U.S. patent number 3,584,971 [Application Number 04/828,553] was granted by the patent office on 1971-06-15 for bladed rotor structure for a turbine or a compressor.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to Ralph J. Ortolano.
United States Patent |
3,584,971 |
Ortolano |
June 15, 1971 |
BLADED ROTOR STRUCTURE FOR A TURBINE OR A COMPRESSOR
Abstract
This invention comprises rotor structure for a turbine or
compressor having an annular row of blades thereon, the rotor
having a peripheral groove and the blades having root portions of
the radial entry type received in the groove. The blade roots are
machined to absolute pitch dimension or slightly less and the
blades are disposed in groups, each group having an arcuate shroud
segment riveted to the tenons of the blades in the group. Total
accumulated deficiency due to undersize pitch dimensions in each
group is made up by a thin liner member interposed between blade
roots in adjacent groups.
Inventors: |
Ortolano; Ralph J. (Saratoga,
CA) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
25252145 |
Appl.
No.: |
04/828,553 |
Filed: |
May 28, 1969 |
Current U.S.
Class: |
416/218;
416/191 |
Current CPC
Class: |
F01D
5/3038 (20130101); F01D 5/32 (20130101); F01D
5/225 (20130101) |
Current International
Class: |
F01D
5/00 (20060101); F01D 5/22 (20060101); F01D
5/30 (20060101); F01D 5/12 (20060101); F01d
005/32 () |
Field of
Search: |
;416/218,220,215--217,191 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
872,949 |
|
Mar 1942 |
|
FR |
|
1,005,530 |
|
Apr 1957 |
|
DT |
|
19,009 |
|
1906 |
|
GB |
|
Primary Examiner: Powell, Jr.; Everette A.
Claims
I claim:
1. A turbine rotor, comprising,
a rotor disc having a circumferential groove,
an annular array of blades carried by said disc and having root
portions of the radial entry type,
said root portions engaging said groove,
said blades being disposed in arcuate groups having generally an
equal number of blades in each group,
said blades being provided with tenons,
an arcuate shroud segment having equally spaced apertures adapted
to mate with said tenons for joining the blades of each group so
that the associated root portions of the blades within each group
are disposed in end-to-end abutment,
the number of blades in each group being generally equal to the
number of blades that can mate with the equally spaced apertures of
said shroud segment and remain in end-to-end abutment,
said tenons being firmly connected to their associated shroud
segments, and
thin liner members interposed between the root portion of adjacent
blade groups to adjust the thickness of the groups to a
predetermined thickness.
2. The structure recited in claim 1, wherein
the groove is provided with an enlarged opening to permit entry of
the roots of the blades in the groove,
the last blade is disposed in said enlarged opening, and
means is provided for securing the last blade to the disc.
3. The structure recited in claim 1, wherein
the arcuate segments are disposed in spaced end-to-end relation
with each other and jointly encompass the annular array of
blades.
4. The structure recited in claim 1, wherein
the groove is of T-shaped cross section and the liners are of
similar shape and size.
5. The structure recited in claim 1, wherein
the thickness of at least some of the blade roots in each group is
less than the theoretical predetermined thickness, and
the thickness of the liner members is chosen in a manner to make up
the difference.
Description
BACKGROUND OF THE INVENTION
Turbine and compressor rotor blades of the radial entry type, i.e.,
having roots of the type that are inserted in a peripheral locking
groove on the rotor, are usually formed in such a manner that their
root width is held to close tolerances. This is necessary because
the width of the root establishes the pitch of the blade and any
deviation from the absolute pitch dimension is troublesome,
especially when the blades are of the shrouded type arranged in
groups held together by arcuate shroud segments riveted to tenons
on the blades.
Blades of the radial entry type are inserted in the locking groove
through an enlarged entrance opening in the groove and after they
are translated or rolled into abutment with each other, the gap
left for the "closing" or "last" blade is measured. The last blade
is then custom fitted by grinding down the width of the root to fit
the gap and secured in any suitable manner. With this arrangement,
the accumulated deviation from true pitch of the blades is
compensated for at the last blade.
