Method for verifying the conformity of an abradable coating in the outer casing of an aircraft turbojet engine

Abstract

Method for checking the conformity of an abradable coating in an aircraft turbojet outer casing Upstream three-dimensional template (14) and downstream three-dimensional template (15) intended for use within an outer casing (3) of a turbojet whose internal surface (2) is equipped with a layer of abradable coating (7), upstream fixing means (12) for an upstream acoustic attenuation ring (10) and downstream fixing means (13) for a downstream acoustic attenuation panel (11).Each upstream / downstream three-dimensional template is in the form of at least one cylindrical sector capable of being mounted on at least one of the respective upstream / downstream fastening means, and has, on its inner face (24, 30), at its respective upstream / downstream end (25, 31), an annular collar (26, 32), which has on its respective upstream or downstream face (28, 34) a visual reference zone (29) intended to visually check the aerodynamic step height located between each three-dimensional template and the abradable coating layer. Figure to be published with the abbreviation: Figure 4.

Description

Title of the invention: Method for checking the conformity of an abradable coating in an outer casing of an aircraft turbojet TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of the conformity control of a coating made of abradable material in an external casing of a turbojet engine, and in particular that of the conformity control of such a coating after it has been repaired. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] In an aircraft turbojet engine, whether at the compressor or turbine level, blades mounted on a rotor are driven in rotation within an outer casing of round section. Particularly at the compressor and turbine level, the blade of these blades is preferably provided as close as possible to the internal part of the outer casing. Indeed, by minimizing the clearance between the blades and the outer casing, the efficiency and performance of the turbojet engine are increased.

[0003] In certain exceptional circumstances, in particular in the case of static loads, maneuvering loads or unbalance within the turbojet, it may happen that the free end of the blades strikes the internal surface of the outer casing. This can damage not only the blades, but also the outer casing.

[0004] At the blade level, the internal surface of the outer casing of turbojets is therefore sometimes protected by a rigid protection, usually cylindrical in shape, which may be in the form of a shell of a single continuous piece extending over 360 degrees or be formed by the 360-degree assembly of several cylinder sectors, generally from two to ten, for example five in number. The rigid protection comprises a coating intended to be located opposite the free end of the blades. In order to protect the blades, the protective coating is made of a material with abradable properties, hereinafter referred to as an abradable material, that is to say it is designed so that when it is brought into contact with a moving body, it wears preferentially to this moving body. The abradable coating guarantees the reliability of the device in the event of contact with the blade: it will be hollowed out by the blade and the latter will undergo almost no wear.Without this material, in the event of contact between a rotating blade and the internal surface of the outer casing, the impact could be too violent and could damage the said blade.

[0005] The rigid protection comprising an abradable coating is usually called an abradable material support cartridge. It usually comprises a support fixed on the internal surface of the outer casing, and a layer of abradable coating located on the internal face of this support, that is to say the face directed towards the inside of the turbojet. The role of the layer of abradable coating is both to optimize the radial clearance with the blades and to optimize the air flow between the internal surface of the outer casing and the blades, that is to say that the layer of abradable coating also makes it possible to achieve the continuity of a vein profile corresponding to a correct vein aerodynamic envelope.

[0006] In other unusual circumstances, for example when the turbojet engine ingests foreign bodies such as hailstones or birds, the protective coating of the outer casing may also be damaged. It is in fact sensitive to impacts.

[0007] Following events such as those mentioned above, it is sometimes necessary to repair the damaged abradable coating surface. The procedure for carrying out this repair depends intrinsically on the type of material constituting the abradable coating. Indeed, there are many types of abradable coatings that can be used within the turbojet engine of an aircraft.

[0008] Generally, this repair is carried out by first removing the elements assembled with the outer casing of the turbojet engine, i.e. the compressor, the combustion chamber and the turbine, in order to gain access to the abradable coating located inside said outer casing. A paste is then deposited on the abradable coating, in the damaged areas. This paste of abradable material is then crosslinked at room temperature or in an oven. It then becomes very hard and can be abraded in order to give it the desired profile.

[0009] In order to ensure that the minimum and maximum clearances provided between the blades and the outer casing are respected, it is necessary to measure the distance between the blades and the layer of abradable material at the repair site. It is also necessary to check the steps with the adjacent parts upstream and downstream of the abradable material support cartridge.

[0010] Usually, the step measurement method used consists of taking an impression in the interface areas of the repair on 24 different positions using a hardenable paste. After hardening the impressions by polymerization, each of them gives a topographical representation of the possible difference in level that may exist between the surface of the abradable material resulting from the repair and the surface of the interface parts. Each impression is then analyzed in the laboratory to carry out a depth and / or thickness measurement in order to determine whether the repair has not generated steps whose value is out of tolerance, which in this case requires an additional repair step, and a new measurement following this.

[0011] This measurement method used is extremely long to implement. Indeed, taking the 24 prints generally requires half a day and their analysis in the laboratory is also very time-consuming.

[0012] This is the current method that would be used if step control were required, although it is not.

