BACKGROUND OF THE INVENTION
[0001] This invention relates to turbine stator vanes and, particularly, to a mechanical
attachment between a tip shroud segment and a group of stator vanes.
[0002] Tip shrouds on stator vanes provide a deterministic flow path for the particular
stator stage, and also serve to increase the stiffness of the vanes. It is customary
to assemble arcuate shroud segments over a number of vanes (e.g., 5, 7 or more), with
the segments collectively forming a 360° shroud. The tip shroud segments are typically
welded to the tips of the vanes.
BRIEF SUMMARY OF THE INVENTION
[0003] In accordance with an exemplary embodiment of this invention, each vane within a
group of vanes to be covered by the shroud segment has a projecting tenon at its tip.
The shroud segment is formed with corresponding holes that align with the tenons of
the respective vanes. A bushing is seated in each of the shroud segment holes, and
each bushing is formed with a center opening for receiving a respective one of the
tenons. The center opening is counterbored, leaving an internal shoulder or seat for
the tenon. The bushing is also formed with an external shoulder that allows the bushing
to engage a shoulder surface of the corresponding shroud segment hole. This arrangement
permits the bushing to be inserted into the shroud segment hole in a direction opposite
the insertion direction of the vane tenons, with the external shoulder providing a
stop limit to the bushing insertion. The vane tenons are subsequently welded to the
internal bushing seat. Note that the bushings are not otherwise attached directly
to the shroud segment but are nevertheless held in place radially by the tenon welds
in one direction and the external shoulder engagement in the opposite direction.
[0004] Accordingly, in one aspect, the present invention relates to a stator vane segment
and tip shroud segment assembly comprising: a plurality of vanes, each having an airfoil
portion and a radially inner tip, each tip formed with at least one radially inwardly
projecting tenon; and a tip shroud segment extending over the radially inner tips
of the vanes, said tip shroud segment formed with a plurality of holes, each hole
fitted with a bushing that receives a respective one of the tenons.
[0005] In another aspect, the invention relates to a stator vane segment and tip shroud
segment assembly comprising: a plurality of vanes, each having an airfoil portion
and a radially inner tip, each tip formed with at least one radially inwardly projecting
tenon; a tip shroud segment extending over the radially inner tips of the vanes; the
tip shroud segment formed with a plurality of holes, each hole fitted with a bushing
that receives a respective one of the tenons; wherein the bushing is formed with an
internal shoulder on which the respective tenon is seated; and wherein each bushing
is formed with an external shoulder engaged by the tip shroud segment.
[0006] In still another aspect, the invention relates to a stator vane segment and tip shroud
segment assembly comprising: a plurality of vanes, each having an airfoil portion
and a radially inner tip, each tip formed with at least one radially inwardly projecting
tenon; a tip shroud segment extending over the radially inner tips of the vanes, the
tip shroud segment formed with a plurality of holes, each hole fitted with a bushing
that receives a respective one of the tenons; wherein each bushing is formed with
an external shoulder engaged by the tip shroud; and wherein each bushing is formed
with a center hole counterbored to provide an internal shoulder that provides a seat
for the respective tenon and wherein the tenon is welded to the bushing at the internal
shoulder.
[0007] Embodiments of the invention will now be described, by way of example only, in connection
with the drawings identified below.
BRIEF DESCRIPTION OF THE DRAWING
[0008]
FIGURE 1 discloses a perspective view of a shrouded stator vane segment in accordance
with an exemplary embodiment of the invention;
FIGURE 2 is a cross-section taken along the line 2-2 of Figure 1;
FIGURE 3 is a partial cross-section taken along the line 3-3 in Figure 1;
Figure 4 is a perspective view of another exemplary embodiment of the invention; and
Figure 5 is an enlarged detail similar to Figure 3 but taken from the assembly shown
in Figure 4; and
Figure 6 is a perspective view of still another embodiment of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0009] With reference initially to Figures 1-3, a stator vane and tip shroud segment assembly
10 includes a plurality of stator vanes 12, each of which includes a dove tail mounting
portion 14, an airfoil portion 16, and a radially projecting tenon 18 (Figure 2) that
projects from the radially inner tip 20 of the vane. Typically, the tenon 18 is round
or oval in cross section and is formed approximately intermediate the forward and
trailing edges 22, 24 of the airfoil portion.
[0010] An arcuate tip shroud segment 26 spans and is attached to a selected member of stator
vanes 12, such that the collective stator vane and tip shroud segments will form a
360° stator assembly.
