JPH04220990A - Deep pan for induction heating cooking apparatus - Google Patents

Abstract

PURPOSE:To make precise temp. control of a deep pan specifically dedicated to an induction heating cooking apparatus without equipping the cooking apparatus proper with a temp. sensor by providing the deep pan with function to make self temp. controlling. CONSTITUTION:The body part 1a of a deep pan specifically dedicated to an induction heating cooking apparatus is formed from a non-magnetic metal material, while the bottom of the body part 1a mating with a heater coil 2 is configured with a normal-temp. magnetic metal material having a specific Curie point. When the temp. of the deep pan attains the Curie point, the normal- temp. magnetic metal material is turned non-magnetical, which reduces the effect of being induction heated by the alternating magnetic field generated by the heater coil. When the pan temp. sinks below the Curie point, the normal- temp. magnetic metal material is turned back magnetical, and the induction heating will take place.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pot for induction heating cookers, and more particularly to a pot having a self-temperature control function.

0002

[Prior Art] In an induction heating cooker, a heating coil is arranged under the top plate, and the lines of magnetic force generated by the heating coil cause an eddy current to flow in the bottom of the pot for the induction heating cooker on the top plate, generating heat. It looks like this.

[0003] As such a pot for an induction heating cooker,
Traditionally, metal pots have been used for heating in general gas pots. However, in this case, the electrical characteristics of the pot are constant during normal cooking, so heating continues at a constant firepower, and in order to prevent overheating and automatically adjust the temperature, a temperature sensing means (thermistor) placed through the top plate is required. The induction heating output was controlled by increasing or decreasing the output of the induction heating device (such as a thermostat or a bimetallic thermostat).

0004

[Problem to be Solved by the Invention] However, in this heating output control method, the temperature of the cooking pot is detected through the crystallized glass used in the top plate, so the actual temperature of the cooking pot cannot be detected. There was a large temperature difference between the temperature and the temperature sensitive to the thermistor, resulting in poor thermal response and detection accuracy. As a result, under abnormal usage conditions such as dry cooking, the temperature could not be completely controlled, causing problems such as the oil in the pot catching fire, and pots made of metal causing severe warping or deformation of the bottom.

Furthermore, since conventional temperature detection detects the temperature of a portion of the bottom of the pot, the detection accuracy deteriorates depending on how the pot is placed or when cooking ingredients are placed unevenly. moreover,
Since the temperature rise at the bottom of the pot during dry cooking and the temperature rise during normal cooking vary greatly depending on the part of the bottom of the pot, it has been extremely difficult to always accurately detect the pot temperature under various usage conditions.

[0006] The present invention aims to solve the above-mentioned conventional problems, and provides a constant high level of safety and highly accurate temperature control by realizing a pot for an induction heating cooker in which the pot itself has a self-temperature control function. It is.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the induction cooking pot of the present invention has a Curie temperature set at the temperature used for cooking, and the high frequency electrical resistance of the pot is set before and after the Curie temperature. By using a pot that is integrally formed with a variable temperature-dependent magnetic metal material and a non-magnetic metal material, a pot that automatically controls the temperature so that it does not exceed a desired temperature has been realized.

[0008]

[Operation] In the present invention, a magnetic metal material having a Curie temperature is used as the material of the pot used in the induction heating cooker, and when the temperature is below the Curie temperature, eddy current flows through the magnetic metal material, causing heat generation due to eddy current loss.

[0009] At this time, the eddy current flowing at the bottom of the pot concentrates on the surface near the heating coil, and as it goes deeper into the metal, it becomes difficult for the current to flow. The depth is called the penetration depth and is expressed by the following formula.

0010

[Math 1]

[0011] Since there are few eddy currents at points above the penetration depth, there is little effect of alternating magnetic fields, and even if there is another metal inside a metal whose thickness is above the penetration depth, it does not greatly affect the overall operation. .

On the other hand, since the metal below the penetration depth is also affected by the magnetic field, the effect of the metal on the inside affects the overall induction heating.

In the pot constructed according to the present invention, when the temperature of the pot is below the Curie temperature, the ultra-high frequency alternating magnetic flux radiated from the heating coil flows into the outer magnetic metal material, but because of its high magnetic permeability, the alternating Eddy currents induced by magnetic flux concentrate on the bottom side of the pot due to the skin effect.

As a result, the eddy current flows on the surface of the magnetic metal material (
Since the flow concentrates on the bottom side of the pot, the electrical resistance of the pot becomes equivalently large, the Joule heat generated by the eddy current increases, and the amount of heat generated by induction heating increases. At this time, unless the thickness of the magnetic metal material exceeds the penetration depth at room temperature, sufficient induction heating output cannot be obtained even under normal conditions due to the influence of the non-magnetic metal material.

