JP2000335980A - Graphite-containing monolithic refractory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve spalling resistance and obtain the same durability as brick even in a case where execution range is wide by compounding a mullite raw material specified in particle diameter and alumina content with artificial graphite having a specific particle diameter at a specific ratio. SOLUTION: This monolithic refractory comprises 10-70 wt.% mullite raw material containing 65-90 wt.% alimina having 100 μm to 10 mm particle diameter and 3-20 wt.% artificial graphite having 100 μm to 1 mm average particle diameter. Generally commercialized electrofused product or baked product can directly be used as the mullite raw material and, as necessary, single mullite raw material or plural mullite raw materials are pulverized and classified and compounded and can be used singly or as a mixture of the plural raw materials. It is preferable to add and use 0.5-6 wt.% pitch powder having 100 μm to 1 mm particle diameter and 4-12 wt.% SiC powder having <=100 μm particle diameter as additives to the monolithic refractory. Further, 1-10 wt.% magnesia or sillimanite mineral raw material having 100 μm to 3 mm particle diameter can be added to the monolithic refractory.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amorphous refractory, and more particularly to an amorphous refractory for lining a mixed iron car.

[0002]

2. Description of the Related Art In a steel making process, a mixed iron wheel is used to transport hot metal from a blast furnace to a converter. For more than ten years, pretreatment for removing impurities such as Si, S, and P from hot metal has been performed in a mixed iron wheel. Usually, the lining of a mixed iron car is constructed by stacking refractory bricks. However, in recent years, there has been a shortage of skilled brick-laying workers, and the use of irregular-shaped refractories instead of bricks has been studied. In general, amorphous refractories are used for ladles and blast furnace tapping gutters, contributing to cost reduction and mechanization and automation of construction. However, for refractory linings, it is difficult to apply refractories compared to ladles, etc., or irregular refractories are not sufficiently durable. It has not spread yet.

A lining material for a mixed iron vehicle is required to have erosion resistance capable of withstanding the pretreatment slag generated in the above pretreatment and spalling resistance in an environment where the outer periphery is restricted by a steel shell. From this viewpoint, alumina-SiC-graphite brick is
Since the contained SiC and graphite are effective in preventing wetting with the flux, they have excellent erosion resistance, and also have high spalling resistance due to their low thermal expansion coefficient, low elastic modulus, and high thermal conductivity. I have.

However, in the case of the refractory of the same type as the above-mentioned brick, since graphite has poor wettability with water, it is necessary to use a large amount of added water to ensure pouring workability. As a result, there is a problem that the porosity of the refractory after construction is significantly increased. Conventionally, to solve this problem, a method of pulverizing and adhering an oxide having good wettability with water to graphite (JP-A-6-166574) has been proposed. The problem is to raise costs. A method of applying mechanical impact to artificial graphite (JP-A-8-183666) or scaly graphite (JP-A-8-301667) is also known, but still has a problem of cost. Further, a method using anthracite (JP-A-8-183667) or earth graphite is also known, but it is difficult to obtain erosion resistance and spalling resistance equivalent to scale graphite added to brick. is there.

[0005] The present inventors have developed an amorphous refractory having a low water content, excellent castability, and high erosion resistance and spalling resistance by using a combination of pitch having a specific particle size, artificial graphite and alumina aggregate. (Japanese Patent Application No. 9-357559) and an amorphous refractory (Japanese Patent Application No. 10-106504) improved in spalling resistance by adding magnesia aggregate. However, when the construction range of the irregular-shaped refractory is wide (for example, lining of a mixed iron wheel), higher spalling resistance is desired.

As described above, conventionally, even when the construction range of the amorphous refractory is wide (for example, lining of a mixed iron wheel), the durability (especially the spalling resistance) is comparable to brick.
The fact is that there was no amorphous refractory having

[0007]

SUMMARY OF THE INVENTION The present invention improves the spalling resistance, and has the same durability as the conventional brick even when the range of construction of the refractory is wide. The purpose is to provide things.

[0008]

Means for Solving the Problems The inventors of the present invention have tested an amorphous refractory mainly composed of alumina aggregate containing artificial graphite having relatively good spalling resistance in a mixed iron wheel, Detailed investigation of the factors governing service life led to the present invention. According to trials with mixed iron cars, when an amorphous refractory that does not contain artificial graphite is used, thermal stress creates a crack inside the amorphous refractory parallel to the surface that comes into contact with the hot metal, and as the number of uses increases It was found that spalling accelerated the wear of amorphous refractories. For practical use, it is essential to improve spalling resistance. To achieve this, it is necessary to add a large amount of graphitized carbon material to achieve low elastic modulus, low thermal expansion coefficient, and high thermal conductivity. It is.

