WO2003051090A1

WO2003051090A1 - Radiant electric heater

Info

Publication number: WO2003051090A1
Application number: PCT/GB2002/005507
Authority: WO
Inventors: Alan Broadbelt
Original assignee: Ceramaspeed Ltd
Current assignee: Ceramaspeed Ltd
Priority date: 2001-12-11
Filing date: 2002-12-03
Publication date: 2003-06-19
Anticipated expiration: 2004-06-11
Also published as: GB0129564D0; AU2002347344A1

Abstract

A radiant electric heater comprising a dish-like support (1) having a base (1A) and a peripheral wall (1B) extending substantially perpendicular to the base (1A), a base layer (3) of thermal insulation material covering the base (1A) of the dish-like support (1) and at least one radiant electric heating element (5) supported relative to the base layer (3) of thermal insulation material. An outwardly extending flange member (1C) is provided at an end of the peripheral wall (1B) remote from the base (1A), and a return inwardly extending flange member (1D) is provided overlying the face of the outwardly extending flange member (1C) remote from the base (1A), and at least one covering sheet (11) is spaced from the at least one heating element (5) and secured between the outwardly extending flange member (1C) and the return inwardly extending flange member (1D) of the dish-like support (1).

Description

RADIANT ELECTRIC HEATER

This invention relates to a radiant electric heater and more particularly relates to a radiant electric heater including a protective covering sheet spaced from a heating element .

It is known, for example from GB-A-2 331 688, to provide a fabric cover for a radiant electric heater, the cover being spaced from the heating element, in order to prevent manual contact with energised heating elements and to prevent particulates, such as of food materials, or liquid from contacting the heating element (s) and any insulating and/or reflecting materials provided in the heater. Such particulates and liquids may be splattered towards the heater during cooking operations and vapours may also be emitted towards the heater.

While these problems can be overcome with the fabric cover of GB-A-2 331 688, the cover is held in place on the heater by means of adhesive, staples, or bent-over tags which may be integral with a metal support of the heater.

These known means for holding the cover in place can be costly in that they require additional components, take time to take effect and/or hold the cover in such a way that the edges of the cover are exposed, thus leaving the edges of the cover susceptible to damage when handled. It is therefore an object of the present invention to provide a radiant electric heater which overcomes or at least ameliorates the above disadvantages of known heaters.

According to the present invention there is provided a radiant electric heater comprising:

a dish-like support having a base and a peripheral wall extending substantially perpendicular to the base;

a base layer of thermal insulation material covering the base of the dish-like support; and

at least one radiant electric heating element supported relative to the base layer of thermal insulation material; wherein

an outwardly extending flange member is provided at an end of the peripheral wall remote from the base, and a return inwardly extending flange member is provided overlying the face of the outwardly extending flange member remote from the base; and

at least one covering sheet is spaced from the at least one heating element and secured between the outwardly extending flange member and the return inwardly extending flange member of the dish-like support. The at least one covering sheet may be in the form of a fabric selected from glass filaments, ceramic filaments, metal filaments and mixtures thereof.

The fabric incorporating metal filaments may be of woven form. The metal filaments may comprise a high temperature withstanding alloy, such as stainless steel.

The fabric incorporating glass and/or ceramic filaments may be of woven, knitted or mat form. The ceramic filaments are selected from alumino-silicate material, alumino-boro- silicate material and zirconia and mixtures thereof. The glass filaments may be selected from E glass, C glass, R glass and S glass and mixtures thereof.

The weight per unit area of the covering sheet may be not greater than 1 kg/m², preferably in the range from 50 to 300 g/ ².

The at least one heating element may be supported on or adjacent to the base layer of thermal insulation material. The thermal insulation material may comprise microporous thermal insulation material.

The dish-like support may comprise metal. A peripheral wall of thermal insulation material may be provided. The at least one covering sheet may be arranged to overlie an outer surface of the peripheral wall.

