FR2910826A1 - Device for production of longitudinal ultrasonic acoustic vibrations in user element e.g. tube, comprises electro-acoustic converter with pair of piezo-electric ceramics, and intermediate element between the converter and user element - Google Patents

Abstract

The device for the production of longitudinal ultrasonic acoustic vibrations in a user element e.g. tube, comprises an electro-acoustic converter (20) having a pair of piezo-electric ceramics (21), and an intermediate element (30) placed between the converter and user element. The piezo-electric ceramics vibrate in radial mode and its distal face (31) vibrates in bending mode. The intermediate element is arranged to the distal face of the converter in a contact zone located at a periphery, and to the user element through its plane end face. The device for the production of longitudinal ultrasonic acoustic vibrations in a user element e.g. tube, comprises an electro-acoustic converter (20) having a pair of piezo-electric ceramics (21), and an intermediate element (30) placed between the converter and user element. The piezo-electric ceramics vibrate in radial mode and its distal face (31) vibrate in bending mode. The intermediate element is arranged to the distal face of the converter in a contact zone located at a periphery, and to the user element through its plane end face. A point of the end face is animated by homogenous vibration according to a direction orthogonal to the surface. A part of the intermediate element and an other part of the user element or user ensemble are made of single-piece. A length of the contact zone is 10-15% of radius of the distal face. The intermediate element comprises a metallic cylinder having an opening, and is present in the form of disc. The cylinder has a side intended to come in contact with the converter. The vibration has an amplitude of larger than 90% of the amplitude of an antinode. The converter has an axis orthogonal to an axis of the disc that is parallel to the end surface, and is connected with a generator having alternative electric signal of ultrasonic frequency. Self-frequency of the vibration in the radial mode and self-frequency of the intermediate element are tuned to the ultrasonic frequency (80-200 KHz) of the generator. A frequency band passing through the generator is 100-300 Hz. The generator delivers an ultrasonic power of 50-10000 watt. The converter is disposed in a sealed chamber in which a cool gas or liquid circulates. The user ensemble comprises a speed transformer, a cylindrical rod and/or sonotrode constituted of an axial bar. The user element or a part of the user ensemble presents the self-frequency. A radial friction lining is arranged around the axial bar. An external radius of the friction lining is determined to include an integer of half wavelength in radial vibration mode. A liquid is pulverized by the vibration of surface situated on an external edge of the lining. The tube has two parts each fixed respectively at one of the two parts of the end surface. An independent claim is included for a process the production of longitudinal ultrasonic acoustic vibrations in a user element.

Description

DEVICE FOR PRODUCING ULTRASONIC VIBRATIONS

  relates to the general technical field of devices and methods for ultrasound generation.

  GENERAL PRESENTATION OF THE PRIOR ART

  Devices and methods for the generation of ultrasound have already been proposed. These devices generally comprise an ultrasound generating element, associated with a user element which transmits the ultrasound to a substrate for a given technical effect: welding, cleaning, destruction of cells or cutting of soft food products. User elements, their shape and characteristics depending on the substrate and the desired technical effect are well known to those skilled in the art, such as ultrasound producing elements. Power ultrasonic generation is commonly done from piezoelectric ceramics or more precisely from Langevin triplet electro-acoustic converters. An electro-acoustic converter makes it possible to transform the high frequency electrical energy of an electronic generator 10 into mechanical vibrations. With reference to FIG. 1a, an electro-acoustic converter comprises two piezoelectric ceramics mounted in prestress between two cylindrical metal parts 23, 25: the horn 23 disposed under the two ceramic elements 21, and the counter-mass 25 disposed on both Ceramics 21. It will be understood in the following that when a piece A is mentioned as being on a piece B, it can be directly on the piece B, or can be located above the piece B and separated from said piece B by one or more intermediate pieces. It will also be understood that when a piece A is mentioned as being on a piece B, it may cover the entire surface of the piece B, or a portion of said piece B. The piezoelectric ceramics 21 are generally disk-shaped of small thickness relative to their diameter, or in the form of torus of rectangular section or approaching. The various types of electroacoustic power converters are widely described in books such as Richerson's Modem Ceramic Engineering, Marcel Dekker Inc., page 284, Figure 7.24, or High Intensity Ultrasonics by Brown and Goodman, Iliffe Books Ltd 1965, or still in the book of Crowford Engineering of Frederick and Co. These converters are used in the industry, mainly for welding thermoplastics, or for cleaning complex parts in optics, electronics or mechanics. The electro-acoustic converters as described above can use two distinct modes of vibration of piezoelectric ceramics: the mode producing alternative variations in their thickness (said mode in the thickness of ceramics) and the mode producing alternative variations of their diameter (mode said in the plane of the ceramics, or plane, or radial). The vibration mode of the piezoelectric ceramics 21 said in the thickness generates longitudinal vibrations in the horn 23 so that each point of the distal flat face 24 of the flag 23 that is to say the face opposite to the face the flag facing the ceramic - is animated by a vibration homogeneous and orthogonal to said face 24.

