A device for attaching ring sectors around a turbine
rotor of Lurbomachine
The present invention relates to a device for attaching
ring sectors around a turbine rotor in a turbomanhine,
such as anr aircraft turbojet or turboprop in
particular.
Background of the inventior.
A turbomachine turbine comprises several stages each
including a guide vane element formed in an annular
array of fixed blades supported by a casing of the
T.urbin« and a wheel rotatively mounted downstream of
the guide vane element in a cylindrical or
frustoconical envelope formed by ring sectors attached
circumferentially end-to-end to the turbine casing.
The ring sectors comprise at their upstream ends
circumferential rims engaged with a slight axial
clearance in a radially inner annular groove o£ an
annular casing rail and held radially in this groove by
a C-section annular locking member that is engaged
axially from upstream on the. casing rail and on the
circumferential rims of the rir.q sectors. These sectors
are held axially by abutment of their circumferential
rims en upstream and downstream faces respectively of
the groove of the- rail.
The rims of the ring sectors are "decambered" relative
to the casing rail and the locking ruei'iibeL, LhcL is Lu
say that ^he rims of the ring sectors have a radius of
curvature greater than that of the rasing rail ard of
the locking member, which makes it possible to mount
the rins of the' ring sectors with a certain radial
preatress between the bottom of the groove of the rail
and the locking member and thereby to limit the axial
movements of the rims of the ring sectors in the
groove.
In operation, the differential thermal expansions of
the ring 'sectors and. of the casing cause an increase of
this radial prestress that is applied in zones of point
contact between the rims of the ring sectors and the
casing rail. But this prestress disappears
progressively over time by wear of the rims of the ring
sectors and of the casing in these zones of contact.
When this radial prestress is zero, the rims of the
ring sectors may move axially in the groove of the
casing and wear by friction the upstream and downstream
faces of the casing groove.
When this wear exceeds a certain value, the rims of the
ring sectors may, by moving downstream in the groove,
disengage from the locking member, which has the result
pf tilting the ring sectors toward the axis of the
turbine and risking contact between the ring sectors
anc the turcdne wheel, likely to cause destruction of
-he ring sectors and the wheel,
Sunuiiary of the invention
A particular object of the invention is to provide a
simple, effective and economic solution to this
problem.
Accordingly, it proposes a device for attaching ring
sectors around a turbine wheel in a turbomachine, each
ring sector comprising a frustoconicsl wall that
supports a block of abradable material attached Lo ils
inner surface and the comprioco at its upotrcom end a
circumferential rim engaged in a radially inner annular
groove of an annular casing rail and held radially in
-his groove by a C-section annular locking member that
is engaged axially from upstream on the casing rail and
on the circumferential rims of the ring sectors,
wherein each ring sector comprises at its downstream
enc a oart tnat is fitted and attached to the
frustoconical wall and to the block of abradable
material of the ring sector, this part being able to
press axially'against a fixed element of the"turbine to
prevent the upstream rim from disengaging from the wall
of the locking member, the axial clearance between the
pressing part'and the fixed element being less than the
axial length of the bearing surface of the upstream rim
of the wall on the locking member.
Thanks ~o the invention, the pressing part provided at
the downstream end of each ring sector limits the
possible retraction of the upstream rim of the ring
sector into th« groovs of the casing rail and prevents
this rim from disengaging from the locking member.
Even in the case of considerable wear cf the casing
rail, the ring sec-ors are held axially upstream by
their upstream rims pressing on a matching face of the
casing rail and downstream by the part pressing on the
fixed element.
The pressing part advantageously comprises meana LhdL
can prcoo radially on the fixed clement.
Each ring sector is therefore held in the axial
direction and in the racial direction on the fixed
element.
According to another feature of the invention, the
pressing par:; is attached to the downstream end of the
wall and to the block of abradable material by brazing
or welding.
It is advantageous, from the economic point of view,
for the pressing part to be on the ring sector, because
that prevents modifying the molds for manufacturing
these sectors. In addition, the device according to the
invention makes it possible to couple ring sectors to a
casing rail independently of the wear of the latter.
