US3745290A

US3745290A - Inductively heatable utensils or vessels for heating,serving and storing food

Info

Publication number: US3745290A
Application number: US00230892A
Authority: US
Inventors: J Harnden; W Kornrumpf
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-03-01
Filing date: 1972-03-01
Publication date: 1973-07-10
Anticipated expiration: 1990-07-10

Abstract

Disclosed herein are various single wall and double-walled inductively heatable vessels for heating, serving and storing food. In general, each vessel is comprised of an inductively heatable inner part, or inner section, and an outer part, or outer section, which is not inductively heatable. For example, immediately after the vessel and food contained therein has been inductively cooked, or heated, on an induction appliance, the vessel may be rested directly on the surface of a conventional dining table without fear of burning the surface of the dining table and without fear that any of the diners will burn themselves by touching the outer part of the vessel. Such fears are abated because only the non-heated outer part of the vessel which is near room temperature touches the dining table and is safely accessible to the diners. The inductively heatable inner part, or section, of the vessel may be comprised of a vapordeposited metallic coating, metallic foil or sheet composite thereof, embedded powdered metal or coiled wires while the nonheated outer part or section may be comprised of suitable thermal insulation material such as plastics, glass, or ceramics, etc.

Description

United States Patent 1 Harnden, Jr. et a1.

[ 3,745,290 July 10, 1973 4] INDUCTIVELY IIEATABLE UTENSILS OR VESSELS FOR HEATING, SERVING AND STORING FOOD [75] Inventors: John D. Harnden, Jr., William P.

Kornrumpf, both of Schenectady, N.Y.

[73] Assignee: General Electric Company,

Schenectady, NY.

[22] Filed: Mar. 1, I972 [21] Appl. No.: 230,892

[52] US. Cl. 219/1049, 219/1067, 220/9 F,

[51] Int. Cl. 1105b 1/02 [58] Field of Search 219/1049, 10.75,

219/1079, 10.67; 13/27; 126/390; 220/9 F, 63, 64, 55 D, 55 E, 55 F, 55 G, 94

[56] References Cited UNITED STATES PATENTS 3,530,499 9/1970 Schroeder 219/1049 3,265,851 8/1966 Schroedcr.... 219/1049 X 3,155,304 11/1964 Beerend 220/64 X 3,623,630 11/1971 Rode 220/64 2,625,242 1/1953 Reed 219/1049 3,078,006 2/ 1963 Price et a1 220/64 3,599,575 8/1971 Yurkoski et 220/9 F X 1,680,595 8/1928 Davis 219/1075 X 3,391,823 7/1968 Tijms 220/64 X Primary Examiner-J. V. Truhe Assistant Examiner-B. A. Reynolds Att0rney-.lohn F. Ahern et a1.

[57] ABSTRACT Disclosed herein are various single wall and doublewalled inductively heatable vessels for heating, serving and storing food. In general, each vessel is comprised of an inductively heatable inner part, or inner section, and an outer part, or outer section, which is not inductively heatable. For example, immediately after the vessel and food contained therein has been inductively cooked, or heated, on an induction appliance, the vessel may be rested directly on the surface of a conventional dining table without fear of burning the surface of the dining table and without fear that any of the diners will burn themselves by touching the outer part of the vessel. Such fears are abated because only the nonheated outer part of the vessel which is near room temperature touches the dining table and is safely accessible to the diners. The inductively heatable inner part, or section, of the vessel may be comprised of a vapordeposited metallic coating, metallic foil or sheet composite thereof, embedded powdered metal or coiled wires while the non-heated outer part or section may be comprised of suitable thermal insulation material such as plastics, glass, or ceramics, etc.

15 Claims, 13 Drawing Figures Patented July 10, 1973 3 Sheets-Sheet .L

Patented July 10, 1973 3,745,290

3 Sheets-Sheet :11

Patented July 10, 1973 3 Sheets-Sheet :3

INDUCTIVELY HEATABLE UTENSILS OR VESSELS FOR HEATING, SERVING AND STORING FOOD CROSS-REFERENCES TO RELATED APPLICATIONS A general application of induction cooking, or heating, is to be had by referring to the following US. Pat. applications: Ser. No. 200,526, filed Nov. 19, 1971, in behalf of David L. Bowers et al., titled SOLID STATE INDUCTION COOKING APPLIANCES: Ser. No. 200,424, filed Nov. 19, 1971, in behalf of JD. Harnden, Jr. et al., titled SOLID STATE INDUCTION COOKING APPLIANCES AND CIRCUITS. The entire right, title and interest in and to the inventions described in the aforesaid patent applications, as well as in and to the aforesaid applications, and the entire right, title and interest in and to the invention herein described, as well as in and to the patent application of which this specification is a part, are assigned to the same assignee.

BACKGROUND OF THE INVENTION The subject invention pertains, in general, to utensils, or vessels, which are inductively heatable by a changing magnetic field; and, in particular, to an inductively heatable utensil, or vessel, which may be used for cooking or warming food contained therein as well as for serving and storing heated food.

Conventional cooking utensils or vessels, hereinafter described, are used for cooking or warming food on conventional electric or gas ranges. The conventional electric range has exposed resistance heating elements which can be electrically energized to such a degree that they often glow to incandescence. The conventional gas range uses open flames. In both kinds of ranges the primary heat source (resistance heating elements or open flames) and the cooking vessel are in fairly intimate contact so that heat transfer between the primary heating source and the vessel occur by the processes of conduction and radiation.

Also, a recent innovation in electric cooking has been the introduction of a so-called glass-ceramic electric range with which glass-ceramic vessels, or cookware, are to be used. In the glass-ceramic electric range, electrical resistance heating elements are embedded in a glass-ceramic counter, or cooktop, which has a smooth optically-flat surface on which there is supported a glass-ceramic cooking vessel which also has an optically-flat bottom surface. The optically-flat bottom surface of the cooking vessel is in such close contact with the optically-flat surface of the counter, or cooktop, that they are said to be mated. Heat transfer between the cooktop and the vessel occurs by the process of conduction.

Except for handle portions conventional cooking utensils or vessels (e.g., pots, pans, etc.) are made almost entirely of cast iron, stainless steel, aluminum, copper, copper-cladded stainless steel or aluminumcladded stainless steel, etc. Suffice it to say that a metal, or alloy, having high thermal conductivity is used.

Conventional cooking vessels or utensils as cited above as well as those made of glass and ceramic, especially when used in conjunction. with conventional cooking ranges, have some objectionable limitations, or deficiencies, among which are the following: l The exposed accessible outer surfaces of the conventional vessel get hot; e.g., often as hot as 450 F and sometimes hotter. (2) The exposed accessible outer surface of the conventional vessel or utensil gets too dirty. (3) The exposed accessible outer surface of the conventional vessel often gets scratched or otherwise permanently marked; e.g., by abrasion from the heater elements or grids on the counter of the conventional ranges. (4) The conventional vessel does not efficiently retain heat for sufficiently long periods of time to enable the conventional vessel to be employed for keeping stored foods warm for relatively long periods of time. (5) The conventional vessel does not heat up rapidly enough; nor, of course, does the food contained therein. (6) Because of the nature of the heat transfer process (conduction) intimate contact between the vessel and the primary heating source is helpful, especially for ranges with electrical heating elements.

