EP4013908A1

EP4013908A1 - Method for coating a turbomachine part

Info

Publication number: EP4013908A1
Application number: EP20754794.4A
Authority: EP
Inventors: Stéphane KNITTEL; Léa Rébecca GANI; Florence Ansart; Romain NOIVILLE; Pierre-Louis Taberna; Julien WAGNER
Original assignee: Safran Aircraft Engines SAS; Centre National de la Recherche Scientifique CNRS; Universite Toulouse III Paul Sabatier
Current assignee: Safran Aircraft Engines SAS; Centre National de la Recherche Scientifique CNRS; Universite Toulouse III Paul Sabatier
Priority date: 2019-08-12
Filing date: 2020-07-30
Publication date: 2022-06-22
Anticipated expiration: 2040-07-30
Also published as: EP4013908B1; US20220290320A1; WO2021028628A1; FR3099935B1; CN114302980A; CN114302980B; FR3099935A1

Abstract

The invention relates to a method for coating a turbomachine part (1), comprising the deposition of a paint by electrophoresis on the turbomachine part, the voltage between the part and a counter-electrode (20) being controlled during the deposition by imposing a succession of pulsed voltage cycles.

Description

Title of the invention: Process for coating a part of a turbomachine

Technical area

The present invention relates to a process for coating a part of a turbomachine with a paint, for example with an anti-corrosion paint, by implementing a deposition step by electrophoresis.

Prior art

High strength steels such as Maraging 250 or ML340 can be used to form turbomachine parts. However, these steels can be susceptible to corrosion in operation.

In order to protect the parts from corrosion, it is known practice to coat them with anti-corrosion paints sprayed using a paint gun. With this type of method, controlling the thickness of the paint applied can be relatively tricky, especially if the part has complex geometry. It is then possible to obtain non-conforming coatings which do not exhibit satisfactory corrosion resistance.

It is therefore desirable to have a process for depositing a coating, for example an anti-corrosion coating, which makes it possible to obtain in a simple manner a coating having the desired properties, for example satisfactory anti-corrosion protection.

Disclosure of the invention

The invention relates to a method for coating a part of a turbomachine, comprising:

the deposition of a paint by electrophoresis on the turbomachine part, the voltage between the part and a counter-electrode being controlled during the deposition by imposing a succession of pulsed voltage cycles, each of these cycles having:

(i) a first voltage stabilization phase during which a first potential difference is imposed between the part and the counter-electrode, and a second voltage stabilization phase during which a second difference of potential is imposed between the part and the counter-electrode, the absolute value of the first potential difference being between 0.1V and 30V, and the absolute value of the second potential difference being less than the absolute value of the first potential difference, and

(ii) a ratio R [duration of the first phase] / [duration of the first phase + duration of the second phase] of between 1/10 and 1/2.

For the sake of brevity, the expressions “first phase of voltage stabilization” and “second phase of voltage stabilization” will be referred to below respectively as “first phase” and “second phase”. The ratio R [duration of the first phase] / [duration of the first phase + duration of the second phase] will for its part be referred to below by the expression “ratio R”.

Thanks to the use of the pulsed voltage cycles described above, the invention makes it possible to obtain a homogeneous and dense coating, for example conferring satisfactory protection against corrosion. The invention makes it possible, in particular, to avoid the phenomenon of “bubbling” of the electrolyte associated with the electrolysis of water which may be encountered when a direct voltage is imposed during electrophoresis. This “bubbling” phenomenon results in a coating that is much less homogeneous and therefore significantly less efficient. The invention is based on the implementation of an electrophoresis technique with specific electrical parameters, which makes it possible to obtain the desired coating in a simple manner. The electrophoresis technique implemented in the invention also makes it possible to better control the thickness of the coating deposited with respect to the projection using a paint gun. It is thus of very particular interest for coating parts having a complex geometry.

In an exemplary embodiment, the absolute value of the first potential difference is less than or equal to 15V.

The use of a first potential difference limited in absolute value makes it possible to further improve the homogeneity of the coating obtained.

In particular, the absolute value of the first potential difference may be less than or equal to 10V, for example less than or equal to 7 V. The absolute value of the first potential difference may be between 2V and 15V, for example example between 2V and 10V, for example between 5V and 10V, for example between 5V and 7V or between 2 V and 7 V.

In an exemplary embodiment, the absolute value of the second potential difference is less than or equal to 5V.

