JPH0136238B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to sheathed heaters, and particularly to insulation resistance values at high temperatures during use (hereinafter referred to as insulation resistance values at high temperatures).
The purpose is to provide a sheathed heater that prevents deterioration of the water and has a long life. In recent years, sheathed heaters have been increasingly used in high-temperature regions of 700°C or higher, and there is a growing desire for improved insulation properties and longer life using electrical insulators as fillers. Conventionally, in this kind of high-temperature sheathed heater, as shown in FIG. 1, a heating wire 3 made of a metal resistance heating element with terminal rods 2 at both ends is inserted into a metal pipe 1, and the heating wire 3 is filled with magnesia insulating powder 4. At the same time,
Both ends of a metal pipe 1 were completely sealed with low melting point glass 5 and heat resistant resin 6. This conventional sheathed heater has a
Although the thermal insulation resistance value is high at high temperatures of around 700 to 800℃, metal pipe 1 and heating wire 3 will deteriorate over time as they are used.
An oxidation reaction and a nitridation reaction occur, and the metal pipe 1
The interior of the heater becomes under reduced pressure, causing significant insulation deterioration, making it impossible to put it to practical use, especially in sheathed heaters where the inner diameter of the metal pipe 1 is small or where the length of the metal pipe is long. This insulation deterioration tends to increase as the operating temperature of the sheathed heater increases, and the reality is that the shape or operating temperature of the sheathed heater is limited. Further, the heating wire 3 becomes thinner in diameter due to oxidation reaction or nitriding reaction, and breaks. This tendency is also largely controlled by the operating temperature, and from this point of view as well, the operating temperature must be limited to a low level. The present invention solves the above-mentioned drawbacks of the conventional sheathed heater, and embodiments of the present invention will be described below with reference to FIGS. 2 and 3. In Figure 2, 11 is a metal pipe, Incoloy 800 (trade name) (30~35% Ni, 19~23% Cr).
%, S: trace amount, Mn trace amount, others are iron), and the outer diameter was 6.6 mm and the length was 500 mm. Reference numeral 12 denotes a heating wire that serves as a metal resistance heating element with terminal rods 13 at both ends, and is made of nichrome wire and is a metal pipe 1.
It is inserted in 1. Reference numeral 14 denotes an electrical insulating powder filled in the metal pipe 11, which is made by dissolving nickel oxide in magnesia insulating powder. Specifically, nickel oxide is added to the calcined magnesia powder so that the nickel atoms are 5 at%%,
It was subjected to electromelting treatment at a temperature of 2800°C and pulverized to a particle size of 420 μm or less to obtain the above-mentioned electrical insulating powder. Insert the heating wire 12 into the metal pipe 11 in this way,
After the pipe filled with the electrically insulating powder 14 is rolled through the steps of diameter reduction and annealing, both ends of the metal pipe 11 are completely sealed with glass 15 and resin 16,
Completed a sheathed heater. Five examples of the present invention having the above configuration were manufactured, and their initial characteristics and durability performance at a surface temperature of 950°C were examined, as well as changes over time in thermal insulation resistance at 750°C in a durability test. For comparison,
Five conventional products with the above configuration using magnesia insulating powder as the only electric insulating powder were manufactured.
A similar test was conducted. Among these test results, the initial characteristics and durability performance results are shown in Table 1. In Table 1, durability performance is expressed in terms of the number of days until the heating wire breaks.

【table】

[Table] As is clear from Table 1, the product of the present invention has almost no significant difference in initial characteristics compared to the conventional product, but the number of days until wire breakage is 3 to 4 times longer. Furthermore, as shown in Figure 3, the thermal insulation resistance value of the inventive product shown by characteristic curve A hardly changes, while that of the conventional product shown by characteristic curve B gradually decreases as the number of days of energization increases. It drops to about 1/10 of the initial value in about a week. As described above, in the product of the present invention, the thermal insulation resistance value is greatly improved compared to the conventional product. This is because, in the product of the present invention, the nickel oxide dissolved in the magnesia insulating powder reacts with the metal pipe 11 and the heating wire 12 to form a dense film, and this film is stable. This is because the oxidation reaction and nitriding reaction of the metal pipe 11 and the heating wire 12 do not proceed, and therefore, the pressure reduction inside the metal pipe 11 is suppressed, and the initial insulation resistance value is maintained for a long period of time. Furthermore, since the nickel oxide is dissolved in the magnesia insulating powder, the distribution state is uniform, the surface area is large, and the reaction with the metal pipe 11 and the heating wire 12 is sufficiently carried out, resulting in a large film-forming effect. In the above embodiment, Incoloy 800 is used as the metal pipe 11, but other metals such as stainless steel, heat-resistant steel such as nickel-based alloys may be used. In addition to the above-mentioned nichrome wire, the heating wire 12 may be an iron-chromium-aluminum wire, a nickel wire, or a nickel alloy wire. Furthermore, regarding the electrical insulating powder 14, what is added to the magnesia insulating powder may be the above-mentioned component elements of metal pipes and heating wires or oxides of the same component elements, such as iron, aluminum, chromium, nickel, or oxides thereof. . Further, the amount of these component elements added is preferably within the range of 0.1 atomic % to 10 atomic % of the entire electrical insulating powder.
If it is less than 0.1 atom%, the film forming ability will be small and the effect of the present invention will be weak.On the other hand, if it is more than 10 atom%, the insulation resistance value at room temperature and high temperature will decrease due to the increase in electron conduction of the component elements themselves. Resulting in. Furthermore, the particle size of the electrically insulating powder must be 420 μm or less. As is clear from the above description, according to the present invention, nichrome wire, iron-
A heating wire made of one of chromium-aluminum alloy wire, nickel wire, or nickel alloy wire is inserted, and electrical insulating powder is filled in the metal pipe, and the electrical insulating powder is used as the magnesia insulating powder. Or, use a heating wire in which at least one element or an oxide of the same element is dissolved in solid solution, and the amount of solid solution of the element dissolved in magnesia insulating powder is 0.1 to the whole electric insulating powder. Since it is within the range of atomic% to 10 atomic%, the film forming ability will not be reduced, and the insulation resistance value at room temperature and high temperature will not decrease due to the increase in electron conduction of the component elements themselves. As a result, it is possible to obtain a sheathed heater that does not have a drop in insulation resistance value when heated and has a long life.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway sectional view of a conventional sheathed heater, FIG. 2 is a partially cutaway sectional view of a sheathed heater showing an embodiment of the present invention, and FIG. 3 is a partially cutaway sectional view of the sheathed heater and a conventional sheathed heater. FIG. 3 is a diagram showing the relationship between the number of energizing days and the insulation resistance value at the time of heat. 11...metal pipe, 12...heating wire, 14...
...Electrical insulation powder.

Claims (1)

[Claims] 1. A metal pipe made of heat-resistant steel such as stainless steel or nickel-based alloy, with nichrome wire, iron-
A heating wire made of any one of chromium-aluminum alloy wire, nickel wire, or nickel alloy wire is inserted, and electrically insulating powder is filled, and the metal is added to the magnesia insulating powder as the electrically insulating powder. Using a solid solution containing at least one element or an oxide of the same element as the constituent elements of the pipe or heating wire, and determining the solid solution amount of the element dissolved in the magnesia insulating powder with respect to the entire electrical insulating powder, A sheathed heater within the range of 0.1 atomic% to 10 atomic%. 2. The sheathed heater according to claim 1, wherein the element dissolved in the magnesia insulating powder or the element contained in the oxide is at least one element selected from the group consisting of iron, aluminum, chromium, and nickel.