Also, the glass-ceramic vessels, or utensils, when used in conjunction with the glass-ceramic electric range, are subject to most of the same objectionable limitations, or deficiences, hereinbefore set forth. Moreover, when conventional cooking utensils or vessels are used in conjunction with any induction cooking range, some of the foregoing objectionable limitations apply to some degree.

The first objectionable limitation, hereinbefore stated, relates to the temperature of the exposed outer surface of the conventional vessel or glass-ceramic ves sel. Often, the surface temperature reaches 450 F or higher. Such elevated temperatures are reached because of, inter alia, the nature and proximity of the primary heating source, the construction of the vessel and the conduction method of transferring heat between the primary heating source and the vessel. Because of the elevated temperature of the outer surface of the vessel, it cannot be safely handled, except with insulated pot holders; and it cannot safely be placed on a dining table and used as a serving vessel. It would burn the surface of the dining table, as well as serving to cool the vessel by accelerated heat transfer to the table or support means. A dining table is not ordinarily designed to withstand such high temperatures. In addition, the presence of such a vessel having an exposed accessible surface at such elevated temperatures would present a hazard to persons at the dining table, especially children.

The second objectionable limitation, hereinbefore stated, relate to the fact that the exposed outer surface of the conventional vessel or glass-ceramic vessel tends to get intolerable dirty. When the conventional vessel is used in conjunction with an electric range or a gas range food spilled on the very hot outer surface of the vessel burns, or chars, on the outer surface. On the outer surface the burned or charred food often becomes tacky or sticky. In the event that the conventional vessel is used on a gas range and exposed to open flames carbon black is deposited on the outer surface of the conventional vessel. Because the outer surface of the conventional cooking vessel or glass-ceramic vessel tends to get dirt accumulated thereon in the manner hereinbefore described, their use on a dining room table as serving vessels is precluded. Tacky or charred food and accumulated carbon black would certainly be transferred from the outer surface of the vessel to the table top or tablecloth thereby soiling the surface.

The third objectional limitation, hereinbefore stated, is that neither the conventional vessel nor the glassceramic vessel efficiently retains heat for sufficiently long periods of time to keep stored foods warm. That is to say: in the absence of heat being transferred to the vessel, such as when it is on top of a range, the vessel and the contents thereof cool at a relatively rapid rate.

The fourth objectionable limitation, hereinbefore stated, is that neither the conventional vessel nor the glass-ceramic vessel heat up rapidly enough; nor, of course, does the food contained therein. Such a relatively slow rate of heating up is largely due to the construction of the vessel and to the inefficient method of transferring heat between the conventional ranges primary heating source and the vessel. The conventional vessel is so constructed that it has a large mass of exposed metal which must be heated and this takes a relatively long period of time. As stated hereinbefore, heat transfer takes place by conduction and radiation.

The fifth objectionable limitation, hereinbefore stated, is that because of the nature of the heat transfer process (i.e., conduction and radiation) very close thermal contact is desirable between the conventional ranges primary heating source and the vessel. Thus, anything which prevents close intimate contact between the source and vessel tends to frustrate good heat transfer therebetween by conduction. For example, damage to the vessel surface (e.g., a dent) tends to make heat transfer inefficient. Also irregularly aligned resistance heating elements in the conventional electric range tend to make for inefficient heat transfer. This coupled with the need for improved lateral heat conductivity results in an increasing trend to heavier and more massive vessels.

SUMMARY OF THE INVENTION Although the invention is hereinafter described and illustrated in the accompanying drawing figures as being embodied in inductively heatable vessels, or utensils, which are adapted to be used with an induction cooking range, it is, nevertheless, to be understood that such vessels may be used in conjunction with other types of induction heating apparatus such as, for example, portable counter top warming or cooking appliances such as warming trivets and the like.

One object of the invention is to provide an inductively heatable vessel, or utensil, which can be used for the cooking, warming, serving and storing of food.

Another object of the invention is to provide an inductively heatable vessel having an outer surface which does not rise to temperatures much higher than ambient or room temperature so that the vessel may, if desired, be safely handled, without insulating pot holders, and placed directly on the surface of a dining table immediately after its removal from an energized induction range or similar heating apparatus, without fear of burning the tables surface.

Another object of the invention is to provide an inductively heatable vessel having an outer surface which, because of its relatively low temperature relative to its inner surface and because of the nature of induction heating, can easily be maintained in such a clean condition that the vessel may, if desired, be placed directly on the surface of a dining table without fear or soiling the surface of the dining table after its removal from an energized induction range or similar heating apparatus- Another objectof the invention is to provide an inductively heatable vessel which is capable of efficiently retaining heat for sufficiently long periods of time so that food stored therein may be kept warm for a relatively long period of time.

Another object of the invention is to provide an inductively heatable vessel which can be heated relatively rapidly to elevated temperatures as compared with the aforementioned conventional vessels and glass-ceramic vessels.

Another object of the invention is to provide an inductively heatable vessel which, unlike the aforementioned conventional vessels or glass-ceramic vessels, need not be placed in intimate contact with a primary heating source; the vessel according to the present invention being heated inductively rather than by the process of conduction as in the case with the aforementioned conventional vessels and glass-ceramic vessels.

Another object is to provide the vessel which may be inductively heatable and have a predetermined temperature profile.

According to one illustrative embodiment of the invention there is provided an inductively heatable vessel comprising: a container made of material which has relatively poor thermal conductivity and in which no significant electrical heating current is induced when said container is subjected to a changing magnetic field, said container having an inner surface forming a cavity and an outer surface, said outer surface including at least one portion thereof which is adapted to contact a vessel supporting surface whereby said vessel may rest in a condition of stable equilibrium on said supporting surface; and, means associated with at least part of said inner surface in which electrical heating current is inducible when said container including said associated means is subjected to a changing magnetic field, said cavity including said associated means being adapted for containing food.

In accordance with another embodiment of the invention there is provided an inductively heatable vessel comprising: a container made of material which has relatively poor thermal conductivity and in which no significant electrical heating currents are induced when said container is subjected to a changing magnetic field, said container having an inner surface forming a cavity and an outer surface; a wall member covering said outer surface of said container and defining together with the outer surface of said container an enclosure for a space between said containers outer surface and said wall member, said wall member having an outer surface including at least a portion thereof which is adapted to contact a vessel supporting surface whereby said vessel may rest in a condition of stable equilibrium on said supporting surface, said wall member being made of a material which has relatively poor thermal conductivity and in which no significant heating current is induced when said wall member is subjected to a changing magnetic field; and, means associated with at least a portion of the cavity of the inner surface of said container and in which electrical heating current is inducible when said vessel including said associated means is subjected to a changing magnetic field.

One feature of the invention resides in employing an inductively heatable means in combination with the aforementioned cavity; said inductively heatable means being, for example, a vapor-deposited metallic coating or a metallic foil insert. In the alternative, powdered metal may be embedded in the container member so that when the container is subjected to a changing magnetic field electric currents circulate through the powdered metal material thus enabling sufficient heat to be produced in the cavity region of the container. In the alternative metallic wire coils may be embedded in the container so that circulating current induced therein by a changing magnetic field may generate the required heat.

