A gas path seal suitable for use with a turbine engine or compressor is provided. A shroud wearable or abradable by the abrasion of the rotor blades of the turbine or compressor protects the rotor blades. A compliant backing surrounds the shroud. The backing may be made of corrugated sheets or the like with adjacent layers having off-set corrugations, with axes of the folds parallel to the rotor axis. The sheets may be bonded together at points of contact by brazing, welding or the like. In another embodiment a compliant material is covered with a thin ductile layer. A mounting fixture surrounds the backing

Bill, R. C.

Ludwig, L. P.

English

A gas path seal suitable for use with a turbine engine or compressor is provided. A shroud wearable or abradable by the abrasion of the rotor blades of the turbine or compressor shrouds the rotor blades. A compliant backing surrounds the shroud. The backing is a yieldingly deformable porous material covered with a thin ductile layer. A mounting fixture surrounds the backing

NASA Technical Reports Server

States Patent [I91 
Bill et al. 
[111 4,295,786 
[45] Oct. 20, 1981 
[54] COMPOSITE SEAL FOR 
[75] Inventors: Robert C. Bill, Rocky River; 
TURBOMACHINERY 
Lawrence P. Ludwig, Fairview Park, 
both of Ohio 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 96,255 
[22] Filed: Nov. 20, 1979 
Related U.S. Application Data 
[62] Division of Ser. No. 931,090, Aug. 8, 1978, Pat. No. 
4,207,024, which is a division of Ser. No. 801,290, May 
27, 1977, Pat. No. 4,135,851. 
[51] Int. C1.3 .............................................. FOlD 11/08 
[52] US. Cl. ..................................... 415/174; 415/196 
[58] Field of Search ............... 415/174, 200, 196, 214, 
415/197; 277/96, 96.1, 96.2, 236 
[561 References Cited 
U.S. PATENT DOCUMENTS 
3,887,299 6/1975 Profant ................................ 415/174 
4,022,481 VI977 Long et al. ..................... 415/174 X 
4,135,851 1/1979 Bill et al. ............................. 415/174 
4,207,024 6/1980 Bill et al. ............................. 415/174 
Primary Examiner-Everette A. Powell, Jr. 
Attorney, Agent, or Firm-Normal T. Musial; John R. 
Manning; Gene E. Shook 
1571 ABSTRACT 
A gas path seal suitable for use with a turbine engine or 
compressor is provided. A shroud wearable or abrad- 
able by the abrasion of the rotor blades of the turbine or 
compressor shrouds the rotor blades. A compliant back- 
ing surrounds the shroud. The backing is a yieldingly 
deformable porous material covered with a thin ductile 
layer. A mounting fixture surrounds the backing. 
10 Claims, 1 Drawing Figure 
https://ntrs.nasa.gov/search.jsp?R=19820011666 2020-03-21T16:12:01+00:00Z
atent Oct. 20, 1981 4,295,786 
4,295,786 
1 2 
its worn portion toward its original dimension. In the 
preferred embodiment wherein the compliant backing 
has a ductile top coating, the normal forces are limited 
and the blade wear is reduced. Hence any gap is less 
The invention described herein was made by employ- 5 than in prior instance of such wear, and the useful life of 
the shroud increased. 
COMPOSITE SEAL FOR TURBOMACHINERY 
ORIGIN O F  THE INVENTION 
ees of the U.S. Government and may be manufactured 
and used by or for the Government for governmental 
purposes without the payment of any royalties thereon 
or therefor. 
RELATED APPLICATION 
This application is a division of copending application 
Ser. No. 931,090 filed Auk. 8, 1978, now U.S. Pat. No. 
BRIEF*DESCRIPTION O F  THE DRAWING 
The objects, advantages and novel features of the 
10 invention will be more fully apparent from the follow- 
ing detailed description when read in connection with 
the accompanying drawing which is a schematic view, 
in longitudinal cross section, of a preferred embodiment 
4,207,024, and which, in tGn, is a division of application 
Ser. No. 801,290 filed May 27, 1977 and now U.S. Pat. l5 
No. 4,135,851. 
of theinvention. 
