EP1207014B1 - Method and apparatus for ultrasonic peening of the blade root slots on a rotor - Google Patents

Description

The invention relates to a method of surface treatment and compressive prestressing by shot blasting the wall of at least one substantially dovetail-shaped annular cavity formed at the periphery of a rotor rim, said annular cell opening outwards by an annular lateral mouth and having at least two cell ends which open into respectively at least one blade introduction opening.

In particular, it is necessary to put in compression prestressing the wall of an annular cell for hammer blade attachment on a turbomachine rotor that can contain blade roots whose contact lines between the annular cell and each foot dawn are heavily solicited. Indeed, in operation, turbine blades or blowers locked in an annular cell by various means, are subjected to considerable centrifugal forces resulting in high friction wear at these contact lines. This frictional wear reduces the life of the parts in operation and regularly causes them to change.

To increase the fatigue resistance of the turbine rotor and harden the surface of the annular cells in the vicinity of the contact lines, it is known to blast the annular cells by means of balls ejected by a compressed air nozzle introduced into each cell. The beads cause permanent compression of the treated surface to a small thickness in order to oppose the appearance and progression of cracks on the surface of the room.

These nozzles can project only microbeads whose diameter is less than 1mm, and typically between 0.3mm and 0.5mm. In addition, the distribution of the balls, both in position and speed, is done according to a Gaussian.

This method is necessarily long, because the total surface of the cavity is treated only by a succession of local treatments which can, in addition, introduce unwanted local deformations and the incrustation of bead residues.

In addition, the shot blasting performed is weak so as not to generate a too high roughness in the vicinity of the treated area, resulting in a hardening of the limited surface. Indeed, the diameter of the projected balls being small, the stronger the shot peening, the greater the degradation of the surface state is important.

Finally, the process using many parameters is poorly controllable and difficult to reproduce.

The FR 2689431 discloses a method of surface treatment and compression prestressing by ultrasonically blasting the wall formed at the periphery of a workpiece. Beads are set in motion by a sonotrode in an enclosure formed by the sonotrode, the wall and shutter elements placed against the wall.

The object of the invention is to propose a method of blasting turbine rotor annular cells, which makes it possible to create reproducible prestressing on all the cells, in a shorter time, while allowing a stronger shot blasting, that is to say a thickness of compression of the larger surface without introducing deformation and limiting the degradation of the treated surface. The invention achieves its object by the fact that the blasting process is carried out according to the features of claim 1.

The method makes it possible to obtain a homogeneous distribution of the positions of the balls constituting a fog of balls. The balls of the fog of balls moving in random directions, they come to strike the cavities walls at various angles, which improves the surface state compared to the balls projected by a nozzle in a preferred direction.

The process requires only a small amount of beads. It is therefore possible to use high quality balls in terms of hardness and geometry, for example rolling bearing balls made of steel or ceramic, which makes it possible to better preserve the surface state.

The volume in which the ball fog is distributed is less than the volume obtained when the vibrating surface remains outside the mouth, the process requires a shorter shot blasting treatment time.

Advantageously, at least three successive shot blasts of the wall are made by reversing the direction of rotation of the rotor rim at each approach to one of the ends of the cell.

The entire wall of the annular cavity is not subjected to the impacts of balls at the same time, which entails the risk of deformation of the cavity, in particular of the cell containing the blade root, being given the importance of the diameter of the rim in relation to its thickness. The fact of treating the wall by three successive treatments makes it possible to compensate considerably for the deformations of the rim.

Of course, it is also possible to carry out the three successive shot peening operations while keeping the same direction of rotation of the rotor rim and stopping shot blasting when the shutter cheeks and the vibrating surface arrive in the vicinity of a first end of the rotor rim. mouth, and then reactivating the fog of balls when the shutter cheeks and the vibrating surface are out of the introduction opening again introduced into the mouth.

Advantageously, a deflector is placed in the enclosure.

The deflector may be substantially triangular geometry with sides parallel to the diverging wall portions so as to reduce the effect of shot blasting the area between said baffle and the bottom of the cavity.

