DE4138528C1 - Ultrasonic transducer e.g. for level indicator - has diaphragm held between seals and flange in direct contact with attachment surface or via spacer - Google Patents

Abstract

The ultrasonic transducer has a flat plate diaphragm (6) coupled to a piezo-electric oscillator (4) to transmit and/or receive vibrations. The diaphragm (6) is held on a flange of the transducer housing. A flexible seal (9) is interposed between the diaphragm and the flange (2). The flange can be connected to an attachment surface (22) by connector bolts (21). A flexible seal (24) can be disposed between the attachment surface (22) and the diaphragm. The flange, in its assembled state, lies on the attachment surface (22) directly or via at least one spacer (25). ADVANTAGE - Simple to manufacture, relatively good operating characteristics and improved acoustic decoupling of structure borne vibration.

Description

The invention relates to an ultrasonic transducer the preamble of claim 1.

In the ultrasonic known from DE-GM 86 25 990 The membrane is a converter thanks to central thickness reductions tion of a plate formed so that the membrane is integral with the outer, forming the mounting flange Plate edge is connected. Via the mounting flange is the ultrasonic transducer to an opposite one Screwed mounting flange, the one with the container to be monitored visually is firmly connected. However, it has been shown that in the known ultrasonic transducer in the level monitoring in some cases problems by per Structure-borne noise transmitted ultrasonic interference signals can occur from the ultrasonic transducer Membrane are actually received  Superimpose the useful signal to be evaluated. The Her is also position of the membrane and the surrounding flange pro blematic, because during the plate processing to manufacture development of the membrane must be worked very precisely because with the recess bottom forming the membrane th thickness and thus defined sound propagation time. In addition, for different membrane diameters or thicknesses of appropriately dimensioned semi-finished products Plates in processed or raw form are kept ready, whereby - in processed Semi-finished panels with an already incorporated membrane - increase the storage costs or - if still unbearable processed semi-finished panels - the manufacturing and delivery increase times accordingly.

Furthermore, it is known from DE-GM 86 30 763, a insert a cantilevered membrane protruding downwards, which are attached directly to the flange via their side edges is screwed. Thanks to the protruding membrane design However, this protrudes into the level monitoring the container to be monitored and reduced consequently its maximum filling volume, as a certain The minimum distance between the ultrasonic transducer membrane and the maximum fill surface is not undercut may be. In addition, structure-borne noise Coupling problems occur. Also the manufacture the cup-shaped membrane is more complex.

The one in the main patent 41 26 399 described, the generic term of Claim 1 corresponding ultrasonic transducer the membrane is designed as a flat plate, the zwi two flexible seals is arranged. At the Mount the ultrasonic transducer on the mounting The flexible seals become slightly flanged compressed so that the membrane mounting screws stand out slightly from their contact surface. This will  the ultrasound bridges that are an ultrasound fort planting of the membrane over the membrane holder screw this flange, the connector and the ultrasound transducer Mounting flange allow, largely under broken so that the unwanted, not from the Membrane radiated ultrasound propagation is largely suppressed. However, it was found that the extent of this achieved Structure-borne noise decoupling from the tightening torque of the Ultrasonic transducer flange with the mounting surface tensioning connecting bolt depends and thus in is variable to some extent. This can happen in some Cases may be undesirable.

The invention has for its object an Ultra to create sound transducers that are easy to manufacture and by relatively good company property ten, especially with regard to reducing the Structure-borne noise coupling.

This task is called with the in claim 1 characteristics solved.

Advantageous embodiments of the invention are in the Subclaims specified.

In the ultrasonic transducer according to the invention Membrane formed as a flat plate, which under Zwi position of a seal on the flange. The ins a seal between the membrane and flange has a good acoustic decoupling between the Membrane and the flange so that the ultrasonic waves not or only to a very subdued extent from the Can propagate membrane to the flange. This brings the advantage that hardly any interference signals are sent and consequently no false echoes are received. A  otherwise possible direct structure-borne noise conduction from the membrane over the housing of the ultrasonic transducer and the flange to the wall of the container to be monitored ters, where the container wall as a transmitter for Ultra noise signals could act under presses. Such interference signals, which are the useful echo store and distort it, because of the identical frequency position hardly with reasonable effort can be reliably eliminated so that the measurement is accurate would suffer.

This effect is in the invention by the flexible Avoid seal that the ultrasound propagation largely prevented from the membrane to the flange.

