EP1859436A1 - Rod-shaped ultrasonic resonator for producing ultrasound in liquids - Google Patents

Abstract

The invention relates to a rod-shaped ultrasonic resonator which comprises a heat-transfer element that is coupled to the piezoelectric transducer in a thermally advantageous manner. The heat-transfer element reduces the thermal resistance relative to the surrounding atmosphere or the housing and thereby relative to the bath when the rod-shaped resonator is submerged in said bath.

Description

ULTRASONIC PUSH-BUTCHER FOR THE PRODUCTION OF ULTRASONIC IN LIQUIDS

In order to increase the cleaning effect of baths, the liquid of the baths is excited with ultrasound. For ultrasonic excitation so-called rod vibrators are used, which are either completely submerged, or reach only with the resonator in the bath.

To the ultrasonic rod oscillator includes a resonator on which at least one end of an ultrasonic head is mounted and acts as a radiator. The head forms a housing in which the piezoelectric ultrasonic transducer is housed.

The electrical converter consists of several piezoelectric ceramic discs. The Curie temperature of the ceramic disks is about 300 ^° C. If the ceramic disks are heated to this temperature or higher, the piezoelectric effect disappears irreversibly. If the piezoelectric transducer is to operate in continuous operation, a clear safety margin must be maintained by the Curie temperature. Usually, the temperature at the surface of the ceramic transducer may not exceed about 150 ⁰ C. At a bath temperature of about 130 ⁰ C thus remains a permissible excess temperature of only 2O ⁰ C.

The ceramic piezoelectric transducer show a very high efficiency. However, the supplied electrical energy is not completely converted into ultrasonic energy, but leads in part to the heating of the converter.

The ultrasonic energy to be generated by the transducer is thus limited by the excess temperature of the transducer.

The piezoelectric transducer is cooled in the known devices substantially only via the mechanically coupled resonator, which consists of titanium. Titan is a bad conductor of heat. Other cooling practically does not take place because of ultrasonic reasons, the housing of the head is filled with air, which forms an extremely poor heat conductor, so that the heat is practically dissipated through the housing wall.

Based on this, it is an object of the invention to provide an ultrasonic transducer which can generate a larger ultrasonic energy.

This object is achieved according to the invention with an ultrasonic rod oscillator having the features of claim 1 or claim 20 solved.

The ultrasonic rod oscillator according to the invention has a resonator on which the piezoelectric transducer is coupled by means of ultrasound technology via a coupling element. The coupling element forms partly part of the housing wall at the same time. The attachment of the housing or the housing wall is located at a vibration node, so that the ultrasonic energy is fed exclusively into the resonator, while the housing itself remains virtually free of ultrasound.

The piezoelectric transducer, together with the fastening device, on the coupling device has a length of about λ / 4 and is thus too compact to be able to give off appreciably heat.

Therefore, according to the invention, a heat transfer element is coupled to the piezoelectric transducer. The heat transfer element is designed according to the one solution so that it forms, together with the inner wall of the housing, a very narrow air gap. The narrower the air gap, the smaller the thermal resistance of this air layer, i. the more heat can be transferred from the piezoelectric transducer to the housing and thus to the bath.

According to the other solution, it is provided that a heat transfer element is provided which acts as a heat sink in the case of a ventilated housing. The last arrangement comes into question when the converter is anyway outside the bathroom. This is a solution that is occasionally found. The length of the heat transfer element is chosen in the area that is integrated into the sound paths, so that thereby the acoustic conditions are not disturbed. For example, the heat transfer element may have a length of λ / 2, wherein it is connected immediately adjacent to an end face of the piezoelectric transducer. In this embodiment, the heat transfer element may have a cylindrical shape or a prismatic, wherein the cross section is suitably star-shaped to obtain the largest possible area, can be discharged through the heat to the housing and thus to the bathroom.

Another possibility is to use a cup as a heat transfer element. In this cup, for example, the bottom is formed by the commonly used polished steel sheath which is interposed between the central nut and the piezoelectric transducer to mechanically fix it.

The heat transfer element can not only be arranged on the end remote from the coupling part of the piezoelectric transducer. It has been found that the piezoelectric transducer does not reach its highest temperature directly in the region of the end remote from the resonator, but at a small distance in front of it. For this reason, it is advantageous if the heat transfer element is inserted into the piezoelectric transducer. For this purpose, the heat transfer element again has a length of λ / 2.

