US3248082A

US3248082A - Reinforced gas-turbine blade or vane

Info

Publication number: US3248082A
Application number: US484783A
Authority: US
Inventors: Marshall G Whitfield
Original assignee: WHITFIELD LAB Inc
Current assignee: WHITFIELD LAB Inc; WHITFIELD LABORATORIES Inc
Priority date: 1965-08-19
Filing date: 1965-08-19
Publication date: 1966-04-26
Anticipated expiration: 1983-04-26

Description

April 6, 1966 M. G; WHITFIELD 3,248,082

REINFORCED GAS-TURBINE BLADE OR VANE Filed Aug. 19, 1965 INVENTOR.

Mars/mil "mm-ea a2 :95

United States Patent 3,248,082 REINFORCED GAS-TURBINE BLADE 0R VANE Marshall G. Whitfield, Brookfield, Conn. Whitfield Laboratories, Inc., P1). Box 293, Bethel, Conn.) Filed Aug. 19, 1965, Ser. No. 484,783 3 Claims. (Cl. 253-77) This application is a continuation-in-part of my copending applications Serial No. 257,938 filed February 12, 1963, and Serial No. 424,454 filed January 4,1965, both entitled, Reinforced Gas-Turbine Blade or Vane, both now abandoned.

This invention relates to turbines intended for high temperature service, such as gas turbines, and more particularly to the blade and vane components of such turbines.

Because of the increased efficiency which is attendant higher operating temperatures, present-day turbines are being designed with the thought of enabling the blades and vanes to withstand increasingly higher temperatures. However, under the severe thermal conditions encountered the blade and vane components despite all efforts to date still tend to fail quickly. To meet this situation, improved alloys are continually being developed and tried, for the purpose of combatting the thermal fatigue which results from elevated operating temperatures, as well as combatting stress rupture, growth and deformation.

A certain measure of success is had with alloys of cobalt or of nickel, wherein various percentages of other metals are present. However, all such alloys have one or more weaknesses, and do not fully successfully meet the complex and demanding requirements of turbine use.

For example, it is known that an alloy which has a satisfactory high temperature strength and which is resistant to deformation under thermal stress will show poor oxidation resistance and fail because of thermal fatigue after a period of apparently successful operation. Alloys which come under this category are thoseknown commercially as Waspaloy, W152 and Stellite 31.

On the other hand, alloys which are developed to show good oxidation resistance and to withstand thermal fatigue quite well, lack mechanical strength and resistance to deformation, which characteristics are important in turbine engines. The SM series of alloys falls in this category.

The above disadvantages and drawbacks of prior tur bine blades and vanes fabricated of SM or like alloys are obviated by the present invention, and one object of the invention is to provide an improved reinforced turbine blade or vane structure constituted principally .of highoxidation resistant metal such as SM alloy, which structure also has the necessary mechanical strength and resistance to deformation demanded for high temperature use in gas turbines. In accomplishing this object there is provided by the invention an improved composite blade or vane structure which is cast of SM (Sierra-Metals, division of Martin Marietta Co.) alloys, including cobalt base (manufacturers 300 series) and nickel base (manufacturers 200 series), or'similar alloys in the desired configuration and which has incorporated in it strategically placed reinforcing wires or members especially constituted of a different alloy comprising molybdenum, tungsten, tantalum or columbium and so selected that the casting temperature (when the reinforcing insert is incorporated in the cast piece) will not seriously reduce the strength of the insert nor adversely alter its properties as a reinforcing means. .By such organization an improved composite blade or vane structure is obtained having the necessary oxidation resistance and which will at the same time withstand thermal fatigue sufliciently to meet the exacting requirements of gas turbine use, such composite structure further having the necessary physical strength and resistance to deformation by virtuel of the reinforcing elements of different alloy matena s.

The reinforcement means may be constituted as individual wires having various configurations, or such means may be in the form of perforated sheets or strips. In each case the reinforcement means is arranged to be supported in the mold cavities so as to enable the bladeor vane structure to be cast in the desired configuration.

Further, the reinforcing means preferably has a coeflicient of expansion which is less than that of the blade or vane alloy, whereby a prestressing effect is had during the high temperature operation of the composite component.