On the other hand, above the Curie temperature, the magnetic metal material loses its magnetism, so its magnetic permeability decreases and the penetration depth of eddy currents (the depth from the surface until the surface current decreases to a constant rate) increases. For this reason, the eddy current that was flowing only on the bottom surface of the magnetic metal material now flows further inside the magnetic metal material (although it has lost its magnetism because it has exceeded the Curie temperature), resulting in an electrical resistance Since the value decreases significantly, the Joule heat also decreases significantly. In this way, the induction heating output can be controlled around the Curie temperature.

Furthermore, if the thickness of the magnetic metal material is thinner than the penetration depth above the Curie temperature, the magnetic flux will penetrate the magnetic metal material and reach the non-magnetic metal material when the Curie temperature is exceeded. The generation of Joule heat is further reduced by using a non-magnetic metal material with low resistance, and the change in the amount of heat generated around the Curie temperature is further increased, which is convenient for control.

[0017] The manner in which the electrical resistance value changes due to a change in magnetism will be explained using the case of a temperature-sensitive stainless steel that was subjected to a test.

[0018]

[Table 1]

As can be seen from Table 1, even if the metal has the same characteristics, the electrical resistance decreases to one-tenth depending on whether it is magnetic or not. In other words, since the Joule heat generated at the bottom of the pot is proportional to the electrical resistance, the amount of heat generated by losing magnetism is reduced to one-tenth. Here, if the thickness of the magnetic metal material is thinner than the penetration depth, a large amount of alternating magnetic flux will penetrate the magnetic metal material at room temperature and reach the non-magnetic metal material, so the difference between the output when it exceeds the Curie temperature will become narrower. The control range of heating power becomes narrower, and the thickness of the magnetic metal material needs to be greater than the penetration depth at room temperature.

Furthermore, if the thickness of the magnetic metal material is made below the penetration depth at high temperatures, the magnetic flux will reach even the non-magnetic metal material at temperatures above the Curie temperature, which will greatly reduce the Joule heat and make it possible to widen the control range. be.

[0021] Here, the changes in the heating operation will be explained step by step. First, when heating starts from room temperature, it heats with a large amount of heat until it reaches the Curie temperature, and as a result,
When the pot reaches its Curie temperature, the pot automatically changes its characteristics and generates less heat. Then, when the temperature of the pot drops below the Curie temperature, the metal material regains its magnetism and resumes heating with a large amount of heat.

[0022] Here, when the Curie temperature of the magnetic metal material of the pot is selected to a desired set temperature, the pot itself can automatically control the amount of heat generated by the above-mentioned operation.
For these reasons, it becomes possible to precisely control the Curie temperature to a desired temperature.

[0023] In particular, when used as a pot using oil, a magnetic metal material having a Curie temperature of about 180 to 280°C, which is a high-temperature cooking temperature, is optimal. This temperature can be freely set by adjusting the composition of the ingredients, so it can be selected appropriately depending on the cooking menu. For example, if the Curie temperature is set to 100°C, a kettle that automatically stops heating when water boils and prevents unnecessary evaporation of water after boiling can be realized.

[0024] Nickel alloys and iron-chromium alloys are suitable as magnetic metal materials having a Curie temperature because they allow the Curie temperature to be freely changed and have a large skin resistance that determines the amount of heat generated. Materials such as aluminum, copper, mirrors, etc., and alloys thereof have high thermal conductivity and also function as a cooking container, and are suitable for application to the present invention.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of one embodiment of the induction cooking pot of the present invention. Reference numeral 1 denotes a pot for an induction heating cooker having a plate thickness of 3 mm, which is placed on a heat-resistant insulator 3, and is placed facing the disc-shaped heating coil 2. The pot 1 is made of a non-magnetic metal material, and the main body part 1 is made of aluminum with good heat conduction.
a and a room temperature magnetic metal material 1b which is a nickel alloy having a Curie temperature of 180 degrees. In general, magnetic metal materials have low thermal conductivity, which leads to uneven temperatures when used as a cooking container, but in the present invention, the body portion 1a is integrally formed of a non-magnetic metal material with good thermal conductivity, so the temperature can be made uniform. It is planned.

In the embodiment, the magnetic metal material 1b has a thickness of 0.5 mm and is a Ni alloy containing 40% Ni, 8% Cr, and 52% Fe, and the non-magnetic metal material 1a is aluminum with a thickness of 2.5 mm. be. Therefore, as mentioned above, the penetration depth at room temperature is about 0.28 mm, which changes to 2.75 mm when the Curie temperature is exceeded, and the thickness of the magnetic metal material is about 2 of the penetration depth at room temperature.
This is approximately 0.2 times the penetration depth at high temperatures.

