JPS60218785A - 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 cookers, microwave ovens, rice cookers, and hot plates.

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

However, 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. In general, a sheathed heater is constructed by inserting a coiled heating wire 2 with terminal rods 1 at both ends into the center of a metal pipe 3, as shown in FIG. 4 and sealing both ends of the metal pipe 3 with low melting point glass 6 and heat resistant resin 6. 'In this way, heat-resistant steels such as 5US321 and NC-F2O3, which have the composition shown in Table 1 and have excellent workability, high-temperature strength, and high-temperature oxidation resistance, can be used as metal pipes for sheathed heaters used at relatively high temperatures. is used.

Table 1 However, the 5U conventionally used as a sheathed heater for electric ovens, yakiniku cookers, gabayaki cookers, and yakitori cookers that use a large amount of sauce or are exposed to salt water.
When heat-resistant steel (7) such as S321 and NCF300 is used, the reaction between the salt contained in the sauce and the metal pipe proceeds 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 rapidly progresses, causing the heating wire to break, which poses a problem in actual use. That was the reality.

For this reason, while paying attention to and studying the hollowing treatment described in Japanese Patent Publication No. 58-36821, it was discovered that the use of hollowing treatment has the effect of increasing the corrosion resistance against common salt.

However, in general, when performing the hollow treatment, a base treatment of either (1) nickel plating treatment or (2) plasting treatment is required, which is extremely troublesome.

Further, the hollow layer formed using a general hollow material has various problems such as easy peeling and softening when used in a high temperature range of 7oO to 800°C.

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

Structure of the Invention The present invention involves inserting a coiled heating wire into the center of a metal pipe made of heat-resistant steel, filling it with electrical insulating powder made of magnesia powder, and rolling it in a reducing atmosphere at 1060°C to 1100°C. After heat treatment is performed to form a dense oxide scale containing chromium oxide as a main component on the surface of the metal pipe, a heat-resistant hollow material containing barium oxide and silicon oxide as main components is applied to the surface of the metal pipe. 96 later
It is fired in an air atmosphere at a temperature of 0°C to 1100°C to form a heat-resistant hollow layer with a thickness of 30 to 100 microns on the surface of the metal pipe. As a result, it is different from the conventional sheathed heater manufacturing process. Using almost the same very simple method, it is possible to control the reaction between the salt contained in sauce and the metal pipe, and it is possible to extend the life of the sheathed heater.0 Description of Examples Hereinafter, embodiments of the present invention will be described in comparison with a conventional example with reference to FIG.

NCFsoo (trade name Incoloy 800) was used as the metal pipe 3.

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

Thereafter, heat treatment was performed in a reducing atmosphere at 105° C. for 10 minutes to form a dense oxide scale containing chromium oxide as a main component on the surface of the metal pipe 3.

Next, a heat-resistant hollow slip whose main components are barium oxide and silicon oxide is applied to the surface of the metal pipe 3 on which the oxide scale has been formed by spraying.
A heat-resistant hollow layer 7 having a thickness of 30 to 100 microns as shown in FIG.
was formed on the surface of the metal pipe 3.

Finally, both ends of the metal pipe 3 are sealed with low-melting glass 5 and heat-resistant resin 6, and a diameter of 11 cylinders and a length of 500 tan is formed.
Six sheathed heaters according to the embodiment of the present invention shown in FIG. 2 were completed and designated as sample numbers 6 to 10.

On the other hand, for comparison, sheathed heaters provided with a heat-resistant hollow layer 7 were completed according to a conventional sheathed heater manufacturing method, and were designated as sample numbers 1 to 6.

In order to test the corrosion resistance of each of the above 7-Z heaters against salt, the surface temperature of the metal tube 3 was set to 800°.
The voltage was adjusted to CK, and an intermittent energization test was conducted in a cycle of 20 minutes of reverse energization and 10 minutes of rest.

However, saturated saline 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. Indicated.

As is clear from Table 2 below, the sheathed heaters of sample numbers 1 to 6 using the conventional metal pipe 3 made of NCF300 broke at about 300 to 400 cycles, but the NC
In the sheathed heaters of sample numbers 6 to 1o of the examples of the present invention in which a heat-resistant hollow layer was provided on the surface of the metal pipe 30 of F300, a long disconnection life of 35oO cycles or more was obtained. In the sheathed heater obtained by the sheathed heater manufacturing method according to the example, reaction with common salt can be suppressed by the hollow layer, and the life of the sheathed heater used in such an environment can be significantly extended.

In addition, according to the manufacturing method of this embodiment, there is no need to carry out special treatments such as nickel plating, plasting, or pickling, which are conventionally performed as a pretreatment when forming a hollow layer, and it is not necessary to carry out special treatments such as nickel plating, plasting, or pickling. Annealing or dehumidification, which is one step in the manufacturing process of the heater, is sufficient and very simple.

On the other hand, when the thickness of the heat-resistant hollow layer is 30 microns or less,
It is not very effective for corrosion resistance, and on the other hand, if it is 100 microns or more, it will be weak against thermal shock and the hollow layer will peel off, so 30 to 100 microns is just right.

As for the components of the hollow material, it is best to use a quantized barium-silicon oxide main composition having a high softening temperature in terms of workability.

In addition, in the embodiment of the present invention, the metal pipe 3 is NC
Fsoo was used, but it is not limited to this, and other 5US321, 5US304 or NCF6
There is no particular problem with heat-resistant steel such as 0.00. 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 fill-shaped electric wire is formed in the center of a metal pipe made of heat-resistant steel. Insert a hot wire, fill with electrical insulating powder made of magnesia powder, and after rolling, 1060° and 110σ
After heat treatment in a reducing atmosphere of C (() to form a dense oxide scale mainly composed of chromium oxide on the surface of the metal pipe, a heat-resistant hollow material containing barium oxide and silicon oxide as the main components was heated. It is applied to the surface of a metal pipe. After that, it is fired in an air atmosphere at 960"C to 11oO"C to form a heat-resistant hollow layer with a thickness of 30 to 10 microns on the surface of the metal pipe, and it does not cause any sag, etc. It is possible to provide a method for manufacturing a sheathed heater that has a long life even when used as a heating source for electric ovens used under conditions where salt water is exposed, or cookers for yakiniku, kabayaki, yakitori, etc. Its value is great0

[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. 2...Heating wire, 3...Metal pipe, 4
...Electrical insulating powder, 7...Heat-resistant hollow layer. Name of agent: Patent attorney Toshio Nakao and one other person/Figure 1 Figure 2

Claims (1)

[Claims] After inserting a heating wire and filling with electrical insulating powder made of magnesia powder and rolling, heat treatment is performed in a reducing atmosphere of 106o'C to 1100"C, and the surface of the metal pipe is coated with a dense powder mainly composed of chromium oxide. After forming an oxide scale, a heat-resistant hollow material containing barium oxide and silicon oxide as main components is applied to the surface of the metal pipe.
A method for producing a sheathed heater, which is formed by firing in an air atmosphere at a temperature of 1100 to 1100C to form a heat-resistant hollow layer having a thickness of 3 to 100 microns on the surface of a metal pipe.