Advantageously, after having blasted a first cell, the rotor part is rotated about its axis of rotation, so as to bring the closing means into the blade introduction opening, the sonotrode is moved substantially vertically and the sheath towards the low position, the acoustic assembly comprising the sheath and the sonotrode is displaced substantially horizontally towards the introduction opening of a second annular cavity which is brought opposite the sonotrode, and the sonotrode is again positioned supporting the dose of beads and the sheath in their high shot blast position for shot blasting said second annular cell.

At the end of the treatment, the sonotrode is advantageously moved substantially vertically towards a low position in the sheath, a position in which the dose of beads is able to be driven from the vibrating surface towards a reservoir through openings formed in the sheath after the shot blasting of the annular cells formed on the rotor rim.

Thus, the dose of beads is easily recovered to be reused for subsequent treatment or replaced.

Advantageously, a dose of beads having a diameter greater than 0.8 mm is used.

The beads used in the process according to the invention have a larger diameter than the diameter of the balls that can be projected by a nozzle, so that shot blasting can be stronger while having a less significant surface degradation.

The invention also relates to an installation for implementing the method.

According to the invention, this installation comprises the features of claim 6.

The installation may comprise a plurality of acoustic assemblies each comprising a sonotrode and a sleeve disposed around the rotor rim, said acoustic assemblies being able to move in an axial direction of the rotor rim.

The installation advantageously comprises a fourth clearance smaller than the diameter of the balls formed between one end of the sleeve and the mouthpiece, which when the vibrating surface does not close the mouthpiece makes it possible to guarantee the tightness of the enclosure.

The various elements of the installation are arranged so that no ball can block said elements likely to move. In addition, the sonotrode and the sleeve comprising the closure means, have a geometry adapted to the shape of the cavity to be treated. In particular, the vibrating surface is of complementary shape to the mouth and the sealing means are formed to ensure tightness of the enclosure.

Advantageously, the second moving means are capable of moving together the closure means and the sonotrode.

The first moving means and the second moving means are advantageously able to be controlled simultaneously.

At the start of the treatment, the sheath and the sonotrode are placed in an intermediate position in which the space generated by the closure means of said sheath and the vibrating surface of said sonotrode constitutes a reservoir for the dose of beads. Then, said sleeve and said sonotrode supporting the dose of beads are moved together with the same movement. Finally, the sonotrode and / or the closure means can be moved individually, depending on the geometry of the cavity to be treated until respectively the vibrating surface closes the mouth of the cavity and the closure means seal the openings of the cavity.

Advantageously, the installation comprises support means for supporting the rotor rim to be treated and drive means of said support means for regularly rotating the annular recess.

The installation advantageously comprises means for expelling the dose of balls from the vibrating surface towards a reservoir.

These simple means allow to expel the dose of ball during a treatment if necessary, or at the end thereof, either to refresh the beads, or to replace them.

Advantageously, the installation comprises means for moving the sonotrode and the sheath substantially horizontally.

A plurality of annular cells, arranged indifferently on a rotor rim and having the same sections, can thus be treated with the same installation that is moved so as to position the sonotrode and the sheath opposite the cell considered.

• la figure 1 est une vue frontale d'une jante de rotor,
• la figure 2 est une vue frontale d'une aube de soufflante disposée dans une cavité annulaire formée à la périphérie de la jante de rotor,
• la figure 3 est une vue de l'installation, le fourreau et la sonotrode étant placés en position intermédiaire,
• la figure 4 est une coupe de l'installation selon un plan médian perpendiculaire à l'axe de rotation de la jante de rotor, le fourreau et la sonotrode étant placés en position haute de grenaillage,
• la figure 5 est une coupe de la figure 4 selon la ligne V-V,
• la figure 6 est une coupe du fourreau contenant la sonotrode, dans leur position intermédiaire, et
• la figure 7 est une coupe du fourreau contenant la sonotrode dans sa position basse.

Other features and advantages of the invention will emerge on reading the following description given by way of nonlimiting example and with reference to the appended drawings in which:

• the figure 1 is a front view of a rotor rim,
• the figure 2 is a front view of a fan blade disposed in an annular cavity formed at the periphery of the rotor rim,
• the figure 3 is a view of the installation, the sheath and the sonotrode being placed in the intermediate position,
• the figure 4 is a section of the installation along a median plane perpendicular to the axis of rotation of the rotor rim, the sheath and the sonotrode being placed in a high shot-blasting position,
• the figure 5 is a section of the figure 4 according to the VV line,
• the figure 6 is a section of the sheath containing the sonotrode, in their intermediate position, and
• the figure 7 is a cut of the sheath containing the sonotrode in its low position.

