GB2397102A - Turbine shroud assembly - Google Patents

Abstract

A turbine shroud assembly for an axial flow gas turbine rotor blade stage suitable for incorporation in a gas turbine engine comprises: a ceramic shroud ring 13 composed of a plurality of ceramic segments 19; resilient layers 25,27 and 29; and a metallic carrier ring 21 which holds the ceramic shroud segments 19 in sealing relationship with the tips of the turbine rotor blades 7. The resilient layers, which may comprise woven wire pads, isolate the ceramic shroud segments 19 from direct contact with the carrier ring 21, thereby accommodating differential expansion and protecting the ceramic shroud segments from the effects of vibration and mechanical shock.

Description

1 2397 102 P7TCIFIC,,? IO!T =FIr!E T-T,?CTTD i, ' .-.'PLY The present

invention relates to a turbine shroud assembly for an axial flow gas turbine, and particularly to a shroud Assembly incorporating ceramic shroud segment-.

In order to ensure efficient operation of axial flow gas turbines, it is portent that the running clearances between the tips of the rotor blades and the radially outer wall of the g^-s na.ssae are as small as possible. If the clearances are too great, turbine efficiency is reduced due to excessive gas leakage across the blade tips.

One way to achieve small running clearances is to surround the rotor blade tips with a ceramic shroud ring forming part of the outer wall of the gas pats-age, the ceramic shroud ring comprising a plurality of shroud segments. The segments are shaped to avoid stress concentrations which could cause brittle fracture, and are sufficently massive to obtain a factor of safety a.deanate to account for unavoidable variations in the properties of the chosen ceramic material, such -as silicon nitride then the turbine rotor has reached oper-.tinr temro.ture from a.

cold start, its diameter will have exPn;ed r,,. A correscording Account, and it is arranged that +.ne runnin- cle.qr-r.^.e is miriTrur q. this condition.

JO Due to Ire rqssi.ve rqture of +hr. ceramic shroud rin. and its situation in the ou+er wall of the gas Deserve' it its still heating up when the rrinirr.um running= clearance is attained, and hence the shroud segments are still expanding. however, the chosen ceramic materiel has a low coefficient OT^ thermal expansion and therefore it is possible to arrange for the excursion of the serpents to be accommodated by sealed clearances between adjacent shroud segments so that the overall 2arP.eter of the shroud ring does not cheese substantially. Hence the minimum running clearance can be substantially maintained during further opertlon of the enKir.e.

3: The ceramic shroud segments must of course be supported P.nd located in the correct position adjacent the blonde tips by Preens of other structure Conveniently, this other structure comprises. metallic outer c- rrier Dinto w ich t're cer=..rP.ic shroud sediments are retained, Art i- is -rrn.e 3'^-' 'uric- t r +,io ir WE ice try tu 'ins rector is 'or-, us, ''e carri - rim.-, or:' Any 'tic coror:r.ts;tic; s from' -n';lc to I', exams.-! lo1:, À r-,t.e which -'lot.: ;vle rio,to_r-+; ior'ed hi r TUrL --.r.in ^le?Y rc to be q+tqinr-A. thin c-:r be acti rv=) by -3r crrorite choice o'' --tf -i ells Art --croci tr Collie of +.ne r-rir ring fir'] loo -'tic r-rcr.q!.. ('no ro.l= huh rc-rs ';'.l t. - -rr-r--:Y; - 3 - the nis-match between the coefficients of thermal extension of the metallic carrier rind And the ceramic shroud segments; althou.eh the carrier ring is shielded by the ceramic from the worst effects of the hot glee in the gas psssa.ge, it still expands to greater exier.t then the ceramic shroud segments and at a different rate.

Because ceramics tend to be brittle and lack elasticity, 'the ceramic shroud serpents cannot be corrected rigidly to the carrier ring.

Another problem with this arrangement is again connected with the brittle nature of the ceramic material, this being the nece city to protect the ceramic shroud segments from 'the effects of vibration and mechanical shocks.

The invention is therefore concerned with providing a shroud assembly in which Me shroud segments are adequately supported and located in sealing relationship with the Allude tips, differential expansion between the ceramic shroud segments and the carrier ring being nevertheless accommodated and the shroud segments being protected frc the effects of vibration and mechanical s!1ock.

