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DESCRIPTION

Field of the Invention

The present invention relates to an insert made of an alloy of an amagnetic material and a ferromagnetic or ferrimagnetic material, which insert is adapted to be used in induction cooking. In particular, the present invention relates to an alloy wherein the percentage of ferromagnetic or ferrimagnetic material is very low with respect to the percentage of amagnetic material.

The present invention further relates to a kitchenware for induction cooking comprising such an insert and a method for making such a kitchenware.

Background Art

As it is known, induction cookers comprise a coil, placed below a hob, inside which a time-varying electric current is flowing. Such a variable current produces a magnetic field time-varying too as a function of the generating current. Variations of the flow of magnetic field produce an induced electromotive force, by Faraday effect. When a conductive metal is inside a time-varying magnetic field, the above mentioned induced electromotive force generates induced currents (called parasitic currents) which circulate inside the conductor.

Therefore, when a suitable kitchenware is placed on the hob, i.e. inside the variable magnetic field, said induced currents circulating in the kitchenware dissipate energy in the form of heat (Joule effect cooperating with the dissipative effect re-orienting the magnetic domains known in literature as hysteresis loop which is typical and characteristic of ferromagnetic materials), thus causing the heating of the kitchenware itself.

It is evident that not all of the materials are suitable for making kitchenware for induction cookers. In fact, it is necessary that the material has electric resistance sufficiently low to allow the passage of induced currents and, at the same time, sufficiently high to allow the dissipation of energy necessary for heating the kitchenware, and thus its content. At present, for making kitchenware for induction cooking, the use of ferromagnetic or ferrimagnetic materials such as cast iron or steel or an aluminum and iron alloy is known, as described in EP 2220975. In particular, this document describes a food container suitable to be heated on induction hobs. The bottom of the container is made of an alloy constituted by ferromagnetic material and aluminum. The minimum quantity of ferromagnetic material must be equal to its percolation index of powders.

Such materials, that became de facto standards in the reference market, have been preferred to materials with more suitable mechanical and/or thermal properties, despite they are less performing, because they better respond to magnetic fields in the context of the above described phenomenon .

For example materials such as aluminum, having lower specific weight (and thus resulting in lighter and handier kitchenware) and better thermal conductivity (and therefore proving to be more suitable for cooking) , are not commonly used in this field because they need too high power and/or frequencies for a civil use for triggering the process and optimizing the efficiency.

Basically, materials notoriously used in the present field, are not proving to be optimal neither from the mechanical nor from the thermal point of view, in addition to be expensive.

Furthermore, the kitchenware market uses more and more often alternative materials such as glass, fiberglass, borosilicate glass, ceramic, porcelain, plastics, because of their versatility and low costs.

However, at present such alternative materials are not compatible with the induction cookers. The International Patent Application published with No. WO 2011/064455 describes an aluminum kitchenware to which a bottom element made of ferromagnetic material is mechanically coupled, coated by an aluminum layer. Such a solution only marginally reduces costs due to the material and does not reduce those due to the manufacturing process of the kitchenware. Such a solution further implies the disadvantages due to a mechanical coupling between kitchenware and bottom element. Finally, it does not meet the current market needs of using alternative materials. SuiranarY of the Invention

Therefore, it is a purpose of the present invention to provide an insert for kitchenware for induction cooking that allows obtaining kitchenware for induction cooking made of materials optimal for the concerned use, with reduced manufacturing costs.

Another purpose of the present invention is to provide a cheap insert that makes the above mentioned alternative materials suitable to be used in induction cooking .

A further purpose of the present invention is to provide a kitchenware for induction cooking that is versatile, cheap and at same time efficient.

Another purpose of the present invention is to provide a method for making a kitchenware for induction cooking that is simple and cheap and achieves a kitchenware overcoming the above described drawbacks.

Another purpose of the present invention is to make amagnetic metals compatible with applications that provide for induction heating.

Another object of the present invention is to provide manufactured products that can be more efficiently induction heated and by consuming less power than known solutions .

These and other purposes are achieved by means of an insert for kitchenware for induction cooking comprising at least one film having thickness s made of an alloy of at least one amagnetic material and at least one ferromagnetic or ferrimagnetic material wherein s is lower than, or equal to, 4 cm, and preferably lower than, or equal to, 500 μπι, and wherein said alloy comprises an amount of amagnetic material comprised between 90% and 99% by mass (wt.%) and an amount of ferromagnetic or ferrimagnetic material comprised between 1% and 10% by mass (wt.%), said percentages being referred to the total mass of the alloy.

