JPS5923073B2 - Manufacturing method of sheathed heater - Google Patents

Description

Detailed Description of the Invention The present invention involves applying a water repellent agent made of silicone resin or the like to the inner surface of an exterior metal pipe, inserting a heating wire and filling it with an inorganic insulator, and then heating it to coat the water repellent agent. The present invention relates to a method of manufacturing a sheathed heater made by diffusing in an inorganic insulator.

In general, in a sheathed heater that is equipped with a heating wire inside an exterior metal pipe, filled with insulating powder such as magnesia, and then reduced in diameter, the insulation resistance between the heating wire and the exterior metal pipe decreases due to moisture absorption of the insulating powder. There were flaws.

For this reason, a method is to apply a water repellent such as silicone resin to the inner wall of the exterior metal pipe, fill it, reduce the diameter, and then heat it to diffuse the water repellent into the inorganic insulation material, thereby preventing a drop in insulation resistance due to moisture absorption. is proposed. However, organic water repellents such as silicone resins have the disadvantage of losing water repellency under certain heat conditions.

This state is shown in FIG. FIG. 1 shows an example of a resin having relatively high heat resistance. Therefore, when annealing the exterior metal pipe, brazing the sheathed heater and metal plate, or casting during the manufacturing process of the sheathed heater, the water repellency of the silicone resin will deteriorate under the thermal conditions within the shaded area in Figure 1. is lost. Curve B in Figure 2 shows the change in insulation resistance when a sheathed heater manufactured by such a conventional manufacturing method is placed in a temperature of 40° C. and a humidity of 90%. As is clear from the figure, insulation resistance decreases due to moisture absorption. The present invention provides a method for manufacturing a sheathed heater in which the water repellency of the silicone resin is not lost even after the manufacturing process is subjected to heat conditions such as those described above, and the insulation resistance does not decrease due to moisture absorption of the insulator. It provides:

An embodiment of the present invention will be described below with reference to FIG.

In the figure, 1 is an aluminum wire exterior metal pipe, 2
is a heating wire installed approximately in the center of the exterior metal pipe 1; 3 is a terminal bar connected to the heating wire 2; 4 is an insulating powder such as magnesia powder filled in the exterior metal pipe; 5 is the inner surface of the exterior metal pipe 1 A water repellent made of silicone resin, etc. In the above configuration, the manufacturing method thereof will be described. First, a water repellent agent 5 made of silicone resin is applied to the inside of the exterior metal pipe 1, a heating wire 2 is inserted, and magnesia powder 4 is filled, and then, range. After this, the end opening of the metal pipe 1 is caulked and sealed as shown in FIG.
After heating at 620° C. for 20 minutes and bracing the aluminum plate, the caulked ends are cut off. The above thermal conditions are those within the diagonal lines in FIG. %
Even after the insulator was put into the tank, no decrease in insulation resistance was observed, as shown by curve A in Figure 2. As is clear from the above description, according to the present invention, the water repellent does not lose its water repellency even after undergoing a manufacturing process in which heat exceeding the heat resistance limit of the water repellent is applied, making it possible to apply it to various electrical devices. .

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of the limit conditions for a one-hour temperature under which silicone resin has water repellency, and Figure 2 is a diagram showing an example of the limit conditions for a temperature of one hour under which silicone resin has water repellency.
3 and 4 are cross-sectional views of a sheathed heater showing the manufacturing process of the present invention. 1...Exterior metal pipe, 2...Heating wire, 4...Inorganic insulator, 5...Water storage agent.

Claims (1)

[Claims] 1 A sheathed heater in which a water repellent made of silicone resin or the like is applied to the inner surface of an exterior metal pipe, a heating wire is inserted therein, the pipe is filled with an inorganic insulator, and the pipe is processed under heat conditions that exceed the heat resistance limit of the water repellent. A method of manufacturing a sheathed heater, characterized in that after the end opening of the exterior metal pipe is hermetically sealed, processing is performed by applying the thermal conditions.