Abstrict
A method of manufacturing an electric heater assembly with a plurality
of electric heating units includes the steps of providing a tray-like
support (1) and moulding microporous thermal and electrical insulation
material into the support. The tray-like support (1) is formed with
a number of dish-like recesses (2), each dish-like recess comprising
a base (4) and a surrounding wall (5). The microporous thermal and
electrical insulation material is moulded into each dish-like recess
to form a base layer (6) against the base (4) of each dish-like
recess and an upstanding wall layer (7) against the surrounding
wall (5) of each dish-like recess, the base layer (6) being formed
integrally with the wall layer (7). At least one electric heating
element (12) is provided in each dish-like recess (2), the heating
element being supported on or adjacent to the base layer (6). The
electric heater assembly is adapted for use behind a plate (10)
to provide a plurality of discrete heating zones on the plate.
Claims
I claim:
1. A method of manufacturing an electric heater assembly with a
plurality of electric heating units produced upon a common support,
for use behind a plate to provide a plurality of discrete heating
zones on the plate, the method comprising:
providing a generally planar support having a plurality of concave
recesses therein, each recess comprising a base and a surrounding
wall;
moulding into each recess microporous thermal and electrical insulation
material, in powder form, to thereby form in each recess a structure
consisting of a base layer disposed against the base of each recess
and an upstanding wall layer disposed against the surrounding wall
of each recess, the base layer and wall layer of said structure
in each recess being integrally formed as a single piece; and
providing in each recess at least one electric heating element
supported relative to the base layer.
2. A method according to claim 1, wherein the microporous thermal
and electrical insulation material is moulded into the recesses
one at a time.
3. A method according to claim 1, wherein the microporous thermal
and electrical insulation material is moulded into all the recesses
at the same time.
4. A method according to claim 1, wherein the microporous thermal
and electrical insulation material is moulded into a plurality of
the recesses at the same time.
5. A method according to claim 1, wherein the upstanding wall layer
of insulation material is provided of a height in each recess such
that it has an upper surface for contacting the plate, when the
heater assembly is arranged for operation.
6. A method according to claim 5,, wherein the upper surface of
one or more of the upstanding wall layers is profiled such as to
be higher at the centre thereof than at the edges.
7. A method according to claim 1, wherein the base layer in each
recess is provided having a compaction density substantially the
same as that of the upstanding wall layer.
8. A method according to claim 1, wherein the base layer in each
recess is provided having a compaction density different from that
of the upstanding wall layer.
9. A method according to claim 8, wherein the wall layer has a
compaction density greater than that of the base layer.
10. A method according to claim 1, wherein the base layer in each
recess has a composition substantially the same as that of the upstanding
wall layer.
11. A method according to claim 1, wherein the base layer in each
recess has a composition different from that of the upstanding wall
layer, although formed integrally therewith.
12. A method according to claim 1, wherein at least one of the
base layer and the wall layer in each recess includes reinforcing
glass filaments.
13. A method according to claim 12, wherein the glass filaments
are selected from E glass, R glass, S glass and silica.
14. A method according to claim 1, wherein the at least one electric
heating element provided in each recess is of ribbon form.
15. A method according to claim 14, wherein the at least one ribbon
form heating element is secured to the base layer in each recess
by partial embedding in the base layer.
16. A method according to claim 15, wherein the at least one ribbon
form heating element is secured to the base layer in each recess
during moulding of the insulation material into each recess.
17. A method according to claim 15, wherein the at least one ribbon-form
heating element is provided partially embedded edgewise in the base
layer of each recess.
18. A method according to claim 17, wherein the at least one ribbon-form
heating element is of corrugated form.
19. A method according to claim 1, wherein the support is of metal.
20. A method according to claim 19, wherein the support is comprised
of a plurality of discrete components.
21. A method according to claim 19, wherein the recesses are integrally
formed in the support by a method selected from the group consisting
of stamping, drawing and pressing a sheet metal component.
22. A method according to claim 1, wherein the support is formed
with a peripheral edge adapted to receive the plate.
23. A method according to claim 22, wherein the plate is secured
to the peripheral edge by means selected from an adhesive and mechanical
fixing means.
24. A method according to claim 22, wherein sealing means is provided
between the plate and the peripheral edge.
25. A method according to claim 24, wherein the sealing means comprises
a gasket.
26. A method according to claim 1, wherein the plate comprises
a glass-ceramic plate.
27. An electric heater assembly whenever manufactured by the method
of claim 1.
