WO2004066679A1

WO2004066679A1 - Radiant electric heater

Info

Publication number: WO2004066679A1
Application number: PCT/GB2004/000170
Authority: WO
Inventors: Stuart Lamb
Original assignee: Ceramaspeed Limited
Priority date: 2003-01-18
Filing date: 2004-01-16
Publication date: 2004-08-05
Also published as: GB0301165D0

Abstract

A radiant electric heater (2) is provided for use behind a plate (4) of a material transmissive of visible radiation. The heater (2) comprises a base (8) of thermal and electrical insulation material having a surface supporting at least one electric heating element (10). A peripheral wall (14) of thermal insulation material is provided engaging a rear surface of the plate (4) and defining a heated area (16). The heating element (10) has at least one terminal region (26) passing through at least one aperture (28) in the peripheral wall (14) and electrically connected to at least one electric terminal means (24) at least one connection region (30). At least one screen means (32) is provided overlying at least part of the terminal region (26) of the heating element (10) in the vicinity of the connection region (30), and adapted and arranged to substantially screen from view through the plate (4), outside of the heated area (16), visible radiation from the terminal region (26), during energising of the heater (2).

Description

RADIANT ELECTRIC HEATER

This invention relates to radiant electric heaters, for example for use in cooking appliances behind a sheet of material such as of glass-ceramic.

Radiant electric heaters are well known for use behind glass-ceramic cooking plates. Such heaters can comprise a dish-like support, such as of metal, having therein a base layer of insulation material, such as microporous thermal and electrical insulation material. At least one electric heating element is provided, supported on the surface of the base layer. One form of heating element which has found wide acceptance is an elongate electrically conductive ribbon, supported on edge and secured in the surface of the base layer.

It is known to provide a temperature-responsive device of rod-like form extending at least partly across the heater from an edge thereof and overlying the heating element or elements. Such temperature-responsive device serves to control the operation of the heater, such as to prevent the glass-ceramic material of the cooking plate from reaching a high temperature at which damage would occur thereto.

It has been found advantageous to provide a heater of this kind in which one or more terminal regions of the ribbon-form heating element or elements is or are arranged to exit the heater through one or more apertures in a peripheral wall thereof for direct electrical connection, such as by welding, to electric terminal means provided externally of the heater. Such terminal means may be conveniently provided on a housing means arranged externally of the heater at an end of the rod- like temperature-responsive device. Such housing means suitably encloses one or more switch means associated with the temperature-responsive device.

A problem with this arrangement is that, as a result of the provision of the one or more apertures in the peripheral wall of the heater through which the terminal region or regions of the heating element or elements extends or extend, visible radiation from the heating element or elements within the heater escapes through the aperture or apertures and this may be seen directly through the glass-ceramic cooking plate. Alternatively or additionally, such escaping visible radiation may illuminate features or components arranged externally of the heater, beneath the glass-ceramic cooking surface, and such features or components may then be undesirably visible through the glass-ceramic cooking plate.

A further problem exists in that the terminal region or regions of the ribbon-form heating element or elements emit visible radiation, during operation of the heater, up to the point or points of welding to the one or more electric terminals externally of the heater. Although the operating temperature of the ribbon material in such region or regions is significantly lower than that of the remainder of the ribbon material within the heater, it is still sufficiently high for visible radiation therefrom to be seen through the glass-ceramic cooking plate.

It is an object of the present invention to overcome or minimise one or more of these problems.

According to the present invention there is provided a radiant electric heater for use behind a plate of a material transmissive of visible radiation, the heater comprising: a base of thermal and electrical insulation material having a surface supporting at least one electric heating element; a peripheral wall of thermal insulation material adapted to engage a rear surface of the plate and defining a heated area; the at least one heating element having at least one terminal region passing through at least one aperture in the peripheral wall and electrically connected to at least one electric terminal means at at least one connection region; at least one screen means being provided overlying at least part of the at least one terminal region of the at least one heating element in the vicinity of the at least one connection region, and adapted and arranged to substantially screen from view through the plate, outside of the heated area, visible radiation from the at least one terminal region, during energising of the heater.

The heating element may comprise at least one electrically conductive ribbon.

The at least one electrically conductive ribbon may be supported on edge on the surface of the base and may be of corrugated form.

The at least one electrically conductive ribbon may be provided with a plurality of spaced-apart legs, integral with the at least one electrically conductive ribbon or secured thereto, the legs extending edgewise from the at least one electrically conductive ribbon and being at least partially embedded in the surface of the base.

