Patent Description:
The welding of laminated packing material by means of induction heat is used in the packaging industry. One example of such a laminated material is a carrier layer of paper, aluminium foil and thermoplastic coatings along the inner and outer surfaces of the laminate. The technique of induction welding is based on the fact that the magnetic field around a conductor, generated by an alternating current is capable of inducing a current in an adjoining electrically conducting material, which depending on the resistance of the material, warms up the material. Thus, in induction welding an inductor loop or coil provided against the laminate containing the aluminium foil, and the laminate is pressed together with the material to which it is to be joined. The aluminium foil is heated by means of appropriately chosen current and processing period. The material is heated to a temperature which is high enough to seal adjoining layers of thermoplastic, causing the combined thermoplastic layers to fuse together, thus producing a tight and durable seal.

A problem often encountered in such sealing process is the contamination of the inductor. This is due to the accumulation of packaging material compounds, e.g. polyethylene residues, on the active welding surface of the inductor. The inductor is typically pressed against the packaging material to prevent fluctuations in the electrical parameters of the induction circuit that is formed between the inductor and the metal foil in the packaging material. Fluctuations in e.g. the impedance of the inductive circuit could otherwise impact the control of the sealing process, leading to suboptimal packaging seals or process interruptions due to exceeded impedance thresholds. Accumulation of chemical residues also necessitates frequent cleaning of the inductors, which in turn adds to the wear of the inductors, and reduced lifetime.

Further prior art is <CIT> disclosing an induction heating device for securely laminating a longitudinal strip to a web of carton -based packaging material. It further discloses a way to accurately monitor the heating process due to increased current in order to prevent damage or burning of the packaging material as a result from over-heating.

Another prior art is <CIT> disclosing an arrangement to enable a continuous weld on a laminated packing material to be carried out by means of induction heat requiring no warming-up period.

Hence, an improved inductor would be advantageous and in particular allowing for avoiding more of the above mentioned problems and compromises, including avoiding accumulation of chemical residues and providing for increased lifetime of the inductor. A related sealing machine for sealing a packaging material and a method of welding a packaging material would also be advantageous.

Accordingly, examples of the present invention preferably seeks to mitigate, alleviate or eliminate one or more deficiencies, disadvantages or issues in the art, such as the above-identified, singly or in any combination by providing a device according to the appended patent claims.

According to a first aspect an inductor according to claim <NUM> is provided.

According to a second aspect a sealing machine according to claim <NUM> is provided.

According to a third aspect a method according to claim <NUM> is provided.

Further examples of the invention are defined in the dependent claims, wherein features for the second and third aspects of the disclosure are as for the first aspect mutatis mutandis.

Some examples of the disclosure provide for an inductor for induction welding of a packaging material that is less susceptible to contamination by packaging material residues.

Some examples of the disclosure provide for an inductor for induction welding of a packaging material that has an increased lifetime.

Some examples of the disclosure provide for an inductor for induction welding of a packaging material that requires less maintenance.

Some examples of the disclosure provide for an inductor that allows for increased stability in the electrical parameters of the inductive heating circuit.

Some examples of the disclosure provide for an inductor heating circuit that allows for improved control of the sealing process.

Some examples of the disclosure provide for more reliable sealing of packaging material containers.

Some examples of the disclosure provide for an increased throughput in an inductive sealing production line.

These and other aspects, features and advantages of which examples of the invention are capable of will be apparent and elucidated from the following description of examples of the present invention, reference being made to the accompanying drawings, in which;.

Specific examples of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the examples set forth herein; rather, these examples are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the examples illustrated in the accompanying drawings is not intended to be limiting of the invention.

