JPH0975211A - Induction heating cooker - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To easily generate eddy current in a pan when induction heating the pan and to easily and uniformly transfer the generated heat to the whole pan, and to manufacture the pan. Sometimes it prevents the pot from deforming. An induction heating cooker according to the present invention is provided so as to face an outer bottom surface portion or an outer peripheral surface portion of a pan 3, and the pan 3 is provided.
Induction heating coils 8 and 9 for induction heating
The induction heating coils 8 and 9 are provided with a control means for controlling energization, and the pot 3 is made of graphite having a carbon purity of 99.9% or more. With this configuration, an eddy current is easily generated in the pan 3 during induction heating, and the generated heat is uniformly and quickly transferred to the entire pan 3. Moreover, when the pot 3 is manufactured, unlike the pot made of the clad material, the pot 3 is not scratched or deformed during manufacturing, and the quality of the pot 3 is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating cooker provided with an induction heating coil for induction heating a pot.

[0002]

2. Description of the Related Art In this type of induction heating cooker, for example, an electromagnetic cooker, a top plate for mounting a pan is provided on the upper surface and an induction heating coil is provided on the lower surface side of the top plate. The coil is configured to generate an eddy current in the pot to heat the pot.
In this configuration, it is obligatory to use a pot made of a magnetic metal such as iron or stainless steel in order to easily generate an eddy current in the pot. In recent years, some rice cookers have an induction heating coil instead of the electric heater, and the induction heating coil is used to heat the rice cooking pot. Also in this case, the rice cooking pot is made of magnetic metal such as iron or stainless steel.

The magnetic metal such as iron or stainless steel has a characteristic that the thermal conductivity is not so good, so that the heat cannot be uniformly and quickly transferred to the entire pot. For this reason, the magnetic metal pan has a drawback in that it cannot heat food better than an aluminum or copper pan. On the other hand, it is considered that the outer part of the pan is made of stainless steel and the inner part of the pan is made of aluminum, and if this pan is used, eddy currents are easily generated and heat is generated in the entire pan. Transmission will be uniform and prompt.

[0004]

When manufacturing the above-mentioned pot made of stainless steel and aluminum, first, a clad material in which a stainless steel plate and an aluminum plate are stacked and rolled by heating them while heating them is combined. To form. Then, by pressing this clad material into a pot shape by pressing, the above-mentioned 2
Manufactures pots made of seed metal. In this case, since stainless steel is a very hard metal and aluminum is a very soft metal, the clad material has a characteristic that the hardness difference is large. When the clad material having such a large hardness difference is drawn, there is a problem that the two metal plates are peeled off or the soft metal plate is scratched by the press die, resulting in poor quality.

When applying the fluororesin to the inner surface of the pot, it is necessary to heat the pot to about 400.degree. here,
Since the two types of metal plates forming the clad material have different thermal expansion coefficients, there is a drawback that the pot is easily deformed during the heating. Further, focusing on the outer part of the clad pan, this part is made of stainless steel, so it is difficult for heat to be transferred. That is, there is a drawback that the heat generated by the eddy current loss in the stainless steel portion is difficult to be transferred to the aluminum portion inside the pot. Therefore, the pot made of the above clad material, compared to the pot made entirely of aluminum or copper,
The disadvantage is that heat is not evenly distributed throughout the pan, and the food cannot be heated well.

Therefore, an object of the present invention is to facilitate the generation of an eddy current in the pan when induction heating the pan, and to easily and uniformly transfer the generated heat to the entire pan. An object of the present invention is to provide an induction heating cooker capable of preventing the deterioration of the quality of a pan when it is manufactured.

[0007]

An induction heating cooker according to the present invention is a pan placed on a cooker main body and an induction heating cooker provided so as to face an outer bottom surface or an outer peripheral surface of the pan. It is characterized in that it is provided with an induction heating coil for controlling the induction heating coil and a control means for controlling energization of the induction heating coil, and the pot is made of graphite.

The inventor of the present invention searched for a substance which is likely to generate an eddy current when being induction-heated and has a high thermal conductivity and which can form a pot. As a result, they have found that graphite is suitable as the substance. That is, according to the experiments of the present inventors, when graphite is induction-heated, an eddy current is easily generated, heat is sufficiently generated due to the loss of the eddy current, and graphite is a substance having a high thermal conductivity. It was confirmed that graphite is a material that can be used to make a pot. The present invention has been made paying attention to this point.