The at least one screen means suitably comprises a material substantially impermeable to the visible radiation from the at least one terminal region of the at least one heating element. The at least one connection region may comprise at least one welded area of overlap between the at least one terminal region of the at least one heating element and the at least one electric terminal means .

The at least one electric terminal means may comprise metal and may be of strip or tab form.

A rod-like temperature-responsive device may be provided extending lengthwise at least partly across the heater from an edge thereof, through the peripheral wall and over the at least one electric heating element, the rodlike temperature-responsive device having a housing means at an end thereof externally of the heater and adjacent to the peripheral wall. The housing means may have supported thereon the at least one electric terminal means having electrically connected thereto the at least one terminal region of the at least one heating element at the at least one connection region. The housing means may accommodate at least one electric switch means.

Two electric terminal means may be provided, laterally disposed at opposite sides of the housing means and having electrically connected thereto two terminal regions of the at least one heating element, passing through two apertures in the peripheral wall.

In one embodiment of the present invention, the at least one screen means comprises at least one portion of the peripheral wall at least partially surrounding the at least one aperture in the peripheral wall. In this embodiment, the at least one electric terminal means may extend into the at least one aperture in the peripheral wall, whereby the at least one connection region is provided in the at least one aperture in the peripheral wall.

In another embodiment of the present invention, the at least one screen means comprises at least one component extending laterally from the peripheral wall, externally of the heater, and over the at least one terminal region in the vicinity of the at least one connection region. The at least one component may be formed integrally with the peripheral wall or may be formed separately and secured to the heater. When formed separately, the at least one component may be secured in contact with the peripheral wall and may comprise mica or ceramic material .

The at least one component may be of sheet, strip or block form and may have one or more side and/or end portions of wall-like form extending therefrom and adapted to screen one or more side and/or end regions of the at least one terminal region in the vicinity of the at least one connection region.

In a further embodiment of the present invention, the at least one screen means comprises at least one strip-form or sheet-form component extending laterally from the housing means of the rod-like temperature-responsive device and over the at least one terminal region in the vicinity of the at least one connection region. The at least one strip-form or sheet-form component may have one or more side and/or end portions of wall-like form extending therefrom and adapted to screen one or more side and/or end regions of the at least one terminal region in the vicinity of the at least one connection region. The at least one strip-form or sheet-form component may be provided overlying the housing means of the rod-like temperature-responsive device and extending laterally at one side face, or at two opposite side faces of the housing means, and may comprise mica or ceramic material. With this arrangement, the at least one strip-form or sheet-form component may serve as a cover for the housing means .

In a still further embodiment of the present invention, the at least one screen means comprises at least one strip-like part extending laterally from the at least one electric terminal means over the at least one terminal region in the vicinity of the at least one connection region. The at least one strip-like part may be formed integrally with the at least one electric terminal means and may have one or more side and/or end portions of wall-like form extending therefrom and adapted to screen one or more side and/or end regions of the at least one terminal region in the vicinity of the at least one connection region.

The at least one strip-like part may comprise metal.

The base may comprise microporous thermal and electrical insulation material and may be provided in a dish-like support, such as of metal.

The plate of the material transmissive of visible radiation may comprise glass-ceramic material and may comprise a cooking surface for a cooking appliance.

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 Figures 1 to 5 are perspective views of respective alternative embodiments of a radiant electric heater according to the present invention.

Referring to Figure 1, a radiant electric heater 2 is provided for use underneath a cooking plate 4 comprising a material, such as glass-ceramic, which is transmissive of visible radiation. The heater 2 comprises a metal dish-like support 6 having therein a base layer 8 of thermal and electrical insulation material, for example microporous thermal and electrical insulation material. A radiant electric heating element is provided comprising an elongate corrugated electrically conductive ribbon 10, for example of iron-chromium-aluminium alloy. The corrugated ribbon 10 has spaced-apart legs 12 integral with or secured thereto and extending edgewise therefrom. The ribbon 10 is mounted edgewise on the base layer 8 and secured by at least partial embedding of the legs 12 in the surface of the base layer 8.

A peripheral wall 14 of insulation material is provided in the heater and has a top surface 15 arranged to contact a rear surface of the cooking plate 4, whereby a heated area 16 is defined.