The formation of the membrane as a flat surface also contributes to this Plate in a defined manner on the flexible Seal rests and also only specifically in one emits only direction, so that the radiation in Lateral direction, transverse to the main transmission direction, extreme is negligible. As a result, none in un directional ultrasound energy sent out, which after multiple refle xions then as disturbing, falsify the measurement result transmitting echo signal could be received.

In the ultrasonic transducer according to the invention, the Flange in the assembled state of the ultrasonic transducer thus either directly or via a (or given if several) spacers on the mounting surface at. Through this - direct or indirect - rigid me mechanical attachment between the flange and the fastening supply area ensures that the flexible you independent of the respective tightening torque of the Connecting bolts together to a defined extent are pressing. This removes the membrane holders screws always to a precisely defined extent of  their contact surface on which they are in the pre-assembled state plants, so that the propagation of structure-borne noise in defined, strong extent is suppressed. There are thus always reproducible conditions after assembly of the ultrasonic transducer on the mounting flange. Furthermore, there is the additional advantage that the direct - or indirect - contact between Ultra sound transducer flange and mounting flange too acts immediately as a stop, the excessive togetherness avoids crushing the flexible seals. Here through such, shortening the lifespan stresses on the seals avoided, so that The sealing effect remains stable over a long period of time remains intact. In addition, now is the Holdings exerted on the membrane via the seals always defined, so that the effects of clamping of the membrane caused by the seals on their sending or receiving behavior always the same and are clearly predictable.

The formation of the membrane as a flat plate has in addition your defined sending and / or receiving behavior other advantages too. For example, the plate protrudes and thus the ultrasonic transducer is not in the container into it so that the filling volume of the container maxi times can be exploited without the required Minimum distance between membrane and level surface needs to be undercut. Due to the The membranes can be of extremely simple design any suitable material, so that in addition to steel and VA also plastic membranes, e.g. B. from PVDF, PTFE etc. can be used. Plastic membranes also have significantly higher cold impact strength as an injection molded membrane. Despite the different membrane materials remains the mechanical structure is the same, so that none constructive changes to the support elements or  Like. are required. Even the exchange of one Membrane can be extremely quick at very simple Handling done. The membranes are also extreme inexpensive to manufacture, for example by easy removal from suitable size plates terials and suitable strength. It is not a spray cast a corresponding shape required. The Manufacturing can be extremely simple, for example wise by punching out commercially available plates be accomplished.

Due to the plate-shaped membrane design, the Membrane can also be coated very easily, for example with modified epoxy resin or Plastic "ECTFE", e.g. B. corrosion resistance increase or meet hygiene requirements. At appropriate dimensioning of the density range Ultrasonic transducers equipped with VA membranes also in explosive areas can be used reliably, d. H. Ex-protected.

The smooth membrane surface now also allows the on sentence of the ultrasonic transducer according to the invention in Le food sector, where particularly high requirements insist on keeping it clean.

The direct contact between the ultrasonic transducer flange and mounting flange, when assembled, can by suitable, preferably circumferential projections on Ultrasonic transducer flange and / or on the mounting Flange can be achieved. According to a preferred Ausge staltung, however, the flange is preferably annular recess for receiving the seals and the membrane. In pre-assembled condition the seal (s) and the membrane are consequently at least at least partially housed in the recess and are thus against damage when handling the  mounted ultrasonic transducer largely ge protects. In a preferred embodiment, the depth is Recess smaller than the entire thickness of the seals and the membrane, so that the membrane / seal package protrudes the recess. When assembling the Ultra sound transducer is therefore on the mounting flange outer seal protruding on the mounting flange and is therefore when screwing the connection bolt, like the other seal, together squeezes until the edge of the Flanges completely on the mounting flange. The degree of compression of the seals is thus exactly defined, because the compressed seals including the membrane exactly the height of the recess acceptance. Through the encompassing the recess The edge of the flange is also the side edges the membrane and the seals are no longer free and are accordingly very good against damage protects.

Alternatively, it is also possible between the flange and the mounting surface at least one spacer insert. If the spacer is the membrane and The spacer halves surrounds the seals ter in addition to its primary function of defi positional positioning of the flanges the further function, the side edges of the membrane and act on the seals from the side from the outside shield the influences and thus these components protect against damage.

In a preferred embodiment, the spacer is in the space enclosed by the connecting bolts orderly. The connecting bolts thus cause Centering the spacer so that the one bringing the spacer and its arrangement he relieved.  

