Method for extracting a foreign body lodged in a high-pressure distributor blade

Abstract

A method for extracting at least one foreign body lodged within a blade of a high-pressure distributor of a turbojet engine, the high-pressure distributor including hollow fixed blades between two annular shrouds forming a gas flow path, each blade being coated with a thermal barrier and provided with at least one recess at least partially obstructed by a first soldered closing plate, includes the following operations: cutting off the first closing plate, extracting the foreign body from the recess, carrying out an endoscopic inspection of an internal space of the recess in order to verify that no foreign body remains, positioning a second closing plate on the recess, and soldering the second closing plate directly onto the distributor with the blades coated with the thermal barrier.

Claims

1. 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, the method comprising: cutting the first brazed closing plate, extracting the foreign body out of the cavity, endoscopically inspecting an internal space of the cavity to check that no foreign bodies remain, positioning a second closing plate on the cavity, and brazing the second closing plate directly to the distributor with the blades coated with the thermal barrier.

2. The extraction method according to claim 1, wherein cutting the first brazed closing plate is performed by grinding said plate.

3. The extraction method according to claim 1, wherein positioning the second closing plate is performed by jig boring on the high-pressure distributor.

4. The extraction method according to claim 1, wherein the second closing plate is pre-sintered.

5. The extraction method according to claim 1, wherein brazing the second closing plate is performed in a vacuum furnace at a temperature below 1200° C.

6. The extraction method according to claim 5, wherein brazing the second closing plate includes a thermal cycle performed at a temperature of between approximately 1160° C. and 1200° C. for 10 to 20 minutes, and then a diffusion cycle at a temperature of between approximately 1150° C. and 1200° C. for 2 to 4 hours.

7. The extraction method according to claim 1, further comprising, after brazing the second closing plate, an operation of X-ray inspecting the high-pressure distributor.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further advantages and characteristics of the invention will appear upon reading the description, illustrated by the figures in which:

(2) FIG. 1, already described, schematically represents a partial view of a high-pressure distributor of prior art;

(3) FIG. 2, already described, schematically represents a partial view of a high-pressure distributor blade of prior art;

(4) FIG. 3, already described, represents a block diagram of the usual method for producing high-pressure distributor blades;

(5) FIG. 4 represents a block diagram of the method for extracting a foreign body according to the invention;

(6) FIG. 5 represents an enlarged sectional view of the layers of materials forming the thermal barrier covering a high-pressure distributor blade;

(7) FIGS. 6A and 6B represent enlarged cross-sectional views of a thermal barrier before brazing and after re-brazing, respectively.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT

(8) An example of embodiment of a method for extracting a foreign body lodged in a cavity of a high-pressure distributor blade is described in detail below, with reference to the appended drawings. This example illustrates the characteristics and advantages of the invention. However, it is reminded that the invention is not limited to this example.

(9) In the figures, identical elements are marked by identical references. For reasons of legibility of the figures, scales between the elements represented are not respected.

(10) FIG. 4 represents, as a block diagram, various steps of the extraction method 300 for reworking a blade considered to be non-compliant after the x-ray inspection 260. This method can be applied to any parts of AM1 covered with a thermal barrier such as, for example, a high-pressure distributor blade 110 of the type represented in FIGS. 1 and 2. As previously explained, each high-pressure distributor blade 110—simply referred to as a blade—includes adjacent cavities which can be drilled or have a liner embedded therein. A closing plate 140 is installed by brazing to the open end of each blade cavity to close the cavity and possibly hold the liner therein.

(11) According to the invention, a blade which is considered to be non-compliant at the end of production may be reworked and the foreign body or bodies removed. In order to extract any foreign body detected inside a blade cavity during the x-ray inspection performed at the end of the blade manufacturing method, the extraction method 300 of the invention provides performing a first operation 310 of cutting the original closing plate 140, also referred to as the first plate. This cutting of the closing plate 140 consists in taking off all the material forming the closing plate 140 by means of a grinding wheel. Grinding the closing plate enables only the material forming the closing plate to be removed, without taking off or degrading the thermal barrier coating on the blade.

(12) Once the closing plate 140 has been fully ground, the foreign body or bodies present in the cavity can be removed by means of a suitable tool such as a pin, hook, pliers, etc., during an extraction operation 320. The extraction method 300 can be continued with an endoscope inspection operation 330. This endoscopic inspection 330 makes it possible, by inserting an endoscope into the cavity, to examine the internal space of the cavity and especially its inner walls to check that all foreign bodies have been extracted. It also makes it possible to check whether the grinding operation 310 of the first closing plate has not generated any new dust or other foreign bodies.

(13) After this endoscopic inspection 330, a new closing plate 140, also referred to as the second closing plate, is positioned in front of the cavity opening, approximately at the location where the first closing plate was located. This positioning of the new closing plate 140 is achieved by jig boring and shot-peening said plate on the blade 110 of the high-pressure distributor. The jig boring and shot-peening operation of the closing plate consists in prefixing the plate on the high-pressure distributor blade by means of welding points made, for example, with a solid electrode for jig boring and a hollow electrode for shot-peening.

