FR2763463A3 - Heating food vessel - Google Patents

Abstract

The food vessel such as a plate is able to keep food warm by the action of induced currents (I). The plate stands on a support which comprises a battery and a high speed chopping device to produce current pulses in a coil. The current pulses cause a varying magnetic field (B) to travel through the plate and induce eddy currents (I). The plate is made from a conducting and ferromagnetic material and is covered with a metallic oxide enamel to provide hardness and durability. The induced currents are encouraged to travel along designed paths by grooves (12) in the conducting and ferromagnetic core also by the addition of conducting paths formed by copper deposition.

Description

 The present invention describes a process for producing a food container such as a plate, flat, hollow, dessert or starter, or such as a dish, having the characteristic of keeping the food it contains hot, throughout the duration of the meal, thanks to the joint action of a device for heating a culinary container described in French patent application No. 96 14 475 of 26 11 96.

This device for heating a culinary container such as a plate or a dish, placed on a table, with a view to keeping the food contained in said container warm, is characterized in that it comprises
- a container support, such as a tray or a table set, in which are arranged a power module comprising a rechargeable battery, a high frequency current chopper supplied by said battery and at least one low flat inductor thickness fed by the chopper and creating an electromagnetic field perpendicular to the plane of the table, and
- a flat armature of small thickness consisting of turns closed on themselves and placed in the container parallel to the plane of the table,
- The container being placed on the support and the armature being magnetically coupled with the inductor so that eddy currents flow in the armature.

 According to the invention, and as a main characteristic, it is therefore agreed that the bottom of the container is traversed by eddy currents induced by its support, and therefore that the container comprises a conductive material in which these currents are propagated.

 According to a second original characteristic of the invention, the container confines the lines of the magnetic field and optimizes the inductive coupling with its support.

 Thus, the bottom of the container also comprises a material permeable to the magnetic field, called ferromagnetic.

 According to a third characteristic of the invention, the container guarantees all the standards of hygiene, resistance to heat, to chemical attack and to scratches that a plate or a dish usually respects. To do this it will present a surface of vitrified and inert aspect, of great hardness resistant to intense thermal shocks, abrasion and blows.

 Finally, this container will present the aesthetic appearance of a usual plate or a usual dish, provided where appropriate with patterns and decorations.

 A container made of a pressed sheet of an alloy or a conductive and ferromagnetic metallic sandwich, covered with a vitrified enamel of food quality constitutes a first example of achievement of the criteria set forth, according to a process at moderate cooking temperature: around 900.

 Indeed, a metal container covered with food enamel resists blows and abrasion well, it is almost unbreakable, it is chemically inert, and easily receives pigmented decorations useful for aesthetics.

 A metal sheet made of an alloy or a sandwich has ferromagnetic properties if it contains iron, with a low carbon content, nickel and cobalt.

 Such a sheet is intrinsically conductive, but it is also possible to strengthen the conductivity by depositing copper or brass on the surface if necessary, without compromising its ferromagnetism.

 An example of such a container is made from a sheet of decarburized iron, pure iron, an alloy of iron and nickel or else an alloy of iron of nickel and cobalt, stamped to the shape of the desired container.

 This sheet can be covered with a chemical deposit of nickel used for hanging the enamel.

 In the case where a reinforcement of the conductivity is necessary, a prior deposit of copper or brass, itself covered with nickel, provides this reinforcement.

 For a plate, a thin sheet, about 0.1 to 0.3 mm, has little effect on its weight and its thermal capacity, which is recommended.

 The enamel of such a container is then preferably a “white titanium” which is a particularly hard and resistant titanium oxide. Such a food-grade enamel has the particularity of better resisting the scratches of cutlery than an arcopal, however vitrified at high temperature, of being colored by pigment, and of adhering intimately to the sheet. A thin layer has sufficient elasticity characteristics to accompany minor deformations of the sheet.

 According to the invention, the container placed on the plate or the inductor set is traversed by eddy currents, and by the induced magnetic field.

