METHOD FOR COMPACTING ANTI-CORROSION PAINT ON A TURBOMACHINE PART

Abstract

The invention relates to a method for compacting an anti-corrosion paint comprising metal particles of a mechanical part (1) such as a turbomachine part, the mechanical part (1) extending along a longitudinal axis X and comprising a radially external surface coated with a first layer (4, 4') of anti-corrosion paint. According to the invention, the method comprises at least one step of generating a laser beam (11) on the first layer (4, 4') of anti-corrosion paint so as to bring the metal particles into contact and to make the anti-corrosion paint electrically conductive. Figure for abstract: figure 1

Description

Title of the invention: METHOD FOR COMPACTING AN ANTI-CORROSION PAINT ON A TURBO-MACHINE PART Field of invention

[0001] The present invention relates to the field of surface treatments or preparations of mechanical parts against corrosion. It relates in particular to a method of compacting an anti-corrosion paint covering a part, in particular a turbomachine part. Technical background

[0002] Mechanical parts, in particular those used in aircraft turbomachines, are exposed to harsh environments in terms of temperatures, corrosive elements, and oxidation reactions. The parts, such as compressor and / or turbine shafts, are for example made of a steel or a steel alloy with a reduced cobalt content so as to have high mechanical strength. These steels have a high sensitivity to corrosion phenomena which are mainly manifested by the development of corrosion pits which consist of localized and deep attacks. These parts are also subjected to high mechanical stresses during the operation of the turbomachine which can lead to the development of corrosion. The synergistic stress / corrosion effect leads to a significant increase in corrosion phenomena.

[0003] Some parts have been covered with a paint resistant to high temperatures and various corrosive and oxidative elements (kerosene, oil, etc.) so that they resist the environment in which they operate, and in particular to protect them from corrosion. This paint, being partly composed of chromium trioxide, has been classified as CMR, which is the acronym for Carcinogenic, Mutagenic, Reprotoxic, and is subject to the "REACH" regulation on the Registration, Evaluation, Authorization and Restriction of Chemical Substances.

[0004] In order to overcome the constraints linked to this regulation, a solution consisting of making the paint anodic has been developed. Examples of this solution are described in documents FR-A1-2991216 and FR-A1-3040013. In particular, this solution consists of spraying onto the surface of the part a liquid paint having a mineral binder and loaded with metal particles. This paint is sprayed via a gun manipulated by an operator or a mechanical arm, and the part coated with paint is then heated in an oven to polymerize the sprayed paint. Then, The polymerized paint undergoes a mechanical action such as compaction in order to bring the metal particles into contact without degrading the cosmetic and physical appearance of the paint depending on the type of compaction carried out. This action allows for electrical continuity between the metal particles of the paint and the metal parts to be treated. The paint layer is thus made dense and electrically conductive to make it a sacrificial layer which will corrode preferentially, in place of the metal of the part to be protected. We then speak of an anodic paint to designate the sacrificial layer made conductive.

[0005] Compaction consists of sandblasting or grenadierizing the painted parts after polymerization with particles of white corundum, glass beads, or even plastic particles. However, the particles used for compaction can become embedded in the paint and on its surface. During operation, a release or liberation of these particles can occur, which can damage other parts of the turbomachine (bearings) which are in the path of these particles which can have a very high hardness such as corundum (9.5 on the MOHS scale).

[0006] To limit the release of very hard particles, particularly at very high speeds, some parts are not compacted, which results in a reduction in the anti-corrosion properties of the coating. The other alternative is to cover the compacted anti-corrosion paint with a finishing layer to contain any particles in the paint, which extends the manufacturing time of the part, not to mention the various steps required to prepare the part before, during and after the application of the paint. In addition, controlling the thicknesses of the different layers of paint is difficult, particularly on parts with a complex configuration. Summary of the invention

[0007] The present invention aims in particular to provide a simple and effective solution for ensuring densification of an anti-corrosion paint to increase protection against corrosion without incrustation of hard particles and while avoiding degradation of the anti-corrosion paint.

[0008] We achieve this objective in accordance with the invention by means of a method for compacting an anti-corrosion paint comprising metal particles of a mechanical part such as a turbomachine part, the mechanical part extending along a longitudinal axis X and comprising a radially external surface coated with a first layer of anti-corrosion paint, the method comprising at least one step of generating a laser beam on the first layer of anti-corrosion paint so as to bring the metal particles into contact and to make the paint electronic. highly conductive anti-corrosion paint.

