Abstrict
A base for an electric heater comprises a base layer (13) of compacted
insulation material (12) and a substantially U-shaped electrically
conductive link (6) having upstanding leg portions (8, 9) with an
elongate portion (7) extending therebetween. The link is embedded
in the base layer with the leg portions protruding therefrom. The
base layer (13) incorporates at least one recess (14) extending
from a surface thereof to the elongate portion (7) of the link
Claims
I claim:
1. A base for an electric heater comprising a base layer of compacted
insulation material and a substantially U-shaped electrically conductive
link having upstanding leg portions with an elongate portion extending
therebetween, the link being embedded in the base layer with the
leg portions protruding therefrom, wherein the base layer incorporates
at least one recess extending from a surface thereof to the elongate
portion of the link.
2. A base according to claim 1, wherein the link is selected from
wire, strip and tape form.
3. A base according to claim 1, wherein the at least one recess
is tapered so as to be wider at the surface of the insulation material
than at the elongate portion of the link.
4. A base according to claim 3, wherein the at least one recess
is of substantially truncated conical form.
5. A base according to claim 1, wherein a plurality of recesses
are provided, spaced apart along the elongate portion of the link.
6. A base according to claim 1, wherein the insulation material
comprises microporous insulation material.
7. A base according to claim 1, wherein a dish-like support is
provided for the base layer of compacted insulation material.
8. A base according to claim 7, wherein the dish-like support comprises
a metal.
Description This invention relates to a base for an electric heater and a method
of manufacture. Such a base may be used in a radiant electric heater
for a cooking appliance, which may be a glass-ceramic cooking appliance.
BACKGROUND TO THE INVENTION
Electric heaters of this kind are well known, having a base layer
of insulation material in a support, such as of metal. At least
one elongate electric heating element, such as of bare wire or ribbon
form, is supported on the base layer.
When the heating element is provided of spiral form, extending
from a periphery of the heater to a termination point within the
heater, it is necessary to provide an electrically conducting link,
such as of wire, strip or tape form, extending from the termination
point to the periphery of the heater, for electrically connecting
the heating element to a power supply.
A similar form of connecting link may also be required with any
form of heating element which may have a termination within the
heater or a tapping point intermediate the ends of the element and
where it is necessary to provide an electrical connecting link between
the termination or tapping point and the periphery of the heater.
It is known to provide a connecting link for this purpose in or
under the insulation base of a heater. Such a link may be U-shaped,
having an elongate portion with upstanding opposite end leg portions
which are required to protrude from the surface of the insulation
for connection purposes. Such a connecting link is known from European
Patent Publication No. 0 630 169.
When the insulation base comprises compacted particulate material,
such as microporous insulation material, it would be convenient
and advantageous to embed such a link in the insulation base simultaneously
with compacting particulate, that is powdered, insulation material
into a dish-like support to form the base. A problem with this is
that a link of wire, strip or tape form is not rigid and when held
by the end leg portions and pressed into the insulation, during
compaction thereof, it tends to bend in its elongate portion.
OBJECT OF THE INVENTION
It is an object of the present invention to overcome or minimise
this problem.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided
a method of manufacturing a base for an electric heater comprising
the steps of:
providing a dish-like support;
providing a substantially U-shaped electrically conductive link
having upstanding leg portions and an elongate portion extending
between the upstanding leg portions;
providing a press tool having a major face provided with recesses
for receiving the leg portions of the link, the press tool having
at least one protrusion on the major face for contacting the elongate
portion of the link intermediate the leg portions;
locating the link in the press tool with the leg portions received
in the recesses and the elongate portion contacted by the at least
one protrusion;
introducing powdered insulation material between the press tool
and the dish-like support;
urging the press tool and the dish-like support towards each other
to compact the insulation material into the dish-like support and
embed the link in the insulation material with the leg portions
protruding therefrom; and
separating the press tool and the support.
The link may be of wire, strip or tape form.
The at least one protrusion on the major face of the press tool
may have a surface provided with a groove for accommodating the
elongate portion of the link.
The at least one protrusion may be tapered so as to be narrower
at a region of contact with the elongate portion of the link than
at a region in the vicinity of the major face of the press tool.
The at least one protrusion may be of substantially truncated conical
form.
The at least one protrusion and/or the press tool may comprise
a metal or a ceramic.
A plurality of protrusions may be provided, spaced apart along
the elongate portion of the link.
The insulation material may comprise microporous insulation material.
The dish-like support may comprise a metal.
According to another aspect of the present invention there is provided
a base for an electric heater comprising a base layer of compacted
insulation material and a substantially U-shaped electrically conductive
link having upstanding leg portions with an elongate portion extending
therebetween, the link being embedded in the base layer with the
leg portions protruding therefrom, wherein the base layer incorporates
at least one recess extending from a surface thereof to the elongate
portion of the link.
The link may be of wire, strip or tape form.
The at least one recess may be tapered so as to be wider at the
surface of the insulation material than at the elongate portion
of the link.
The at least one recess may be of substantially truncated conical
form.
