GB2371963A

GB2371963A - Electric heater, particularly for an oven

Info

Publication number: GB2371963A
Application number: GB0102805A
Authority: GB
Inventors: Kevin Ronald Mcwilliams
Original assignee: Ceramaspeed Ltd
Current assignee: Ceramaspeed Ltd
Priority date: 2001-02-03
Filing date: 2001-02-03
Publication date: 2002-08-07
Anticipated expiration: 2021-02-03
Also published as: GB0102805D0; DE20201678U1; GB2371963B

Abstract

An electric heater (2), particularly for use behind a wall (4) (fig 2) of an oven cavity (6), (fig 2) comprises a tray-like support (10) having therein a base layer (12) of microporous thermal insulation material. An elongate metal-sheathed electrical resistance heating element (14) is supported relative to the base layer (12). The base layer may comprise a plurality of tiles of the microporous thermal insulation material arranged in the tray-like support. The wall of the oven may be in contact with, or spaced from, the sheathed heating element. The arrangement is compact and gives good thermal insulation.

Description

ELECTRIC HEATER

This invention relates to an electric heater which finds particular application in an oven, behind a wall of a cavity of the oven. More particularly, the invention relates to such a heater having a heating element comprising an elongate metal-sheathed resistance heating element and which is arranged in compact form on a support with good thermal insulation and efficient performance.

According to the present invention there is provided an electric heater comprising a tray-like support having therein a base layer of microporous thermal insulation material and at least one elongate metal-sheathed electrical resistance heating element supported relative to the base layer.

The supported at least one heating element may be secured relative to the base layer by at least one bracket or clip means engaging the at least one heating element.

Such at least one bracket or clip means may be arranged to extend from the tray-like support through the base layer. The at least one bracket or clip means may be provided integral with the tray-like support and may

comprise at least one cut and bent portion of the traylike support.

The tray-like support may comprise a metal, such as steel, which may be a stainless steel.

The at least one heating element may be supported in contact with the base layer.

The base layer may comprise a plurality of tiles of the microporous thermal insulation material arranged in the tray-like support. Such tiles may be arranged in edgeto-edge configuration in the tray-like support.

The at least one metal-sheathed heating element may be formed with spaced adjacent limbs and elevated regions of the base layer may be provided between adjacent element limbs. Such elevated regions may be formed with ridgelike peaks which may be substantially parallel to the adjacent element limbs. The elevated regions may serve to provide locally increased thermal insulation of the base layer and/or increased robustness of the heater and/or may serve to provide reflection of thermal radiation from the at least one heating element outwardly from the heater.

The heater may be adapted for use in an oven, whereby the heater is overlain by a wall of a cavity of the oven.

The wall of the cavity of the oven may be in contact with, or spaced from, the at least one metal-sheathed heating element.

The wall of the cavity of the oven may be contoured to provide one or more recesses on a side thereof facing the heater, to accommodate the at least one heating element.

Such recess or recesses may be accompanied by one or more corresponding elevated ridges on an opposite side of the wall of the cavity of the oven.

The heater may be provided with elevated regions of the base layer of microporous thermal insulation material which contact the wall of the cavity of the oven.

The arrangement of the heater of the invention provides a compact construction in an oven and excellent thermal insulation and efficiency of operation.

For a better understanding of the 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 perspective view of an embodiment of electric heater according to the present invention ; Figure 2 is a representation of an oven incorporating the heater of Figure 1; Figure 3 is a cross-sectional view of part of the heater of Figure 1, showing bracket or clip means for securing a heating element in the heater; Figure 4 is a cross-sectional view of part of the heater of Figure 1 located against a wall of an oven cavity; Figure 5 is a cross-sectional view of part of the heater of Figure 1 with a heating element thereof located in spaced relationship with a wall of an oven cavity; Figures 6 to 9 are cross-sectional views of alternative constructional arrangements of heating element and base layer of microporous thermal insulation material in the heater of Figure 1, the heater being located against a wall of an oven cavity; and Figures 10 to 12 are cross-sectional views of alternative arrangements of a wall of an oven cavity located with respect to the heater of Figure 1.

Referring to Figures 1 to 4, an electric heater 2 is provided for location behind a wall 4 of a cavity 6 of an oven 8. The wall 4 may, for example, comprise enamelled steel, although other materials could be considered.

The heater 2 comprises a tray-like support 10, such as of stainless steel, having thereon a base layer 12 of compacted microporous thermal insulation material. Such microporous thermal insulation material is known per se and typically comprises a highly dispersed metal oxide powder, such as silica aerogel or pyrogenic silica, mixed with glass filament or ceramic fibre reinforcement, an opacifier such as titanium dioxide, and an optional small quantity of alumina powder to resist shrinkage.

The tray-like support 10 may be quite large, for example 0.5 by 0.5 metres. Since it is quite difficult to provide the base layer 12 by direct compaction of powdered microporous insulation material into a tray-like support 10 of such size, it is preferred to form tiles of the compacted insulation material in a moulding press and then arrange these edge-to-edge in the tray-like support 10 to form the base layer 12.

An elongate metal-sheathed electrical resistance heating element 14 is located on the base layer 12 of microporous

insulation material in the tray-like support 10. As shown particularly in Figure 4, the heating element 14 comprises an electrical resistance heating wire 16 inside a metal sheath 18 and spaced from the metal sheath 18 by compacted powdered high-temperature-withstanding electrical insulation material 20. Such metal-sheathed heating elements are known to the skilled person.

