JPS6362077B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a sheathed heater, and particularly, an object of the present invention is to provide a method for manufacturing a sheathed heater that has a long life and a high insulation resistance value in a used state after long-term use. Generally, sheathed heaters are as shown in Figure 1.
A coiled heating wire 2 with terminal rods 1 at both ends is inserted into a metal pipe 3, and the metal pipe 3 is filled with electrical insulating powder 4 such as fused magnesia, fused silica, fused alumina, etc. Both ends of the metal pipe 3 are sealed with glass 5 or heat-resistant resin 6 as required. This sheathed heater has been rapidly used as a heating component due to its excellent performance, quality, and simplicity, and is used in home appliances, various industries, space exploration, nuclear power, and other special applications. Since then, its market scope has been expanding. Among these, the use of high-temperature sheathed heaters is expected to continue to grow in the future. However, when we look at the current state of performance and quality of sheathed heaters from a global perspective, we find that the disadvantage is that the insulation resistance value in use (hereinafter referred to as insulation resistance value when hot) decreases over time, and that the heating wire is The drawback was that the lifespan before disconnection was short. The present inventors focused on the electrical insulating powder 4, and as a result of various studies, added nickel oxide powder as the electrical insulating powder to significantly suppress the evaporation phenomenon of the component elements of the heating wire 2, thereby achieving the intended purpose. It has been concluded that it is possible to manufacture a sheathed heater that has a high insulation resistance value when hot after a certain long period of use, and has a long life. However, when considering the actual manufacturing method of sheathed heaters, the nickel oxide powder added to the electrical insulating powder 4 must meet many conditions such as uniform dispersibility, no segregation due to external stress, and high specific resistance. is required. On the other hand, nickel oxide powders currently on the market can be broadly classified into the following two types. The first method is by roasting nickel metal powder, and the second method is by roasting various nickel salts. However, when considering the application of sheathed heaters, each has manufacturing disadvantages. The material obtained by the first method has a bulk specific gravity close to that of the electrically insulating powder, so it is easily dispersed in the electrically insulating powder. However, the nickel oxide powder tends to segregate due to vibrations during filling. On the other hand, in the second method, the primary particles are very fine and aggregate as large secondary particles, making it difficult to uniformly disperse the particles when mixed with electrical insulating powder. Such segregation and agglomeration of nickel oxide powder
In the production of sheathed heaters, this is not preferable because it significantly reduces work efficiency and causes a decrease in the characteristics of the sheathed heater, particularly the withstand voltage and insulation resistance value when heated. The present invention aims to provide a method for manufacturing a sheathed heater that can eliminate the drawbacks that occur in a method for manufacturing a sheathed heater using electrically insulating powder containing nickel oxide powder and achieve the intended purpose. . The manufacturing method of the present invention is characterized by the use of nickel oxide powder produced by simultaneously roasting metal nickel and nickel salt in air. The nickel oxide powder produced by the above method has all the advantages of conventionally commercially available nickel metal powders and nickel oxides obtained from nickel salts as starting materials, and can be easily added to electrical insulating powders. It is possible to obtain a stable electrically insulating powder that is not easily segregated even if it is dispersed and subjected to vibration after dispersion. For this reason, the deterioration of withstand voltage and the low insulation resistance value when heated, which were observed when using conventional commercially available nickel oxide powder, are no longer observed. For these reasons, by using the above-mentioned nickel oxide, it is possible to provide a sheathed heater that has a high insulation resistance value when hot after long-term use and has a long life. Examples of the present invention will be described below. (Example) The weight ratio of nickel salt and metal nickel powder is
A mixture of 3:1 was heated to 1100℃ in air.
A nickel oxide powder was prepared by roasting for 2 hours and then pulverizing to 5 microns or less. On the other hand, fused magnesia powder is used as the main component of electrical insulating powder 4, and 1% by weight of nickel oxide powder produced by the above method is added and mixed to this fused magnesia powder, and this is prepared as electrical insulating powder 4. did. Incidentally, the fused magnesia powder having the composition ratio shown in Table 1 was used. Table 1 MgO 96 ~ 97 wt% CaO 0.2 ~ 0.3 〃 SiO ₂ 2 ~ 3 〃 Al ₂ O ₃ 0.4 ~ 0.5 〃 Fe ₂ O ₃ 0.14 ~ 0.16 〃 In addition, as the heating wire 2, a nichrome wire with a wire diameter of 0.29 mm was used. Using type 1, it is made into a coil shape with a winding diameter of 2 mm,
Terminal bar 1 was connected to both ends. Additionally, metal pipe 3 has a length of 413 mm and an outer diameter of 8.
mm, wall thickness 0.46mm NCF2P (product name Incoloy 800)
was used. The heating wire 2 with the terminal bar 1 connected to both ends is inserted into the metal pipe 3, the metal pipe 3 is filled with the electrical insulation powder 4 prepared in advance, and the metal pipe 3 is rolled to reduce its diameter and annealed at 1050°C. , 10 minutes), the metal pipe 3 is made into a metal pipe with a length of 500 mm and an outer diameter of 6.6 mm.
Then, both ends of the metal pipe 3 were sealed with low melting point glass 5 and heat resistant resin 6 to complete a sheathed heater. For comparison, as a conventional example, when only fused magnesia powder was used as electrical insulating powder 4, in addition, 1% by weight of commercially available nickel oxide powder produced by roasting metallic nickel powder was added. Sheathed heaters were similarly completed using fused magnesia powder and fused magnesia powder to which 1% by weight of commercially available nickel oxide, which was produced by roasting nickel salt, was added as electrical insulating powder 4. For each completed sheathed heater, the insulation resistance value at room temperature at the initial stage of completion, the insulation resistance value at a pipe surface temperature of 750°C (hereinafter referred to as insulation resistance value during heating), and the limit withstand voltage at room temperature were measured. The results are shown in Table 2. In addition, a life test and a heat insulation resistance value test of the sheathed heater shown below were conducted. [Lifetime Test] For each of the above-mentioned sheathed heaters, the heating wire 2 was energized so that the surface temperature of the metal pipe 3 was maintained at 950° C., and the number of days until the heating wire 2 broke was examined. [Insulation resistance value test when heated] For each of the above-mentioned sheathed heaters, the heating wire 2 was energized so that the surface temperature of the metal pipe 3 was maintained at 950° C., and changes in the insulation resistance value when heated were examined. In addition,
When measuring the insulation resistance value under heat, the surface temperature of the metal pipe 3 was lowered to 750°C. The results of the above life test and the thermal insulation resistance value after 11 days in the thermal insulation resistance value test are
Shown in the table.