[0009] Thus, this solution makes it possible to achieve the aforementioned objective. In particular, the use of at least one laser beam avoids the use of media (plastics, ceramics, metals, etc.) likely to be released or released when the mechanical part is rotated. This type of compaction, causing the contact of the aluminum-based metal particles, to obtain electrical conductivity and therefore anti-corrosion properties, is obtained by an energy input at the surface. This energy input will make it possible to modify the state of the material of the particles so that they agglomerate with each other. The physical integrity of the paint is thus preserved. Finally, this process is easily automated and makes it possible to overcome the release or release of foreign particles without the need to apply a top coat and consequently a gain in terms of manufacturing time and cost.

[0010] The method also comprises one or more of the following features or steps, taken alone or in combination:

[0011] - the method comprises a step of installing the mechanical part in a enclosure intended to receive an inert gas such as nitrogen or argon.

[0012] - the contact of the metal particles is determined by heating metal particles at a threshold temperature value less than or equal to the melting temperature of the metal particle material.

[0013] - the power of the laser beam is between 200 and 1000 W.

[0014] - the power of the laser beam is preferably 400 W.

[0015] - the laser beam consists of a single beam of a wavelength emission between 1000 and 1500 nm.

[0016] - the laser beam generates pulses each having a duration of between 4 and 8 ms.

[0017] - the laser beam scans the first layer of anti-corrosion paint on the part following a helical trajectory.

[0018] - the method comprises a step of moving the following laser beam a first direction orthogonal to the longitudinal axis X, the mechanical part being rotated around the longitudinal axis and translated along the longitudinal axis.

[0019] - the mechanical part is hollow.

[0020] - the mechanical part comprises a radially internal surface coated with a second layer of anti-corrosion paint, and in that the laser beam is generated inside the mechanical part and reflected inside the mechanical part so as to reach the second layer of anti-corrosion paint, the laser beam scanning the second layer of anti-corrosion paint following a he- licoidal.

[0021] - the mechanical part is a turbomachine shaft.

[0022] - the method comprises a step of moving the laser source along a first direction orthogonal to the longitudinal axis and following a second direction parallel to the longitudinal axis, the mechanical part being rotated around the longitudinal axis.

[0023] - the laser is of the Nd:YAG type.

[0024] - the metallic particles of the paint include aluminum.

[0025] - the anti-corrosion paint is applied by spraying a liquid paint loaded with metal particles on at least one surface of the mechanical part and polymerization of the paint sprayed onto the part so as to obtain a layer of anti-corrosion paint intended to protect the part.

[0026] The invention relates to a method for producing an anodic coating, the method comprising the following steps: - supply of a mechanical part with a longitudinal axis, - projection of a liquid paint loaded with metallic particles onto at least one surface of the mechanical part, - polymerization of the paint sprayed onto the part in order to obtain a layer of anti-corrosion paint intended to protect the part, - compacting the anti-corrosion paint so as to obtain an anodic paint, the compacting comprising at least one projection of a laser beam towards said anti-corrosion paint so as to bring the metal particles into contact and to make the anti-corrosion paint electrically conductive.

[0027] The invention also relates to the use of a laser beam from at least one laser source to compact anti-corrosion paint coating a mechanical part, and in particular a turbomachine part.

[0028] The invention also relates to a mechanical part, in particular a turbomachine, covered at least in part with an anti-corrosion paint compacted according to the aforementioned method.

[0029] Finally, the invention relates to a compacting installation for carrying out a method of compacting a mechanical part comprising: - an enclosure,

[0030] - a mechanical part with a longitudinal axis comprising at least one surface ra- externally which is coated with a first layer of anti-corrosion paint containing metallic particles, the mechanical part being installed in the enclosure, and

[0031] - a compacting device comprising a laser source intended to generate at at least one laser beam towards the first layer of paint so as to bring the metal particles into contact and make the anti-corrosion paint electrically conductive. Brief description of the figures

[0032] The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly on reading the detailed explanatory description which follows, of embodiments of the invention given as purely illustrative and non-limiting examples, with reference to the appended schematic drawings in which:

[0033] [Fig-1] [Fig.l] is a schematic view of an axial section of a part mechanical, such as a turbomachine shaft, installed in an enclosure of a compacting installation according to the invention;

[0034] [Fig.2] [Fig.2] is a schematic view, in radial section, of a mechanical part comprising layers of paint on its radially internal and external surfaces according to the invention;

[0035] [Fig.3] [Fig.3] represents the arrangement of the compacting device for making a layer of paint, arranged inside a hollow part, electrically conductive according to the invention;

[0036] [Fig.4] [Fig.4] schematically represents the trajectory of the laser scan on a radially external surface of the mechanical part according to the invention; and

[0037] [Fig.5] [Fig.5] schematically illustrates a layer of anti-corrosion paint with zones thermally affected by the laser according to the invention. Detailed description of the invention

[0038] Figures 1 to 3 respectively represent, in an axial section, a mechanical part 1, and in particular a mechanical part of an aircraft turbomachine in an installation for compacting an anti-corrosion paint which covers at least one surface of the mechanical part 1.

