US2925250A - Blades for compressors, turbines and the like - Google Patents

Description

Feb. 16, 1960 L. T. WHITEHEAD 2,925,250

BLADES FOR COMPRESSORS, TURBINES AND THE LIKE 5 Sheets-Sheet 1 Filed May 25. 1953 Feb. 16, 1960 L. T. WHITEHEAD 2,925,250

BLADES FOR COMPRESSORS, TURBINES AND THE LIKE Filed May 25. 1953 5 SheetsSheet 2 Pi g. S.

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BLADES FOR COMPRESSORS, TURBINEZS AND THE LIKE 5 Sheets-Sheet 3 Filed May 25. 1955 26 (I! x //l Fig. 6.

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BLADES FOR COMPRESSORS, TURBINES AND THE LIKE Filed May 25. 1953 5 Sheets-Sheet s l/l/l/I/I/l. 7 [III/ SKI/III:

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Attorney's United States Patent O BLADES FOR COMPRESSORS, TURBINES AND THE LIKE Leslie Thomas Whitehead, Famborough, England assignor to Power Jets (Research and Development) limited, London, England, a British company Application May 25, 1953, Serial No. 357,007

Claims priority, application Great Britain May 30, 1952 2 Claims. (Cl. 253-77) This invention relates to the mounting of blades and particularly rotor blades for fluid fiow machines, particularly compressors and turbines. An object of the invention is to provide a construction which will be cheap and light, and can be readily mass produced. The invention is not necessarily intended to be suitable for steam and gas turbines operating at high temperatures.

The manufacture of compressor and turbine blades is usually a major source of expense owing to the complicated machining operations involved. Hence it is desirable to make the blades out of preformed material, such as solid or tubular strip of appropriate cross-section and twisted if so required by the design, or from sheet metal bent to shape on a former. The use of such a method of manufacture involves difliculty in providing an adequate root fixing, and it is this problem with which the present invention is particularly concerned.

Accordingly the invention provides a rotor carrying a row of radially extending blades, each of which comprises a blade part proper consisting of a strip of material of aerofoil cross-section having a lateral notch in its root end, in which notch a part of the rotor engages, and a root block cast on to said end of the strip. In another aspect the invention provides a blade comprising a length of tubular sheet metal material having a lateral notch in its root end, the metal in the notch being cut and bent outwardly to form a projection, and said end being embedded in cast metal.

The invention will now be more fully described with reference to the accompanying drawings, of which:

Figure 1 is an axial half section of a single stage bladed compressor rotor.

Figure 2 is a side elevation of one of the blades, part of the root being shown as broken away.

Figure 3 is a plan view of the blade shown in Figure 2.

Figure 4 is a section on the lines IV--IV in Figures 2 and 3.

Figures 5, 6 and 7 are axial half-sections of the upstream ends of three multistage axial flow compressors.

Figure 8 is a fragmentary view of the rotor of a further multistage axial flow compressor.

Figure 9 is an axial half-section of the upstream end of yet another multistage axial fiow compressor.

Referring to Figure 1, a rotor for an axial flow compressor comprises two similar coaxial sheet metal discs 1, 2 having their peripheries bent towards one another to form axially directed flanges 1a, 2a. Annular brackets 3, 4 are fixed, e.g. by welding, to the adjacent faces of the discs, so as to form further axially directed flanges radially within the peripheral flanges, and a ring is shrunk on to these inner flanges to hold the discs together. Reinforcing rings 6, 7 are fitted within the peripheral flanges 1a, 2a, and are secured thereto by spot welding ice at a number of positions around the rotor circumference.

Referring now to Figures 2, 3 and 4, each blade includes a blade part proper 11, which is a strip of tubular material of the appropriate aerofoil cross-section, being twisted if so required by the design, and a root block 12. Rectangular notches 15 are cut in the leading and trailing edges of the blade towards one end, so that a T-root is formed, and this end is cast into the root block 12. The block is formed with notches 16 at opposite ends corresponding to the notches in the blade.

The metal in the notches 15 in the blade is not cut away altogether, but is left attached along the upper edges of the notches. The tabs so formed are bent outwards and upwards to form projections in the shape of approximately semi-circular gutters 13, which are embedded in the cast metal of the root block 112.