The at least one heating element may be selected from heating elements of bare wire, ribbon, sheathed wire or ribbon and lamp form.

An apertured member may be provided in contact with the at least one covering sheet. The apertured member may comprise a perforated sheet or a lattice arrangement, of metal, ceramic or other refractory material.

The return inwardly extending flange member may be formed with a flange portion at an inner end thereof extending towards the base of the heater.

The outwardly extending flange member and the return inwardly extending flange member with the or each covering sheet secured therebetween may be crimped between their inward and outward boundaries .

Thus the present invention provides a radiant electric heater in which the protective cover is secured in place by means of a return flange of a dish-like member of the heater. Such a means of securement ensures correct positioning of the protective cover in a cost-effective manner in that no additional components are required. In addition, the edges of the protective cover are retained within the return flange and susceptibility to damage is therefore reduced.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which:

Figure 1 is a plan view, partly cut away, of one embodiment of a radiant electric heater according to the present invention;

Figure 2 is a cross-sectional view of the radiant electric heater shown in Figure 1;

Figure 3 is a cross-sectional view of part of another embodiment of a radiant electric heater according to the present invention; and

Figure 4 is a cross-sectional view of part of a further embodiment of a radiant electric heater according to the present invention.

The radiant electric heater shown in Figures 1 and 2 comprises a metal dish-like support 1 provided with a base layer 3 of compacted microporous thermal insulation material. The metal dish-like support comprises a generally planar base 1A with an upstanding (as shown in the figures) peripheral wall IB having at an upper end thereof an outwardly extending flange IC.

A heating element 5 is provided secured to the base layer 3. As shown, the heating element 5 comprises a corrugated metal ribbon mounted edgewise on the base layer 3 and secured by partial embedding in the base layer. Such a heating element is well known to the skilled person. The heating element 5 could alternatively be of coiled bare wire or coiled ribbon form or of sheathed wire or ribbon form or of lamp form or of any other form known to the skilled person secured in or adjacent to the base layer. More than one form of heating element could also be provided in the heater.

A terminal block 7 for the heating element 5 is mounted on the dish-like support 1 and allows the heating element to be connected to a voltage supply for operation.

A peripheral wall 9 of thermal insulation material is provided in the heater within the upstanding peripheral wall of the dish-like support 1 and has a height such that an upper surface of the insulating peripheral wall is at a level somewhat below the upper end of the peripheral wall of the dish-like support 1. As shown, the wall 9 is integral with the base layer 3. However, the insulating wall could be provided as a separate member, as is well known in the art .

In order to prevent contact with the internal components of the heater, such as the heating element 5 and insulation layer 3, by particulate materials and to reduce ingress of vapours, during operation of the heater, for example in a cooking appliance, at least one cover sheet 11 is provided spaced from the heating element 5, the cover sheet being partly cut away in Figure 1 to show the underlying components. The cover sheet 11 may comprise any suitable material such as a fabric comprising glass filaments, ceramic filaments or metal filaments. The filaments may be of a woven, knitted or mesh form.

When metal filaments are employed, these suitably comprise a suitably high temperature withstanding alloy, such as a stainless steel, and fine wire filaments, which may be as little as 25 microns in diameter, woven together to form a fabric.

When glass or ceramic filaments are employed, these may be woven, knitted or matted to form a fabric.

The ceramic filaments may comprise alumino-silicate materials, such as supplied by the Carborundum Company Ltd., under the trade names Fibertex and Fibersil. A fabric of woven alumino-borate-silicate filaments may be employed, such as supplied by 3M Company under the trade name Nextel .

A zirconia cloth fabric may also be employed, for example as supplied by Zircar Products, Inc.

The glass filaments may comprise filaments of E glass, C glass, R glass or S glass or modifications thereof. For example, the boron oxide in E glass may be replaced by magnesium oxide, such a glass being commercially available under the trade name Advantex from OCF Corporation.