DESCRIPTION O F  THE PREFERRED 
EMBODIMENT 
Referring to the FIGURE, a rotor blade 10 of a tur- 
In the design of turbines or compressors or the like, bine compressor, for example, rotates about an axis 12 
especially those of high speed, it is understood that 2o tending to force the fluid in which it operates along this 
close tolerance between the tips of the blades and the axis. A shroud surrounds the blade 10 and is substan- 
surrounding shroud or housing which seals one side Of tially concentric with the axis 12. The shroud may be of 
the blades from the other is desirable. Such a seal re- suitable material abradable relative to the material of 
duces the return flow of fluid from the high pressure to the blade 10. 
the low pressure side. The closer the shroud surrounds 25 backng surrounds the shroud. The 
the tips of the blades, the more efficient is the turbine or abradable shroud is bonded to the concave, inner face of 
compressor. Aerodynamic losses are also reduced by the backing. The backing is inserted and bound to a 
closer fitting of the blade tips to the shroud. housing 22. 
BACKGROUND OF THE INVENTION 
A 
the clearance dh'nensions are dynamic. Previous abradable seals, even though various materi- 
They increase and decrease with temperature and with 30 als for the shroud have been proposed, such as sintered 
metals, metal honeycombs, and porous ceramics, have and forces and may increase 
Or decrease faster than the rotor* The 'learance may 
also decrease, for example in one direction, under so- 
called shock loading when an airplane makes a sudden 
maneuver that subjects the parts to unusual acceleration 35 
forces, causing a differential expansion or movement of 
the parts. 
The prior attack on such problems has been to design 
the shroud to fit closely, say within 20 to 30 mils. (i.e. 
not provided a desirable flexibility. After abrasion due 
to a transient condition such as a thermal transient or 
shock loading, the gap or wear produced by the rub or 
contact is generally larger than the interference depth 
because of tearing out, galling, and spalling. 
The drawing illustrates the preferred embodiment in 
which the blade 10 is shown at an instant when forces 
about 5 to 7 mm.) about the tips ofthe blades at ambient 40 have Caused the tip of the blade to contact the shroud* 
temperature. Moreover, the shroud about the blade has The compliant backing in this is com- 
been designed to be wearable or abradable relative to pressed, the compression as illustrated in the drawing in 
the blade tips. Then if there is a thermal transient or exaggerated fashion* 
shock loading that a blade tip to strike the The material of the shroud 34 may be a relatively thin 
shroud, the blade material flakes off or abrades the 45 layer 36 of deformable metallic material. The backing 
shroud material, which may be a sprayed coating or 38 is a compliant material, such as low density sintered 
sintered material of low density. Thus, the shroud mate- metal, or gas blown plastic. The metal or metal alloy 
rial is abradable (or wearable) with respect to the blade layer 36 may be a dense Plasma sprayed soft 
material. However, such wear is not readily achieved in as aluminum, or a bonded metal sheet or foil. 
practice. By the arrangement of the present invention 50 When the blades, as a result of forces 
the blade tip may be designed to rotate in close proxim- 
ity to the shroud without fear of cataclysmic destruc- 
tion of either blade or shroud, should contact between 
the two occur due to thermal transient or shock load- 
ing. 
as de- 
scribed hereinbefore, rub against the shroud, the thin 
metallic layer 36 is deformed into the Compliant sub- 
strate material 38. In effect because Of the Compliant 
substrate material 38 the magnitude of a force normal to 
55 the surface of the shroud is limited. This normal force is 
SUMMARY OF THE INVENTION 
measured in the radially inward direction. A larger 
displacement simply causes a greater deformation with- 
According to the present invention, there is provided out greatly increasing the normal force. Therefore, in 
in combination for a turbine rotor or the like a stator effect, the compliant substrate material limits the magni- 
shroud of material wearable relative to the blades, a 60 tude of the normal force which can be developed be- 
compliant backing of a yieldingly deformable porous tween the blade tip and the shroud. The more porous 
material with a thin ductile layer, and a rigid mounting and yieldingly deformable the substrate 38 and the thin- 
surrounding the compliant backing. The compliance of ner the shroud layer 36, the smaller will be the normal 
the backing tends to cause the shroud when tipped or force. Because the normal force is low when the blades 
touched by the rotating blade because of some transient 65 rub against the shroud, blade wear is reduced. 