  This mode makes it possible to propagate longitudinal vibrations of high intensity through devices vibrating in resonance with the electro-acoustic converter and the associated generator 10, generically called sonotrodes and attached to the distal face 24 of the horn 23, the contact performing the entire extent of said distal face, according to the prior art. In this case, the piezoelectric ceramics are fed by a generator providing an electrical signal whose bandwidth is tightened (100 or 200 Hz) and which is centered on a frequency which must be remote from the natural resonance frequency of the piezo ceramics -electrical in their radial mode of vibration. The so-called vibration mode in ceramics is used in most industrial applications of power ultrasounds, for example, welding, spraying, cell destruction or the cutting of soft food products, such as foie gras. It is well known to those skilled in the art that the dimensions of such electroacoustic power converters using the so-called vibration mode in the thickness of ceramics vary inversely with the frequency used. In practice, the length of this type of electro-acoustic converter 20 will be of the order of a half-wavelength, while its diameter will be much smaller than a quarter of a wavelength in order to avoid the superposition of a transversal vibration preferential mode of vibration, the superposition of the two vibrations can lead to the destruction of ceramics. Thus, beyond 40 kHz, the diameter of the ceramics is considerably reduced which significantly limits the allowable power, so that, for example, at 80 kHz, this diameter is about 15 mm with a permanent operating power limited to about 20 watts. A disadvantage of such devices is the fact that they are unsuitable for transmitting a significant useful power, that is to say of the order of 100 Watt minimum, at frequencies greater than or equal to 60 kHz, a user element and are therefore not usable in the case of industrial applications requiring such power / frequency pairs. The second mode of vibration of piezoelectric ceramics, called planar or radial, is obtained by choosing their dimensions, as well as the piezoelectric characteristics of their material, in such a way that their natural frequency, according to this mode of vibration, is equal to that of the generator. Those skilled in the art know that, in the case of toric ceramics, this natural frequency F is given by the following formula: F = C / (Dext-Dint), in which: C is the radial vibration coefficient of the material used, Dext is the outer diameter of ceramics, Dint is the inside diameter of ceramics.

  The dimensions of the electro-acoustic converters, whose ceramics vibrate in plane or radial mode, can be much larger than those of converters whose ceramics vibrate in thickness mode, at equal frequency, because of their respective modes of vibration. .

  Thus, it is common to find, for example, electro-acoustic converters whose ceramics vibrate in plane mode, 100 kHz of eigenfrequency, having piezoelectric ceramics with a diameter of the order of 40 mm and allowing a level power much higher than converters of the same frequency but working in mode in the thickness of ceramics. This mode of vibration of the ceramics generates bending vibrations at the distal face 24 of the horn 23. Thus this type of converter is specifically intended for vibrating according to the bending mode, large flat surfaces particularly sought after for cleaning by ultrasound. In this case, several electro-acoustic converters are generally directly attached to the cleaning tank, or glued inside an immersible sealed housing, through their entire distal end face 24 of the roof 23 in order to transmit to the liquid contained in the tank the ultrasonic vibratory energy required for the ultrasonic cleaning process.

  The electro-acoustic converters are then electrically connected in parallel to form an assembly having a broad electro-acoustic impedance curve and very flattened and electrically powered by a frequency sweeping generator, covering a wide range of frequencies (several kHz) around the target frequency. Those skilled in the art who know, on the one hand, the need existing in the industry to generate longitudinal ultrasonic vibrations in a user element at frequencies greater than or equal to 60 kHz and powers greater than or equal to 100 Watt and on the other hand, the existence of electro-acoustic converters, whose ceramics vibrate in said plane or radial mode and the distal face in bending mode, and which are capable of operating at such power / frequency pairs, is then brought to ask the following problem: how to use such converters to generate the longitudinal ultrasonic vibrations thus sought? An object of the invention is to provide a solution to this problem.

PRESENTATION OF THE INVENTION

  For this purpose, it is therefore proposed to use the capacity of the electro-acoustic converters 20, as described above and whose piezoelectric ceramics 21 vibrate in said plane or radial mode and the distal face 24 in bending mode, transmit at the desired frequencies a high power. Bending mode is a deformation mode of the material well known to those skilled in the art in which the distal face bends in response to stress. The flexural vibration of the distal end 24 of the converter is well illustrated by Figs. 1b and 1c. For example, the converter shown in Figures 1 is calculated to vibrate at 80 kHz in this mode of vibration ceramics; the diameter of its cylindrical flag 23 is 41 mm. The curve of FIG. 1d represents the amplitude of the vibration of each point of the distal face 24 of the horn 23 as a function of its distance to the center of the face. This curve shows that the bending vibration of the distal face has two amplitude bellows located respectively at the center and at the outer edge of said face; these two bellies are separated by an amplitude node located on a circle concentric to said face and about 26 mm in diameter. The belly of central amplitude is much more marked than the belly of peripheral amplitude. In the vicinity of each belly, the amplitude curve is flattened, so that in a small area 26 around each belly, the amplitude is constant in first approximation. Thus, in a disc 26a concentric to the distal face of about 6 mm in diameter, the amplitude is in all points greater than 90% of the central belly amplitude; in this case, the ratio of the radius of the disk 26a to the radius of the distal face is 3 / 20.5 = 14.6%. Similarly, in a ring 26b concentric to the distal face, located at its periphery and about 2.5 mm wide, the amplitude is in all points greater than 90% of the amplitude to the peripheral belly; in this case the ratio between the width of the ring 26b and the radius of the distal face is 2.5 / 20.5 = 12.2%. These two ratios are between 10 and 15%. A first aspect of the device according to the invention consists in using this particular characteristic to recover the vibratory energy produced by the converter by means of at least one of these zones where the vibration is in first approximation homogeneous and of high amplitude. We will then place an integral connection between, on the one hand, one of these zones 26a or 26b and, on the other hand, either an intermediate element 30, or directly a user element 40, 50. This makes it possible to generate the longitudinal vibrations desired in the user element, to the desired power / frequency pairs and thus to bring to the problem the solution sought.