The figure 1 shows a rotor rim 1 comprising three annular cavities 2, formed at the periphery of the rotor rim 1 and distributed over different diameters of said rotor rim 1. These annular cavities 2 are substantially dovetail shaped and have a mouth 2A of substantially annular shape.

In order to allow the mounting of the substantially dovetail-shaped legs 4, fan blades 6 in the cell 2, said cell 2 has a blade opening opening 5 visible on the figure 3 .

Each blade root 4 is successively mounted by sliding in the insertion opening 5. One or more blade attachment device (not shown) makes it possible to block the blades 6.

The figure 2 shows that the support between the walls of the cell 2 and the blade root 4 results in two lines of contact 2B.

The object of the invention is to propose a method and an installation for compressively preloading the wall 2C of each cell 2 and in particular the zones of the two contact lines 2B, so as to increase the wear resistance of these contact lines 2B caused by the friction between the blade root 4 and the wall of the cell 2 and thus increase the fatigue resistance of the rotor rim 1.

The figure 3 shows an example of installation used for the implementation of the method and in which a single acoustic assembly is used, said acoustic assembly positioned below the rotor rim 1 being able to move vertically and horizontally.

The rotor rim 1 is held by a mandrel 7 which can drive said rotor rim 1 in rotation about its axis of rotation 1A, disposed horizontally.

A sonotrode 8, whose vibrating surface 8A is placed in an intermediate position in a sleeve 16, is mounted movably under the rotor rim 1. A dose of beads is placed above the vibrating surface 8a. The acoustic assembly comprising the sonotrode 8 and the sleeve 16 is moved horizontally until the vibrating surface 8A of the sonotrode 8 is opposite the cell 2 to be treated.

The rotor rim 1 is rotated about its axis 1A so as to place the insertion opening 5 facing the vibrating surface 8A.

Then, the sonotrode 8 and the sheath 16 are moved vertically towards their high shotblasting position and the rotor rim is rotated to bring the vibrating surface 8A close to a first cell end, 5A for example, so that shutter cheeks 14A and 14B formed on the sleeve 16 are placed in the cell 2 so as to form a closed mobile enclosure 12.

As indicated on the figure 4 said movable enclosure 12 is delimited by the wall portion 2'C, the vibrating surface 8A which closes the mouth portion 2A, the closure cheeks 14A and 14B and the sleeve 16.

The spacing L1 between the two closure flanges 14A and 14B is substantially equal to the circumferential extent L2 of the insertion opening 5.

Beads 10 with a diameter of between 0.8 mm and 5 mm, preferably equal to 1 mm, are projected by the vibrating surface 8A, facing upwards, of the sonotrode 8 into the chamber 12.

The figure 5 shows that the vibrating surface 8A is excited by a vibration generator 18, for example quartz, in order to create a ball fog 10 in the chamber 12. A deflector 15 which is carried by the closure cheeks 14A and 14B can be placed in the ball fog 10 to mitigate the effect of shot blasting the bottom of the cell and increase the blasting of the inner flanks of the mouth 21. Said deflector 15 is triangular with sides substantially parallel to the wall portions 2'C and at the bottom of the cell.

The clearance e1 formed between the sonotrode 8 and the sleeve 16 is smaller than the diameter of the balls 10, so that no ball 10 can pass between the vibrating surface 8A and said sleeve 16.

The shutter cheeks 14A and 14B shaped dovetail have axial sections substantially complementary to those of the cell 2, so that in the high shot blasting position, the game e2 formed between each cheek 14A shutter 14B, and the wall portion 2'C to be shot-blasted is smaller than the diameter of the balls 10. Thus, no ball 10 can escape from the enclosure 12.