 Depending on the characteristics of the container associated with the set or the heating plate, the induced currents will circulate in the plate in indifferent directions or else according to a preferential circuit which determines the variable inductive coupling according to the rotation of the plate.

 By using a uniform ferromagnetic sheet, covered with a homogeneous and uniform conductive deposit, an attitude with invariant coupling is produced.

 By using a ferromagnetic sheet of non-homogeneous thickness, or covered with a non-uniform conductive deposit, it is easy to make the circuit allowing variable coupling.

 Indeed, a copper-plated or brass-based deposit on the sheet itself which is not very conductive creates a preferred circuit for induced currents.

 Likewise, a chemical attack or a locally thinning machining of the sheet produces insulation zones, hardly crossed by currents. These are then confined along the tracks thus delimited.

FIG. 1 describes the structure of such a sheet 11, traversed by currents I, a variable magnetic field
B, and hollowed out with a network of grooves 12 isolating preferred conduction bands.

 Note that the field B is guided in the sheet and that it does not cross a groove.

 A container made of a ferrite (ceramic comprising iron, nickel and cobalt oxides) covered with an ultra hard enamel vitrified at high temperature (1350 "C) constitutes the basis of the second embodiment of the invention.

 In fact, ferrite is a material with high magnetic permittivity used as a transformer core. It is also a ceramic fired at high temperature, resistant to very high vitrification temperatures of surface porcelain enamels used to protect plates.

 Such a ceramic is compatible with the processes for producing dishes and plates, in particular with decorations. However, it is not or not very conductive.

 Thus, the conduction of the structure will be ensured by a metallic conductive deposit made on the bottom of the container, on the back, in an area out of food contact and protected from erosion and shocks from cutlery.

 This deposit is made on the back of the container by inlaying a sheet of conductive metal, for example copper, brass, silver or aluminum.

For better attachment of the conductive metal to the base plate, it would preferably be spared vitrification enamel. The deposition of the conductive sheet can then be accompanied by its compatible protective enamel, the whole being cooked at moderate temperature (between 500 and 9000C)
Such an embodiment is not detrimental to the chemical food and resistance characteristics of the container, since only the bottom is enamelled at low temperature.

 A container produced by this process has the characteristics of conventional porcelain, but also the magnetic and conductive properties necessary for the transmission of heating power by induction.

 FIG. 2 represents a container produced by this method. Ferrite is represented at 21, it constitutes the body of the container, a porcelain enamel is deposited at high temperature on the food side at 22, a conductive metallic deposit is applied to the back at 23, itself is covered by a protective enamel 24 cooked at low temperature.

Claims (8)

Claims 1) Culinary heating container, suitable for the tray or table set heating by induction the culinary containers, characterized in that  - The container has a conductive and ferromagnetic bottom in which propagate the currents induced by the plate or the inductor set, and in which the induced magnetic fields are guided and confined.  - The surface of the container is covered with a material of great hardness, resistant to abrasion and impact, chemically inert and capable of receiving a decorative marking. 2) A container according to claim 1 characterized in that it is formed from a ferromagnetic and conductive sheet, in the shape of the container, covered with a metallic protective enamel. 3) A container according to claim 2 characterized in that the sheet contains iron or nickel or cobalt, and in that the enamel is a titanium oxide. 4) A container according to claim 3 characterized in that a conductive deposit on the surface of the sheet strengthens the conduction and performs a circuit for receiving the induction. 5) A container according to claim 4 characterized in that the conductive deposit is made of copper. 6) A container according to claim 3 characterized in that the sheet has a network of grooves isolating preferred conduction bands which provide an electrical circuit adapted to the induction transmitted by the tray or the table set. 7) A container according to claim 1 characterized in that the ceramic which constitutes it is a ferrite having a high magnetic permittivity, first covered on the food side with a porcelain enamel fired at high temperature and then on the back by a sheet of '' a conductive metal covered with a protective enamel cooked at moderate temperature. 8) A container according to claim 7 characterized in that the metal sheet is machined or undergoes a chemical attack (Figure 1).