Method of restoring worn turbine components

The method of restoring the worn edge surfaces of the shroud portion of a turbine component, such as a blade of the type having a ribbed mounting base at one end, which involves the steps of applying welding material to the worn edges of the shroud portion so as to build up the same beyond the dimensions of the shroud of a new component, and thereafter clamping the blade by its base in a fixture having a reference surface with a fixed position-relationship with respect to one edge of the shroud of a new blade of the type being refurbished when said new blade is similarly clamped in the fixture, and grinding off the added or overlay metal from the one edge of the built-up shroud until such edge is restored and duplicates the fixed relationship with respect to the reference surface. Thereafter the blade is clamped in a second fixture which has a supporting surface so arranged as to back up the one restored edge and thereby accurately position the blade with respect to the fixture, and then a remaining one of the built-up edges is restored. Finally, the blade is clamped in a third fixture having multiple surfaces backing up respectively the one restored edge and the remaining restored edge, while a third edge of the shroud is resurfaced. The method is characterized by high accuracy and good repeatability; excellent uniformity between successive units being refurbished thereby results.

BACKGROUND 
This invention relates generally to methods and means for refurbishing worn 
turbine components, and more particularly to methods and means for 
refurbishing the shrouds of worn turbine blades. 
After a period of operation, the blades employed in turbine engines and the 
like tend to become worn, especially in the vicinity of the trailing edge 
of the airfoil surface and at the location of the shrouds which serve as 
mountings for ends of the blades. The circularly arranged blades of a 
turbine stage extend radially and are supported at their outer ends by an 
air seal ring which engages the blade shrouds, while at their inner ends 
the blades are clamped in a suitable hub. 
In the past, when the shrouds of the blades have become worn, they were 
usually refurbished by building up one set of edges of all the blades, 
usually a corresponding set of edges which all faced in the same direction 
when the blades were assembled in radial fashion, and then ground down an 
extent so as to produce a surface on each set of edges which was slightly 
higher than that of the original. Other edges which were worn only 
minimally were allowed to remain so. The reasoning was that the lesser 
worn edges could be used as a reference in providing an indication as to 
how much of the built-up edges should be removed. 
Problems occurred when such procedures were employed, however. Ideally the 
shrouds were refurbished with respect to the stacking line of the blade, 
which is an imaginary line extending through a central portion of the 
blade longitudinally. When accurately restored with respect to this 
stacking line, the shrouds of the successive blades can nest with one 
another in the turbine rotor. However, improper build-up of material on 
one set of edges of the shrouds gave rise to dissymmetry of the shrouds 
with respect to these stacking lines, tending to forcibly shift the outer 
portions of the blades in a circumferential direction when the blades were 
installed. Since the inner, base portions of the blades were firmly held 
in the hub, there resulted undue stresses being developed in the airfoil 
structure; frequently this structure would crack transversely if the 
stresses which occurred were of sufficient magnitude. Such failures, due 
to imprecise refurbishing of the turbine blade shrouds, often had 
catastrophic results and accordingly could not be tolerated. 
Where attempts were made to add welding material to all of the edges of the 
shroud, accurate refinishing of these built-up edges was difficult to 
achieve since there was no reference on the built-up blade by which to 
gauge the first grind. Frequently the airfoil structure of the blade was 
worn, and thus any attempt to use this airfoil as a reference in making 
the first grind on the built-up shroud would result in imprecise 
restoration, leading to further problems when the blades were re-installed 
in the turbine. 
SUMMARY 
The above disadvantages and drawbacks of prior methods and means for 
refurbishing turbine blades are obviated by the present invention which 
has for an object the provision of a novel and improved method and means 
for refurbishing the shroud of a turbine component such as a blade, the 
method being simple to carry out and providing a highly reliable 
refurbished product which meets the strict standards of usage required by 
turbine components. Still another object is the provision of a method and 
means as above, which produce refurbished blades of high precision, 
closely duplicating the characteristics and dimensions of new parts. Yet 
another object is the provision of a method and means which produce blades 
of high uniformity from unit to unit, and which can maintain such 
uniformity even over extended periods of time. Accordingly, undue stresses 
in the blades, resulting from imprecise or sloppy refurbishing operations, 
is virtually eliminated, and the reliability of the resulting turbine 
assembly incorporating the refurbished blades is thereby enhanced. 