Preferably also the reinforcement means are coated with either the base metal of the blade alloy or else with one of its alloying additions, whichever is found to be most suitable for protecting the reinforcement while in the mold cavity, and found to be suitable to alloy readily with the blade or vane metal during the casting of the latter. exposure of the reinforcing means when the composite structure is in use, especially at those locations which experience the highest operating temperature. The prestressing action mentioned above is of considerable advantage in minimizing distortion and combatting thermal shock or fatigue, at such elevated operating tempera tures.

Another object of the invention is to provide an improved composite reinforced blade or vane structure for gas turbines and the like, which structure is comparatively simple, economical to fabricate, and effective in accomplishing the desired increased strength and resistance to deformation.

A feature of the invention resides in the provision of an improved reinforced blade or vane structure as above set forth, wherein no rigid limitations are placed on the blade configuration nor the casting process, so that full freedom is had in the design and fabrication of the blades.

Another feature of the invention resides in the provision of a reinforced turbine blade or vane structure as above characterized, wherein an effective bond is had between the imbedded reinforcing means and the cast metal of the blade structure.

Other features and advantages will hereinafter appear.

In the drawings accompanying this specification, similar characters of reference are used to designate like components throughout the several views, in which:

FIG. 1 is a top plan view of an improved reinforced blade structure as provided by the invention.

FIG. 2 is a side elevational view of the blade structure of FIG. 1.

FIG. 3 is a bottom plan FIGS.-1 and 2.

FIG. 4 is a left endelevational view of 'the blade structure.

FIG. 5 is a right end elevational view of the blade structure. I

FIG. 6 is a transverse section, enlarged, taken on the line 66 of FIG. 2.

FIG. 7 is a top plan view of a composite blade structure illustrating a modification of the invention.

FIG. 8 is a perspective view of the reinforcing means incorporated in the blade structure of FIG. 7.

FIG. 9 is a plan view of one type of reinforcing wire element, which may be incorporated in the blade structures of FIGS. 1-3.

view of the blade structure of FIG. 10 is a plan view of another type of reinforcing wire element, which is incorporated in the blade Patented Apr. 26, I966 Means are provided for subsequently preventing Considering first FIGS. 1-6, the composite bladestructure showin therein is designated generally by the numeral 10. The bladestructure comprises a curved body portion 12 having somewhat the shape of an air foil section, such body portion having

end plates

14 and 16 which are depicted as being of substantially rectangular configuration. The exact shape of the

end plates

14 and 16 is subject to alteration, to adapt the blade to various supporting means as provided in the particular turbines under consideration. The blade 10 is cast of an alloy having high resistance to oxidation and heat, such as the SM series .of alloys.

In accordance with the invention, reinforcing stitfening elements 18a of a special alloy which is not especially resistant to oxidation but which instead has excellent mechanical strength at high temperatures are incorporated in the blade structure 10. The elements 18a may have any desired configuration. In FIGS. 1-6 they are constituted as straight wires, one such wire being illustrated in FIG. 10. The Wire 18a in this figure is shown as having a smooth surface and end enlargements 18b. Preferably the wire is provided with a protective coating, as by electroplating of a noble metal, aluminum or the nickel series. In place of the wires 18a, wires 18 with roughened surfaces as indicated in FIG. 10 may be employed. The wire 18a has the enlargements or shoulders 18b constituted as anchorage means. The shoulders 18b have special utility where the reinforcement wire has a smaller coefficient of expansion, since it will -reliably insure a tensional stressing of the reinforcements as the blade temperature increases. This is due to the following action: When the casting initially is solidifying and I cooling, the shrinkage of the cast metal in directions laterally of the reinforcement rods causing lateral compression of the rods, takes precedence over shrinkage in longitudinal directions because of the thin or blade-like configuration of the casting and the presence of the anchorage shoulders 18b. As a consequence, when the cast composite blade structure becomes hot during use, there is not a direct reversal of such shrinkage but instead the tendency is for the blade structure to elongate longitudinally, and this results in a tensional stressing of the reinforcement rods and a condition wherein the blade structure itself is held under continual longitudinal compression at the operating temperature. Thus, under actual conditions of use where very high temperatures are encountered, the increased stressing of the reinforcement means will tend to minimize distortion, thermal shock or fatigue of the blade structure.

