SE513009C2 - The ultrasound unit - Google Patents

Abstract

The disclosure relates to an ultrasound unit comprising an annular tool (4) or sonotrode intended for welding packaging containers with circular cross section. The tool (4) has a mass plane (10) located at a right angle to the centre axis (8) of the tool, and with a mean circumference (6) whose length is adapted to the wavelength of the ultrasound source. With a view to making possible the welding of packaging containers with a circumference which is larger than the mean circumference of the sonotrode, a circular working surface (7) is employed which is located in a working plane (9) a distance from the mass plane (10).

Description

i- fifi s _.._.... t ._.._ u .... i ......._. u l_n ... d '- .. ß a h. 10 15 20 25 30 35 513 00? l i I i i i i l provide an annular working part with an internal dimension, which mainly corresponds to the external dimension of the packaging container at the welding point. With the help of an abutment located in the packaging, which e.g. may be slightly conical or expandable, the weldable parts of the dry packing container are pressed against the annular working part in the work surface, after which the ultrasonic source is activated so that the working part vibrates and the damaged welding frequency. This technique has been tried with limited results. In t. X. U -PS 3,438,824 is illustrated i.a. an assembly which utilizes an annular working part 1, which is radially connected via a feed part to a conventional ultrasonic source which generates reciprocating oscillations transmitted axially through the feed part to the working part n. In an annular working part the oscillations are spread substantially evenly around the circumference of the working part, the axial, along the feed part cent um line linear and reciprocating ultrasonic waves due to the sono of the sonotrode being converted to radial waves, which move back and forth along those from the working part stretching radii. The annular working part is dimensioned in such a way that its average circumference, i.e. the mean value of the outer and inner diameters of the working part, above corresponds to a wavelength of the ultrasound. The causes of the ultrasound in the working part can be seen as compression and decompression waves, which alternately lengthen and shorten the ring in its circumferential direction. This causes each individual point of the workpiece material to move radially back and forth, resulting in the desired radial movement of the work surface. It is here by special will: that the circumference of an annular working part is matched to the actual wavelength, as generated by the ultrasonic source. More specifically, the working part must have an average diameter which is chosen so that exactly one wavelength of the ultrasound fits around the average circle of the working part. Since the oscillation pattern and frequency of the working part are to some extent also influenced by the material of which the working part is made (usually titanium), some adjustment of the noble diameter and average circumference can be made by suitable material choice. Of course, it is also possible to manufacture ultrasonic sources with varying ultrasonic frequency, but in particular the ultrasonic sources are manufactured with certain standard frequencies with advantages in terms of, for example, efficiency and the suppression of noisy, audible sound. 20 kHz is a common frequency. the standard frequencies determined in practice and only limited possibilities for selecting materials in the process, it will thus be necessary to adapt the diameter and circumference of the pre-eels to be sealed instead to the possibilities available with current types of ultrasonic devices, which obviously is a disadvantage which limits the freedom d it is necessary to design e.g. packaging container. It is thus a general wish to provide an ultrasonic assembly, which comprises an annular working part with a working surface whose diameter and circumferential length can be easily adapted to the current work task n, i.e. to the circumference and diameter of the object to be welded. An object of the present invention is thus to provide an ultrasonic assembly with an annular working part, which has a working surface whose circumferential length and diameter within certain limits can be chosen freely adapted to the operating frequency of a connected ultrasonic source.

A further object of the present invention is to provide an annular working part for an ultrasonic assembly, which working part, despite the possibility of varying the circumferential length of the working surface, does not require special adjustment of either the frequency of the ultrasonic source or the material of the working part. Given an ultrasonic source and working material (usual design conditions), the invention thus gives greater freedom of choice than before with regard to the diameter of the pre-packing.

A further object of the present invention is to provide an annular working part for an ultrasonic assembly, which working part despite the freedom of choice in terms of circumferential length and diameter of the work surface makes it possible to efficiently and without unnecessary losses transmit oscillations from the ultrasonic source to desired parts of a machined object, e.g. . a packaging container.