In fact, it has been found that, by combining said respective amounts of materials with the specific thickness of the film, it is possible to obtain an insert able to optimally respond to the magnetic field, and thus able to be effectively used in induction cooking and, at the same time, provided with good thermal and mechanical properties.

But above all, with such a combination of features, it is possible to obtain an insert that can be embedded in kitchenware made of a great number of materials, comprised the above-mentioned materials which more and more often the kitchenware market is making use of, i.e. glass, fiberglass, borosilicate glass, ceramic, porcelain, plastics .

In particular, it has been found that it is sufficient to add a very small percentage of ferromagnetic or ferrimagnetic material inside an alloy made of amagnetic materials, to impart ferromagnetic features to the insert.

This is only happening if the thickness of the film is in the above-mentioned value range.

Such features, i.e. the percentages of materials in combination with the claimed thicknesses, allow obtaining light, easy to handle and cheap kitchenware for induction cooking .

Furthermore, the proportions between the used materials and the thickness of the insert make it possible to be easily embedded in different types of kitchenware by simple and cheap manufacturing processes.

Preferably, the amagnetic material comprises at least one material selected from silver, copper, aluminum, platinum, boron and the ferromagnetic or ferrimagnetic material comprises at least one material selected from nickel, iron, cobalt.

The combination of such materials responds particularly well to the magnetic field, in the context of the phenomena described above.

The amagnetic material can contain at least one rare- earth element or oxide of rare-earth elements, preferably in content lower than 1% by mass. The rare-earth elements in small amounts, as mentioned, allow to refine the metal structure of the alloy and to make it fluid.

In an embodiment, in addition to the just described metals, the alloy used for making the insert also comprises non-metals, such as carbon, and/or metalloids, such as silicon, in amounts lower than, or equal to, 1% by mass (wt.%) . Some non-metals and some metalloids have amagnetic or ferromagnetic behavior. Therefore, the non-metals and/or metalloids content in the alloy will take into account this aspect. The choice of the nature and quantity of non-metals and/or semi metals depends upon the result you want to achieve. For example, the alloy can contain less than 1% by mass (of the total mass) of carbon to increase the melting point of the alloy itself.

Advantageously, the insert also comprises one or more additional layers coupled with the film, that have the purpose of improving the mechanical, thermal and/or electric resistance features of the insert.

In particular, by applying two additional layers respectively at the top surface and the bottom surface of the film, it is possible to obtain a multilayer insert in which the film is mechanically shielded.

Furthermore, if the film is made of materials having relatively low melting temperatures (such as for example aluminum) , and if the additional layers are made of insulating materials, the film would also be thermally shielded by the additional layers.

In an application, the film is sandwiched between layers of electrically insulating material, in the absence of air, i.e. is confined under vacuum. In this solution, the film can be induction heated until completely melted, switching to the liquid state. A subsequent cooling brings the film back to the solid state. In other words, it is possible to use the film as an insert of kitchenware also to exploit the latent heat of fusion and solidification.

The purposes of the present invention are also achieved by the described and claimed methods that allow obtaining kitchenware for induction cooking in a simple and cheap way and that allow embedding the insert in the kitchenware with evident manufacturing and maintenance advantages .

For the purposes of the present invention, the term "alloy" is used to identify the materials in which the mixing of metals or other constituents is intentional. Therefore, the term "alloy" is irrespective of undesired impurities being present or not that can derive from the nature of minerals from which the compounds are extracted and/or from the mining and metallurgical processes used.

Furthermore, in the present invention by "amagnetic materials" is meant all of those materials, such as diamagnetic or paramagnetic materials, not appreciably interacting with magnetic fields.

Conversely, by "ferromagnetic or ferrimagnetic materials" are meant all of those materials appreciably interacting with magnetic fields. Commonly, such materials are also called magnetic materials.

In the present context, metals are respectively classified as diamagnetic, paramagnetic or ferromagnetic or ferrimagnetic, depending on the relative magnetic permeability at room temperature and further, when talking about ferromagnetic behavior, the behavior at room temperature is always meant.