I In place of the wire-

like reinforcements

18 and 18a shown in FIGS. 1-6, 9 and 10, a perforated strip type of reinforcement may be employed, such as the strip 38 shown in FIGS. 7 and 8. Such stiff strip may be of the plate 38. The blade 30 has a curved body portion 32 providing stiffness, which is similar in shape to the body portion 12, and has

end plates

34 and 36 similar to the

plates

14, 16. Imbedment of the reinforcing plate 38 is effected by casting the blade alloy substance about the reinforcing plate, as the latter is suitably supported in a mold.

In effecting the support of the insert pieces 18, 18aor 38in the mold, the latter may be supported at either one end or at both ends. By virtue of such support, the insert piece will have a projecting portion when the cast blade structure is removed from the mold; Such projecting portion may be removed by any suitable machining process, as by milling, grinding, etc. This will leave an exposed surface of the insert means, at one or both ends of the blade structure. Such exposed surface is not an especially serious consideration at the end plate 16 comprising the base end of the blade 10, or at the end plate 36 comprising the base end of the blade 30. Such base ends operate at a lower temperature than the other or i 7 but ends of the blades, whereby oxidation of the reinforcement means does not represent a serious problem.

However, in accordance with the invention,

end cover plates

20, 22 may be welded orotherwise secured to the end plates 14-16 respectively of the blade structure,

thereby to cover any exposed ends or portions ofthe reinforcement means. In FIGS. 7 and 8,

cover plates

40, 42 are secured to the

end plates

34, 36 respectively, for this purpose.

of the insert members are bad.

The reinforcement means as provided by the invention is stiff and continuous and unbroken throughout virtually the full length of the casting and is resistant to bending forces applied to it adjacent the ends of the casting; thus such means greatly strengthens the blade structures, tendt ing to minimize distortion under the effects of heat and mechanical stress. By virtue of the insert members havt ing a different composition especially chosen to provide great mechanical strength without regard to the adverse effects of oxidation, the composite blade structure is great- I ly superior to purely monolithic structures involving but a single. alloy. The blade structure as provided herein may be economically fabricated, and the increased cost is more than offset by the extended life interval of the blade,

whereby the servicing period for the gas'turbine is ap-' (b) said alloy having high oxidation and thermal fatigue resistance,

(c) said casting having a curved cross section,

(d) all exposed surfaces of said casting being constituted of the said refractory metallic alloy of high oxidation and thermal fatigue resistance,

(e) reinforcement and stiffening insert means cast within said casting and bonded thereto,

(f) said insert means comprising a metal alloy ofthe group of metals including tantalum, molybdenum, columbium and tungsten and being less refractory but mechanically stronger than the said alloy of the SM series,

(g) said insert means being coated with a metallic substance of the group of metals including noble metals, aluminum, and the nickel series, by which the insert means is bonded to the casting,

(h) said insert means having a lesser coefficient of expansion than that of the alloy of the casting, (i) said insert meansbeing continuous and unbroken throughout virtually the full length of the casting and comprising stiff elongateelements each resistant to bending forces applied to it adjacent the ends of the casting and each extending longitudinally of and for the full length of the casting and having surfaces at their end portions which surfaces are adjacent the ends of the casting and which face toward the center portions of the elements,

(j) said casting including integral portions disposed between and on opposite sides of said elongate ele- Thus, with the completed blade struc-. tures illustrated in FIGS. 1-5, and 7, no exposed portions ments at all points between the extremities of the latter,

(k) said elongate elements being under continual lateral compression. from the casting when cold,

(1) said casting being under continual longitudinal compression from the said end-portion surfaces of the elongated-elements when the casting is at operating temperature,

(In) said casting including supporting formations at its ends,

(n) the said end-portion surfaces of the said elongate reinforcing elements being disposed adjacent the said supporting formations of the castings, thereby to maintain major portions of the casting under longitudinal compression. I

2. A composite reinforced turbine blade structure as in claim 1, wherein:

(a) the reinforcement insert means comprises a plurality of separate stiflFening rods.

3. A composite reinforced turbine blade structure as 20 in claim 1, wherein:

(a) the reinforcement insert means comprises a perforated stiffening metal strip of curved cross section, interiorly disposed in the blade and having longitudinally extending rows of perforations, some of said perforations comprising the said end-portion surfaces.

