GB2492121A

GB2492121A - Induction Cookware with polymeric contact surface

Info

Publication number: GB2492121A
Application number: GB1110559.0A
Authority: GB
Inventors: Christopher Lawson
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-06-22
Filing date: 2011-06-22
Publication date: 2012-12-26
Also published as: GB201110559D0

Abstract

The present invention relates to cookware vessels suitable for use with induction heating comprising a base 103, wherein the base comprises a ferromagnetic material such as stainless steel, cast iron or carbon steel. A contact surface 104 which in use faces one or more induction elements comprises a polymeric support layer which comprises one or more organic polymers. The organic polymer may be selected from fluoropolymers, such as PTFE or silicone polymers. The side walls of the cookware may comprise, for example, aluminium, copper or stainless steel. In use, the polymeric support layer helps prevent abrasion damage to a support surface such as a hob, stovetop or range.

Description

Induction Cookware The present invention relates to cookware vessels suitable for use with induction heating.

Induction heating is the process of heating an electrically conducting object, typically a metal, by electromagnetic induction, whereby eddy currents are generated within the electrical conductor and resistance leads to Joule heating of the electrical conductor. Heat may also be generated by magnetic hysteresis losses in materials that have significant relative permeability. An induction heater consists of an electromagnet, through which a high-frequency alternating (AC) current is passed. The frequency of AC used depends upon the dimensions of the electrically conducting object, the electrically conducting material and the coupling between the electromagnet and the electrically conducting object.

Cookware vessels have been fabricated from a variety metals, including laminations of different metals to provide selected improvements in at least one of strength, thermal conductivity, weight, and durability among other properties, without detriment to the other properties.

The use of induction heating for cooking (induction cooking) is now commonplace and gaining in popularity because it is fast, energy efficient and safer to use than direct heating methods, which utilise an open flame or hot electric heating element. For induction cooking, typically a ferromagnetic or ferromagnetic-coated cookware vessel is placed on top of a support surface of a hob, stovetop or range. The support surface typically consists of a plate of dielectric material, such as glass or glass-ceramic. The induction heating element is typically a conductive electric coil disposed beneath the support surface. The induction heating element is a usually sealed and isolated from the support surface. An AC current passed through coil produces eddy currents within the ferromagnetic material in the cookware vessel. These eddy currents within the ferromagnetic portion of the cookware vessel create heat from the resistance of the metal because of induction. This heats the remainder of the cookware vessel, but no heat is generated from the actual support surface. Various patents describe the desirability of particular materials and constructions which include one or more metals that act as a receiver of the energy from the coil, with other materials of construction improving heat transfer or imparting other physical properties to the cookware vessel. These include: US 3,966,426; US 4,544,818; US 4,646,935; US 4,705,727; EP0672520; us 6,926,971 and EP1952735.

As described hereinabove, the support surface on a hob, stovetop or range upon which the cookware is supported in use, is typically glass or glass ceramic. Such glass or glass ceramic surfaces are easily scratched or scuffed. It is a problem with known cookware that repeated placing and the inevitable movement of the cookware on the support surface during use causes abrasion damage to the latter which is clearly undesirable.

As described hereinabove with respect to induction heating, in contrast to direct heating, no heat is generated from the actual support surface. However, a proportion of the heat generated in the cookware is transferred to the support surface via thermal conduction. It is clearly desirable to minimise the heat lost by conduction to the support surface to maximise energy efficiency. Moreover it is desirable that heating of the support surface is minimised to prevent accidents occurring when someone or something inadvertently comes in contact with a hot surface once the cookware has been removed.

The present invention provides an article of cookware for use with induction heating comprising a base, wherein the base includes a ferromagnetic material and has a contact surface which in use faces one or more induction elements; characterised in that the contact surface of the base comprises a polymeric support layer wherein the support layer comprises one or more organic polymers.