Another feature-of the invention resides in spatially distributing the inductively heatable means so as to enable a predetermined temperature profile to be attained.

Another feature of the invention resides in the using of foamed plastic materials for either or both the container and wall member.

Still another feature of the invention resides in the employment of thermal insulation material or dead air or vacuum within the space defined by the wall member and outer surface of the container.

Other objects and features, as well as a fuller understanding of the invention, will appear by referring to the following detailed description, claims and drawing figures.

DESCRIPTION OF THE DRAWING FIGURES FIG. 1 is an elevation view in cross section showing an inductively heatable vessel, such as a saucepan, with a detatched lid or cover illustrative of one embodiment of the invention.

FIG. 2 is an elevation view in cross section showing a modification of the inductively heatable vessel of FIG. 1.

FIG. 3 is an elevation view in cross section showing another modification of the inductively heatable vessel of FIG. 1.

FIG. 4 is a fragmentary elevation view in cross section showing another modification of the inductively heatable vessel of FIG. 1. I

FIG. 5 is a fragmentary elevation view in cross section showing another modification of the inductively heatable vessel of FIG. 1.

FIG. 6 is an elevation view in cross section showing an inductively heatable double-walled vessel, such as a pot, with a detatched lid or cover, illustrative of another embodiment of the invention.

FIG. 7 is an elevation view in cross section showing an inductively heatable double-walled pot illustrating a modification of the vessel shown at FIG. 6.

FIG. 8 is an elevation view in cross section showing an inductively heatable double-walled pot illustrating a modification of the vessel shown at FIG. 6.

FIG. 9 is an elevation viewv in cross section showing an inductively heatable double-walled pot illustrating another modification of the vessel shown at FIG. 6.

FIG. 10 is an elevation view in cross section showing an inductively heatable double-walled pot showing another modification of the vessel shown at FIG. 6.

FIG. 1 l is a fragmentary elevation view in cross section showing a modification of the doublewalled potof FIG. 8.

FIG. 12 is a fragmentary elevation view in cross section showing a modification of the double-walled pot shown at FIG. 7.

FIG. 13 is an elevation view in cross section showing still another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Shown at FIG. 1 is an inductively heatable singlewalled vessel, or saucepan, designated, generally, by reference number 20. For purposes of clarity a lid 21, or cover, is shown detatched from the saucepan 20. The saucepan 20 is comprised of a single wall member 22 which has been formed into the shape of a container having a central cavity designated, generally, by the reference number 23. The wall member 22, forming the container, includes an annular wall section which surrounds the cavity 23. The wall member 22, forming the container, also defines an inside wall surface 24 and an outside wall surface 25. As shown in FIG. 1 the inside wall surface 24 immediately adjacent the cavity 23 while the outside wall surface 25 is more remote from the cavity 23; i.e., wall surface 25 is separated from wall surface 24 by the thickness of the material comprising the wall member 22. The cavity 23 which is bounded by the inside wall surface 24, among other things, is adapted for containing food (not shown). Attached to the outside surface 25 of the wall member 22 is a handle 26.

The wall member 22, in accordance with the invention, is fabricated from a material, or materials, having relatively poor thermal conductivity. Also, the material, or materials, are of a kind in which no significant heating currents are induced when the material is subjected to a changing magnetic field. Since the saucepan 20 of FIG. 1 is intended for use on an induction range for cooking food contained within its cavity 23 the material of wall member 22 should be able to withstand temperatures of approximately 550 F. Many materials and composite materials meeting the foregoing specifications are available. For example, plastics, epoxies, polyimides, glass and ceramics, among others, are among the many abundantly available materials. The material may be homogeneous or non-homogeneous. It may contain voids as illustrated at FIG. 4 where a cellular. foamed plastic material is employed.

As shown in FIG. 1 the inside surface 24 of the wall I member 22 is provided with a metallic coating 27 or lining. The coating 27 may be a vapor-deposited metallic coating which is bonded to the inside wall surface 24 of wall member 22. Alternatively, the coating may be a metallic foil liner or sheet 27a which may be adhesively bonded to the surface 24 or it may be an unbonded metallic foil insert formed as a cup-like insert which may be disposed of after a certain amount of use and replaced by a fresh insert.

Many materials, such as metals or alloys, may be used for the coating 27 of the liner 270. In general, the material chosen should be one in which sufficient electrical current will circulate in closed paths in the material to produce sufficient I R losses; the current resulting from the induced voltages developed in the material when the material is subjected to a changing magnetic field. The thickness of the coating 27 or liner 27a will generally depend on, among other things, the material chosen and the IR loss or dissipated heat required. Ferromagnetic materials, such as magnetic stainless steel, are among those which are suitable because they have a desirable relative magnetic permeability which is greater than unity. However, other materials such as thin aluminum foil can be used. Although vapor deposited coatings and foil liners have bee mentioned herein- 7 before, it is to be understood that other forms of coatings may be used. For example, the coating 27 may be a coating of sintered metal or alloy material. Suffice it to say that the process of induction heating is well known to those skilled in the art as are the characteristics of many inductively heatable materials including metals and alloys which are suitable for use in connection with inductively heatable cooking vessels. See, for example, the patent applications hereinbefore identified.

Food is not illustrated as being within the cavity 23 in FIG. 1 in order that the structural details of the vessel 20 may appear more prominently and, thus, more clearly. The vessel 20 (and its contents) are intended to be placed on the counter of an induction cooking range (not shown). The induction range includes an induction coil, situated under the counter, which when electrically energized from a relatively highfrequency A.C. source (e.g., ultrasonic or higher) produces a high frequency electromagnetic field which includes magnetic field and electric field components. Lines of magnetic flux pass through the metallic coating 27 or liner 27a which, in effect, functions as a short-circuited single-turn secondary winding of a transformer. As a result, voltages are induced in the coating 27, or liner 27a, and heating current circulates in the coating or liner. I R losses are dissipated as useful heat for cooking food in the cavity 23 which, as illustrated at FIG. 1, is bounded by the coating 27 or liner 27a.

Although the relative thicknesses of the coating 27, or liner 27a,,and the wall member 22 are illustrated in FIG. 1 such that the coating or liner is much thinner than wall member 22, it is to be understood that the relative cross-sectional dimensions of the coating, liner and wall member may be much different than illustrated, depending on the materials chosen for the wall member 22, the coating 27 or the liner 27a.

In the event that the coating 27 or liner 27a is of a magnetizable material (magnetic permeability greater than unity) the lines of magnetic flux created by the induction coil will tend to be denser in the magnetizable material and will tend to be less dense in the adjacent wall member 22 and in the surrounding air space. Hence a relatively more efficient heating of such material is achievable. However, non-magnetizable material such as aluminum foil can be used for the liner 27a. Such material can present sufficient electrical resistance to allow sufficient IR losses to occur. The thickness, or thinness, of the aluminum foil can be chosen to provide the required R loss.