[0009] Graphitized carbon raw materials include scaly graphite, quiche graphite and artificial graphite. When scaly graphite and quiche graphite are used, a large amount of added water is required to ensure pouring workability, so that the porosity of the refractory after construction is high and is not suitable for practical use. However, when artificial graphite is used, the amount of added water required to ensure pouring workability has a correlation with the particle size of artificial graphite, and fine particles require a large amount of added water, while coarse particles require a small amount of added water. It became clear that it was enough.

The present invention relates to an artificial graphite having a particle size of 100 μm to 10 mm, containing 10 to 70% by weight of a mullite raw material containing 65 to 90% by weight of alumina, and having an average particle size of 100 μm to 1 mm.
It is an amorphous refractory containing up to 20% by weight.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
If the average particle size of the artificial graphite is less than 100 μm, the amount of added water necessary to ensure pouring workability increases, and oxidation occurs in the air, and the silica component in the mullite raw material, which is an additive, is reduced to reduce the usefulness. It may cause a loss of performance. On the other hand, if the average particle size of the artificial graphite exceeds 1 mm, the effect of improving spalling resistance is reduced due to the localization of the graphite, and it is difficult to obtain, which is not preferable in terms of cost. Therefore, it is necessary to use artificial graphite having a particle size in the range of 100 μm to 1 mm.

Regarding the addition amount of artificial graphite in the amorphous refractory, if the addition amount of artificial graphite is less than 3% by weight, low elastic modulus, low coefficient of thermal expansion, and high thermal conductivity cannot be maintained, and spalling resistance is low. The effect of improvement is poor. On the other hand, if the added amount of artificial graphite exceeds 20% by weight, the amount of added water necessary for ensuring the workability of pouring even coarse-grained graphite increases, which causes a deterioration in durability. Therefore, refractories of irregular shape
It is necessary to use one containing 3 to 20% by weight of artificial graphite.

The addition of the mullite raw material has the effect of reducing the coefficient of thermal expansion of the amorphous refractory. The decrease in the coefficient of thermal expansion increases the thermal shock resistance, and thus has the effect of improving the spalling resistance. In the case of refractories in which the periphery such as the lining of a mixed-iron car is strongly constrained by a steel shell, the thermal expansion coefficient decreases, which reduces the compressive thermal stress of the inner surface during heating. Sometimes the occurrence of cracks can be suppressed because the tensile stress on the inner surface is reduced. Further, there is an effect of improving spalling resistance by improving mechanical properties at high temperature (particularly, lowering the elastic modulus).

Mullite has a composition of 3Al ₂ O ₃ .2SiO ₂ (alumina component: about 70% by weight). When the composition is alumina-rich, mullite becomes a mixture of a mullite phase and an alumina phase. Phase and a silica phase. If the alumina component in the mullite raw material is less than 65% by weight, the low melt is increased due to the silica phase, and the corrosion resistance is reduced. 90% by weight of alumina component in mullite material
If it exceeds, the mullite phase decreases and the effect of lowering the thermal expansion coefficient is small. Therefore, it is necessary to use a mullite raw material containing 65 to 90% by weight of an alumina component.

[0015] Mullite has lower corrosion resistance than alumina, and the silica contained therein is reduced to carbon, which is a cause of impairing the durability. If the particle size of the mullite is less than 100 μm, the dissolution rate in slag is increased and the corrosion resistance is remarkably reduced, and the reduction rate by carbon is also increased, which is not suitable for practical use. On the other hand, if the particle size of the mullite exceeds 10 mm, there is a problem that the aggregate is easily separated at the time of casting. Therefore, it is necessary to use a mullite material having a particle size of 100 μm to 10 mm.

If the content of the mullite raw material in the amorphous refractory is less than 10% by weight, the effect of lowering the coefficient of thermal expansion is small due to the small amount of the mullite phase, and the effect of improving the mechanical properties at high temperatures is also small. On the other hand, the amount of mullite
If the content is more than 10% by weight, the fluidity of the amorphous refractory is impaired. Therefore, the content of the mullite raw material in the amorphous refractory must be 10 to 70% by weight.

As the mullite raw material, a commercially available electrofused product or calcined product (also referred to as a synthetic product) can be used as it is, or if necessary, pulverized, classified, blended, or a mixture of a plurality of raw materials. Can be used as In addition, the natural raw material sillimanite minerals
Mullite can be obtained by heat treatment at 00 to 1750 ° C., and it can be used alone or as a mixture of a plurality of raw materials in the same manner as an electrofused product or a calcined product.

