The present invention refers to an ultrasound welding device, in particular for welding flexible packages optionally made of a plastic material.
Another object of the present invention is a machine for packaging food products provided with such an ultrasound welding device.
The object of the present invention is used in the industrial field of ultrasound welding devices and, in particular, is suitable for being used on machines and apparatuses for packaging food products and/or similar products.
As known in the industrial field of packaging of food products, it is very common to use flexible packages made through thin films of thermoplastic polymers. Such packages can be of different shapes and sizes according to the type of food product to be packaged and/or the contingent requirements of the manufacturers.
Generally, the aforementioned packages are formed and closed immediately after the filling in step by suitable automated machines.
The prior art provides that such machines carry out the hermetic closure of the filled in packages through suitable thermowelding stations or devices.
In particular, the thermowelding stations and devices are provided with suitable metal bars that are heated at a sufficient temperature to melt the material which the packages consist of. Once in contact with the portions of thermoplastic material to be joined, the heated metal bars transfer part of own heat to the package being welded, causing a partial melt and, therefore, the welding thereof.
With reference to the packaging of food products, the aforementioned thermowelding of packages has various problems.
A first problem that can be encountered concerns the quality of the airtight seal of the weld made on the package. Indeed, it is not rare for a part of the food product to be packaged to be at the welding area, compromising the fusion of the parts of the packaging in contact at one or more points. In this case, the welding obtained has unwelded areas or openings in fluid communication with the outside so that the package is not able to ensure adequate protection of the product from foreign polluting agents and inevitably allows the product to fall out through such openings.
In the case in which the food products to be packaged contain fats or oils, like for example cheeses, cold meats, soups, sauces and/or similar, the welding surfaces of the metal bars incur undesired contaminations that make the welding difficult with repercussions also on the quality of the hermetic seal of the welding itself.
When the food products to be packaged are fresh, like for example salads, vegetables, cheeses and similar, and/or sensitive to high temperatures, like for example chocolate and other analogous products, the high heat of the metal bars can alter and compromise the chemical and organoleptic characteristics of such products that are thus subject to changes in flavour, aroma, as well as appearance.
In the case in which the products to be packaged have a powdered or granular structure, like for example flour, sugar, powdered yeast, coffee, cereals, animal food and similar, it may happen that the powders or granules become trapped in the welds with undesired repercussions on the quality thereof and also on the outer appearance of the package obtained.
In order to solve the aforementioned problems it is common practice to replace the thermowelding stations and devices with ultrasound welding stations and devices.
In practice, an ultrasound frequency mechanical vibration is applied to the portions of thermoplastic material to be welded, said vibration generating, by molecular friction, localised heat, consequently melting the material only in contact with the welding bars.
An example of an ultrasound welding device of the known type that is normally used in industrial machines and apparatuses for packaging food products is illustrated in the attached
The ultrasound welding device 1 represented in
The transducer 2 normally has an elongated shape that develops mainly along a longitudinal direction X.
In order to amplify the vibrations generated by the transducer 2, the ultrasound welding device 1 of the traditional type is also equipped with two mechanical components connected in series to the transducer 2, namely along the longitudinal direction X of development of the latter.
The first mechanical component consists of an amplifier 3 of substantially elongated, cylindrical or frustoconical configuration. The second mechanical component consists of a sonotrode 4 that has a support portion 4a defining, on the opposite side with respect to the transducer 2 and to the amplifier 3, said welding bar 5 on which a respective welding surface 5a is made.
The ultrasound welding device of the conventional type is also provided with at least one contrast bar 6 on which a respective contrast surface 6a is defined against which the welding surface 5a of the sonotrode 5 operates during the ultrasound welding in order to weld the portions in contact of the package being formed. Although the use of welding devices like the one described above and represented in
In particular, the Applicant has found that the bulk of conventional ultrasound welding devices like the one illustrated in
Conventional welding devices are in fact designed and made so as to amplify the vibrations generated through a mechanical configuration that has a longitudinal dimension equal to 3l/2, where l corresponds to the wavelength that propagates in the medium.
The excessive bulk of the traditional configuration of the aforementioned ultrasound welding devices inevitably has an impact on the overall configurations and dimensions of the machines and apparatuses for packaging food products that house them.
In order to maximise the vibrations generated by the transducer, the Applicant found that the longitudinal bulk of the ultrasound welding device must be equal to a multiple of l/2, where l corresponds to the wavelength that propagates in the medium.
The main aim of the present invention is to propose an ultrasound welding device and a machine for packaging food products provided with such an ultrasound welding device, capable of solving the problems encountered in the prior art.
An aim of the present invention is to amplify and transmit the longitudinal vibrations generated by the transducer effectively through a device having a reduced longitudinal bulk, in other words reduced with respect to the longitudinal bulk of traditional ultrasound welding devices.
A further aim of the present invention is to make machines and apparatuses for packaging food products that are of reduced dimensions and limited bulks, less than those of similar packaging machines and apparatuses.
The aforementioned aims and others are substantially accomplished by an ultrasound welding device and by a machine for packaging food products provided with such an ultrasound welding device, as expressed and described in the following claims.
A preferred but not exclusive embodiment of an ultrasound welding device and of a machine for packaging food products provided with such an ultrasound welding device in accordance with the present invention will now be described as an example. The description will be made hereinafter with reference to the attached drawings, provided for exclusively indicating and therefore not limiting purposes, in which:
With reference to
The ultrasound welding device 10 comprises at least one power generator (not illustrated in the attached figures) arranged to generate at least one electric signal, in particular sinusoidal at a predetermined frequency, preferably comprised between 20 kHz and 35 kHz.
Advantageously the power generator is arranged to generate a sinusoidal electric signal having a programmable amplitude, a minimum power of about 1 kW and a maximum power of about 5 kW.
