JPH0148626B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a sheathed heater that is widely used as a heating source for general cooking utensils, industrial electric furnaces, etc., and particularly relates to an incompletely sealed type sheathed heater. Conventional configurations and their problems Sheathed heaters have been widely used in general cooking utensils such as toaster ovens, microwave ovens, rice cookers, and hot plates, as well as for heating plastic molds and as a heating source for electric furnaces. ing. This is because the sheathed heater is simple, highly safe, and has excellent corrosion resistance. In general, a sheathed heater consists of a coiled heating wire with terminal bars at both ends inserted into the center of a metal pipe. It is sealed with melting point glass and heat-resistant resin. However, recently, incompletely sealed sheathed heaters, in which both ends of the metal pipe are not completely sealed with the low-melting glass and heat-resistant resin, have been reconsidered. In this way, incompletely sealed sheathed heaters do not pose any problems in practical use, especially when not used in a humid atmosphere or have a double insulation structure, and can significantly reduce costs. Recently, it is often used. However, if a partially sealed type sheathed heater is used in a high temperature range of 700°C to 800°C, the insulation resistance value when energized may decrease and the lifespan of disconnection may decrease, similar to the fully sealed type sheathed heater. Due to these problems, it is desired to develop a sheathed heater with a longer lifespan without disconnection. On the other hand, in a completely sealed type sheathed heater, to solve the above problem, a method has already been proposed in Patent Publication No. 34551-1971 - namely, a method of adding nickel oxide or iron oxide to fused magnesia powder. − is very effective. However, when the above method is applied to an incompletely sealed sheathed heater, the chromium element, which is a component of the heating wire, reacts with nickel oxide and iron oxide through oxygen in the atmosphere, resulting in composite oxidation of chromium. A phenomenon was observed in which the heating wires were easily formed, significantly deteriorating the heating wires, and conversely shortening the disconnection life. In this way, for incompletely sealed sheathed heaters that allow atmospheric oxygen to penetrate relatively easily, the method of significantly extending the disconnection life is as follows:
The reality is that it has not yet been discovered. OBJECTS OF THE INVENTION The present invention provides an incompletely sealed type sheathed heater that eliminates the above-mentioned conventional drawbacks and has a long disconnection life. Structure of the Invention The present invention provides a sheathed heater formed by incompletely sealing both ends of a metal pipe, in which sintered magnesia powder and at least one of nickel oxide powder and iron oxide powder are added as electrical insulating powder. using electrofused magnesia powder, the amount of the sintered magnesia powder added is equal to or more than the total amount of nickel oxide powder and iron oxide powder, and the total amount of nickel oxide powder and iron oxide powder is 0.1% by weight.
By adding the sintered magnesia powder, the chromium element, which is a component element of the heating wire, reacts with the sintered magnesia powder, forming a dense oxide film on the surface of the heating wire. , it is possible to prevent the heating wire from deteriorating. In addition, the added nickel oxide powder or iron oxide powder has a high oxygen dissociation pressure, so it releases oxygen according to the degree of decompression inside the sheathed heater, and has the effect of preventing depressurization inside the sheathed heater. It is possible to prevent the evaporation phenomenon of elements). As a result of the above, it is possible to provide an incompletely sealed sheathed heater with a long disconnection life. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. As electrical insulating powder 4, fused magnesia powder was prepared in which nickel oxide powder or iron oxide powder of 250 microns or less and sintered magnesia powder of 250 microns or less were added as shown in Table 1. In addition, as the metal pipe 3, NCF800 (trade name Incoloy 800) was used. On the other hand, a heating wire 2 made of a coiled nichrome wire (wire diameter 0.29 mm) with terminal rods 1 at both ends is prepared, inserted into the center of a metal pipe 3, and filled with electrical insulating powder 4 prepared in advance. The diameter was reduced by rolling. After this, the metal pipe 3 is annealed and left completely unsealed at both ends, with a diameter of 6.6 mm as shown in the figure.
Completed incompletely sealed sheathed heaters with a length of 500mm and a capacity of 100V-400W, each with sample numbers 4 to 26.
And so. On the other hand, for comparison, as shown in Table 1, there are cases in which only fused magnesia powder is used as electrical insulating powder 4, cases in which fused magnesia powder to which 1% by weight of nickel oxide powder is added, and oxide Using fused magnesia powder to which 1% by weight of iron powder was added, incompletely sealed sheathed heaters were similarly completed, and the sample numbers were 1, 2, and 3, respectively. In this way, the voltage was adjusted so that the surface temperature of the metal pipe 3 of each completed sheathed heater was 900°C, and an intermittent energization test was performed by accelerating the cycle of energizing for 20 minutes and stopping for 10 minutes. The number of cycles until the heater broke was determined and shown in Table 1. As is clear from Table 1, sample numbers 2 and 3, in which nickel oxide powder or iron oxide powder was added to electrofused magnesia powder as electrical insulating powder,
The disconnection life was shorter than that of Sample No. 1, which contained only electrofused magnesia powder without the addition of the oxide. In addition, sample numbers 9, 10, 16, 18, 21, and 24 where the amount of sintered magnesia powder added is less than the total amount of nickel oxide powder and iron oxide powder, and the total amount of nickel oxide powder and iron oxide powder is 0.1. Sample numbers 4, 5, 21, which are less than or equal to 10% by weight
No. 22, 23, 24, 25, and 26 showed no effect on extending the disconnection life, and showed 500 to 1600 cycles.

