Note: Descriptions are shown in the official language in which they were submitted.
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1 FIELD OF THE INVENTION
2 The present invention relates to the construction of 2
3 the cooking surfaces used for electrical hot plates for cook- 3
4 ing devices. In particular the invention describes the novel 4
means of fabricating a cooking plate for fitting into 5
counters and the like.
6 6
Electrical hot plates are normally manufactured from
cast iron and have a number of disadvantages. Cast iron
rusts, thereby leading to considerable cavitation of the 8
9 surface. Cast iron has poor strength criteria and com-
paratively small heat conductivity r thereby leading when 10
11 uneven-ly loaded to over-heating of the electrical heating 11
12 elements so that the life duration of these elem~nts is 12
13 shortened. Overheating of the cast iron plate can cause 13
local expansion resulting in the deformation or cracking
14 14
of the plate. It is also known that it is difficult to
make a cast iron plate able to retain an even surface. An 15
16 area in the centre of a cast iron plate is, therefore, 16
1~ usually slightly depressed causing poor cooking charac- 1~
18 teristics. 18
19 PRIOR ART 19
It is known that the disadvantages as outlined above 20
21 can be overcome by producing hot plates of cast stainless 21
steel madecf a special alloy (Norwegian Patent No. 119954).
22 22
Special alloy hot plates are comparatively expensive to
23 produce and, therefore, the invention herein provides a 23
24 better solution to the known weaknesses of cast iron heating 24
elements. 25
26 An electric: hot plate could be made of aluminium 26
2~ with cast-in electrical heating elements, and with a thin 2
28 plate of stainless steel on each side. The stainless steel 28
plates would be metallurgically connected to the aluminium
29 29
plate.
The above solution provides a cast warming or hot
CECIL C. KENT & ASSOCIATE5
PATENT ATTORNEYS
378~3
plate. The heating element is cast in the aluminium and is placed
between the said two stainless steel plates. It is an object of the
present invention to provide a combined system of protection rim and
hot plate, and a system of inter-connecting several plates together.
It is already known that a top plate combined with a hot plate
can be produced from glass. A cooking means fabricated from glass has
marked limitations such as the size of the glass plate, number of
hot plates per glass plate, and the surface temperature allowed at
the plates.
It is also an object of the present invention to provide hard-
ware of the highest quality to perform efficiently and with maximum
constructive simplicity without the disadvantages of cast iron or the
cost of other known combinations of components.
It is a further object of the invention to provide a large surf-
ace having heating zones thereon connected to heating elements and
protected against radiation to other portions of the surface outside
the zones.
SUMMARY OF THE INVENTION
In the present invention the visible part~of the cooking surfaces
consists of a continuous plate of metal, such as stainless steel, with
one or more hot and cold zones. The lower surface that comes into
contact with the frame of a bQnch or counter in a home or restaurant
will always be a continuous cold zone.
The metal plate or cooking surface herein disclosed consists of
a uniform material or a laminate and preferably three layers of two
different kinds of metal. A comparatively thick layer of one metal
with a good heat conductivity, such as aluminum is provided in the
middle, and a relat:ively thin layer of metal with a heat conductivity
less than 50 k cal.~/m.h.C is provided on either side of the aluminium
such as stainless steel.
Aluminium has a heat conductivity number of lgO k cal/m.h.
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C and stainless steel 15 k cal./m.h. c The thickness of
2 the various metal layers will depend on the choice of material2
3 The middle layer will if of aluminium, have a thickness of 3
0,5 mm up ~ lO mm. The outer layers, if of stainless steel, 4
will have a thickness of 0,l mm up to 2 mm.
It is a particular object of this invention to provide
6 a cooking surface or plate that is all one piece on the 6
upper side. The hot areas of the plate can be slightly
8 raised or lowered in relation to remaining part of the 8
g plate to indicate cooking area on the surface. 9
The present inventive concepi consists of and is 10
11 hereby claimed to reside in the means, method, construc- 11
tion and arrangement and combination of parts exemplified
12 12
inthe embodiment of such concept, reference being had to
13 the accompanying drawings in which one embodiment of the 13
14 present invention is given and where like characters of
re~erence designate like parts. 15
16 Fig. l shows a sectional side view through the
1~ cooking surface of the invention, using aluminium 17
18 with stainless steel plates covering top and 18
bottom.
19 19
Fig. 2 shows a cooking surface consisting of `~
an aluminium plate with one top covering of -
21 21
stainless steel.