  By associating, as the case may be, several electro-acoustic converters 20 and several intermediate elements 30, the present invention makes it possible in particular to produce, in a user element (part 40 or set of parts 50), the natural frequency of vibration of which is tuned to that of the converters. , high-intensity longitudinal vibrations necessary to achieve, in the case of high frequencies greater than or equal to 60 kHz, the power level required for industrial applications such as spraying, welding, machining, liquid processing, cutting, etc.

  Other preferred but non-limiting aspects of the device according to the invention are the following: the natural frequency of vibration in the radial mode of the piezoelectric ceramics of the converter and the natural frequency of vibration of the intermediate element are given to the same ultrasonic frequency F; - The converter 20 is then connected to a generator 10 capable of producing an alternating electrical bandwidth signal narrow width and between 100 and 300 Hz around said ultrasonic frequency F; - In a first embodiment, an intermediate element 30 is attached to the converter integrally by the contact zone 26a located in the center of the distal face; this intermediate element may comprise a cylindrical metal bar intended to come into contact with the user element 40, 50 via the flat end surface 31, which is animated at all points with a homogeneous vibration orthogonal to the surface ; in a second embodiment, the intermediate element 30 and the horn 23 of the piezoelectric converter are made in one piece; in a third embodiment, the intermediate element 30 and the user element 40 are made in one piece, so that the user element 40 is directly attached to the converter integrally by the contact zone 26a located in the center of the distal face; in a fourth embodiment, the intermediate element 30 is attached to the converter integrally by the contact zone 26b located at the periphery of the distal face; this intermediate element may comprise a metal cylinder having a recess, the face 32 of the cylinder comprising the recess being intended to come opposite the face 24 of the electro-acoustic converter, so as to allow the two facing faces 32 and 24 to vibrate freely without touching each other; in a fifth embodiment, a plurality of electroacoustic converters 20 are associated with the intermediate element 30; this intermediate element may, for example, be in the form of a thick disk at the periphery of which the converters are fixed integrally regularly spaced, the axes of the converters being orthogonal to the axis of the disk and the end surface 31 being parallel to the axis of the disc; Other preferred aspects of the device according to the invention are the following: the ultrasonic frequency F is between 20 kHz and 400 kHz, preferably 40 kHz and 200 kHz, and still more preferably between 80 kHz and 200 kHz; ultrasonic delivered by the generator 10 is between 50 and 10000 Watt, - at least one end face 31 of the intermediate element 30 is flat, the vibration at any point of this face being homogeneous and orthogonal to said end face the converter is arranged in a sealed chamber in which a gas or a cooling liquid circulates, the device further comprises a user element comprising a part 40 or a set of parts 50 disposed at the end face 31. of the intermediate element 30.

  According to a first variant, the user element 40 comprises a sonotrode formed of a cylindrical rod 41.

  According to a second variant, the user element 50 comprises a speed transformer 52, and / or a cylindrical rod 51, and / or a sonotrode 54, 58, 59. In a preferred, but not limiting, case, the various components of the user element 40, 50 taken separately, have a natural frequency of vibration tuned to that of the generator 10.

  According to a third variant, the sonotrode 53 implemented comprises an axial bar 57 around which is arranged a radial ring 56 disposed around the bar 57 orthogonal to the axis of the bar. The bar vibrates longitudinally and the crown radially, the outer radius of the ring 56 being determined to comprise an integer number of half-wavelengths in radial vibration mode of the ring 56 at the frequency F.

  The vibration of the surface 55 which constitutes the outer edge of the ring 56 allows, for example, the spraying of liquid, which allows the production of atomizing devices. In such a case, the device according to the invention may advantageously be located partly inside a sealed enclosure 61, the penetration being at a node 511 of the vibration. Such a device makes it possible, for example, to atomize molten metal alloys, the droplets thus formed giving cooling in the chamber metal powders with narrow granulometry.

  According to a fourth variant, the intermediate element 30 is in the form of a ring on the periphery of which a plurality of converters 20 are fixedly fixed in a regularly spaced manner, the axes of the converters being orthogonal to the axis of the ring and the surface 31 is constituted by a part of the crown. The user element 40 is a hollow tube of revolution whose axis is the same as that of the ring, whose length is chosen so that it vibrates in resonance at the frequency F and which is fixed integrally to the surface 31. The tube may preferentially be in two parts 45 and 46, on either side of the ring 30.

  The invention also relates to a method for producing longitudinal ultrasonic acoustic vibrations comprising the steps of: -conversion of an alternating electrical signal into radial mechanical vibrations of piezoelectric ceramics which are the constituents of an ultrasonic transducer, - transformation of the vibrations radial mechanical ceramics bending vibrations of the distal face of the transducer, - use of the vibratory energy of the distal face of the transducer, to generate longitudinal mechanical vibrations in a user element by means of an intermediate element.

  PRESENTATION OF THE FIGURES Other features, objects and advantages of the present invention will become apparent from the description which follows, which is purely illustrative and nonlimiting and should be read with reference to the accompanying drawings in which: FIG. 1a illustrates a schematic view in perspective of an electro-acoustic converter of the Langevin triplet type of the prior art; FIGS. 1b and 1c illustrate, in section, a modeling operation in the mode of excitation of piezoelectric ceramics said radial or plane, in the two positions of maximum amplitude which are in phase opposition of the electro-acoustic converter illustrated in Figure la; FIG. 1d shows the amplitude of the vibration of each point of the distal face of the electro-acoustic converter illustrated in FIG. 1a, as a function of its distance from the axis of revolution; FIGS. 2 to 13 illustrate various embodiments of the device according to the invention.

