CA1256748A - Electromagnetic induction heating cooking utensil - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A cooking utensil for heating by electromagnetic induction comprises an aluminum or aluminum alloy vessel having at its bottom a spray coated layer of iron and a spray coated layer of aluminum or an aluminum alloy cover-ing the iron layer.

Description

~LZ~74~3 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 ~d~

~2~ll!3 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.

~;251~i;7~3 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.

Claims (3)

WHAT IS CLAIMED IS:

1. A cooking utensil for heating by electromagnetic induction comprising a vessel made of a material selected from the group consisting of aluminum and an aluminum alloy, said vessel having at its bottom a spray coated layer of a magnetic material and a spray coated layer of a material selected from the group consisting of aluminum and an aluminum alloy covering said layer of a magnetic material.

2. A cooking utensil as set forth in claim 1, wherein said layer of a magnetic material has a thickness of 0.37 to 0.71 mm and said layer covering it has a thickness of 0.062 to 0.20 mm.

3. A cooking utensil as set forth in claim 1 or 2, wherein said magnetic material is iron.