The use of a second potential difference limited in absolute value makes it possible to further improve the homogeneity of the coating obtained.

In an exemplary embodiment, the ratio R is between 1/10 and 1/3.

The use of these values for the ratio R makes it possible to further improve the homogeneity of the coating obtained.

In particular, the ratio R can be between 1/10 and 1/4. The ratio R can also be between 1/6 and 1/3 or between 1/6 and 1/4.

In an exemplary embodiment, the pulsed voltage cycles are repeated with a frequency less than or equal to 1 kHz during the deposition by electrophoresis.

Limiting the repetition frequency of the pulsed voltage cycles is advantageous in order to increase the relaxation time of the system between two successive first phases, which makes it possible to further improve the homogeneity of the coating obtained.

In particular, said frequency may be less than or equal to 100 Hz, or even less than or equal to 10 Hz.

In an exemplary embodiment, the paint is inorganic.

The use of an inorganic paint is advantageous when the turbomachine part is intended to operate at relatively high temperatures outside the stability range of organic paints.

In an exemplary embodiment, the paint is an anti-corrosion paint.

In an exemplary embodiment, the part is a part of an aircraft turbomachine.

Brief description of the drawings

[Fig. 1] FIG. 1 schematically and partially illustrates the implementation of a method according to the invention.

[Fig. 2] FIG. 2 schematically and partially illustrates the implementation of a method according to the invention. [Fig. 3] FIG. 3 illustrates an example of a succession of pulsed voltage cycles that can be implemented within the framework of the invention.

[Fig. 4] FIG. 4 illustrates an example of a succession of pulsed voltage cycles that can be implemented within the framework of the invention.

[Fig. 5] FIG. 5 schematically represents a turbomachine blade which can be coated by the process according to the invention.

[Fig. 6] FIG. 6 is a photograph showing the coating obtained in the context of a process according to the invention.

[Fig. 7] FIG. 7 is a photograph showing the coating obtained in the context of a process outside the invention.

[Fig. 8] FIG. 8 is a photograph showing the coating obtained in the context of a process according to the invention.

[Fig. 9] FIG. 9 is a photograph showing the coating obtained in the context of a process according to the invention.

[Fig. 10] FIG. 10 is a photograph showing the coating obtained in the context of a process according to the invention.

[Fig. 11] FIG. 11 is a photograph showing the coating obtained in the context of a process according to the invention.

[Fig. 12] FIG. 12 is a photograph showing the coating obtained in the context of a process according to the invention.

[Fig. 13] FIG. 13 is a photograph showing the coating obtained in the context of a process according to the invention.

[Fig. 14] FIG. 14 is a photograph showing the coating obtained in the context of a process according to the invention.

[Fig. 15] FIG. 15 is a photograph showing the coating obtained in the context of a process according to the invention.

[Fig. 16] FIG. 16 is a photograph showing the coating obtained in the context of a process according to the invention.

[Fig. 17] FIG. 17 is a photograph showing the coating obtained in the context of a process according to the invention. Description of embodiments

Referring to Figures 1 and 2, the part 1 to be coated is immersed in a bath of a paint 10 which is for example an anti-corrosion paint. The surface of the part 1 intended to be coated with the paint may have been prepared beforehand in a conventional manner by a chemical and / or mechanical pickling step.

The surface of the part 1 intended to be coated comprises an electrically conductive material. The part 1 can be made of a metallic material, for example aluminum or an aluminum alloy, steel or a nickel or cobalt-based superalloy. Part 1 may be an aircraft turbomachine part. The part 1 can be a turbine engine blade, such as a turbine blade or a compressor blade, a turbine shaft or part of a turbine shaft, a compressor shaft or part of a compressor shaft.

Part 1 constitutes an electrode which is connected to a first terminal of a voltage generator G. A counter-electrode 20 is present opposite the surface of the part 1 to be coated and is also immersed in the paint bath 10. The counter-electrode 20 is connected to a second terminal of the voltage generator G, different from the first thick headed.

During the deposition by electrophoresis, the generator G imposes specific pulsed voltage cycles between the part 1 and the counter-electrode 20 which will be illustrated in more detail below in connection with FIGS. 3 and 4. A stirring means ( not shown) may be present in the paint bath 10 in order to ensure mixing of this bath during the deposition.

