Abstrict
A radiant electric heater comprises at least first and second adjacent
heating zones (8, 12), the first heating zone (8) including a first
heating element (6) and the second heating zone (12) including a
second heating element (10). The heating elements are supported
relative to a base (4) of thermal and electrical insulation material.
Terminal means (30) is provided at a periphery of the heater for
connecting the first and second heating elements (6, 10) to a source
of electrical energy. The heating elements (6, 10) are formed from
a single elongate electrically conductive material, the heating
elements having a conjoined first terminal region (20) connected
to a first electrical connector (32) at the terminal means (30),
having a free second terminal region (18) connected to a second
electrical connector (34) at the terminal means (30), and having
a free third terminal region (16) connected to a third electrical
connector (36) at the terminal means (30). At least one of the first,
second and third terminal regions (20, 16, 18) traverses the second
heating zone (12) for connection to the respective electrical connector
(32, 34, 36).
Claims
I claim
1. A radiant electric heater comprising at least first and second
adjacent heating zones, the first heating zone including a first
heating element and the second heating zone including a second heating
element, the heating elements being supported relative to a base
of thermal and electrical insulation material, and terminal means
provided at a periphery of the heater for connecting the first and
second heating elements to a source of electrical energy, wherein
the heating elements are formed from a single elongate electrically
conductive member, the heating elements having a conjoined first
terminal region connected to a first electrical connector at the
terminal means, having free second terminal region connected to
a second electrical connector at the terminal means, and having
a free third terminal region connected to a third electrical connector
at the terminal means, wherein at least one of the first, second
and third terminal regions traverses the second heating zone for
connection to the respective electrical connector.
2. A heater as claimed in claim 1, wherein the heating elements
are in the form of a ribbon secured upright into the base of thermal
and electrical insulation material.
3. A heater as claimed in claim 1, wherein the first heating zone
is circular and the second heating zone is at least part-circular
and at least partially surrounds the first heating zone.
4. A heater as claimed in claim 3, wherein the conjoined terminal
regions of the heating elements comprise a looped distal region
of the second heating element welded to a portion of the first heating
element.
5. A heater as claimed in claim 1, wherein a peripheral wall is
provided around the external periphery of the heater.
6. A heater as claimed in claim 1, wherein a dividing wall is provided
between the adjacent heating zones.
7. A heater as claimed in claim 1, wherein a temperature-responsive
device is provided for sensing the temperature in the region of
at least the first heating zone.
8. A heater as claimed in claim 1, wherein the at least one of
the first, second and third terminal regions traversing the second
heating zone comprises a plurality of portions of the elongate electrically
conductive member electrically connected in parallel.
9. A heater as claimed in claim 8, wherein the plurality of portions
of the elongate electrically conductive member electrically connected
in parallel comprise a plurality of elongate close meanders of the
elongate electrically conductive member traversing the second heating
zone and electrically interconnected thereacross at least at opposite
ends thereof.
10. A heater as claimed in claim 9, wherein the plurality of elongate
close meanders of the elongate electrically conductive member are
electrically interconnected thereacross at least at opposite ends
thereof by means selected from welding, folding and crimping.
11. A heater as claimed in claim 9, wherein the meanders comprise
elongate substantially straight sections interconnected by at least
one looped end.
12. A heater as claimed in claim 11, wherein the at least one looped
end of the meanders has been severed subsequent to electrical interconnection
of the meanders in parallel.
13. A heater as claimed in claim 1, wherein at least one of cuts
and welds is provided at at least one portion of the elongate electrically
conductive member.
14. A heater as claimed in claim 13, wherein the at least one of
cuts and welds is provided to respectively disconnect and reconnect
at least one portion of the elongate electrically conductive member.
15. A heater as claimed in claim 14, wherein the at least one of
cuts and welds is provided to respectively disconnect and reconnect
at least one portion of the elongate electrically conductive member
at the terminal regions thereof.
16. A heater as claimed in claim 1, wherein the at least one of
the terminal regions of the elongate electrically conductive member
traverses the second heating zone such as to overlie the second
heating element and be spaced therefrom.
17. A heater as claimed in claim 16, wherein the at least one of
the terminal regions of the elongate electrically conductive member
is provided in at least one recess formed in the base of thermal
and electrical insulation material underlying the second heating
element.
18. A heater as claimed in claim 1, wherein the at least one of
the terminal regions of the elongate electrically conductive member
traverses the second heating zone such as to underlie the second
heating element and be spaced therefrom.