Such an arrangement has numerous advantages. In use, the polymeric support layer forms the outermost layer of the cookware and contacts the support surface of a hob, stovetop or range to prevent abrasion damage to the support surface when the article of cookware is in use. Moreover, this polymeric support layer thermally insulates the article from the support surface and reduces the amount of heat lost by thermal conduction from the article to the support surface.

The polymeric support layer may be a continuous layer across substantially the entire surface area of the contact surface, or it may be a discontinuous layer located in separate discrete areas. A skilled person will appreciate that the polymeric support layer prevents direct contact between the metallic elements of the base and a support surface. Thus, the polymeric support layer spaces the metallic elements of the base from the support surface and provides a non-abrasive contact surface.

A skilled person will appreciate that in the case of direct heating methods which use an open flame or a hot electric element, the contact surface of the base reaches temperatures above the melting point of conventional organic polymers.

In one embodiment, the one or more organic polymers include fluoropolymers and silicone polymers.

In a further embodiment, the one or more organic polymers include silicone polyester resin.

In a further embodiment, the one or more organic polymers include polytetrafluoroethylene, perfluoroalkoxy polymer, fluorinated ethylene propylene and polyethylenetetrafluoroethylene.

In a particular embodiment, the support layer comprises polytetrafluoroethylene. In a further embodiment, the support layer consists essentially of polytetrafluoroethylene. In a yet further embodiment the support layer consists of polytetrafluoroethylene.

A skilled person will appreciate that polytetrafluoroethylene is also known as PTFE, Teflon®, Algoflon® and Polymist®; perfluoroalkoxy polymer is also known as PFA, Teflon® PFA and Hyflon®; fluorinated ethylene propylene is also known as FEP and Teflon® FEP; and polyethylenetetrafluoroethylene is also known as ETFE, Tefzel® and Fluon®.

In one embodiment the ferromagnetic material is stainless steel.

Stainless steel is an iron alloy containing a minimum of 10.5% chromium. Although it has many desirable properties for the fabrication of cookware such as resistance to acid or alkali, it is relatively poor heat conductor.

Aluminium is a lightweight metal with excellent thermal conductivity. A disc of aluminium is typically incorporated into the base of an article of stainless steel cookware.

Copper provides the best thermal conductivity of common metals and a disc of copper may be incorporated into the base of stainless steel cookware.

In another embodiment, the base further comprises aluminium.

Additionally or alternatively, the base further comprises copper In one embodiment, the base has a cooking surface opposed to the contact surface, wherein the base comprises an organic coating across substantially the entire surface area of the cooking surface, wherein the organic coating comprises one or more organic polymers.

The organic coating prevents adhesion of food to the cooking surface during use.

In a particular embodiment, the organic coating comprises polytetrafluoroethylene. In a further embodiment, the organic coating consists essentially of polytetrafluoroethylene. In a yet further embodiment the organic coating consists of polytetrafluoroethylene.

In one embodiment, the article of cookware comprises the base which defines a closed base end; an open upper end; and a side wall extending from the base to the open upper end, the base and the side wall thereby defining a vessel with an interior surface and an exterior surface.

In a further embodiment, the base and the sidewall comprise aluminium.

Aluminium cookware, and in particular anodized aluminium cookware, has become popular because it is light in weight, compared to steel or iron cookware. However, aluminium cookware has several disadvantages, not least that aluminium is not ferromagnetic and cannot therefore be used alone in the fabrication of cookware for induction heating.

An anodised finish provides an alumina or ceramic like aluminium oxide coating that is harder and hence more scratch and acid resistant than the unprotected aluminium metal.

In a further embodiment, at least a portion of the interior surface is anodised.

In a yet further embodiment, the interior surface and at least a portion of the exterior surface is anodised.

In a yet further embodiment, the interior and exterior surfaces excluding the contact surface are anodised.

Although the alumina that forms the anodized finish is hard, the anodized aluminium finish is readily stained by acidic foods.