Previously to the above arrangement, the deviation from true blade
pitch was made up by insertion of liners or shims between roots on
a random basis in sufficient numbers and thickness to render
unnecessary custom fitting of the last blade.
With both of the above arrangements, the spacing of the apertures
in the arcuate shroud segments (for securement to mating tenons in
the blades by riveting) cannot be predetermined nor can the
apertures be "prepitched." Instead the aperture spacing is
determined by calipering or otherwise measuring the individual
spacing between adjacent blade tenons and drilling the apertures in
the shroud segments to suit.
The above arrangements are expensive and involve considerable time
to provide even at the manufacturing plant, where full facilities
are available. However, when repairs in the field are subsequently
required, the above arrangements are even more time consuming and
difficult to provide, because of lack of proper facilities.
BRIEF SUMMARY
The present arrangement is an improvement over the above-described
prior art and facilitates fabrication at the manufacturing plant
and service in the field.
According to the invention, the radial entry blade roots are
machined to a width as close as economically feasible to the
theoretical pitch, but not exceeding such width. The blades are
provided with tenons extending radially outwardly and are connected
to each other in groups by arcuate shroud segments having apertures
spaced equally from each other to coincide with the spacing between
adjacent tenons. The shroud segments are secured to blades by
riveting of the tenons.
The aggregate width of all of the blades in each blade group is
measured and the deficiency is made up by a thin liner having a
thickness substantially equal to such deficiency. The liners are
disposed between adjacent blades at the ends of neighboring blade
groups, so that they do not effect the pitch of the blade roots and
therefore permit employment of shroud segments that have apertures
that are prepunched to the theoretical pitch of the blades. With
this arrangement, manufacture is facilitated, as well as service in
the field where reblading of a rotor may be required, since
individual blade width measurement for custom fitted shroud
installation is eliminated.
THE DRAWINGS
The invention, along with its objects and advantages, will be more
apparent from reading the following detailed description in
connection with the accompanying drawings in which:
FIG. 1 is a fragmentary end view of a bladed rotor structure
incorporating the invention, with portions cut away to show further
detail;
FIG. 2 is an enlarged sectional view taken on line II-II of FIG. 1;
and
FIG. 3 is a perspective fragmentary view of the rotor structure
during fabrication.
PREFERRED EMBODIMENT
Referring to the drawings in detail, in FIG. 1 there is shown a
portion of a rotor structure 10 for an axial flow elastic fluid
turbine or compressor, formed in accordance with the invention.
The rotor structure 10, is only partially shown, since it may be of
a well-known type. The rotor structure comprises a rotor disc 12
having an annular array of radially extending blades 14 connected
to its circumferentially peripheral portion 15.
The blades 14 are unitarily connected to each other in groups (six
blades to a group, in the example shown) by arcuate shroud segments
17, and the shroud segments are disposed in annular spaced
end-to-end relation with each other.
The blades 14 are of the well-known "radial-entry" type and
comprise an air foil or vane portion 18, a platform portion 19 and
a root portion 20 of T-cross section The outer tips of the blades
14 are provided with radially extending tenon portions 21, which as
illustrated are of circular cross section, but may be of any other
suitable cross section, as known in the art.
The rotor disc 12 is provided with a peripheral groove 22 in its
peripheral portion 15 and the groove is of T-shaped cross section
to closely coincide with the T-shaped blade root portions 20. As
illustrated, the groove 22 is slightly larger in cross section than
the root portions to facilitate assembly, as will later be
described, but a snug or sliding fit between the two may be
provided, if desired.
As best seen in FIGS. 2 and 3 the T-shape cross section of the
groove 22 is partially defined by a pair of circumferential flanges
24 disposed in mutually opposed and spaced relation with each
other. These flanges extend across the T of the blade roots 20 and
are effective to retain the blades in the groove.