  DESCRIPTION OF THE INVENTION As described above, the dimensions of the electro-acoustic converters excited according to the second mode of excitation of their piezoelectric ceramics, that is to say whose ceramics vibrate in plane mode ( or radial), can be much larger than those of converters excited according to the first mode, that is to say whose ceramics vibrate mode in the thickness.

  However, and as illustrated in FIGS. 1b and 1c, an electro-acoustic converter whose ceramics vibrate in plane (or radial) mode produces a bending vibration of the distal face 24 of the horn 23-that is to say the opposite face on the face of the pavilion next to the ceramics. However, this does not allow to vibrate in longitudinal mode a user element (part 40 or set of parts 50) attached to said distal face 24 according to the same methods as those used in the case of ceramics vibrating in the mode in which thickness, let alone to transmit significant useful ultrasonic power. This is true even when the natural vibration frequency of the user element (part 40 or set of parts 50) is given to that of the converter 20. In fact, it is known to those skilled in the art that for such significant ultrasonic power is transmitted to the user element (part 40 or assembly of parts 50), vibrating in longitudinal mode, it is necessary that each point of the distal plane face 24, which is at the interface between the flag 23 ( source of the vibrations) and the user element (part 40 or set of parts 50) of the vibrations, vibrates homogeneously and orthogonally to the distal face 24. To overcome this drawback, the invention proposes a device for producing ultrasonic acoustic vibrations. as shown in Figures 2 to 13. This device comprises: - at least an electro-acoustic converter 20, as shown in Figure la and comprising a pair of piezoelectric ceramics 21, ceramics 21 vibrate in radial mode and the distal face 24 in bending mode, as illustrated in FIGS. 1b and 1c, a user element 40, 50, an intermediate element 30, which is placed between the converter 20 and the user element 40, 50 and is attached, on one side, integrally to the distal face 24 of the converter 20 in a contact zone 26 located around a belly of amplitude of vibration of the distal face 24 and, of the another side, to the user element 40, 50 by its flat end surface 31, any point of the end surface 31 being animated with a homogeneous vibration orthogonal to said surface.

  Referring to Figure 2a, there is illustrated an embodiment of the device according to the invention. In this embodiment, the device comprises a generator 10, an electro-acoustic converter 20, and an intermediate element 30. The generator 10 allows the generation of an ultrasonic frequency alternating electrical signal F. The generator 10 is electrically connected to the electro-acoustic converter 20 in a manner known to those skilled in the art. The electro-acoustic converter 20 is of the Langevin triplet type.

  This converter 20 comprises two piezoelectric ceramics 21a, 21b contiguous. The two ceramics 21a, 21b are arranged between a first metal part 23 - hereinafter referred to as a bell - integral with one 21a of the two ceramics, and a second metal part 25 - hereinafter referred to as counter-mass - integral with the other ceramic 21b. In the embodiment illustrated in FIG. 2a, the horn 23 and the counter-mass 25 are of cylindrical shape, and the two ceramics 21a, 21b of toroidal shape with a rectangular section. However, the flag 23, against the mass 25, and / or the ceramics 21a, 21b may have other forms than those illustrated in Figure 2a. Ceramics 21a, 21b are able to vibrate in radial mode. More particularly, the piezoelectric characteristics of the material constituting the ceramics and the dimensions of the ceramics 21a, 21b are chosen so that the frequency F of the generator 10 corresponds to their resonance frequency (or natural frequency) in the radial vibration mode. .

  The vibration of the ceramics 21a, 21b in the radial mode induces bending vibrations at the distal face 24 of the horn 23. In the embodiment illustrated in FIGS. 1a to 1d, the distal face 24 of the horn 23 comprises two bellows of vibration: a central belly 26a, located in the center of the distal face 24, and a peripheral belly 26b, located at the periphery of the distal face 24. In the context of the present invention, the term "vibrational belly" refers to a region of the distal face 24 where the amplitude of displacement of the distal face 24 of the horn 23 is maximum when the ceramics 21 vibrate in radial mode.

  The central belly 26a and the peripheral belly 26b are separated by a nodal region of the distal face 24 corresponding to a circle, as illustrated in Figures lb to 1d. In the embodiment illustrated in FIG. 2a, the intermediate element 30 is integral with the horn 23 at a contact zone 26a, in the form of a disc concentric with the distal face 24 and thus located at the central belly of said face. Advantageously, the radius of this contact zone is between 10% and 15% of the radius of the distal face 24, so that, according to FIG. 1d, the amplitude of the vibration at any point of said zone is greater than 90 % of the amplitude of the vibration in the center. The intermediate element 30 illustrated in FIG. 2a consists of a metal cylindrical bar coaxial with the horn 23, the material and dimensions of which have been chosen so that it presents a natural mode of vibration, in longitudinal mode, in resonance at frequency F.

  It is fixed to the horn 23 via a small cylinder coaxial with the bar, whose section has the same dimension as the contact zone 26a and the height is about 1 mm; this arrangement limits the contact between the two parts to the desired contact area 26a. The fixing means of the intermediate element 30 to the roof 23 may be of any nature known to those skilled in the art such as: screwing, welding, gluing, crimping, hooping, ... In a particular non-limiting embodiment of the invention the intermediate element 30 and the horn 23 are in one piece. The intermediate element 30 also comprises a flat end face 31. This end face corresponds to the face of the intermediate element 30 opposite to the contact zone between the intermediate element 30 and the horn 23. A user element 40, 50 can be attached to the end face 31 of the intermediate element 30. The operating principle of the device illustrated in Figure 2a is as follows. The generator 10 generates an ultrasonic frequency alternating electric signal F which vibrates the piezoelectric ceramics 21a, 21b of the converter 20. The ceramics vibrate in radial mode.

