JPS60166284A - Manufacture of carbonaceous refractories - 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 The present invention relates to a method for producing carbonaceous refractories by oxidative firing.

Examples of carbonaceous refractories include carbon magnesia carbon,
Refractories manufactured from alumina carbon, magnesia silicon carbide carbon, etc. or a combination thereof are known.These refractories have good electrical and thermal conductivity and excellent thermal shock properties, so they are used in steel manufacturing, Steelmaking furnace materials,
It is often used in crucibles, etc.

It is generally known that when carbonaceous refractories are subjected to oxidation firing, practically unfavorable results appear at relatively low temperatures, for example, around 450°C.

Therefore, in the production of carbonaceous refractories, a method of reduction firing at an appropriate temperature is used. The reason why reduction firing is used is that carbon is oxidized due to excess oxygen in the firing gas, and the resulting carbonaceous refractories have significantly deteriorated thermal shock properties and are significantly less resistant to erosion by molten materials. This is because it deteriorates.

However, reduction firing generally requires more work to adjust the reduction conditions than oxidation firing, requires higher equipment costs, requires more careful attention to quality control, and lowers fuel costs. It is known to take quite a while.

Furthermore, reduction firing is known to have poor furnace durability and low productivity.

Regarding the method for manufacturing large carbonaceous refractories by oxidation firing, the present inventors have proposed that the oxidation of carbonaceous refractories by oxidation firing can be achieved by coating the surface of the carbonaceous refractories with one or more glazes containing a low-temperature axis with a low softening temperature. We found that this can be prevented. Patent application No. 58-1'7040 filed prior to this application
In No. 1, because a low-temperature glaze was applied on top of other medium- and high-temperature glazes, certain conditions were required for the thickness of the glaze layer, the rate of heating and cooling during firing, etc.

During firing, when the top layer low-temperature glaze is melted due to the firing coordination, the lower medium (high) abuse glaze remains unmelted, but at this time, the relationship between the thickness of the lower glaze layer It was observed that the lower glaze was pulled by the melted upper layer low-temperature glaze, causing cracks 7 in the lower glaze, and that oxidation progressed through these cracks.

This drawback was overcome by using the manufacturing method described below.

That is, this is a method in which the glaze is coated on the surface of the refractory in the order of low temperature glaze, medium temperature glaze, high temperature glaze, or low temperature glaze, medium temperature glaze, further low temperature glaze, and high temperature glaze.

The low-temperature glaze used in the present invention is a leaded glaze with an extremely low softening temperature and the following composition: pbo 65-8
5% 5i02 5-14q6 B203 12-18% Na2O0-2% CaOO-1% and 20 4 for phosphoric acid glaze with the following composition:
~8% Na2O7~11% Li2O2~6% MgO'3 ~7% 2007~13% Ano2033 ~7chi p2o555 ~65%. These have softening temperatures of about 450°C or less. As the medium-temperature glaze, for example, lead-free or lead-based borosilicate frit can be used, and generally commercially available frits for ceramic glazes and frits for enamel can also be used. The temperature range in which this medium temperature glaze can be used is approximately 00°C to 1200°C.
Furthermore, if the refractory is fired at a high temperature, the low temperature glaze or medium temperature glaze is coated with a high temperature glaze whose operating temperature range is 800°C to 1500°C.

As high temperature glazes, commonly available porcelain glazes and N
ano, CaO, AJ203, B2O3, 81
Glass cullets containing 02 as a main component can be used.

Furthermore, it has been found that adding an appropriate amount of a suitable reducing agent such as carbon, silicon carbide, nitride, etc. to this low-temperature glaze is also effective in preventing oxidation of the carbonaceous refractory.

Low-temperature glazes volatilize at a temperature of around 111'00°C, although this varies depending on the thickness of the glazed layer, firing time, etc., so if higher temperatures or longer firing times are required, use medium-temperature glazes as mentioned above. A glaze with a higher softening temperature and volatilization temperature, such as one for high temperatures, is used on top of the coating layer of the glaze for low temperatures to prevent oxidation.

The coating method for each glaze may be a spray method, a brush coating method, a dipping method, or the like, and can be selected depending on the size, shape, etc. of the target carbonaceous refractory.

During firing, the glaze reacts with the refractory, but the resulting layer does not in any case affect the product.

Examples are shown below.

Example The following was used as the glaze.

The composition is expressed in Sodel notation.

Low-temperature glaze (softening temperature approx. 400℃) Medium-temperature glaze (softening temperature approx. 650℃) High-temperature glaze (softening temperature approx. 850℃) These glazes are applied to magnesia carbon bricks measuring 25mm x 25mm x 60mm at a low temperature from the surface. for medium temperature,
Glazes were applied in the order of high-temperature glazes in order of glaze thickness of about 0.5 to 1.5, and fired by heating to 1400°C at a heating rate of 6°C/min.

After firing, the sample was cut and the cross section was observed, and the refractory was not oxidized and was in good condition.

Agent Asamura Hako

Claims (1)

[Claims] A method for producing a carbonaceous refractory in which the surface is coated with a glaze and oxidized and fired, characterized in that the glaze is coated on the refractory surface in the order of low temperature glaze, medium temperature glaze, high temperature glaze or high temperature glaze, medium temperature glaze. A method for producing carbonaceous refractories.