<FIG> schematically illustrates an inductor <NUM> for induction welding of a packaging material <NUM> having at least one layer of metal foil. The inductor <NUM> comprises a welding surface <NUM> configured to be arranged opposite the packaging material <NUM> for heating thereof. At least one spacing element <NUM>, <NUM>', <NUM>", <NUM>‴, is arranged to protrude from the welding surface <NUM> in a first direction <NUM> towards the packaging material <NUM>, when the packaging material <NUM> is arranged opposite the welding surface <NUM>. The at least one spacing element <NUM>, <NUM>', <NUM>", <NUM>‴ (denoted <NUM> - <NUM>‴ for short below), thereby separates the packaging material <NUM> from the welding surface <NUM> by an off-set distance <NUM>. By having at least one spacing element <NUM> - <NUM>‴ protruding from the welding surface <NUM> the packaging material <NUM> is prevented from contacting the welding surface <NUM>, and is instead kept at the off-set distance <NUM> from the welding surface <NUM>. Build-up of residues from the packaging material <NUM> on the welding surface <NUM>, e.g. from polyethylene that is formed due to the high temperature exposed to the packaging material <NUM>, can thus be prevented. This advantageously provides increasing the service interval, since less cleaning of the inductor <NUM> is required. At the same time, the at least one spacing element <NUM> - <NUM>‴ protruding from the welding surface <NUM> provides for achieving stable characteristics of the electrical parameters of the induction circuit since the packaging material <NUM> can be readily arranged against the at least one spacing element <NUM> - <NUM>‴ and thereby be kept at the well-defined off-set distance <NUM> from the welding surface <NUM>. Having such defined separation minimizes the risk of fluctuations in e.g. the impedance of the induction heating circuit, which provides for optimized control of the welding process. The sealing procedure of the packaging containers may thus be made more reliable and completed in a shorter amount of time, since it is possible to more accurately control the power delivery to the inductor, thanks to the improved stability of the electrical characteristics involved the process. The lifetime of the inductor <NUM> can also be increased, due to the optimized power control and due to less wear on the inductor, which is a result of less exposure to contaminants and partly also because of fewer cleaning operations which contribute to the overall wear of the inductor <NUM>. Thus, having at least one spacing element <NUM> - <NUM>‴ protruding from the welding surface <NUM> provides for a more robust inductor with increased lifetime, as well as improved control of the induction sealing process. The protrusion from the welding surface <NUM> by the least one spacing element <NUM> - <NUM>‴ should be construed as an extension from a plane in which the welding surface <NUM> of the inductor lies. turning to e.g. <FIG>, the spacing element <NUM> extends or protrudes beyond such plane (which extends in the feed direction <NUM>) in the first direction <NUM>. In the example of <FIG> it is clear that the spacing element <NUM> may not need to be in abutment with the welding surface <NUM>, but should regardless be construed as protruding or extending form the welding surface <NUM> in the first direction <NUM> towards the packaging material <NUM> as discussed.

As schematically illustrated in e.g. <FIG>, the at least one spacing element <NUM> - <NUM>‴ comprise at least one roller <NUM> - <NUM>‴ being pivotally fixed to the inductor <NUM> and being rotatable around a rotational axis <NUM>, which is further illustrated in the top-down view of the inductor <NUM> in <FIG>. The at least one roller <NUM> - <NUM>‴ is configured to convey the packaging material <NUM> across the welding surface <NUM> at the off-set distance <NUM>. Having at least one roller <NUM> - <NUM>‴ provides for attaining the off-set distance <NUM> with the advantages as elucidated above while allowing for an efficient conveying of the packaging material <NUM> across the welding surface <NUM> with a minimum of frictional force exerted between the packaging material <NUM> and the welding surface <NUM>. The at least one roller <NUM> - <NUM>‴ may thus freely rotate relative the welding surface <NUM>. It is also conceivable however that the at least one spacing element <NUM> - <NUM>‴ may comprise a static, i.e. not rotating, low friction material that provides for an efficient sliding movement between the packaging material <NUM> and the at least one spacing element <NUM> - <NUM>"'. A static spacing element <NUM> - <NUM>‴ may provide for an inductor <NUM> requiring a minimum of maintenance, albeit at least one roller <NUM> - <NUM>‴ may provide for advantages in terms of providing a minimum of frictional force against the packaging material <NUM>. A static spacing element <NUM> - <NUM>‴ may comprise a material having a low friction coefficient while being highly resistant to contaminations and abrasion. It is further conceivable that at least one static spacing element <NUM> - <NUM>‴ may be combined with at least one movable spacing element <NUM> - <NUM>‴ in certain applications of the inductor <NUM> to provide for a balance between maintenance, manufacturing costs and movability. It is further conceivable that other movable spacing elements <NUM> - <NUM>‴ may be provided, such as spherical elements which may rotate relative to the welding surface <NUM>.