【table】

[Table] However, the amount of sintered magnesia powder added is equal to or greater than the total amount of nickel oxide powder and iron oxide powder, and the total amount of nickel oxide powder and iron oxide powder is 0.1% to 10% by weight. Sample number 6, which is %
Each of the sheathed heaters No. 7, 8, 11, 12, 13, 14, 15, 17, 19, and 20 had a lifespan of more than 3,000 cycles before disconnection, and a remarkable effect was obtained. In this way, the amount of sintered magnesia powder added is equal to or greater than the total amount of nickel oxide powder and iron oxide powder, and the total amount of nickel oxide powder and iron oxide powder is 0.1% by weight to 10.0% by weight. By using the electrofused magnesia powder, it is possible to obtain the effect of lengthening the disconnection life in so-called incompletely sealed type sheathed heaters, such as those in an unsealed state or in a simple sealed state. If the amount of sintered magnesia powder added is less than the total amount of nickel oxide powder and iron oxide powder,
The effect of suppressing the reaction between the chromium element, which is a component element of the heating wire, and the added nickel oxide powder and iron oxide powder is reduced, and no effect can be obtained. On the other hand, if the total amount of nickel oxide powder or iron oxide powder added is less than 0.1% by weight, the depressurization prevention effect will be small, and if it is more than 10% by weight, the electrical insulation will be shortened due to a decrease in packing density and thermal conductivity, leading to a decrease in disconnection life and a decrease in electrical insulation. Sexually, it causes problems and is not desirable. In addition, in the present invention, the added sintered magnesia powder is very active compared to the fused magnesia powder and the nickel oxide powder and iron oxide powder that are added at the same time, so it penetrates into the mouth of the metal pipe very little. The oxygen reacts with the chromium element, which is a component element of the heating wire, to form a stable oxide film on the surface of the heating wire. reaction and prevent the deterioration of the oxygen supply ability of the above oxides, making it possible to prevent pressure reduction inside the sheathed heater, which was previously seen in completely sealed and incompletely sealed sheathed heaters. It is possible to suppress the evaporation phenomenon of the heating wire component elements (mainly chromium) due to the reduced pressure inside the sheathed heater, and significantly increase the disconnection life. In addition, although a sheathed heater was used as an example of the present invention, the present invention is not particularly limited to this.
A similar effect can be obtained with a cartridge heater. Effects of the Invention As is clear from the above description, according to the incompletely sealed sheathed heater of the present invention, at least one of sintered magnesia powder, nickel oxide powder, and iron oxide powder can be used as the electrical insulating powder. The amount of the sintered magnesia powder added is equal to or greater than the total amount of nickel oxide powder and iron oxide powder, and The amount added is 0.1% to 10% by weight, and as a result, it is possible to obtain a sheathed heater with a long disconnection life, and its practical value is great.

[Brief explanation of drawings]

The figure is a sectional view of a sheathed heater according to an embodiment of the present invention. 2... Heating wire, 3... Metal pipe, 4... Electrical insulation powder.

Claims (1)

[Claims] 1.Equipped with a metal pipe and a heating wire inserted into the metal pipe, both ends of the metal pipe are incompletely sealed,
As the electrical insulating powder, fused magnesia powder to which at least one oxide powder selected from the group of sintered magnesia powder, nickel oxide powder and iron oxide powder is added is used, and the amount of the sintered magnesia powder added is nickel oxide powder. A sheathed heater in which the total amount of addition of nickel oxide powder and iron oxide powder is equal to or greater than the total addition amount of nickel oxide powder and iron oxide powder, and the total addition amount of nickel oxide powder and iron oxide powder is 0.1% by weight to 10% by weight.