According to the present invention, a turbine shroud ssembly for Ad. xlel flow gas '.u-'::ine rotor blade stage comprises AC a. ceramic -out ring composed of plurality of ceramic shroud se,T.er. s, resilient and, And a metallic carrier rind- which Folds the ceramic Shroud segments in sealing relationship with the rotor blades; the ceramic shroud segments being isolated from direct contact with 'he carrier ring by said resilient men. ns.

In the preferred embodiment the carrier ring defines a circum ferer. tially exterdin channel and the ceramic shroud segments have radially outer portions which are housed and held therein, The carrier TIC ring includes a 'etachable ring portion or another means to facilitate insertion of the radially outer portions of the ceramic shroud segments into the circumferentially extending channels -referarly, the circumferenti-lly extending channel has a radial cross- section with '? reentrant Profile and the radially outer portions O,r the cer,q.mic shroud,eents have a profile which is complementary to Chat. of the charnel, 'he resilient means feint-' sandwiched between the c-q--el cvile And We profile of the outer portions of t,hr ceramic shroud slants, Thc- c>- oral crofi].r ray adv?nta-eoucly include a q''y ou+Prost sJrfce Provided with rPsilien+ firers er-.?r.,rine radially outer surfaces of the outer portions of the ceramic shroud segments, and forward and rearward oppositely inclined surfaces provided with resilient means engaging respective forward and rearward surfaces of the outer portions of the ceramic shroud sentiments. Sphere provided, the detachable ring portion of the carrier ring may bear one of the oppositely inclined surfaces of the channel.

It is advantageous for satisfactory location of the ceramic shroud segments that the carrier ring holds the ceramic shroud segments such that the resilient means is in a partly compressed condition.

The resilient means Gray comprise] yers of resilient material such as pads of resiliently woven or aimed wire stands. alternatively, the resilient means may comprise a laminated plate,sprin'T comprising a stack of flexible Plates, +,he plates being spaced apart from =.Ach other by means effecting r?. plurality of Points of contract between adjacent l- Ayers.

sealing between adjacent ceramic shroud segments may be effected by means of compressible sealing wire located in corresponding Grooves provided in on end '-?C of each ceramic s'rnud semen+,. 'the sealing wire may comprise asbeso-. her heat stable String braided with metA..l wire.

the carrier ring is preferably provided with means fcilitqtin, coolin- of at least t('P outer portions of the carrier rin', and 'he ceramic shroud., ements.

The inversion also includes a ceramic shroud Pediment or a carrier ring for incorporation in a turbine shroud nsse,chly according to 'e bore paragraphs.

An embodiment Or Me invention will now be described by,,r.oy of example only witch reference to the accomp,nyin drains in which: Figure 1l, is a. secron,,l side elevation of' Pert of iris turbine incorporatir, +hc invention; Figure 1 is On erlarFPd view of area in Figure 1N illustr.tinT or ali,en.ti- embo8Ai=n+. of Land invntlon; Figure 2 is 'lien on.-. =ction --O in 'figure ^';.win.- only cPr'.-Ain coponerts In iso'-. L ion from o' her tract ore; Fit 'CHAR e is a \.[i=W or. sec.ior;-P in ''i '-\A re 1, The:2-w'r.- e not to -Celia.

R F Mauri-- Tic 1 i = 1, G - A. i " / r rt n. q r. U t i i! ; -I]i -LlO art ACT --at Jo tUrT.Ofqn ^OFrf -me TIFF L.lA--.1'r.C 1 r -n r I; r.- -a r -, F; r -A 1 h - In,- ^; ' ' .- ,1 i Al | - lr -' . ., r I dry. - _: 1 r. - 5 -

^nfs q, only.rts of these fe-^tures binf shown. Combustion (tu.bi^.e) s^s 11 from.- co-..bus.ion ctarber (not show) flo',r throu-Y +he ^nr.ul array of..o%'le,,uide v^nes 5' ?re uidei t^ereby onto the trbine -o+or bl- 7es 7, .n rrom +hence p?SS throuPh 'he ?nnular array of st?tor v-nes 9 to the next stage of turbine bldes (not shown).

In acco-dtr.ce À^ith the invention, a cer.^-.ic sroud ring 13 is po;-ided tc surroun' +he r.^dially ou+er tips of turbire '-.'-:des 7 -r.d form a sec?1 c?gainst th.en in or'er to,revent excessive le-k^,.fe ^f +'-e turbine r-^nes over the bl?de tips between the high pres^.u-e.r.d low pressure sides ^f the '.^l^,des. The cer-;mic srcud rin: 13, to-ther '+h the ^hrouds 1r,, 17 of vnes 5 ?rd " re^pectivel-, defires the ou+eboundary o ''-. turbine ss-^e 7.