condition to yield somewhat. Then, even though Currently used shroud materials such as sintered 
abraded or worn, the compliance of the backing pro- metal or felt metals have disadvantages of low erosion 
vides a restorative force tending to return the shroud at resistance, aerodynamic roughness and porosity which 
4,295,786 
3 
permit back leakage. An arrangement as described in 
connection with the drawing with the shroud layer as 
suggested herein provides an aerodynamically smooth 
surface and high erosion resistance and is substantially 
less permeable from a leakage standpoint. Furthermore, 
any wear debris produced in the rub is less than that 
produced in other shroud arrangements. Wear debris 
tends to plug up turbine cooling holes and to plate out 
or stick on compressor blades causing aerodynamic 
losses. 
Various modifications may be made. For example, 
metallic sheets (not illustrated) may be distorted by 
wires aligned parallel to axis 12 to form corrugations for 
the compliant backing, or these corrugations might 
extend at angles of less than 90" to the axial direction. 
The compliant backing 38 may use fibermetal, and in- 
stead of the thin metallic layer, material such as high 
temperature resistant ceramic may be used. 
What is claimed is: 
1. A gas path seal for a turbine or the like having a 
plurality of blades mounted for rotation about an axis 
comprising 
a stator shroud having an aerodynamic smooth sur- 
face on a thin layer of a deformable metallic mate- 
rial that is wearable relative to said blades and 
closely spaced to the blade tips whereby said 
shroud is deformed when said blades rub against 
said surface, 
4 
a yieldingly deformable porous backing surrounding 
said layer to receive said deformed shroud thereby 
reducing said blade wear by limiting the magnitude 
of normal forces measured radially inward which 
are developed between the blade tips and the 
shroud, and 
a rigid mounting housing surrounding said backing 
and being secured to the outermost surface of said 
backing. 
2. The combination as claimed in claim 1, said shroud 
being substantially cylindrical. 
3. The combination as claimed in claim 2, said mount- 
ing housing being also cylindrical. 
4. The combination as claimed in claim 1, said yield- 
15 ingly deformable porous backing being metal. 
5. The combination as claimed in claim 4, said metal- 
lic backing material comprising a thermal sprayed layer. 
6. The combination as claimed in claim 5, said metal- 
lic backing material comprising porous sintered metal. 
7. The combination as claimed in claim 1, said yield- 
ingly deformable backing material comprising a gas 
blown plastic material. 
8. The combination as claimed in claim, 1, said stator 
shroud material comprising a dense plasma sprayed 
9. The combination as claimed in claim 1, said shroud 
10. The combination as claimed in claim 9, said 
5 
10 
20 
25 aluminum layer. 
material comprising sheet metal. 
shroud material comprising aluminum foil. * * * * *  30 
35 
40 
45 
50 
55 
60 
65 


Composite seal for turbomachinery

A gas path seal suitable for use with a turbine engine or compressor is provided. A shroud wearable or abradable by the abrasion of the rotor blades of the turbine or compressor shrouds the rotor blades. A compliant backing surrounds the shroud. The backing is a compliant material covered with a thin ductile layer. A mounting fixture surrounds the backing

United States Patent [191 
Bill et al. 
u 1 1  4,20'7,,024 
[45] Jm, IO, 1980 
COMPOSITE SEAL FOR 
TURBOMACHINERY 
Inventors: Robert C. Bill, Hocky River; 
Lawrence P. Ludwig, Fairview Park, 
both of Ohio 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Assignee: 
Appl. No.: 931,090 
Filed: Aug. 4, 1978 
Related US. Application Data 
Division of Ser. No. 801,290, May 27, 1977, Pat. No. 
4,135,851. 
