Classifications

• • A—HUMAN NECESSITIES
  • A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
  • A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
  • A47J36/00—Parts, details or accessories of cooking-vessels
  • A47J36/02—Selection of specific materials, e.g. heavy bottoms with copper inlay or with insulating inlay
  • A47J36/04—Selection of specific materials, e.g. heavy bottoms with copper inlay or with insulating inlay the materials being non-metallic
• • A—HUMAN NECESSITIES
  • A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
  • A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
  • A47J27/00—Cooking-vessels
  • A47J27/002—Construction of cooking-vessels; Methods or processes of manufacturing specially adapted for cooking-vessels
• • A—HUMAN NECESSITIES
  • A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
  • A47J—KITCHEN EQUIPMENT; COFFEE MILLS; SPICE MILLS; APPARATUS FOR MAKING BEVERAGES
  • A47J27/00—Cooking-vessels
  • A47J27/004—Cooking-vessels with integral electrical heating means

Definitions

• the present invention relates to a ceramic cooking utensil. More particularly, the present invention relates to a ceramic vessel for induction heating.
• the field of the invention is that of ceramic cookware.
• the object of the invention is to provide a ceramic cooking utensil capable of being heated by induction, and having improved resistance to expansion and / or deformation, while maintaining a good continuity of the currents induced in the bottom.
• EP 0 695 282 discloses a solution for using the ceramic containers on the induction plates.
• this document proposes to deposit on the bottom of a ceramic container by painting, screen printing or decalcomania, a thin layer of material having electrically conductive properties and / or magnetic properties leading to the production of heat by exposure to an electromagnetic field.
• EP 0 695 282 proposes to use a metal layer based on silver powder, knowing that silver is known for its resistance to hot oxidation.
• silver as the base of the metal layer to produce heat through exposure to an electromagnetic field, is not obvious.
• silver like copper is known as "diamagnetic".
• yield is a ratio between the power delivered by the induction plate and the heating power obtained. Ferromagnetic metals, such as iron, nickel, cobalt or ferritic steel, have in particular a sufficiently high magnetic susceptibility to obtain a satisfactory yield.
• EP 0 695 282 does not describe the yield obtained with a metal powder-based silver layer.
• the following publications are known that deal with the magnetic properties of silver:
• “Sintered” can acquire unexpected magnetic properties, close to those of ferromagnetic metals, when subjected to an intense magnetic field, substantially greater than 1 Tesla.
• the inductors used in the induction plates generate a magnetic flux, such as the induced currents, which are predominant over a part of the layer. metallic and not important elsewhere. Having a nonhomogeneous heat flow can cause thermal shock between the hot spots and the cold spots of the ceramic container, which can cause it to break. Indeed, ceramic materials are quite sensitive to thermal shock and mechanical stress due to their low elasticity.
• the invention is precisely intended to meet this need while overcoming the disadvantages of the techniques described above.
• the invention provides a cooking utensil for use on an induction plate, having a very good thermal conductivity for optimum use and being relatively simple to achieve.
• the invention provides a cooking utensil comprising a ceramic container and a bottom obtained from a paste containing silver powder. Said bottom is deposited outside the base of the container.
• a mastery of the design and sizing of the bottom allows to obtain, with the current cooking plates, a heating power suitable for cooking over high heat.
• the geometry of the deposit is determined so as to optimize the magnetic properties of the silver deposit by homogeneously distributing the heating power delivered by the induction plate.
• the thickness of the deposit is defined according to the desired heating power.
• the coefficient of expansion of the container is very low.
• the utensil of the invention has a silver powder base for use on induction systems and good heat conduction.
• the variation of the deposit width disposed on the set of the outer base of the container allows rapid heat spread to the entire container.
