US2805838A - Rotors for turbines and similarly bladed fluid flow machines - Google Patents

Description

Sept. 10, 1957 G, PICKUP 2,805,838

ROTORS FOR TURBINES AND SIMILARLY BLADED FLUID FLOW MACHINES Filed June 15, 1951 :5 She ets-Sheet 1 Fig a? U1: l M r H 2,805,838 ROTORS 'FOR TURBINES AND SIMILARLY BLADED FLUID FLOW MACHINES Filed Jun 15, 1951 G- PICKUP Sept 1957 3 Sheets-s 2 1 Fig. 6.

Sept. 10, 1957 e. PICKUP 2,805,838

ROTORS FOR TURBINES AND SIMILARLY BLADED FLUID FLOW MACHINES Filed June 15, 1951 s'sheets-sneet s [nvenfor Cue-r30. PAW? Aftorney s iudb 2,895,338 7 RGTQRS FOR AND SEMILARLY BILABED FL'UH) FLQW MACHINE George Pickup, St. Albans, England, assignor to Power Jets {.Research reloprnent) Limited, London,

England, a company Application .lune 15, 3""5 erial No. 231,698

priority, Great Britain June 22, Edi

All or the claime subject matter of the said application has been ded' a to the free of People in the 1 lbs of America to take effect on the or patent and to persist for the entire term thereof This invention relates to rotors for turbines and similarly bladed fluid flow machines having separately fabricated blades mounted on a rotor disc or drum. In general, bladed rotors may be regarded as composed of three portions distinct with respect to their functions and their ability to withstand centrifugal and other loads in operation, the portions comprising: firstly, the rotor disc or drum which may conveniently be of peripherally continuous form to afiord resistance to circumferential or hoop stresses and so be self-supporting with respect to its own centrifugal loads in operation; secondly, the working portions ofthe blades which, being of necessity of peripherally non-continuous form, are not therefore self-supporting with respect to their own centrifugal loads; and, thirdly, an intermediate portion whereby the non self-supporting blade working portions are attached to the self-supporting disc or drum. The selfupporting disc or drum must, therefore, be designed with a reserve or surplus of strength against its self-imposed loads so that it is capable of supporting the blade working portions; similarly, a still greater reserve of strength must be provided if the intermediate portion affording the attachment between the blade working portions and the rotor disc or drum is peripherally discontinuous and so also requires supporting against its own centrifugal loads. It is apparent, therefore, that the requisite strength and consequently bulk weight of the rotor disc or drum is dependent on the degree to which the intermediate portion of the rotor is capable of supporting itself against self-imposed centrifugal loads. If a small measure of self-support can be obtained without an increase in the weight of each blade and its means of attachment to the rotor, then an advantage is gained in that the reserve of strength required in the disc, and therefore its weight, may be reduced. Thus the value of the ratio of non self-supporting material to self-supporting material has an appreciable effect on the weight of the complete rotor assembly.

It is very desirable, therefore, to eliminate the intermediate portion of the rotor in so far as it is non selfsupporting centrifugally and it is toward this general object that the present invention is directed.

This object is, of course, fulfilled in rotors of the known kind in which the blades are integral with the disc or drum, but such rotors present, with regard to their initial manufacture, considerable practical difficulties, especially in cases where differing mechanical and t ermal properties are required in the materials of the blades and the rotor dis or drum, and, in addition, integral blades do not conveniently permit replacement of any one or all of the blades.

The general object is also fulfilled in another known kind of rotor in which separately manufactured blades are first melded together at their roots to form a complete ring which is then fitted round a self-supporting disc and secured by a circum erential weld. Here, again, however, the choice of materials of the respective elements of the rotor is restricted, in th they must be capable of being 2,8@5,833 Patented Sept. 18, 1957 welded together and the blades are not readily replaceable. Furthermore, the intermediate portion of the rotor formed by the blade roots remains self-supporting centrifugally only in so far as it remains a continuous ring. In the event of the failure of the weld between any two blades the loads of the whole ring are thrown on to the disc. This consideration is of particular importance in cases where high temperature conditions obtain in the region of the blades as, for example, in rotors for gas turbines which are particularly prone to such welding failures. Thus the use of welded rotors in such circumstances is desirably to be avoided.