Recesses 14 are cut or east in each side of the root block 12 to reduce the weight. These recesses are such that a layer of metal is left on each side of the blade in the centre of the block, and the full width of the block is left around the notches 16 in the ends.

As can be seen from Figure l, the peripheral fianges 1a, 2a on the discs, and their reinforcing rings 6, 7 fit into the end notches 16 of the root block which is accordingly held firmly clamped between them.

Since the rotor disc flanges 1a, 2a engage directly in the notches 15 in the blade strip 11 reliance is not placed solely on the cast material for carrying the radial blade load. It will be seen that the load which can be so transmitted to the rotor is limited by the tensile strength of the neck between the notches 15. A further part of the end load is taken in shear by the turned-up gutters 13, and this part of the load is transmitted to the rotor through the cast material of the block 11. It will be seen that at the level of the top of the notches, the whole cross-sectional area of the blade is available to take the end load, the part forming the neck taking the load in tensilon, and the part forming the gutters taking the load in s ear.

It will be noted that the blade strip cannot be pulled bodily out of the root block without deforming the 1'- root. Further, pulling out the strip would involve straigthening out the gutters 13, and resistance to separation of the blade and root is thereby increased. The resistance provided by these features is in addition to that provided by any adhesion which may obtain between the metal of the strip and the root block.

The tube forming the blade part proper 11 may be made by deforming circular or other suitably shaped, e.g. elliptical, tube, to the required aerofoil cross-section, or by bending a sheet of metal to shape around a former, and welding up along the seam, say, at the trailing edge. Solid strip material might alternatively be used, although in that case it would not be possible to provide projections for increasing the load carrying capacity of the blade.

To reduce weight, the root block 12 may conveniently be made of a lighter material than the blade itself. Thus the blade may be of sheet steel, while the root block may be of aluminium alloy.

Referring to Fig. 5, the compressor rotor comprises a number of bladed rotor elements, each of which comprises two similar sheet metal discs 1, 2 centrally dished towards one another and having their peripheries bent towards one another to form axially directed flanges 1a, 2a. Annular brackets 3, 4, which may also be made of sheet metal, are fixed, e.g. by spot welding, to the adiaeent, i.e. the inner, faces of the discs, and rings 9, 10 are fitted around the brackets 3, 4, and are secured thereto by spot welding at a number of points around the circumference of the brackets. These brackets 3, 4 and the rings 9, 10 thus form flanges radially within the peripheral flanges, and a further ring 5 is shrunk on to these flanges, thus serving to hold the discs together. Reinforcing rings 6, 7 are fitted within the peripheral flanges la, 2a, and are secured thereto by spot welding at a number if positions around the rotor circumference.

Each rotor blade is of the type with reference to Figures 2-4, and comprises a blade part proper 11, consisting of a strip of solid or tubular material, and a root block 12 cast onto the end of the strip. The peripheral flanges 1a, 2a of the rotor disc and their reinforcing rings 6, 7 fit into the notches 16 in the ends of the root block, which is accordingly held firmly clamped between them.

Each rotor element is thus generally the same as the single stage rotor shown in Fig. 1. The adjacent rotor elements are held together in the same way as the two discs of each rotor element. The adjacent discs of adjoining rotor elements are provided with annular brackets 21, 22, also made of sheet metai,- fixed, e.g. by welding, to their adjacent, i.e. their outer faces, at positions radially between the periphery and the brackets 3, 4. Rings 23, 24 are fitted around the flanges, and secured thereto by spot welding, and a ring 25 is shrunk on to the flanges so formed, and accordingly serves to hold the rotor elements together. The rotor thus comprises a number of axially spaced sheet metal discs held together by shrink rigns 5, 25 fitting on to axially directed flanges on each disc.

The surface of the rotor between the blade rows, is formed by a sheet metal spacer ring 26, the central portion of which is flush with the surfaces of the blade roots, and the ends of which are of reduced diameter and fit into the end notches 16 of the blade roots 12. A filler ring 27 is fitted into the notches in the blade roots at the end of the rotor.