Description This invention concerns a method of manufacturing an electric heater
assembly with a plurality of electric heating units, for use behind
a plate such as a glass-ceramic plate in a cooking appliance, to
provide a plurality of discrete heating zones on the plate.
DESCRIPTION OF PRIOR ART
For many years it has been most common practice to design glass-ceramic
top cooking appliances in which a plurality of discrete electric
heating units are provided underneath and in contact with a sheet
of glass-ceramic and in which each heating unit is formed in an
individual metal dish-like support and individually held against
the underside of the glass-ceramic sheet. Recent trends have been
aimed at simplifying manufacture by forming a plurality of heating
units directly on a common supporting tray which is then secured
in contact with the underside of the glass-ceramic sheet. One such
arrangement is described in European Patent Publication No. 0757508
in which individual components of a plurality of heating units are
built up on a common tray-like support. In this arrangement, for
each heating unit a tablet-form base of insulation material and
a separate insulating wall are assembled on the base of the support,
one or more heating elements being secured to the base.
An arrangement of securing clips is used to secure the components
to the support.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a method of
manufacturing a heater assembly in which rather than separately
form the insulation components and then build them up on the tray-like
support, the insulation components are integrally formed directly
on the support and no securing clips are required.
SUMMARY OF THE INVENTION
The present invention provides a method of manufacturing an electric
heater assembly with a plurality of electric heating units, for
use behind a plate, in particular a glass-ceramic plate, to provide
a plurality of discrete heating zones on the plate, the method comprising:
providing a tray-like support having formed therein a plurality
of dish-like recesses, each dish-like recess comprising a base and
a surrounding wall;
moulding into each dish-like recess microporous thermal and electrical
insulation material to form a base layer against the base of each
dish-like recess and an upstanding wall layer against the surrounding
wall of each dish-like recess, the base layer being formed integrally
with the wall layer; and
providing in each dish-like recess at least one electric heating
element supported relative to (that is, on or adjacent to) the base
layer.
The microporous thermal and electrical insulation material may
be moulded into the dish-like recesses one at a time, or all or
a plurality thereof at the same time.
The upstanding wall layer of insulation material may be provided
of a height in each dish-like recess such that it has an upper surface
for contacting the plate, such as the glass-ceramic plate, when
the heater assembly is arranged for operation. The upper surface
of one or more of the wall layers may be profiled such as to be
higher at the centre than at the edges.
The base layer in each dish-like recess may be provided having
a compaction density substantially the same as, or different from,
that of the upstanding wall layer. It may be preferred for the wall
layer to have a compaction density greater than that of the base
layer.
The base layer in each dish-like recess may have a composition
substantially the same as, or different from, that of the upstanding
wall layer, although formed integrally therewith.
The base layer and/or the wall layer in each dish-like recess may
include reinforcing glass filaments. Such filaments may, for example,
be selected from E glass, R glass, S glass and silica.
The microporous insulation material may be moulded into each dish-like
recess as described in British Patent Application No. 9705923.2.
The at least one electric heating element provided in each dish-like
recess may be of ribbon form and may be secured to the base layer
in each dish-like recess by partial embedding in the base layer.
Such partial embedding of the at least one heating element may be
effected during moulding of the insulation material into each dish-like
recess.
The at least one ribbon-form heating element may be provided partially
embedded edgewise in the base layer of each dish-like recess and
may be of corrugated form.
The tray-like support may be of metal and may be fabricated from
component parts or the plurality of dish-like recesses may be formed,
for example, by stamping, drawing, pressing, or otherwise shaping,
a basic sheet-form metal component.
The tray-like support may be formed with a peripheral edge adapted
to receive the plate. The plate may be secured to the peripheral
edge by means of an adhesive or may be secured by mechanical fixing
means. Sealing means, such as a gasket, may be provided between
the plate and peripheral edge.
The plate may preferably be a glass-ceramic plate and may be for
use in a cooking appliance.
The invention is now described by way of example, with reference
to the accompanying drawings; in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A, 2A and 3A, are perspective views of an electric heater
assembly during various manufacturing stages thereof according to
the method of the invention; and
FIGS. 1B, 2B and 3B are cross sectional views of the assembly of
FIGS. 1A, 2A and 3A respectively.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIGS. 1A and 1B, a tray-like support 1 is provided
for use in an electric heater assembly, starting with a metal sheet,
such as of steel, which is processed such as by pressing, stamping
or drawing, to form a plurality of dish-like recesses 2 therein
and, optionally, an upturned edge rim 3. Alternatively the tray-like
support 1 with the recesses 2 may be fabricated from component parts.
