Masking agent for covering a surface area of ​​a component of a turbomachine and method for machining a component of a turbomachine

Abstract

The invention relates to a masking agent (14) for covering a surface area (12) of a component (10) of a turbomachine, in particular for covering a thermal spray coating, wherein the masking agent (14) comprises at least one crosslinkable elastomer precursor with a dynamic viscosity at 25 ± 0.2 °C between 21,000 mPas and 39,000 mPas. The invention further relates to a method for processing a component (10) of a turbomachine, in which at least one surface area (12) of the component (10) is first covered with such a masking agent (14) and the component (10) is then processed.

Description

The invention relates to a masking means for covering a surface region of a component of a turbomachine and to a method for processing a component of a turbomachine.Components of turbomachines, in particular components for aircraft engines, generally require a plurality of processing steps. For example, surface areas of certain components are coated with thermal spray coatings in order to make the surface of the component more resistant to thermal stress, corrosive influences and abrasion. Frequently, however, such components must be subjected to further processing steps and, for example, mechanically and / or chemically post-processed. In these machining operations, tools or media can be used, against which the surface or a coating of the component is not resistant, whereby the functional properties change. In order to protect the surface of the component at least in critical regions during these subsequent processing steps, the surface of the component is usually protected with a coolant during mechanical processing and with masks during chemical processing or a cleaning process.However, hitherto thermal sprayed layers have not been protected from this cooling medium, for example, before rotation with cooling medium. If the coating must not come into contact with the cooling medium during the turning, the layers are turned without the use of a cooling medium, which can lead to damage to the component. If a cooling medium is used on an already coated component, which cooling medium influences the coating properties, the sprayed layer must subsequently be removed and newly produced. In particular in the case of thermal spray coatings and other porous surfaces, there is, conversely, the risk that masking agent penetrates into the open porosity and remains there at least partially even after removal of the masking. The functional property of the component can thus likewise be adversely affected.The object of the present invention is to provide a masking agent which ensures reliable masking on the one hand, but on the other hand does not lead to damage to the surface during removal. A further object of the invention is to specify a method for machining a component of a turbomachine which avoids the aforementioned problems with respect to sensitive surface regions of the machined component.The objects are achieved according to the invention by a masking means having the features of claim 1 and by a method according to claim 5. Advantageous embodiments with expedient developments of the invention are specified in the respective dependent claims, wherein advantageous embodiments of the masking means are to be regarded as advantageous embodiments of the method and vice versa.A first aspect of the invention relates to a masking means for covering a surface region of a component of a turbomachine, in particular for covering a thermal spray layer of the component. A more reliable masking of the surface region without the risk of damage to the masked surface region during the removal of the masking agent is provided according to the invention in that the masking agent comprises at least one crosslinkable elastomer precursor having a dynamic viscosity at 25±0.2° C. between 21000 mPas and 39000 mPas. In other words, the masking agent according to the invention contains at least one elastomer precursor which can be thermally, photochemically and / or ionically crosslinked to form an elastomer. In the simplest configuration, the masking agent according to the invention can also consist exclusively of this elastomer precursor. The crosslinkable elastomer precursor for its part already has a high dynamic viscosity at 25±0.2° C. between 21000 mPas and 3900 mPas (at 20 U / min), which can be further increased by crosslinking the elastomer precursor to form an elastomer. The masking means thus enables an accurate and effective covering of the surface region of the component. The defined dynamic viscosity ensures targeted application and good adhesion to the surface even in the case of porous surfaces of sprayed layers, but without penetrating deeply into the latter. By using this masking means, the surface of the component is then effectively protected during subsequent processing steps. It forms a protective layer which protects against possible damage to the surface, which can have a thermal spray layer, for example. The masking agent can also be removed easily and generally without residue after crosslinking. This