JPH11180762A - Production of magnesia-chromium refractory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable to dry at a low temp., to secure excellent strength property in a temp. region up to a high temp. and to improve corrosion resistance and thermal spalling resistance by blending sodium aluminate and sorbitol with a refractory composition containing a magnesia raw material and a chromia raw material. SOLUTION: Water, 0.5-3.5 pts.wt., preferably 0.5-3 pts.wt. sodium aluminate expressed in terms of NaAlO2 and 0.1-1 pts.wt. sorbitol are added into 100 pts.wt. refractory composition containing the magnesia raw material and the chromia raw material, which are controlled to 5-1 mm for coarse particles, 1-0.1 mm for middle particles and <=0.1 mm for fine particles, kneaded, molded and heated to 100-500 deg.C to be dried. Next, the magnesia-chromium refractory is obtained by firing at 1700-1750 deg.C at need. As a result, initial molding density is increased, a multiple spinel is formed at a relatively low temp. and production cost is remarkably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a magnesia-chromium refractory having excellent corrosion resistance and heat resistance.

[0002]

2. Description of the Related Art Magnesia refractories have been widely used as refractories for lining metal refining vessels because of their excellent erosion resistance to basic slag. However, although magnesia refractories are excellent in corrosion resistance, they are inferior in heat resistance and structural spall resistance, and there is a drawback that a container lined with magnesia refractories has a short life. Structural spalls are formed by a slag infiltration, a transformed part whose structure is greatly different from that of the raw part, and this transformed part suddenly rises and falls during the use of the metal smelting vessel. It refers to the phenomenon of peeling.

As a measure for preventing the above-mentioned structural spall, a magnesia-chromium refractory has been considered by combining a magnesia raw material and a chromium ore raw material. Magnesia-chromium refractories have excellent corrosion resistance and heat-resistant spall resistance, and have been conventionally used in steelmaking processes as lining materials for molten steel vacuum degassing furnaces such as RH and DH and AOD furnaces. Magnesia-chromium refractories are classified into direct bond refractories and ribboned refractories according to the raw material composition. Direct-bond refractories use high-purity synthetic magnesia clinker as a magnesia source and natural chromium ore as a chromium source. It is manufactured by firing at high temperature. On the other hand, ribboned refractories are molded and fired in the same manner as the former, using a sintered magcroclinker in which magnesia clinker and chromite are sintered in advance in a rotary kiln or tunnel kiln, or an electrofused electromagnet clinker. It can be obtained by

[0004] Improvements in the quality of magnesia-chromium fired refractories for the purpose of improving the corrosion resistance have been actively carried out. For example, Japanese Patent Publication No. Sho 63-31428 uses a high-purity magnesia clinker and a chromium ore having a small amount of silica, and Japanese Patent Application Laid-Open No. 2-19663 uses a chromium oxide, and a strong chromium oxide is used between the chromium oxide and the magnesia clinker. A magnesia-chromium refractory that forms a picrochromite bond and satisfies corrosion resistance and heat resistance spall is introduced. Recently, Japanese Unexamined Patent Publication (Kokai) No. 3-141148 discloses a refractory in which the surface of a coarse-grained magnesia clinker is preliminarily coated with a fine-grained chromium raw material so that picrochromite can be easily formed. Japanese Patent Application Laid-Open No. Hei 9-52755 discloses a refractory in which ferrochrome powder is blended with an ore refractory composition, such as an Fe-Cr alloy and a refractory impregnated with chromium oxide after firing, which simultaneously satisfy both corrosion resistance and heat resistance spall. Magnesia
There are chromium fired refractories.

[0005]

In recent years, as the demand for high-grade steel has increased, magnesia-chromium fired refractories have become
It is used in special refining furnaces such as secondary refining furnaces, and its use under severe conditions such as slag and molten steel wear is increasing. More recently, oxygen injection operations have increased for the prevention of metal adhesion by splash and the production of ultra-low carbon steel, and conventional magnesia-chromium refractories have not been able to provide a sufficient life. On the other hand, however, as the production volume of crude steel declined, magnesia was inexpensive with excellent corrosion resistance and heat resistance.
Chromium fired refractories are also required and currently imported from China and Southeast Asia.