Yet another object of the invention is the provision of a series of novel 
and unique clamping fixtures for use in carrying out the above method, the 
fixtures being simple in construction, and providing an especially 
accurate and precise positioning of the blade, which is necessary for 
critical finishing operations normally associated with such turbine 
components. 
Still another object of the invention is the provision of a series of 
clamping fixtures in which the blade can be readily installed with a 
minimum of effort and wherein no judgment is required on the part of the 
operator, for effecting proper seating in the respective fixture. As a 
result, operator-related error is virtually eliminated. 
The above objects are accomplished in one aspect of the invention, by a 
novel method for restoring the worn edges of the shroud of a turbine 
component such as a blade of the type having a mounting base portion at 
one end and a shroud at the other end, wherein the method includes the 
steps of building up the shroud of the worn blade by fusing metal to the 
worn portions thereof, and mounting the worn blade by its base portion in 
a fixture which includes a reference surface disposed so as to have a 
predetermined fixed parallel relationship with respect to one given edge 
of the shroud of a new blade where the latter is similarly mounted in the 
fixture. Thereafter portions of the added metal are removed from the 
corresponding edge of the built-up shroud of the worn blade until the 
corresponding edge essentially reproduces the fixed relationship with 
respect to the reference surface. 
The objects are further accomplished in a method of restoring turbine 
blades of the type having a mounting base portion at one end and a shroud 
at the other end, which includes the steps of building up a multiplicity 
of edges of the shroud of the worn blade by fusing metal to worn portions 
thereof, mounting the worn blade by its base portion in a fixture 
associated with a surface grinder of the type having an abrasive member, 
bringing one built-up edge of the shroud into engagement with the abrasive 
member to restore the one edge to its original geometry with respect to 
the base portion of the blade, and thereafter mounting the worn blade in a 
second fixture and placing the same on a surface grinder of the type 
having an abrasive member. The second fixture includes a supporting 
surface adapted for direct engagement with the one restored edge of the 
shroud, and the step of mounting the worn blade in the second fixture 
comprises the step of resting the one restored edge directly on the 
supporting surface to thereby accurately position a remaining one of the 
built-up edges of the shroud with respect to the abrasive member of the 
second-mentioned surface grinder. Thereafter the said one remaining edge 
of the shroud is brought into engagement with the abrasive member of the 
second-mentioned surface grinder to remove carefully controlled amounts of 
the one remaining edge, so as to restore it to its original geometry with 
respect to the one restored edge of the shroud and with respect to the 
blade base. 
The above objects are further accomplished by a simple and unique clamping 
fixture adapted for use with a surface grinder apparatus of the type 
having an abrasive member and a work supporting table, the fixture being 
adapted to hold a turbine blade of the type having a mounting base portion 
which has a series of parallel ribs on its opposite surfaces, a 
convex-concave airfoil portion, and a shroud, for enabling the shroud of 
the blade to be engaged by the abrasive member of the grinder. The 
clamping fixture secures the blade in novel positions with respect to the 
grinder table. One such fixture is characterized by a base, means on the 
base defining a resting surface for engagement with the surface of the 
work supporting table, means carried by the base and including a vise for 
clamping the base portion of a blade such that the parallel ribs thereof 
are disposed askew with respect to the table surface, shoulder means 
carried by the fixture base engageable with at least one edge of the 
shroud, for backing up the latter in a predetermined position with respect 
to the base, and adjustable means carried by the fixture base and 
engageable with the convex-concave airfoil portion of the blade, providing 
a supplemental back-up therefor, to support that end of the blade adjacent 
the shroud and thereby to enable an edge of the shroud opposite said one 
edge to be engaged by the abrasive member of the surface grinder as the 
fixture base is moved with respect to the abrasive member. 
