Refractory ramming mass are made of a high proportion of granular and powdery materials and a low proportion of binders and other components, or even all of them are composed of granular and powdery materials. They are bulk materials that need to be constructed by strong ramming.
The refractory materials for induction furnace linings should meet certain conditions to cope with the harsh working environment of the lining. The refractoriness of steelmaking refractory materials should be ≥1700℃, and the refractoriness of smelting cast iron refractory materials should be ≥1500℃.
The refractory materials used have good high temperature stability and strong corrosion resistance, and the basicity difference with slag is small; they have a certain strength at room temperature and high temperature; they have low resistance, good insulation and low specific resistivity. The lining materials should avoid the introduction of ferromagnetic materials that can significantly reduce the specific resistivity and insulation of the materials. Materials that are easy to form low melting point phases in the raw materials can also play a similar role. The lining materials have good thermal insulation properties, and the refractory materials used should be economical and environmentally friendly.
The refractory lining of the induction furnace uses ramming materials. According to whether water is added, the ramming mass for induction furnace can be divided into dry and wet ramming mass. At present, dry ramming mass is recognized by most induction furnace manufacturers. Wet ramming is for reusing furnace lining crucibles or smelting certain metals with very low melting points (such as Zn).
Dry ramming mass has many advantages that wet ramming mass does not have: it does not contain any liquid binder (water), has short drying and sintering time, and does not require exhaust; it has good stability, fast construction speed, and convenient furnace dismantling, which saves the material trapping time and pouring maintenance time of wet ramming, and the shutdown cycle is relatively short; the sintered-semi-sintered-unsintered structure of the furnace lining can maintain the volume stability of the furnace lining, resist slag penetration, prevent the formation of large cracks, and improve the safety of the furnace lining.
According to different chemical properties, ramming mass can be divided into three types: neutral ramming mass, alkaline ramming mass and acidic ramming mass. The main component of alkaline ramming mass is alkaline oxide. At present, the alkaline material used in large quantities is magnesium material, which has the advantages of excellent corrosion resistance, high melting point, high load softening temperature, and no reaction with alkaline slag or alkaline melt.
However, magnesium ramming mass has poor thermal shock stability and relatively high sintering temperature. Thermal shock during operation will cause cracking and peeling of furnace lining materials, and is only suitable for small-capacity induction furnaces.
The main component of acidic dry ramming mass is SiO2. In the presence of other impurities, the crystal transformation of SiO2 is complex, and excessive heating rate during furnace baking will greatly reduce the melting temperature of the material. Silica dry ramming mass can be used in various induction furnace lining materials, but its refractoriness and purity limit its use.
The main components of neutral dry ramming mass are neutral oxides such as Al2O3 or their complexes. Corundum dry ramming mass has the characteristics of high temperature resistance, good slag corrosion resistance, no effect on molten steel quality, short construction time and no need for baking during construction. It is widely used in various alloy steel smelting.
Corundum dry ramming mass currently still has the disadvantages of low service life, difficulty in sintering and difficulty in controlling thermal expansion. Magnesium-aluminum spinel has good resistance to slag penetration. Adding fused magnesia sand to corundum material to generate magnesium-aluminum spinel in situ can reduce the penetration of molten iron or slag into refractory materials and improve the slag resistance of materials. The secondary spinelization reaction during the use of aluminum-magnesium materials can effectively inhibit the cracking of the furnace lining. Aluminum-magnesium ramming mass for furnace lining can weaken the thermal cracking of the furnace lining material and reduce the generation of microcracks in the material.
In addition, according to the type of materials used, ramming mass can be divided into silicon ramming mass, corundum ramming mass, magnesium ramming mass, magnesium-calcium ramming mass, magnesium-aluminum ramming mass, aluminum-magnesium ramming mass and Al2O3~SiC~C ramming mass; according to the different parts of use, ramming mass can be divided into tundish working lining, electric furnace bottom and power frequency melting groove dry ramming mass.
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