Ceric shroud rinf- 13.s cc.rosed of -.. r.u.mb r Or c r mic s',roud 1' se.en'.s 19 (1-a ---19d, e.c, s shown in iOure 37. In the r es n' e. rbodi.rnt, hr nU- - r- ot^ sr-r-nts is. -bou+ ' ir'T, 'h d'ietrr -^ the:urbine p.^.?re '.-ein= l^-rr.e, hut es;^eci.'.ly for s-2ller turtines r.e number of.^.er+s could be much less.

the urb n ge '..ein l.?re, u' ''o- s.--'l^r 'urbir.rc; 'he numb^- of Sc-reri,s 'cu11 ',e Inuch 'ess.

h ser-mic ^efen+s 1 corrosinf +he shroud rinF '7 re c-r'e from ? ^-3lic crri^r rin-- 21, -: subst-.rtilly dove-t^il ^'>.--red r.-^di-^-'ly ou-r rorti.on 7 Or e'?ch se:ert 9 b^irr hel2 i+'-in c--- = rin^ 71, '^ut isol+ ^d f-o=. .icct contac with it by mesr.s o resi'iert '.yers or pads 5,?7 -rc'. 29. Desilient la.yers 25, 27' r.d 29 gre circumferentially coextensive ith the c?rrier ring 21 ^s can re.-4ily be seen rom Figure 1, te ccrrier ring,'1 is shaped to rovide a circumferentially exendirg ch?nr,el into which r,roject the dove- ti] s'e.?cl portions 23 of segments 9, t'e channel 3: hving a rdil cross-srction rith reentrnt rofile w1nh is complement.ary to tie r,rofile of the corions 3.o ht they cn be housed end cositively ret;ned in it. he resilient 1?yers 5, ?7 nd 2'? re s-.ndwichr-r. u-tween he c.?r.ncl rrofile ard the rrofile of '-e portions 23 of se:ments '9, he crofile of the chrnel ircl'',in.a rdilly nuierost substntially cylir. dricl s'rface 31 rovided wih resilient lyer 25,.rd two r,?dially ir. nrr:'rusto-conial surfces 73,32 nroid,d with re-ilier'. l-yrrs ?7 nd ?9 rrs.ecti'.,rly. 'nine -6tally innrr surf nes 33,3 of t'e chrnel r= in fore;nd ft positions on orpo ir.- ides of te outh -f te cw-nrl -1 re irnlln d ir ^-T:osl', -erses wit. rP^rect -^ e'ch oie- h rr, 'i's - 6 - of the portions 23 of ceramic segments 19 have "bearing" or load tkin surfaces 35,26 and 37 corresponding respectively to the radially outer and inner lo-ding-taking surfaces 31,32 and 33 of the channel.

Note, however that the load-taking surfaces of the outer portions of the shroud segments engage the respective resilient layers 25,27 and 29, not the internal surfaces of the carrier ring.

The resilient layers 25,27 and 29 ray comprise pods of resiliently coven or nitted +ran:ls of wire, -such Is -e sold under the trade name "Vibrashock" by Delaney Gallay Lid of Edgeware Road, Crcklewood, Londor The wire must I've of such a constitution that it will retain its resiliency at t e temp-rqures it experiences during operation of the turbine. The wire pods nay be bonded to the urfaces 31 to 33 of the carrier rind 19 by any suitable Process such as brazing, diffusion bonding o- elcirF.

As an alterr.--ve to the use of wire pads, resilient layers,27 and 29 may comprise a,?e of laminated Plate spring 38 as illustrated in Figure 1B, in Which a stack of flexible sorinfy plates 39 are secured together, the plates 39 being spaced from each other and bonded to each other by re.-r.c of feature 41 provided at intervals over the surf-ices of t'e plates, th.Pce features Living a plurality of points of contact between ad Scent p'.=tes 39 bu+ allowing flexing of the Plates between the points of contact. Features 41 on adjacent plates are staggered with re-cec+ to each other is shown in order to ensure that the flexibility and -resiliency of the plate spring 38 as a whole is evenly distributed over the area of contact between the plate spring and the surface 35 of the shroud segment 19 Plates 30 ivy be of any suit-tile metal or high temperature composite construction such as carbon.

