Device for fastening a moving blade to the rotor of a turbomachine

Abstract

A device for fastening a moving blade (3) to a rotor (2) of a thermal turbomachine is described. The moving blade (3) has a blade root (36), a blade leaf (32) and a platform (31) arranged between the blade root (36) and the blade leaf (32) and having at least two side flanks (33, 34). The idea, on which the invention is based, of avoiding axial forces occurring on the rotor (2) on account of bearing faces set obliquely to the rotor axis (4) between two adjacent moving blades (3) is that adjacent moving blades (3) meet solely at axially oriented bearing faces (52).

Description

TECHNICAL FIELD

[0001] The invention relates to a device for fastening a moving blade to the rotor of a thermal turbomachine according to the preamble of claim 1.

PRIOR ART

[0002] Moving blades which are fastened in circumferential grooves on rotors of turbomachines are to be positioned in a suitable way as a function of the respective flow conditions, but, in particular, are to be secured reliably against coming loose from the circumferential groove completely while the turbomachines are in operation as a result of maladjustments which may possibly occur.

[0003] There is the risk of individual moving blades coming loose completely from the respective fastening measures when the moving blades inserted within the circumferential grooves and fastened in a way known per se are capable of being displaced unevenly along the circumferential groove on the rotor in the circumferential direction within the respective assembly play. Owing to peripheral maladjustments of this kind in the case of a multiplicity of moving blades inserted along the circumferential groove, a considerable gap may be established between two adjacent moving blades, such a gap being sufficiently large for a moving blade to be capable of coming loose from the circumferential groove as a result of radial twisting, thus causing considerable damage to the entire turbomachine plant.

[0004] Securing measures, known per se, against individual moving blades coming loose independently from the circumferential groove are concerned, in general, with reducing the play between two adjacent blade roots within the circumferential groove in the circumferential direction. Use is made, for this purpose, of special intermediate pieces which can fill the play which has remained in a circumferential direction from assembly, the intermediate pieces having to be installed very closely together in the remaining intermediate gap.

[0005] The use of specially shaped intermediate pieces, which reduce the assembly-related play in the circumferential direction to an amount which is very much smaller than would be necessary for the free thermal expansion of the individual moving blades along the circumferential groove, gives rise, when the turbomachine is in operation, to thermally induced constraints which are brought about at least longitudinally in the circumferential direction between the individual adjacent moving blades. If the blade roots of the individual moving blades or the platforms provided, as a rule, between the blade roots and blade leaves are designed to be contoured obliquely in such a way that two adjacent moving blades come into contact via oblique bearing faces oriented with respect to the rotor axis, the abovementioned thermally induced mechanical constraints lead, within the bearing faces oriented obliquely to the rotor axis, to additional axial forces which lead to a distortion of the rotor and consequently to vibrations.

[0006] Irrespective of the design of the platforms of respective moving blades, it is also conceivable that two blade roots arranged adjacently within the circumferential groove have blade-root flanks running obliquely to the rotor axis and are contiguous with one another, the vibration phenomena explained above occurring in the same way.

[0007] U.S. Pat. No. 4,684,325 describes generic turbine moving blades which, in a multiplicity lined up with one another along the circumferential groove, are directly contiguous with one another via the side flanks of rhombically designed platforms. The rhombic design of the platforms, on the one hand, is due to the oblique position of the respective turbine leaf in relation to the throughflow direction and, on the other hand, is motivated by an increase in the packing density of moving blades to be arranged along the circumferential groove. If, then, due to the operating conditions prevailing in a turbomachine, turbine moving blades designed in this way come into force-exposed active connection via the bearing faces not oriented parallel to the axis of rotation, the axial forces arising along the individual bearing faces between the adjacent moving blades lead to unavoidable vibrations within the rotor arrangement, due to which corresponding bearings supporting the rotor arrangement are subjected to considerable load. It is expedient to counteract effectively this very situation by means of appropriate measures.