19. A heater as claimed in claim 18, wherein the at least one of
the terminal regions of the elongate electrically conductive member
is provided in at least one recess formed in the base of thermal
and electrical insulation material underlying the second heating
element.
20. A heater as claimed in claim 1, wherein the free first terminal
region is provided in the second heating zone at an end of the second
heating element remote from the conjoined terminal region, with
the free second terminal region being provided at an end of the
first heating element remote from the conjoined terminal region,
the conjoined terminal region and the free first terminal region
traversing the second heating zone.
21. A heater as claimed in claim 1, wherein the at least one of
the terminal regions traversing the second heating zone is adapted
to be substantially non-visibly radiating when the heater is energised.
22. A heater as claimed in claim 1, wherein the at least one of
the terminal regions traversing the second heating zone is adapted
to be of reduced visible radiance relative to the remainder of the
heating elements when the heater is energised.
23. A heater as claimed in claim 1, wherein the third electrical
connector is positioned intermediate the first and second electrical
connectors.
24. A heater as claimed in claim 1, wherein the terminal regions
of the heating elements are connected to the respective first, second
and third electrical connectors by welding.
25. A heater as claimed in claim 1, wherein the terminal means
comprises at least one terminal block supported at the periphery
of the heater and accommodating the first, second and third electrical
connectors.
26. A heater as claimed in claim 1, wherein the elongate electrically
conductive member forming the first and second heating elements
with their conjoined and free terminal regions is provided as a
pre-formed component for supporting relative to the base of thermal
and electrical insulation material.
27. A heater as claimed in claim 1, wherein a dish-like support
is provided, receiving the base of thermal and electrical insulation
material.
28. A heater as claimed in claim 27, wherein the dish-like support
comprises metal.
29. A heater as claimed in claim 27, wherein the terminal means
is supported at a peripheral rim of the dish-like support.
Description [0001] This invention relates to a radiant electric heater and
in particular relates to a radiant electric heater, for example
for a glass-ceramic cooking appliance, comprising at least first
and second adjacent heating zones.
DESCRIPTION OF PRIOR ART
[0002] It is known to manufacture radiant electric heaters for
glass-ceramic top cooking appliances which are provided with two
heating zones in the form of an inner, circular, heating zone and
an outer, annular, heating zone extending around the inner zone.
The inner and outer heating zones may, or may not, be separated
by a dividing wall of thermal insulating material so as to define,
if desired, separate and distinct heating zones on the glass-ceramic
cooking surface. The inner and outer heating zones are each constituted
by a heating element in the form of a ribbon or coil material which
is configured to occupy the space allotted to the heating zone concerned
and which is supported on a base of thermal insulation material
provided in a dish-like support. Thus, a first heating element is
provided in the inner heating zone and a second heating element
is provided in the outer heating zone. A probe-type temperature
sensor, or other suitable type of temperature sensor, extends over
the outer and inner heating zones and is adapted to be responsive
in particular to the temperature of the glass-ceramic cooking surface
in the region of the inner heating zone. The heating elements are
connected to the temperature sensor and to a source of electrical
power by way of a terminal block provided at a peripheral wall of
the supporting dish. The terminal block is provided adjacent to
the temperature sensor and is formed with three electrical connectors,
a first connector adjacent to the temperature sensor, a second connector
remote from the temperature sensor and a third connector intermediate
the first and second connectors. It is common practice in such heaters
to connect the first connector externally of the supporting dish
directly to an electrical connector of the temperature sensor, for
example by means of welding, and internally of the dish to one end
of each of the first and second heating elements. It is also common
practice to connect the other end of the second heating element
to the second connector within the dish and to connect the other
end of the first heating element to the third connector within the
dish, the connection between the end of the first heating element
and the third connector being by way of a link which is secured
at one end of the first heating element, passes over the end of
the second heating element, and is connected to, or integral with,
the third connector.
[0003] Disadvantages of such known radiant electric heaters are
that the presence of two separate heating elements and the manner
in which the heating elements are secured to the electrical connectors,
particularly involving one or more separate links, render the insertion
of the heating elements into their positions on the base of insulating
material in the supporting dish unsuitable for automatic production
methods.
OBJECT OF THE INVENTION
[0004] It is an object of the present invention to overcome or
minimise the above problems.
SUMMARY OF THE INVENTION
[0005] According to the present invention there is provided a radiant
electric heater comprising at least first and second adjacent heating
zones, the first heating zone including a first heating element
and the second heating zone including a second heating element,
the heating elements being supported relative to a base of thermal
and electrical insulation material, and terminal means provided
at a periphery of the heater for connecting the first and second
heating elements to a source of electrical energy, wherein the heating
elements are formed from a single elongate electrically conductive
member, the heating elements having a conjoined first terminal region
connected to a first electrical connector at the terminal means,
having a free second terminal region connected to a second electrical
connector at the terminal means, and having a free third terminal
region connected to a third electrical connector at the terminal
means, wherein at least one of the first, second and third terminal
regions traverses the second heating zone for connection to the
respective electrical connector.