The at least one roller <NUM> - <NUM>‴ may be extend across at least half of the width <NUM> of the welding surface <NUM>, in the direction of the rotational axis <NUM>. This may provide for further ensuring that the packaging material <NUM> is maintained at the off-set distance <NUM> from the welding surface <NUM> and that the packaging material <NUM> can be effectively and reliably conveyed over the welding surface <NUM>.

As illustrated in e.g. <FIG> and <FIG>, the welding surface <NUM> may have an elongated extension in a feed direction <NUM> in which the packaging material <NUM> is conveyed, when arranged opposite the welding surface <NUM>. The rotational axis <NUM> may extend parallel with the welding surface <NUM>, i.e. in the plane of the welding surface <NUM>, and perpendicular to the feed direction <NUM>. Having the rotational axis <NUM> extending in the plane of the welding surface <NUM> may provide for further enduring that the packaging material <NUM> is kept at a constant off-set distance <NUM> across the welding surface <NUM>. By having the rotational axis <NUM> extending perpendicular to the feed direction <NUM> the packaging material <NUM> may be exposed to a minimum of frictional force from the at least one roller <NUM> - <NUM>"'.

The at least one roller <NUM> - <NUM>‴ may be arranged in a corresponding recess <NUM>, <NUM>', <NUM>", <NUM>‴, in the welding surface <NUM>, as illustrated in e.g. the side-views of <FIG> and <FIG> or the perspective view of <FIG>. Arranging the at least one roller <NUM> - <NUM>‴ in a recess allows for selecting an optimized diameter of the roller <NUM> - <NUM>‴ in order to provide for the desired dynamics of the relative movement between the roller <NUM> - <NUM>‴ and the packaging material <NUM>, while being able to set the off-set distance <NUM> to the desired value.

The inductor <NUM> may comprise at least one support <NUM> in which the at least one roller <NUM> - <NUM>‴ is pivotally fixed, as schematically illustrated in <FIG>. The at least one support <NUM> may be movably fixated to the inductor <NUM> and thereby be movable relative to the welding surface <NUM> such that the corresponding roller <NUM> - <NUM>"', pivotally fixed to the support <NUM>, has a variable position in the first direction <NUM>, perpendicular to the welding surface <NUM> and the rotational axis <NUM>. The off-set distance <NUM> may thus be readily varied and set to a range of values by moving the support <NUM> and the corresponding roller <NUM> - <NUM>‴ in the first direction <NUM>, towards the packaging material <NUM>. In case of having a plurality of rollers <NUM> - <NUM>"', each of the rollers <NUM> - <NUM>‴ may be individually moved relative to each other to optimize the trajectory of the packaging material <NUM> across the welding surface <NUM>. It is also conceivable that in case of having static spacing elements <NUM> - <NUM>"', as discussed above, the position of the static spacing elements <NUM> - <NUM>‴ in the first direction <NUM> may be individually adjusted.

The at least one roller <NUM> - <NUM>‴ may comprise a cylindrical surface covered by a resilient material (not shown). Such resilient material may accommodate slight movements of the packaging material <NUM> in the first direction <NUM> and thereby smoothen out possible vibrations occurring in the packaging material <NUM> when conveyed over the welding surface <NUM>. This may provide for increased stability in the trajectory of the packaging material <NUM> relative to the inductor <NUM> and further process stability with regards to the electrical characteristics of the inductive heating circuit established via the magnetic coupling of the inductor <NUM> to the metal foil of the packaging material <NUM>.

