The mold residue moisture is divided into two categories: adsorbed water and crystal water. Moisture can make mold powder agglomerate and deteriorate its quality. Moisture should be limited to less than 0.5%. Certain substances in the base material, such as soda, solid, and body water glass, have a strong ability to absorb water. When water is absorbed, the powder slag is rolled into a ball, which brings trouble to the continuous casting operation. The water absorption of mold slag is mainly determined by the type and particle size of raw materials. The finer the particle size, the greater the water absorption rate. At 200 mesh, the cement water absorption rate is 0.41%, the solid water glass is 3.24%, the fluorite is 0.45%, the soda is 15.9%, and the graphite is trace. Moisture control method: the baking temperature of raw materials is not lower than 110 ℃. Properly extend the baking time. The raw materials after baking should be batched and mixed in time, and the prepared slag powder should be sealed and packaged in time. For steel grades with higher quality requirements, it is best to bake the mold flux raw materials to above 800 °C to remove crystal water, or to use pre-melted mold flux.