  This mode of vibration of the ceramics 21 induces alternating variations in their diameters which excite the vibration of the horn 23 into a bending mode at its distal face 24. The intermediate element 30, which is integral with the horn 23 at the level of the contact zone 26a located at the central belly of the distal face 24, is excited by the vibration of said horn 23. The amplitude of the vibration of the distal face 24 in the contact zone is almost homogeneous, since in every point of said zone, the amplitude is between 90% and 100% of the amplitude in the center of the zone. This makes it possible to vibrate the intermediate element 30 at the frequency F according to its longitudinal self-mode, so that any point on its end face 31 is then animated by a vibration that is homogeneous and orthogonal to said face.

  Any user element 40, 50 attached to the end face 31 can then be vibrated in the longitudinal mode at the frequency F, since it was designed, according to the prior art, to do this. Thus, the invention provides a device for producing homogeneous longitudinal vibrations used in most industrial applications such as welding, spraying and industrial cutting to transmit a significant power output greater than or equal to 100 Watt. Referring to Figure 2b, there is illustrated another embodiment of the device according to the invention. In this particular embodiment, the intermediate element 30 is integrated with the user element 40, which in this case is a sonotrode of the prior art; for the rest, the device is identical to that shown in Figure 2a.

  Referring to Figure 3, there is illustrated another embodiment of the device according to the invention. In the case presented in FIG. 3, the contact zone 26 between the horn 23 and the intermediate element 30 is located at the peripheral belly of the distal face 24.

  The intermediate element 30 and the horn 23 are two separate parts fixed by screwing, welding, gluing, crimping or hooping or any other means known to those skilled in the art to ensure a rigid connection between the flag 23 and the intermediate element 30. The intermediate element 30 comprises a first metal cylinder of diameter substantially equal to the diameter of the horn 23, and intended to come into contact with the horn 23 at the peripheral belly of the distal face 24, the contact zone 26b being in the shape of a crown. Advantageously, the width of this ring is between 10% and 15% of the radius of the distal face 24, so that, according to FIG. 1d, the amplitude of the vibration at any point of said zone is greater than 90% the amplitude of the vibration at the periphery. The first cylinder comprises a recess whose depth is provided sufficient for the distal face 24 of the horn 23 and the facing face 32 of the intermediate element 30 to vibrate freely in their respective modes without touching other than in the contact zone. 26b. This allows the decoupling of the vibrations of these two faces that vibrate in phase opposition with respect to each other. More generally, the geometry of the intermediate element 30 is chosen so that the contact between the intermediate element 30 and the horn 23 takes place only at the level of the contact zone 26 retained, when the device is in operation, so as not to interfere with the vibration of these two parts according to their own mode of resonance. The material (for example aluminum, titanium, ...) of the intermediate element 30 is chosen, and its geometry is calculated, so that it enters into resonance vibration at the same frequency F and that the end face plane 31 of the intermediate element 30 is animated at every point of a homogeneous vibration movement orthogonal to said end face 31.

  The operating principle of the embodiment illustrated in FIG. 3 is similar to that of the embodiment illustrated in FIG. 2. The generator 10 generates an ultrasonic frequency alternating electric signal F which vibrates the ceramics in radial mode.

  The vibration of the ceramics 21a, 21b excite the vibration of the horn 23 in a bending mode at its distal face 24. The intermediate element 30, which is integral with the horn 23 at the contact zone 26b located at the peripheral belly of the distal face 24 is excited by the vibration of said horn 23.

  The amplitude of the vibration of the distal face 24 in the contact zone is almost homogeneous, since at any point in said zone, the amplitude is between 90% and 100% of the amplitude at the center of the zone. This makes it possible to vibrate the intermediate element 30 at the frequency F according to its own mode, so that any point of its end face 31 is then animated by a vibration that is homogeneous and orthogonal to said face.

  Referring to Figure 4, there is illustrated another embodiment of the device according to the invention. In this embodiment, the intermediate element 30 comprises a circular plate and at least one cylindrical protuberance extending towards the outside of the plate, and concentric with the axis of revolution of the plate, the end of the protuberance forming the flat end face 31 of the intermediate member 30 for receiving the user assembly. The material and the geometrical characteristics of the plate are carefully selected so that it has a natural mode of resonance vibration at the frequency F such that the circular plate vibrates in radial mode and the protrusion 31 vibrates in longitudinal mode in opposition of phase (Poisson effect) according to the prior art, as described, for example in US Pat. No. 3,696,259 of 03/10/1972. A plurality of identical converters 20 is associated with the plate via contact zones 26a situated in the central belly of the distal face 24 of each converter 20. These converters 20 are fixed outside the plate and protrude radially. , so that the axis of revolution of the plate is orthogonal to the axes of revolution of the converters 20.

  The converters 20 are regularly spaced around the plate, and connected to the same generator 10, so that all the converters vibrate in phase at the frequency F of the generator. Of course, the geometry of the intermediate element 30 of FIG. 4 is determined so that the operating contact between the intermediate element 30 and each converter 20 takes place only at the level of the contact zone 26 retained, c that is to say at the central belly or the peripheral belly of the distal face 24 of the horn 23 of each electro-acoustic converter 20. Thus, the horns 23 of the electro-acoustic converters will vibrate at their distal face 24 in phase in flex mode; through the contact zones 26 where the vibration is homogeneous, they will excite the vibration of the plate in its own mode, so that it will be animated by a radial vibration. The operating principle of the embodiment illustrated in Figure 4 is as follows.