Finally, in the present description and claims below, when talking about rare-earth elements, the IUPAC definition is always meant.

Brief List of the Figures

Further characteristics and advantages of the present invention will be more evident from the review of the following specification of some preferred, but not exclusive, embodiments shown for illustration purposes only and without limitation, with the aid of the attached drawings, in which:

- figure 1 shows a schematic perspective view of a first embodiment of the insert according to the invention;

figure 2 shows a sectional view of a second embodiment of the insert according to the invention;

- figure 3 shows a sectional view of a third embodiment of the insert according to the invention;

- figure 4 shows a sectional view of a kitchenware according to an embodiment of the invention;

- figure 5 shows a sectional view of a kitchenware according to a further embodiment of the invention.

Detailed Description of the Invention

The following detailed description refers to an insert for kitchenware for induction cooking, a kitchenware for induction cooking and a method for making a kitchenware for induction cooking.

With reference to figures 1-5, an insert for kitchenware for induction cooking is denoted as a whole with the reference number 1.

The insert 1 comprises a film 2 having thickness s comprised in the range 0 cm < s ≤ 4 cm. In particular, the minimum value is excluded from the range, whereas the maximum value is comprised. Preferably, the thickness s is lower than 500 μπι, for example comprised between 5 μπι and 200 μπι, and still more preferably between 5 μπι and 100 μπι.

Such a film 2 is made of an alloy of at least two materials or mixtures of materials: the first material is an amagnetic material, such as for example a diamagnetic or paramagnetic material, or a mixture of amagnetic materials compatible between each other, whereas the second material is a ferromagnetic or ferrimagnetic material or a mixture of ferromagnetic or ferrimagnetic materials compatible between each other.

As known, a material is called ferromagnetic when its relative magnetic permeability is much higher than the unit; diamagnetic when it is lower than the unit and paramagnetic when it is slightly higher than the unit.

According to the present invention, the content of amagnetic material in the alloy is comprised between 90% and 99% by mass (wt.%), preferably between 95% and 99% by mass (wt.%), even more preferably between 97% and 99% (wt.%), with respect to the total mass of the alloy. Whereas the content of ferromagnetic material is comprised between 1% and 10% by mass (wt.%), preferably between 1% and 5% by mass (wt.%), even more preferably between 1% and 3% by mass (wt.%), still with respect to the total mass of the alloy.

In an embodiment, the percentages of the amagnetic material and magnetic material are such that, if summed, they constitute 100% of the alloy, i.e. no additional material is provided.

The amagnetic material is preferably selected from gold, silver, copper, aluminum, platinum; the ferromagnetic material is selected from nickel, iron, cobalt.

Titanium and boron allow obtaining a satisfying refining of the alloy, since they allow the formation of smaller and substantially spherical pellets and, consequently, improve the overall mechanical features. However, the content of boron, if present, is lower than 0.5% by mass, and is preferably comprised in the range 0.1% - 0.2% and the content of titanium, if present, is lower than 0.5% by mass, and is preferably comprised in the range 0.1% - 0.2%.

The amagnetic material can contain at least one rare- earth element or an oxide of rare-earth elements, but with content preferably lower than 1% by mass.

The alloy is preferably obtained by a technique selected from: melting, sintering, dispersing a powdered metal in a liquid metal phase.

The film 2 can easily be made by methods know to the technician of the art, for example by rolling. Such a film 2, if placed in a variable magnetic field having suitable intensity, in a few seconds is able to reach temperatures of several hundred degrees, thanks to the induced currents generated therein. Therefore, it proves being optimal for the use in induction cooking.

In order to strengthen the insert 1 or to impart it particular mechanical, thermal or electric features, it is possible to couple at least one additional layer 3 to the film 2. The embodiment depicted in figure 1 shows a film 2 coupled to an additional layer 3.

Such an additional layer 3 is preferably made of electrically insulating material, such as for example glass, fiberglass, borosilicate glass, porcelain, resin, ceramic, polymeric materials. Thereby, it is possible to maximize the heat exchange of the insert 1 by protecting the film 2, i.e. avoiding its approach the melting point. Such additional layer 3 made of insulating material also serves to avoid overheating the hob due to the heating of the kitchenware.

In accordance with the embodiment showed in figure 2, the additional layers 3 are two and are respectively located at the top surface and the bottom surface of the film 2.

