GB2154110A - Improvements in or relating to cooking apparatus - Google Patents

Abstract

A hob has a surface plate (1) of a glass-ceramic material transparent to infrared radiation from heating units located beneath the plate (1). Each unit comprises at least one tungsten halide filament lamp (2) mounted above a reflector (3) which may be clad externally with thermal insulation. Disposed between the plate (1) and the lamp or lamps of each heating unit is a screen of optically transparent heat resistant material that is also transparent to infra-red radiation. The presence of the screen reduces the extent to which the plate (1) is heated by convection. A further reduction can be effected by directing a flow of cooling air over the screen. In some cases, the screen can be omitted and reliance placed solely on the cooling air flow. <IMAGE>

Description

SPECIFICATION Improvements In or Relating to Cooking Apparatus This invention relates to cooking apparatus and has particular reference to electrically-energised cooking apparatus for domestic use.

It has already been proposed to employ as a heating element in cooking apparatus a source of infra-red radiation arranged to direct radiation through a specified part of a surface of glass, ceramic or glass ceramic material permeable to such radiation. Such sources also emit a considerable amount of energy in the visible spectrum and it has been suggested that some of such energy can be prevented from reaching the eyes of a user by employing a surface of a coloured glass, ceramic or ceramic glass, red-brown being an acceptable colour. However, such materials tend to be poor transmitters of the infra-red radiation and therefore the specified part tends to become very hot and, because of the thermal properties, of the materials, tends to take a considerable time to return to a 'safe' temperature, i.e. a temperature that allows the part to be touched without risk of injury.

According to the present invention, cooking apparatus comprises a plate of a heat-resistant material permeable to infra-red radiation, and beneath the plate, one or several spaced sources of infra-red radiation each located beneath a specified area of the plate, means being provided for reducing the transference of heat by convection from the or each source to the plate and further means for controlling the emission of infra-red radiation from the or each source.

The means for reducing heat transfer by convection may comprise a screen of heat-resistant material permeable to infra-red radiation disposed between the plate and the or each source. The screen may be part of a source and may be mounted upon or secured to a reflector forming part of the source, or it may be common to some or all of the sources where there are several sources.

Alternatively, the means for reducing heat transfer by convection may comprise an arrangement for directing a cooling airflow between the plate and the or each source to convey heat from the latter to a suitable exit in the hob.

The screen may also have the property of absorbing to a required extent optically visible radiation from the sources and thus forms an optical filter. In such an arrangement, the plate may be of an optically-transparent, heat resistant material that is also permeable to infra-red radiation.

The optical filter may be located directly beneath the plate or at a position between the plate and the source. The filter may be common to some or all of the sources where there are several sources. In addition, an optical filter may be used as well as the screen or screens. Alternatively, the optical filter may be embodied in the source, for example when the source comprises one or more tungsten lamps, the envelopes of the latter may comprise or incorporate the optical filter.

According to another aspect of the invention, cooking apparatus comprises a plate of a heat resistant material permeable to infra-red radiation, and, beneath the plate one or several spaced sources of infra-red radiation, the or each source comprising an infra-red emitter and a reflector disposed to direct emission incident upon it from the source on to a specified part of the plate, the or each source and its reflector being spaced from the plate and being provided with means for controlling the emission in infra-red radiation from the source.

Means may also be provided for reducing the transference by convection of heat from the or each source to the plate. Such means may comprise a screen of heat-resistant material permeable to infrared radiation disposed between the source and the plate and the screen may form part of a source or it may be common to some or all of the sources where there are several sources. Where individual screens are provided, these may be mounted upon or secured to the reflector.

Alternatively, the means for reducing heat transfer by convection may comprise an arrangementfordirecting a cooling airflow between the plate and the or each source.

The screen may also have the property of absorbing to a required extent optically visible radiation from a source and thus form an optical filter. In such an arrangement, the plate will be of an optically-transparent, heat-resistant material that is also permeable to infra-red radiation.

The optical filter may be embodied in the source, for example where the source comprises one or more tungsten lamps, the envelopes of the latter may comprise or incorporate the optical filter.

An optical filter may be used in addition to the screen and may be located directly beneath the plate or at a position between the plate and the source. The optical filter may be common to some or all of the sources where there are several sources.

