Central bolt ultrasonic atomizer

Description

BACKGROUND OF THE INVENTION

1. Technical Field.

[0001] The present invention relates to piezoelectric ultrasonic atomizers, particularly of the type having an atomizing surface at a tip of a reduced diameter amplifying probe at one end of a transducer and a coaxial fluid delivery channel extending from the other end of the transducer to the atomizing surface.

2. Background Art.

[0002] Piezoelectric ultrasonic atomizers are finding increasing use in industrial applications where liquid materials must be delivered in the form of a very fine spray or mist. The design and construction of such atomizers is described in U.S. Patent No. 4,337,896 of BERGER et al. A typical arrangement is to sandwich a flat electrode between two disks or piezoelectric material, such as lead zirconate titanate, to form a driving element, and then to clamp the driving element between a cylindrical front amplifying horn and a cylindrical rear dummy section. The amplifying horn is provided with a reduced diameter probe having an atomizing surface at its tip. The amplification of vibrational amplitude obtained at the atomizing surface is approximately equal to the ratio between the respective cross-sectional areas of the cylindrical portion of the front horn and of the end of the probe.

[0003] In the type of atomizer shown in U.S. Patent No. 4,337,896, the necessary clamping pressure on the driving element is obtained by providing circumferential flanges on the adjacent ends of the front and rear sections and drawing the flanges together with a circle of bolts. The flanges also provide an annular bearing area for compressing an elastomeric gasket ring, to prevent liquid spray from contacting the outer peripheries of the piezoelectric disks. The sealing effectiveness of such a gasket is an important factor in extending the operating life of the atomizer.

[0004] The clamping flange design has drawbacks, however. To reduce internal losses, the front and rear horns should each be made as a single piece. It is wasteful to have to start with stock having an outer diameter equal to the flange diameter and then machine as much as two-thirds of it away. More importantly, the size of droplets formed by an ultrasonic atomizer varies inversely with the frequency of the unit. To obtain very small particles in the micron range, it is necessary to use very high frequencies, well over 100 kHz. To avoid significant transverse wave motion in the transducer, however, the transverse dimensions of the front and rear sections should be less than one-quarter wavelength.

[0005] As an example, in titanium a quarter wavelength at frequencies above 100 kHz is less than one centimeter. It is desirable to have the ratio between cylindrical section diameter and probe tip diameter be as large as possible, for increased amplification. At the same time, the atomizing surface should be large enough to handle a reasonable flow and the probe must be sturdy enough to resist breaking in operation. These factors make it undesirable to use up part of the diametral dimensions for clamping flanges.

[0006] An alternative arrangement for clamping a cylindrical atomizing transducer and concurrently protecting the piezoelectric elements from liquid contamination is disclosed in U.S. Patent No. 3,861,852 of BERGER. In this arrangement, a cylindrical transducer is inserted into a cup, and the transducer elements are clamped together by force exerted upon a flange on the rear dummy section by a cap threaded into the cup, with the front face of the transducer bearing against the base of the cup. O-rings at the clamping surfaces seal the transducer inside the cup from liquid spray delivered from the tip of a probe extending through an opening in the base of the cup. It is difficult to apply and maintain the proper clamping pressure on the piezoelectric driving element with this arrangement, however, and the end clamping can introduce significant damping and thereby reduce efficiency of the transducer.

[0007] Although liquid is fed to the above-described atomizers through a radial passage that intersects an axial channel in the front horn of the transducer, it is also known, for example from U.S. Patent No. 4,352,459 of BERGER et al., to feed the liquid axially through the rear section of a flange-clamped transducer. It is necessary in this design, however, to provide an annular sealing gasket between the feed tube and the inner circumferences of the piezoelectric disks, thus reducing the potential cross sectional area of the disks and thereby the available vibrational driving power. It is also known to clamp the driving element of a piezoelectric transducer by means of a solid central bolt, as in U.S. Patents No. 3,368,085 of McMASTER et al., No. 3,396,285 of MINCHENKO, No. 3,689,783 of WILLIAMS, and No. 3,694,675 of LOVEDAY. The transducers of these patents are not fluid feed atomizers, however.

SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to improve an ultrasonic liquid atomizing transducer assambly as disclosed in U.S. Patent No 4.352.459 of BERGER and to provide a piezoelectric atomizer design having a maximum practical amplification and adapted for high frequency operation above 100 kHz.

[0009] It is another object of the present invention to provide an axial feed piezoelectric atomizer that provides effective internal sealing without reducing the cross-sectional area available for the piezoelectric elements.

