JPH0288468A - Magnesia-calcia refractories - Google Patents

Abstract

PURPOSE:To obtain refractories having superior spalling and thermal shock resistances by blending MgO-CaO refractory aggregate contg. synthetic clinker made of CaO coated with MgO with aragonite type calcium carbonate. CONSTITUTION:100 pts.wt. refractory aggregate consisting of 20-95wt.% MgO and 80-5wt.% CaO and contg. synthetic MgO-CaO clinker made of 60-40wt.% CaO coated with 40-60wt.% MgO is blended with 0.5-5 pts.wt. aragonite type calcium carbonate of 0.5-10mm diameter to obtain magnesia-calcia refractories. The aragonite type calcium carbonate is converted into calcite type at 330-480 deg.C at the time of calcining in the production of the refractories. Since the conversion is accompanied by about 8% volume expansion, many microcracks occur in brick. These microcracks produce a stress propagation preventing effect at the time of use and are very effective in preventing the extension of cracks due to spalling.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnesia-calcia refractory having excellent digestion resistance, spalling resistance and corrosion resistance.

Prior art and its problems Dolomite refractories have been widely used as lining materials for various furnaces such as converters, steelmaking furnaces, and cement rotary kilns. However, in recent years, operating conditions have become more severe, and more specifically, for example, converters have become larger, operating temperatures have increased,
With the reduction of blowing time, there is a growing demand for refractories with superior spalling resistance, thermal shock resistance, and the like.

In response to this situation, for example, magnesia (hereinafter M
A basic refractory whose main component is a raw material (gO) has been developed. Although this refractory has excellent erosion resistance against highly basic slag, it has a serious drawback of poor spalling resistance.

In other words, since the reactivity between MgO and slag is low, the slag penetrates into the interior of the brick, which has a temperature corresponding to the melting point of the slag that has entered, loosening the connective tissue of MgO crystals (periclase) present in the penetrated area. . As a result, when the temperature of the brick decreases, differences in physical properties (thermal expansion coefficient, porosity, strength, etc.) occur between the slag permeated area and the non-permeated area, making spalling more likely to occur. It is. In addition, since MgO has a high coefficient of thermal expansion, the difference in expansion between the inside of the brick furnace (high temperature side) and the back side (low temperature side)
Spalling is likely to occur. Therefore, in MgO-based bricks, various causes such as slag action, thermal distortion due to the furnace body structure, thermal shock and mechanical shock caused by the furnace usage cycle (repetitive heating and cooling), etc. overlap. hand,
The bricks undergo thermal and structural spalling and gradually flake off from the furnace body, eventually rendering the furnace unusable.

In order to eliminate the above-mentioned drawbacks of MgO-based bricks, MgO-based bricks
Along with gO raw materials, dolomite raw materials and calcia (CaO
) MgO-CaO refractories blended with raw materials have been developed and are frequently used. Although such refractories have high strength, their spalling resistance and thermal shock resistance are still far from satisfactory. In addition, C in refractories
In some cases, aO is digested by reaction with moisture in the air, embrittles the tissue, and causes the refractory itself to collapse. When such refractories are used as lining materials in cement rotary kilns, a coating layer made of cement components is usually formed on the refractory surface near the firing zone, which can be expected to extend the life of the refractories. However, in reality, as the coating layer repeatedly desorbs and desorbs due to the rotation of the kiln, the refractory surface receives significant thermal shock, causing spalling. Further, when the kiln is idle, the air flow passes through the refractory surface while being in contact with the surface of the refractory, which may cause severe damage to the refractory due to the extinguishing phenomenon.

Means for Solving the Problems As a result of various studies in view of the current state of the technology as described above, the present inventor has developed an MgO-CaO synthetic linker with excellent digestion resistance in which MgO is coated with CaO. M g including -
By blending a specific amount of aragonite-type calcium carbonate into the O-CaO refractory aggregate, spalling resistance can be improved without impairing the excellent properties (such as high strength) originally possessed by MgO-CaO refractories. It has been found that corrosion resistance can be improved.