Although the amorphous refractory of the present invention is sufficiently effective only with the above basic configuration, this basic configuration can be combined with other techniques. Hereinafter, preferred technologies to be combined with the present invention will be described. First, pitch powder can be added. The addition amount of the pitch powder is desirably 0.5 to 6% by weight. According to the results of the erosion test using pig iron and pre-treated slag, it was found that pitch powder suppressed slag penetration with the smallest amount of addition compared to other carbon materials and improved erosion resistance. It has been confirmed that sufficient resistance to erosion can be ensured by adding a small amount of pitch powder even in trials with mixed iron cars. However, if the added amount of the pitch powder is less than 0.5% by weight, the effect of improving the erosion resistance is small, and if it exceeds 6% by weight, the porosity increases due to heating, and the erosion resistance is impaired.

As the pitch powder, a coal tar pitch powder containing 50% by weight or more of fixed carbon can be used. Since the pitch powder is liquefied when heated and moves into nearby fine pores by capillary action, the particle size of the pitch powder does not significantly affect the properties of the amorphous refractory. Therefore, the particle size of the pitch powder is not particularly limited, but if the particle size exceeds 1 mm, the pitch powder is unevenly distributed even after liquefaction. On the other hand, if it is less than 100 μm, the amount of added water must be increased, which is not preferable. Therefore, it is necessary to use a pitch powder having a particle size of 100 μm to 1 mm.

Further, SiC powder can be added. It is desirable that the particle size of the SiC powder be 100 μm or less, and the amount added be 4 to 12% by weight. In the atmosphere, graphite oxidizes at high temperatures. Particle size 100
In the case of artificial graphite of μm to 1 mm, it does not oxidize up to about 1000 ° C., but at higher temperatures, oxidation proceeds in a high oxygen atmosphere. Therefore, when the SiC powder is added, the SiC powder is oxidized before the artificial graphite, so that the oxidation of the artificial graphite can be suppressed. This effect is remarkably exhibited at 1300 ° C. or higher.

It is not preferable to use SiC powder having a particle size exceeding 100 μm because the effect of suppressing the oxidation of graphite is small. If the amount of the SiC powder having a particle diameter of 100 μm or less is less than 4% by weight, the effect of suppressing the oxidation of graphite is small, which is not preferable. On the other hand, if the addition amount exceeds 12% by weight, the effect of suppressing oxidation is saturated, and at the same time, the amount of added water necessary for ensuring the pouring workability increases, and the durability is impaired.

The SiC powder suppresses the oxidation of graphite,
It has the effect of increasing the thermal conductivity. Therefore, from the viewpoint of improving the spalling resistance, the addition of the SiC powder is preferable. Further, when 1 to 10% by weight of a raw material of magnesia or a sillimanite group mineral having a particle size of 100 μm to 3 mm is added, the residual expandability can be added and the generation of cracks can be reduced. As magnesia, a calcined product, a calcined product, or the like can be used, and an electrofused product is particularly desirable.

The effect of the additive used in the irregular refractory material of the present invention is as described above. However, as a material to be used in place of or in combination with mullite, a particle diameter of 0.1 μm to
10mm alumina can be used. The particle size is 0.1μm ~ 10mm
Magnesia-alumina spinel can also be added. The fused alumina or magnesia-alumina spinel having a particle size of 0.1 μm to 10 mm is preferably an electrofused product.

As the magnesia-alumina spinel, a spinel containing about 25% by weight of MgO or a raw material having a mixed phase of spinel and corundum can be used. When the basicity (CaO / SiO ₂ ) of the slag is lower than 2, it is preferable to use alumina alone, and when the basicity is higher than 2, it is preferable to use magnesia-alumina spinel.

The particle size distribution is adjusted by mixing raw materials of various particle sizes as required. For the adjustment of the particle size, the balance of each particle size is important. When creating a graph of the particle size distribution, if the horizontal axis of the graph is the particle size and the vertical axis is the cumulative volume ratio from the fine particle side, and the graph is created using logarithm on each axis, a linear particle size distribution (Andreasen And the slope of the straight line is preferably in the range of q = 0.2 to 0.28.

Other small amounts of raw materials to be added include alumina cement for providing strength without heating, metals such as Si for supplementing strength, carbon black, clay for adjusting fluidity of amorphous refractories, and the like. Silica fine powder and various dispersants, water reducing agents, and cement setting modifiers may be added.