The end disc 1 of the rotor has attached to it, e.g. by welding, a frusto-conical bearer member 28 secured to a stub shaft 29 for supporting the rotor in bearings.

For assembly, each rotor disc will first be made up into a subassembly with its brackets 3, 4, 21, 22, the rings 9, 10, 23, 24 on these brackets and the reinforcing rings 6, 7. The disc 1 at the end of the rotor is set up on a stand with its axis vertical, and the first row of blades is fitted with the root notches engaging with the peripheral flange of the disc. The shrink ring 5 is then heated and dropped over the inner flange 3. The next disc 2 is then immediately placed in position with its peripheral flange fitting into the notches in the other ends of the blade roots and the inner flange 4 fitting into the shrink ring 5. n cooling, the ring shrinks on to the inner flanges thus serving to hold the discs together, and at the same time causing the blade roots to be held firmly clamped between the peripheries of the discs.

The end of the spacer ring 26 is then inserted in the end notches of the blade roots. The shrink ring 25 is heated and dropped over the inner flanges on the outer face of the disc 2 and the first disc 1 of the next rotor element is placed in position, so that the ring 25 shrinks on to and grips the inner flanges of the disc to hold them together. The next row of blades is fitted on to the peripheral flanges of the last mentioned disc and the end of the spacer ring 26, and assembly of the remainder of the rotor is carried out in the manner already described.

The stator comprises a row of stator blades, each of which, like the rotor blades, comprises a strip-31 of solid or tubular material having its end cast into a root block 32. These blocks are slid into the end of a semi-circular channel member 33, two of which are assembled around the rotor between the rows of rotor blades. Around each row of rotor blades, there is a channel section spacer ring 34, having its open side facing outwards. The spacing and blade carrying channel members are enclosed in a tubular casing 35. As shown, the casing and channel members taper towards the outlet end of the compressor.

The stator can be assembled around the rotor while it is set up in a vertical position with its upstream end, i.e. the end shown in the drawings, lowermost. The first of the stator members 34 is placed around the first row of rotor blades, and the two half channel members 33 carrying the stator blades are placed on top of the channel member 34. The remainder of the stator and blade carrying channel members are addedalternately in a like manner, and the outer casing 35 is then slid over the whole assembly. If necessary the channel members may be secured in position in the casing by welding or the like.

The embodiment shown in Fig. 6 is similar in most respects to that of Fig. 5 and the same reference numerals have been used for corresponding parts. The diflerence lies in the means whereby the rotor discs are connected together. The discs 1, 2 have attached to their inner surfaces cast brackets 3, 4, the axially extending arms of which are somewhat thicker than the arms attached to the disc faces. These arms are screwed externally to receive an internally threaded ring 5a which accordingly serves to draw them together. Cast annular brackets 21, 22 are similarly secured to the outer faces of the discs, and their axially extending arms are also externally screwed to receive an internally screwed ring 250 which likewise serves to draw the rotor elements together. The ends of the brackets 21, 22 are formed with radially extending flanges which abut with one another when the screwed joint is made. Thus the rotor is made up of a number of axially spaced sheet metal discs held together by screwed rings 511, 25a, which screw on to axially directed flanges on each disc. The screw threads are all on the same hand and are such that rotation of the rotor tends to tighten the joints.

In this embodiment, the discs are formed with central apertures, and the metal around these apertures is bent outwardly in an axial direction to form axially directed flanges, around which fit reinforcing rings 30.

Fig. 7 shows a variant of the embodiment of Fig. 6. The discs are similarly provided with cast brackets 3, 4 and 21, 22, but of each pair of brackets, one of them 3, 21 is screwed internally and the other 4, 22 is screwed externally. These brackets screw direct together and the screwed rings 5a, 25a shown in Fig. 6 are thus dispensed with. It will'be noted that the end of the bracket 22 abuts with the radially extending part of bracket 21. This serves to increase the stiffness of the rotor.

The rotors shown in Figs. 6 and 7 may be readily assembled by setting up the end disc of the rotor with its axis vertical and fitting on the blades, the screwed rings (in Fig. 6) and the discs in order.