reduces the amount of work required for preparing and preparing the component for different processing steps and increases the efficiency of the process. The defined dynamic viscosity of the elastomer precursor also enables precise control of the application behavior and the layer thickness of the masking agent. This allows a uniform and consistent covering of the surface region to be protected to be achieved. By means of the precise protection of the surface region to be masked, the need for complicated preliminary work, such as the removal of coatings, and also for post-work, such as the repair of damaged spray layer regions and the like, is additionally reduced or ideally completely avoided. This results in corresponding time and cost savings in the manufacturing process. If the viscosity of the elastomer precursor is already sufficient, it is possible in certain cases to dispense with crosslinking. In general, "a / an" in the context of this disclosure should be read as indefinite articles, that is to say without expressly stated to the contrary always also as "at least one / at least one". Conversely, "a / an" can also be understood as "only one / only one".In an advantageous embodiment of the invention, it is provided that the at least one elastomer precursor is photocrosslinkable and that the masking agent additionally comprises at least one photoinitiator. In contrast to thermal crosslinking, photocrosslinking is substantially less time-intensive and energy-intensive, environmentally friendly and emission-free and requires significantly less machine complexity. In addition, it can be avoided in this way that the viscosity of the elastomer precursor changes significantly due to temperature, since no heating of the elastomer precursor is necessary, since the crosslinking reaction can be carried out at room temperature. In addition, complex three-dimensional geometries, as occur regularly in components for turbomachines, can also be provided with the masking agent reliably and without problems with locally different heating and the masking agent can then be cured quickly by exposure to UV light.Further advantages result from the fact that the masking agent additionally comprises a fluorescent additive. With the aid of a fluorescent additive, both the application and the later removal of the masking agent from the component can be easily monitored and monitored. In particular, it is particularly easy to check whether residues of the masking agent still remain on the component after the removal, which can then be removed in a targeted manner in a corresponding cleaning step until no fluorescence signal can be detected any longer. The cleaning can be effected, for example, with the aid of solvents and / or by burning out the thermoplastic masking residues.In a further advantageous embodiment of the invention, it is provided that the at least one elastomer precursor comprises (meth)acrylate monomers, in particular hexanediol di(meth)acrylate and / or isobornyl (meth)acrylate and / or trimethylolpropane tri(meth)acrylate, and / or (meth)acrylate oligomers, in particular urethane (meth)acrylate oligomers. As a result, a masking can be produced which has a high tensile strength, extensibility, hardness, chemical resistance and adhesion to the component. Within the scope of the present disclosure, the term (meth)acrylate is to be understood as meaning in principle corresponding acrylates, methacrylates and any desired mixtures thereof.A second aspect of the invention relates to a method for machining a component of a turbomachine, in which at least one surface region of the component is first covered with a masking agent according to the first aspect of the invention and the component is subsequently machined. The method according to the invention brings about a particularly simple and reliable masking of surface regions of the component to be protected during the subsequent processing step or steps. Owing to the high viscosity of the masking agent, the masking agent does not penetrate, or penetrates only slightly, into layers such as, for example, porous thermal spray layers. The masking agent can be applied optionally with the hand and / or with a robot, so that accurately fitting masking of different components is possible. After the processing, the masking can be removed again from the component by hand and / or mechanically, because of its elastic properties, quickly and reliably. Further features and their advantages can be gathered from the descriptions of the first aspect of the invention.In an advantageous embodiment of the invention, it is provided that the surface region of the component is cleaned before the masking agent is applied. This ensures reliable application and reliable adhesion of the masking agent to the surface. Alternatively or additionally, the surface region is covered with a covering agent, in particular an adhesive tape, to which the masking agent is then applied. This allows additional protection of sensitive and / or porous surface regions of the component. Furthermore, the adhesion of the masking agent to the surface can also be improved as a result. Likewise, the removal of the masking means can