The axial clearance between the pressing part and the
fixed element is less than the axial" length of the
bearing surface of the upstream rim of the ring sector
on thft locking member. This makes it possible to ensure
that the maximum retraction position of the rinq sector
is defined by the axial pressure of the part on the
fixed element. This axial clearance between the
pressing part and the fixed element lies for example
between 0.3 and 1.2 mm approximately.
In a preferred embodiment of the invention, the
pressing part has an F-ahaped section and comprises two
rirns in a portion of a cylinder that extend in the
downstream direction, one of these rims being attached
to a radially inner surface of the wall of the ring
.sector and the other of these rims being able to press
radially on a radially outer face of a cylindrical rim
of the fixed element.
The fixed element of the turbomacnine consists
advantageously of a turbine guide vdue element situated
downstream of the ring sector.
The invention also relates to a turbomachine turbine
and a turbomachins, such as en aircraft turbojet or
turboprop, comprising at least one device as described
above.
Finally, the invention relates to a ring sector for a
turbomacnine turbine, comprising a frustoconical wall
that supports a block of abradable material attached to
its inner surface and that comprises at its upstream
end a rim for coupling to a casing, wherein it
comprises at its downstream end an axial and radial
pressing part that is fitted and attached to the wall
and to the block of abradable material of -he ring
sector.
The pressing part is preferably attached by weiding or
brazing to the block of abradable material and to the
downstream end of the wall af th'e ring sector.
Brief description of the drawings
The invention will be better understood and other
features, details and advantages of the latter will
appear more clearly en reading the following
description, given as a nonlimiting example and with
reference to the appended drawings in which:
- figure 1 is a partial schematic view in axial section
of a device for attaching ring sectors according to the
prior art;
- figure 2 is a partial schematic view in axial section
of a device for attaching ring sectors according to the
invention.
Description o: the preferred embodiments
The turbine 10 partially represented in figure 1
comprises several stages each including s. guide vane
element 12, 13 formed of an annular array of fixed
blades 14 supported by a casing 16 of the turbine, and
a wheel 18 mounted downstream of the guide vane element
12, 13 and rotating in a substantially frustoconical
envelope formed by ring sectors 20 supported
circumferentially end-to-end by the casing 16 of the
turbine.
The guide vane elements 12, 13 comprise an outer wall
of revolution 22 and an inner wall of revolution (not
visible] respectively, that delimit between them the
annular stream of gas flow in the turbine and between
which the blades 14 extend radially. The means for
attaching the guide vane elements comprise at least one
outer cylindrical rim 24 oriented in the upstream
direction and to be engaged in an annular groove 26
oriented in the downstream direction of the casing 16.
The rotors 18 are supported by a turbine shaft (not
shown) . They comprise an outer ring 28 and an inner
ring (not visible) respectively, the outer ring 28 of
each wheel comprising outer annular ribs 30 surrounded
externally with a slight clearance by the ring sectors
20.
Each ring sector 20 comprises a frustoconical wall 32
and a block 34 of abradable material attached by
brazing and/or welding to the radially inner surface of
the wall 32, this block 34 being of the honeycomb type
and being adapted to wear by friction en the ribs 30 of
the wheel to minimize the radial clearances between the
rotor and the ring sectors 20.
The downstream ends of the ring sectors 20 are engaged
from upstream in an annular space 36 delimited by a
cylindrical rim 38 oriented in the upstream direction
of the outer wall 22 of the guide vane element 13
situated downstream of the ring sectors, on the one
hand, and by a cylindrical rim 39 of the casing to
which this guide vane element is coupled, on the other
hand.
The ring sectors 20 are held radially at their
downstream ends by radial outward pressure of their
walls 32 on a radially inner cylindrical face of the
rim 39 of the casing, and by radial inward pressure of
their blocks 34 of abradable material on a radially
outer cylindrical face of the cylindrical rim 38 of the
guide vane element.