To permit insertion of the blades 14 in the groove 22, arcuate
opposed portions of the flanges 24 are cut away (see FIG. 3)
thereby forming an entrance slot or opening 26 permitting "radial
entry" of the blades 14, one at a time, into the groove 22. After
entry, the blades 14 are "rolled" or translated laterally to form
the annular array that completely fills the peripheral extent of
the groove.
Since the entrance opening 26 is devoid of the locking flanges 24,
a special blade called a "closing" blade or "last" blade is
employed to complete the annular array and blades. This blade is
not shown, since it may be of any well-known type and forms no part
of this invention. However, it may be pointed out that the "last"
blade employs locking means that do not rely on the shape of the
groove 22.
As thus far described, the structure is substantially
conventional.
In accordance with the invention, the width A of the roots 20 is
machined as closely as economically feasible to the theoretical
pitch dimension taken to three decimal places, but not to exceed
this dimension. Hence when the total required number of blades 14
are inserted and rolled into abutment with each other, a void or
gap in the blade row will remain that normally is of a width equal
to the total number of blades multiplied by the average deficiency
or negative departure per blade root from the theoretical pitch
dimension.
This gap is preferably resolved on a blade group basis and may be
divided by the number of blade groups in the blade array to arrive
at a gap B per blade group. The gap B is preferably expressed as a
linear measurement carried to three decimal places. To take up the
gap B between blade groups, a shim or liner member 29 is inserted
between adjacent blade roots at the ends of neighboring blade
groups. The liners 29 are of T-shape as best seen in FIG. 2 and are
of a thickness equal to the thickness of the gap B. They may be
inserted at any point in the periphery of the groove 22 by turning
sideways during insertion, thereby their facilitating assembly at
the ends of each blade group.
With this arrangement the accumulation of individual deviations
from the theoretical width A is limited to each blade group and
compensated for by the liners 29. Since the liners 29 are disposed
between adjacent blade groups the shroud segments 17 may be
preformed with uniform pitch dimensions or spacing between the
apertures 30. The number of blades in each group is generally equal
to the number of blades that can mate with the preformed apertures
of the shroud segment and remain in end-to-end abutment when the
width A of a blade root is expressed in a measurement carried to
three decimal places, thereby facilitating manufacture and assembly
of the shroud segments onto the tenons 21 of the blades. This
factor becomes even more significant when repair in the field is
required since equipment and special tools are lacking to make the
shroud segments with the customized or individually fitted
apertures.
Also, since the liners are uniformly distributed about the
circumference of the rotor disc 12, balance of the rotor (both
dynamic and static) is maintained.
In the example shown, the blades 14 are initially loose fitting in
the groove 22 to facilitate positioning, but after positioning the
root portions 20 are wedged against the annular flanges 24 by
suitable caulking strips 31, as well known in the art.
To more clearly explain the invention, the following examples is
given:
Assuming 24 groups of blades in a row, each group consisting of six
blades, the total number of blades equals 6 .times. 24 or 144
blades.
Assuming a linear dimension of 0.500 inch for pitch A and
manufacture of the blades with a 0 plus tolerance and a 0.003 inch
negative tolerance, expressed as:
+ 0.000
- 0.003
0.500
If the blades are formed with the greatest acceptable deficiency,
their width A= 0.0497 inch and the total accumulated negative error
per group is 6 .times. 0.003 inch or 0.018 inch. Accordingly, the
thickness of the liners in this instance should be 0.018 inch.
However, in actual manufacture the width A is usually maintained
closer than the maximum tolerance prescribed, so that the liner
thickness may be somewhat less than 0.018 inch in this example.
It will be seen that, in this example, the total accumulated error
for the entire blade row can be as great as 144 .times. 0.003 or
432 inch, which is almost the width of another blade and would have
undesirable effects if compensated for by a single liner at a
single gap.
It will also be seen that the accumulated error of 0.018 for a
blade group if compensated for by insertion of a liner between
blades within the group would prevent installation of a prepunched
liner with uniform spacing between apertures.
Although only one embodiment of the invention has been shown, it
will be seen that the invention is not so limited, but is
susceptible of various other changes and modifications without
departing from the spirit thereof.
* * * * *