[0013] Following numerous studies, the applicant has further discovered that the control method used for the minimum clearance provided between the blades and the outer casing was not sufficient, because it does not make it possible to detect a difference in height between the surface of abradable material of the abradable material support cartridge and the internal surface of the elements provided upstream or downstream of said abradable material support cartridge.

[0014] Indeed, as shown in [Fig. 1], the abradable material support cartridge is usually bordered upstream by an upstream acoustic attenuation ferrule and downstream by a downstream acoustic attenuation panel.

[0015] Just like the abradable material support cartridge, the upstream acoustic attenuation ferrule and the downstream acoustic attenuation panel can be in the form of a single continuous part extending over 360 degrees or be formed from the 360-degree assembly of several cylinder sectors. Unlike the abradable material support cartridge, the upstream acoustic attenuation ferrule and the downstream acoustic attenuation panel are not parts subject to wear.

[0016] The inner surface of the upstream acoustic attenuation shell, that of the abradable material support cartridge and that of the downstream acoustic attenuation panel are intended to be substantially at the same level in order to form an aerodynamic vein profile. Indeed, the abradable coating layer makes it possible to guarantee continuity of the aerodynamic profile at the interfaces with the upstream acoustic attenuation shell and the downstream acoustic attenuation panel. A difference in thickness at one of these interfaces results in a step.However, studies carried out by the applicant have revealed that such a step, located between the abradable material support cartridge and the upstream acoustic attenuation shroud and / or between the abradable material support cartridge and the downstream acoustic attenuation panel, creates a disturbance in the flow of fluid between the blades and the internal surface of the outer casing, which reduces the efficiency and performance of the turbojet. This is referred to as an aerodynamic step.

[0017] There is therefore a need for a method for checking the conformity of the height of each of the aerodynamic steps after repair of the abradable coating, in order to determine whether or not their value is within a range of values ​​that can be considered acceptable. Such a method is therefore based on checking the conformity of the continuity of the profile of the abradable coating with the parts in interface, for example with the sound attenuation panel and the sound attenuation shroud.

[0018] A difficulty is represented by the fact that the upstream acoustic attenuation shroud and the downstream acoustic attenuation panel cannot act as reference surfaces for measuring and controlling the height of an aerodynamic step. Indeed, the upstream acoustic attenuation shroud and the downstream acoustic attenuation panel have wide shape and positioning tolerances. The method for controlling the aerodynamic step height after repair of the abradable coating must therefore not be based on a comparison with the internal diameter of the upstream acoustic attenuation shroud and the downstream acoustic attenuation panel at their interface with the coating layer of the abradable material support cartridge.

[0019] Furthermore, during the life of the outer casing of a turbojet engine, the upstream acoustic attenuation shroud and the downstream acoustic attenuation panel may each be replaced respectively by a new upstream acoustic attenuation shroud or by a new downstream acoustic attenuation panel, the internal diameter of which may be slightly different from that of the shroud or panel that they replace. Indeed, the manufacturing requirements for these parts are low, and many dimensional variations may exist from one acoustic attenuation shroud to another or from one acoustic attenuation panel to another.

[0020] Thus, the method for checking the conformity of the aerodynamic step height after repair of the abradable coating must advantageously also make it possible to check whether the internal diameter of the repaired abradable coating is within the tolerance range determined by the different possible internal diameters for the upstream acoustic attenuation shell and the downstream acoustic attenuation panel.

[0021] The conformity control method according to the invention must advantageously be reliable, precise, simple and quick to implement, and it must not require the removal of the abradable material support cartridge, nor the removal of the external casing, to allow in situ control of the vein profile. Summary of the invention

[0022] The invention offers a solution to the problems mentioned above by providing a new method for controlling the vein profile intended to control the height of the aerodynamic step provided between an upstream acoustic attenuation ferrule and an abradable material support cartridge, and to control the height of the aerodynamic step provided between a downstream acoustic attenuation panel and said abradable material support cartridge after repair of the abradable coating of said abradable material support cartridge.

[0023] Generally speaking, the method of the invention makes it possible to control the conformity of the height of the aerodynamic step provided between an abradable material support cartridge and any upstream or downstream element located in the immediate vicinity thereof, this element being a part in interface with the abradable material support cartridge. This upstream or downstream element is usually an acoustic attenuation element. For reasons of clarity of the description, such an upstream element will be designated as an upstream acoustic attenuation shell and such a downstream element will be designated as a downstream acoustic attenuation panel, which corresponds to the most usual case.

[0024] The control method of the invention is based on the use of two three-dimensional templates, replacing the upstream acoustic attenuation shell and the downstream acoustic attenuation panel and each making it possible to provide one or more visual markers making it possible to control the aerodynamic step height that a repaired abradable material support cartridge is likely to generate with the upstream acoustic attenuation shell and the downstream acoustic attenuation panel.

[0025] Also, the invention relates to both the step height control method and the three-dimensional templates used in this method.

[0026] One aspect of the invention relates to a three-dimensional template, such as: • it is in the form of at least one cylinder sector having a first face called the internal face, a second face called the external face opposite the first face, a first end and a second end opposite the first end; • on its first face, called the internal face, at one of its ends, it comprises a collar in the form of at least one annular sector having a first face, called the upstream face, and a second face, called the downstream face, opposite the first face; and • the collar has at least one visual identification zone.

