JPS5942435B2 - Manufacturing method of meads heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention prevents a decrease in insulation resistance due to moisture absorption, and
The present invention relates to a heat treatment method for a sheathed heater that can also be used as a high temperature heater.

Conventionally, as shown in Fig. 3, a sheathed heater in which a heating wire 2 is housed in a metal pipe 1 and is filled with an insulating powder 3 such as magnesia to reduce the diameter has many excellent features. However, due to moisture absorption of the insulating powder, the heating wire 2
The insulation resistance between the metal pipe 1 and the metal pipe 1 sometimes decreased.

In order to prevent this decrease in insulation resistance, a method has been proposed in which a water repellent such as a silicone resin is mixed in to prevent the insulating powder from absorbing moisture. However, organic water repellents such as silicone resins lose their water repellency under certain temperature conditions for one hour, as shown in FIG. The conditions shown in FIG. 1 are an example of a resin having relatively high heat resistance. On the other hand, sheathed heaters have a metal pipe 1
When an electric heating plate is formed by annealing, brazing with the metal plate 4 as shown in Fig. 3, or casting, etc., it is exposed to high temperatures. When the temperature inside the gland was maintained for one hour, the water repellency of the silicone resin etc. mixed into the insulating powder was lost. Curve B in FIG. 2 shows the change in insulation resistance when such a conventional sheathed heater is placed in an atmosphere of 40° C. and 90% humidity. As is clear from the figure, the insulation resistance decreases due to moisture absorption. Therefore, the present invention provides a heat treatment method for a sheathed heater that does not lose its water repellency even after undergoing the above-described manufacturing process in which high temperatures are applied, and therefore does not cause a decrease in insulation resistance due to moisture absorption of the insulator. It is something. That is, the present invention is characterized in that a sheathed heater filled with an insulating powder made of an inorganic insulating material and an organic water repellent mixed into a metal pipe is heat-treated in an inert atmosphere.

The following is a specific example of a case where a sheathed heater is brazed to an aluminum plate to form an electric heating plate. Insulating powder 3 is a mixture of magnesia powder mixed with 1 to 10% silicone resin and filled into an aluminum pipe. The sheathed heater is heated to a typical blazing temperature of 620℃.
℃ and held for 20 minutes to remove the aluminum metal plate 4.
In the step of brazing, the brazing is performed in an inert atmosphere, for example, a nitrogen atmosphere. After this brazing, the entire sheathed heater was placed in an atmosphere with a temperature of 40°C and a humidity of 900 tons), and the change in insulation resistance between the heating wire 2 and the metal pipe 1 was measured. The results are shown in the curve Ai in Fig. 21. .

From this characteristic diagram, it can be seen that the sheath heater according to the embodiment of the present invention still exhibits higher insulation resistance even after processing at a high temperature than the conventional example. Note that in annealing a sheathed heater using an iron pipe as a metal pipe, the same results as in the brazing of the aluminum pipe can be obtained by annealing in an inert atmosphere.

As is clear from the above description, since the heat treatment method of the present invention is heat-treated in an inert atmosphere, the water-repellent effect of the water-repellent can be maintained even if heat conditions exceeding the heat-resistant temperature limit of the water-repellent are applied. It has a high insulation resistance and is extremely effective.

[Brief explanation of the drawing]

Figure 1 shows an example of the temperature and time limit conditions under which silicone resin has water repellency, and Figure 2 shows a sheathed heater at a temperature of 4.
It is a diagram showing the change in insulation resistance value when the sheathed heater is placed in an atmosphere of 0°C and 90% humidity. In the diagram, curve A shows the change in insulation resistance value of the sheathed heater according to the heat treatment method of the present invention, and curve B shows the change in insulation resistance value when placed in an atmosphere of 0°C and 90% humidity. FIG. 3 is a cross-sectional view of the sheathed heater soldered to a metal plate. 1...Metal pipe, 3...Insulating powder.

Claims (1)

[Claims] 1. A heat treatment method for a sheathed heater, which comprises heat-treating a sheathed heater in which a metal pipe is filled with insulating powder made of an inorganic insulator mixed with an organic water repellent in an inert atmosphere. . 2. The method for heat treatment of a sheathed heater according to claim 1, wherein the inert atmosphere is a nitrogen atmosphere.