[0006] The heating elements may be in the form of a ribbon secured
upright into the base of thermal and electrical insulation material.
[0007] The first heating zone may be circular, with the second
heating zone being at least part-circular and at least partially
surrounding the first heating zone. The conjoined terminal regions
of the heating elements may comprise a looped distal region of the
second heating element welded to a portion of the first heating
element.
[0008] A peripheral wall may be provided around the external periphery
of the heater.
[0009] A dividing wall may be provided between the adjacent heating
zones.
[0010] A temperature-responsive device may be provided for sensing
the temperature in the region of at least the first heating zone.
[0011] The at least one of the first, second and third terminal
regions traversing the second heating zone may comprise a plurality
of portions of the elongate electrically conductive member electrically
connected in parallel.
[0012] The plurality of portions of the elongate electrically conductive
member electrically connected in parallel may comprise a plurality
of elongate close meanders of the elongate electrically conductive
member traversing the second heating zone and electrically interconnected
thereacross at least at opposite ends thereof, such as by welding,
folding or crimping.
[0013] The meanders may comprise elongate substantially straight
sections interconnected by one or more looped ends and may have
one or more looped ends thereof which has or have been severed subsequent
to electrical interconnection of the meanders in parallel.
[0014] One or more of cuts and welds may be provided at one or
more portions of the electrically conductive member, in particular
to respectively disconnect and reconnect one or more portions of
the elongate electrically conductive member, particularly at the
terminal regions thereof.
[0015] The at least one of the terminal regions of the elongate
electrically conductive member may traverse the second heating zone
such as to overlie or underlie the second heating element and spaced
therefrom.
[0016] The at least one of the terminal regions of the elongate
electrically conductive member may be provided in one or more recesses
or grooves formed in the base of thermal and electrical insulation
material underlying the second heating element.
[0017] The free first terminal region may be provided in the second
heating zone at an end of the second heating element remote from
the conjoined terminal region, with the free second terminal region
being provided at an end of the first heating element remote from
the conjoined terminal region, the conjoined terminal region and
the free first terminal region traversing the second heating zone.
[0018] The at least one of the terminal regions traversing the
second heating zone may be substantially non-visibly radiating,
or of reduced visible radiance relative to the remainder of the
heating elements, when the heater is energised.
[0019] The third electrical connector may be positioned intermediate
the first and second electrical connectors.
[0020] The terminal regions of the heating elements may be connected
to the respective first, second and third electrical connectors
by welding.
[0021] The terminal means may comprise at least one terminal block
supported at the periphery of the heater and accommodating the first,
second and third electrical connectors.
[0022] The elongate electrically conductive member forming the
first and second heating elements with their conjoined and free
terminal regions may be provided as a pre-formed component for supporting
relative to the base of thermal and electrical insulation material.
[0023] A dish-like support, such as of metal, may be provided,
receiving the base of thermal and electrical insulation material.
The terminal means may be supported at a peripheral rim of the dish-like
support.
[0024] By means of the present invention, a cost-effective radiant
electric heater is provided having at least two heating zones and
in which at least two heating elements and their associated terminal
regions are integrally provided for assembly onto a base of thermal
and electrical insulation material, to form the heater. An assembly
of the heating elements and their associated terminal regions is
readily provided by automated techniques, suitably comprising the
use of a jig means into which the integral heating elements are
wound, and their terminal regions formed. The assembly is then readily
transferred from the jig to the base of insulation material and
into the surface of which it is suitably impressed and secured.
[0025] For a better understanding of the present 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:
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a plan view of an embodiment of a radiant electric
heater according to the present invention;
[0027] FIG. 2 is a perspective view of a portion of ribbon form
heating element material as used in the heater of FIG. 1;
[0028] FIG. 3 is a perspective view of part of a jig in which is
formed the integral heating elements and terminal regions thereof
of the heater of FIG. 1; and
[0029] FIG. 4 is a plan view of another embodiment of a radiant
electric heater according to the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0030] Referring to FIG. 1, a radiant electric heater comprises
a dish-like support 2, for example of metal, containing a base 4
of thermal and electrical insulation material, for example compressed
microporous thermal and electrical insulation material. Secured
to the base 4 is a first heating element 6 of ribbon form material
inserted upright into the base, the first heating element 6 occupying
a substantially circular inner first heating zone 8 in the central
region of the heater. Also secured to the base 4 is a second heating
element 10 of ribbon form material inserted upright into the base,
the second heating element 10 occupying a substantially annular
outer second heating zone 12 around the peripheral region of the
heater. The first and second heating elements 6, 10 are integral,
formed of a single elongate electrically conductive member in the
form of a length of the ribbon form heating element material. The
integral ribbon form heating elements 6, 10 may be of corrugated
from, such as shown in FIG. 2 and may be provided with legs 14,
integral therewith or secured thereto, for insertion into the base
4 of insulation material.
