GB2187836A

GB2187836A - Cooking hob

Info

Publication number: GB2187836A
Application number: GB08705517A
Authority: GB
Inventors: Graham Howlett Goodchild; Peter William Crossley
Original assignee: Thorn EMI Appliances Ltd
Current assignee: Thorn EMI Appliances Ltd
Priority date: 1986-03-11
Filing date: 1987-03-09
Publication date: 1987-09-16
Anticipated expiration: 2007-03-09
Also published as: GB9011917D0; GB8605948D0; GB2230852B; GB2187836B; GB8705517D0; GB2230852A

Abstract

A cooking hob comprises a cooktop 2 with a heating element 3 mounted beneath the underside of the cooktop, the heating element 3 comprising a substrate 8 having a resistive heater track 9 deposited on a surface thereof, and means 10 to provide enhanced thermal contact between the heating element and the underside of the cooktop 2. Said means 10 may comprise a resilient compressible material to compensate for irregularities in the undersurface of cooktop 2, or a rigid metal plate. The cooktop 2 may be glass ceramic or stainless steel. <IMAGE>

Description

SPECIFICATION Cooking hob This invention relates to cooking hobs and in particularly to electric cooking hobs.

For many years, electric cooking hobs have comprised a number, usually four, hotplates, each consisting of a metal sheathed, electric resistance heater coil in a spiralled formation, set in an enamelled metal surround.

More recently, it has been found advantageous to mount four open, spiralled, resistance heater coils in a cooking hob having a single continuous sheet of glass ceramic as an upper surface for supporting cooking utensils to be heated by the heater coils through the glass ceramic. The coils may each be mounted in a heating unit containing a base layer of a suitable thermally insulative material.

Glass ceramic hobs of this type have proved to be successful due, inter alia, to the provision of a substantially smooth, flat cooktop, which can easily be cleaned. However, there tends to be a considerable lag in thermal response of these hobs, because heat to the cooking utensils is transferred by thermal convection and radiation from the heater coils to, and thermal conduction through, the glass ceramic cooktop, the underside of which is generally spaced from the heater coils.

Furthermore, it is now generally considered to be desirable to provide a cooking hob, which is as shallow as possible, so that it can easily be fitted into the thickness of a worktop, for example, and the depth of known glass ceramic hobs tends to be considerably restricted by their construction.

It is therefore an object of the present invention to provide a cooking hob, which alleviates the above-mentioned problems associated with known hobs, whilst maintaining the significant advantages of such known hobs.

According to the present invention there is provided a cooking hob comprising a cooktop with a heating element mounted beneath the underside of said cooktop, said heating element comprising a substrate having a resistive heater track deposited on a surface thereof, and means to provide enhanced thermal contact between the heating element and the underside of the cooktop.

Preferably, the thermal contact enhancing means is made of a resilient, compressible material to at least partially compensate for irregularities in the surface of the underside of the cooktop.

Preferably, the cooktop is made of a ceramic material.

Preferably, the thermal contact enhancing means is made of a rigid metallic material to inhibit distortion of the cooktop when heated.

Preferably, the upper surface of the cooktop is formed from a single sheet of metallic material.

Preferably, the upper surface of the cooktop is raised above the surrounding area of the said upper surface in the region above the heating element.

The invention will now be further described by way of example only with reference to the accompanying drawings, wherein: Figure 1 shows a schematic sectional view of one embodiment in accordance with the invention, Figure 2 shows a schematic sectional view of another embodiment in accordance with the invention, Figure 3 shows an underside plan view of a heating element having a resistive heater track deposited thereon, as employed in the embodiments shown.

Fig. 1 shows a sectional view of a cooking hob having a base 1, a cooktop 2, made of a glass ceramic material, and a heating unit, shown generally at 3, mounted beneath the cooktop 2 and biassed towards the underside of the cooktop by leaf springs 4 or any other suitable resilient biassing arrangement.

Preferably, the cooking hob includes four heating units, which are preferably circular in plan view, all mounted beneath a single plate of glass ceramic forming the cooktop, thereby providing four respective hotplate regions of the hob.

The heating unit 3 consists of a shallow, metallic, open-topped casing 5 containing a base layer 6 of a thermally-insulative material, such as a microporous insulation material. A heating element, shown generally at 7, is supported on the upper surface of the insulative layer 6 and consists of a substrate 8 having a resistive heater track 9 deposited on the underside thereof.

The substrate 8 may consist of a glass ceramic plate or a metal plate made from stainless steel, for example, coated with a suitable high temperature-resistant, electricallyinsulative, ceramic material. The heater track 9 can be made from any suitable metal and is preferably printed onto the substrate by, for example, thick film or screen printing. Fig. 3 shows an underside plan view of a suitable substrate 8 with a heater track 9 printed thereon.

