JPH03141157A - Refractory for blast furnace having low heat conductivity - Google Patents

Abstract

PURPOSE:To obtain the title refractory having remarkably improved alkali resistance, spalling resistance, abrasion resistance and oxidation resistance by adding prescribed amount of sintering agent and antioxidant to a mixture containing beta-Al2O3, C and SiC at prescribed weight ratio, further adding a binding agent thereto, kneading the mixture and forming and burning the kneaded material. CONSTITUTION:2-10wt.% sintering agent and 1-5wt.% antioxidant are added to 100wt.% mixture consisting of 10-80wt.% beta-Al2O3, 5-25wt.% carbon and 15-85wt.% SiC. A binding agent is further added to the mixture and the mixture is kneaded, formed and burned to provide the aimed blast refractory having low heat conductivity. In the above-mentioned ingredients, it is especially required to use a carbon having dense structure having <=60% graphitization degree as the carbon. The above-mentioned refractory has low heat conductivity, small heat loss and excellent acid resistance and alkali resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low thermal conductivity refractory for blast furnaces which has significantly improved alkali resistance, spall resistance, wear resistance and oxidation resistance.

[Conventional technology] β-alumina, carbon, and silicon carbide have traditionally been used as aggregates,
Japanese Patent Publication No. 56-35630 proposes a refractory for blast furnaces that has improved corrosion resistance, spalling resistance, and alkali resistance by adding metallic silicon to create silicon carbide bonds or carbon bonds between particles. .

However, while the above-mentioned refractories have improved many physical properties,
It has a high thermal conductivity and has the disadvantage of being easily consumed by oxidation at high temperatures.

Therefore, when used on the walls of a blast furnace, there is a large amount of heat loss to the outside of the furnace, and it is desired to improve the thermal economy of blast furnace operation.

Furthermore, the protection of the blast furnace walls was not sufficient due to oxidation damage to the refractories.

[Problems to be Solved by the Invention] Blast furnaces have recently become longer-lived due to improvements in operating technology, repair technology, and cooling methods from the shell.

Accordingly, high durability of refractories is required, and cooling from the steel shell is being implemented to protect the refractories and extend their lifespan.

Carbon-containing refractories with high thermal conductivity are often used as materials suitable for this cooling.

Protecting the furnace body by cooling in this way causes an extremely large amount of heat loss to be released to the outside of the furnace, which is not desirable from a thermoeconomic standpoint.

The present inventors focused on refractories with excellent thermoeconomics without relying on the protection of the furnace body through cooling, that is, refractories with low thermal conductivity that are resistant to damaging effects such as alkali attack, thermal shock, abrasion due to charges, and steam oxidation. , repeated experiments.

[Means for solving the problem] As a result of various experiments to solve the above problem, β-
Select alumina-silicon carbide-carbon based materials, and in this system, carbon with a low degree of graphitization has a low thermal conductivity, and raw materials with a dense structure are susceptible to alkali attack, heat impact and charging. It was discovered that this material has excellent durability against wear, and the present invention was completed.

In other words, the feature of the present invention is that β-alumina 10
~80wt%, carbon 5~25wt%, and silicon carbide 15~85wt% mixture LQQ it%, externally sintering agent 2~10wt% and antioxidant 1~5w
This is a low thermal conductivity refractory for blast furnaces, which is characterized in that it is made by adding a binder to this, kneading it, shaping it, and firing it.

Conventionally, carbon-containing refractories have had insufficient durability because the carbon is oxidized, the structure becomes brittle, and when the refractory is used, the carbon dissolves into hot metal and disappears.

For this reason, in order to impart oxidation resistance to the refractory, a method of adding a small amount of ultrafine silicon carbide to the refractory was disclosed in JP-A-58-11507.
This is proposed by Publication No. 3.

Although several proposals have been made in other literature, there is still room for improvement in their durability.

In the present invention, carbon having a dense structure is used,
Further, a sintering agent and an antioxidant are added and fired to reduce the pore diameter of the refractory and turn the open pores into sealed pores. Furthermore, by minimizing the amount of carbon used, oxidative wear is suppressed.

The carbon used in the present invention includes calcined anthracite coal, coal pitch coke, petroleum pitch coke, earthy graphite, etc. having an appropriate degree of graphitization, and calcined anthracite coal is particularly preferred. Its purity is preferably 80 wt% or more, more preferably 90 wt% or more.

Further, carbon having a dense structure with a degree of graphitization of 60% or less as determined from Franklin's P value is used.

If the degree of graphitization exceeds 60%, the thermal conductivity will increase, which is not desirable.The reason why we limited the amount of 1° carbon to the range of 5 to 25 t% is that if the degree of graphitization exceeds 25*t%, the oxidation resistance will decrease, and the thermal conductivity will increase. rate becomes higher.

Moreover, if it is less than 5 wt%, the coefficient of hot linear expansion becomes large and the spalling resistance decreases.

β-alumina is a material mainly composed of a β-alumina phase obtained by stabilizing Al2O3 with Na, O, or 20, and is a material with much better alkalinity than the α-alumina phase.

The reason why β-alumina is limited to the range of 10 to 80+vt% is that below 10 wt%, the thermal conductivity is 8 kcal/m.
hr becomes higher and the oxidation resistance decreases.

If it exceeds 80 wt%, there will be less silicon carbide and carbon, and the spall resistance will decrease.

It is preferable to use β-alumina powder with a thickness of 0.3 mm or more, and if it is 0.3 mm or less, it is easy to turn into α-alumina by firing.

The purity of silicon carbide is preferably 80wt% or higher, and 90w
More preferably, it is t% or more. Corrosion resistance and alkali resistance decrease as purity decreases.

