FR3042090A1 - HEATING DEVICE FOR COOKING APPARATUS - Google Patents

Abstract

Heating device (3) for a cooking appliance comprising a resistive platen (7) containing a metal substrate (8) and three plasma-obtained layers (9, 10, 11) which cover said substrate (8), a foil equalization (12) in contact with said metal substrate (8) of the resistive platen (7), and an insulating element in contact with said three layers (9, 10, 11) obtained by plasma method.

Description

Technical field and state of the art

The present invention relates to the field of food cooking appliances and relates, in particular, to a device for heating such a cooking appliance. The invention more particularly relates to heating devices which incorporate a heating element comprising an electric circuit fixed on a metal substrate by plasma method.

One way of cooking food is to heat a cooking chamber with a hotplate. Controlling the rise in temperature and obtaining a homogeneous heat in the cooking chamber is often difficult to achieve in this way. Known systems propose a device incorporating a heating plate fixed directly on the bottom of the enclosure to be heated. The major disadvantage attributed to such systems is their poor durability, because they are subject to high heat losses and must be maintained at high temperatures that cause irreversible damage.

Patent FR 2 938 416 discloses a heating element fixed directly in contact with the bottom of a pan made of a multilayer material. The heating element has a heating element layer containing a plurality of heating resistors made by a printing process, a mica layer and a pressure plate. The heating element must not include an equalizing layer, such as a graphite plate, between the heating element layer and the bottom of the pan. The absence of such an equalization layer is detrimental to optimal heat transfer, and is not compatible with the manufacture of heating resistors obtained by plasma process with deposition of several layers for which it is necessary to correct the irregularities. of surfaces.

Description of the invention

The object of the present invention is to overcome all or part of these disadvantages and to propose a heating device for a cooking appliance, in particular for a cooking cooking appliance, comprising a resistive plate containing a metal substrate and three layers obtained. by plasma process which cover said substrate, an equalizing sheet in contact with said metal substrate, and an insulating element in contact with said three layers obtained by plasma process.

Thus, the part of the device that fulfills the function of heating resistance integrates at least three layers obtained by plasma process. Each of these three layers plays a specific role: the layer directly deposited on the substrate electrically isolates the second layer which covers it. This second layer has a role of temperature rise Joule effect, and it supports the third layer which covers the entire and whose role is to provide electrical insulation.

The term "plasma process" in the sense of the present invention is a process made from thermal projections of different powders (in English "thermal spray") on a substrate. The plasma process used in the context of the present invention is more particularly the blown arc plasma method, which implements the use of air at atmospheric pressure as a projection medium, and which is described as APS (of the invention). English "Atmospheric Plasma Spraying"). Such a method provides resistive layers for receiving an electric current to generate heat by causing a rapid rise in temperature of a food warming surface. In the following description, the layers obtained by plasma process will be called "plasma layers".

Such a resistive platinum obtained by plasma process is advantageously thin, which guarantees a low thermal inertia and corresponds well to the requirements of temperature control for cooking food. The combination of the resistive platinum and the equalization sheet makes it possible to optimize the heat transfer. This equalization sheet has a high heat transfer capacity which allows the resistance to exchange the best with the bottom of the container to be heated, and because of its ability to crush, to fill the imperfections of flatness and roughness of the two parts coming into contact.

Thanks to the insulating element, the heat generated by the resistive plate is redirected towards the bottom of the container to be heated and thermal losses are avoided.

The equalizing sheet is preferably made of graphite, and has a preferred thickness of 0.1 to 2 mm. This material is a stable form of carbon that is able to keep its heat transfer material properties at temperatures close to 400 ° C and not to deteriorate over time despite significant thermal variations. Graphite is a flexible material with a low shore hardness (defined by the ISO 868 standard) and absorbs well the imperfections of the substrate. Graphite is inert and therefore perfectly meets heat dissipation requirements, and its black color gives it increased emissivity. The advantage of applying graphite in the form of a sheet is that it is easy to cut and easy to position.