• the invention thus relates to a cooking utensil comprising a ceramic container, said utensil comprising on an outer base of the container a coating layer based on silver powder,
• the layer is deposited in a geometrical shape configured so as to optimize the magnetic properties of the silver powder by homogeneously distributing on the container a heating power delivered by the induction plate,
• a thickness of the layer is defined as a function of the maximum heating power to be reached by the base of the container.
• the geometric shape comprises a succession of protuberances of the layer based on silver powder.
• a local width of said protuberances of the layer is defined as a function of the local magnetic field. In this way, it is possible to locally modulate the heating power.
• the geometric shape further comprises a succession of air channels. Said air channels are delimited by two consecutive protuberances. More preferably, a bottom of said channels is formed by the outer base of the ceramic container.
• the alternation protuberances / air channels is configured so that the current induced by the induction plate circulates within the protuberances comprising the silver powder.
• the protuberances and the air channels have a shape of concentric rings or spirals around a center of the coating layer, said rings or said spirals being circular or elliptical.
• the coating layer comprises a succession of projecting point protuberances separated by the air channels.
• the outer base of the container has on its periphery a capillary barrier, said barrier comprising at least two projections in relief by relative to the coating layer, said at least two projections delimiting at least one groove.
• Such projections form a support foot which makes it possible to prevent any thermal shocks on the bottom of the container, following overflow or liquid runoff.
• This liquid, especially water, is trapped in the foot by capillarity and does not flow to the coating layer being heated.
• This foot also makes it possible to slightly elevate the utensil relative to the plate. This elevation of the utensil, for example a few millimeters, prevents marking of the induction plate.
• the ceramic is not very conducive to heat and the induction plate locally produces a very intense heat flow. This temperature may exceed 900 ° C in some areas. Such a temperature may cause a softening of the protective vitreous layer of the induction plate, which may be deformed when in direct contact with the cookware.
• the shape of the projections and the groove adapts to the shape of the periphery of the base of the ceramic container. More preferably, the projections and the groove have a concentric shape. Even more preferentially, this shape is circular or elliptical, depending on the shape of the base of the container.
• the barrier comprises three projections delimiting two grooves.
• the embodiment implementing protuberances of the coating layer may advantageously be combined with the embodiment implementing the capillary barrier. These two embodiments can also be made independently.
• the thickness of the coating layer is greater than or equal to approximately 10 ⁇ m.
• the coefficient of thermal expansion of said container is ultra-low in particular of the order of 2.10 "6 K " 1 from 20 to 200 ° C.
• the maximum heating power on the base of the container for cooking over high heat is greater than about 3 Watts / cm 2 .
• the thickness of the protuberances is greater than or equal to approximately 10 ⁇ m.
• the utensil is capable of being subjected to cooking on an induction hob.
• said utensil is also able to undergo cooking performed by cooking means other than induction, for example microwave ovens, flame or convection.
• the invention also relates to a method of producing a utensil as described above.
• the deposition of the coating layer on the base of the ceramic container is carried out by decal.
• Figure 1 shows an axial sectional view of a ceramic cooking utensil according to one embodiment of the invention.
• Figure 2 shows an axial sectional view of the cooking utensil shown in Figure 1, illustrating more precisely the outer base of this utensil.
• Figures 3 and 4 show a bottom view of a cooking utensil according to two embodiments of the invention.
• Fig. 5 is a diagram showing the relationship between the radius of a deposit on the outer base of the cookware and the heating power of three induction cookers having different diameters.
• Figures 6, 7 and 8 show another embodiment of the invention, wherein the outer base of the utensil comprises a capillary barrier.
• cooking means the possibility of cooking over high heat.
• This cooking over high heat can be achieved by means of a minimum average heat flux of the order of three Watts / cm 2 on the base of the container placed on the cooking plate.
• FIG 1 shows a cooking utensil 10 heated by an induction plate 14.
• the utensil 10 comprises a ceramic container 11.
• the ceramic container 11 may be porcelain, faience, terracotta, vitroceramic, sandstone etc ....
