Put simply blown polythene extrusion is the process through which polymer pellets are melted, formed and then cooled to make a continuous state. The basic process sounds very simple, however the actual manufacturing side can be very complicated.

In a typical process, blown film manufacturing involves feeding raw polymer pellets from a hopper to a heated extruder (1). Once inside the extruder, the polymer is pushed through a rotating screw and heated up until it enters a soft melted state or ‘melt’ as it is called (2). This soft ‘melt’ material is then pumped under continuous pressure through a ring shaped opening called a die (3). This material then leaves the die in the form of a tube, the tube is inflated with air to form a bubble.

When the desired thickness of the film is reached it is then air cooled into a solid state, then guided by collapsing boards into a ‘pinch’ or ‘nip’ roller at the very top of the bubble. From there the film travels back down the outside of the tower (4). At this point the film is known as Lay Flat Tube or LFT for short.

From here the film can then enter slitting stations which gives the option of converting it into different film variations. For example slitting both sides of the original flat tube can make two separate layers which can be separated and wound onto their own separate reels. The film can then be wound onto corrugated or plastic cores for shipment to the customer (5).

polythene extrusion diagram

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