US 3891351 A
This disclosure is directed to turbine machinery discs having improved elevation and contouring of the disc rim lugs and blade attachment slots local to the outer diameter blade attachment lug and slot surfaces of said discs thus providing a strain-conforming and restraining surface for redistributing and resisting the transmission of blade shank tang stresses and strains as they develop in the root attachment lands and transition zones of the turbomachinery blades.
Description (OCR text may contain errors)
United States Patent [1 1 Norbut June 24, 11975 1 TURBINE DISC  Inventor: Theodore J. Norbut, 3 141 Claydor Dr., Dayton, Ohio 45431  Filed: Mar. 25, 1974  Appl. No.: 454,372
 US. Cl. 416/219; 416/241; 416/244; 416/248  Int. Cl. FOld 5/30  Field of Search 416/219, 244, 248, 241 B, 416/214 [5 References Cited UNITED STATES PATENTS 3,294,364 12/1966 Stanley 416/219 3,612,718 10/1971 Palfreyman et a1 416/193 X 3,809,495 5/1974 Stahl 416/24 B FOREIGN PATENTS OR APPLICATIONS 920,641 11/1954 Germany 416/500 United Kingdom 416/241 B U.S,S.R 416/219 Primary Examiner-Everette A. Powell, Jr. Attorney, Agent, or Firm-Joseph Patrick Burke 5 7] ABSTRACT This disclosure is directed to turbine machinery discs having improved elevation and contouring of the disc rim lugs and blade attachment slots local to the outer diameter blade attachment lug and slot surfaces of said discs thus providing a strain-conforming and re straining surface for redistributing and resisting the transmission of blade shank tang stresses and strains as they develop in the root attachment lands and transition zones of the turbomachinery blades.
11 Claims, 14 Drawing Figures TURBINE DISC This invention is directed to improved discs with rims having blade attachment slots and lugs with smoothly radiused raised outer rim lug surfaces adjacent the rim slots to mitigate or reduce the generation of severe stress-strain concentrations and non-uniform load distributions in turbomachinery blading. According to this invention, these disc rims, suitable for use in turbomachinery attachment devices, exhibit restraining surfaces different from prior art rims in that they afford additional restraining surfaces due to the elevated rim lug height at the uppermost portions of the rim lugs thereby providing additional, smooth contacting lug surfaces for absorbing and distributing stresses, such as, centrifugal, centrifugal untwist, gas bending, vibratory, foreign object impact and other forms of complex stresses.
This integral disc of this invention is characterized by the following composite features:
1. The outer portions of the disc rim lugs are raised (elevated) adjacent to the slots in contrast with lower disc rim portions between said raised lugs.
2. These raised portions have a gradual radius of curvature, which is substantially equal and symmetrical for each rim lug set accommodating each blade.
3. The curvature of the outer rim lugs is more gradual than that of the lower ends of the rim slots which accommodate the blade tang portions.
4. Each symmetrical rim slot, accommodating each peripherally mounted blade, has a pair of extended (raised) lug portions, the height (diameter) of which approximately equals that of each other.
5. Each disc rim has symmetrical approximately equal respective lower intermediate portions (between the raised lugs), said lower portions being of approximately equal diameter.
6. There is no direct sharing of tension or compres sion forces between adjacent blades.
In the drawings, the features of the invention are contrasted with typical prior art configurations.
FIG. I of the drawing is a perspective view, partly in section, illustrating an individual turbine blade in its individual disc attachment. It will be realized that actual turbine rotors have a plurality of such blades and disc attachments customarily spaced peripherally about the rim portion of a disc for rotation. These blades are arranged circumferentially in fluid flow machines such, for example, as turbomachinery compressors and turbines.
FIGS. 2 and 3 are likewise perspective views, partly in section, showing further configurations of prior art devices evidencing similar disc rim and blade root attachment relationships.
