This application claims priority to German Patent Application DE102009021561.1 filed May 15, 2009, the entirety of which is incorporated by reference herein.
This invention relates to a method and an apparatus for etching the surfaces of integrally bladed rotors (blisks) of aircraft gas turbines.
The surfaces of the rotors of turbines or compressors of aircraft gas turbines are, as is generally known, subjected to an etching process after finish machining by mechanical or chemical removal processes to enable a structural examination to be subsequently made and structural defects, if any, to be better imaged and revealed and, finally, the in-service failure safety of critically classified rotary components to be improved. Surface etching of rotors made of nickel-base material can, among others, be accomplished by immersion in an etchant. The etching effect of this process is, however, not strong enough to enable a satisfactory structural examination to be made and positively and reliably detect all structural defects. It has also been proposed that the surface of unbladed rotor disks made of nickel-base material be etched electrolytically. Here, the electrochemical removal of surface material is effected by the transfer of electric charge between the metallic material of the workpiece and a liquid electrolyte. In this process, the rotor disk is immersed into the electrolyte and connected as anode (positive pole of a direct-current source). The flow of current via the electrolyte and a cathode, in connection with the electrolyte, causes material to be removed from the metal surface by metal ions going into solution. The apparatus provided for the performance of the etching process includes a container which is filled with electrolyte and has cathodes arranged on the sidewalls and, disposed above the container and suspended from a contact bar forming the positive pole, a holding device for the rotor disk thus acting as anode. On unbladed disks, electrolytic etching using this apparatus, as compared to pure immersion etching, enables a stronger etching effect to be obtained and structural examination to be improved. For the structural examination or the safe detection of structural defects of bladed rotors (blisks) in nickel-base material, electrolytic etching using the known apparatus is only restrictedly useful because the etching effect in the blade area, due to the complex blade geometry and the current losses occurring from the contacts at the rotor disk to the blade tips, is inconsistent and also lower in relation to the disk surface. Therefore, the removal of surface material from blisks for the purpose of subsequent structural examination is performed by use of the more consistent, but less intense, immersion etching process by which, however, reliable structural examination is not ensured.
A broad aspect of this invention is to provide a method and an apparatus for etching the surfaces of integrally bladed rotors (rotor disks) in nickel-base material such that a reliable detection of structural defects in ensured in all surface areas.
The present invention provides that nickel-base, integrally bladed rotors for aircraft gas turbines are electrolytically etched for structural examination in that, from all parts of the rotor connected as anode, a uniform current flow via the electrolyte to the main and auxiliary cathodes is produced in the blade areas remote from the electrical contact points at the rotor disk by providing additional auxiliary cathodes disposed aside the main cathodes, thereby obtaining a sufficiently strong and consistent etching effect for blisks made of nickel-base material and ensuring reliable structural examination also in the bladed area.
According to the present invention, an apparatus for obtaining uniform current flow from the entire surface of the rotor connected as anode via the electrolyte includes an electrolyte-filled container with main cathodes arranged therein and, suspended from a contact bar, a holding device with contacting and retaining pins for retaining and electrically contacting the rotor at the rotor disk. In the area of the blades integrally formed onto the rotor disk, auxiliary cathodes are arranged which are adaptable in form, size and arrangement to the blade geometry and the current flow to be obtained via the electrolyte to control the etching effect in the blade area. Besides uniform etch attack, the auxiliary cathodes related to the blades also provide for protection against burning of the blade tips.
In a further development of the present invention, the auxiliary cathodes for influencing the current flow and the etching effect are arranged at one or both blade edges and/or at the blade tips and/or each between the blades at a distance corresponding to the respective requirements.
In a further development of the present invention, the auxiliary cathodes are provided as an annular disk spaced from the blade side edges or as a tubular section spaced from the blade tips or also as a ring with a certain, for example circular, cross-sectional shape. The auxiliary cathodes may also include a plurality of individual cathode sections arranged beside, above, beneath or between the blades.
In a further development of the present invention, the holding device has a retaining bracket at whose bottom end first and second retaining arms are provided. Arranged at the mutually facing free ends of the retaining arms are the contacting and retaining pins engaging on both sides with the thickened inner area of the rotor disk and connecting to the positive pole of a direct-current source. Thus, the wetting of the rotor is only interrupted at the points of engagement between the contacting and retaining pins and the rotor disk.
In development of the present invention, the auxiliary cathodes are attached to the retaining bracket in an electrically insulated manner and connected to an electric conductor routed in an insulated manner on the retaining bracket and connecting to the negative pole of a direct-current source.
The first retaining arms are attached directly to the retaining bracket, and the second retaining arms are threadably attachable to the retaining bracket by a threaded connection to clamp the rotor disk between the contacting and retaining pins.
The present invention is more fully described in light of the accompanying drawings showing a preferred embodiment. In the drawings,
The etching apparatus illustrated in
The holding device 5 exemplified in
After being cleaned, the rotor 6 (blisk) is etched upon attachment to the holding device, immersion in the electrolyte 1 kept under agitation by a stirrer (not shown) and application of a specific voltage. The flow of current from the workpiece acting as an anode via the electrolyte to the cathode will not take place in the blade area via the more remotely situated main cathodes 3, but directly via the auxiliary cathodes 10 positioned closer to the blades 9 or the blade area, respectively, and designed in accordance with the blade geometry, thus enabling a material removal to be specifically set via the auxiliary cathode parameters (shape, size, distance, arrangement) which in all blade parts is uniform and appropriate for structural examination. Upon removal from the electrolyte 1 and the holding device 5, the rotors 6 (blisks) thus etched are multiply rinsed/cleaned and subsequently dried, being then reliably structurally examinable in all areas of the rotor disk 7 and the blades 9.
Number | Date | Country | Kind |
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10 2009 021 561.1 | May 2009 | DE | national |