[0031] As will be described in detail hereinafter, the first heating
element 6 has a free terminal region 16 and the second heating element
10 has a free terminal region 18. The first and second heating elements
6, 10 also have a conjoined terminal region 20.
[0032] In practice, the first heating element 6 is arranged to
be energised whenever the heater is energised, irrespective of the
size of a cooking utensil placed on a cooking surface (not shown)
below which the heater is arranged, while the second heating element
10 is only energised in conjunction with the first heating element
6, and only when a relatively large cooking utensil is used such
that the cooking utensil overlies both the first and second heating
elements 6, 10.
[0033] A peripheral wall 22 of thermal insulation material extends
around the periphery of the heater between the outer second heating
zone 12 and an upstanding rim of the dish-like support 2.
[0034] A dividing wall 24 of thermal insulation material may optionally
be provided between the first 8 and second 12 heating zones.
[0035] A probe-type temperature-responsive device 26 extends from
a periphery of the heater, a temperature-sensing portion 28 of the
device 26 extending substantially over the first heating element
6 in the inner first heating zone 8.
[0036] A terminal block 30 is mounted on the upstanding peripheral
rim of the dish-like support 2 adjacent to the temperature-responsive
device 26 and is provided with a first electrical connector 32 adjacent
to the temperature-responsive device 26, a second electrical connector
34 remote from the temperature-responsive device and with a third
electrical connector 36 intermediate the first and second electrical
connectors.
[0037] Externally of the dish-like support 2, the first electrical
connector 32 may be connected directly, for example by welding,
to an electrical connector of the temperature-responsive device
26.
[0038] The conjoined terminal region 20 of the first and second
heating elements 6, 10 comprises meanders of the ribbon form heating
element material traversing the second heating zone 12 and consisting
of two elongate substantially straight sections 38, 40 interconnected
by a loop 42. Such two elongate substantially straight sections
38, 40 may traverse the second heating zone 12 such that they overlie
or underlie and are spaced from the second heating element 10. They
are preferably arranged to underlie the second heating element 10
and are provided in one or more recesses or grooves pressed into
the base 4 of insulation material underneath the second heating
element 10. The two elongate substantially straight sections 38,
40 are electrically connected in parallel by welding them together
at regions 44 and 46 at opposite ends thereof. They are also welded
to the first electrical connector 32 inside the heater. The loop
42 is effectively redundant and is removed by severing, suitably
prior to locating the integral heating elements 6, 10 on the base
4.
[0039] The free terminal region 16 of the first heating element
6 likewise comprises meanders of the ribbon form heating element
material traversing the second heating zone 12 and consisting of
two elongate substantially straight sections 48, 50, interconnected
by a loop 52. Section 48 is open-ended. The sections 48, 50 traverse
the second heating zone 12, preferably underlying and spaced from
the second heating element 10 in the same way as described for the
sections 38, 40 of the conjoined terminal region 20. The two elongate
substantially straight sections 48, 50 are electrically connected
in parallel by welding them together at regions 54, 56 at opposite
ends thereof. They are also welded to the third electrical connector
36 inside the heater. The loop 52 is effectively redundant and is
removed by severing in the same way as the loop 42.
[0040] The free terminal region 18 of the second heating element
10 in the outer second heating zone 12 is electrically connected
by welding to the second electrical connector 34.
[0041] The heater is operated either by electrically connecting
a power supply (not shown) to the electrical connectors 32 and 36
to energise only the first heating element 6, or by electrically
connecting the power supply to the electrical connectors 34 and
36 to energise both the first heating element 6 and the second heating
element 10 in parallel.
[0042] Because the terminal regions 16 and 20 comprise two sections
of ribbon form material connected in parallel, they emit substantially
no visible radiation, or less visible radiation than the remainder
of the heating elements 6, 10 when energised, thereby eliminating
any requirement for providing shielding or screening of these terminal
regions.