be facilitated by removing it from the component together with the masking means. Alternatively or additionally, it is provided that the masking agent is crosslinked, preferably photochemically, after application to the surface region. This additionally increases the viscosity of the masking agent and ensures a particularly reliable masking effect and a simple removability.In a further advantageous embodiment of the invention, it is provided that the masking agent is applied to the surface region by means of bead application, wherein beads adjoining one another are preferably arranged offset with respect to one another. A bead application allows contactless application with a certain "flying height", i.e. with a certain distance between a bead application nozzle tip and the component surface. The bead can optionally also be pushed into the width in order to produce a flat masking. By arranging adjacent or adjacent caterpillars offset with respect to one another, a particularly reliable masking without gaps can be ensured. Alternatively or additionally, it is provided that the masking agent is applied to the surface region with a layer thickness of at least 0.5 mm. This also ensures gapless, continuous and thus reliable masking of the relevant surface region.In a further advantageous embodiment of the invention, it is provided that an Ni-based plasma spray layer and / or a thermally sprayed running-in coating and / or a thermally sprayed wear protection layer of the component is or are covered at least in regions by means of the masking means. This allows the numerous advantages of the masking according to the invention to be realized for various surface regions that have hitherto been difficult to mask.Further advantages result from the fact that the component is chemically processed, in particular cleaned, de-coated and / or coated with a test agent and / or a cooling lubricant and / or an anti-splashing layer, after covering the surface region. This allows many different components for turbomachines to be masked and processed in different ways.In a further advantageous embodiment of the invention, it is provided that the masking agent is at least partially removed from the component after the processing of the component, in particular by pulling off and / or by applying a solvent and / or by burning out. This allows simple and complete removal of the masking agent from the component after it has been used.Further features of the invention are evident from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description, and the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respectively specified combination but also in other combinations without departing from the scope of the invention. Therefore, embodiments of the invention are also to be considered as included and disclosed which are not explicitly shown and explained in the figures, but which emerge from the explained embodiments and can be generated by separate combinations of features. Embodiments and combinations of features are also to be considered as disclosed, which therefore do not have all features of an originally formulated independent claim. Furthermore, embodiments and combinations of features, in particular by the embodiments set forth above, are to be considered as disclosed which go beyond or deviate from the combinations of features set forth in the references of the claims. The following shows: FIG. 1 shows a perspective detailed view of a blade cluster of an aircraft engine with a Ni-based plasma sprayed layer; FIG. 2 is a perspective view of the blade cluster in which the Ni-based plasma sprayed layer is covered with a masking agent; FIG. 3 is a perspective view of the blade cluster, wherein the masking agent is removed without residue after the processing of the blade cluster; FIG. 4 shows a perspective detailed view of an intake lining of a housing part of an aircraft engine; FIG. 5 shows a perspective detailed view of the housing part, wherein the running-in covering is covered with the masking agent; FIG. 6 shows a perspective detailed view of a fin coating of a rotor of an aircraft engine; FIG. 7 shows a perspective detailed view of the fin coating, which is covered with the masking agent; FIG. 8 shows a perspective detailed view of an intake lining of a rotor of an aircraft engine; and FIG. 9 shows a perspective detailed view of the running-in covering which is covered with the masking means.FIG. 1 shows a perspective detailed view of a component 10 of an aircraft engine, which component is designed as a blade cluster and has a surface region 12 which has a Ni-based plasma spraying layer. In the event of damage to such titanium-based blade clusters 10, solidification blasting is prescribed after the screening. In order subsequently to remove the impurities from the titanium material by the blasting, cleaning with cleaning agents containing nitric acid is subsequently provided. However, the nitric acid used attacks the already present Ni-based plasma sprayed layer 12. A mechanical device for protecting the plasma sprayed layers 12 cannot be used due to the complex geometry. Mechanical cleaning, on the other hand, is very complicated and