[0039] By mechanical part we mean parts intended to ensure, in service, a mechanical function, which implies that these parts have good mechanical strength as well as good resistance to corrosion and wear. Turbomachine shafts, and in particular compressor and / or turbine shafts are thus non-exhaustive examples of mechanical parts concerned by the invention. Typically, turbomachine shafts are made of a metallic material or a metallic alloy. The metallic material or the metallic alloy includes steel for example.

[0040] As can be seen in Figures 1 to 3, the mechanical part 1 is a turbomachine shaft which extends along a longitudinal axis X. The turbomachine shaft is hollow here. The shaft comprises a radially external surface 2 and a radially internal surface 3 opposite each other along a radial axis Z perpendicular to the longitudinal axis. X.

[0041] We recall that, prior to the compacting process, the radially external surface of the part 1 is coated with a first layer 4 of anti-corrosion paint illustrated schematically in [Fig.2]. The paint is an inorganic paint or any paint comprising metal particles. In particular, a liquid paint loaded with metal particles is sprayed onto the surface of the part. Advantageously, the metal particles are aluminum particles. Examples of anti-corrosion paints applied to the surface of the parts are those known under the brand name Sermetel W® or Maberbind CF®.

[0042] After spraying the paint, the coated part 1 is polymerized so that the paint hardens and forms the anti-corrosion paint intended to protect the part.

[0043] The anti-corrosion paint is then compacted. For this, the compaction is carried out in a compaction installation 5. By the term compaction, in the present invention, we mean the use of external energy on the surface of the part coated with the layer of paint with metal particles so as to at least partially modify the state of the material and to bring the metal particles into contact. In this way, the anti-corrosion paint is densified and the contact of the metal particles of the paint increases its corrosion resistance. The paint is made electrically conductive. We then obtain an anodic coating.

[0044] The installation 5 comprises a compacting device 6 which is equipped with a head 7 connected to an energy source intended to supply energy to the surface of the first layer 4 of anti-corrosion paint. The energy source is controlled by an electronic control system 8 of the installation. Typically, the electronic control system 8 is equipped with at least one microcontroller 9 and a memory 10 where numerous compacting parameters are recorded.

[0045] In the present example, the energy source is configured to generate or project at least one primary laser beam 11 onto the paint coating the mechanical part of the turbomachine. The output emission wavelength of the laser beam is between ultraviolet (UV) and infrared (IR). The power of the laser is between 100 and 1200 Watt (W). Advantageously, the laser beam provides pulses that are between 0.3 and 50 ms.

[0046] According to yet another advantageous characteristic, the laser beam which is emitted has a frequency between 0 and 500 Hertz (Hz).

[0047] The compacting device 6 is advantageously installed in an enclosure 12 provided for this purpose. The enclosure 12 is closed for example by means of a door through which the part 1 is introduced. The generation of the laser beam 11 is carried out under gas protection in order to avoid any oxidation of the paint during heating or raising of the temperature of the metal particles and to preserve the properties an corrosion of the paint. The gas used is an inert gas such as Argon or Nitrogen.

[0048] Advantageously, the inert gas flow is projected by means of at least one nozzle 13 coaxial with the laser beam so that the most critical zone (which receives the laser beam directly) is constantly protected by a neutral atmosphere. The electronic control system 8 is also connected to the inert gas flow projection nozzle. Alternatively, the inert gas flow is projected by means of a nozzle which is arranged close to the laser beam so that the gas flow protects the critical zone and its immediate environment as well.

[0049] The contacting of the metal particles is determined by heating the metal particles to a threshold temperature value less than or equal to the melting temperature of the material of the metal particles. In the present example, the melting temperature of the metal particles in the case of aluminum is of the order of 660°C. The threshold temperature value lower than the melting temperature of the metal is possible thanks to the thermal shrinkage of the binder (contraction of the silicate network) and the creep of the metal particles.