A further object of the present invention is to provide an annular working part for an ultrasonic assembly, which working part has a working surface with an average diameter which differs from the average diameter of the working part.

A further object of the present invention is finally to provide an annular working part for an ultrasonic assembly, which working part has an uncomplicated shape, is easy to manufacture and is not subjected to excessive stresses in connection with ultrasonic welding. The above and other objects have been achieved according to the invention by giving an ultrasonic assembly of the type described in the introduction to the features set out in claim 1. Preferred embodiments of the ultrasonic assembly according to the invention have further been given the features set forth in the subclaims.

By placing the annular working surface of the ultrasonic unit on a projection, the mass of which constitutes only a small part of the total mass of the working part, it becomes possible to provide a working surface with an average diameter greater than the average diameter of the circumference (at a center facing the working part). diameter is smaller than the average diameter (at a work surface facing away from the center of the workpiece). In this way, the annular working part can be adapted to the circumference and diameter of the object to be welded without previous inconveniences arising.

Preferred embodiments of the ultrasonic assembly according to the invention will now be described in more detail with particular reference to the accompanying drawings, which only show the details which are indispensable for understanding the invention.

Fig. 1 shows diagrammatically from the side an ultrasonic assembly according to the invention. 10 15 20 25 30 35 513 ÛÛ9 4 Fig. 2 shows on a larger scale and in section a section through a part of the working part of the ultrasonic assembly as shown in Fig. 9.1.

Fig. 3 shows on a larger scale and in section a section through a second embodiment of the working part of the ultrasonic saw assembly according to Fig. 1.

An ultrasonic assembly 1 according to the invention is in its preferred embodiment intended for welding cross-sections, which is a typical packaging industry. One example of packaging container parts with annular or circular examples of the use of ultrasonic welding technology in sliding so that ultrasonic technology can be used for welding together ear packing material is that at least one of the constituent material layers contains a material that can be plasticized by ultrasonic waves. In practice, for packaging containers, in any case those intended for wholly or partly liquid filling goods, often layers of thermoplastic material, which is particularly suitable for ultrasonic etching, the material layers to be joined together must in this case comprise a contact surface containing thermoplastic material. , e.g. polyethylene, which enables the working surface of the welding assembly, preferably after pressing the two layers of material against by means of some form of abutment, to ultrasonically vibrate the material so that the term plastic layers are plasticized and fused together to cool and solidify again at the end of the ultrasonic heating. the constituent packaging container parts with each other. This technique is well known e.g. from the previously mentioned meri PCT / lB98 / 00897, to which reference is made for further information and technical details. Fig. 1 shows an ultrasonic assembly 1 according to the invention. The unit includes an ultrasonic source or! converter 2 of known type, which by means of e.g. a piezoelectric crystal converts electrical current variation into mechanical motion in the form of reciprocating ultrasonic waves or vibrations as in the described application, i.e. welding of paper / plastic packaging, typically has a frequency range of approx. 15-50 kHz, usually 20 ki-lz 'The ultrasonic source 2, which is connected in a known (not shown) manner to a current source, is either amplified or mechanically connected to a supply part or booster 3 for ng of the ultrasonic waves generated by the ultrasonic source.

The supply part 3 also defines the node point of the waves and is used in a conventional manner also for the suspension of the ultrasonic assembly 1 in a stand (not shown). The feed part 3 is thus mechanically connected at its one end of the feed part 3 m to the ultrasonic source 2, and the end is mechanically connected to a closed or annular working part 4 (sonotro), which by its indirect mechanical connection to the ultrasonic source 2 is torn via the feed part 3 so that the annular working member is subjected to radially directed ultrasonic vibrations around its entire circumference.