Int. Cl .2  .............................................. FOlD 11/08 
U.S. Cl. ..................................... 415/174; 415/196 
Field of Search ............... 415/174, 200, 208, 217, 
415/218,214, 197, 196; 277/96,96.1,96.2,236; 
29/404; 428/462,492 
References Cited 
U.S. PATENT DOCUMENTS 
3,423,070 VI969 Corrigan .............................. 415/20 
3,519,282 7/1970 Davis ............................... 277/236 X 
3,545,944 12/1970 Emanuelson et al. ........ 415/174 UX 
3,880,550 4/1975 Corey et al. ......................... 415/174 
3,887,299 (91975 Profant ................................. 415/174 
4,022,481 5/1977 Long et al. ........................... 415/174 
4,063,742 12/1977 Watkins, Jr. ..................... 415/174 X 
4,135,851 1/1979 Bill et al. .............................. 415/174 
4,139,376 2/1979 Erickson et al. ................ 415/174 X 
FOREIGN PATENT DOCUhlENTS 
660610 4,4963 Canada ...................................... 277/96 
1576942 7/1970 Fed. Rep. of Germany ........... 418/153 
Primary Examiner-Everette A. Powell, Jr. 
Attorney, Agent, or Firm-Musial, N .  T.; J. R. Manning; 
G. E. Shook 
WI ABSTRACT 
A gas path seal suitable for use with a turbine engine or 
compressor is provided. A shroud wearable or abrad- 
able by the abrasion of the rotor blades of the turbine or 
compressor shrouds the rotor bIades. A compliant back- 
ing surrounds the shroud. The backing is a compliant 
material covered with a thin ductile layer. A mounting 
fixture surrounds the backing. 
2,952,442 9/1960 Wamken ....................... 415/174 UX 6 Claims, 1 Drawing Figure 
https://ntrs.nasa.gov/search.jsp?R=19800018159 2020-03-21T02:58:09+00:00Z
U.S. Patent Jun. 10, 1980 
‘36 
4.207.024 
1 
COMPOSITE SEAL FOR TURBOMACHINERY 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the U.S. Government and may be manufactwred 
and used by or for the Government for governmental 
purposes without the payment of any royalties thereon 
or therefor. 
RELATED APPLICATION 
This application is a division of copending application 
Ser. No. 801,290 which was filed May 27, 1977 and is 
now U.S. Pat. No. 4,135,851. 
BACKGROUND OF THE INVENTION 
In the design of turbines or compressors or the like, 
especially those of high speed, it is understood that 
close tolerance between the tims of the blades and the 
2 
are limited and the blade wear is reduced. Hence any 
gap is less than in prior instance of such wear, and the 
useful life of the shroud is increased. 
5 BRIEF DESCRIPTION OF THE DRAWING 
The objects, advantages and novel features of the 
invention will be more fully apparent from the follow- 
ing detailed description when read in connection with 
the accompanying drawing which is a schematic view, 
10 in longitudinal cross section, of a preferred embodiment 
of the invention. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
Referring to the FIGURE, a rotor blade 10 of a tur- 
bine compressor, for example, rotates about an axis 12 
tending to force the fluid in which it operates along this 
axis. A shroud surrounds the blade 10 and is substan- 
_ _  tially concentric with the axis 12. The shroud may be of 
l 5  
surrounding shroud or housing which seals one side of 2u suitable material abradable relative to the material of 
the blades h m  the other is lesirable. Such a seal re- 
duces the return flow of fluid from the high pressure to 
the low pessure side. The closer the shroud surrounds 
the tips of the blades, the more efficient is the turbine or 
compressor. Aerodynamic losses are also reduced by 25 
closer frtting of the blade tips to the shroud. 
Nevertheless the clearance dimensions are dynamic. 
They increase and decrease with temperature and with 
mechanical and aerodynamic forces and may increase 
or decrease faster than the rotor. The clearance may 30 
also decrease, for example in one direction, under so- 
called shock loading when an airplane makes a sudden 
maneuver that subjects the parts to unusual acceleration 
forces, causing a differential expansion or movement of 
The prior attack on such problems has been to design 
the shroud to fit closely, say within 20 to 30 mils. (Le. 