[0010] Another object of the invention is to provide external sealing of the piezoelectric elements in an atomizer as characterized above without exially loading the transducer element.

[0011] The above and other objects are achieved in an ultrasonic liquid atomizing transducer assembly comprising
   a driving element including a pair of annular piezoelectric disks and an annular electrode coaxially positioned therebetween;
   terminal means for feeding ultrasonic frequency electrical energy to said electrode;
   a cylindrical rear dummy section having a front end contacting one piezoelectric disk of the driving element and a rear end;
a front section having a cylindrical portion, the cylindrical portion having a rear end contacting the other piezoelectric disk of the driving element and a front end, and an amplifying portion extending from the front end of the cylindrical portion, the amplifying portion comprising a probe having a tip that forms an atomizing surface, an axial passage being provided through the length of the transducer assembly from the rear end of the rear dummy section to the atomizing surface, and a portion of the passage adjacent the driving element in the front atomizing section being enlarged and internally threaded;
a tubular central bolt formed as a hollow stud having an externally threaded portion engaging said internally threaded portion of the passage in the front atomizing section, a rear feed tube portion of the bolt being located in the rear dummy section and extending axially beyond the rear end of the dummy section; and
means for sealing the piezoelectric disks from contact with the liquid being atomized. In accordance with the invention the rear dummy section having a constant outside diameter from the front end to the rear end, and a portion of the passage in the rear dummy section also being enlarged and internally threaded;
the externally threaded portion of the tubular bolt engaging the internally threaded portion of the rear dummy section as well as the internally threaded portion of the front section with sufficient torque to connect the front atomizing section and the rear dummy section under a tension that provides all of a predetermined total compressive preload on the driving element, the externally threaded portion extending from a front end portion of the bolt located in the front atomizing section and formed with a smooth cylindrical sealing surface;
the means for sealing the piezoelectric disks comprising an annular sealing member disposed between said sealing surface and the axial passage to prevent liquid flowing in the passage from reaching the inner circumferential surfaces of the piezoelectric disks; and
the means for sealing the piezoelectric disks from contact with the liquid being atomized comprising an enclosed shell surrounding the transducer assembly, the shell having a front end wall provided with a first cylindrical passage that loosely receives the cylindrical portion of the front section, and an annular sealing means (41) disposed between the inner surface of the cylindrical passage and the circumference of the cylindrical portion of the front section, the radial spacing between the cylindrical portion of the front section and the cylindrical passage being less than the radial thickness of the annular sealing means when unconstrained, so that the annular sealing means (41) is radially compressed between said passage and said cylindrical portion, and wherein said annular sealing means is unconstrained in the axial direction.

[0012] The above and other objects, features and advantages of the present invention will be more readily apparent from the following description of the preferred embodiments when considered with the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawing in which like numerals indicate the same or similar parts and in which:

Fig. 1 is a partially cut away perspective view of an ultrasonic atomizing transducer assembly according to the invention, and

Fig. 2 is a view in longitudinal cross section of the transducer assembly of Fig. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0014] With reference to the figures, an embodiment of an ultrasonic atomizing transducer assembly 11 includes a transducer 12 having a driving element 13, a rear dummy section 14, and a front atomizing section 15.

[0015] The driving element 13 is assembled from a washer-shaped metal electrode 16 sandwiched between a pair of annular piezoelectric disks 17 and 18. The electrode may be made of copper or any other suitable metal having high electrical conductivity, and it is provided with a terminal 19 for attachment to a source of electrical energy at the resonant frequency of the transducer. The piezoelectric disks are made of any material conventionally used for such service, such as barium titanate or lead zirconate titanate.

[0016] The rear dummy section 14 is a metal cylinder, preferably titanium, having a length equal to a quarter wavelength at the designed operating frequency of the transducer. A front end 20 of the rear section 14 contacts the rear piezoelectric disk 18, and a rear end 21 of the rear section is free to vibrate as an antinodal plane. The front atomizing section 15 includes a cylindrical portion 22 having a rear end 23 that contacts the front piezoelectric disk 17 and a front end 24 that lies in a nodal plane, the cylindrical portion 22 being designed to be one-half wavelength long at the operating frequency of the transducer. From the front end of the cylindrical portion 22, a quarter wavelength amplifying probe 25 extends to a frustoconical tip 26 having an atomizing surface 27. The front atomizing section preferably is made of the same material as the rear dummy section, although a different material could be used if desired, so long as the appropriate wavelength dimensions were used to match the operating frequency of the rear section.