The reason why silicon carbide is used at 15 to 85 wt% is 85 wt%.
If it exceeds this, the thermal conductivity will increase and the spall resistance will deteriorate. If it is less than 15 wt%, alkali resistance and strength will decrease.

Sintering agents are metallic silicon, metallic aluminum, ferrosilicon, and their alloys, as well as borides such as boron carbide and boron nitride, which transform into oxides, oxynitrides, etc. during firing, and reduce the pore diameter. Bonds between particles to create high strength.

The reason why the amount is 2 to 10*t% is because if it exceeds 10 wt%, the effect cannot be expected to increase in proportion to the amount added, which is uneconomical and the anti-spall property decreases. If it is less than 2 wt%, the number of interparticle bonds is small and no strengthening of the structure is observed.

The antioxidant is 0. Na, 0,820. ．． 510. ,
These include low-melting point powders containing CaO and the like as main components, glass powder, feldspar, borax, and clay.

These coat the particle surfaces and the interparticle spaces during firing, sealing the pores and blocking them from the outside air.

The amount added is limited to 1 to 5 wt%; if it exceeds 5 wt%, the fire resistance of the refractory will decrease and its durability will decrease. 1wt
This is because if the amount is less than %, a sufficient antioxidant effect cannot be obtained.

In addition, for the kneading, molding, firing, etc. with the addition of a binder in the present invention, it is almost sufficient to use the general conditions for manufacturing this type of refractory, so detailed descriptions of the conditions will not be given here. Although omitted, it is preferable that the binder is organic and that the firing is performed in a reducing atmosphere at a temperature of 1,000 to 1,600°C.

[Example] Examples will be described below.

Table 1 shows the blending ratios of Examples (A-F) and Comparative Examples (I-I).

An organic binder such as pitch, anthracene, or synthetic resin is added to each of the mixtures, kneaded, and reduced after molding;
It was fired at a temperature of ~1400°C.

The β-alumina used here is an electrically fused product with a β-alumina conversion rate of 90% or more.

The carbon used was calcined anthracite, pitch coke, and natural phosphorous graphite was used in the comparative example. The purity of silicon carbide, metallic silicon, and metallic aluminum was 91.4%, 97.5%, and 98.5%, respectively.

The chemical components of each raw material used are shown in Table 2.

In Examples A, B, D, and E, a phenolic resin was added to the mixture, and after kneading and molding, baking was performed at 1350° C. in a reducing atmosphere.

In Examples C and F, 4 wt % of hard pitch containing 8% anthracene was added to the mixture, heated and kneaded at 130°C, and after molding, baked at 1100°C in a reducing atmosphere.

Moreover, Comparative Examples I to I were produced in the same manner as Examples A, B, D, and E.

Thermal conductivity, oxidation resistance, alkali resistance, spalling resistance and erosion resistance of each of the specimens produced as described above were measured, and the results are shown in Table 3.

Thermal conductivity was measured by cutting each specimen into a cylinder of 20φ x 150mm by direct heat flow method, and expressed as a value at 600°C.

Regarding oxidation resistance, each specimen was cut into a cube of 40 mm on a side, kept in an electric furnace at 1400° C. for 30 minutes, taken out, and comparatively evaluated by observing the cut surfaces.

For alkali resistance, each specimen was cut into a 20 x 20 x 80 mm square column, and the reagents potassium carbonate and coke powder 20:
80 in a container filled with the mixture, the container is sealed, and kept in an electric furnace at 1300° C. for 5 hours. This is 5
After repeating the test several times, the specimens were taken out and compared based on the dimensional change rate.

For spall resistance, each specimen was measured at 40x 50x 180mm.
It was cut into square columns and placed in hot metal at 1500℃ in an induction furnace.
Comparative evaluations were made by observing the external appearance and cut surface of the specimens which had been immersed for 0 seconds and then cooled in water.

Regarding erosion resistance, each specimen was shaped like a trapezoid (upper side 70mm x
Base 150mm x Height 70mm x Length t: +omm)
It was cut into pieces, laminated with a comparative amount, and heated to 1500°C using an oxygen-propane gas burner. Pig iron and blast furnace slag were put into it at a ratio of 50:50, and the temperature was kept at that temperature for 3 hours while rotating. After that, it was dismantled and the amount of damage was compared and evaluated.

As is clear from Table 3, Examples A to F use a predetermined amount of carbon with a low degree of graphitization, so their thermal conductivity is 3 to 7 kcal/low compared to Comparative Example G.
It is in the range of m, h o ℃.

The oxidation resistance is superior to Comparative Examples A, C, H, and G.

In terms of alkali resistance, it is superior to Comparative Examples 1, 2, and 5.

In terms of spall resistance, it is superior to Comparative Examples 2 and E.

In terms of erosion resistance, it is superior to Comparative Examples A, C, II, Po, H, and G.

As described above, Examples A to F of the present invention are novel refractories that have low thermal conductivity and excellent oxidation resistance, and also have alkali resistance, spall resistance, and erosion resistance (wear resistance).

[Effect of the invention] The refractory of the invention has low thermal conductivity, low heat loss,
In addition, it has excellent acid resistance and alkali resistance, as well as spall resistance and erosion resistance (wear resistance), and has many uses, especially as embedded refractories for blast furnace walls and stave coolers. As such, it is highly suitable in terms of both furnace wall protection and thermoeconomic efficiency.

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Claims (1)

[Claims] 1 β-alumina 10-80wt%, carbon 5-25
2 to 10 wt% of a sintering agent and 1 to 51% of an antioxidant are added to 100 wt% of a mixture consisting of 15 to 85 wt% of silicon carbide, a binder is added thereto, and after kneading, molding, A refractory for blast furnaces with low thermal conductivity characterized by being fired.