Because the material of wall member 22 has relatively poor conductivity (i.e., is a good thermal insulation material) there will be a large temperature difference between the inner surface 24 and the outer surface 25 of the wall member 22. The inner surface 24 will be at a much higher temperature; e.g., at or near the temperature of the coating 27 or liner 27a. The outer surface 25, on the other hand, will be at or near room temperature. As a result, the vessel 20 may be placed directly on the surface 28 of a dining table. Because of the relatively lower temperature of the outside surface 25 there is no danger of damaging the surface 28. In FIG. 1 the surface 28 may represent the wood surface of a conventional dining table or it may represent a conventional tablecloth. In any event, the surface 28 will not be destroyed or damaged by excessive temperatures because the outside surface 25 of vessel 20 is, as stated before, relatively cool (at or near room temperature) whereas the coating 27 or liner 27a is at a substantially higher temperature; e.g., 450 F or higher. Also, because of the relatively low temperature of the outside surface 25 there is no danger that a person touching the outside surface 25 will be burned. In addition, if food should actually be spilled on the outside surface 25 it will not, because of the relatively lower temperatures involved, burn or char. Thus, the vessel 20 may have its outside surface wiped clean with ease and the surface 28 will not be dirtied by burned, carmelized or charred foods transferred thereto from the surface 25. Moreover, because the coating 27 or liner 27a is thermally insulated by the wall member 22 and because the lid 21 is also of thermal insulation material food located in the cavity 23 adjacent the high temperature coating 27, or liner 27a, will remain hot for a relatively long period of time.

Hence, for the foregoing reasons the cooking vessel 20 may, immediately after cooking, be placed directly on the surface 28 of a dining table. While resting on the surface 28 of the dining table, the vessel 20 may be used as a serving vessel. Also, when the lid 21 is replaced on the vessel 20 the remaining food in cavity 23 may be kept warm until such time as second servings are to be dispensed from the vessel.

Shown in FIG. 2 is another inductively heatable vessel, or saucepan, designated generally by the reference number 20A. A lid or cover such as the lid 21 (FIG. 1) is intended to be used with the vessel 20A but is not shown in FIG. 2. Since the vessel 20A shown in FIG. 2 is in many respects like the vessel 20 shown at FIG. 1 elements and portions which are common to both vessels are identified with like reference numbers. As shown, the vessel 20A is comprised of a single wall member 22 which has been formed into a container having a central cavity 23. The wall member 22 includes an annular wall section which surrounds the cavity 23. The wall member 22 which forms the container also defines an inside wall surface 24 and an outside wall surface 25. As illustrated in FIG. 2 the inside surface 24 is adjacent cavity 23 while the outside wall surface 25 is more remote from the cavity 23; the outside surface 25 is spaced apart from the inside surface 24 and from cavity 23 by the thickness dimension of the wall member 22. As suggested, the cavity 23 is adapted for the containment of food (not shown). Attached to the outside surface 25 of the wall member 22 is a conventional handle 26. The material from which the wall member 22 is formed is the same material as hereinbefore described with respect to FIG. 1.

As indicated at FIG. 2 there is embedded in the wall member 22 near the inside surface 24 thereof metallic material. The embedded metallic material is designated, generally, by the reference number 29. In vessel 20A the embedded metallic material 29 serves the same purpose as the metallic coating 27 or metallic liner 27a of the vessel 20 of FIG. 1. That is, electric heating current is inducible in the embedded metallic material 29 by the action of a changing magnetic field produced by an induction coil. The metallic material 29 may be in powder or granular form; i.e., particulate form. The metallic particles need not be totally embedded; i.e., the particles adjacent the surface 24 may be partially exposed. The particle density is greatest at that portion of the wall member 22 which is closest to the inside surface 24. This has been done so that most of the heat will be generated by the circulating currents in the region closest to the cavity 23. The particles 29 may be chosen from the same materials as hereinbefore discussed; e.g., magnetizable or non-magnetizable metallic materials such as, for example, magnetic stainless steel, aluminum, etc. As was the case with the vessel (FIG. 1) circulating currents are not induced in the wall member 22, per se, but only in the mass of metallic particles 29.

Although the relative thicknesses of the mass of particles 29 and the wall member 22 are illustrated in FIG. 2 in such a way that the overall thickness of wall member 22 is substantially greater than the overall thickness of the mass of particles 29, it is to be understood that the relative thicknesses will depend on, among other things, the materials chosen for the particles 29 and for the wall member 22.

Because the material comprising the wall member 22 is of poor thermal conductivity (or is a good thermal insulation material) there will be a large temperature difference between the outer surface of wall member 22 and that portion of the wall member 22 which contains the mass of particles 29. That portion containing the particles 29, including the inside surface 24, will be at a much higher temperature than the outside surface 25. As a result the vessel 20A like the vessel 20 of FIG. 1 may be placed on the surface 28 of a dining table immediately after cooking and while the inside surface 24, the contained food in cavity 23 and the mass of particles 29 are at a relatively high temperature. Because of the relatively low temperature of the outside surface 25 of vessel 20A, the surface 28 will not be damaged because of elevated temperatures. Moreover, because of the relatively cool temperature of the surface 25 diners seated around the dining table will not be injured by touching the vessel 20A, nor will potholders or hot mats be required for moving or lifting the vessel. Food spills coating the surface 25 can be easily and safely wiped clean without fear that the surface 25 will be marked with burned, carmelized or charred foods which, on occasion, are sticky or tacky. Hence, the surface 28 will not be dirtied by such materials adhering to the outside surface 25 of the vessel 20A. Because of the thermal insulation qualities of the wall member 22 and because a lid or cover such as the lid 21 (FIG. 1) is intended to be used with the vessel 20A food contained therein may be kept warm for a relatively long period of time. As is the case with vessel 20 in FIG. 1 the vessel 20A is adapted for use as a serving vessel when placed on a surface 28 of a dining table.

Another feature of the vessels 20 and 20A shown in FIGS. 1 and 2, respectively, is that because of the nature of the induction heating process they can be heated up relatively rapidly as compared with conventional cooking vessels, used with conventional electric and gas ranges, and glass-ceramic vessels used with the glass-ceramic electric range.

Although in FIG. 2 the mass of metallic particles 29 is shown as being more or less evenly, or uniformly, distributed within the wall member 22 near the inside surface 24 thereof, it is to be understood that a nonuniform distribution of the particles 29 may be employed. For example, a non-uniform distribution of the particles 29 may be employed for the purpose of maintaining a relatively uniform temperature over the botthe wall member 22.

tom portion of the vessel along the inside surface 24 of Shown at FIG. 3 is another inductively heatable single wall vessel 20B, or saucepan, which is a modification of the saucepans 20 and 20A shown at FIGS. 1 and 2, respectively. The vessel 20B is intended to be used with a cover or lid 21 like that shown in FIG. 1. The vessel 20B, as shown, is comprised of a single wall member 22 which has been formed into a container having a central cavity 23 which is bounded by an annular wall section. The wall member 22 forming the container also defines an inside wall surface 24 and an outside wall surface 25. As shown in FIG. 3 the inside wall surface 24 is adjacent the cavity 23 while the outside wall surface 25 is more remote from the cavity; the inside and outside wall surfaces 24 and 25, respectively, being separated by the thickness of the wall member 22. The cavity 23 is adapted for the containment of food (not shown). Attached to the outside wall surface 25 is a conventional handle 26. Like the vessels illustrated at FIGS. 1 and 2 the vessel 20B is also adapted for being rested directly on the surface 28 of a dining table. The wall member 22 is similar to the wall member 22 used for the vessel shown at FIGS. 1 and 2 and is made from the same material or materials hereinbefore discussed.