PRESENTATION OF THE INVENTION

[0008] The object on which the invention is based is to develop a device for fastening a moving blade of the generic type described above, in such a way that axial forces on the rotor which occur due to thermal distortions within the moving blades are to be avoided completely. Care is to be taken, at the same time, to show that a coming loose of individual moving blades on account of gap interspaces which may possibly be formed can be ruled out completely. The measures to be taken are not to require any structurally complicated work or precautions and, in particular, are to allow retrofitting in the case of already existing rotor arrangements.

[0009] According to the invention, the device for fastening a moving blade according to the preamble of claim 1 is designed such that, in the region of the blade root extending into the circumferential groove, bearing faces are provided which are actively connected to said blade root and are oriented parallel to the rotor axis, and adjacently inserted moving blades come into a loose force-exposed connection directly or indirectly with one another, in each case within the circumferential groove, via the bearing faces oriented parallel to the rotor axis.

[0010] The idea, on which the invention is based, of avoiding axial forces occurring on the rotor due to bearing faces set obliquely to the rotor axis between two adjacent moving blades is the avoidance of those very oblique bearing faces. The idea of the invention is therefore of particular importance especially in the case of moving blades with a large angle of incidence in relation to the throughflow direction in turbomachines, especially since the platforms of moving blades of this kind have, not least for reasons of space and weight, obliquely running side flanks, via which the directly adjacent moving blades or similarly configured intermediate pieces, inserted, as a rule, within the circumferential groove, are contiguous with one another.

[0011] To avoid those very contact faces oriented obliquely to the rotor axis, there is in a particularly advantageous way, for each individual moving blade, a shim which is introduced radially between the blade root and the rotor within the circumferential groove and which makes at least one releasably firm active connection with the respective blade root. The shim has bearing faces which are oriented parallel to the rotor axis and which project beyond the side flanks of the platform of the moving blade in the circumferential direction of the rotor. What is achieved thereby is that two adjacent moving blades butt against one another solely via the bearing faces, assigned to them, of the respective shims, said bearing faces being oriented parallel to the rotor axis. By virtue of the geometric design of the shims, during operation, only stresses in the circumferential direction occur on account of differences in thermal expansion between the rotor and the shims arranged in the circumferential direction within the circumferential groove, but said stresses are entirely uncritical for the rotational behavior of the rotor. Any axial forces directed onto the rotor can be avoided because of the axial or parallel orientation of the bearing faces in relation to the rotor axis.

[0012] The releasably firm active connection between the individual moving-blade roots and the shims assigned to them is made from the sides of the shim preferably by means of a force-exposed bolt, preferably a spring-force-exposed bolt, which engages into a corresponding recess within the blade root, as a result of which, on the one hand, movement-free fixing of the moving blade in the circumferential direction is ensured, but, on the other hand, there is sufficient play between the rotor and the blade root, so that the blade root can thermally expand essentially freely within the circumferential groove. Thermal distortions within the blade root seated in the circumferential groove can thereby be largely avoided.

BRIEF DESCRIPTION OF THE INVENTION

[0013] The invention is described by way of example below, without the general idea of the invention being restricted, by means of exemplary embodiments, with reference to the drawings in which:

[0014] FIG. 1 shows a top view of a moving blade inserted into a circumferential groove, with two adjacently arranged shims,

[0015] FIG. 2 shows a cross-sectional illustration along the sectional line in FIG. 1, and

[0016] FIG. 3 shows an illustration of a detail regarding the connection between shim and blade root.

[0017] Only the elements essential for the invention are illustrated. Like elements are designated identically in the various figures.