A commercial paint known per se can be used. The paint 10 is typically in the form of a suspension comprising solid particles 11 dispersed in a liquid medium. Advantageously, the paint 10 can be devoid of chromium at the oxidation degree + VI in order to be compatible with the “Registration, evaluation and authorization of chemicals” (“REACH”) regulation. The paint 10 may contain chromium with the oxidation degree +111. As an example of a paint that can be used, there may for example be mentioned the paint sold under the reference SERMETEL W® by the company PRAXAIR.

The particles 11 of the paint 10 may comprise one or more pigments, for example one or more anti-corrosion pigments in the case of an anti-corrosion paint. corrosion. These pigments are typically chosen from: metal phosphates, for example zinc phosphate, metal chromates, such as magnesium chromate, or halo-zirconates, or from mixtures of such compounds. Electrically conductive particles, such as aluminum particles, can be added to the pigment (s). The addition of these conductive particles makes it possible to give the layer 6 an electrically conductive character, which makes it possible to avoid a self-limiting effect of the deposition by electrophoresis and to be able, if desired, to deposit a layer 6. relatively thick. In the event that such conductive particles are not present, the treated surface may become more and more insulating as the layer 6 is deposited, naturally slowing or even stopping the formation of the latter. By way of illustration, the thickness e of the deposited layer 6 may be greater than or equal to 35 μm, for example between 35 μm and 70 μm.

By way of illustration, the average size D50 of the particles 11 of the paint 10, optionally agglomerated, may be less than or equal to 10 μm, for example between 0.1 μm and 10 μm. The liquid medium of the paint can typically include a binder and a solvent. The paint 10 can optionally further comprise one or more additives making it possible to adjust its properties, such as its viscosity or the stability of the suspension.

During the deposition, the generator G imposes a variable potential difference between the part 1 and the counter-electrode 20. Due to the application of an electric field between the part 1 and the counter-electrode 20, the particles 11 of electrically charged paint moves and is deposited on part 1 in order to obtain layer 6. The example illustrated in Figures 1 and 2 concerns the case where part 1 is negatively charged during the first phases of voltage cycles, the particles 11 being positively charged. The particles 11 are thus deposited on the part 1 during the first phases of the voltage cycles. However, it does not depart from the scope of the invention if the part 1 is positively charged during the first phases of the voltage cycles and the negatively charged particles. By way of illustration, when the particles 11 are positively charged, they may have a zeta potential greater than or equal to 1 mV, for example greater than or equal to at 10 mV. The zeta potential of the particles 11 can typically be between 1 mV and 100 mV, for example between 10 mV and 30 mV.

The preceding description has attempted to describe the electrophoretic system and the formation of layer 6 in connection with FIGS. 1 and 2. We will now describe FIGS. 3 and 4 which illustrate examples of pulsed voltage cycles that can be put into operation. work within the scope of the invention.

According to the example of FIG. 3, each voltage cycle C1 comprises a first phase PI of stabilization in positive voltage during which a first constant potential difference DDP1 is imposed between the part 1 and the counter-electrode 20. Unless stated otherwise, the potential differences correspond to the following difference: [(electrical potential of part 1) - (electrical potential of counter-electrode 20)]. The first potential difference DDP1 is between 0.1V and 30V, for example between 5V and 7V. FIG. 3 relates to the case where the part 1 is positively charged during the first phases PI at a potential greater than that of the counter-electrode 20 but it is not beyond the scope of the invention when the part is negatively charged during these phases as illustrated in Figure 4 which will be discussed below. Each voltage cycle C1 further comprises a second voltage stabilization phase P2 during which a second constant potential difference DDP2 is imposed between the part 1 and the counter-electrode 20. Each voltage cycle C1 comprises a single first phase PI and a single second phase P2. The absolute value of the second potential difference DDP2 is less than the first potential difference DDP1. The absolute value of the second potential difference DDP2 can be less than or equal to half of the first potential difference DDP1. The absolute value of the second potential difference DDP2 can be less than or equal to 5V. In the example illustrated in FIG. 3, the case of a second negative potential difference DDP2 has been shown. This case corresponds to the application of an alternating voltage between the part 1 and the counter-electrode 20 during the deposition by electrophoresis. As a variant, we could have a zero or positive potential difference DDP2. During the deposition by electrophoresis, there is alternation between the first phases P1 of voltage stabilization and the second phases P2 of voltage stabilization. There are thus successively: realization of a first phase PI of stabilization in voltage of a first cycle, then of a second phase P2 of stabilization in voltage of this first cycle, then realization of a first phase PI of stabilization in voltage of a second cycle, then of a second phase P2 of voltage stabilization of this second cycle and so on.