about 5 to 7 mm.) about the tips of the blades at ambient 
temperature. Moreover, the shroud about the blade has 
been designed to be wearable or abradable relative to 40 
the blade tips. Then if there is a thermal transient or 
shock loading that causes a blade tip to strike the 
shroud, the blade material flakes off or abrades the 
shroud material, which may be a sprayed coating or 
sintered material of low density. Thus the shroud mate- 45 
rial is abradable (or wearable) with respect to the blade 
material. However, such wear is not readily achieved in 
the parts. 35 
practice. By the arrangement of the present invention 
the blade tip may be designed to rotate in close proxim- 
ity to the shroud without fear of cataclysmic destruc- 
tion of either blade or shroud, should contact between 
the two occur due to thermal transient or shock load- 
ing. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided 
a combination for a turbine rotor or the like a stator 
shroud of material wearable relative to the blades, a 
compliant backing with a thin ductile layer, and a rigid 
mounting surrounding the compliant backing. The com- 
pliance of the backing tends to cause the shroud when 
tipped or touched by the rotating blade because of some 
transient condition to yield somewhat. Then, even 
though abraded or worn, the compliance of the backing 
provides a restorative force tending to return the 
shroud at its worn portion toward its original dimen- 
sion. In the preferred embodiment wherein the compli- 
ant backing has a ductile top coating, the normal forces 
50 
55 
60 
65 
the blade 10. 
A compliant backing surrounds the shroud. The 
abradable shroud is bonded to the concave, inner face of 
the backing. The backing is inserted and bound to a 
housing 22. 
Previous abradable seals, even though various materi- 
als for the shroud have been proposed, such as sintered 
metals, metal honeycombs, and porous ceramics, have 
not provided a desirable flexibility. After abrasion due 
to a transient condition such as a thermal transient or 
shock loading, the gap or wear produced by the rub or 
contact is generally larger than the interference depth 
because of tearing out, galling, and spalling. 
The drawing illustrates the preferred embodiment in 
which the blade 10 is shown at an instant when forces 
have caused the tip of the blade to contact the shroud. 
The compliant backing in this case is slightly com- 
pressed, the compression as illustrated in the drawing in 
exaggerated fashion. 
The material of the shroud 34 may be a relatively thin 
layer 36 of deformable metallic material. The backing 
38 is a compliant material, such as a porous rubber or 
rubber-like material, for example, sponge rubber, low 
density sintered metal, or gas blown plastic. The metal 
or metal alloy layer 36 may be a dense plasma sprayed 
soft metal, such as aluminum, or a bonded metal sheet or 
foil. 
When the blades, as a result of forces such as de- 
scribed hereinbefore, rub against the shroud, the thin 
metallic layer 36 is deformed into the compliant sub- 
strate material 38. In effect because of the compliant 
substrate material 38 the magnitude of a force normal to 
the surface of the shroud is limited. This normal force is 
measured in the radially inward direction from the 
shroud. A larger displacement simply causes a greater 
deformation without greatly increasing the normal 
force. Therefore, in effect, the compliant substrate ma- 
terial limits the magnitude of the normal force which 
can be developed between the blade tip and the shroud. 
The more porous and yieldingly deformable the sub- 
strate 38 and the thinner the shroud layer 36, the smaller 
will be the normal force. Because the normal force is 
low when the blades rub against the shroud, blade wear 
is reduced. 
Currently used shroud materials such as sintered 
metal or felt metals have disadvantages of low erosion 
resistance, aerodynamic roughness and porosity which 
4,207,024 
3 
permit back leakage. An arrangement as described in 
connection with the drawing with the shroud layer as 
suggested herein provides an aerodynamically smooth 
surface and high erosion resistance and is substantially 
less permeable from a leakage standpoint. Furthermore, 5 
any wear debris produced in the rub is less than that 
produced in other shroud arrangements. Wear debris 
tends to plug up turbine cooling holes and to plate out 
or stick on compressor blades causing aerodynamic 
losses. 10 
Various modifications may be made. For example, 
metallic sheets (not illustrated) may be distorted by 
wires aligned parallel to axis 12 to form corrugations for 
the compliant backing, or these corrugations might 
extend at angles of less than 90" to the axial direction. 15 
Instead of sponge rubber in the compliant backing 38 
we may use fibermetal and instead of the thin metallic 
layer, material such as high temperature resistant ce- 
ramic layer may be used. 
What is claimed is: 20 
1. A gas path seal for a turbine or the like having a 
plurality of blades mounted for rotation about an axis 
comprising 
a stator shroud having an aerodynamically smooth 
surface on a thin layer of a deformable metallic 25 
4 
material that is wearable relative to said blades and 
closely spaced to the blade tips whereby said 
shroud is deformed when said blades rub against 
said surface, 
a yieldingly deformable rubber backing surrounding 
said layer to receive said deformed shroud thereby 
reducing said blade wear by limiting the magnitude 
of normal forces measured radially inward which 
are developed between the blade tips and the 
shroud, and 
a rigid mounting housing surrounding said backing 
and being secured to the outermost surface of said 
backing. 
