JPH054796B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a sheet heating element for a microwave oven that generates heat by irradiation with microwaves emitted from a magnetron of a microwave oven and browns food to be cooked. It is.

<Prior art> Generally, a microwave oven is a cooking device that cooks food by guiding microwaves emitted from a magnetron into the oven chamber and irradiating the food to be cooked, thereby generating heat in the food itself. . Therefore, since the food to be cooked is not browned, for example, fish dishes have the disadvantage that the lack of browned food does not stimulate the appetite. Therefore, there is a microwave oven that has a built-in sheathed heater so that the heat generated by the heater is directly applied to the food to be cooked in parallel with the heating of the food by microwaves.

However, since two types of heating means are used as described above, a magnetron and a heater are required as heat sources, which increases costs, complicates the structure, and increases the size of the entire device. Recently, with the aim of improving these problems, the heating element that generates heat when irradiated with microwaves can be dielectrically heated by microwaves alone using a plate with a double structure made by polymerizing an insulating base material as a heating element. A proposal has been made by the same applicant to provide both heating effects by thermal radiation. (Jitsukai 61-
149372) <Problems to be solved by the invention> However, this proposal does not specify a specific material for the exothermic substance, and attempts to put it into practical use using commonly known metal oxide ferrites, silicon carbide, etc. In this case, the following problems occurred.

1 The heat generation efficiency is poor and the effect of browning is not good.

2 There is a marked tendency to generate heat locally, and the heat generating area is insufficient.

3. Extreme heat generation tendency is significant, and the heat generating layer may crack or deteriorate.

<Purpose of the Invention> The present invention was devised in view of the above-mentioned problems, and aims to improve heat generation efficiency, reduce local heat generation tendency, and expand heat generation area, thereby creating a practical planar heat generation system for microwave ovens. The purpose is to provide the body.

<Means for Solving the Problems> A heating element is made by firing a silicon carbide ceramic into a plate shape, containing 5 to 30% silicon nitride as a sintering binder to create pores.

<Function> Since it contains 5 to 30% silicon nitride as a sintering binder, the binding force between the silicon carbide particles is strong, and the binder itself has excellent thermal conductivity, heat resistance, and thermal shock resistance. There is. Also, since it has pores inside, it absorbs microwaves well, generates heat over a wide area, and has improved thermal shock resistance.
As described above, the heat generation efficiency is high, and the tendency to generate heat locally can be reduced, and the heat resistance and thermal shock resistance of the heating element itself are improved, and cracking and deterioration do not occur even after long-term use.

<Example> An example of the present invention will be described below based on the drawings.

Figure 1 shows a heat insulating material 1 made of a material that easily transmits microwaves emitted from the magnetron of a microwave oven and has heat insulating properties, such as ceramic fiberboard or a ceramic molded product with high porosity.
1 is a sectional view of a planar heater 1 for a microwave oven in which a heating element 11 of the present invention is embedded with only one surface (lower surface) exposed.

In the heating element 11, as shown in FIG. 2, silicon carbide particles 11a are bound together by a binder 11b made of silicon nitride. Moreover, pores 11c exist between each particle.

Generally, silicon carbide has a high melting point and is difficult to sinter and shape, so silicate-based or oxide-based ceramic raw materials are usually used as the sintering binder, but in the case of molded products using these binders, the binder Because it has poor heat resistance, thermal shock resistance, and thermal conductivity, when it is irradiated with microwaves and generates heat, it tends to generate heat locally, resulting in poor heat generation efficiency, as well as cracking and thermal deterioration due to thermal distortion of the heat generating part. Ru.

These problems have been solved in the heating element 11 of the present invention because it contains 5 to 30% silicon nitride as a sintering binder and has appropriate pores inside. If the content of silicon nitride as a sintering binder is less than the above range, the bonding strength will be insufficient, and if it is more than this, the content of silicon carbide will decrease and microwave absorption will deteriorate.

Next, an outline of a standard manufacturing method of the heating element of the present invention will be explained.

The raw material is 80 parts of silicon carbide raw material (coarse grain, medium grain, fine grain), 20 parts of fine powder silicon nitride raw material, and a small amount of bentonate, and about 1 part of PUA and an appropriate amount of Add water and mix the powder using a ball mill. This is dehydrated and granulated using a spray dryer, put into a press mold of a predetermined size, and then press-molded into a plate shape. After that, the molded product is completely dried in a drying oven and then heated to 1450℃ in a firing oven.
Sintering is carried out under the conditions of holding at ℃ for 2 hours.

FIG.
2 is a front sectional view of a microwave oven employing the heater 1 shown in the figure, in which a magnetron 2 serving as a heat source for microwave heating and an oven chamber 3 are connected by a waveguide 4. FIG. A microwave radiation port 5 is provided at the tip of the waveguide 4, and the heater 1 is placed along the top of the oven 3 in the middle thereof. Moreover, the microwave radiation port 5 and the heater 1
A microwave reflection damper 6 is rotatably disposed in the middle of the oven chamber 3. When the damper 6 is moved downward, it is blocked and the microwaves are guided to the radiation opening 5, causing the inside of the oven chamber 3 to be blocked. Microwave M is radiated to perform cooking using normal microwave heating. Also, when the damper 6 is moved upward,
The microwave is guided to the heater 1, and the heater 1 absorbs the microwave, becomes red hot through thermal conversion, and radiates infrared rays (heat rays) R into the oven chamber 3 to perform infrared radiant heating.

Figure 4 shows the microwave irradiation time when heating element A of the present invention of the same size and heating element B made of a silicon carbide ceramic plate using an oxide binder are placed in a microwave oven with an output of 500 W. It is a relationship diagram showing the surface temperature of the heating element, and it is clear at a glance that the heating efficiency of the heating element A of the present invention is high.

<Effects> As described above, the heating element of the present invention has high heat generation efficiency due to microwave absorption in microwave ovens, and has a reduced tendency to generate heat locally, so that the heat generating area can be expanded and the heating element can be used as a surface for microwave ovens. It is an optimal heating element as a shaped heating element.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a heater incorporating the heating element of the present invention, FIG. 2 is an enlarged sectional view of the heating element of the present invention,
FIG. 3 is a sectional view of a microwave oven employing the heating element of the present invention, and FIG. 4 is a relationship diagram showing the heating element surface temperature with respect to the microwave irradiation time. Code, 11: heating element, 11a: silicon carbide particles,
11b: silicon nitride, 11c: pores.

Claims (1)

[Scope of Claims] 1. A heating element that generates heat by microwave irradiation in a microwave oven, which contains 5 to 30% silicon nitride as a sintering binder and has pores to form a silicon carbide ceramic into a plate shape. Baked sheet heating element for microwave ovens.