The walls 32 of the ring sectors each comprise at their
downstream ends a lug 40 extending axially in the
downstream direction and adapted to bs engaged in a
matching cavity 42 of the downstream guide vane element
13 to prevent the ring sectors 20 from rotating about
the axis of the turbine.
The frustoconical walls 32 of the ring sectors 20 disc
comprise at their upstream enc's cylindrical rims 44
oriented in the upstream direction than are engaged
with a slight axial clearance in a radially inner
annular groove 46 of an annular rail 48 of the casing
16. These rims 44 are held radially in this groove by
means of a locking member 50 formed of a C-section
split ring engaged from upstream on the annular rail 48
of the casing and on the upstream rims 44 of the ring
sectors .
The locking member SO cotnprsesi two cylindrical
branches 52 and 54 extendinq in the downstream
(direction, radially outer and radially inner
respectively, that are connected together at their
upstream ends by a radial wall 56, and that are pressed
respectively to a radially outer cylindrical face of
the rail 48 and to the circumferential rims 44 of the
ring sectors 20.
In the example shown, the locking member 50 is
prevented from moving ax. tally in the upstream Hi recti on
by axial pressure of its radial wall 56 on a radial
annular rim 58 of the outer wall 22 of the guide vane
element 12 situated upstream of the ring secrors 20.
The radius of curvature of the locking member 50 and of
the rail 48 is less than that of the rims 44 of the
tiny beclurb 20, which makes it possible to mount with
a certain radial prestreaa the rims 44 of the ring
sectors in the groove 46 of the rail, these ring
sectors . pressing locally on the bottom of the groove
anc on the radially inner branch 54 of the locking
member, respectively.
In operation, the rims 44 of the ring sectors 20
vibrate axially and coins to wear by friction the
upstream ' end downstream faces of the groove" 4'G of the
rail .
When the downstream face of the groove 46 is very worn
(as is shown in dashed line$ 60) , the rims 44 can move
in the downstream direction by sliding on the radially
inner branch 54 of the locking member, and disengage
from the locking member, which may in particular cause
the destruction of the blocks 34 of abradable material
of the ring sectors that come into contact with the
annular ribs 30 of the wheel 10.
The invention makes it. possible to provide a simple
solution to this problem thanks ~o a pressing part
.fitted and attached to the downstream end of each ring
sector.
In an embodiment of the invention represented in figure
2, the pressing part 70 has an F-snaped section ana!
comprises two rims 72 anc 74 in a portion of a cylinder
oriented in the downstream direction, radially outer
and radially inner respectively, that are connected
tcge-her at their upstream ends by a radial wall 76.
The radially outer face of the outer rim 72 is pressed
and attached by welding or brazing to s. downstream end
portion of the radially inner surface of the wall 32 of
the ring sector, and the radial wall 76 is pressed and
attached by brazing or welding to a radial ±ace ot the
block 34 of abradable material ol the ring seclor 20,
ring sector .is held radially flt. its downstream end
by radial pressure of the inner rim 74 of the part 70
on the, cylindrical rim 38 of the downstream guide vane
element, and by radial pressure of its wall 32 on the
radially inner face of the cylindrical rim 39 of the
casing 16.
The ring sectors are held axlally at their upstream
ends aa described above with reference to figure 1, and
at their downstream ends by axial pressure in the
downstream direction of the radial wall 76 of the part
on the upstream end of the cylindrical rim 38 of the
downstream guide vane element 13.
The radial walls 76 of the parts 70 are separated from
the cylindrical rim 38 of the guide vane element 13 by
an axial clearance 78 that is less than the axial
lenylh 80 on which the rims 44 of the ring sectors are
pressing on the locking member 50, so that, in the
event of considerable wear of the downstream face of
the groove 46 of the rail, the radial walls 76 of the
part 70 come to press axially on the cylindrical rim 38
of the guide vane element and limit the possible
retraction of the rims 44 of the ring sectors in the
groove, preventing them from disengaging from the
locking member 50. The axial clearance lies for example
between 0,3 and 1.2 mm'approximately.
