US2777666A - Turbine nozzle structure - Google Patents

Description

Jan. 15, 1957 J. E. CORR ETAL TURBINE NOZZLE STRUCTURE Filed Dec. 6, 1951 Inventors:

e. t o im @J m e CL /O Em HH A Inh@ op .m Jwme h. iv VJ bv United States Patent O TURBINE NozzLE STRUCTURE John E. Corr, Scotia, and Joseph H. Ouellette, Albany,

N. Y., assignors to General Electric Company, a corporation .of New York Application December 6, 1951, Serial No. 260,229

Claims. (Cl. 253-78) This turbine relates to elastic uid turbines, particularly to the construction of the nozzle member used to direct the motive uid into the buckets of the moving wheel.

As will be appreciated by those familiar with the steam turbine art, nozzles and diaphragms ordinarily are fabricated largely by welding, from a comparatively heavy plate member having at least one arcuate opening through the outer circumferential portion thereof, in which opening are disposed a pair of radially spaced arcuate bands suitably sealed and secured to the disk member and having a plurality of circumferentially spaced airfoil-shaped partitions or blades extending radially across the arcuate nozzle passage defined between the bands. Nozzle diaphragms of this general type and arrangement are disclosed, for instance, lin the United States patents to Haigh-2,373,558 issued April 10, 1945, and 2,264,877 issued December 2, 1941, and the patent to Truex- 2,245,237 issued June 10, 1941.

In the modern high-temperature, high-pressure steam turbine, the nozzle partitions are subjected to substantial bending stresses due to the pressure differential existing across the partitions in normal operation. The stresses in the partitions are further increased by any residual stresses remaining from the Welding operation and by diierential thermal expansion which takes place between the comparatively thin blades and the relatively massive bands and adjacent disk portions. This problem is particularly serious in the very thin exit edge portions of the nozzle blades. if these thin discharge edge portions are rigidly fixed to the bands, then when loaded by the pressure differential across the partitions, they behave as a beam fixed at both ends. This loading, taken with the differential thermal expansion stresses, may very well produce failure Yin the thin exit edges of the blades unless special means are provided for permitting some elasticity in the end portions of the blade so that it does not behave as a beam fixed at both ends. The construction described herein provides elasticity or freedom for the partition discharge edges so that the high stresses which otherwise occur in conventional constructions do not appear.

Accordingly, the object of the present invention is to provide an improved nozzle diaphragm structure, arranged to provide such elasticity in the means for securing the blades to the bands as to prevent over-stressing of the thin exit edge portions of the blades.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawings, in which Figure 1 is a longitudinal section through the outer circumferential portion of a nozzle diaphragm incorporating the invention, Figure 2 is a cross section of a single nozzle blade, taken on the plane 2 2 in Figure l, Figure 3 is a side view in elevation of a blade, Figure 4 is an end view of the blade taken in the direction 4 4 in Figure 3, Figure 5 is a perspective view of one blade by itself, and Figures 6 and 7 are detail views of two possible modifications.

Generally stated, the invention is practiced by using comparatively thick arcuate bands which are welded to 2 the adjacent portions of the diaphragm disk. Each blade is provided with comparatively massive root and tip portions with special slots arranged to introduce flexibility at the trailing edges of the blades.

Referring now more particularly to Figure 1, the invention is disclosed as appliedto a diaphragm disk 1 deiining an arcuate nozzle inlet passage 2 and having an outer circumferential portion 1a adapted to be received in a suitable circumferential groove in the turbine casing (not shown). The nozzle structure proper comprises spaced arcuate bands 3, 4 firmly secured by comparatively massive welds 5, 6 respectively to the adjacent portions of the disk 1 to form wall portions of the nozzle passage. The inlet portions of the bands 3, 4 are sealed against uid leakage by smaller concentric' circumferential welds 7, 8.

The nozzle blade comprises an airfoil-shaped intermediate portion 9 with a root section 10 and a tip section 11. The configuration of each nozzle blade is shown in Figures 2, 3, 4, and the perspective view in Figure 5.

The thickened root and tip portions 10, 11 are provided because of the extremevdiiiiculty which would bel experienced in trying to machine in the comparatively massive bands 3, 4 a hole having the precise configuration of the airfoil portion 9 with its extremely thin exit edge 9a.

In accordance with the invention, the required degree of liexibility is providedfin the blade attachment by axially slotting the thickenedroot and tip portions 10, 11. These slots may be conveniently formed by drilling transverse holes shown at 12, 13 respectively and then outting apertures through from th'eedge as indicated at 12a, 13a respectively.

As will be apparent from the assembly view shown in Figure l, the outer portions of the bands 3, 4 are firmly secured by the massive welds 5, 6. On the other hand, by reason of the presence of the holes 12, 13, and apertures 12a, 13a the comparatively thin exit edge portion 9a of the airfoil section A9 is substantially free to deect radially of the nozzle inlet passage to a limited extent. Thus elastic deformation of the exit edge of the blade prevents the creation of stresses sulcient to cause cracking and eventual failure. At the same time, the thickened portions 10, 11 of the discharge edge serve to prevent'the thin trailing edge 9a of the blade from uttering since these enlarged'blade portions tit the cooperating openings machined in the bands 3, 4. As shown in Fig. 1, the thickened end portions of the blade, at the sides of the holes 12, 13 remote from the thin vane edge 9a, are fused to the band members 3, 4 to positively 1ocate the blades relative to the bands.

