JPS6185792A - Manufacture of sheathed heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a sheathed heater, which is widely used as a heating source for general cooking utensils and commercial cooking utensils.

Conventional structure and its problems Sheathed heaters have been widely used as a heating source for general cooking utensils such as toaster ovens, microwave ovens, rice cookers, and hot plates, as well as commercial cooking utensils such as Kabayaki and baked pottery. .

This is because the sheathed heater is simple, safe, and has excellent corrosion resistance.

In general, a 7-Z heater inserts a coiled heating wire with terminal rods on both sides into the center of a metal pipe, fills the metal pipe with electrically insulating powder made of fused magnesia powder,
Roll to reduce diameter. Thereafter, it is manufactured by sealing with low melting point glass and heat resistant resin.

On the other hand, recently, electric ovens and cookers such as yakiniku, kabayaki, and yakitori, which use sauces containing a large amount of salt or are used under conditions where they are exposed to salt water, have become widely available. A sheathed heater is also used as a heating source. In this way, 7
-5US321 and NGF800, which have excellent workability, high-temperature strength, and high-temperature oxidation, are used as metal pipes for heaters.
Heat-resistant steels such as

However, under the above-mentioned usage environment, if heat-resistant steels such as S[Ta205 and NCF 800, which have been used conventionally, are used as sheathed heaters for electric ovens, yakiniku cookers, and Kabayaki cookers, dripping may occur. The reaction between the salt contained in such foods and metal pipes progresses in an extremely short period of time, causing cracks in the metal pipes.

Furthermore, following the above reaction, salt enters through cracks in the metal pipe, and the reaction between the heating wire and the salt progresses rapidly, causing the heating wire to break, which poses a problem in actual use. Ta.

For this reason, by applying an oxide scale to the surface of the metal pipe in advance through annealing treatment, which is one of the processes for manufacturing a sheathed heater, and then treating it with a heat-resistant hollow material to form a heat-resistant hollow layer on the surface of the metal vibrator. has already proposed that the corrosion resistance of conventional sheathed heaters to salt can be improved.6 However, the heat-resistant hollow layer formed by this method
It is relatively weak against water, and if water or sauce drips at high temperatures of 700 to 800°C, fine or large racks will occur.
A problem arose in that corrosion resistance decreased.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned conventional drawbacks and provides a complete method for manufacturing a 7-Z heater that has excellent thermal shock resistance and high corrosion resistance against common salt.

Structure of the Invention In order to achieve the above-mentioned object, the present invention uses heat-resistant steel as a metal pipe, and after filling and rolling diameter reduction, the surface of the metal pipe is blasted and annealed, and bent into a predetermined shape. . After that, a heat-resistant hollow layer is formed on the surface of the metal pipe by treating it with a heat-resistant hollow material, and the oxide scale with excellent adhesion formed by blasting and annealing is bonded between the metal pipe and the heat-resistant hollow material. It is possible to manufacture a sheathed heater that has excellent thermal shock resistance and high corrosion resistance against salt by increasing the bonding between the layers. This will be explained in comparison.

Example: N c F 800 (trade name: Incoloy 80o) was used as the metal pipe 3. On the other hand, a heating wire 2 made of a coiled nichrome wire (wire diameter 0.5511+) with terminal rods 1 at both ends was prepared. It was then inserted into the center of a metal pipe 3, filled with electrical insulating powder 4 made of electrofused magnesia powder, and rolled to reduce its diameter.

Afterwards, it is sand blasted with molten alumina,
Subsequently, an annealing treatment was performed at a temperature of 1050'C for 10 minutes, and a commercially available heat-resistant hollow slip mainly composed of BaO and 5in2 was applied by spraying.
Heat-treated at 80°C for 10 minutes to form the heat-resistant hollow layer 7 shown in the figure.
was formed on the surface of the metal pipe 3.

Finally, both ends of the metal pipe 3 are sealed with low melting point glass 6 and heat resistant resin 6, and the diameter is 11,501 mm. Length 6oOII
Six sheathed heaters of the embodiment of the present invention shown in Figure II were completed and designated as sample numbers 11 to 16.

On the other hand, for comparison, a sheathed heater using a conventional metal pipe 3 without a heat-resistant hollow layer 7 was prepared, and in particular, an oxide scale was formed only by annealing without blasting, and then heat-resistant hollow was applied. Six sheathed heaters each provided with a heat-resistant hollow layer were prepared, and the sample numbers were 1 to 6 and 6 to 10, respectively.

In order to simultaneously test both the salt corrosion resistance and thermal shock resistance of each of the above 7-Z heaters, the voltage was adjusted so that the bare surface temperature of the metal pipe 3 became Boo" (:, and after the surface temperature was saturated, , 2CG of saturated saline was added dropwise once every 2 minutes.

Continue dripping until the metal pipe 3 cracks,
Thermal shock resistance and corrosion resistance were evaluated by determining the number of drops that caused pipe cracking.

The results are shown in Table 1.

As is clear from Table 1, the conventional NCFso.

In the sheathed heaters of sample numbers 1 to 6 using metal pipes 3 made of For the sheathed heaters with sample numbers 6 to 10, 3Q○~
The pipe cracked within 400 cycles.

On the other hand, in the sheathed heater manufactured by the manufacturing method of the present invention, pipe cracking occurred after more than eoo cycles, and a remarkable effect was observed.

This is because the heat-resistant hollow layer 7 created by the conventional manufacturing method using only annealing treatment is weak against thermal shock, and when evaluated using the above test method, cracks have already appeared in the heat-resistant hollow layer 7 after about 200 times, resulting in poor corrosion resistance. decreases.

However, in the manufacturing method of the present invention, the oxide scale formed on the surface of the metal nozzle 3 is 0r20. The film layer, which is the main part of f, is formed of plasto in an uneven state and is richer in 0r20° compared to the case of oxide scale formed only by conventional annealing treatment, so the heat-resistant hollow layer 7 and The adhesion of the material is greatly increased, the material is resistant to thermal shock, and as a result, the corrosion resistance is also improved.
Although sandblasting was performed, the method is not particularly limited to this, and shortblasting may also be used.

Further, as the heat-resistant hollow material, a material whose main components are B&0 and 5in2 was used, but other heat-resistant hollow materials may also be used.

On the other hand, in the embodiments of the present invention, bending was not particularly performed, but if bending is performed, it may be performed after performing the blasting and annealing treatments.

Effects of the Invention As is clear from the above explanation, according to the method for manufacturing a 7-Z heater of the present invention, heat-resistant steel is used as the metal pipe,
After filling and rolling to reduce the diameter, the surface of the metal pipe is subjected to a blast treatment and annealing treatment, and then bent into a predetermined shape. After this,
By treating with a heat-resistant hollow material, a heat-resistant hollow layer is provided on the surface of the metal pipe, and it is possible to provide a method for manufacturing a 7-Z heater that has excellent thermal shock resistance and high corrosion resistance against common salt. Value is great.

[Brief explanation of the drawing]

The figure is a sectional view of a sheathed heater according to an embodiment of the present invention.

Claims (1)

[Claims] Heat-resistant steel is used as the metal pipe, and after filling and rolling,
A sheathed heater characterized in that the surface of the metal pipe is blasted and annealed, bent into a predetermined shape, and then treated with a heat-resistant hollow material to provide a heat-resistant hollow layer on the surface of the metal pipe. Production method.