JP2000128650A - Amorphous refractory for casting application - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amorphous refractory for casting application, capable of being used for the linings of steel-melting vessels, etc., and having excellent durability. SOLUTION: This amorphous refractory for casting application comprises refractory aggregates and refractory coarse granules containing alumina and MgO.Al2O3-based spinel as main materials. Therein, organic fibers are added, and 3-20 wt.% of the MgO.Al2O3-based spinel comprises calcined MgO.Al2 O3-based spinel ultrafine powder having an average particle diameter of <=5 μm, wherein the total amount of the refractory aggregates and the refractory coarse granules is 100 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an irregular-shaped refractory for casting, which is particularly suitable for lining a molten steel container.

[0002]

2. Description of the Related Art Amorphous refractories (hereinafter referred to as "casting materials") for casting are used for lining of molten steel containers such as molten steel ladle, tundish, and molten steel vacuum degassing furnace.
Spinel has been proposed (JP-A-1-87577,
JP-A-2-225379, JP-A-4-59665, JP-A-5
-238838). This material exhibits excellent durability due to the corrosion resistance and volume stability of alumina and the slag penetration resistance of spinel.

[0003]

However, in recent years, the conditions of use of molten steel containers are that the durability of conventional lining materials is not sufficient due to increased temperature of molten steel, prolonged stagnation time, and harshness due to gas blowing and stirring. I can't get it. Therefore, there is a strong demand for providing a more durable casting material than the above-mentioned conventional materials.

[0004]

A feature of the present invention is that the refractory aggregate mainly composed of alumina and MgO.Al ₂ O ₃ -based spinel and the refractory coarse-grained refractory for casting. In the above method, 3-20 wt% of the MgO.Al ₂ O ₃ -based spinel is calcined with an average particle size of 5 μm or less in a ratio of 100 wt% of the total amount of the refractory aggregate and the refractory coarse particles, while adding organic fibers. MgO / Al
A construction for monolithic refractories poured which was ₂ O ₃ spinel micronized.

[0005] It is known that the composition of the casting material is such that refractory coarse grains are added separately from the refractory aggregate (Japanese Patent Laid-Open No. 4-5966).
No. 5). The refractory coarse grains cut the growth of cracks generated in the refractory structure and prevent the growth of cracks, thereby improving the spalling resistance of the cast material.

[0006] However, the refractory coarse particles reduce the fluidity of the cast material during construction. This decrease in fluidity causes problems such as difficulty in quick construction, difficulty in filling small places, and inferior compactness of the construction body.

Therefore, MgO.Al _{2 having} a particle size of 5 μm or less
It has been proposed to improve the fluidity as well as the slag permeation resistance by adding ultrafine powder of O ₃ -based spinel (hereinafter referred to as spinel) (Japanese Patent Laid-Open No. 5-238838). However, durability is not enough.

[0008] The present invention uses ultra-fine spinel powder, particularly ultra-fine calcined spinel powder. The addition of the ultrafine calcined spinel powder provides excellent durability by improving hot strength in addition to fluidity.

Generally, a refractory raw material is produced by strong firing at a high temperature for the purpose of improving the degree of fire resistance and denseness. The firing temperature of spinel as a refractory raw material is usually 1800 to 2000 ° C.
Conventionally used spinel ultrafine powder is also obtained by finely pulverizing this strongly fired product. On the other hand, the calcined spinel ultrafine powder used in the present invention has been calcined at a low temperature of, for example, 1600 ° C. or less.

[0010] The material using the refractory coarse grains is liable to generate fine cracks starting from the interface of the refractory coarse grains in the wear-out process of the refractory, peeling of the refractory coarse grains, and the like. The calcined spinel ultrafine powder is chemically active because it is produced by low-temperature sintering, and its sintering effect firmly holds the refractory coarse grains, prevents the fine cracks and spalling described above, and sets the hot strength of the cast material. Improve. In addition, the refractory coarse grains and the strongly sintered spinel structure exist around the refractory coarse grains, thereby preventing the slag from penetrating into the interface of the refractory coarse grains.

However, if the calcined spinel ultrafine powder is added in an amount sufficient to overcome the decrease in fluidity due to the use of refractory coarse grains, its reactivity leads to oversintering of the cast material structure, resulting in spalling resistance. It may cause a decline in sex. If the lining of a molten steel ladle or the like is inferior in spalling resistance, peeling damage occurs due to thermal shock caused by receiving and discharging molten steel, and improvement in durability cannot be expected. The present invention prevents the spalling resistance from lowering by adding an organic fiber.

Organic fibers are known as drying aids for casting materials. It is also known as a sintering inhibitor (Japanese Patent Application Laid-Open No. 2-225379). However, it has not been known to add organic fibers for the purpose of preventing oversintering due to ultra-fine calcined spinel powder.

