JPS6019118B2 - Manufacturing method of sheathed heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a sheathed heater containing silicone resin as a filler, and in particular, aims to prevent thermal decomposition of silicone resin during the heating process and obtain a sheathed heater with high insulation resistance. do.

By adding silicone resin to the filler of a sheathed heater, it has been attempted to utilize the water repellency of the silicone resin to suppress the hygroscopicity of the filler, magnesia, and to obtain a sheathed heater with high edge supply resistance. There is.

However, this silicone resin has a low heat resistance limit, and it is known that, for example, when the temperature exceeds 35,000 in the atmosphere, it decomposes and its water repellency decreases. On the other hand, in the manufacturing process of a sheathed heater, after a filler is filled between a heating coil and a metal pipe, the weight of the sheathed heater is reduced in order to increase the density of the filler, but this reduction in diameter causes the metal pipe to work harden. After this, it is transformed through the Akatsuki Anchor process. The sintering process is performed to make work-hardened metal pipes easier to deform in subsequent processes, and is usually heated to 50°C using a high-frequency heater.
It is heated to a high temperature of 0 to 700 qo. For this reason, the silicone resin contained in the filler is thermally decomposed during the dulling process.
The loss of high insulation properties could not be avoided. The higher the heating temperature and the longer the heating time in this dulling step, the greater the deterioration of the insulation performance. The present invention eliminates the drawbacks of the conventional sheathed heater manufacturing method described above, and one embodiment of the present invention will be described below.

In the figure, 1 is a heating wire with terminals 2 at both ends,
It is inserted into a metal pipe 3 made of iron, copper, aluminum, etc.

Between the metal pipe 3 and the heating wire 1, a silicone resin such as methyl-based silicone resin, phenyl-based silicone resin, methyl-phenyl-based silicone resin is used as an insulating material such as fused magnesia with a particle size of 37 to 420 French. Powdered filler 4 added in an amount of 0.2 to 5% is filled. In order to improve the thermal conductivity between the heating wire 1 and the metal pipe 3, the sheathed heater is reduced in diameter by 10% or more by rolling, swaging, or the like. After this, in order to solidify the silicone resin, first heating is performed at a temperature of 200 to 30,000 ℃ for 0.5 to 3 hours in an N2 gas atmosphere. Further, in order to anneal the metal pipe 3, instantaneous second heating is performed at a temperature of 500 to 700° C. in an N2 gas atmosphere, and after that, bending processing or the like is performed to complete the sheathed heater. When the silicone resin is heated in an N2 gas atmosphere, the weight of the silicone resin decreases from 10,000 to 250 oo as the resin solidifies, as shown by the dotted line A in Fig. 2.
There is almost no decrease in the temperature range up to oo. In addition, 7
When it exceeds 5,000, it shows a rapid decrease, indicating that thermal decomposition has occurred. On the other hand, when heating is performed in the atmosphere, as shown by the solid line B in Figure 2, in the temperature range of 250 qo to 50,000 qo, the weight gradually decreases due to gradual thermal decomposition, and when the temperature exceeds 55,000 qo, the decomposition becomes severe. , it shows a rapid weight loss, indicating that the properties of silicone resin have disappeared. Thus, it can be seen that when silicone resin is heated in an N2 gas atmosphere, thermal decomposition hardly occurs at a temperature of 750 qo or less. In addition to N2 gas, an inert gas such as Ar gas or a reducing gas such as ammonia decomposition gas may be used, as long as it is a non-oxidizing gas. As is clear from the above explanation, according to the present invention, the heating process in the sheathed heater manufacturing process is performed in a non-oxidizing gas atmosphere, so thermal decomposition of the silicone resin contained in the filling hardly occurs, and the water repellency of the silicone resin is improved. The sheathed heater can be completed without any damage.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part of a sheathed heater showing an embodiment of the present invention, and FIG. 2 is a characteristic diagram of weight change depending on temperature of silicone resin. 1... Heating wire, 3... Metal pipe, 4... Insulating filler. Figure 1 Figure 2

Claims (1)

[Claims] 1. A method for manufacturing a sheathed heater, in which a metal pipe filled with an insulating filler containing silicone resin between a heating wire is heated in a non-oxidizing gas atmosphere, and then cooled. 2. The method for manufacturing a sheathed heater according to claim 1, wherein the cooling treatment is an annealing process.