JP6467635B2 - Electromagnetic induction heating cooker - Google Patents

Description

The present invention relates to an electromagnetic induction heating cooker used for general household use and business use using ink having excellent infrared transparency and visible light permeability.

  The electromagnetic induction heating cooker that heats the cooking vessel placed on the top plate placed on the top surface of the electromagnetic induction heating cooker with a heating coil is widely recognized for its excellent features of safety, cleanliness, and high efficiency. It is popular.

  The electromagnetic induction heating cooker has a control circuit for connecting an inverter circuit to a heating coil formed in an annular shape and supplying a high-frequency current from the inverter circuit to the heating coil. The inverter circuit supplies a high-frequency current to the heating coil by the control circuit, thereby generating a high-frequency magnetic flux in the heating coil. By supplying this high-frequency magnetic flux to a pot or the like placed on the top plate in the vicinity of the heating coil, an eddy current is generated at the bottom of the cooking container, and the pot is based on the eddy current and the specific resistance of the pot or the like. The isolator is inductively heated. Here, there is one that includes means for detecting the temperature of the cooking container (load) and controls the output of the inverter circuit.

  In an electromagnetic induction heating cooker, a function of detecting the temperature of a cooking container and automatically adjusting the temperature to a desired temperature has been required. Particularly in oil cooking, a function of preventing oil ignition due to overheating is indispensable. Accurate and quick temperature detection means are indispensable.

  Conventionally, this type of electromagnetic induction heating cooker uses heat-resistant glass or ceramic as a top plate, detects the temperature of the lower part of the top plate, and controls the heating operation. This is because a temperature sensor such as a thermistor is provided at the bottom of the top plate so that the temperature of the cooking container is detected via the top plate and a signal is sent to the control circuit to control the heating operation so that it reaches a predetermined temperature. Since this is a temperature detection based on heat conduction through heat-resistant glass or ceramic that cannot be said to have high heat conductivity, this method is not necessarily an accurate and quick temperature detection means.

  For this reason, in recent years, an infrared sensor is provided to control the output of the inverter circuit in order to more accurately and quickly detect the temperature of the cooking vessel placed on the top plate (see, for example, Patent Document 1). ).

  3 and 4 show a conventional electromagnetic induction heating cooker described in Patent Document 1, and FIGS. 3 and 4 are diagrams of an electromagnetic induction heating cooker provided with an infrared sensor. 3 and 4, a top plate 2 made of heat-resistant glass is provided on the upper portion of a main body 1 that constitutes the outer shell of the electromagnetic induction heating cooker.

  A cooking container 3 that is an object to be heated is placed on the top plate 2, and an infrared sensor 4 is provided below the top plate 2 in order to detect the temperature of the cooking container 3. A light guide 5 for guiding the infrared rays to the infrared sensor 4 is provided.

  The infrared sensor 4 is attached toward the top plate 2. The light guide 5 guides infrared radiation from the cooking container 3 to the infrared sensor 4, and the infrared sensor 4 detects temperature.

Below the top plate 2, a control circuit 7 having an inverter circuit for supplying a high-frequency current to the heating coil 6 formed in an annular shape is provided. The control circuit 7 causes the inverter circuit to supply a high frequency current to the heating coil 6, thereby generating a high frequency magnetic flux in the heating coil 6. By supplying this high-frequency magnetic flux to the cooking container 3 placed on the top plate in the vicinity of the heating coil 6, an eddy current is generated at the bottom of the cooking container 3, and based on the eddy current and the specific resistance of the cooking container 3. The cooking container 3 is induction-heated.

  In addition, as shown in FIG. 5, in the electromagnetic induction heating cooker, the operation content, the cooking process, the heating state, etc. are displayed on the display unit 21 such as the operation unit by electronic light emission, and the operation is induced, There are attempts to make the heating status easy to understand or to provide a display with higher appearance.

  Conventionally, the display unit 21 such as the operation unit in the electromagnetic induction heating cooker has been generally disposed on the front surface of the main body 1, but recently, for reasons such as ease of display and ease of operation. Things that place emphasis on the placement of the top surface on the top plate 2 are becoming mainstream.

  As an example, there is one in which the light emitting display unit 22 provided in the vicinity of the outer periphery of the heating coil is turned on when induction heating is started.

