US2715011A

US2715011A - Ceramic blade for turbine engine

Info

Publication number: US2715011A
Application number: US135580A
Authority: US
Inventors: Schorner Christian
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1949-07-19
Filing date: 1949-12-29
Publication date: 1955-08-09
Anticipated expiration: 1972-08-09

Description

Aug. 9, 1955 Filed Dec. 29, 1949 INVENTOR ATTORNEYS United States CERAMIC BLADE FOR TURBINE ENGINE Christian Schtirner, Augsburg, Germany, assignor to Maschinenfabrik Augsburg-Numberg A. G., Augsburg, Germany, a corporation of Germany Application December 29, 1949, Serial No. 135,580 Claims priority, application Germany July 19, 1949 4 Claims. (Cl. 253-77) This invention relates to a moving blade for turbine engines, more particularly, gas turbines, of ceramic masses.

Ceramic blades are adapted to substantially improve the thermal efficiency of internal combustion plants, e. g., exhaust gas turbines, without requiring complicated methods for cooling the constructional elements owing to the increased working temperatures. Their low price also is an advantage. Of course, a ceramic blade is exposed to very high mechanical stresses, apart from the required insensitivity to changes of temperature and the usual requirements as regards high speed, capacity, etc. However, the blade shapes cannot be simplified as much as it would be desirable for the ceramic material, and the tensions resulting by the firing and shrinking as a consequence of the requisite shapes, call for measures for improving the rated fatigue limit. For fixing the blades in the wheel body of steel (with due regard to the requirements for a tight mutual engagement of the seating surfaces irrespective of the different heat expansions) approximately axially directed wedge-shaped grooves have proved good, in which the complementarily shaped dovetail roots of the blades are seated. However, in order to ensure an efficient guidance or conversion of the gas in the blade grid, relatively wide blades are required in order that a suficient strength may be left for the roots of the blades at the rim of the rotor between the grooves. These wide blades with their substantialy curved and partly even twisted surfaces, however, contrast with the straight roots of the blades which engage in the wedge-shaped grooves of the rim of the rotor. Substantial parts of the blade project beyond the base of the root of the blade, whereby ceramic structures are resulting which are particularly unfavorable as to their mechanical rated fatigue limit.

It is the object of the present invention to improve the strength of the ceramic blades.

With this object in View, according to the present invention the vane is subdivided in its width and the roots of the two blade elements have different inclinations with respect to the circumferential direction of the wheel body in conformity with the average inclination of the skeleton line of these blade elements. Thus the blade portion of the single vane element becomes smaller in width. The resulting components of the profile are less and more uniformly curved and the appertaining root portions with their plane wedge shape can be better adapted thereto. The more gradual transition from the blade portion to the root portion which is thereby ensured, no matter whether the blade is produced by casting or by pressing, is favorable for a high rated fatigue limit, since the preliminary tensions produced in the constructional element by the firing and shrinking are thereby reduced. Owing to the more shallow curvature the preliminary tension at the transition to the root portion is also reduced, and the measures of the profile can be more accurately adhered to. The partial profiles can be joined in such a way without expensive mechanical 2,715,0ll Patented Aug. 9, 1955 ice working that discontinuities in the curvature of the profile are avoided. Also the staggering between the partial profiles can be chosen in such a way that no substantial leakage will result between the front and rear faces of the blade. Finally also the lift of the profile is not substantially affected, since energy will be fed to the field of vorticity at the back of the tail through a possible joint, so that the excess velocity will fade at the end of the back contour of the thick inlet or leading part of the blade.

Other and further objects, features and advantages of the invention will be pointed out hereinafter and appear in the appended claims forming a part of the application.

In the accompanying drawing a now preferred embodiment of the invention is shown by way of illustration and not by way of limitation.

In the drawing:

Fig. 1 is a side view of a subdivided or split blade,

Fig. 2 is a development of the rim of a rotor with a subdivided blade,

Fig. 3 is a fragmentary rear view, in the direction A, on the rotor as per Fig. 2, and

Fig. 4 is a development of the rim of a rotor with an undivided blade in accordance with the conventional design.

Similar reference numerals denote similar parts in the different views.

It Will be seen from Fig. 2 that the joint '7 extending through the vane portions 1, 2 and the root portions 8, 9 of the blade advantageously does not form a plane but is staggered as indicated by the line 7. The rotor may also be subdivided, in the form of two halves 10, 11, on the line 7, or it may be made in one piece. Since the profile of the blade near the root (Fig. 2) consists of a thick leading element 1 with a center line of the profile of a practically axial direction and a thin tail element 2 with a center line on the profile which is rather inclined, at an angle a, with respect to the axial direction, the widths a1, cm of the companion wedge-shaped root portions 8 and 9 may be different. The advantage of the subdivision of the blade in accordance with the invention will be realized particularly clearly by comparison with a through-going wedge-shaped root having a width and an average inclination 61 to the circumferential direction as per Fig. 4, which angle e1 is smaller than the angle a. In this case, freely overhanging portions 3 and 4 of the blade are present at the thick leading part of the profile and at the thin tail part 13 thereof, respectively, which overhanging portions are difficult to evaluate as to their stress, being moreover at a disadvantage as to their strength and liable to be damaged by their protruding position. In the blade according to the invention, on the contrary the whole vane part of the blade falls within an imaginary radially directed prism whose base is formed by the companion root portion of the vane.

