JP6578750B2 - Electric rice cooker - Google Patents

Description

  The present invention relates to an induction heating type electric rice cooker, and more particularly to an induction heating type electric rice cooker using a non-metallic inner container, for example, a ceramic earthen pot.

  In general, an electric rice cooker has a plurality of heating means such as a work coil and a heat insulation heater, and uses these heating means to automatically cook rice and keep it warm, providing the user with the most suitable rice etc. Widely known as an instrument.

  Conventionally, for an electric rice cooker, as an inner pot for cooking rice, for example, a stainless steel outer wall, an aluminum inner wall, and a metal having a multilayer structure with a fluorine coating on the inner side of the aluminum inner wall are used. When cooking rice, what cooks the contents in the inner pot by induction heating the inner pot is known.

  By the way, such a metal inner pot has the property that it is easy to heat and cool easily, and the temperature of rice is rapidly raised during cooking, so it cannot be said that it fully draws out the deliciousness when cooked. It was. Moreover, since it is easy to cool after cooking rice, some energy is required in order to heat rice.

  The present applicant has already proposed an electric rice cooker using a ceramic earthen pot to compensate for the drawbacks of such a metal inner pot. This ceramic product has a larger heat capacity than metal products, so the rate of temperature rise during cooking is relatively mild and heat storage is good, so you can cook rice deliciously, It is possible to reheat with a microwave oven while putting on, and since there is good heat storage, there is an advantage that a warm state can be kept long after reheating.

  However, clay pots generally have a low thermal conductivity of about 1 W (watts) / m (meters) K (Kelvin), so that the heat generated by the bottom heating element is difficult to reach the whole area and the temperature rises locally. For example, in the case of rice cooking, the color unevenness of the rice tends to occur, the detection of the center sensor at the bottom tends to be delayed, and it has a problem that it is easy to crack when dropped because it has low impact resistance. Yes.

  In order to reduce such a problem, the present applicant has applied for the invention of the earthenware pot structure shown in FIG. The outline is as follows.

  That is, the earthenware pot 1 has a horizontal bottom wall portion 1a having a heating element 3 facing the work coil 4, an arcuate ring-shaped curved wall portion 1b, and a cylindrical side wall portion 1c. It is a conventionally well-known bottomed container-like thing which has the annular protrusion 5 with the low height which hangs down between the part 1a and the curved wall part 1b, and is the wall thickness of the bottom wall part 1a and the curved wall part 1b. The thickness of the side wall portion 1c is made thinner than that of the side wall portion 1c to improve the heat conduction performance of the heat generating element 3, and an aluminum die cast portion 2 having high heat conductivity is provided on the outer peripheral surface of the bottom wall portion 1a to conduct heat. (For example, refer patent document 1).

  However, the structure for changing the thickness of the wall portion of the present invention is only to produce a clay pot using a mold having such a shape, and there is no extra effort and cost increase compared to the same thickness. Providing the aluminum die cast part greatly contributes to the improvement of the thermal conductivity, but on the other hand, a new problem arises in that it takes time and cost to be provided.

JP 2009-45194 A

  The present invention has a predetermined amount of silicon carbide having a thermal expansion coefficient substantially the same as that of a conventional clay pot, for example, cordierite mineral, and having a very high thermal conductivity compared to the clay pot. It aims at providing the electric rice cooker which raises the heat conductivity of a clay pot, without providing the above-mentioned conventional aluminum die-casting part by containing.

  In order to achieve the above object, the present invention adopts the following configuration.

In the invention which concerns on Claim 1, the inner pot made from a ceramic, the heat generating body provided in the said inner pot, the inner case which accommodates the said inner pot, the outer case which accommodates and fixes the said inner case, The said inner case, In the electric rice cooker provided with the electromagnetic induction heating means provided between the outer case and generating heat from the heating element, the inner pot contains silicon carbide and contains cordierite mineral as a main component. a ceramic member, the content of silicon carbide in said pot, Ru der than 20% by weight configuration.

In the invention which concerns on Claim 2 , the heat conductivity of the said inner pot is a structure which is 2.0 W / mK or more.

  By containing a predetermined amount of silicon carbide in the earthenware pot, the thermal conductivity of the earthenware pot can be increased. As a result, rice cooking efficiency and heat retention efficiency can be increased, white rice cooking can produce more delicious rice cooking, and rice cooking can reduce uneven color of rice cooking. In addition, it seems that color unevenness reduces because the local heat_generation | fever of the inner peripheral part of the clay pot facing a heat generating body is eased, and cooking temperature falls.

  Moreover, the detection accuracy in the inner pot by the center sensor at the bottom can be increased. As a result, more appropriate cooking rice and heat insulation can be performed.

