JPS581991A - Sea heater - 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 The present invention provides a long-life, high-quality sheathed heater that has insulation resistance at high temperatures, high dielectric strength voltage, and little change over time.

Magnesia is generally used as an insulating filler for sheathed heaters. Since this magnesia absorbs moisture and lowers the insulation resistance when cold, it is not possible to simply use magnesia alone as an insulating filler, and various ideas have been devised. For example, in a low-temperature sheathed heater with a surface temperature of about 400° C. or lower, the surface of magnesia powder is coated with silicone resin to provide water repellency, thereby preventing a decrease in cold insulation resistance due to moisture absorption. Therefore, the openings at both ends of a low-temperature sheathed heater do not need to be sealed with glass or the like, but can be simply sealed with resin, and gas can easily enter and exit at the sealing part. Since the resistance is also high, there are few problems in terms of life, gate edge resistance during heat, and dielectric strength.

On the other hand, in a sheathed heater for medium and high temperatures with a surface temperature of about 850'C or less, water repellency cannot be imparted by the above method because it exceeds the heat resistance temperature of silicone resin. Therefore, the openings at both ends of the sheathed heater are sealed with glass to prevent moisture from entering, thereby preventing the insulation resistance from decreasing when cold. However, by providing a glass sealing cap, gas does not enter and exit the sealing portion, and the air pressure inside the sheathed heater decreases, resulting in deterioration of insulation resistance when hot, dielectric strength voltage, and life.

The present invention solves the drawbacks of the sheathed heater that is airtightly sealed with a glass seal, as described above, and is characterized by adding a sulfate compound to the insulating filler layer.

Here, the above-mentioned sulfate is sodium.

Alkali metals such as calcium, magnesium.

Sulfates of alkaline earth metals such as calcium, nickel, transition metals such as iron are used.

The present invention will be explained below with reference to Examples. .

Figure 1 shows an example of the configuration of a sheathed heater. 1 is a metal pipe, 2 is a coiled heating wire, 3 is a terminal connected to the heating wire, 4 is an insulating filler made of magnesia, and 6 is a glass sealing layer. It is. In the present invention, sulfate is added to the filler 4.

Since the sheathed heater with the above configuration has a glass seal, there is no gas (air) going in or out at the sealing part, so when the heater is energized, oxidation of the heating wire occurs as in the conventional example. As the oxygen partial pressure inside the sheathed heater decreases, the sulfate added to the insulating filler dissociates, and its products react with the heating wire to generate oxides and sulfides. Therefore, it is possible to prevent the internal pressure of the sheathed heater from decreasing, and it is possible to prevent deterioration of the insulation resistance and dielectric strength voltage at the time of heat over a long period of time, and the life span is accordingly increased several times or more.

Figure 2 shows a sheathed heater in which magnesium sulfate is added to the insulating filler in various proportions, and the difference between the terminals is c1ooV? The results of comparing the changes in insulation resistance between the pipe and the heating wire over time when a voltage is applied are shown. If the amount of sulfate added is less than 0.01% by weight, there is no effect, and if the amount of sulfate added is less than 0.01% by weight,
When added above, there is almost no deterioration, but the insulation resistance is low from the beginning, making it impractical. Similar trends were observed when other metal sulfates were added.

Next, the results of comparing various characteristics of the sheathed heater B of the present invention in which 1.0% by weight of magnesium sulfate is added to the insulating filler and the conventional heater B to which no sulfate is added are shown.

Figure 3 shows that a voltage of 100v is applied between the terminals,
Figure 4 shows the change in dielectric strength between the pipe and the heating wire after energization under the same conditions. In addition, FIG. 6 shows the lifespan (J) expressed in number of energized days until disconnection under the same conditions.As described above, according to the present invention, the insulation resistance under heat.

A sheathed heater with a long life and less change in dielectric strength over time can be obtained.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the main parts of the sheathed heater of the example, Figure 2 is a diagram showing changes in insulation resistance during heating when various proportions of sulfate are added to the filler, and Figures 3- Figure 6 is a diagram comparing various characteristics with the conventional example. 1...Pipe, 2...Heating wire, 3. Old terminal, 4...・Insulating filler, 6...
...Sealing layer. Name of agent: Patent attorney Toshio Nakao and 1 other person
1yJ Mouse 2 drawing fl, g Atsushi (El) WA3 drawing 41!1 a5yA 481-

Claims (3)

[Claims] (1) A sheathed heater characterized in that a sulfate compound is added to a filler layer that insulates a metal pipe and an electric or hot wire. (2) The sheathed heater according to claim 1, wherein the sulfate compound is an alkali metal sulfate, an alkaline earth metal sulfate, or a transition metal sulfate. (3) The ratio of the sulfate added to the filler. The sheathed heater according to claim 1, wherein the content is 0.01 to 10% by weight.