JP2551844B2 - Hot plate for heating element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hot plate for a heating body such as an electric heater, which has excellent durability and moldability at high temperatures.

[Conventional technology and problems]

A hot plate for an electric heater, which has been conventionally generally used for cooking or kitchen, is obtained by kneading a naturally-occurring ceramic material powder with water, molding and firing it. This product is widely used because it uses a naturally occurring clay-based material and is easy to mold and inexpensive, but it is not satisfactory in terms of thermal efficiency. In addition, a heater called smooth stop has been developed in which the upper surface of the device is covered with ceramic glass. This product has a smooth surface and is easy to clean, and is preferred by consumers as a clean instrument. For the hot plate of the heater, a molded product composed of a composition mainly composed of ultrafine silica powder having a low thermal conductivity and a low specific heat is often used in order to improve the thermal efficiency and the responsiveness to increase / decrease of heating. ing. However, although this hot plate has good thermal efficiency, it has a drawback of being poor in heat resistance. When it is used at a temperature of about 900 ° C. or higher for a long time, there is a problem that a portion in contact with a heating source is cracked. Further, the ultrafine silica powder has poor moldability, and particularly in the case of a hot plate having a high peripheral edge formed, the peripheral edge is easily damaged when taken out from the press-molding die.

For this reason, there is a demand for a hot plate having good thermal efficiency, excellent heat resistance, and good moldability. For example, the temperature of a nichrome coil or a halogen lamp, which is a heating source, often exceeds 1000 ° C. Therefore, a hot plate that can withstand use at a high temperature of 1000 ° C. is required.

[Knowledge of problem solving]

In the present invention, by using a molding material mainly composed of ultrafine particle alumina, it is possible to achieve excellent heat resistance and moldability which cannot be obtained by a hot plate composed of a conventional molding material mainly composed of ultrafine particle silica. Was found.

[Structure of Invention]

According to the present invention, there is provided a hot plate for a heating body, which is made of a molding material in which an infrared ray impermeable agent and a fibrous reinforcing material are mixed with ultrafine particulate alumina powder.

Further, in the present invention, the molding material mainly composed of ultrafine particle alumina powder may contain ultrafine particle silica powder, and further, ultrafine particle alumina powder and ultrafine particle silica powder are laminated in layers. However, according to the present invention, a hot plate for a heating element is provided, which is made of these mixed molding materials or laminated molding materials.

The ultrafine particulate alumina used in the present invention is called fumed alumina, which is produced as fumed alumina by burning a volatile or sublimable aluminum compound in a flame, and a typical example is West Germany Degussa. "Aluminum Oxide C" manufactured by the company is known and has an average primary particle diameter of about 0.02 micron and a specific surface area of 100 m ² / g.

The ultrafine-particulate alumina is suitable as a heat insulating material in a high temperature region, particularly in a high temperature region because it has heat resistance of 900 ° C. or higher, has very little heat shrinkage, and has a small thermal conductivity. In the present invention, an infrared ray opaque agent is added to the ultrafine particulate alumina powder in order to further improve the heat insulating property of the hot plate in a high temperature range.

As the infrared ray opaque agent, titanium oxide, iron oxide, zirconium oxide, carbon black and other heat-resistant substances having a large infrared refractive index, reflectance or scattering effect are used. Among them, titanium oxide is preferable because it has a large effect, is easily available, and is inexpensive. The infrared opaque agent has an average particle size of several microns, for example, 0.5 to 25 microns, and is 10 to 70% by weight based on the total weight of the ultrafine particulate alumina composition.
By adding (volume 0.2 to 8%), the thermal conductivity of the molded body can be lowered. The infrared ray impermeable agent scatters infrared rays (radiant heat from the heating source) inside the heat insulating material and prevents the radiant heat from passing through the heat insulating material, so that the heat insulating effect of the molded body is significantly improved.

The above-mentioned ultrafine-particle alumina powder has better moldability than silica powder, but in the present invention, a fibrous reinforcing material is added to further enhance the moldability and strength. The fibrous reinforcing material used in the present invention is asbestos, rock wool, and various other heat-resistant fibrous substances, and particularly bulk ceramic fibers have excellent reinforcing properties,
It is also suitable in terms of heat resistance and economy. The content is 3 to 30% by weight, usually 5 to 10% by weight based on the total weight of the composition. Alumina fibers have better heat resistance and slightly lower thermal conductivity than ceramic fibers, but they are extremely expensive and poor in economic efficiency.

The hot plate of the present invention is formed mainly by the above-mentioned ultrafine particle alumina powder, but a material obtained by further mixing ultrafine particle silica may be used as this forming material. The ultrafine silica is called fumed silica, which is produced as fumed silica by burning a volatile silicon compound in a flame, and as a typical one, for example, manufactured by Nippon Aerosil Co., Ltd. Aerosil "is known, and the average diameter of its primary particles is about 0.01 to 0.02 μm, and the specific surface area is 100 to 400 m ² / g.
Is. The ultrafine particle silica powder has excellent heat insulating properties, and the heat insulating property of the hot plate is improved by mixing with the ultrafine particle alumina powder. The mixing amount of the ultrafine silica powder is preferably 75% by weight or less, particularly preferably 50% by weight or less. If the mixing amount of the silica powder exceeds 80% by weight, the heat shrinkage of the molded body increases, which is not preferable.

