JPS6060993A - 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. More specifically, the present invention relates to a method for producing carbonaceous refractories by oxidation firing.

As carbonaceous refractories, carbon, magnesia carbon,
Refractories manufactured using alumina, carbon, magnesia, silicon carbide, carbon, or a combination thereof are known. This refractory has good electrical and thermal conductivity and excellent thermal shock properties, so it is used in iron and steel manufacturing, furnace materials for steelmaking, crucibles, and the like.

In the production of carbonaceous refractories, a method of reduction firing at an appropriate degree is generally used. Oxidation occurs due to the oxygen in reduction firing, and the carbon burns out and becomes porous, which causes the obtained carbonaceous refractory to have significantly deteriorated thermal shock properties and corrosion resistance due to molten material. be.

However, in general, reduction firing requires more work to adjust reduction conditions than oxidation firing, requires more installation costs, requires more careful attention to quality control, and requires considerable fuel costs. It is known. In addition, reduction firing is known to have poor furnace durability (and low productivity).

In order to avoid the above-mentioned disadvantages, the inventors explored the possibility of oxidative calcination. As a result of extensive research, it has been found that, in general, when carbonaceous refractories are subjected to oxidation firing, practically unfavorable results occur at relatively low temperatures, for example, about 450° C. or higher. That is, in the initial stage of firing, oxygen penetrates from the surface of the refractory to a considerable depth, oxidizes the carbon content, and reduces the electrical conductivity and thermal shock resistance of the refractory, resulting in a low glaze. By coating the surface of the refractory, it is possible to cut off contact between the refractory and oxygen and perform oxidation firing.

According to the present invention, a leaded glaze having the following composition: pbo 65-85 81025-14% B2O 312-18% Na2O 0-2φ CaO 0-1 and a phosphorus glaze having the following composition: 204 ~8
Row Na2O7-11% Li2O2-6T.

MgO 6-7 modulus Zn0 7-16 modulus 203 6-7% P2O 555-65% had a melting point of about 450°C or less, and very good results were obtained.

When the above glaze is coated on the surface of a refractory and fired in an oxidizing atmosphere, it begins to soften at around 400°C, and at around 4'50°C, where the refractory begins to oxidize, it has already leaked through the surface of the refractory, causing the refractory to oxidize. When contact with oxygen is cut off and the temperature is further raised, it gradually begins to volatilize and is completely exhausted at about 1000°C.

The degree of volatilization depends on the amount of glaze covered and the firing time, so in some cases it may be sufficient to cover only the glaze mentioned above, but if firing needs to be continued for a longer period of time,
In addition to the above glazes, another type of glaze that melts at a higher temperature can also be used. For example, PbO,5i02, At!
203, Cab, MgO%' Bad.

Contains at least one of K2O, 1'Ja20, B2O
A lead-free or lead-based borosilicate frit containing C.3 as a main component is preferred, and other generally commercially available frits for ceramic glazes or frits for enamel can also be used. These glazes should be called medium-temperature glazes if the glaze of the present invention, which melts at the above-mentioned low temperature, is a low-temperature glaze.
℃, it is as high as 600-1200℃. Furthermore, if it is necessary to bring the refractory to a high temperature for firing, there are commercially available glazes that can be used in a temperature range of 800 to 1500°C and can be called high-temperature glazes. Cover with porcelain glaze. High temperature glazes include Na2O, CaO1AA203
, SiO□ is the main component, but Lascarets can also be used.

As mentioned above, when carbonaceous refractories are fired in an oxidizing atmosphere, oxidation starts at a relatively low temperature, so it is necessary to cover the above-mentioned low-temperature glaze.T1 Medium- and high-temperature glazes are necessary. It is only necessary to switch according to the situation.

It is recommended that the surface of the refractory be coated with glazes for high temperature, medium temperature, and low temperature in that order, starting from the surface. Further, the coating method for each glaze is not particularly limited and may be a spray method, a brush coating method, or a dipping method.

The amount of coating can be arbitrarily changed depending on the type of cypress used as the refractory to be fired, the kiln filling method, the firing temperature, and the firing time.

During the process, the lees chemical reacts with the refractories, but the layer formed by the reaction is about 1 to 2 degrees thick in each case, and this part has no effect on the product because it is ground after firing. .

Examples and comparative examples of the present invention are shown below.

The following glazes were used in the examples. The composition is expressed in Sodel notation.

Low-temperature glaze (softening temperature approx. 400°C) Medium-temperature glaze (softening temperature approx. 650'O) High-temperature glaze (softening temperature approx. 85000°C) These glazes were glazed with magnesia carbonate as shown below to make four samples. It was created. Glazing was done by dipping.

Sample 1... Glaze only for low temperature glaze (present invention) 2... Glaze only for medium temperature glaze (comparison) 6... Glaze only for high temperature glaze (comparison) 4... High temperature, medium temperature, low temperature Each glaze was applied in this order (according to the present invention). The size of each sample was 25mm x 25mm x 60mm, and the thickness of the glaze was about 0.5mm to 1mm.

After glazing, all samples were heated and fired to 1400°C in an oxidizing atmosphere at a heating rate of 6.5°O/min. After firing, the sample was cut and the cross section was observed with the naked eye.

A photograph showing the cross-sectional appearance is shown in the drawing.

Figure 1 shows that when only the low-temperature glaze was applied (sample 1), the carbonaceous matrix in the 10th part of the matrix remained black before firing and was not oxidized, and the 20th part of the matrix showed that the carbonaceous matrix was not oxidized from the surface to the inside. This indicates that oxidation has progressed slightly. rThe oxidized parts were caused by insufficient glazing.

Either or both of the causes of uneven firing temperature may have been caused by not paying enough attention to filling the kiln, but in any case, if these causes are removed, the glaze using only the low-temperature glaze of the present invention will not work. It was found that it can be fired in an oxidizing atmosphere.

Figure 2 shows the case where only medium temperature glaze is applied (Sample 2)'t
-(1) The unoxidized portion 1 only remained in the center of the sample, and the surrounding area was mostly gray oxidized portion 2. The figure shows the case where only the glaze was applied (sample filtration) and the case where each glaze was applied in this order for high 6, medium temperature, and I vortex (sample 4), and sample 6 was gray over the entire cross section. This shows that the matrix was completely oxidized, and in (sample 4), the entire surface was a black matrix, indicating that it was not oxidized.

The white particles in the scheme are magnesia.

In the end, it was impossible to oxidize a sample that did not use the low-temperature glaze of the present invention, and the present invention made it possible for the first time to oxidize a carbonaceous refractory.

It is clear that the low i crystal glaze of the present invention can be used not only for carbonaceous refractories but also for oxidizing and firing other carbonaceous articles.

[Brief explanation of the drawing]

u', Figures 1 to 6 are photographs showing the particle structures of Examples of the present invention and Samples of Comparative Examples. 1゛°°oxidized? , C part 2... Oxidized partial agent Asamura Hiroshi・1 diagram

Claims (1)

[Claims] A method for producing a carbonaceous refractory, which comprises coating the surface with a glaze and oxidizing it.