JPH02111657A - Production of magnesia-calcia refractory brick - Google Patents

Abstract

PURPOSE:To obtain a calcined refractory brick having excellent heat-resistance and structural spalling resistance by adding heated and melted thermoplastic resin to coarse grains of heated refractory aggregate, kneading the mixture to coat the grain with the resin, adding fine powder and then a thermosetting resin to the kneaded mixture and kneading, forming and calcining the mixture. CONSTITUTION:Coarse grains (having particle diameter of preferably <=5mm, especially >=3.5mm) such as natural dolomite clinker and seawater magnesia clinker are mixed with molten thermoplastic resin such as polypropylene. The amount of the resin is usually 3-10wt.%, preferably about 3-7wt.%. When the temperature of the mixture is lowered to <=40 deg.C, the mixture is added with fine grains and fine powder of refractory, kneaded further, added with (usually 0.1-1 pts.wt., preferably 0.5-0.7 pts.wt. of) a thermosetting resin such as phenolic resin and kneaded to obtain a body, which is formed and then calcined in an oxidizing atmosphere at about 1400-1700 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing magnesia-calcia refractory bricks.

[Conventional technology and its issues]

Magnesia bricks are widely used as lining materials for various furnaces used in various fields such as iron manufacturing, steel manufacturing, and nonferrous metal manufacturing.

Generally, the melting point of MgO in magnesia bricks is approximately 2800.
Although it has excellent slag resistance due to its low solubility in slag, it has an important drawback of poor spalling resistance. In other words, the reactivity of MgO with slag is low, , the slag penetrates into the interior of the brick and loosens the connective tissue of MgO crystals (periclase) present in the permeated part.As a result, when the temperature of the brick decreases, physical properties (thermal properties) between the permeated part and the non-penetrated part Spalling is likely to occur due to differences in coefficient of expansion (expansion coefficient, porosity, strength, etc.). Also, since MgO has a large coefficient of thermal expansion, the inner side (high temperature side) and back side (low temperature side) of the brick Spalling is also likely to occur due to the expansion difference between Thermal shock caused by 〒8, mechanical shock 1
The combination of these factors causes thermal spalling and structural spalling, and the bricks gradually fall off from the furnace body, eventually rendering the furnace unusable.

There have also been attempts to improve spalling resistance by using magnesia and calcia in combination. That is, CaO and M
Since it hardly reacts or forms solid solution with gO, it is expected that the crystal growth of MgO isolated by CaO will be suppressed and the spalling resistance of bricks will be improved. Furthermore, Ca
When using O, CaO itself reacts with the slag penetrating into the bricks due to its promoting action, raising the melting point of the slag, thereby preventing the slag from penetrating into the bricks. In this case, the rate of corrosion of the bricks increases, but the damage to the bricks changes from spalling rate-limiting to melting rate-limiting, extending the life of the bricks, making it particularly promising as a furnace material operated at temperatures above 1,700℃. .

However, new problems arise when using CaO. In general, CaO sources include natural and synthetic dolomite clinker-1Mg0.CaO clinker, Ca
O clinker etc. are used. Natural dolomite clinker contains about 2 to 5% of flux components such as Sin, Fex 03, A120s, etc., and synthetic dolomite clinker - 1Mg0.CaO clinker and CaO clinker have a dense sintered body obtained during the production of tallinker. SiO2, Ti derived from sintering aids added to
O2, A1203, Few Ox, etc. are 0°8 to 2.5
Contains about %. In magnesia-calcia bricks, their flux component or sintering aid is MgO
-CaO is concentrated in the interstices of the CaO crystals or at the boundaries of the CaO crystal grains, and reacts with CaO or MgO to produce low-melting compounds. Furthermore, when increasing the CaO content in the brick, the amount of the above-mentioned flux component or sintering aid also increases, resulting in oversintering when the brick is sintered. Bricks that have been oversintered become highly elastic and have a small amount of deformation in response to stress, so they do not deform when stress occurs and are more likely to crack, resulting in lower heat spalling resistance. In particular, when the CaO content exceeds 60%, the increase in elasticity due to oversintering becomes remarkable, and not only does the heat spalling resistance drop significantly, but also Fe, 0. or A1□0. There is a problem in that the corrosion resistance against slag that accumulates in the steel is significantly reduced.