The individual measures regarding surface shape, insertion or cup shape or This figure can be combined in a variety of ways.

In the case of an air-permeable housing for the resonator head, it is advantageous if the heat transfer element has a large surface area, wherein the surface serving for the cooling is expediently oriented parallel to the flow path of the air due to the convection effect.

Incidentally, developments of the invention are the subject of subclaims.

When reading the figure description, it is clear that a number of modifications are possible, which result from the respective requirements. In addition, a number of combinations of the disclosed features are possible. Describing any conceivable combination would unnecessarily increase the scope of the description of the figures. The description of the figures is therefore limited to a few basic variants.

In the drawings, embodiments of the subject matter of the invention are shown, in which:

1 shows an ultrasonic rod oscillator, in a simplified perspective view;

FIG. 2 shows the head of the bar oscillator according to FIG. 1 in a side view with the housing open; FIG.

Fig. 3 shows the head ^"of the rod oscillator in a representation similar to Fig. 2 with a different positioning the heat transfer element;

Fig. 4 shows the head of the bar oscillator of Figure 1, a view similar to Figure 2 with a cup-shaped heat transfer element.

5 shows a section through a head of a rod vibrator with a star-shaped heat transfer element and a housing adapted thereto and

Fig. 6 shows the head of a bar oscillator of a representation similar to Fig. 2 using a heat transfer element with cooling fins.

FIG. 1 shows an ultrasound rod oscillator 1 in a perspective representation that is not to scale. The ultrasonic rod oscillator 1 includes a resonator 2 and a head 3 connected to the resonator 2. The resonator 2 is continuously cylindrical over its length with a constant diameter. At its end remote from the head 3, it has a conical tip 4.

The head 3 is provided at its rear with a threaded pin 5 which is tubular and from which leads out an electrical cable 6, via which the electrical energy is fed into the head 3. The structure of the head is shown in Fig. 2.

The head 3 includes a connecting element 1, a piezoelectric transducer 8, a heat transfer element 9 and a cup-shaped housing cover 10.

The connecting element 7 is a one-piece body made of titanium with a cylindrical extension 11 whose outer diameter corresponds to the outer diameter of the resonator 2. In the cylindrical extension 11, a blind bore 12 is arranged coaxially with an internal thread. With the help of the blind bore 12 of the resonator 2 is attached to the connecting element.

The connecting element 7 forms following the extension 11, a flange 13, which merges via a recess in a threaded extension 14 and is the part of the housing of the head 3. The threaded extension 14 is tubular and surrounds a pin 15 which is mechanically fixedly connected to the cylindrical extension 11.

Between the pin 15 and the threaded part 14, a kind of membrane is formed to decouple the flange 13 and the thread 14 from the vibrations, which are fed by the piezoelectric transducer 8 in the extension 11 maximum.

The connecting element 7 is a piece of titanium worked from the solid and thus in one piece.

The projection 11 to the coaxial pin 15 forms a plane surface 16 on which the piezoelectric transducer 8 rests. The piezoelectric transducer 8 is composed in the illustrated embodiment of a total of β piezoelectric ceramic discs 17, between which electrodes 18 are inserted. The electrodes 18 are each provided on one side with terminal lugs 19, to which power supply lines 20 are connected. In the embodiment shown, three of the terminal lugs 19, based on Fig. 2, upwards and a total of three downwards. Each lying on one side terminal lugs 19 are electrically connected in parallel, which, in electrical terms, results in a dipole, in which the feeding or stimulating AC voltage with a frequency of üblicherwiese greater than 25 kHz is fed.

Both the ceramic discs 17 and the disc-shaped electrodes 18 are disc-shaped rings with flat end faces.

The electrode 18 lying furthest to the right in FIG. 3 forms the right front end of the piezoelectric transducer 8, while the leftmost ceramic disk 17, which bears directly against the pin 16, represents the left front end. As can be seen, the piezoelectric transducer 8 is substantially cylindrical with planar end faces.

The heat transfer element 9 is designed in the form of a cylindrical tube with flat front end 22 and 23. The lateral surface 24 is cylindrical.

On the side remote from the piezoelectric transducer 8 side of the heat transfer element 9 is a friction-reducing steel plate 25 which is pressed by means of a nut 26 against the piezoelectric transducer 8. The nut 26 is screwed onto a threaded pin 27 indicated by dashed lines, which is anchored at the other end in the pin 16 of the connecting element 7. Both the threaded pin 27 and the nut 26 are made of titanium, while the heat transfer element 9 is made of aluminum. As a result of this arrangement, the rightmost electrode 18 is an electrode which simultaneously feeds the leftmost ceramic disk 17 as well.

