Ladle unburned alumina magnesia bricks

With the advent of oxygen-blown converters and continuous casting, ladle-lined clay bricks (even high-alumina bricks) are no longer applicable. In the initial stage of high alumina and alkalinization of the ladle lining, the successful development of unburned magnesia bricks and the successful development and application of alumina magnesia carbon bricks took a long time, even in the overall package of pure aluminum-magnesium castables. During the promotion of lining, aluminum magnesia carbon brick is still an important material for lining.

Ladle unburned alumina magnesia brick is a unburned refractory product for ladle lining made of high alumina bauxite clinker and magnesia as raw materials. With the increase of molten steel temperature in the ladle and the prolongation of residence time, the lining of clay bricks is seriously eroded. While using high-alumina bricks, alumina-magnesia non-fired bricks can replace clay bricks and low-grade high-alumina bricks. This unburned magnesia brick is made of special or first-grade high alumina bauxite and first-grade brick-making magnesia, and water glass is used as a binding agent, and is mixed with a certain proportion of fine magnesia powder and bauxite powder. It is finely ground, formed by mixing and brick press, dried to 200°C and passed the quality inspection to be the finished product. The typical physical and chemical properties of this brick: Al2O372%, MgO9.8%, bulk density of 2.63~2.85g/cm3, apparent porosity of 20%~21%, compressive strength at room temperature of 52.2~117MPa, load softening start temperature of 1420°C. Since the amount of MgO added in the batch is calculated based on the SP composition of all the substrates, the unburned magnesia brick has good thermal shock resistance and alkali slag corrosion resistance. However, due to the introduction of low melting point substances such as Na2O into the water glass binder, its high temperature strength and load softening temperature are low. In addition, because the thermal conductivity of this kind of brick is higher than that of clay brick, it is easy to form cold steel and sticky slag in the bag, so preheating and heat insulation measures should be taken during use.

Broadly speaking, refractories with alumina, magnesia and carbon as the main components can be collectively referred to as aluminum-magnesium-carbon refractories. Aluminum-magnesium-carbon bricks are unfired shaped refractory products combined with high-alumina bauxite clinker (or corundum), magnesia (or magnesia-alumina spinel SP) and graphite as the main raw materials, combined with asphalt or resin. Aluminum-magnesium-carbon refractory products can be divided into two categories according to the content of alumina or magnesia: one is alumina-magnesium-carbon bricks with alumina as the main component, commonly expressed by AMC or LMC; the other is mainly magnesia The composition of magnesia-alumina-carbon bricks is usually expressed by MAC or MLC.

With the emergence of continuous casting ladle and out-of-furnace refining ladle, the temperature of molten steel in the ladle increases and the residence time is prolonged, and the original clad-lined clay bricks, high-alumina bricks and alumina-magnesium unburned bricks can no longer meet the requirements for use. Alumina magnesia carbon bricks are non-burning bricks developed in the late 1980s. In order to improve the performance of non-burning magnesia bricks combined with water glass for small and medium capacity ladles, graphite was added, and the service life was improved, but it was quickly replaced by resin-bonded magnesia-carbon bricks.

Aluminum-magnesium-carbon bricks are developed on the basis of carbon-containing bricks such as magnesia-carbon bricks and aluminum-carbon bricks, absorbing the characteristics of aluminum-magnesium-based refractories, and have both the advantages of carbon-containing refractories and aluminum-magnesium-based refractories. This carbon composite non-burning brick not only has excellent chemical and thermodynamic stability, but also has excellent thermal and mechanical properties:

(1) High resistance to penetration of molten steel and slag. Due to the reaction between MgO fine powder and alumina fine powder in the matrix during high temperature use, SP is generated in situ with controllable volume expansion, which is beneficial to the densification of bricks and prevents molten steel and slag from flowing from the working face and joints of the bricks. penetration.

(2) Excellent resistance to slag erosion. In addition to the anti-erosion effect of graphite, in-situ generation of SP can absorb FeO in the slag and form a solid solution during use; Al2O3 reacts with CaO in the slag to form a high melting point CaO-Al2O3 compound, which can block the pores of the brick and increase the The effect of large melt viscosity can achieve the purpose of inhibiting slag penetration and resisting slag erosion.

(3) High mechanical strength. Compared with MgO-C bricks and Al2O3-C bricks, the amount of graphite added to alumina-magnesia-carbon bricks is less, generally 6% to 12%, so it has the characteristics of large bulk density, low porosity and high strength.

The production process of aluminum magnesia carbon bricks is the same as that of MgO-C bricks. Taking measures to make the mixing uniform and increasing the molding pressure are the basic conditions to ensure the excellent performance of the aluminum-magnesium-carbon brick in the process. The purity of the main raw materials of alumina-magnesia-carbon bricks has a wide range of fluctuations. The alumina-containing raw materials can be first-grade high-alumina bauxite clinker, super-grade high-alumina bauxite clinker, brown corundum, sintered corundum and fused corundum. The raw materials containing magnesia can be sintered magnesia and fused magnesia. The carbon raw material is mainly natural flake graphite. The binder is commonly used to synthesize aldehyde resin. Antioxidants use SiC and Al powders.

Alumina-containing raw materials generally account for 80% to 85% of the total ingredients of aluminum-magnesium-carbon bricks, and the ingredients can be added in granular and fine powder. There are many kinds of alumina-containing raw materials, but high alumina bauxite contains high impurities such as SiO2, which can reduce the slag resistance of bricks. Comparing sintered corundum with fused corundum, the former has small crystals and many grain boundaries, and the slag resistance of the aluminum-magnesium-carbon bricks made with it is not as good as that of the aluminum-magnesium-carbon bricks made with fused corundum under the same conditions.

Among the magnesia-containing raw materials, compared with sintered magnesia, fused magnesia has larger grain size, larger bulk density and higher MgO content, so it has strong slag erosion resistance. Fused magnesia is generally added to the ingredients of unburned magnesia-carbon bricks, and it is mainly added in the form of fine powder, and the addition amount is generally controlled within 15%. Appropriate amount of magnesia fine powder added, the volume expansion effect produced by in-situ SP during use is beneficial to block the pores of the brick. However, when the amount of magnesium oxide fine powder is too much, too much SP generation will cause excessive volume expansion, and excessive thermal stress and cracks will occur inside the brick, reducing the strength of the brick.

The carbon raw materials of aluminum magnesia carbon bricks are generally based on natural flake graphite. In order to avoid low temperature oxidation of graphite in actual use and excessive temperature drop of molten steel in the ladle due to the high thermal conductivity of graphite, the amount of graphite added is generally controlled within 10%.

Like other carbon-containing refractory materials, the binder used in aluminum-magnesium-carbon bricks is mainly synthetic phenolic resin, and the amount added depends on the molding equipment, generally 4% to 5%.