  The light emitting display part of the conventional electromagnetic induction heating cooker has, for example, a structure as shown in FIG. 5 (only the top plate is shown), and transmits the light provided on the main body case forming the outer shell and the upper surface of the case. A light emitting component is provided in the main body of the electromagnetic induction heating cooker provided with a top plate 2 formed of a material such as heat-resistant glass and a heating coil for induction heating of the cooking vessel 3 below the top plate 2. .

JP 2005-038660 A

  As described above, in the electromagnetic induction heating cooker, the temperature detection of the cooking container 3 by the infrared sensor 4 is performed accurately and quickly, and the operability and design of the top plate 2 are improved by optical display. Is required.

  However, when trying to realize these required characteristics at the same time, it sometimes includes conflicting elements.

  Usually, if the detection of the infrared sensor 4 is to be performed well, the top plate 2 needs to transmit infrared rays well. Therefore, the top plate 2 is made of heat-resistant glass that is colorless or transparent and is almost colorless and transparent. It is desirable that the sensor window immediately above the arrangement of the infrared sensor 4 is not subjected to any processing for generating color.

  If the top plate 2 is not subjected to any color treatment, it is possible to obtain good infrared transmission, but the internal components of the electromagnetic induction heating cooker are exposed through colorless and transparent glass, resulting in an adverse appearance. Therefore, it is usually printed with heat-resistant inks of various colors except for the portion directly above the infrared sensor arrangement, which gives a design.

However, in the upper part of the infrared sensor arrangement, when processing the color to the top plate, make sure that the ink has sufficient infrared transparency, and not to expose the internal components from the outside through the sensor window. It is necessary to have high visible light shielding properties, that is, it is necessary to simultaneously realize high infrared transmittance and low visible light transmittance for color processing of the sensor window.

  Further, in recent years, a display unit such as an operation unit is configured to transmit information such as heating power and operation contents to a user of an electromagnetic induction heating cooker with a light emitting diode. These indications are not necessary when the electromagnetic induction heating cooker is not operated, and it is desirable that the display content is clearly displayed only by light emitted from the light emitting diode only during use. It is important in terms of operability and design that the components of the light emitting peripheral part are not visible from the outside, and that visible light emitted from the light emitting diode is sufficiently transmitted.

  As described above, in the top plate, the required optical characteristics differ depending on the part, in particular, the infrared and visible light transmittance is the detection performance of the infrared sensor, the display properties of the display unit such as the operation unit, Development of technology to control infrared and visible light to the desired transmittance according to the site is a major issue because it has a great influence on designability. Furthermore, it is difficult to satisfy the above issues with a single surface treatment. It was a big issue.

SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide an electromagnetic induction heating cooker using ink that realizes infrared transparency and visible light transparency at the same time.

  In order to solve the above-mentioned conventional problems, the present invention invents an ink for adjusting optical characteristics for controlling the transmittance of infrared light and visible light for the top plate of an electromagnetic induction heating cooker, and treats this on the top plate. This is an electromagnetic induction heating cooker.

  The ink used for the top plate of the induction heating cooker of the present invention is an ink for adjusting optical properties, and the ink contains gold as an organic compound or colloid, and iron, bismuth, and titanium contain organic compounds or colloids. In addition, a silicon compound is contained, these substances are added to an organic solvent, and a thickening component is further added.

  The ink according to this configuration is printed on a top plate, baked at 600 to 850 ° C., and after removing organic components, a thin film forming portion having a thickness of 0.05 to 5 μm is provided, and in the thin film, gold, iron, bismuth, It contains titanium and silicon, and exhibits colors such as black, green, and red depending on the film thickness, component amount, and firing conditions, and can control the transmittance of infrared rays and visible light.

  As described above, the top plate on which the ink of the present invention is printed and the thin film forming portion is provided can control infrared rays and visible light to a desired transmittance. Because it transmits well, accurate and quick temperature detection is possible with an infrared sensor, and good cooking performance is obtained, and parts placed in the electromagnetic induction heating cooker body to moderately suppress visible light transmission are sensors There is no exposure through the window and the effect of ensuring good design is achieved.