The weight per unit area of the cover sheet 11 should be as small as practicable to ensure optimum thermal efficiency of the heater. In general, the weight per unit area of the cover sheet should be less than 1 kg/m , with a typical weight per unit area being in the range from 50 to 300 g/m² for glass and ceramic filament fabrics, but somewhat greater for metal filament fabrics.

The cover sheet or sheets 11 are at least partially translucent to allow the transmission therethrough of visible and infra-red radiation from the heating element 5. Additionally, especially in the case of metal filament fabrics, the fabric may absorb and re-radiate radiation from the heating element 5. The or each cover sheet 11 overlies the upper surface of the peripheral wall 9 and the outwardly extending flange IC of the dish-like support and is retained in place by a return inwardly extending flange ID of the dish-like support. Thus the or each cover sheet 11 is sandwiched between the outwardly extending flange IC and the return inwardly extending flange ID. In this way the or each cover sheet 11 is securely held in place and the edges thereof are enclosed between the two flanges IC and ID and are therefore protected against damage. Further, no additional components are required to secure the or each cover sheet 11 in place and securement can be effected quickly and efficiently.

As shown in Figure 2, the inner end of the return inwardly extending flange ID is formed with a downwardly extending flange portion IE which has the effect of lowering the or each cover sheet 11 so as to be close to the upper surface of the peripheral insulating wall 9. Thus, the or each cover sheet 11 is effectively recessed into the dish-like support 1.

As can be seen, the heating element 5 is spaced from the or each heating cover sheet 11 and there is no direct contact therebetween. The spacing eliminates direct contact between the heating element 5 and the cover sheet or sheets 11 so as to minimise the thermal capacity of the heating element and to enable the same to reach full operating temperature as quickly as possible. The spacing also protects the user from the electrical potential of the heating element 5, especially when the cover sheet or sheets 11 are of metal filaments.

An apertured sheet 13 is optionally provided overlying the one or more cover sheets 11 of the fabric and sandwiched between the outwardly extending flange IC and the return inwardly extending flange ID of the dish-like support 1. The apertured sheet 13 is shown partly cut away in Figure 1 to reveal the underlying components. Such apertured sheet 13 may serve more than one purpose. It may provide support and/or protection for the cover sheet or sheets 11 of the fabric, enabling the thickness of the sheet or sheets to be minimised and also minimising the risk of manual contact with internal components of the heater. The apertured sheet 13 can comprise perforations 15 in a metal or ceramic sheet or the sheet can be of expanded metal form 17 (both forms being shown in Figure 1) , or other appropriate lattice-form. The apertured sheet 13 could alternatively comprise any suitably apertured refractory material .

The radiant electric heater of the present invention may be used, for example, in cooking appliances such as grills and ovens, and in general heating applications such as space heating and industrial thermal processing. In applications of the radiant electric heater in microwave ovens, where electrical screening of the heater is required in respect of electromagnetic radiation generated elsewhere in the appliance, the apertured sheet 13, formed of metal, also or alternatively fulfils the screening function.

The radiant electric heaters shown in Figures 3 and 4 differ from that shown in Figures 1 and 2 in a number of respects .

As shown in Figure 3, the peripheral insulating wall 9 is substantially the same height as the upstanding peripheral wall IB of the dish-like member and no downwardly extending flange IE is provided, with the result that the or each cover sheet 11 is not recessed into the dish-like member in the manner of Figures 1 and 2.

Further as shown in Figure 3 , the outwardly extending flange IC and the return inwardly extending flange ID with the or each cover sheet 11 secured therebetween are crimped at 19 between their inward and outward boundaries so as to increase the security of the fastening of the or each cover sheet between the two flanges.

