JPH02311358A - Non-baked magnesia-carbon brick - Google Patents

Abstract

PURPOSE:To improve safely the subject brick in oxidation resistance by incorporating non-baked magnesia-carbon brick with a specified amount of alloy powder free from hazards such as explosion produced by coating with pitch the surface of Mg-Al alloy powder with a regulated content, granular size, etc. CONSTITUTION:Firstly, pitch is put into a vessel equipped with a steam heating jacket, heated and melted. Second, Mg-Al alloy powder >=40wt.% in magnesium content and <=150mum in granular size is added to the resultant molten pitch followed by mixing to coat the surface of said powder with the pitch to produce Mg-Al alloy powder free from hazards such as explosion or ignition. Thence, 0.5 to 10wt.% of the alloy powder is incorporated into non-baked magnesia- carbon brick, thus obtaining the objective non-baked magnesia-carbon brick of high oxidation resistance in a safe manner.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to refractory bricks, and particularly to unburnt acid magnesia abacarbon bricks.

[Conventional technology]

Unfired magnesia carbon bricks are recognized for their usefulness and are widely used as refractories for converters, electric furnaces, and secondary refining ladles.

However, one of the drawbacks of unfired magnesia carbon bricks is that they are free from oxygen in the atmosphere, lower oxides (e.g. Fe) in the slag.
An example of this is tissue embrittlement due to oxidation caused by O, MnO, etc.).

In order to improve oxidation resistance, various metals such as Aj2.
It is well known that Si and the like are widely used.

SiOz, which is produced by oxidation, reacts with magnesium, which is the main constituent of unfired magnesia carbon bricks, to produce low melting point compounds (for example, MgO・2SiO□), so even higher corrosion resistance is required. In some cases, its usage will also be limited.

Also, Aj! Since its oxide, alumina, reacts with magnesium to create spinel minerals, it cannot necessarily be considered a harmful component as mentioned above, but aluminum and carbon dioxide are formed by reacting with the carbon and graphite that make up bricks during high-temperature use. Carbide (8β.

C3) reacts with moisture in the air as shown in the formula below immediately after the furnace cools, causing a digestive reaction and embrittling the brick structure.

AI! aCs + 1 2 H2O-3CH, ↑
+4 A 7! It is also known to use Si in combination to suppress the formation of (OH)3 aluminum carbide, but when Si is mixed, the corrosion resistance deteriorates as described above.

[Problem to be solved by the invention]

As an alternative to A1 and Sj as metals for preventing oxidation of carbon (graphite) in magnesia carbon bricks, which have the following drawbacks, AA-Mg alloy is used, for example, as described in Japanese Patent Publication No. 303-1983. Some unfired magnesia
It came to be used in carbon bricks.

However, as disclosed in Japanese Patent Application Laid-Open No. 60-108363, both magnesium and aluminum metals comply with Fire Service Act 2.
Magnesium metal is a dangerous substance designated as Class 8 metal, but it is much more ignitable than aluminum metal, and as a result, A'fi-Mg alloy has a much higher risk of ignition and explosion than Aβ metal. . Therefore, there is a risk of ignition and explosion from the flame of the burner that heats the mixer, for example, and its usage is extremely limited.

In addition, in order to eliminate the above-mentioned drawbacks of magnesium, JP-A-60-108363 describes magnesia carbon bricks that use metallic magnesium coated with magnesium oxide, but There is no disclosure of a method for coating with magnesium, and even if it could be realized, it would of course be economically expensive.

The present invention was proposed in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide an unfired magnesia carbon brick that is easy to handle and is made of magnesium or a magnesium-aluminum alloy.

[Means to solve the problem]

In order to achieve the above object, the present invention employs the following means. In other words, if the particle surface is coated with a pinch and the magnesium content is 40% or more, the particle size is 15.
Magnesium-aluminum alloy powder of 0μm or less
．． It contains 5 to 10%.

[For production]

As shown in the binary phase diagram of aluminum-magnesium alloy, the range of magnesium content from 35% to 65% has the lowest melting point (450°C), and 450°C corresponds to the oxidation start temperature of natural graphite, etc. Therefore, this composition is preferable in order for the alloy to melt and fully exhibit its oxidation-resistant effect.

Additionally, magnesium has a superior affinity for oxygen compared to aluminum, and exhibits greater oxidation resistance at low temperatures, making it usable in practice by applying a pinch coating.
゛The particle size of magnesium-aluminum alloy powder is 150μ
If it is 150 μm or more, uniform dispersibility is insufficient and sufficient oxidation resistance effect cannot be observed. The amount added is preferably 0.5 to 10%; if it is less than 0.5%, no effect will be seen, and if it is more than 10%, it will be economically disadvantageous.

As a coating material, coal tar pitch with a softening point of 130 to 135 DEG C. and a fixed carbon content of 42% by weight has excellent coating properties and is the most economical.

Mg in a pinch, -A7!7! As a method for coating the powder, a method of adding a pinch to the Mg-A48 alloy powder and kneading it is preferable, and coating by transfer is also possible.

〔Example〕

Table 1 shows the formulations of the products of the present invention and comparative products. Pinch has a softening point of 130-135°C1 fixed carbon 42% by weight
Mg-A4 alloy powder and Mg powder were added thereto, mixed and coated to a film thickness of 0.051 m. did. Add 4% phenol resin externally as usual, and make 1000 kg r/
After molding with Cl, after hardening treatment at 250°C for 40 hours, after heat treatment at 1500°C for 3 hours, the porosity of the sample, and the thickness of the oxide layer after heat treatment at 1200°C, and at 1200°C.
A comparison was made of the oxidative wear rate.

As shown in Table 1 above, the decarburized layer due to oxidation is smaller than that of Aβ alone, and the oxidative wear rate is also smaller than that of A1 alone.

Table 1 [Effects of the Invention] As explained above, the present invention achieves excellent oxidation resistance for the first time by pinch-coating magnesium-aluminum alloy powder, especially one with a composition of 40% or more of magnesium content. It is possible to safely commercialize unfired magnesia carbon bricks.

Claims (1)

[Scope of Claims] [1] Unfired magnesia containing 0.5 to 10% of magnesium-aluminum alloy powder whose particle surface is coated with pitch and has a magnesium content of 40% or more and a particle size of 150 μm or less・Carbon brick.