JPS60101897A - 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 sheathed heater that is widely used as a heating source for general cooking utensils, industrial electric furnaces, and the like.

Conventional Structure and Problems Conventionally, sheathed heaters have been widely used as a heating source for general cooking appliances such as toaster ovens, microwave ovens, rice cookers, and hot plates.

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

2 bake Also, 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.

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. The metal pipe 3 is filled with powder 4 and both ends of the metal pipe 3 are sealed with low melting point glass 6 and heat resistant resin 6.

In this way, 5US321 and N, which have the compositions shown in Table 1, have excellent workability, high-temperature strength, and high-temperature oxidation properties as metal pipes for sheathed heaters used at relatively high temperatures.
Heat-resistant steel such as CF300 is used.

Below Margin 3 '<--ji Table 1 However, it can be used as a sheathed heater for electric ovens, yakiniku cookers, kabayaki cookers, and yakitori cookers that use a large amount of sauce or are used under conditions where they are exposed to salt water. , traditionally used! 3
When heat-resistant steel such as US3'21 or NCFaoo 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, 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. That was the reality.

For this reason, we paid attention to the hollow treatment described in Japanese Patent Publication No. 58-36821, and while conducting studies, we discovered that the use of hollow treatment has the effect of increasing the corrosion resistance against common salt. .

However, in general, when performing the hollow treatment, it is necessary to perform one of the following base treatments: (1) Nisokelmetal treatment, (2) Plasting treatment, and this is extremely troublesome.

Purpose of the Invention The present invention solves the above-mentioned conventional drawbacks and uses a very simple method, even in an environment where common salt is used.
This provides a sheathed heater with a long life.

Structure of the Invention The present invention provides a heat-resistant hollow layer on the surface of the metal pipe by heat-treating a metal pipe made of heat-resistant steel in advance to form an oxide scale on the surface of the metal pipe, and then treating it with a heat-resistant hollow agent. As a result, the reaction between the salt contained in sauces and metal pipes can be suppressed using a much simpler method than before, making it possible to extend the life of the sheathed heater. It is.

DESCRIPTION OF EMBODIMENTS Hereinafter, a practical example of the present invention will be described with reference to FIG.
This will be explained in comparison with a conventional example.

NCF300 (product name Incoloy 8) as metal pipe 3
00) was used.

On the other hand, a coiled nichrome wire (
A heating wire 2 having a wire diameter of 0.55 mm) was prepared, inserted into the center of a metal pipe 3, filled with electrical insulation powder 4 made of fused magnesia powder, and rolled to reduce its diameter.

After this, in order to form oxide scale on the metal pipe 3, it was heat treated at a temperature of 105°C for 10 minutes, and applied by spraying using a commercially available heat-resistant hole pick and knob.
Heat treatment was performed at 980° C. for 10 minutes to form a heat-resistant hollow layer 7 shown in FIG. 2 on the surface of the metal pipe 3.

Finally, both ends of the metal pipe 30 were sealed with low-melting glass 5 and heat-resistant resin 6 to complete five sheathed heaters of the embodiment of the present invention shown in Fig. 2 with a diameter of 11 m and a length of 6 mm and 500 mm. Sample numbers 6 to 1o were used.

On the other hand, for comparison, samples Nos. 1 to 5 were prepared in the same manner as the sheathed heater using the conventional metal pipe 3 without the heat-resistant hollow layer 7.

In order to test the corrosion resistance of each of the above-mentioned sheathed heaters against salt, the voltage was adjusted so that the surface temperature of the metal pipe 3 was 800°C, and a continuous energization test was conducted in a cycle of 20 minutes of energization and 10 minutes of rest. Ta.

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 2.

As is clear from Table 2 on page 7, the sheathed heaters of sample numbers 1 to 6 using the conventional metal pipe 3 made of NCF 8o○ broke at about 300 to 400 cycles. but,
A heat-resistant hollow layer 7 is placed on the surface of the gold 4 pipe 3 of NCF300.
In the sheathed heaters of sample numbers 6 to 10 of the examples of the present invention provided with the above, a long disconnection life of 360 o 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, blasting, or pickling, which are conventionally performed as a pretreatment when forming a hollow layer. The heat treatment step of annealing or firing, which is one step in the manufacturing process of the sheathed heater, is sufficient and is very simple.

On the other hand, in the examples, a commercially available heat-resistant hollow material was used as the heat-resistant hollow material, but the material is not limited to this.Also, NCF300 was used as the metal pipe 3, but it was also possible to use other heat-resistant hollow materials such as 5US321. There is no particular problem if it is made of steel.

Effects of the Invention As is clear from the above explanation, the present invention has the following advantages. - According to Dajita, a metal pipe made of heat-resistant steel is heat-treated on page 9 to form oxide scale on the surface of the metal pipe, and then treated with a heat-resistant water-blasting agent to form a heat-resistant hollow layer on the surface of the metal pipe. and
To provide a sheathed heater that has a long life even when it is used as a heating source for an electric range used with sauce or salt water, or a cooker for grilled meat, kageyaki, yakitori, etc. can be done, and its value is great.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional sheathed heater, and FIG. 2 is a sectional view of a sheathed heater according to an embodiment of the present invention. 3...Metal pipe, 7...Heat-resistant hollow layer. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
figure

Claims (1)

[Claims] A sheathed heater characterized in that a metal pipe made of heat-resistant steel is heat-treated in advance to form an oxide scale on the surface of the metal pipe, and then treated with a heat-resistant hollow agent to provide a heat-resistant hollow layer on the surface of the metal pipe.