The invention further provides another clamping fixture adapted for use 
with a surface grinder apparatus of the type having an abrasive member and 
a work supporting table, the fixture being adapted to hold a turbine blade 
characterized by a mounting base portion having a series of parallel ribs 
on its opposite surfaces, and a shroud, while the latter is engaged by the 
abrasive member of the grinder. The fixture comprises a base, means on the 
base defining a resting surface for engagement with the surface of the 
work supporting table, means carried by the fixture base and engageable 
with at least one edge of the shroud, for supporting the latter on the 
base, means carried by the fixture base and engageable with a second edge 
of the shroud, for supplementing the support provided by the first 
supporting means, means carried by the base and including a clamping jaw 
engageable with still another edge of the shroud, to hold the latter 
tightly in a predetermined position on the base, and a cradle carried by 
the base, adapted to receive the mounting base portion of the blade. 
In addition, there is provided means pivotally mounting the cradle to 
enable it to swivel within limits when the clamping jaw is tightened, 
thereby assuring that the cradle does not interfere with proper seating of 
the first mentioned supporting means and the supplementary supporting 
means on the respective edges of the shroud. 
The arrangement is such that the blade can be readily installed on the 
fixtures with a minimum of effort; in addition, errors in the finished 
product resulting from operator-related judgments are virtually 
eliminated. 
The method and means as above set forth are seen to be extremely simple, 
while providing excellent uniformity and repeatability between different 
blades of the same type. As a consequence, there is thus eliminated from 
the turbine assembly all stresses in the airfoil surfaces of the blades 
due to improper dimensioning of the shrouds thereof. The resultant blades 
can thereby meet the stringent requirements of usage set forth for new 
parts, at a fraction of the cost. 
Other features and advantages will hereinafter appear.

FIGS. 1-4 illustrate a turbine blade of the type adapted to be refurbished 
according to the methods and grinding fixtures of the present invention. 
The blade is generally designated by the numeral 10, and includes a convex 
airfoil surface 12, and a concave airfoil surface 14 (FIG. 2). As the 
blade is traversed lengthwise, the shape of the airfoil section changes, 
this giving rise to the double airfoil (dotted) outline shown in FIG. 2. 
The blade further comprises a mounting base portion 15 which is tapered as 
shown in FIG. 1, with a series of ribs 16 on one side and a second series 
of ribs 18 on the other side. The mounting base portion 15 is commonly 
known in the trade as a "fir tree". At the opposite end of the blade is a 
shroud of irregular outline, particularly shown in FIGS. 2 and 7. The 
shroud is indicated by the numeral 20, and comprises edge portions 22, 24 
and 26. Refurbishing of the blade in accordance with the invention 
involves a build-up of these three edges 22, 24 and 26, followed by 
grinding operations on these same edges in a succession of grinding 
fixtures to be described below. As shown in FIG. 2, the edge 22 is seen to 
be disposed opposite the location of the leading edge of the airfoil of 
the blade. The remaining straight edge portions of the shroud 20 are 
indicated in FIG. 7 by the numerals 28, 30, 32, 34, 36 and 38. The showing 
of FIGS. 1-4 represents a new blade, whereas the blade illustrated in FIG. 
7 has become worn through extended periods of use wherein the edges of the 
shroud have considerably smaller dimensions than those of a new part. 
Referring to FIGS. 7-17 and in accordance with the present invention there 
is provided a novel and improved method for refurbishing the worn shroud 
of a turbine blade by which there is first added beads of welding material 
to the worn edges of the shroud to thereby build them up beyond their 
original dimensions, and thereafter the edges are ground one at a time, 
namely those edges indicated by the numerals 22, 24 and 26 in three 
separate grinding fixtures, the three fixtures being respectively 
illustrated in FIG. 8, FIGS. 9-11, and FIGS. 12-17. 
FIG. 5 illustrates turbine rotor 40 in dotted outline, including a shaft 42 
and a rotor hub 44, the latter having a series of radially extending 
recesses 46 in its periphery, the recesses being adapted to receive the 
ribbed base portions 15 of the turbine blades 10. A series of such blades 
10 is illustrated in FIG. 5, occupying the positions they would appear in 
during normal operation of the turbine. As illustrated in FIG. 6, the 
shrouds of the blades are seen to nest with one another, and the ribs 21 
on each shroud align with one another. A suitable sealing ring 48 extends 
around and engages the nested shrouds, thereby holding captive the blades 
10 in their operative positions. The ring 48 is illustrated in FIG. 5. 
