JPH0815113B2 - Manufacturing method of sheathed heater - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sheathed heater that is widely used as a heating source for general household appliances and industrial electric furnaces, and particularly has excellent electrical insulation properties in a humid atmosphere. The present invention relates to a method for manufacturing a middle-high temperature type sheathed heater.

2. Description of the Related Art Conventionally, as a heating source used in a temperature range of 400 ° C. or higher such as an oven, a microwave oven, and an electric stove,
The sheathed heater is widely used.

This type of sheathed heater generally has a coil-shaped heating wire provided with electrical outlet terminals at both ends inserted into the central portion of a metal pipe, and this metal pipe is filled with an electrically insulating powder made of electro-fused magnesia powder. Then, after the rolling was reduced in diameter, an annealing heat treatment was carried out to bend it into a predetermined shape.
Then, the electro-melted magnesia powder was dehumidified, and finally the end portion of the metal pipe was sealed with a low melting point glass and a heat resistant resin.

However, such a sheathed heater has problems such as cracks in the glass sealing portion and complexity of the sealing process.

For this reason, non-sealing and simple sealing of the end portion of the metal pipe have been studied, and an electrically insulating powder obtained by adding a powder made of a CaO-SiO ₂ compound to the electro-fused magnesia powder is used. Sealed with silicone resin (Japanese Patent Publication No. 55-49396), electro-fused magnesia powder, CaO
-B ₂ O ₃ using the electrical insulating powder added a powder consisting of -SiO ₂ based glass, a heat treatment is performed to melt soften the glass, covered with fused magnesia powder (JP-B-56-5036 No. gazette) has been proposed.

On the other hand, in a sheathed heater used at a relatively low temperature, a magnesia powder mixed with a silicone resin as an electrically insulating powder and heated and melted (Japanese Patent Publication No. 527576).
There are also various types of proposals for improving moisture resistance, such as those impregnated with heat resistant oil (silicone oil etc.) (Japanese Patent Publication No. 55-10116).

Invention however a problem to be solved is, in the sheathed heater as described above, the reaction reduced life and by the heating wire and the CaO-SiO ₂ compound in the high temperature _{region, CaO-B 2 O 3 -SiO} 2 based glass solidifies However, there is a problem that a sheath heater having a complicated shape cannot be manufactured due to cracking of the metal pipe due to the bending process after the heat treatment.

On the other hand, a sheathed heater with improved moisture resistance using silicone resin or silicone oil has low heat resistance
0 ~ 500 ℃ is the upper limit of use, and because the stainless steel pipe used as a metal pipe in the medium and high temperature range cannot withstand the annealing heat treatment (around 1050 ℃) and carbonizes, it causes problems such as deterioration of insulation performance. There was a point.

The present invention solves such problems, and an object of the present invention is to provide a method of manufacturing a sheathed heater, which has a relatively easy manufacturing process, has high insulation properties, and can be used in a medium to high temperature range. is there.

Means for Solving the Problems In order to solve the above problems, the present invention includes an insertion step of inserting a heating wire into a metal pipe via an electrically insulating powder,
After the inserting step, an impregnation step of impregnating the electrically insulating powder with silicone oil, a gelation step of gelling the silicone oil, and an annealing heat treatment at a temperature of 800 ° C. or higher due to generation of Joule heat by passing an electric current through the metal pipe. And a annealing step for producing a sheathed heater.

Traditionally, irons, rice cookers, hot plates, etc.
The sheathed heater used in the low temperature region of 400 ° C or less uses ultra-low carbon steel that is extremely hard to work harden as a metal pipe (Japanese Patent Publication No. 59-23232), and uses electro-fused magnesia powder as the electrically insulating powder. It was processed and impregnated with silicone oil.

With such sheathed heaters, since there is no treatment in the temperature range where silicone oil deteriorates during the manufacturing process, this type of sheathed heater exhibits excellent moisture resistance due to the water repellency of silicone oil, and It was simple.

