The material change from initial state to the state that fitted the dry condition.
Ⅱ.Constant drying period
The surface and the central temperature of materials are kept by the equivalence, and the period which water content decreases linearly with time.
The material that is stable hard like a ceramic material, it shift to Ⅲ period (Decreasing drying rate period) from Ⅱ period (Constant drying period) as soon as possible is required.
Conversely, at the liquid paint, if the suitable temperature gradient is not kept, coating film defects will occur, such as bubble, wrinkles, dimple.
Ⅲ.Decreasing drying rate period first half
The surface temperature rises rapidly, and central temperature also follows and rises.
Ⅳ.Decreasing drying rate period second half
The surface temperature of the material will rise slowly to near the heat source temperature.
The material approaches the equilibrium moisture content, central temperature rises rapidly, and finally approaches the temperature of the heat source.
Ⅴ.Equilibrium drying rate period
The surface temperature and central temperature of the material are close to the heat source temperature.
The dry weight moisture content of the material (water content) becomes the equilibrium moisture content, there is no movement of the water any more.
As above, five phases (period) appear in the ustulation.
However, depending on the material, five phases do not necessarily appear.
Only either can appear the Decreasing drying rate period and the Equilibrium drying rate period.