A rod-like temperature-responsive device 18 is provided, extending at least partly across the heated area 16 of the heater, from an edge of the heater. The rod-like temperature-responsive device 18 is supported at the edge of the heater and suitably comprises differentially- expanding components which operate one or more switch means 20 provided in a housing 22 located externally of the heater adjacent the peripheral wall 14. Two metal electric terminal means 24 of strip or tab form are supported one on each side of the housing 22, at opposite sides of the housing, although only one such electric terminal means 24 is visible in Figure 1.

The electrically conductive ribbon 10 is provided with terminal regions 26 which pass through apertures 28 provided in the peripheral wall 14 and a rim of the dishlike support 6. The terminal regions 26 of the ribbon 10 overlap corresponding electric terminal means 24 and are electrically connected thereto, by welding, at connection regions 30. Again it is to be noted that only one of the two terminal regions 26 is visible in Figure 1, passing through its associated aperture 28 in the peripheral wall 14 and electrically connected to its corresponding electric terminal means 24 at the connection region 30. However, the arrangement for connection of the other terminal region 26 at the other side of the housing 22 is exactly the same.

When the electrically conductive ribbon heating element 10 is electrically connected to a power supply and energised therefrom, it heats up to a red heat condition and is visible through the cooking plate 4 in the heated area 16. There is, however, a disadvantage in that visible radiation also occurs from the terminal regions 26 of the ribbon 10, outside of the heated area 16. Although such visible radiation from the terminal regions 26 may be less than that from the remainder of the ribbon 10 within the heated area 16, it still tends to be seen through the cooking plate 4 and this is aesthetically unsatisfactory.

In order to solve this problem, screen means 32 are provided overlying at least part of each of the terminal regions 26 of the ribbon 10 in the vicinity of their connection regions 30. Such screen means 32 are arranged to substantially screen from view through the plate 4, outside of the heated area 16, visible radiation from the terminal regions 26, during energising of the heater 2.

The screen means 32 are suitably of sheet or strip form, extending laterally from the peripheral wall 14. They suitably comprise a material such as mica or ceramic and are secured to the peripheral wall 14 or between the peripheral wall 14 and either a rim of the dish-like support 6 or the base layer 8. The screen means 32 of sheet or strip form may have one or more side and/or end portions 34 of wall-like form integral therewith and extending therefrom at any desired angle and serving to screen one or more side and/or end regions of the terminal regions 26 of the ribbon 10, to minimise visibility of radiation therefrom.

Referring now to Figure 2, this shows an arrangement which is similar to that of Figure 1, with an exception that, instead of the screen means 32 being of sheet or strip form secured to the heater 2, the screen means 32 are formed integrally with the peripheral wall 14 and extend laterally in block form over the terminal regions 26 of the ribbon 10 in the vicinity of the connection regions 30. As before, one or more side and/or end portions 34 of wall-like form may be provided integral with and extending at any desired angle from the block- form screen means 32.

Referring now to Figure 3, another embodiment of a radiant electric heater 2 according to the present invention is provided, which is similar to those of Figures 1 and 2 with a main exception that the screen means 32 comprise portions of the peripheral wall 14 at least partially surrounding the apertures 28 in the peripheral wall 14. Furthermore, with this arrangement the electric terminal means 24 are adapted so that they extend into the apertures 28 through the peripheral wall 14 and such that the connections to the terminal regions 26 of the ribbon 10, at the connection regions 30, are provided within the apertures 28. Any portions of the terminal regions 26 of the ribbon 10 which may extend beyond the connection regions 30 and outside of the peripheral wall 14 of the heater emit little or no visible radiation.

Referring now to Figure 4, a further embodiment of a radiant electric heater 2 according to the present invention is of substantially the same basic construction as described with reference to Figure 1, with the exception of the screen means 32. In the arrangement of Figure 4, the screen means 32 comprises a cover of the housing 22 of the rod-like temperature-responsive device 18 and which is extended laterally beyond opposite side faces of the housing 22, to overlie the terminal regions 26 of the ribbon 10. Here the screen means 32 is suitably of sheet form and suitably comprises mica or ceramic material. Once again, one or more side and/or end portions 34 of wall-like form may be provided, integral with and extending from the screen means 32 at any desired angle and serving to screen one or more side and/or end regions of the terminal regions 26 of the ribbon 10, to minimise visibility of radiation therefrom.