fitre reinforced.rahite, -and features 41 may comprise excrescences in the surfaces of the plates 19, or small discs of material secured to JO the surfaces of the plates. The plate spring 38 is secured to the cylindrical surface 31 of carrier ring 31 through bonding of the features 41 on the adjacent plate 39 to that surface 31 To Prevent ur.-:nted Movement of the Shroud segments 19 within carrier ring 21, resilien+ layers 2S, 7 qr.d:9 are in a Curtly corcressrd condition against surfaces 35 to 37 Of +?e shroud portions.?3. In order o.c?ive this ?.qr.lol co?T. rres.ion o t A?. F? r? S i | lent l;yc?r,-, o',.cr shroud r?ortions 27.- ?re in effect cleared into position ?r?ir..t the resilience of the red ilie-- layers, clr?ir. >arcing enabled by wrens of a detachable ring portion 43 of carrier ring 21, which also enables insertion of the outer shroud portions ?3 into the carrier ring' channel during assembly.

Detachable ring portion 43 is bolted to the main body of the carrier ring 21 by bolts 45 as shown, and bears the frusto-conical surface 32 having resilient layer 27.

Halving' now described the way in which:eramic shroud segments 19 are held in carrier ring 21, the way in w ich the carrier ring 21 is held and located in relation to other structure will now be considered, It will be seen from Figure 1A that at its rearmost side, the carrier ring 21 is supported from a flange 47 Provided on the outer shroud portion 17 of stator vane 9, Stator vane 9 is in turn supported from turbine casing 49 through another flange 51 extending from shroud portion 17, and from other static structure (not shown), In order to provide circumferential location of carrier rink' 21 and to prevent it moving circumferentially in the event of the tips Or rotor blades rubbing against shroud segments 19, the carrier ring is provided withy plurality of circumferentailly spaced lugs 55 on its outer surface, these being dodged against corresponding projections 56 which are welded to a static ring 53. Static ring' 53 is in turn Secured to other turbine casing' members 49, 50 through its flange 54.

The static ring 53 his frusto-coni.cl/cylindricl extension 7 projecting forwardly of florae 54, the forward cylindircal portion of which Dears a.rinst a cylir.Aricl surface of circumferentilly exter.1inr land 59 on carrier ringer 21, This provides Positive radial loo tion for carrier ring 21 at its forw-rd side and, since there is some r?silier.cy in extension 57, also provides some d.,rinr of vibrations snA shock loadings experienced TV carrier ring 21.

Carrier ring; .'1 is further carried ndloc-ted -at its forward side bv hearts of cylinrrical 1octinr ring 61 Schick has plurality 0 circufer.nt i?] ]y spaced lifted rojctions 63, The lips 65 on projections 63 ergapre corresponlinr, steered nortlon 66 on carrier ring 1, thus providing. radial loc-.ion which is copl=.ntry to that provided by exter.sion 57 of static ring '>3, Positive axial location of c.;rrl=r rind i' is rovird By enfrer?fnt of r-1i11y inr,er annul r flange 67 on crri-?r retry' ?1 with annular groove (,9 in static rinser 71, <static ring 71 i in learn molted to forage 73 of oyli.dricnl. amber 75, - 8 - Figure 2 is a view on section C-C in Figure 1A from which all - structure other than locating ring 61 and carrier ring 21 has been eliminated. Referring now to Figures 1A and 2 together, it will be seen that the lipped projections 63 are equi-angularly spaced around the circumference of the locating ring 61 and project radially inwards from it to engage step 66 in the forward side of ring 21 by means of lips 65, The projections 63 are formed by cutting out segments of circles fir.,, a flange orignally formed on locating ring 61.

