GB2214767A - Ceramic hot-plates - Google Patents

Abstract

Spring 24 biasses the base of dish 1 containing tungsten halogen lamps 3-6 and thermal insulation 2 against quartz or ceramic plate 8 and so reduces the chance of breakage. The strength of the bias may be adjusted by screw 25 and the position of supporting bar 17 by screws 22. <IMAGE>

Description

HEAT SOURCE RETAINING APPARATUS This invention relates to heat source retaining apparatus and also to such apparatus incorporated in heat source apparatus.

The heat source apparatus may be of the kind described in UK Patents Nos. 2132060 and 2148678 of Thorn EMI Appliances Limited, incorporating one or more sources of infra-red radiation. Heating apparatus of this kind consists of, in one example, a shallow, circular tray member containing thermally insulative material and supporting four tubular, infra-redemitting, tungsten-halogen lamps. The tray member, together with typically three similar members may b mounted beneath a continuous layer of glass ceramic, so as to form a cooking hob.

Heat source apparatus comprising frangible material, such as a glass ceramic, is subject to breakage, for instance by impact, for example if a cooking pan is dropped onto the heat source apparatus.

It is a principal object of the invention to overcome this problem.

It may be desirable to incorporate heating apparatus of this kind into a conventional cooking hob, wherein a number of electrical heating elements or gas burners are mounted and which is generally provided with an upper surface of enamelled steel, stainless steel or other such materials, which may not be transmissive to infra-red radiation.

According to the present invention there is provided heat source retaining apparatus comprising resilient biassing means, which is arranged so as to act on means comprising a said heat source so as to securely support said heat source means.

The major advantage of this is that frangibility of heat source apparatus incorporating said heat source retaining apparatus is considerably reduced due to resilience afforded by the resilient biassing means.

This obviates the inconvenience and expense of repairing or replacing the heat source apparatus and furthermore allows a heat source housing to be set in and securely supported within a desired surround in a cooking hob. The construction of the heat source housing is not part of the present invention.

These advantages especially apply to tungstenhalogen heat source apparatus which is itself frangible and preferably that which employs a frangible cooking surface in the form of a heat-transmission layer occupying the space provided by the surround and attached to a tungsten-halogen heat source housing on its inner face. The cooking surface can be used as a cooking utensil itself or as a support for cooking pans; it also serves to protect the tungsten-halogen heat source. The cooking surface is preferably smooth so that it can be easily cleaned. Guarding against breakage of such heat source apparatus according to the invention avoids ingress of extraneous matter beneath the heat-transmission layer, for example spilt liquid or food or broken crockery. As a result of the invention this apparatus can be effectively set into a cooking hob.

Preferred features of the invention are given in the dependent claims. Adjustability of said biassing means allows a certain biassing force to be set during manufacture according to the material(s) of the heat source apparatus to be supported and a certain degree of resilience may thereby be imparted to the heat source apparatus. The resilience is also useful to allow a certain amount of movement caused by expansion and contraction of the apparatus during use.

An advantageous preferred embodiment of the invention uses a retaining member, for example a bar to extend around the inset walls of the heat source apparatus and meet a desired surround, and the biassing means comprises a spring to be connected between the retaining member and the heat source apparatus through a variable fastening so as to be able to adjust the clamping of the heat source apparatus to a certain degree. To be able to further alter the degree of clamping of the heat source means the retaining member may also be adjustable.

The apparatus of this invention therefore enables frangible heat source apparatus, especially of the tungsten-halogen kind, to be incorporated in one or more surrounds in a desired cooking hob, for example an all tungsten-halogen hob or a hob having more than one kind of heat source.

The surround may be made of enamelled steel, stainless steel or other suitable material. The peripheral edge of the heat source apparatus may be provided with a trimming ring of stainless steel or other material, which joins and covers the space between the edge of the apparatus and the edge of the surround.

