Note: Descriptions are shown in the official language in which they were submitted.
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SHEET METAL PANEL
This invention relates generally to sheet metal
panels in gas turbine engines. More particularly, it
relates to arcuate panels with small radii bends,
especially where such bends are substantially normal to
the direction of arc.
BACKGROUND OF THE INVENTION
Gas turbine engines have numerous annular areas,
including combustor, high pressure turbine and low
pressure turbine. Each of these areas is bounded by a
liner or shroud which defines a flow path. Typical
liners/shrouds may be segmented into a number of arcuate
panels with a means for attaching each panel to a support.
In the past, such panels have been formed by
rough casting of the part followed by precision machining.
These panels tend to be heavy due to casting limitations
requiring minimum thicknesses. They also may exhibit
weaknesses due to voids created during the casting
process. Furthermore, the machining operation requires
additional time resulting in more expensive panels.
Panels may also be formed by alternative
fabrication techniques. for example, in low pressure
turbine shrouds, sheet metal members may be joined
together to form the panel. Again, as with machining,
such techniques are time consuming and expensive.
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OBJECT OF THE INVENTION
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It is an object of the present invention to
provide a new and improved arcuate sheet metal panel for
use in a gas turbine engine.
It is another object of the present invention to
provide a less expensive flow path liner than those
heretofore known.
It is a further object of the present invention
to provide a new and improved arcuate sheet metal shroud
for use in a high pressure turbine
SUMMARY OF THE INVENTION
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In accordance with the present invention, a sheet
metal panel in a gas turbine engine comprises a stressed
region, The region defines a first arc of intersection
with a first plane, The region further defines a second
arc of intersection with a second plane. The second arc
has an inner radius of less than twice the thickness of
the panel.
In a specific embodiment of the present invention,
a sheet metal shroud panel comprises a generally arcuate
shroud backing, a first web and a first rail. The first
web extends outwardly from the backing and the first rail
extends from the first web. The first rail includes
first and second sections wherein the second section is
folded back on the first section thereby forming a
stressed region. This stressed region defines a first
arc of intersection with a first plane and defines a
second arc of intersection with a second plane. The
second arc has an inner radius of less than the thickness
of the panel.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic view of a gas turbine
engine.
FIGURE 2 is a cross-sectional view of a shroud
panel and mounting according to one form of the present
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invention.
FIGURE 3 is a perspective view of the shroud
panel in Figure 2.
FIGURE 4 is a cross-sectional view of the shroud
panel in Figure 2.
FIGURE 5 is a perspective view of a stressed
region of a sheet metal panel.
FIGURE 6 is a perspective view of another
stressed region of a sheet metal panel.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows a gas turbine engine 10 with
compressor 12l combustor 14, high pressure turbine 16,
and low pressure turbine 18~ Each of these annular
areas is radially bounded by a structure which defines
a flow path. Compressor 12 is bounded by casing 20,
combustor 14 by liner 22r and turbines 16 and 18 by
shrouds 23 and 26. Each of these structures must be
connected to a support. In addition, each structure may
be segmented into a number of arcuate panels for varying
engineering and assembling reasons. Although the
requirements for strength, heat resistance, weight, etc.
for each of these structures may differ, they all have
a common need for strong, reliable, and relatively
inexpensive means for attaching to a support.
One embodiment of the present invention is shroud
panel 24 which is an arcuate segment of high pressure
turbine shroud 23. Shroud panel 24r a view of which is
shown in Figures 2, or and I is formed from a single
piece of sheet metal. Numerous materials may be
advantageously employed for the sheet metal. The
preferred material will consist of a high temperature
alloy including singularly or in some combination the
elements Nickel, Cobalt, and Chromium. For example,
commercially available materials with these features are
Hostile X, HS188, L605, Renew 41~ Wasp alloy, MOE, and
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MOE. The thickness T of the sheet metal will be
determined by the application. In one embodiment,
thickness T will be greater than 25 miss and in a
preferred embodiment will be between 25 miss and 60 miss.
Panel 24 includes a generally arcuate shroud
backing 38. The arcuate shape generally conforms to the
circumferential direction 40 of the turbine as bounded
by shroud panels 24. Panel 24 also includes forward
attachment structure 42 and aft attachment structure 44.
It will be clear that the attachment structures shown are
by way of illustration only and that many alternative
configurations are within the scope of the present
invention.
As shown in Figure 4, forward attachment structure
42 comprises first attachment component 92 and second
attachment component 94. Component 92 includes first web
member 96 which extends outwardly from the forward end of
shroud backing 38 and first rail section 98 which extends
from first web member 96~ Component 94 includes second
rail section 100 and second web member 102. As described
more fully hereinafter, component 94 is folded back on
component 92 so that first web member 96 and first rail
section 98 substantially conform to second web member 102
and second rail section 100, respectively. Web members 96
and 102 thereby form a well and rail sections 98 and 100
form a forward rail 30.