EMBODIMENTS OF THE INVENTION, COMMERCIAL PRACTICABILITY

[0018] FIG. 1 shows a top view of the circumferential groove 1 of a rotor 2 of a thermal turbomachine, such as a compressor or a gas or steam turbine. For the sake of greater clarity in the illustration, only one moving blade 3 (middle position) with a rhombically designed platform 31 and with a blade leaf 32 set at an angle .alpha. is illustrated within the circumferential groove 2. In the exemplary embodiment illustrated, the side flanks 33, 34 of the platform 31 are directed essentially parallel to one another and form the same angle of incidence .alpha. with respect to the coparallel, marked by broken lines, to the axis of rotation 4. It may be pointed out, merely for the sake of completeness, that the blade leaf 32 has a wrenched design in its radial extent, that is to say the blade tip 35 has a larger angle of incidence .alpha. than the blade-leaf region near the platform 31.

[0019] Furthermore, the blade root, not illustrated, which is completely covered by the platform 31 in the illustration of a top view according to FIG. 1, is in engagement with a holding contour which is incorporated within the circumferential groove 1 and may be gathered in detail from the cross-sectional illustration according to the FIG. 2, which will also be dealt with in detail.

[0020] Provided radially below the moving blade 3, within the circumferential groove 1, is a shim 5, a multiplicity of which are arranged, distributed in the circumferential direction, in each case directly contiguously with one another. The shims 5 have in each case bearing faces 52 oriented parallel to the rotor axis 4. For the sake of clearer illustration, the associated moving blade 3 is depicted merely in terms of the middle shim 5 in FIG. 1, said moving blade being connected via a connection means at least releasably firmly to the shim 5 associated with it. The connection means 6 is connected such that the moving blade 3 is fixed securely in the circumferential direction longitudinally in relation to the circumferential groove 1. A special design of the connection means 4 will be dealt with below in FIG. 3.

[0021] In the exemplary embodiment according to FIG. 1, the shims 5 connectable in each case to a moving blade 3 are designed preferably in the manner of an obliquely set "H" and have a middle connecting web 51, in which the corresponding connection means 6 can be integrated. The side limbs directed in the circumferential direction in relation to the circumferential groove 1 terminate in each case in the regions having the bearing faces 52 which are oriented parallel to the rotor axis 4 and which all project beyond the moving blade 3 in radial projection, thus ensuring that two moving blades arranged adjacently in the circumferential groove 1 are in force-exposed contact preferably solely in each case via the bearing faces 52. In particular, as a result of the very high temperatures prevailing when a turbomachine is in operation, even the shims 5 expand in relation to the rotor material, thus giving rise, however, to only mechanical constraints in the circumferential direction between the individual shims 5, whereas any axial forces on the rotor are avoided owing to the parallel orientation of the bearing faces in relation to the rotor axis.

[0022] The idea, on which the invention is based, of avoiding axial forces occurring on the rotor 2 due to bearing faces set obliquely to the rotor axis 4 between two adjacent moving blades 3 is, in general, that adjacent moving blades 3 meet only at axially oriented bearing faces 52, irrespective of whether these bearing faces 52 are fastened to a shim 5 or directly to the blade root 36 or are connected in another active way to the blade root 36. The bearing faces is oriented parallel to the rotor axis project beyond the side flanks 33, 34 of the platform 31 of the moving blade 3 in the circumferential direction of the rotor for the inventive purpose.

[0023] FIG. 2 illustrates a sectional diagram along the sectional line A-A according to FIG. 1. This shim 5 assigned to the moving blade 3 is located in an intermediate gap 7 between the blade root 36 and the rotor 2. The platform 31, the top side of which is flush with the rotor top side, may likewise be gathered from the cross-sectional illustration according to FIG. 2. A spring-force-exposed bolt 7, by means of which the moving blade 3 is fixed in relation to the shim 5, is provided centrally in relation to the blade root 36 as a connection means 6.

[0024] FIG. 3 illustrates a corresponding cross-sectional illustration of the connection means 6. Here, the shim 5 has a press fit by means of a sleeve 62, within which is provided a spring element 63 which can drive a bolt 61 vertically upwards. The bolt 61 and the sleeve 62 project, in association with the moving blade 3, into a corresponding recess 64 within the blade root 36.