FIG. 7 diagrammatically shows a welding apparatus including a conductor bar 
50 and welding electrode 52 in the form of a welding rod. The welding rod 
is preferably constituted of a metal alloy known in the trade as Haynes 
Alloy #25 or #31, available commercially as type L-605. The rod has 
essentially the same composition as the alloy of which the turbine blades 
are constituted with the parts by weight being essentially as specified by 
the table below: 
ESSENTIAL CHEMICAL ANALYSIS OF HAYNES ALLOY #25 
Parts of weight: 
1. Carbon--0.09 
2. Silicon--0.22 
3. Manganese--1.55 
4. Phosphorus--0.018 
5. Sulfur--0.007 
6. Chromium--20.32 
7. Nickel--10.56 
8. Tungsten--14.30 
9. Iron--2.25 
10. Cobalt--50.685 
FIG. 7 further shows a series of beads 54, 56 and 58 which have been added, 
by fusing, to the worn edges 22-26 respectively of the shroud in order to 
build them up, such that the built-up dimensions substantially exceed 
those of a new blade component. The remaining edges can also be built-up 
at the same time, as necessary, in the same manner illustrated in FIG. 7. 
Following the build-up of the edges 22-26 and in accordance with the 
invention, the blade 10 is then clamped in position on a grinding fixture 
particularly illustrated in FIG. 8, the fixture being designated by the 
numeral 60. The fixture is adapted to be used in a surface grinder or 
grinding machine having a substantially flat work supporting surface or 
movable table 62 and a power driven grinding wheel 64. The table 62 moves 
with respect to the wheel 64 of the grinder, in the usual manner. The 
fixture 60 includes a base 66 having a reference surface 80, an angle 
block 68, and a substantially flat support block 70 carrying a vise 72. 
The latter includes a fixed jaw 74 having a ribbed configuration to 
receive the ribs 16 of the blade base portion 15. A movable jaw 76 is 
provided, also of ribbed configuration, to clamp against the ribs 18 of 
the blade base portion 15. The jaw 76 includes an advancement screw 77. 
Disposed adjacent to the jaws 74, 76 is a stop or stop shoulder in the 
form of a block 78 which constitutes a positioning device against which 
the base 15 bears. With the blade 10 clamped in position on the fixture 
60, the base 66 can be moved (with the table 62) such that the edge 22 
engages the wheel 64. This results in removal of carefully controlled 
quantities of the welding bead 54 from the edge 22, such that the latter 
is effectively restored to a dimension closely resembling that of a new 
blade. 
In accomplishing proper positioning between the blade 10 which is being 
refurbished and the wheel 64, it will be understood that a new blade 10 
having the desired shroud dimensions is first mounted or clamped in place 
on the fixture 60 and the table 62 adjusted with respect to the grinding 
wheel 64 such that the latter just barely engages the edge 22. 
Subsequently, the new blade is removed, and the blade being refurbished 
substituted in the fixture, following which the grind is made. The taper 
of the wedge block 68 is determined experimentally, to bring the edge 22 
of a new blade into parallelism with the table 62. Accordingly, by the 
invention there is established a fixed relationship between the edge 22 of 
the shroud of a new blade 10, and the bottom planar surface 80 of the base 
66 of the fixture 60 such that when a worn blade having the edges of its 
shroud built-up by welding is placed in the fixture 60, and thereafter 
engaged by the wheel 64 as the fixture 60 is drawn past the wheel, the 
edge 22 will be ground down to the point wherein its dimensions are 
essentially the same as those of a new blade. Thus, there is established, 
between the reference surface 80 and the edge 22 the said fixed 
relationship. It is seen that this grinding operation does not depend on 
the dimensions of any of the remaining edges of the shroud, which are not 
of any value since they are either worn, or may have been built-up by 
welding for subsequent refinishing. Nor does it depend upon the dimensions 
of the concave or convex airfoil surface. Such surfaces are typically 
inaccurate after a blade has been in use, due to considerable wear and 
abrasion. Instead, the reference between the edge 22 and table 62 is 
established through the base 15 of the blade, which generally remains 
intact throughout the life of the blade and which retains its original 
geometry even after prolonged periods of use. Accordingly, an especially 
accurate dimensioning of the edge 22, closely resembling the geometry of 
the new blade, is possible. 