In a yet further embodiment the article further comprises an organic coating across substantially the entire surface area of the interior surface, wherein the organic coating comprises one or more organic polymers.

Cladding is a technique for fabricating cookware with a layer of heat conducting material such as aluminium or copper, covered by a non-reactive material such as stainless steel. Rather than just a heat distributing disk in the base, the aluminium and/or copper may extend over the entire article of cookware.

In a further embodiment, the base and the sidewall comprise aluminium and stainless steel.

In a further embodiment, the base and the sidewall comprise copper and stainless steel.

In a further embodiment, the base and the sidewall comprise copper, aluminium and stainless steel.

Cast iron cookware is slow to heat but once at temperature provides even heating.

In another embodiment, the ferromagnetic material is cast iron.

Carbon steel is malleable and can be rolled into thin sheets whilst maintaining high strength and heat resistance. Carbon steel cookware allows rapid and high heating.

In another embodiment, the ferromagnetic material is carbon steel.

Bare untreated cast iron and carbon steel react with acidic foods and are subject to rusting. Cast iron and carbon steel may be enamelled, i.e. at least a portion of the surface area is coated with a vitreous (porcelain) enamel layer, to overcome the reactivity whilst maintaining the heat distribution profile.

In a further embodiment, at least a portion of the interior surface is enamelled.

In a yet further embodiment, the interior surface and at least a portion of the exterior surface is enamelled.

In a yet further embodiment, the interior and exterior surfaces excluding the contact surface are enamelled.

In another aspect, the present invention provides a method of fabricating an article of cookware for use with induction heating comprising a base, wherein the base includes a ferromagnetic material and has a contact surface which in use faces one or more induction elements; characterised in that the contact surface of the base comprises a polymeric support layer wherein the support layer comprises one or more organic polymers; comprising the step of applying a coating comprising one or more organic polymers to the base.

In one embodiment, the coating is heat cured following application to the base to form the polymer support layer.

A skilled person will appreciate that the articles of the present invention can may be fabricated using techniques which are well known in the fabrication of cookware such as lamination using impact bonding and/or brazing techniques, anodising, vitreous enamelling and application of organic coatings.

It should be appreciated that the terms "embodiment" and "an embodiment of the invention" should be understood to refer to any embodiment or aspect of the invention as defined or described herein. Therefore, it should be understood that the features of specific embodiments can be combined with one or more other specific features described herein or be combined with any aspect or embodiment of the invention described herein. All such combinations of features are considered to be within the scope of the invention defined in the claims.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a vertical cross-sectional view of a first embodiment of an article of cookware; Figure 2 is a vertical cross-sectional view of a second embodiment of an article of cookware; Figure 3 is a vertical cross-sectional view of a third embodiment of an article of cookware; and Figure 4 is a vertical cross-sectional view of a fourth embodiment of an article of cookware.

For the avoidance of doubt, the skilled person will appreciate that in this specification, the terms "up", "down", "front", "rear") "upper", "lower", "width", etc. refer to the orientation of the components as found in the article of cookware in normal use as shown in the Figures An article of stainless steel cookware 1 according to the invention is shown in Figure 1.

The article of stainless steel cookware 1 comprises a stainless steel vessel 101, a thermally conductive aluminium disc 102, a stainless steel base plate 103 and PTFE support layer 104.

The aluminium disc 102 is prefabricated to conform substantially to the diameter of the bottom of the stainless steel vessel 101. The disc 102 is laminated between the bottom of the vessel 101 and the base plate 103. The PTFE support layer 104 coats the base plate 103 and forms a continuous contact surface.

An alternative embodiment of the invention in the form of an article of aluminium cookware 2 is shown in Figure 2.

The article of aluminium cookware 2 comprises an aluminium vessel 201, a thermally conductive aluminium disc 202, a stainless steel base plate 203 and PTFE support layer 204.