As shown in FIG. 3, there is embedded in the wall member 22 near the inside surface 24 thereof at the bottom portion of the vessel 208 a set of concentrically arranged circular metallic wires. Only the two end sections of each of the concentrically arranged circular metallic wires are shown in FIG. 3. In FIG. 3 six circular wires are illustrated. The ends of the sectioned first circular wire are designated by the reference numbers 30 and 30', respectively. The ends of the other circular wires are similarly identified by the reference numbers 31-31, 32-32, 33-33, 34-34 35-35 and 3636. Each of the embedded wires forms a closed path in which induced currents generated by an induction coil may flow and produce I R losses which are dissipated as heat. Although in FIG. 3 each of the concentrically arranged metallic wires is illustrated as being wholly embedded within the wall member 22 near the inside surface 24, it is to be understood that they need not be entirely embedded but may be partially exposed and visible at the bottom of the inside surface 24 of the vessel 203. The concentrically arranged metallic wires embedded wholly or partially in the wall member 22 may be made from the same materials as hereinbefore discussed with reference to the metallic particles 29 (FIG. 2) or the metallic coating 27 or liner 27a (FIG. 1). The concentrically arranged wires of vessel 20B serve the same purpose as hereinbefore discussed with reference to the metallic particles 29 and the coating 27 or liner 27a. The relative cross section dimension or diameter of each of the concentric wires as compared with the thickness of the wall member 22 in FIG. 3 is such that the diameter of each of the wires is but a fraction of the thickness of the wall member 22. However, it is to be understood that the relative thicknesses of the wires and of the wall member 22 will depend upon, among other things, the specific materials chosen for the wires and for the wall member 22.

The vessel 208 shown at FIG. 3 may be used in the same manner as hereinbefore discussed with reference to the use of the vessels 20 and 20A of FIGS; 1 and 2, respectively. In brief, the vessel 20B may be used for cooking food as well as for serving it from the surface 28 of a dining table immediately after removal of the vessel from an induction range. In addition, the vessel 20B may keep food contained therein warm for a relatively long period of time. Moreover, because of the nature of induction cooking and because of the construction of the vessel 2013 the concentrically arranged wires are heated up rather rapidly. As a result, the vessel 20B will be brought up to a relatively high temperature much quicker than the conventional vessel used with electric or gas ranges, and, also, much quicker than the glass-ceramic vessels employed with the glass-ceramic electric range.

FIG. 4 is a fragmentary elevation view of the vessel 20 of FIG. 1. In FIG. 4 the wall member 22 is illustrated as being fabricated from a closed cell cellular or foamed plastic material which may advantageously have a sealed smooth skin forming its inside surface 24 and its outside surface 25. It is intended that the metallic coating 27 or liner 27a be bonded or otherwise placed next to the inside surface 24 over the closed smooth skin thereon. The cellular material from which the wall member 22 is fabricated is designated generally by the reference number 22a.

FIG. is a fragmentary elevation view of a modified form of the vessel shown at FIG. 1. As shown at FIG. 5 the wall member 22 is provided with feet 22b. Advantageously, the feet 22b may be molded as an integral part of the wall member 22 when the vessel is fabricated. The feet 22b serve a decorative purpose as well as a functional purpose. Functionally, the feet 22b enable an air space to be provided between the outside surface of the vessel and the surface 28 of the table on which it rests. As a result, an even greater thermal barrier is presented to insure that the surface 28 of the dining table not receive excessive heat transferred from the vessel by conduction.

Illustrated in FIG. 6 is another inductively heatable vessel, or pot, designated generally by the reference number 40. As shown, the vessel 40 is a double-walled vessel. For purposes of clarity a lid 41 or cover is shown as being detatched from the vessel 40. The pot 40, as shown, is comprised of an outer wall member 42 which has been formed into the shape of a container having a central cavity therein. The wall member 42 includes an inside wall surface 43 and an outside wall surface 44. Located within the confines of the large central cavity of the outer wall member 42 is an inner wall member 45. The inner wall member 45 is formed into the shape of a container having a large central cavity 46. The inner wall member 45 includes an inside wall surface 47 and an outside wall surface 48. The cavity 46 of the wall member 45 is adapted for containing food (not shown). As indicated in FIG. 6 an enclosed space is defined between the outside surface 48 of inner wall member 45 and the inside wall surface 43 of the outer wall member 42. This space may be air-filled, evacutated or it may be filled with thermal insulation material. The inside wall member 45 may be secured to the outside wall member 42 by means of a suitable adhesive applied between the surfaces 48 and 43 at the upper portion of the vessel 40 near the rim thereof. In the alternative, the inner wall member 45 may be an easily removable insert to be placed within the wall member 42 as needed. It may, for example, be a disposable insert which may be replaced from time-to-time, as required. Fastened to the outside wall surface 44 of the outer wall member 42 are handles 49.

The outer wall member 42, according to the invention, is made of a material which has a relatively poor thermal conductivity or, stated another way, is made of thermal insulation material. In addition, the material of the wall member 42 is such that no significant heating currents are induced therein when the wall member 42 is subjected to a changing magnetic field. Since the vessel 40 is intended for use with an induction cooking range, the wall member 42 should be able to withstand temperatures of about 550 F Many materials and composite materials meeting the foregoing specifications are available. Plastics, epoxies, polyimides, glass and ceramics, among others, are some of the materials available. The material may be homogeneous or nonhomogeneous. It may contain voids. For example, a cellular or foamed plastic material may be employed for fabrication of the wall member 42. The lid 41 or cover is fabricated from the same materials or materials similar to those used for the fabrication of the wall member 42.

Many materials such as metals or alloys may be used for fabricating the inner wall member 45. It general, the material chosen should be one in which sufficient electrical current will flow in closed paths in the material to produce sufficient I R losses; such electrical currents attend the induced voltages developed in the material when the material is subjected to a changing magnetic field. The thickness dimension of the wall member 45 will depend upon, among other things, the material chosen and the R loss, or dissipated heat, required. Ferromagnetic materials such as magnetic stainless steel are suitable because they have a relative magnetic permeability which is greater than unity. However, other materials such as aluminum may be employed. In the vessel construction shown in FIG. 6 there will be a relatively large temperature difference between the outside surface 48 of the inner wall member 45 and the outside surface 44 of the outer wall member 42. The thickness of the wall member 42 and the thermal insulation material of which it is made and the space between the surfaces 43 and 48 constitute a high thermal impedance or thermal barrier. Thus, the wall member 45 will remain at a relatively high temperature while the outside surface 44 of the wall member 42 will be at or near room temperature. As a result, the vessel 40 may be safely placed on the surface 28 of a dining table. Hence, the vessel 40 may be used for the cooking or heating, serving and storage of food contained in the cavity 46. Since the outer surface 44 of wall member 42 is at, or near, room temperature, the surface 28 of the dining table will not be subjected to burns. In addition, diners at the table need not fear being burned because of touching the outer surface 44 of the vessel 40. Moreover, food spilled on the outside surface 44 will not burn or char thereby presenting a rather messy, sticky or tacky stain which would otherwise soil the surface 28 of the dining table. Because of the thermal barrier between the wall member 45 and the outer surface 44, food may be retained within the cavity 46 in a heated state for relatively long periods of time. In addition, because of the nature of induction cooking, the inner metallic wall member 45 will be raised to elevated temperatures rather rapidly as compared with conventional cooking vessels employed with conventional electric or gas ranges and as compared with glass ceramic vessels employed in conjunction with glassceramic electric ranges.