[0027]

EXAMPLES The effects of the present invention will be described in detail below with reference to examples. After adding a predetermined amount of added water to artificial graphite and mullite raw materials shown in Tables 1 and 2, and kneading with a universal mixer,
Using a flow table, the tapping flow was measured 15 times (the target was 180 mm), and the flowability was examined. Table 1,
Except for the components shown in 2, 2, 10% by weight of SiC, 2% by weight of pitch powder, 0.5% by weight of carbon black, 2% by weight of metal silicon powder, 3% by weight of alumina cement, 1% by weight of clay , Containing 15% by weight of calcined alumina fine powder, with the balance being fused alumina. Further, 0.1% by weight of a dispersant was added.

[0028]

[Table 1]

[0029]

[Table 2]

Thereafter, the mixture was poured into a 40 × 40 × 160 mm prismatic metal frame, cured for 24 hours, deframed and dried at 110 ° C. for 24 hours. Then, at 1400 ° C in a coke breeze,
The sintering was carried out for a period of time, and the porosity and the coefficient of thermal expansion were measured. It was poured into a trapezoidal column-shaped metal frame, cured for 24 hours, deframed and dried at 110 ° C. for 24 hours. And then
The melt erosion test was performed by cooling in a coke breather at 500 ° C. for 3 hours. In the erosion test, a crucible was assembled with eight test pieces, hot metal was put inside, the temperature was raised to 1600 ° C in a nitrogen flow, and then hot metal pretreatment slag (basicity 1.8) was charged and scraped every hour. The cooling was carried out for a total of 3 hours.

After cooling, each test piece was cut in the vertical direction (perpendicular to the surface in contact with the hot metal), and the maximum depth of erosion (the interface between the hot metal and slag) was compared with a standard sample. . Here, the standard sample is a current brick for a mixed iron wheel, and its composition is alumina-7% by weight SiC-15% by weight scale graphite. In addition, some samples, after deframing and drying,
After firing in a coke breeze at 1400 ° C. for 3 hours, the porosity was investigated.

Further, the composition having excellent fluidity and erosion index obtained in the above-mentioned investigation (hereinafter referred to as evaluation in the experimental stage) was kneaded with a mortar mixer for 3 minutes, and the conical portion was removed from the straight body portion of the mixed iron wheel. 20m thick in the area of 2m x 4m
Pour at 0mm, after curing for 24 hours, remove the frame and use a burner for 48
After drying for an hour, the durability was evaluated by actually using 250 charges (hereinafter referred to as actual furnace evaluation).

In the actual furnace evaluation, the presence or absence of cracks perpendicular to the surface in contact with the hot metal (hereinafter referred to as the operating surface) was examined by external appearance observation. Also collect the refractories after use,
A comparison was made with the remaining thickness of the surrounding brick. When cutting the refractory for recovery, the existence of internal cracks parallel to the working surface was investigated. The results are shown in Tables 1 and 2. Table 1 summarizes the performance of the present invention, and Table 2 summarizes the performance of the comparative example.

First, the effect of artificial graphite will be described. When the average particle size of the artificial graphite is less than 100 μm (Comparative Example 1:
(Average particle size 30 μm), a large amount of added water is required to ensure fluidity, and this causes an increase in porosity. As a result, it showed inferior characteristics in the evaluation of erosion at the experimental stage,
Not practical. When the average particle size of artificial graphite exceeds 1 mm (Comparative Example 2: average particle size of 1.5 mm), spalling resistance is not improved due to uneven distribution of graphite. As a result, in the actual furnace evaluation, many cracks were generated and the wear was fast.

On the other hand, the artificial graphite has an average particle size of 100 μm to 1 μm.
In the case of mm (Invention Examples 1 to 3), the porosity was low in the evaluation at the experimental stage and an excellent erosion index was exhibited, and no crack was observed in the actual furnace evaluation of 250 charges, indicating a residual thickness comparable to brick. Was. When 2% by weight of artificial graphite was added (Comparative Example 3), although the erosion index was excellent in the evaluation at the experimental stage, many internal cracks occurred in the evaluation in the actual furnace, and the residual thickness was larger than that of the brick. Was significantly less. Further, when 22% by weight of artificial graphite was added (Comparative Example 4), poor properties were exhibited in the evaluation of erosion at the experimental stage, which was not suitable for practical use.