FIGS. 4(A) and 4(8) are both side views showing a characteristic prior art disc rim having a plurality of rim slot and lug portions in christmas tree arrangement.
FIG. 5 is a sectional view taken along the line 55 of FIG. 4( B) illustrating in detail the dead rim, live rim, web and bore portions of such a disc rim.
FIGS. 6 and 7 are perspective views, partly in section, illustrating the disc rims of this invention resulting in the improved features which will be pointed out hereinafter.
FIG. 8(A) is a schematic showing of a typical positioning of a prior art turbine blade in relation to the characteristic root attachments, surfacing and disc rim attachment configuration typical of FIGS. 1, 2 and 3.
FIG. 8(B) is a schematic view of the blade attachment of FIG. 8(A) in perspective showing the blade attachment land surface 5.
FIG. 9 is a diagrammatic view vectorially illustrating the strain distribution typically occurring on the blade root attachment tang, adjoining blade shank and transition surfaces resulting from steady centrifugal body forces during rotation of turbine blades mounted in prior art rims. A high strain gradient results at this point where the local tensile and compressive strains become additive and reinforce each other. The strain field is entirely tensile above the point of contact and changes to compression as the load is introduced into the disc lug at the zone of contact.
FIG. 10 is a similar diagrammatic view showing in section the strain field amplification to which prior art devices are subjected when a bending moment is applied in conjunction with centrifugal body forces. Such bending moments are characteristically introduced by such causes as steady and unsteady gas dynamic pressure forces, airfoil untwist, natural resonance vibrations and instantaneous impacts from foreign object debris.
FIGS. 11 and 12 diagrammatically illustrate by vectorial notation the effect of the devices of the invention in providing a reduction in the magnitude of the peak strains through redistribution.
Referring to the drawings, and more particularly to FIGS. 1 and 8(8), turbine blade 1 has a platform portion 2. Beneath the blade platform is a centrally located blade shank 3 which merges into a root attachment transition zone shown at 4 and thence downwardly to the root attachment land surfaces, viz., such as at surfaces 5, FIG. 8(B), of the blade tang portions 6. The blade root attachment is thus made up of blade shank portion 3 and tang portions 6 which underlie transition zone 4.
The blade root attachment is received in the cavities or slot portions 9 of disc rim portions 7 of disc 8. See FIGS. 4(A) and 4(8). The mounting disc 8 has a disc rim portion 7 in which there are a plurality of circumferentially located slots 9, of varying configurations depending on blade configuration. The rim portion 7 of the disc can be further divided into an upper (dead) rim portion R and a lower live rim portion R as shown in FIG. 5. The disc portions underlying the rim are the web portion W and the bore portion B. Each disc rim has lug portions 11. As will be noted from FIGS. 1 5, and 8(A), the upper portions U of the prior art disc rim lugs are of generally uniform. height (diameter) and curvature in the outer rim periphery.
In contrast thereto, the discs of this invention have rims whose outer periphery have raised (elevated) lug portions 13 adjacent to the slots and lower intermediate rim portions 12 between raised portions 13.
As will be noted from FIG. 2, some turbine blades do not have a platform. Instead, the disc rim cavities or lugs 9 receive the root attachment in a position where the shank to root attachment transition zone 4 lies closer to the upper portion of blades 1. As illustrated in FIG. 2, the zones of immediate stress-strain reaction are the blade root attachment tang zones shown by cross-hatching at 10. Such stress-strain reaction zones 10 are shown on both the left and right hand sides of the root attachment for blade 1 of FIG. 2.
FIGS. 3, 4(A) and 4(8) illustrate characteristic prior art blade root and disc lug attachment configuration referred to in the art as a Christmas tree. In such blade root attachments, the blade root attachment is defined by a plurality of blade tang portions 6 (FIG. 3), each such portion having mating lugs 11 (FIG. 4(A)) defining the slot portions 9 in the disc rim 7 which terminate upwardly at the outer rim periphery in outermost portions U of uniform height (diameter) and curvature in the outer rim periphery.