However, if silicone oil is used for sheathed heaters used in the medium to high temperature range of 400 ° C or higher, ultra-low carbon steel has a problem in heat resistance as a metal pipe, and as a result, metal pipes are made of stainless steel and heat and corrosion resistant super Since an alloy is used, work hardening occurs due to rolling reduction in the sheath heater manufacturing process, and therefore annealing heat treatment is required.However, in this annealing heat treatment process, the metal pipe ruptures or deforms due to rapid evaporation of silicone oil. It was impossible to use because it caused various problems such as occurrence of electric shock and deterioration of insulation due to carbide.

The present invention uses the silicone oil, which has hitherto been said to be impossible to be applied to the medium to high temperature region, and is treated under predetermined conditions to gel, and then the metal pipe is treated in an extremely short time. A sheathed heater that has been subjected to a special annealing heat treatment has improved moisture resistance and can be applied to medium and high temperature regions.

Using electro-fused magnesia powder as an electrically insulating powder, filling it according to the conventional manufacturing process, and rolling and reducing the diameter, then impregnating it with silicone oil, or filling it with electro-fusing magnesia powder and then impregnating it with silicone oil. Then, the diameter is reduced by rolling, and a linear sheathed heater is manufactured in which the inside is sufficiently impregnated with silicone oil. In order to sufficiently impregnate the entire inside with the silicone oil, it is possible to impregnate the molten magnesium in a shorter time after the filling while the density of the electrofused magnesia powder is low. When impregnating after rolling impregnation, impregnation for several days is required.

Such a linear sheathed heater is heat-treated to gel the silicone oil. The gelation can be carried out under the conditions of 200 to 400 ° C. for 1 to 4 hours for dimethyl silicone oil and 100 to 250 ° C. for 5 to 30 minutes for methyl hydrogen silicone oil.

Further, the metal pipe of the sheathed heater is subjected to annealing heat treatment. Since the annealing heat treatment causes the above-mentioned problems when the treatment is performed by a conventional electric furnace, means for directly and rapidly generating heat in the metal pipe, that is, annealing heat treatment by generation of Joule heat by directly passing an electric current through the metal pipe, Alternatively, heat treatment such as annealing heat treatment by induction heating using high frequency is performed for several seconds to a predetermined temperature. To anneal
Since heating at 800 ° C or higher is required and the heating time is short, 1050 ° C to 1200 ° C is desirable.

After gelling the silicone oil as described above, by directly heating the metal pipe and performing annealing heat treatment in a short time, the metal pipe does not burst or deform due to rapid evaporation of the silicone oil, and the metal pipe is Since it expands first, a gap is created between the metal pipe and the electrically insulating powder solidified by rolling to form an air layer, and no carbide is generated inside the metal pipe, but it burns and becomes a gas, and goes out. At this time, the silicone oil decomposes into amorphous silica, and this decomposed amorphous silica reacts with the electro-melted magnesia powder to form a reaction layer with excellent moisture resistance on the surface of the electro-melted magnesia powder, and the central portion of the sheathed heater. The gelled silicone oil of (3) does not decompose and becomes water-repellent, and becomes a layer having excellent moisture resistance. Therefore, it is possible to prevent insulation deterioration due to intrusion of moisture in the atmosphere.

When the annealing heat treatment is performed using an electric furnace as in the conventional case,
Even if the silicone oil is gelled, the entire sheath heater is gradually heated, so there is almost no gap between the metal pipe and the electronic insulating powder, and the entire temperature is high, so carbide is formed throughout the sheath heater. As a result, the insulation deteriorates and, of course, lacks moisture resistance, so that it cannot be put to practical use.

Examples Hereinafter, specific examples of the present invention will be described with reference to the drawings.

A heating wire 2 made of a coil-shaped nichrome wire having electrical extraction terminals 1 at both ends is prepared, inserted into the center of a metal pipe 3 made of SUS321, filled with an electrically insulating powder 4 made of electro-fused magnesia powder, and methyl. After dipping in hydrogen silicone oil and impregnating for 10 minutes, the diameter was reduced by rolling to prepare a linear sheathed heater having an outer diameter of φ6.6 mm and a length of 500 mm as shown in the figure.

