JPH0147870B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a far-infrared heater that is used as a heat source for space heaters, cookers, drying equipment, etc., and that efficiently radiates far-infrared rays. Conventional configurations and problems Conventional far-infrared heaters that emit far-infrared rays include infrared lamps, ceramics with heating wires embedded and fired, and sheathed heaters with far-infrared radiation layers formed on the surface. However, from the viewpoint of radiation characteristics, mechanical strength, and longevity, many sheathed heaters were manufactured with a far-infrared radiation layer formed on the surface. Generally, in a sheathed heater, as shown in Fig. 1, a coiled heating wire 2 with terminal rods 1 at both ends is inserted into a metal pipe 3, and this metal pipe 3 is filled with electrically insulating powder 4 such as fused magnesia. If necessary, cover both ends of the metal pipe 3 with glass 5 or heat-resistant resin 6.
It was sealed. On the other hand, as a far-infrared heater, there was one in which a far-infrared radiation layer 7 was formed on the surface of a sheathed heater, as shown in FIG. and far infrared radiation layer 7
In this case, the zircon content should be 60% or more.
A fired mixture of oxides such as Fe ₂ O ₃ , CoO, NiO, Cr ₂ O ₃ , MnO ₂ and clay, or a mixture of elements from group 2 of the periodic table and elements from group 3 of the periodic table. There were compounds containing 30% by weight or more of complex compounds with elements and complex oxides selected from the group of zirconium silicate. However, the former, which is mainly composed of zircon,
Since it is a type of porcelain, it is mechanically weak and cracks occur during cooling and heating cycles of 500°C or higher, which is unfavorable in terms of lifespan.There was also a problem that the emissivity in the wavelength region of 8 μm or less was low. In addition, the latter containing a complex oxide,
There was a large difference in coefficient of thermal expansion from metal, which caused peeling and cracking during cooling and heating cycles, which was an undesirable problem in terms of lifespan. The present invention solves these conventional problems and has a high emissivity in the far infrared region, is thermally stable even when used in high temperature regions up to 800°C, has excellent adhesion to metals, and has a high emissivity in the far infrared region. The present invention aims to provide a far-infrared heater that can sufficiently withstand cycles. Structure of the Invention The present invention uses metallic nickel powder as a far-infrared emitting material after being roasted at a temperature of 800°C or higher.
This product uses nickel oxide powder crushed to a size of 10μ to 44μ, and coats the surface of a metal pipe made of an iron-based alloy with this nickel oxide powder.
Nickel oxide has a high emissivity in far-infrared rays, and has a large coefficient of thermal expansion as it is close to that of metal.Furthermore, nickel oxide is coated with iron-based alloy metal pipes, such as SUS321, which has traditionally been used as metal pipes for sheathed heaters. It has excellent high-temperature oxidation compared to stainless steel such as SUS304, so even when used at high temperatures of 800℃, the far-infrared emitting layer made of nickel oxide does not peel off, and it has excellent far-infrared emissivity. It is possible to obtain a heater. Description of Examples Examples of the present invention will be described below. The nickel oxide powder used is generally obtained by two methods: roasting metal nickel powder or roasting nickel salt, but nickel oxide powder obtained by roasting nickel salt In addition to being expensive, it is not suitable for thermal spraying, which is a typical method of coating treatment described below, because the particle size is very fine and the fluidity of the powder is very poor. However, nickel oxide powder obtained by roasting nickel metal has a relatively large particle size and good fluidity, but nickel oxide powder roasted at temperatures below 800°C can be used as a far-infrared emitting material. If the surface of the metal pipe of a sheathed heater is coated and used at high temperatures around 800°C, the color may change from black to green. However, those baked at a temperature of 800℃ or higher,
The above-mentioned discoloration phenomenon is not observed and the nickel oxide powder remains green or blackish green, so nickel oxide powder is prepared by roasting metallic nickel powder at a high temperature of 800°C or higher and pulverizing it to a size of 10μ to 44μ. is preferred. The coating method for the nickel oxide powder may be any method such as a coating method or a thermal spraying method, but the thermal spraying method is particularly suitable. Currently, metal pipe 3 has a length of 413 mm and an outer diameter of 8.
SUS304, SUS321 stainless steel, and iron-based alloy NCF800 (JISG4902, trade name Incoloy 800) with a wall thickness of 0.46 mm are used. As the heating wire 2, a first class nichrome wire with a wire diameter of 0.29 mm was used, which was formed into a coil shape with a winding diameter of 2 mm, and the terminal rod 1 was connected to both ends. A heating wire 2 with the terminal rod 1 connected to both ends is inserted onto each metal pipe 3, and the metal pipe 3 is filled with fused magnesia powder as an electrical insulating powder 4, and the steps of rolling diameter reduction and annealing are performed. After that, the metal pipe 3 was made to have a length of 500 mm and an outer diameter of 6.6 mm. After that, the surface of each metal pipe is blasted with corundum (#60) abrasive, and various nickel oxide powders shown in the table are directly coated on the metal pipe surface by plasma spraying to form a far-infrared emitting layer. 7 was formed, and far infrared heaters of sample numbers 2 to 12 (the configuration is shown in FIG. 2) were completed.