[0009] Further, far infrared rays are sufficiently emitted from graphite by heating it. Even in this far infrared, especially wavelength 1
The one having a size of 0 to 30 μm has a function of heating the material from the inside, and in particular has a function of making the rice fluffy from the inside, so that the effect becomes more significant when applied to the rice cooker.

According to the above construction, since the pot is made of graphite, when the pot is induction heated, eddy current is likely to be generated in the pot and the generated heat is uniformly and quickly transferred to the entire pot. Become. Moreover, when manufacturing such a pot, unlike a pot made of clad material, the pot is not damaged or deformed during production, so it is possible to prevent deterioration of the pot quality. .

In the above construction, it is preferable that the graphite forming the pot has a carbon purity of 99.9% or more. Furthermore, it is a good configuration that the pan is formed by cutting the graphitized block material. With this configuration, a graphite pot can be easily manufactured. In this case, the block material is preferably formed by graphitizing a block-shaped molded product molded by CIP molding. It is also preferable that the block material is formed by graphitizing a block-shaped molded product molded by extrusion molding.

Furthermore, it is also a good constitution to construct a pot by firing a pan-shaped molded product formed of a phenolic resin and graphitizing it. On the other hand, it is also preferable to apply a fluororesin to the surface of the pot. It is also a good configuration to apply glassy carbon to the surface of the pot. Further, a kneaded material obtained by kneading powdery coke and pitch is subjected to CIP molding or extrusion molding to mold a block-shaped molded product, and the block-shaped molded product is heated at 800 to 1000 ° C. while repeating pitch impregnation. Firing the primary firing,
It is a preferable configuration that the block material is graphitized by heating the primary fired product at 2500 to 3000 ° C.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to a rice cooker will be described below with reference to FIGS. 1 to 7. First, in FIG. 2 showing the schematic overall configuration of the rice cooker,
An inner case 2 is arranged inside the rice cooker body 1,
A graphite pot 3 is housed in the inner case 2 so as to be detachable from above. The method for manufacturing the pan 3 will be described later. A lid 4 is provided on the top of the rice cooker body 1 so as to be rotatable upward through a hinge 5. The lid 4 is configured to open and close the upper openings of the rice cooker body 1 and the inner case 2. When the lid 4 is closed, the inner lid 6 attached to the inner surface side of the lid 4
The upper opening of the pan 3 is closed by the above.

A temperature sensor 7 is arranged at the center of the bottom of the inner case 2 so as to contact the bottom of the pot 3. The temperature sensor 7 is configured to detect the temperature of (the bottom of) the pan 3. Then, the first induction heating coil 8 is disposed in a flat portion (a portion surrounding the temperature sensor 7) in the outer bottom portion of the inner case 2, and the second induction heating coil 9 is disposed in a corner portion of the outer periphery. . This allows
The first and second induction heating coils 8 and 9 are arranged so as to face the outer bottom surface portion and the outer peripheral surface portion (corner portion) of the pot 3. The first and second induction heating coils 8 and 9
Ferrite 10 is disposed below the coil so as to form a magnetic circuit with the induction heating coils 8 and 9.

Further, an inverter circuit section 11 for supplying a high frequency current to the induction heating coils 8 and 9 is arranged on the inner bottom of the rice cooker body 1, and the cooling fan unit 1 is also provided.
2 are provided. In addition, the control circuit unit 13 is provided in the lower portion on the front side in the rice cooker body 1, and the operation unit 14 is provided in the upper portion. Various operation switches and various indicators are arranged on the operation unit 14 so as to be exposed outside the front surface of the rice cooker body 1. The control circuit unit 1
3 includes a microcomputer,
It has a function (control program) to control the rice cooking operation. The control circuit unit 13 is the same as the inverter circuit unit 11 described above.
The induction heating coils 8 and 9 are configured to be energized by drivingly controlling the switching element therein. The control circuit section 13 constitutes a control means. Further, the control circuit unit 13 is configured to receive each switch signal from each operation switch of the operation unit 14 and control each display of the operation unit 14.

A drum heater 15 for keeping the rice in the pot 3 warm is arranged on the outer peripheral surface of the inner case 2. A heater 16 for keeping the rice in the pan 3 warm is also provided on the upper surface of the inner lid 6. The heaters 15 and 16 are configured so that energization is controlled by the control circuit unit 13.