Two preferred embodiments of the working part 4 according to the invention are shown in Figs. 2 and 3, where Fig. 2 is illustrated in Figs. n working part for external welding and Fig. 3 illustrates a working part adapted for internal welding. The two working parts 4 ', 4 "in Fig. 2 and Fig. 3 are annular and as shown in Fig. 1 at their one part via a radial feed part 3 connected to the conventional ultrasonic source 2. Depending on the frequency of the ultrasonic vibrations generated by the ultrasonic source 2, an average diameter 5 determined by the mass distribution is selected for the working parts 4, which average diameter is so adapted that the length of the average circumference 6 corresponds to an ultrasonic wavelength, i.e. a wavelength of the ultrasound. the actual length depends on the material from which the working part 4 is made, but in the case of a commonly used material, e.g. titanium, and with a standard type ultrasonic source that generates ultrasonic vibrations with a frequency of 20 kHz, the average diameter becomes approx. 80 mm. This means that packaging containers which are welded with one of the known devices under these conditions must have a diameter of a maximum of approx. 70 mm if a working surface at the inside of the working part 4 is used and a diameter of at least approx. 90 mm if a working surface at the outside of the working part is used. Thus, in the two known prior art constructions referred to herein (US-PS 3,438,824 and PCT / IB98 / 00897), both of which utilize a working surface at the inside of the working part 4, the packaging containers to be welded must have a largest diameter of approx. 70 mm. If it is to be possible with the aid of this type of device to weld packaging containers with a larger or smaller diameter than approx. 90 and 70 mm, respectively, either a different material must be selected for the working part 4 or an ultrasonic source with a different frequency must be used. Both of these options present disadvantages. The commonly used material for working parts for ultrasonic use (sonotrodes) is titanium, which has superior properties in terms of vibration transmission and strength, and it is in practice black to find any other material that is correspondingly suitable for this type of use. The ultrasonic sources used for ultrasonic welding are usually of a standard type and then usually operate at the frequency 20 kHz, which has been shown to provide good efficiency while avoiding that the frequency is within the audible range, which places less demands on shielding to avoid harmful hearing. A decrease in the frequency below the accepted standard range places the ultrasonic oscillations within the audible range, and an increase in the frequency above said range results in reduced efficiency, so that the frequency of the ultrasonic source used is not easily adjusted so that ultrasonic welding of packaging containers with other diameters previously used can be done. In the two previously known methods, to which reference is made, a conventional, annular working part with an inner cylindrical or conical working surface and an average diameter 5 which is located substantially between the inner and outer surface of the working part are thus used. This design of annular working parts for ultrasonic welding has so far been dominant.

In order to make it possible to vary the diameter of the annular working part without changing the standard frequency of the ultrasonic source and without changing the material in the annular working part, 10 15 20 25 30 35 513 00960 annular working part in which case the work surfaces have been moved or displaced from the usual positions hitherto used. This makes it possible to depart from the previously prevailing principle of drying the work surface centered around the mass distribution of the measuring part consisting of the plane of symmetry or mass and thus the part located in the mass plane. longer to constitute a limit in the choice of the diameter of the ring ormi a work surface.

From both Fig. 2 about fi. 3 shows how a radial section through the annular working part in the two embodiments is given a cross-sectional shape which no longer coincides with the usual, mainly rectangular or square cross-sectional shape. Herein it becomes possible to place the work surfaces 7 in an unconventional manner in relation to the average circumference 6, which will be explained in more detail in the following with separate reference to the respective embodiment.

Although the two embodiments of the annular feed part 3 shown in Figs. 3 according to the invention are intended for annular welding, the embodiment according to the figure is intended for external welding, while the embodiment according to the figure is intended for internal welding of e.g. packaging container. Corresponding parts to the two embodiments have been given identical reference numerals, except that if necessary the suffix 'has been used to indicate reference numerals relating to the first embodiment (Fig. 2) and the suffix' has been used to indicate reference numerals relating to the second embodiment. (Fig. 3).