cost-intensive. Masking with a masking agent 14 according to the invention made it possible to clean the component 10 with nitric acid-containing cleaners without having to damage the spray layer 12 already present or to have to be repaired anew after cleaning. The masking agent 14 is based on crosslinkable elastomer precursors having the highest possible dynamic viscosity between 21,000 and 39,000 mPas (cps) at 25±0.2° C. and 20 U / min (rpm). As a result, the masking agent 14 can be applied uniformly and with good adhesion to the surface region 12 of the component 10 to be protected without, for example, running down on vertical surfaces.If the masking agent 14 were not resistant to subsequently used media or in the case of adhesion problems, generally a tape or tape can also be arranged first on the surface region 12 and the highly viscous masking agent 14 applied thereto. Likewise, other special preparations can be carried out, for example, when applied to the edges of the surface region 12 to be protected, in order reliably to prevent the penetration of the masking agent 14 into corresponding component regions. Before application, the surface region 12 can be cleaned in order to reliably remove protective agents or lubricants and to ensure good adhesion of the masking agent 14. Application is generally preferably effected initially at the boundary regions of the surface to be covered. Application in the coating area is preferably effected in contactless fashion with immediate (UV) light transmission. In the case of bead application, the individual beads are preferably applied offset in order to guarantee tightness. Curing in this case basically also takes place after each bead and / or layer ply. The layer thickness is generally at least 0.5 mm.The masking agent 14 can preferably be polymerized out photochemically, as a result of which it acquires its final dimensional stability, cohesion and adhesion, in order to be able to optimally protect the surface region 12 for subsequent processing steps. Masking agent 14 preferably contains crosslinkable monomers and / or oligomers (in particular urethane acrylate) and optionally one or more photoinitiators, modifiers and / or (fluorescent) dye(s). As a result, the masking agent 14 is particularly resistant chemically and mechanically, at least in the fully polymerized state, without significantly infiltrating surface regions 12 with open porosity.FIG. 2 shows a perspective view of the blade cluster 10 in which the surface region 12 of the Ni-based plasma spray layer is covered with the masking agent 14 according to the invention. It can be seen that the masking agent 14, despite the complex surface geometry, covers the surface region 12 with a uniform layer thickness and protects it from damage during subsequent chemical and / or mechanical processing steps.FIG. 3 shows a perspective view of the blade cluster 10, wherein the masking agent 14 is removed without residue from the surface region 12 with the Ni-based plasma sprayed layer after the processing of the blade cluster 10. The pulling-off can generally take place manually and / or mechanically. Since the masking agent 14 does not penetrate into the open porosity of the plasma spray layer because of its high viscosity, no masking agent residues remain there either after the removal. If, unexpectedly, residues of the masking agent 14 remain, they can be removed by cleaning, optionally with a solvent and / or by burning off. When an optional fluorescent dye is added to the masking agent 14, it is easily visually checked whether all residues have been completely removed.FIG. 4 shows a perspective detailed view of a thermally sprayed running lining of a component 10 of an aircraft engine designed as a housing. The high open porosity of this surface region 12 can be seen. Deviations can be detected on such components 10 which make it necessary to reprocess the dimension correction layers (not shown). If the dimension correction layers of these components 10 are remachined, the following process steps, among other things, must be carried out:pre-turning the region to be coated (dimension correction layer) with cooling lubricant (KSS);cleaning; andColor Penetration (FPI) test.If these processing steps are carried out, no media such as KSS or FPI penetrants may enter the existing running-in pad 12. Up to now, this condition could not be fulfilled, which has the consequence that, in addition to the dimension correction layers, the abradable coating 12 also had to be de-coated and re-applied. By masking the abradable coating 12 with the aid of the masking agent 14 according to the invention, partially the repair of the dimension correction layers can be carried out, whereas a complicated and cost-intensive decoating and resurfacing of the abradable coating 12 can be prevented.FIG. 5 shows a perspective detailed view of the housing part 10 in this regard, wherein the intake covering 12 is covered with the masking agent 14. The composition and use of the masking agent 14 are as in the preceding example. Removal of the masking agent 14 after performing the processing steps may again be accomplished by simple manual and / or machine