The Inductor <NUM> may comprise a plurality of spacing elements <NUM>, <NUM>', <NUM>", <NUM>‴, as illustrated in <FIG>. The number of spacing elements <NUM> - <NUM>‴ may be selected depending on the particular application which may dictate varying requirements with respect to e.g. the dimensions of the inductor <NUM>. <FIG> illustrate examples with four spacing elements <NUM> - <NUM>‴, i.e. four rollers <NUM> - <NUM>‴ in these examples, which should however not be seen as limiting but instead mere examples of a number of spacing elements <NUM> - <NUM>‴. Thus, it is conceivable that the number of spacing elements may be more or less than shown in the provided examples, depending on e.g. the length of the inductor <NUM> in the feed direction <NUM>. The plurality of spacing elements <NUM> - <NUM>‴ may be separated from each other by a set separation distance <NUM> defined such that the packaging material <NUM> remains separated from the welding surface <NUM> along the separation distance <NUM> when conveyed in the feed direction <NUM>. Thus the separation distance <NUM> is chosen such that the packaging material <NUM> does not abut the welding surface <NUM> between the spacing elements <NUM> - <NUM>‴ given a particular application. the speed by which the packaging material <NUM> is conveyed in the feed direction <NUM> over the welding surface <NUM> may be different in various applications, as well as the properties of the packaging material itself, which may affect the amount of flexing of the packaging material <NUM> between two spacing elements <NUM> - <NUM>‴. The separation distance <NUM> may thus be varied to accommodate such factors and prevent flexing of the packaging material <NUM> to such extend it touches the welding surface <NUM>. It is also conceivable that the spacing elements <NUM> - <NUM>‴ may be movable in the feed direction <NUM>, i.e. being configured to be fixated at different separation distances <NUM>, to provide for substantially maintaining the off-set distance <NUM> across the welding surface <NUM> while having separation distances <NUM> that minimize friction on the packaging material <NUM>.

The plurality of spacing elements <NUM> - <NUM>‴ may comprise a plurality of rollers <NUM>, <NUM>', <NUM>", <NUM>‴, each arranged in a corresponding recess <NUM>, <NUM>', <NUM>", <NUM>‴ in the welding surface <NUM>, as schematically illustrated in the examples of <FIG>. Such configuration may provide for a particularly advantageous inductor <NUM> with improved lifetime and stable electrical characteristics of the inductive heating circuit.

The at least one spacing element <NUM> - <NUM>‴ may be arranged such that the off-set distance <NUM> is substantially constant over the welding surface <NUM> along a feed direction <NUM> in which the packaging material <NUM> is conveyed, when arranged opposite the welding surface <NUM>. A constant off-set distance <NUM> may further provide for achieving optimal stability and control of the electrical parameters of the inductive heating circuit.

The at least one spacing element <NUM> - <NUM>‴ may be thermally insulated from the welding surface <NUM>. Thermally insulated should be construed as decreased thermal coupling between the at least one spacing element <NUM> - <NUM>‴ and the welding surface <NUM> so that the amount of thermal power transferred therebetween is reduced. The at least one spacing element <NUM> - <NUM>‴ may be thermally insulated from the welding surface <NUM> by having a thermally insulating material arranged inbetween the at least one spacing element <NUM> - <NUM>‴ and the welding surface <NUM>, i.e. a material having a lower heat transfer coefficient than the welding surface <NUM>. Alternatively, the at least one spacing element <NUM> - <NUM>‴ may be separated from the welding surface <NUM> as in the case of having at least one roller <NUM> - <NUM>‴, shown in the examples of <FIG>. The air gap between the at least one roller <NUM> - <NUM>‴ and the welding surface <NUM> may be varied to achieve the desired amount of thermal insulation, so that the packaging material <NUM> is not heated excessively when in contact with the at least one roller <NUM> - <NUM>"'. Formation of compound residues such as polyethylene on the at least one roller <NUM> - <NUM>‴ may thereby be prevented.

