JPH04294087A - heating element - 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]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-temperature heating element, ie, an electric heater, used in electric heating appliances such as space heaters and cookers.

0002

BACKGROUND OF THE INVENTION Conventionally known heating elements of this type include mica heaters in which heating wires are wound around mica plates, sheathed heaters, and quartz tube heaters.

0003

However, conventional heating elements have tube walls and side walls around the heating wire, and heating of the object to be heated is carried out through these tube walls and side walls. Therefore, the heat generated by the heating wire is not directly radiated as radiant energy, and although there are some heaters such as quartz tube heaters that transmit short wavelength infrared rays, in most cases, the heat is not radiated directly to the tube wall or side wall. After heat is transferred, it becomes secondary radiation from that part. Therefore, the magnitude of infrared radiant energy is basically determined by the temperature of the tube wall and side wall. Therefore, from the perspective of utilizing radiant heating, if the radiant temperature is set to, for example, 800°C, which is optimal for radiant heating of a cooker, it is necessary to set the temperature of the heating element to a higher temperature, for example, 1000°C. As a result, heat resistance requirements for heating wires have become severe, and there has been no practical heating wire material that can withstand these requirements.

[0004] Furthermore, in terms of the heat capacity of the heating element, heating of the tube wall and side wall is added to the heat capacity in addition to the heating element, which is disadvantageous in terms of temperature rise after energization.

[0005] Furthermore, if the heating element is used in its bare state, there are problems with corrosion resistance and uneven radiation heating distribution due to the small radiation area.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and provide a heating element which has a short heating start-up time, is highly reliable, and can be used at high temperatures, which is advantageous for the use of infrared radiation.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the heating element of the present invention uses a heat-resistant metal foil patterned and arranged in a planar shape, and on the surface of the metal heating element, a borosiloxane polymer or A film containing a titanocarbosilane polymer and a nickel-aluminum alloy is formed and used. That is, a paint film containing a nickel-aluminum alloy powder is applied and baked on the surface of a metal heating element using a borosiloxane polymer or a titanocarbosilane polymer as a binder.

[0008]

[Operation] The present invention is used as it is without special tube walls or side walls, with the main coating layer formed on the patterned surface of the metal foil. Therefore, since the heat capacity is small, the temperature rise speed after energization is relatively fast. Furthermore, even when used under harsh environmental conditions at high temperatures, a film with high heat resistance and excellent corrosion resistance is formed on the surface, so it has excellent corrosion resistance as a heater element. In addition, for various applications, the spatial arrangement of the heater is spread out on a flat surface compared to conventional rod-shaped heaters such as sheathed heaters, which allows for a larger heat radiating area, improving uneven heating and achieving uniform radiant heating. I can do it. Furthermore, compared to the case where metal is used as is, the heat emissivity from the surface of the heating element is high and high radiation is possible.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the heating element of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a heating element, in which a coating film 3 is formed on the surface of a patterned heat-resistant metal foil 2. This is obtained by first patterning a heat-resistant metal foil sheet, and then coating and baking a paint containing nickel-aluminum alloy powder on the heating element using a borosiloxane polymer or titanocarbosilane polymer as a binder. It will be done.

[0010] As the heat-resistant metal foil, iron-chromium-aluminum type, nickel-chromium type, various stainless steel sheets, etc. are used. The thickness of the metal foil used is 30 μm to 200 μm. Considering the specific resistance value of the heat-generating metal normally used and its resistance characteristics as a heater for AC100V power supply, if the thickness of the metal exceeds 200 μm, it must be used in a narrow and long state, that is, a wire-wound type method is required. This is disadvantageous from the viewpoint of thermal radiation distribution. Further, if the thickness is less than 30 μm, processing becomes extremely difficult. To form a circuit as a heater element, a pattern may be obtained by pressing or etching a foil of a required size, or a necessary pattern may be formed using a wire material of a predetermined width.

Methods for forming a metal alloy film on a heat-resistant metal include methods such as successive cladding of nickel and aluminum on a base material and firing the cladding to form an alloy, or plasma spraying. All of these methods are expensive, and in the case of the former in particular, when cutting the plate after cladding, the base metal is inevitably exposed on the end face, resulting in variations in corrosion resistance. . Additionally, there is a problem in that it is difficult to increase the thickness of the surface alloy layer due to workability conditions in cladding processing.

FIG. 2 shows a heating element of the present invention, and this heating element 1 is supported by a support 4 made of ceramics or the like for practical use. It has a large radiation area compared to conventional rod-shaped heaters such as sheathed heaters. The surface also has excellent infrared radiation properties.

The reason why the heating element of the present invention exhibits excellent corrosion resistance at high temperatures is estimated as follows. In general, the corrosion behavior that governs the corrosion resistance of heating elements at high temperatures is 2.
There are two types of corrosion: one is corrosion due to high-temperature oxidation, and the other is wet corrosion due to moisture containing salt. High-temperature oxidation is a form of corrosion in which scale of oxidation products is formed on the metal surface and progresses by desorption. Wet corrosion is the electrochemical corrosion of metals in aqueous solutions. Metals are ionized and dissolved as a simultaneous reaction of hydrogen ion reduction. This is accelerated by being energized as a heating element.

The coating film of the present invention acts as a barrier to the diffusion of oxygen to the element metal surface during high-temperature oxidation, thereby preventing the progress of oxidation. Further, the aluminum-nickel alloy as an additive component is stable in an oxidizing atmosphere and has a property of being resistant to abnormal oxidation. This makes it resistant to high temperature oxidation. It is also believed that the nickel-aluminum alloy powder contained in the coating is electrochemically less noble than the heat-generating metal of the usual base material and acts as a sacrificial anode with respect to wet electrochemical corrosion. Therefore, wet corrosion is also prevented and overall excellent corrosion resistance is exhibited at high temperatures.

