In order to ensure that there is always a corresponding thickness of liquid slag film along the entire length of the mold, the melting temperature of the protective slag should be lower than or equal to the surface temperature of the billet shell at the lower mouth of the mold, which is related to the length of the mold, the drawing speed and the cooling water amount. In order to keep the slag moving along the shell in the mold, the corresponding thickness of the liquid slag layer is always maintained. In continuous casting production, the melting temperature of the protective slag is usually controlled below 1200 degree , and the melting temperature of most of the slab continuous casting protective slag is controlled between 1050-1200 degree .