Next, the process of manufacturing the graphite pan 3 will be described with reference to FIGS. As shown in FIG. 4 among them, first, the raw coke 17 made of, for example, petroleum coke or coal coke is pulverized by the pulverizer 18 and then the pulverized coke is pulverized by the fine pulverizer 19 into fine powder. . Subsequently, after performing a step of sieving the coke pulverized into the fine powder by the sieving device 20, the coke is stored in the storage tank 21. Then, a step of kneading the fine coke stored in the storage tank 21 and the binding material 22 made of, for example, pitch by the binding device 23 is performed.

After that, a step of forming the kneaded material into a predetermined shape, for example, a block shape is performed. In this case, 3
One molding method, specifically, one of CIP molding (CIP molding device 24), mold molding (mold molding device 25), and extrusion molding (extrusion molding device 26). Of these, CIP molding (CIP molding device 24)
Alternatively, in the case of molding by molding (molding molding device 25), coke pulverized into fine powder by the fine pulverizing device 19 is added as necessary.

An example of the CIP molding device 24 is shown in FIG. By using this CIP molding, it is possible to produce a material (graphite) which is isotropic and has no difference in characteristics depending on the processing direction, and which is homogeneous, dense and strong. An example of the molding device 25 is shown in FIG. Using this mold molding, C
Similar to IP molding, it is possible to produce a material (graphite) that has small particles and is homogeneous, dense, and strong. This material is suitable for fine processing and is less anisotropic than the extruded material. Further, an example of the extrusion molding device 26 is shown in FIG. By using this extrusion molding, a long material (graphite) can be easily manufactured, and the material has a coarser structure than the materials obtained by CIP molding and extrusion molding, but the thermal expansion coefficient is small and it is resistant to thermal shock. It is possible to produce extremely strong materials (graphite). The CIP molding may be referred to as a rubber press, and the mold molding may be referred to as a mold molding.

Then, as shown in FIG. 4, the block-shaped molded product molded as described above is baked by the primary baking device 27. In this case, the block-shaped molded product is
It is heated at 1000 ° C. to generate a primary fired product (carbonaceous material) 28. At this time, the pitch infiltration device 29 is configured to fire the block-shaped molded article while repeatedly impregnating the block.

Subsequently, the primary fired product 28 is heated by the graphitizer 30 to be graphitized. In this case 2500
The block-shaped graphitized material 31 is generated by heating at 3000 ° C. Then, the graphitized material (block material) 31 is cut by the processing device 32 to manufacture the pot 3 having a shape as shown in FIG. Further, when it is desired to increase the purity of carbon of the graphitizing material 31, the purification device 33 is configured to highly purify the carbon. Here, the graphite constituting the pot 3 of the present embodiment is configured so that the purity of carbon is 99.9% or more.

Graphitized material 3 produced as described above
The characteristics of No. 1 are shown in Table 1 below. In Table 1, sample product types A to F have different manufacturing conditions (molding method of kneaded product, kneading ratio, heating temperature, heating time, etc.).

[0023]

[Table 1] From the above table, it can be seen that the thermal conductivity of graphite is 8 to 10 times better than that of stainless steel (14 kcal / mh ° C.). In particular, sample types D to F using extrusion molding
Has very good thermal conductivity. On the other hand, the sample product types A to C using CIP molding have excellent characteristics that the material is hard and is difficult to crack.

Then, the surface of the pot 3 formed by cutting the graphite as described above, particularly the inner surface, is coated with a fluororesin. In this case, EK-1909BKN (manufactured by Daikin Industries, Ltd.) is used as the undercoating material for the fluororesin, and EK-
It is preferable to use 4398SLN (manufactured by Daikin Industries, Ltd.). This makes it easier to clean the pot 3 and to easily take out the food (rice) contained in the pot 3. In the state where the fluororesin is not coated, the surface of the pan 3 made of graphite alone is fragile and the carbon particles are easily separated from the surface, that is, the carbon particles are easily attached to the food (rice) contained in the pan 3. However,
The above-mentioned fluororesin coating can surely prevent such adhesion of carbon particles.

The outer surface, which is the surface of the pot 3, is coated with glassy carbon. In this case, as the glassy carbon paint, it is preferable to use a paint in which carbon particles are added to FDS paint (manufactured by Okitsumo Co., Ltd.). By such a coating process,
The surface hardness of the pot 3 becomes high, and the work of cleaning the pot 3 becomes easy.