[0015] Although this coating film is not a complete film without pinholes, the presence of these pinholes can be avoided because the coating film as a whole is contributed by the nickel-aluminum alloy powder and acts as a sacrificial anode. does not have much of an adverse effect on corrosion resistance.

[0016] Here, the significance of using the heating element at high temperatures will be explained. The reason why a temperature of 800 to 900°C is advantageous in the application of radiation heating is that the infrared absorption of water as a heated object is at 3 μm, and if this absorption characteristic is to be utilized, Planck's radiation 800~ from the law
This is because a radiator temperature of 900° C. is advantageous. The reason why it has not been used in the past, despite its advantages, is that it has a problem with corrosion resistance.

The paint used in the present invention is prepared by stirring nickel-aluminum alloy powder and a binder such as a borosiloxane polymer together with a solvent using a dispersing machine such as Attritor (trade name). The paint may contain additives for glass, ceramics, metals, etc. to adjust thermal expansion with the base metal, and surfactants added for the purpose of stabilizing the paint, that is, preventing sedimentation. .

The borosiloxane polymer is a heat-resistant polymer composed of a mixture of 6-, 8-, and 10-membered rings composed of Si-B-O, which is synthesized using diphenyldichlorosilane and boron hydroxide as starting materials. It is. In the case of titanocarbosilane, it is a heat-resistant polymer obtained by adding titanium alkoxide to polycarbosilane and polymerizing it. All of them have excellent handling properties as binders for heat-resistant paints as polymers derived from organic substances at room temperature, and when the temperature exceeds several hundred degrees Celsius, they thermally decompose and become extremely stable inorganic substances, that is, ceramic substances at temperatures above 600 degrees Celsius. During this time, approximately 1/2 of the polymer weight remains as a cured product.

The paint used in the experiment had the following formulation. Ube Industries Co., Ltd.'s "Tyranopolymer" is used as a binder.
100 parts by weight (however, as polymer solid content, 50 parts by weight)
%) and an average particle size of 1 μm.
20 parts by weight of alumina and 20 parts by weight of borosilicate glass as fillers were stirred and mixed together with 100 parts by weight of xylene as a solvent for 10 hours using a paint dispersion machine "Attritor" to form a paint.

The heating element samples are FCH-1 and NCH.
-1 as a base material with a thickness of 50 μm, a tape shape of 8 mm width, and a length of 20 cm. After degreasing the base material by heating at 400°C for 30 minutes, the above paint was sprayed to 100 μm. Dry for 10 minutes at 300℃, then 10 minutes at 300℃ for 60 minutes.
It was created by firing at 0°C for 10 minutes and finally at 900°C for 1 hour. It was carried out in the same way on both sides.

The average thickness of the coating film was 3 μm. The infrared emissivity of this surface was measured and found to be 0.83.

[0022] The heating element was evaluated by energizing the heating element which had been subjected to the above treatment, and the surface temperature was set at 800°C. In this state, 0.5 cc of 5% saline solution was dropped every 2 minutes, and the corrosion resistance was evaluated by the number of drops until the heating element broke. The number of drops was as follows. FCH-1 (base material only): 10 times, NCH- (base material only): 15 times, FCH-
1 (this treated product): 120 times, NCH-1 (this treated product):
It was 138 times.

[0023] The reason why the corrosion resistance was improved is considered to be due to the reason estimated above. Although titanocarbosilane polymers have been described as examples, similar effects can be obtained by using borosiloxane polymers as the binder.

[0024] Here, the film thickness was tested at 3 μm on each side, but this film thickness can be increased or decreased as necessary. Regarding corrosion resistance, from the perspective of preventing wet corrosion, the thicker the film, the better the corrosion resistance can be expected, but due to the difference in thermal expansion coefficient with the base material, there is a risk that the paint film will peel off if the film is too thick. . In terms of film thickness, a range of 2 to 10 μm is desirable.

[0025]

Effects of the Invention As is clear from the description of the embodiments above, the following effects can be obtained according to the present invention. (1) Since only a coating film is formed on the surface of the heating element made of patterned metal foil, a heater with a small heat capacity and a fast temperature increase rate can be obtained. (2) Because a coating film with excellent corrosion resistance at high temperatures is formed on the surface of the heating element, it could not be used conventionally.
It is now possible to use it in harsh corrosive environments at temperatures above 00°C. (3) Because the metal foil heating element is patterned, the radiation area is larger than that of conventional rod-shaped heaters, and the surface infrared emissivity is expected to be more than double that of conventional metals, providing heating with an advantageous radiation distribution. can. (4) Since there are no tube walls or side walls around the heating element, high-temperature radiation heating can be achieved with a quick temperature rise time. (5) Compared to other film forming methods, later steps such as terminal attachment can be simplified by masking the terminal portion in particular. (6) Since the coating film is formed by painting, the heating element has excellent productivity and can be manufactured at low cost.

[Brief explanation of drawings]

[Fig. 1] Cross-sectional view of a heating element in one embodiment of the present invention

[Figure 2] Top view of the heating element

[Explanation of symbols]

1 Heating element 2 Patterned heat-resistant metal foil 3 Coating film

Claims (1)

[Claims] Claim 1: A coating film containing a borosiloxane polymer or a titanocarbosilane polymer and a nickel-aluminum alloy is formed on the surface of a metal heating element that is used by patterning heat-resistant metal foil and arranging it in a plane. heating element.