The aluminium disc 202 is prefabricated to conform substantially to the diameter of the bottom of the aluminium vessel 201. The disc 202 is laminated between the bottom of the vessel 201 and the base plate 203. The PTFE support layer 204 coats the base plate 203 and forms a continuous contact surface.

An alternative embodiment of the invention in the form of an article of anodised aluminium cookware 3 is shown in Figure 3.

The article of anodised aluminium cookware 3 is similar to that shown in Figure 2 and described hereinabove, but further comprises an anodised layer of aluminium oxide 305 on both the inner and outer surface of the aluminium vessel 301. Thus, the article 3 comprises aluminium vessel 301, a thermally conductive aluminium disc 302, a stainless steel base plate 303 and PTFE support layer 304.

The aluminium disc 302 is prefabricated to conform substantially to the diameter of the bottom of the aluminium vessel 301. The disc 302 is laminated between the bottom of the vessel 301 and the base plate 303. The PTFE support layer 304 coats the base plate 303 and forms a continuous contact surface An alternative embodiment of the invention in the form of an article of enamelled cast iron cookware 4 is shown in Figure 4.

The article of enamelled cast iron cookware 4 comprises a cast iron vessel 401, a vitreous enamel layer 405 and a PTFE support layer 404.

The entire surface area of the cast iron vessel 401 (i.e. both the inner surface and the outer surface) is coated with the vitreous enamel layer 405. The PTFE support layer 404 coats the bottom surface of the vessel 401 to form a continuous contact surface for the article.

Claims

Claims 1. An article of cookware for use with induction heating comprising a base, wherein the base includes a ferromagnetic material and has a contact surface which in use faces one or more induction elements; characterised in that the contact surface of the base comprises a polymeric support layer wherein the support layer comprises one or more organic polymers.
2. An article according to claim 1 wherein the one or more organic polymer is selected from fluoropolymers and silicone polymers.
3. An article according to claim 2 wherein one or more organic polymer is selected from polytetrafluoroethylene, perfluoroalkoxy polymer, fluorinated ethylene propylene and polyethylenetetrafluoroethylene.
4. An article according to any preceding claim wherein the support layer comprises polytetrafluoroethylene
5. An article according to claim 2 wherein the one or more organic polymers is selected from silicone polyester resin.
6. An article according to any preceding claim wherein the ferromagnetic material is stainless steel.
7. An article according to any of claims 1 to 5 wherein the ferromagnetic material is cast iron.
8. An article according to any of claims 1 to 5 wherein the ferromagnetic material is carbon steel.
9. An article according to any preceding claim wherein the base further comprises aluminium.
10. An article according to any preceding claim wherein, the base further comprises copper
11. An article according to any preceding claim wherein, the base has a cooking surface opposed to the contact surface, wherein the base comprises an organic coating across substantially the entire surface area of the cooking surface, wherein the organic coating comprises one or more organic polymers.
12. An article according to any preceding claim comprising the base which defines a closed base end; an open upper end; and a side wall extending from the base to the open upper end, the base and the side wall thereby defining a vessel with an interior and an exterior surface.
13. An article according to claim 12 wherein the base and the sidewall comprise aluminium.
14. An article according to claim 13 wherein the interior and exterior surfaces excluding the contact surface are anodised.
15. An article according to claim 12 or 13 wherein the base and the sidewall comprise copper.
16. An article according to claim 12, 13 or 15 wherein the base and the sidewall comprise stainless steel.
17. An article according to claim 12 wherein the base and the sidewall comprise cast iron or carbon steel
18. An article according to claim 17 wherein the interior and exterior surfaces excluding the contact surface are enamelled.
19. An article according to any of claims 12 to 18 which further comprises an organic coating across substantially the entire surface area of the interior surface, wherein the organic coating comprises one or more organic polymers.
20. A method of fabricating an article of cookware according to any preceding claim comprising the step of applying a coating comprising one or more organic polymers to the base.
21. A method of claim 20 further comprising the step of heat curing the coating to form the polymeric support layer following application of the coating to the base.