JPS6231982A - Silicon carbide heat generating body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a silicon carbide heating element used as a heating source for various industrial furnaces.

[Conventional technology]

Generally, a silicon carbide heating element is composed of a heat generating part having a uniform resistance value and low resistance terminal parts formed at both ends of the heat generating part.

Since silicon carbide heating elements are composed of ceramic members, they exhibit characteristics not found in metal heating elements.

For example, a silicon carbide heating element exhibits a negative temperature coefficient from room temperature to 700°C, and has a positive temperature coefficient in the higher temperature range;
Use above is recommended. Silicon carbide is relatively stable in the atmosphere, but is sensitive to water vapor and alkali vapor.
It is weak and causes shortening of the life of the heating element. In silicon carbide heating elements, the surface of the heating part has been coated with various ceramic materials.

The manufacturing conditions for new ceramic products and electronic components are very strict, and especially in firing furnaces, it is required to be able to finely control the temperature distribution inside the furnace. In electric resistance furnaces that use silicon carbide heating elements as a heat source, temperature distribution in the width direction within the furnace has become a problem. In other words, no matter how uniform a heating element with a surface temperature is used, the temperature drops from the center of the furnace toward the side walls due to heat dissipation from the side walls of the furnace. However, due to differences in firing positions, uneven baking and shrinkage occur, leading to poor yields and improvements in temperature distribution have been desired.

12. [Problems to be solved by the invention] As an improvement method for the above, Publication of Utility Model Publication No. 48-22750,
It has been proposed to arbitrarily connect elements with different resistance values to form a heat generating part and change the temperature distribution.

Although the above-mentioned method is an effective means for improving the temperature distribution within the furnace, it has a major drawback. In other words, in order to join heating elements with different resistance values (
Because the joint part enters the furnace, and because the heat generating parts are joined together, the strength of the joint part deteriorates significantly, oxidation occurs, and the life of the heating element is short.In addition, during manufacturing, heating elements with different resistance values are used. The number of man-hours involved in manufacturing and combining and joining them increases, which is disadvantageous in terms of workability and cost.

An object of the present invention is to provide a heating element that can relatively easily and inexpensively improve the temperature distribution in a method for improving the temperature distribution in a furnace.

[Means for solving problems]

That is, the present invention is characterized in that, in a silicon carbide heating element, a part of the heat generating part is coated with one or more types of ceramic material having a different emissivity from silicon carbide.

It has been known that the emissivity of furnace bricks and the like varies depending on their color (blackness). Generally, in high-temperature ranges, heat is primarily transferred to the heated object through radiation. According to Stefan Boltzmann's law, radiant heat is greatly influenced by the blackness of the material, and in the case of a heating element, a black surface is preferable.

However, when it comes to refractory materials used for the walls of electric furnaces, etc., it is being considered to conversely reduce the amount of heat received in order to save energy, and materials with a low degree of blackness are often used, so the surface of the heating element As a result of examining methods for arbitrarily changing the temperature, it was found that the amount of radiant heat dissipated could be controlled by coating the surface of the heat generating part with silicon carbide and a 6-ceramic material with an emissivity of cQ%.

That is, although the emissivity of silicon carbide is generally about 0.871, for example, if the surface of the heat generating part is partially coated with a material having a low emissivity, the temperature near the coated surface will decrease. As a result, uniform temperature distribution within the furnace can be achieved.

[Example 1] Diameter 25 mm, heat generating section 300 mm, end section 300 m
m rod-shaped silicon carbide heating element, as shown in FIG. 1, a white mullite substance (emissivity ε=0.
4) A covering area 3 of 75 yn thickness is formed using the coating material, and on both sides of the covering area 3, a silicon carbide heating element consisting of a heating part 1 consisting of an uncoated area 4, both terminal parts 2, and an electrode part 5 is attached with an electric capacity. 15Kw, inner furnace dimensions 300mm, depth 600m
The temperature inside the electric furnace was set to 1200° C., and the temperature was maintained for 1 hour after the temperature was raised by electricity, and the temperature distribution inside the furnace was measured. In the measurement, as shown in FIG. 3, a thermocouple was installed at a position 75 mm below the heating element, and the temperature was measured at five points in the width direction of the furnace. The measurement results are shown in Table 1.

[Example 2] Four U-shaped silicon carbide heating elements shown in Fig. 2 with a diameter of 20 mm, a heat generating part of 300 mm, an end part of 300 mm, and a pitch of heat generating parts of 50 mm were installed in the same electric furnace as in Example 1 above. . A part of the heat generating part of the U-type silicon carbide heating element (a position slightly closer to the tip than the center of the heat generating part) is coated with mullite having a width of 75 mm and an emissivity of ε-0.4. there were. Table 1 shows the results of measuring the temperature distribution in the furnace at a temperature of 1200°C using the same method as in Example 1.

[Comparative Example 1] The same rod-shaped silicon carbide heating element as in Example 1, but not coated with mullite, was used in the same electric furnace to measure the temperature distribution inside the furnace. The measurement results are shown in Table 1.

[Comparative Example 2] The same U-type silicon carbide heating element as in Example 2, but not coated with mullite, was used in the same electric furnace to measure the temperature distribution inside the furnace.

The measurement results are shown in Table 1.

[Comparative Example 3] A silicon carbide heating element having the same dimensions and the same material as in Example 1. Instead of the Nimlite material, a black chromium-based coating (emissivity ε-0,
9) was applied to the central 75-width area of the heat-generating area.

The chromium-based coat described above had approximately the same emissivity as silicon carbide. The temperature distribution in the furnace was measured in the same manner as in Example 1.

The measurement results are shown in Table 1.

The silicon carbide heating element of the present invention, as shown in the examples,
In the conventional product, the temperature difference inside the furnace, which was 10°C or more, could be reduced to within ±2°C. In the example, the coating was applied to one location on the heating element, but depending on the purpose of use, it is easy to apply the coating to multiple locations.

〔Effect of the invention〕

By using the silicon carbide heating element of the present invention, it became possible to perform firing that could not be done conventionally, for example, firing a mix with strict upper and lower allowable temperature limits, and it was possible to prevent uneven firing and shrinkage.

Moreover, simultaneous double-row firing is possible, which has the effect of achieving mass production with stable quality of processed materials.

The present invention can be expected to have great effects in the field of heating furnaces for ceramics and metals, where high precision, especially precision in temperature distribution, is required in recent years, and the industrial benefits are immeasurable.

[Brief explanation of the drawing]

FIG. 1 is a front view showing one embodiment of the silicon carbide heating element of the present invention. FIG. 2 is a plan view showing another embodiment of the silicon carbide heating element of the present invention. FIG. 3 is a sectional view showing the temperature measurement position in the furnace in the example. ■---Heating part 2-1 to 1 terminal part 3--1 covering area 4-11 terminal covering area 5--m-electrode part 1st figure 2nd figure 3rd figure

Claims (1)

[Claims] A silicon carbide heating element used as a heating source for various industrial furnaces is characterized in that a part of the surface of the heating part of the silicon carbide heating element is coated with one or more ceramic materials having a different emissivity from silicon carbide. Silicon carbide heating element.