Likewise, when the vibrating surface 8A closes the mouth 2A in the high shot-blasting position, a third clearance e3, formed between the vibrating surface 8A of the sonotrode 8 and the mouth 2A, is smaller than the diameter of the balls 10 so that no ball 10 can come out of the chamber 12. If the vibrating surface 8A does not close the mouth, a fourth set e4 between an end 16A of the sleeve 16 and the mouth 2A ensures the sealing the enclosure 12.

A first slide 20 makes it possible to carry out the vertical displacements of the sonotrode 8 by sliding said sonotrode 8 into the sleeve 16. A second slide 22, carried by a frame 24, makes it possible to move the sonotrode 8 vertically and the sheath 16. Control means (not shown) make it possible to control said first slide 20 and said second slide 22. Means (not shown), for example rails, make it possible to displace the acoustic assembly comprising the sonotrode 8 and the sheath 16 horizontally, so as to position it opposite a cell to be treated.

The first slide 20 can be carried either by the second slide 22, as indicated on the figure 5 or by the frame 24, in which case the control of the two slides 20 and 22 must be synchronized to mount together the sonotrode 8 and the sleeve 16 to the high shot blasting position.

Before starting the treatment operation of an axial cavity 2, the sonotrode 8 is placed in an intermediate position in the sleeve 16, in which position the space defined by the sleeve 16 and the vibrating surface 8A constitutes a container 26. which makes it possible to contain the dose of beads 10 which is deposited on the vibrating surface 8A, as shown in FIG. figure 6 .

After fixing the rotor rim 1 by holding means comprising the mandrel 7, the sonotrode 8 and the sleeve 16 are moved in the vicinity of a first cell 2 to be treated and the introduction opening 5 of said first cell 2 is introduced. cell 2 opposite the sonotrode 8, by rotating the rotor rim 1 about its axis of rotation 1A with the aid of drive means (not shown). The drive means comprise for example a motor.

The sonotrode 8 and the sleeve 16 are moved towards their high shot-blasting position by simultaneously moving, with the help of the slide 22, the shutter cheeks 14A and 14B and the vibrating surface 8A in the insertion opening 5, then rotate the rotor rim 1 until the two cheeks 14A and 14B are in the end 5A for example. Therefore, the wall portion 2'C of the first cell 2 is blasted by operating the vibration generator 18 which generates a fog of balls 10 in the sealed mobile enclosure 12 and the rim is rotated regularly. rotor 1 about its axis of rotation 1A so as to blast the entire wall 2C.

When the first flange 14A arrives in the vicinity of the mouth end 5B 2A, the direction of rotation of the rotor rim 1 is reversed and the wall portion 2'C is blasted to the other end. SA mouthpiece 2A. The process is repeated once again until reaching the 5B end again. It is understood that the process may comprise more than three shot peening passages as mentioned above.

As soon as the blasting of the first cell 2 is completed, the rotor rim 1 is rotated, so that the shutter cheeks 14A, 14B are placed in an opening 5 for introducing blades, the sonotrode 8 is released and the shutter cheeks 14A and 14B outside the introduction opening 5, then horizontally moving the acoustic assembly comprising the sonotrode 8 and the sheath opposite a second cell 2, the treatment is repeated according to the aforementioned method and so on until the treatment of all the axial cells 2 formed on the rotor rim 1 is completed.

At the end of the treatment, the sonotrode 8 is withdrawn to its lower position, represented figure 7 , in which the release of the dose of balls 10 is carried out. The balls 10 are, for example, blown from the surface 8A with the aid of a blower 28 through openings 30 formed in the sleeve 16 and recovered in a reservoir 32 Said beads may then be refreshed or replaced for further processing.

Claims (12)

1. A method of surface treating and compressively prestressing by peening a wall (2C) of at least one annular recess (2) approximately in the shape of a dovetail, formed in the periphery of a rotor rim (1), said annular recess opening to the outside via an annular lateral mouth (2A) and having at least two recess ends (5A, 5B) opening into, respectively, at least one blade introduction opening (5), said method comprising the steps of:

   a) providing a sonotrode arranged within a sleeve (16), said sonotrode (8) having a vibratory surface (8A) and ultrasonic means (18) for vibrating said vibratory surface, and said sleeve having opposed closing-off means (14A, 14B) capable of sliding in the recess (2); placing a plurality of beads (10) of a predetermined diameter on said vibratory surface (8A) of said sonotrode with said sonotrode arranged in an intermediate position in which said sleeve surrounds said vibratory surface;