The heat transfer element 9 has between its two end faces 22 and 23 an acoustic length of λ / 2. The length of the piezoelectric transducer 8, including the disk 25 of the nut 26 and the pin 16, which extends to the housing wall, has a length of λ / 4. The right end of the nut 26 is thus on a vibration at the resonant frequency.

The housing cover 10 is, as shown, cup-shaped and is composed of a collar 28 and a cup bottom 29, from which the threaded pin 5 protrudes. At its free end, the collar 28 is provided with an internal thread 31 which is screwed in the assembled state with the thread 14.

The collar 28 forms a cylindrical housing inner wall 32. The diameter that the housing inner wall 32 is defined is slightly larger than the outer diameter of the outer peripheral surface 24 of the heat transfer element 9. In the assembled state, the housing inner wall 32 lies in a position as shown in FIG Dashed lines 33 is illustrated. The inner wall 32 thus forms, with the outer peripheral surface 24, a narrow, cylindrical gap 34 having a thickness between 0.5 mm and 5 mm and the length of the heat transfer element 9. As a result, the thermal resistance to the outside of the housing 10 is greatly reduced.

As the figure further shows, the maximum is Outer diameter of the piezoelectric transducer 8, including the protruding terminal lugs 19, smaller than the outer diameter of the heat transfer element 9 and the inner diameter of the inner space 32 corresponds.

In order to pass the electrical connection lines past the heat transfer element 9, this contains two longitudinal grooves, which are not visible because of the representation. The connecting cable 6 passes through the tubular threaded pin 5 therethrough.

When the ultrasonic rod vibrator 1 equipped with the head 3 of FIG. 2 is operated, heat is generated in the piezoelectric transducer 8. This heat is derived in part via the pin 16 and connected to the extension 11 resonator 2 in the bath. In this way, the left end of the piezoelectric transducer 8 receives some cooling. The right end releases its heat to the heat transfer element 9. The heat transfer element 9 in the form of the aluminum tube transports the heat through the narrow air gap 34 to the collar 28 of the housing cup 10 and from there into the bath.

The right end of the piezoelectric transducer 8 thus experiences a much better cooling than in the prior art. In the prior art, the right end would only be cooled to the extent that it would conduct over the poorly heat conductive because the titanium pin 27 would dissipate heat toward the resonator 2. By using the heat transfer element 9, the housing cup 10 is additionally used to transfer heat from the piezoelectric transducer 8 into the bath. The ceramic discs 17 are not good heat conductors. The arrangement according to FIG. 2 will consequently show the maximum excess temperature in a region which lies between the two front ends of the piezoelectric transducer, it is advantageous if the heat transfer element 9 according to FIG. 3 is inserted into the piezoelectric transducer 8. As the figure reveals, a total of four ceramic discs 17 are located between the heat transfer element 9 and the connecting element 7, while two ceramic discs 17 are arranged between the heat transfer element 9 and the washer 25. Thereby, the right front end of the divided piezoelectric transducer 8 is cooled via the nut 26 and the bolt 27, the intermediate part by means of the heat transfer member 9 toward the housing 10 and the left end of the piezoelectric transducer 8 via the connecting member 7 to the resonator second

The thermal resistance in the embodiments according to FIGS. 2 and 3 is determined by the area of the annular gap 34 and its thickness. The thermal resistance is inversely proportional to the surface and inversely proportional to the thickness.- The thickness of the gap 34 can not be reduced for manufacturing reasons below a certain technical level, without the risk that the heat transfer element 9 touches the inside 32. This effect must be avoided at all costs, because otherwise ultrasonic energy would be coupled into the housing 10. With regard to the surface of the gap, there are also limits, because the head can not grow arbitrarily in diameter.

An enlargement of the cooling surface can be with the Achieve embodiment of FIG. 4.

In the embodiment of Fig. 4, the heat transfer element 9 has the shape of a cup with a bottom 36 and a collar 37. The collar of the cup faces away from the piezoelectric transducer 8, i. in Fig. 4 to the right. The bottom 36 lies between the right end of the piezoelectric transducer 8 and the central mounting nut 26. The bottom 36 replaces the steel disk 25, i. the cup 37 is preferably at least in the region of the bottom 36 of the polished steel disc.

