METHOD FOR TREATING A SURFACE OF A METALLIC PART OF A TURBOMACHINE

Abstract

A method for treating a surface of a metallic part in particular of a turbomachine includes a step of shot-peening a surface of the metallic part using metallic beads and a step of cleaning the surface of the metallic part after the shot peening. The cleaning comprises step includes applying a magnetic cleaning paste to the surface of the metallic part in such a way as to remove any residues of metallic beads.

Claims

1. A method for treating a surface of a metallic part, in particular of turbomachine, the method comprising a step of shot-peening a surface of the metallic part using metallic beads and a step of cleaning the surface of the metallic part after the shot-peening, wherein the cleaning comprises applying a magnetic cleaning paste, comprising at least one polymer and a magnetic powder to the surface of the metallic part so as to remove any residues of the metallic beads.

2. The method according to claim 1, wherein the metallic part is made of titanium or a titanium alloy.

3. The method according to claim 1, wherein the material of the metallic beads comprises steel.

4. The method according to claim 1, further comprising a degreasing step subsequent to the cleaning step.

5. A paste for cleaning a metallic part, in particular of a turbomachine, comprising at least one polymer and a magnetic powder configured so as to remove any residues of metallic beads when applied to a surface of the metallic part in order to clean said metallic part.

6. The cleaning paste according to claim 5, wherein the polymer is comprised in the group polyurethane, polyester-polyurethanes, polyether-polyurethane, polyester, polyamide, epoxyester resin, polyesteramides and/or alkyds, polysiloxanes and mixtures thereof.

7. The cleaning paste according to claim 5, wherein the magnetic powder comprises magnetite or iron filings.

8. The cleaning paste according to claim 5, wherein the magnetic powder is present in the cleaning paste in an amount of between 40% and 80% by weight compared to a total weight of the paste.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0019] The invention will be better understood, and other purposes, details, characteristics and advantages thereof will become clearer on reading the following detailed explanatory description of embodiments of the invention given by way of purely illustrative and non-limiting examples, with reference to the attached schematic drawings in which:

[0020] FIG. 1 is a schematic axial cross-sectional view of a shot-peening installation to which the invention applies; and

[0021] FIG. 2 shows a schematic perspective view of the application of a cleaning paste to the surface of a segment of a “shot-peened” metallic part to be treated according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022] FIG. 1 shows an installation 1 for the surface treatment of a metallic part, in particular a turbomachine. Of course, the invention is not limited to the turbomachine parts.

[0023] The installation 1 for the surface treatment is a shot-peening installation. More specifically, the installation comprises an enclosure 2 and a bead projecting device 3. The enclosure comprises lateral walls 4, one of which comprises an opening 5 allowing the installation of the part in the enclosure 2. The projecting device 3 is installed inside the enclosure 2 and comprises nozzles 6 for spraying beads as projectiles onto the surface of the part to be treated at high speed. A support 7 intended to hold a metallic part 8 is arranged within the enclosure. In other words, the walls of the enclosure surround the metallic part. The support 7 can be movable in rotation to drive the metallic part in rotation. A door 4a allows to close off the opening 5 to prevent beads from being sprayed out of the enclosure during the shot-peening operation.

[0024] Alternatively, the beads are sprayed onto the surface 10 of the part using ultrasound. In this case, the bead projecting device comprises one or more sonotrodes (not shown) each comprising a vibrating surface which is intended to move the beads towards the surface of the part.

[0025] The beads are metallic. These are advantageously, but not necessarily, made of steel. The beads have a diameter of between 0.5 and 2 mm and a hardness of between 8 and 10 Mohs.

[0026] The metallic part 8 to be treated can be a turbine vane, a movable wheel intended to carry vanes or another member of the turbomachine. The material of the metallic part is comprised in the group comprising titanium or titanium alloy, steel, aluminium, and nickel-based super-alloys. Advantageously, but not restrictively, the metallic part is made of titanium or titanium alloy.

[0027] In a method for treating the surface of a metallic part, in particular for a turbomachine, it comprises a step of shot-peening the surface of the metallic part to be treated. The shot-peening step is carried out by means of a shot-peening installation as described above.

[0028] The method then comprises a step of cleaning the surface of the metallic part to remove any embedded beads 9 or metallic residue deposits from the surface of the metallic part. In the case of steel beads, the deposit comprises ferrous residues.

[0029] With reference to FIG. 2, the cleaning step comprises the application of a magnetic cleaning paste 11 to the surface 10 of the part. As the cleaning paste 11 is magnetic, it will be able to “attract” the beads 9 or residues of the material of the beads more easily.

[0030] In the present invention, the term “paste” is taken to mean a composition which is soft, i.e. which has a viscosity between a solid and a liquid and which is easily malleable.

[0031] The cleaning paste 11 is flexible or soft so that it can access all the hard-to-reach areas of the surface of the metallic part. Typically, the cleaning paste 11 is malleable by hand at room temperature.

[0032] In the present application, the cleaning paste 11 comprises at least one polymer and a magnetic powder.

[0033] The polymer allows on one hand to hold the magnetic powder together in the paste and, on the other hand, to adhere to the part to loosen the beads 9 or residues of the material of the beads.

[0034] The polymer is selected from the group comprising polyurethane, polyester-polyurethanes, polyether-polyurethane, polyester, polyamide, epoxyester resin, polyesteramides and/or alkyds, polysiloxanes and mixtures thereof. Advantageously, the polymer is silicone (polysiloxane).

[0035] The magnetic powder comprises an amount by weight between 40% and 80% of the total weight of the paste 11 comprising the polymer.

[0036] The magnetic material is selected from the group comprising magnetite or iron filings. The iron has a high magnetic susceptibility compared to the titanium. The magnetite allows the iron of the steel beads to be easily attracted to the part made of titanium. The magnetic susceptibility is the ability of a part to become magnetised under the action of a magnetic excitation.

[0037] In particular, the material of the beads has a higher magnetic susceptibility than that of the material of the metallic part.

[0038] The magnetic powder comprises particles with a particle size of between 200 μm and 800 μm.

[0039] In the cleaning step, the cleaning paste 11 is “rolled” onto the surface 10 of the part 8 so that the magnetic particles trap the residues of the metallic beads in the cleaning paste. We understand that there is no friction which allows the physical integrity (e.g. scratches) of the part to be maintained after the paste has passed through. At each passage, the operator kneads the paste 11 and the residues to obtain a homogeneous mixture and to apply this mixture again on the surface of the part to be treated.

[0040] Finally, the method comprises a degreasing step after the cleaning step. The degreasing step allows to remove all greasy residues and metallic deposits from the surface of the part. The greasy residues are related to the handling of the part and the nature of the cleaning paste.

[0041] The degreasing step is carried out using a cleaning or degreasing bath that is compatible with the material of the metallic part. The cleaning bath consists of immersing the part for a specific time in alkaline solutions and under defined temperature and concentration conditions.

[0042] Alternatively, the surface of the part is sprinkled with the cleaning bath under the same time and temperature conditions.

[0043] The cleaned (decontaminated) and degreased surface of the metallic part is free of all residues and is ready to be put into service or put back into service under the intended conditions of use. The treated part will not undergo galvanic cutting during its operation.