On the other hand, when artificial graphite was added in an amount of 3 to 20% by weight (Inventive Examples 4 to 6), a large amount of added water was not required, and the porosity was low in the evaluation at the experimental stage, indicating an excellent erosion index. Was.
Furthermore, no cracks were observed in the actual furnace evaluation, and the durability was comparable to that of brick. Next, the effect of the mullite raw material will be described. When the particle size of the mullite raw material is less than 100 μm (Comparative Example 5: particle size of 10 to 100 μm), the solubility of the mullite raw material in slag increases, and the mullite raw material reacts with the graphite added in combination. It shows poor characteristics in evaluation and is not suitable for practical use. When the mullite raw material has a particle size of more than 10 mm (Comparative Example 6: particle size of 10 to 30 mm), the mullite raw material is coarse and tends to separate in the evaluation of fluidity in an experimental stage, which is not suitable for practical use.

On the other hand, the mullite raw material has a particle size of 100 μm to 10 μm.
In the case of mm (Invention Examples 7 and 8), the corrosion resistance to slag is sufficient and the reactivity with graphite is low, so that a high erosion evaluation is obtained in the experimental stage, and a tendency to separate even in the evaluation of fluidity is observed. Did not. No cracks were observed in the actual furnace evaluation of 250 charges, and the remaining thickness was comparable to that of brick. When the mullite raw material was added in an amount of 8% by weight (Comparative Example 7), although the thermal expansion coefficient was high and the erosion index evaluated in the experimental stage was excellent, many cracks were generated in the actual furnace evaluation, and compared with brick. The remaining thickness was small. Further, when 75% by weight of the mullite raw material is added (Comparative Example 8), a large amount of added water is required to secure fluidity, and the porosity increases. As a result, not only do the erosion evaluations at the experimental stage show inferior properties, but also there is a tendency to separate in the evaluation of the fluidity, which is not practical.

On the other hand, when the mullite raw material is added in an amount of 10 to 70% by weight (Inventive Examples 9 to 11), the coefficient of thermal expansion can be sufficiently reduced, and a large amount of added water is not required. as a result,
In the evaluation at the experimental stage, the porosity is low and shows an excellent erosion index,
No tendency for separation was observed in the evaluation of fluidity.
Further, no cracks were observed in the actual furnace evaluation, the residual thickness was comparable to that of brick, and excellent durability was exhibited.

Further, the alumina component in the mullite raw material is 65
If the amount is less than 10% by weight (Comparative Example 9: 63% by weight of alumina component), the amount of low melt is increased due to the silica phase, and the corrosion resistance is undesirably reduced. When the alumina component in the mullite raw material exceeds 90% by weight (Comparative Example 10: Alumina component
93% by weight), which is not preferable because the effect of lowering the coefficient of thermal expansion is reduced because the amount of the mullite phase is reduced.

On the other hand, when the alumina component in the mullite raw material is 65%
In the case of 9090% by weight (Inventive Examples 12 and 13), the coefficient of thermal expansion is sufficiently reduced without impairing the corrosion resistance. No cracks were observed in the actual furnace evaluation, showing a residual thickness comparable to that of brick, and excellent durability. As shown in Table 1, the mullite raw material can be used for both electrofused and calcined products.

[0041]

According to the present invention, artificial graphite having an average particle size of 100 μm to 1 mm is used as an amorphous refractory for lining a mixed iron car.
10 to 70% by weight of mullite raw material containing ~ 20% by weight, having a particle size of 100µm to 10mm and containing 65 to 90% by weight of alumina
The use of the contained refractory material prevented the occurrence of cracks inside the refractory material and achieved a durability equivalent to that of brick.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masato Kumagai 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Research Institute (72) Inventor Akitoshi Urushiya 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture ( No address) Inside the Mizushima Works of Kawasaki Steel Corporation (72) Inventor Satoshi Terayama 1576 Nakahiro, Higashi-oki, Higashi-Oki 2 Kawasaki Furnace Materials Co., Ltd. (72) Inventor Noboru Komatsubara Naka, Ako City, Hyogo Prefecture F-term in Kawasaki Reactor Co., Ltd., 1576, Hiroki Higashi-oki, F-term (reference) 4G033 AA02 AA15 AB01 BA01 4K014 AD21 4K051 AA06 AB03 AB05 BB03 BE03 GA01 LA02 LA11 LC01

Claims (1)

[Claims] Claims: 1. Alumina having a particle size of 100 μm to 10 mm and alumina
An amorphous refractory comprising 10 to 70% by weight of a mullite raw material containing 65 to 90% by weight and 3 to 20% by weight of artificial graphite having an average particle size of 100 μm to 1 mm.