The present invention has been proposed in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a method for producing fired refractory bricks that are excellent in heat spalling resistance and structural spalling resistance.

[Means to solve the problem]

In order to achieve the above object, the present invention employs the following means. That is, the refractory brick of the present invention is made by kneading heated coarse particles of refractory aggregate and a thermoplastic resin dissolved by heating until the temperature drops from 40°C to room temperature, coating the coarse particles with resin, and then adding fine powder. Finally, a thermosetting resin is added, kneaded, molded, and fired.

[For production]

According to the manufacturing method of the present invention, voids are formed on the surface of the coarse grains due to volatilization of the resin coated on the coarse grains during firing, and these voids absorb thermal stress and contribute to improving thermal shock resistance. discovered.

As the magnesia raw material used in the present invention, any known material can be used, such as natural magnesia clinker-1 seawater magnesia clinker, fused magnesia, and the like. Any known calcia raw material can be used, such as natural dolomite clinker.
-5 Synthetic dolomite clinker 1 Electrofused dolomite clinker: Synthetic magnesia calcia clinker, etc. can be mentioned. In the present invention, one or two of these refractory aggregates are used.
Mixtures of more than one species can be used.

The particle size of the refractory aggregate is not particularly limited and may be selected as appropriate, but it is usually about 5 mm or less, especially 3.5 m.
It is also more preferable that the force be less than or equal to m.

As the thermoplastic resin, polypropylene, wax, etc. can be used, and the amount added may be determined as appropriate, but usually 3~
The amount is preferably about 10 parts by weight, preferably about 3 to 7 parts by weight. If the amount added exceeds 10 parts by weight, the voids formed may become too large and the strength may decrease. Also, 3
If the amount is less than 3 parts by weight, voids capable of absorbing thermal stress will not be formed, which is not preferable, and about 3 to 7 parts by weight is preferable.

As the thermosetting resin, polyurethane-based, evoquin-based, and phenol-based resins can be used, and the amount added may be determined appropriately, but it is usually 0.3 to 1 part by weight, preferably 0.5 to 1.
The amount is preferably about 0.7 parts by weight. If the amount added exceeds 1 part by weight, there may be a difference in quality between the first molded product and the final molded product of one batch of clay due to curing of the resin.

If the amount is less than 0.3 parts by weight, the thermoplastic resin coating on the surface of the coarse particles will collapse during molding, which is undesirable.

The refractory of the present invention is produced in accordance with a conventional method, for example, by kneading the above-mentioned refractory aggregate and binder, molding the mixture, and firing it at about 1400 to 1700° C. in an oxidizing atmosphere.

〔Example〕

Examples will be given below to further clarify the present invention.

40 parts by weight of natural dolomite clinker with a particle size of 3 to 1 mm heated to 100°C and 20 parts by weight of seawater magnesia clinker
Polypropylene, which is a thermoplastic resin heated to 160°C (the amount added is shown in Table 1), is added to the weight part, and the mixture is kneaded until the temperature reaches 35°C, followed by seawater magnesia clinker with a particle size of 1 mm or less. 40 parts by weight was added, and polyurethane, which is a thermosetting resin (the amount added is shown in Table 1), was added, kneaded, molded into a dish shape, and fired at 1650° C. to obtain a refractory of the present invention.

Table 1 Addition amount (parts by weight) Table 2 shows the physical properties of the obtained bricks.

As a comparative example, the mixing ratio of fireproof aggregate was the same as in the example,
Polypropylene 1, a thermoplastic resin, as a binder
．． Bricks to which 5 parts by weight (Comparative Example 1) and 1.5 parts by weight of polyurethane which is a thermosetting resin (Comparative Example 2) were added were manufactured in a conventional manner. These physical properties are also shown in Table 2.

Table 2 [Effects of the Invention] According to the present invention, fired refractory bricks having excellent heat spalling resistance can be obtained without reducing strength.

Claims (1)

[Scope of Claims] [1] Adding and mixing a molten thermoplastic resin to coarse refractory aggregate, and when the temperature of the mixture drops to 40°C or less, adding fine refractory powder and continuing kneading; A method for producing a magnesia-calcia refractory brick, which comprises further adding and kneading a thermosetting resin to form a clay, which is then molded and then fired.