Aa long as the casing rail 48 is not worn or is
slightly worn, th0 ring sectors 20 are held axially on
the casing 16, as described above with reference to
figure 1, that is to say by axial pressing cf the rims
44 of the ring sectors on the upstream and downs-ream
faces respectively of the groove 46 of the rail.
When the face oriented in the upstream direction of the
groove is heavily worn or has even corap-etely
disappeared (as shown in dashed lines 82), the ring
sectors 20 are held sxially in the downstream direction
by axia" prftRsnre of the radial walls 76 of the parts
70 on the cylindrical rim 38 of the downstream quide
vane element.
The part 70 may be fitted and attached to the
downstream end of an existing ring sector of the prior
art. For this it is sufficient to remove a downstream
end portion of the block 34 of abradable material of
the ring"sector and to attach to it instead "by brazing
or welding an axial and radial pressing part 70.
As a variant,'the pressing part may comprise only axial
means of pressing on the upstream rim 38 of the guide
vane element, the ring sectors being held radially
toward the inside at their downstream ends by radial
pressure of the blocks 34 on this upstream rim, as is
the case in the prior art.

CLAIMS
1, A device' for attaching ring sectors (20)1' around a
turbine wheel in a turbomachine, each ring sector
(?0) comprising a f rnsf nrnri r.fll wall (32) that,
supports' a block of abradable material (34)
attached to its inner surface and that comprises
at its upstream end a circumferential rim (44)
engaged in a radially inner annular groove of an
annular casing rail (48) and held radially in this
groove by a C-section annular locking member (50)
that is engaged axially from upstream on the
casing rail end on the circumferential rims of the
ring sectors, wherein each ring sector (20)
comprises at its downstream end a part (70) that
is fitted and attached to the frustoconical wall
(32) and to the block of abradable material of the
ring sector, this part being able to cone to press
axially against a fixed element of the turbine to
prevent the upstream rim (44) of the wall from
disengaging from' the locking member, the axial
clearance (78) between the pressing part and the
fixed element being less than the axiai length
(80) of the bearing surface of the upstream rim
(44) of the wall (32) on the locking nembar (50.
2. The device as claimed in claim 1, wherein the
pressing par- (70) comprises means that can press
radially on the fixed element..
3. The device as claimed in claim 1 or 2, wherein the
part (70) is attached to the downstream end of the
well (32) and to the block of abradable ma-erial
by brazing or welding.
4. The device as claimed in one of the preceding
claims/ wherein the axial clearance (~8) between
the pressing part (70) and the fixed element lies
between 0.3 and 1.2 mm approximately.
5. The device as claimed in one of the prececing
claims, wherein Lhe plessiny pa-fL "(70) has an Fshaped
section.
6. The device as claimed in claim 5, wherein the
pressing part (70) comprises two rims (12, 74).in
a portion of a cylinder that extend in the
downstream direction, one of these rims (72) being
attached to a radially inner surface of the wall
(32) of the ring sector (20) and the other of
these rims being able to come to press radially on
a radially outer face of a cylindrical rim (38) o£
the fixed element.
7. The device as claimed in one of the preceding
claims, wherein the fixed element ferns part of a
turbine guide vane element (13) .
8. A turbomachine, such as an aircraft turbojet or
turboprop, which comprises at least one device as
claimed in one of the preceding claims.
9. A ring sector (20) for a tuxbomachinc turbine,
comprising a frustorornacal wall (3?) that supports
a block of abradable material (34) attached to its
inner surface and "hat comprises at its upstream
end a rim '(44) for coupling to a casing (16),
wherein it comprises at its downstream end an
axial and radial pressing part (70) that is fitted
and attached to the wall and to the block of
abradable material of the ring sector,
10. The ring sector (20) .as claimed in claim 9,
wherein the pressing part (70) is attached by
welding or brazing to the block of abradable
material ana to the downstream end of the wall of
the ring sector (32).
11. A turbcmachine turbine, wherein it comprises at
least one device as claimed in one of claims 1