JPH06104892B2 - Method for producing sulfur-resistant electric heating element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an electric heating element that is resistant to oxidation at high temperatures, and particularly to a high temperature gas containing sulfur.

[Prior Art and its Problems] Nickel-chromium alloys and iron-chromium alloys are the most commonly used materials that generate heat by electric current, which have been widely used in various industries that utilize high temperatures. It consists of: In particular, for linear wires, the composition is determined by JIS (C 2520) as a heating wire as follows.

The latter of these contains 2-6% aluminum, which was once known as an epoch-making product in the heating wire field, and still boasts a global market. Cantal Gadelius of Sweden ( Kanthal Gaderius) product, commonly known as Kanthal wire composition (3.5-6% Al, 19-25% Cr, 0.5-3)
% Co, rest Fe) was developed with reference.
This simple wire is famous for its extremely high heat resistance, especially for high-temperature sulfur-containing gas, which is extremely durable. But,
When the same product is installed in an electric heating device and then energized and heated for a long time, even if it is the standard heating specified by the manufacturer,
It has a drawback that its mechanical strength is greatly changed, it becomes extremely brittle after cooling, and rewinding or other reworking is impossible at the time of repair.

In general, we know that increasing aluminum content helps improve sulfur resistance, but it is limited by the adverse effects on drawing and other practical processing, and here we are struggling with the delicate composition of Kanthal wire and JIS-compliant products. Know how is hidden. On the other hand, Nichrome wire consisting mainly of nickel and chromium can be freely deformed and regenerated even after heating, so it has higher heat resistance than iron-chromium wire, and its high price and sulfur resistance. Despite its low drawbacks, it still has wide application.

Here, if it is possible to form an aluminum alloy layer having a thickness that hardly affects the mechanical strength of the nichrome wire on the surface of the nichrome wire, the sulfur resistance of the nichrome wire should be significantly improved. In the case of iron-chromium wire, it is also possible to avoid the subtle difficulty of compounding the composition at the time of manufacturing the raw material, manufacture a raw material with a composition that is easy to process, draw or wind, and then aluminum alloy only the surface layer Should be desirable.

The inventors hereof filed a prior application developed by the inventors (JP-A-58-1).
The invention of No. 73994) was applied and the object was achieved.

[Summary of the Invention] In the above-mentioned prior application, the inventors of the present invention have proposed a paint in which powdery aluminum as fine as possible, particularly aluminum metal foil, or powder is finely pulverized in the coexistence of stearic acid and mineral spirits. Aluminum paste (JIS K 5910) for organic use is soluble in an organic solvent, dried to form a film, and more than 95% of the organic content in the film is thermally decomposed by heating up to around the melting point of aluminum (about 660 ° C) ( Prepare a paint-type stock solution that is uniformly dispersed in a solution of an organic polymer compound that undergoes combustion decomposition in air)
By coating the surface of a substrate made of copper, nickel, chromium and other metals and their alloys, drying it, and then heating it to 650 ° C or higher in air or an inert gas, or in a vacuum, the surface layer of the substrate becomes extremely simple. It has been disclosed that an alloy layer of a base metal and aluminum can be formed.

It will be easily understood that this method can be applied to a linear or strip-shaped electric heating element made of a nickel-chromium alloy, an iron-chromium alloy, or the like. In fact, as disclosed in the examples below, an aluminum alloy layer is formed on the surface layer of a nichrome electric heating element, an iron-chromium electric heating element, and has high heat resistance and sulfur resistance, which are the main objects of the present invention, Moreover, an electric heating element having a mechanical strength that can withstand re-deformation after cooling was obtained.

Organic polymer compound (resin) required for carrying out the method of the present invention
(1) The solution or the dispersion can form a film that adheres to the metal surface, and (2) the thermal decomposition at the temperature suitable for each resin causes the film to be substantially removed from the film. Volatilized and disappears.

An organic polymer compound that forms a general organic practical paint film was sufficient as the one having the characteristics of (1) above. However, in order to have the characteristic of (2), it was necessary to have a special chemical structure.

The present inventors have found that among organic polymer compounds, a thermogravimetric analysis curve (TGA curve) measured in air, more preferably in nitrogen, shows a decomposition rate of 95% or more at 200 to 700 ° C. As a result of a test study on many organic polymer compounds, it was confirmed that those compounds meet the object of the present invention as expected. However, the TGA curve changes depending on the morphology of the measurement sample, heating rate, etc., and even for the same compound, it shows a difference depending on the degree of polymerization distribution.
Although it may be difficult to make a determination only from the same curve, the following are suitable for carrying out the method of the present invention.

