CA1191457A

CA1191457A - System for keying blade discs to a shaft

Info

Publication number: CA1191457A
Application number: CA000394662A
Authority: CA
Inventors: Ralph D. Brown; William E. Howard
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1981-01-30
Filing date: 1982-01-21
Publication date: 1985-08-06
Also published as: ES279679U; ES279679Y; JPS5857602B2; DE3202905A1; GB2092268B; IT8219332A0; FR2499148A1; KR890001168B1; IT1149496B; MX155288A; BR8200449A; KR830009351A; FR2499148B1; GB2092268A; JPS57143102A; ZA82415B

Abstract

ABSTRACT OF THE DISCLOSURE
A face disc keyed to the shaft and keyed to a peripheral flange on a turbine blade disc eliminates stress concentrations at the highly stressed juncture of the blade disc and the shaft.

Description

~3~t-'7 1 ~9,~58 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 '`'~k 5'~

2 49,458 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;

q?~ r~

3 49,458 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-~a~ r-~

~ 49,458 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.

Claims

What is claimed is:

1. A rotor for an elastic fluid machine, said rotor comprising:
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 circumferential step;
a plurality of face discs each having a bore which fits a particular circumferential step, and a first plurality of rectangular shpaed keys fastened thereto adjacent the outer periphery thereof;
each blade disc having a plurality of rectangular shaped notches disposed on an outer peripheral surface thereof for receiving the first plurality of keys;
each face disc also having a plurality of grooves disposed at the bore which register with a plurality of grooves in the shaft; and a second plurality of keys which are received by the registering grooves in the bore of the face disc and the shaft to positively prevent rotation of the blade disc with respect to the shaft.

2. A rotor as set forth in claim 1, wherein the blade disc has a flange on the end adjacent the associated face disc and the notches are disposed in the outer peripheral surface of the flange.

3. A rotor as set forth in claim 1, wherein the face disk has a button disposed therein, the button having a thickness predetermined to axially space the blade discs when the blade discs are assembled on the shaft.

4. A rotor as set forth in claim 1, wherein the first plurality of keys are fastened to the face disk by mechanical fasteners.

5. A rotor as set forth in claim 1, wherein the first plurality of keys are fastend to the blade disc by fitted bolts which fit tightly into bolt holes disposed in the face disk and in the first plurality of keys.