  Further, when a thin film is formed by printing the ink of the present invention on a top plate in a display unit (including a light emitting display unit of a light emitting diode) such as an operation unit, visible light emitted from the light emitting diode is emitted from the top plate when the light emitting diode emits light. Since the display can be recognized by the user through transmission, good operability is obtained, and the thin film forming part suppresses the transmission of visible light, so that the parts inside the main body are exposed from the outside There is no effect and high design properties are secured.

Cross-sectional schematic diagram of relevant parts showing an electromagnetic induction heating cooker according to Embodiment 1 of the present invention. Cross-sectional schematic diagram of relevant parts showing an electromagnetic induction heating cooker according to Embodiment 1 of the present invention. Sectional view of a conventional induction heating cooker equipped with an infrared sensor An enlarged schematic cross-sectional view of the vicinity of an infrared sensor in a conventional electromagnetic induction heating cooker Top view of an electromagnetic induction heating cooker equipped with a conventional infrared sensor

  In the present invention, an ink for adjusting optical characteristics for controlling the transmittance of infrared rays and visible light is invented for the top plate of the electromagnetic induction heating cooker, and this is processed into the top plate.

  In the first invention, gold is contained as an organic compound or colloid, and iron, bismuth, titanium is contained as an organic compound or colloid, and further contains a silicon compound, and these substances are added to an organic solvent. Furthermore, the ink is adjusted by adding a thickening component.

  Since the ink of this configuration is composed of an inorganic substance, it can be fired at a high temperature.Solvents and thickening components are lost during firing, and the inorganic substance mainly remains after firing. Since it is formed, it has durability suitable for a member exposed to a high temperature such as a top plate of an electromagnetic induction heating cooker.

  In addition, this ink can form a thin film mainly composed of an inorganic substance having a thickness of 0.05 to 5 μm, and this thin film maintains the stress balance of a heat-resistant glass having a normal thickness of 3 to 6 mm constituting the top plate. And high impact strength can be maintained.

  In addition, the thin film contains gold, iron, bismuth, titanium, and silicon. Depending on the film thickness, component amount, component ratio, and firing conditions, it exhibits colors such as black, green, and red, and transmits infrared and visible light. Gender can be controlled.

  In particular, the second invention is an ink that uses, as the silicon compound of the first invention, any one of colloidal silica, aerosil, which is a form of silicon oxide, or a silane compound such as silicon ethylhexanoate or tetraethoxysilane. It is.

  The above-mentioned silicon-containing substance plays an important role particularly for stabilizing the infrared transmission at a high level and stabilizing the color tone, and by adding an appropriate amount to the ink of the present invention, the optical characteristics can be stabilized.

  Specifically, it is desirable to add 2.6 to 14 wt% as the amount of silicon in the fired thin film. However, if it is less than 2.6 wt%, the infrared transmission performance becomes unstable, and if it exceeds 14 wt%, the color tone is changed. There is a tendency to change greatly and to transmit visible light too much, and there is a tendency that the concentration in the coating film is too high and problems such as cracking and peeling of the coating film occur.

  In the third invention, in particular, the ink of the first or second invention is printed on at least a part of transparent crystallized glass or borosilicate glass by a method such as screen printing, and then baked at 600 to 850 ° C. , An electromagnetic induction heating cooker using a top plate provided with a colored and opaque thin film forming portion containing iron, bismuth, silicon, and titanium.

Since the thin film forming part is made of an inorganic substance, the heat resistance is extremely high.
Since it is a thin film having a thickness of 5 μm, the stress balance of the heat-resistant glass constituting the top plate can be maintained, and high impact strength can be maintained.

  In the fourth invention, in particular, the thin film forming portion of the third invention transmits infrared light having a wavelength of 910 to 1550 nm by 70% or more, and the transmittance in the visible light region of wavelength 380 to 750 nm is 5% or more and 30%. It is the following electromagnetic induction heating cooker.

  Thin film forming parts that are fired under appropriate conditions and have an appropriate film thickness contain gold, iron, bismuth, titanium, and silicon in the film, so that optical characteristics corresponding to the distribution of these elements can be obtained. .

  The thin film forming section can transmit infrared light having a wavelength of 910 to 1550 nm by 70% or more, thereby efficiently transmitting infrared light emitted from the cooking container placed on the top plate, and directly below the top plate. Infrared sensor temperature detection can be performed accurately and quickly.