Shown in FIG. 7 is a modification of the vessel shown in FIG. 6. In FIG. 7 is there is illustrated an inductively heatable double-walled vessel, or pot, designated generally by the reference number 40A. A lid or cover, such as the lid 41 shown in FIG. 6, is intended to be used with the vessel 40A of FIG. 7. The vessel 40A employs the same wall member 42 as is employed with the vessel 40 of FIG. 6. The outer wall member 42 includes an inside wall surface 43 and an outside wall surface 44 which, as indicated, is in contact with the surface 28 of a dining table. Secured to the outside surface 44 of the outer wall member 42 are the handles 49. Located within the large central cavity within the outer wall member 42 is an inner wall member 50. The inner wall member 50 has been formed into the shape of a container having a central cavity 51. The wall member 50 also includes an inside wall surface 52 and an outside wall surface 53. The wall member 50 is fabricated from the same or similar materials as the wall member 42. That is, the wall member 50 is made of a material having a relatively poor thermal conductivity or one which is a relatively good thermal insulator. In addition, the material of the wall member 50 should be such that no significant heating currents are induced therein when the wall member 50 is subjected to a changing magnetic field. The inner wall member 50 may be adhesively bonded to the outer wall member42 at the upper or rim portion of the wall member 42. In the alternative, the inner wall member 50 may be a removable insert.

The inside wall surface 52 of the inner wall member 50 is provided with a metallic coating 54 or lining. The inner wall member 50 having the coating 54 on the inside surface thereof is, in effect, a different form of the vessel shown at FIG. 1. The coating 54 may be a vapor-deposited metallic coating which is bonded to the inside wall surface 52 of the wall member50. Alternatively, the coating may be in the form of a metallic foil liner 54a. The metallic foil liner 54a may be adhesively bonded to the surface 52 or it may be an unbonded metallic foil insert formed as a cup-like insert, which may be disposed of after a certain amount of use and replaced with a fresh insert. Many materials, such as metals or alloys, may be used for the coating 54 or liner 54a. In general, the material chosen should be one in which sufficient electrical current will flow in closed paths in the material to produce sufficient I R losses; the electrical currents attend the induced voltages developed in the material when the material is subjected to a changing magnetic field. Although the relative thicknesses of the coating 54 and liner 54a in relation to the thickness of the wall member 50 are indicated in FIG. 7 in such manner that the thickness of the wall member 50 is greater than that of the coating or liner, it is to be understood that the relative thicknesses of these elements will depend on, among other things, the materials chosen and on the IR loss, or dissipated heat, required. The coating 54 or liner 54a may be fashioned from ferromagnetic material such as magnetic stainless steel. Magnetic stainless steel is considered suitable because it has a desirable relatively magnetic permeability which is greater than unity. However, other materials such as aluminum may be employed. The enclosed space between the outer wall member 42 and the inner wall member 50 (i.e., the space between the surfaces 53 and 43) may be evacuated, air-filled or filled with suitable thermal insulation material.

Thus, the vessel 40A depicted at FIG. 7 may be used for the cooking or heating, serving and storing foods in the same manner as the vessel 40 or in the same manner as the vessel 20, both of which are hereinbefore described.

The vessel 40B, illustrated at FIG. 8, is the same as the vessel 40A shown at FIG. 7 with the exception that the coating 54 or liner 54a is placed on the surface 53 of the inner wall member in FIG. 8. In the embodiment shown in FIG. 8 the thickness of the wall member 50 may be reduced somewhat so that heat developed in the coating 54 or liner 540 may be more readily transferred to the contents of the cavity 51. In the embodiment shown in FIG. 8 the advantage of placing the metallic material in the space enclosed between the

wall members

50 and 42 is that heat will be retained by the vessel 40B for a longer period of time.

The vessel 40B of FIG. 8 may be used in the same manner for heating, serving and storing foods as hereinbefore discussed with reference to the

vessels

40A, 40, 20B, 20A and 20.

Shown in FIG. 9 is another inductively heatable double wall vessel, or pot, designated, generally, by the reference number 40C. The vessel 40C is intended to be used with a lid or cover, such as the lid 41 shown in FIG. 6. The vessel 40C is a modification of the vessel 40 shown in FIG. 6. The vessel 40C is comprised of the same outer wall member 42 as employed in the

vessels

40, 40A and 408. It is comprised of the same or similar materials which have been discussed hereinbefore. As indicated, the outer wall member 42 includes an inside wall surface 43 and an outside wall surface 44 which is adapted to be placed on the surface 28 of a dining table. As shown in FIG. 9 the vessel 40C is comprised of an inner wall member 55 which has been formed into the shape of a container with a central cavity 59 therein. The inner wall member 55 includes an inside wall surface 56 and an outside wall surface 57. Embedded in the wall member 55 near the inside surface 56 thereof is a mass 58 of metallic particles or granules. The wall member 55 is fabricated from the same materials as the wall member 42. That is, the wall member 55 is fabricated from thermal insulation material. The metallic particles 58 distributed near the inside surface 56 of the wall member 55 serve the same purpose as the particles 29 embedded in the .wall member 22 of vessel 20A (See FIG. 2). The metallic particles 58 may be of the same materials as were employed for particles 29 (FIG. 2). Moreover, the particles 58 may be wholly or partially embedded in the member 55 near the inside surface 56 thereof. In effect, the container formed by the inner wall member 55 is similar to the vessel 20A. The inner wall member 55 may be adhesively bonded and thereby secured to the outer wall member 42 at the rim thereof. In the alternative, the container formed from the wall member 55 may be a removable insert. The space between the outside surface 57 of wall member 55 and the inside surface 43 of the wall member 42 may be evacuated, air-filled or filled with a thermal insulation material. Thus, the vessel 40C may be used for the heating, storage and service of food in the same manner as herein discussed with reference to the

vessels

40 and 20. In addition, the vessel 40C is rapidly heated inductively as compared with conventional vessels employed with conventional electrical or gas ranges or as compared with the glass-ceramic vessels employed with the glass-ceramic electric range.

