METHOD FOR COMPACTING A CORROSION PROTECTION COATING ON A PART OF A TURBO ENGINE

Description

1. Scope of the invention

[0001] The present invention relates to the field of surface treatments of mechanical parts against corrosion. It relates in particular to a method of compacting an anti-corrosion paint covering a part, especially a turbomachine part. 2. State of the art

[0002] Mechanical components, particularly those used in aircraft turbomachinery, are exposed to harsh environments in terms of temperature, corrosive elements, and oxidation reactions. Components such as compressor and low-pressure turbine shafts are made of steel or a steel alloy with a reduced cobalt content to achieve high mechanical strength. These steels are highly susceptible to corrosion, which manifests primarily as pitting corrosion, consisting of localized and deep attacks. These components are also subjected to significant mechanical stresses during turbomachine operation, which can lead to corrosion. The synergistic effect of stress and corrosion results in a substantial increase in corrosion phenomena.

[0003] Some parts were coated with a paint resistant to high temperatures and various corrosive and oxidizing elements (kerosene, oil, etc.) to withstand their environment and, in particular, to protect them from corrosion. This paint, which contains chromium trioxide, has been classified as CMR (Carcinogenic, Mutagenic, Reprotoxic) and is subject to the REACH regulation on the registration, evaluation, authorization, and restriction of chemical substances.

[0004] To overcome the constraints of this regulation, a solution involving anodic coating was developed. Examples of this solution are described in documents FR-A1-2991216 and FR-A1-3040013. Specifically, this solution consists of spraying a liquid paint containing a mineral binder and metallic particles, such as aluminum, onto the surface of the part. This paint is sprayed using a gun operated by a technician. The coated part is then heated in an oven to polymerize the sprayed paint. The polymerized paint then undergoes a mechanical action, such as compaction, to bring the metallic particles into contact without degrading the cosmetic and physical appearance of the paint. This action establishes electrical continuity between the metallic particles and the metal parts being treated.The paint layer is thus made dense and electrically conductive, creating a sacrificial layer that will corrode preferentially, instead of the metal of the part being protected. This conductive sacrificial layer is then referred to as an anodic paint.

[0005] Compaction involves sandblasting or shot-blasting the painted areas after polymerization with particles of white corundum, glass beads, or plastic particles. Compaction densifies the paint and gives it sacrificial properties responsible for its high-performance anti-corrosion properties. Alternatively, anodic painting can also be achieved by polishing. Polishing is a time-consuming process involving manually sanding the part with sandpaper.

[0006] The step of making the paint anodic is optional when the paint contains chromium trioxide. However, it is essential for paints that do not contain it.

[0007] However, the particles used for compaction can become embedded in and on the surface of the paint. During operation, these particles can be released, potentially damaging other components of the turbomachine that are in their path. Some particles, such as corundum, a mineral element, have a high hardness of around 9.5 on the Mohs scale. Therefore, for parts like turbine and compressor shafts, the compaction step is not performed to avoid the release of these very hard particles at high speeds, which would reduce the paint's corrosion protection. Indeed, since the paint layer is not conductive without compaction, it provides less corrosion protection, merely forming a barrier on the surface of the part.The anti-corrosion effect provided by this barrier layer is highly dependent on its porosity. Furthermore, as soon as the part is scratched or dented, the protection ceases and the part becomes susceptible to corrosion. In addition, for these parts with non-compacted coatings, the paint is applied manually in at least two coats to minimize porosity. This increases the manufacturing time of the part, not to mention the various preparation steps required before, during, and after painting. Controlling the thickness of the different paint layers is a delicate matter, especially on parts with complex configurations.

[0008] EP1598444A1 discloses a method for compacting an anti-corrosion paint according to the preamble of the feature of claim 1. 3. Objective of the invention

[0009] The present invention aims in particular to provide a simple and effective solution for ensuring the densification of an anti-corrosion paint to increase corrosion protection without the encrustation of hard particles and while avoiding the degradation of the anti-corrosion paint. 4. Description of the invention

[0010] This objective is achieved in accordance with the invention by means of a compaction process of an anti-corrosion paint comprising metallic particles and covering a mechanical part such as a turbomachine part, the process comprising the characteristics of claim 1 including a step of at least one projection of solid ice particles onto the part so as to densify and make the paint electrically conductive.