  Further, the thin film forming portion is colored and opaque because the transmittance in the visible light region with a wavelength of 380 to 750 nm is not less than 5% and not more than 30%, and components in the main body cannot be seen from the outside through the thin film forming portion. However, since the visible light has a certain level of transparency, visible light emitted from the light emitting diodes arranged in the main body can be confirmed from the outside, and thus the display by the light emitting diodes can be seen well.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
The ink of the present embodiment is for forming a thin film forming portion for adjusting the optical characteristics of the top plate of the electromagnetic induction heating cooker.

  In the ink preparation example of the present embodiment, 10 parts by weight of 20% gold-containing gold resinate, 6% iron-containing tris (2-ethylhexanoic acid) iron (III) / mineral spirit liquid 40 parts by weight, and 25% bismuth containing Bismuth 2-ethylhexanoate (III) 10 parts by weight of 2-ethylhexanoic acid solution, 4 parts by weight of 40% silica-containing toluene-dispersed colloidal silica, 3 parts by weight of 7.7% titanium-containing titanium 2-ethylhexanate These were added to 16.5 parts by weight of a 5: 1 mixed solvent of 3-methoxy-3-methyl-1-butanol and benzyl alcohol, and further, 16.5 parts by weight of rosin was added to make a total amount of 100 parts by weight of ink. The printability was improved by adding trace amounts of auxiliary agents such as antifoaming agents and leveling agents as necessary.

  The ink with the components as described above was printed on a transparent crystallized glass having a thickness of 4 mm by screen printing, and then a thin film forming part was provided in the printing part by baking at 800 ° C. for 20 minutes. Almost all organic components were burned out, and the thin film forming part contained an inorganic substance composed of gold, iron, bismuth, silicon, and titanium, and was a film having a thickness of about 1 μm that had a black-green appearance.

  The ink raw material component may contain chlorine or sulfur as impurities, but there is no particular problem.

In consideration of the elements of gold (Au), iron (Fe), bismuth (Bi), silicon (Si) and titanium (Ti) in the ink components, the weight ratio is 25.4: 30.5.
: 31.7: 9.5: 2.9 (100 in total), as will be described later, it is possible to impart desired optical properties to the glass by controlling the element ratio and film thickness.

  In this embodiment, gold uses gold resinate as a raw material component, but there is no problem even if it is a gold colloid, and other organic compounds such as resin acid metal salts and colloids are used as the raw material component of iron, bismuth and titanium. It is also possible. Here, in the present embodiment, gold uses gold resinate as a raw material component, but gold colloid can also be implemented by replacing gold resinate with gold colloid in the above-described ink preparation examples.

  In addition to the above-mentioned colloidal silica, any of the above-mentioned colloidal silica, aerosil, or a silane compound such as silicon ethylhexanoate or tetraethoxysilane can be used as the silicon raw material component. It is an indispensable element for the stabilization of characteristics, and it is important to select materials and determine the amount of addition in consideration of compatibility with other raw material components.

  When silicon oxide such as aerosil is used in addition to colloidal silica as a raw material component of silicon, the ink printability is improved and stable optical characteristics are obtained particularly by using particles having an average particle size of 50 nm or less.

  Furthermore, in this embodiment, rosin is added as a thickening component to the ink to improve the appropriate viscosity and dispersibility of the component. In addition to rosin, modified rosin, cellulosic thickener, castor oil In addition, synthetic resins such as acrylic can be used, and the solvent component for dissolution can be changed according to the solubility of the resin component.

  Here, the optical characteristics of the thin film forming portion formed by printing and baking the ink of the present embodiment on transparent crystallized glass were measured. For infrared transmittance, the spectral transmittance at a wavelength of 910 to 1550 nm was measured. As for the visible light transmittance, the spectral transmittance of 380 to 750 nm was measured, and as a result, the infrared ray had a transmittance of 83% and the visible light had a transmittance of 26%.

  If the infrared transmittance is too low, there is a high possibility that the temperature detection of the infrared sensor will not be performed correctly. Therefore, a transmittance of 70% or more is necessary. On the other hand, if the visible light transmittance is 30% or more, visible light is easily transmitted. Although it is easy to transmit, the concealment property is low, so the main body storage parts directly under the glass can be seen through, and the appearance is impaired, so it is necessary to be within 30%, but it is good by appropriately transmitting the light of the light emitting diode In order to obtain a good display state, a visible light transmittance of at least 5% is required.