The at least one spacing element <NUM> - <NUM>‴ may be removably fixated to the inductor <NUM>. It is thus possible to allow for efficient and facilitated maintenance and optimization of the at least one spacing element <NUM> - <NUM>‴ on the inductor <NUM>. It is also conceivable that the number of spacing element <NUM> - <NUM>‴, e.g. rollers <NUM> - <NUM>‴, may be varied as desired, by removing or attaching rollers <NUM> - <NUM>‴ to the inductor <NUM> depending on the particular application. A high degree of customizability of the inductor <NUM> is thus provided and replacement of the inductor <NUM> as a whole can be avoided.

A sealing machine for sealing a packaging material <NUM> is provided. The sealing machine comprises an inductor <NUM> as described above in relation to <FIG>. In the sealing machine, the packaging material <NUM> is conveyed to be arranged opposite a welding surface <NUM> of the inductor <NUM>, and at least one spacing element <NUM>, <NUM>', <NUM>", <NUM>‴, is arranged to protrude from the welding surface <NUM> in a first direction <NUM> towards the packaging material <NUM>, whereupon the least one spacing element <NUM> - <NUM>‴ separates the packaging material <NUM> from the welding surface <NUM> by an off-set distance <NUM> while being conveyed in sealing machine. This thus provides for a sealing machine with the advantages as described above in relation to the inductor <NUM> and <FIG>.

<FIG> illustrates a flow chart of a method <NUM> of welding a packaging material <NUM> having at least one layer of metal foil with an inductor <NUM>. The order in which the steps of the method <NUM> are described and illustrated should not be construed as limiting and it is conceivable that the steps can be performed in varying order. The inductor <NUM> has a welding surface <NUM> configured to be arranged opposite the packaging material <NUM> for heating thereof. The method <NUM> comprises conveying <NUM> the packaging material <NUM> over the welding surface <NUM> at an off-set distance <NUM> from the welding surface <NUM> by moving <NUM> the packaging material <NUM> over at least one spacing element <NUM>, <NUM>', <NUM>", <NUM>‴ arranged to protrude from the welding surface <NUM>. A method <NUM> of welding a packaging material <NUM> with an inductor <NUM> is thus provided with the associated advantages as described above in relation to the inductor <NUM> and <FIG>.

The at least one spacing element <NUM> - <NUM>‴ may comprise a plurality of rollers <NUM>, <NUM>', <NUM>", <NUM>‴. The method <NUM> may comprise rolling <NUM> the packaging material <NUM> on the rollers <NUM> - <NUM>‴ over the welding surface <NUM> to maintain the off-set distance <NUM> between the packaging material <NUM> and the welding surface <NUM> along a feed direction <NUM> in which the welding surface <NUM> extends and in which direction the packaging material <NUM> is conveyed.

The present invention has been described above with reference to specific examples. However, other examples than the above described are equally possible within the scope of the invention. The different features and steps of the invention may be combined in other combinations than those described. The scope of the invention is only limited by the appended patent claims.

Claim 1:
An inductor (<NUM>) for induction welding of a packaging material (<NUM>) having at least one layer of metal foil, the inductor comprising
a welding surface (<NUM>) configured to be arranged opposite the packaging material for heating thereof, and
at least one spacing element (<NUM>, <NUM>', <NUM>", <NUM>‴) arranged to protrude from the welding surface in a first direction (<NUM>) towards the packaging material, when the packaging material is arranged opposite the welding surface, whereupon the least one spacing element separates the packaging material from the welding surface by an off-set distance (<NUM>), and
wherein the at least one spacing element comprises at least one roller (<NUM>, <NUM>', <NUM>", <NUM>"') being pivotally fixed to the inductor and being rotatable around a rotational axis (<NUM>), whereby the at least one roller is configured to convey the packaging material across the welding surface at the off-set distance.