[0050] The heating of the metal particles (and the paint layer) is defined by a focusing of the laser beam and a linear energy. In particular, the focusing of the beam is controlled by adjusting the opening of a diaphragm which makes it possible to manage the size of the laser beam. The heating of the particle material causes a change in orientation as explained below.

[0051] The linear energy (EL) of the laser (known in English by the expression "Linear Energy Density") is adjusted according to the parameters of the paint (thickness, behavior, etc.) and the conductivity properties thereof. In the present invention, the linear energy corresponds to the ratio between the power of the laser P (expressed in Joule (J) / second (s)) and the scanning speed of the laser V expressed in millimeter (mm) / s. The linear energy is expressed in J / mm. Indeed, too low a linear energy could create defects such as lack of bonding between the particles and possibly a degradation of the quality of the conductive properties of the sacrificial layer. Conversely, too high an energy could cause excessive melting of the aluminum particles and result in a heterogeneous layer of the paint (porosity, thickness).

[0052] Advantageously, but not limited to, the laser source is of the Nd:YAG (yttrium-aluminum garnet) type doped with neodymium. This type of laser generates energy compatible with the energy requirement for this application. The emission wavelength of the laser beam is of the order of 1064 nanometers (nm). The power of the laser beam is between 200 and 400 Watts (W). Preferably, the power of the laser beam is 400W.

[0053] With reference to [Fig.4] and in order to provide uniform conductivity in the paint layer 4, the laser scanning on the anti-corrosion paint is carried out along a helical 110 or corkscrew trajectory. The paint here has a thickness of between 20 and 100 pm. The laser beam is applied to the surface of the paint with a coverage rate Re of the order of 10% and a bandwidth Lb of the order of 1 mm. The linear energy depends on the source, the focusing of the laser beam and the type of paint.

[0054] In the present invention, we understand by the expression "helical trajectory" the path of the laser beam on the anti-corrosion paint corresponding to a translational movement in a first direction and a rotational movement in a plane orthogonal to the first direction of the laser beam relative to the part or of the part relative to the laser beam.

[0055] In one embodiment, the turbomachine shaft is rotated about the longitudinal axis X and moves along the longitudinal axis and preferably simultaneously. Advantageously, the movement of the shaft is a translation. For this, the compacting installation 5 comprises a rotation element 14 of the shaft which is mounted on a frame 15. Guide bearings 16 mounted on the frame allow the rotation of the shaft relative to the frame. The rotation element 14 is advantageously an electric or thermal motor. The motor is connected to the electronic control system 8 which controls the rotation of the motor in one direction or another. Similarly, the laser generation head 7 moves in a direction r which is parallel to the radial axis Z. This is also a translation. In other words, the laser generation head will be fixed in the directions 1 and t.The head is placed at a distance d between 50 and 200 mm.

[0056] The head 7 will move along the direction r so as to adjust the focus of the laser and to adapt to the geometry of the turbomachine shaft. The rotating shaft advances according to a predetermined step. The step can be of the order of 1 mm / revolution. The concatenation of the rotation and the translation of the turbomachine shaft will allow scanning of the laser along the helical trajectory. Advantageously, but not limitingly, the electronic control system is connected to the compacting device 6 so as to control the movement of the head 7.

[0057] According to another embodiment, the turbomachine shaft is rotated around the longitudinal axis and the head 7 of the compacting device 6 moves in the direction r and in a direction parallel to the longitudinal axis X so as to obtain the scanning of the laser along a helical trajectory.

[0058] In the present embodiment, the radially internal surface 3 of the shaft also comprises a layer of anti-corrosion paint called “second layer of paint” 4' comprising metal particles. This second layer 4' of anti-corrosion paint is identical to the first layer 4. Alternatively, the first and second layers 4, 4' are different.

[0059] In order to reach the second layer 4, 4' of paint (located inside the shaft), a deflection member 17 is installed inside the turbomachine shaft. The deflection member 17 is pivotally mounted inside the shaft and its pivoting is controlled by the electronic control system 8 to which it is connected. Advantageously, the deflection member 17 is a deflecting mirror. In this way, the laser beam which reaches the mirror is reflected onto the second layer of paint. The scanning of this second layer 4' of paint is carried out in the same way as for the first layer of paint 4, that is to say following a helical trajectory.