Shown in FIG. 10 is another modification of the vessel shown in FIG. 6. Shown in FIG. 10 is an inductively heatable double wall vessel, or pot, designated, generally, by the reference number 40D. The vessel 40D is intended to be used with a lid or cover such as the lid 41 shown in FIG. 6. The vessel 40D employs an outer wall member 42 similar to the wall member 42 shown in FIG. 6. The wall member 42 has an inside surface 43 and an outside surface 44 as shown. Located within the large central cavity of the wall member 42 is an inner wall member 60 which has been formed into the shape of a container having a central cavity 63. The wall member 60 forming the container has an inside wall surface 61 and an outside wall surface 62. Embedded in the wall member 60 is a set of concentrically arranged metallic wire rings. Thus, the inner wall member 60, including the set of metallic rings, is similar to the vessel B shown in FIG. 3. The wall member 60 is fabricated from the same materials, or similar materials, used for the fabrication of the wall member 42. Such materials have been discussed hereinbefore. As indicated, a concentric set of six rings is employed and in FIG. 10 only the end sections of each of the concentric rings appear as being embedded in the wall member 60. For example, the end sections 64 and 64' of one ring are shown. The end sections of the other concentric rings are designated by the reference numbers 65-65, 66-66, 67-67, 68-68 and 69-69. The relative diameter of each of the concentric rings in relation to the overall thickness of the wall member 60 is determined by, among other things, the materials chosen for the metallic rings and for the wall member as well as by the desired IR losses required. The inner wall member 60 forming the inner container may be adhesively bonded to the outer wall member 42 at the rim thereof, near the upper portion of wall member 42. In the alternative, the inner wall member 60 defining the inner container may be a removable insert. The concentric metallic rings perform the same function as the concentric rings in the wall member 22 of the vessel 20B of FIG. 3; i.e., induced heating currents circulate therein. The concentric rings may be wholly embedded within the wall member 60 or they may be partially exposed.

Thus the vessel 40D with a lid such as the lid 41 of FIG. 6 may be used for the heating, warming, serving and storing of food. In addition, the vessel 40D may be heated very rapidly relative to the prior art cooking vessels, as hereinbefore discussed. Also, the space between the inner and outer wall members 60 and 42 (between the surfaces 62 and 43) may be evacuated, airfilled or filled with thermal insulation material.

It is to be understood that the material, or elements, on which heating current is inducible to produce the required IR losses, as heat, may be appropriately distributed or arranged to provide a desired temperature profile or gradient along the surface adjacent the foodholding cavity. In FIG. 1, for example, the coating 27 (of vessel 20) may be vapor-deposited with a suitable mask so as to make coating 27 thicker at the center'and bottom of the surface 24 than at the more remote or peripheral zones, or regions, thereof. By doing so it is possible to produce a more nearly uniform temperature profile radially across the circular bottom area of the inner surface 24. The same result can be achieved in vessel 20A, FIG. 2, by selective distribution of the bulk of particles 29. Similarly, in vessel 2013, FIG. 3, the concentric rings 30-36 may be selectively sized and spaced to provide more, or less, heat loss material where desired to obtain the desired temperature profile or lateral gradient. From the foregoing discussion and the examples given, it is clear that the same or similar spatial distribution of FR loss material can be accomplished in the

vessels

40, 40A, 40B, 40C and 40D. Also, in vessel 72 of FIG. 13, hereinafter described in more detail, the thickness of wall member 74 may be varied from point to point or zone to zone to allow for the attainment of a desired temperature profile; such as a uniform one, for example.

Also, ribs (not shown) may be molded in the inside surface of the outer wall members (such as surface 43 of wall 42) to provide additional structural support for the inner containers.

The fragmentary cross-sectional elevation view shown in FIG. 11 represents a modification of the vessel 40B shown in FIG. 8. In FIG. 11 the vessel 40B has an outer wall member 42 which is provided with legs 70. The legs 70 serve at least two purposes. They provide a decorative effect and, in addition, have a functional feature; namely, an additional thermal barrier (air space) is provided between the outside surface 44 of the wall member 42 and the surface 28 of the dining table. The air space between the surfaces 44 and 48 insure the maintenance of a relatively low temperature at the surface 28.

In FIG. 12 a modification of the vessel 40A of FIG. 7 is shown in a fragmentary elevation view in cross section. Between'the surfaces 53 and 43 of the inner and

outer wall members

50 and 42, respectively, there is inserted cellular or foamed thermal insulation material designated generally by the reference number 71. Alternatively, glass fibers or the like may be used.

It is to be understood that the modifications of FIG. 11 (legs 70) and FIG. 12 (cellular or foam thermal insulation 71) may be applied to any of the double wall vessels disclosed herein. Also, if desired, the space may be evacuated entirely and the double-walled vessels formed in a manner similar to the way a vacuum bottle is constructed, with the two walls hermetically sealed. Instead of vacuum the space may be a dead air space.

Shown at FIG. 13 is a vessel designated generally by the reference number 72. The vessel 72 is comprised of a single wall member 74 of metallic material which is formed in the shape of a container having a central cavity 75 for the containment of food (not shown). The vessel 72 is provided with conventional handles 73. The vessel 72 is in the form of a pot and its wall member 74 may be magnetic stainless steel, cast iron or aluminum. The material of which the wall member 74 is made is one in which heating currents may be induced when the wall member 74 is subjected to a changing magnetic field. That is to say, the wall member 74 is one which is capable of being inductively heated in that it develops the required I R loss created by circulating currents induced therein. However, the wall member 74 is provided with a plurality of pedestals or legs such as the legs 76. The legs 76 are fabricated from a suitable plastic or other thermal insulation material. Being of thermal insulation material the legs 76 separate the wall member 74 from the surface 28 of a dining table by a large air gap, or space so that the hot wall member 74 will not burn the surface 28. Although the outside surface of the wall member 74 is hot the vessel 72 can, nevertheless, be placed on the surface 28 of a conventional dining table because of the legs 76. Without the legs 76 the vessel 72 could not be placed on the table. Moreover, a pot such as the pot 72 could not be used with the conventional electric or gas range. Nor could the pot 72 be used with the glass-ceramic electric range. The vessel 72 can, nevertheless, be used with an induction cooking range. This is so because of the nature of the induction cooking process. The legs 76 are of thermal insulation material and, in addition, they separate the outside surface of the wall member 74 from the surface 28 by providing an air gap therebetween. The air gap serves as a high thermal impedance or thermal barrier so that the vessel can be used on a conventional dining table as a serving vessel.

Although the invention has been described and illustrated in the accompanying drawings with the aid of specific embodiments thereof, it is to be understood that many changes in details of construction and in the combination and arrangements of parts and components, as well as changes in configurations and in materials, may be made without departing from the spirit and scope of the invention which is hereinafter claimed.

What is claimed is:

1. An inductively heatable vessel for cooking food, storing heated food and adaptable for use as a heated food serving vessel while supported on a vessel support means comprising: a first wall member forming a first container with a first cavity which is adapted for receiving food, said first wall member having an inner wall surface adjacent the first cavity and an outer wall surface, said first wall member being of a material in which no significant heating current is induced when the material of said first wall member is subjected to a changing magnetic field; inductively heatable means covering at least a part of the first walled members inner wall surface, said inductively heatable means being of a material in which significant electrical heating current is induced when said material is subjected to a changing magnetic field; and, a second wall member forming a second container defining a second cavity and having an inner wall surface and an outer wall surface, said second wall member being of a thermal insulation material in which no significant electrical heating current is induced when said material is subjected to a changing magnetic field, said first container being received in the second cavity of said second container such that the outer wall surface of the first wall member and the inner wall surface of the second wall member enclose a space between said first and second containers, said outer wall surface of the second wall member including a portion which is adapted to contact the vessel support means whereby said second container with said first container received therein may be supported in a condition of stable equilibrium on the vessel support means.