• the container 11 may be a hollow utensil for containing, storing or transporting any substance (liquid, gaseous or solid). It can also be a flat plate. This container 11 can take various shapes and sizes.
• the container 11 is made according to the traditional process of manufacturing ceramic objects. In order to be used effectively as a cooking utensil, the container 11 must have good resistance to thermal shock. For this purpose, the container 11 preferably has an ultra-low thermal expansion coefficient. In a preferred embodiment, the coefficient of expansion of the container 11 is of the order of 2.10 -6 K -1 from 20 to 200 ° C.
• the utensil 10 has a coating layer 12 on an outer base 13 of the container 11.
• the base 13 is preferably of planar shape.
• the layer 12 is for example made of silver powder and a binder comprising a glass powder. The amount of silver powder is much greater than that of the binder. In a preferred embodiment, the layer consists of about 90% silver and about 10% binder. Glass powder is a bonding agent that allows to fix the silver powder.
• This paste is then affixed to the container 11 according to traditional techniques in the field of ceramics.
• This layer 12 is deposited on the container 11, preferably by decal.
• the layer 12 may, in a variant, be applied by screen printing.
• the container 11 with the layer 12 is then fired at a temperature, for example of the order of 850 to 900 degrees Celsius.
• the layer 12 is advantageously covered with a uniform protective layer.
• This protective layer is essentially composed of a glass frit, colored or not.
• the layer 12 has substantially a disc-shaped outline. It may also have an outline having any other geometric shape for carrying out the invention.
• the layer 12 is deposited as a decoration in a geometry intended to optimize the properties magnetic of said layer.
• the layer 12 comprises a succession of protuberances 15 on a face 19 of contact with the induction plate 14.
• the protuberances 15 are seen here in section.
• the induction heating power is proportional to the area occupied by the layer 12 in which the current is induced. A reduction of the heating power is obtained by leaving voids in the layer 12.
• the protuberances 15 are separated by channels 17, where the air can circulate.
• the shape of the air channels 17 and the protuberances 15 define a crenellated profile of the contact face of the layer 12 with the plate 14.
• the heating power is proportional to the thickness of the layer 12, up to the thickness of the layer 12. limit of the depth of penetration of the magnetic field. In one embodiment of the invention, the penetration depth is approximately 20 ⁇ m.
• the air channels 17 form cavities each having a bottom formed by the ceramic base 13 of the container 1 1. Said air channels 17 are delimited by two successive protuberances. The protuberances 15 form protruding parts of the layer 12.
• the geometry of the layer 12 is preferably configured so that the induced current circulates, within the protuberances 15 comprising the silver powder, in a substantially tangential direction, in a cylindrical coordinate system oriented perpendicularly to the base 13 of the container 11.
• the layer 12 has a substantially symmetrical shape of revolution around a center 16 of the base 13, especially in the case where this base has a circular contour or elliptical.
• Figure 2 shows a perspective view of the axial section of the cooking utensil shown in Figure 1.
• the container 11 has a base 13 of substantially circular contour.
• the protuberances 15 are formed by a relief, continuous or not, which winds in a first spiral around a center 16 of the base 13.
• the channels 17 are in the form of a second spiral interposed between the turns of the first spiral.
• the base 13 and the spirals may have an elliptical profile rather than circular.
• Figure 3 shows a bottom view of a utensil 10 according to a variant of the invention.
• the contact face of the layer 12 with the induction plate 14 may be formed of protuberances 15 and air channels 17 in the form of concentric rings around the center 16 of the layer 12.
• the protuberances 15 and the channels 17 of air have a circular shape. An elliptical shape can also be realized.
• the contact face of the layer 12 comprises a succession of projecting point protuberances 15 separated by channels 17 of air.
• the layer 12 is in the form of a disk having spot empty spaces.
• the protuberances 15 and the air channels 17 can have all the geometric shapes that make it possible to optimize the magnetic properties of the silver powder.
• the air channels 17 also make it possible to control the thickness of the protuberances 15.
