JPS6237511B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a heating element using electrical contact resistance. Conventionally, carbon particles are used as this type of heating element, but since carbon particles have the characteristic that their resistance decreases rapidly in high temperature ranges, it is difficult to control the temperature when they are filled between electrodes and energized. Another disadvantage is that current control becomes complicated because the interelectrode voltage fluctuates greatly when the temperature rises. The present invention provides a method for manufacturing a heating element that can eliminate such disadvantages. The method of the present invention will be described in detail below.
The first step is to carbonize the plant and make it into fine particles to obtain carbon grains, and the second step is to mix fine particles of an inorganic heat-resistant material, which exhibits insulating properties at low temperatures and becomes a conductor or semiconductor at high temperatures, with the carbon grains, which can be carbonized. It has a second step of adding and mixing an adhesive solution, a third step of sintering the mixed dough, and a fourth step of crushing the sintered dough after cooling. be. As the inorganic heat-resistant material, metal compounds may be used, particularly monocalcium phosphate, dibasic calcium phosphate, tribasic calcium phosphate, calcium hydroxide, calcium oxide, calcium carbide, calcium silicate, alumina, molten alumina, D-soda. Alumina, alumina white, alumina silicate, aluminum oxide, silicate compounds, silicon nitride, zeolites, tungsten compounds, boron compounds such as borax, boron nitride, boron silicate, zirconium, zirconium oxide, etc. are considered. This metal compound only needs to be contained in the starting heating element, so in the initial second step, calcium,
Silicic acid or silicon may be used so that these substances are oxidized into metal compounds during the sintering process in an electric furnace, or the sintering process may be performed in a carbonizing or nitriding atmosphere. Then, these substances may be made into carbides or nitrides. Examples are shown below. Example 1 5 parts of vegetable carbonized material with particle size of 500 mesh
Add 1 part of mesh silica, mix this with a mixed solution of 0.5 part of polyvinyl alcohol and 1 part of water,
Next, this mixed piece was placed in an electric furnace and heated at 1500℃ for 1 hour.
Sintered for a time, further cooled, crushed and sorted to 0.1~
A heating element with a size of 1 m/m was obtained. This heating element was filled in a furnace with a width of 50 m/m, a length of 100 m/m, and a depth of 50 m/m, and electricity was applied between the electrodes on both sides in the longitudinal direction. Results as shown in Table 1 were obtained.

[Table] Next, the same furnace was filled with only plant carbon particles and energized in the same manner as before, and the results were as shown in Table 2.

[Table] In the above experiment, the initial voltage and current values were regulated to be constant, but in reality, such regulation is not done, so the initial current value varies from furnace to furnace depending on the contact resistance of the heating element. Through the above experiments, it was confirmed that the heating element obtained by the method of the present invention has gentle voltage drop characteristics and current increase characteristics over time compared to conventional carbon particles, and the furnace temperature was also lower than that of conventional carbon particles. was found to be higher than that of Example 2 To 4 parts of charcoal powder with a particle size of 500 mesh or less,
Add 1 part of tricalcium phosphate with a particle size of 500 mesh or less and 1 part of silica with a particle size of 500 mesh or less, mix this with a solution of 0.1 part of polyvinyl alcohol and 2 parts of water, mold it into a piece, dry it, and heat it at 1500℃. Sintered for an hour, then cooled and crushed to 0.1~1
A heating element with a size of m/m was obtained. This heating element was filled in the furnace used in Experiment 1 and energized using a graphite electrode, and the following results were obtained.

[Table] In this experiment, a commercial power source was used, so electricity was applied at a constant voltage, but as mentioned above, the initial current value was not constant due to changes in contact resistance for each furnace. The following results were obtained by filling the furnace used in this experiment with a conventional heating element made only of carbon particles and energizing it.

[Table] Through this experiment, it was confirmed that the current change characteristics and temperature rise characteristics of the heating element obtained by the method of the present invention had linear characteristics compared to conventional heating elements. Example 3 4 parts of charcoal with a particle size of 500 mesh and 1 part of zirconium oxide with a particle size of 500 mesh were mixed, and this was mixed with a solution of 0.5 part of polyvinyl alcohol and 2 parts of water.
After that, it was fired at a temperature of 1800°C for 1 hour, and after further cooling, it was pulverized to obtain a heating element having a size of 0.5 to 1 m/m. This heating element was filled in the furnace used in Experiment 1, and the voltage was controlled during the elapse of time to energize the furnace, and results as shown in Table 5 were obtained.

[Table] This experiment confirmed that the temperature inside the furnace can be easily controlled by controlling the voltage value. Since the heating element obtained by the method of the present invention has the above characteristics, the following effects can be expected. The heating element obtained by this method is composed of carbon particles and an inorganic heat-resistant material, and while this inorganic heat-resistant material has electrical insulation properties up to a predetermined high temperature, it becomes a semiconductor or As a conductor, it has an electrical resistance value. Therefore, the calorific value of the heating element increases in the high-temperature range, and the subsequent change in resistance of the entire heating element is constant due to the inorganic heat-resistant material, so the temperature inside the furnace increases at a large rate in the high-temperature range. On the other hand, it is thought that the change in resistance of the heating element will be gentler than in the case of conventional carbon particles only. Since the heating element of this method contains an inorganic heat-resistant material, it has good heat retention properties, so it can be improved to accelerate the temperature increase in the furnace in the high temperature range, and the resistance change in the high temperature range is gradual. Voltage and current can be easily controlled.

Claims (1)

[Claims] 1. Mix and mix fine particles of a carbonized plant with fine particles of an inorganic heat-resistant material that exhibits electrical insulation at a certain temperature or below, but becomes a conductor or a semiconductor at a certain temperature or above. A method for manufacturing an electric resistance heating element, which comprises sintering, then cooling and pulverizing the powder to select and collect particles of a required size.