  The generator 10 generates an ultrasonic frequency alternating electric signal F which vibrates the ceramics of the converters 20 in radial mode. The vibration of the ceramics 21a, 21b excite the vibration of the horn 23 of each converter 20 in a bending mode at its distal face 24. The intermediate element 30, which is fixed to the horns 23 of the converters at the central belly 26a or peripherals 26b of the distal faces 24, is excited by the vibrations of the horns 23. The vibrations of the horns 23 induce the contraction and the expansion of the plate, the latter inducing the contraction and the expansion of the protuberance in opposition of the phase (effect Fish). Thus, the plate vibrates radially and the protrusion vibrates longitudinally at the same frequency. In fact, the end surface 31, to which the user assembly 40, 50 is fixedly attached, makes it possible to vibrate in longitudinal mode this assembly. The embodiment shown in FIG. 4 makes it possible to obtain a particularly high acoustic power by setting the electro-acoustic converters 20 in parallel, which all operate in phase. The intermediate element 30 illustrated in FIG. 4 thus simultaneously carries out: the paralleling of several electro-acoustic vibrators 20 vibrating in phase, the transformation of the vibration mode of the piezoelectric converters 20 into a radial mode of platinum, - the transformation of the radial vibration mode of the platen into a longitudinal mode at the end face 31, - the transformation of the amplitude of the vibrations. By choosing the number of electroacoustic converters and their geometry, it is thus possible to cover a frequency range from 20 to 400 kHz and a power range from 50 to 10,000 watts. Referring to Figure 5, there is illustrated another embodiment of the device according to the invention. In this embodiment, the device according to the invention illustrated in FIG. 2a is disposed in a sealed chamber 60 in which a gas or a cooling liquid circulates. Indeed, the (case of Figures 2 and 3), or the (case of Figure 4), converter (s) electro-acoustic (s) give off in operation of heat which causes the raising of their temperature.

  This rise in the temperature of the converters can lead to their destruction. To overcome this drawback, it is possible to place the electro-acoustic converter (s) inside a cooling chamber 60, the cooling means being provided by a circulation of air, of gas or of circulating water, in the latter case, in a sealed envelope, or by any other means conceivable. In the case of Figure 5, the cooling is provided by a compressed air flow entering through the opening 601 and out through the opening 602.

  The output junction of the device according to the invention and the cooling chamber 60 is made at a node of amplitude 33 of the vibration of the intermediate element 30.

  A user element (part 40 or set of parts 50) which is going to be vibrated at the same frequency, can then be solidarily attached, according to principles well known to those skilled in the art, to the end face 31. than the preceding parts, the vibrations created in the part in contact with the end face 31 being longitudinal and propagating in the user element (part 40 or set of parts 50) per plane of equal phase, at least in its initial part. The links between the flag 23 and the intermediate element 30, on the one hand, and between the intermediate element 30 and the user element (part 40 or set of parts 50), on the other hand, can be realized, according to the prior art, by any appropriate means such as screwing, welding, gluing, crimping, shrinking or any other appropriate mechanical means ensuring a rigid connection.

  In this regard, a variant of the connecting mode between two consecutive parts consists of making them in one piece, in the same block of material. Without the present invention being limited to the following cases, the user element (the part 40, or as the case may be, each part constituting the set of parts 50) can be preferentially chosen so that it has a natural frequency of vibration. granted to the natural frequency F common to the generator 10, the electro-acoustic converter 20 and the intermediate element 30, the assemblies thus composed constituting a resonant vibrating assembly at the frequency F of the electrical signal delivered by the generator 10. The user element (part 40 or assembly of parts 50) may comprise a sonotrode, or a cutting blade, or a sprayer, or an ultrasonic reactor, or any other resonant assembly depending on the intended application: welding, machining, cutting, spraying , treatment of liquids and solid / liquid mixtures such as homogenization, dispersion, disintegration, destruction of biological cells, degassing.

  As a result, the present invention advantageously finds application in all industrial applications of power ultrasound and especially welding, machining, cutting, spraying, cleaning, sieving, treatment of liquids, etc.

  Other features and advantages of the present invention will appear on reading the detailed description given below of a number of particular embodiments of the present invention. Figures 6 to 8 relate to the vibration of simple sonotrodes. Figure 6 shows a sonotrode 40 whose geometry can be adapted to any particular use. It comprises a cylindrical bar 41 with a circular section which is fixed integrally with the end face 31 of the intermediate element 30.

  The invention allows propagation in the cylindrical bar 41 of longitudinal ultrasonic vibrations which propagate along the generatrix of the cylindrical bar in equal phase planes. FIG. 7 implements a user assembly 50, consisting of a speed transformer 52 - also commonly known by those skilled in the booster art - and a sonotrode 58, which can, for example, be used for agitation / homogenization of a liquid; the two ends of the booster 52 are connected to the other elements of the user assembly in the vicinity of amplitude amplitude of displacement of the vibration.

  FIG. 8 implements a user assembly 50, consisting of a speed transformer or booster 52 and a sonotrode 59, which can, for example, be used for cutting soft or fragile materials (foie gras, mille- sheet, etc.). Figures 9 to 11 relate to spraying devices of liquid substances or solid / liquid mixtures according to the invention.