• the air channels 17 have a depth corresponding to a thickness of the protuberances 15.
• a distance such that 18 (see FIG. 2) separating two successive protuberances 15 may be variable depending on the zone of interest of the layer 12.
• a distance 18 between two consecutive protuberances 15 is constant on the layer 12.
• the width of the air channels 17 is also constant.
• the alternation of the protuberances 15 and the air channels 17 makes it possible to form a heating power divider between the coldest points, corresponding to the center and the ends of the layer 12, and the hottest points of the layer 12
• This power divider makes it possible to vary the temperature received by the protuberances so as to reduce the thermal gradients generated by the induction. This function will be explained below by the description of FIG.
• the thickness of the protuberances 15 is adjusted so as to obtain sufficient heating power. This thickness is determined so that it is substantially greater than the depth of penetration of the magnetic field generated by the induction plate.
• Table 1 below shows an example of the result obtained with these tests.
• This table shows a maximum heating power to be reached by the container according to the thickness of the silver layer. This maximum power is substantially equal to a percentage of the theoretical nominal power of the induction plate. This percentage depends in particular on the type of material of the container.
• Table 1 is obtained after several tests, for a theoretical nominal power of the induction plate of about 2800 Watts.
• the heating power obtained through the protuberances 15 is of the order of 70% of the theoretical rated power. Only when the thickness of the protuberances 15 is greater than or equal to substantially 20 ⁇ m, is observed an optimum heating power of the layer 12 of the order of 90% of the nominal theoretical power of the plate. induction.
• FIG. 5 is a diagram showing the relationship between the surface heating power expressed in Watt / cm 2 of three induction plates having different diameters and the radius of the layer 12 expressed in centimeters.
• the abscissa axis corresponds to the radius of the layer 12 and the ordinate axis to the heating power delivered by the induction plate.
• the electric field E is calculated by solving the Maxwell-Faraday equation This equation gives the rotation of the electric field as a function of the time derivative of the magnetic field:
• the magnetic field B is obtained by summation of all the turns of the induction plate, whose respective contributions are given by the law of Biot and Savart.
• Curve 30 represents this evolution for an induction plate having a diameter of 16 centimeters and a theoretical rated power of the order of 2000 Watts.
• Curve 31 represents this evolution for an induction plate having a diameter of 18 centimeters and a theoretical nominal power of the order of 2800 Watts.
• Curve 32 represents this evolution for an induction plate having a diameter of 21 centimeters and a theoretical nominal power of the order of 3100 Watts.
• FIG. 5 shows that the power delivered by the three plates around the center 16 of the layer 12 is almost zero. Since the center of the plate does not heat up, it is therefore not necessary to deposit protuberances near the center 16. As one moves further away from the center 16, the power increases.
• the heating power delivered has a bearing where it is at the maximum on the layer 12. This level is around 2.4 to 2.6 centimeters radius. The further away from this plateau, the more the power delivered decreases to zero at about 7 centimeters of radius of the layer 12.
• the heating power delivered has a bearing where it is at the maximum on the layer 12. This level is around 2.5 to 3 centimeters radius. The further away from this plateau, the more the power delivered decreases, until it is nil at about 8 cm of radius of the layer 12.
• the heating power delivered has a bearing where it is at the maximum on the layer 12. This level is approximately 2.5 to 4 centimeters radius. The further away from this plateau, the more the delivered power decreases to zero at about 9 centimeters radius of the layer 12.
• the thickness of the protuberances 15 is greater when these protuberances are deposited around the center 16. This thickness is then decreased as we approach the bearing. to be increased as we move away from this plateau.
• the number and size of the protuberances 15 on the layer 12 are determined as a function of the reduction of the desired heating power. For example, if it is desired to reduce the heating power received by layer 12 by 25%, the silver powder protrusion coverage rate on layer 12 should be about 75%.