The heating element 14 is secured relative to the base layer 12 by brackets or clips 22 which are suitably provided integral with the tray-like support 10 and, as shown in Figure 3, comprise portions of the tray-like support 10 which are cut out and bent so as to extend through apertures in the base layer 12 and engage the heating element 14.

End regions 24 and 26 of the heating element extend through apertures in the tray-like support 10 and terminals 28 and 30 are provided for connecting the heating element 14 to a power supply (not shown).

As shown in Figure 4, the heater 2 is arranged with the heating element 14 in contact with the outside of the wall 4 of the oven cavity. Although this provides a very compact construction, it may be desirable for some applications to provide clearance between the heating

element 14 and the wall 4 of the oven cavity. Such an arrangement is illustrated in Figure 5 and may result in improved heat distribution as well as avoiding risk of local overheating of the wall 4 and damage to an enamel coating when provided thereon.

Another compact arrangement is illustrated in Figure 6.

Here the heating element 14 is provided in recesses 32 in the base layer 12 of microporous thermal insulation material. This also enables the thickness of the base layer 12 to be increased, thereby providing increased robustness thereof and improved thermal insulation.

Figures 7,8 and 9 show further arrangements in which elevated regions 34 of the base layer 12 are formed between adjacent spaced limbs 14A, 14B of the heating element 14. Such elevated regions can be rounded, as shown in Figure 7, and provide increased thermal insulation.

Alternatively the elevated regions 34 can be formed with ridge-like peaks, as shown in Figure 8 and as also shown by the dotted outlines 34 at the left hand side of Figure 1. In addition to providing increased thermal insulation these elevated regions 34 also serve to reflect, towards the wall 4 of the oven cavity, thermal radiation emitted

laterally by adjacent limbs 14A, 14B of the heating element 14. Such reflected thermal radiation is indicated by the arrows 36 in Figure 8.

In the arrangement of Figure 9, the elevated regions 34 of the base layer 12 contact the wall 4 of the oven cavity. This results in increased robustness of the assembly as well as providing increased thermal insulation.

Figures 10,11 and 12 show arrangements in which the wall 4 of the oven cavity is contoured to provide recesses 38 on a side thereof facing the heater, to accommodate the heating element 14. Such recesses 38 result in complementary elevated ridges 40 on the opposite side of the wall 4. In the arrangement of Figure 10, clearance is provided between the heating element 14 and the wall 4 at the recess 38. The arrangement of Figure 11 is more compact, with the heating element 14 being in contact with the wall 4 at the recess 38.

In the arrangement of Figure 12, the recesses 38 are formed in such a way that the wall 4 of the oven cavity closely follows the contour of the heating element 14.

Claims

1. An electric heater comprising a tray-like support having therein a base layer of microporous thermal insulation material and at least one elongate metalsheathed electrical resistance heating element supported relative to the base layer.

2. A heater as claimed in claim 1, wherein the supported at least one heating element is secured relative to the base layer by at least one bracket or clip means engaging the at least one heating element.

3. A heater as claimed in claim 2, wherein the at least one bracket or clip means is arranged to extend from the tray-like support through the base layer.

4. A heater as claimed in claim 3, wherein the at least one bracket or clip means is provided integral with the tray-like support.

5. A heater as claimed in claim 4, wherein the at least one bracket or clip means comprises at least one cut and bent portion of the tray-like support.

6. A heater as claimed in any preceding claim, wherein the tray-like support comprises a metal.

7. A heater as claimed in claim 6, wherein the metal comprises steel.

8. A heater as claimed in claim 7, wherein the steel comprises a stainless steel.

9. A heater as claimed in any preceding claim, wherein the at least one heating element is supported in contact with the base layer.

10. A heater as claimed in any preceding claim, wherein the base layer comprises tiles of the microporous thermal insulation material arranged in the tray-like support.

11. A heater as claimed in claim 10, wherein the tiles are arranged in edge-to-edge configuration in the traylike support.

12. A heater as claimed in any preceding claim, wherein the at least one metal-sheathed heating element is formed with spaced adjacent element limbs.

13. A heater as claimed in claim 12, wherein elevated regions of the base layer are provided between adjacent element limbs.

14. A heater as claimed in claim 13, wherein the elevated regions of the base layer are formed with ridgelike peaks.

15. A heater as claimed in claim 14, wherein the ridgelike peaks are substantially parallel to the adjacent element limbs.

16. A heater as claimed in claim 13,14 or 15, wherein the elevated regions serve to provide locally increased thermal insulation of the base layer and/or increased robustness of the heater and/or serve to provide reflection of thermal radiation from the at least one heating element outwardly from the heater.

17. A heater as claimed in any preceding claim, adapted for use in an oven, whereby the heater is overlain by a wall of a cavity of the oven.

18. A heater as claimed in claim 17, wherein the wall of the cavity of the oven is contoured to provide one or

more recesses on a side thereof facing the heater to accommodate the at least one heating element.

19. A heater as claimed in claim 18, wherein the recess or recesses is or are accompanied by one or more corresponding elevated ridges on an opposite side of the cavity of the oven.

20. A heater as claimed in claim 17,18 or 19, wherein elevated regions are provided on the base layer of microporous thermal insulation material which contact the wall of the cavity of the oven.

21. An electric heater substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

22. An oven provided with an electric heater as claimed in any preceding claim.