GB2333680A

GB2333680A - Electric toaster elements

Info

Publication number: GB2333680A
Application number: GB9801243A
Authority: GB
Inventors: Peter Ravenscroft Wilkins
Original assignee: Ceramaspeed Ltd
Current assignee: Ceramaspeed Ltd
Priority date: 1998-01-22
Filing date: 1998-01-22
Publication date: 1999-07-28
Anticipated expiration: 2018-01-22
Also published as: GB9801243D0; GB2333680B; DE29900776U1

Abstract

An electric toaster comprises a housing (1) having at least one slot (2) for receiving at least one food item to be toasted. At least two radiant electric heating means (4A, 4B) are disposed in facing spaced relationship in the housing with the at least one slot (2) therebetween, each radiant electric heating means comprising at least one heating element (7) disposed on or adjacent to a layer (6) of microporous thermal insulation material.

Description

Electric Toaster This invention relates to electric toasters.

Electric toasters are well know which comprise a housing having at least one slot for receiving at least one food item, such as bread, to be toasted. Radiant electric heating means are disposed in facing spaced relationship in the housing with the slot therebetween. Such radiant electric heating means commonly comprise a sheet-like support of electrically insulating material, such as mica, on which is wound, woven, or othenvise secured, a wire or narrow ribbon form heating element. while such heating means are relatively inexpensive to manufacture, they suffer from disadvantages in that they heat up slowly and also emit substantial thermal radiation in a direction opposite to that of the food item being toasted.

Such radiation is inefficient and may also result in heating up of the housing itself to the extent that the housing may become dangerously hot to touch, particularly when comprising metal.

It is an object of the present invention to overcome or minimise these disadvantages.

The present invention provides an electric toaster comprising: a housing having at least one slot for receiving at least one food item to be toasted; at least two radiant electric heating means disposed in facing spaced relationship in the housing with the at least one slot therebetween, each radiant electric heating means comprising at least one heating element disposed on or adjacent to a layer of microporous thermal insulation material.

The microporous thermal insulation material may incorporate an infra-red radiation-reflective opacifier material.

The microporous thermal insulation material may be provided in a support, such as a dish or frame, which may comprise a metal.

The at least one heating element may be of ribbon form and may be of corrugated ribbon fonn.

The ribbon form at least one heating element may be secured edgewise to the layer of microporous thermal insulation material by partial embedment therein.

At least one of the radiant heating means may be provided for location in a central region of the housing and comprising heating elements disposed on or adjacent to opposite faces of a layer of the microporous thermal insulation material. Such layer of the microporous insulation material may suitably be supported in a frame.

Each radiant electric heating means may be provided with at least one protective covering sheet selected to have required high temperature withstanding property and to allow adequate transmission of thermal radiation for effecting toasting.

The at least one covering sheet may comprise mica. particularly at least partly transparent mica.

Alternatively, the at least one covering sheet may comprise an apertured metal or ceramic material.

Alternatively, the at least one covering sheet may comprise a fabric comprising glass and/or ceramic and/or metal filaments.

The fabric comprising glass and/or ceramic filaments may be of woven, knitted or mat form.

The fabric comprising metal filaments may be of woven form.

The glass filaments in the fabric may be selected from E glass, C glass, R glass and S glass, and modifications thereof.

The ceramic filaments in the fabric may be selected from aluminosilicate, aluminoborosilicate and zirconia materials.

The weight per unit area of the fabric comprising glass and/or ceramic filaments mas be not greater than 1 kg/m2 The weight per unit area of the fabric comprising glass filaments may be preferably from 50 to 300 g/m2 The metal filaments in the fabric may comprise a stainless steel.

The toaster of the invention provides rapid heat-up of the heating elements therein with efficient radiation towards the food item or items being toasted as a result of the use of the microporous insulation material. The microporous insulation material also minimises thermal radiation in a direction opposite to that of the item or items being toasted, resulting in a cool exterior of the housing, even when this is of metal.

The invention is now described by way of example with reference to the accompanying drawings in which: Figures 1A and 1B are sectional views of an electric toaster according to the invention; Figure 2 is a plan view of radiant heating means for use in the toaster of Figure 1; Figure 3 is a cross-sectional view of the heating means of Figure 2; and Figure 4 is a cross-sectional view of radiant heating means for use in a central location in the toaster of Figure 1.

