Why Blown Film Needs Cooling Air and Controlled Exhaust
Hot polymer leaves a circular die and expands into a moving film bubble. Inflation gives it shape, but cooling must also remove heat from the newly formed film.
Follow the air through the process
The outside ring cools the outer surface
A blower feeds the annular cooling ring around the die. Air leaves its opening and travels along the outside of the film. This is an external cooling route.
Fresh air also reaches inside the bubble
With internal bubble cooling, a separate passage through the die supplies cooler air inside. The air moves along the inner surface and absorbs heat from the film.
Heated internal air needs an exit
An internal exhaust tube removes the warmed air. Supply and exhaust therefore allow continued air exchange, instead of leaving the same warm air trapped inside.
Exchange and bubble size must stay balanced
Too much supply relative to exhaust can enlarge the bubble; the opposite can reduce it. Diameter feedback adjusts the inlet or exhaust flow while cooling air continues to move.
Airflow function
- Supply air along the outer film surface through the annular ring.
- Exchange internal air using distinct supply and exhaust duties.
- Work with bubble-diameter feedback while maintaining the required cooling flows.
What can change the result
- An unbalanced internal inlet and exhaust can change bubble diameter.
- Blocked cooling passages can reduce heat removal even while the blower runs.
- Changing only one circuit can disturb the coordinated film process.
Start with the complete air path
Share your layout and the information you already have. Unknown values can be identified before a configuration is selected.
Match the fan to this air path
LONGWELL centrifugal families include plastic and film-blowing applications. Share the cooling flow, passage resistance, air conditions and control requirements for the supply and exhaust duties.
Where it sits
Review the external cooling-ring supply, internal cooling-air supply and warm internal exhaust as separate duties. Each route has its own passages and air conditions.
Why consider this configuration
The documented plastic-machinery family is a starting point for supplying cooling air through restricted passages. Internal supply and exhaust also need compatible control ranges.
Check the result in your equipment
Application questions
Is internal bubble cooling the same as inflation air?
It continuously replaces warmed internal air through supply and exhaust passages. Their balance must also maintain the intended bubble size.
Does the outer air ring replace internal exhaust?
The outer ring cools the outside surface. Warm air inside a bubble with internal cooling leaves through its separate exhaust route.
Can the same fan be selected for all three routes?
Compare the actual duty and air conditions for each route. Different passage losses, temperatures and control ranges may require different configurations.
Discuss your film-cooling air paths
Share the cooling-ring and die passage layout, the three airflow duties and internal-air temperature. Add the required control signals and bubble operating range.
A layout, installation photos or your existing model is enough to start the discussion.