An embodiment of the invention will now be described by way of example only, with reference to the drawings, in which: Figure 1 shows a partial plan view of heat source apparatus, in accordance with the present invention.

Figure 2 shows a sectional view through Y-Y of the apparatus of Figure 1, Figure 3 shows a sectional view through X-X of the apparatus of Figure 1, and Figure 4 shows a plan view of a cooking hob incorporating four of such heating apparatus.

Referring to Figure 1, heating apparatus consists of a generally circular tray 1, preferably formed from metal, which has a layer 2 of thermally insulative material, which may be fabricated from a microporous material, for example MICROTHERM (Registered Trade Mark), disposed therewithin, on the base thereof. A number, preferably four, sources of infra-red radiation, 3 to 6, which preferably each consist of a tubular infra-red-emitting, quartz or glass ceramic halogenated lamp with a tungsten filament (not shown) are supported above the layer 2, so that they extend across the circular area of the tray 1. A moulding 7 of ceramic fibre material is arranged around the periphery of the tray 1, to act as packing material therefor, and the tray is urged upwardly, by support means described below.Such a heat source housing arrangement F is generally known as a "flan".

The ceramic fibre moulding 7 is sufficiently flexible to allow a certain amount of movement, caused by expansion and contraction of other parts of the apparatus, whilst providing positive location for the lamps.

The heating apparatus is urged upwardly into abutting relation with a disc 8 of an infra-red transmissive material, which is preferably glass ceramic and the extent of which is preferably substantially confined to the circular area directly above the tray 1, within which the infra-red lamps are supported. The disc 8 is mounted in a surround 9 of stainless steel, which forms the support surface of a conventional cooking hob, via a trim ring 10 which is raised above the surface level of the surround 9 and extends around the periphery of the disc 8.

The trim ring 10 which is made of stainless steel or another suitable material, has a lower limb 10a attached beneath the glass ceramic disc 8 and an external, sloping limb 10b, which covers the inner edge of the surround 9. The lower edge of the periphery of the glass ceramic disc is seated on silicone rubber pads on the outer face of the lower limb of the trim ring and the cir-cumferential edge is attached to an intermediate shoulder 10c of the trim ring by a resilient silicone or other heat-and fluid-resistant adhesive sealant A. This mounting prevents ingress of extraneous matter to the interior in normal use. The inner face of the lower limb of the trim ring is in abutting relation with a shoulder on the heating apparatus.A saucepan, or other cooking utensil, containing food to be cooked, may be placed upon the external face of the glass ceramic disc 8, so that it may be heated by infra-red radiation emitted from the lamps 3 to 6, which is transmitted through the glass ceramic.

As is known, the properties of the glass ceramic material provide optimum transmission of infra-red radiation emitted from the infra-red lamps by matching the frequency of infra-red transmission through the glass ceramic with frequency of emission of the lamps.

The transmission characteristics of glass ceramic material are such that wavelengths below 0.6 m are substantially absorbed. However, some visible radiation above this wavelength is transmitted, as red light, thus providing a visible indication of power level.

Figure 4 shows a plan view of a cooking hob incorporating four heat sources as just described and having an enamelled or stainless steel upper surface 9, which surrounds the four glass ceramic discs, 11 to 14, each having a said trim ring 10 provided therearound.

A thermal limiter, which is intended to limit the operating temperature of the glass ceramic layer to e.g.

below 700 C, comprises a bimetallic rod 15 arranged so as to operate a microswitch 16. The limiter is provided between the lamps and the layer 2 of insulative material and is adjusted so that expansion of the rod, due to heat emitted by the lamps, causes one end of the rod to operate the microswitch 16 when the temperature has reached a threshold value, thereby disconnecting the power to the lamps.

Figures 2 and 3, in which like parts are labelled, show sectional views of the apparatus shown in Figure 1, indicating the shape of the features thereof, particularly of the tray 1, as well as showing overall shallowness of the apparatus.