Such dish-like recesses 2 form the basis of electric heating units
and although four are shown in FIG. 1A, any required number could
be provided. Each dish-like recess 2 comprises a base 4 and a surrounding
wall 5.
Referring now to FIGS. 2A and 2B, microporous thermal and electrical
insulation material is moulded into each dish-like recess to form
a base layer 6, against the base 4 of each dish-like recess 2, and
an upstanding wall layer 7, against the surrounding wall 5 of each
dish-like recess 2. The base layer 6 of insulation material is formed
integrally with the wall layer 7 in each dish-like recess 2. The
insulation material may be moulded into the dish-like recesses 2
either one at a time, or all or a plurality thereof at the same
time.
Each wall layer 7 of insulation material is provided of such a
height that it has an upper surface 8 which protrudes slightly above
the top 9 of the surrounding wall 5 of each dish-like recess 2.
The upper surface 8 of each wall layer is optionally arranged for
subsequently contacting the rear surface of a plate 10, such as
a glass-ceramic plate, and may be profiled 11 such as to be higher
at the centre than at the edges.
The microporous insulation material, which is well known to the
skilled person, is moulded into the dish-like recesses 2 to form
the base layers 6 and wall layers 7 by compacting powdered insulation
material into the dish-like recesses 2. A particularly suitable
method for providing the integral base layers 6 and wall layers
7 in a common processing operation is described in British Patent
Application No. 9705923.2. The base layer 6 in each recess 2 may
be provided having a compaction density substantially the same as,
or different from that of the wall layer 7. It may be preferred
for each wall layer 7 to have a greater compaction density than
that of each corresponding base layer 6. For example, the wall layers
7 may have a compaction density of about 350 kg/m.sup.3 and the
base layers 6 may have a compaction density of about 300 kg/m.sup.3.
The base layer 6 in each recess 2 may have a composition substantially
the same as, or different from, that of the wall layer 7, although
formed integral therewith. An example of a particular composition
for each wall layer 7 is:
Pyrogenic silica 62 percent by weight Opacifier (Rutile) 27 percent
by weight E glass filaments 11 percent by weight
Each base layer 6 may, for example, comprise:
Pyrogenic silica 60 percent by weight Opacifier (Rutile) 37 percent
by weight Ceramic fibres 3 percent by weight
However, glass filaments, such as for example filaments of S glass
or silica, may be used in place of the ceramic fibres. Alternatively,
E glass or R glass filaments may be incorporated as permitted by
operating temperatures of the heater units in the heater assembly
being manufactured.
Referring now to FIGS. 3A and 3B, at least one heating element
12 is provided in each dish-like support 2, on or adjacent to the
base layer 6 of microporous insulation material. Any of the well-known
forms of heating element may be considered, such as, for example:
coiled wire or ribbon; or flat or edgewise mounted ribbon of planar
or corrugated form; or one or more heating lamps, particularly halogen
lamps. However it is particularly convenient to provide one or more
ribbon elements, particularly of corrugated form, partially embedded,
particularly edgewise, in the surface of each base layer 6. Such
one or more heating elements may be secured by partial embedding
in each base layer 6 during the process of moulding the microporous
insulation material into the recesses 2 to form the base layers
6 and upstanding wall layers 7. This is achieved, for example, as
described in British Patent Application No. 9705923.2.
A well-known form of temperature limiter 13 is provided, extending
over the heating element or elements 12 in each dish-like recess
2, the surrounding wall 5 of each recess 2 and also the wall layer
7 being cut away to facilitate location of each limiter.
As a result, four heating units are provided formed in the four
dish-like recesses 2 of the tray-like support 1.
Electrical connecting leads 14 are provided in the tray-like support
and extending from each resulting heating unit to a terminal block
15 on the rim 3 of the support, whereby the resulting heater assembly
may be connected to an external power supply.
The resulting heater assembly may be supported against the rear
side of a plate 10, such as a glass-ceramic cooking plate of well
known form, in a cooking appliance.
The peripheral edge 3 of the tray-like support 1 may be suitably
adapted to receive the plate 10. The plate 10 may be secured to
the peripheral edge by means of an adhesive or by mechanical fixing
means (not shown). If required, sealing means, such as a gasket,
may be provided between the plate 10 and the peripheral edge 3.
|