[0027] According to one aspect of the invention, a three-dimensional template is in the form of a single continuous cylindrical piece extending over 360 degrees.

[0028] According to another aspect of the invention, a three-dimensional template is in the form of a 360-degree cylindrical assembly of several cylinder sectors.

[0029] According to an additional aspect of the invention, at least one visual identification zone is delimited by at least two arcs belonging to concentric circles.

[0030] According to one aspect of the invention, the collar has an internal face and this internal face constitutes one of the arcs.

[0031] According to another aspect of the invention, at least one visual identification zone is delimited by a strip.

[0032] According to an additional aspect of the invention, at least one collar extends inside the outer casing along an axis orthogonal to the internal face of the three-dimensional template on which it is provided.

[0033] According to one aspect of the invention, one of the arcs is materialized by the periphery of the internal face of the collar.

[0034] According to another aspect of the invention, at least one visual identification zone differs from the rest of the collar by its color, its texture, its depth or its relief.

[0035] According to an additional aspect of the invention, along the axis A, the upstream three-dimensional template has a length substantially equal to that of the upstream acoustic attenuation ferrule.

[0036] According to one aspect of the invention, along axis A, the downstream three-dimensional template has a length substantially equal to that of the downstream acoustic attenuation panel.

[0037] According to another aspect of the invention, the annular collar of the upstream three-dimensional template has an internal diameter smaller than that of the upstream acoustic attenuation ferrule, and the annular collar of the downstream three-dimensional template has an internal diameter smaller than that of the downstream acoustic attenuation ferrule.

[0038] Another aspect of the invention relates to an assembly formed from an outer casing of an aircraft turbojet engine and a set of three-dimensional templates as described above, in which: • the outer casing extends along a longitudinal axis of revolution A and has an internal surface which is equipped with a layer of abradable material, upstream fixing means and downstream fixing means; • the set of three-dimensional templates comprises an upstream three-dimensional template mounted on at least one of the upstream fixing means and a downstream three-dimensional template mounted on at least one of the downstream fixing means; • the visual identification zone of the upstream three-dimensional template is provided on the downstream face of the collar; • the visual identification zone of the downstream three-dimensional template is provided on the upstream face of the collar; and • the layer of abradable material is located between the upstream three-dimensional template and the downstream three-dimensional template.

[0039] According to one aspect of the invention, the assembly is such that: • at the level of the upstream fixing means, the outer casing has a location provided to house an upstream acoustic attenuation element, in which the upstream three-dimensional template is housed; • at the level of the downstream fixing means, the outer casing has a location provided to house a downstream acoustic attenuation element, in which houses the downstream three-dimensional template.

[0040] According to another aspect of the invention, the layer of abradable material has an internal face located opposite the visual identification zone of each of the three-dimensional templates.

[0041] An additional aspect of the invention relates to a conformity control method intended to be used within an outer casing of a turbojet engine having an internal surface equipped with a layer of abradable material having an internal face which delimits an internal diameter, an upstream acoustic attenuation element fixed by means of upstream fixing means and a downstream acoustic attenuation element fixed by means of downstream fixing means, the method being intended to control the conformity of the height of an upstream aerodynamic step M1 and the height of a downstream aerodynamic step M2 of the layer of abradable material, which method comprises the following steps: • removal of the upstream acoustic attenuation element and the downstream acoustic attenuation element, • mounting an upstream three-dimensional template on at least one of the upstream fixing means and a downstream three-dimensional template on at least one of the downstream fixing means, the three-dimensional templates being upstream and downstream three-dimensional templates as described previously, • visual inspection of the internal diameter of the abradable material layer: • by comparison, at the interface between the upstream three-dimensional template and the layer of abradable material, of the position of the internal face of the layer of abradable material relative to the visual identification zone located on the downstream face of the collar of the upstream three-dimensional template, and • by comparison, at the interface between the downstream three-dimensional template and the layer of abradable material, of the position of the internal face of the layer of abradable material relative to the visual identification zone located on the upstream face of the collar of the downstream three-dimensional template, • validation of the conformity of the internal diameter of the layer of abradable material if the position of the internal face of the layer of abradable material is located opposite the visual identification zone of each of the three-dimensional templates, or non-validation otherwise.

[0042] The advantages of the invention are numerous.

[0043] Each three-dimensional template being intended to be mounted on at least part of the fixing means of the upstream acoustic attenuation ferrule and the downstream acoustic attenuation panel, no additional fixing means or any tool no special is required, and when checking the conformity of the abradable coating, any error that could be caused by incorrect positioning of the three-dimensional templates is avoided, for better reliability of the control.

[0044] Due to the simplicity of their shape and design, the three-dimensional templates can be manufactured easily and at low cost. No other parts are required for implementing the vein profile conformity control method according to the invention, so it is an inexpensive method.