[0011] The arcuate tip shroud segment 26 is formed with a plurality of holes 28 that are
appropriately located to align with the stator tenons 18. As best seen in Figure 3,
the holes 28 are counterbored in a radially outward direction to create a radially
inwardly facing shoulder 30 that is adapted to be engaged by a corresponding radially
outwardly facing shoulder 32 on a bushing 34. The bushing 34 is correspondingly shaped
to be received in the segment hole 28 (i.e., round or oval), and, as already indicated
above, is formed with an external shoulder 32 that engages the corresponding shoulder
30 on the arcuate tip shroud segment 26. The bushing 34 is also formed with a center
opening 36 that is counterbored to provide an annular (or oval)-shaped, radially outwardly
facing seat 38 that is adapted to be engaged by the marginal edge of a respective
tenon end face 40.
[0012] With the bushings 34 inserted in the segment holes 28 in direction A (Figure 3),
the airfoil tenons 18 are inserted into the bushing in direction B until the tenons
are fully engaged with the seats 38. Subsequently, each airfoil tenon 18 is fixed
to the bushing at the seat 38 by weld 42. It is significant that the bushing is not
otherwise fixed to the tip shroud segment 26. As a result, some degree of movement
between the airfoil portion 16 and the tip shroud segment 26 is permitted via bushing
34, thereby reducing stresses during operation. Note that the bushing is recessed
relative to the radially inner face of the shroud segment so as not to protrude into
the gas flowpath
[0013] In the exemplary embodiment, the bushing may be constructed of 316 Stainless Steel
while the airfoil portion 16 (including the tenons 18) and the tip shroud segment
26 may be constructed of a harder 403 Stainless Steel, but the material compositions
may vary.
[0014] Figures 4 and 5 illustrate another embodiment of a vane and tip shroud segment assembly
110 where the shapes of the tip shroud segment, bushing, and airfoil tenon as shown
vary somewhat from the embodiment shown in Figures 1-3. Otherwise, the components
and the interaction between the tip shroud segment, airfoil portion and bushing remains
as previously described. For convenience, similar reference numerals are used, but
with the prefix "1" added, to designate corresponding features, but no further description
is required.
[0015] Figure 6 illustrates another vane segment configuration that incorporates the subject
invention. In this figure, similar reference numerals are used to designate similar
components, where applicable, but with the prefix "2" added. The vane and tip shroud
segment assembly 210 incorporates bushings 234 as described in connection with Figures
1-3 and this aspect of the assembly need not be repeated here. In this embodiment,
the portion (or dovetail mounting portions) 214 of the vanes are ganged together via
a strap 244 and a plurality of bolts 246.
[0016] In an alternative arrangement that does not require welding, the tenons could be
formed with subtenons that project beyond the tenon end face and the extended subtenon
may then be cold formed about the bushing end face. In yet another variation, the
tenon could be formed with a tapped hole with a bolt passing through the center opening
of the bushing and into a threaded hole in the tenon.
[0017] While the invention has been described in connection with what is presently considered
to be the most practical and preferred embodiment, it is to be understood that the
invention is not to be limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements included within
the spirit and scope of the appended claims.
1. A stator vane segment and tip shroud segment assembly (10) comprising:
a plurality of vanes (12), each having an airfoil portion 16 and a radially inner
tip (20), each tip formed with at least one radially inwardly projecting tenon (18);
and
a tip shroud segment (26) extending over the radially inner tips (20) of the vanes,
said tip shroud segment (26) formed with a plurality of holes (28), each hole fitted
with a bushing (34) that receives a respective one of said tenons (18).
2. The assembly of claim 1 wherein said tenons (18) are attached directly to said bushings
(34).
3. The assembly of claim 1 wherein said bushing (34) is formed with an internal seat
(38) on which the respective tenon is seated.
4. The assembly of claim 1 wherein each bushing (34) is recessed relative to a radially
innermost surface of said tip shroud segment (26) such that said bushing does not
protrude into a flowpath along the airfoil portions of the vanes (12).
5. The assembly of claim 3 wherein each bushing (34) is recessed relative to a radially
innermost surface of said tip shroud segment (26) such that said bushing does not
protrude into a flowpath along the airfoil portions of the vanes (12).
6. The assembly of claim 1 wherein each bushing (34) is formed with an external shoulder
(32) engaged by said tip shroud segment (26).
7. The assembly of claim 3 wherein each bushing (34) is formed with an external shoulder
(32) engaged by said tip shroud segment (26).
8. The assembly of claim 1 wherein each bushing (34) is formed with a center hole counterbored
to provide an internal shoulder that provides a seat (38) for the respective tenon
(18) and wherein said tenon (18) is welded to said bushing at said internal shoulder.
9. The assembly of claim 2 wherein said bushings (34) are not otherwise attached to said
tip shroud segment.
10. The assembly of claim 1 wherein said tenons (18) are welded to said bushings.