The disc rims of FIGS. 6 and 7, illustrating the present invention, characteristically show disc rim lugs 11 and corresponding disc rim slots 9 having both elevated, raised or extended portions 13 above the lower intermediate rim portions 12 (which are the adjacent and lower lying portions of the disc rim periphery).
The elevated rim lug portions 13 provide increased restraint for reducing the bending deflections reacted as moments in the blade shank/transition regions. Positioning of the extended disc rim lugs in close proximity to the blade shank provides restraint of the shank which limits movement of the blade attachment tangs when centrifugal body forces load the blade attach ment tangs against the disc raised lugs portions 13 during rotation. This provides more uniform strain distribution for the attachment surfaces. The smoothly radiused raised lug surfaces 13 of this invention tend to avoid stress/strain concentrations on blade shank surfaces such as occur when the shank comes in contact with the upper uniform surface portions U of the disc lug 11 typical of FIGS. 1 3, 4(A), 4(3) and 5. The smoothly radiused surfaces provide, at a distance removed from the local origins of normal high strain intensity, non-linear contact surfaces that absorb bending induced contact pressure forces in a graduated manner. In accordance with this invention, the uniform geometric contouring of the elevated rim lug portions 13 is proportioned to accommodate the magnitude and rate of blade deflection during bending.
The net effect of the features of this invention is to reduce or substantially eliminate abrupt stress/strain transitions and load non-uniformities as compared with known art root attachments such as shown in FIGS. 1, 2, 3, 4(A), 4(8), and 5.
Prior art FIGS. I, 2, 3, 4(A), 4(8) and feature abrupt changes in contour in the disc rim lug portions 11 at upper portions U which produce localized Hertzian stress/strain concentrations when the sides of the blade shank come in contact with the disc lug portions 11 when bending of the blade occurs. Such concentrated stress/strain fields are normally accommodated by the inherent ductility of conventional materials such as steel, titanium and nickel-based, so-called superalloys. Brittle materials such as ceramics and composites possess limited ductility and must avoid such abrupt contour changes to prevent stress concentrations from interacting. As shown in FIG. 2., there can exist a zone of comparatively severe stress-strain interaction in a deflected blade.
A further advantage of this invention resides in the fact that not only monolithic materials but also ceramics and composite material systems can be utilized to make integral discs within the purview of this invention. Thus, materials such as composites and ceramics, while usually classified as brittle because they possess little or no ductility for redistributing local stress-strain concentrations, can be utilized in turbomachinery in-- corporating this invention.
The successful application of these materials to turbomachinery blading depends to a great extent upon the ability to avoid abrupt stress-strain concentrations, e.g., as introduced by non-uniform loading. Conventional metals such as titanium tend to exhibit distress in blade root attachments from local load nonuniformities. However, such distress can be, and customarily is, manifested in the form of fretting wear, induced fatigue or limited low cycle fatigue life as a consequence of concentrated high contact stresses.
Thus, the more gradual transition afforded by the present invention in the blade attachment to shank transition region and the central shank section of rotating turbine-compressor blading offers a more flexible approach to materials in the compressor blading art.
The restraining effect provided by this invention suppresses load shifting from one blade root attachment to its opposing partner. The elevated rim lug 11 can be in intimate contact with the blade shank portion prior to rotation or separated therefrom by a normal assembly tolerance gap.
FIGS. 9 and 10 depict characteristic prior art stressstrain relationships vectorially and illustrate contrasts between disc rims of FIGS. 1, 2 and 3. Such relationships can be compared with those characteristic of this invention as illustrated by the diagrams of FIGS. 11 and 12 with FIG. 11 referring to FIG. 6 and FIG. 12 illustrating the general effect of FIG. 7s configuration on strain distribution.