To channel the heat source towards the bottom of the container to be heated, the insulating element is an insulating sheet of mica. This insulating material withstands high temperatures thanks to its calorific value.

Advantageously, the metal substrate of the resistive platinum is stainless steel or aluminum. These materials have the rigidity adequate for the desired use, and have sufficient thermal resistance to support the plasma process.

Advantageously, the total thickness of the three plasma layers of the resistive platinum is less than 1 mm, preferably less than 0.7 mm, or even less than 0.5 mm. Such thickness ranges guarantee a low thermal inertia and correspond well to the requirements of temperature regulation for cooking food.

The heating device according to the invention advantageously comprises a dimensionally stable metal stiffener. Said stiffener is advantageously a rail with a section having the shape of a "W", which shape provides a great mechanical inertia and makes it dimensionally stable. The creation of air gaps harmful to thermal transfer is thus avoided, and a uniform plating over the entire pressure surface is ensured. The stiffener can be placed in direct contact with the insulating element and is intended to allow the heating device to be fixed in compression on the bottom of a food container.

In the stiffener, at least one bore adapted for the passage of a threaded rod is advantageously provided to ensure a pressurization on a support reliably.

The present invention also relates to a heating assembly of a cooking appliance comprising a heating device as described above in the context of the invention and a bottom integrated in the base of the enclosure of said cooking appliance intended to contain food. The bottom is brought into contact with the equalizing sheet of the heating device.

The bottom is advantageously a stainless steel with a thickness of 5 to 15 mm. The heating device according to the invention is particularly suitable for heat transfer on the monometallic bottoms despite a reduced thermal conductivity. Stainless steel is particularly advantageous for the intended application because it is a food material.

As seen above, the stiffener advantageously comprises bores adapted for the passage of threaded rods. A fixing by screwing on the bottom of the heating assembly can thus be provided and allow compression of the heating device on said bottom.

The bottom advantageously comprises threaded rods adapted to cooperate by screwing with nuts optionally with washers. The heating device can thus be easily clamped to the bottom of the enclosure of the cooking appliance. Clamping is advantageously carried out using eight threaded rods integral with the bottom to be heated. The clamping is intended to strongly and uniformly plating the different layers of the heater on the bottom. The creation of air gaps harmful to thermal transfer is avoided.

BRIEF DESCRIPTION OF THE FIGURES Other features and advantages of the invention will become apparent in the light of the detailed description which follows, made on the basis of the accompanying drawings. These examples are given in a non-limiting manner. The detailed description is to be read in conjunction with the accompanying drawings in which: - Figure 1 shows a perspective view of an exploded embodiment of a heating assembly according to the invention; - Figure 2 shows a sectional view of the resistive plate of a heating device according to the invention or are shown in particular the superposition of the three plasma layers; - Figure 3 shows the resistive plate provided with three electrical outlets for operation in three-phase mode; and - Figure 4 shows a detail seen in section of the device according to the invention at the stiffeners.

Description of Embodiments of the Invention

Figure 1 shows an embodiment, in exploded configuration, of a heating assembly 1 incorporating a bottom 2 of a food cooking vessel and a heating device 3 which must be mounted on the bottom by screwing.

The bottom 2 is a metal support made of stainless steel (or stainless steel) with a thickness of between 5 and 15 mm. Stainless steel is a food material compatible with the heating of food for consumption. The stainless steel used has an increased conductivity and a low coefficient of expansion. The stainless steel used is duplex steel, a term used to designate a steel category belonging to the family of ferrito-austenitic or austenitic-ferritic steels. Duplex stainless steels are advantageously used in this context in particular because they have a high capacity for corrosion resistance.

The bottom 2 comprises eight threaded rods 4 (four of which are shown in FIG. 1) uniformly distributed over the face of the bottom intended to be pressed onto the heating device 3. The eight threaded rods 4 must receive nuts 5 and their washers 6 by their ends, in order to compress the heating device 3 on the bottom 2.

