This requires the glass phase softening temperature to be high, so in addition to AI2O3, ZrO2, SiO2, Na2O in the brick, other components are less. 

 

However, because of the use of graphite lining bricks and graphite electrodes during the melting of the electric furnace, a reducing atmosphere will be generated. C and CO will reduce a part of the Fe2O3, TiO2, and SiO2 in the melt into low-priced oxides, which will increase the composition of components. 

According to the basic principles of phase ratio, this will reduce the liquidus limit temperature. When such a brick is used at high temperature, the viscosity of the glass phase is greatly reduced, a high-viscosity protective layer cannot be formed, and the glass phase has a low viscosity, and it is easy to diffuse to the high-temperature glass liquid.

Will fall into the glass liquid, which will cause streaks and stones in the glass liquid.