What Is The Working Principle Of A Blown Film Machine?

A blown film extruder is a key equipment for processing plastic materials into film and is widely used in food packaging, agricultural mulching and industrial packaging. It works on the basis of plastic melt extrusion blow molding technology, its core steps are as follows:
1.Material Preparation and delivery of raw materials
Material type: Common plastic granules (such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), etc.).
Conveying System: Plastic particles enter the hopper either through a feeder or manually, and the pressure from a rotating screw pushes the material into the heating zone.
2.Melt Extrusion
Heating and melting: The raw material enters the screw extruder and is propelled through multiple heating zones by a rotating screw (typically between 150 and250 degrees Celsius depending on the material type). The plastic granules gradually melt to form a uniform melting state.
Screw Function: Screw can not only transport raw materials, but also compress and homogenize the melt through compression and metering segments to ensure uniformity of melt density and temperature.
3. Molding
Ring mold: Molten plastic enters the ring mold through a screw tip (the mold structure determines the number and thickness of film layers). The flow divider inside the die distributes the melt evenly into the annular gap.
Extrusion into a tube: The melt is extruded from the annular gap of the mold to form a continuous tubular molten preform (i.e., a "molten tube"). In order to avoid melting breakage or uneven thickness, precise Precise temperature control of the die is needed.
4. Inflation and cooling
Expansions: Compressed air (typically 0.1-0.3 MPa) is blown into the tube melt through a ring above the mold to preform, causing it to expand horizontally and form film bubble (up to 2-5 times the diameter of the mold).
Cooling and molding: The air ring also blows cool air to the outer surface of the film bubble, rapidly cooling and solidifying the melt to maintain expansion. The cooling speed affects the transparency and crystallinity of the films.
V. Towing and winding
Traction Roller: The cooled film bubble are clamped by a traction roller and stretched downward to form a flat film strip. The towing speed must match the blowing speed to control film thickness.
Reel system: After passing through the guide rollers, by the winding machine winding into a cylindrical finished product. The winding tension must be uniform to avoid deformation or wrinkling of the film.
6. Auxiliary Controls (Key Parameters)
Temperature control: The temperature of each heating zone needs to be adjusted according to the material characteristics to ensure melt flowability.
Blow-up Ratio: The ratio of film bubble diameter to mold diameter affects the transverse stretch and thickness uniformity of the film.
The Traction Ratio traction speed to extrusion speed controls the longitudinal stretch and thickness of the film.
Cooling Efficiency: air flow, air temperature and cooling distance affect the crystallinity and physical properties films.
Application Scenarios and Advantages
Uses: Production of shopping bags, plastic film, agricultural film, industrial packaging film.
Advantages: Single or multilayer composite films can be produced (extruded jointly by multiple extruders).
Thickness, strength and transparency of the film can be controlled by adjusting process parameters such as blow-out ratio and traction ratio.
Highly automated and suitable for large-scale continuous production.
In short, blown film machines is the process of transforming plastic granules into continuous films by the process of molding → ring molding → blowing and cooling → traction winding. At its core, temperature, pressure and velocity parameters are precisely controlled to ensure uniformity and performance stability of the film. The process combines the principles of rheology, thermodynamics and mechanics of plastics and is one of the basic techniques of modern packaging industry.