[0025] As indicated diagrammatically in FIG. 1 below the moving blade 3, at least one intermediate piece 8 may be inserted within the circumferential groove 1 between two moving blades 3, as a spacer piece which has a blade root as fastening element and also a platform which is flush with the rotor 2 and with the platforms 31 of two adjacent moving blades 3.

[0026] The measure according to the invention is suitable in a particularly advantageous way as a retrofit set in the case of turbomachines which are already in operation. It is expedient merely to enlarge the axial and, if appropriate, circumferential play in the region of the blade roots by remachining, for example by regrinding, in order to provide sufficient space for inserting the shims.

1 List of reference symbols 1 Circumferential groove 2 Rotor 3 Moving blade 31 Platform 32 Blade leaf 33, 34 Side flanks 35 Blade leaf tip 36 Blade root 4 Rotor axis 5 Shim 51 Connecting web 52 Bearing faces 6 Connection means 61 Bolt 62 Sleeve 63 Spring element 64 Recess 7 Intermediate gap 8 Intermediate piece

Claims

1. A device for fastening moving blades (3) along a circumferential groove (1) running within a rotor (2) of a thermal turbomachine, in which the moving blades (3) have a blade root (36), a blade leaf (32) and a platform (31) arranged between the blade root (36) and the blade leaf (32) and having at least two side flanks (33, 34), the circumferential contour (1) provides an inner contour designed for receiving the blade roots (36), and the side flanks (33, 34) of the platform (31) of the moving blades (3) located in the circumferential groove are inclined obliquely to the rotor axis (4), characterized in that, in the region of the blade root (36) extending into the circumferential groove (1), bearing faces (52) are provided which are actively connected to said blade root and are oriented parallel to the rotor axis (4), and adjacently inserted moving blades (3) come into a loose force-exposed connection directly or indirectly with one another, in each case within the circumferential groove (1), via the bearing faces (52) oriented parallel to the rotor axis (4).

2. The device as claimed in claim 1, characterized in that an intermediate gap (7), in which is introduced a shim (5) having the bearing faces (52), is provided radially within the circumferential groove (1) between the blade root (36) and the rotor (2), the shim (5) extending beyond the two side flanks (33, 34) in the circumferential direction.

3. The device as claimed in claim 2, characterized in that the shim (5) has a connection means (6) by which the shim (5) is capable of being connected releasably firmly to the blade root (36).

4. The device as claimed in claim 3, characterized in that the connection means (6) is a force-exposed bolt (61) which engages from the sides of the shim (5) into a recess (64) provided correspondingly within the blade root (36).

5. The device as claimed in claim 2, characterized in that the shim (5) is joined firmly to the blade root (36) or is connected in one piece to the blade root (36).

6. The device as claimed in one of claims 2 to 5, characterized in that the shim (5) is designed in the manner of an "H", the connecting limb (51) of which is oriented essentially parallel to the side flanks (33, 34) of the platform (31) and has four bearing faces (52) oriented parallel to the rotor axis (4).

7. The device as claimed in one of claims 1 to 6, characterized in that, in the state in which the moving blade (3) is joined to the rotor (2), that surface of the platform (31) which is directed radially to the blade leaf (32) is flush with said rotor.

8. The device as claimed in one of claims 1 to 7, characterized in that an intermediate piece which is flush with the rotor (2) is inserted between two adjacent moving blades (3) into the circumferential groove (1) and fits snugly, essentially free of force, against the side flanks (33, 34) of the platform (31) of the two adjacent moving blades (3).

9. The device as claimed in one of claims 1 to 8, characterized in that the platform (31) has a rhombically designed shape in which the side flanks (33, 34) extend along the width of the blade leaf (32).

10. The device as claimed in one of claims 1 to 9, characterized in that at least one intermediate piece is inserted between two adjacent moving blades (3) within the circumferential groove (1) and has a blade root (36) and also a platform (31) which is flush with the rotor (2) and with the platforms (31) of two adjacent moving blades (3).