JPH0155554B2 - - 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, 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 metal 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 metal 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, metal oxide powders currently on the market can be broadly classified into the following two categories. The first method is by roasting metal powder, and the second method is by roasting various metal 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 electrical insulating powder, it is easily dispersed in the electrical insulating powder, but segregation of the metal oxide powder is likely to occur 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 metal oxide powder is not preferable because it significantly reduces work efficiency in the production of sheathed heaters and causes a decrease in the characteristics of the sheathed heater, especially the withstand voltage and insulation resistance when hot. do not have. The present invention aims to provide a method for manufacturing a sheathed heater that can eliminate the manufacturing defects that occur in the manufacturing method of a sheathed heater using electrically insulating powder to which metal oxide powder is added, and that can achieve the intended purpose. It is something. The manufacturing method of the present invention is characterized by using a metal oxide powder produced by roasting metal salts, and adding this metal oxide powder to the electrical insulating powder base material in advance at a mixing ratio that is higher than the final concentration. The mixed powder is then added to the electrically insulating powder base material and mixed to obtain a predetermined concentration. As described above, the metal oxide powder obtained by roasting the metal salt has very fine primary particles, but it quickly aggregates into a large powder, which deteriorates the characteristics of the sheathed heater. However, according to the method of the present invention, in advance,
Mix electrical insulating powder and the above metal oxide powder,
After adhering or dispersing these metal oxide powders on the surface of the electrically insulating powder, they are further diluted with the electrically insulating powder base material to the required concentration to prepare the electrically insulating powder. The segregation and agglomeration phenomena observed by using metal oxide powder obtained by roasting metal salts are significantly suppressed. In addition, metal oxide powder is added to electrical insulating powder,
When mixing, it is even better to include a pulverizing process using a grinder, pot mill, etc. Further, the powder used as the electrically insulating powder base material is preferably fused magnesia powder, but in particular, the electrically insulating powder base material in the mixture of the initial metal oxide powder and the electrically insulating powder base material is In addition to fused magnesia powder, silicon oxide, aluminum oxide, or an equivalent electrical insulating powder may be used. For the above reasons, it is possible to stably manufacture 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 Commercially available nickel oxide powder obtained by roasting nickel salt was mixed with fused magnesia powder at a weight ratio of 10
%, and was uniformly ground and mixed using a Raikai machine to prepare a mixed powder. This mixed powder was diluted with fused magnesia powder so that the content of nickel oxide powder was 1% by weight to prepare electrical insulation powder 4. In addition, a first type nichrome wire with a wire diameter of 0.29 mm was used as the heating wire 2, and this was made into a coil shape with a winding diameter of 2 mm.
Terminal bar 1 was connected to both ends. Furthermore, as the metal pipe 3, NCF2P (product name Incoloy) with length 413 mm, outer diameter 8 mm, wall thickness 0.46 mm
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 step (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. Example 2 Commercially available nickel oxide powder produced by roasting nickel salt was blended with fused alumina powder at a weight ratio of 20%, and uniformly ground and mixed using a grinder. A mixed powder was prepared. The content of nickel oxide powder in this mixed powder is
Electrical insulation powder 4 was prepared by diluting it with electrofused magnesia powder to a concentration of 1% by weight. Thereafter, a sheathed heater was completed in the same manner as in Example 1. Example 3 Commercially available nickel oxide powder produced by roasting nickel salt was added to fused silica powder in a weight ratio.
The mixture was blended to a concentration of 30% and uniformly ground and mixed using a grinder to prepare a mixed powder. The content of nickel oxide powder in this mixed powder is
Electrical insulation powder 4 was prepared by diluting it with electrofused magnesia powder to a concentration of 1% by weight. Thereafter, a sheathed heater was completed in the same manner as in Example 1. For comparison, as a conventional example 1, only electrofused magnesia powder was used as the electrical insulating powder 4, and as a conventional example 2, a commercially available nickel oxide powder produced by roasting a metallic nickel powder was used. When using fused magnesia powder to which 1% by weight of is added, and conventional example 3, fused magnesia powder to which 1% by weight of commercially available nickel oxide produced by roasting nickel salt is added as electrical insulating powder 4. Similarly, a sheathed heater was also completed. The insulation resistance value of each completed sheathed heater 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 the insulation resistance value at room temperature) were measured, and the withstand voltage at room temperature was measured. 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 1. In addition, the following life tests and insulation resistance tests were conducted on the sheathed heaters of Examples 1 to 3 and the conventional example, respectively. [Lifetime 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 examined. [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 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 FIG. 2, A indicates the first embodiment, B the second embodiment, C the third embodiment, D the first conventional example, E the second conventional example, and F the third conventional example.

[Table] As is clear from Table 1, Conventional Examples 2 and 3 using commercially available nickel oxide powder were significantly more effective than Conventional Example 1 using only fused magnesia powder as electrical insulating powder 4. Although the defective rate was high, Examples 1 to 3 of the present invention exhibited a defective rate as low as that of Conventional Example 1. Moreover, as is clear from Table 1 and FIG. 2, in the sheathed heaters of Examples 1 to 3 of the present invention,
Compared to conventional example 1, the lifespan is approximately 10 times longer, and
The thermal insulation resistance value after 11 days also showed a high value, and the effects obtained by adding the nickel oxide powder seen in Conventional Examples 2 and 3 were maintained as they were. 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. Further, in the above examples, nickel salt was used, but the same tendency can be obtained even if at least one metal salt selected from the group of cobalt salt, tungsten salt, copper salt, gallium salt, tin salt, and iron salt is used. Indicated. As is clear from the above explanation, a metal oxide powder obtained by roasting nickel salt is mixed with an electrically insulating powder base material, and this is further mixed with the electrically insulating powder base material to be used as an electrically insulating powder. By the method of manufacturing a sheathed heater of the invention, 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]

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. In a method for manufacturing a sheathed heater, which involves inserting a heating wire into a metal pipe and filling it with electrically insulating powder, the method comprises: A metal oxide produced by roasting at least one selected metal salt is mixed into an electrically insulating powder base material,
A method for producing a sheathed heater, characterized in that a mixture of this powder and an electrically insulating powder base material is used as the electrically insulating powder.