   b) placing said introduction opening (5) facing said sonotrode (8);

   c) moving said sonotrode (8) together with said sleeve (16) substantially vertically toward said blade introduction opening (5) to place them in a peening position in which said closing-off means (14A, 14B) face said recess ends (5A, 5B) that open into said opening (5);

   d) turning said rotor rim (1) about an axis of rotation (1A) arranged horizontally in such a way as to bring said closing-off means (14A, 14B) into a first recess end (5A) so as to form a closed moving chamber (12) containing said beads (10);

   e) moving said sonotrode (8) substantially vertically so that said vibratory surface (8A) is level with said lateral mouth of said recess (2), and

   f) operating said ultrasonic means to vibrate said vibratory surface of said sonotrode (8) whereby said beads are mobilized in said moving chamber, and, by uniformly turning said rotor rim (1) about said axis of rotation (1A) until said second recess is reached, ultrasonically peening the entirety of said wall of said recess.
2. A method according to claim 1, wherein said peening step is conducted at least three successive times on said wall (2C) by reversing the direction of rotation of said rotor rim (1) each time one of said recess ends is neared.
3. A method according to claim 1 or 2, including the step of placing a deflector (15) in said moving chamber (12).
4. A method according to any claims 1 to 3, further including the steps of:

   rotating said rotor part (1) about said axis of rotation so as to bring said closing-off means into said blade introduction (5) opening after peening said first recess;

   moving said sonotrode (8) and said sleeve (16) substantially vertically toward a lowered position; moving said sleeve (16) and said sonotrode (8) together substantially horizontally toward an introduction opening (5) of a second annular recess (2);

   bringing said opening up to face said sonotrode (8);

   and positioning said sonotrode (8), supporting said beads (10), and said sleeve (16) in said raised peening position to peen said second annular recess (2).
5. A method according to any claims 1 to 4, wherein said predetermined diameter of said beads (10) exceeds 0.8 mm.
6. An apparatus for use in carrying out the method according to any claims 1 to 5, comprising a sonotrode (8) mounted in a sleeve (16) equipped with closing-off means (14A, 14B), said sonotrode being capable of projecting beads (10) of a predetermined diameter into a moving chamber (12) delimited by a wall portion of said annular recess, said vibratory surface of said sonotrode, arranged near said mouth of said recess, and said closing-off means;
   means (18) for producing ultrasonic oscillations capable of exciting said sonotrode (8); first means (20) for moving said sonotrode (8) substantially vertically; and
   second means (22) for moving said closing-off means substantially vertically (14A, 14B);
   a first clearance (e1), smaller than said diameter of said beads (10), being formed between said sonotrode (8) and said sleeve (16);
   a second clearance (e2), smaller than said diameter of said beads (10), being formed between said closing-off means (14A, 14B) arranged in said annular recess (2) and said annular recess (2), and
   a third clearance (e3), smaller than said diameter of said beads (10), being formed between said mouth (2A) of said recess and said vibratory surface (8A) arranged in said mouth.
7. An apparatus according to claim 6, wherein a fourth clearance (e4), smaller than said diameter of said beads (10), is formed between an end of said (16A) sleeve (16) and said mouth (2A).
8. An apparatus according to claim 6 or 7, wherein said second means (22) for moving said closing-off means are capable of moving said closing-off means (14A, 14B) and said sonotrode (8) at the same time.
9. An apparatus according to any claims 6 to 8, wherein said first means (20) for moving said sonotrode and said second means for moving said closing-off means (22) can be operated simultaneously.
10. An apparatus according to any claims 6 to 9, which further comprises support means for supporting said rotor rim (1) that is to be treated, and means for driving said support means to cause said annular recess (2) to rotate uniformly.
11. An apparatus according to any claims 6 to 10, which further comprises means (28) for driving said plurality of beads (10) from said vibratory surface (8A) toward a reservoir (32).
12. An apparatus according to any claims 6 to 11, which further comprises means for moving said sonotrode (8) and said sleeve (16) substantially horizontally.

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