There is no urgent need in this embodiment of the heat transfer element 9 to make the bottom 36 and collar 37 integral. It is sufficient if it is ensured that the thermal resistance at the transition from the bottom 36 to the cup collar 37 is small compared to the thermal resistance, the heat transfer element 9 relative to the housing 10 shows.

The collar 37 is both cylindrical outside and inside, i. he limits a cylindrical interior. In order to obtain the desired large heat transfer surface, the housing cup 10 is provided deviating from the previous embodiment with an inwardly projecting cylindrical pin 38. The pin 38 is designed as a hollow structure, so that the bath liquid can circulate therein.

In the assembled state, the collar 28 of the housing cup 10 forms the cylindrical gap 34 with a small width, as in the embodiment of Figures 2 and 3. Another cylinder gap with similarly small gap width arises between the cylindrical inner wall of the collar 37 and the pin 38th

Thus, the cup-shaped heat transfer element 9 is able to dissipate heat to the housing cup 10 and from there into the bath both on the outside and on the inside of the collar 37.

Another way to increase the area of the air gap between the heat transfer element 9 and the cup-shaped housing 10 is illustrated in FIG. 5.

While in the previous embodiments, the heat transfer element 9, except for grooves for electrical connections, is largely rotationally symmetrical, has the heat transfer element 9 of FIG. 5 seen in cross-section on a star-shaped structure. Fig. 5 shows a section through the head 3 at right angles to the longitudinal axis or parallel to the axis along which propagate the ultrasonic waves, by the heat transfer element 9. Evident is the middle draw bolt 27 and the star-shaped heat transfer element 9. It settles mentally composed of a circular ring and of this outgoing triangular spikes together.

The collar 28 of the housing 10 has an inner wall 32 which is complementary star-shaped. Such a structure can be produced for example by sinking EDM or by punching of corresponding slats.

In place of the screw through the thread 14 and the thread 31 enters a connection via tie rods, the pass through holes 41 therethrough. The mutually aligned bores 41 are provided both on an overhanging collar of the bottom 29 of the housing 10 and in the flange 13.

The embodiments according to FIGS. 2 to 5 relate to ultrasonic rod vibrators which can be used fully submerged. In these bar vibrators, the head 3 is also in the bathroom.

Fig. 6 shows an embodiment of an ultrasound rod vibrator 1, the head 3 is arranged outside the bath. With the flange 13 of the head 3 is fixed to the container wall. The housing 10 is in the free atmosphere. It is sufficient if the further description is limited to the differences from the previous embodiments.

In order to achieve a good cooling effect, the collar 28 is provided the housing cup 10 having a plurality of air holes 42 through which the outside atmosphere can pass circulates ^• lose. In order to cool the piezoelectric transducer 8 better, a heat transfer element 9 is used, which carries on its outer side a plurality of cooling fins 43. In this embodiment, it is not important to get the gap between the heat transfer element and the housing 10 as small as possible. On the contrary, it is a question of giving as much heat as possible via the cooling ribs 43 to the air circulating through the air holes 42.

The heat transfer member 9 of Fig. 6 is arranged in the same manner as in the embodiment It can also be positioned centrally in the piezoelectric transducer 8, corresponding to FIG. 2.

The length of the heat transfer element 9 in the axial direction is in turn chosen so that at the end of the clamping nut 26 of the antinode of the standing wave is. While the passage point through the wall, which is formed in the connecting element 7, is located on the position of the vibration node.

The cooling fins are shown in Fig. 6 only schematically. It is understood that the cross-sectional shape and the diameter of the cooling fins 43 is also dimensioned according to sound technical aspects, in order to avoid a break due to the induced sound vibrations.

An ultrasonic rod oscillator has a heat transfer element that is thermally coupled well with the piezoelectric transducer. It ensures that the thermal resistance to the surrounding atmosphere or to the housing, and thus to the bath is reduced with submerged rod oscillators.