By the provided in a preferred embodiment Vent channels can be the container medium at egg any leakage rate into the atmosphere derived so that it does not get inside the ultrasonic Converters arrive and for example as explosive atmosphere can accumulate.

In particular, to be able to hold the membrane on the flange re in pre-assembled condition with the membrane still not between the flange and a counter bearing flange is clamped, the membrane is preferably equipped with threaded bolts that have a screw connection allow with the flange. The assembly of the ultrasound Transducer on site, for example one to be monitored appropriate container, takes place in a preferred embodiment via another flexible seal that is between the Membrane and the mounting surface facing this is arranged. This additional seal brings white Other advantages in that a direct Ultra sound coupling to the receiving container or the like. un is suppressed. At the same time, there is also the surprisingly favorable effect that the flexible seal between membrane and flange and also, if existing the, the seal between the membrane and fastening surface together slightly when tightening the connecting bolts be pressed. This reduces the distance slightly between the membrane and the flange. Here lift them up with the threaded bolts of the membrane standing nuts or bolts slightly from the previous contact surface on the flange. By this Ab this remaining sound bridge will also lift between Diaphragm and flange largely interrupted, so that in the subsequent operation a reproduction of the ul traschalls from the membrane to the flange and over it and the connecting bolts to the mounting surface and the device connected to it is essentially complete  dig is suppressed. An unwanted ultrasound radiation from components other than the membrane consequently suppressed automatically. This posi tive effect results automatically when the Ultrasound transducer on the components carrying this te. The membrane is spring-loaded on both sides protects them in addition to effective ultrasonic decoupling also against damage due to external influences, Temperature tensions or the like from the flexible you at least to a certain extent can. This effect is optimal if the two Seals face each other, since then the stress Chung the membrane with respect to shear forces and the like. is minimized. In a preferred embodiment, the Thickness of the seal or seals a maximum of 2 mm, so that the displacement of the membrane when screwing the Ultrasound transducer limited to the external carrier remains and at the same time a sufficient increase in me mechanical strength of the seal or seals is achieved due to their compression. If you a minimum sealing width Have 20 mm, is further achieved that the Converter is explosion-proof and therefore also in explosion-proof hazardous areas can be used.

The structure-borne noise decoupling can be further ver better if the membrane threaded bolts and / or the nuts or bolts to be screwed with them Plastic is made because plastic only uses ultrasound very poorly conductive and also the change of material type at the transitions membrane / threaded bolt and / or Screws / flange a strong damping of the ultrasonic Forwarding entails. The structure-borne noise decoupling This can also be done additionally or alternatively improve that additional washers used will. Particularly good results are achieved when the washers are made of plastic.  

A further improvement in structure-borne noise decoupling tion can also be achieved in that the thread bolts and / or the courage to be screwed to them tern or screws at least partially through sleeves are surrounded. The structure-borne noise must therefore have several limits run through layers, which dampens it. In particular special if the sleeves are made of plastic effective structure-borne noise suppression.

The flange of the ultrasonic transducer can be made in one piece, e.g. B. be formed as a thick plate. But it is also possible to insert a flange ring for fastening set so that defined clamping behavior can be achieved leaves. Through suitable shaping and material selection a stable connection can be made more adequate Ensure strength, with a clear savings material and processing costs can be achieved. Especially with a U-shaped cross-section Flange ring high stability. If the flange egg NEN has all-round, raised edge, lets achieve high rigidity of the flange connection. With a suitable length adjustment of the height of the raised edge and the length of at least the inside the leg of the U-shaped flange ring can be these with correct positioning in close mutual bring to engagement so that a heavy duty ka sten-shaped system is reached. With mutual Ab stood between the raised edge and the inside between the legs of the flange ring a room enclosed on all sides, in which z. B. which are engaged with the membrane threaded bolts Nuts or screws can be accommodated. Here through they are exposed to outside influences would propagate directly to the membrane.

The invention is described below with reference to an embodiment Example with reference to the drawings nä described here. Show it:

Fig. 1 shows an embodiment of the erfindungsge MAESSEN ultrasonic transducer,

Fig. 2 to 4 modified embodiments of the inventive ultrasonic transducer.

The exemplary embodiments of the ultrasonic transducer according to the invention shown in the drawings and designated by the reference numeral 1 have a flange 2 in the form of a plate which has a central through opening 3 . In this through opening 3 , a piezo oscillator 4 is accommodated, which sits on webs 5 on a membrane 6 . Between the piezo oscillator 4 and the membrane 6 , a filling material 7 for impedance matching is available.

