JPS58157079A - Method of producing sheathed 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 relates to a method for manufacturing a sheathed heater, which has a long life, high insulation resistance when heated, high dielectric strength voltage, and is of high quality with little change over time in insulation resistance and dielectric strength voltage when hot. The present invention attempts to provide a manufacturing method for producing a sheathed heater.

Magnesia is generally used as an insulating filler for sheathed heaters. This magnesia absorbs moisture and its insulation resistance decreases, so in most sheathed heaters, the openings at both ends are sealed with glass or resin to prevent moisture from entering, thereby preventing the insulation resistance from decreasing due to moisture absorption. .

However, by sealing the openings at both ends in this way,
There will be no moisture intrusion, but at the same time there will be no air inflow.

Therefore, in the sheathed heater for medium and high temperatures, after the heating wire consumes the air inside the 7-piece heater in a short period of time, the heating wire components are diffused, and the insulation resistance during heating deteriorates. Therefore,
The insulation deteriorated rapidly and the lifespan was short.

SUMMARY OF THE INVENTION In order to eliminate the drawbacks of the conventional examples, the present invention provides a sheathed heater in which metal oxides such as iron, copper, nickel, cobalt t, or tin are formed on the inner surface of the pipe. FIG. 1 shows the configuration of a sheathed heater according to the manufacturing method of the present invention. In Figure 1, 1 is a stainless steel pipe, 2 is iron, copper, nickel, and cobalt supported inside the pipe, metals that can be oxidized by heating such as tin, and 3 are magnesia filled in the pipe 1. 4/fi heating wire.

By heat-treating the sheathed heater with this configuration, part or all of the metal 2 coated on the inner surface of the pipe 1 is oxidized,
Oxide f generated on the inner surface of the vibrator 1. Thereafter, glass sealing is performed to prevent moisture absorption from the openings at both ends of the sheathed heater.

The metal oxide that forms inside the stainless steel pipe is decomposed when the oxygen inside the sealed sheathed heater is consumed as an oxide film on the heating wire, and the partial pressure of oxygen inside decreases, which is always constant. This is to maintain the oxygen partial pressure of the sheathed heater.This prevents the heating wire components from dissipating and extends the life of the sheathed heater.

FIG. 2 shows the relationship between the energization time of the sheathed heater and the change in insulation resistance in the heating state. In FIG. 4, reference numbers M, B, C, D, lf, F, and G indicate the characteristics of the sheathed heater shown in Table 1, respectively.

(k′ bottom #, white) Table 1 The amount of oxygen in the oxide is the amount that can oxidize the amount of chromium contained in the nichrome wire used as a heating wire (
The amount of chromium oxidized/the amount of chromium before oxidation).

As is clear from Figure 2, the stereoless pipe
It can be seen that the change in insulation resistance of the sheathed heater with gold maple oxide layer formed inside the square is smaller than that of the conventional sheathed heater.

In particular, when the amount of oxygen in the oxide is such that the amount of chromium contained in the heating wire can be converted into chromium oxide, the insulation resistance value is 1MΩ as a guideline for use as a sheathed heater. The time required to reach this temperature is more than 10 times that of conventional sheathed heaters, and the lifespan can be greatly extended. This is a characteristic diagram showing the relationship, and reference numbers M, B, and G in FIG. 3 indicate the same reference numbers as shown in Table 1, respectively.

From FIG. 3, it can be seen that the sheathed heater according to the present invention exhibits a slower change in internal pressure over time than the conventional one.

In the conventional completely sealed sheathed heater G, the oxidation reaction of the heating wire progresses during the relatively early energization time, and the oxygen inside the sheathed heater is completely removed, and the heating wire continues to be heated even after that. Therefore, the heating wire forms a nitride film, the pressure inside the sheathed heater continues to decrease, and there is nothing inside the sheathed heater that reacts with the heating wire. Therefore, the metal of the heating wire is diffused, and the insulation resistance gradually deteriorates. Furthermore, since there are few oxidized and nitride films to prevent this diffusion, the heating wire thins out quickly and has a short lifespan.

However, in the sheathed heater according to the present invention, as shown in FIG. 3, the internal pressure of the sheathed heater shows a constant value at 415 atm (air temperature measurement), and nitriding does not proceed. this is,
The oxygen inside the sheathed heater is consumed as an oxide film on the heating wire, the internal oxygen partial pressure decreases, and when it reaches the decomposition pressure of the metal oxide generated inside the pipe, the metal oxide decomposes and the oxygen is released into the heating wire. This is because even if the oxygen is consumed, a constant oxygen partial pressure is maintained at all times. Therefore, while the generated metal oxide exists, nitridation does not occur inside the sheathed heater and the pressure is maintained at 415 atmospheres.

This reaction ends when all the metal oxides are reduced to metals, and then nitridation occurs like in a normal sheathed heater, the internal pressure decreases, and the electric current is removed when there are no reactants with the heating wire. Metal dissipation from the hot wire occurs, and the insulation resistance gradually deteriorates as shown in FIG. However, compared to conventional sheathed heaters, a large amount of oxygen is put inside the sheathed heater, and the chromium oxide film that is generated when the heating wire (chromium wire) is at high temperatures will continue to be formed for a long time. Even inside the heater, the same effect as when used in air is exhibited, and the life of the heating wire itself is extended. In addition, at the point when oxygen and nitrogen are consumed, a thick film is formed on the heating wire, so the rate of metal diffusion from the heating wire is very low, and the insulation after the air is consumed is reduced. The rate of deterioration of the resistor also becomes very slow.

In addition, when comparing a sheathed heater in which metal oxides are generated on the inner surface of a stainless steel pipe as in the above example, and a case in which oxides are uniformly dispersed in the insulating filling material of a /-sheathed heater, the amount of oxides is In the same case, the lifespan shows almost the same effect, but the insulation resistance under heat shows a value lower than the initial value when oxide is uniformly added, but the sheathed heater according to the present invention shows a lower value than the initial value. The value indicates the insulation resistance value due to magnesia, similar to conventional sheathed heaters.
After that, this value will continue for a long time, and a sheathed heater with good insulation properties can be obtained from the beginning.

Note that Fe is used as the metal oxide in the above examples.

Although only the metal oxide of Cu has been described, it has been confirmed that substantially the same effect can be obtained by using other metal oxides such as tin, nickel, and cobalt.

As is clear from the above explanation, according to the manufacturing method of the present invention, it is possible to obtain a sheathed heater that is insulated at high temperatures and has a long life.In addition, it is possible to obtain a sheathed heater that is insulated at high temperatures and has a long life.In addition, the inner surface of the pipe is simply coated with a metal material that can be oxidized by heating. It can be produced using conventional processes.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the essential parts of a sheathed heater according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the change in insulation resistance over time of the sheathed heater with respect to the energization time, and Fig. 3 is an internal diagram of the sheathed heater with respect to the energization time. FIG. 3 is a characteristic diagram showing changes in pressure. , 1... River/stainless steel pipe, 2... Metal, 3... Insulating filler 1, 4... Heating wire.

Claims (1)

[Claims] A method for manufacturing a sheathed heater, comprising storing a heating wire and a filler in a pipe whose inner surface is coated with metal, and oxidizing the metal by heat treatment.