[0017] Except for a narrow circumferential flange 28 at the rear end of the front section, the outer diameter of the transducer is equal to the diameters of the front and rear sections. These sections are clamped against the driving element 13 with a predetermined compressive stress by a central tubular bolt 29 that is formed as an enlarged threaded stud on the end of a liquid feed tube 30. The tubular bolt engages an internally threaded enlarged portion 31 of an axial passage 32 that extends through the transducer from the rear end of the rear dummy secton 14 to open onto the atomizing surface at the tip of the probe 25.

[0018] To prevent liquid flowing through the delivery tube 30 into the passage 32 from penetrating past the threaded portion of the front section and contacting the internal surfaces of the piezoelectric disks, an O-ring seal 33 is provided between a smooth sealing surface 34 machined on the front end of the central bolt 29 and the inner surface of the passage 32. As illustrated, the O-ring is fitted into a circumferential groove machined into the wall of the passage to assure that the O-ring is properly located with respect to the sealing surface 34. The groove could equally well be formed on the end of the bolt, or any other conventional sealing arrangement could be used between the end of the bolt and the inner surface of the passage in the front section.

[0019] An additional O-ring 35 is provided to seal between the outer circumference of the feed tube 30 and the inner circumference of the axial passage. This second O-ring prevents ingress of moisture from the environment surrounding the atomizer.

[0020] Because there are no clamping flanges on the transducer body to provide an annular area for a compressed ring gasket around the outside of the driving element, the outer peripheries of the piezoelectric disks are protected by an enclosed shell 36. This shell is in the form of a cylindrical cup 37 having a screw cap 38. The cup 37 has an end wall 39 provided with an opening 40 which receives the cylindrical portion 22 of the front section of the transducer. This opening is sealed by a radially compressed O-ring 41 disposed between the outer circumference of the cylindrical portion 22 and a counterbore 42 in the opening 40. The screw cap 38 has an end wall 43 with a similar but smaller opening 44. An O-ring 45 in a counterbore 46 seals this opening in the same way as O-ring 41 seals the front opening. As illustrated, O-ring 45 is radially compressed between the counterbore 46 and a cylindrical collar 47 extending from the end 21 of the rear dummy section.

[0021] Alternatively, the dimensions of the collar and the counterbore could be revised so that the O-ring 45 could seal radially against the outer periphery of the feed tube 30 and abut against the end of the collar. It is important, however, that there be no axial compression force exerted by the shell against the transducer body via the O-rings 41 and 45. In this connection, the narrow flange 28 at the rear of the front section serves merely to locate the O-ring 41 as close as possible to the nodal plane defined by the electrode 16. There should be no axial force exerted against this flange by the O-ring since the O-ring 45 at the rear of the shell has room to float axially. Consequently, the transducer is supported in the shell substantially purely radially, with no axial force exerted between the shell and the transducer.

[0022] The procedure for assembling the transducer is as follows. After the O-ring 33 is installed into its groove in the front section 22, the central bolt is screwed into the front section until it bottoms. The piezoelectric disks and the center electrode are then passed over the bolt. If desired, a sleeve of electrical insulating material (not shown) may be inserted between the bolt and the inner circumferences of the disks and electrode. This will help to center the driving element as well as to prevent a short circuit of the driving element. It also may be desirable to add a second annular electrode (not shown) between the rear piezoelectric disk and the rear dummy section to provide a second terminal to facilitate completing the electrical circuit across the piezoelectric disks.

[0023] After the driving element is assembled onto the bolt, the O-ring 35 is fitted over the feed tube 30, and the rear dummy section is then screwed down against the driving element. The proper compression force is obtained by applying a torque wrench to two diametrically spaced detent holes 48 drilled in the rear end 21 of the rear dummy section.

[0024] Following assembly of the transducer, the shell can be mounted by first installing O-ring 45 on the collar 47 (or on the tube 30 in the above-mentioned alternative arrangement) and then sliding the threaded cap 38 over the tube 30 into place over the rear dummy section. A lead wire 49 attached to a hermetically sealed coaxial fitting 50 mounted on the end wall of the cap is then clipped or soldered to terminal 19 of the center electrode 16. If a second electrode is provided, as described above, a second lead wire (not shown) from a second coaxial fitting (not shown) should be similarly attached to the second electrode. Finally, the O-ring 41 is placed on the cylindrical portion 22 of the front atomizing section, and the cup 37 is slipped onto the cylindrical section 22 and screwed into the cap 38 until it bottoms. The cap can be tightened by means of a spanner wrench fitting the detent holes 51 in the end wall of the cap.