Referring now to Fig. 8, the rotor again comprises a number of rotor elements, each of which comprises two discs 1, 2. As before the discs are formed with peripheral flanges la, 2a, but instead of brackets fixed to the disc faces, axially directed flanges, 3a, 4a are formed integrally with the discs. The discs with their flanges may conveniently be formed by a die-casting process. A shrink ring 5 fits on to the inner flanges 3a,

Between each pair of rotor elements, there is provided a spacer ring 26a which forms the surface of the rotor between the blade rows. The ends of this ring are formed with hooked lips 26b, which hook over the peripneral flanges 1a, 2a on the discs, and themselves fit into the end notches 16 in the blade roots. It will be appreciated that when the discs of a rotor element are brought to gether, the hooked lip 26b will be tightly clamped between the blade roots and the peripheral flange of the disc, and hence it can serve as a rigid spacing member connecting adjacent rotor elements.

' faces of the discs themselves.

To assemble this rotor, the disc at one end thereof is set up with its axis vertical, and the blades of the first row are fitted on with their root notches engaging withthe peripheral flange of the disc. A sub-assembly i then made up of the disc 2 of the first rotor element, the disc 1 of the second rotor element and the spacer ring 26a. The hooked lip 26b at one end of the ring is formed with gaps at diametrically opposite positions, of such a size that the ,two discs can be placed together back to back and slid edgeways into the spacer ring. The two discs are then turned through 90 (so that they lie coaxial with the ring) and the peripheral flange 2a of the disc 2 is allowed to engage in the hooked lip 26b at one end of the ring. The shrink ring 5 is heated and placed in position around the inner flange 3a of disc 1, and the sub-assembly described above is placed in position so that the inner flange 4a of disc 2 fits within the shrink ring 5, and the hooked lip 26b engages in the notches 16 in the ends of the blade roots. After the shrink ring 5 has cooled and gripped the flanges 3a, 4a, the other disc of the sub-assembly is pulled upwards so that its peripheral flange engages in the lip 26b at the other end of the ring 26a. To facilitate this last operation, flange 3a is provided with a lip 3b with which a suitable tool can engage. The rest of the rotor is assembled in a like manner.

In all the embodiments described above the discs on each rotor element are slightly dished towards each other so that at high speeds, their peripheries tend to approach one another and so clamp the blades more firmly between them. Dishing of the discs also serves to stiffen them against lateral vibration. The shrink rings 5, 25 and the screwed rings 5a, 25a serve to prevent the flanges on which they are fixed belling out under centrifugal force. The peripheral flanges la, 2a and reinforcing rings 6, 7 are a close fit in the notches 16 in the blade roots so that there is no tendency for the flanges to bend under centrifugal loads and so to be pulled out of the notches. It will be noted that the T-roots of the blades extend under the peripheral flanges of the discs almost to the This tends to ensure that the radial loads on the blades are applied to the discs in tension rather than in bending of the peripheral flanges. Further the flanges of the discs engage in the notches in the blade strips 11, so that they cannot be pulled out of the root block without deforming the T-root.

It may in some cases be more convenient for the rings 5, 5a, 25, 25a described above to fit within their respective flanges. In the embodiments of Figs. 1, 5 and 8, the outer surface of the ring could be a shrink fit with the inner surfaces of the flanges, and for assembly the ring would be cooled and allowed to expand into the flanges. In the embodiment of Fig. 6, the rings could be externally screwed and engage with internally screwed portions of the brackets 3, 4.

A somewhat different embodiment is shown in Fig. 9. A multi-stage axial flow compressor includes a number of coaxial, axially spaced discs 41 having integral peripheral flanges 42, extending axially on either side thereof. The discs may conveniently be made by a die-casting process. Slots are cut right through the flange of each disc so as to expose the edge of the disc itself.

Each disc carries a row of rotor blades 11, the roots 12 of which have circumferentially and radially extending notches 44 cut in the base and circumferentially and axially extending notches 16 cut in each side. These blades are of the type described above with reference to Figs. 24, and so the notches 16 in the root 12 correspond to the notches in the blade strip. The blade roots 12 fit into the slots in and protrude within the flange 42, and the notches 44 on the base of the root l2 fit over the exposed edge of the disc 41, while the side notches 16 lie radially within the disc flange 42. The angle at which the slots are set relative to the axis of the rotor is such that the blades are set at the required stagger angle.