Instead, in the embodiment showed in figure 3, one additional layer 3 is placed between two films 2. It is possible to provide inserts 1 without additional layers 3, or multilayer inserts 1 provided with three or more additional layers 3, having features equal or different between each other and being interposed between films 2 or in contact with one another, depending on the features you want to give to the insert 1.

The additional layers 3 can be coupled with the film 2 prior to the making of a kitchenware 4 or concurrently.

Said coupling can be carried out by a known process, such as compression molding or thermoforming or welding (preferably ultrasonic bonding) . Alternatively, the coupling can be made by injection molding or additive methods or spraying (the material constituting the additional layer 3 is sprayed onto the film 2), or by dipping in a bath of material (the film 2 is dipped in a bath of material constituting the additional layer 3) .

In an application exploiting the latent heat of fusion and solidification, the insert is directly made in a cavity between two layers of electrically insulating material. The insert remains confined, in vacuum conditions. For example, the alloy is casted in the cavity in vacuum conditions and the cavity is then isolated from the outside. Thereby an insert is obtained, that during the normal use can be induction heated until melted, then solidifying in the cavity when the induced magnetic field has ceased. Therefore, the kitchenware embedding this solution also exploits the latent heat of fusion/solidification of the alloy .

In figures 4 and 5 two embodiments of a kitchenware 4, according to the present invention, are depicted.

The kitchenware 4 comprises a bottom wall 5 and a lateral wall 6 which define a compartment 7 adapted to contain liquids or solids intended to be heated.

The kitchenware 4 can have any shape. The bottom part 5 is preferably flat or anyway defines a plane, so that to provide an optimal support on an induction hob.

In accordance with the present invention, the kitchenware 4 comprises at least one insert 1 as described above, which is placed at least at the bottom wall 5.

In the embodiment of figure 4, the insert 1 is placed at the bottom wall 5 and lateral wall 6, whereas in the embodiment of figure 5, the insert 1 is only placed at the bottom wall 5. In both cases, the insert 1 substantially has the same extent of the wall on which it is applied. Obviously, it is possible to provide for variants to such embodiments, for example, it is possible to apply an insert 1 of dimensions smaller than the walls to which it is applied, or it is possible to apply several inserts 1 (placed on the plane of the wall or on a plane perpendicular to the wall) to the same wall. The insert 1 is advantageously embedded in the kitchenware 4, i.e. the two items make a single piece. In the kitchenware 4 of figure 5, the insert 1 is placed inside the bottom wall 5, however it could be placed at the higher surface or at the lower surface of the bottom wall, but in any case it is embedded in the kitchenware 4 itself.

It is also possible to provide a kitchenware 4 wherein the insert 1 is glued by means of glues or resins, at one or more of its internal and/or external surfaces, but such an embodiment still being very cheap as it can be applied to already existing kitchenware, have not all the advantages of the kitchenware 4 in which such an insert 1 is embedded.

The kitchenware 4 of figure 5 also comprises handles 8 to handle the kitchenware 4. They can be made of thermally non-conductive material or anyway be isolated from the body of the kitchenware 4, in a known manner.

The kitchenware 4 can comprise the insert 1 only, i.e. can be obtained by shaping the insert 1 as showed in figure 4, or also comprise a portion made of electrically insulating material, as showed in figure 5. In such an embodiment, said insulating material constitutes the body of the kitchenware 4, in which the insert 1 is embedded.

Such electrically insulating material is preferably selected from: polymeric materials, glass, fiberglass, borosilicate glass, ceramic, porcelain, resins, ceramics, stones .

Obviously, the material must be suitable for cooking edible, solid or liquid substances, i.e. it must tolerate temperatures in the order of some hundreds of Celsius degrees without releasing substances harmful to health.

When an induction cooker is switched on, i.e. the magnetic field is activated, induced currents inside the insert 1 heat the substances contained in the kitchenware 4. In other words, the insert 1 confers ferromagnetic and electrical conductivity features to the kitchenware 4, thus making it suitable for induction cooking and preserving at the same time the features peculiar to its constituent materials .

The insert 1 allows converting the energy of the magnetic field into heat and replacing traditional sources, such as gas or electric cookers, in the interest of safety.