[0045] Since the removal of the upstream acoustic attenuation ferrule and the downstream acoustic attenuation panel is easy and quick, as is the mounting of the three-dimensional templates, the conformity control method according to the invention is also easy and quick to implement. This control method is all the faster because it can be done in situ, and does not require any removal or handling of the abradable material support cartridge.

[0046] The conformity control method according to the invention advantageously makes it possible to quickly check, by a simple visual examination, whether the thickness of the abradable coating, at the interface between an upstream three-dimensional template and the layer of abradable material, is within a tolerance range or not. By providing a suitable visual marking zone on each three-dimensional template, this range can easily be adapted to the different upstream acoustic attenuation shrouds and to the different downstream acoustic attenuation panels which can be mounted in the outer casing of the turbojet engine, these upstream acoustic attenuation shrouds and downstream acoustic attenuation panels being able to have a slightly different internal diameter.

[0047] Furthermore, during the life of the outer casing of a turbojet engine, the upstream acoustic attenuation shroud and the downstream acoustic attenuation panel may each be replaced respectively by a new upstream acoustic attenuation shroud or a new downstream acoustic attenuation panel, the internal diameter of which may be slightly different from that of the shroud or panel which they replace.

[0048] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0049] [Fig.l] is a schematic cross-sectional view in right perspective of an outer casing of a turbojet engine at the level of an abradable material support cartridge bordered by an upstream acoustic attenuation shroud and by a downstream acoustic attenuation panel, a blade being shown opposite the abradable material support cartridge.

[0050] [Fig.2] is a detail view of the circled portion on the left in [Fig.l].

[0051] [Fig.3] is a detail view of the circled part on the right in [Fig. 1].

[0052] [Fig.4] is a schematic sectional view in right perspective of the casing of [Fig.l] , in which the upstream acoustic attenuation shell and the downstream acoustic attenuation panel have each been replaced by a three-dimensional template according to the invention.

[0053] [Fig.5] is a detail view of the circled portion on the left in [Fig.4].

[0054] [Fig.6] is a view similar to [Fig.5], but in which a portion of the layer of abradable coating located on the inner face of the abradable material support cartridge has been removed.

[0055] [Fig.7] is a schematic sectional view in left perspective of the assembly shown in [Fig.4].

[0056] [Fig.8] is a detail view of the circled part on the right in [Fig.7].

[0057] [Fig.9] is a view similar to [Fig.8], but in which part of the layer of abradable coating located on the inner face of the abradable material support cartridge has been removed.

[0058] [Fig. 10] is a schematic perspective view of a three-dimensional template according to the invention in the form of an assembly of several cylinder sectors. DETAILED DESCRIPTION

[0059] The figures are presented for information purposes only and in no way limit the invention.

[0060] Conventionally, in an aircraft turbojet, air circulates between a casing forming an external envelope - designated as the outer casing - and an internal envelope - designated as the inner casing. In conventional operation, this air enters the turbojet through an air inlet located on the so-called upstream side, and leaves the turbojet at an exhaust located on the so-called downstream side.

[0061] In the remainder of this text, by internal face or surface, we mean the face or surface of a part which is directed towards the inside of the outer casing, and conversely by external surface, we mean the face or surface of a part which is directed towards the outside of the outer casing.

[0062] Similarly, by upstream element or face is meant an element or face which is located on the upstream side of the aircraft turbojet engine, i.e. on the side of its air inlet, while by downstream element or face is meant an element or face which is located on the front side of the aircraft turbojet engine, i.e. on the side of its exhaust.

[0063] As shown in Figures 1 to 3, at the level of certain rotating blades 1 of the turbojet, the internal surface 2 of the outer casing 3 may comprise an abradable element 4. This abradable element 4 is usually in the form of a cartridge supporting abradable material 5 comprising a support 6 fixed on the internal surface 2 of the outer casing 3 and on which is provided a layer of abradable material 7 whose internal face 8, in the event of contact with the free end 9 of a rotating blade 1, is hollowed out by the latter.

[0064] The outer casing 3 is generally in the form of a solid of revolution with a longitudinal axis of revolution A and comprising substantially cylindrical zones and substantially conical zones.

[0065] Upstream, the abradable material support cartridge 5 is bordered by an upstream part, generally an upstream acoustic attenuation part 10 for example in the form of a ferrule, also said upstream part will be designated as an “upstream acoustic attenuation ferrule” in the remainder of this text. Downstream, the abradable material support cartridge 5 is bordered by a downstream part, generally a downstream acoustic attenuation part 11 for example in the form of a panel, also said downstream part will be designated as a “downstream acoustic attenuation panel” in the remainder of this text. The upstream acoustic attenuation ferrule 10 is fixed on the internal surface 2 of the outer casing 3 by means of upstream fixing means 12, while the downstream acoustic attenuation panel 11 is fixed on the internal surface 2 of the outer casing 3 by means of downstream fixing means 13.

[0066] The abradable material support cartridge 5, the upstream acoustic attenuation ferrule 10 and the downstream acoustic attenuation panel 11 are usually cylindrical in shape, and may be in the form of a single continuous cylindrical piece extending over 360 degrees or be formed from the 360-degree assembly of several cylinder sectors. The abradable material support cartridge 5, the upstream acoustic attenuation ferrule 10 and the downstream acoustic attenuation panel 11 are centered inside the outer casing 3 and extend along the axis A.