It will be noticed that carrier ring 21 is divided into a number of segments 21a, 21b, 21c to allow for circumferential thermal expansion as was explained in reerect of the ceramic shroud ring. To facilitate a. ssebly ?rd disassembly the number of shroud ring segments should be an integer multiple of the number of carrier ring sediments. In the present instance the number of carrier rin.' segments is half the r fiber of ceramic shroud. segments, each carrier rir.,: serpent housing To shroud ring elements, but this ratio or the number of carrier ring segments to the robber of shroud ring segments is not mandatory, and indeed by judicious choice of materials, coo1ing arrarFeents And support era location featuresj,i.t would be possible to lesion carrier ring So diving many fewer segments then he pre.-,ent one or nerh.ps even a carrier ri'.,-;.hich is effectively unitary.' In order to seal the radially extending Arcs 77 between 1,acent carrier rinser segments (the gals Me recesry to allow for expansion and contraction of the segmer.'s) circumferentially ad,iacent ends of the carrier ring segments are rovided with matching opposed slots 79, within which are located sealing.' strips 81. This sealing arrangement on the forward side of the carrier ring 21 is necessary to help r,revent unwanted air flows in the radially outward direction, As explained later. Similar sealing a.rranements (not shown) ae r.rcessary on the rear side of the carrier ring between carrier ring 3C Presents, As can be seen in Figure 1t, . sealing- wire 83 is retained in a c'cul r groove 8c provided in the forward ir.'ernal face of carrier Al- 21 at the Couth of the chnnr.el in which portior,s 23 of shroud ring e-ens 19 Are retained. Compressible stalling wire 83, which Way _ 9 _ be made from asbestos string braided with nickel wire, is held comrre-sed against the forward faces of the shroud ring segments 19 and also seals slots 79 in carrier ring 21 (Figure 2), A similar wire seal 87 is provided between the front external face of carrier ring 21 and the rear face of ring 71, Silica or alumina. fibre strings could also be used AS sealing wires, Further similarly constituted wire seals are provided between adjacent ceramic shroud segments, Referring to Figures 1A and 3 together' i+ will be seen that radially extending gaps 88 between adjacent shroud segments 19a. to 19d, etc. are sealed by means of selling wires 92 and 94, which are held in respective grooves 96 and 98 provided in an end face of each shroud segment, The grooves 96 and 98 are approximately at right angles to each other, grooves 96 running in an axial Erection across the mouth of the channel defined by carrier ring 21 so that sealing wires 92 prevent gases from the turbine passage 3 flowing up Caps 88 between shroud sediments 19 into the interior of.

the carrier ring. Grooves 98 runs radially outward from the middle of grooves 96 so 'hat sealing wires 94 prevent direct flow of n.i.r through gnus 88 between front and rear interns sides ofthe carrier ring 21, :0 as will be explained below, In Fi-ure 1., here will be seen an a.nnul, r chamber 89 Defined -etween carrier ring 71, static ring 71, and the front face of ceramic shroud ring 13, The chamber 89 is fed hind Pressure air from an annular chamber 90 surrounding noz.;Tle Guide vane shrouds 15 ty means of many circvrerentially spaced drilling 91 through ring 71. This air is at a hither pressure than i.he clasps in the turbine passage 3.

Sealing' wires fl3,87 and 92 prevent any very larvae flow of the high Pressure Sir in the radially outward direction, and it therefore -.ost2y escapes from chamber P,9 rearwardly and inwardly. he?rw?rdly, 3C, the --,ir from chamber 89 flows through Haps 88 between adjacent shroud ser.=nts towards the rear fore of the shroud ring 13,grndually entering e turbine Passage 3 at stations between the front of the shroud ring 13.-nd the shroud 17 Or s+,-tor vane Q. The air from chamber 89 alto flows ir,w.-dly directly into the turbine passage 3 borough the -arrow And bPt,een the rear equips of line 71 and roz.'le guide vine shared 1 r on one tide And the front face of shroud rin' 13 on the other-, There airflows rrPvPnt 'tot Uses Fronhe turbine.is--r,e co,i'. l'to cost c' ; ith.svtic ring 7 And. '.hP c.rriPr ring ?1, -ran -'.so Act tc cool We rdi1ly ir,rrr ro-tion or the -proud ring I' 12. the -arc rat.-P,sllic coror.Pr..

- lo - Annular chamber 93, between locating ring 61 and cylindrical flanged member 75, also receives pressurised air, but At lower pressure then chamber 90. Air from chamber 93 enters the interior of the carrier ring 21 through holes 94, only some of which are shown in Figure A, and portions of gaps 77 (between Scent carrier ring segments) which are outboard of sealing strips 81. Luring operation of the ermine, . flow of ? ir is established from chamber 93 to the turbine pzss.qge 3 downstream of the shroud ring 13, where the pressure is lower After expansion of the turbine gives through rotor blades 7.

