Thermal cut-out device for radiant heaters

Details Thermal cut-out device for radiant heaters Thermal cut-out device for radiant heaters

1985-05-08

1987-05-12

Miller, Jr., George H.

Electric heating

Heating devices

Combined with container, enclosure, or support for material...

219461, 219443, 219462, 219512, 337394, H05B 368

Patent

active

046653074

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to thermal cut-out devices for radiant heaters and to radiant heaters incorporating such thermal cut-out devices.
In a radiant heater, for example for a glass ceramic top cooker, thermal energy emitted by an electric heating element or by an infra-red lamp is transmitted, partly by convection and conduction and partly by radiation, to and through the glass ceramic and is absorbed by a cooking utensil positioned on the cooking surface above the heater. It is conventional in such heaters to include a thermal cut-out device to prevent the exposed surface of the glass ceramic rising above about 600.degree. C. which could cause damage to or discolouration of the cooking surface. We have found, however, that under certain circumstances the thermal cut-out device can be caused to operate at an undesirably low temperature due to incident radiation.
It is therefore an object of the present invention to provide a thermal cut-out device which is less sensitive to incident thermal radiation. It is a further object of the present invention to provide a radiant heater which incorporates such a thermal cut-out device.
According to one aspect of the present invention there is provided a thermal cut-out device for a radiant heater, which thermal cut-out device comprises a probe-type thermally responsive assembly, characterised in that at least a part of the thermally responsive assembly is coated with and/or is surrounded by a radiation reflective material.
According to a further aspect of the present invention there is provided a radiant heater, for example for a glass ceramic top cooker, which heater comprises at least one heating element and a thermal cut-out device comprising a probe-type thermally responsive assembly which extends across the heater, characterised in that at least a part of the thermally responsive assembly is coated with and/or is surrounded by a radiation reflective material.
The heating element, for example, may be in the form of a helically coiled bare wire or may be an infra-red lamp. The heating element may be arranged on a base layer of thermally insulating material or may be supported above a reflector. A peripheral wall of thermal insulation material may surround the at least one heating element.
In one embodiment of the present invention, the thermal cut-out device includes a snap-acting switch assembly and the probe-type assembly comprises a first element of material having a relatively high coefficient of thermal expansion and a second element of material having a relatively low coefficient of thermal expansion, one of which elements is coupled with the snap-acting switch assembly.
Preferably, the thermally responsive assembly comprises a metal rod coupled with the snap-acting switch assembly and arranged within a high temperature resistant glass tube.
The metal rod may be coated with a metal such as gold or a suitable element from Group VIII of the Periodic Table, or with a high temperature resistant powder, for example a metal oxide such as aluminum oxide, magnesium oxide, titanium dioxide or tin oxide. Additionally, or alternatively, the glass tube may be coated with metal or metal foil or, preferably, coated at least partly with a suitable powder. Instead of, or in addition to, coating the metal rod or the glass tube, a radiation reflective barrier may be positioned between the metal rod and the glass tube and/or may be positioned around the glass tube. Such a barrier may be made of or may be coated with a metal such as gold or a suitable element from Group VIII of the Periodic Table or may be made of or coated with a powder such as aluminium oxide, magnesium oxide, titanium dioxide or tin oxide. For example, gold in liquid form or as a paste may be coated onto a ceramic tube made of a material such as magnesium silicate.
Instead of providing a radiation reflective barrier, the tube itself may be made of a radiation reflective particulate material.
Where the barrier or the tube is made of or coated with a powder, the particle size of the powder is preferabl

REFERENCES:
patent: 2559372 (1951-07-01), Rike
patent: 2626755 (1953-01-01), Tidd
patent: 3710076 (1973-01-01), Frazier
patent: 3883719 (1975-05-01), Hurko
patent: 4267815 (1981-05-01), Gossler

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