JPS6119089A - Method of producing 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, industrial electric furnaces, and the like.

Conventional Structure and Problems Sheathed heaters have been widely used as heating sources for general cooking appliances such as open stoves, microwave ovens, rice cookers, and hot plates.

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

Generally, a sheathed heater has a coiled heating wire 2 with terminal rods 1 at both ends inserted into the center of a metal pipe 3, as shown in FIG. , and both ends of the metal pipe 3 are sealed with low melting point glass 6 and heat resistant resin 6.

On the other hand, recently electric ovens, yakiniku, and kabayaki have become popular.

Using a sauce containing a large amount of salt such as yakitori,
Cooking appliances that can be used under saline conditions are widely available in the market, and sheathed heaters are also used as the heating source for these appliances.

Heat-resistant steels such as 5US321 and NCF300, which have excellent workability, high-temperature strength, and high-temperature oxidation resistance, are used as metal pipes for sheathed heaters used at relatively high temperatures.

However, the 5U, which has traditionally been used as a sheathed heater for electric ovens, yakiniku cookers, kabayaki molds, and yakitori cookers that use a large amount of sauce or are exposed to salt water,
When heat-resistant steel such as S321 or NCF 800 is used, the reaction between the common salt contained in the sauce and the metal pipe progresses in an extremely short period of time, causing cracks in the metal pipe.

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

For this reason, the authors have already begun to pay attention to hollowing treatment, and have begun using sheathed heaters without performing special surface treatments such as nickel plating and blasting, which have traditionally been used as pretreatments for hollowing. The corrosion resistance against common salt is improved through a relatively simple manufacturing method in which oxide scale is formed on the surface of the metal pipe through the annealing process, which is a step in the manufacturing process of I am proposing that it can be done.

However, the above manufacturing method cannot be applied to items with dimensions or shapes that do not require a firing furnace, or items with complex shapes, and requires a large firing furnace or special heater fixing jig, which significantly increases costs. ,There's a problem.

OBJECTS OF THE INVENTION The present invention provides a method for manufacturing a sheathed heater with a long life even in an environment where common salt is used, by a simple method, and which eliminates the above-mentioned conventional drawbacks.

Structure of the Invention The present invention involves positioning a coiled heating wire in the center of a metal pipe made of heat-resistant steel, filling the gap between the metal pipe and the heating wire with electrical insulating powder made of magnesia powder, and performing heat treatment after rolling to reduce the diameter. Then, an oxide scale is formed on the surface of the metal and pipe, and the pipe is bent into an arbitrary shape.

After this, the hollow material is applied to the surface of the metal pipe, a predetermined current is applied to both ends of the metal pipe, and the metal pipe is heated by Joule heat, thereby firing the hollow material and forming a hollow layer on the surface of the metal pipe. As a result, a hollow layer can be formed in a very simple method even in a sheathed heater with an extremely complicated shape or size that cannot be placed in an electric furnace, and it is possible to form a hollow layer using a very simple method. Since the reaction between the salt and the metal pipe can be suppressed, it is possible to manufacture a sheathed heater with a long life.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to FIGS. 2 and 3.

Metal pipe 3 has an outer diameter of smm and a length of 1600mm.
CFsoo (trade name Incoloy 800) was used.

On the other hand, a coiled nichrome wire (
A heating wire 2 with a wire diameter of 0.55 mrn is prepared, inserted into the center of a metal pipe 3, filled with electrical insulation powder 4 made of magnesia powder, and reduced in diameter by rolling to an outer diameter of 6.6 m.
m, length 2,000 (11+11).

Thereafter, in order to form oxide scale on the metal pipe 3 and to bend it, it was heat treated at a temperature of 1000°C for 10 minutes, and bent as shown in FIG.

Subsequently, using a commercially available heat-resistant hollow slip, the coating was applied by spraying, leaving both ends of the metal pipe 3 (a=3 omm portions) intact.

Next, as shown in FIG.
Then, sandwich both ends (part a) of the bent sheathed heater, adjust the applied voltage with the voltage regulator 11 so that the surface temperature of the metal pipe 3 is 1000°C, and heat-treat for 3 minutes to bake the hollow material. A hollow layer 7 was formed on the surface of the metal pipe 30.

Finally, both ends of the metal pipe 3 were sealed with a low-melting glass 5 and a heat-resistant resin 6 to complete six sheathed heaters according to the embodiment of the present invention shown in FIG. 2, designated as sample numbers 6 to 10.

On the other hand, for comparison, sheathed heaters having the shape shown in FIG. 2 using a conventional metal pipe 3 without a hollow layer 7 were prepared according to a conventional manufacturing method, and designated as sample numbers 1 to 5.