  As a result of further examination of the optical characteristics, the thin film forming portion of the top plate has an infrared transmittance of 70% or more at a wavelength of 910 to 1550 nm, and a transmittance of visible light of a wavelength of 380 to 750 nm is 5% or more and 30%. In order to realize the following, the ink should be adjusted by precisely designing the ratio of each element of gold (Au), iron (Fe), bismuth (Bi), silicon (Si), and titanium (Ti). Turned out to be important.

  Further, the total addition amount as elements of gold (Au), iron (Fe), bismuth (Bi), silicon (Si), and titanium (Ti) in the ink is adjusted to be 6 to 10 g in 100 g ink. Then, the ink suitable for printing can be adjusted, and if it is less than 6 g, the density is too thin and the color tone does not come out, and if it exceeds 10 g, the density is too high and cracks may occur in the thin film forming portion.

The optical characteristics when the addition amount of each element is varied using the same raw materials as in this embodiment are shown in (Table 1). The element composition ratio in (Table 1) is gold (Au), iron (Fe ), Bismuth (Bi), silicon (Si), and titanium (Ti).

  In addition, the solvent and the resin component in the ink were 25 ± 10 parts by weight in total, the solvent / resin component weight ratio was 50:50, and the solvent was a 3-methoxy-3-methyl-1-butanol / benzyl alcohol weight ratio of 5 : 1 mixed solvent.

  The determination in (Table 1) is a case where the transmittance of infrared light with a wavelength of 910 to 1550 nm is 70% or more and the transmittance of visible light with a wavelength of 380 to 750 nm is 5% or more and 30% or less. did.

  From the above results, since Au has a great influence on the visible light transmittance, it is desirable that the abundance ratio is 23.3 wt% or more, but even if it is excessive, the optical characteristics are adversely affected, so that it is within 39.1%. It is desirable.

  Fe is an important component for controlling the transmission of light together with Au, and the ratio of Au / Fe is preferably about 0.7 to 1.6, but Fe has selectivity for infrared transmission, and the larger one is preferable. However, if it is excessive, the color tone will become reddish and the transmission of visible light will increase. For this reason, Fe can adjust color tone moderately by mixing and using Au, and can aim at optimization of visible light and infrared rays transmission.

Bi is an important component for film formation, and if it is less than 20 wt%, the film formability deteriorates. Therefore, it is desirable to contain at least 20 wt%. Since there is a possibility of adversely affecting the characteristics, it is desirable to make it within 35.6%.

  Further, if Ti is too much or too little, both infrared transmittance and visible light transmittance are adversely affected, and 1.2 to 4.5 wt% is an appropriate value.

  In the present embodiment, it has been found that Si is an important trace additive element particularly for stabilizing the optical characteristics, but in keeping with the abundance ratio of Au, Fe, Bi, Ti described above, By adding Si of 2.6 to 14.0 wt%, infrared transmittance can be improved and stabilized, and a desired visible light transmittance can be obtained.

  If Si is less than 2.6 wt%, the infrared transmittance is less than 70%, and the desired detection performance cannot be obtained. On the other hand, if it exceeds 14.0 wt%, the visible light transmittance is increased and the desired concealability cannot be obtained. Therefore, it is necessary to set the amount of Si to 2.6 to 14.0 wt%.

  Next, the form which applied the ink obtained by this Embodiment to the electromagnetic induction heating cooking appliance is demonstrated using FIG. 1 and FIG. 2 below. FIG. 1 is a schematic cross-sectional view of an essential part showing an electromagnetic induction heating cooker in Embodiment 1 of the present invention, and FIG. 2 is a schematic cross-sectional view of an essential part showing an electromagnetic induction heating cooker in Embodiment 1 of the present invention. is there.

  Here, No. of (Table 1). The transparent crystallized glass for a top plate having a thickness of 4 mm is used for the ink according to the present embodiment, in which the infrared transmittance at a wavelength of 910 to 1550 nm is 83% and the visible light transmittance at 380 to 750 nm is 26%. On the lower surface, after screen printing on the sensor window 24 and the display unit 21 such as the operation unit, the top plate 2 baked at 800 ° C. for 20 minutes to form the black-green thin film forming unit 25 is used as the main body 1 of the electromagnetic induction heating cooker. The performance was confirmed by assembling it.

