JPS5855632B2 - Sea heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sheathed heater formed by sealing both ends of a metal pipe, and an object of the present invention is to prevent insulation deterioration during use at high temperatures.

Generally, this type of sheathed heater is completely sealed with a leakage rate of 10-7 CC/see or higher to prevent moisture from entering from the outside.

A completely sealed sheathed heater will not exhibit the phenomenon of a decrease in insulation resistance or withstand voltage when used at low temperatures, such as when used underwater or in aluminum die-casting. , exhibiting very good characteristics.

However, when used at high temperatures, the more complete the seal is, the more the insulation resistance value decreases and the withstand voltage decreases.

These phenomena occur because the air inside the metal pipe decreases due to oxidation and nitridation reactions at high temperatures in the heating wire, resulting in a decrease in dielectric breakdown voltage, and also because the metal components of the heating wire, mainly iron components, diffuse onto the surface of the insulating material powder. It is known that this is because the insulation resistance value decreases.

The present invention solves the above-mentioned drawbacks of the conventional sheathed heater, and embodiments 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 the metal pipe 3.

A mixture 6 made by mixing an insulating material 4 such as magnesia powder and silica gel 5 in equal proportions is filled between the metal pipe 3 and the heating wire 1.

Reference numeral 7 denotes an elastic body such as heat-resistant silicone rubber attached to the terminal 2, and seals both ends of the metal pipe 30.

Reference numeral 8 denotes a pressurizing body provided on the terminal 2, which presses the elastic body T against the end of the metal pipe.

In the above configuration, the degree of sealing by the elastic body 7 is 10-2~
It is about 10-7cC/SeC and is not completely sealed.

Therefore, when the pressure inside the metal pipe 3 is reduced, air flows in from the outside.

Although this inflowing air contains moisture, this moisture is absorbed by the silica gel 5 and is not adsorbed by the insulating material 4.

Therefore, insulation deterioration due to moisture and decrease in dielectric breakdown voltage due to oxygen deficiency do not occur.

Thereafter, when the heating wire 1 is energized, water is separated from the silica gel 5 due to the temperature rise and moves toward the terminal 2 side.

Moreover, by applying electricity, a gap is created between the elastic body T and the metal pipe 3 due to an increase in internal pressure, and the moisture released from the silica gel 5 is diffused to the outside.

At this time, the pressurizing body 8 prevents the elastic body I from being pushed out more than necessary.

Note that after the energization ends, when the temperature reaches room temperature, the elastic body I returns to its original state and seals the end of the metal pipe 3.

The sheathed heater A of this example and the sheathed heater B, which has the same sealing structure and does not contain silica gel in the insulating material, were placed in a thermostat at a temperature of 40°C and a relative humidity of 90φ to observe changes in insulation resistance over time. The results of the investigation are shown in Figure 2.

As is clear from Fig. 2, the insulation resistance of the sheathed heater mixed with or without silica gel decreases over time, but the sheathed heater of this example has a resistance of 1000 MΩ or more even after 30 days. The resistance value was maintained.

This is because the silica gel 5 absorbs moisture and the insulation resistance value of the insulating material 4 does not decrease.

Similarly, when the sheathed heaters A and B are energized and the change in insulation resistance value over time is examined, as shown in Fig. 3,
In a sheathed heater that does not contain silica gel, the insulation resistance value decreases rapidly, but in the sheathed heater of this example, the insulation resistance value temporarily decreases, but then recovers and maintains a high resistance value of 1000 MΩ or more.

This is because the moisture that has moved to the terminal 2 side is discharged to the outside.

As is clear from the above explanation, since the sheathed heater of the present invention is made of an insulating material mixed with silica gel, moisture is adsorbed by the silica gel and the insulating material is prevented from absorbing moisture, resulting in a high insulation resistance value. can be maintained for a long period of time, and its industrial value is great.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the essential parts of a sheathed heater showing an embodiment of the present invention, Fig. 2 is a characteristic diagram showing changes in insulation resistance value over time when the same sheathed heater and a conventional sheathed heater are left unused, and Fig. 3 The figure shows the same characteristics when both the sheathed heaters are energized. 1... Heating wire, 2... Terminal, 3...
...metal pipe, 4...-insulating material, 5...-silica gel, I...-elastic body.

Claims (1)

[Claims] 1. In a sheathed heater made of a heating wire with terminals at both ends and an insulating material filled between a metal pipe, silica gel is mixed with the insulating material, an elastic body is attached to the terminal, and the elastic body is used to heat the metal. A sheathed heater made by sealing both ends of a pipe.