Also, the conventional design presents corner portions 5 and 6 of the wedge-shaped root which are less utilized as to their strength, and a smaller tensile cross section of the wedge-shaped heads 12 of the rotor between the dovetail grooves 13 therein.

While the invention has been described in detail with respect to a now preferred example and embodiment of the invention it will be understood by those skilled in the art after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention and it is intended, therefore, to cover all such changes and modifications in the appended claims.

Having'thus described 'my invention, I claim as new and desire to secure by Letters Patent? 1. In a gas turbine having-,a metal rotor and a plurality of composite ceramic blades mounted around the rim thereof, the combination Which ',comprises a plu-, ralityof transverse grooves in the rim of said rotor for receivin'g said' blades, eachof said grooves havinga portion disposed 'substantially'axially of said rotor and a second portion disposed 'at an angle" to said axial IP01:

tion, a plurality, of separateceramic blade elements .a

assembled in edge-to-edge arrangement on said rotor forming eachfsaid blade,'.each of said elements having a vane part and a root part which completely underlies the entire cross section of said vane part, means for aflixin'g the root, part of one; of .said elements, in said axial .portion ofijsaid "groove .in' said rotor, and means foratfixing theroot part ofanother of said elements in said second portion of said groove, the vane parts of saidassembled elements forming for each said blade a continuous curved working surface and the rootpartsof I said elementsab'utting ata substantial anglejandhaving a substantially rectilinear transverse cross section.

2. "In a gas turbine having a metal rotor and a ,plurality of. composite ceramic blades mounted around the rim thereof,"the combination, which comprises a plurality of transverse grooveshaving a substantially rectilinear, transverseaxial cross section in,the rim of t said rotor for receiving said blades, each of said grooves having a first portion and a second portion which meets said 'first portion at an angle, a plurality of separate ceramic blade elements assembled in edge-to-edge arrangernent on said rotor forming each said blade, each of i'said elements having a vane part and a root part which completely underlies the entire .cross section of said yane part, meansfor afiixing the root part of one of saidf'elements in said,first portion of saidjgroove in said rotor, means for affixing the rootpart of another of said 'elements in said.second portion of said groove,

and corresponding projections and depressions on adjacent radial meeting edges of said elements forming staggered joints between said elements ineach said blade,

the vane parts of said assembled elements forming for each "said blade, a continuous working surface having a substantial curvature and (the root parts of said elements abutting at an angle'andhaving a substantially rectilinear 5 transverse cross section.

3;In' a gas turbine having'a metal rotor and a plu rality of composite ceramic blades mounted around the rim thereof, the combination which comprises a plurality of substantially transverse grooves in the rim of said rotor forrrc e vi g sa d.b a es, hlofis i igrp v ha e a ing, afirst p rti nand a sccondhportionwhich meets said, t p on. t, an, v r gleta p u ality f parat a c.

l de. el me s a semb ed. in dg rt -e gq rr ngemen on said-rotor forming eachfiaid ,blade, -ea,C 1 of said ele: mentshaving a yane part and? ,root part ,Which .corn

pletely underlies, the. entire. ,cross section of .said vane P m an f r. flix n the r p rt, of: on f, id 161 ments. in said first portion of said groove in saidrotor, meansfor afii'xing-flhe, rootpart of another, of said elements said second ,portionpf; saidgroove, and co operating projections: and depressions on adjacent; meet,- dsesot i flidflane, partsforming, staggered joints, be-

tween said elements in each said blade substantially radially of said rotor, the vane parts of said assembled elements forming for each said blade a continuous working surface having a substantial curvature radially outwardly of said rotor and the root parts of said elements abutting at an angle and having a substantially rectilinear transverse cross sectiomthe aggregate axial cross-sectional areas of said root parts in each said blade being sub- 'stantially lessthan the area of a rectangle underlying the entire curvature ,of '1 said assembled vane elements ;providing increased rotor. rimsurface between saidzblades.

4. Ina, gas turbine having a metal rotor and a plurality of composite ceramic blades mounted around the rim thereof, the combination which comprises a plurality of transverse grooves in the rim of said rotor for receiving said blades, each'of said grooves having a portion disposed substantially axially of said rotor and a second portion. disposed at a substantial angle to the axisof said .rotor, a plurality. of separate cerami blade elements,

including a leading element and a tail element assembled in ,edge to-edge; arrangement: on said rotor forming each said blade, each ,of said elements having ;a vanepart and,

a root .partv whichcompletely; underlies the. entire cross section of saidyanepart, means including a trapezoidal configurationmfsaid root .part formounting the: root, part ofzsaid lead ng element. in said axialliportion of said a groove in said rotor, means including a trapezoidal configuration. of saidroot part for mountingtherootpart of said tail element in saidsecondportion of said groove,

and cooperating projections and depressions on adjacent;- radial meeting edgesof said elements forming staggered joints, therebetween in each said blade v substantially ra-a dially of said-rotor, the vane-parts of said assembled, elements forming for each, said blade a continuous work-,

ing. surface having I substantial curvature ,and the root parts of.said ,elements abuttingt at, an angle, and the rag-, gregate. axial, cross-sectional areaof said root .partsin each said blade being substantially less than, the area; of a rectangle enclosing said entire substantialtcurvature of,

saidassembled vane parts providing increased rotor rim surface between adjacent said blades.

References Cited in the fileofthis patent UNITED STATES PATENTS OTHER REFERENCES Ser. No.,,385,333, Schutte (A. P. C.),, published,May-- Ser. No, 385,334, Schutte V-(A. P.- 0.), published May