That is, the present invention provides the following magnesia-calcia refractory: "MgO consisting of 40 to 60% by weight of MgO and 60 to 40% by weight of CaO, and in which MgO covers CaO.
-Contains CaO fruit synthesis linker-, MgO20-9
A magnesia-calcia refractory made by blending 0.5 to 5 parts by weight of aragonite type calcium carbonate with a particle size of 0.5 to 10 mm to 100 parts of refractory aggregate consisting of 5% by weight and 80 to 5% by weight of Ca. thing. ” The MgO-CaO fruit synthetic linker used in the present invention consists of 40 to 60% by weight of MgO (hereinafter simply referred to as %) and 60 to 40% of CaO.
As schematically shown in the figure and FIG. 2, the structure is characterized in that MgO surrounds CaO. Due to this unique structure, this synthetic linker is particularly resistant to digestion. When the MgO content in the synthetic linker exceeds 60%, the strength decreases;
If it is less than 0%, the digestive resistance will decrease. A synthetic linker having such a structure can be produced, for example, by adding a solution of a water-soluble iron compound to an MgO raw material, then adding a CaO raw material or its hydrate to form a precipitate mainly consisting of magnesium hydroxide. , is produced by mixing the precipitate and a calcium compound and calcining the mixture.

The refractory aggregate used in the present invention is the above-mentioned MgO-C
aO-based synthetic linker alone or together with MgO and/or
Alternatively, it is composed of a mixture with a known basic refractory material containing CaO. If a mixture of synthetic linker and basic refractory material is used, the amount of the former should be at least 20% of the mixture in order to achieve the desired effect. The basic refractory materials are not particularly limited, and include dolomite clinkers such as natural dolomite clinker, synthetic dolomite clinker, electrically excited dolomite clinker, natural magnesia clinker, seawater magnesia clinker, fused magnesia clinker, etc. Magnesia clinkers: Examples include sintered or fused mag lime clinker. In the present invention, the above-mentioned MgO-CaO fruit synthetic linker alone or a synthetic linker and one or more of these are used in combination to obtain 20 to 95% of MgO and 80% of CaO.
Adjust so that the ratio is ~5%. When MgO is less than 20%, the digestion resistance becomes insufficient and the slag resistance decreases. On the other hand, when MgO exceeds 95%, spalling resistance and slag erosion resistance decrease. The particle size of the refractory aggregate is usually about 10 mm or less, more preferably about 5 mm or less.

As the aragonite type calcium carbonate used in the present invention, any known aragonite type calcium carbonate can be used.
You can use one type of both. This aragonite-type calcium carbonate has a temperature of 330 to 4
At 80°C, it transforms into a calcite type, with a volumetric expansion of about 8%.

Therefore, many microcracks occur inside the brick. According to research conducted by the inventor of the present application, it has been found that these microcracks exhibit an effect of preventing stress propagation during use, and are extremely effective in preventing the propagation of cracks due to spalling. Such an effect in the present invention is achieved only when aragonite-type calcium carbonate is used. For example, when using calcite-type calcium carbonate, spherical gaps that do not exhibit the effect of preventing crack propagation are produced. was formed, and no improvement in spalling resistance was observed. The amount of aragonite type calcium carbonate to be blended is 0.5 to 5 parts per 100 parts by weight (hereinafter simply referred to as parts) of the refractory aggregate. If the amount of aragonite-type calcium carbonate is less than 0.5 part, the amount of microcracks generated within the brick will be too small, and the effect of improving spalling resistance will be insufficient. On the other hand, if it exceeds 5 parts, the structure becomes porous and the fire resistance of the brick decreases. The particle size of aragonite-type calcium carbonate is not particularly limited, but is usually 0. 5-10
It is about mm+, and it is more preferably 1 to 3II11. Aragonite type calcium carbonate particle size is 0
．． When it is less than 5ma+, the occurrence of microcracks tends to decrease, and when it exceeds 10mm, cracks other than microcracks tend to occur, and the effect of improving spalling resistance tends to be diminished. .

The refractory of the present invention is produced by blending aragonite-type calcium carbonate with MgO-CaO-based refractory aggregate, and further adding known non-aqueous binders such as tar, liquid phenol resin, polyurethane, polypropylene, and wax according to a conventional method. It is manufactured by kneading, molding, and firing 1 to 5 parts (usually about 1 to 5 parts per 100 parts of refractory aggregate). The process from adding the non-aqueous binder to firing is the same as usual, so it will not be described in detail.
It is preferable to carry out the heating at about 700°C.

