US2949278A

US2949278A - Turbine blade retention

Info

Publication number: US2949278A
Application number: US595874A
Authority: US
Inventors: Hamilton L Mccormick
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1956-07-05
Filing date: 1956-07-05
Publication date: 1960-08-16
Anticipated expiration: 1977-08-16
Also published as: GB808258A

Description

Aug. 16, 1960 Filed July 5, 1956 United TURBINE BLADE RETENTION Filed July 5, 1956, Ser. No. 595,874

3 Claims. (Cl. 253-77) My invention relates to wheel and blade assemblies such as are used in axial flow compressors and turbines and is particularly directed to providing an improved means of retention of blades on wheels.

By way of background, it may be pointed out that axial flow compressors and turbines commonly are made up of one or more wheels, each of which has a number of blades mounted around the rim of the wheel. Commonly, the wheel has slots cut across the rim into which the blades are inserted, there being some form of dovetail engagement between the root of the blade and the walls of the slot. Usually, the blades are retained from sliding out of the slots by some structure which keys or pins the blades to the wheel. Perhaps the most common mode of retention involves the use of a pin which extends more or less radially through the wheel rim-into the base of the blade. Other structures which have been proposed (see, for example, US. Patents 2,434,935 and 2,686,656) involve keys which lie under the base of the blade at the bottom of the blade slot and are fixed in some way to the wheel and blade. While such structures may provide adequate blade retention, they have the disadvantage that they weaken the wheel at a point of very high stress at the blade root, with the result that the entire wheel must be made heavier than would otherwise be necessary.

In distinction to these prior proposals, the blade locking structure of the present invention involves structure disposed at the rim of the wheel between the blade slots in a region of low stress, with the result that the weight of the wheel and, consequently, of the other parts of the engine, need not be increased to compensate for stress inducing conditions presented by blade locking means located at the bottom of the blade slot.

The principal objects of the invention are to provide an improved turbine wheel assembly; to decrease the weight and increase the strength of such assemblies; to provide a turbine wheel and blade assembly with locking means which is readily applied and removed and does not weaken the wheel; and to provide a simple, effective, and convenient blade locking means for such installatio'ns.

The nature of the invention and the advantages thereof will be clearly apparent to those skilled in the art from the succeeding detailed description of the preferred embodiment of the invention and the accompanying drawings in which:

Fig. 1 is a fragmentary perspective view of a wheel and blade assembly according to the invention;

Fig. 2 is a framentary sectional view of the same taken on a plane containing the axis of the turbine wheel, as indicated by the line 22 in Fig. 1;

Fig. 3 is a fragmentary sectional view on a plane at right angles to the axis, as indicated by the line 3--3 in Fig. 2; and

Fig. 4 is a view similar to Fig. 2 illustrating a modified structure.

The invention is shown and described herein as ap plied to a typical turbine structure and the structure tates Patent hereinafter will be referred to as a turbine, but the term is not intended as one of limitation, since the invention is readily applicable to various machines of similar configuration.

Referring to Fig. 1, there is illustrated a fragmentary portion of a turbine wheel 10 including the rim 11, the central po'rtion of the wheel not being illustrated, since it may follow any suitable known configuration and the invention is not concerned with the disk or hub of the wheel. Blades 12 are mounted in the wheel, each blade comprising an airfoil or blade portion 13, a root 14, and a blade platform 15, projecting circumferentially of the wheel immediately adjacent the rim thereof, between the blade portion and root portion of the blade. As illustrated, the blade roots are of the common multiple dovetail form and are mounted in serrated slots 17 in the rim of the wheel. It will be understood that the particular slot and root form is immaterial. These slots extend across the rim from the forward face of the wheel (not shown) to the rearward face 19 thereof.

The wheel illustrated is one in which the periphery or radially outer surface 16 of the wheel is conical or tapered, in which case the serrations on the wheel and blade root are likewise at an angle to the axis of the wheel, which axis may be considered as horizontal in Figs. 2 and 4. It is immaterial to the invention whether the serrations are so inclined or not. It will also be understood that the blade slots may be either straight across the rim of the wheel or skewed. Ordinarily, the blade roots are a slightly loose fit in the slots in the turbine wheel. The blades are mounted by sliding them axially of the wheel into the grooves.