In connection with the detailed design of a nozzle diaphragm incorporating the invention, it may be noted that, with bands of a thickness on the order of it is considered that the minimum diameter of the holes 12, 13 should be on the order of j". It will be seen from Figure l that welds 7, 8 eifectively prevent leakage of motive iluid around the outside of the bands 3, 4 while the welds 5, 6 seal against leakage radially outward between the blade end portions 10, 11 and the cooperating surfaces of the openings formed in the bands.

Thus it will be apparent that the invention provides a simple and rugged nozzle diaphragm construction which is eifectively sealed against leakage and incorporates the degree of resiliency required to prevent excessive stresses in the thin trailing edges of the blades.

While only one embodiment of the invention has been described specifically, it will be apparent to those skilled in the art that many minor alterations and substitutions of mechanical equivalents may be made.' For instance, in some applications it may be found that only one end of the blade need be slotted, as illustrated in Fig. 7, in order to give the required degree of flexibility. Further- 'Patented Jan. 15, 1957 i ures i115.

.. Patent-,ofy the ,United'Statesisz s Y ,1. 5A ,tu rbine g nozzl,e- .structure i including aV ,first member 1110,12, therequired exibiltygina the connecting means `for the thin disc!12tlg@ 4 edges -of the kblades v may .beprovided in other equivalent ways. Figure 6 shows one of these. In this modification, the blade 9 isexactly asV shown in Figure 45,errcept that l the rmeans -tfor-eipansionl consists of having the ,zcornerzofthe thickened ,-.root tor tip pnrton Y sawed away, as. ndicatedfby .Ihetcurued separation ssurface i Y 11a .to form a clearancelspace for-recess .lleff'lhetde- Y f tached tinsertgportion 11b is l loosely placed in the :slotein i band ,d duringthe weldingoperation, -sothattthe weld metal i Y .becomes fused 'to `the 'ysparate portion 11b, Y, leaving .the remaining-,thickened .edge-,portion -11c completely q freeto expand and contnactfradiallyrelativettoithenozzle inlet-passagepfthe.weldedgportion The process vof sawllgiofthaportion 11b .will ofcourse,l removefenough metal Y Yto insure (that ztherefwll `be tafsmall clearance vspace as showmatflld. This;modiiication isssubstantiallyrthemechariical l equivalent Lof :the iblade :form f illustrated in Fig-V Qther Vequivalents twill occur-,to those skilled t in the art. .vllrt'siof courseintended tofeoverrbyttheappended claims all ,such fmodicationsias 4fall within the true spirit and scopeofttheginvention. Y y "Whatl claim .as .Lnewr'and .desire to-secure by Letters provided ivvith an arcuate nozzlepassage :extending V,air-

'ially therethrough,f,a pairof radiallyspacedaarcuate band' members. fused to,the.rstimember tozform radially; spaced inner. and-'outer wall portionsgof fthe nozzlepassage, and

' band members fused to said lirst member to 'formradially each blade being ethickened adjacent -thefexitfedge.endoc- V Vcnpyinggrecessesof similar zshapeiin the respective band Y. members, said thickened edge portions withintthe con-y y ,2.A`nozzIe-structure v:in .accordance v.with claim f1` in which -,the :slot in Y-the fthiekenededge portion vcomprises ka {transverse tdrilledshole,communicating .with an aperture-.- of lan :axial widths less than the diameter .of the Yhole Y and textendingthronghfthe -discharge tedgeofithe .,blade.Y

g3. A turbine nozzle structutge. including ea -irstmember adapted toabe disposed transversely `.in a .turbine-.casing and lprovided Withuan .arcuate nozzlevpassage extending I axiallytherethrongh, ;a jpair tof radially rspacedxarcuate spaced inner `and outer wallmportions or' the nozzle -passage, and a plurality ofl circumferentally spaced nozzle blades extending radially across'the nozzle passage, each blade having a thin exit edge portion, the Yroot and tip portions of each blade being'thickenedradjacent the exit edge and occupying recesses of similar shape in the respective band members, the extreme endstof the root and tip portions t' of said blades :being fused .to theircooperatingV band members, at least one of said thickened edgek port-ions y being" provided withA anaxiallyr extending separation surface spaced radiallybetween 'the-adjacentrwall portion of said nozzle passage andthe lfusedends offthe blades,;,saidtseparatiorrsurfaces extendinginwardlyfa substantial distance from the exit edge, whereby said thinV bladesextending radiallyacross the nozzle passage, reach" bladehaving atthin ,exit edgeportion,..thexroot and tip ,por-

Vtion .fof .each-,blade being ',thickenedadjacent .the .exit edge andoccupyingarecess of,sirnilar shapelin the respective band members, A`the ,extremeends .of .the root and .tip ,portions of :the bladeslbeing Ifused vto the respective .band members, said Vthickenede'dge portions Within the rconfines sof fthe .recess ,in said -band rmember each .being 5,. 4rA =nozzle.structure .accordance with `claim 4 in whichlheiinserts .disposed inthe recessesV of the .thickened blade ledge portions, have the same .external contour/as the thickened vedge portions ofvr the. blade.

' References Cited in the Lle ofthisvpatent UNITED ,STATES PATENTS 2,11056-79 :2,378L7711 Howard June '119,-' 1945 iHoward Dec. `l-7, 19,46

*Robinson z -Mar;r=8,'1938

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