After heat treatment at 150 ° C for 15 minutes to gel the silicone oil, fix both ends of the metal pipe 3 with clamps and energize for 15 seconds in the city gas combustion gas atmosphere under the condition of 10V200A (2000W). And annealing heat treatment, U
The sheathed heater was completed by bending into a letter shape.

On the other hand, in the same manner as above, after filling with the electrically insulating powder 4 and reducing the diameter by rolling, it was immersed in dimethyl silicone oil for 3 days to impregnate it, and then heat treated at 300 ° C. for 2 hours to gel the silicone oil, 5 with induction heating device using high frequency
Annealing heat treatment was performed in the temperature range up to 1150 ° C for 2 seconds. Induction heating was performed by passing a sheathed heater through the heating coil at a speed of 1 m / min. At this time, a ceramic guide was provided in the heating coil so that it could flow through the center of the heating coil. When it deviates from the center, local heating occurs and the metal pipe 3
In the extreme case, it may melt, and sufficient management was required.

In addition, without impregnating silicone oil in the conventional process,
A sheathed heater filled with electro-melting magnesia was produced, one of which was sealed with a low melting point glass, and the other was completed without sealing, to obtain a comparative sample.

The insulation resistance and the withstand voltage at the initial stage of completion of the four kinds of sheathed heaters thus prepared were measured. Then, put in a humid atmosphere at 40 ° C and 95% relative humidity for 14 days and 30 days.
The insulation resistance after a day was measured and evaluated. The results are shown in Table 1.

As is clear from Table 1, one embodiment of the present invention is shown.
No. 1 and No. 2 showed the same level of moisture resistance as the No. 3 conventional sheathed heater with a glass seal.

Furthermore, while measuring the insulation resistance during heating while using electricity using the sheathed heater, a surface temperature of 800 ° C was used for one cycle of 20 minutes of electricity and 10 minutes of rest. The insulation resistance was measured. This sheathed heater is placed in a humid atmosphere at 40 ° C and 95% relative humidity.
The insulation resistance was measured by leaving it for 14 days and 30 days. Table 2 shows the results.

As is clear from Table 2, one embodiment of the present invention is shown.
In No. 1 and No. 2, the insulation resistance during heat at the initial stage of completion is the same level as the No. 3 conventional sheathed heater with a glass seal,
The insulation resistance during heat after 3000 cycles of durability test is superior to that of No.3 conventional sheathed heater with glass sealing. Furthermore, it was found that the insulation characteristics in a humid atmosphere after the durability test were at the same level as the sheathed heater with a conventional glass seal, and it had durability at 800 ° C.

In this way, the sheathed heater impregnated with silicone oil, gelled by heat treatment, heated the metal pipe 3 and annealed at 800 ° C or higher, has excellent insulation resistance during heat and moisture resistance, and does not require a glass sealing. A low-cost and highly reliable sheath heater can be obtained.

Although methyl hydrogen silicone oil and dimethyl silicone oil were used in the examples of the present invention, other silicone oils such as phenyl silicone oil, methyl / hydroxyl group-containing silicone oil, and methyl / vinyl group-containing silicone oil were used. And so on. Further, the metal pipe 3 is not limited to SUS321 and may be stainless steel or corrosion resistant heat resistant superalloy.

Effects of the Invention As is clear from the description of the above examples, the method for manufacturing a sheathed heater of the present invention is one in which after impregnating silicone oil, the silicone oil is gelated by heat treatment and further annealed at 800 ° C. or higher. Therefore, it is particularly excellent in moisture resistance, and since it can be manufactured by a relatively simple method, it can be provided at a low cost.

[Brief description of drawings]

FIG. 1 is a sectional view of a sheathed heater showing an embodiment of the present invention. 2 ... Heating wire, 3 ... Metal pipe, 4 ... Electrically insulating powder.

Claims (1)

[Claims] 1. An inserting step of inserting a heating wire into a metal pipe through an electrically insulating powder, an impregnating step of impregnating the electrically insulating powder with silicone oil after the inserting step, and a gelling treatment for gelating the silicone oil. 800 ℃ due to the process and Joule heat generated by passing an electric current through the metal pipe
A method for manufacturing a sheathed heater, comprising: an annealing step of performing annealing heat treatment at the above temperature.