2. The combination as claimed in claim 1, said shroud 
3. The combination as claimed in claim 2, said mount- 
being substantially cylindrical. 
ing housing being also cylindrical. 
4. A gas path seal as claimed in claim 1, said thin layer 
of stator shroud material comprising flexible sheet 
metal. 
5. A gas path seal as claimed in claim 1, said thin layer 
of stator shroud material comprising foil. 
6. A combination as claimed in claim 5, said thin layer 
of stator shroud material comprising aluminum foil. 
* * * * i t  
30 
35 
40 
45 
50 
55 
60 
65 


United States Patent [191 
Bill et al. 
[I11 4,135,851 
[MI Jan. 23, 1979 
[54] COMPOSITE SEAL FOR 
[75] Inventors: Robert C. Bill, Rocky River; 
TURBOMACHDWRY 
Lawrence P. Ludwig, Fairview Park, 
both of Ohio 
[73] Assignee: The United States of America 88 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 801,290 
[22] Filed: May27,1977 
[51] Int. c1.2 .............................................. M)lD 11/08 
[52] US. c1. ..................................... 415/17+ 415/200 
[58] Field of Search ........... 415/174, 200, 199.4, 
4W199.5, 217, 218; 277/96, 96.1, 96.2 
[56l References Cited 
U.S. PATENT DOCUMENTS 
2,477,852 8/1949 Bacon ........................... 415/174 UX 
2,994,124 8/1961 Denny et al. ................. 60/200 A X 
3,423,070 1/1969 Comgan .............................. 415/200 
4,063,742 12/1977 Watkins, Jr. ........... 415/174 X 
Primary Examiner--LouiS J. Casaregola 
Asisrant Examiner-Donald S. Holland 
Attorney, Agent, or Firm-N. T. Musial; J. R. Manning; 
G. E. Shook 
PI ABSTRACT 
A gas path seal suitable for use with a turbine engine or 
compressor is provided. A shroud wearable or abrad- 
able by the abrasion of the rotor blades of the turbine or 
compressor shrouds the rotor blades. A compliant back- 
ing surrounds the shroud. The backing may be made of 
corrugated sheets or the l i e  with adjacent layers hav- 
ing off-set corrugations, with axes of the folds parallel 
to the rotor axis. The sheets may be bonded together at 
points of contact by brazing, welding or the like. In 
another embodiment a compliant material is covered 
with a thin ductile layer. A mounting fmture surrounds 
the backing. 
5 c1pims, 3 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19790010147 2020-03-20T18:10:33+00:00Z
U.S. Patent ~ m .  23, 1979 Sheet 1 of 2 4,135,851 
'16 
20 
I 
U.S. Patent ~ m .  23,1979 Sheet 2 of 2 4,135,85 1 
I 
38 
34’ ‘36 
I 
IO - 
36 
\ /” 
‘22 
4,135,85 1 
1 
COMPOSITE SEAL FOR TURBOMACHINERY 
ORIGIN OF THE INVENTION 
The invention described herein was made by employ- 
ees of the United States Government and may be manu- 
factured and used by or for the Government for govern- 
mental purposes without the payment of any royalties 
thereon or therefor. 
BACKGROUND OF THE INVENTION 
In the design of turbines or compressors of the like, 
especially, those of high speed, it is understood that 
close tolerance between the tips of the blades and the 
surrounding shroud or housing which seals one side of 
the blades from the other is desirable. Such a seal re- 
duces the return flow of fluid from the high pressure to 
the low pressure side. The closer the shroud surrounds 
the tips of the blades, the more efficient is the turbine or 
compressor. Aerodynamic losses are also reduced by 
closer fitting of the blade tips to the shroud. 
Nevertheless the clearance dimensions are dynamic. 
