Abstrict
A radiant electric heater includes a base (2) of insulation material
and a lamp-form heating element (3) supported adjacent to a surface
of the base. The lamp-form heating element is in the form of a filament
(4) inside an elongate envelope (5). The surface of the base (2)
is locally depressed (dished or ramped) beneath the envelope (5).
A corrugated ribbon heating element (7) is supported on edge relative
to the surface of the base (2). A portion of the corrugated ribbon
heating element (7) crosses the at least one lamp-form heating element
(3) beneath the envelope (5) and substantially conforms to the contour
of the locally depressed surface and is free from contact with the
envelope (5).
Claims
I claim:
1. A radiant electric heater comprising a base of insulation material;
at least one lamp-form heating element supported adjacent to a surface
of the base, the at least one lamp-form heating element comprising
a filament inside an elongate envelope and the surface of the base
being locally depressed beneath the envelope; and at least one corrugated
ribbon heating element supported on edge relative to the surface
of the base, at least one portion of the at least one corrugated
ribbon heating element crossing the at least one lamp-form heating
element beneath the envelope and transversely relative to a longitudinal
direction of the envelope, with the at least one portion of the
corrugated ribbon heating element substantially conforming to a
contour of the locally depressed surface and being free from contact
with the envelope, the at least one portion of the at least one
corrugated ribbon heating element substantially conforming to the
contour of the locally depressed surface of the base by means of
a corrugation pitch, at least one region of the at least one portion
of the at least one element having a different corrugation pitch
at a location in the vicinity of the surface of the base from that
at a corresponding location remote from the surface of the base.
2. A heater according to claim 1, wherein the locally depressed
surface of the base is of substantially channel form, having sloping
entry and exit sections.
3. A heater according to claim 2, wherein the sloping entry and
exit sections are curved.
4. A heater according to claim 2, wherein the sloping entry and
exit sections are stepped.
5. A heater according to claim 1, wherein the at least one portion
of the at least one corrugated ribbon heating element is arranged
to cross the at least one lamp-form heating element beneath the
envelope thereof at least at one region of the envelope at which
the filament therein is substantially inactive.
6. A heater according to claim 1, wherein the base comprises microporous
thermal and electrical insulation material.
7. A heater according to claim 6, wherein the insulation material
is provided in a dish-like support.
8. A heater according to claim 7, wherein the dish-like support
comprises metal.
9. A heater according to claim 1, wherein the at least one lamp-form
heating element comprises a tungsten filament inside a quartz glass
envelope.
10. A heater according to claim 9, wherein the envelope is sealed.
11. A heater according to claim 10, wherein the envelope contains
a halogenated atmosphere.
12. A heater according to claim 1, wherein the elongate envelope
of the at least one lamp-form heating element is substantially straight.
13. A heater according to claim 1, wherein the elongate envelope
of the at least one lamp-form heating element is of a non-straight
shape.
14. A heater according to claim 13, wherein the non-straight shape
comprises a substantially circular shape.
15. A heater according to claim 1, wherein the at least one corrugated
ribbon heating element is provided with leg portions extending edgewise
therefrom and at least partly embedded in the surface of the base.
16. A heater according to claim 1, wherein the at least one corrugated
ribbon heating element is arranged for electrical connection in
series with the at least one lamp-form heating element.
Description This invention concerns radiant electric heaters particularly for
use in cooking appliances such as glass-ceramic cooking appliances.
The invention is particularly concerned with such heaters which
incorporate one or more lamp-form heating elements together with
one or more ribbon heating elements.
DESCRIPTION OF PRIOR ART
Radiant electric heaters are known which comprise a base layer
of insulation material having supported adjacent thereto one or
more lamp-form heating elements. The or each lamp-form heating element
generally comprises a filament, such as of tungsten, inside an elongate
envelope, such as of quartz glass, the elongate envelope being either
straight or substantially circular. Such radiant electric heaters
are known, for example, from European Patent Publication No. 0 176
027 in which a coiled wire heating element is additionally supported
relative to the base in the region of the lamp-form heating element.