[0011] Thus, this solution achieves the aforementioned objective. In particular, these solid ice particles densify the paint coating the mechanical part, bringing the metallic particles within the paint into contact with it and thereby increasing its corrosion resistance. The solid ice particles also eliminate the problems of encrustation and release of foreign particles, such as glass beads or corundum particles, during operation, as these particles sublimate upon impact with the paint. In this way, the physical integrity of the paint is preserved. Finally, this process is easily automated, reducing manual operations such as applying multiple coats of paint to address the encrustation of foreign particles, and consequently saving on manufacturing time and costs.

[0012] Preferably, the process also includes one or more of the following features or steps, taken alone or in combination: said solid particles include carbon dioxide particles, said solid particles are sublimated after impact on the paint, the solid particles are projected at a pressure of between 2 and 8 bar, the distance between the surface of the part and the nozzle is between 20 and 100 mm, the solid particles are projected along at least one beam whose general direction has an inclination relative to the surface of the part of between 30° and 90°, the solid particles are projected along at least one beam which moves at a speed of between 40 and 60 mm / s, the process comprises two stages of projecting the particles onto the surface of the part, the part is a turbomachine shaft, said solid particles may be projected by sandblasting or shot blasting devices, the projection of the solid particles is carried out in a closed chamber, preferably at ambient temperature,The hardness of the solid ice particles is between 2 and 2.5 MOHS, the sublimation temperature of the solid ice particles after impact is approximately -78.9°C, and the metallic particles include aluminum.

[0013] Preferably, the invention relates to a method for producing an anodic coating, the method comprising the following steps: projection of a liquid paint loaded with metallic particles onto a surface of the part, polymerization of the paint projected onto the part so as to obtain an anti-corrosion paint layer intended to protect the part, compaction of the anti-corrosion paint so as to obtain an anodic paint, the compaction including at least one projection of solid ice particles towards said anti-corrosion paint so as to densify the anti-corrosion paint and make it electrically conductive. 5. Brief description of the figures

[0014] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent upon reading the detailed explanatory description that follows, of embodiments of the invention given by way of purely illustrative and non-limiting examples, with reference to the accompanying schematic drawings in which: There figure 1 is a schematic front view of an example of a workpiece compaction device for a process according to the invention; The figure 2 is a schematic, top view of the compaction device of the figure 1 ; There figure 3 represents an image of a test tube coated with paint that has not hardened after aging; The figure 4 represents an image of a test tube coated with a paint compacted with solid particles of dry ice according to the invention; The figure 5 illustrates a scanning electron microscope image of a painting that has not undergone compaction; and The figure 6illustrates an image taken by SEM of a paint that has undergone compaction with ice particles according to the invention. 6. Description of embodiments of the invention

[0015] THE figures 1 and 2 Figures 1 and 2 respectively represent, in front and top views, a compaction device for an anti-corrosion paint coating the surface of a mechanical part 2, and in particular a mechanical part of an aircraft turbomachine. By mechanical part, we mean parts intended to perform a mechanical function in service, 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 examples of mechanical parts covered by this invention, though they are not exhaustive.

[0016] We remind you that, prior to the compaction process, part 2 is coated with an anti-corrosion paint. The paint is an inorganic paint or any paint containing metallic particles. In particular, a liquid paint containing metallic particles is sprayed onto the surface of the part. Advantageously, the metallic particles are aluminum particles. Examples of anti-corrosion paints applied to the surface of parts are those known under the brand names Sermetel W® or Maberbind CF®.

[0017] After the paint is sprayed, the coated part is polymerized so that the paint hardens and forms the anti-corrosion paint intended to protect the part.

[0018] The anti-corrosion paint is then compacted. This compaction is achieved using the compaction device 1. In the present invention, compaction refers to the process of projecting materials, possibly abrasive, at high speed onto the surface of the coated part to make the paint conductive. This densifies the anti-corrosion paint, bringing the metallic particles of the paint into contact and increasing its corrosion resistance. The paint is thus rendered electrically conductive, resulting in an anodic coating.