According to this embodiment having such a structure, the pot 3
Since it is composed of graphite (specifically, graphite having a carbon purity of 99.9% or more), induction heating of the pot 3 facilitates the generation of an eddy current in the pot 3, and further, the generated vortex Eddy current loss occurs due to the electric current and the specific resistance of the pan 3 (graphite) itself, and sufficient heat is generated. In this case, as shown in FIG. 2, the portion of the pan 3 corresponding to the induction heating coils 8 and 9, that is, the flat portion of the outer bottom portion and the lower portion (corner portion) of the outer peripheral portion, generate heat intensively. Is configured. Since the graphite forming the pot 3 has a high thermal conductivity, the generated heat can be uniformly and quickly transferred to the entire pot 3. As a result, the food (rice and water) in the pan 3 can be efficiently heated without uneven heating, that is, the thermal efficiency can be increased.

Here, the heating operation of the rice and water contained in the pan 3 when the rice is cooked by the pan 3 of the above embodiment will be described with reference to FIG. As shown in FIG. 1, since the induction heating coils 8 and 9 raise the temperature of the flat portion of the outer bottom surface of the pot 3 and the lower portion (corner portion) of the outer peripheral surface portion, the water in the pot 3 moves in the direction of the arrow in FIG. Convection as shown in. Specifically, the water in the pan 3 rises along the peripheral wall (rising part) of the pan 3 and descends at the center of the pan 3, so that the whole rice in the pan 3 is generated. Is heated evenly. As a result, the rice in the pan 3 is cooked from the upper surface thereof, and is cooked downward as the amount of hot water in the pan 3 is reduced.

FIG. 3 (a) shows the result of measuring the temperature distribution in the pan 3 when the rice is cooked using the pan 3. In addition, the result of having measured the temperature distribution in the pan when rice was cooked using the conventional pan (clad material pan) 34 is shown in FIG. In this case, as shown in FIGS. 3A and 3B, the temperature is measured at nine points P1 to P9 in the pot. The temperature measurement point P1 is the lower center, the temperature measurement point P2 is the middle center, the temperature measurement point P3 is the upper center, and the temperature measurement point P4.
Is the middle lower part, temperature measurement point P5 is the middle middle part, temperature measurement point P
6 is an intermediate upper part, temperature measurement point P7 is a lower part near the peripheral wall part, temperature measurement point P8 is a middle part near the peripheral wall part, and temperature measurement point P9 is an upper part near the peripheral wall part.

3 (a) and 3 (b) show the temperature distribution when the temperatures at four or more temperature measuring points in the pot reach 100.degree. Specifically, in FIG. 3A, P1 is 99 ° C., P2 is 99 ° C., and P3 is 100 ° C.
℃, P4 96 ℃, P5 99 ℃, P6 100 ℃, P
7 is 100 ° C, P8 is 100 ° C, and P9 is 100 ° C. Further, in FIG. 3B, P1 is 86 ° C. and P2 is
88 ° C, P3 100 ° C, P4 100 ° C, P5 8
7 ℃, P6 is 100 ℃, P7 is 98 ℃, P8 is 96 ℃,
P9 is 100 ° C.

From FIG. 3A, the maximum temperature difference (maximum temperature (100 ° C.) and minimum temperature (96
It can be seen that the difference) is 4 ° C. On the other hand, FIG.
From (b), the maximum temperature difference (difference between the maximum temperature (100 ° C) and the minimum temperature (86 ° C)) of the conventional pot 34 is 14 ° C.
It can be seen that it is. Therefore, it can be seen from FIGS. 3 (a) and 3 (b) that the pot 3 of the present embodiment can have a much more uniform temperature distribution than the pot 34 of the conventional configuration.

Further, far infrared rays are sufficiently emitted from graphite by heating it. Even in this far infrared, especially wavelength 1
The one having a size of 0 to 30 μm has a function of heating the material from the inside, and particularly has a function of making the rice fluffy from the inside. Therefore, when graphite is applied to the pan 3 of the rice cooker, the effect becomes more significant.

On the other hand, when the pot 3 of this embodiment is manufactured, the block material 31 is graphitized and
Since the pot 3 is manufactured by cutting the clad, unlike the conventional clad pot made of clad material, two types of metal are peeled off during manufacturing, the pot is damaged, or the pot is deformed. This can be eliminated and the quality of the pot 3 can be improved. In particular, in this embodiment, since the cutting process is adopted, the dimensional accuracy of the shape of the pot 3 can be increased.

In the above embodiment, the inner surface of the pot 3 is coated with the fluororesin and the outer surface of the pot 3 is coated with the glassy carbon. However, the present invention is not limited to this. The entire surface (inner surface and outer surface) may be coated with the fluororesin, or the entire surface of the pot 3 (inner surface and outer surface) may be coated with glassy carbon.