The membrane 6 is formed as a thin, preferably round plate made of steel, VA, suitable plastic or other mate rial. On the membrane 6 , a Thermofüh ler 8 is attached, which is used for temperature detection and emits corresponding signals to a control circuit, not shown, by means of which this can compensate for temperature-related changes in transit time of the ultra sound waves. This is of particular interest when using the ultrasonic transducer for level monitoring. The ultrasonic transducer can also be used in any other application.

Between the membrane 6 and the flange 2 a device 9 is arranged, which is formed as a circumferential ring seal and is made of soft, flexible material, ie forms a soft seal.

The piezo oscillator 4 is parallel to the diaphragm 6 and there so arranged that it radiates essentially all of its energy downwards to the diaphragm 6 and further down into the container, so that high efficiency with good bundling characteristics of the ultrasonic waves is achieved .

To the membrane 6 also in which the ultrasonic transducers are not left to in terms of its filling level to be monitored container or another, is set with ultrasonic waves to be powered forming apparatus to reliably on the flange in the pre-assembled condition, are on the diaphragm threaded bolt 10 firmly attached, of which only one is shown in the drawing. In order to achieve symmetrical relationships, a plurality of threaded bolts, for example eight, are attached symmetrically to the membrane 6 at the same circumferential distances. The threaded bolts 10 are formed as internal threaded bolts, which engage with slight play in corresponding underside recesses in the flange 2 . From the other side of the flange 2 , screws 11 are screwed into the threaded bolts 10 , the screw heads of which correspond to the bottom of the bottom of the membrane 6 opposite the flanged side Sacklö cher 12 . Alternatively, the threaded bolts 10 can also be designed as externally threaded bolts, the length of which is dimensioned so large that they penetrate the entire flange 2 and project outwards on the other flange side. Nuts, for example cap nuts, can then be screwed onto the protruding thread end in order to clamp the membrane 6 with the flange 2 .

The threaded bolts 10 are welded to a steel or VA membrane 6 by a stud welding process using an energy stored in a capacitor, while in a plastic membrane they are firmly connected to the membrane 6 by high-frequency welding. Such fastening methods are easy to control with little effort and high reliability.

For the passage of the threaded bolt 11 , the device 9 has corresponding through openings, the diameter of which is adapted to that of the threaded bolt 11 .

On the flange 2 , a cover 13 is arranged, which is designed as a plate with an inner through opening and is screwed to the flange 2 by means of screws 14 . Although only a single screw 14 is shown in the drawing, a plurality of screws 14 are present at the same circumferential intervals. A narrow ring seal 15 is attached between the flange 2 and the cover 13 . On the lid 13, a further pot-shaped cover 16 is arranged which is screwed by screws 17 to the lid. 13 Between the covers 13 and 16 there is also an annular seal 18 . The cover 16 has a central through-hole 19 for the passage of electrical lines 20 , via which the electrical signals to the piezoelectric oscillator 4 and thermocouple 8 are guided or passed by these to a control circuit (not shown).

The ultrasonic transducer 1 is a plurality of connecting bolts 21 , of which only one is shown in the drawing, with a mounting flange 22 screws, which forms part of a support frame or a container wall.

In order to be able to couple the ultrasonic energy into the object to be monitored or supplied with ultrasonic energy, the fastening flange 22 surrounds an annular passage opening 23 , the diameter of which is slightly larger than that of the passage opening 3 .

Between the mounting flange 22 and the membrane 6 , a seal 24 is inserted, which is formed as a ring seal made of flexible material, ie as a soft seal. The seal 24 is arranged so that it faces the seal 9 on the other side of the membrane. When tightening the threaded bolts 21 , the ring seals 9 and 24 are pressed together somewhat, so that the screw heads of the screws 11 bores lift off from the bottom of the bag, so that no ultrasound bridges are formed as a result. The flexible clamping of the membrane 6 also effectively suppresses the undesired transmission of ultrasonic vibrations to other device parts on all other sides. The flexible seals 9 and 24 also cause no significant ultrasound transmission because they are made of soft material that cannot conduct ultrasound well.

The flexible seal 24 can be placed on the mounting flange 22 prior to the assembly of the ultrasonic transducer 1 or else previously, for example by means of adhesive, attached to the membrane 6 .

