GB2258273A

GB2258273A - Rotor blade locking arrangement.

Info

Publication number: GB2258273A
Application number: GB9116774A
Authority: GB
Inventors: Raymond Eaton
Original assignee: Alstom Power UK Holdings Ltd
Current assignee: Alstom Power UK Holdings Ltd
Priority date: 1991-08-02
Filing date: 1991-08-02
Publication date: 1993-02-03
Anticipated expiration: 2011-08-02
Also published as: GB9116774D0; GB2258273B

Abstract

In a locking arrangement for the rotor blades of a gas turbine, a plate 15 extends circumferentially over the roots 3 of several blades. The plates 15 are trapped, in the assembled position, between retaining hooks 13 and 9 respectively integral with the rotor disc 7 and the blade roots 3. The plates 15 each have a resiliently mounted dog 21 which, when in position, prevents rotation of the plate 15. The plate 15 is inserted in one rotational position, by deflection of the dog 21, and then moved rotationally to engage the plate with both sets of hooks and, at the same time to allow the dog 21 to snap into its locking position. The plate covers and seals the gaps between blade roots and rotor disc, the locking is positive and at the same time can be released by depression of the dog. <IMAGE>

Description

Rotor Blade Locking Arrangement This invention relates to locking arrangements for the rotor blades of axial flow machines and particularly but not exclusively to such locking arrangements for gas turbines.

Rotor blades are comnonly mounted in the periphery of a rotor disc by means of a 'jig-saw' fit between the root of an individual blade and a complementary slot into which the blade root is fitted axially, as shown in the accompanying drawings, Figures 1 and 2. It is necessary to prevent the blade moving in the slot in operation and it has therefore been common to provide some locking arrangement. One proposed arrangement employed a metal member in the form of a castellated wire which was trapped in a groove formed between the blade and the disc. Such an arrangement requires the wire to be inserted before the blade is fitted and this may be an inconvenience.Other disadvantages are the absence of a really positive locking arrangement, no sealing facility (preventing escape of fluid past the blade roots), and particularly, the difficulty of dismantling the locking wires, since they have to be straightened. It follows therefore that it is not practical to re-use the wires after a dismantling process. Aero engine components are expensive and re-usability of the parts can provide a significant saving.

Simplification of the assembly process is also inherently desirable.

An object of the present invention is to provide a locking arrangement which overcomes some or all of these problems.

According to the present invention, in a rotor blade locking arrangement for an axial flow rotary machine which includes a rotor disc having slots in its periphery adapted for the insertion of the root of a rotor blade in an axial direction, the disc and the blade roots include complementary retaining members adapted to trap between them a plurality of segmental plates which on assembly lie on the axial face of the disc, each plate being shaped to permit, in a first rotational position, axial insertion of the plate between the retaining members, and each plate has a resiliently mounted dog member which is radially stressed by the insertion in the first rotational position and which is released into a blade locking position by rotational movement of the plate.

The plate may comprise two leaves one of which is so formed as to provide resilience in the plane of the plate and on which the dog member is mounted. The dog member may be an extension of the one leaf.

The two leaves of the plate may be connected together at the inner radial edge of the plate, the dog member extending from the one leaf in an outward radial direction.

The one leaf may comprise a resilient portion which extends circumferentially along the plate and which is fixed at its ends to the other leaf of the plate, the dog member extending radially from the centre of the portion. The two leaves may be formed from a single sheet of metal by folding.

The plate may extend er at least three blade roots and preferably over seven or more.

The dog member may be prevented from rotational movement in the blade locking position by engagement with portions of the blade root, or portions of the disc, particularly adjacent ones of the disc-mounted retaining members.

The one leaf may comprise a strip portion which extends out of the plane of the one leaf to permit deflection of the resilient portion and insertion of the plate between the retaining members, the strip portion being deformed into the plane of the one leaf to prevent deflection of the resilient portion and thus removal of the plate from the locking position. The strip portion may be cantilever mounted from the radially inward edge of the plate and when deformed into the plane of the one leaf engage the resilient portion. The resilient portion may then have a flange extending for a small proportion of the length of the resilient portion and projecting perpendicular to the plane of the plate to form an abutment for engagement by the end of the strip portion in its deformed position.

A rotor blade locking arangement In accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, of which; Figure 1 is a perspective view of a conventlonal rotor blade and blade root; Figure 2 is a similar view of the complementary slot in the rotor disc; Figures 3 and 4 are corresponding views of a rotor blade and disc slot according to the invention; Figure 5 is an elevation of a locking plate; Figure 6 is an axial view of part of the periphery of a disc rotor showing a locking plate in position; Figure 7 is a part section in an axial plane on the line VII-VII of Figure 6; Figure 8 is a part section in an axial plane on the line VIII-VIII of Figure 6; Figure 9 is a part section on the line VII-VII showing a modification of the plate of Figure 5;; Figure 10 is a perspective view of a locking plate and part of the disc periphery axially aligned for assembly; and Figures 11 and 12 are axial sections through a blade root with blade in successive stages of assembly of the plate.