  Moreover, the local heat_generation | fever of a clay pot can be suppressed. As a result, it is possible to reduce the peeling of fluorine coated on the inner peripheral surface of the earthenware pot and improve the durability of the earthenware pot.

  Moreover, the heat transfer speed to the side wall portion without the heating element can be increased. As a result, the heat retention performance can be improved.

  Moreover, the heating nonuniformity with respect to rice can be reduced. As a result, cooking unevenness can be reduced.

  Moreover, the impact resistance of the earthenware pot can be improved. As a result, the durability of the clay pot can be improved.

Sectional view of the electric rice cooker without the lid Temperature change with time of the current earthenware pot Temperature change with time of clay pot containing silicon carbide Cross section of a conventional electric rice cooker

  FIG. 1 is a longitudinal sectional view of an electric rice cooker with a clay pot set in an inner case and no lid, FIG. 2 is a temperature change diagram with respect to time of the current clay pot, and FIG. 3 is silicon carbide. It is a temperature change figure with respect to time of a containing clay pot.

  The electric rice cooker 30 includes a container body 31 and a lid (not shown) that opens and closes the upper opening of the container body 31. The container body 31 forms an outer case 32 that forms an outer wall, an inner case 33 that is located in the outer case 32 and forms an inner wall, a shoulder member 34 that forms the upper ends of both cases 32 and 33, and a bottom. A bottom member 35 is provided.

  The outer case 32 is made of a metal such as stainless steel and is a cylindrical member having an upper and lower opening, and forms a body portion of the electric rice cooker 30. The outer case 32 may be made of resin instead of metal.

  The shoulder member 34 is made of resin, for example, polypropylene (PP) or the like, and forms an upper end portion of the container body 31 and has a hinge mechanism and a handle 36 for opening and closing a lid (not shown).

  The inner case 33 forming the inside of the container body 31 is a bottomed dish-shaped member made of resin, and has a metal cylindrical case 37 above it, and the inner case 33 and the cylindrical case 37 will be described later. An internal space for storing the earthenware pot 50 is formed.

  The inner case 33 and the shoulder member 34 are connected by screws (not shown), but the cylindrical case 37 is sandwiched between the members 33 and 34 when the inner case 33 and the shoulder member 34 are connected. Moreover, the outer periphery of the cylindrical case 37 has a heat retaining coil 38, and a later-described clay pot 50 housed inside is warmed from the side.

  A sensor opening 39 is provided at the center of the bottom of the inner case 33, and a hole having the same diameter as that of the sensor opening 39 is formed at the center of the upper surface of the bottom of the inner case 33 so as to surround the sensor opening 39. A doughnut-shaped ceramic plate 45 having the above is disposed.

  The ceramic plate 45 is a glossy heat insulating member that reflects the heat from the earthenware pot 50 and prevents the heat from being transmitted downward, and improves the appearance of the inside when the earthenware pot 50 is removed.

  In addition, three substantially rectangular recesses 46 are formed on the outer inner surface where the ceramic plate 45 is disposed at the bottom of the inner case 33, and substantially rectangular silicon members 47 are press-fitted into the recesses 46, respectively. When the earthenware pot 50 is stored in the inner case 33, the low-profile annular protrusion 54 formed in a form that hangs on the bottom lower surface of the earthenware pot 50 is placed on the silicon member 47, and the earthenware pot 50 has Prevent rattling and rotation.

  A bottom coil 40 and a bending portion coil 41 which are electromagnetic induction heating means and work coils for performing induction heating are provided below the bottom portion and the bending portion of the inner case 33, respectively.

  The bottom coil 40 and the bending portion coil 41 are fixed by a coil base 42. The bottom coil 40 and the bending portion coil 41 are formed by connecting a copper wire concentrically a plurality of times in series to the central portion and its outer peripheral portion.

  The bottom member 35 is a resin-made bottomed dish-like member made of polypropylene (PP) or the like, like the shoulder member 34, and forms a bottom outer shell, and has a plurality of leg portions 43 on the bottom surface. The bottom member 35 is attached to the inner case 33 with a screw (not shown). At this time, the outer case 32 is sandwiched between the shoulder member 34 and the bottom member 35.

  Reference numeral 44 denotes a temperature sensor as a center sensor, which is attached in such a manner that its tip protrudes upward from the sensor opening 39 of the inner case 33, and is pressed by the clay pot 50 when the clay pot 50 is stored in the inner case 33. .

  The temperature sensor 44 is a well-known sensor comprising a reed switch for detecting the set state of the earthenware pot 50 and a thermistor for detecting the temperature of the earthenware pot 50, and has a function of a safety device and a function of temperature detection.