[0025] Since the transducer is connected to the shell only radially through the "axially floating" O-rings 41 and 45, the transducer can be mounted by clamping or fastening to the shell in any desired way without adversely affecting either the compression preload on the driving element 13 or the resonant frequency of the transducer. Liquid can be delivered to the rear of the unit via a flexible hose (not shown) connected to the delivery tube 30 by the standard coupling connectors 52 (see Fig. 1). Alternatively, the assembly can be supported by a rigid liquid supply pipe coupled to the delivery tube 30.

[0026] To test the above-described design, an atomizing transducer was built and tested. The dimensions were chosen for an operating frequency of about 56 kHz. The front and rear transducer sections were made of titanium and the central bolt was made of 316 stainless steel, to provide corrosion resistance for a wide variety of operating liquids. Due to the relatively low yield strength of this material, however, it is a marginal choice particularly for higher frequencies, because the bolt may have to be torqued beyond its yield point to obtain the required compression on the piezoelectric disks. Thus, in applications where corrosion resistance is not a prime consideration, it may be preferable to use a stronger steel for the central bolt material.

[0027] In testing the completed assembly, it was found to be essential to avoid any axial loading on the O-rings of the shell; otherwise, the electrical impedance of the unit would vary over a wide range with time, making it impossible to maintain operation at peak efficiency. With purely radial compression of the O-rings, however, stable operation and repeatable results were easily obtained. The shell was leak-free even when the unit was operated submerged under water.

[0028] Accordingly, the design of the present invention is adapted to provide an ultrasonic atomizing transducer that is simple to manufacture and is completely shielded from damp or hazardous environments, such as explosive atmospheres. By eliminating the clamping flanges of prior designs, it is possible to obtain a high amplification factor without having the transverse dimensions of the transducer body exceed the practical limit for achieving substantially one-dimensional vibration.

[0029] Certain changes and modifications of the disclosed embodiment will be readily apparent to those skilled in the art. For example, the central bolt could be integrally formed as part of the rear or front section in applications where the material of the section is strong enough to carry the necessary tensile stress for preloading the piezoelectric disks. In addition, it is possible to provide many different sealing arrangements within the prescribed limitations.

Claims

1. An ultrasonic liquid atomizing transducer assembly comprising:
a driving element (13) including a pair of annular piezoelectric disks (17,18) and an annular electrode coaxially positioned therebetween;
terminal means (19) for feeding ultrasonic frequency electrical energy to said electrode;
a cylindrical rear dummy section (14) having a front end (20) contacting one piezoelectric disk (18) of the driving element (13), and a rear end (21);
a front section (15) having a cylindrical portion (22), the cylindrical portion having a rear end (23) contacting the other piezoelectric disk (17) of the driving element and a front end (24), and an amplifying portion extending from the front end of the cylindrical portion, the amplifying portion comprising a probe (25) having a tip (26) that forms an atomizing surface (27), an axial passage (32) being provided through the length of the transducer assembly (11) from the rear end (21) of the rear dummy section to the atomising surface (27), and a portion (31) of the passage adjacent the driving element (13) in the front atomising section being enlarged and internally threaded;
a tubular central bolt (29) formed as a hollow stud, having an externally threaded portion engaging said internally threaded portion of the passage in the front atomizing section, a rear feed tube portion of the bolt being located in the rear dummy section and extending axially beyond the rear end of the dummy section; and
means (33) for sealing the piezoelectric disks (17, 18) from contact with the liquid being atomized, wherein the transducer assembly is characterized by:
   the rear dummy section (14) having a constant outside diameter from the front end to the rear end, and a portion of the passage (32) in the rear dummy section also being enlarged and internally threaded;
   the externally threaded portion of the tubular bolt (29) engaging the internally threaded portion of the rear dummy section as well as the internally threaded portion of the front section with sufficient torque to connect the front atomizing section and the rear dummy section under a tension that provides all of a predetermined total compressive preload on the driving element, the externally threaded portion extending from a front end portion of the bolt located in the front atomizing section and formed with a smooth cylindrical sealing surface (34);
   the means for sealing the piezoelectric disks comprising an annular sealing member (33) disposed between said sealing surface (34) and the axial passage (32) to prevent liquid flowing in the passage from reaching the inner circumferential surfaces of the piezoelectric disks (17, 18); and
   the means for sealing the piezoelectric disks from contact with the liquid being atomized comprising an enclosed shell (36) surrounding the transducer assembly (11), the shell having a front end wall (39) provided with a cylindrical passage (40) that loosely receives the cylindrical portion (22) of the front section (15) and an annular sealing means (41) disposed between the inner surface of the cylindrical passage and the circumference of the cylindrical portion of the front section, the radial spacing between the cylindrical portion of the front section and the cylindrical passage being less than the radial thickness of the annular sealing means when unconstrained, so that the annular sealing means (41) is radially compressed between said passage and said cylindrical portion, and wherein said annular sealing means is unconstrained in the axial direction.

