1. Field of the Invention
The present invention relates to assembling distributor sectors, bearing fixed blades, and ensuring correction of a gas flow in a casing enclosing stators of a turbomachine.
2. Description of the Related Art
The external flow of gases in turbomachines is delimited by distributor and ferrule sectors alternately mounted on the casing via overlapping hooks along the machine. With reference to
This assembly holds the sectors 1 against the movements produced by the radial and axial forces oriented towards the rear during operation. Assembling these conventional devices is difficult to carry out, as the inclined sectors 1 have to be disposed in the casing 7 so that the rear flange 3 can be inserted in the second hook 10 before making them pivot about the end hook 4 at the front, so that the end hook 5 can be inserted behind the hooks 10 with a radial movement towards the outside. In order to effect this assembly, it is necessary to have two major sets of rotor-stator in the internal stream, with such a requirement being detrimental to the seals between rotor and stator. Finally, probably the most serious disadvantage of this assembly is the fact that the hooks 6 and 10 are integrally formed with the casing 7, being subjected to significant mechanical and thermal stresses since they are near the stream of hot gases. As such, it becomes necessary to construct the hooks 6 and 10 and the casing 7 from a sufficiently resistant material even though the casing 7 is subjected to a lower temperature. In addition, due to the integral construction, fatigue cracking can appear in the hooks 6 and 10 and spread to the point where the entire casing 7 needs to be replaced.
Therefore, a need exists to rectify the design of the above-described casing, which is both costly and fragile, while enabling straightening sectors to be mounted more simply and producing a more rigid and less complex assembly. The instant invention satisfies these various requirements.
In its most general form, the present invention relates to the assembly of sectors of a distributor ring on a casing, the sectors comprising two flanges fitted with support faces on the casing, a hook being disposed beneath a curved edge of one of the flanges to support the sectors against centripetal movements, characterised in that the assembly comprises a support plate placed between the flanges; and means for fixing the support plate to the casing, the hook being placed on the support plate, the support plate and the casing comprising flat mutual support faces oriented in an axial direction, fixing means comprising slugs passing radially through the casing, the support plate being retained between the casing and the slugs, and the support plate having a mounting direction towards the flange having said curved edge.
The hook, which is the most stressed part of the assembly, may now be constructed with increased freedom for the choice of materials because it is disposed on a support plate and thus separated from the casing; it may be more easily replaced, if required; and finally, mounting is effected via linear movement of the sole support plate rather than the more complicated joint pivoting movement of the sectors in conventional assemblies.
The assembly may be further simplified if the hook comprises a conical external face at least on a central portion under the curved edge tapering towards the flange having the curved edge.
It should be noted that documents U.S. Pat. No. 3,892,497 and U.S. Pat. No. 5,618,161 disclose arrangements where distributor sectors are retained by carriers of a hook which is thus separated from the casing, but the end plates are placed otherwise and are not mounted by translation, but by tilting. They must be divided into sectors: the arrangement and mounting remain complicated.
Other arrangements, which can be adapted in addition to the above, multiply the advantages, which the invention provides. Its various aspects will emerge better from the following description of the figures, in which:
The casing is now designated by reference numeral 21, but its general form resembles that of the previous one; its diameter decreases towards the front and its form is thus slightly conical at the point of the invention.
The new straightening sectors are designated by reference 20 and comprise, as before, flanges 22 and 23 at the front and at the rear are fitted with end hooks 24 and 25, both curved towards the rear; the end hooks 24 and 25 are here supported on the casing 21 by mutual support faces 26 and 27, oriented in a radial direction, and by flat support faces 28 and 29, axially oriented and opposite to each other. Contrary to the above-noted conventional design, assembly of the new straightening sectors is simplified and made more stable. An essential element of the invention is a support plate 30 supported on the casing 21 by flat mutual support faces 31 and oriented in an axial direction, the support plate 30 comprising on its edge a hook 32 facing the front and passing under the end hook 24 of the first flange 22. The support plate 30 extends on a full turn. As previously, the straightening sectors 20 bear towards the front a projection 33 for retaining the adjacent ferrule sectors 34 underneath. Another projection 35 can be noticed; it is found under the second end hook 25 and its purpose is to support ferrule sectors 35 opposite the preceding.
Slugs 37 are adjusted through the casing 21 in a radial direction, and keep the support plate 30 supported against the casing 21 by engaging behind the latter to block it axially.
The hook 6 of the conventional casing 7 has been eliminated, with the hook 32 of the support plate 30 replacing it, such that a weak point of the casing 7 has been eliminated. The hook 10 for the other flange 3 has not been eliminated completely, since the second end hook 25 is placed behind a groove 19 of the casing 21, which ensures the same support functions for the flange 23, but it should be emphasised that the groove 19, more massive and less protruding than the hook 10, is much less stressed. Such modification of the hook 10 in the design of
Eliminating hooks 6 and 10 or replacing them by simpler structures decreases stress and the risk of failure of the casing 21, while, at the same time, simplifying the casing manufacture process. The casing 21 now may be constructed from a less resistant material than the one used for casing 7. Only the hook 32 and its support plate 30 remain subjected to high temperatures, thus requiring the use of a more resistant material.
As shown in
The movement of the support plate 30 towards the front can be made very simply by a special tool, as often found for carrying out assembly and disassembly work of turbomachines. An appropriate tool would comprise a platen mounted in the casing supporting the straightening sectors 1, as well as thrusters for pressing on the rear of the support plate 30 through holes 42 hollowed through the other flange 23.
It should be emphasised that one of the main stresses being exerted on the straightening sectors 1 or 20 is a force to the rear, produced by the flow of air across the latter. This force is translated by a tilting motion around support points of the sectors on the casing 7 or 21 and by a centripetal radial force on the hook 6 or 32, which makes it vulnerable, but the consequences of breaking would be less serious on the hook 32 than on the hook 6, since it would be enough to replace the support plate 30 instead of the entire casing 7. The hook 32 offers radial support to the inside on sectors 20, just like the hook 6 on the sectors 1, since the end hook 24 is placed on the latter, but it offers more rigid assembly than the hook 6, even though it is not all in one with the casing 21, by keeping the end hook 24 pressed against the casing 21 on the support faces 26. The diameter of a surface portion of the rear portion 39 can be selected to exert the desired pressing force at this point.
The conicity of the surface 38 always allows the support plate 30 to be placed without difficulty, with the hook 32 acting as a corner. Assembly is still stiff, while being simplified, if the ferrule sectors 36 to the rear comprise a projecting front end 43 placed on the projection 35 and introduced on the end hook 25 of the flange 23 in the place of the clip 12.
If the support plate 30 must be replaced, it is easy to extract it if tapping points are put in place, such as internal screw threads 53, which allow it to be gripped by threaded axes introduced through the holes 42, and to be extracted by drawing it to the rear until the straightening sectors 20 are released.
It should be noticed that the end hook 24 of the first flange 22 was directed to the rear, and the hook 32, with which the first flange is assembled, was directed towards the front, contrary to the traditional arrangement as in
Number | Date | Country | Kind |
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01 11830 | Sep 2001 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR02/03091 | 9/11/2002 | WO | 00 | 2/25/2004 |
Publishing Document | Publishing Date | Country | Kind |
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WO03/023193 | 3/20/2003 | WO | A |
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