The heating device 3 for a cooking appliance comprises a resistive plate 7 containing a metal substrate 8 made of stainless steel or aluminum. The resistive plate 7 also comprises three layers 9, 10 and 11 obtained by plasma process which cover the metal substrate 8 (see FIG. 2). The three plasma layers 9, 10 and 11 have a total thickness of 0.5 mm. Each of these three layers plays a specific role: the layer 9 directly deposited on the substrate electrically isolates the second layer 10 which covers it. This second layer 10 has a role of temperature rise Joule effect, and it supports the third layer 11 which covers the entire and whose role is to provide electrical insulation.

A graphite equalizing sheet 12, 0.1 to 2 mm thick, is pressed into contact with the substrate 8. An insulating element, in the form of a mica sheet 13, is applied in contact with the three layers plasma 9, 10 and 11 of the resistive plate 7.

A metal stiffener 14, integrates with the heating device 3 to allow a firm clamping hold and a uniform compression of all the elements of the device on the bottom. The stiffener 14 is advantageously a rail whose section has the shape of a "W", as can be seen in Figure 4, which form provides a great mechanical inertia and makes it dimensionally stable. Indeed, this specific form can effectively plaster the elements on the bottom of the device while leaving flexibility for the expansion of the different layers. Thanks to the "W" stiffener, the creation of air gaps harmful to thermal transfer is avoided.

In the stiffener, at least two bores 15 adapted for the passage of threaded rods 4 of the bottom 2, are formed. The complete tightening is ensured by means of the nuts 5, and their washers 6, in brass in order to avoid seizing. The various heating cycles to which the assembly is subjected cause successive expansions conducive to causing seizure, jam that must be avoided to promote disassembly for maintenance of the equipment.

Figure 3 shows three electrical outlets 18 of the heater assembly for operation in three-phase mode. Each socket 18 is connected to a plasma layer 10 interposed between two other plasma layers 9, 11.

Nomenclature (1) heating assembly (2) bottom of a cooking vessel (3) heating device (4) threaded rod (5) nut (6) washer (7) resistive plate (8) metal substrate (9, 10 , 11) plasma layers (12) equalizing sheet (13) mica sheet (14) metal stiffener (15) bore (18) electrical socket

Claims (10)

A heating appliance (3) for a cooking appliance comprising a resistive platen (7) containing a metal substrate (8) and three plasma-obtained layers (9, 10, 11) which cover said substrate (8), a foil equalizer (12) in contact with said metal substrate (8) of the resistive platen (7), and an insulating element in contact with said three layers (9, 10, 11) obtained by plasma method. 2 heating device (3) according to claim 1, characterized in that the equalization sheet (12) is graphite. 3 heating device according to one of claims 1 to 2, characterized in that the insulating member is a mica sheet (13). 4 Heating device (3) according to one of claims 1 to 3, characterized in that the metal substrate (8) of the resistive plate (7) is stainless steel or aluminum. Heating device (3) according to one of claims 1 to 4, characterized in that the total thickness of the three plasma layers (9, 10, 11) of the resistive plate (7) is less than 1 mm, of preferably less than 0.7 mm. 6 heating device (3) according to one of claims 1 to 5, characterized in that said device comprises a metal stiffener (14) dimensionally stable. 7 Heating device (3) according to claim 6, characterized in that the metal stiffener (14) comprises a bore (15) adapted for the passage of a threaded rod (4). 8 heating assembly (1) of a cooking appliance comprising a heating device (3) according to one of claims 1 to 7, and a bottom (2) integrated in the base of the enclosure of said cooking appliance for to contain food, which bottom (2) is in contact with said equalizing sheet (12). 9 heating assembly (1) according to claim 8, characterized in that the bottom (2) is a stainless steel with a thickness of 5 to 15 mm. 10 heating assembly (1) according to one of claims 8 or 9, characterized in that said bottom (2) comprises threaded rods (4) adapted to cooperate by screwing with nuts (5).