2. An ultrasonic liquid atomizing transducer assembly according to claim 1 wherein the annular sealing member (33) comprises an O-ring.

3. An ultrasonic liquid atomizing transducer assembly according to claim 1 wherein the threaded stud has a rear end located in the rear dummy section (14), and the tubular central bolt (29) further comprises an integral liquid feed tube (30),having a smooth exterior surface extending axially from the rear end of the threaded stud beyond the rear end of the dummy section.

4. An ultrasonic liquid atomizing transducer assembly according to claim 3 wherein the means for sealing the piezoelectirc disks (17, 18) comprises an additional annular sealing member (35) disposed between the smooth exterior surface of said liquid feed tube (30) and the axial passage (32) to prevent moisture in the environment surrounding the transducer assembly from reaching the inner circumferential surfaces fo the piezoelectric disks.

5. An ultrasonic liquid atomizing transducer assembly according to claim 4 wherein the additional annular sealing member (35) comprises an O-ring.

6. An ultrasonic liquid atomizing transducer assembly according to claim 1 wherein the means for sealing the piezoelectric disks (17, 18) from contact with the liquid being atomized further comprises:
the shell (36) further having a rear wall provided with an additional cylindrical passage that loosely receives an axial feed tube extending from the rear end of the rear dummy section and an additional annular sealing means (45) disposed between the additional cylindrical passage and the feed tube (30), the radial spacing between the additional cylindrical passage and the feed tube (30) being less than the radial thickness of the annular sealing means when unconstrained, so that the annular sealing means is radially compressed between said additional passage and said feed tube, and wherein said annular sealing means (45) is unconstrained in the axial direction.

7. An ultrasonic liquid atomizing transducer assembly according to claim 6 wherein said first mentioned and additional radially compressed sealing means (45) comprise O-rings.

8. An ultrasonic liquid atomizing transducer assembly according to claim 6 wherein said enclosed shell (36) comprises a cylindrical cup (37) and a cylindrical cap (38) threadedly fitting on said cup.