Referring to Figures 1A and 1B, an electric toaster comprises a housing 1 of metal or plastics material of well knows form of construction having slots 2 in the top thereof for receiving one or more food items (not shown), such as bread, to be toasted.

The housing overlies a base 3, which supports standard mechanisms for receiving and holding the food items and ejecting them from the toaster after being toasted. Such mechanisms do not form part of the present invention and, apart from carriage means 30, are omitted from the drawings to aid simplicity.

Radiant electric heating means 4A, 4B are secured in the housing I on the base 3 such that the heating means face each other with the slots 2 therebeaveen. Two heating means 4A are provided at opposite sides of the housing 1, with a heating means 4B in a central region of the housing spaced therefrom by the slots 2. Details of the construction of the heating means are shown in Figures 2, 3 and 4.

Referring to Figures 2 and 3, the heating means 4A each comprise a metal support dish 5 provided with a base layer 6 of compacted microporous thermal and electrical insulation material.

The term 'microporous' is used herein to identify porous or cellular materials in which the ultimate size of the cells or voids is less than the mean free path of an air molecule at NTP, i.e. of the order of 100 nm or smaller. A material which is microporous in this sense will exhibit very low transfer of heat by air conduction (that is, due to collisions between air molecules).

Such microporous materials include aerogel, which is a gel in which the liquid phase has been replaced by a gaseous phase in such a way as to avoid the shrinkage which would occur if the gel were dried directly from a liquid. A substantially identical structure can be obtained by controlled precipitation from solution, the temperature and pH being controlled during precipitation to obtain an open lattice precipitate. Other equivalent open lattice structures include pyrogenic (fumed) and electro-thermal types in which a substantial proportion of the particles have an ultimate size less than 100 nm. Any of these materials, based, for example on silica, alumina, other metal oxides, or carbon, may be used to prepare a composition which is microporous as defined above.

Optionally a binder may be added to provide increased strength, in which case a heat treatment may be necessary in order to cure the binder.

A knonvn form of high performance microporous thermal insulation material comprises microporous silica particles compacted to consolidate the material into a handleable form, and topically includes ceramic fibre or glass filament reinforcement and an opacifier, such as rutile, which improves infra-red radiation reflective properties of the material.

Examples of microporous insulation materials are to be found, for example, in GB-A-1580909 and EP-A-0560479.

A radiant electric heating element 7 is provided secured to the base layer 6 of microporous insulation material. The heating element 7 comprises a corrugated metal ribbon mounted edgewise on the base layer 6 and secured by partial embedding in the base layer 6.

A terminal block 8 for the heating element is mounted on the heating means and allows the heating means to be connected to a voltage supply for operation.

A peripheral wall 9 of thermal insulation material is provided in the heating means. As shown, this wall is of microporous insulation material and integral with the base layer 6. However it could be provided as a separate member In order to ininimise risk of contact with internal components of the heating means by particulate materials and to at least reduce ingress of vapours during operation, at least one protective covering sheet 10 is optionally provided, selected to have required high temperature withstanding property and to allow adequate transmission of thermal radiation for effecting toasting. The covering sheet 10 may be arranged to overlie the top surface of the peripheral wall 9 and be secured thereto if desired.

Various materials may be selected for the covering sheet 10. It may comprise mica. particularly at least partly transparent mica.

Alternatively the covering sheet 10 may comprise an apertured, for example perforated, metal or ceramic material.

As a further altemative, the covering sheet 10 may comprise a fabric comprising glass and/or ceramic and/or metal filaments. Such a fabric comprising glass and/or ceramic filaments mas be of woven, knitted or mat form.

The fabric comprising metal filaments may be of woven form and man, for example, comprise a stainless steel. The metal filaments may have a diameter down to about 25 microns.

A fabric with glass and/or ceramic filaments should have a weight per unit area not greater than 1 kg/m2 A fabric with glass filaments has a preferred weight per unit area between about 50 and about 300 g/m2 Examples of ceramic filament fabric materials are aluminosilicate materials (such as materials supplied by Carborundum Co. Ltd having the trade names Fibertex and Fibersil) and aluminoborosilicate materials (such as a material supplied b 3M Co. having the trade name Nextel).

A fabric comprising zirconia ceramic filaments is also suitable for this application, such a fabric being available from Zircar Products Inc.

A fabric may also be used comprising filaments of E-glass, C-glass, R-glass, or S-glass, or modifications thereof. For example, E-glass filaments having boron oxide replaced by magnesium oxide is available from OCF Corporation under the trade name Advantex.