The ultrasound welding device 10 comprises at least one transducer 11 operatively associated with the power generator in order to transform the electric signal generated by the latter into mechanical vibrations, in particular having the same frequency as the electric signal generated by the power generator.
As visible in
Still with reference to
The sonotrode 12 is structured and configured so as to amplify and transmit the mechanical vibrations generated by the transducer 11 to a welding surface 13 defined on the sonotrode 12 itself.
Advantageously, the transducer 11 and the sonotrode 12 are engaged so as to amplify and transmit the mechanical vibrations generated by the transducer 11 to the welding surface 13 of the sonotrode 12 in the absence of interposition of an amplifier or a similar intermediate device for the amplification of vibrations.
In particular, the transducer 11 and the sonotrode 12 are directly engaged to one another, preferably through at least one threaded coupling 14.
Alternatively, the sonotrode 12 can also be integrated to the transducer 11 so as to form a unique vibrating entity.
Advantageously, the sonotrode 12 comprises a first portion 12a defining the aforementioned welding surface 13 and a second portion 12b that extends from the first portion 12a, on the opposite side with respect to the welding surface 13.
As visible in
According to a preferred aspect of the present invention, the second portion 12b of the sonotrode 12 comprises at least one pair of amplification arms 12c that extend substantially parallel to one another from the first portion 12a in the opposite direction with respect to the welding surface 13. The second portion 12b of the sonotrode 12 also comprises at least one support cross member 12d that develops transversely to the amplification arms 12c, preferably perpendicular to the development of the latter.
As visible in
In even greater detail, the amplification arms 12c and the support cross member 12d of the second portion 12b of the sonotrode 12 define a substantially U-shaped structure that delimits, with the first portion 12a of the sonotrode 12, a housing area 15 for the stay of the transducer 11 screwed or integrated in the threaded seat 14a of the support cross member 12d.
As visible in
Advantageously, the mutual engagement between the transducer 11 and the sonotrode 12 through the threaded coupling 14 is such as to allow the transfer of the mechanical vibrations generated by the transducer 11 along the longitudinal development X of the latter, towards the support cross member 12d of the second portion 12b of the sonotrode 12 and on the opposite side with respect to the welding surface 13 thereof.
The particular configuration of the support cross member 12d and of the amplification arms 12c allows the amplified transfer of the vibrations generated by the transducer 11 towards the first portion 12a of the sonotrode 12 and, consequently, of the welding surface 13 of the latter.
In other words, the mechanical vibrations generated by the transducer 11 propagate longitudinally in the opposite direction with respect to the welding surface 13 of the sonotrode 12 in order to be reflected and directed towards the welding surface itself by the particular structure of the sonotrode 12, which consists of the support cross member 12d and of the amplification arms 12c. The structure 12c, 12d of the sonotrode 12 provides for transmitting and amplifying the movements, generating, on the structure itself, a flexional motion that is firstly amplified, so as to then be converted into an axial motion capable of producing homogeneous movements of the welding surface 13.
As represented in
As visible in
In detail, the supply station 101 comprises at least one supply reel 102 from which the packaging material in the form of a continuous band Y′ is unwound and a plurality of idlers 103 that define the path of the packaging material Y′ towards the following station of the machine 100.
Operatively downstream of the supply station 101 of the machine 100, at least one transformation station 104 for transforming the flexible packaging material in the form of a continuous band Y′ into a flexible packaging material in the tubular form y″ is provided.
In detail, the transformation station 104 comprises a tubular element 105 on which the flexible packaging material in the form of a continuous band Y′ takes up a tubular configuration Y″. In other words, the flexible packaging material in the form of a continuous band Y′, while advancing, wraps the tubular element 105, reproducing its tubular shape Y″.
As illustrated in
Still with reference to
Advantageously, the loading station 107 is operatively arranged at least at the transformation station 104, and in particular also at the longitudinal sealing station 106.
In detail, the loading station comprises at least one loading hopper 107a in fluid communication with the tubular element 105 so that the insertion of a predetermined amount of food product into the loading hopper 107a causes the fall of the product itself by gravity along the tubular element 105 and, consequently, along the flexible packaging material in the tubular form Y″.
Downstream of the longitudinal sealing station 106, the machine is advantageously equipped with at least one pair of conveyor belts 108 that facilitate the advancement of the flexible packaging material in the tubular form Y″ towards an ultrasound welding station 109 that, in fact, is operatively arranged downstream of the longitudinal sealing station 106 in order to make at least one weld on the flexible packaging material in the tubular form Y″, the weld being transversal to the longitudinal development of the flexible packaging material.
Specifically, in the ultrasound welding station 109, the flexible packaging material in the tubular form Y″ is welded transversally while it advances so as to form single packages inside which the food product coming from the loading hopper 107a of the loading station 107 is hermetically sealed.
As schematically represented in
During each welding operation, the flexible packaging material in the tubular form Y″ is pressed between the welding surface 13 of the sonotrode 12 and the contrast surface 16a of the contrast element 16 and the ultrasound device 10 is initiated to weld the portions of material in contact.
The object of the present invention solves the problems encountered in the prior art and allows achieving important advantages.
Firstly, the particular configuration of the sonotrode along with the type of direct connection between the latter and the transducer allows an optimal amplification of the mechanical vibrations generated by the transducer in the absence of bulky intermediate amplification devices.
In particular, the threaded coupling of the transducer with the support cross member of the sonotrode allows the elimination of the intermediate amplifiers and allows a substantial reduction in the longitudinal dimensions of the transducer/sonotrode assembly that translates into a significant reduction in the overall bulks of the ultrasound welding device, as well as of the machine or apparatus on which it is mounted.