However, recently, Japanese Patent Laid-Open Publication No.
7, an unfired magnesia-chromium refractory obtained by adding alumina, titania, etc. to the raw materials of magnesia, chromium ore, and chromia is introduced.

In view of the above-mentioned social situation, the present invention provides an inexpensive magnesia-chromium unfired refractory (hereinafter referred to as an unfired product) instead of a conventional expensive magnesia-chromium fired refractory (hereinafter referred to as a fired product). ), Which enables drying at low temperatures, and in the temperature range up to high temperatures, secures excellent strength characteristics, corrosion resistance and heat resistance equal to or higher than conventional fired products, and improves durability. The purpose is to aim.

[0008]

On the basis of the above-mentioned problems, the present inventor has studied possible alternatives to the conventional baked products, which can be used as inexpensive unfired products. For unfired products, picrochromite spinel products are generated from the refractory operating surface at an extremely high temperature used for lining metal refining vessels, etc., and the corrosion resistance and heat resistance spoil property are improved at least as much as fired products. confirmed. To that end, it was found that the point is to generate picrochromite spinel at lower temperatures during use and to exhibit higher refractory strength characteristics up to the temperature during use, and completed the present invention. It is. The fired product is fired at an ultra-high temperature in order to generate a large amount of spinel products such as picrochromite in order to improve the corrosion resistance and heat resistance spall resistance. However, the sintering process affects the production cost, and the price is high. In the present invention, unsintered products are sufficient, and these problems have been solved. That is, the present invention provides 0.5 to 3.5 parts by weight of sodium aluminate in terms of NaAlO ₂ and 0.1 to 0.1 parts by weight of sorbitol, based on 100 parts by weight of the refractory composition containing the magnesia-based material and the chromia-based material. A method for producing a magnesia-chromium refractory, wherein 1 part by weight is blended.

Hereinafter, the present invention will be described. As the magnesia raw material that can be used in the present invention, one or two or more types selected from calcined products or electrofused products of natural raw materials or artificial raw materials can be used. Although the purity does not particularly affect the effect of the present invention, it is desirable to use a high purity MgO component of 95% or more, that is, a material having few impurities. The particle size is preferably adjusted to 5 to 1 mm for coarse particles, 1 to 0.1 mm for medium particles, and 0.1 mm or less for fine particles so as to obtain a close-packed structure similarly to a conventional fired product.

As the chromia material, chromite, chromium oxide and magcroclinker can be used. As the chromium ore, for example, machine rock chrome ore, transvar chrome ore, turquoise ore, or the like can be used, and it is desirable to use one having little impurities. The constituent components of the chromium ore react with the MgO component of the magnesia raw material during use to form a composite spinel structure, and have an action of firmly bonding the aggregates. As the chromium oxide, a commercially available product having a purity of 90% or more can be used similarly to the conventional material. Chromium oxide has the effect of preventing slag and molten steel from penetrating. The chromium oxide needs to be fine powder, and is preferably added to the joint from the above-mentioned effects. Further, as the magcroclinker, an electrofused magcroclinker obtained by electromelting a mixture of magnesia clinker and chromite or chromium oxide, or a calcined magcroclinker fired in a rotary kiln or the like can also be used.

The particle size composition of the magnesia raw material and the chromia raw material may be the same as that of a normal calcined product, but since the bonding portion is easily sintered from a relatively low temperature during use, it is resistant to sintering. It is necessary to provide sportiness. As the coarse particles such as chromium ore and magcroclinker having a smaller coefficient of thermal expansion than the joint portion, it is preferable to use crushed particles having a particle size of about 5 to 30 mm. Due to the composition of the coarse particles, even if thermal stress occurs at the joint, microcracks occur at the boundary between the coarse particles and the joint, dispersing the thermal stress to preferably prevent cracks and peeling due to stress concentration. Can be.