[0019] The compaction device 1 includes at least one nozzle 3 for projecting a beam or jet 4 of solid particles, enabling surface treatment of the turbomachine part. In this example, the device 1 comprises a single nozzle 3 with an outlet 5 located at a distance from the part 2. The nozzle 3 is connected to a conduit 6 that is supplied with solid particles. The solid particles are stored in a reservoir (not shown). In particular, the outlet 5 of the nozzle is located at a distance d from the surface of the part, which is between 20 and 100 mm. Advantageously, but not exclusively, the predetermined distance d is between 30 and 60 mm. Preferably, the distance is 50 mm. The nozzle 3 has a general direction that is inclined relative to the surface of the part so as to prevent premature wear of the solid particles. This inclination is between 30° and 85°.The minimum angle of 30° prevents paint stripping. Ideally, the nozzle angle relative to the workpiece should be between 45° and 90°. One to two passes of the solid particle beam over the workpiece surface are recommended to maintain the paint's physical and cosmetic integrity.

[0020] To perform particle projection, the nozzle 3 is moved along the part, following its height, and around its circumference, maintaining at all times the same geometry for the relative position of the nozzle and the surface of the part.

[0021] Of course, the invention is not limited to the use of this compaction device, which is described only by way of example. The compaction device could, for example, comprise two nozzles, each emitting a jet or beam of particles 3 oriented between 30° and 90° with respect to the surface of the workpiece 1, the two beams propagating in the same plane. The general directions of the two nozzles are oriented at 90° to each other. The two beams converge at a focal point 4 located on the workpiece 1; that is, they both reach the same point to be treated. Given the solid angle characterizing the divergence of the beams 3, the surface swept at each instant by the sandblasting has the shape of a circle of diameter "I".

[0022] The compaction device 1 here is a high-pressure cryogenic cleaning system.

[0023] The compaction device 1 is advantageously installed in an enclosure 7 designed for this purpose. The enclosure 7 is closed by means of a door through which the part is introduced. Advantageously, an ambient temperature and humidity are maintained inside the enclosure to prevent condensation of water on the part. Of course, it is not necessary for the enclosure to be completely closed.

[0024] The solid particles used to compact the anti-corrosion paint coating this turbomachine part are dry ice particles. These solid dry ice particles are advantageously, but not exclusively, composed of solid carbon dioxide (CO2). Solid carbon dioxide is also known as dry ice.

[0025] Solid ice particles are propelled towards the surface of the part (which is coated with paint) with sufficient energy to densify the paint covering it. Once the solid particles have impacted the anti-corrosion paint, they sublimate. This is made possible by the ambient temperature of chamber 7. The solid carbon dioxide transforms into a gas, thus preventing any particles from remaining embedded in the anti-corrosion paint. The sublimation temperature of the ice particles after impact is between 75°C and 80°C. Advantageously, but not limitingly, the sublimation temperature is around -78.9°C.

[0026] Advantageously, but not exclusively, a drying step can be implemented after compaction to control condensation that may form after the sublimation of dry ice solid particles. This can take place before the enclosure is opened.

[0027] According to the invention, the solid particles have dimensions ranging from 1 mm to 30 mm. Advantageously, but not limitingly, the dimensions of these particles are between 1 and 10 mm. Preferably, the dimensions of the solid particles are on the order of 3 mm. The particles may be spherical in shape.

[0028] Solid ice particles are delivered at a pressure between 2 and 8 bar, preferably between 5 and 8 bar. Even more preferably, the pressure at which the particles are delivered is between 6 and 8 bar. This allows the paint to be densified without being damaged. There is no paint stripping with this operating range. Similarly, in order to preserve the physical and cosmetic integrity of the paint, the ice particles are projected at a mass flow rate between 0.8 kg / h and 2 kg / h. Preferably, the mass flow rate is between 1 and 1.5 kg / h.

[0029] The particle beam moves across the surface of the part at a speed between 40 mm / s and 60 mm / s. Preferably, the nozzle travel speed is 50 mm / s.

[0030] The projection of ice particles at a constant pressure is facilitated by an airflow projected simultaneously with the particles into the nozzle, thus aiding particle ejection. Nozzle 3 moves at a speed between 40 mm / s and 60 mm / s to propel the beam of ice particles.

[0031] Alternatively, a suction-feed shot blasting machine, with appropriate air pressure and mass flow rate, can be used to project the solid ice particles. This machine is, for example, equipped with one or two round nozzles of 10 to 14 mm.

[0032] Salt spray tests (according to ISO 9227) to evaluate the corrosion resistance of the compacted paint demonstrated that it maintained its anti-corrosion properties on the substrate after 168 hours of aging. The ice particles also have the advantage of sublimating upon contact with the paint, leaving no trace of embedded elements, unlike the particles used in prior art.

