JPS6185790A - Sea 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 the Invention The present invention relates to a sheathed heater that is widely used as a heating source for general cooking utensils and commercial cooking utensils.

Conventional configuration and its problems 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, as well as commercial cooking appliances such as Kabayaki and Yakiniku grills. . This is because sheathed heaters are simple, highly safe, and have excellent corrosion resistance.

Generally, a sheathed heater uses a coiled heating wire with terminal rods at both ends inserted into the center of a metal pipe.

This metal pipe is filled with electrically insulating powder made of fused magnesia powder, and both ends of the metal pipe are sealed with low-melting 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, K has excellent workability as a metal pipe for sheathed heaters used at relatively high temperatures, and has excellent high-temperature strength and high-temperature oxidation l1C16i! Heat-resistant steels such as 5US321 and NCFSOO are used.

However, under the above-mentioned usage environment, if heat-resistant steel such as 5US321 or NCF 800, which has been used conventionally, is used as a sheathed heater for electric ovens, yakiniku grills, and kahayaki grills, it may cause sauces. The reaction between the contained salt 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, and the reality is that there is an interlayer during actual use. Met.

For this reason, it has already been shown that the corrosion resistance of conventional sheathed heaters against salt can be improved by providing oxide scale on the surface of the metal pipe in advance, and then treating it with a heat-resistant hollow material to form a heat-resistant hollow layer on the surface of the metal pipe. is suggesting.

However, the heat-resistant hollow layer formed by this method is relatively weak against thermal shock, and when water or sauce drips at high temperatures of 700 to 800 degrees Celsius, fine or large racks are formed, resulting in the problem of reduced corrosion resistance. Ta.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned conventional drawbacks and provides a sheathed 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 the metal nozzle, and coats the surface of the metal nozzle with Cr2O3.
B containing 0.1 to 10% by weight of silicon nitride whiskers is provided thereon.
By providing a heat-resistant hollow layer containing aO and S-O2 as main components, it is possible to form a heat-resistant hollow layer that simulates thermal shock resistance, and a 7-Z heater with high corrosion resistance against common salt is made possible.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 1 in comparison with a conventional example.

Example As the metal pipe 3, NCF300 was used.

On the other hand, a coiled nichrome wire (
A heating wire 2 having a wire diameter of 0.551j+) 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 provide the oxide scale layer 7 mainly composed of 0r2O3 on the surface of the metal pipe 3,
Heat treatment was performed at a temperature of 0° C. for 10 minutes.

Note that the atmosphere at this time was a reducing gas containing CO and H2 as main components.

Next, silicon nitride whiskers were added in a range of 0.01 to 16% by weight as shown in Table 1 to a commercially available heat-resistant hollow slip containing BaO and SiO 1CQ was applied and heat treated at 0° C. for 5 minutes to form a heat-resistant hollow layer 8 shown in FIG.

Finally, both ends of the metal pipe 3 were sealed with a low-melting glass 6 and a heat-resistant resin 6 to complete the sheathed heater of the embodiment of the present invention shown in the figure with a diameter of 11 B and a length of 5 mm. And so.

On the other hand, for comparison, a sheathed heater using a conventional metal pipe 3 without a heat-resistant hollow layer 8 and a sheathed heater with a heat-resistant hollow layer 8 that does not contain silicon nitride whiskers were prepared in the same manner. were set to 1 and 2, respectively.

In order to simultaneously test both the corrosion resistance and thermal shock resistance of each of the sheathed heaters mentioned above, the voltage was adjusted so that the surface temperature of the metal pipe 3 reached 800°C, and after the surface temperature was saturated, the 2CQ saturation 1 saline solution every 2 minutes
It was added dropwise at a rate of 3 times.

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.

Note that the above test was conducted with the sheathed heater continuously energized.

The results are shown in Table 1.

As is clear from Table 1, in the sheathed heater of sample number 1 using the conventional metal pipe 3 made of NCF300, pipe cracking occurred after 82 cycles.

In addition, a sheathed heater of sample number 2 provided with a conventional heat-resistant hollow layer 8 containing no silicon nitride whiskers,
Furthermore, in the sheathed heaters of sample numbers 3 and 4 containing 0.1% by weight or less of silicon nitride whiskers, 2O0 to 3
Pipe cracking occurred after 00 cycles.

However, in the sheathed heaters of sample numbers 5, 6, 7, 8, and 9, which were provided with the heat-resistant hollow layer 8 containing silicon nitride whiskers in the range of 0.1% to 10% by weight, long pipes cracked more than 600 times. A significant effect on corrosion resistance was observed.

On the other hand, in the sheathed heater of sample number 10 in which the content of silicon nitride whiskers is 10% by weight or more, the adhesion of the heat-resistant hollow layer 8 decreases, and the heat-resistant hollow layer 8 cracks or peels off after several tens of drops. Therefore, pipe cracking occurred almost as often as in the sheathed heater of sample number 1, and no effect was obtained.

In this way, in the sheathed heater according to the embodiment of the present invention,
The reaction with salt can be suppressed by the heat-resistant hollow layer,
In addition, even if salt water is applied during red heat, the inclusion of silicon nitride whiskers and the formation of an oxide scale layer mainly composed of Cr2O5 increase thermal shock resistance and prevent the heat-resistant hollow layer from peeling off easily. The lifespan of sheathed heaters used in environmental conditions can be significantly increased.

Note that the content of silicon nitride whiskers is preferably in the range of 0.1 to 10% by weight, and in other ranges.

Adhesion becomes weaker, and no improvement in thermal shock resistance is observed.

Also, as heat-resistant hollow materials, those whose main components are BaO and SiO□ have high heat resistance, and Cr2O.

It has good adhesion to the oxide scale layer whose main component is .

In addition, in the embodiment of the present invention, as the metal pipe 3,
Although NGF800 was used, the material is not particularly limited to this, and any other heat-resistant steel such as 5US321 may be used without any problem.

Effects of the Invention As is clear from the above explanation, according to the sheathed heater of the present invention, heat-resistant steel is used as the metal pipe, an oxide scale layer mainly composed of Cr2O and gold is provided on the surface of the metal pipe, and 0.1 silicon nitride whiskers on top
It is a heat-resistant hollow metal whose main components are BaO containing ~10% by weight and 5in2), Yl, and is used for electrolytic corrosion (microwave, grilled meat, It is possible to provide a sheathed heater that has excellent thermal shock resistance even when used as a heating source for cookers for Kabayaki, Yakitori, etc., and has high corrosion resistance against salt, and its value is invaluable.

[Brief explanation of drawings]

The figures show a sectional view and a partially enlarged sectional view of a sheathed heater according to an embodiment of the present invention. 3...Metal pipe, 7...Oxide scale layer, 8...Heat-resistant hollow layer

Claims (1)

[Claims] Heat-resistant steel is used as the metal pipe, and an oxide scale layer containing Cr_2O_3 as the main component is provided on the surface of the metal pipe, and silicon nitride whiskers are further added thereon by 0.1 to 1.
A sheathed heater characterized by providing a heat-resistant hollow layer whose main components are BaO and SiO_2 containing 0% by weight.