JP2917526B2 - Pot for induction heating cooker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In an induction heating cooker, a heating coil is disposed below a top plate, and eddy currents are generated in the bottom surface of the induction heating cooker on the top plate by lines of magnetic force generated by the heating coil to generate heat. It has become.

[0003] Such induction heating cooker pots include:
Conventionally, metal pots have been used for heating among general pots used for gas and the like. However, in this case, since the electric characteristics of the pot are constant during normal cooking, heating is continued with a constant heating power, and temperature detection means (thermistor) disposed via a top plate to prevent overheating and automatic temperature control. Or bimetal thermostat) to control the induction heating output.

[0004]

However, in such a heating power control method, since the temperature of the pot is detected through the crystallized glass used for the top plate, the actual temperature of the cooking pot is controlled. The temperature difference between the temperature and the temperature sensed by the thermistor was large, resulting in poor thermal response and detection accuracy. As a result, the temperature cannot be completely controlled in an abnormal use state such as empty cooking, and oil in the pot ignites, and a problem such as remarkable warpage or deformation of the bottom of a pot using a metal material occurs.

Further, in the conventional temperature detection, since the temperature of a part of the bottom of the pot is detected, the accuracy of detection is poor when the pot is placed or when the cooking material is imbalanced. further,
Since the rise in the temperature of the pot bottom during empty cooking and the rise in the temperature during normal cooking vary greatly depending on the location of the pot bottom, it has been extremely difficult to always accurately detect the pot temperature under various use conditions.

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned conventional problems, and always provides high safety and high-precision 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]

In order to achieve the above object, a pot for an induction heating cooker according to the present invention sets a Curie temperature at a temperature used for cooking, and a high-frequency electric resistance of the pot before and after the Curie temperature. The temperature-dependent magnetic metal material and the non-magnetic metal material that change are integrally formed, and the thickness of the room-temperature magnetic metal
Is greater than the eddy current penetration depth below the Curie temperature and
To a pot that is below the penetration depth above the temperature
Thus, a pot that is automatically controlled so as not to exceed a desired temperature is realized.

[0008]

According to the present invention, a magnetic metal material having a Curie temperature is used as a material of a pot provided for an induction heating cooker. At a temperature lower than the Curie temperature, an eddy current flows through the magnetic metal material and heat is generated by eddy current loss.

At this time, the eddy current flowing in the bottom of the pot concentrates on the surface near the heating coil, and has a property that the current hardly flows as it goes into the metal. The depth is called penetration depth and is expressed by the following equation.

[0010]

(Equation 1)

[0011] Since the eddy current is small at a point higher than the penetration depth, the influence of the alternating magnetic field is also small. Even if another metal exists inside the metal having a thickness larger than the penetration depth, the overall operation is not significantly affected.

On the other hand, metals below the penetration depth are also affected by the magnetic field inside, so that the effects of the metals inside affect the overall induction heating.

In the pot of the present invention, when the temperature of the pot is lower than the Curie temperature, the super-ultra-frequency alternating magnetic flux radiated from the heating coil flows to the outer magnetic metal material, but the alternating magnetic flux has a high magnetic permeability. The eddy current induced by the magnetic flux is concentrated on the bottom side of the pot due to the skin effect.

As a result, the eddy current flows intensively on the surface (bottom side of the pan) of the magnetic metal material, so that the electric resistance of the pan becomes equivalently large, the Joule heat generated by the eddy current is large, and The calorific value increases. At this time, if the thickness of the magnetic metal material is not more than the penetration depth at room temperature, a sufficient induction heating output cannot be obtained due to the influence of the non-magnetic metal material even under normal conditions.

On the other hand, when the temperature is higher than the Curie temperature, the magnetic metal material loses magnetism, so that the magnetic permeability decreases and the penetration depth of the eddy current (the depth from the surface until the surface current decreases to a certain rate) increases. As a result, the eddy current flowing only on the bottom surface of the magnetic metal material flows further inside the magnetic metal material (although the magnetism has been lost because the temperature has exceeded the Curie temperature). Since the value is greatly reduced, Joule heat is also significantly reduced. In this way, the induction heating output before and after the Curie temperature can be controlled.