The heat flan F is retained in accordance with the invention by a device comprising a retaining bar 17 spaced apart from and extending around the inset walls of the flan. The retaining bar 17 consists of an elongate portion 18 extending across the base side of the flan, and turned-over elongate sides 19 which are disposed around the sides of the flan and have curved ends 20 which abut the interior face of the surround 9.

The retaining bar 17 is fastened to the interior face of the lower limb 1Oa of the trim ring 10 by means of a pair of rods 20, each disposed between each side of the bar and the flan. The head of each rod 21 is welded to the interior face of the lower limb 1Oa of the trim ring 10 and the other end of the rod passes through a confronting hole in the retaining bar and is fastened by a threaded nut 22. Tightening of the threaded nut on each rod clamps the retaining bar to the underside of the hob surface 9. Thus, the position of the retaining bar can be set during manufacture. The elongate portion 18 of the bar 17 includes a flange 23 on each side to give the bar additional rigidity.

A U-shaped leaf spring 24 is disposed centrally beneath the flan, attached to the inner face of the retaining bar via a screw fastening 25. The arms 26 of the spring pass through apertures 27 in the elongate portion 18 of the retaining bar 17 and rest against the inner face of the base wall of the flan.

The upward force on the flan due to the spring action can be controlled by the degree of tightness of the screw, whereby the clamping of the flan can be controlled as required in order to provide a specified resilience to the apparatus to offset its frangibility.

Thus, the chance of breakage of the frangible parts of the heat source apparatus can be minimised according to the principle of the invention.

The area of the hob surface illuminated by the lamps is not, of course, limited to a substantially circular shape but may be varied by using different shapes and/or sizes of the tray, such as a square or rectangular shape, as well as other suitable shapes and/or configurations of the lamps, such as circular, semi-circular, horse-shoe shape, concentric rings with aligned end portions, or lamps which can be tapped at various points along their lengths.

Heating apparatus in accordance with the present invention may be suitably oriented so that it may be employed in a selected one of various applications, such as microwave ovens, grills, barbecues, toasters, electric fires and rotisseries.

Claims (1)

1. Heat source retaining apparatus comprising resilient biassing means, which is arranged so as to act on means comprising a said heat source so as to securely support said heat source means.

2. Apparatus according to claim 1, wherein said biassing means is adjustable so as to alter the biassing force applied to the said means comprising a said heat source.

3. Apparatus according to claim 2, comprising a retaining member, which is arranged to assist in supporting said heat source means.

Apparatus according to claim 3, wherein said adjustment of the biassing means is achieved through a variable fastening between said biassing means and said retaining member, 5. Apparatus according to claim 4, wherein said variable fastening comprises a screw fastening and said biassing means comprises a U-shaped leaf spring attached to the inner face of said retaining member via said screw fastening, with its arms arranged to act on the inner face of said heat source means.

6. Apparatus according to any preceding claim, wherein said biassing means is arranged to act on the inner face of said heat source means.

7. Apparatus according to any one of claims 3 to 6, comprising means for adjusting the clamping of said retaining member.

8. Apparatus according to claim 8, wherein the means for adjusting the clamping of the retaining member comprises at least one elongate fastener for connecting the retaining member and means comprising a heat source surround and means for adjusting the relative positions of the retaining member and the elongate fastener.

9. Heat source apparatus incorporating retaining apparatus according to any preceding claim.

10. Apparatus according to claim 9, comprising a heat source, accommodated in a housing and set in a surround, and a heat-transmission plate mounted at the exposed side of the heat source.

11. Apparatus according to claim 10, wherein the plate is attached to the surround via means comprising a fluid-resistant seal.

12. Apparatus according to any one of claims 9 to 11, wherein the heat source housing is attached to the heattransmission plate inner face.

13. Apparatus according to claim 12, wherein the heattransmission plate comprises glass ceramic material.