Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROMAGNETIC INDUCTION HEAT-
ING COOKING UTENSIL
BACKGROUND OF THE INVENTION
1. Field of the Invention:
This invention relates to a cooking utensil which
is suitable for heating by electromagnetic induction.
2. Description of the Prior Art:
There is known a cooking utensil of the type which
is subjected to a magnetic field induced by an exciter and
heated by the heat appearing as a result of eddy-current
loss. The conventional cooking utensils of this type used
to be made of iron, e.g. cast iron or enameled iron, or
18Cr-8Ni or 18Cr stainless steel. The housewives, however,
complained that they were heavier than those made OL other
materials. ~oreover, the utensils made of iron were liable
to rusting, and those made of enameled iron were likely to
have the enamel separated from the iron.
There has been proposed the use of aluminum, which
has been used for making a variety of cooking utensils, for
making a cooking utensil for heating by electromagnetic in-
duction, too. It comprises a vessel made of aluminum and
having a bottom to which a different magnetic metal is
- bonded. It, however, still has a-lot of drawbacks. The
metal bonded to the bo-ttom is liable to rusting and separa
tion from the aluminum body. The bonding of the metal makes
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the utensil awkward in appearance and expensive to manufac-
ture. Moreover, it is not comparable to a cooking pan of
iron or enameled iron in heating efficiency unless its mag-
netic metAl layer has a considerably large thickness. `There-
fore, it does not contribute very much to reducing the weight
of an iron or stainless steel utensil.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a cook-
ing utensil for heating by electromagnetic induction which
is comparable to any conventional iron or enameled iron
utensil in heating efficiency, and yet lightweight and easy
to handle by the housewife, which is free from any possibi-
lity of rusting or layer separation, and which is easy and
inexpensive to manufacture.
This object is attained by a cooking utensil compris
ing a vessel made of aluminum or an aluminum alloy and hav-
ing at its bottom a spray coated layer of a magnetic mate-
rial, such as iron, and a spray coated layer of aluminum or
an aluminum alloy formed on the magnetic material layer.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a vertical sectional view of a cook-
ing utensil embodying this invention, in which a part there-
of is enlarged.
_ TAILED DESCRIPTION OF THE INVENTION
Referring to the drawing, a cooking utensil embody-
ing this invention comprises a vessel 1 made of aluminum.
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The vessel l has at its bottom a magnetic layer 2 formed
by spray coating from a magnetic material, such as iron
or cast iron, and a nonmagnetic layer 3 formed by spray
coating from aluminum on the magnetic layer 2.
The heating efficiency and power consumption of
the utensil depend on the thicknesses of the magnetic and
nonmagnetic layers 2 and 3. The inventors of this inven-
tion have conducted a lot of tests in this connection and
found that the utensil would achieve the highest heating
efficiency with the smallest power consumption if the mag-
netic layer 2 has a thickness of 0.37 to 0.71 mm and the non-
magnetic layer 3 has a thickness of 0.1 mm. The tests and
their results will hereunder be described.
Test Series I - Comparison of different types of utensils
in time required for heating 0.5 liter of
water from 20C to 90C.
Utensil Heating time
Aluminum pan formed at its bottom with 4 min. 31 sec.
a spray coated layer of iron having a
thickness of 0.60+0.04 mm
Aluminum pan formed at its bottom with a 3 min. 36 sec.
spray coated layer of iron having a thick-
ness of 0.60+0.04 mm and a spray coated
layer of aluminum formed on the iron layer
and having a thickness of 0.10+0.02 mm
Enameled iron pan 3 min. 25 sec.
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Aluminum pan formed at its bottom with 3 min. 35 sec.
a spray coated layer of iron having a
thickness of 1.0~1.2 mm
As is obvious from these results, no aluminum pan
having only a layer of a magnetic material, such as iron,
was comparable to the enameled iron pan in heating efficiency,
unless the layer had a thickness of at least about 1.0 mm.
The layer of such thickness not only added to the weight of
the pan, but also was easy to separate from the aluminum
body. On the other hand, if the layer had a thickness of
0.5 to 0.6 mm, it was unliable to easy separation and easy
and inexpensive to produce. The aluminum pan having only
an iron layer of such small thickness was, however, lower
in heating efficiency.
As a result of further study, therefore, the in-
ventors have found that if a nonmagnetic layer of aluminum
having a thickness not exceeding 1 mm is formed on the iron
layer having a thickness of, say, 0.4 to 0.6 mml the aluminum
pan is comparable to the enameled iron pan in heating effi-
ciency, as is obvious from the table which has hereinabove
appeared. This construction contributes to reducing the
weight of the pan and preventing any easy separation of the
iron layer. It also enables an improvement in productivity
and a reduction in the cost of production. It is also
helpful for lowering the power consumtion of the pan, as
is obvious from the test results which will hereunder appear.
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Test Series II - Comparison in power consumption of various
combinations of 120 mm square aluminum sheets
having various thicknesses and iron sheets
having various thicknesses.
Sheet thickness (mm) Power consumption (W)
Fe 0.30+0.02; Al 0.10+0.02 No heating was possible.
Fe 0.40_0.07; Al 0.05+0.008 440
Fe 0.40+0.07; Al 0.07 0.008 820
Fe 0.40_0.07; Al 0.10+0.02 820
Fe 0.40+0.07; Al 0.17+0.03 820
Fe 0.40+0.07; Al 0.24+0.03 No heating was possible.
Fe 0.70+0.10; Al 0.05+0.008 450
Fe 0.70+0.10; Al 0.07+0.008 820
Fe 0.70+0.10; Al 0.10+0.02 820
Fe 0.70_0.10; Al 0.17+0.03 8~0
Fe 0.70+0.10; Al 0.24+0.03 No heating was possible.
Fe 1.00+0.18; Al 0.10+0.02 830
Fe 1.00+0.18; Al 0.24+0.03 No heating was possible.
Basically the same results were obtained when the
magnetic layer was of materials other than iron, and also
when the pan was made of an aluminum alloy.
The following advantages were found to be available
when the magnetic layer had a thickness of 0.4 to 0.7 mm,
and was covered by an aluminum layer having a thickness of
0.062 to 0.20 mm:
(1) The pan of this invention has the following advan-
tages over the conventional pan to which a layer of a mag-
netic material, such as iron, is bonded:
(a) It is free from any separation between the two
metals or corrosion caused by their difference in coefficient
of thermal expansion, and is, therefore, very good in appear-
ance;
(b) It is free from any possibility of rusting or corro-
sion by a brazing material; and
(c) It is higher in productivity and less expensive.
(2) It has the following advantages over any other pan
made by spray coating:
(a) A higher heating efficiencyi
(b) There is no possibility of separation of the spray
coated layer or its rusting; and
(c) A more pleasant appearance.