(14) Once the new closing plate is correctly positioned, the insert can be brazed to the high-pressure distributor during a brazing operation 350. During this brazing operation 350, the new closing plate is brazed directly to the distributor blade coated with the thermal barrier. The new closing plate 140 is a conventional pre-sintered closing plate, identical to the original closing plate. Brazing is performed under vacuum, in an adapted furnace, at a brazing temperature not exceeding 1180° C. +/−10° C. Brazing conditions for the new closing plate 140 are conventional brazing conditions, in which the new closing plate includes a sinter (i.e. a powder agglomerated by simultaneous compression and heating below the melting temperature), and is subjected, together with the high-pressure distributor, to a thermal cycle and a diffusion cycle bringing the assembly to a processing temperature which is below its melting temperature but sufficient for the sinter to be melted and conglomerate the plate with the high-pressure distributor. The thermal cycle may include, for example, a 15-minute vacuum firing at 1180° C. The diffusion cycle, initiated following the thermal cycle, may include, for example, a 3-hour vacuum firing at 1175° C.

(15) In contrast to the brazing operation of the first closing plate, when brazing 350 the new closing plate, the thermal barrier is present on the high-pressure distributor 100. An example of an enlarged sectional view of a blade portion of AM1 coated with this thermal barrier is represented in FIG. 5. This example shows an AM1 layer 110c forming the blade 100, covered with an AlPt underlayer 110b and with a ceramic layer 110a forming the thermal barrier.

(16) In the method of the invention, the high-pressure distributor blade, which has been previously brazed with the original closing plate, is brazed a second time during the brazing operation 350. During this second brazing operation 350, the blade 100 is coated with its thermal barrier. Although those skilled in the art would think that the thermal cycle generated to solder the new closing plate would have a damaging effect on the thermal barrier of the high-pressure distributor, especially through diffusion of the underlayer, the applicant was surprised to find that this was not the case. Indeed, on the one hand, the AM1 blade is adapted to withstand a second thermal cycle with no risk of modification of its structure. On the other hand, the ceramic layer (ZrO2/Y2O3) of the thermal barrier is adapted to undergo a thermal cycle at approximately 1180° C. since its melting temperature exceeds 1200° C. Finally, as shown in FIGS. 6A and 6B, the underlayer of the thermal barrier does not migrate inside the blade of AM1. Indeed, even if, under the brazing conditions stated above, the underlayer 110b slightly changes by diffusion, this has no impact on the compliance of the blade 100 of the high-pressure distributor. An example of the structure of AM1 with thermal barrier before the second thermal cycle is represented in FIG. 6A. An example of the same structure of AM1 with thermal barrier after the second thermal cycle (i.e. after re-brazing) is represented in FIG. 6B. A comparison of the two FIGS. 6A and 6B shows that, although the underlayer 110b has slightly migrated into the part of AM1 110c and into the ceramic layer 110a, the thickness c1+c2 of underlayer 110b is only slightly smaller than before the first thermal cycle and is therefore large enough to enable the thermal barrier to adhere to and protect the blade of AM1.

(17) The applicant has performed further re-brazing tests with modulated temperatures and firing times—for example a thermal cycle for 10 to 20 minutes at temperatures between approximately 1160° C. and 1200° C. and a diffusion cycle for 2 to 4 hours at temperatures between 1150° C. and 1200° C.—and found that the underlayer 110b hardly changes much and that the microstructure is not modified either by aluminium depletion or by transformation to gamma prime. The precipitate in AM1 remains between 0.3 and 0.7 micron. The thickness c1+c2 of the underlayer remains between 40 μm and 75 μm and the proportion c2/(c1+c2) between 50% and 80%. Similarly, the proportion of platinum (Pt) remains between 23% and 40% and the proportion of aluminium (Al) between 17% and 25%, these thicknesses and proportions being compliant with technical requirements DMP32-021.

(18) The operation 350 of brazing the new closing plate 140 therefore enables the new plate to be conglomerated on the high-pressure distributor blade without generating any damaging effect on the structure of the high-pressure distributor. The reworked high-pressure distributor will therefore have the same performance as a standard high-pressure distributor.

(19) The extraction method 300 just described can be supplemented by an operation 360 of x-ray inspecting the high-pressure distributor blade cavity. This inspection operation 360 is implemented at the end of the extraction method 300 to check whether all foreign bodies have been removed from the cavities of the high-pressure nozzle blade.

(20) Although described through a number of examples, alternatives and embodiments, the method for extracting foreign bodies according to the invention includes various, modifications and improvements which will be obvious to those skilled in the art, it being understood that these alternatives, modifications and improvements are within the scope of the invention.