JPH0439196B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a sheathed heater that is widely used as a heating source for general cooking appliances, industrial electric furnaces, and the like. Conventional Structure and Problems Sheathed heaters have been widely used as a heating source for general cooking appliances such as toaster ovens, microwave ovens, rice cookers, hot plates, and irons. This is because the sheathed heater is simple and has high safety and excellent corrosion resistance.
By the way, in general cookers equipped with the above-mentioned sheathed heater, sauces containing a large amount of salt are often used for grilled meat, kabayaki, and yakitori. Generally, as shown in Fig. 1, a sheathed heater has a coil-shaped heating wire 2 with terminal rods 1 at both ends inserted into the center of a metal pipe 3, and an electrically insulating powder made of fused magnesia powder is inserted into the metal pipe 3. 4, and both ends of the metal pipe 3 are sealed with low-melting glass 5 and heat-resistant resin 6. The metal pipe 3 of the sheathed heater is made of austenitic stainless steel or iron-based alloy such as SUS321 or NCF800, which has the composition shown in Table 1 and has excellent workability, high-temperature strength, and high-temperature oxidation resistance. However, NCF800, an iron-based alloy, is mostly used.

[Table] However, when using austenitic stainless steels and iron-based alloys such as SUS321 and NCF800, which have traditionally been used as sheathed heaters for yakiniku, kabayaki, and yakitori dishes that use a large amount of seasoning sauce, it is extremely short. In reality, the salt contained in the sauce corrodes the metal pipe over time, causing the heating wire to break, which poses a problem in actual use. Purpose of the Invention The present invention solves the above-mentioned conventional drawbacks and provides a sheathed heater that has a long life even when used as a heating source for cooking dishes such as yakiniku, kabayaki, and yakitori that use sauces. . Structure of the Invention In order to achieve the above object, the present invention provides a coating layer mainly composed of activated silica formed by reactions such as decomposition or dehydration of water glass, colloidal silica, silica sol, organic silicate, etc.
It is installed on the surface of a metal pipe made of an iron-based alloy such as NCF800, and the salt contained in the sauce reacts with activated silica, forming a glass layer on the surface of the metal pipe, so it does not penetrate inside the metal pipe. The reaction of common salt can be suppressed, and as a result, it is possible to provide a sheathed heater with a long life. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to FIG. Note that the same components as in FIG. 1 are given the same reference numerals. In this embodiment, as the metal pipe 3
NCF800 (trade name Incoloy 800) was used. On the other hand, a heating wire 2 made of a coiled nichrome wire (wire diameter 0.55) with terminal rods 1 at both ends is prepared, inserted into the center of a metal pipe 3, and filled with electrical insulating powder 4 made of fused magnesia powder. After rolling and annealing,
Both ends of the metal pipe 3 were sealed with low melting point glass 5 and heat resistant resin 6. After this, a coating layer 7 mainly composed of activated silica is formed on the surface of the metal pipe 3 using water glass, colloidal silica, silica sol, organic silicate, etc. shown in Table 2, and the coating layer 7 is made to have a diameter of 11 mm and a length of 50 mm. of
100V-800W sheathed heaters of the present invention shown in FIG. 2 were prepared and designated as sample numbers 2 to 5. The water glass was diluted with about 10 times as much water, applied with a brush, and then dried at 100°C to form the coating layer 7. Colloidal silica was mixed with an inorganic adhesive (trade name Sumiceram) and dried at 100℃ after application, and silica sol was soaked and dried at 100℃ in the same way as the metal pipe 3. A coating layer 7 was formed on the surface. In addition, an organic silicate was similarly formed by immersing it in an ethyl silicate solution and drying it at 100°C. On the other hand, for comparison, a sheathed heater using a conventional metal pipe 3 of NCF800 without the above-mentioned coating layer mainly composed of activated silica was prepared and designated as sample number 1. In order to test the corrosion resistance of each sheathed heater to salt, the surface temperature of the metal pipe was
The voltage was adjusted to 800°C, and an intermittent energization test was conducted in a cycle of 20 minutes of energization and 10 minutes of rest. However, saturated saline was applied once every 48 cycles. Using the above test method, determine the cycle until each sheathed heater breaks, and use this result as the second test method.
Shown in the table. As is clear from Table 2, the sheathed heater of sample number 1 using the conventional metal pipe made of NCF800 broke after only about 500 cycles.
The sheathed heaters of the present invention of sample numbers 2 to 5, in which a coating layer containing activated silica as a main component was provided on the surface of the NCF800 metal pipe, exhibited long adiabatic cycles of 1500 to 3000 cycles.

[Table] The reason why the effects of the present invention were obtained is that the coating layer mainly composed of activated silica provided on the surface of the metal pipe reacts with the highly corrosive common salt contained in the sauce. It is presumed that this is to prevent the formation of Na ₂ O--SiO ₂ -based glass and the diffusion of common salt into the metal pipe. In the embodiments of the present invention, NCF800 is used as the metal pipe 3, but the metal pipe 3 is not limited to this, and other iron-based alloys may be used. Effects of the Invention As is clear from the above explanation, according to the sheathed heater of the present invention, by providing a coating layer containing activated silica as a main component on the surface of a metal pipe made of an iron-based alloy such as NCF800, dripping can be prevented. It is possible to provide a long-life sheathed heater that can be used as a heating source for cooking equipment such as yakiniku, kabayaki, and yakitori, 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...Coating layer containing activated silica as a main component.

Claims (1)

[Claims] 1 Water glass, colloidal silica, silica sol,
A coating layer mainly composed of activated silica formed by the decomposition or dehydration reaction of organic silicates, etc.
A sheathed heater characterized by being installed on the surface of a metal pipe made of an iron-based alloy such as NCF800.