In the present invention, the spalling resistance due to the refractory coarse grains and the effect of improving the fluidity and hot strength due to the calcined spinel ultrafine powder are exhibited only by the addition of the organic fiber.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing the ultrafine calcined spinel powder used in the present invention is not particularly limited. For example, an alumina source such as calcined alumina or aluminum hydroxide and a magnesia source such as lightly-baked magnesia or magnesium hydroxide are mixed at an arbitrary ratio, fired in a low temperature range, and then finely pulverized. The specific firing temperature is preferably 1600 ° C. or lower. If it exceeds 1600 ° C., the activity decreases and the sintering effect of the cast material is poor.
The lower limit of the sintering temperature is preferably 1100 ° C. in order to cause spinel bonding by mutual reaction between alumina and magnesia.
The most preferable firing temperature is 1100 to 1500 ° C.

The chemical composition of the calcined spinel ultrafine powder is, for example,
MgO: 10-35 wt%, the balance being Al ₂O₃Be the subject.
If there is too much MgO, there is a problem of hydration with construction water,
Not good.

The average particle size of the ultrafine spinel powder is 5 μm or less. If the average particle size exceeds 5 μm, the sintering effect is poor,
The effect of improving hot strength in the present invention cannot be obtained. A more preferred average particle size is 0.2 to 3 μm. Average particle size
Although the effect of the present invention can be obtained even when the thickness is 0.2 μm or less, it is not preferable in terms of productivity due to the labor required for pulverization.
The average particle size can be specified by, for example, a laser type particle size distribution analyzer.

The proportion of the ultrafine spinel powder is the proportion of the total amount of the refractory aggregate and the refractory coarse particles in the total amount of 100 wt%. If it is less than 3 wt%, the hot strength and the fluidity are inferior. And the spalling resistance decreases.

As the spinel, in addition to the above-mentioned ultrafine powder, a spinel having a larger particle diameter than the ultrafine powder may be used in combination. In that case, the ratio of the entire spinel including the ultrafine powder described above is 100 wt.
% Is preferably not more than 40 wt%. If it exceeds 40 wt%, the spalling resistance is poor. Further, as the spinel other than the calcined spinel ultrafine powder, an ordinary strongly fired product or an electrofused product can be used.

Alumina as a refractory aggregate is used for electrofusion, firing
Any of the products may be used. In addition, calcined product is used for fine powder part
May be. Natural raw materials such as sand shale and bauxite
Is Al₂O₃Due to the low purity,
If only a part, Al₂O ₃Mainly synthetic products with high purity
Is preferable.

The proportion of alumina as the refractory aggregate is 3% in the total amount of 100 wt% of the refractory aggregate and the refractory coarse particles.
5 to 85 wt% is preferred. If it is less than 35 wt%, the spalling resistance is poor, and if it exceeds 85 wt%, the slag penetration resistance is poor.

As the refractory aggregate, for example, magnesia may be used in combination in addition to spinel and alumina.
When combining magnesia, the total amount of refractory aggregate and refractory coarse particles should be 100 to avoid lowering spalling resistance.
It is preferably at most 10 wt% as a percentage of wt%. Also,
When magnesia is combined, it is preferable to reduce the proportion of spinel other than the calcined spinel ultrafine powder.

In addition, silica, mullite, calcia, magnesia-calcia, zircon, zirconia, chromia,
Carbon, carbide, nitride, boride, clay, mullite, etc. may be partially combined.However, if the amount is large, the hot strength is reduced.
It is preferable that the content is 5% by weight or less as a proportion of 0% by weight.

The particle size of each refractory aggregate is adjusted to coarse particles, medium particles, and fine particles in the same manner as in the conventional casting material, taking into account the calcined spinel ultrafine powder used in the present invention.

As the material of the refractory coarse particles, a sintered product such as alumina or spinel or an electrofused product, or a refractory waste material containing these as a main material can be used.

The ratio of the refractory coarse particles is a ratio of 10 to 35 watts in the total amount of 100 wt% of the refractory aggregate and the refractory coarse particles.
t% is preferred. If the amount is small, the effect of spalling resistance of the refractory coarse particles becomes insufficient. If it is too large, a tightly packed structure cannot be obtained due to a decrease in fluidity during construction.

The maximum particle size of the refractory aggregate is generally 3 to 8 mm. The refractory aggregate is adjusted to coarse, medium, and fine particles within the range of the maximum particle size or less. The particle size of the refractory coarse particles is even larger than that of the refractory aggregate.

The specific particle size of the refractory coarse particles depends on the maximum particle size of the refractory aggregate, but is usually 10 to 50 mm. If the particle size of the coarse particles is too small, the spalling resistance of the coarse particles cannot be obtained. If it is too large, it will not be possible to fill narrow locations, and the fluidity will be significantly reduced.

The organic fiber is a polymer organic material such as vinylon (including polyvinyl alcohol), rayon, polyester, nylon, polypropylene and polyethylene. The length is preferably 1 to 10 mm. In addition, the ratio is 100 w combined amount of refractory aggregate and refractory coarse particles.
0.05 to 1 wt% is preferable to t%. If the amount is too small, the effect of spalling resistance cannot be obtained, and if it is too large, the corrosion resistance decreases.

The binder is most preferably alumina cement, but is not limited thereto and may be magnesia cement or the like. The ratio depends on the type of the binder, but is preferably 1 to 15 wt% with respect to 100 wt% of the total amount of the refractory aggregate and the refractory coarse particles.