【table】

[Table] On the other hand, for comparison, a conventional sheathed heater without thermal spraying of nickel oxide powder was also completed and designated as sample number 1. The far infrared heaters for sample numbers 1 to 12 completed as above were turned on for 20 minutes at 100V-400W.
Electricity was applied in a 10-minute off cycle (pipe temperature was about 800°C), and the far-infrared radiation layer 7 was tested for peeling and the degree of discoloration was evaluated, and the results are shown in the table. Peeling was checked after 100 cycles, 500 cycles, and 1000 cycles, and discoloration was checked after 100 cycles. Furthermore, the results of measuring the emissivity at each wavelength when the pipe surface temperature was set at 750° C. for sample numbers 1 and 5 are shown in FIG. In addition, in the table, the ○ mark in the peel test column indicates that no peeling occurred, the × mark indicates that peeling occurred, and the ○ mark in the discoloration column indicates that no discoloration occurred. The x mark indicates that discoloration has occurred. Further, in FIG. 3, a indicates the measurement results of sample number 1, and b indicates the measurement results of sample number 5. As is clear from the table, NCF800 is applied to metal pipes.
Sample numbers 2, 3, 5, 7, and 8 using nickel oxide powder with a particle size of 10μ to 44μ
No peeling occurred up to 1000 cycles, but sample numbers 2 and 3, where the baking temperature of the nickel oxide powder was 800°C or lower, did not peel off, but
Significant discoloration of the far-infrared radiation layer was observed. On the other hand, sample numbers 5, 7, and 9 treated at 800° C. or higher did not peel off and no discoloration was observed. Further, Sample Nos. 4 and 6, in which the nickel powder was roasted at 800° C. and the particle size of the nickel oxide powder was outside the range of 10 μm to 44 μm, could not be successfully thermally sprayed. In addition, in sample numbers 9, 10, 11 and 12, which used metal pipes other than NCF800, even if nickel oxide powder baked at a temperature of 800℃ or higher was used,
In SUS304, the far-infrared emitting layer peeled off within 100 cycles, and in SUS321, within 500 cycles, so they were unusable. Also, as is clear from Figure 3, sample number 5
It can be seen that the far-infrared heater represented by 1 shows a higher emissivity at each wavelength compared to sample number 1, which is a conventional sheathed heater. As is clear from the above explanation, far infrared heaters in which 10μ to 44μ nickel oxide powder, which is obtained by roasting metal nickel powder at a temperature of 800°C or more, is sprayed onto NCF800 metal pipes, are more effective than conventional sheathed heaters. It has a high far-infrared emissivity and will not peel or discolor even when used at high temperatures of 800℃. Effects of the Invention As described above, the present invention provides a method for coating the surface of an iron-based alloy metal pipe with metal nickel powder.
By coating with nickel oxide powder obtained by roasting at a temperature of 800℃ or higher and pulverizing it to a size of 10μ to 44μ, it has a high emissivity in the far infrared region and can be used in high temperature regions up to 800℃. It is possible to provide a far-infrared heater that is thermally stable and sufficiently resistant to cooling and heating cycles even when used, and whose far-infrared radiation layer does not peel off, and has great practical value.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional sheathed heater, FIG. 2 is a sectional view of a sheathed heater according to an embodiment of the present invention, and FIG. 3 is a radiation characteristic diagram of the sheathed heater. 2... Heating wire, 3... Metal pipe, 4... Electrical insulation powder, 7... Far-infrared radiation layer.

Claims (1)

[Scope of Claims] 1. A coiled heating wire is inserted into a metal pipe made of an iron-based alloy coated with nickel oxide powder obtained by roasting and pulverizing nickel metal powder at a temperature of 800°C or higher. A far-infrared heater made by filling magnesia powder between the and heating wire. 2. The far infrared heater according to claim 1, wherein the nickel oxide powder has a particle size of 10μ to 44μ.