Referring now to Figure 5, a still further embodiment of a radiant electric heater 2 according to the present invention is again of substantially the same basic construction as described with reference to Figure 1, with the exception of the screen means 32. In the embodiment of Figure 5, two screen means 32 are provided, one at either side of the housing 22 and each comprising a metal strip-like part integral with and extending laterally from the electric terminal means 24 and overlying the associated terminal region 26 of the ribbon 10. Again, one or more side and/or end portions 34 of wall-like form may be provided, integral with and extending from the screen means 32 at any desired angle and serving to screen one or more side and/or end regions of the terminal regions 26 of the ribbon 10, to minimise visibility of radiation therefrom.

Although in the foregoing description reference has been specifically made to a heater in which two terminal regions of the electrically conductive ribbon heating element are provided, passing through apertures in the peripheral wall of the heater and electrically connected to the terminal means at two opposite sides of the housing of the temperature-responsive device, such an arrangement is not essential. The present invention is applicable to any arrangement where one or more terminal regions of the ribbon heating element pass through one or more apertures in the peripheral wall of the heater and is or are electrically connected to one or more electric terminal means provided either on the housing of the temperature-responsive device or on one or more terminal block means provided at one or more exterior regions of the heater.

Claims

1. A radiant electric heater for use behind a plate (4) of a material transmissive of visible radiation, characterised in that the heater (2) comprises:

a base (8) of thermal and electrical insulation material having a surface supporting at least one electric heating element (10) ;

a peripheral wall (14) of thermal insulation material adapted to engage a rear surface of the plate (4) and defining a heated area (16) ;

the at least one heating element (10) having at least one terminal region (26) passing through at least one aperture (28) in the peripheral wall (14) and electrically connected to at least one electric terminal means (24) at at least one connection region (30);

at least one screen means (32) being provided overlying at least part of the at least one terminal region (26) of the at least one heating element (10) in the vicinity of the at least one connection region (30), and adapted and arranged to substantially screen from view through the plate (4), outside of the heated area (16), visible radiation from the at least one terminal region (26) , during energising of the heater (2) .

2. A heater as claimed in claim 1, characterised in that the heating element (10) comprises at least one electrically conductive ribbon (10) .

3. A heater as claimed in claim 2, characterised in that the at least one electrically conductive ribbon (10) is supported on edge on the surface of the base (8) .

4. A heater as claimed in claim 2 or 3, characterised in that the at least one electrically conductive ribbon (10) is of corrugated form.

5. A heater as claimed in claim 2, 3 or 4, characterised in that the at least one electrically conductive ribbon (10) is provided with a plurality of spaced-apart legs (12), the legs (12) extending edgewise from the at least one electrically conductive ribbon (10) and being at least partially embedded in the surface of the base (8),.

6. A heater as claimed in claim 5, characterised in that the legs (12) are integral with the at least one electrically conductive ribbon (10) .

7. A heater as claimed in claim 5, characterised in that the legs (12) are secured to the at least one electrically conductive ribbon (10) .

8. A heater as claimed in any preceding claim, characterised in that the at least one screen means (32) comprises a material substantially impermeable to the visible radiation from the at least one terminal region (26) of the at least one heating element (10) .

9. A heater as claimed in any preceding claim, characterised in that the at least one connection region (30) comprises at least one welded area of overlap between the at least one terminal region (26) of the at least one heating element (10) and the at least one electric terminal means (24).

10. A heater as claimed in any preceding claim, characterised in that the at least one electric terminal means (24) comprises metal.

11. A heater as claimed in any preceding claim, characterised in that the at least one electric terminal means (24) is of a form selected from strip and tab form.

12. A heater as claimed in any preceding claim, characterised in that a rod-like temperature-responsive device (18) is provided extending lengthwise at least partly across the heater (2) from an edge thereof, through the peripheral wall (14) and over the at least one electric heating element (10) .

13. A heater as claimed in claim 12, characterised in that the rod-like temperature-responsive device (18) has a housing means (22) at an end thereof externally of the heater (2) and adjacent to the peripheral wall (14).

14. A heater as claimed in claim 13, characterised in that the housing means (22) has supported thereon the at least one electric terminal means (24) having electrically connected thereto the at least one terminal region (26) of the at least one heating element (10) at the at least one connection region (30) .

15. A heater as claimed in claim 13 or 14, characterised in that the housing means (22) accommodates at least one electric switch means (20) .