. The Ausführungsbei shown in Figures 2 to 4 games have the advantage over that shown in Figure 1, for example approximately exporting the special feature that the flange 2 -. At least partially rests directly on the Be festigungsflansch 22 - in the assembled state. In the exemplary embodiment according to FIG. 2, this is achieved by a recess 29 on the underside of the flange 2 . The recess 29 is slightly larger than the outer diameter of the membrane 6 and the seals 9 , 24 and their cross-sectional shape adapted, preferably round. The Ausneh mung 29 is located on the sealing surface of the flange 2 and has a depth which is smaller by a defined amount all the height of the elastic, annular seals 9 , 24 and the membrane 6th The diameter of the recess 29 is so large that the flange 2 is not touched by the membrane 6 . When tightening the connecting bolts or screws 21 , the elastic seals 9 , 24 are pressed together until the flange 2 abuts the mounting flange 22 . In the exemplary embodiment shown, this contact takes place between the flanges 2 and 22 via the part of the sealing surface of the flange 2 lying radially outside the recess 29 . The force acting on the seals 9 , 24 in the assembled state is so great that the tightness is ensured.

In the recess 29 on the outside encompassing step of the flange 2 , one or more ventilation channels 30 are provided, via which a leakage of the container medium that may occur can escape into the atmosphere. This protects the interior of the ultrasonic transducer against such immissions. The ventilation channels 30 are hen at the location of the through holes for the connecting bolts or screws 21, respectively. However, it is also possible to introduce the ventilation channels at a suitable other point. In the embodiment shown, the ventilation channels only start radially outside of the seals 9 , 24 , so that the device 24 rests continuously on the sealing surface of the mounting flange 22 and thus good sealing effect bezüg Lich shielding the escape of ultrasound energy is maintained.

The other features of the embodiment of FIG. 2 - as well as the embodiments of FIGS. 3 and 4 - correspond to those of the game Ausführungsbei according to FIG. 1, unless otherwise specified ben.

The embodiment according to FIG. 3 differs from that of FIGS . 1 and 2 by an additional union spacer 25 , which is preferably configured in a ring shape and is arranged radially inside the connecting bolts or screws 21 . The spacer 25 is arranged between the flange 2 and the mounting flange 22 . The spacer 25 surrounds the membrane 6 and the seals 9 , 24 on the outside with from. Through the connecting bolts or screws 21 , the distance holder 25 encompassed by these on the outside is automatically brought into a concentric position, so that it is ensured that he does not touch the membrane 6 at any point.

The thickness of the spacer 25 is slightly smaller than the total thickness of the membrane 6 including the seals 9 , 24 , so that the seals 9 , 24 are squeezed together until the flanges 2 and 22 are completely open when the connecting bolts or screws 21 are screwed together rest on both sides of the spacer 25 . The spacer 25 is made of solid material, in particular metal or hard plastic.

Vent channels 31 are provided on the top and / or bottom of the spacer 25 , via which any medium escaping from the container to be monitored can flow into the atmosphere.

In the illustrated embodiments, the Ge threaded bolt 10 and the screws 11 made of plastic be. Alternatively or additionally, washers 27 ( FIG. 2) made of plastic can be used, which are introduced between the heads of the screws 11 and the flange 2 . Alternatively or additionally, plastic sleeves 28 can be used, which are pushed over the threaded bolts 10 and / or over the thread and / or the head of the screw 11 . The plastic sleeves 28 each have a diameter that is adapted to the part to be surrounded. This plastic sleeves any direct contact between the threaded bolt 10 and the screws 11 on the one hand and the flange 2 on the other hand is avoided. This enables effective structure-borne noise decoupling.

Similar to the exemplary embodiment according to FIG. 3, a spacer 25 is also used in the exemplary embodiment according to FIG. 4. This embodiment differs from the exemplary embodiment according to FIG. 3 in several respects, in particular with a view to the configuration of the flange 2 . In this embodiment, the flange 2 consists of a formed sheet metal part, which has an annular shape and U-shaped cross section with a significantly shorter outer leg. The lid 13 is out as a thin plate, which closes the top of the flange 2 and is welded to it, so that the parts 2 , 13 have a hat-shaped shape. The lid 16 ( Fig. 1) is omitted in the embodiment of FIG. 4, so that this embodiment has a shorter overall axial length than the other games Ausführungsbei.