In this embodiment, sodium aluminate is added to and mixed with the above raw material composition. Sodium aluminate is represented by NaAlO ₂ or Na ₃ AlO ₃ as a typical composition, and the molar ratio of Na ₂ O to Al ₂ O ₃ is 1.2.
/ 1 to 2.6 / 1. Further, sodium aluminate is easily dissolved in water and has high solubility.

[0013] Sodium aluminate has a function of reacting and sintering magnesia, chromium ore, chromium oxide, and the like blended in the joint from a relatively low temperature to form a composite spinel and generate strength. Therefore, even in the temperature range during use, there is no large change in strength from the working surface to the back surface, no cracking or peeling due to heat-resistant spalls, and more corrosion-resistant composite spinel is generated, so that the corrosion resistance is high.

The amount of sodium aluminate to be added is 0.5 to 3.5 parts by weight in terms of NaAlO _{2 based} on 100 parts by weight of the refractory composition containing the magnesia-based material and the chromia-based material. If the addition amount of sodium aluminate is 0.5 parts by weight or less, sufficient strength as a refractory cannot be obtained,
If it exceeds 3.5 parts by weight, oversintering occurs during use, and the spall resistance becomes poor. Preferably it is 0.5 to 3 parts by weight.

The inventors of the present invention have already proposed the effect of the addition of sodium aluminate. However, in order to improve them, the present invention has been applied to the above raw material composition as a molding aid. Sorbitol is added and mixed. Sorbitol is mainly composed of D-sorbitol and is represented by HOCH ₂ (CHOH) ₄ CH ₂ OH, and is easily dissolved in water as a powder. Generally, it is used as a surfactant or a food additive. The same effect can be obtained by adding and dissolving in the binder aqueous solution or adding it as a powder in the raw material composition. The addition of sorbitol improves the filling properties of the kneaded clay, the lubricity between the particles, reduces the secular change of the clay, suppresses the slaking, and produces a molded body with no toxicity and high molding density. Further, the high density acts more effectively on the improvement of the bending strength and the sintering during use, and gives high strength.

The amount of sorbitol added as a molding aid is 0.1 to 1 part by weight with respect to 100 parts by weight of the refractory composition containing the magnesia-based material and the crucia-based material.
If the amount is less than 0.1 part by weight, the effect of filling and lubricating properties is hardly obtained, and if it is more than 1 part by weight, it is undesirably lost because it is an organic substance due to sintering during use, leaving pores.

In the present invention, the unsintered product is produced by kneading, molding, and drying the above refractory composition. In the case of a fired product, firing is performed, and the same effect can be obtained in that case. The method of kneading, molding and drying is the same as the ordinary refractory manufacturing method, but the preferred kneading method is to disperse water or sodium aluminate in coarse or medium magnesia raw material and chromia raw material and sorbitol into alumina. A method of adding and kneading an aqueous solution or sorbitol dissolved in an acid soda as a powder and adding and kneading a small amount of a magnesia-based material, a chromia-based material and / or a sodium aluminate powder while coating the surface of the particles is preferred. In the present invention, sorbitol includes mannitol as a similar substance. The molding is performed by pressure molding with a friction press, an oil press, a rubber press, or the like according to the use of the refractory. What is necessary is just to dry at 100-500 degreeC. In the case of a baked product, the calcination temperature may be low because it is easy to dry, and calcination is performed at 1700 to 1750 ° C.

[0018]

EXAMPLES Examples of the present invention and comparative examples are shown below. Table 1 shows examples of the present invention and test results thereof, and Table 2 shows comparative examples and test results thereof. In each example, sodium aluminate (Na) was added to a composition using the magnesia raw material, chromite, magcroclinker, chromium oxide, etc. shown in Tables 1 and 2.
₂ O / Al ₂ O ₃ molar ratio 1.2 / 1) Powder and sorbitol were powdered, and the mixture was added and mixed (wt%).
After adding t% (outer hook) and kneading, the mixture was pressure-formed (1000 kg / cm ² ) into a parallel shape by a friction press.
Thereafter, it was dried at 200 ° C. for 24 hours to obtain a test refractory.

