Explain in detail the application fields of magnesia bricks

Ordinary magnesia-chrome bricks are made of sintered magnesia and chrome ore as raw materials, mixed in appropriate proportions, formed and fired at high temperature. The mineral composition of the product is periclase, spinel and a small amount of silicate.

The production of ordinary magnesia-chrome bricks uses brick-making magnesia and general refractory grade chrome ore as raw materials. Using sulfite pulp waste liquid as a binder, after kneading and molding, it is fired at about 1600 ℃. In order to prevent abnormal expansion of products during firing, a weak oxidizing atmosphere must be maintained in the kiln.

(1) Chemical composition of the product: SiO2 2.98% 4.50%, MgO 61.75% ~ 72.69%, Cr2O3 10.04% 14.9%.

(2) The physical properties of the product: the apparent porosity is 18% and 21%, the compressive strength at room temperature is 36.150. 0MPa, and the softening temperature under load is 16001640℃.

Ordinary magnesia-chrome bricks have strong resistance to alkaline slag, better resistance to acid slag than magnesia bricks, better thermal shock resistance than magnesia bricks, higher softening temperature under load, and good volume stability at high temperature. Reburn line shrinks small. This series of products are mainly used in the firing zone of small and medium-sized rotary kilns below φ4.0m

The refractoriness of magnesia bricks is above 2000 ℃, and the softening temperature under load varies greatly with the melting point of the cemented phase and the number of liquid phases produced at high temperatures. Generally, the softening starting temperature of magnesia bricks under load is between 1520 and 1600°C, while high-purity magnesia bricks can reach 1800°C. The starting temperature of magnesia brick softening under load is not much different from the collapse temperature. The linear expansion rate of magnesia bricks at 1000-1600 ℃ is generally 1.0%-2.0%, and it is approximately linear. Among the refractory products, the thermal conductivity of magnesia bricks is second only to carbon-containing bricks, and it decreases with the increase of temperature. Under the condition of 1100℃ and water cooling, the thermal shock resistance of magnesia brick is only 1 to 2 times. Magnesia bricks can resist the erosion of alkaline slag such as iron oxide and calcium oxide, but are not resistant to the erosion of acid slag such as silicon oxide. The conductivity of magnesia bricks at room temperature is very low, but when it reaches high temperatures, such as 1500 °C, it cannot be ignored. It should be paid attention to when it is used in the bottom of electric furnaces, especially when it is wet.

The microstructure of magnesia brick is actually a combination of magnesia microstructure. The microstructure of magnesia brick made of a magnesia is the simplest, but the matrix part is relatively loose and there are many pores. The microstructure of magnesia bricks made of different grades of magnesia is obviously different. The magnesia brick made of magnesia with high impurity content has many silicate phases, MgO crystals are round, and the direct bonding rate is low. The content of impurities in the raw materials is low. The magnesia bricks fired at ultra-high temperature have less silicate and high direct bonding rate. In the magnesia bricks with a MgO content of more than 98%, the MgO crystals are euhedral or semi-hedromorphic. True direct intergranular bonding can only be maximized in materials that do not contain silicates and intergranular pores.

The performance of magnesia bricks varies greatly due to the use of raw materials, production equipment, and technological measures.

Because of its good high temperature performance and strong resistance to metallurgical slag, magnesia bricks are widely used in steelmaking linings in the iron and steel industry, ferroalloy furnaces, non-ferrous industrial furnaces for iron mixing furnaces, linings for copper, lead, tin, zinc furnace linings, building materials industry, lime calcining kilns; glass Industrial regenerator lattices and civil heat exchangers; high temperature calcining kilns in the refractory industry, such as high temperature shaft kilns for calcining magnesia, high temperature tunnel kilns for firing basic refractory bricks, etc.

In addition to the commonly used carbon-based refractory linings in submerged arc furnaces, basic magnesia bricks and magnesia sand-based magnesia refractory linings have also been widely used. For example, in nickel-iron ore furnace, magnesia refractory lining is mainly used.

Nickel-iron submerged arc furnace, as the name suggests, is mainly used to smelt nickel-iron alloys. The nickel-iron submerged arc furnace is different from the submerged arc furnace for smelting other ferroalloys. Most of the domestic smelting methods of nickel-iron alloys adopt the "rotary kiln-submerged arc furnace method", that is, the raw materials are preliminarily dried and reduced in the rotary kiln. The nickel slag at 900~1000℃ is poured into the submerged arc furnace for smelting.

In the smelting process, the lining of nickel-iron ore furnace not only has to bear strong high temperature, but also bear the physical, chemical erosion and mechanical erosion of charge, high temperature gas, molten iron and high temperature slag. In the selection of lining refractory materials for nickel-iron ore furnace, the main requirement is that the lining refractories have low thermal conductivity, mainly magnesia lining, magnesia brick or magnesia chrome brick + magnesia ramming material for furnace bottom, magnesia brick for furnace Masonry, slag, iron mouth area with magnesia-chrome bricks.

The main raw material for making magnesia bricks is magnesite, and the binder is water and brine or sulfite pulp waste liquid. The main performance characteristics of magnesia bricks are: high refractoriness, excellent resistance to alkaline slag; but the thermal conductivity and electrical conductivity at high temperature are large, and the softening temperature under load is low, and the resistance to rapid cooling and rapid heating is poor. Pulverization occurs when exposed to water or steam at high temperatures.

In the production of ferroalloys, magnesia bricks are used to build the furnace walls and bottoms of high-carbon ferrochromium reduction electric furnaces, medium and low carbon ferrochromium converters, rocking furnaces and refining electric furnaces, and ladles containing ferrochromium and medium and low carbon ferromanganese. Lining etc. Use magnesia alumina bricks instead of magnesia bricks to build the furnace roof. Magnesia has high refractoriness. In ferroalloy production, magnesia is often used to knot the bottom of the furnace, make and repair the furnace wall and bottom, and can be used as a material for plugging holes or making knotted ingot molds.