JPS6362075B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sheathed heater and a method for manufacturing the same, and particularly aims to provide 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, 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 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, 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. The first method has a bulk specific gravity close to that of the electrically insulating powder and is therefore easily dispersed in the electrically insulating powder. However, 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, work efficiency is significantly reduced, and the characteristics of sheathed heaters
In particular, this is not preferable because it causes a decrease in withstand voltage and insulation resistance value when heated. The present invention aims to provide a sheathed heater and a method for manufacturing the same that can eliminate the manufacturing defects that occur when using electrically insulating powder containing nickel oxide powder and achieve the intended purpose. . A feature of the present invention is that a nickel oxide powder produced by roasting nickel salt is used as the nickel oxide powder, and at least one kind selected from aluminum oxide, iron oxide, and chromium oxide is added to the nickel oxide powder. The process involves adding oxides and firing them. Nickel oxide powder produced by roasting nickel salt is a highly reactive powder with very small primary particles. This nickel oxide powder, aluminum oxide,
When iron oxide or chromium oxide is added and fired, it easily reacts and forms on the surface of the nickel oxide particles.
A compound layer with the above oxide is formed, and the surface of the nickel oxide particles is modified and stabilized. As a result, the agglomeration phenomenon, which was a drawback of nickel oxide powder obtained by roasting nickel salt, is suppressed, and by using this nickel oxide powder,
It is possible to obtain a homogeneous electrical insulating powder, and it is possible to prevent the deterioration of withstand voltage and the decrease in insulation resistance value when heated when completed, which were observed when using conventional commercially available nickel oxide powder. For these reasons, it is possible to stably 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 1) Aluminum oxide, iron oxide,
Alternatively, chromium oxide was blended to have the composition ratio shown in Table 2, and the mixed powder was fired at 1200°C. After firing, it was ground to 250 microns or less to prepare nickel oxide powder. On the other hand, fused magnesia powder was used as the main component of electrical insulating powder 4, and 1% by weight of nickel oxide powder produced by the above method was added and mixed to this fused magnesia powder to prepare 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. 1 type is used, and 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, the length is 413mm, the outer diameter is 8mm, and the wall thickness is 0.46mmNCF2P (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 sintered (1050°C). , 10 minutes), the metal pipe 3 was made to have a length of 500 mm and an outer diameter of 6.6 mm, and both ends of the metal pipe 3 were coated with low-melting glass 5.
Then, the sheathed heater was completed by sealing with heat-resistant resin 6. For comparison, Conventional Example 1 uses only fused magnesia powder as electrical insulating powder 4, and Conventional Example 2 uses commercially available nickel oxide powder produced by roasting metallic nickel powder. 1% by weight of fused magnesia powder was used as electrical insulating powder 4, and conventional example 3 used fused magnesia powder to which 1% by weight of commercially available nickel oxide produced by roasting nickel salt was used for electrical insulation. The powder used as Powder 4 was completed. For each completed sheathed heater, the insulation resistance value at room temperature at the initial stage of completion, insulation resistance value at pipe surface temperature of 750℃ (hereinafter referred to as insulation resistance value at room temperature), and withstand voltage at room temperature were measured. 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. In Table 2, sample number 1 indicates conventional example 1, sample number 2 indicates conventional example 2, and sample number 3 indicates conventional example 3.

[Table] As is clear from Table 2, the sheathed heaters of sample numbers 2 and 3 using commercially available nickel oxide powder are more effective than sample 1, which uses only fused magnesia powder as electrical insulating powder 4. , Despite the markedly high defective rate, sample numbers 9~
Sheathed heater No. 23 showed a similar low defect rate as sample number 1. However, for sample numbers 4 to 8, no effect was observed on the defective rate. This is assumed to be due to the following reasons. If the amount of various oxides such as aluminum oxide, iron oxide, and chromium oxide added, which act as modifiers on the surface of nickel oxide powder, is less than 0.05%, the modification of nickel oxide particles will be insufficient, and conventional nickel oxide powder will This is because the aggregation phenomenon cannot be suppressed. (Example 2) Aluminum oxide, iron oxide, or chromium oxide is added to nickel oxide powder obtained by roasting nickel salt.
Samples 10, 16, 18, and 20 were blended to have the composition ratio shown in the table, and these mixed powders were fired at a temperature of 700°C to 1500°C. After firing, it was ground to 250 microns or less to prepare nickel oxide powder. Thereafter, a sheathed heater was completed in the same manner as in Example 1. The defect rate of each completed sheathed heater was determined in the same manner as in Example 1, and is shown in Table 3.

[Life test]

For each sheathed heater, 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 investigated. [Insulation resistance value test when heated] For each sheathed heater, 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 fourth table.
Shown in the table. Further, FIG. 2 shows the change in the insulation resistance value during heat as a result of the above-mentioned insulation resistance value test during heat. In Figure 2, A is sample 10 and B is sample 10.
16, C indicates sample 18, D indicates sample 20, and E indicates sample 1.

[Table] As is clear from Table 4 and Figure 2, the lifespan is approximately 10 times longer than that of Sample 1, which is a conventional example, and the thermal insulation resistance value after 11 days is also higher. The effect obtained by adding nickel oxide powder was maintained. In the examples, fused magnesia powder was used as the main component of the electrical insulating powder, but similar trends were observed when fused alumina powder or fused silica powder was used instead of fused magnesia powder. . As is clear from the above description, according to the present invention, at least one oxide selected from aluminum oxide, iron oxide, and chromium oxide is mixed with nickel oxide powder produced by roasting nickel salt, By firing to produce stable nickel oxide powder and using electrical insulating powder to which this stable nickel oxide powder is added, a sheathed heater with a long life and high insulation resistance when hot after long-term use can be made stable. and can be provided.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a typical sheathed heater, Figure 2
The figure is a time characteristic diagram of the insulation resistance value at the time of heat in the sheathed heater of the embodiment of the present invention and the sheathed heater of the conventional example. 2... Heating wire, 3... Metal pipe, 4... Electrical insulation powder.

Claims (1)

[Claims] 1. A sheathed heater in which a heating wire is inserted into a metal pipe and the electrically insulating powder is filled with at least one kind selected from the group of aluminum oxide, iron oxide, and chromium oxide as the electrically insulating powder. A sheathed heater made of nickel oxide stabilized by the oxide of. 2 In a sheathed heater formed by inserting a heating wire into a metal pipe and filling it with electrically insulating powder, at least one oxide selected from the group of aluminum oxide, iron oxide, and chromium oxide and nickel salt are roasted. mixed with nickel oxide,
A method for manufacturing a sheathed heater, characterized in that a stable nickel oxide powder is produced by firing, and an electrical insulating powder to which this stable nickel oxide powder is added is used.