They increase and decrease with temperature and with 
mechanical and aerodynamic forces and may increase 
or decrease faster than the rotor. The clearance may 
also decrease, for example in one direction, under so- 
called shock loading when an airplane makes a sudden 
maneuver that subjects the parts to unusual acceleration 
forces, Causing a differential eXpanSi0n Or movement Of sheets 38 with corrugations 20 extending substantially 
the parts. 30 longitudinally parallel to the axis 12. The sheets may be 
The Prior attack on Such Problems has been to deign bound to each along the lines of contact of the corruga- 
the shroud to fit closely, say Within 20 to 30 mi ls  tions by brazing or welding, and preferably formed to 
about 5 to 7 mm.) about the tips of the blades at ambient the as-installed radius of curvature. abradable 
temperature. Moreover the shroud about the blade has shroud is bonded to the concave, inner face of the back- 
been designed to be wearable or abradable relative to 35 ing 16. The backing 16 is inserted and bound to a hous- 
the blade tips. Then if there is a thermal transient or ing 22. 
shock loading that causes a blade tip to strike the Previous abradable seals, even though various materi- 
shroud, the blade material flakes off or abrades the als for the shroud have been proposed, such as sintered 
shroud material, which may be a sprayed coating or metals, metal honeycombs, and porous ceramics, have 
sintered material of low density. Thus the shroud mate- 40 not provided a desirable flexibility. After abrasion due 
rial is abradable (or wearable) with respect to the blade to a transient condition such as a thermal transient or 
material. However such wear is not readily achieved in shock loading, the gap or wear produced by the rub or 
practice. By the arrangement of the present invention contact is generally larger than the interference depth 
the blade tip may be designed to rotate in close proxim- because of tearing out, galling, and spalling. 
ity to the shroud without fear of cataclysmic destruc- 45 The seal illustrated in FIGS. 1 and 2 has a certain 
tion of either blade or shroud, should contact between elasticity. On any incident of contact or rub, the compli- 
the two occur due to thermal transient or shock load- ant backing 16 tends to be compressed in response to the 
ing. pressure created by the contact of the blade tip to the 
shroud 14. As a result the amount of material worn is 
50 reduced, and the shroud 14 tends to resume its original SUMMARY OF THE INVENTION 
According to the present invention, there is provided dimension at the worn area. Hence the gap resulting 
in combination for a turbine rotor or the like a stator from each contact is reduced and the useful life of the 
shroud of material wearable relative to the blades, a shroud is lengthened for a design of comparable clear- 
compliant backing of corrugated backing sheets or a ance of blade to shroud. 
compliant backing with a thin ductile layer, and a rigid 55 The compliance of the backing depends not only 
mounting surrounding the compliant backing. The com- upon the material but also the spacing L between corru- 
pliance of the backing tends to cause the shroud when gations, the depth d of the corrugations and the number 
tipped or touched by the rotating blade because of some of corrugated sheets used. 
transient condition to yield somewhat. Then, even Referring to FIG. 3 which illustrates a preferred 
though abraded or worn, the compliance of the backing 60 embodiment, the blade 10 is shown at an instant when 
provides a restorative force in the embodiment utilizing the forces mentioned above have caused the tip of the 
the corrugated construction tending to return the blade to contact the shroud. The compliant backing in 
shroud at its worn portion toward its original dimen- this case is slightly compressed, the compression as 
sion. In the embodiment wherein the compliant backing illustrated in the drawing in exaggerated fashion. The 
has a ductile top coating, the normal forces are limited 65 material of the shroud 34 may be a relatively thin layer 
and the blade wear is reduced. Hence any gap is less 36 of deformable metallic material. The backing 38 may 
than in prior instance of such wear, and the useful life of be of a compliant material, such as a porous rubber or 
the shroud is increased. rubber-like material, for example, sponge rubber, low 
BRIEF DESCRIPTION OF THE DRAWING 
The objects, advantages and novel features of the 
invention will be more fully apparent from the follow- 
5 ing detailed description when read in connection with 
the accompanying drawing in which: 
FIG. 1 is a schematic view, in transverse cross sec- 
tion, of an arrangement for a turbine or compressor 
embodying the invention, 
FIG. 2 is a perspective view, partly in section, of the 
shroud, compliant backing and mounting of the ar- 
rangement of FIG. 1, and 
FIG. 3 is a schematic view, in longitudinal cross 
section, of another, preferred embodiment of the inven- 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
10 
15 tion. 