In each of the shown embodiments of the working part 4 according to the invention there is thus an annular projection 15 with a preferably cylindrical working surface 7 which in the case of the external part for welding is facing the working part 8 of the working part and at the other, for the internal welding intended embodiment is wet from the center axis 8 of the working part 8. The working surface 7 is mainly centered along a working plane 9, which extends at right angles to the respective center 'max 1 8. Both embodiments of the feed part 3 also comprise a distance f the plane of symmetry or mass 10 located on the etching plane 9, which is likewise oriented in an angle to the center axis 8 and so positioned in the axial direction that the radial section shown in the figures through the annular working part is divided into two sectors, namely the upper sector A and a lower sector B, which are balanced in relation to the product in terms of surface area (mass) and geometric shape (decisive for the rigidity of the feed portion). In the two shown preferred embodiments a of the feed part according to the invention, the cross-sectional sectors A and B located on either side of the mass planet fb have both identical shape and equal surface (mass) ¿which is preferable because it results in a uniform, symmetrical wave propagation in the feeding part. In the case of asymmetrical design, e.g. about objects, e.g. packaging container to be welded is used according to the invention. sector A has a smaller surface area than sector B, for the sake of balance the sector B must instead have a geometric shape which gives this part of the annular feed part a greater rigidity and thus compensating for the imbalance caused by the smaller surface area (mass) of sector A. In other words, the two sectors A and B axially separated by the mass plane 10 must be mutually balanced with respect to a factor determined by both the mass of the sector and the stiffness of the sector determined by the geometric shape.

Due to the described, substantially symmetrical construction of the annular working part 4, the propagation and amplitude of the ultrasonic waves are not adversely affected by the fact that the working surface is not centered around the mass plane, i.e. of the axial distance between the mass plane and the working plane. The projection 15 which in the two embodiments supports the working surface 7 has a mass which is negligible in relation to the total mass of the working part 4, which preferably amounts to only approx. 10% of the total mass of the working part 4. It has been shown in practice that the wave propagation in the mass plane 10 is not negatively affected by the distance between the mass plane 10 and the working plane 9 if the mass of the committee 15 amounts to less than approx. 20% of the total mass of the working part 4. Preferably, the design of the working part 4 is symmetrical about the mass plane 10, but it is also possible to allow some asymmetry provided that the two sectors A and B are mutually balanced with respect to mass and rigidity.

Larger mass in one sector thus requires that the opposite sector has a smaller stiffness, which balances out the otherwise uneven oscillation relations between the two sectors located on either side of the mass plane 10. It is also essential that the supply part 3 of the ultrasonic source connects in the mass plane 10, since otherwise the oscillation balance between the two sectors is shifted.

Figures 2 and 3 indicate how the two embodiments of the device according to the invention are intended to be used for sealing parts of the packaging container, preferably a cylindrical or conical casing part in the form of a sleeve 11 and an end end 12 located at one end thereof. which the end gable 12 are preferably made of laminated material comprising e.g. a central layer of fibrous material, e.g. paper, which on both sides is coated with heat-sealable material, e.g. a thermoplastic such as polyethylene. Figures 2 and 3 also indicate how an abutment 13 is used to compress one end of the sleeve 11 and a folded edge of the end end 12 between the abutment and the working surface 7 of the respective working part 4 during the sealing.

When operating the first embodiment of the device according to the invention illustrated in Fig. 2, one end of the cylindrical sleeve 11 is placed in the upper end of the annular working part 4 and with the outside of the sleeve end in contact with the likewise cylindrical working surface 7. The lower part of the sleeve 11 end positioned end end 12 is pressed with its folded edge against the inner surface of the sleeve by means of the abutment 13, which as shown in fig. 2 e.g. can be slightly conical and thus achieve the desired <, W .. »-.-. w“ ...._...... »___- n un; 10 15 20 25 30 35 513 0089 compressive force at axial downward movement, as indicated by the arrow 14. The abutment 13 'may also be of some other known type, e.g. expandable, and comprise a number of tightly arranged segments, which are pressed radially outwards by means of a suitable power source, e.g. pneumatics. Thus, when the sleeve 11 and the end end 12 are placed in the correct position and in adjacent parts pressed against each other by means of the abutment 13 ', the ultrasonic source 2 is activated so that axial ultrasonic oscillations are propagated and amplified via the feed part 3, transmitted to and distributed in the annular working part 4. .