Revendications

1. Un ensemble transducteur à ultrasons pour l'atomisation de liquide et comportant:
   un élément pilote (13) comportant une paire de disques piézo-électriques annulaires (17, 18) et une électrode annulaire positionnée coaxialement entre les deux disques;
   des moyens de connectique pour alimenter ladite électrode en énergie électrique de fréquence ultrasonique;
   une section cylindrique arrière isolante (14) comportant une paroi frontale (20) venant au contact d'un disque piézo-électrique (18) de l'élément pilote (13) et une partie arrière (21);
   une section frontale (15) comportant une partie cylindrique (22), cette partie cylindrique comportant une extrémité arrière (23) venant au contact de l'autre disque piézo-électrique (17) de l'élément pilote, et une extrémité frontale (24), et
une partie d'amplification s'étendant depuis l'extrémité frontale de la partie cylindrique, la partie amplificatrice comportant une sonde (25) pourvue d'une pointe (26) qui forme une surface d'atomisation (27), un alésage axial (32) étant prévu à travers la longueur de l'ensemble transducteur (11) depuis l'extrémité arrière (21) de la section arrière isolante jusqu'à la surface d'atomisation (27) et une partie (31) du passage voisin de l'élément pilote (13) dans la partie frontale d'atomisation étant élargie et filetée intérieurement;
   un boulon central (29) sous forme d'un goujon creux comportant une partie filetée extérieurement engagée dans ladite partie filetée de l'alésage de la partie frontale d'atomisation, un canal arrière d'alimentation venu du boulon étant logé dans la section arrière isolante et s'etendant axialement au-delà de l'extrémité terminale de ladite section isolante, et
   des moyens (33) pour isoler les disques piézo-électriques (17, 18) de tout contact avec le liquide en voie d'atomisation, dans lequel l'ensemble transducteur est caractérisé par:
   la section arrière isolante (14) présente un diamètre extérieur constant depuis sa paroi frontale jusqu'à son extrémité arrière et une partie de l'alésage (32) dans ladite section isolante arrière étant également élargie et filetée intérieurement;
   la partie extérieurement filetée du boulon tubulaire (29) est engagée dans la partie filetée intérieurement de ladite section isolante arrière comme dans la partie filetée intérieurement de la partie frontale avec un couple suffisant pour relier la section frontale d'atomisation et la section arrière isolante sous une contrainte qui procure la totalité d'une charge prédéterminée de compression sur l'élément pilote, la partie extérieurement filetée du boulon s'étendant depuis la partie frontale de ce dernier située dans la section frontale d'atomisation et étant prévue avec une surface extérieure cylindrique lisse offrant une surface d'étanchéité (34);
   les moyens pour isoler les disques piézo-électriques comprennent un joint annulaire (33) disposé entre ladite surface d'étanchéité (34) et l'alésage axial (32) pour empêcher l'écoulement du liquide depuis ledit alésage et qui pourrait atteindre la surface circonférentielle extérieure des disques piézo-électriques (17, 18); et
   les moyens pour assurer l'étanchéité des disques piézo-électriques et les protéger de tout contact du liquide atomisé comportent une coquille d'enveloppement (36) entourant l'ensemble transducteur (11), la coquille comporte une paroi frontale(39) pourvue d'un passage cylindrique (40) qui reçoit intérieurement de façon lâche la portion cylindrique (22) de la section frontale (15) et un joint annulaire d'étanchéité (41) est disposé entre la surface intérieure du passage cylindrique et la circonférence de la partie cylindrique de la section frontale, l'espace radial entre la partie cylindrique de la section frontale et l'alésage cylindrique étant inférieur à l'épaisseur radiale du joint annulaire lorsqu'il n'est pas comprimé, de sorte que le joint annulaire (41) est soumis à une compression radiale entre ledit passage et ladite partie cylindrique et dans lequel ledit joint cylindrique n'est pas comprimé dans une direction axiale.

2. Un ensemble transducteur à ultrasons pour l'atomisation de liquide selon la revendication 1, dans lequel le joint annulaire d'étanchéité (33) comporte un joint torique.

3. Un ensemble transducteur à ultrasons pour l'atomisation de liquide selon la revendication 1, dans lequel le goujon fileté comporte une extrémité arrière située dans la section arrière isolante (14) et le boulon tubulaire central (29) comporte en outre un tube d'alimentation de liquide (30)
comportant une surface extérieure lisse s'étendant axialement depuis l'extrémité arrière du goujon fileté au-delà de l'extrémité arrière de la section isolante.

4. Un ensemble transducteur à ultrasons pour l'atomisation de liquide selon la revendication 3, dans lequel les moyens d'étanchéité des disques piézo-électriques (17, 18) comportent un joint additionnel annulaire (35) disposé entre la surface extérieure lisse dudit tube d'alimentation de liquide (30)et l'alésage axial (32) pour empêcher l'humidification de l'environnement. entourant l'ensemble transducteur et empêcher l'humidité d'atteindre les surfaces circonférentielles intérieures des disques piézo-électriques.

5. Un ensemble transducteur à ultrasons pour l'atomisation de liquide selon la revendication 4, dans lequel le joint annulaire additionnel comporte un joint torique.

6. Un ensemble transducteur à ultrasons pour l'atomisation de liquide selon la revendication 1, dans lequel les moyens pour assurer l'étanchéité des disques piézo-électriques (17, 18) de tout contact avec le liquide atomisé comportent en outre: la coquille d'enveloppement (36) présente une paroi arrière prévue avec un passage cylindrique additionnel qui reçoit de façon lâche un tube d'alimentation s'étendant depuis la partie arrière de la section arrière isolante et un joint annulaire d'étanchéité (45) est disposé entre le passage cylindrique additionnel et ledit tube d'alimentation (30), l'espace radial entre le passage cylindrique additionnel et le tube d'alimentation étant inférieur à l'épaisseur radiale du moyen d'étanchéité annulaire lorsqu'il n'est pas comprimé de sorte que le moyen d'étanchéité annulaire est comprimé radialement entre ledit passage additionnel et ledit tube d'alimentation et dans lequel ledit joint annulaire d'étanchéité (45) n'est pas sous tension dans une direction axiale.