The cooking apparatus may be a hob or a cooker or a small readily portable cooking unit.

By way of example only, embodiments of the invention will now be described in greater detail with reference to the accompanying drawings which show the embodiments in schematic form only.

In Fig. 1 there is shown part 1 of the surface plate of a hob which may be an independent unit or part of a cooker. The plate is of a red-brown coloured glass-ceramic material transparent to infra-red radiation for example that known under the Trade Mark "Ceran".

Beneath the plate are disposed several spaced sources of infra-red radiation, for example tungsten filament lamps preferably those containing a suitable halogen to enable them to operate at a high temperature. The filaments of such lamps have a low thermal mass and therefore they respond quickly to changes in the rate at which electrical energy is supplied to them.

Each source is disposed beneath a specified area of the plate and may comprise a single lamp of suitable power or it may comprise several lamps which may be of tubular form, the latter arrangement is shown in Fig. 1 where several tubular lamps 2 are disposed in parallel side-by-side relationship.

Beneath the lamps 2 is a reflector 3 contoured to reflect upwardly through the specified area of the part, radiation incident upon the reflector 3 from the lamps. To reduce the emission of heat from the reflector which will inevitably absorb a proportion of the infra-red radiation, the external surface of the reflector may be clad with a thermal insulating material as shown at 4 in Fig. 1.

As can be seen from Fig. 1, the reflector 3 is generally cup-shaped and across the top is fitted a screen 5 of optically transparent heat resistant material that is also transparent to infra-red radiation for example the material known underthe Trade Mark "Robax".

The unit comprising the lamps, reflector (plus insulation) and screen is spaced from the plate to avoid transferring heat from the unit to the plate by conduction.

The effect of the screen 5 is to minimise transfer of heat from the lamps to the plate by convection. In that way, the temperature of the specific area of the plate is kept low and the area will rapidly reach a safe temperature when the lamps are de-energised.

The extent to which the plate is heated by convection can be reduced still further by arranging an airflow between the plate and the units disposed beneath it. Such an arrangement is illustrated in Fig.

2, the air flow being indicated by the arrows 6. The force airflow is provided by a suitable fan or impeller positioned to one side or the front or back of the hob, and the flow exhausting to atmosphere via a suitably located exit in the hob.

The embodiment shown in Fig. 2 is otherwise similar to that shown in Fig. 1.

By employing an air flow of sufficient intensity, it is possible to dispense with the screen 5. In that case, reliance is placed on the forced airflow to keep to a minimum the transference of heat to the plate by convection.

Each source is controllable separately from the other sources, control being provided for example by switches which effect a sequential de energisation of the several lamps to reduce the output of the source, or by means of a series-parallel connecton of combinations of the lamps or by suitable energy controllers employing for example solid state switching devices for example triacs or thyristors.

The plate employed in the embodiments of Figs. 1 and 2 is of a coloured (normally red-brown) glass ceramic material, the colour serving to absorb to a required extent optically visible radiation from the sources. The degree of absorption allows a user to see that a source is energised and to use the visible radiation as a guide to effecting a required reduction in infra-red output of the source.

In another embodiment arranged substantially as shown in Fig. 1,the plate is of an optically transparent glass-ceramic material that is also permeable to infra-red radiation for example the material "Robax", and the screen 5 is an optical filtertransparentto infra-red radiation. The filter may absorb all visible radiation from the source, or sufficient of the visible radiation may be transmitted through the filter to provide the visible effect referred to in the preceding paragraph.

The filter also assists in reducing heat transfer by convection to the plate and this may be helped by the use of a forced airflow as described above with reference to Fig. 2.

It is not essential that the filter be a part of the source. As shown in Fig. 3, the optical filter could be secured to the undersurface of the plate directly above the source and could be used with and without a source employing a screen 5 forming part of the source. Fig. 3 shows an embodiment with the screen 5 and also a forced air flow between the filter and the screen 5. The forced airflow could be omitted however.

Although Fig. 3 shows the use of an optical filter for each source, this is not essential and the filter may be of a size such that it extends over all the sources thus being common to them all.

Another alternative position for the optical filter is shown in Fig. 4 where it occupies a position between the plate and the source. The position may be central or nearer the plate or the source. The source may also incorporate a screen 5 as shown in Fig. 4 but could be used without a screen and forced air flow may be provided between the filter and the plate or between the filter and both the plate and the source, this latter arrangement being shown in Fig.