Dispersants, curing accelerators, curing retarders, drying accelerators, and A
metal powder such as l, volatile silica, basic aluminum lactate,
Glass powder, pitch powder, carbon fiber, metal fiber (for example, stainless steel fiber), ceramic fiber, etc. may be added.

Among these, dispersants are most commonly used for imparting fluidity. Specific examples of the dispersant include, for example, sodium tripolyphosphate, sodium hexametaphosphate, sodium ultrapolyphosphate, sodium acid hexametaphosphate,
Inorganic salts such as sodium borate and sodium carbonate; sodium citrate; sodium tartrate; sodium polyacrylate; sodium sulfonate; polymetaphosphate; polycarboxylate; It is added in an amount of about 0.01 to 0.5 wt% with respect to 100 wt% of the total amount of the refractory aggregate and the refractory coarse particles.

When metal fibers are added, the ratio is preferably 4 wt% or less based on 100 wt% of the total amount of the refractory aggregate and the refractory coarse particles.

The casting of the casting material of the present invention is carried out as usual.
About 4 to 8 wt% of construction water is added to and mixed with the entire composition described above, and the construction is poured. At the time of construction, it is preferable to apply vibration with a vibrator in order to enhance the filling property. In addition to directly using a core in a molten steel container or the like, a precast block obtained by casting in advance may be lined.

[0034]

EXAMPLES Table 1 shows the particle diameters, chemical analysis values and firing temperatures of the ultrafine spinel powder used in the examples of the present invention and the comparative examples. Table 2 shows the composition and test results of the inventive examples and comparative examples. For the tests shown in Table 2,
The test method is as follows.

Fluidity: 6 wt% of the working water was added to the composition shown in Table 2 and kneaded with a mixer, and the tap flow value was measured. The numerical value is the diameter of the base after flowing, and the larger the numerical value, the higher the fluidity.

Hot bending strength: To the composition shown in Table 2, 6% by weight of the working moisture was added and kneaded with a mixer.
Pour into a vibrating formwork, cure and dry.
The bending strength was measured at a temperature of 0 ° C. to evaluate the hot strength.

Spalling resistance: The cast molded article obtained in the same manner as above was heated at 1650 ° C. for 30 minutes, air-cooled, repeated 6 times, and evaluated for the occurrence of cracks. ◎
… No cracks, ○… Minimal cracks, Δ… Small cracks, ×… Large cracks.

Corrosion resistance: The cast molding obtained above was tested. A steel slab: converter slag (FeO content; 20% by weight) = 1: 1 by weight ratio as an erosion agent, 1650 ° C. ×
A 4-hour rolling erosion test was performed to measure the erosion size.

Slag penetration resistance: After the above-mentioned rotational erosion test,
The slag penetration size was measured. Durability: The core was poured into a 100-ton molten steel ladle using a core, cured, heated and dried at about 1000 ° C., and used, and the number of usable charges was measured. If the column of the test result is blank, the test was not performed.

[0040]

[Table 1]

[0041]

[Table 2]

As shown by the test results in Table 2, the examples of the present invention show that fluidity, hot strength, spalling resistance, corrosion resistance,
The slag penetration resistance is excellent, and as a result, the improvement of the durability in actual equipment is very remarkable. On the other hand, in Comparative Example 1, since the calcined spinel ultrafine powder has a large average particle size, sufficient effects on hot strength and corrosion resistance cannot be obtained.

In Comparative Example 2, the calcined spinel ultrafine powder was not used, and calcined alumina was used as the ultrafine powder, and was inferior in hot strength, corrosion resistance and slag penetration resistance. In Comparative Example 3, the ratio of the ultra-fine calcined spinel powder was too large, and the spalling resistance was poor.

Comparative Examples 4 and 5 using the ultrafine sintered spinel powder are inferior in hot strength, corrosion resistance and slag penetration resistance. Comparative Example 6 in which no organic fiber was added and Comparative Example 7 in which no refractory coarse particles were contained were both inferior in spalling resistance.

[0045]

The cast material of the present invention exhibits excellent effects on the fluidity, spalling resistance, corrosion resistance and hot strength in addition to the slag penetration resistance inherent in alumina-spinel. As a result, it shows sufficient durability even under recent severe use conditions in a molten steel container or the like.

Claims (2)

[Claims] 1. An irregular shaped refractory for casting including a refractory aggregate mainly composed of alumina and MgO.Al ₂ O ₃ -based spinel and refractory coarse grains, wherein an organic fiber is added, and the refractory aggregate and Total amount of refractory coarse grains 100
3 to 20 wt% of the MgO.Al ₂ O ₃ -based spinel is a calcined Mg having an average particle size of 5 μm or less.
O.Al ₂ O ₃ -based spinel ultra-fine powder, refractory for casting. 2. The irregular shaped refractory for casting according to claim 1, wherein the calcined MgO.Al ₂ O ₃ -based spinel ultrafine powder has a firing temperature of 1600 ° C. or less.