The heating means 4B, provided in the central region of the housing 1 is illustrated in Figure 4 and differs from the heating means 4A in the following respects. As shown in Figure 4, the microporous thermal insulation 6A is supported in a metal frame 5A with both opposite faces of the insulation material exposed. This is compared with the arrangement of heating means 4A in Figures 2 and 3 where the insulation 6 is provided in a metal support dish 5 with one face of the insulation exposed. As shown in Figure 4, a heating element 7 is provided on each face of the insulation material 6A, each heating element 7 being the same as the corresponding heating element 7 of each heating means 4A as shown in Figures 2 and 3. A pair of terminal blocks 8A and 8B serve for connection of the tsvo heating elements to a voltage supply and peripheral walls 9 and protective covering sheets I 0A and 1 0B are provided in the same way and of the same construction as the wall 9 and covering sheet 10 provided for the two heating means 4A and described with reference to Figures 2 and 3.

When the toaster is energised, the heating elements 7 heat up to radiant temperatures ver) rapidly and provide ven efficient radiation towards the food item or items being toasted. The microporous insulation material serves as a reflector of radiation. It also minimises thermal radiation in a direction opposite to that of the food item or items being toasted. resulting in a cool exterior of the housing 1, even when this is of metal. In this regard, the peripheral wall 9. particularly when of microporous insulation material, assists in maintaining the top surface of the housing 1 at a low temperature.

Claims

Claims 1. An electric toaster comprising: a housing having at least one slot for receiving at least one food item to be toasted; at least two radiant electric heating means disposed in facing spaced relationship in the housing with the at least one slot therebetween, each radiant electric heating means comprising at least one heating element disposed on or adjacent to a layer of microporous thermal insulation material.
2. A toaster according to claim 1, in which the microporous thermal insulation material incorporates an infra-red radiation-reflective opacifier material.
3. A toaster according to claim 1 or 2, in which the microporous thermal insulation material is provided in a support.
4. A toaster according to claim 3, in which the support comprises a dish or frame.
5. A toaster according to claim 4, in which the dish or frame comprises a metal.
6. A toaster according to any preceding claim, in which the at least one heating element is of ribbon form.
7. A toaster according to claim 6 in which the ribbon fonn at least one heating element is corrugated.
8. A toaster according to claim 6 or 7 in which the ribbon form at least one heating element is supported on edge on the layer of microporous thermal insulation material.
9. A toaster according to claim 8, in which the ribbon form at least one heating element is secured edgewise to the layer of microporous thermal insulation material by partial embedment therein.
10. A toaster according to any preceding claim, in which at least one of the radiant heating means is provided for location in a central region of the housing and comprising heating elements disposed on or adjacent to opposite faces of a layer of the microporous thermal insulation material.
11. A toaster according to claim 10, in which the laxer of the microporous insulation material is supported in a frame.
12. A toaster according to any preceding claim, in which each radiant electric heating means is provided with at least one protective covering sheet selected to have required high temperature withstanding property and to allow adequate transmission of thermal radiation for effecting toasting.
13. A toaster according to claim 12. in which the at least one covering sheet comprises mica.
14. A toaster according to claim 13, in which the mica is at least partly transparent mica.
15. A toaster according to claim 12, in which the at least one covering sheet comprises an apertured metal or ceramic material.
16. A toaster according to claim 12, in which the at least one covering sheet comprises a fabric comprising glass and/or ceramic and/or metal filaments.
17. A toaster according to claim 16, in which the fabric comprising glass and/or ceramic filaments is of woven, knitted or mat form.
18. A toaster according to claim 16, in which the fabric comprising metal filaments is of woven form.
19. A toaster according to claim 16 or 17, in which the glass filaments in the fabric are selected from E glass, C glass, R glass and S glass, and modifications thereof.
20. A toaster according to claim 16 or 17, in which the ceramic filaments in the fabric are selected from aluminosilicate. aluminoborosilicate and zirconia materials.
21. A toaster according to any of claims 16, 17, 19 or 20, in which the weight per unit area of the fabric comprising glass and/or ceramic filaments is not greater than 1 kg/m2.
22. A toaster according to claim 21. in which the weight per unit area of the fabric comprising glass filaments is from 50 to 300 g/m2
23. A toaster according to claim 16 or 18, in which the metal filaments in the fabric comprise a stainless steel.
24. An electric toaster constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.