It will beunderstood that the structure so far described is 'old and well known. In connection with prior structures, however, it has been customary to extend a pin through the rim 11 of the wheel into the blade root 14 or to dispose retainers in the bottom of the groove 17. Structures of both these types weaken the wheel at the base of the groove, which is a point of high stress. V

The blade retaining means of this invention comprises keys 20;, which may be rectangular plates, disposed in key slots 21 cut through the rim of the wheel at the margin 16 in the portions 22 of the wheel rim between the blade slots 14. As will be apparent, the key slots 21 are directed generally radially and circumferentially of the rotor although they may be inclined to the radial or circumferential direction, and, if the blade slots are inclined or skewed, it may be desirable to have the slots and the keys in them disposed perpendicular to the blade slots. In the form illustrated in Figs. 2 and 3, however, the key 20 is radial to the axis. The outer end of the key projects approximately to the level of the outer surface of the blade platform 15 and is received in notches 23 in the edges of the blade platforms. The key, by its engagement with the

abutting surfaces

23 and 23" on the blade platform, locks the blade against movement in either direction in the blade slot 17. Some slight clearance to provide for ready insertion of the key and prevent binding of the key in the slot 21 and notches 23 should be provided.

The key 20 must'be retained against displacement by centrifugal force when the engine is operating. This is accomplished by a pin 26 which is a loose fit in a bored hole 27 in the rotor and a press fit in a hole 28 in the key 20. The inner end portion 29 of the pin is tapered to facilitate its insertion, which may be accomplished by driving the pin with a press or hammer. A bore 31 on the axis of bore 27 and of slightly smaller diameter continues to the forward face of the wheel to admit a drift pin by which the pin 26 may be removed when it is necessary to remove the blades.

semble the rotor, the blades are slid into place in the slots and, after two adjacent blades. are in place, the key 20 is dropped into place in the slot 21. Pin 26- is then inserted into the bore 27 and driven through the hole 28 in the key, locking the key in place.v To remove any blade, it is necessary only to drive out the pins 26'on each side of it and lift out the keys 26 so that the blade can be slid out of the wheel.

The blade lock shown in Fig. 4 difiers in certain. features of constructure from that of Figs. 2 and 3. In Fig. 4, the axis of the bore 27 in the wheel rim' 11' is parallel to the axis of the blade slot 17 and thus the key 20 is inclined to the axis of the rotor, the plane of the key being perpendicular to the axis of the blade slot. Key 20 fits in slot 21 in the same manner as previously described and egages with notches 23 in the platforms 1'5 of blades 12, as previously described. In the form of Fig. 4, however, the bore 27 is a blind bore and the pin 37 includes a projecting head 38 joined to the body of the pin by a neck 39, the head providing for engagement of the pin by an extracting device.

Figure 4 also illustrates external splines or ridges 41 which may conveniently be formed by a knurling operation (in the pin 37 and which extend over the part of the pin which is received in the hole 42 in the key. The knurled or ridged surface provides conveniently a satisfactory interference fit between the pin and the key for tight frictional engagement between them, Without requiring precise machining of the pin and hole 42. This feature may be employed also with the pin 20 of Figs. 2 and 3. t

The advantages of the invention will be apparent to those skilled in the art. The blade lock is simple in structure, easy to apply, and avoids weakening of the wheel and blade at critical stress areas.

The detailed description of the preferred embodiment of the invention, for the purpose of explaining the principle thereof, is not to be regarded as limiting the invention, as many modifications may be made by the exercise of skill in the art within the. scope of the inventron.

I claim:

1. A turbine wheel assembly comprising, in combination, a wheel having faces and including a rim and having dovetail blade slots extending continuously transversely of the rim between the faces; turbine blades including dovetail blade roots mounted in the blade slots with dovetail engagement therein and blade platforms projecting circumferentially of the wheel rim from the blade roots adjacent the Wheel rim; and means for retaining the blades against displacement longitudinally of the blade slots, the retaining means comprising means defining a key slot extending radially and circumferentially of the wheel rim intersecting the blade slots; means on the blade platforms defining notches therein aligned with the key slot having axially facing walls; a plurality of keys, received in the key slot between adjacent blade slots and extending into the notches, abutting the axially facing walls of the key slots in the wheel and the axially facing walls of the notches in the blade platforms; each key being substantially a rectangular parallelepipedand having a hole therein extending transversely of the rim; the rim having holes therein between the blade slots aligned with the holes in the keys; and a pin located References Cited in the file of this patent UNITED STATES PATENTS 1,545,495 Holzwarth July 14, 1925 2,751,189 Ledwith June 19, 1956 FOREIGN PATENTS 313,027 Switzerland Apr. 30, 1956 725,461 Great Britain Mar. 2, 1955 767,889 France May 7, 1934 837,495 Germany Apr. 28, 1952 1,121,732 France May 7, 1956