JPS6362076B2 - - 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 industrial applications, and special applications such as space exploration and nuclear power. 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, if we look at the current state of performance and quality of sheathed heaters from a global perspective, we find that their insulation resistance value (hereinafter referred to as hot insulation resistance value) decreases over time during use, and that the heating wire The disadvantage 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 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. required. On the other hand, currently available nickel oxide powders are broadly classified into the following two categories. The first method is by roasting nickel metal powder, and the second method is by roasting various nickel salts. However, when considering application to sheathed heaters,
Each has its own manufacturing drawbacks. In the case of the first method, since the bulk specific gravity is close to that of the electrically insulating powder, it is easily dispersed in the electrically insulating powder, or the nickel oxide powder tends to be segregated 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 aggregation of nickel oxide significantly reduces work efficiency in the production of sheathed heaters, and also causes a decrease in the characteristics of the sheathed heater, especially the withstand voltage and insulation resistance value when heated, leading to defects in the sheathed heater. This is not a desirable factor as it increases the rate. The present invention aims to provide a method for manufacturing a sheathed heater that eliminates manufacturing defects that occur in a method for manufacturing a sheathed heater using electrically insulating powder to which nickel oxide powder is added, and that can achieve the intended purpose. It is something. The manufacturing method of the present invention is characterized by agglomerating nickel oxide particles that have been crushed so that the primary particles are 5 microns or less, producing nickel oxide powder of 250 microns or less by granulation, and producing nickel oxide powder of 250 microns or less. The powder is added to the electrical insulation powder. When the above-mentioned nickel oxide powder is added to electrical insulating powder, it is easily and uniformly dispersed. At this time, since the granulated nickel oxide powder is only agglomerated, it is easily separated to near primary particles and firmly adheres to the surface of the electrically insulating powder. As a result, segregation does not occur even when stress such as vibration is applied. For the above reasons, it is possible to obtain an electrical insulating powder to which nickel oxide is added which has uniform dispersibility and does not cause segregation. For this reason, the segregation and non-uniform dispersion of nickel oxide powder that occur in conventional manufacturing methods that only add nickel oxide powder do not occur, making it possible to significantly reduce the defective rate.
In addition, it is possible to stably produce a sheathed heater with a high insulation resistance value when hot after long-term use, which has not been possible with conventional electrical insulating powders, and which has a long life. Examples of the present invention will be described below. (Example 1) Metallic nickel powder (average particle size 3 to 7 microns) was roasted at 900°C for 2 hours and then ground.
Nickel oxide particles were produced. The nickel oxide particles were classified into three groups: 10 microns or more, 10 microns to 5 microns, and 5 microns or less. Thereafter, the particles were granulated to a size of 250 microns or less using water as a binder to prepare nickel oxide powder. On the other hand, fused magnesia powder is used as the main component of the electrical insulating powder 4, and this fused magnesia powder contains
1 nickel oxide powder produced by the above method
% by weight was added and mixed, and this was prepared as electrical insulating powder 4. 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. Furthermore, as metal pipe 3, length 413 mm, outer diameter 8 mm, wall thickness 0.46 mmNCF2P (product name Incoloy 800)
was used. The heating wire 2 with the terminal rod 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 reduced in diameter and annealed (1050°C, After each process (10 minutes), the length of the metal pipe is 500mm and the outer diameter is 6.6mm, and both ends of the metal pipe are covered with low-melting glass 5.
Then, the sheathed heater was completed by sealing with heat-resistant resin 6. (Example 2) Nickel metal powder (average particle size 3 to 7 microns) was roasted at 900°C for 2 hours, pulverized to 5 microns or less, and then granulated using water as a binder to prepare nickel oxide powder. . In addition, granulation is 420 microns to 350 microns, 350 microns
The measurements were carried out in the following ranges: micron to 297 micron, 297 micron to 250 micron, 250 micron to 177 micron, 177 micron to 105 micron, and 105 micron or less. Thereafter, a sheathed heater was completed in the same manner as in Example 1. (Example 3) After crystallizing nickel sulfate from a nickel sulfate solution, the crystalline nickel sulfate was roasted at 1000°C for 2 hours, pulverized to 5 microns or less, and then granulated to 250 microns or less using water as a binder. Then, nickel oxide powder was prepared. Thereafter, a sheathed heater was completed in the same manner as in Example 1. For comparison, as a conventional example, only electrofused magnesia powder was used as electrical insulating powder 4, and as an example, 1% by weight of commercially available nickel oxide powder produced using metallic nickel powder as a starting material was added. Sheathed heaters were similarly completed using fused magnesia powder, commercially available nickel oxide produced using nickel sulfate as a starting material, and fused magnesia powder to which 1% by weight was added, respectively, as electrical insulating powder 4. The nickel oxide powders to which the completed sheathed heaters of Examples 1 to 3 and the conventional example were added were classified as shown in Table 2 according to the size of the primary particles and the size when granulated. For each completed sheathed heater, the insulation resistance value at room temperature at the initial stage of completion and the insulation resistance value at a pipe surface temperature of 750°C (hereinafter referred to as insulation resistance value at the time of heat), and the withstand voltage at room temperature were measured. When the insulation resistance value is 1MΩ
Below, those with a withstand voltage of 1000V or less were detected as defective products, and the defect rate for each group was determined. The results are shown in Table 2.

[Heat insulation resistance test]

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 during heating 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 results of the heat insulation resistance value after 11 days in the heat insulation resistance test are shown in the third table.
Shown in the table.

[Table] As is clear from Table 2, the defect rate is significantly higher in L and M, which use commercially available nickel oxide powder, than in K, which uses only magnesia powder as electrical insulating powder 4. Despite this, the nickel oxide particles are less than 5 microns,
Groups C, G, H, I, and J in Examples 1 to 3 in which nickel oxide powder granulated to a size of 250 μm or less was added showed almost the same defect rate as K. However, if particles larger than this are used, or if powder larger than 250μ is used due to granulation, the dispersibility will be poor when mixed with magnesia powder, and nickel oxide may exist as large particles or be filled. Nickel oxide powder may segregate in a part of the sheathed heater due to vibrations, etc.
A non-uniform phenomenon was observed, and the defective rate was extremely high in terms of insulation resistance under heat and especially withstand voltage, which became a major problem in manufacturing. On the other hand, in Table 2, C, which had a low defective rate,
A life test and a heat insulation resistance test were conducted on G, H, I, J and the conventional K, and the characteristics of the sheathed heaters were compared. As shown in Table 3, the conventional K using only magnesia powder The lifespan was approximately 10 times longer than that of the previous model, and the insulation resistance value when heated after 11 days was also high. In addition, in Examples 1 to 3, fused magnesia powder was used as the main component of the electrical insulating powder, but
Similar trends were observed when fused alumina powder and fused silica powder were used instead of fused magnesia powder. As is clear from the above description, the method for manufacturing a sheathed heater of the present invention involves pulverizing nickel oxide particles to 5 microns or less and granulating them to 250 microns or less.
This is a manufacturing method in which this is added to electrical insulating powder.
As a result, it is possible to stably provide a sheathed heater that has a long life 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 oxide particles crushed to 5 microns or less are granulated to 250 microns or less, and the electrically insulating powder is used as the electrically insulating powder. A method for manufacturing a sheathed heater, characterized in that the granulated nickel oxide powder is added thereto.