As soon as the grinding operation illustrated in FIG. 8 has been completed, 
and in accordance with the present invention, the blade 10 is removed from 
the fixture 60 and placed in a second fixture particularly illustrated in 
FIGS. 9-11. The second fixture is generally designated 82, and includes a 
pair of upstanding wedge-shaped legs or support portions 84, 86 and a 
connecting yoke portion 88 on which there is carried a vise 90 having a 
base 100. The latter includes a first jaw 92 which is adjustable but which 
is adapted to remain stationary once a suitable predetermined position has 
been obtained. A threaded hole 94 in the base of the vise 90 includes an 
adjustment screw 96 by which the jaw 92 may be advanced and retracted. The 
latter is movably carried in suitable slide grooves 98 of the base 100 of 
the vise 90. In addition, a second, movable jaw 102 is provided, also 
carried in suitable slide grooves 104 in the vise base 100, and adjustable 
by means of positioning screw 106 carried in a threaded hole 108 in the 
base 100. As particularly shown in FIG. 9, the jaws 92, 102 have 
cross-sections substantially in the form of the letter "T", with the 
extremities which engage the base 15 of the blade having semi-cylindrical 
contact surfaces which engage adjacent pairs of ribs 16 or 18 of the base 
15, to thereby hold the base captive once the screw 106 is advanced as in 
FIG. 9. In addition, a stop shoulder 110 and positioning pin 111 are 
provided, against which the base 15 bears, for effecting proper 
positioning thereof with respect to the fixture 82. 
Referring again to FIG. 10, there is attached to the yoke portion 88 an 
intermediary member 112 which carries a shroud support member 114 having a 
tip portion 116 constituted of hardened steel. The latter is referred to 
in the appended claims as a supporting surface, and is adapted to bear 
against or provide a backing for the edge 22 which has just been 
refurbished in the fixture illustrated in FIG. 8. In addition, in order to 
effect additional support of the blade adjacent to the shroud 20, there is 
provided an adjustable slide 118 having a base 120 which is slidable in a 
groove 122 of an upstanding member 124 carried by the yoke 88. A set screw 
126 is provided, engageable with the slide 118 for holding the latter in a 
predetermined fixed, adjusted position. As clearly illustrated in FIG. 9, 
the upper edge 128 of the slide is engageable with the convex side 12 of 
the blade, thus constituting a second supporting surface therefor, 
providing a supplemental back-up during the grinding operation to be 
described below. 
Also carried by the intermediary member 112 is a gauging surface 130 for 
supporting a micrometer device 132 of the type illustrated in dotted 
outline in FIG. 10. The device includes a base 134, an indicator 136, and 
a feeler arm 138. The latter is adapted to engage the edge 24 of the 
shroud 20 periodically during the grinding operation, in order to monitor 
its dimension. The edge 24 is referred to in some of the appended claims 
as "said one remaining edge", and is also considered to be opposite the 
edge 22 of the shroud. 
In operation, with the gauge 132 removed, the fixture 82 is placed on a 
suitable support surface of a surface grinder machine having a table 83, 
with the fixture being oriented generally as shown in FIG. 9. The leg 
portions 84, 86 are seen to have slightly different dimensions, such that 
when they are placed on the table 83 of the grinder, the yoke portion 88 
will be at a slight angle with respect to the table surface. 
The proper dimensions and configurations of the legs 84, 86 are determined 
experimentally, as is the proper position of the slide 118. Prior to 
grinding of a worn blade which has had certain of the edges of the shroud 
built-up by welding, a new blade is clamped in the fixture 82 of FIGS. 