• the protuberances 15 have a width of 1 to 10 millimeters and the distance 18 of the air channels is greater than or equal to about 0.5 millimeters.
• the particular shape, distribution and thickness of the protuberances can give rise to many variations, guided essentially by the optimization of the magnetic properties of the layer 12 and by the homogeneity of the heat flow on the container.
• the protuberances 15 and the air channels 17 are respectively twelve in number.
• the layer 12 deposited on the base 13 has an external diameter of the order of 152 millimeters.
• a central vacuum located in the center of the layer 12 has a diameter of the order of twenty millimeters.
• the invention provides a silver powder-based layer of a predetermined thickness so that sufficient heating power can be achieved for optimum use in cooking.
• the silver layer is further deposited in a geometric shape configured both to control the deposited thickness and to limit gradients on the utensil. This limitation of gradients makes it possible to preserve the integrity of the utensil and to limit the risks of charring food.
• the layer 12 may have a diameter greater than about twelve centimeters, which can reach a maximum heating power of the order of 5 to 7 Watts / cm 2 .
• the maximum power can reach 10 Watts / cm 2 .
• Figures 6, 7 and 8 show another embodiment of the invention.
• the outer base 13 of the container 11 comprises a capillary barrier 40, in addition to the layer 12.
• This capillary barrier 40 provides an improvement to the embodiments in which the outer base 13 of the container 11 is of planar shape . Indeed, in certain circumstances, this flat shape may have disadvantages.
• the ceramic is a relatively low heat conducting material compared to metals, with a conductivity of the order of 2 Wm -1 .K “1 , against for example 30 Wm " 1 .K “1 for a steel.
• the rate of heat transfer towards the contents of the container 11 is reduced.
• the bottom of said container 11, when heated by induction, may have very high temperature zones, close to 900 ° C.
• the temperature reached locally on the outer base 13 of the container 11, during its heating on the induction plate 14, can reach the softening temperature of the fusible mineral materials of the layer 12.
• the layer 12 to Silver base comprises vitrifiable mineral materials, fuse at about 900 ° C, to ensure fixation by cooking and protection of silver particles. Therefore, if there is contact between the layer 12 and the induction plate 14, it is then likely to mark said plate.
• the cooling of the ceramic is relatively slow.
• rapid passage of the container 11 from the induction plate 14, where it is being heated, to a support such as a worktop or a service table, there is a risk of burning the support, or even heat shock potentially damaging to the container 11, particularly if the support is wet.
• a capillary barrier 40 can be made.
• Figure 6 shows an example of a schematic representation of a view of the outer base 13 provided with such a barrier 40. This barrier is shown in more detail in Figures 7 and 8.
• this barrier 40 is conventionally obtained by the shape of the mold, regardless of the technique of shaping the ceramic paste, whether in particular casting or pressing.
• the barrier 40 of the invention comprises an outer protrusion 41 in the form of a relief, located near the outer wall of the container 11, delimited by a hollow formed by a first groove 42.
• the barrier 40 also comprises an intermediate projection 43, in shape of relief, delimited by the first groove 42 and by another hollow formed by a second groove 44.
• This barrier finally comprises an internal projection 45 in the form of relief, delimited by the second groove 44 and a bottom wall 46 of the container 11 intended for receive the layer 12.
• the outer base comprises a single barrier 40, the three projections 41, 43 and 45 and the two grooves 42 and 44 are annular and concentric.
• the barrier 40 shown is made on the entire outer periphery of the base 13 of the container 11, near the periphery. In this example, the barrier 40 is made about three millimeters from the periphery, so as to maximize the surface of the layer 12 and provide better stability of the container 11 on the induction table.
• the three projections 41, 43 and 45 have a height above the layer
• the container 11 bears on the plate 14 only through said projections.
• Said projections (41, 43, 45) form a support foot.
• the height of the protrusions is about 0.5 mm above the layer 12.
• zones 47 between the induction plate 14 and the top of the projections form the horizontal capillary traps.