The present invention also relates to a method for making a kitchenware 4 for induction cooking. Such a method comprises the steps of:

- preparing an insert 1 as described above;

- applying the insert 1 to a shape, mould or item;

- heating the insert 1 up to reach the softening or melting point, so that the insert 1 adheres to the surfaces of the shape, mould or item; cooling the insert 1 up to solidification and separating the manufactured product or item, with the obtained insert, from the shape or mould.

Preferably, the heating step is carried out by subjecting the insert 1 to a time-varying magnetic field to generate, in the insert 1 itself, parasitic currents dissipating the heat by Joule effect, which cooperates with the dissipative effect re-orienting the magnetic domains known in literature as hysteresis loop which is typical and characteristic of ferromagnetic materials and the cooling step is carried out by ceasing the magnetic field.

The invention further relates to a method for making a kitchenware 4 for induction cooking, comprising the steps of:

- making an insert 1 as described above;

coupling the insert 1 with an electrically insulating material by compression moulding, thermoforming, welding, injection molding, additive method, spraying or bath submersion, in order to obtain the kitchenware 4.

If in the step of making the insert the same insert 1 is expected to be provided with additional layers 3, the insulating material to which it will be coupled in the following step will be that constituting the body of the kitchenware 4, such as for example in figure 5. If instead the step of making the insert is not expected to provide the insert 1 with additional layers 3, the insulating material to which it will be coupled in the following step will constitute such additional layers 3, and the insert 1 will constitute the kitchenware 4 itself, such as for example in figure 4.

The electrically insulating material is preferably selected from: polymeric materials, glasses, fiberglasses, borosilicate glasses, porcelains, resins, ceramics, stones.

The step of making the insert 1 can provide for processing the insert 1 itself, which are adapted to improve its mechanical and/or thermal properties, such as for example the embossing.

The step of coupling the insert 1 to the insulating material can comprise the following sub-steps:

a. providing a shaping mold of the desired shape;

b. pre-heating the mold;

c. possibly placing an electrically insulating material, previously prepared, inside the mold;

d. placing the insert 1 inside the mold;

e. closing under pressure the mold;

f. extracting the obtained kitchenware 4.

In particular, step c is carried out to obtain kitchenware 4 such as those of figure 5, i.e. provided with a body or at least one portion made of insulating material. In other words, the insulating material that will constitute the body of the kitchenware 4 of figure 5, is loaded in the mold together with the insert 1, so that to obtain the embedding of the insert 1 in the kitchenware 4 during the molding of the kitchenware 4, rapidly, simply and cheaply.

On the contrary, if kitchenware 4 such as those of figure 4 is desirably obtained in which the insert 1 itself constitutes the kitchenware 4, step c is not carried out. In such a case, the molding serves to couple the film 2 and additional layers 3 and to give the desired shape to the kitchenware, rapidly, simply and cheaply.

If you would like to make additional layers 3 made of materials having very high melting temperature, such as for example borosilicate glass, then the method for making a kitchenware 4 will comprise the following steps of:

- making a film 2 ;

- coupling at least one additional layer 3 to said film 2 by welding;

- coupling the so obtained insert 1 to an electrically insulating material by thermoforming, in order to obtain the kitchenware 4.

In other words, the step of making the insert 1 is carried out by making the film 2 and subsequently weld- coupling the additional layers 3, whereas the step of coupling an insulating material is carried out by thermoforming .

The welding is preferably an ultrasonic and under vacuum bonding.

An illustrative and not limitative example of how an insert 1 can be prepared follows:

- preparing the film 2 by using an alloy comprising between 98% and 99% aluminum and between 1% and 2% iron;

- optionally, embossing the film 2 ;

- coupling two additional layers 3 made of polymeric material, each at a surface of the film 2.

The invention refers to any kitchenware 4 obtained by one of the above described methods.

In the scope of the description above and in the following claims, all numerical quantities indicating amounts, parameters, percentages, and so on, are to be construed as preceded in all circumstances by the term "about", if not otherwise indicated. Furthermore, all ranges of numerical quantities include all of the possible combinations of maximum and minimum numerical values and all of the possible intermediate ranges, in addition to those specifically referred in the text.

Obviously, the skilled person, with the purpose of satisfying contingent and specific requirements, will be able to make further modifications and variants to the insert, kitchenware and method according to the present invention, all of which are however contained within the scope of protection of the present invention.