a) Polyacetal resin (260 ° C [95% thermal decomposition point, the same applies below]) b) Acrylic acid, acrylic acid methyl-, ethyl-,
Isopropyl-, n-butyl-, 2-ethylhexyl-, 2-hydroxyethyl-, hydroxypropyl-ester, methacrylic acid, methyl methacrylic acid-, ethyl-, isopropyl-, n-butyl-, n-hexyl-, lauryl Polymer of one compound selected from esters of acrylic acid and methacrylic acid such as-, 2-hydroxyethyl-, hydroxypropyl-ester, hydroxyesters, fumaric acid, maleic acid, and itaconic acid ( 350-450 ° C) c) Polyethers such as adducts of polyoxypropylene and sucrose (350-400 ° C) d) Polyesters or polyethers, 2,4
-Or 2,6-Tolylene diisocyanate and a polymer having a urethane bond such as an addition polymer with other polyisocyanates (380 to 500 ° C) e) Urea resin (350 ° C) f) Melamine resin (350 ° C) ) G) Benzoguanamine resin (370 ℃) h) Alkylation-modified urea resin (400 ℃) i) Alkylation-modified melamine resin (400 ℃) j) Alkylation-modified benzoguanamine resin (420 ℃ k) Polycarbonate resin (530 ℃) l ) Aromatic polyesters (580 ℃) m) Butyral resin (600 ℃) n) US General Electric
aromatic polyester imides (63
0 ℃) p) Kapton H (Kapt) manufactured by Dupont, USA
on H) Aromatic polyimides (670 ° C) alone, or a mixture or copolymer thereof. Each of the above organic polymer compounds is soluble in one or a mixture of water, alcohol groups, ketones, esters, cellosolves, carbitols, dimethylformamide, dimethylacetamide, dimethylsulfoxide and the like. The solution, after volatilization of the solvent, forms a film on the surface of the metal, and is thermally decomposed in the temperature range in the above () to substantially disappear from the coating system. On the other hand, polyvinyl chloride, which is also soluble in organic solvents and has film-forming properties, epoxy-based resins that do not contain urethane bonds, and fibrin-based resins are 700 times when heated in a nitrogen stream.
Even if the temperature reaches ℃, there is a residual content of 20-65%, and if heated in air, oxidative combustion accompanies it, so the residual content will decrease, but it will not completely burn, especially in a coating in which a heat resistant material coexists. Since a considerable amount of carbon and the like remains, it is not suitable as a material for carrying out the present invention.

The above-mentioned organic polymer compound suitable for carrying out the present invention can be used as a colloidal dispersion liquid in water or an organic solvent, in addition to the water or organic solvent solution described above. In particular, an aqueous undiluted solution of a resin produced by the so-called emulsion polymerization method from the compound belonging to the above (a) can be directly used as a suitable raw material for carrying out the present invention.

The aluminum-containing coating used in the practice of the present invention has the same physical properties as the coating of a general metal coating, and in particular its flexibility withstands the deformation of the substrate after the coating is formed. After drying, it can be processed into the final form before heating and firing, for example, it can be wound into a coil and placed in an electric heating device, and it can be alloyed by the first red heat (650 ° C or higher). It can be said that the greatest advantage of the law. Therefore, it is possible to commercialize the aluminum-containing film as it is applied.

The first heat treatment including red heat is carried out in order to achieve uniform and effective diffusion.
℃) or more is desirable. As a matter of course, the upper limit is equal to or lower than the melting point of the electric heating material.

[Examples] Examples will be described below.

Example 1 130 parts of methacrylic resin liquid (heating residue 25%) and 50 parts of n-butylated modified melamine resin liquid (heating residue 60%) were dissolved in 350 parts of ethyl cellosolve, and aluminum paste for coating (heating residue) (Paint 65%) 450 parts were evenly dispersed to prepare a paint type stock solution. This is a commercially available Nichrome heating wire (JIS C
2520 2 kinds) and dried. After heating it at 900 ° C for 150 hours in an electric furnace, it was left to cool, lightly polished in water to remove the outer skin, and a gray-blue surface layer appeared, which clearly became a metal phase different from the original line. It was The obtained heat transfer wire was not cut even when repeatedly wound on a glass rod having an outer diameter of 8 mm.

In addition, an imported commercial Kanthal wire is used at the same temperature as above, but at 150 ° C at 150 ° C.
The product that had been heated for a period of time and then cooled was broken by winding several times to demonstrate its embrittlement.

Example 2 (Comparative Experiment) A commercially available iron-chromium heating wire (JIS C 2520 type 2) was uniformly coated with the aluminum-containing resin solution described in Example 1 and treated in the same manner as in Example 1. , Markedly brittle,
The effect of increasing aluminum content was shown.

EFFECTS OF THE INVENTION According to the present invention, by applying a coating material in which finely powdered aluminum is dispersed and then heating it, it has high heat resistance and sulfur resistance, and has a mechanical strength that can withstand re-deformation after cooling. There is an advantage that the heat transfer material having the above can be easily obtained, and its industrial value is extremely great.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Shimada 3-3 Kashiwara, Ishioka City, Ibaraki Prefecture (3) Inventor Shinichi Nishiyama 712-56 Inariyama, Nakanuki-cho, Tsuchiura City, Ibaraki Examiner Masaki Okui (56) References Sho 55-38984 (JP, A) Japanese Patent Sho 58-26432 (JP, B2)

Claims (3)

[Claims] 1. 95% at 750 ° C. or lower on the surface of an electric heating element made of an alloy whose main component is a combination of iron, chromium and nickel.
After coating a solution or dispersion containing at least one organic polymer compound that undergoes thermal decomposition in which finely powdered aluminum is dispersed, the whole is heated to form an alloy layer containing aluminum on the surface layer of the electric heating element. A method for producing a sulfur-resistant electric heating element, which is characterized by being formed. 2. The organic polymer compound is selected from acrylic acid, acrylic acid ester, acrylic acid ester hydroxy derivative, methacrylic acid, methacrylic acid ester, methacrylic acid ester hydroxy derivative, maleic acid, fumaric acid and itaconic acid. Polymers of raw materials containing one kind or a mixture of two or more kinds, polymers having urethane bonds, urea resins, alkylated modified urea resins, melamine resins, alkylated modified melamine resins, benzoguanamine resins, alkylated modified benzoguanamine resins, The method according to claim 1, which is at least one selected from the group consisting of butyral resin, polyacetal resin, polycarbonate resin, aromatic polyester and aromatic polyesterimide, or a mixture of two or more thereof. 3. The method according to claim 1, wherein the alloy layer is formed by passing an electric current through the electric heating element and heating the electric heating element by the heat generated in the electric heating element.