In the first stage, the temperature of the drying room shall keep at 70°C, and the drying process shall carry out for 1 hour.

In the second stage, the temperature of the drying room is set at 40°C-45°C, and drying is performed for 2-3 hours.

In the third stage, the temperature of the drying room is set to about 50°C and should maintain for 15 hours.

In the fourth stage, the temperature of the drying room keeps at 55°C to 60°C for 8 hours.