Using the test refractories thus obtained, the physical properties shown in Tables 1 and 2 were evaluated. Test items,
The measuring method is as follows. The bulk specific gravity was measured by a normal refractory test method (based on JIS R2205). Table 1
The heat treatment method “dry” in Table 2 was obtained by drying at 200 ° C. for 24 hours, and “baking” was obtained by firing at 1700 ° C. for 5 hours. The bending strength is 30 x 1
Cut out a 5 × 20 mm test piece, 1000 ° C.,
After heating for 3 hours in an electric furnace maintained at each temperature of 1500 ° C., it was taken out and subjected to a three-point bending test.

The heat-resistant spalling property was 5
A 5 × 55 × 230 mm prismatic test piece was cut out and placed in an electric furnace having one side maintained at 1400 ° C.
Hold for 5 minutes. Next, the heat shock by the heating-cooling cycle of taking out of the furnace and forcibly air-cooling at room temperature for 15 minutes was repeated up to 25 times. Evaluate by the number of times until it comes off,
The heat-resistant spalling property is better when the number of times until the spalling is increased is larger. In addition, what did not peel off at the time of repeating 25 times was represented as 25+.

The corrosion resistance index and the slag penetration thickness are determined by cutting and polishing a plurality of trapezoidal column-shaped test pieces from the refractory to be tested to a predetermined size, lining them in a rotating drum, and rotating the drum while rotating the drum axis. Oxygen propane flame was blown in the direction and heated to 1700 ° C. Steel and slag (CaO / SiO
The ratio of ₂ is 3: 1) and the ratio is 5: 5.
Eroded for 30 minutes. After the completion, the erosion material was tilted and discharged, and forced cooling with compressor air was performed for 20 minutes. The operation from heating by the oxygen-propane flame to forced cooling by the compressed air was repeated five times. Thereafter, the test piece is taken out, cut, and the amount of erosion (mm)
The slag penetration thickness (mm) was measured at each part of the test piece and expressed as an average value. In Tables 1 and 2, the amount of erosion of each example when the amount of erosion of Comparative Example 12 is set to 100 is represented as a corrosion resistance index, and the smaller the index, the better.

The examples shown in Table 1 show that there is little change in the strength characteristics at each temperature as compared with the comparative examples 14 and 15 of the fired products of the prior art. The heat resistance spall, the corrosion resistance index, and the slag penetration thickness as a total result of these physical properties also show good results.

Comparative Examples 10 and 11 shown in Table 2 are examples containing a large amount of sorbitol of the present invention. Comparative Examples 12 and 13 are conventional unfired products. Comparing the above comparative example with the present example, the comparative example shows that the bulk specific gravity is small and the number of pores is large, the strength at medium and high temperatures is low, and as a result, the corrosion resistance and the spalling resistance are inferior.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

According to the present invention, the initial compaction density, that is, the interparticle bond is increased by adding sodium aluminate and sorbitol, and a composite spinel is formed at a relatively low temperature. As a result, it exhibits corrosion resistance and heat spalling resistance equal to or higher than those of conventional baked products, and has high durability. In the case of an unfired product, a firing step is not required, and related fuel and labor costs are not required, so that not only the production cost can be significantly reduced, but also the number of production days can be shortened, and the economic effect is further increased.

Claims (1)

[Claims] A sodium aluminate is added to 100 parts by weight of a refractory composition containing a magnesia-based material and a chromia-based material.
O ₂ 0.5 to 3.5 parts by weight in terms of, magnesia, characterized in that sorbitol 0.1-1 parts by compounding - method for producing chromium refractories.