  Inside the inner case 33, a clay pot 50 (which may be made of ceramics) which is a non-metallic inner container is detachably stored. The earthenware pot 50 includes an upper thick portion 51, a curved portion thin portion 52, and a bottom thin portion 53.

  The upper thick part 51 is a cylindrical part that forms the upper side wall part of the earthenware pot 50, and has a grippable flange 51a at its upper end.

  The said curved part thin part 52 is a curved part which forms the downward direction of the upper thick part 51 of the clay pot 50, and is thinned in order to improve heat conduction. The bottom thin portion 53 is a horizontal portion that forms the bottom wall portion of the earthenware pot 50, and is thinned to increase heat conduction in the same manner as the curved thin portion 52.

  On the lower surface between the curved thin portion 52 and the bottom thin portion 53, an annular protrusion 54 having a low height is formed so as to hang downward. The protrusions 54 are placed on a plurality of silicon members 47 provided on the bottom of the inner case 33. By such a mounting form, rattling of the earthenware pot 50 is reduced and stabilized.

  In addition, between the shoulder member 34 and the cylindrical case 37, a plurality of, for example, three support pieces 48 made of an elastic material for positioning the clay pot 50 are provided on the outer periphery, and the side surface of the clay pot 50 is Direct contact with the cylindrical case 37 or the inner case 33 is prevented.

  Since the earthenware pot 50 has many irregularities on its surface, it is formed by applying glaze which is a glossy material on its outer surface and firing, but before the firing, the lower surface of the curved thin part 52 and the bottom thin part 53 The heating element 55 is provided in the form as shown in FIG.

  The heating element 55 is formed by, for example, applying a silver paste made of a mixture of silver particles of several tens of microns and a resin to a necessary portion by screen printing, and then firing the paste, and the heating element 55 includes a bottom coil. 40 and the bending portion coil 41 are opposed to each other, generate heat by Joule heat caused by eddy currents induced by the bottom coil 40 and the bending portion coil 41, and the earthenware pot 50 is heated by the heat.

  The heating element 55 may be one in which a metallic object such as copper foil or stainless steel net is embedded in advance in the earthenware pot 50 in advance.

(Ingredients of clay pot) An example of the ingredients of a clay pot is as follows. The substrate is a ceramic cordierite-based, for example, SiO ₂ is 46 to 51% _Al 2 _{O 3} is 35-40% MgO is 9-14%, those KNaO of 0-5% .

In general, “cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ )” is known as a crystalline ceramic having a small coefficient of thermal expansion and excellent thermal shock resistance.

  The glaze is composed mainly of, for example, lithia β-spodumene, and the heating element is composed mainly of silver paste composed of, for example, silver powder, flux, and medium.

(Manufacturing method of earthenware pot) An example of the manufacturing method of earthenware pot is as follows. First, sandy cordierite mineral is mixed with finely divided silicon carbide and water to make a clay, and the clay is put into a mold to form a clay pot.

  After molding, firing (unbaked) at about 1300 ° C., then applying glaze and firing at about 1300 ° C., then transferring the silver paste to the heated part, for example, the bottom and the curved part, removing air and removing about 900 again. Bake at ℃ to complete the clay pot.

By the way, the present inventor has the following effects (a) to (d) by containing a predetermined amount, for example, 20% by weight of silicon carbide in a clay pot and firing it. Was confirmed by experiments.

(A) A clay pot having high thermal conductivity (2.5 times higher thermal conductivity as will be described later) can be produced by containing a predetermined amount of silicon carbide in the clay pot. The reason seems to be due to the fact that, generally, clay pots have a low thermal conductivity of 1 W / mK or less, and silicon carbide has a very high thermal conductivity of 270 W / mK.

  That is, when silicon carbide is fired, it changes to silicon dioxide (thermal conductivity is 1.38 W / mK, which is considerably smaller than silicon carbide), but the oxidation start temperature is as high as 700 ° C. Only the surface is oxidized and changed to silicon dioxide, and the oxidized surface becomes a protective film to prevent further oxidation inside so that the high thermal conductivity of silicon carbide is sufficiently maintained. Seem.

(B) Finely divided silicon carbide is suitable as a component contained in a clay pot. The reason for this seems to be that silicon carbide generally has a high chemical stability at a decomposition temperature of about 2500 ° C., and there is little chemical change even during earthen pot firing (firing temperature of about 1300 ° C.). .

(C) Formability can be ensured even if silicon carbide is contained, and even if the earthenware pot is fired, cracks and cracks during firing due to differences in the coefficient of thermal expansion do not occur. The reason is that the coefficient of thermal expansion (4.5 × 10 ⁻⁶ / ° C.) of the components of clay pots, for example, cordierite-based minerals as the main component is generally the same as that of silicon carbide. Seems to be attributed.