Since the average circumference 6 located in the mass 23, determined by the average diameter 5, has a length which corresponds to an entire wavelength, the annular working part 4 as a whole will vibrate or pulsate radially with sufficient amplitude to heat the intermediate surface 7 and the abutment 13 the parts of the packaging container to such a temperature that the surface layer of the packaging material of thermoplastic fuses into the abutment surface between the sleeve 11 and the folded edge of the end end 12. After the desired heating time, the supply of current to the ultrasonic source 2 is cut off, whereby the vibrations cease and the temperature of the molten thermoplastic layers drops until the fused layers: solidify and form a liquid-tight seal between the lower end of the sleeve 11 and the end 13. and packaging container elarn can be jointly removed from the working part 4.

Workflow in the second embodiment of the device according to the invention shown in Figure 3 is similar with the difference that the contact between the working part 4 "and the packaging layer holder whose sleeve 11 and end end 12 are to be welded takes place at the end of the end end 1, i.e. by contact between the end end 12 folded edge and the working surface 7 "located at the side of the work part 4. More specifically, an end end 12 is placed over the upper end of the work portion 4 so that the end end rests against it and the folded end of the end end abuts the external working surface 7 ". Thereafter, the cylindrical sleeve 11 of the packaging container is slid down until its lower edge is flush with the the lower end of the folded-down edge region of the end end 12, after which an outer face 11 "13 compresses the overlapping parts of the sleeve 11 and the end end 12 while simultaneously pressing against the working surface. The abutment 13 can e.g. In this position the ultrasonic source 2 is activated so that ultrasonic waves are spread via the measuring part 3 and distributed in the working part 4, the radial vibrations of which heat each other up. adjacent thermoplastic layers so that the sleeve 11 and the end end 12 are welded together and, after cooling the heated, joined thermoplastic layers, form a liquid-tight seal at the bottom end of the packaging container. Then the abutment is removed 13 "and the packaging container is lifted axially upwards and detached from the working part 4.

By displacing the working plane axially in relation to the mass plane in accordance with the invention while maintaining the balance around the mass plane important for the propagation of the ultrasonic waves and with maintaining an optimal average circumference, it thus becomes possible to seal objects with different diameters, which has not previously been possible. essentially coincident mass and work plan has been changed by the more or less given average circumference. This expands the possibilities of using ultrasonic welding without costly or impractical reconstructions of either the ultrasonic source or the working part being necessary.

Claims (9)

ÅqÉl-iHÜ-lmu flfi.-. n ... _, Anni, Ulm., 10 15 20 25 30 PATENTKRAV Ultrasonic assembly lfl ris 00910 comprising an annular working part (4) and a feed part (3), which is connectable to an ultrasonic source (2) for generating ultrasound with a predetermined wavelength d, the working part (4) having a right angle to the central axis (8) of the working part (8) located mass plane (10) with an average circumference (6), the length of which is adapted to said working plane (9) 2. Ultrasound unit divides each radial s which are mutually bala 'wavelength and a working plane (9) with a working surface (7), the right angle being towards the center axis (8) of the working part (4) and on the "let (1 D), characterized therefrom , that the working surface (7) is supported by a 1 of the mass of the working part (4) amounts to less than 20%. ), based on a factor determined by both the mass of the sector and the stiffness of the sector determined by the geometric shape. Ultrasonic assembly according to one of Claims 1 to 2, characterized in that the working surface (7) has a circumference which is different from the average circumference (6). Ultrasonic assembly according to one of Claims 1 to 3, characterized in that the working surface (7 ') faces the central axis (8) of the working part (4'). Ultrasonic assembly according to Claim 4, characterized in that the diameter of the working surface (7 ') is larger than the diameter of the average circumference (6). Ultrasonic assembly according to one of Claims 1 to 3, characterized in that the working surface (7 ") faces the center axis (8) of the working part (4"). Ultrasonic assembly according to Claim 6, characterized in that the diameter of the working surface (7 ") is smaller than the diameter of the average circumference (6). Ultrasonic assembly according to one of Claims 1 to 7, characterized in that the feed part (3) connects radially to the working part (4). 513 009 11 Ultrasonic assembly according to claim 8, characterized in that the feed part (3) connects in the mass plane (10).