In contrast to the known kinds of rotors above described, having integral or integrated blades, are those commonly used in which the blades are separately fabricated, the blade roots and the rotor disc or drum having complementary interengaging surfaces whereby the centrifugal blade loads are transmitted to the disc or durm. These comprise broadly two types: firstly, those having a series of axially extending grooves disposed round the periphery of the self-supporting portion of the rotor; and,

econdly, those having one or more peripheral grooves. In each of these types, however, the intermediate portion constituted by the blade roots and complementary disc or drum formation is wholly or partially non-selfsupporting as regards to self-imposed centrifugal loads. In the first type both the blade roots and the complementary formations are peripherally discontinuous and thus non-self-supporting, and in the second type the blade roots are non-self-supporting and the complementary grooved formation, although ofiering the possibility of peripheral continuity, is in fact commonly gapped to permit insertion of the blade roots in the groove. The more general use of rotors of this kind as compared with those previously described having integral or integrated blades may be attributed, at least in p rt, to the comparative freedom of choice of materials of the respective components and the ease of replacement of any component which they permit.

More specifically stated, the general object of the present invention, determined by the foregoing considerations, is to provide an improved means of assembling blades on a rotor in a manner to provide increased strength or alternatively reduced bulk and weight of the rotor assembly as a whole.

Accordingly, the invention proposes a rotor for a turbine or similarly bladed fluid flow machine having at least one circumferential row of separately fabricated blade I elements mounted on a rotor disc or drum, wherein each blade element of a row is detachably secured to the adjacent blade elements of the row, in addition to the attachment of the blade elements to the disc or drum; thus in this way the blades form an unbroken ring about the disc or drum which is self-sustaining against circumferential tension and hence centrifugal loads. The term detachably secured is intended to include all cases where two blades are interlocked either by mutual engagement or by means of one or more fastening elements and parting of the blades is opposed by reaction between abutting surfaces, but to exclude the case where the blades are themselves fused or welded. The invention is to be regarded, of course, as including blades adapted for se curing to other blades and so is appropriate for use in a rotor as above described.

In the preferred form of rotor according to the invention it is proposed that each blade be provided with a root portion adapted to fit in a peripheral groove in the rotor disc or drum ,(so afiording the possibility of peripheral continuity in the rotor), each blade having one set of formations providing for securing same to adjacent blades and another set for securing the blade to the rotor by 3 engagement with corresponding formations in the rotor groove.

By way of illustration, some constructional embodiments of the invention are now described with reference to the accompanying drawings in which Figures 1a, lb, lc, 4a, 4b, a, 5b and 8 represent various root formations of individual axial flow rotor blades, while Figures 2, 3, 6, 7 and 9 represent part sectional views of axial flow turbine rotors.

Figure 7 represents an elevation, partly cross-sectioned, of a turbine rotor typical of the kind to which the invention has application. The rotor comprises a single disc 21 adapted for mounting on a shaft 22 and having at'its periphery a circumferential groove formed between side walls 9 which groove accommodates the roots 1 of a circumferential row of blades 2. For the purposes of the invention the roots of the blades'are shaped in a particular manner as shown in Figures 1a, 1b and which represent respectively top plan, side elevation and under bottom plan views of the rotor blades 2 of Figure 7 on an enlarged scale. The blade root 1 is shaped to provide on one side a tongue 3 and on the opposite side a groove 4- of complementary shape so as to mate with similar tongues and grooves of adjacent blade roots; the blades are secured together by pins passing through holes 5 in the interleaving portions of the roots. Although as illustrated, the blade root has only one tongue and groove, it is apparent that several tongues and grooves'could be provided per blade, thereby increasing the number of shearing planes and so distributing sheer stresses in the securing pin. The end faces 6 of the root 1 may be shaped in any desired manner to engage the sides of a rotor groove as is shown, for example, in Figure 2 which represents on an enlarged scale a part section of the rim of the axial flow rotor disc shown in Figure 7, and showing blades, as described with respect to Figures la, 11) and 1c, which are mounted in the peripheral groove in the disc 21, the blade ends 6 and the groove sides 7 having complementary circumferential serrations. As is also shown in Figure 2, the pin 8, in addition to passing through the holes 5 in the blade roots, may also extend through sides 9 of the rotor grooves. Figure 3 represents a part section in an axial plane through an axial flow rotor drum having a peripheral groove accommodating blades which, while generally similar to those described with reference to Figure 1, have end projections 42 which engage complementary recesses in the sides 41 of the peripheral groove. In this case the pins 49 are co-terminous with the blade root. r