A plurality of recesses may be provided, spaced apart along the
elongate portion of the link.
The insulation material may comprise microporous insulation material.
A dish-like support, such as of metal, may be provided for the
base layer of compacted insulation material.
The base may be further processed by providing an elongate heating
element supported on the base layer and electrically connecting
a termination thereof to an upstanding leg portion of the link.
In the method of the invention, as a result of the location of
the link in the press tool with the elongate portion of the link
in contact with the one or more protrusions on the major face of
the press tool, the link can be embedded in the insulation material
without bending of the link occurring.
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 cross-sectional view of a press tool with a located
electrically conductive link;
FIG. 2 is a cross-sectional view of a dish-like support for a base
of an electric heater and into which insulation material is to be
compacted with the press tool of FIG. 1 and the link of FIG. 1 embedded;
FIG. 3 is a cross sectional view of the base of the invention comprising
the dish-like support of FIG. 2 having compacted insulation material
therein and in which the link of FIG. 1 is embedded;
FIG. 4 is a plan view of an electric heater produced from the base
and method of the invention; and
FIG. 5 is a cross-sectional view of the heater of FIG. 4.
DESCRIPTION OF PREFERRED EMBODIMENT
As shown in FIG. 1, a press tool 1 is provided, such as of metal
or ceramic, having a major face 2. A plurality of tapered protrusions
3, suitably of truncated conical form, are provided spaced apart
in line on the major face 2 of the press tool and two recesses 4,
5, in the form of holes, are provided in the major face 2 in line
with the protrusions 3.
A substantially U-shaped electrically conductive link 6 of wire,
strip or tape form is provided, having an elongate portion 7 and
upstanding opposite end leg portions 8 and 9. The link 6 is located
in relation to the press tool 1 with the leg portions 8, 9 inserted
in the recesses 4, 5 and with the elongate portion 7 in contact
with the free ends 10 of the tapered protrusions 3. The free ends
10 of the tapered protrusions 3 are preferably grooved as illustrated
by dashed lines in FIG. 1 to accommodate the profile of the link
6 and ensure reliable contact with the link.
As shown in FIG. 2, a metal dish-like support 11 for the base of
an electric heater is provided.
The dish-like support 11 of FIG. 2 and the press tool of FIG. 1
with the link in position are located between plates of a well known
form of press (not shown) and powdered insulation material 12 is
introduced between the press tool 1 and the dish-like support 11.
The insulation material is suitably microporous insulation material,
although other materials could be considered, such as powdered vermiculite
or perlite. Mixtures of materials could also be used. The press
is operated to urge the press tool 1 and the dish-like support 11
towards each other to compact the insulation material 12 into the
dish-like support 11 and embed the link 6 into the insulation material.
During this compaction and embedding process, contact between the
protrusions 3 on the press tool and the elongate portion 7 of the
link 6 prevents bending of the link from occurring. The press tool
1 and the dish-like support 11 are then separated leaving a base
layer 13 of compacted insulation material in the dish-like support
11, as shown in FIG. 3, with the link 6 embedded therein. The leg
portions 8 and 9 of the link extend from the surface of the base
layer 13.
The conical form of the protrusions 3 on the press tool 1 allow
the press tool to separate readily from the compacted base layer,
leaving spaced apart clean recesses or holes 14 of complementary
conical shape in the surface of the base layer 13 and with the link
6 exposed at the bottom of the recesses or holes. The recesses or
holes 14 are tapered so as to be wider at the surface of the insulation
material than at the elongate portion of the link.
An electric heater may then be completed from the resulting base,
as shown in FIGS. 4 and 5. An electric heating element 15 of substantially
spiral form is supported on the surface of the insulating base layer
13. As shown, this heating element comprises a ribbon which is supported
on edge and partially embedded in the base layer 13. However other
forms of heating element, such as coiled wire, could be provided.
One end of the heating element, at the periphery of the heater,
is connected to a terminal in a terminal block 16. The other end
of the heating element, remote from the periphery of the heater,
is connected to one upstanding leg portion 9 of the link 6, such
as by welding. The other upstanding leg portion 8 of the link 6
is situated at the periphery of the heater and is connected to a
terminal in the terminal block 16, such as by welding.
A peripheral wall 17 of insulation material, such as vermiculite,
is provided on the heater and has an upper surface 18 adapted to
contact a plate, such as a glass-ceramic plate (not shown) in a
cooking appliance.
A well-known form of rod-like temperature-responsive device 19
is provided to prevent overheating and/or for providing control
of the heater.
Although in the foregoing description specific reference has been
made to a heating element of substantially spiral shape the invention
is not limited thereto but is applicable wherever there is a requirement
to provide a connecting link between a termination or tapping point
on one or more heating elements, of whatever shape, within a heater,
and a peripheral region of the heater. The invention is applicable
to heaters having a plurality of heating elements, such as in concentric
arrangement, and where it is required to connect an end or ends
of one or more such elements within the heater to a terminal location
at the periphery of the heater. |