The hot plate of the present invention also includes a hot plate having a structure in which the molding material mainly containing the ultrafine particle alumina powder and the molding material mainly containing the ultrafine particle silica are laminated in two layers. In this case, an ultrafine alumina powder layer having excellent heat resistance is provided on the side in contact with the heater. A hot plate having a double structure of an ultrafine particle alumina layer and an ultrafine particle silica layer has slightly better heat resistance and moldability than a hot plate made of a material in which these double fine powders are uniformly mixed. Are better.

The hot plate for a heating element of the present invention is manufactured by press molding using the above molding material.

At the time of molding, place a metal dish with a high edge around the bottom of the mold, put the molding material in this and press-mold, and take out the molded product together with the plate, it is easy to remove from the mold and subsequent processing It's easy. Since the thickness of the molded product has a so-called dimensional return, it is necessary to take into consideration the return amount at the time of pressure molding. In addition, when the metal dish is not used, a dimensional return occurs in the radial direction of the molded body.

First example of molded products obtained by press molding various molding materials
~ Fig. 4 shows. FIG. 1 is a cross-sectional view of a heating plate for a heater such as a nichrome coil using a molding material of ultrafine particle alumina, and FIG. 2 is a heating of a nichrome coil of the same shape using a molding material of ultrafine particle silica. Sectional drawing of the heating plate for heaters is shown, respectively. When fine powder of silica is used, the moldability is poor. Therefore, unless the peripheral wall portion A'is made low and the inner peripheral surface B'is made slant and the heater groove C'is not set shallow, it is removed from the mold. When molding, the peripheral wall portion A'is damaged. Therefore,
In order to manufacture a molded body having a high peripheral wall portion using silica powder, conventionally, a molded body having a low peripheral edge portion A'is manufactured in advance, and then the lacking portion D'is separately molded and joined with another material. However, in the present invention, since a material mainly composed of ultrafine particulate alumina is used, the strength of the molded body is large, the peripheral wall portion A can be preliminarily formed high as shown in FIG. 1, and the peripheral wall portion A to the hot plate surface extends. The inner peripheral surface B can also have a steep angle, and the groove C for accommodating a heating body such as a heater can be deeply formed.

FIG. 3 (a) is a plan view of a hot plate E for halogen lamps, FIG. 3 (b) is a cross-sectional view of a hot plate according to the present invention mainly containing ultrafine alumina powder, and FIG. FIG. 3 is a cross-sectional view of a hot plate of the same shape mainly containing ultrafine silica powder. The hot plate according to the present invention in FIG. 3 (b) can be molded as an integrally molded product. However, since the conventional hot plate in FIG. 4 is mainly composed of fine particle silica powder, the moldability is poor and when the peripheral edge is high. In many cases, the whole body cannot be integrally molded unless the inclination angle of the inner peripheral surface is set to a considerably large value, and therefore, the peripheral part G separately molded must be joined after the lower base part F is previously molded.

Next, in order to produce a molded product having a two-layer structure, first, ultrafine silica powder is charged in the bottom of the mold, and ultrafine alumina powder is filled on the upper side of the mold and pressure molding is performed. The amount of ultrafine silica powder is 3 parts by weight or less, preferably 1 part by weight or less, based on the amount of ultrafine alumina powder.

〔The invention's effect〕

The heating plate for a heating element produced by using a molding material mainly composed of ultrafine particulate alumina powder according to the present invention withstands use at a high temperature of 1000 ° C. or higher, and in that case the thermal contraction is small and the thermal conductivity is extremely high. Low (for example, 0.03 to 0.04 Kcal / m · hr · ° C at an average temperature of 500 ° C). Also, it has good mold releasability from the mold after molding, dimensional stability, and is extremely superior in both heat resistance and moldability to a hot plate manufactured using a conventional molding material composed of ultrafine particulate silica powder. The advantages in use and use are significant.

[Examples and Comparative Examples]

Examples 1 to 6, Comparative Examples, 2 Using the raw materials shown in Table 1, the raw materials were sealed in a propeller-type high-speed stirrer with a capacity of 50 and mixed for 10 minutes to prepare molding materials. Next, a test mold 10 having a quadrilateral shape as shown in FIG. 5 in which the width of the outer peripheral edge, the slope of the inner wall, and the shape of the groove are different for each side is mounted on a press molding machine, and the mold is subjected to the above. Each raw material was charged and pressure-molded for about 5 minutes so that the volume density after molding was 0.35 g / ml, the thickness of the central portion was 15 mm, and the height of the inner wall was 15 mm. The composition of the molding material of each sample, the characteristics of the molded body,
The evaluation of the moldability and the like are summarized in Table 1.