This flow of air passes through those portions of the carrier ring./cer. qmic shroud ring assembly which are outboard of sealing wire 92, .?r.d helps to cool the Grater portions of carrier ring 21 and the outer portions 23 of shroud segments 19. Cooling of carrier ring 21 is made more effective by the presence of sealing wires 94' which encourage circ, 'qtion of the air around the periphery of shroud portions 23 through the resilient layers 25,27 and 29. Effective cooling for carrier ring 21 and the reslliPr.t layers ensures a satisfactory service life for these comr) onPnt s, Notetht the resilient layers 25,27 and 29, if made of pads O' resilient wire strzr.ds' mcqy each form an ?r.nulu extending completely ground the carrier rind 21, or -^y ?lte-n.qtively comprise desecrate circumferPn.'iqlly -paced sf-gmen1 portions Provided that they Hire sufficient supporttothecPr?mic -proud segments. Forever, if the resilient layers comprise the l-min-ted sprir s shown in Figure 1B, they must be circumferentizlly discorin uous in order to quo for thermally induced strains between 'the spring plates 39. 3o 11 _

Claims (1)

1. what lle Claim Is: 1. A turbine shroud assembly for an axial flow gas

   turbine rotor blade stage, the assembly comprising a ceramic shroud ring composed of a r, lurqlity of chromic shroud segments, resilient means, and a metallic carrier ring which holds the ceramic shroud segments in se,=*lin relationship with the rotor blades; the ceramic shroud senents being isolated from direct contact with the carrier' ring by said resilient means.

   2. A turbine shroud assembly according to cla-i.m 1 in which the carrier ring defines a circumferentially extending channel and the ceramic shroud segments have radially outer portions which are housed end held therein.

   3. A turbine shroud assembly according to claim 2 in which the Currier rinds includes An,. etq,chable ring portion to facilitate insertion of the radially cute- Portions of We ceramic shroud segments into the circumferentially extending channel defined by the carrier ring, 4. A turbine shroud assembly according to claim 2 or claim 3 in which the circumferer.tially extending channel has a. radial cross-section with q reentrant profile, the radially outer portions of the ceramic shroud seamen's 'saving a Profile which is co,nplem.entary to that o^ the channel, .h rPsil.-nt Herons being ^-nd,'!;.ched b- ten Mid c>,nr.=' refile ard said Profile of the outer portions of the cer-;nic shroud segments.

   I. A turbine shroud assembly according to claim 4 in which the reentrant profile of the circumferer.tially extending channel includes: q radially outermost surface Provided with resilient means engqginr" rdi.a].ly outer surfaces of the outer portions of the ceramic shroud segments; end for,/=rd and rearward oppositely inclined surf ces Provided with resilient news ergqPin respective forward and rearward surfaces of the outer portions of the ceramic shroud segments, (. A turbir.q' shroud "=senbly according to claim 5 in which the detachable rind Fort on 'rears one or the oppositely inclined suffices o^ the channel.

   7. A tubir.e shroud as early according to any one Or cl.qis 1 to 4 in.

   which the Currier rind holds the= ce--mic shroud rip;- sPg=en+.s such th t Bee rPsili-.t genres is in n Tartly comr=s^d conflation, a, t. 'u-birq s'>rcud.q-enPlv qccodins, to any one or claims A to 7 - which the. -=sil ent rein, comr-i es layers of resilient n,tqriql. _ 12

   9. A turbine shroud,qs-em.bly according to claim 8 in whic resilient m. ?teriRl comprises pads of resiliently woven or wire strands.

   0. A turbine shroud assembly according to any one of claims 1 to 7 in which the resilient.eans comprises a laminated plate spring Comprising a stack of flexible plates' the plates N eing spaced apart Prom each other by mears effecting a plurality of points of contact bat ween adjacent orates, points of contact between adjacent plates being s aggered with repert to each other, 11, 5. turbine shroud s^-embly according to any one of claims 1 to 10 in which adjacent cer-q.m ^ shroud segments are provided with sealing Means t'r.erebatween on Weir circumferentially zdjrqcent end feces.

   12, ..turbir.e shroud assembly according to cl-im 11 in which the sealing means comprises compressible sealing wire means located in corres?ondirg groove e-.s provided in an end face of each ceramic shroud s a 2ment.

   13, ,urblne shroud -^^embly qcco-dlnr to claim 4 in which the -=alir.g wire means con-- ses asbestos string braided metal wire,.