[0043] The integral first and second heating elements 6, 10 with
their terminal regions 16, 18 and 20 are advantageously produced
as a pre-formed component for securing into the base 4 of insulation
material. Such a pre-formed component is suitably prepared by winding
the integral first and second heating elements 6, 10, with their
terminal regions 16, 18, 20, into a jig and then transferring the
resulting pre-formed component from the jig to the base 4 of insulation
material by appropriate pressing. Part of such a jig is shown in
FIG. 3. The jig 58 has grooves 60 into which the second heating
element 10 is first wound. This is followed by winding in of the
first heating element 6 and the conjoined terminal regions 20 and
the free terminal region 16.
[0044] Only the conjoined terminal regions 20 are shown in FIG.
3, the free terminal region 16 being similarly arranged. As shown
in FIG. 3, the two elongate substantially straight sections 38,
40 of the conjoined terminal regions 20 are located in grooves 62
in the jig 58, overlying the outer heating element 10. The welds
44 and 46 are formed by means of welding heads 64, 66 and the loop
42 is then removed by suitable cutting means 67.
[0045] The jig 58 is then located with the face 68 thereof in contact
with the base 4 of insulation material in the dish-like support
2 of the heater and pressure is applied to transfer the pre-formed
assembly of the heating elements 6, 10, together with their terminal
regions 16, 18, 20, to the base 4 and to secure the assembly to
the base 4, with the terminal regions 16, 20 deeply recessed into
the base 4 and with the outer heating element 10 overlying and spaced
from the terminal regions 16, 20.
[0046] Another embodiment of a radiant electric heater according
to the present invention, with an alternative arrangement of the
terminal regions, is illustrated in FIG. 4. Here, as in FIG. 1,
a dish-like support 2 is provided, with a base 4 of thermal and
electrical insulation material, a peripheral wall 22, and an optional
dividing wall 24. First and second heating elements 6 and 10 are
integrally provided in an inner first heating zone 8 and an outer
second heating zone 12 respectively. Conjoined terminal regions
20 are provided for the heating elements 6, 10 and free terminal
regions 16 and 18 are provided for the first 6 and second 10 heating
elements respectively.
[0047] The terminal regions 16 and 20 comprise meanders of the
ribbon form heating element material traversing the second heating
zone 12, one consisting of three elongate substantially straight
sections 70, extending at one end region of the first heating element
6, interconnected by loops 72, 74, the other consisting of three
elongate substantially straight sections 76, extending at the other
end region of the first heating element 6, and interconnected by
loops 78, 80. The terminal regions 16, 20 traverse the second heating
zone 12 in the same way as previously described with reference to
FIG. 1.
[0048] The elongate substantially straight sections 70 of the conjoined
terminal regions 20 are electrically connected in parallel by welding
them together at regions 82, 84 at opposite ends thereof. A looped
distal region 86 of the second heating element 10 is also electrically
connected by the weld 84 to one of the end regions of the first
heating element 6 to form the conjoined terminal regions 20. The
elongate substantially straight sections 76 of terminal region 16
are also electrically connected in parallel by welding them together
at regions 88, 90 at opposite ends thereof. The loops 72, 74, 78,
80 are effectively redundant and may be removed by cutting, if required.
[0049] The conjoined terminal region 20 is welded to electrical
connector 32 of the terminal block 30, inside the heater and the
terminal region 16 is welded to electrical connector 36 of the terminal
block 30, inside the heater. A free end terminal region 18 of the
second heating element 10 is welded to electrical connector 34 of
the terminal block 30, inside the heater.
[0050] As a consequence of the arrangement of the first and second
heating elements 6, 10 in the heater of FIG. 4 and the provision
of the heating elements and the terminal regions 16, 18, 20 thereof
as an integral component, it is necessary to cut the ribbon form
heating element material at region 92 and to weld a resulting free
end portion 94 to the free end terminal region 18 of the second
heating element 10 at a weld region 96.
[0051] The radiant electric heater shown in FIGS. 1 and 4 can be
modified in a number of respects. For example, the radiant electric
heater need not be circular, but could be, for example, oval in
configuration with the first heating element 6 occupying a substantially
circular heating zone 8 and the second heating element 10 occupying
a part-circular (or crescent shaped) heating zone 12 adjacent to
the circular heating zone 8. Furthermore, a heater could be provided
having more than two, for example three, heating zones, such as
in concentric arrangement.
[0052] Instead of welding being used to electrically connect in
parallel the sections of the terminal regions 16 and 20 traversing
the second heating zone 12, other techniques, such as crimping or
folding could be used. |