References Cited by the Examiner UNITED STATES PATENTS 2,077,959 4/1937 Smith 170159 3,098,723 7/1963 Micks 25377 X FOREIGN PATENTS 235,304 6/ 1925 Great Britain.

574,770 1/ 1946 Great Britain.

619,634 3/ 1949 Great Britain.

833,261 4/ 1960 Great Britain.

SAMUEL LEVINE, Primary Examiner.

E. A. POWELL, 111., Assistant Examiner.

Claims

1. A COMPOSITE REINFORCED TURBINE BLADE STRUCTURE COMPRISING, IN COMBINATION: (A) AN ELONGATED CASTING OF A REFRACTORY METALLIC ALLOY OF THE SM SERIES KNOWN TO BE DEFICIENT IN MECHANICAL STRENGTH AS COMPARED WITH KNOWN STRUCTURAL METALS, (B) SAID ALLOY HAVING HIGH OXIDATION AN THERMAL FATIGUE RESISTANCE, (C) SAID CASTING HAVING A CURVED CROSS SECTION, (D) ALL EXPOSED SURFACES OF SAID CASTING BEING CONSTITUTED OF THE SAID REFRACTORY METALLIC ALLOY OF HIGH OXIDATION AND THERMAL FATIGUE RESISTANCE, (E) REINFORCEMENT AND STIFFENING INSERT MEANS CAST WITHING SAID CASTING AND BONDED THERETO, (F) SAID INSERT MEANS COMPRISING A METAL ALLOY OF THE GROUP OF METALS INCLUDING TANTALUM, MOLYBDENUM, COLUMBIUM AND TUNGSTEN AND BEING LESS REFRACTORY BUT MECHANICALLY STRONGER THAN THE SAID ALLOY OF THE SM SERIES, (G) SAID INSERT MEANS BEING COATED WITH A METALLIC SUBSTANCE OF THE GROUP OF METALS INCLUDING NOBLE METALS, ALUMINUM, AND THE NICKEL SERIES, BY WHICH THE INSERT MEANS IS BONDED TO THE CASTING, (H) SAID INSERT MEANS HAVING A LESSER COEFFICIENT OF EXPANSION THAN THAT OF THE ALLOY OF THE CASTING, (I) SAID INSERT MEANS BEING CONTINUOUS AND UNBROKEN THROUGHOUT VIRTUALLY THE FULL LENGTH OF THE CASTING AND COMPRISING STIFF ELONGATE ELEMENTS EACH RESISTANT TO BENDING FORCES APPLIED TO IT ADJACENT THE ENDS OF THE CASTING AND EACH EXTENDING LONGITUDINALLY OF AND FOR THE FULL LENGTH OF THE CASTING AND HAVING SURFACES AT THEIR END PORTIONS WHICH SURFACES ARE ADJACENT THE ENDS OF THE CASTING AND WHICH FACE TOWARD THE CENTER PORTIONS OF THE ELEMENTS, (J) SAID CASTING INCLUDING INTEGRAL PORTIONS DISPOSED BETWEEN AND ON OPPOSITE SIDES OF SAID ELONGATE ELEMENTS AT ALL POINTS BETWEEN THE EXTREMITIES OF THE LATTER, (K) SAID ELONGATE ELEMENTS BEING UNDER CONTINUAL LATERAL COMPRESSION FROM THE CASTING WHEN COLD, (1) SAID CASTING BEING UNDER CONTINUAL LONGITUDINAL COMPRESSION FROM THE SAID END-PORTION SURFACES OF THE ELONGATED ELEMENTS WHEN THE CASTING IS AT OPERATING TEMPERATURE, (M) SAID CASTING INCLUDING SUPPORTING FORMATIONS AT ITS ENDS, (N) THE SAID END-PORTION SURFACES OF THE SAID ELONGATE REINFORCING ELEMENTS BEING DISPOSED ADJACENT THE SAID SUPPORTING FORMATIONS OF THE CASTINGS, THEREBY TO MAINTAIN MAJOR PORTIONS OF THE CASTING UNDER LONGITUDINAL COMPRESSION.