Further, when the thickness of the magnetic metal material is thinner than the penetration depth above the Curie temperature, the magnetic flux penetrates the magnetic metal material and reaches the non-magnetic metal material when the temperature exceeds the Curie temperature. The generation of Joule heat is further reduced by the non-magnetic metal material having a small resistance, and the change in the calorific value before and after the Curie temperature is further increased, which is convenient for control.

The state of the change in the electric resistance value due to the change in the magnetism will be described in the case of a temperature-sensitive stainless steel subjected to a test.

[0018]

[Table 1]

As can be seen from Table 1, even if the metals have the same characteristics, the electrical resistance is reduced to one-tenth depending on whether they are magnetic or not. In other words, since the Joule heat generated at the bottom of the pot is proportional to the electric 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, the alternating magnetic flux penetrates the magnetic metal material in large quantities at room temperature and reaches the non-magnetic metal material, so the difference from the output when the Curie temperature is exceeded is narrowed. The control range of the thermal power becomes small, and the thickness of the magnetic metal material needs to be greater than the penetration depth at room temperature.

Further, when the thickness of the magnetic metal material is set to be equal to or less than the penetration depth at a high temperature, the magnetic flux reaches the nonmagnetic metal material at a temperature higher than the Curie temperature, so that Joule heat is greatly reduced and the control range can be widened. is there.

Here, the state of the change of the heating operation will be described step by step. First, when heating is started from room temperature, heating is performed with a large amount of heat until the Curie temperature is reached. As a result, when the pot reaches the Curie temperature, the pot itself changes its characteristics automatically and the amount of generated heat decreases. Then, when the temperature of the pot falls and becomes equal to or lower than the Curie temperature, the metal material regains magnetism and restarts heating with a large calorific value.

Here, when the Curie temperature of the magnetic metal material of the pan is selected to a desired set temperature, the pan itself can automatically control the calorific value by the operation described above.
For this reason, the Curie temperature can be accurately controlled to a desired temperature.

Particularly 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 material, so that it can be appropriately selected in the cooking menu. As an example, if the Curie temperature is selected to be 100 ° C., heating is automatically interrupted when water boils, and a kettle that prevents wasteful evaporation of water after boiling can be realized.

Further, nickel alloys and iron-chromium alloys as magnetic metal materials having a Curie temperature are optimal because they can freely change the Curie temperature and have a large skin resistance which determines the calorific value. Since materials such as aluminum, copper, mirrors, and alloys thereof have high thermal conductivity and are provided with an element as a cooking vessel, they are suitable for application to the present invention.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of an embodiment of the induction cooking pot of the present invention. Reference numeral 1 denotes a 3 mm-thick induction heating cooker placed on a heat-resistant insulator 3, which is placed opposite to a disk-shaped heating coil 2. The pot 1 is a non-magnetic metal material, and a main body 1a made of aluminum having good heat conductivity.
And a room temperature magnetic metal material 1b which is a nickel alloy having a Curie temperature of 180 degrees. Generally, a magnetic metal material has a low thermal conductivity, which leads to temperature unevenness as a cooking vessel. However, in the present invention, since the main body portion 1a of a non-magnetic metal material having good heat conductivity is integrally formed, 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 of 40% Ni, 8% Cr and 52% Fe, and the non-magnetic metal material 1a is 2.5 mm thick aluminum. is there. Therefore, as described above, the depth of penetration at room temperature is about 0.2.
When it exceeds the Curie temperature at 8 mm, it changes to 2.75 mm, and the thickness of the magnetic metal material is about twice the penetration depth at normal temperature and about 0.2 times the penetration depth at high temperature.