In the above embodiment, when the pan 3 is manufactured, the block material 31 is graphitized and the block material 31 is cut to manufacture the pan 3. However, instead of this, the pan 3 is manufactured. It may be manufactured as described below. That is, for example, a true spherical phenol resin (for example, a true sphere having a particle size of about 5 to 800 μm) mainly composed of phenol, formalin, or the like is heated and melted in an injection molding machine and molded into a pot shape. Subsequently, the molded pot-shaped molded product is heated in a firing furnace to be graphitized. In this case, for example, the heating temperature is 1500 to 2000 in a nitrogen gas atmosphere.
It is configured to be baked at a temperature set to ° C. In this case, it is known that when the molded product of the phenolic resin is graphitized, the volume of the molded product shrinks by about 17%. For this reason, in this example, when molding a pot-shaped molded product with a phenolic resin, the volume was 10 to 10 in consideration of shrinkage during firing.
It is configured to be molded to a size of about 20%.

In the case of the above construction, since a general resin molding device can be used when molding the pot-shaped molded product, the pot-shaped molded product can be molded into a stable shape. Further, since the cutting process is unnecessary, the number of manufacturing processes can be reduced and the manufacturing cost can be reduced.

Although the above-mentioned embodiment is applied to the rice cooker,
It may be applied to other induction heating cookers, for example, an electromagnetic cooker (a cooking heater installed on a cooking table) and a pan used in the electromagnetic cooker.

[0037]

As is apparent from the above description, according to the present invention, since the pot for induction heating is made of graphite, eddy current is easily generated in the pot and the generated heat is evenly distributed over the entire pot. It is possible to quickly transmit, and when manufacturing such a pot, the pot is not damaged or deformed during production, so it is possible to prevent deterioration of the pot quality. Produce an effect.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view around a pan and an induction heating coil showing an embodiment of the present invention.

[Figure 2] Vertical side view of the entire rice cooker

FIG. 3 (a) is a diagram showing a temperature distribution inside the pot when the pot of the present embodiment is heated, and FIG. 3 (b) is a diagram showing a temperature distribution inside the pot when the pot having the conventional structure is heated.

FIG. 4 is a diagram showing a pot manufacturing process.

FIG. 5 is a vertical sectional view of a CIP molding device.

FIG. 6 is a vertical cross-sectional view of the molding apparatus.

FIG. 7 is a vertical sectional view of an extrusion molding device.

[Explanation of symbols]

1 is a rice cooker main body, 2 is an inner case, 3 is a pot, 4 is a lid, 8 is a first induction heating coil, 9 is a second induction heating coil, 1
3 is a control circuit unit (control means), 17 is a raw material coke, 1
8 is a crushing device, 19 is a fine crushing device, 20 is a sieving device, 21 is a storage tank, 22 is a binding material, 23 is a welding device, 2
4 is a CIP molding device, 25 is a mold molding device, 26 is an extrusion molding device, 27 is a primary firing device, 28 is a primary firing product, 29 is a pitch infiltration device, 30 is a graphitization device, 31 is a graphitization material (block material). ), 32 is a processing device, and 33 is a high-purification device.

Claims (9)

[Claims] 1. A pan placed on the cooker main body, an induction heating coil provided to face the outer bottom surface or the outer peripheral surface of the pan to induction heat the pan, and the induction heating coil is energized and controlled. An induction heating cooker, characterized in that the pan is made of graphite. 2. The induction heating cooker according to claim 1, wherein the graphite constituting the pan has a carbon purity of 99.9% or more. 3. The induction cooking device according to claim 1, wherein the pan is formed by cutting a graphitized block material. 4. The induction heating cooker according to claim 3, wherein the block material is formed by graphitizing a block-shaped molded product molded by CIP molding. 5. The induction heating cooker according to claim 3, wherein the block material is formed by graphitizing a block-shaped molded product formed by extrusion molding. 6. The induction heating cooker according to claim 1, wherein the pan is formed by baking a pan-shaped molded product formed of a phenolic resin to graphitize it. 7. The induction heating cooker according to claim 1, wherein the surface of the pot is coated with a fluororesin. 8. The induction heating cooker according to claim 1, wherein the surface of the pot is coated with glassy carbon. 9. A block material is formed by CIP molding or extrusion molding of a kneading material obtained by kneading powdery coke and pitch, and the block material is repeatedly impregnated with a pitch of 800. ~ 1000 ° C
The primary fired product is fired by heating at
The induction heating cooker according to claim 3, wherein the induction heating cooker is graphitized by heating at 00 to 3000 ° C.