The magnesia-calcia refractory of the present invention is useful as a refractory for lining various types of furnaces.

Effects of the Invention According to the present invention, a magnesia-calcia refractory having excellent spalling resistance, corrosion resistance and extinguishing resistance can be obtained. Moreover, other physical properties such as strength are equivalent to or better than conventional products.

EXAMPLES Comparative examples and examples are shown below to further clarify the features of the present invention.

Examples 1 to 3 and Comparative Examples 1 to 3 Each raw material was blended in the proportions (parts) shown in Table 1, and the mixture 1
00 parts and 2 parts of polypropylene as a binder were added, kneaded, molded into a sub-mould, and fired at 1650°C.

In addition, each symbol in Table 1 indicates the following materials.

■...Natural magnesia clinker - 1 particle size 3ma+ or less ■...Natural dolomite clinker - 1 particle size 3IllIB
Below, MgO 40%, CaO 60% m・MgO-CaO based synthetic linker - 1 particle size 5 mm or less, MgO 50%, CaO 60% ■... Aragonite type calcium carbonate, particle size 3 to 1 m Raw material Implementation Table 1 Example Ratio Comparison Example I 60 -20 606060II
-40404040 m 406040 - -40rV
111 1 In addition, the above natural dolomite clinker (n) and M g O-Ca
In order to determine the digestion resistance of the O-based linker (m), both materials were placed in an autoclave and the water vapor pressure was 4 kg/
When held at cJ (gauge pressure) and temperature of 152°C for 3 hours, the results shown in Table 2 were obtained.

Table 2 Weight increase rate Powdering rate (%) (%) II 6. 1 44.8III
1.8 4. 7 The properties of the refractory obtained above were investigated as follows.

A: Porosity (%), according to JIS R2205.

B... Bulk specific gravity, according to JIS R2205.

C-...Compressive strength (kgf/cd), JIS
According to R2206.

D...Bending strength (kg f/cd, 1400℃)
, according to JIS R2213.

E: Spalling resistance: A refractory was inserted into an electric furnace maintained at 1200°C, and a cycle of heating for 15 minutes and air cooling for 15 minutes was repeated to determine the number of cycles until the refractory peeled off.

F: Digestion resistance: A refractory was placed in a thermostatic chamber maintained at a temperature of 30° C. and a humidity of 80%, and the number of days until it powdered or disintegrated was measured.

G: Corrosion resistance, a rotary slag tester was lined with refractory material and tested at 1650°C for 5 hours. The slag used was a mixture of Portland cement:alumina=1=1. After the test, (1) the melted area of the refractory and (2) the permeation area of the slag were measured, and expressed as an index with that of Comparative Example 1 set as 100.

The results are shown in Table 3.

Characteristics Implementation Example G ■ ■ 14.3 2.98 〉20 30-day powdering 12.4 3.01 〉20 30-day powdering ratio 16.4 2.89 Comparison of 15-day disintegration Example 18.6 2.91 〉15 10-day disintegration 14.0 2.97 Compared to conventional magnesia-calcia refractories, the 30-day powdered product has
It is clear that it is particularly excellent in spalling resistance, thermal shock resistance and digestion resistance.

[Brief explanation of drawings]

Figures 1 and 2 show MgO-CaO used in the present invention.
FIG. 2 is a cross-sectional view schematically showing a system-synthesized linker. (Above) From the results shown in Table 3, the magnesia-calcia fire resistance chart of the present invention containing an MgO-CaO-based composite linker and aragonite-type calcium carbonate is shown.

Claims (1)

[Claims] (1) MgO consisting of 40-60% by weight of MgO and 60-40% by weight of CaO, with MgO covering CaO
-Contains CaO-based synthetic clinker, MgO20-95
Refractory aggregate 10 consisting of % by weight and 80-5% by weight of CaO
A magnesia-calcia refractory comprising 0.5 to 5 parts by weight of aragonite type calcium carbonate having a particle size of 0.5 to 10 mm to 0 parts by weight.