FIG. 8(A) depicts one of the typical disc-to-blade root attachment configurations known within the art in reference to FIGS. 1 and 2. FIG. 9 illustrates the strain distribution existing on the outer portions of the blade attachment surfaces under uniformly loaded conditions for the same configuration as FIG. 8(A).
As will be observed from FIGS. 9 12, a strain reversal occurs at the initial point of contact of the disc rim lug (upper portion) with the blade attachment shank. The reversal occurs as the blade shank load is transferred to the root attachment tang. The outer surface strain distribution shown in FIGS. 9 12 is tensile as it approaches the contact point and it then converts to compression With the introduction of nonuniform loads arising from centrifugal, centrifugal untwists, vibratory, gas bending, foreign object impact and others, one side ofthe blade attachment is forced to absorb the loads relieved by its partner. The intensity of the strain reversal is illustrated in FIG. 10 and occurs as a consequence of load redistribution in the form of bending.
FIG. 11 illustrates the effect of the configuration of FIG. 6 on load distribution. The magnitude of the stress reversal is reduced (as compared with FIG. I as illustrated in FIG. 9) and taken up over a greater distance upwards along the shank surface.
FIG. 12 illustrates the effect of the configuration of FIG. 7 on load distribution. Similarly, the magnitude of the stress reversal is reduced (as compared with FIG. 2 as illustrated in FIG. 10) and is distributed over a significantly greater distance upwards along the blade shank surface in like manner to that shown in FIG. II.
The present invention differs significantly from conventional prior art disc rims which differ from one another based on metal characteristics which provide stress redistributing capability through inherent ductility of the metal. This invention offers a distinct advantage of flexibility in choice of materials because these configurations avoid the generation of strain gradients critical to material having low ductility such as composites and ceramics. The significance of this is that the present invention permits the utilization of not only monolithic materials but also ceramics, and composite material systems of ceramics and metals,-viz., ceramets in addition to the so-called superalloys. Thus, the present invention can utilize such integral disc materials as: monolithic material, such stainless steel; titanium alloys customarily usable at temperatures of 900F. to lOOOF.; nickel and cobalt-based so-called superalloys, viz., metal alloys containing nickel and/or cobalt and having a melting point range of approximately 2400F. to 2500F. and usable at temperatures up to 1800F.; ceramics stable at temperatures up to about 2500F.; fiber-reinforced metallic or inorganic and organic composite material systems, such as Boron/Aluminum, Graphite/Epoxy, Borsic Titanium etc. Other organic polymeric materials can be used, e.g., silicone resins.
What is claimed is:
l. A turbine machinery disc having bore, web and rim portions, the rim portion of which is comprised of:
a plurality of circumferentially arranged symmetrical slots for accommodating blades, each slot having blade tang-accommodating portions of given radius of curvature;
a set of symmetrical rim lugs adjacent to each slot, each lug having raised outer portions which are substantially of the same height and gradual radius of curvature, which radius of curvature exceeds that of said blade-tang accommodating slot portions; and
lower symmetrical rim portions of approximately equal diameter between said raised rim lugs;
said disc being further characterized as avoiding direct sharing of tension and compression between adjacent blades.
2. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of ceramic material.
3. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of ceramic and metal material.
4. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of a metal alloy containing nickel and having a melting point ranging from approximately 2400F. to 2500F.
5. A turbine machinery disc as in claim ll wherein said bore, web and rim portions are integral and comprised of a metal alloy containing cobalt and having a melting point ranging from approximately 2400F. to 2500F.
6. A turbine machinery disc as in claim 4 wherein said metal alloy includes cobalt.
7. A turbine machinery disc as in claim 5 wherein said metal alloy includes nickel.
8. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of monolithic material.
9. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of fiber-reinforced metallic composite material.
10. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of fiber-reinforced organic polymeric composite material.
11. A turbine machinery disc as in claim 1 wherein said bore, web and rim portions are integral and comprised of fiber-reinforced inorganic composite material.