9-11. The table 83 on which the fixture 82 rests can now be raised with 
respect to the grinding wheel (shown in FIG. 10 in dotted outline) 
designated by the numeral 140, until it just barely engages the surface 24 
of the new blade. The latter is then removed, and a worn blade having had 
its edge 24 built-up, and having had its edge 22 refurbished in the 
fixture shown in FIG. 8, is then substituted. Accordingly, there is thus 
established a fixed relationship between the edge 24 of the new blade and 
a reference or resting surface which in this case is a plane containing 
the bottom edges 142, 144 of the legs 84, 86 respectively. Restoration of 
the edge 24 of the worn blade is now readily accomplished by moving the 
fixture 82 (on the table) so as to bring the edge into engagement with the 
grinding wheel 140. When a point is reached wherein no further material is 
being removed, the edge 24 will closely resemble the edge of a new blade, 
particularly with respect to its dimension relative to the edge 22. During 
the grinding process, of course, the dimension of the edge 24 can be 
checked periodically by means of the gauge 132. 
By the above arrangement it is seen that the second or a "remaining" edge 
24 of the shroud has now been carefully restored to a predetermined 
dimension with respect to the first edge 22. Subsequent blades which have 
first been refurbished in the fixture of FIG. 8 can then be installed in 
the fixture 82 of FIGS. 9-11 and refurbished in the manner discussed 
above. Excellent uniformity and repeatability are thus realizeable between 
different units of the same type. 
Referring to FIG. 7 again, following the refurbishing of the edge 24 in the 
fixture shown in FIGS. 9-11, the worn blade having a built-up edge 26 is 
transferred to a third fixture illustrated particularly in FIGS. 12-17. 
The fixture is generally designated by the numeral 146, and is used to 
clamp the blade in a position wherein the edge 26 (FIG. 7) can be ground 
down to thereby restore its dimension to that of a new blade. 
In accordance with the present invention, this third fixture enables a 
blade to be clamped in a position wherein a third edge of the shroud of 
the blade can be resurfaced. In FIGS. 12 and 13, this third fixture 146 is 
seen to have a base comprising a mounting plate 148 having an upstanding 
end block 150 at one end, and a second upstanding end block 152 at its 
other end. The first end block 150 is shown in FIG. 12, and includes a 
transverse hole 154 in which there is received the boss 156 of a base 
carrier block or swivel cradle 158. The boss 156 includes a threaded hole 
which receives a cap screw 160, carrying a pair of washers 162 which are 
maintained spaced apart by means of a spring 164. This mounting 
arrangement for the carrier block 158 enables it to turn or swivel within 
limits. It is adapted to receive the base 15 of a turbine blade in the 
manner of FIG. 12. As shown in FIG. 13, a stationary guide arm or flange 
166 is carried on the block 158, and a resilient arm or flange 168 is 
disposed at the opposite end of the block 158 for holding the base 15 
captive. The face of the block 158 includes a hollow recess 169 to thereby 
provide a seat for the end of the base 15. 
The second upstanding block 152 of the base carries a clamp comprising a 
pivotal jaw 170 which can swivel about a pin 172 in the block 152. Carried 
by the jaw 170 is an actuator screw 174 having a knurled knob portion 175. 
The screw 174 is received in a threaded hole 176 in the jaw 170. As 
particularly shown in FIG. 16, the jaw 170 includes a face 180 which bears 
against the protruding part of the shroud located between the edges 36 and 
38 of the shroud (FIG. 7). 
Also carried by the block 152 is a hardened steel pin 182 constituting a 
supporting surface for the edge 24 of the shroud, (which has been 
refurbished in the fixture of FIGS. 9-11) when the blade is clamped in 
position as shown. A second screw 184, constituting a clamping screw and 
having a knurled knob 186, is carried in the block 152 of the base. It has 
a hardened steel end piece 188 secured thereto. The piece 188 bears 
against the rib 21 of the shroud (FIG. 6) when the screw 184 is tightened. 
In FIGS. 13 and 15, a supplementary support surface is provided, in the 
form of a block 202, constituting a shoulder on which the restored edge 22 
of the blade can rest. In some of the appended claims, the pin 182 is 
referred to as a supporting surface which backs the edge 24 (the 
"remaining" edge), and the block 202 referred to as a supplementary 
support surface which backs the edge 22 (the "one" edge). 