It is known additionally to provide one or more corrugated ribbon
heating elements supported edgewise on the base layer. Such one
or more ribbon heating elements may be arranged for electrical connection
in series with the one or more lamp-form heating elements and may
serve to damp inrush current through the latter when energised,
such inrush current resulting from the large positive temperature
coefficient of resistance of the filament material, such as tungsten.
With heaters of this construction there is a requirement for one
or more portions of the one or more ribbon heating elements to cross
the one or more lamp-form heating elements, particularly to allow
electrical connection to terminal means at the edge of the heater.
This has been solved hitherto by welding a wire or flat metal strip
to the ribbon heating element and passing the wire or flat metal
strip beneath the lamp envelope. This is disadvantageous since it
requires an additional process step and unreliability can occur
in the welded junction between the ribbon and the wire or flat strip.
OBJECT OF THE INVENTION
It is an object of the present invention to overcome or minimise
this problem.
SUMMARY OF THE INVENTION
The present invention provides a radiant electric heater comprising
a base of insulation material; at least one lamp-form heating element
supported adjacent to a surface of the base, the at least one lamp-form
heating element comprising a filament inside an elongate envelope,
the surface of the base being locally depressed (dished or ramped)
beneath the envelope; and at least one corrugated ribbon heating
element supported on edge relative to the surface of the base, at
least one portion of the at least one corrugated ribbon heating
element crossing the at least one lamp-form heating element beneath
the envelope with the at least one portion of the corrugated ribbon
heating element substantially conforming to the contour of the locally
depressed surface and being free from contact with the envelope.
The at least one portion of the at least one corrugated ribbon
heating element may substantially conform to the contour of the
locally depressed (dished or ramped) surface of the base by means
of a corrugation pitch at one or more regions of the at least one
portion of the at least one element having a different value at
a location in the vicinity of the surface of the base from that
at a corresponding location remote from the surface of the base.
The locally depressed (dished or ramped) surface of the base may
be of substantially channel form, for example including sloping
entry and exit sections, which may be curved or stepped.
The at least one portion of the at least one corrugated ribbon
heating element may be arranged to cross the at least one lamp-form
heating element beneath the envelope thereof at one or more regions
of the envelope at which the filament therein is substantially inactive.
The base may comprise microporous thermal and electrical insulation
material which may be provided in a dish-like support, such as of
metal.
The at least one lamp-form heating element may comprise a tungsten
filament inside a quartz glass envelope which may be sealed and
may contain a halogenated atmosphere.
The elongate envelope of the at least one lamp-form heating element
may be substantially straight or may be of a non-straight shape,
including a substantially circular shape.
The at least one corrugated ribbon heating element may be provided
with leg portions extending edgewise therefrom and at least partly
embedded in the surface of the base.
The at least one corrugated ribbon heating element may be arranged
for electrical connection in series with the at least one lamp-form
heating element.
By means of the invention, the edgewise-supported at least one
ribbon heating element is able to flex in its corrugations to descend
on one side of the local depression in the surface of the base,
to pass under the envelope of the at least one lamp-form heating
element and to ascend on the other side of the local depression
at the other side of the lamp-form heating element without contact
with the envelope. The need for a separate wire or flat tape connecting
link welded to the ribbon heating element and passing under the
envelope of the lamp-form heating element is avoided.
The invention is now described by way of example with reference
to the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a radiant electric heater according to
the invention; and
FIGS. 2A and 2B are cross-sectional views of the heater of FIG.
1.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring to the drawings, a radiant electric heater comprises
a metal dish-like support 1 containing a base 2 of insulation material,
suitably comprising well-known compacted microporous thermal and
electrical insulation material. A lamp-form heating element 3 is
supported adjacent to a surface of the base 2. The lamp-form heating
element 3 suitably comprises a tungsten filament 4 inside a substantially
circular elongate envelope 5, suitably of quartz glass. The envelope
is sealed and contains a halogenated atmosphere. A groove 6 is optionally
provided underneath the lamp envelope.
A corrugated ribbon heating element 7 is supported on edge and
partly embedded in the surface of the base 2. The ribbon heating
element 7 is of known form and includes leg portions 7A integral
therewith and extending edgewise therefrom and which are at least
partly embedded in the surface of the base 2 for securing the ribbon
heating element thereto.