[0067] It will be noted that the outer casing 3 can be a single piece, or composed of several parts assembled longitudinally along the axis A. In the example shown in the figures, the outer casing 3 is notably formed of an air inlet casing 3a, a fan casing 3b and an intermediate casing 3c.

[0068] As already mentioned previously, during the life of a turbojet, the upstream acoustic attenuation shroud 10 and the downstream acoustic attenuation panel 11 may each be replaced by new parts whose internal diameter may be slightly different from that of the shroud or panel that they replace. In addition, when repairing the layer of abradable material 7, the thickness thereof may vary. Thus, there may be a difference in internal diameter between the layer of abradable material 7 and the upstream acoustic attenuation shroud 10 and the downstream acoustic attenuation panel 11 located nearby. Seen in section, this difference in internal diameter is materialized by a difference in height forming an upstream step M1 at the interface between the layer of abradable material 7 and the upstream acoustic attenuation shroud 10 and a downstream step M2 at the interface between the layer of abradable material 7 and the downstream sound attenuation panel 11. These steps M1 and M2 can be better seen in Figures 2 and 3. In these figures, the upstream step M1 is a rising step while the downstream step M2 is a falling step for the airflow circulating in the outer casing 3 from upstream to downstream, i.e. from left to right in the figures. Of course, there are multiple possibilities, and each of the steps M1 and M2 can be a rising step or a falling step. Furthermore, although in the figures the step height is the same for the steps M1 and M2, the step height is generally different for each of these steps M1 and M2. These steps M1 and M2 cause a disturbance for the airflow along the internal surface 2 of the outer casing 3, they are usually referred to as aerodynamic steps.

[0069] Depending on its height, negative or positive, one of the aerodynamic steps M1 and M2 may present a disturbance deemed too significant, because it significantly harms the efficiency and performance of the turbojet. In such a case, the thickness of the layer of abradable material 7 must be rectified.

[0070] The method according to the invention aims to check whether the aerodynamic steps M1 and M2 have a height that can be judged as acceptable or not according to specificities defined by the manufacturer and / or the user of the turbojet.

[0071] This conformity control method is based on the use of at least two parts, each of which temporarily replaces, for the duration of the control, the upstream acoustic attenuation shell 10 and the downstream acoustic attenuation panel 11.

[0072] Thus, during this conformity control method, the upstream acoustic attenuation shell 10 is replaced by a dummy acoustic attenuation shell designated as an upstream three-dimensional template 14, while the downstream acoustic attenuation panel 11 is replaced by a dummy acoustic attenuation panel designated as a downstream three-dimensional template 15.

[0073] According to a preferred embodiment of the invention, each three-dimensional template 14, 15 has a length along the axis A which is substantially equal to that of the part whose place it can take during the conformity check of the height of the aerodynamic steps M1 and M2, namely the upstream acoustic attenuation shroud 10 and the downstream acoustic attenuation panel 11.

[0074] Between the external face 16 of the upstream three-dimensional template 14 and the internal surface 2 of the outer casing 3 are provided fixing means 17 which are constituted by all or part of the upstream fixing means 12, or which are capable of collaborating with all or part of the latter. Similarly, between the external face 18 of the downstream three-dimensional template 15 and the internal surface 2 of the outer casing 3 are provided fixing means 19 which are constituted by all or part of the downstream fixing means 13 or which are able to collaborate with all or part of the latter.

[0075] On its external face 16, the upstream three-dimensional template 14 preferably has an upstream wedging portion 20 capable of coming to bear against the internal surface 2 of the outer casing 3, while on its external face 18, the downstream three-dimensional template 15 preferably has a downstream wedging portion 21 capable of coming to bear against the internal surface 2 of the outer casing 3. By way of example, in the figures, the upstream wedging portion 20 is provided at the upstream end 22 of the upstream three-dimensional template 14, while the downstream wedging portion 21 is provided at the downstream end 23 of the downstream three-dimensional template 15.

[0076] On its internal surface 24, at its downstream end 25, the upstream three-dimensional template 14 comprises an annular collar 26, having an upstream face 27 and a downstream face 28. When the upstream three-dimensional template 14 extends over 360 degrees, this collar 26 preferably has an internal diameter smaller than that of the upstream acoustic attenuation ferrule 10 so as to extend further towards the inside of the outer casing 3 than the internal face 8 of the layer of abradable material 7, that is to say that when considered in section, the collar 26 is higher than the internal face 8 of the layer of abradable material 7. On its downstream face 28, the collar 26 of the upstream three-dimensional template 14 has a visual identification zone 29. This visual identification zone 29 is preferably located in the part of the collar 26 which extends beyond the layer of abradable material 7.