Figures 4a and 5a represent in top plan and Figures 4b and 5b represent in side elevation two forms of blade; roots designed to interlock with similar blade roots in a manner such as to resist parting loads between the blades. Thus, in Figures 4a and 4b, the blade root 43 is provided at one side with a part-circular recess 11 and,

at the other side with a complementary part-circular projection 12. The recess, being deeper than its radius, has re-entrant sides which retain the projection12 of an adjacent interlocked blade. As shown in the Figure 4b, the projection 12 may have a central hole through which'a pin may pass into the sides of a rotor groove in wh ch the blade is seated in the manner described with reference to Figure 2; in this case, however, the pin makes no contribution toward securing the blades together. In ,Figures 5a and 5b, the blade root 47 has complementary dovetailed recesses 13, 14 and projections 15, 16l0n opposite sides of the root. I

In either of the embodiments illustrated in Figures 4a, .4b and 5a, Sb,'the ends 44 and 46, respectively, of the blade may be formed in any desired manner for attach- V ment to the rotor disc or drum.

in orderto permit the assembly of a ringof blades of any. one, of the typesdescribed in a rotor groove itmay be necessary to provide a gap' in the sideofthe groove, :as,*for instance, where theblades are interlocked by relative sliding in a direction axially of the rotor. The presence of such a gap is of course undesirable in that it reduces the capacity of the gapped groove wall to support itself against centrifugal loads. Figure 6, which represents an isometric view of a single rotor disc, illustrates a method for restoring the continuity of the groove wall in these circumstances. In the figure, the gap 17 in the wall 48 is provided at each circumferential extreme with serrations l8 and a closure piece 19 which is provided with corresponding serrations. Thus, after insertion of the ring of blades into the groove 20, the closure piece is entered into the gap 17 and affords a tie between the ends of the Wall 48 bounding the same.

The invention may have application, as well as to those parts of'blade roots affording attachment of the blades to a rotor, also to other parts of the blade roots normally radially intermittent when mounted on the rotor, such as cooling fins. For example, Figure 8 represents an isometric view of a rotor blade having a root formation comprising hooking members generally similar to that of the blade shown in Figure 1 in having a tongue 4-9 having an angularly disposed upper face 61 and a complementary shaped groove 50 having an angularly disposed downwardly extending or lower face 68 adapted to receive the upper face of the next adjacent hooking member. In

this case however, the interleaving portions of the roots have additionally, at their radially inner ends, groups of spaced fins, the group 23 on the tongue 49 of one blade being adapted to interleave between the remaining groups 24 on an adjacent blade. Figure 9 shows an isometric view of apart of a rotor fitted with blades as shown in Figure 8, the rotor being sectioned in a' radial plane transverse to its rim. The rotor comprises a pair of axially spaced discs 25 having rims 51 projecting laterally into the cavity between the discs and between which the blades are retained. The blades are drilled to accommodate firstly, pins 26 passing through the interleaved groups of fins on adjacent blades and, secondly, bolts 27 passing through the unfinned parts of the blade roots. The bolts 27 pass also through the rims 9 of the rotor discs 25 and are tensioned by nuts 23. The groups of fins 23 and .24, on successive blades, together define a series of peripheral channels 29 extending inwardly from the blades. A current of cooling air is arranged to flow through the space 30 between the discs 25 and outwardly through the channels 29. By suitable manipulation of the clearance between adjacent blade roots, gaps are afforded between them as at 31 allowing the cooling air to pass into th turbine working fluid stream.

What I claim is:

1. A bladed rotor comprising two co-axial discs axially spaced to define a peripheral cavity each of said discs having at least one grooved circumferential rim projecting laterally into said cavity, and a circumferential row of axial fiow blade elements each having aroot portion provided with disc abuttingends entered in said cavity and against which said discs each abut, the disc-abutting ends of each of said root portions being recessed to afford grooves complementary to and engaging said grooved circumferential rims of the discs, each root portion being provided with circumferentially and oppositely extending complementary hooking members having upper and lower faces each overlapping a corresponding complementary member on an adjacent blade element of the row, the overlapping hooking members of adjacentblade elements being secured together by axially extending pins held in place by the circumferential rims of the discs. 7

2. A bladed rotor according to claim 1, wherein at least one of said hook members on each root portionhas its radially inner surface slotted in radially extending planes and affording with the correspondingly slotted members of the other blade elements of the row a pluraiity of circumferentialiy,continuous cooling fins bound: in the peripheryof said cavity.

3. The bladed rotor according to claim 1 wherein the References Cited in the file of this patent 5 UNITED STATES PATENTS Fedeler May 20, 1902 Ray Oct. 16, 1928 Doran Nov. 12, 1940 10 6 Doran Feb. 3, 1942 Kroon Aug. 10, 1943 Buck May 15, 1951 Constant Aug. 28, 1951 Birmann Dec. 30, 1952 FOREIGN PATENTS Great Britain Sept. 16, 1921 Great Britain Jan. 22, 1941

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