Separately, a 25 mm thick plate-shaped sample of the same density is manufactured using the same raw material, and this is used as a sample for measuring the change in the thickness of the molded body, the thermal conductivity by the cylindrical method, the shrinkage factor during heating, and the bending strength. did.

The change in thickness at the time of molding is obtained by pressing the raw material charged in the close bag to a certain thickness and comparing the thickness when the molded body returns when the pressure is released and the thickness when pressed. It was

The thermal conductivity was determined by the cylindrical method. That is, outer diameter and height
A cylindrical sample having a thickness of 100 mm and a thickness of 25 mm was produced, and a heat source was installed inside the sample to heat the sample, and the temperature was calculated when the inner surface temperature and the outer surface temperature of the sample became constant and the heating calorie.

Heat shrinkage is performed by inserting an iron rod through a hole provided at the center of a sample on a disc having a diameter of 100 mm and a thickness of 25 mm, supporting both ends of the iron rod into an electric furnace, heating at 1100 ° C. for 2 hours, The change was measured and determined.

Bending strength uses a sample of 200 × 400 × 25 mm,
The sample was placed on fulcrums at intervals of 300 mm, and a load was applied to the center of the upper surface of the sample through a 20 mm square rod, and the load when the sample was broken was measured.

Examples 1 to 6 of the present invention are the changes in the thickness of the molded body,
Good results were obtained in terms of thermal conductivity, shrinkage upon heating, and bending strength. Furthermore, the hot plate according to the present invention had very few damages during the demolding after pressing, and the demolding was easy.

Comparative Example 1 is a molded article using a molding material made of ultrafine silica powder, which is easily broken when taken out from the mold and has a large heat shrinkage, which is not suitable for use. The molded product made of the ultrafine particulate titania of Comparative Example 2 is significantly inferior to the examples of the present invention in heat shrinkage and thermal conductivity. Since the raw material price of ultrafine particulate titania is almost the same as that of ultrafine particulate alumina, there is no advantage in using ultrafine particulate titania from the viewpoint of price.

[Table 1 Note] Dimension of sample: Square plate (150mm in cross section shown in Fig. 5)
× 150mm), central thickness 15mm, edge height 30mm, thickness change during molding: thickness at press / product thickness × 100% heat shrinkage: diameter after heating / diameter before heating × 100 % Weight ratio of the first layer and the second layer of Example 5: 1: 1 Example 6 uses an iron dish during pressing Overall evaluation: ○ Suitable × Inappropriate Example 7 and Comparative Examples 3 and 4 (a) A commercially available natural ceramic material, (b) a molding material made of ultrafine silica powder, and (c) a molding material made of fine alumina powder were used, respectively, and a diameter of 180 mm was obtained. A disc-shaped hot plate substrate having a thickness of 15 mm was formed. Outer diameter 18 on each board
A ring made of ceramic fiber board having a diameter of 0 mm, an inner diameter of 150 mm and a height of 20 mm was attached to form hot plates, and nichrome heaters were attached to the hot plates. Table 2 shows the effect of placing an enameled pot containing 1 of water on the hot plate and heating the nichrome heater with electric power of 1 kw / hr. It can be seen that the hot plate (c) of the present invention can be used even when the surface temperature reaches 1,100 ° C., has good thermal efficiency and excellent heat resistance.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a hot plate for a heater such as a nichrome coil of the present invention made of a molding material using ultrafine particle alumina powder, and FIG. 2 is made of a conventional molding material using ultrafine particle silica powder. A cross-sectional view of a hot plate for a heater such as a nichrome coil, Fig. 3 (a) is a plan view of a hot plate for a halogen lamp of the present invention, which is made of a molding material using alumina powder,
FIG. 3 (b) is a sectional view taken along line XX 'in FIG. 3 (a), FIG. 4 is a sectional view of a hot plate for a halogen lamp made of a molding material using silica powder, FIG. 5 (a) and FIG. (B) is a plan view and a side view of the pressure plate, and (c) is a sectional view of the mold. In the drawing, A, A '... peripheral wall part, B, B' ... inner peripheral surface, C, C '...
… Groove, D ′ …… Joint part, E …… Molded body, F …… Base part, G …… Peripheral part, H …… Heating body, 10 …… Test mold, 11 …… Pressure plate, 12 …… Outer frame.

Claims (3)

(57) [Claims] 1. A heating plate for a heating body, which is made of a molding material in which an infrared ray opaque agent and a fibrous reinforcing material are mixed with ultrafine particulate alumina powder. 2. A heating plate for a heating element, which is made of a molding material in which an infrared ray opaque agent and a fibrous reinforcing material are mixed in a mixture of ultrafine particle alumina powder and ultrafine particle silica powder. 3. An ultrafine-particulate alumina powder and an ultrafine-particulate silica powder are respectively mixed with an infrared ray impermeable agent and a fibrous reinforcing material, which are laminated, and the ultrafine-particulate alumina layer is located on the heater side. Hot plate for heating element.