[0077] Similarly, on its internal face 30, at its upstream end 31, the downstream three-dimensional template 15 comprises an annular collar 32, having an upstream face 33 and a downstream face 34. When the downstream three-dimensional template 15 extends over 360 degrees, this collar 32 preferably has an internal diameter smaller than that of the downstream acoustic attenuation panel 11 so as to extend further towards the inside of the outer casing 3 than the internal face 8 of the layer of abradable material 7, that is to say that when considered in section, the collar 32 is higher than the internal face 8 of the layer of abradable material 7. On its upstream face 33, the collar 32 of the downstream acoustic attenuation panel 11 has a visual identification zone 35. This visual identification zone is preferably located in the part of the collar 32 which extends beyond the layer of abradable material 7.

[0078] According to a preferred embodiment of the invention, each collar 26, 32 extends inside the outer casing perpendicular to the internal surface 24, 30 of the three-dimensional template on which it is provided 14, 15.

[0079] In the figures, by way of example, the wedging part 20, 21 of a three-dimensional template 14, 15 is connected to the collar of said three-dimensional template 14, 15 by an intermediate part 36, 37. Each intermediate part 36, 37 can be of any shape. In the figures, it is represented by a piece of straight section, which is a simple and economical form.

[0080] The role of the visual marking zones 29, 35 is to delimit a conformity range for the internal diameter of the layer of abradable material 7 at the level of each aerodynamic step M1, M2. As will be seen later, the control of this conformity is carried out visually by controlling at which level of the visual marking zones 29, 35 the nose 38, 39 of each aerodynamic step M1, M2 is located. By nose 38, 39 of each aerodynamic step M1, M2 is meant respectively the internal downstream edge and the internal upstream edge of the layer of abradable material 7.

[0081] For each visual identification zone 29, 35, several variants can be envisaged.

[0082] According to a first variant shown in the figures, a visual identification zone 29, 35 is delimited by at least two arcs 40a, 40b, 41a, 41b each belonging to a circle centered on the axis A, these circles being concentric. Within each pair of arcs 40a, 40b, 41a, 41b, the internal arc 40a, 41a is thus distinguished from the external arc 40b, 41b.

[0083] According to another variant not shown in the figures, one of the arcs 40a, 40b, 41a, 41b, namely the internal arc 40a, 41a of a visual identification zone 29, 35 is materialized by a rim located on the internal face 42, 43 of the collar 26, 32.

[0084] According to another variant not shown in the figures, at least one visual identification zone 29, 35 is delimited by a band, that is to say a visual identification zone 29, 35 formed by a strip whose height materializes a conformity range for the internal diameter of the layer of abradable material 7. Thus a strip differs from two arcs in that the arcs are each materialized by a simple curve of reduced thickness, while a band is materialized by a strip whose thickness is defined between said arcs.

[0085] Thus, if a visual identification zone 29, 35 is for example obtained by a hollow shape in the collar 26, 32, each arc 40a, 40b, 41a, 41b can be materialized by a fine engraved curve, while each band can be materialized by a much thicker engraved curve.

[0086] According to another additional variant not shown in the figures, at least one visual identification zone 29, 35 may have a graduation, for example accompanied by numerical values.

[0087] In order for each visual identification zone 29, 35 to be clearly visible and easily distinguished from the face of the collar where it is located, the visual identification zones 29, 35 may have a color, a texture, a hollow part or a protruding part which differentiates them from the rest of the collar, at least at the level of the face of the collar 26, 32 where they are located.

[0088] According to a first variant of the invention, such as the acoustic attenuation ferrule upstream 10 and the downstream acoustic attenuation panel 11, the upstream three-dimensional template 14 and the downstream three-dimensional template 15 may be in the form of a single continuous substantially cylindrical piece extending over 360 degrees or be formed from the 360-degree assembly of several cylinder sectors.

[0089] According to a second variant of the invention, the upstream three-dimensional template 14 and the downstream three-dimensional template 15 can be in the form of a single cylinder sector which, when checking the conformity of each aerodynamic step M1, M2, will then be successively mounted and then dismounted in several circumferential positions so as to check the conformity of each aerodynamic step M1, M2 over its entire circumference.

[0090] The first variant has the particular advantage of being able to check the conformity of the entire perimeter of each aerodynamic step M1, M2 during a single step, while the second variant has the particular advantage of being more economical and less bulky, since it only requires a set of three-dimensional templates comprising two small three-dimensional templates 14, 15.

[0091] The invention is more particularly concerned with the part of the outer casing 3 provided at the air inlet of a turbojet, also referred to as the fan casing, and which is substantially cylindrical. However, the invention can be adapted to any other part of the outer casing 3 which is capable of being equipped with an abradable element 4. In the case where this other part is not substantially cylindrical, but comprises one or more conical parts, it is obvious to those skilled in the art to adapt the sectional profile of the upstream three-dimensional template 14 and the downstream three-dimensional template 15 so that these parts have a shape close to the upstream acoustic attenuation shroud 10 and the downstream acoustic attenuation panel 11 which they are intended to replace.

[0092] Now that we have described the set of three-dimensional templates 14, 15 necessary for the invention, we will describe the method for checking the conformity of the height of the aerodynamic steps M1 and M2 themselves.