  1 shows a schematic cross-sectional view of light transmission particularly in the vicinity of the sensor window 24, and FIG. 2 shows a schematic cross-sectional view of light transmission particularly in the vicinity of the display unit 21. Except for the sensor window 24 and the display unit 21 such as the operation unit (in other words, other than the thin film forming unit 25), the crystallized glass is colorless and transparent on the lower surface or upper surface of the crystallized glass that is the base material of the top plate 2. The normal printing unit 30 is provided so that there is no part.

  Infrared sensor 4 is arranged below thin film formation part 25 in sensor window part 24 shown in FIG. A light emitting diode 26 is disposed below the thin film forming portion 25 in the display portion 21 such as the operation portion shown in FIG.

  As a result, it was confirmed that the infrared sensor 4 in the main body 1 senses the temperature of the cooking container 3 with extremely high sensitivity, and the visible light transmission is also suppressed in the display unit 21 such as the sensor window 24 and the operation unit. Since it is controlled, it is highly concealed and the main body housing parts directly below the crystallized glass are not seen through. The display unit 21 appropriately transmits light from the light emitting diodes 26 arranged inside the main body 1. A good display state can be obtained when necessary, realizing high operability and aesthetics.

  As described above, in the present embodiment, it is possible to obtain the ink for adjusting the optical characteristics for controlling the transmittance of infrared light and visible light for the top plate of the electromagnetic induction heating cooker, and the obtained ink is used as the top plate. Processed into plates.

In the present embodiment, gold is contained as an organic compound or colloid, and iron, bismuth and titanium are contained as an organic compound or colloid, and further contain a silicon compound, and these substances are added to an organic solvent, Furthermore, the ink is adjusted by adding a thickening component.

  Since the ink of this configuration is composed of an inorganic substance, it can be fired at a high temperature.Solvents and thickening components are lost during firing, and the inorganic substance mainly remains after firing. Since it is formed, it has durability suitable for a member exposed to a high temperature such as a top plate of an electromagnetic induction heating cooker.

  In addition, this ink can form a thin film mainly composed of an inorganic substance having a thickness of 0.05 to 5 μm, and this thin film maintains the stress balance of a heat-resistant glass having a normal thickness of 3 to 6 mm constituting the top plate. And high impact strength can be maintained.

  In addition, the thin film contains gold, iron, bismuth, titanium, and silicon. Depending on the film thickness, component amount, component ratio, and firing conditions, it exhibits colors such as black, green, and red, and transmits infrared and visible light. Gender can be controlled.

  In the above-described embodiment, the configuration in which the ink is printed on the crystallized glass for the top plate has been described. However, borosilicate glass may be used instead of the crystallized glass.

  As described above, since the ink and the electromagnetic induction heating cooker according to the present invention can control the infrared transparency and the visible light transmission, not only the electromagnetic induction heating cooker but also a temperature detection means, The present invention can be applied to various devices that emit light by using a light emitting means.

DESCRIPTION OF SYMBOLS 1 Main body 2 Top plate 3 Cooking container 4 Infrared sensor 21 Display part 24 Sensor window part 25 Thin film formation part 26 Light emitting diode

Claims (1)

Gold is contained as an organic compound or colloid, and iron, bismuth, titanium is contained as an organic compound or colloid, and further contains a silicon compound. These substances are added to an organic solvent, and a thickening component is further added. A top plate provided with a colored opaque thin film forming portion containing gold, iron, bismuth, silicon, and titanium, which is printed and baked on at least a part of transparent crystallized glass or borosilicate glass after adding and adjusting the ink. An electromagnetic induction heating cooker used,
The thin film forming portion transmits infrared light having a wavelength of 910 to 1550 nm by 70% or more, and transparency in a visible light region having a wavelength of 380 to 750 nm is 5% or more and 30% or less.
With
The abundance ratio of the gold, the bismuth and the titanium is
The gold is 23.3 wt% or more and 39.1% or less,
The bismuth is 20 wt% or more and 35.6% or less,
The titanium is 1.2 wt% or more and 4.5% or less,
Is an electromagnetic induction heating cooker .

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