Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2001-03-30
2001-10-09
Paik, Sang (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S448190, C219S460100, C219S462100
Reexamination Certificate
active
06300605
ABSTRACT:
The present invention relates to radiant electric heaters, such as for use in cooking appliances and especially for use in cooking appliances having glass-ceramic cooking surfaces.
DESCRIPTION OF PRIOR ART
It is well known to provide a radiant electric heater for use in a cooking appliance beneath a glass-ceramic cooking surface and in which at least two concentrically-arranged heating elements, separated by a dividing wall of thermal insulation material, are supported on or adjacent to a base of thermal insulation material, such as microporous thermal and electrical insulation material. An outer heating zone and an inner heating zone are thereby provided, the inner heating zone having one or more heating elements which are generally arranged to be energisable independently of the heating element or elements of the outer heating zone.
A peripheral wall of thermal insulation material is generally arranged around the edge of the heater and a rod-like temperature-responsive device extends from a periphery of the heater across the heater to a position at least partly across the inner heating zone.
In order to meet a requirement that the temperature-responsive device should be responsive substantially only to heat from the inner heating zone, even when both inner and outer heating zones are energised, it is known to provide a tunnel of thermal insulation material covering the rod-like temperature-responsive device in the outer heating zone between the peripheral wall and the dividing wall. The heating element in the outer heating zone is arranged to stop short of the tunnel at either side thereof and hence do not intrude into the tunnel. The temperature-responsive device is thus thermally isolated from the heating element in the outer heating zone.
It is further known to provide one or more portions of the heating element of the inner heating zone extending into the tunnel through an aperture in the dividing wall. It has been found expedient to lead such one or more portions of the heating element through the tunnel to a terminal region, or terminal block, at the edge of the heater for electrically connecting the element of the inner heating zone to a power supply. Although the provision of the portion or portions of the heating element passing through the tunnel enables the rod-like temperature-responsive device to be influenced by heat from the element of the inner heating zone over substantially its entire length, a problem can arise in that overheating can occur in the portion or portions of the heating element inside the tunnel. Although the problem applies to all forms of heating elements, it has become particularly apparent with heating elements in the form of corrugated ribbon material, with a risk of premature failure of the portion or portions of an element of such material inside the tunnel. The temperature of the portion or portions inside the tunnel may reach a level about 20 to 50 degrees Celsius higher than the highest temperature in the body of the heater.
OBJECT OF THE INVENTION
It is an object of the present invention to overcome or minimise this problem.
SUMMARY OF THE INVENTION
According to the present invention there is provided a radiant electric heater comprising:
a base of thermal insulation material having supported relative (on or adjacent) thereto at least two concentrically-arranged heating elements separated by a dividing wall of thermal insulation material to form an outer heating zone and an inner heating zone, the heater having a peripheral wall of thermal insulation material;
a tunnel formed of thermal insulation material extending between the peripheral wall and the dividing wall across the outer heating zone and such that the at least one heating element of the outer heating zone is substantially absent from an area occupied by the tunnel;
a rod-like temperature-responsive device extending from a periphery of the heater through the tunnel and at least partly across the inner heating zone, through an aperture provided in the dividing wall;
at least one portion of at least one heating element of the inner heating zone extending into the tunnel; and
ventilation means provided for the tunnel intermediate the ends thereof to reduce temperature within the tunnel to a desired level.
The ventilation means may comprise one or more apertures extending into the tunnel from the outer heating zone.
The one or more apertures may be provided at a base region of side walls of the tunnel.
The tunnel may be of substantially inverted U-shaped cross section and supported on lower edges thereof.
The tunnel may be supported such that one or more apertures is or are provided between the tunnel and the base. The tunnel may be supported on spaced-apart protrusions provided on the base and which may be integral with the base. Alternatively, the tunnel may have one or both lower edges of substantially castellated form. As a further alternative, one or more pedestal regions may be formed by one or more lower regions of the peripheral wall and/or the dividing wall, the tunnel being spaced from the base at one or both ends thereof by the one or more pedestal regions. As a still further alternative, one or more recesses (grooves or holes) may be provided in the base of thermal insulation material extending beneath one or both lower edges of the tunnel.
The tunnel may be integral with the dividing wall and/or the peripheral wall.
The tunnel may comprise bound vermiculite.
The one or more portions of the one or more heating elements of the inner heating zone may extend through the tunnel to a terminal region at the edge of the heater. In this respect, the tunnel may be provided with a laterally-extending portion proximate the peripheral wall to shield the one or more portions of the one or more heating elements in the vicinity of the terminal region.
The one or more heating elements of the inner heating zone may be energisable independently of the heating element or elements of the outer heating zone.
The heating elements may be of ribbon form and may be supported edgewise on the base.
The base may comprise microporous thermal and electrical insulation material.
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:
REFERENCES:
patent: 4350875 (1982-09-01), McWilliams
patent: 5498854 (1996-03-01), McWilliams
patent: 5977523 (1999-11-01), Scott
patent: 6018149 (2000-01-01), Higgins
patent: 2339376 (2000-01-01), None
Search Report Aug. 30, 2000.
Ceramaspeed Limited
Dorman Ira S.
Paik Sang
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