GENERAL TECHNICAL FIELD

The invention relates to the general field of turbomachines and more particularly turbomachine elements comprising anti-rotation notches in particular those of low-pressure turbine distributor sectors and more particularly those of fastening structures of such sectors.

STATE OF THE ART

A turbomachine comprising one or several air compression sections admitted in the engine (generally a low-pressure section and a high-pressure section).

Typically, a low-pressure turbine includes several successive expansion stages. Each of these stages exhibits a mobile wheel (rotor) and a stationary wheel (also called distributor or stator).

FIGS. 1 and 2illustrate a low-pressure turbine oriented longitudinally from upstream to downstream according a direction F.

In a known manner, a low-pressure turbine comprises mobile wheels10and distributors11. Each distributor11is divided into sectors, that is to say, formed of several radial sectors12, each bearing a plurality of stationary blades20. The radial sectors12are each fastened on a casing13at their farthest end from the central axis by an outer annular platform14. The outer platform14exhibits from upstream to downstream, upstream cylindrical hooks16and downstream cylindrical hooks15making it possible to fasten the platform14onto the casing13.

The upstream and downstream are defined here by the flow direction of the gases in the turbine (arrow F onFIGS. 1 and 2).

Due to the axial symmetry of the distributors and the tangential forces resulting from the gaseous flow that crosses them, it is necessary to provide means for locking the sectors in rotation. For that, the downstream hook15of the outer platform is shaped so as to create anti-rotation notches in which anti-rotation pins are inserted. These pins take the form of a head placed in these notches, thus, preventing any movement of rotation of the distributor segment around its axis X.

FIG. 3illustrates a sector12whereof the downstream hook16comprises a U-shaped anti-rotation notch17.

A problem with this notch17is that it is subject to wear by pressure of bearing stress and friction.

This wear implies thatthe low-pressure distributor is not sufficiently maintained and can move about inside the casing;the tangential and axial positions of the distributors are no longer compliant, thus, damaging the clearances in the turbine with risks of friction with the mobile wheels and deteriorating turbine performance.

Such wear typically requires a repairing operation by welding, which causes problems of cracks around and in the repaired area, due to the significant heat gradient during the placing of the metal welding.

PRESENTATION OF THE INVENTION

The invention proposes to overcome at least one of these drawbacks.

To this end, the invention proposes a distributor sector of a turbine of a turbomachine, comprising an outer platform comprising a downstream cylindrical hook adapted to engage with the turbomachine casing, the hook comprising a part in which is formed a U-shaped anti-rotation notch comprising a bottom and two lateral walls extending from said bottom, said notch being at least partially covered by a wear insert inserted in said notch, the insert being removeable.

The invention is advantageously completed by the following characteristics, taken alone or in any technically feasible combination possible:the wear insert has a U shape and is of complementary shape with the notch, said insert being inserted according to an axial direction facing the bottom of the notch, the insert comprising an inner base in contact with the bottom of the notch and two lateral walls extending perpendicularly from the base of the insert, the lateral walls of the insert being in contact with the lateral walls of the notch;the base of the insert is clipped to the bottom of the notch the insert comprising an upper lip and a lower lip, said lips extending according to an axial direction from the base of the insert such as to encircle the base of the notch;each lateral wall of the insert comprises an upper lip and a lower lip, said lips extending tangentially from each wall such as to encircle each lateral wall of the notch;the insert is positioned iso-statically on the notch:at least the upper lip forming a flat support for the insert according to a radial direction,the inner base forming a lineic contact for the insert according to an axial direction;the lateral wall forming an abutment for the insert according to a tangential direction.the insert is a U shape inserted in the notch according to a radial direction, the insert further comprising two wings extending from each lateral wall of the U shape according to a direction perpendicular to the radial direction, said wings resting on the outer annular surface of the upper annular platform of the hook;the insert is positioned iso-statically on the notch:the wings in contact with the annular surface forming a flat support for the insert according to a radial direction;one of the lateral walls forming a lineic contact for the insert according to an axial direction;an end of one of the wings forming an abutment for the insert according to a tangential direction.the L shaped insert inserted into the notch according to a tangential direction in flat support with an inner annular surface of the outer platform of the hook;the insert is iso-statically positioned on the notch:a contact between the inner annular surface forming a flat support for the insert in the radial directionone of the lateral walls of the notch forming a lineic contact for the insert in the tangential direction;the bottom of the notch forming an abutment for the insert in the axial direction.the insert is a U shape inserted in the notch according to a tangential direction perpendicular to an axial direction facing the bottom of the notch, the insert comprising an inner base in contact with a lateral wall of said notch, two lateral walls extending from said inner base.the insert is positioned iso-statically on the notch:one of the lateral walls forming a flat support for the insert in the radial direction;one of the lateral walls of the notch forming a lineic contact for the insert in the tangential direction;the bottom of the notch forming an abutment for the insert in the axial direction.

the insert is of a Cobalt based metal alloy material, for example of type HA188, MAR-M-509, HS25.the insert is formed in a piece of sheet metal of a thickness ranging between 0.08 mm and 4 mm.it comprises an upper annular platform comprising the part.

The invention also relates to a low-pressure turbine of a turbomachine comprising a distributor section according to the invention.

The invention has many advantages.

The insert is removeable so that, once worn, it can easily be changed, thus, greatly simplifying the reparation of low-pressure turbines.

The insert efficiently protects the walls of the anti-rotation notch.