Also carried by the base is a third upstanding block 190 on which there is 
disposed an end plate 192 having a substantially flat reference surface 
194. The arrangement is such that the fixture 146 can be turned from the 
position of FIG. 15 through an angle of 135.degree. to the position of 
FIG. 17, and the reference surface 194 set upon a table or support 196 of 
a grinding machine. The machine includes a grinding wheel 198 shown in 
FIG. 17 in dotted outline, having a shaft 200 driven by suitably powered 
means (not shown). In this third fixture, there is thus established a 
predetermined fixed relationship between the reference surface 194 and the 
edge 26 of a new blade. 
In use, a new blade 10 is first clamped in position on the fixture 146 and 
the fixture thereafter placed with its reference surface 194 resting on 
the table 196. Subsequently, with the grinding wheel 198 not running, the 
position of the table can be adjusted such that it barely engages the edge 
26 of the new blade as illustrated in FIG. 17. The blade to be 
refurbished, having a built-up edge 26 then substituted for the new blade, 
and the edge 26 ground down until a point is reached wherein no further 
material is being removed from the edge. By such an arrangement, a 
dimension of the refurbished edge 26 will closely resemble that of a new 
blade, and the relationship (both angular and dimensional) with respect to 
the previously refurbished edges 22 and 24 will closely duplicate that of 
a new blade component. 
By the above arrangement involving three fixtures, namely that of FIG. 8, 
that of FIGS. 9-11 and that of FIGS. 12-17, there is established a very 
precise, highly uniform and highly accurate and repeatable relationship 
between the stacking line of the turbine blade and the shroud edges 22, 24 
and 26, as well as between the shroud edges themselves. Following the 
refurbishing of these three edges, any remaining edges requiring 
reconstruction or repair can be readily refurbished in different clamping 
fixtures (not shown). It is noted that the edge 22 is first refurbished 
and restored with respect to the base 15 of the blade. Thereafter, in the 
fixture of FIGS. 9-11 the blade is clamped by its base, a portion of the 
refurbished edge 22 is rested upon the supporting surface 116 in effecting 
proper dimensioning of a second or a remaining edge, namely that indicated 
by the numeral 24. Simultaneously, the convex face 12 of the blade is 
supported at a location adjacent the shroud 20 on a second supporting 
surface, in the form of the slide 118. The vise jaws 92, 102 are elongate 
and disposed at an angle with respect to the table 83, such that the base 
portion 14 of the blade is skewed with respect thereto, and the edge 24 is 
generally parallel to the table, so as to remain tangent to the grinding 
wheel 140 during its engagement therewith. Thereafter, the third fixture, 
illustrated in FIGS. 12-17 clamps the blade by its base portion 15 and 
also employs the refurbished edge 24 which was restored in the fixture of 
FIGS. 9-11 in accomplishing a refurbishing of the edge 26. The supporting 
surface, in the form of the pin 182, backs this refurbished edge 24 when 
the latter rests on the pin, and the supplementary support surface, 
comprising the block 202, tightly engages the restored edge 22 when the 
screw 174 is turned to actuate the jaw 170. 
Prior to the present invention, the shrouds of such blades have been 
built-up by welding, and the grinding procedure carried out without regard 
to precise refinishing with respect to the blade stacking line. 
Accordingly, the dimensions of the shroud of a refurbished component, as 
well as the dimensional relationship of the shroud to the stacking line, 
was sometimes quite different from those proportions characterizing a new 
blade. Accordingly, substitute parts often did not fit well in original 
equipment, and excessive stresses frequently developed in the airfoil 
surface of the blade, resulting from compound errors in the dimensions of 
the shrouds of the stacked blades. This can be appreciated from an 
inspection of FIGS. 5 and 6 wherein it can be seen that close tolerances 
are required in order to enable all the turbine blades to nest properly, 
since such blades are secured not only by their bases, but also by their 
nesting shrouds. 
It is seen that the present invention provides refurbished blades which 
closely resemble the dimensions of new parts, and there is thus insured 
high reliability and low stress operation over extended periods of use. 
The method of the invention is thus seen to provide a distinct advance and 
improvement in the technology of turbine blade repairs. 
Each and every one of the appended claims defines a distinct aspect of the 
invention separate from the others, and each claim is accordingly to be 
treated in this manner when the prior art devices are examined in any 
determination of novelty or validity. 
Variations and modifications are possible without departing from the spirit 
of the invention, and certain portions of the invention can be used 
without others.