Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
  • B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
  • B24C1/10—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods for compacting surfaces, e.g. shot-peening
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
  • B24C5/00—Devices or accessories for generating abrasive blasts
  • B24C5/005—Vibratory devices, e.g. for generating abrasive blasts by ultrasonic vibrations
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/47—Burnishing
  • Y10T29/479—Burnishing by shot peening or blasting

Definitions

• the present invention relates to a process for treating and compressing surfaces comprising areas of difficult access, more specifically the axial retaining hooks of turbomachine blades comprising a groove between the hook and the root of the blade.
• the axial retaining hooks of the vanes in the housing thereof on a turbine disk and the rims of the turbine disks comprising a radial axial retaining groove of the vanes are highly stressed.
• the blade hooks undergo a high level of static stress, as to the grooves of the discs, there are problems of contact and wear between the disc and the flange applied against the face of the disc.
• the prestressing shot peening operation is a mechanical treatment intended to improve the properties of a metal part by surface hardening. It is based on the structural transformation of materials.
• the conventional method is to put the mechanical parts under superficial compression, by the projection of small steel balls, glass or ceramic. This micro-grinding operation creates a compressed zone which is the seat of internal compressive stresses by which the resistance is increased.
• the surface is hammered by spraying BA 315 steel balls (0.315 mm diameter steel ball) with an intensity F15A (according to the Almen number).
• a gas flow is used, produced by expansion through a nozzle, then the nozzle is moved parallel to the surface of the workpiece, or the workpiece relative to the nozzle, to cover the surface to be treated.
• shot blasting Given the difficulty of accessibility of certain areas, this type of shot blasting can not be done in optimal conditions. Indeed, the shot blast can not be directed directly on the surface and shot blasting is done by rebound, in the best case.
• Reball shot blasting is much less efficient because the balls arrive at the surface with a lower kinetic energy. Also, in in some cases, the level of compression is not sufficient to treat the surface of the room.
• Laser shock treatment is a process that aims to generate plasticizing shock waves in a material, in order to also improve its surface properties.
• the shock waves are obtained by focusing on the surface of the material a very intense laser pulse (GW / cm2) in the presence of a confinement medium for very short durations (a few nanoseconds).
• the treatment is capable of inducing residual compressive stresses of thicknesses up to several hundred micrometers on a wide variety of materials, particularly for applications in the field of steels, aluminum alloys or titanium .
• the treatment allows the improvement of surface properties, such as resistance to fatigue, wear or corrosion.
• One of the advantages of this technique lies in the fact that the surface states of the pieces are little modified.
• the applicant has set a goal of treating surfaces on a turbomachine blade axial retention hook having areas of difficult access to gas turbine engine parts using the ultrasonic shot blasting process.
• the ultrasonic shot blasting process makes it possible to compress and thereby harden the surface layers of metallic materials, the purpose of this technique being to improve the service life of the parts.
• the method consists of vibrating a sonotrode, at frequencies close to the ultrasonic frequency, via acoustic elements, connected to a generator. Beads of different types are propelled towards the material to be shot, via the sonotrode.
• the invention consists in applying the ultrasonic blasting process on said areas, such as blade grooves, for which processes such as conventional shot blasting or laser shock do not allow a complete recovery of the surface.
• the method of ultrasonic blasting, by means of a fog of balls set in motion in contact with a sonotrode, of a metal surface comprising a difficult access zone is characterized in that the surface being that of an axial retaining hook of a turbomachine blade comprising a groove formed between the hook and the root of the blade and a surface portion external to said groove, the ball mist is contained in an enclosure enclosing said surface.
• the application of the method gives the possibility of a deeper compression in the areas of difficult access and, consequently, allows the improvement of the tolerance to damage (fatigue, fretting, ..).
• the shot peening process targets parts made of a material of the group steel, titanium alloy or nickel-based superalloy or aluminum
• the invention is of interest when said hook groove has a width of between 1.5 mm and 10 mm and a depth of between 1.5 mm and 20 mm.
• They have a diameter less than or equal to 2.5 mm and a mass greater than or equal to 0.5 g, and a diameter of between 300 ⁇ m and 2.5 mm.
• the treatment time is between 5 and 200 seconds.
• the sonotrode forms a portion of the wall of the enclosure.
• Patent FR2816538 discloses a method for increasing the life of the blade fasteners on a turbine rotor using ultrasonic blasting of the grooves and blade roots. Shot peening is carried out with an Almen arrow at least equal to F8A in order to increase the compression prestressing of the surfaces in contact without increasing the roughness.
• the balls are projected by the percussion of a vibrating thankrode and contained in a chamber formed by the annular or axial groove, the sonotrode being introduced into the mouth of the latter and two ears covering the lateral openings.
• the accessibility of the areas to be treated is not in question in the teaching of this patent since the housing grooves of the blades allow the formation of enclosures with their wall.
• the patent FR 2873609 relates to ultrasonic blasting and the use of projectiles to obtain a sufficient intensity of treatment on concave surfaces having a radius of curvature lower than that of the projectiles.
• the projectiles have both a high hardness and a density while being of small dimension and their use makes it possible to treat areas that are difficult to access with conventional projectiles having small radii of curvature. These projectiles are capable of acquiring kinetic energy large enough to generate the desired level of stress in the room.