【table】

[Table] As is clear from Table 2, metal nickel,
By using nickel salt as a starting material,
In the manufacturing method of adding the generated nickel oxide, each sample shows non-uniform dispersion and segregation due to vibration during filling, so the sample number
As seen in the sheathed heaters No. 13, 16, 24, 25, 27, 28, and 30, when the insulation resistance value and withstand voltage during the initial stage of completion are significantly adversely affected, making it impossible to withstand actual use. However, it has the drawback of significantly increasing the defective rate. However, the manufacturing method of the sheathed heater according to the embodiment of the present invention can reduce the defective rate and also shorten the lifespan by approximately
We were able to obtain a sheathed heater with insulation resistance 10 times higher and one digit higher in insulation resistance after 11 days. As is clear from the above explanation, according to the manufacturing method of the sheathed heater of the present invention, the use of electrically insulating powder to which nickel oxide powder produced by simultaneously roasting nickel metal and nickel salt is used increases the longevity of the sheathed heater. It is possible to stably provide a sheathed heater that has a long insulation resistance value and a high insulation resistance value when hot after long-term use.

[Brief explanation of drawings]

The figure is a cross-sectional view of a typical sheathed heater. 2... Heating wire, 3... Metal pipe, 4... Electrical insulation powder.

Claims (1)

[Claims] 1. In a method for manufacturing a sheathed heater in which a heating wire is inserted into a metal pipe and electrically insulating powder is filled, nickel metal and nickel salt are simultaneously roasted to produce nickel oxide powder, and the electrically insulating powder is used as the electrically insulating powder. A method for manufacturing a sheathed heater, characterized by using a sheathed heater to which nickel oxide powder is added.