Operational Parameter
The speed at which water is evaporated from a wet textile during the drying process determines the movement of chemicals within the substrate. In continuous finishing lines, moisture reduction rate governs the transit of dye particles from the interior to the exterior of the fabric. This parameter is measured in kilograms of water evaporated per hour per square metre of fabric.
System Mechanism
Raising the temperature of the drying air increases the vapor pressure gradient between the wet fabric and the surrounding atmosphere. This gradient drives the water molecules out of the fibres into the air stream. When the moisture reduction rate is too high in the early drying stages, the rapid liquid flow draws the dye particles toward the surface, causing migration defects.
A controlled, lower rate in the pre-dryer allows the moisture to decrease to a safe level where the dye particles remain stable before the final dry zone.
Operational Control
Adjusting the fan speed and heater output in each chamber maintains the moisture reduction rate within the specified process window. Humidity sensors in the exhaust ducts measure the moisture level to automate the air dampers. Technicians use online moisture meters at the exit of the pre-dryer to verify the residual moisture content of the fabric.
Calibrating the line speed ensures the fabric spends the correct amount of time in each drying zone.
Process Constraint
Thick, heavy fabrics require a much slower rate to prevent surface overdrying while the core remains damp. This constraint limits the maximum production speed of the continuous line for heavyweight materials.