  FIG. 9a uses a device for vibrating a user assembly 50 successively comprising a cylindrical rod 51 fixed to the flat end face 31 of the intermediate element 30 and of length equal to an integer multiple of half wavelengths (longitudinal mode of vibration), a speed transformer 52 or booster and a sputtering sonotrode 53. The sonotrode 53, which is illustrated in detail in FIG. 9b, comprises a disc 56 and cylindrical excrescences of revolution. 57 concentric to the axis of the disk 56 and extending on either side of the latter. The material and the geometry of the sonotrode 53 are chosen so that the cylindrical protrusions 57 vibrate longitudinally in resonance at the frequency of the generator 10 and the disc 56 vibrates radially in resonance at the same frequency.

  The radius of the disk is thus precisely determined so that at frequency F, the radial vibration which animates it comprises an integer of half-wavelengths. The outer face 55, which constitutes the edge of the disc 56, is vibrated orthogonal to said outer face 55, which allows the spraying of liquid by the outer face 55 in a homogeneous and industrially productive manner. The European patent EP 0 588 609 describes such a sonotrode 53 The radius of the disc 56 can, in particular embodiments of the present invention, be more or less important, since it allows a radial vibration of said disc 56 in resonance with the frequency F of the generator and that, by this very fact, the vibration which animates it comprises a whole number of half-wavelengths. FIG. 10 uses the spray assembly of FIG. 9 mounted inside a sealed enclosure 61 in which any suitable atmosphere can be established, from the point of view of composition, temperature and pressure. , in order to constitute a spray atomization atomization device, spray drying type, or any other type. In the case of Figure 10, the penetration of the device according to the invention inside the sealed chamber 60 is in a node amplitude 511 of the vibration of the cylindrical rod 51. The atomizer of the figure 10, in which a flow of cold gas has been established, allows, for example, to produce metal alloy powders having a fine particle size spectrum and constricted by atomization solidification.

  This metal alloy, previously carried to a temperature above its melting point, is atomized within the atomizer into fine droplets. These droplets then cool down by falling within the enclosure and solidify to produce the desired powders.

  For example, an assembly according to Figures 9 and 10, and operating at 80 kHz, rated power 350 Watt, will be described in detail below. This set comprises an electro-acoustic converter 20, equipped with two ceramics 21 diameters 38 mm outside / 12 mm inside and 6 mm thickness excited in so-called radial or plane mode. This converter 20 is connected, via an intermediate element 30, to a straight cylindrical coupling rod 51 of diameter 15 mm, made of titanium alloy TA6V of a length corresponding to 6 half-wavelengths, or 300 mm.

  This assembly further comprises a booster 52, with a ratio 2.25, which makes it possible to obtain a peak-to-peak vibration of the order of 2 to 6 microns at its point of attachment (vibration belly) to the sonotrode of spraying 53. The spray horn is of the type shown in FIG. 9b and vibrating in resonance with the assembly described previously.

  This set allows the production of tin-based fusible metal alloy spherical powder having an average diameter of the order of 30 microns under an alloy flow rate of the order of 100 kg / h. The device illustrated in FIG. 11 implements a user element 50 successively comprising a cylindrical rod 51 fixed to the flat end face 31 of the intermediate element 30, a booster 52 and a spray horn 54 having a section cylindrical bar circular whose free face (ie the farthest from the converter 20) 55 allows the spraying of a liquid.

  A sheath 62 surrounds the user element 50, which enters the sheath at a node of amplitude 511 of the vibration of the cylindrical rod 51. This sheath 62 allows the liquid to be sprayed to be fed to the sonotrode 54 via an orifice 63.

  Referring to Figure 12, there is illustrated another embodiment of the device according to the invention for forming a tubular ultrasonic reactor. In this embodiment, the intermediate element 30 is in the form of a ring.

  A plurality of identical converters 20 are associated with the ring via contact zones 26a located at the central belly of the distal face 24 of each converter 20. These converters 20 are fixed on the outside of the ring and make radially projecting, so that the axis of revolution of the ring is orthogonal to the axes of revolution of the converters 20. The converters 20 are regularly spaced around the ring, and connected to the same generator 10, so that all the converters vibrate in phase at the frequency F of the generator. To the rings 31 internal to the ring, are fixed on either side of the ring 30, two tubes 45 and 46, which may be, in a preferred embodiment but not limited to, integrated with the ring 30, in a unique piece.

  The materials and the geometric characteristics of the ring 30 and the tubes 45, 46, constituting together the user element 40, are chosen so that, at the frequency F, the ring vibrates in resonance in radial mode and the tubes in longitudinal mode.

  The operation of the device according to the invention illustrated in FIG. 12 is then as follows. The converters vibrate in phase at the frequency F delivered by the generator and vibrate the ring 30 in radial mode. By Poisson effect of the ring, the tubes 45 and 46 are vibrated in the longitudinal mode. A liquid that circulates within the tubes then receives the ultrasonic energy. Finally, FIG. 13 uses an ultrasonic reactor vibrated by electro-acoustic converters 20 and their intermediate elements 30. European patent EP0567579 discloses such an ultrasonic reactor, consisting of a tubular metal body 43 and a bulge ring 42 in the middle part of the tube 43, each vibrating in resonance at the same ultrasonic frequency.

  FIG. 13 according to the present invention shows the general diagram revealed by this document: it comprises a tubular metal body 43 and the annular bulge 42, made in one piece 40. In the particular case represented by FIG. 13, only two converters 20 are represented, but a plurality of converters also distributed around the annular bulge 42 can also be implemented. The connection between each electro-acoustic converter 20 and its associated intermediate element 30 is arranged, in the case of FIG. 13, at the belly of peripheral amplitude 26b, but could equally well be located at the belly of central amplitude 26a. The reader will appreciate that many modifications can be made to the invention as described above without departing materially from the teachings of this document. For example, the distal face 24 of the electro-acoustic converter may comprise more than two vibration bellies, the contact zone, whose radius (in the case of a central disk) or the width (in the case of a peripheral ring) has been preferably between 10% and 15% of the radius of the distal face may be smaller or larger. Finally, the shape of the intermediate element 30 may vary. For example, the cylinder having the recess as shown in Figure 3 may have notches at its outer wall.