2. The vessel according to claim 1 wherein said inductively heatable means covering at least part of the first wall members inner wall surface is a metallic material which is a vapor-deposited coating bonded to said inner wall surface.

3. The vessel according to claim 1 wherein said inductively heatable means covering at least part of said first wall members inner wall surface is a lining of metallic material on said inner wall surface and is bonded thereto.

4. The vessel according to claim 1 wherein said inductively heatable means covering at least part of said first wall members inner wall surface is a disposable liner of metallic material positionable on said inner wall surface.

5. The vessel according to claim 1 wherein said inductively heatable means is spatially distributed to enable achievement of a predetermined temperature profile along said inner wall of said first wall member.

6. An inductively heatable vessel for cooking food, storing heated food and adaptable for use as a heated food serving vessel while supported on a vessel support means comprising: a first wall member forming a first container with a first cavity which is adapted for receiving food, said first wall member having an inner wall surface adjacent the first cavity and an outer wall surface, said first wall member being of a material of which no significant heating current is induced when the material of said first wall member is subjected to a changing magnetic field; inductively heatable means covering at least part of the first wall members outer wall surface, said inductively heatable means being of a material in which significant electrical heating current is induced when said material is subjected to a changing magnetic field; and, a second wall member forming a second container with a second cavity and having an inner wall surface and an outer wall surface, said second wall member being of a thermal insulation material in which no significant electrical heating current is induced when said material is subjected to a changing magnetic field, said first container being received in the second cavity of the second container such that the outer wall surface of the first wall member including said inductively heatable means and the inner wall surface of the second wall member enclose a space between said first and second containers, said outer wall surface of said second wall member including a portion which is adapted to contact the vessel support means whereby the second container and the first container therein may be supported in a condition of stable equilibrium on the vessel support means.

7. The vessel according to claim 6 wherein said inductively heatable means is comprised of a metallic material which is a vapor-deposited coating bonded to said outer wall surface of the first wall member.

8. The vessel according to claim 6 wherein said inductively heatable means is a lining comprising metallic material bonded to said outer wall surface of said first wall member.

9. The vessel according to claim 6 wherein said inductively heatable means in a disposable liner comprising metallic material positionable on said outer wall surface of said first wall member.

10. The vessel according to claim 6 wherein said inductively heatable means is spatially distributed to enable a predetermined temperature profile to be achieved.

11. An inductively heatable vessel for cooking food, storing heated food and adaptable for use as a heated food serving vessel while supported on a vessel support means comprising: a first wall member forming a first container with a first cavity which is adapted for receiving food, said first wall member having an inner wall surface adjacent the first cavity and an outer wall surface, said first wall member being of a material in which no significant heating current is induced when said material of said first wall member is subjected to a changing magnetic field; inductively heatable means at least partially embedded in said first wall member in the region of said inner wall surface thereof adjacent the first cavity, said inductively heatable means being of a material in which significant electrical heating current is induced when said material is subjected to a changing magnetic field; and, a second wall member forming a second container with a second cavity and having an inner wall surface and an outer wall surface, said second wall member being of a thermal insulation material in which no significant electrical heating current is induced when said material is subjected to a changing magnetic field, said first container being received in the second cavity of the second container such that the outer wall surface of the first wall member and the inner wall surface of the second wall member enclose a space between the first and second containers, said outer wall surface of the second wall member including a portion which is adapted to contact the vessel support means whereby the second container including the first container therein may be supported in a condition of stable equilibrium on the vessel support means.

12. The vessel according to claim 11 wherein said inductively heatable means is comprised of a mass of distributed metallic particles.

13. The vessel according to claim 11 wherein said inductively heatable means is comprised of a set of concentrically arranged metallic rings.

14. The vessel according to claim 11 wherein said inductively heatable means has a relative magnetic per meability greater than unity.

15. The vessel according to claim 11 wherein said inductively heatable means is spatially distributed to enable a predetermined temperature profile to be achieved.

Claims

1. An inductively heatable vessel for cooking food, storing heated food and adaptable for use as a heated food serving vessel while supported on a vessel support means comprising: a first wall member forming a first container with a first cavity which is adapted for receiving food, said first wall member having an inner wall surface adjacent the first cavity and an outer wall surface, said first wall member being of a material in which no significant heating curreNt is induced when the material of said first wall member is subjected to a changing magnetic field; inductively heatable means covering at least a part of the first walled member''s inner wall surface, said inductively heatable means being of a material in which significant electrical heating current is induced when said material is subjected to a changing magnetic field; and, a second wall member forming a second container defining a second cavity and having an inner wall surface and an outer wall surface, said second wall member being of a thermal insulation material in which no significant electrical heating current is induced when said material is subjected to a changing magnetic field, said first container being received in the second cavity of said second container such that the outer wall surface of the first wall member and the inner wall surface of the second wall member enclose a space between said first and second containers, said outer wall surface of the second wall member including a portion which is adapted to contact the vessel support means whereby said second container with said first container received therein may be supported in a condition of stable equilibrium on the vessel support means.

2. The vessel according to claim 1 wherein said inductively heatable means covering at least part of the first wall member''s inner wall surface is a metallic material which is a vapor-deposited coating bonded to said inner wall surface.

3. The vessel according to claim 1 wherein said inductively heatable means covering at least part of said first wall member''s inner wall surface is a lining of metallic material on said inner wall surface and is bonded thereto.

4. The vessel according to claim 1 wherein said inductively heatable means covering at least part of said first wall member''s inner wall surface is a disposable liner of metallic material positionable on said inner wall surface.

6. An inductively heatable vessel for cooking food, storing heated food and adaptable for use as a heated food serving vessel while supported on a vessel support means comprising: a first wall member forming a first container with a first cavity which is adapted for receiving food, said first wall member having an inner wall surface adjacent the first cavity and an outer wall surface, said first wall member being of a material of which no significant heating current is induced when the material of said first wall member is subjected to a changing magnetic field; inductively heatable means covering at least part of the first wall member''s outer wall surface, said inductively heatable means being of a material in which significant electrical heating current is induced when said material is subjected to a changing magnetic field; and, a second wall member forming a second container with a second cavity and having an inner wall surface and an outer wall surface, said second wall member being of a thermal insulation material in which no significant electrical heating current is induced when said material is subjected to a changing magnetic field, said first container being received in the second cavity of the second container such that the outer wall surface of the first wall member including said inductively heatable means and the inner wall surface of the second wall member enclose a space between said first and second containers, said outer wall surface of said second wall member including a portion which is adapted to contact the vessel support means whereby the second container and the first container therein may be supported in a condition of stable equilibrium on the vessel support means.

14. The vessel according to claim 11 wherein said inductively heatable means has a relative magnetic permeability greater than unity.