Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM FOR KEYING BLADE I)ISCS TO A SHAFT
CROSS-REFERENCE TO RELATED APPLICATIONS
This is an improvement on United States Patent
entitled "System For Keying Discs To Shaft", No. 4,330,236
issued May 18, 1982, assigned to this same assignee.
BACKGROUND OF THE INVENTION
This invention relates to a system for keying
discs to a shaft and more particularly to a system for
keying blade discs to a shaft in a steam turbine.
In large steam turbines the last stage of the
turbine become extremely large with blades in the neigh-
borhood of 4 feet long extending ~rom a spindle which is
approximately 4 feet in diameter. Therefore, it is desir-
able to fabricate this spindle u-tilizing a relatively
small diameter shaft with discs shrunk onto the shaft.
Even though the discs are shrunk on the shaft with an
interference fit, because of differential heating and the
large torque transmitted between the disc and the shaft it
has become co~non practice to key the disc to the shaft.
The keys had a rectangular cross section with relative
sharp corners, which resulted in very high stress concen-
tration at the corners and after many hours of opera-tion
cracks be~an to form radiating from the corners of the
keyways. To reduce the concentration of stresses in the
keyways, round keys were used and round holes were drilled
at the juncture oE the disc and shaft as this eliminated
the sharp corners in the rectangular keyways and thus
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reduced stress concentration; however, the area adjacent
the bore of the disc have very large stresses. The round
keys did produce lower stress concentrations, but have
resulted in cracking emanating from the round keyways.
Therefore an object of this invention is to eliminate any
type of stress concentration in the bore of the disc and
prevent relative movement between the blade discs and the
shaft during periods o~ differential heating or overspeed
ing
SUMMARY OF THE INVEMTION
In general a rotor for an elastic fluid machine
when made in accordance with this invention comprises a
shaft having a plurality of circumferential steps which
ascend from at least one end thereof, a plurality of blade
discs each having a bore which fits a particular circum-
ferential step and a plurality of face discs each having a
bore which fits a particular circumferential step. The
rotor also comprises a first plurality of keys fastened to
the face disc adjacent their outer diameter. Each blade
disc has a plurality of notches for receiving the ~irst
plurality of keys. Each face disc also has a plurality of
grooves disposed at the bore which register with a plural-
ity of grooves in the shaft and a second plurality of keys
are received b~ the registering grooves in the bore of the
face disc and the sha~t to positively prevent rotation of
the blade disc with respect to the shaft.
BRIEF DESCXIPTION OF T~E DRAWINGS
The objects and advantages of this invention
will become more apparent from reading the following
detail description in conjunction with the accompanying
drawings, in which:
Figure 1 is a partial sectional view of a tur-
bine and rotor incorporating this invention;
Figure 2 is a partial sectional view taken on
line II-II of Figure 3;
Figure 3 is a partial sectional view taken on
line III-III o~ Figure 2;
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Fi~ure 4 is an enlarged partial sectional view
taken on line IV-IV of Figure 2; and
Figure 5 is a partial sectional view taken on
line V-V of Figure 4.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings in detail and in
particular to Figure 1 there is shown a low pressure steam
turbine or elàstic fluid machine 1, which comprises an
~enclosed housing or casing 3 with a rotor 5 disposed
therein. The casing 3 has journal bearings 7 disposed on
opposite ends thereof for rotatably supporting the rotor
5. A steam inlet nozzle 9 is disposed in the central
portion of the casing to supply steam to circu].ar arrays
of stationary and rotatable blades 13 and 15, respec-
tively, affixed to the casing 3 and rotor 5. The station-
ary blades are disposed in blade rings or diaphragms 17,
which attach to the casing producing pressure stages as
the steam expands through the turbine 1. The casing 3,
journal bearing 7 and blade diaphragms 17 are split hori-
~onta~ly so that the upper half of the casing may beremoved to permit removal of the rotor 5.
The rotor 5 comprises a shaft having a plurality
of circumferential steps 23, which ascend from each end
thereof. Disposed on the circumferential steps 23 are
blade discs 25, which have a central hub 27 and one or
more circular arrays of rotatable blades 15 attached to
their outer periphery. The hubs 27 each have a central
bore 29 sized to fit a particular or mating step 23 on the
shaft 21. The bore 29 is normally slightly smaller than
the diameter of the mating step over which it slides
producing an interference or shrink fit therebetween.
As show~ in Figures 2 through 5 the hubs 27 of
the blade disc 25 have a counterbore 31 and a radially
extending rim or flange 33 on one end thereof, the end
adjacent the next smaller diameter step. A face disc 35
is disposed adjacent the hub 27. The face disc 35 has a
bore 37 which ~its a mating step 23. A boss 38 is dis-
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posed adjacent the bore 37 and f:i-ts into the counterbore
31 and the Eace disc 35 extends radially ou-twardly beyond
-the periphery of the flan~e 33 on the blade disc. A
plurali-ty of finger keys 41 are fastened to -the face disc
35 by fas-tening means such as fitted bolts 43, which fit
tightly into reamed holes in the face disc 35. The keys
41 are elongated so as to accommodate 4 bolts each and
have a milLed out portion 45 forming a rectangular shaped
finger portion 47, which fits a registering rectangular
shaped notch 49 in the flange 33 of the blade disc 25.
The radially inner end of the finger 47 is chamfered and
the notch 49 has a large radius at the corners in order to
reduce stress concentrations.
The shaft 21 and bore 37 of the face disc 35
each have regist.ering or aligned grooves 53 and 55,
respectively, which form openi.ngs for receiving dowel pi.ns
or keys 57 for keying the face disc 35 to the shaft 21 and
cooperate with the keys 41 and notches 49 to positively
prevent rotation of the blade disc 25 with respect to the
shaft 21 even during thermal gradients or when the rotor
is subjected to overspeeding at which times the inter-
ference fit between the blade disc and the shaft may
loosen.
Buttons 61 are disposed in holes 63 disposed in
the face disc 35. The buttons 51 have a predetermined
thi.ckness greater than the thickness of the face disc 35
to set the axial clearance in the blade disc assembly.
The buttons 51 have a peripheral lip 62 machined therein
so that it can be pressed into the holes 63 wi-thout induc-
ing high stresses in the face disc 35 and yet be heldsnugly therein.
The face disc 35 hereinbefore described advan-
tageously provide an intermediary member for keying blade
disc 25 to the shaft 21 to eli.minate stress concentrations
in the bore of the blade disc 25. The notches 49 in the
blade disc 25 which receive the keys 41 are disposed in an
area where the longitudinal stress is sufficiently lower
than that of the bore, thus reducing the possibility of
stress cracks originating at the notches.
