Typical properties of three refractory materials used commonly for making induction furnace lining.
|Silica (SiO2)||Alumina (A12O3)||Magnesia (MgO)|
|Melting Point (C)||1723||2050||2800|
|Free Energy at 14500 C (kJ/mol)||-594||-758||-732|
|Avg. thermal conductivity between 0 C and 12000 C (W/mK)||1.7||2.6||4.0|
|Expansion coefficient between 0 C and 12000 C||12.2||8.2||13.8|
|Relative thermal shock resistance (R + 6K/Ea)||715||480||345|
|Relative cost (taking silica cost as unity)||1||5 – 10||5 – 10|
6 = Tensile Strength; K = Thermal Conductivity; E = Modulus of Elasticity; a = thermal expansion coefficient
Typical Size Grading of Silica Ramming Mass
|Size||Typical Content (%)|
|Coarse||-4 mm + 0.85 mm||33|
|Medium||-0.85 mm + 0.20 mm||30|
|Fine||-0.20 mm + 0.063 mm||17|
The ultrafine and fine particles combine with boric oxide to form a low-melting-point glassy phase which fills in the gaps between the coarse and medium size quartz grains and binds these grains with one-another.
Note: The bond is complete in the inner-most sintered layer which has been heated to above 13000C. in the middle fritted layer, which has been exposed to a temperature between 9000C and 13000C, the bond is partial. The outermost layer in contact with asbestos Sheet is not heated beyond a few hundred degrees centigrade, and the bond does form in This Layer.