22 Fig. 3 shows a heating plate made of a homogeneous 22
23 material of low heat conductivity. 23
24 IN THE DRAWINGS 24
In the drawings a cooking surface 15 is shown and 25
26 in Figs. l and 2 it consists o~ an aluminium plate 14 26
27 is shown, both sides are covered with a relatively thin 27
plate of stainless steel 16 and 17. The lower plate is
28 28
disconnected by a groove 4, the zone in the middle 9 is
29 2
connected to the heating element 5, and the regulating
-- 3
CECIL C. KENT & ASSCICIATES
PATENT ~TTn R N EYS
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7~43
thermostat 6. Radiation from the heating elements 5 is arrested by
the asbestos plate 7, and the bottom cover 8. The hot zone 9 is
connected with the cold zones 10 across the bridge 11 of the stainless
steel plate. The guarantee against overheating towards the outer rims
18 is secured by the reset thermostat 12.
The cold and the hot zones are separated by circular or linear
grooves 4 having been made, when referring to laminate, through the
bottom layer of stainless steel 17 and through the core of aluminium 14,
right through to the upper layer of stainless steel 16. These grooves
:
~. will act as a barrier against transfer of thermal energy. The groove
~. i
`~' could have a width of 5mm. up to 100 mm. depending on the choice of
' material, the thickness of the various layers, and the stability of
the plates.
A heat loss will occur across the bridges 11 of stainless steel
between a hot and cold zone, but of a quantity which is of negligible
~ practical importance. The thickness of the stainless steel 16, for
-'~ instance, across the bridge 11, should preferably be from 0,2- 0,3 mm.
` even if the same layer outside the bridge has a greater thickness.
Measurements prove that after 8 hours continuous heating, the
bridge of a comparatively thick dimensions, 0,9 mm x 80 mm will have
a temperature of 45C in the outer rim 20 when the inner edge 21 has
a temperature of 200C.
The heat transfer is directly proportional to the cross section
of the conductor. By reducing this from o,9 to o,3 mm for instance,
the heat transmission will thus be reduced to one third.
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From this it would appear that with a thickness o~ 0.9 mm,
2 width 80 mm, a temperature difference of 150C and time for 2
obtaining stable condition 2 hours, the loss of energy will 3
be 3.7 watt, that is to say less than l/2% of the energy 4
input.
S
; Because of the characteristics of alluminium the heat
energy will be evenly distributed in the heated zone 9 of the
7 aluminium core. The two outer layers keep each other in
8 balance in such a way that no bimetallic action occurs. It is 8
g found that the linear expansion of the diameter of the hot 9
zone will be absorbed over the grooves 4. The bridge ll of 10
11 thin stainless steel will act as a hinge preventing the plate 11
from warping ~rhen in use.
12 12
;~ By providing the grooves 4 and the bridge ll to
13 13
prevent distortion and warping of the heating surface the
actual surface will not change but remain as when cool and the
heating zone will stay even.
16 In use it will be seen that only the heated zones 1~
17 will rise or sink in relation to the temperature variations. 17
18 The bridges ll between the warm and cold zones are preferably 18
made as an angled line or irregular line to assist in the 19
20 absorption of the distortion and to keep the cooking zone flat.20
The amount of heat passing over the bridge ll will be dis-
21 21
tributed over the entire cold zone 14 and continuously given
22 off to the surrounding areas. If necessary, an extra bridge 22
23 may be arranged as a frame midway around the outer rim. It 23
24 can also be arranged so that the hot zones consist of triple 24
laminate whilst the cold zones are of double laminate. A 25
26 greater heat production can thus be obtained from the cold 26
27 zones as is shown in Figure 2 where zone 14 has no lower steel 2
cover and thereby can conduct to the outside
28 28
The advantages of the invention compared with prev-
29 29
iously known constructions may be summarized as follows:-
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1 A continuous plate of metal has both hot and cold zones,
2 making it possible to use the same surface for several oper- 2
3 ations, such as cooking, simmering and food preparation at a 3
cooking counter or table. The surface will be impervious to 4
water and the heating unit protected from food spills. The
draining board of a stainless steel bench can be combined in
6 the function as both cooker, drying table and draining board.
7 In a home kitchen the whole counter work space could be made 7
8 from one complete surface of stainless steel with sink, work 8
g area and cooking plates provided therein and thereunder. A 9
]0 system could be arranged with quadratic squares as hot zones. 10
11 Each zone Could be given a different surface treatment, for 11
12 instance chromium plated, from the remaining part of the plate,
and thus made possible architectural and decorative designs
~ 13 in the planning of the cooking areæ which have not previously
; been possible with the known constructions. 14
An additional advantage of the invention is that it 15
16 employs a plate of stainless steel which is decorative, 1~
1~ corrosion resistant, durable and cannot be broken as for in- 17
18 stance a plate of glass. 18
19 The inner core of aluminium 14 will conduct the heat 19
so well that it is unnecessary to take the usual precautions 20
in the choice of the correct pan size for any particular plate. -
21 21
The aluminium core will evacuate heat away from the element
22 to the cooled parts of the heated zone. 22
23 The invention is not limited to cooking surfaces,
24 electric stoves and hot plates but aims at other utilizations 24
of this principle, for instance used as a variable heat panel, 25
26 or as a restaurant table with hot zones. 26
27 2~
28 28
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