Referring to the drawings, Figure 1 shows the blade 1 and root 3 of a conventional gas turbine blade. The root is a sliding fit in an axial direction In the slot 5 of the periphery of a disc rotor 7, this disc being one of a number of stages in the turbine.

In the embodiment now described, the root 3 is formed with a retaining member In the form of a hook, 9. When the blade is in position this hook 9 stands proud of the disc face. At the outer part of the blade root two lugs 11 are formed, also projecting from the disc face and forming between them a slot 12.

The disc 7 is also formed with retaining members provided by an overhang 13 from the disc periphery. An intermittent groove 14 is thus formed around the periphery complementary to the groove 10 In the blade root provided by the hook 9.

The complementary retaining members 9 and 13 so provided, accommodate a locking and sealing plate 15 shown in Figure 5. This plate has two leaves formed by folding a pressed out sheet in (approximate) half. It may however be formed of separate leaves fixed together. The front leaf comprises a long resilient portion 17 joined to the back leaf 19 at its ends. Extending from the centre of this portion 17 Is a rectangular piece 21 integral with the 'beam' 17, which engages the slot 12 in the blade root and thus constitutes a 'dog' preventing rotation of the plate 15 around the periphery. The thickness of the material and the length and radial depth of the portion 17 are such that the central portion of this 'beam' can be pressed radially Inwards, by hand, until the dog 21 does not protrude beyond the edge of the back leaf. This condition is shown in broken lines 17'. In the example shown in Figure 5 the plate 15 extends circumferentially over only three blades. The resilient beam 17 has therefore to be relatively narrow to permit the necessary deflection.

In a practical embodiment, eg as shown in Figure 6, the plate 15 would extend over seven or more blades. The beam 17 would then be correspondingly long and resilient deflection would be an easier matter. Figure 5 shows a plate for three blades merely for convenience of illustration.

The resilient beam 17 is connected (by folding) to the back leaf 19 at two positions 23 which correspond to the endmost blades of those which the plate 15 covers. The two-leaf thickness of the plate is a close fit in the groove 10 of the blade root.

At each blade pitch between the end positions 23 the front leaf of the plate Includes a folded-over portion 25 which also Is a close fit in a corresponding groove 10 in a blade root. Thus the lower edge of the locking plate can engage a series of perhaps 8 or 10 blade roots. The upper edge of the resilient beam 17 lies substantially In line with that of the back leaf 19 and again the resulting double-leaf thickness is a close fit in the disc grooves 14.

The back leaf 19 is relieved along the lower (radially inner) edge at positions 27 between double-thickness positions. These relieved positions or cut-outs, are such that, when aligned with the blades, they would, but for the dog 21, allow the plate to be inserted into the disc grooves and then ride over the hooks 9 of the blade roots. Figure 10 shows the plate 15 positioned for assembly, with the cut-outs 27 axially aligned with the blade roots 3 and in particular the hooks 9.

Figures 11 and 12 show the manner of Inserting the locking plate. The plate is positioned as in Figure 10 and then the dog 21 inserted under the hook 13 as in Figure 11 which is a section through the cut-out 27 and blade root 3. By pressing the plate 15 upwards (ie radially outward) under the hook 13, the beam 17 is deflected downwards and the cut-outs 27 can ride over the blade-root hooks 9 and into the groove 10. The beam 17 is still flexed In this condition (as shown in broken lines in Figure 5). By sliding the plate around the periphery by half a blade pitch the dog 21 will ride out of the groove 14, between the lugs 11 and snap into the slot 12. At the same time, the double leaf portions 25 and 23 will slide Into the blade root grooves 10.The plate is then locked in position between the complementary retaining hooks 9 and 13 and prevented from rotating by the engagement between the dog 21 and the lugs 11.

Reverting to Figure 6, this shows the locking plate 15 in position on the rotor disc face (what might be called the axial face, as opposed to the curved, peripheral, face of the disc). In the illustrated example the resilient beam portion 17 extends over seven blades although only part of the plate is shown. It will be clear that the plate may extend for several blade pitches beyond the end of the beam 17 the length of which is preferably chosen Independently of th plate length. It is not, of course, necessary that the beam 17 is associated with the double-leaf portions 23, since the beam 17 may be fixed to the back leaf 19 in various ways and at various positions.

The portions 23 may then be formed similarly to the double thickness portions 25.

Figure 7 shows, In a section through the centre of the dog 21, the plate 15 In operative position. Figure 8 shows, in the same condition, a section midway between two blades.