(D) When silicon carbide is contained, the hardness is increased as compared with the conventional one. The reason seems to be that, in general, the hardness of hydrocarbons is 13 as the new Mohs hardness and the third highest on the earth.

  As described above, the present invention can contain silicon carbide in a conventional earthenware pot component, or can make a earthenware pot with high thermal conductivity by containing silicon carbide, or has moldability even if silicon carbide is contained. It has an operational effect or technical significance that it can be secured or that hardness can be increased by containing silicon carbide.

(Thermal conductivity measuring device) The thermal conductivity was measured by using a thermal conductivity measuring device (TPS 2500S, manufactured by Kyoto Electronics Industry Co., Ltd.), which is an open device of "Toyama Prefectural Industrial Technology Center, Life Engineering Laboratory". .

  The measurement method of the device is the “hot disk method”. When the sensor is sandwiched between measurement samples, and the sample holder is sandwiched and fixed, and the measurement is started by operating a personal computer, the measurement ends after several tens of seconds. This is how the result is displayed on the display.

As a result of the measurement by the above method, the current material clay pot has a thermal conductivity of 1.2 W / mK, whereas the clay conductivity containing silicon carbide (contains approximately 20% by weight) has a thermal conductivity of 3 0.0 W / mK. That is, the thermal conductivity increased 2.5 times. The density of the silicon carbide-containing earthenware pot is 2.1 g / cm ³ , which is 1.2 times that of the current earthenware pot.

(Experimental result) FIG. 2 is a temperature change diagram with respect to the time of the current clay pot, FIG. 3 is a temperature change diagram with respect to the time of the silicon carbide-containing clay pot, and both figures are shown by solid lines in the outer periphery of the bottom wall of the clay pot. It is the temperature change with respect to the time of a surface, and the figure shown with a broken line is the temperature change with respect to the time of the internal peripheral surface of a clay pot bottom wall part.

  In the experiment, using the electric rice cooker JPX-A100 manufactured by the present applicant, cooked white rice in a standard mode with extremely white rice, heating and reducing strength, and the inner wall surface of the bottom wall and the inner wall surface of the inner pot. The temperature of was measured.

  The results are shown in FIGS. That is, during the cooking process, the temperature difference between the outer peripheral surface and the inner peripheral surface of the bottom wall portion is about 50 ° C. as shown in FIG. 2 in the current clay pot, whereas as shown in FIG. 3 in the silicon carbide-containing clay pot. About 20 ° C. and about 30 ° C. lower. That is, the thermal conductivity of the silicon carbide-containing earthenware pot is improved.

  Further, in the steaming process, the temperature difference between the outer peripheral surface and the inner peripheral surface of the bottom wall portion is about 50 ° C. as shown in FIG. 2 in the current clay pot, whereas in the clay pot containing silicon carbide, as shown in FIG. The temperature was about 20 ° C. or lower and about 30 ° C. or lower. That is, similarly, the thermal conductivity of the silicon carbide-containing earthenware pot is improved.

  By the way, if the content of silicon carbide is more than 20% by weight, the moldability is deteriorated, and cracks are easily generated during firing. Therefore, 20% or less which does not contain zero by weight ratio is preferable.

  Moreover, content of silicon carbide should just be 20% or less by weight ratio, and the heat conductivity of an inner pot should just be 2.0 W / mK or more.

  The present invention is not limited to the configuration of the above-described embodiment, and can be appropriately changed in design without departing from the gist of the invention.

DESCRIPTION OF SYMBOLS 30 Electric rice cooker 31 Container main body 32 Outer case 33 Inner case 34 Shoulder member 35 Bottom member 36 Handle 37 Cylindrical case 38 Heat retention coil 39 Sensor opening 40 Bottom coil 41 Bending part coil 42 Coil stand 43 Leg part 44 Temperature sensor 45 Ceramic plate 46 Concave portion 47 Silicon member 48 Support piece 50 Earthen pan 51 Upper thick portion 51a Flange 52 Curved portion thin portion 53 Bottom thin portion 54 Annular projection 55 Heating element

Claims (2)

An inner pot made of ceramic, a heating element provided in the inner pot, an inner case for storing the inner pot, an outer case for storing and fixing the inner case, and provided between the inner case and the outer case In an electric rice cooker equipped with electromagnetic induction heating means for heating the heating element,
The inner pot is a ceramic member containing silicon carbide and mainly composed of cordierite mineral,
The content of silicon carbide in said pot, electric rice cookers, characterized in der Rukoto than 20% by weight. The electric rice cooker according to claim 1, wherein the inner pot has a thermal conductivity of 2.0 W / mK or more.

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