CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of PCT/FR2019/052105, filed Sep. 12, 2019, which in turn claims priority to French patent application number 1858353 filed Sep. 17, 2018. The content of these applications are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a method for extracting a foreign body from a high-pressure distributor blade of a turbomachine. It also relates to a method for detecting the presence of a foreign body in a cavity of a high-pressure distributor blade.

The invention finds applications in the field of aeronautics and, in particular, in the field of manufacturing high-pressure distributor blades.

STATE OF THE ART

In an aircraft turbojet engine, the high-pressure distributor100, an example of which is represented inFIG. 1, is a set of fixed blades110arranged between two coaxial annular platforms120, called shrouds, and delimiting a gas flow stream between the outlet of the combustion chamber and the inlet of the high-pressure turbine. Blades110, which are generally hollow, each include two adjacent cavities, one end of which opens outside the gas flow stream. They also include holes extending between each cavity and the stream.

In some high-pressure distributors, each blade100includes a liner embedded in each of the cavities, and drilled with a plurality of holes opening into the cavity, over its entire surface extending between the annular platforms120. The purpose of this liner is especially to cool the blade in which it is embedded. In some high-pressure distributors, such as the one represented inFIG. 2, it is the hollow blades that are drilled. Whether drilled or provided with a liner, each blade cavity is closed by a closing plate140which ensures cooling regulation of the blade by controllably obstructing the cavity apertures.

Airplane engine turbine blades are conventionally made of a nickel-based metal superalloy called AM1 (NiCr7Co8W5A15Ta8Ti). However, due to their location, blades of high-pressure distributors—also known as HPD—are subject to very high gas temperatures, especially during the so-called “hot” operating phases of the engine, such as, for example, the take-off phase. In order to resist these very high temperatures, HPD blades of AM1 are generally covered with an insulating coating forming a thermal barrier—also called TB. It is known that the thermal barrier consists of several layers, each having a different function. The external layer, i.e. the layer most exposed to hot gases, of the thermal barrier is usually a ceramic layer. The main function of this ceramic layer is heat insulation. The internal layer of the thermal barrier, i.e. the layer in contact with the AM1, is an underlayer usually of an aluminium-platinum alloy such as AlPt. The function of this underlayer is to protect the blade from oxidation and maintain thermal barrier on the AM1.

Generally, HPD blades are manufactured according to the method represented inFIG. 3. This method first consists of a step210of producing an as cast blade form. At the end of this step210, the as cast blade includes two cavities which are drilled in step220so that they can subsequently cool the blade. When each cavity is fitted with a liner, the liners are inserted into the cavities of the blade in step230. A closing plate is then brazed over each cavity to close said cavities (step240). Once the blade cavities are closed, a thermal barrier is deposited on the outer surface of each blade to protect the blade, in particular from heat. An x-ray inspection is then performed, in step260, to check whether the blade is in compliance with the specifications. This x-ray inspection is especially used to detect whether the cavities are free of any foreign bodies resulting from manufacturing operations.

Indeed, it is possible, in the casting step as well as in the drilling, brazing or thermal barrier installing steps, that dust or other residues may have settled inside the blade, generating a defect on said blade. But, most defects result in the blade not complying with current technical requirements and a non-compliant blade is discarded.

To date, it is actually common practice to discard any blade considered to be non-compliant as a result of detection of a foreign body in a cavity, as it is considered that in order to remove the foreign body, the thermal barrier covering the blade would first have to be removed. One solution contemplated by airplane engine manufacturers for reworking a HPD blade is as follows:Pickling the non-compliant blade so as to remove the thermal barrier covering said blade or at least the ceramic layer of said thermal barrier;Taking off the closing plate;Removing the foreign body from the cavity;Brazing a new closing plate to the bare blade;Depositing a new thermal barrier; andPerforming a new x-ray inspection.

However, such a reworking method would have many drawbacks and, in particular, it would have an impact on the dimension of the blade insofar as pickling the part is equivalent to chemically machining said part of AM1. Another drawback would be the risk of residue when pickling the thermal barrier (especially if the underlayer of AlPt is not removed), which could cause excessive thickness when the new thermal barrier is installed. A further drawback would be the risk of increased non-compliance of the blades due to the installation of the new coatings. Furthermore, implementing such a rework method would be expensive because, as the cost of a thermal barrier is high, it is expensive to install this thermal barrier twice.

SUMMARY OF THE INVENTION

In order to address the problem discussed above of discarding non-compliant blades due to foreign body in a cavity, the applicant provides a method for extracting foreign body wherein only the closing plate is cut and replaced by a new closing plate directly brazed to the blade coated with the thermal barrier.

According to a first aspect, the invention relates to a method for extracting at least one foreign body lodged within a blade of a high-pressure distributor of a turbojet engine, said high-pressure distributor including fixed hollow blades between two annular shrouds forming a gas flow stream, each blade being coated with a thermal barrier and drilled with at least one cavity at least partially obstructed by a first brazed closing plate. This method is characterised in that it includes the following operations of:cutting the first closing plate,extracting the foreign body out of the cavity,endoscopically inspecting an internal space of the cavity to check that no foreign body remains,positioning a second closing plate on the cavity, andbrazing the second closing plate directly to the distributor with the blades coated with the thermal barrier.

This extraction method makes it possible to rework a blade, considered to be non-compliant at the end of production, by removing the foreign bodies lodged in said blade and causing its non-compliance, without any removing or pickling operation of the thermal barrier.

A “foreign body” is any dust, manufacturing residue or particle deposited or caught in a cavity in a high-pressure distributor blade.

Advantageously, cutting the first plate is performed by grinding said plate.

The extraction method according to the invention may include one or more of the following characteristics:positioning the second closing plate is performed by jig boring and shot-peening on the high-pressure distributor;the second closing plate is pre-sintered;brazing the second plate is performed in a vacuum furnace at a temperature below 1200° C.;brazing includes a thermal cycle performed at a temperature between approximately 1160° C. and 1200° C. for 10 to 20 minutes, and then a diffusion cycle at a temperature between approximately 1150° C. and 1200° C. for 2 to 4 hours;it includes, after the brazing operation of the second closing plate, an x-ray inspection of the high-pressure distributor.