As shown in Figure 4, the peripheral insulating wall 9 is substantially the same height as the upstanding peripheral wall IB of the dish-like member and no downwardly extending flange IE is provided, with the result that the or each cover sheet 11 is not recessed into the dish-like member in the manner of Figures 1 and 2 . The or each cover sheet 11 is therefore simply sandwiched between the outwardly extending flange IC and the return inwardly extending flange ID.

Claims

1. A radiant electric heater comprising:

a dish-like support (1) having a base (1A) and a peripheral wall (IB) extending substantially perpendicular to the base (1A);

a base layer (3) of thermal insulation material covering the base (1A) of the dish-like support (1) ; and

at least one radiant electric heating element (5) supported relative to the base layer (3) of thermal insulation material; characterised in that

an outwardly extending flange member (IC) is provided at an end of the peripheral wall (IB) remote from the base (1A) , and a return inwardly extending flange member (ID) is provided overlying the face of the outwardly extending flange member (IC) remote from the base (1A) ; and

at least one covering sheet (11) is spaced from the at least one heating element (5) and secured between the outwardly extending flange member (IC) and the return inwardly extending flange member (ID) of the dish-like support (1) .

2. A radiant electric heater as claimed in claim 1, characterised in that the at least one covering sheet (11) is in the form of a fabric selected from glass filaments, ceramic filaments, metal filaments and mixtures thereof.

3. A radiant electric heater as claimed in claim 2, characterised in that the fabric incorporating metal filaments is of woven form.

4. A radiant electric heater as claimed in claim 2 or 3 , characterised in that the metal filaments comprise a high temperature withstanding alloy.

5. A radiant electric heater as claimed in claim 4, characterised in that the alloy comprises stainless steel.

6. A radiant electric heater as claimed in claim 2, characterised in that the fabric incorporating glass and/or ceramic filaments is of woven, knitted or mat form.

7. A radiant electric heater as claimed in claim 2 or 6, characterised in that the ceramic filaments are selected from alumino-silicate material, alumino-boro-silicate material and zirconia and mixtures thereof.

8. A radiant electric heater as claimed in claim 2 or 6, characterised in that the glass filaments are selected from E glass, C glass, R glass and S glass and mixtures thereof.

9. A radiant electric heater as claimed in any preceding claim, characterised in that the weight per unit area of the covering sheet is not greater than 1 kg/m².

10. A radiant electric heater as claimed in claim 9, characterised in that the weight per unit area of the covering sheet is in the range from 50 to 300 g/m².

11. A radiant electric heater as claimed in any preceding claim, characterised in that the at least one heating element (5) is supported on or adjacent to the base layer (3) of thermal insulation material.

12. A radiant electric heater as claimed in claim 11, characterised in that the thermal insulation material comprises microporous thermal insulation material.

13. A radiant electric heater as claimed in any preceding claim, characterised in that the dish-like support (1) comprises metal.

14. A radiant electric heater as claimed in any preceding claim, characterised in that a peripheral wall (9) of thermal insulation material is provided.

15. A radiant electric heater as claimed in claim 14, characterised in that the at least one covering sheet is arranged to overlie an outer surface of the peripheral wall (9) .

16. A radiant electric heater as claimed in any preceding claim, characterised in that the at least one heating element (5) is selected from heating elements of bare wire, ribbon, sheathed wire or ribbon and lamp form.

17. A radiant electric heater as claimed in any preceding claim, characterised in that an apertured member (13) is provided in contact with the at least one covering sheet (11) .

18. A radiant electric heater as claimed in claim 17, characterised in that the apertured member (13) comprises a perforated sheet or a lattice arrangement, of metal, ceramic or other refractory material .

19. A radiant electric heater as claimed in any preceding claim, characterised in that the return inwardly extending flange member (ID) is formed with a flange portion at an inner end thereof extending towards the base of the heater.

20. A radiant electric heater as claimed in any preceding claim, characterised in that the outwardly extending flange member (IC) and the return inwardly extending flange member (ID) with the or each covering sheet (11) secured therebetween are crimped between their inward and outward boundaries .