[0093] This method makes it possible to check the conformity of the height of the upstream aerodynamic step M1 provided between the upstream acoustic attenuation shell 10 and the layer of abradable material 7, and to check the conformity of the height of the aerodynamic step M2 provided between the abradable material support cartridge 7 and the downstream acoustic attenuation panel 11.

[0094] As already mentioned, during the repair of the layer of the abradable material coating 7, elements initially housed in the outer casing 3 of the turbojet engine were removed in order to be able to access the abradable coating located inside said outer casing. This also allows easy access to the attenuation shroud. upstream acoustic panel 10 and downstream acoustic attenuation panel 11.

[0095] Firstly, the upstream acoustic attenuation sleeve 10 and the downstream acoustic attenuation panel 11 must be removed and replaced respectively by the upstream three-dimensional template 14 and the downstream three-dimensional template 15.

[0096] It is then possible to carry out a visual inspection of the internal diameter of the layer of abradable material 7 at each of the interfaces located between the abradable material support cartridge 5 and the upstream acoustic attenuation ferrule 10 and the downstream acoustic attenuation panel 11. This visual inspection is carried out by checking at which level of the visual identification zones 29, 35 the nose 38, 39 of each nearest aerodynamic step M1, M2 is located.

[0097] Thus, the visual inspection of the internal diameter of the layer of abradable material 7 at the interface located between the abradable material support cartridge 5 and the upstream acoustic attenuation ferrule 10 is carried out by visually looking at the level at which the nose 38 of the upstream aerodynamic step M1 is located relative to the visual reference zone 29 of the upstream three-dimensional template 14. Similarly, the visual inspection of the internal diameter of the layer of abradable material 7 at the interface located between the abradable material support cartridge 5 and the downstream acoustic attenuation panel 11 is carried out by visually looking at the level at which the nose 39 of the downstream aerodynamic step M2 is located relative to the visual reference zone 35 of the downstream three-dimensional template 15.

[0098] If the nose 38, 39 of an aerodynamic step M1, M2 is located in the visual identification zone 29, 35 defining the conformity range for the internal diameter of the layer of abradable material 7, this means that for this step M1, M2, the internal diameter of the layer of abradable material 7 is considered acceptable according to specifications defined by the manufacturer and / or the user of the turbojet.

[0099] Otherwise, the internal diameter of the layer of abradable material 7 is not considered acceptable and must be rectified.

[0100] For example, the nose 38, 39 of an aerodynamic step M1, M2 is located in the visual identification zone 29, 35 defining the conformity range if, when the abradable material support cartridge 5 is considered in profile as in the figures, it is located at a height between the internal arc 40a, 41a and the external arc 40b, 41b of the visual identification zone 29, 35 considered.

[0101] In the case where the compliance range is materialized by a band, the nose 38, 39 of an aerodynamic step M1, M2 is located in the visual identification zone 29, 35 defining the compliance range if it is located between the two edges which delimit said band.

[0102] It will be noted that the conformity range defined and delimited by the visual reference zone 29, 35 is chosen in order to take into account the maximum and minimum dimensions that the upstream acoustic attenuation shell 10 and the downstream acoustic attenuation panel 11 may have, taking into account their manufacturing tolerances. Thus, the thickness values ​​tolerated for the layer of abradable material 7 at the interfaces with the upstream acoustic attenuation shell 10 and the downstream acoustic attenuation panel 11, defining minimum and maximum values ​​delimited by each visual identification zone 29, 35, must be considered as generating aerodynamic steps M1, M2 acceptable for the entire range of possible dimensions for the upstream acoustic attenuation shell 10 and the downstream acoustic attenuation panel 11.

[0103] According to a variant of the invention, the visual control indicating at what level the nose 38, 39 of an aerodynamic step is located relative to a visual reference zone 29, 35 can be facilitated by the use of an additional tool, for example by the use of a rod, a laser pointer, a set square, a ruler or a shim. It can also be assisted by the use of a thickness control tool, for example a glitter shim or a graduated ruler.

[0104] It will be noted that the conformity check of steps M1 and M2 is not necessarily carried out at the same time for all steps M1 and M2.

[0105] For example, it is possible to first dismantle the upstream acoustic attenuation shroud 10, then replace it using the upstream three-dimensional template 14 before carrying out the conformity check at the upstream aerodynamic step M1. The upstream three-dimensional template 14 can then be removed to replace the upstream acoustic attenuation shroud 10 before carrying out similar operations for the downstream acoustic attenuation panel 11 and the downstream three-dimensional template 15 to check the conformity of the layer of abradable material 7 at the downstream aerodynamic step M2.

[0106] It is also possible to dismantle, during the same step, the upstream acoustic attenuation shell 10 and the downstream acoustic attenuation panel 11 to replace them with the upstream three-dimensional template 14 and the downstream three-dimensional template 15 in order to check the conformity of the layer of abradable material 7 at the level of the aerodynamic steps M1 and M2 during the same step.

[0107] It has been seen previously that each three-dimensional template 14, 15 can be a single continuous piece extending over 360 degrees or be formed from the 360-degree assembly of several cylinder sectors as shown in [Fig. 10].