In the embodiment shown in FIG. 4, there is an additional flange ring 26 which has a U-shaped cross section and is mounted in such a way that its legs protrude downward to the mounting flange 22 . The length of the radially inner leg of the U-shaped flange ring 26 is as large as the length of the upwardly bent outer portion of the flange 2 , so that the flange ring 26 rests at the same time with both its inner underside on the upper side of the bent edge of the flange 2 and is also supported on the flange 2 with the underside of its radially inner leg. The leg of the flange ring 26 and the curved outer edge run parallel at a distance, so that an all around closed ring space is formed, in which in this case designed as nuts parts 11 are housed, which are designed to be bolted in this embodiment as Außenge Threaded bolts 10 are screwed up. Below the nuts 11 there is a washer 27 , while the threaded bolts 10 are each surrounded by a sleeve 28 , preferably made of plastic.

The threaded screws 21 penetrate both the flange ring 26 (via corresponding openings) and through holes in the mounting flange 22 and are screwed on the underside by nuts.

The flange ring 26 is rotatable and ensures easy installation. By using deformed sheet metal parts 2 and 26, he can achieve sufficient strength with very low material and processing costs.

All others are also within the scope of the invention standing not described, but from the drawing he visible features.

Claims (16)

1. Ultrasound transducer with a membrane formed as a flat plate, which is coupled to a piezoelectric oscillator in order to be able to emit and / or receive vibrations, and which is furthermore interposed with a flexible seal on a flange of the housing of the ultrasound Transducer is applied, the flange via connecting bolts with a fastening surface ver bindable and a flexible seal can be attached between the fastening surface and the membrane, characterized in that the flange ( 2 ) in the assembled state directly or via at least one spacer ( 25 ) on the mounting surface ( 22 ). 2. Ultrasonic transducer according to claim I, characterized in that the flange ( 2 ) has a preferably annular recess ( 29 ) for receiving the seals ( 9 , 24 ) and the membrane ( 6 ). 3. Ultrasonic transducer according to claim 2, characterized in that the depth of the recess ( 29 ) is smaller than the total thickness of the seals ( 9 , 24 ) and the membrane ( 6 ). 4. Ultrasonic transducer according to one of the preceding claims, characterized in that the spacer ( 25 ) surrounds the membrane ( 6 ) and the seals ( 9 , 24 ) on the outside. 5. Ultrasonic transducer according to one of the preceding claims, characterized in that the spacer ( 25 ), seen in the radial direction, between the membrane ( 6 ) and the connecting bolt ( 21 ) is angeord net. 6. Ultrasonic transducer according to one of the preceding claims, characterized in that in the contact surface between the flange ( 2 ) and the fastening supply surface ( 22 ) and / or on the top and / or underside of the spacer ( 25 ) ventilation channels ( 30 , 31 ) are formed. 7. Ultrasonic transducer according to one of the preceding claims, characterized in that on the membrane ( 6 ) threaded bolts ( 10 ) are attached, via which the membrane ( 6 ) with the interposition of the seal ( 9 ) with the flange ( 2 ) screw-connected is. 8. Ultrasonic transducer according to claim 7, characterized in that the threaded bolts ( 10 ) and / or with them for fastening to the flange ( 2 ) to screw nuts or screws ( 11 ) are made of plastic. 9. Ultrasonic transducer according to claim 7 or 8, characterized in that between the flange ( 2 ) and with the threaded bolts ( 10 ) to be screwed Mut tern or screws ( 11 ) washers ( 27 ) are seen before. 10. Ultrasonic transducer according to claim 9, characterized in that the washers ( 27 ) consist of plastic. 11. Ultrasonic transducer according to one of claims 7 to 10, characterized in that the threaded bolts ( 10 ) and / or with them to be screwed Mut tern or screws ( 11 ) at least partially surrounded by sleeves ( 28 ), preferably made of plastic are. 12. Ultrasonic transducer according to one of the preceding claims, characterized by a flange ring ( 26 ) in contact with the flange ( 2 ) which is penetrated by the connecting bolts ( 21 ). 13. Ultrasonic transducer according to claim 12, characterized in that the flange ring ( 26 ) has a U-shaped cross section. 14. Ultrasonic transducer according to one of the preceding claims, characterized in that the flange ( 2 ) is an outer circumferential bent edge sits. 15. Ultrasonic transducer according to claim 13 and 14, characterized in that the height of the bent edge of the flange ( 2 ) speaks ent the length of the inner leg of the U-shaped flange ring ( 26 ). 16. Ultrasonic transducer according to claim 15, characterized in that the bent edge of the flange cal ( 2 ) and the flange ( 2 ) adjacent leg of the U-shaped flange ( 26 ) run parallel and at a mutual distance.