[0060] [Fig.5] illustrates a layer 4 or 4' of anti-corrosion paint with aluminum particles having a thickness of the order of 20 to 90 pm. Depending on the focusing of the laser beam, it will diffuse more or less throughout the entire thickness of the paint layer. For example, a focusing of 100% generates a zone ZI whose depth is substantially equal to the thickness of the paint layer. On the other hand, a focusing of the order of 40% generates a zone Z2 whose depth is less than the thickness of the layer 4, 4' of paint.

[0061] Advantageously, but not limitatively, the diameter of the laser beam is between 0.2 and 5 mm.

[0062] We will now describe the method of compacting the turbomachine part, using the installation 5 described above. The method comprises a step of installing the mechanical part in the enclosure 12. The part is rotated by the electronic control system 8. Simultaneously with or after the rotation step, a laser beam is generated on the layer 4 of paint coating the part 1. The laser beam is oriented towards the paint by making an angle of approximately 90° with the rotation axis. This also provides several pulses. The duration of each pulse is between 4 and 8 ms during the generation step. The mechanical part 1 is also moved in translation along the longitudinal axis so that the laser scans the layer of paint along the helical trajectory.During this generation step, the energy input will bring the temperature of the aluminum particles to a value corresponding to their melting temperature or to a value lower than this so that the particles are melted or partially melted and can agglomerate with each other. We understand that this allows a change of orientation or displacement of the metal particles for contact. The particles in contact achieve electrical continuity. Similarly, the inert gas is projected into the enclosure concomitantly with the laser generation step.

[0063] Subsequently, the mirror (deflection member 17) is installed inside the room hollow and the second layer 4' is scanned with the laser beam also following a helical trajectory.

[0064] With a laser beam emitting laser pulses of 4 to 8 ms duration and generated at a power of 400W, the resistivity of the anodic paint layer, measured with an ohmmeter (Ohm), is less than 5 Ohms. This confirms that the paint compacted with the laser beam is made conductive. The paint has a uniform, defect-free appearance, and homogeneous in thickness (with a reduction in thickness of a few micrometers).

[0065] Outside the pulse duration range between 4 and 8 ms and the power range of 300 to 500 W, the paint may be damaged by stripped or burned portions.

Claims

Claims

1. Method for compacting an anti-corrosion paint comprising metal particles of a mechanical part (1) such as a turbomachine part, the mechanical part (1) extending along a longitudinal axis X and comprising a radially external surface (2) coated with a first layer (4, 4') of anti-corrosion paint, characterized in that the method comprises at least one step of generating a laser beam (11) on the first layer (4, 4') of anti-corrosion paint so as to bring the metal particles into contact and to make the anti-corrosion paint electrically conductive, the power of the laser beam being between 200 and 1000 W, and preferably is 400 W, and the laser beam generating pulses each having a duration of between 4 and 8 ms.

2. Method according to the preceding claim, characterized in that it comprises a step of installing the mechanical part (1) in an enclosure (12) intended to receive an inert gas such as nitrogen or argon.

3. Method according to any one of the preceding claims, characterized in that the contacting of the metal particles is determined by heating the metal particles to a threshold temperature value less than or equal to the melting temperature of the material of the metal particles.

4. Method according to any one of the preceding claims, characterized in that the laser beam consists of a single beam with an emission wavelength between 1000 and 1500 nm.

5. Method according to any one of the preceding claims, characterized in that the laser beam scans the first layer (4, 4') of anti-corrosion paint on the mechanical part (1) following a helical trajectory.

6. Method according to the preceding claim, characterized in that it comprises a step of moving the laser beam (11) in a first direction orthogonal to the longitudinal axis X, the mechanical part (1) being rotated around the longitudinal axis X and in translation along the longitudinal axis X.

7. Method according to any one of the preceding claims, characterized in that the mechanical part (1) is hollow.

8. Method according to the preceding claim, characterized in that the mechanical part (1) comprises a coated radially internal surface (3)

9.

10. of a second layer (4') of anti-corrosion paint, and in that the laser beam (11) is generated inside the mechanical part (1) and reflected inside the mechanical part so as to reach the second layer (4') of anti-corrosion paint, the laser beam (11) scanning the second layer (4') of anti-corrosion paint following a helical trajectory. Method according to any one of the preceding claims, in which the mechanical part is a turbomachine shaft. Method according to any one of the preceding claims, in which the anti-corrosion paint is applied by spraying a liquid paint loaded with metal particles onto at least one surface of the mechanical part and polymerizing the paint sprayed onto the part so as to obtain a layer of anti-corrosion paint intended to protect the part.

Images