   14, .t turbine shroud =e-N-lv according to any one of claims 1 to 13 -.'hhiCn the carrier is provided with means facilit.qUin flow of r-essused cooling al- -on pressured sir supply means into the -bier. o -a e' said if:- of presurised cooling air bain'" routed to cool at led t the c,e- portions of the carrier ring and the ceramic strolls segme-.ts.

   5, ceramic shroud -----her., for incorporation in.= 'urbira shroud asse:. blv-.qccordin to -ny one of claims 1 to 1d, 6. carrier ring c i-cooor.=tior in a turbine spread = embly according.c any one Of claims 1 JO 14, 47. A turbid shroud -s-em'cly substantially as described in this sreclf cat on with reference to ard as illustrated Hal Figures 1 to 3 of ' e accomo,qnyirlp d-^-ins, A 3, ce-?ric shroud segment substantially as described in this c!eciicqticr. with reference.-a and as illustrated by Figures 1 to 3 of He cccomn,=.nyinr 1--i-. -so.

   ma, car- or rinser so ar.tially -he described in this scecific-tion +; reference 'o and -s llistrted by l<'itrurs 1 to 3 of t,>:e -.ccorrn; nyir.f -I rewinds, Amendments to the claims have been filed as follows 1. A turbine shroud assembly for an axial flow gas turbine rotor blade stage, the assembly comprising a ceramic shroud ring composed of a plurality of ceramic shroud segments, resilient means, and a metallic carrier ring comprising a circumferentially extending channel which receives and holds radially outer portions of the ceramic shroud segments so that their radially inner portions are in sealing relationship with the rotor blades; the ceramic shroud segments being isolated from direct contact with the carrier ring by said resilient means.

   2. A turbine shroud assembly according to claim 1 in which the carrier ring includes a detachable ring portion to facilitate insertion of the radially outer portions of the ceramic shroud segments into the circumferentially extending channel defined by the carrier ring.

   3. A turbine shroud assembly according to claim 1 or claim 2 in which the circumferentially extending channel has a radial cross section with a reentrant profile, the radially outer portions of the ceramic shroud segments having a profile which is complementary to that of the channel, the resilient means being sandwiched between said channel profile and said profile of the outer portions of the ceramic shroud segments.

   4. A turbine shroud assembly according to claim 3 in which the reentrant profile of the circumferentially extending channel includes: a radially outer..ost surface provided with resilient means engaging radially outer surfaces of the outer portions of the ceramic shroud segments; and forward and rearward oppositely inclined surfaces provided with resilient means engaging respective forward and rearward surfaces of the outer portions of the ceramic shroud segments.

   5. A turbine shroud assembl according to claim 4 in which the detachable ring portion bears one of the oppositely inclined surfaces of the channel.

   6. A turbine shroud assembly according to any one of claims 1 to 3 in which Ale carrier ring holds the ceramic shroud ring segments such that the resilient heirs is in Partly compressed condition. lo

   A turbine shroud assembly according to any one of claims 1 to 6 in which the resilient means comprises layers of resilient material.

   8. A turbine shroud assembly according to claim in which the resilient material comprises pads of resiliently woven or knitted wire 5' strands.

   9. A turbine shroud assembly according to any one of claims 1 to 6 in which the resilient means comprises a laminated plate spring comprising a stack of flexible plates, the plates being spaced apart from each other by means-effecting a plurality of points of contact between adjacent plates, points of contact between adjacent plates being staggered with respect to each other.

   1.. A turbine shroud assembly according to any one of claims 1 to 9 in which adjacent ceramic shroud segments are provided with sealing means therebetween on their circumferentially adjacent end faces, the sealing means comprising compressible sealing wire means located in corresponding groove means provided in an end face of each ceramic shroud segment.

   11. A turbine shroud assembly according to claim 70 in which the sealing wire means comprises asbestos string braided Faith metal wire.

   12, A turbine shroud assembly according to any one of claims 1 to 11 in which the carrier ring is provided with means facilitating flow of Fressurised cooling air from pressured air supply means into the turbine passage, said flow of pressurized cooling air being routed to cool at least the outer portions of the carrier ring and the ceramic shroud segments.

   13. A turbine shroud assembly substantially as described in this specification with reference to and as illustrated by Figures 1 to 3 of the accompanying drawings.