In order to test the corrosion resistance of each sheathed heater against salt, the surface temperature of the metal pipe 3 was set at 800'C.
A continuous energization test was conducted using a cycle of 20 minutes of reverse energization and 10 minutes of rest.

However, the saturated saline solution was applied to the metal pipe 3 of the sheathed heater once every 48 cycles.

Using the above test method, the cycles until each sheathed heater broke were determined, and the results are shown in Table 1.

(Left below) Table 1 As is clear from Table 1, the sheathed heaters of sample numbers 1 to 6 using the conventional metal pipe 3 made of NCF300 broke at about 3oo to 400 cycles, but the Joule heat In the sheathed heaters of sample numbers 6 to 1o of the examples of the present invention, in which the hollow layer 7 was provided on the surface of the metal pipe 3 made of NCF 800 by a firing method using heat generation of 3.5
A long disconnection life of 00 cycles or more was obtained.

In this way, in the sheathed heater according to the embodiment of the present invention,
Reaction with common salt can be suppressed by the hollow layer, and the lifespan of sheathed heaters used in such environments can be significantly extended.

Furthermore, according to the manufacturing method of this embodiment, there is no need to perform special treatments such as nickel plating, plasting, or pickling, which are conventionally performed as a pretreatment when forming a hollow layer. Annealing, which is one step in the manufacturing process of the sheathed heater, is sufficient and is very simple.

Furthermore, in the firing of hollow metal, a large furnace or the like is not required, and a small-capacity transformer is required, which is economical, and even heaters with complicated shapes or extremely long dimensions can be fired easily.

For example, the metal pipe 3 has an outer diameter of 6.6 mm and a length of 3.
When it is desired to raise the surface temperature to 1 oOo'C and fire the hollow material using a material made of 5US321 with a diameter of 0.00 mm, the result is as shown in Table 2, and a small-capacity transformer is sufficient.

Table 2 Specific resistance value of 5US321 70X10 Ω・σ10
Watt surface density at 00°C 1o W/, J Required power eoo w Required current 141A Required voltage 4.2V On the other hand, although a commercially available enameled material was used as the enameled material in the example, it is not limited to this. Although NCF300 was used as the metal pipe 3, there is no particular problem with this as long as it is a heat-resistant steel such as 5US321.

Furthermore, the manufacturing method of the present invention is not only applicable to firing hollow materials, but can also be widely applied to general surface treatments of metal pipes 3 of sheathed heaters, such as heat treatment of heat-resistant paints and heat-treated heat-resistant inorganic adhesives. be.

Furthermore, since the applied hollow layer is heated from the inside, this method has the advantage that it has fewer defects such as pinholes and blowholes, and can produce a film of extremely high quality. .

Effects of the Invention As is clear from the above explanation, according to the method for manufacturing a sheathed heater of the present invention, a coiled heating wire is positioned in the center of a metal pipe made of heat-resistant steel, and the gap between the metal pipe and the heating wire is reduced. The metal pipe is filled with electrically insulating powder made of magnesia powder, rolled to reduce its diameter, and then heat treated to form an oxide scale on the surface of the metal pipe and bent into an arbitrary shape.

After this, the hollow material is applied to the surface of the metal pipe, and a predetermined current is applied to both ends of the metal pipe, causing the metal pipe to generate heat using Joule heat, thereby firing the hollow material and forming a hollow layer on the surface of the metal pipe. Even if it is used as a heating source for cooking appliances such as electric ovens that are used in conditions such as using sauces or salt water, or cooking equipment such as Yakiniku, Kabayaki, Yakitori, etc., it will not last long. It is possible to provide a manufacturing method for long-lasting sheathed heaters, and its value is great.

[Brief explanation of drawings]

Figure 1 is a sectional view of a conventional sheathed heater, Figure 2 (a)
, (b) shows an external view and a partially enlarged view of a sheathed heater according to an embodiment of the present invention. FIG. 3 is a plan view showing the Joule heating principle in one embodiment of the present invention. 2...Heating wire, 3...Metal pipe, 4
・・Electric insulating powder, ・・・・ Holo layer.

Claims (1)

[Claims] A coiled heating wire is placed in the center of a metal pipe made of heat-resistant steel, the gap between the metal pipe and the heating wire is filled with electrical insulating powder made of magnesia powder, and the diameter is reduced by rolling, followed by heat treatment. Then, an oxide scale is formed on the surface of the metal pipe, and the metal pipe is bent into an arbitrary shape. After this, the hollow material is applied to the surface of the metal pipe, a predetermined current is applied to both ends of the metal pipe, and the metal pipe is heated by Joule heat, thereby firing the hollow material and forming a hollow layer on the surface of the metal pipe. A method for manufacturing a sheathed heater characterized by: