The preparation technology of coated sand mainly includes cold, warm and hot methods. At present, almost all the production of coated sand is hot method. The process of thermal film coating is that the sand is heated to a certain temperature, then mixed with resin, Urotropine aqueous solution and calcium stearate, and then cooled, crushed and screened. Because of the difference of formulation, the mixing process is different. At present, there are many kinds of coated sand production lines in China. There are about 2000-2300 semi-automatic production lines with manual feeding and nearly 50 fully automatic production lines with computer control, which effectively improve production efficiency and product stability. For example, the automatic visual production line of XX foundry co., Ltd. has accurate feeding time control to 0.1 seconds, heating temperature control to 1/10 C, and can observe the sand mixing state through video time, the production efficiency reaches 6 tons/hour.