Claims

Claims: 1. Ultrasonic rod oscillator (1) for generating ultrasound in liquids, comprising a housing (10, 13) which delimits an interior space and which has at least one outer wall (28, 29) whose inner side (32) faces the interior, with a piezoelectric transducer device (8) having two ends and housed in the housing (10) with a resonator (2) located outside the housing (10, 13) with a connector (7) in that the transducer device (8) is connected to the resonator (2) and that projects at least in part from an outer wall (13) of the housing (10, 13), with a heat transfer element (9) which is heat-conducting with the piezoelectric transducer (8). is connected and which has at least one surface (24) extending adjacent to the inside (32) of an outer wall (28) forming a gap (34) to transfer the heat loss of the piezoelectric transducer (8) to the outer wall (28) , 2. ultrasonic rod vibrator according to claim 1, characterized in that the interior has a cylindrical cross-section. • 3. Ultrasonic rod vibrator according to claim 1, characterized in that the heat transfer element (9) is cylindrical on its outer side. 4. Ultrasonic rod vibrator according to claim 2, characterized in that the heat transfer element (9) has a deviating from the cylindrical shape prismatic shape, preferably a star-shaped shape. 5. ultrasonic rod vibrator according to claim 1, characterized in that the interior has a deviating from the cylindrical shape prismatic cross section, wherein the base surface of the prism, at least approximately, is star-shaped. 6. Ultrasonic rod oscillator according to claim 1, characterized in that the star-shaped base surface is composed of a central surface and outgoing from this central surface arms. 7. ultrasonic rod vibrator according to claim 1, characterized in that the arms have mutually the same shape. 8. ultrasonic rod vibrator according to claim 1, characterized in that the arms, seen in cross section, are approximately triangular. 9. ultrasonic rod vibrator according to claim 1, characterized in that the housing (10,13) has a cylindrical outer surface (28). 10. Ultrasonic rod oscillator according to claim 1, characterized in that a housing part (10) has substantially the shape of a cylindrical cup (28,29). 11. Ultrasonic rod transducer according to claim 10, characterized characterized in that the housing part (10) in the cylindrical cup (28,29) contains an insert which defines a prismatic interior. 12. Ultrasonic rod oscillator according to claim 1, characterized in that the width of the gap (34) is between 0.5 mm and 3 mm. 13. Ultrasonic rod transducer according to claim 1, characterized in that the connecting element (7) has a collar (13,14),. whose outer diameter is greater than the inside diameter of the interior. 14. Ultrasonic rod oscillator according to claim 1, characterized in that the piezoelectric transducer device (8) is formed from a number of juxtaposed piezoelectric discs (17), between which electrodes (18) are inserted. 15. Ultrasonic rod oscillator according to claim 1, characterized in that the piezoelectric transducer device (8) has two front ends and that the heat transfer element (9) is arranged at a front end. 16. Ultrasonic rod vibrator according to claim 1, characterized in that the piezoelectric transducer device (8) has two sections which are acoustically connected in series and that the heat transfer element (9) is inserted between the two sections. 17. Ultrasonic rod transducer according to claim 1, characterized in that the heat transfer element (9) in the direction parallel to the axis of oscillation, a length of has λ / 2. 18. Ültraschall-rod transducer according to claim 1, characterized in that the heat transfer element (9) has the shape of a cup, wherein the bottom (36) of the cup-shaped heat transfer element (9) with an end face of the piezoelectric device (8) is coupled acoustically and thermally conductive , 19. Ültraschall rod vibrator according to claim 18, characterized in that the housing (10,13) has a recess (38) which engages to form a narrow gap in the interior of the cup-shaped Wärmeübertragungs- elemnets (9). 20. Ültraschall rod oscillator (1) for generating ultrasound in liquids, comprising a piezoelectric transducer means (8) having two ends, with a resonator (2), with a connecting element (7) for connecting the transducer means (8) with the Resonator (2), comprising a heat transfer element (9), which is thermally conductively connected to the piezoelectric transducer (8) and which has at least one surface which forms a lower thermal resistance to the surrounding atmosphere than the piezoelectric device (8). 21. Ültraschall rod vibrator according to claim 20, characterized in that a housing (10) which is ventilated. 22. Ültraschall rod vibrator according to claim 20, characterized in that the housing (10) for ventilation contains ventilation holes (42). 23. Ultrasonic rod vibrator according to claim 20, characterized in that the heat transfer element (9) has an articulated surface in the manner of a heat sink. 24. Ultrasonic rod transducer according to claim 20, characterized in that the piezoelectric transducer means (8) comprises a stack of individual piezoelectric discs (17), between which electrodes (18) are arranged. 25. Ultrasonic rod vibrator according to claim 20, characterized in that the heat transfer element (9) in the piezoelectric transducer means (8) is inserted. 26. Ultrasonic rod vibrator according to claim 1 or 20, characterized in that the connecting device (7) is located partly outside the housing (10, 13).