GB2092268A

GB2092268A - System for Keying Blade Discs to a Shaft

Info

Publication number: GB2092268A
Application number: GB8202569A
Authority: GB
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1981-01-30
Filing date: 1982-01-29
Publication date: 1982-08-11
Also published as: GB2092268B; JPS5857602B2; KR830009351A; ES279679U; IT1149496B; FR2499148A1; CA1191457A; BR8200449A; MX155288A; FR2499148B1; IT8219332A0; KR890001168B1; ZA82415B; ES279679Y; DE3202905A1; JPS57143102A

Abstract

A face disc 35 keyed to the shaft 21 and keyed to a peripheral flange on a turbine blade disc 25 eliminates stress concentrations at the highly stressed juncture of the blade disc and the shaft of a turbine. <IMAGE>

Description

SPECIFICATION System for Keying Blade Discs to a Shaft 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 becomes extremely large with blades in the neighborhood of 1.2 m long extending from a spindle which is approximately 1.2 m in diameter.

Therefore, it is desirable to fabricate this spindle utilizing 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 common 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 concentration at the corners and after many hours of operation cracks began 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 of the disc and shaft as this eliminated the sharp corners in the rectangular keyways and thus 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 the principal object of this invention is to eliminate any type of stress concentration in the bore of the disc of a turbine rotor and to prevent relative movement between the blade discs and the shaft during periods of differential heating or overspeeding.

With this object in view, the present invention resides in 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, eacn 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 keys fastened thereto adjacent the outer periphery thereof, characterized in that each blade disc has a plurality of notches for receiving the first plurality of keys, each face disc has a plurality of grooves disposed at the bore which register with a plurality of grooves in the shaft, and a second plurality of keys 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.

The invention will become more readily apparent from the following description of a preferred embodiment herein shown, by way of example only in the accompanying drawings, in which: Figure 1 is a partial sectional view of a turbine 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 Ill-Ill of Figure 2; Figure 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.

Referring now to the drawings in detail and in particular to Figure 1 there is shown a low pressure steam turbine or elastic 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 stem to circular arrays of stationary and rotatable blades 13 and 15, respectively, affixed to the casing 3 and rotor 5. The stationary 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 horizontally so that the upper half of the casing may be removed 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 1 5 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 shown 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 step. A face disc 35 is disposed adjacent the hub 27. The face disc 35 has a bore 37 which fits a mating step 23. A boss 38 is disposed adjacent the bore 37 and fits into the counterbore 31 and the face disc 35 extends radially outwardly beyond the periphery of the flange 33 on the blade disc. A plurality of finger keys 41 are fastened to the face disc 35 by fastening 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 finger portion 47, which fits a registering notch 49 in the flange 33 of the blade disc 25.The radially inner end oi 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 registering or aligned grooves 53 and 55, respectively, which form openings for receiving dowel pins or keys 57 for keying the face disc 35 to the shaft 21 and cooperate w'tF the keys 41 and notches 49 to positively prevent a.iQn of the blade disc 25 with respect to the Stl&commat; < e.ven during thermal gradients or when the rotor isaubiected to overspeeding at which times the interference fit between the blade disc and the shaft may loosen.

Buttons 61 are disposed in holes 63 disposed in the face disc 35. The button 51 have a predetermined thickness 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 without inducing high stresses in the face disc 35 and yet be held snugly therein.

The face disc 35 hereinbefore described advantageously provide an intermediary member for keying blade disc 25 to the shaft 21 to eliminate 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 ofthe bore, thus reducing the possibility of stress cracks originating at the notches.

Claims

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 keys fastened thereto adjacent the outer periphery thereof, characterized in that each blade disc had a plurality of notches (40) for receiving the first plurality of keys (47), each face disc (35) has a plurality of grooves (55) disposed at the bore which register with a plurality of grooves (53) in the shaft (29), and a second plurality of keys 57 are received by the registering grooves (53, 55) in the bore (37) of the face disc (53) and the shaft (21) to positively prevent rotation of the blade disc (27) with respect to the shaft (21).

2. A rotor as claimed in claim 1, characterized in that the blade disc (27) has a flange (33) on the end adjacent the associated face disc (35) and the notches (40) are disposed in the flange (33).

3. A rotor as claimed in claim 1, characterized in that the face disc (35) has a button (61) disposed therein, the button (61) having a predetermined thickness to provide for axial clearance when the blade discs (27) are assembled on the shaft (21).