4, the flows being indicated by the arrows 7.

It will be appreciated that the embodiments described above with reference to Figs. 3 and 4 will also include individual controls for the various sources and that these controls may be of one or other of the forms described above.

The screen and filter may be of a suitable glass-ceramic material or of toughened glass, a borosilicate glass or quartz for example.

The embodiments described above may be incorporated in a hob unit orthey may be part of an electric cooker. Additionally, the embodiments may be included in small readily portable cooking apparatus which may be simply a hob unit or it may include a small oven andlor grill.

Claims (24)

1. Cooking apparatus comprising a plate of a heat-resistant material permeable to infra-red radiation, and, beneath the plate, one or several spaced sources of infra-red radiation each located beneath a specified area of the plate, means being provided for reducing the transference of heat by convection from the or each source to the plate, and further means for controlling the emission of infrared radiation from the or each source.

2. Apparatus as claimed in claim 1 in which the means comprises a screen of heat-resistant material permeable to infra-red radiation disposed between the plate and the or each source.

3. Apparatus as claimed in claim 2 and including several sources and in which the screen is common to all the sources.

4. Apparatus as claimed in claim 2 in which the screen is a part of the source.

5. Apparatus as claimed in claim 4 in which the or each source includes a reflector for reflecting radiation incident upon it towards the specified area of the plate, and in which the or each screen is mounted upon the reflector.

6. Apparatus as claimed in claim 1 in which the means for directing a cooling airflow between the plate and the or each source.

7. Apparatus as claimed in any one of claims 2-5 in which means are provided for directing a cooling flow of air between the plate and the or each screen.

8. Apparatus as claimed in any one of claims 2--5 and 7 in which the plate is of a material that is also transparent to visible radiation, and in which the screen is also an optical filter impermeable to some at least of visible radiation from a source.

9. Apparatus as claimed in claim 8 and comprising several sources, and in which the optical filter is common to all the sources.

10. Apparatus as claimed in any one of claims 2--5 and 7 in which the plate is of a material that is also transparent to visible radiation, and in which there is located between the plate and the or each source an optical filter impermeable to some at least of visible radiation from a source.

11. Apparatus as claimed in claim 10 in which the optical filter is incorporated in the source.

12. Cooking apparatus comprising a plate of heat-resistant material permeable to infra-red radiation, and, beneath the plate, one or several spaced sources of infra-red radiation, the or each source comprising an infra-red emitter and a reflector disposed to direct emission incident upon it from a source on to a specified part of the plate, the or each source and its reflector being spaced from the plate and being provided with means for controlling the emission of infra-red radiation from the source.

13. Apparatus as claimed in claim 12 in which additional means are provided for reducing the transference by convection of heat from the or each source to the plate.

14. Apparatus as claimed in claim 12 in which the additional means comprises a screen of heat resistant material permeable to infra-red radiation disposed between the plate and the or each source.

15. Apparatus as claimed in claim 14 and including several sources and in which the screen is common to ail the sources.

16. Apparatus as claimed in claim 14 in which the screen is a part of the source.

17. Apparatus as claimed in claim 16 in which the or each screen is mounted upon the reflector of a source.

18. Apparatus as claimed in claim 13 in which the additional means comprises an arrangement for directing a cooling flow of air between the plate and the or each source.

19. Apparatus as claimed in any one of claims 14--18 in which the plate is of a material that is also transparent to visible radiation, and in which the screen is also an optical filter impermeable to some at least of visible radiation from a source.

20. Apparatus as claimed in claim 18 and comprising several sources, and in which the optical filter is common to all the sources.

21. Apparatus as claimed in any one of claims 14--17 in which the plate is of a material that is also transparent to visible radiation, and in which there is located between the plate and the or each source an optical filter impermeable to some at least of visible radiation from a source.

22. Apparatus as claimed in claim 21 in which the optical filter is incorporated in the source.

23. Apparatus as claimed in claim 21 or 22 in which the optical filter is located immediately beneath the plate.

24. Cooking apparatus as herein described with reference to and as illustrated by Fig. 1, 2, 3 or 4 of the accompanying drawings.