More than one lamp-form heating element 3 and more than one corrugated
ribbon heating element 7 may be provided in the heater if required.
Shapes, other than circular, for the lamp-form heating element 3
may also be considered. For example, a substantially straight shape,
or any other required shape, may be considered for the envelope
5.
The corrugated ribbon heating element 7 may serve as a ballast
resistance element to damp inrush current through the filament of
the lamp-form heating element when the latter is electrically energised
for operation. For such purpose the ribbon heating element 7 is
arranged to be electrically connected in series with the lamp-form
heating element 3.
The heating elements 3 and 7 may, however, be arranged for independent
operation in the heater.
The corrugated ribbon heating element 7 is required to cross the
lamp-form heating element 3 beneath the envelope 5 thereof. Such
crossing is required at region 8 to enable an end 9 of the ribbon
heating element to be connected to a terminal block 10 at the edge
of the heater. Crossing of the lamp-form heating element 3 is also
required at region 11 to accommodate a reversal in the pattern arrangement
of the corrugated ribbon heating element 7.
Regions 8 and 11 are advantageous crossing points because there
the filament 4 is substantially inactive, being connected to terminations
4A. This minimises undesirable heating of the underlying ribbon
heating element by the lamp-form heating element 3.
FIG. 2A shows how the crossing beneath the lamp envelope 5 at region
8 is achieved, the crossing under the lamp envelope 5 at region
11 being substantially the same and will not be separately described
in detail, although illustrated in FIG. 2B.
The surface of the base 2 is locally depressed (dished or ramped)
12 beneath the envelope 5. Such locally depressed surface is conveniently
of substantially channel form and includes sloping entry and exit
sections which can be of curved or stepped form. A portion of the
corrugated ribbon heating element 7 is partly embedded edgewise,
by means of its leg portions 7A in the depressed surface 12, conforming
to the contours of the surface and passing beneath the envelope
5 without contact therewith.
The corrugated ribbon heating element 7 is compliant and conforms
to the contours of the locally depressed surface of the base by
appropriate accommodation by the corrugations of the element. At
region 13 of the ribbon heating element, the element is supported
on a substantially planar major surface of the base 2 and the corrugations
in the element have a corrugation pitch which is the same at a location
14 thereof adjacent to the surface of the base 2 as at a location
15 thereof remote from the surface of the base.
At region 16, the ribbon heating element is flexed to change from
the planar major surface of the base and descend on the sloping
section 17 of the locally depressed surface of the base. To accommodate
the flexing, the corrugations change so that the corrugation pitch
at a location 18 adjacent to the surface of the base 2 is smaller
than the corrugation pitch at a corresponding location 19 remote
from the surface of the base 2.
At region 20 of the ribbon heating element, flexing of the element
in the opposite sense occurs. Here the corrugation pitch at a location
21 adjacent to the surface of the base 2 is larger than that at
a corresponding location 22 remote from the surface of the base
2.
After passing under the envelope 5 of the lamp-form heating element
at region 20, the ribbon heating element ascends on the sloping
section 23 of the locally depressed surface of the base and is flexed
at region 24 in a similar manner to that previously described with
reference to region 16. After further flexing, the end 9 of the
ribbon element is then connected to terminal block 10.
In manufacturing the heater, the ribbon heating element 7 is secured
to the base 2 before the lamp-form heating element 3 is located
in position. The base 2 is pre-formed with the required locally
depressed region or regions and the ribbon heating element 7 is
partly embedded in the surface of the base, including the one or
more depressed surface regions, in a single operation using an appropriately-shaped
press tool in which the element 7 is temporarily supported.
Alternatively, the base 2 can be pre-formed without the required
locally depressed regions which are then formed during subsequent
embedding of the ribbon heating element 7 using the press tool.
The lamp-form heating element 3 is then fitted to the heater.
A peripheral wall 25 of insulation material is provided on the
heater and is arranged to contact the underside of a glass-ceramic
cooking plate (not shown) of a smooth top cooking appliance.
A well-known form of temperature limiter 26 is also provided on
the heater.
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