Similarly, aft attachment structure 44 comprises
third attachment component 104 and fourth attachment
component 106. Component 104 includes third web member
108 which extends outwardly from the aft end of shroud
backing 38, and third rail section 110 which extends from
web member 108~ Component 106 includes fourth rail
section 112 and fourth web member 114. As with forward
attachment structure 42, structure 44 is formed by folding
component 106 back on component 104 so that third web
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member 108 and third rail section 110 substantially
conform to fourth web member 114 and fourth rail section
112, respectively. Web members 108 and 114 thereby form
a web, and rail sections 110 and 112 form an aft rail 32.
As shown in Figure 2, each panel 24 is attached
to support 28 by the capture of forward rail 30 and aft
rail 32 of panel 24 by forward slot 34 and aft slot 36
of support 28, respectively In addition to the
generally arcuate shape of panel 24 in direction 40,
bends aye, 46b, 46c, 46d, eye, 46f, 46g, and 46h are
formed substantially normal to direction 40. In the
neighborhood of each bend, a stressed region is formed
where tension and/or compression stresses result from
both the arcuate shape and the normal bend thereto.
Figure 5 shows more detail of the stressed region
48 of panel 24 in the neighborhood of bend 46g.
Stressed region 48 defines a first arc 50 of intersection
with first plane 52. Plane 52 is generally parallel to
a plane tangent to the apex 49 of bend 46g. The radius
of arc 50 is the distance to the center line of the
engine. Stressed region 48 further defines a second arc
54 with second plane 56. Plane 56 is taken as normal to
first plane 52 in a preferred embodiment. Arc 54 is the
image of inner surface 59 of stressed region 48 and
corresponds to the inner radius of bend 46g. In general,
the radius 64 of arc 54 will be less than twice the
thickness (IT) of panel 24. In the case of bend 46g,
wherein panel 24 is folded back on itself, radius 64 of
arc 54 is much less than the thickness (lo) of panel 24
and approaches zero The measure of arc 54 will be
approximately 180 since panel 24 folds back on itself
at bend 46g~
Various reasons may exist for maintaining a small
radius bend on bend 46g. As shown in Figure 2, forward
rail 30 must be received by forward slot 34. Close
dimensional control must be maintained at this
interface. Consequently, a large radius bend creating a
bulbous end on rail 30 would adversely affect this mating.
In addition, the gap 66 between rail sections 68 and 70
will be brazed In order to achieve good strength, gap
66 must be narrow throughout its length.
Typically in the past, the inner radius 64 of
such bends must be greater than or equal to twice the
thickness (IT) of panel 24 to avoid fracturing. In the
present invention, tighter bends of less than IT and
approaching zero have been achieved. The sheet metal
panel is first stressed by forming it to its
circumferential arcuate shape. This establishes tensile
and compressive stresses in the panel in the
circumferential direction This arc is held while the
piece is bent to a very small radius arc in a second
direction. A biaxial stress condition is created by this
process thereby allowing these small radii bends to be
achieved.
Although folding a panel back on itself, such as
shown in Figures 2-5 may be necessary to form rails 30
and 32, other tight radius bends may be required
elsewhere in the panel. For example, a stressed region
72 in the neighborhood of bend 46d is shown in Figure 6.
Region 72 defines a first arc 74 of intersection with a
first plane 76. Region 72 defines a second arc 78 of
intersection with a second plane 82. Arc 78, which is
the inner radius of bend 46d, has a radius 84 of less
than twice the thickness (IT) of panel 24. In a
preferred embodiment, radius 84 is approximately lo,
although smaller radii are attainable if required.
Tight bends may be achieved wherever necessary to
duplicate the contours of prior art cast panels. For
example, bends aye and 46c may be tight to increase the
amount of surface area of aft rail 32 which contacts aft
slot 36. Bend 46d may be tight to increase the area
bonding contact between web members 108 and 11~ of web
90. As with bend 46g, shown in Figure 4, the radii of
tight bends may approach zero where required.
It may be desirable to braze joints 60 and 61
shown in Figure 4, where attachment components 92 and
94, and 104 and 106 conform, respectively. One method
by which these joints may be brazed is vacuum bonding.
More particularly, the process as described in Keller
et at, Us S. Patent No. 4,098,450 issued July 4, 1978,
may be advantageously employed
It will be clear to those skilled in the art that
the present invention is not limited to the specific
embodiments described and illustrated herein. Nor is the
invention limited to turbine shrouds in gas turbine
engines. Rather, the invention applies equally to any
arcuate sheet metal panel with a tight radius bend in a
gas turbine engine.
It will be understood that the dimensions and
proportional and structural relationships shown in the
drawings are illustrated by way of example only and
those illustrations are not to be taken as the actual
dimensions or proportional structural relationships used
in the panel of the present invention.
Numerous modifications, variations, and full and
partial equivalents can be undertaken without departing
from the invention as limited only by the spirit and
scope of the appended claims.