stripping.FIG. 6 shows a perspective detailed view of a thermally sprayed fin coating 12 (wear protection layer) of a component 10 of an aircraft engine, which component is designed as a rotor (slide). The surface of this slide 10 could not be wetted during crack testing for reasons which cannot be understood. The cleaning carried out several times for the fin coating 12 already present on the component 10 using a cleaning agent without problems for the fin coating 12 did not lead to the desired wettability. Alternative cleaning with an alkaline cleaner would damage unprotected fin coating 12. By masking the fin coating 12 with the masking agent 14 according to the invention, the component 10 with the more effective alkaline cleaning agent could be cleaned without having to damage the fin coating 12 or to remove and renew the fin coating 12. FIG. 7 shows a perspective detailed view of the fin coating 12 which is covered with the masking agent 14 in order to be able to perform cleaning with the alkaline cleaning agent. After cleaning, the masking agent 14 could be removed again easily.FIG. 8 shows a perspective detailed view of a surface region 12 of an aircraft engine component 10 designed as a rotor, said surface region being designed as an abradable coating. The open-porous structure of the abradable coating 12 can be seen again, which has previously made masking or masking difficult to impossible due to the risk of invading, conventional masking agents. As already mentioned, a tape or tape (not shown) can optionally also be applied here first, to which the masking agent 14 according to the invention is then applied. However, with a sufficiently high viscosity of the (uncrosslinked) masking agent 14, a direct application can also take place here. FIG. 9 shows a perspective detailed view of the running-in pad 12 which is directly covered with the masking means 14.The parameter values specified in the documents for defining process and measurement conditions for characterizing specific properties of the subject matter of the invention are also to be considered included within the scope of the invention within the scope of deviations-for example on account of measurement errors, system errors, scale-in errors, DIN tolerances and the like.List of reference numbers:10 Component 12 Surface region 14 Masking means

Claims

Masking agent (14) for covering a surface region (12) of a component (10) of a turbomachine, in particular for covering a thermal spray layer, characterized in that it comprises at least one crosslinkable elastomer precursor having a dynamic viscosity at 25±0.2°C of between 21000 mPas and 39000 mPas.Masking agent (14) according to Claim 1, characterized in that the at least one elastomer precursor is photocrosslinkable and in that the masking agent (14) additionally comprises at least one photoinitiator.Masking agent (14) according to claim 1 or 2, characterized in that it additionally comprises a fluorescent additive.Masking agent (14) according to one of Claims 1 to 3, characterized in that the at least one elastomer precursor comprises (meth)acrylate monomers, in particular hexanediol di(meth)acrylate and / or isobornyl (meth)acrylate and / or trimethylolpropane tri(meth)acrylate, and / or (meth)acrylate oligomers, in particular urethane (meth)acrylate oligomers.Method for machining a component (10) of a turbomachine, in which at least one surface region (12) of the component (10) is first covered with a masking means (14) according to one of Claims 1 to 4 and the component (10) is subsequently machined.Method according to Claim 5, characterized in that the surface region (12) of the component (10) is cleaned before application of the masking agent (14) and / or is covered with a covering agent, in particular an adhesive tape, to which the masking agent (14) is then applied, and / or in that the masking agent (14) is crosslinked, preferably photochemically, after application to the surface region (12).Method according to claim 5 or 6, characterised in that the masking agent (14) is applied to the surface region (12) by means of bead application, wherein beads adjoining one another are preferably arranged offset to one another, and / or in that the masking agent (14) is applied to the surface region (12) with a layer thickness of at least 0.5 mm.Method according to one of Claims 5 to 7, characterized in that the masking means (14) is used to cover at least in regions an Ni-based plasma spray layer and / or a thermally sprayed running-in coating and / or a thermally sprayed wear protection layer of the component (10).Method according to one of Claims 5 to 8, characterized in that, after covering the surface region (12), the component (10) is chemically processed, in particular cleaned, decoating and / or coated with a test agent and / or a cooling lubricant and / or an anti-splashing layer.Method according to one of Claims 5 to 9, characterized in that the masking agent (14) is at least partially removed from the component (10) after the processing of the component (10), in particular by pulling off and / or by exposure to a solvent and / or by burning out.

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