[0033] THE figures 3 and 4 present a comparison after 168 hours of aging between a test specimen (representing the mechanical part) coated with a single layer of uncompacted paint and a test specimen coated with a single layer of paint compacted with dry ice. According to the invention, the paint layer is on the order of 50 µm. We see on the figure 3that thick, dense rust had developed in several areas on the surface of the test specimen. Conversely, the test specimen whose paint was compacted with dry ice particles from the figure 4 There are no signs of rust on the surface of the part. This clearly demonstrates that the ice particles help to thicken the paint layer and improve its resistance to corrosion.

[0034] THE figures 5 and 6 These are images captured by a SEM (scanning electron microscope) and allow observation of the densification of the paint applied in two layers to a 20 mm test specimen, respectively with and without compaction. According to the invention, each layer has a thickness of between 50 µm + / - 10%. On the figure 5representing an uncompacted paint, we observe that the paint exhibits numerous porosities between the surface of the specimen 20 and the external surface of the paint. The second paint layer (top layer) 10a, located approximately 37 µm from the external surface of the part, contains more porosities, or is even almost completely filled with porosities, than the first paint layer (bottom layer) 10b in contact with the surface of the specimen 20.

[0035] Regarding the paint compacted with ice particles shown on the figure 6We can see that the size and quantity of pores have significantly decreased in the second layer 10b. We also note that there is no encrustation of foreign particles. The compaction operation with ice particles did not degrade or strip the paint, since the measured paint thickness only decreased by 5 to 10 µm (maximum allowable of 10 µm) according to the invention. It follows that compaction with solid dry ice particles eliminates the risk of release or dispersal of particles used in the compaction process, since the dry ice particles are sublimated upon contact with the part after impact.

[0036] In an example using a paint layer approximately 50 µm thick, dry ice particles were projected at an angle of approximately 90° to the surface of the part. The particles were projected a maximum of two times onto the surface of the part. Following a salt spray test after 168 hours of aging, the specimen showed no red corrosion streaks or localized corrosion (pitting).

Claims

1. Method of compacting an anti-corrosive paint (10a, 10b) comprising metal particles and covering a mechanical part (2, 20) such as a turbine engine part, the method comprising a step of projecting at least one paint layer loaded with metallic particles onto the surface of the part and to at least one step of spraying solid ice particles on the part (2, 20) so as to densify and to make the paint layer electrically conductive while preserving the physical integrity of the anti-corrosion paint, characterized in that the paint layer has a thickness of between 50 µm + / - 10%, the solid particles have dimensions of between 1 and 30 mm, and preferably, 3mm and in that the projection of solid ice particles reduces the thickness of the paint layer by 5 to 10 µm.

2. Method according to the preceding claim, characterised in that said solid particles comprise carbon dioxide particles.

3. Method according to one of the preceding claims, characterised in that the solid particles are sprayed at a pressure of between 2 and 8 bars.

4. Method according to any one of the preceding claims, characterised in that the solid particles are sprayed according to at least one beam (4), of which the general direction has an inclination with respect to the surface of the part which is between 30° and 90°.

5. Method according to any one of the preceding claims, characterised in that the distance between the surface of the part (2, 20) and the nozzle (3) is between 20 and 100 mm.

6. Method according to any one of the preceding claims, characterised in that the solid particles are sprayed according to at least one beam (4) which is moved at a speed of between 40 and 60mm / s.

7. Method according to any one of the preceding claims, characterised in that it comprises two steps of spraying particles over the surface of the part (2, 20).

8. Method according to any one of the preceding claims, characterised in that the metal particles comprise aluminium.

9. Method according to any one of the preceding claims, wherein the mechanical part is a turbine engine shaft.

10. Method according to any one of the preceding claims, characterised in that the solid ice particles are sprayed with a mass flow of between 0.8kg / h and 2kg / h, preferably, between 1 and 1.5kg / h.

11. Method according to any one of the preceding claims, characterised in that the ice particles are projected simultaneously with an airflow and at a constant pressure.

12. Method according to any one of the preceding claims, characterised in that the hardness of the solid ice particles is between 2 and 2.5 Mohs.

13. Method according to any one of the preceding claims, characterized in that the projecting of solid ice particles reduces the size and quantity of pores in the paint layer.