Steelmaking Electric Furnace Top High Aluminum Products

High-aluminum bricks for electric furnace roof

Refractory products with an Al2O3 content of more than 65% made of bauxite clinker and a small amount of clay, used for electric furnace roof.

Performance The technical performance of high-aluminum bricks for electric furnace roof is divided into three grades in China according to the Al2O3 content: DL-80, DL-75, and DL-65, with standardized design for brick type and masonry.

The crystal phase of high-aluminum bricks for furnace roof is mullite-corundum. The high-grade DL-80 is mainly composed of corundum phase, with high refractoriness and good resistance to various slags.

The thermal expansion coefficient of high-aluminum bricks for furnace roof increases with increasing temperature, especially high-grade bricks can reach 0.8%~0.9% at 1200℃. Due to the crystal structure of the main crystal phase, the number and viscosity of the glass phase of high-aluminum bricks for furnace roof are different, and their elastic modulus is also different, and the strain generated by stress under high temperature is also different. For example, the elastic modulus of high-alumina bricks made of bauxite with an Al2O3 content of 85% to 86% changes with temperature. The maximum elastic modulus (6.69MPa and 8.97MPa) appears when the temperature reaches 1230℃ and cools to 850℃, and the elastic modulus value during cooling is higher than that during heating.

 

Key points of the process The high-alumina bricks for the electric furnace roof are made of high-grade, high-purity and well-sintered bauxite materials. The amount of combined clay with good plasticity and low impurity content such as K2O, Na2O and Fe2O3 should be small. Clay is added in the form of mud, and the maximum critical particle size of clinker is 4~3mm. Use a high-tonnage press to form to prevent particle segregation of the mud entering the mold. The size of the brick is strictly manufactured according to the drawings to avoid distortion and cracks.

Use When building the furnace roof, the force must be balanced, and appropriate expansion joints must be left in the radial and circumferential directions. Bake before use. When peeling and damage occur during the smelting operation, it is appropriate to use bricks of lower grades; when the damage is mainly caused by melt erosion, it is appropriate to use bricks of higher grades, and when the high-temperature smelting is continued, add soot blowing on the furnace roof.

It is usually divided into three categories:

Grade I: Al2O3 content ≥75%;

Grade II: Al2O3 content 60%~75%;

Grade III: Al2O3 content 48%~60%;

It can also be classified according to its mineral composition, generally divided into five categories: low mullite (sillimanite), mullite, mullite-corundum, corundum-mullite and corundum.

One of the important working properties of high-alumina refractory bricks is the structural strength at high temperature, which is usually evaluated by the load softening deformation temperature. Its high-temperature creep is also measured to reflect its high-temperature structural strength. The test results show that the load softening temperature increases with the increase of Al2O3 content.

For high-alumina refractory bricks with Al2O3 content below 70%, the load softening temperature depends on the ratio of the amount of mullite crystal phase and liquid phase, and increases with the increase of the amount of mullite. The amount and properties of the liquid phase have a significant effect on the load softening temperature. Therefore, reducing the impurity content in the raw materials is conducive to improving the load softening temperature and high-temperature creep.

Production process

The molding production methods of high-aluminum refractory bricks and clay bricks are basically the same. Only some process parameters are different. There are also processes such as crushing → mixing → molding → drying → firing → inspection → packaging. Its compressive stress is better at low temperatures, but it is slightly reduced at high temperatures, so the stacking in the kiln is less than 1 meter. The production process of high-aluminum refractory bricks and multi-clinker clay bricks is similar. The difference is that the proportion of clinker in the ingredients is higher, which can be as high as 90%~9%. The clinker needs to be graded, sorted and screened before crushing to remove iron. The firing temperature is relatively high. For example, high-aluminum refractory bricks such as Ⅰ and Ⅱ are generally 1500~1600℃ when fired in tunnel kilns.

Production practice has proved that strict selection and grading of high-aluminum clinker before crushing and graded storage using alumina clinker and combined clay fine grinding can improve the quality of high-aluminum refractory bricks.

Process points Natural bauxite materials require good calcination and strict grading. The iron oxide content in chemical analysis is controlled below 1.2%, and no concentrated iron points or iron cores are allowed. High grade and high purity are required. The bricks are formed by high-tonnage brick presses. The bricks have a regular shape and are not allowed to have surface network cracks or internal layer cracks. The high density of the bricks is guaranteed, and the firing temperature is not less than 1500℃.

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