[0108] It has also been seen that each three-dimensional template 14, 15 can also be in the form of a single cylinder sector such as one of the cylinder sectors as shown in [Fig. 10]. According to this variant of the invention, when checking the conformity of the layer of abradable material 7 at the level of the aerodynamic steps M1 and M2, the three-dimensional template 14, 15 is then mounted successively in several circumferential positions on the internal surface 2 of the external casing 3 thanks to the fixing means 17, 19. It is then possible to control each aerodynamic step M1, M2 sector by sector, over its entire circumference.

[0109] Unless otherwise specified, the same element appearing in different figures has a single reference.

Claims

Claims

1. Assembly formed of an outer casing (3) of an aircraft turbojet and a set of three-dimensional templates (14, 15), characterized in that: - the outer casing (3) extends along a longitudinal axis of revolution A and has an internal surface (2) which is equipped with a layer of abradable material (7), upstream fixing means (12) and downstream fixing means (13); - the set of three-dimensional templates (14, 15) comprises an upstream three-dimensional template (14) mounted on at least one of the upstream fixing means (12) and a downstream three-dimensional template (15) mounted on at least one of the downstream fixing means (13); - the visual identification zone (29) of the upstream three-dimensional template (14) is provided on the downstream face (28) of the collar (26); - the visual identification zone (35) of the downstream three-dimensional template (15) is provided on the upstream face (33) of the collar (32);- the layer of abradable material (7) is located between the upstream three-dimensional template (14) and the downstream three-dimensional template (15); and in that. - each three-dimensional template (14, 15) is in the form of at least one cylinder sector having a first face called the internal face (24, 30), a second face called the external face (16, 18) opposite the first face, a first end (22, 31) and a second end (23, 25) opposite the first end; on its first face called the internal face (24, 30), at one of its ends (22, 23, 31, 25), it comprises a collar (26, 32) in the form of at least one annular sector having a first face called the upstream face (27, 33) and a second face called the downstream face (28, 34) opposite the first face; and the collar (26, 32) has at least one visual identification zone (29, 35).;

2. An assembly according to claim 1, characterized in that a three-dimensional template (14, 15) is in the form of a single continuous cylindrical piece extending over 360 degrees.

3. An assembly according to claim 1, characterized in that a three-dimensional template (14, 15) is in the form of a 360-degree cylindrical assembly of several cylinder sectors.

4. Assembly according to any one of the preceding claims, characterized in that at least one visual identification zone (29, 35) is delimited by at least two arcs (40a, 40b, 41a, 41b) belonging to concentric circles.

5. Assembly according to the preceding claim, characterized in that the collar (26, 32) has an internal face (42, 43) and in that this internal face (42, 43) constitutes one of the arcs (40a, 40b, 41a, 41b).

6. Assembly according to any one of the preceding claims, characterized in that at least one visual identification zone (29, 35) is delimited by a strip.

7. Assembly according to any one of the preceding claims, characterized in that: - at the level of the upstream fixing means (12), the outer casing (3) has a location provided for housing an upstream acoustic attenuation element (10), in which the upstream three-dimensional template (14) is housed; - at the level of the downstream fixing means (13), the outer casing (3) has a location provided for housing a downstream acoustic attenuation element (11), in which the downstream three-dimensional template (15) is housed.

8. Assembly according to any one of the preceding claims, characterized in that the layer of abradable material (7) has an internal face (8) located opposite the visual identification zone (29, 35) of each of the three-dimensional templates (14, 15).

9. Conformity control method intended to be used within an outer casing (3) of a turbojet engine having an internal surface (2) equipped with a layer of abradable material (7) having an internal face (8) which delimits an internal diameter, an upstream acoustic attenuation element (10) fixed by means of upstream fixing means (12) and a downstream acoustic attenuation element (11) fixed by means of downstream fixing means (13), the method being intended to control the conformity of the height of an upstream aerodynamic step (M1) and the height of a downstream aerodynamic step (M2) of the layer of abradable material (7), which method comprises the following steps: - removal of the upstream acoustic attenuation element (10) and the downstream acoustic attenuation element (11), - mounting an upstream three-dimensional template (14) on at least one of the upstream fixing means (12) and a downstream three-dimensional template (15) on at least one of the downstream fixing means (13), the three-dimensional templates (14, 15) being upstream and downstream three-dimensional templates (14, 15) according to any one of claims 1 to 6, - visual inspection of the internal diameter of the abradable material layer (7): • by comparison, at the interface between the upstream three-dimensional template (14) and the layer of abradable material (7), of the position of the internal face (8) of the layer of abradable material (7) relative to the visual identification zone (29) located on the downstream face (28) of the collar (26) of the upstream three-dimensional template (14), and • by comparison, at the interface between the downstream three-dimensional template (15) and the layer of abradable material (7), of the position of the internal face (8) of the layer of abradable material (7) relative to the visual identification zone (35) located on the upstream face (33) of the collar (32) of the downstream three-dimensional template (15), - validation of the conformity of the internal diameter of the layer of abradable material (7) if the position of the internal face (8) of the layer of abradable material (7) is located opposite the visual identification zone (29, 35) of each of the three-dimensional templates (14, 15), or non-validation otherwise.

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