In order to evaluate the induction cooking pot 1 of the present invention, oil was put into the induction cooking pot 1 of the present invention.
This was placed on top plate 2 of an induction heating cooker and tempura cooking was performed. The state at this time will be explained with reference to FIG. At timing a, induction heating of the room temperature magnetic metal material 1b in the pot 1 containing oil is started. The heat generated in the room temperature magnetic metal material 1b is conducted to the main body portion 1a and heats the oil. The output of induction heating at that time was 1200W. After that, the oil temperature rises almost linearly as it continues to be heated with a constant firepower, and when the pot temperature reaches the preset Curie temperature of 180℃, the pot 1 rapidly changes to a non-magnetic material, and the oil temperature increases almost linearly. The heating power is reduced to 250W. The output value when the power decreases (250 W in this case) can be varied depending on the material, thickness, shape, etc. of the main body portion 1a made of magnetic metal material. After the pot 1 reaches the Curie temperature, the heat power is significantly reduced and the oil temperature continues to gradually drop to 175°C (point c). At this time, the room-temperature magnetic metal material 1b restores its magnetism again, so the heating power automatically rises to 1200 W again and the oil temperature rapidly rises toward the Curie temperature of 180°C. Add ingredients such as tempura to the oil until the temperature of the pot reaches 175.
Similarly, if the temperature drops to ℃, the firepower will be turned on and off automatically.
Keep oil temperature constant.

[0029] Generally, induction heating cookers are equipped with a mechanism to prevent small objects from generating heat, and if the input value is significantly lower than that of a normal pot, heating is automatically stopped. In the above example, if the input exceeds the Curie temperature and is less than the small object detection level, heating is temporarily stopped, but for a predetermined period of time (
After 1 to 3 seconds (usually 1 to 3 seconds) have passed, it will automatically restart and the pot temperature will rise to 1.
If the temperature is 75°C or lower, heating is automatically started at 1200W. Also, if the pot temperature has not decreased to 175℃,
Since there is little input, heating is interrupted again when a small object is detected. Therefore, although the input when the temperature exceeds the Curie temperature changes depending on the characteristics of the pot, automatic control of the pot temperature is possible even if it is higher or lower than the small object detection level.

In the embodiment shown in FIG. 1, the explanation is based on a pot having a structure in which a clad plate integrally formed with a non-magnetic metal material and a magnetic metal material is pressed, but as shown in FIG. 3, an aluminum pot 4a is used. The pot 4 may be constructed by attaching a magnetic metal material 4b to the bottom portion (the portion opposing the heating coil) or integrally forming it by explosive bonding, and the same function as in FIG. 1 can be obtained. In this embodiment, the strength of the bottom of the pot is high, so the bottom is always flat even when the pot is empty, and it is stable even when placed on the top plate, and the pot can be weighed, which is very convenient.

[0031] As described above, the induction cooking pot of the present invention has a self-temperature control function, which not only improves cooking performance and safety from oil ignition, but also improves safety by reducing temperature distribution. A significant effect on cooking performance can be expected.

Further, although a nickel alloy is used as a magnetic metal material having a Curie temperature, the material is not limited to this, and can be appropriately selected depending on the set temperature, mechanical strength, workability, etc.

Furthermore, although 180 degrees has been explained as the Curie temperature, it is not limited to this temperature, for example, the Curie temperature can be set to 100 degrees Celsius for a kettle or 260 degrees Celsius for a teppanyaki grill. The desired temperature required above can be selected.

[0034]

[Effects of the Invention] As is clear from the above description, the induction cooking pot of the present invention has the following effects.

(1) Since heating is performed at maximum output until the set temperature is reached, the start-up time (preheating time) can be minimized.

(2) Since induction heating is used, there is no heat capacity, so there is no overshoot in the pan temperature after reaching the set temperature.

(3) Even if the temperature of the pot drops suddenly due to the addition of food, heating is automatically started at the maximum heating power without any time delay, and the temperature accuracy is extremely high.

(4) Since it does not depend on the temperature detection accuracy of the induction heating cooker body, the combination of the pot and the body is free. (Constant temperature accuracy can be obtained even if the cooker itself changes)
(5) Since it works based on the average temperature of the bottom of the pot, accuracy and operation are not affected by the way the pot is placed or the unevenness of the ingredients.

(6) Since non-magnetic metal materials have good thermal conductivity, there is little temperature unevenness to the food being cooked.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a pot for an induction heating cooker according to an embodiment of the present invention.

[Figure 2] Explanatory diagram of the same operation

[Fig. 3] Cross-sectional view of a pot for induction heating cooker showing another embodiment

[Explanation of symbols]

1, 4 Pot for induction heating cooker 1a, 4a
Main body part (non-magnetic metal material) 1b, 4b Room temperature magnetic metal material 2 Heating coil

Claims (2)

[Claims] 1. A cold magnetic metal having a predetermined Curie temperature is integrally formed on the outside of a cooking container made of a non-magnetic metal, at least in a portion facing a heating coil, and the cold magnetic metal has a thickness of a Curie temperature. A pot for induction heating cookers whose penetration depth is greater than or equal to the eddy current penetration depth at temperatures below. 2. A room-temperature magnetic metal having a predetermined Curie temperature is integrally formed on at least the portion facing the heating coil on the outside of the cooking container made of a non-magnetic and highly thermally conductive metal, and the room-temperature magnetic metal has a prescribed Curie temperature. A pot for an induction heating cooker, wherein the thickness of the metal is greater than the penetration depth of an eddy current at a temperature below the Curie temperature and below the penetration depth at a temperature above the Curie temperature.