Claims (20)

  Apparatus for producing longitudinal ultrasonic acoustic vibrations in a user element (40, 50), comprising, at least, an electro-acoustic converter (20), comprising a pair of piezoelectric ceramics (21), characterized in that the piezoelectric ceramics (21) of the converter vibrate in radial mode and its distal face (24) in bending mode, an intermediate element (30) is placed between the converter (20) and the user element (40, 50), the intermediate element is attached, on one side, integrally to the distal face (24) of the converter (20) in a contact zone (26) located around a belly of amplitude of vibration of the distal face (24), the intermediate element (30) is attached on the other side to the user element (40, 50) by its flat end face (31), and any point of the end face (31) is animated with a homogeneous vibration in a direction orthogonal to said surface .   2. Device according to claim 1, characterized in that the electro-acoustic converter (20) and the intermediate element (30) are in one piece.   3. Device according to claim 1, characterized in that the intermediate element (30), on the one hand, and the user element (40) or a part of the user assembly (50), on the other hand, are in one piece.   4. Device according to one of claims 1 to 3, characterized in that the contact area (26) is located at the center (26a) of the distal face (24) of the converter (20).   5. Device according to claim 4, characterized in that the radius of the contact zone (26a) is between 10 and 15% of the radius of the distal face (24) of the converter (20).   6. Device according to one of claims 1 to 3, characterized in that the contact area (26) is located at the periphery (26b) of the distal face (24) of the converter (20). 10   7. Device according to claim 6, characterized in that the width of the contact zone (26b) is between 10 and 15% of the radius of the distal face (24) of the converter (20).   8. Device according to claim 6, characterized in that the intermediate element (30) comprises a metal cylinder having a recess, the face of the cylinder having the recess being intended to come opposite the electro-acoustic converter.   9. Device according to one of claims 1 to 8, characterized in that the extent of the contact zone (26) is such that at each of its points, the amplitude of the vibration is greater than 90% the amplitude at the belly around which the contact zone (26) is located. 25   10. Device according to one of claims 1 to 9, characterized in that it comprises a plurality of electro-acoustic converters (20) associated with the intermediate element (30), the intermediate element (30) being shaped of disk and the converters (20) being integrally fixed in a regularly spaced manner at the periphery thereof, the axes of the converters being orthogonal to the axis of the disk and the end surface 31 being parallel to the disk.   11. Device according to one of claims 1 to 10, wherein the (or) converter (s) (20) is (are) connected (s) to a generator (10) of alternating electric frequency signal ultrasonic frequency F, the natural frequency of vibration in radial mode of the piezoelectric ceramics (21) of the converter and the natural frequency of the intermediate element (30) being tuned to the ultrasonic frequency F of the generator (10) and the bandwidth of said generator being width between 100 and 300 Hz around the frequency F.   12. Device according to claim 11, characterized in that the ultrasonic frequency F is between 20 kHz and 400 kHz, preferably 40 kHz and 200 kHz, and even more preferably between 80 kHz and 200 kHz.   13. Device according to one of claims 11 or 12, characterized in that the ultrasonic power delivered by the generator (10) is between 50 and 10000 Watt.   14. Device according to one of claims 1 to 13, characterized in that the (or) converter (s) (20) is (are) arranged in a sealed chamber (60) in which a gas circulates or a coolant.   15. Device according to one of claims 1 to 14, characterized in that the user assembly (50) comprises a speed transformer (52), and / or a cylindrical rod (51), and / or a sonotrode (53). ).   16. Device according to one of claims 11 to 15, characterized in that the user element (40), or each piece of the user unit (50) taken separately, has a natural frequency tuned to the ultrasonic frequency F of the generator (10).   17. Device according to claim 16, characterized in that the user assembly (50) comprises at least one sonotrode (53) consisting of an axial bar (57) around which is arranged a radial ring (56), arranged around the bar (57) orthogonal to the axis of the bar, the bar (57) vibrates longitudinally and the crown radially, the outer radius of the ring (56) being determined to comprise an integer number of half-wavelengths in radial mode of vibration of the crown (56) at the frequency F.   18. Device according to claim 17, characterized in that a liquid is sprayed by the vibration of the surface (55) located on the outer edge of the ring (56).   19. Device according to one of claims 11 to 16, which can be used as an ultrasonic reactor modular unit, in which the disc-shaped intermediate element (30) is a corona recessed in its center, the surface (31) is in two parts which are respectively on either side of the element (30) and are themselves in the form of an inner ring concentric with the element (30), the user element (40) is a two-part tube (45) and (46), each of which is respectively fixed to one of the two parts of the surface (31), whose characteristics are chosen so that it resonates in the longitudinal vibration mode at frequency F.   20. A method for producing longitudinal ultrasonic acoustic vibrations comprising the steps of: converting an alternating electrical signal into radial mechanical vibrations of piezoelectric ceramics which are the constituents of an ultrasonic transducer, transformation of the radial mechanical vibrations of the ceramics into vibration bending the distal face of the transducer, using the vibratory energy of the distal face of the transducer, to generate longitudinal mechanical vibrations in a user element by means of an intermediate element.