General Vacuum Dryer mostly drying heat-sensitive materials, which is the low-temperature drying. Calcination temperature generally in the 250°C above this called calcination, calcination select Rotary Vacuum Dryer benefits are: 
A, the same temperature in a high vacuum state affirmative; 
B, which is the closed type; 
C, and a solution of hazardous gas may be recycled. 
So again it comes to solving coefficient of expansion coefficient of expansion is the key, Yuntai took six months to put the expansion coefficient of the cylinder resolved.