The rotor discs 41 are spaced apart by spacer rings 46, the ends of which are shown as parallel in section but which may be taperd. These ends fit under the flanges of the discs on either side, and engage with the notches 16 in the sides of the blade roots, thus acting as retaining or wedging members retaining them in position against centrifugal loads. The flanges 42 are a shrink fit on the ends of the spacer rings 46 so that theflanges 42 and rings 46 together constitute a rigid rotor drum assembly. The rings thus ensure concentricity of the discs. The central portion 47 of each spacer ring 46 is enlarged so that its surface is flush with the surface of the flanges of the two adjacent discs and forms the rotor drum periphery between them. Rather than heat the discs and allow the flanges 42 to shrink on the spacer rings 46, it may be more convenient to freeze the rings 46 and allow them to expand into the flanges.

Between each pair of disc's, there is provided a light tube 48, lying along the rotor axis and fitting at its ends over projections 49 on the hubs of the discs 41. The tubes 48 serve to damp out vibrations of the discs, but are not rigid enough to have any locating function.

The end discs of the rotor are mounted on frustoconical bearer members 50 secured to stub shafts for supporting the rotor in bearings (not shown).

The stator consists of a number of diametrically split rings 51, each having a circumferentially extending undercut recess into which the roots 32 of stator blades 31 can he slid from the end. These stator blades again consist of strips of tubular or solid material 31 cast into a root block 32. The rings are generally tapered in form towards the outlet end of the compressor, but each ring has on its outer surface at each end a parallel section 52 of the same diameter as the adjoining parallel section 53 on the next ring. Shrink rings 54 are fitted over these parallel sections 52, 53 so as to make up a rigid stator drum assembly.

It will be observed that in this embodiment, the rings 46 engage in the notches 16 in the blade roots 12, and hence in the corresponding notches in the blade strip 11. Thus they serve to retain the blade strip against being pulled out bodily without deforming the T-root.

I claim:

1. A rotor for a turbo-machine comprising disc structure and a row of rotor blades disposed around the periphery of the disc structure, each blade comprising a radially extending length of metal strip of aerofoil crosssection having leading and trailing edges and side faces, and formed with a notch in at least one of its edges towards but spaced from its radially inner end, said notch having an edge extending trasversely to the axis of the strip on the side of the notch furthest from said radially inner end of the strip, and having an integral projection from at least one of its side faces extending along said edge of the notch; a root block of cast metal, said radially inner end and the projection of at least one of said lengths of strip being embedded in the root block and the root block having a side face formed with a notch corresponding to the notch in the length of strip; and the disc structure comprising a part engaging in said notch in the block and projecting in a direction transverse to the length of strip into said notch in the length of strip.

2. A rotor for a turbomachine comprising disc structure and a row of rotor blades disposed around the pe riphery of the disc structure, each blade comprising a radially extending length of metal strip of aerofoil crosssection having leading and trailing edges and side faces, and formed with a rectangular notch in each of its edges towards but spaced from its radially inner end and hav ing projections from at least one of its side faces extending along the edga of the notches extending transversely of the length of strip furthest from said radially inner end thereof and a root block of cast metal, said radially inner end of said length of strip and its projections being embedded in the root block and the root block having opposite side faces each formed with a notch corresponding to said notches in the length of strip; and the disc structure comprising annular axially extending parts engaging in said notches in the root blocks and projecting 5 in a direction transverse to the lengths of strip into said notches in the lengths of strip.

References Cited in the tile of this patent UNITED STATES PATENTS 10 1,620,974 Klenk Mar. 15, 1927 A 1,939,357 Lorenzen --.1-- Dec. 12, 1933 8 Dimberg May 7. 1935 Warren Oct. 29, 1935 Soderberg Dec. 8, 1936 Werther Dec. 8, 1942 Eastman July 3, 1951 Riddiford Nov. 6, 1951 Meyeer --a-- June 3, 1952 Sollinger Oct. 20, 1953 FOREIGN PATENTS Germany Sept. 14, 1921 Great Britain June 19, 1933

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