As indicated above, the relative durations of the first phases PI and of the second phases P2 are controlled within the framework of the invention. Thus for each cycle C1 of pulsed voltage, the ratio R, which corresponds to the ratio Tl / [Tl + T2], is fixed at a predetermined value between 1/10 and 1/2, where Tl denotes the duration of the first phase PI and T2 the duration of the second phase P2. The ratio R is, for example, between 1/6 and 1/4.

Pulsed voltage cycles C1 can be repeated periodically during electrophoretic deposition as illustrated. The repetition frequency of the pulsed voltage cycles may be less than or equal to 1 kHz, for example less than or equal to 100 Hz, for example less than or equal to 5 Hz. This frequency may be between 0.1 Hz and 1 kHz, for example between 0.1 Hz and 100 Hz, for example between 1 Hz and 100 Hz, for example between 1 Hz and 10 Hz, or even between 1 Hz and 5 Hz.

Pulsed voltage cycles C1 can be applied for a period greater than or equal to 1 minute. This duration may be less than or equal to 30 minutes, for example less than or equal to 10 minutes. This duration can be between 1 minute and 30 minutes, for example between 1 minute and 10 minutes. FIG. 4 shows a variant in which the part is negatively charged during the first phases P10 of voltage stabilization. Thus in this case, each voltage cycle CIO comprises a first phase P10 of stabilization in negative voltage during which a first constant potential difference DDP10 is imposed between the part 1 and the counter-electrode 20. The absolute value of the potential difference DDP10 checks the values given above. Each voltage cycle CIO further comprises a second phase P20 of voltage stabilization during which a second constant potential difference DDP20 is imposed between the part 1 and the counter-electrode 20. This second potential difference DDP20 verifies the conditions mentioned above. In the example of FIG. 4, the case of a second positive potential difference DDP20 has been shown, but it is not beyond the scope of the invention whether DDP20 is zero or negative. The durations T10 and T20 of the stabilization phases P10 and P20, for their part, satisfy the same relative ratio condition as Tl and T2.

In general, the ratio R can vary between 1/10 and 1/2. It will be noted that for relatively high values of the ratio R, close to 1/2, it may be preferable to implement first potential differences limited in absolute value in order to improve the homogeneity of the layer formed.

The method of the invention can be implemented for the coating of a blade 21 of a turbomachine, comprising for example a root 22, a blade 24 and a head 26, like that illustrated very schematically in FIG. 5. The invention applies of course to other types of turbomachine parts, such as those listed above for example.

Examples Example 1

An anti-corrosion paint was applied using a two-electrode electrophoretic system comprising a platinum electrode and a 15CDV6 steel electrode. The anti-corrosion paint deposited was the paint sold under the reference SERMETEL W® by the company PRAXAIR.

A first test according to the invention was carried out by imposing a succession of pulsed voltage cycles, each pulsed voltage cycle had a first phase of stabilization in positive voltage at 10V and a second phase of stabilization in voltage at 0V. The part to be coated was positively charged during the first phases. Each pulse voltage cycle had an R ratio of 1/3. The voltage cycles were repeated at a frequency of 1 Hz and the deposition by electrophoresis was carried out for a period of 5 minutes. FIG. 6 is a photograph showing the appearance of the coating obtained.

By way of comparison, a second test outside the invention was carried out with the same electrophoretic system but by imposing a direct voltage at 10 V for 1 minute 40 (no alternation with second phases at zero voltage). This duration of 1 minute 40 corresponds to the cumulative duration of application of the voltage of 10V during the first test (= 5 minutes / 3). FIG. 7 is a photograph showing the appearance of the coating obtained.

It is observed that the deposit associated with FIG. 7 is much less homogeneous than that associated with FIG. 6. There was in fact a phenomenon of “bubbling” during the DC voltage deposition of FIG. 7 which led to a coating. heterogeneous.

Example 2

Additional tests were carried out using the same electrophoretic system as in Example 1 and using the same succession of pulsed voltage cycles as in the first test described in Example 1 except for the ratio R that has been changed.

FIG. 8 is a photograph showing the appearance of the coating obtained for a ratio R of 1/6 (coating thickness = 43 μm). FIG. 9 shows the result obtained for a ratio R of 1/4 (coating thickness = 31 μm).

In these two cases, a particularly homogeneous anti-corrosion deposit was obtained, even having an even better homogeneity compared to that of the first test of Example 1 using a ratio R of 1/3.