In Figure 9 Is shown a modification of the locking plate which prevents it being unintentionally released. The front leaf of the double thickness portion 25 is extended upwards (29) so as just to reach the resilient beam 17. This extended portion 29 is bent outwards to permit assembly (ie to permit the beam 17 to deflect downwards). Once assembled, the extension 29 Is forced back against the back leaf 19 so preventing deflection of the beam 17. A short flange 31 formed on the under-edge of the beam 17 facilitates the bending back of the extension 29. It will be clear that the flange 31 must be short, eg, no longer than the dog 21, so as not to stiffen the beam 17 unduly.

In the above described embodiment the dog 21 is directed outwardly and engages the slot 12 in the blade root. In a first modification the lugs 11 may be removed and the dog 21 widened until it engages the adjacent hooks 13 of the disc. Again, the plate 15 may be reversed, the dog 21 facing (radially) inwardly and engaging suitable abutments on the blade root or disc. There may also be more than one dog, as long as they are not too close to the ends of the beam 17.

In assembling the blades and locking plates, because of the half-blade-pitch movement of the plate necessary between Insertion of the plate and snapping in of the dog 21, there are two possible approaches: (a) to Insert all of the plates around the periphery and then move them around the periphery to their locking positions in unison (or at least, allow a tolerance between each pair and 'inch' them around progressively); and (b) allow a half-blade-pitch tolerance between each pair so that each one can be fitted (and removed) independently. This would mean removing that part of the back leaf 19 that extends beyond the front leaf portion 23.

The embodiment described provides a locking arrangement which can be easily dis-mantled, the dog 21 being pressed downwards and the plate slid along between the hooks 9 and 13 until the cut-outs 27 coincide with the hooks 9.

Partial sealing of the gaps between the blade roots and the disc slots 5 is achieved by the back leaf 19 of the plate 15 which lies flat against the axial face of the disc. The gap under the base of the blade root 3 will not be so covered and this will admit a controlled amount of fluid which is useful for cooling purposes. In some designs this amount of cooling may not be sufficient and the back leaf 19 may be perforated In line with the current line of the blade root side flanks.

More commonly however, the greater degree of sealing provided by the continuous back leaf 19 pressed against the disc face.

Claims

1. A rotor blade locking arrangement for an axial flow rotary machine which Includes a rotor disc having slots in its periphery adapted for the insertion of the root of a rotor blade in an axial direction, wherein the disc and the blade roots include complementary retaining members adapted to trap between them a plurality of segmental plates which on assembly lie on the axial face of the disc, each plate being shaped to permit, In a first rotational position, axial Insertion of the plate between the retaining members, and each plate has a resiliently mounted dog member which is radially stressed by said insertion in said first rotational position and which is released into a blade locking position by rotational movement of the plate.

2. A locking arrangement according to Claim 1, wherein said plate comprises two leaves one of which is so formed as to provide resilience in the plane of the plate and on which said dog member is mounted.

3. A locking arrangement according to Claim 2, wherein said dog member is an extension of said one leaf.

4. A locking arrangement according to Claim 2 or Claim 3, wherein the two leaves of said plate are connected together at the inner radial edge of the plate, said dog member extending from said one leaf in an outward radial direction.

5. A locking arrangement according to Claim 2, 3 or 4, wherein said one leaf comprises a resilient portion which extends circumferentially along the plate and which is fixed at its ends to the other leaf of the plate, said dog member extending radially from the centre of said portion.

6. A locking arrangement according to any of Claims 2 to 5, wherein said two leaves are formed from a single sheet of metal by folding.

7. A locking arrangement according to any preceding claim, wherein said plate extends over at least three blade roots.

8. A locking arrangement according to Claim 7, wherein said plate extends over seven or more blade roots.

9. A locking arrangement according to any preceding claim, wherein said dog member Is prevented from rotational movement by engagement with portions of said blade root in said blade locking position.

10. A locking arrangement according to any of Claims 1 to 8, wherein said dog member Is prevented from rotational movement by engagement with portions of the disc in said blade locking position.

11. A locking arrangement according to any of Claims 1 to 8, wherein said dog member is prevented from rotational movement by engagement with adjacent ones of the disc-mounted retaining members.

12. A locking arrangement according to Claim 5 or any of Claims 6 to 11 appendent to Claim 5, wherein said one leaf comprises a strip portion which extends out of the plane of said one leaf to permit deflection of said resilient portion and insertion of said plate between said retaining members, said strip portion being deformed into the plane of said one leaf to prevent deflection of said resilient portion and thus removal of the plate from the locking position.

13. A locking arrangement according to Claim 12, wherein said strip portion is cantilever mounted from the radially inward edge-of the plate and when deformed into the plane of said one leaf engages said resilient portion.

14. A locking arrangement according to Claim 13, wherein said resilient portion has a flange extending for a small proportion of the length of the resilient portion and projecting perpendicular to the plane of the plate to form an abutment for engagement by the end of said strip portion In its deformed position.

15. A locking arrangement for turbine rotor blades substantially as hereinbefore described with reference to the accompanying drawings.