The heating element 7 is positioned in thermal contact with the underside of the glass ceramic cooktop 2 via a layer 10 of a resilient heat sink material, which enhances thermal conduction from the heating element 7 to the cooktop 2 and also allows for any irregularities in the smoothness of the underside of the cooktop 2, which may otherwise be detrimental to good thermal contact.

Preferably, one or more temperature sensors (not shown) are printed on the upper side of the substrate 8 to monitor the temperature of the glass ceramic cooktop 2, which may be damaged by overheating. The heat output of the heater track 6 can then be controlled, in known manner, in accordance with the output of the temperature sensor or sensors.

It is also preferable that an earth connection is provided to the substrate 8 and it is also necessary to ensure that electrical terminal connections to the heater track 9 do not impede the thermal contact between the heating element 7 and the cooktop 2.

The power output of the heating element 7 is preferably 1500-1800W at mains voltage, in order to achieve an operating temperature of 650-700"C within approximately 30 secs.

from initial energisation.

Fig. 2 shows part of a cooking hob, in accordance with the second aspect of the invention, wherein the cooktop consists of a single pressed sheet 11, of metal, preferably stainless steel. In a hotplate region 13 of the cooktop, a resistive heater track 14 is printed, but thick film or screen printing, for example, onto the underside of a metallic disc 15 preferably also made of stainless steel, and metallic core construction 16 of preferably aluminium or copper, having higher thermal conductivity than the sheet 11, is sandwiched between the disc 15 and the pressed sheet 11.

The core construction 16 inhibits localised distortion by the sheet 11 when heated by the heater track 14, and also aids in inhibiting lateral thermal conduction through the sheet 11 thereby confining a considerable proportion of the heat output of the heater track 14 to the hotplate region 13.

The heater track 14 may be confined as shown by the track in Fig. 3 or any other suitable configuration. It is also preferably made from a suitable metal and has a power output of 1800W at mains voltage and an operating temperature of 500"C attained within 30 secs. of initial energisation.

A cooking hob consisting of four hotplate regions, each in accordance with the region 13 shown in Fig. 2, can therefore be provided with an upper surface formed from a single pressed sheet of stainless steel, thereby forming a continuous smooth surface over the whole cooking hob.

A layer or pad of thermally insulative material (not shown), such as a microporous material, may be mounted adjacent the underside of each hotplate region 13 beneath the heater track 14 to inhibit dissipation of heat in a downward direction and thereby aid in enhancing thermal conduction through the metal core 16.

Instead of the hotplate region 13 being raised above the surrounding area of the upper surface, the metal core 16 may be formed beneath the level of the surrounding part 12, so that the upper surface may be made flat.

Each hotplate region of both of the cooking hobs shown in Figs. 1 and 2 may be any shape or size, although in a preferred arrangment each region is circular. Moreover, each heater track may also be any suitable size or configuration.

It can thus be envisaged that by utilising a heater track, deposited either on a substrate or the underside of the cooktop, the present cooking hob can be constructed so as to have a considerably reduced depth, as compared with conventional hobs. In fact, the hob shown in Fig. 1 can be made so as to have a depth of only 30mm and the hob in Fig. 2 is evidently of minimai depth.

The present cooking hob also provides greater thermal contact between the heater and cooktop than known hobs, thereby encouraging a decrease in thermal response time.

Furthermore, as well as these additional advantages over known cooking hobs, the present invention maintains the important feature of a smooth cooktop, which can easily be cleaned.

Claims

1. A cooking hob comprising a cooktop with a heating element mounted beneath the underside of said cooktop, said heating element comprising a substrate having a resistive heater track deposited on a surface thereof, and means to provide enhanced thermal contact between the heating element and the underside of the cooktop.

2. A cooking hob according to Claim 1, wherein the thermal contact enhancing means is made of a resilient, compressible material to at least partially compensate for irregularities in the surface of the underside of the cooktop.

3. A cooking hob according to Claim 2, wherein the cooktop is made of a ceramic material.

4. A cooking hob according to Claim 1, wherein the thermal contact enhancing means is made of a rigid metallic material to inhibit distortion of the cooktop when heated.

5. A cooking hob according to Claim 4, wherein the upper surface of the cooktop is formed from a single sheet of metallic material.

6. A cooking hob according to Claim 5, wherein the upper surface of the cooktop is raised above the surrounding area of the said upper surface in the region above the heating element.

7. A cooking hob substantially as hereinbefore described with reference to and as illustrated in Fig. 1 or Fig. 2 or Figs. 1 and 3 or Figs. 2 and 3 of the accompanying drawings.