• the trickling liquid falling at the foot of the container 11 placed on the cooking plate 14 is pumped by capillary action between said plate and said apex of the protrusions, possibly passing through the recessed zones constituted by the grooves 42 and 44.
• the barrier 40 thus allows to trap the liquid by capillarity and constitutes a watertight barrier which prevents any penetration of said liquid to the layer 12.
• the projections 41, 43 and 45 are ceramic. When heated on the induction plate 14, they remain at a moderate temperature, less than 100 ° C. These protrusions are capable of retaining the runoff liquids without undergoing thermal shock which may damage the container 11.
• the ceramic is indeed capable of withstanding thermal shocks such as soaking in water at 20 ° C. test piece previously heated to 300 ° C.
• the furrows 42 and 43 constitute, for their part, so-called vertical capillary traps. Their role is to store liquids between pumping areas. Their presence is useful especially when the container 11 is raised from the cooking plate 14. In their absence, the water which stagnates with horizontal capillary traps could be sucked up during the lifting and then trickle down to the layer 12, the horizontal capillary protection being suppressed by the simple fact of raising the utensil.
• the grooves 42 and 44 thus constitute permanent capillary traps, taking over the horizontal capillary traps constituted by the interface between the flat tops of the projections 41, 43 and 45 and the cooking plate 14, which only exist in the the container 11 rests on the cooking plate 14.
• the grooves 42 and 44 have a height h of about 2 mm.
• the dimensions of these grooves 42 and 44 are determined so that the hollow of said grooves can not be clogged, during the enameling operation that takes place during the manufacture of the utensil 10.
• the internal width Lint of the grooves 42 and 44 is for example of the order of 1.5 mm.
• the outer width Lext grooves 42 and 44 is for example of the order of 2 mm.
• the terms inner and outer mean with respect to the direction of contact of the container 11 on the induction plate 14 and the container position of the container 11.
• the lower width Lint of the grooves 42 and 44 is smaller than the outside width Lext of said grooves. This type of sizing grooves 42 and 44 facilitates the demolding of the container 11, after shaping the dough.
• the grooves 42 and 44 have a trapezoidal cross section of approximately 3.5 mm 2 in area. In other embodiments, the grooves may have a rectangular or hemispherical section.
• the dimensioning of the barrier 40 is determined so as to ensure perfect stability of the container 11 without degrading the aesthetic while allowing the formation of a capillary dam whose water retention capacity by the furrows are quite effective.
• the number of protrusions and furrows of a barrier may be different from that of the embodiment illustrated in FIGS.
• the barrier 40 may comprise a single groove 42, framed by two projections (41, 43).
• the barrier 40 may comprise more than two grooves.
• the width of the barrier 40 would then be increased, which could excessively and unnecessarily reduce the surface of the bottom wall of the container that should accommodate the layer 12.
• the layer 12 may have any geometric shape and any thickness capable of providing the container with a heating power suitable for cooking.
• the layer 12 comprises protuberances 15 and air channels 17, as shown in FIGS. 1 to 4.
• the cooking utensil obtained according to the invention can also be adapted for any other conventional cooking means than induction.
• These conventional means can be selected from microwave ovens, gas burners, radiant, oven, barbecue etc ....

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• Engineering & Computer Science (AREA)
• Food Science & Technology (AREA)
• Manufacturing & Machinery (AREA)
• Cookers (AREA)

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• 2009
  • 2009-11-06 FR FR0957863A patent/FR2952289B1/fr active Active
• 2010
  • 2010-06-10 FR FR1054611A patent/FR2952290B1/fr not_active Expired - Fee Related
  • 2010-11-08 WO PCT/FR2010/000743 patent/WO2011055043A2/fr active Application Filing
  • 2010-11-08 US US13/508,396 patent/US20120273482A1/en not_active Abandoned
  • 2010-11-08 EP EP10787821A patent/EP2496120A2/de not_active Withdrawn

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