Example 3

Additional tests were carried out using the same electrophoretic system as in Example 1 and using the same succession of pulsed voltage cycles as in the first test described in Example 1 except for the value voltage of the first phases which has been modified.

FIG. 10 is a photograph showing the appearance of the coating obtained for a voltage of 7 V during the first phases (thickness of the coating = 23 μm). FIG. 11 shows, for its part, the result obtained when this voltage is 5V coating thickness = 28 μm).

In these two cases, a particularly homogeneous anti-corrosion deposit was obtained, even having an even better homogeneity compared to that of the first test of Example 1 using a voltage of 10V during the first phases . Example 4

Additional tests were carried out using the same electrophoretic system as in Example 1 and using the same succession of pulsed voltage cycles as in the first test described in Example 1 except for the value voltage of the second phases which has been modified.

FIG. 12 is a photograph showing the appearance of the coating obtained for a voltage of -2 V during the second phases (coating thickness = 38 μm).

In this case, a particularly homogeneous anti-corrosion deposit is obtained, even having an even better homogeneity compared to that of the first test of Example 1 using a voltage of 0 V during the second phases.

Example 5

Additional tests were carried out using the same electrophoretic system as in Example 1 and using the same succession of pulsed voltage cycles as in the first test described in Example 1 except for the duration. deposition by electrophoresis which was set at 1 minute. Several voltage values of the first phases were evaluated with this treatment time, namely: 10V (figure 13, coating thickness = 43 µm), 12V (figure 14, coating thickness = 31pm) and 15V (figure 15, thickness coating = 28 µm).

In all cases, an anti-corrosion deposit having good homogeneity is obtained.

Example 6

Additional tests were carried out using the same electrophoretic system as in Example 1 and using the same succession of pulsed voltage cycles as in the first test described in Example 1 except for the duration the deposition by electrophoresis which was set at 1 minute and the frequency which was changed. FIG. 16 shows the result obtained for a cycle repetition frequency of 2 Hz (coating thickness = 26 μm) and FIG. 17 the result obtained for a cycle repetition frequency of 5 Hz (coating thickness = 31 μm). In all cases, an anti-corrosion deposit having good homogeneity is obtained.

The expression "between ... and ..." should be understood as including the limits.

Claims

[Claim 1] A method of coating a part (1; 21) of a turbomachine, comprising:

- deposition of a paint by electrophoresis on the turbomachine part, the voltage between the part and a counter-electrode (20) being controlled during the deposition by imposing a succession of pulsed voltage cycles (Cl; CIO), each of these cycles having:

(i) a first phase (PI; P10) of voltage stabilization during which a first potential difference (DDP1; DDP10) is imposed between the part and the counter-electrode, and a second phase (P2; P20) of stabilization in voltage during which a second potential difference (DDP2; DDP20) is imposed between the part and the counter-electrode, the absolute value of the first potential difference being between 0.1V and 30V, and the absolute value of the second difference of potential being less than the absolute value of the first potential difference, and

[Claim 2] A method according to claim 1, wherein the absolute value of the first potential difference (DDP1; DDP10) is less than or equal to 15V.

[Claim 3] A method according to claim 2, wherein the absolute value of the first potential difference (DDP1; DDP10) is less than or equal to 10V.

[Claim 4] A method according to claim 3, wherein the absolute value of the first potential difference (DDP1; DDP10) is less than or equal to 7 V.

[Claim 5] A method according to any one of claims 1 to 4, wherein the absolute value of the second potential difference (DDP2; DDP20) is less than or equal to 5V.

[Claim 6] A method according to any one of claims 1 to 5, wherein the ratio R is between 1/10 and 1/3.

[Claim 7] A method according to claim 6, wherein the ratio R is between 1/10 and 1/4.

[Claim 8] A method according to any one of claims 1 to 6, wherein the pulsed voltage cycles (Cl; CIO) are repeated with a frequency less than or equal to 1 kHz during electrophoresis deposition.

[Claim 9] A method according to claim 8, wherein said frequency is less than or equal to 100 Hz.

[Claim 10] A method according to any of claims 1 to 9, wherein the paint is inorganic.

[Claim 11] A method according to any of claims 1 to 10, wherein the paint is an anti-corrosion paint.

[Claim 12] A method according to any one of claims 1 to 11, in which the part (1; 21) is an aircraft turbomachine part.