16. A heater as claimed in claim 13, 14 or 15, characterised in that two electric terminal means (24) are provided, laterally disposed at opposite sides of the housing means (22) and having electrically connected thereto two terminal regions (26) of the at least one heating element (10), passing through two apertures (28) in the peripheral wall (14).

17. A heater as claimed in any preceding claim, characterised in that the at least one screen means (32) comprises at least one portion of the peripheral wall (14) at least partially surrounding the at least one aperture (28) in the peripheral wall (14).

18. A heater as claimed in claim 17, characterised in that the at least one electric terminal means (24) extends into the at least one aperture (28) in the peripheral wall (14), whereby the at least one connection region (30) is provided in the at least one aperture (28) in the peripheral wall (14).

19. A heater as claimed in any one of claims 1 to 16, characterised in that the at least one screen means (32) comprises at least one component extending laterally from the peripheral wall (14), externally of the heater (2), and over the at least one terminal region (26) in the vicinity of the at least one connection region (30) .

20. A heater as claimed in claim 19, characterised in that the at least one component is formed integrally with the peripheral wall (14).

21. A heater as claimed in claim 19, characterised in that the at least one component is formed separately from the peripheral wall (14) and is secured to the heater (2) .

22. A heater as claimed in claim 21, characterised in that the at least one component is secured in contact with the peripheral wall (14).

23. A heater as claimed in claim 21 or 22, characterised in that the at least one component comprises material selected from mica and ceramic material.

24. A heater as claimed in any one of claims 19 to 23, characterised in that the at least one component is of a form selected from sheet, strip and block form.

25. A heater as claimed in any one of claims 19 to 24, characterised in that the at least one component has one or more side and/or end portions (34) of wall-like form extending therefrom and adapted to screen one or more side and/or end regions of the at least one terminal region (26) in the vicinity of the at least one connection region (30) .

26. A heater as claimed in any one of claims 13 to 16, characterised in that the at least one screen means (32) comprises at least one component of form selected from strip-form and sheet-form extending laterally from the housing means (22) of the rod-like temperature-responsive device (18) and over the at least one terminal region (26) in the vicinity of the at least one connection region (30) .

27. A heater as claimed in claim 26, characterised in that the at least one component has one or more side and/or end portions (34) of wall-like form extending therefrom and adapted to screen one or more side and/or end regions of the at least one terminal region (26) in the vicinity of the at least one connection region (30) .

28. A heater as claimed in claim 26 or 27, characterised in that the at least one component is provided overlying the housing means (22) of the rod-like temperature- responsive device (18).

29. A heater as claimed in claim 26, 27 or 28, characterised in that the at least one component extends laterally at one side face of the housing means (22) .

30. A heater as claimed in claim 26, 27 or 28, characterised in that the at least one component extends laterally at two opposite side faces of the housing means (22).

31. A heater as claimed in any one of claims 26 to 30, characterised in that the at least one component comprises material selected from mica and ceramic material .

32. A heater as claimed in any one of claims 26 to 31, characterised in that the at least one component serves as a cover for the housing means (22) .

33. A heater as claimed in any one of claims claim 1 to 16, characterised in that the at least one screen means (32) comprises at least one strip-like part extending laterally from the at least one electric terminal means (24) over the at least one terminal region (26) in the vicinity of the at least one connection region (30) .

34. A heater as claimed in claim 33, characterised in that the at least one strip-like part is formed integrally with the at least one electric terminal means (24)

35. A heater as claimed in claim 33 or 34, characterised in that the at least one strip-like part has one or more side and/or end portions (34) of wall-like form extending ζ therefrom and adapted to screen one or more side and/or end regions of the at least one terminal region (26) in the vicinity of the at least one connection region (30) .

36. A heater as claimed in claim 33, 34 or 35, characterised in that the at least one strip-like part comprises metal.

37. A heater as claimed in any preceding claim, characterised in that the base (8) comprises microporous thermal and electrical insulation material.

38. A heater as claimed in any preceding claim, characterised in that the base (8) is provided in a dishlike support (6) .

39. A heater as claimed in claim 38, characterised in that the dish-like support (6) is of metal.

40. A heater as claimed in any preceding claim, characterised in that the plate (4) of the material transmissive of visible radiation comprises glass-ceramic material.

41. A heater as claimed in any preceding claim, characterised in that the plate (4) of the material transmissive of visible radiation comprises a cooking surface for a cooking appliance.