In order to evaluate the induction cooking pot 1 of the present invention, oil is put into the induction cooking pot 1 of the present invention.
This was placed on the top plate 2 of the induction heating cooker to perform tempura cooking. The state at this time will be described with reference to FIG. At the timing a, the induction heating of the room-temperature magnetic metal material 1b of the pot 1 containing the oil is started. The heat generated by the room-temperature magnetic metal material 1b is conducted to the main body 1a to heat the oil. The output of induction heating at that time is 1200 W. Then, the oil temperature rises almost linearly because it is continuously heated with a constant heating power, and when the pan temperature reaches the preset Curie temperature of 180 ° C., the pan 1 rapidly changes to a non-magnetic material,
The output of induction heating drops to 250W. The output value when reduced (250 W in this case) can be changed by the material, thickness, shape, etc. of the main body portion 1a of the magnetic metal material. After the pot 1 has reached the Curie temperature, the thermal power is greatly reduced, so that the oil temperature gradually decreases to 175 ° C (point c). At this time, since the room-temperature magnetic metal material 1b regains magnetism again, the thermal power automatically rises again to 1200 W and the oil temperature rapidly rises toward the Curie temperature of 180 ° C.
Add ingredients such as tempura in oil and let the temperature of the pot rise to 175
Similarly, when the temperature drops to ℃, the thermal power is automatically turned on and off,
Keep oil temperature constant.

In general, the induction heating cooker is provided with heat prevention for small items, and when the input value is much smaller than that of a normal pot, heating is automatically stopped. In the above embodiment, if the input when the temperature exceeds the Curie temperature is less than the small object detection level, the heating is temporarily stopped, but after a predetermined time (usually 1 to 3 seconds) has elapsed, the heating is automatically restarted and the pot temperature is reduced. If it is 175 ° C. or lower, heating is automatically started at 1200 W. If the temperature of the pot has not dropped to 175 ° C., the input is small and the heating is interrupted again by detecting the small object. Therefore, the input when the temperature exceeds the Curie temperature changes due to the characteristics of the pan, but the pan temperature can be automatically controlled whether it is higher or lower than the accessory detection level.

The embodiment of FIG. 1 has been described based on a pot having a structure formed by squeezing and processing a clad plate in which a non-magnetic metal material and a magnetic metal material are integrally formed. However, as shown in FIG. The pan 4 may be formed by attaching or bombarding the magnetic metal material 4b to the bottom portion (the portion opposing the heating coil), and the same operation as in FIG. 1 is obtained. In this embodiment, the bottom of the pot is high in strength, so that the bottom is always flat even in empty cooking, and is stable even when placed on the top plate.

As described above, the pot for the induction heating cooker of the present invention has a self-temperature control function, and in addition to enhancing cooking performance and safety such as ignition of oil, the temperature distribution is reduced and the safety is reduced. And the remarkable effect of cooking performance can be expected.

Although a nickel alloy was used as the magnetic metal material having a Curie temperature, the present invention is not limited to this, and it can be appropriately selected according to the set temperature, mechanical strength, workability, and the like.

Further, the description has been given of a 180 ° Curie temperature, but this is not particularly limited to this temperature. For example, a cooking temperature of 100 ° C. for kettles and a Curie temperature of 260 ° C. for teppanyaki are used. What is necessary is just to select the desired temperature required above.

[0034]

As is apparent from the above description, the pot for an induction heating cooker according to the present invention has the following effects.

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

(2) Since there is no heat capacity due to induction heating, there is no overshoot in the pot temperature after reaching the set temperature.

(3) Even if the temperature of the pot suddenly drops due to the input of foodstuffs, heating is automatically started at the maximum heating power with no time delay, and the temperature accuracy is extremely good.

(4) Since it does not depend on the accuracy of detecting the temperature of the induction heating cooker main body, the combination of the pot and the main body is free.
(Constant temperature accuracy can be obtained even if the cooking device body is changed.) (5) Since the operation is performed at the average temperature at the bottom of the pan, the accuracy and operation are not affected by the way of placing the pan or the bias of the material.

(6) Since the non-magnetic metal material has good heat conduction, there is little unevenness in the temperature of the food.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an induction cooking pot according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram of the operation.

FIG. 3 is a cross-sectional view of a pot for an induction heating cooker showing another embodiment.

[Explanation of symbols]

 1,4 Induction cooker pot 1a, 4a Main body (non-magnetic metal material) 1b, 4b Room temperature magnetic metal material 2 Heating coil 3 Heat resistant insulating material

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05B 6/12

Claims (1)

(57) [Claims] 1. A room-temperature magnetic metal having a predetermined Curie temperature is integrally formed at least in a portion facing a heating coil outside a cooking container made of a nonmagnetic good heat conductive metal, A pot for an induction heating cooker, wherein the thickness of the metal is not less than the penetration depth of the eddy current below the Curie temperature and less than the penetration depth above the Curie temperature.