wax pattern of the inner post 19 is first invested with a suitable investment material (ceramic material, or the like); and thereafter, the invested wax pattern is supported in a suitable mold material (sand, or the like). Then the composite mold is preheated so that the wax pattern of the inner post 19 is melted and removed from the investment material, leaving a corresponding void in the supporting mold material; and thereafter, the mold material is completely cured. Finally, the high-stress metal is cast into the mold filling the void defined by the investment material so that, upon cooling, the inner post 19 is in a finished condition after rem-oval thereof from the mold and the breaking-away of the investment material. When the inner post 19 is .thus cast, the series of teeth 27 are formed integrally with the body thereof; and also the notches for the ultimate production of the

ducts

29 and 30 are formed therein incident to this casting step.

Then the cast inner post 19 is prepared for the casting thereonto of the associated outer shell 20. More particularly, suitable cores (formed of ceramic material, or the like) are arranged upon the outer end of the inner post 19 in the notches mentioned for the ultimate production of the

ducts

29 and 30 in the finished bucket 14. Then a wax pattern of the outer shell 20 is cast in place upon the outer end of the inner post 19; and then both the inner post 19 and the wax pattern of the outer shell 20 are invested with a suitable investment material; and thereafter, the composite invested pattern is supported in a suitable mold material. Then the composite mold material is preheated so that the wax pattern of the outer shell 20 is melted and removed from the investment material, leaving a corresponding void in the supporting mold material; and thereafter, the mold material is completely cured.

Finally, the heat-resistant metal is cast into the mold filling the void defined by the investment material so that, upon cooling, the outer shell 20 is in a finished condition after removal thereof, with the inner post 19, from the mold and the breaking-away of the investment material. When the outer shell 20 is thus cast, the series of teeth 28 are formed integrally with the body thereof; and also the notches for the ultimate production of: the

ducts

29 and 30 are formed therein incident to this casting step. Of course, the cores supported by the inner post 19 in the .casting of the outer shell 20 define the

ducts

29 and 30 in the composite bucket 14 after the breaking and removal of these cores. Moreover, in this casting of the outer shell 20, the outer surface [thereof is in a smooth and finished condition directly defining the gasfoil, and without further finishing operation.

In view of the foregoing, it will be understood that the required plurality of the composite buckets 14 are fabricated; and then they are arranged in a mold in proper position in ci-rcumferentially spaced-apart relation extending radially outwardly with the inner ends of the inner posts 19 extending radially inwardly; and then the metal of the disk 12 is cast into the mold so that the inner ends of the inner posts 19 are encompassed thereby, whereby the inner ends of the inner posts 19 are fused into the metal of the disk 12 forming the periphery thereof and providing a corresponding plurality of rigid connections between the disk 12 and the plurality of buckets 14. After cooling of the disk 12, the partially completed wheel 10 is removed from the mold.

The annular members 15 may be cast or fabricated in any conventional manner; and thereafter, they are brought into place and assembled upon the hub 13 of the disk 12. Subsequently, the annular members 15 are secured to the hub 13 in any suitable manner, such as: welding, induction melting, etc.; whereby the wheel 10 is ready for certain final finishing operations, including balancing, etc.

In view of the foregoing, it is apparent that there has been provided a turbomachine wheel of improved and simplified construction and arrangement, as well as an improved method of making the same. The improved wheel also includes a plurality of composite buckets of improved and simplified construction and arrangement; and similarly, the overall method includes improved and simplified method steps of making the composite buckets.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A turbomachine wheel comprising a disk and a plurality of circumferentially spaced-apart .and radially outwardly extending buckets disposed about the periphery of said disk; each of said buckets including a post rigidly secured to the periphery of said disk, a shell surrounding said post and provided with an outer surface defining a gasfoil, means including a first series of teeth formed integrally with said post and a second series of teeth formed integrally with said shell and cooperating with each other to define an interference fit therebetween for rigidly securing said shell to said post, said first series of teeth being provided on the outer surface of said post adjacent to the outer end thereof and said second series of teeth being provided on the inner surface of said shell intermediate the ends thereof, whereby the inner end of said shell projects radially inwardly toward the periphery of said disk and the outer end of said shell projects radially outwardly beyond the outer end of said post, means defining a first duct between said post and the leading wall of said shell, means defining a second duct between said post and the trailing wall of said shell, means including a first flange carried by the inner end of said shell and extending outwardly therefrom in the leading dirfiction and spaced radially outwardly fromthe periphcry of said .disk for directing cooling air into saidfirst duct," and means including a secondflange carried by the inner end of said shell and extending outwardly there from in the trailing direction and spaced radially outwardly from the peripheryiof said disk for directing eool ing air into said second duct.

2. The turbornachine Wheel set forth in claim 1, wherein the first flange carried by each shell cooperates with the second flange carried by the adjacents'nell to provide a substantially continuous circumferentially extending bridge therebetween.

3. Thetturbomachine heel set forth inclaim 1, Wherein the first and second flanges carried by each shell re spectively carry first and second sets of-radially inwardiy directed supporting ribs engaging the periphery of said disk.

References Cited .in the file of this 1 patent UNITED STATES PATENTS Buchi Nov. 29, .Klenk Mar. 15, Dimberg Mar. 15, ,Dirnberg -Mar. l5, Fransson Mar.t2 1, Franz .S ept. 2 5, .Johnstone May'27, Schmitt Aug. 11, Williams Nov. 3, Grantham July 27, Bruckman Jan. 29,

FOREIGN PATENTS Great Britain Jan. 20,