How to Reduce Moisture After Film Washing

Why film is different

Washed rigid flake drains well. Water sits on the surface and runs off, so a centrifuge or a screen can remove most of it quickly. Film does not behave that way. It folds, it layers, it holds water in the gaps between layers and in the texture of the surface, and it does not drain under gravity.

That is the whole problem. It is not that film is wetter in principle — it is that the water is held in a structure that gravity cannot drain.

Mechanical dewatering comes first

The economical sequence is always mechanical first, thermal second. Mechanical dewatering removes the bulk of the free water using force rather than heat, and the cost per litre removed is a fraction of what a dryer costs for the same job.

Mechanical options:

• Squeezing — the material is compressed between a screw and a perforated barrel or cone. For

film this is the most effective single stage, because it removes water from between the layers rather than only from the surface.

• Centrifuging — effective for flake and for material that flows; less effective for film that

mats.

• Drainage and vibration screens — useful as a first step to remove free water before the

mechanical stage, and cheap to run.

The film squeezer exists because of this specific problem. It is not a general-purpose dryer; it is a machine designed to remove water from film mechanically, and it is normally the stage that decides whether thermal drying is affordable at all.

Thermal drying removes what is left

Thermal drying — hot air, usually in a staged or belt dryer — removes the remaining surface moisture. Three practical points:

1. Size it after the mechanical stage. A dryer sized for the moisture content leaving the

squeezer is much smaller than one sized for the moisture content leaving the washing tank.

1. Airflow matters as much as temperature. Film mats easily, and a mat has a dry outside and a

wet inside. Good airflow through the material is what makes the dryer work.

1. More heat is not more drying. Excess temperature can soften or degrade film without

removing additional water, and it raises energy cost for no benefit.

What moisture level is "dry enough"

There is no universal target. It is set by what happens next:

Because the target depends on the destination, the drying configuration is decided with the whole process route, not on its own.

Degassing is the backstop

Where moisture cannot be removed economically before extrusion, the extruder can be configured to remove it — vacuum venting, or a two-stage arrangement that exposes the melt twice. This is a legitimate route, but it is more expensive to run than removing water mechanically, so it is normally the second choice rather than the first.

A practical order of checks

1. Is the dewatering stage actually working, or is material bypassing it?
2. Is the material reaching the dryer in a mat, or spread enough for air to pass through?
3. Is the dryer airflow adequate, and are the air paths clear?
4. Is the moisture target being set by the downstream process, or has it been assumed?
5. If moisture still exceeds the target, is degassing the right answer — or is the drying stage

undersized?

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