Film Extruders: Design, Parameters and How to Choose

Blown film extrusion lines are the core business of Plastic Expert. Here we explain what a line consists of, how it works, which parameters to look at when choosing, and how single-layer extrusion differs from multilayer.

What is an extrusion line

An extruder for blown film production is a complex but straightforward system: it turns pellets into a finished product — film.

Main units of the line

• extrusion module: screw and barrel with a gearbox and motor;
• extrusion die head (die);
• film winding unit;
• auxiliary units: corona treater, knives, winding system.

How it works

An extruder is like a heated meat grinder with a long worm — the screw — inside. Pellets are fed into the loading hopper, the screw carries them to the die head, and ring heaters melt them. The melt leaves through the die, is inflated with air to the required width and thickness, and the film is then wound in the required form.

Parameters to consider when choosing equipment

• Screw diameter and length — the L/D ratio, for example 30:1: the screw length equals 30 of its diameters.
• Die head diameter — determines the possible film width.
• Roller width — determines the maximum film width.
• Processed material — LDPE (high-pressure polyethylene) or HDPE (low-pressure).

Winding unit

Winding can be single or “back to back”. The second option allows the film to be not only wound as a tube but also slit into two webs, each wound separately. Two-strip tooling winds both streams at the same time. Automatic roll removal is also available.

Auxiliary units

• corona treater — activates the film surface so that printing adheres well;
• knives — turn the tube into half-tube or flat web;
• printing machines — built into the line or standalone (see below).

Multilayer extrusion

Single-layer film is produced by one extrusion module. The next step is ABA extrusion: two modules produce a three-layer film, where one extruder makes the outer layers and the other makes the middle layer. If all three layers must have different properties, ABC extrusion is used: three modules form three layers on a three-layer die head. Multilayer lines can have 2, 3, 5 or more extrusion modules.

Printing machines

There are two types of printing. An inline machine is built into the line: the film comes out already printed. An offline machine stands separately: the roll is unwound, passes over guide rollers, is printed, then passes through the drying unit and is wound onto the take-up shaft. Flexographic printing machines differ in the number of colors and the arrangement of the printing sections.

What to read and see next

• Extruders in the catalog and used blown film extruders.
• Flexographic printing machines.
• Overview of blown film extruders.
• Three-layer ABA/ABC films: how to reduce thickness and gain more properties.

A Plastic Expert manager will help you select a line for your film: 8 (800) 700-49-01.

How to maintain the line daily, weekly and monthly — see the extruder maintenance schedule.