7. Un ensemble transducteur à ultrasons pour l'atomisation de liquide selon la revendication 6, dans lequel lesdits premiers joints d'étanchéité et joints d'étanchéité additionnels, comprimés radialement, sont constitués de joints toriques.

8. Un ensemble transducteur à ultrasons pour l'atomisation de liquide selon la revendication 6, dans lequel ladite coquille d'enveloppement (36) comporte une coupelle cylindrique (37) et un opercule cylindrique (38) engagé et s'adaptant par un pas de vis sur ladite coupelle.

Ansprüche

1. Wandlereinrichtung für einen Flüssigkeitsultraschallzerstäuber mit:

einem Antriebselement (13) mit einem Paar von ringförmigen piezoelektrischen Scheiben (17, 18) und einer ringförmigen Elektrode, die koaxial dazwischen angeordnet ist;

einem Anschlusselement (19) zur Einleitung ultraschall-frequenter elektrischer Energie in die Elektrode;

einem zylindrischen hinteren Ansatzstück (14), welches ein vorderes Ende (20), das mit der einen piezoelektrischen Scheibe (18) des Antriebselements (13) in Verbindung steht, und ein hinteres Ende (21) aufweist;

einem vorderen Bereich (19) mit einem zylindrischen Abschnitt (22), wobei der zylindrische Abschnitt ein hinteres Ende (23), das mit der anderen piezoelektrischen Scheibe (17) des Antriebselements in Verbindung steht, und ein vorderes Ende (24) aufweist, und einem sich verstärkenden Bereich, der vom vorderen Ende des zylindrischen Bereichs absteht, wobei der sich verstärkende Bereich eine Sonde (25) aufweist, mit einer Spitze (26), welche eine Zerstäubungsoberfläche (27) bildet, einem axialen Durchlass (32), welcher sich über die Länge der Wandlereinrichtung (11) von deren hinterem Ende (21) des hinteren Ansatzstückes bis zur Zerstäubungsoberfläche (27) erstreckt, und mit einem Bereich (31) des Durchlasses, welcher dem vorderen Zerstäubungsabschnitt des Antriebselements (13) benachbart und aufgeweitet ist, und ein Innengewinde aufweist;

einem rohrförmigen Zentralbolzen (29), der als hohle Stiftschraube ausgebildet ist und einen äusseren mit einem Gewinde versehenen Bereich aufweist, der mit dem Innengewinde des Durchlasses im vorderen Zerstäubungsabschnitt in Verbindung steht, wobei ein hinterer Speiseleitungsabschnitt des Bolzens im hinteren Ansatzstück vorgesehen ist und sich axial über das hintere Ende des Ansatzstückes hinauserstreckt;

Mittel (33) zum Abdichten der piezoelektrischen Scheiben (17, 18) gegenüber der zu zerstäubenden Flüssigkeit,

dadurch gekennzeichnet,

dass das hintere Ansatzstück (14) vom vorderen Ende bis zum hinteren Ende einen konstanten Aussendurchmesser aufweist und ein Abschnitt des im hinteren Ansatzstück sich befindenden Durchlasses aufgeweitet ist und ein Innengewinde aufweist;

dass der äussere, mit einem Gewinde versehene Abschnitt des rohrförmigen Bolzens (29) sowohl mit dem mit einem Innengewinde versehenen Abschnitt des hinteren Ansatzstückes als auch mit dem mit einem Innengewinde versehenen Abschnitt des vorderen Bereichs mit ausreichender Drehkraft in Verbindung steht, um den vorderen Zerstäubungsbereich und das hintere Ansatzstück mit ausreichender Spannkraft zu verbinden, wobei die Spannkraft vollständig die ganze vorbestimmte Druckvorspannung auf das Antriebselement zur Verfügung stellt, und dass der mit einem Aussengewinde versehene Abschnitt, welcher von einem vorderen Endabschnitt des Bolzens absteht, im vorderen Zerstäubungsabschnitt angeordnet ist und mit einer glatten zylindrischen Dichtfläche (34) versehen ist;

dass die Mittel zum Abdichten der piezoelektrischen Scheiben ein ringförmiges Dichtelement (33) aufweisen, welches zwischen der Dichtfläche (34) und dem axialen Durchlass (32) angeordnet ist und verhindert, dass im Durchlass strömende Flüssigkeit die innere Umfangsfläche der piezoelektrischen Scheiben (17, 18) erreicht; und