• This patent describes several embodiments of enclosures adapted to the configuration of the surfaces to be treated. However his teaching does not include the treatment of parts having a part with a throat of small opening.
• FIG. 1 shows schematically a turbomachine blade hook.
• FIG. 2 represents the schematization of the X-ray diffraction stress analysis zones.
• FIG. 3 shows the stress profile obtained by conventional shot blasting, on the analysis zone A of FIG. 2, with the abscissa depth in microns and the ordinate the value of the residual stress in MPa.
• Figure 4 shows the tooling for ultrasonic blasting of blade hooks.
• FIG. 5 shows the stress profile obtained by ultrasound shot blasting, on the analysis zone A of FIG. 2.
• the rotor discs comprise a rim, on the periphery of which is mounted a plurality of removable blades.
• the blades are mounted in axial grooves, dovetail for example, machined in the rim, and comprise a foot, also dovetail, machined at the base of the blade, the assembly being effected by the fitting of the foot into the groove.
• the blade roots are nested in the grooves by sliding, with limited play.
• the feet are immobilized axially by means of axial retaining hooks integral with the blade root. The hooks cooperate with a transverse rod disposed between the root of the blade and the hook.
• the grooves contain the axial movement of the feet of dawn.
• the material is included in the group steel, titanium alloy, superalloy based on nickel or aluminum.
• Figure 1 shows the geometry concerned by application of the method of the invention.
• the surface to be treated comprises the interior of the groove 5 formed between the hook 20 and the foot 13 of the blade as well as the adjacent outer surface portion 7. It consists of an inverted U-shaped zone 5. The width of this zone varies between 1.5 mm and 10 mm, and the depth varies between 1.5 mm and 20 mm.
• the surface to be treated also comprises the surface portion 7 of the outer hook at the groove 5.
• the hooks are highly stressed; the high level of static stresses on said hooks can cause problems of breakage and wear.
• FIG 4 shows the tooling developed to allow ultrasonic blasting of the hooks.
• the blade 10 comprises, schematically a blade 11, a foot 13, section for example dovetail, and possibly a stilt.
• a platform is interposed between the foot 13 and the blade 11.
• the tooling 30 comprises a support plate with a vibrating surface 32 and a sonotrode, excited by means for producing vibrations at an ultrasonic frequency, not shown in the drawings.
• Said vibrating surface constitutes the active wall of an enclosure 25.
• an opening 26 is formed, through which the hook 20 has been introduced. dawn 10.
• the opening 26 is closed by the face of the foot of the blade with the hook.
• the hook 20 is thus included in the enclosure.
• the groove 5 and the surface portion 7 of the hook, adjacent and external to the groove, are included in the enclosure.
• the throat here has a width of 3.2 mm and a depth of 7.26 mm.
• the vibrating surface 32 is situated at a short distance from the hook 20. It is wider than the groove 5 and at least partially sees the surface portion of the external hook at the groove 5.
• Balls 2 with a diameter of 1.5 mm, are introduced into the chamber 25 through the opening 26.
• a ball fog is created. in the chamber 25.
• the balls are propelled towards the hook 20, striking the wall of said groove 5 and the adjacent surface portion 7.
• the frequency of the ultrasonic oscillations, the dimensions of the vibrating surface 32, as well as the diameter, the material and the mass of the balls are chosen so that the zone of the groove of the hook but also the portion of the outer surface at the groove is shot blast homogeneously for a very short time.
• a significant advantage of ultrasound blasting is that its implementation requires only a small amount of beads. In the present case, it is therefore possible to use high quality balls such as steel rolling balls. These beads have a higher hardness than tungsten carbide balls.
• the steel bearing balls do not break, they are perfectly spherical, and therefore do not produce sharp stops that can increase the roughness of the surface of the shot blasted part.
• the blasting time is determined according to the recovery rate, the recovery ratio being the ratio between the impacted surface and the total surface exposed to shot blasting.
• the development of ultrasonic shot blasting was carried out on a hook 20 over an area 3.2 mm wide and 7.26 mm deep.
• the parameters used for the process were as follows: diameter of the beads between 300 ⁇ m and 2.5 mm, with a mass of between 0.5 and 5 grams, an amplitude of between 20 and 500 ⁇ m, and with a treatment time varying between 5 and 200 seconds.
• FIG. 5 shows the stress profile obtained by ultrasonic peening, object of the invention, in zone 2 of the hook 20 represented in FIG.
• zones A and B of FIG. 2 SEM analyzes were carried out in order to verify the overlap obtained by ultrasonic shot blasting.
• SEM analysis provides a reflected image of the sample (magnified up to 100,000 times or more), highlighting details that can not be detected otherwise.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Laser Beam Processing (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)
• Turbine Rotor Nozzle Sealing (AREA)
• Rolling Contact Bearings (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)
• Crushing And Pulverization Processes (AREA)
• Disintegrating Or Milling (AREA)

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• 2008
  • 2008-04-18 FR FR0802178A patent/FR2930184B1/fr not_active Expired - Fee Related
• 2009
  • 2009-04-17 JP JP2011504478A patent/JP5511789B2/ja active Active
  • 2009-04-17 AT AT09732287T patent/ATE541673T1/de active
  • 2009-04-17 US US12/988,436 patent/US8627695B2/en active Active
  • 2009-04-17 CN CN200980118191.9A patent/CN102123828B/zh active Active
  • 2009-04-17 RU RU2010146976/02A patent/RU2507055C2/ru active
  • 2009-04-17 EP EP09732287A patent/EP2288473B1/de active Active
  • 2009-04-17 ES ES09732287T patent/ES2379577T3/es active Active
  • 2009-04-17 WO PCT/EP2009/054595 patent/WO2009127725A1/fr active Application Filing
  • 2009-04-17 CA CA2721642A patent/CA2721642C/fr active Active
  • 2009-04-17 BR BRPI0910574-3A patent/BRPI0910574B1/pt active IP Right Grant

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