Referring to the figures, a rotor blade 10 of a turbine 
20 compressor, for example, rotates about an axis 12 in a 
counter-clockwise direction as viewed in FIG. 1, tend- 
ing to force the fluid in which it operates in a direction 
into the paper. A shroud 14 surrounds the blade 10 and 
is substantially concentric with the axis 12. The shroud 
25 14 may be of suitable material abradable relative to the 
material of the blade 10. 
A compliant backing 16 surrounds the shroud 14. The 
backing 16 may be formed of high-temperature metal 
4,135,85 1 
3 4 
density sintered metal, or gas blown plastic. The metal What is claimed is: 
or metal alloy layer 36 may be a dense plasma sprayed 1. In a turbine having a rotor with a plurality of 
soft metal, such as aluminum, or a bonded metal sheet or blades thereon mounted for rotation about an axis and a 
foil. shroud of abradable material surrounding said blades in 
When the blades, as a result of forces such as de- 5 close relationship to the tips thereof to reduce aerody- 
scribed hereinbefore, rub against the shroud, the thin namic losses, the improvement comprising 
metallic layer 36 is deformed into the compliant sub- a plurality of corrugated sheets surrounding said 
strate material 38. In effect because of the compliant shroud with the corrugations extending longitudi- 
substrate material 38 the magnitude of a force normal to nally substantially parallel to said axis of rotation of 
shroud, the innermost sheet being bonded to said is measured in the radially inward direction from the shroud and the remaining sheets being bonded to shroud.) A larger displacement simply causes a greater each other along the lines of contact of the respec- deformation without greatly increasing the normal tive corrugations with the corrugations of one 
sheet being offset with respect to those of the next force. Therefore in effect the compliant substrate mate- 
adjacent sheet, and rial limits the magnitude of the normal force which can be developed between the blade tip and the shroud. The 
backing and being secured to the outermost corru- more porous and yieldingly deformable the substrate 38 
gated sheet. and the thinner the shroud layer 36, the smaller will be 
the normal force. Because the normal force is low when 2o 2. The as claimed in claim wherein the 
the blades rub agahst the shroud, blade wear is re- 
duced. 3. The combination as claimed in claim 1, said shroud 
Currently used shroud materials such as sintered being cylindrical. 
metal or felt metals have disadvantages of low erosion 4. The as in 3, said mount- 
resistance, aerodynamic roughness and porosity which 25 ing fixture being also cylindrical. 
permit back leakage. An arrangement as described in 5. A gas path seal for a turbine or the like having a 
connection with FIG. 3 with the shroud layer as sug- plurality of blades mounted for rotation about an axis 
gested herein provides an aerodynamically smooth sur- comprising 
face and high erosion resistance and is substantially less a shroud of material wearable relative to said 
permeable from a leakage standpoint- blades and closely spaced to the blade tips, 
wear debris produced in the rub is less than that pro- a plurality of corrugated sheets surrounding said 
duced in other shroud arrangements. Wear debris tends shroud with the corrugations extending longitudi- 
to plug up turbine cooling holes and to plate out or stick nally substantially parallel to said axis of rotation, 
on compressor blades causing aerodynamic losses. the innermost sheet beiig bonded to said shroud 
and the remaining sheets being bonded to each 
metallic sheets (not illustrated) may be distorted by other along the lines of contact of the respective 
wires aligned parallel to axis 12 to form corrugations fpr corrugations with the corrugations of one sheet 
the compliant backing of FIGS. 1 or 2, or these corru- beiig offset with respect to those of the next adja- 
gations might extend at angles of less than 90" to the cent sheet, and 
axial direction. Instead of sponge rubber in the compli- 40 a rigid mounting fixture surrounding said corrugated 
ant backing 38 we may use fibermetal and instead of the sheets and being secured to the outermost corru- 
thin metallic layer, material such as high temperature gated sheet. 
the surface of the shroud is limited. (This normal force 10 said rotor to form a compliant backing for 
. 
. 
' 15 
a rigid mounting fixture surrounding said * 
sheets are 
30 
Various modifications may be made. For example 35 
resistant ceramic layer may be used. * * * * *  
45 
50 
55 
65 


Composite seal for turbomachinery

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