dass die Mittel zum Abdichten der piezoelektrischen Scheiben gegenüber einer Kontaktierung mit der zu zerstäubenden Flüssigkeit ein Gehäuse (36) aufweisen, welches die Wandlereinrichtung (11) umgibt und mit einer vorderen Stirnwand (39) versehen ist, die mit einem zylindrischen Durchlass (40) versehen ist, der lose den zylindrischen Abschnitt (22) des vorderen Bereichs (15) und ein Dichtelement (41) aufnimmt, welches zwischen der Innenoberfläche des zylindrischen Durchlasses und der Umfangsfläche des zylindrischen Abschnitts des vorderen Bereichs angeordnet ist, und dass dar radiale Abstand zwischen dem zylindrischen Abschnitt des vorderen Bereichs und dem zylindrischen Durchlass kleiner ist als die radiale Dicke des ringförmigen, unverformten Dichtelements, so dass das ringförmige Dichtelement (41) zwischen dem Durchlass und dem zylindrischen Abschnitt radial komprimiert wird und in axialer Richtung frei ist.

2. Wandlereinrichtung für einen Flüssigkeitsultraschallzerstäuber nach Anspruch 1, dadurch gekennzeichnet, dass das ringförmige Dichtelement (33) einen O-Ring aufweist.

3. Wandlereinrichtung für einen Flüssigkeitsultraschallzerstäuber nach Anspruch 1, dadurch gekennzeichnet, dass die mit einem Gewinde versehene Stiftschraube ein hinteres, im hinteren Ansatzstück (14) sich befindendes Ende aufweist und der rohrförmige Zentralbolzen (29) zudem eine integrale Flüssigkeitsspeiseleitung (30) aufweist, die eine glatte Aussenoberfläche besitzt und axial vom hinteren Ende der mit einem Gewinde versehenen Stiftschraube über das hintere Ende des Ansatzstückes hinweg absteht.

4. Wandlereinrichtung für einen Flüssigkeitsultraschallzerstäuber nach Anspruch 3, dadurch gekennzeichnet, dass die Mittel zum Abdichten der piezoelektrischen Scheiben (17, 18) ein zusätzliches ringförmiges Dichtelement (35) aufweisen, welches zwischen der glatten Aussenoberfläche dar Flüssigkeitsspeiseleitung (30) und dem axialen Durchlass (32) angeordnet ist, um die die Wandlereinrichtung umgebende Feuchtigkeit davon abzuhalten, an die innere Umfangsfläche der piezoelektrischen Scheiben zu gelangen.

5. Wandlereinrichtung für einen Flüssigkeitsultraschallzerstäuber nach Anspruch 4, dadurch gekennzeichnet, dass das zusätzliche ringförmige Dichtungselement (35) einen O-Ring aufweist.

6. Wandlereinrichtung für einen Flüssigkeitsultraschallzerstäuber nach Anspruch 1, dadurch gekennzeichnet, dass die Mittel zum Abdichten der piezoelektrischen Scheiben (17, 18) gegenüber einer Kontaktierung mit der zu zerstäubenden Flüssigkeit ausserdem aufweisen:

dass das Gehäuse (36) ferner eine hintere Wand besitzt, welche mit einem zusätzlichen zylindrischen Durchlass versehen ist, der lose eine axiale, vom hinteren Ende des hinteren Ansatzstückes aus sich erstreckende Flüssigkeitsspeiseleitung und ein zusätzliches ringförmiges Dichtelement (45) aufnimmmt, welches zwischen dem zusätzlichen zylindrischen Durchlass und der Speiseleitung (30) angeordnet ist, dass der radiale Abstand zwischen dem zusätzlichen zylindrischen Durchlass und der Speiseleitung (30) kleiner ist als die radiale Dicke des ringförmigen unverformten Dichtelements, so dass das ringförmige Dichtelement zwischen dem zusätzlichen Durchlass und der Speiseleitung radial komprimiert wird und in axialer Richtung frei ist.

7. Wandlereinrichtung für einen Flüssigkeitsultraschallzerstäuber nach Anspruch 6, dadurch gekennzeichnet, dass das zuerst erwähnte und das zusätzliche, radial komprimierte Dichtelement (45) O-Ringe aufweisen.

8. Wandlereinrichtung für einen Flüssigkeitsultraschallzerstäuber nach Anspruch 6, dadurch gekennzeichnet, dass das geschlossene Gehäuse (36) eine zylindrische Büchse (37) und eine zylindrische Kappe (38) aufweist, die über ein Gewinde auf die Büchse aufgesetzt ist.

Drawing