Comprehensive Breakdown of the Blown Film Process Workflow

Blown film process

(1) Raw material treatment: the plastic granules are mixed according to a certain proportion and dried to remove the moisture in the granules to ensure that no air bubbles will be produced during the extrusion process.

(2) Extrusion film: plastic granules are melted in the extruder, forming continuous molten plastic.

(3) Blowing and Cooling: The fluid from the die head is cooled and blown by the wind ring to form film bubbles.

(4) Herringbone clamping: The film bubble is extruded into a sheet to facilitate the subsequent process.

(5) Traction stretching: The cooled and cured film is pushed through the stretching mechanism to make the film more uniform and transparent.

(6) Edge-cutting and winding: after cutting off a certain width of waste edges on both sides of the film, the film is wound up online using two winders.

Blown film key process parameters

(1) Temperature

Temperature includes extruder temperature and die head temperature. Generally, the extruder temperature must be adjusted according to different plastic materials' melting points and characteristics. In contrast, the die head temperature must be uniform to ensure the melt's fluidity at the die head's exit and the film's thickness uniformity.

(2) Frost line position

The frost line is the demarcation line of the plastic from the molten state into the highly elastic state, and its position affects the crystallization and orientation of the film. The height of the frost line affects the transparency and mechanical properties of the film.

(3) Wind ring cooling

The cooling wind ring cools the just-extruded melt quickly to form a film. The airspeed and volume of the cooling air ring need to be precisely controlled to avoid uneven film thickness.

(4) Haul-off temperature

Temperature control during the haul-off process is also significant. Too high a haul-off temperature may lead to uneven stretching of the film, affecting its uniformity.

(5) Blow-up ratio

Control of the blowing ratio (the diameter of the film bubble to the diameter of the mold opening): the appropriate blowing ratio can improve the film's lateral tensile strength while maintaining the film's uniformity.

(6) Draw ratio

Adjust the ratio of haul-off speed to extrusion speed to ensure uniform film stretching in the longitudinal direction.

Main equipment in blown film

(1) Extruder

The extruder is the core equipment of the blown film process, mainly composed of a screw, barrel, hopper, reducer, and drive motor. It melts and plasticizes the plastic granules through the rotary movement of the screw to form continuous molten plastic.

(2) Die head

The die head is a component installed at the front end of the extruder. It determines the shape and size of the film, and its design has an important effect on the uniformity of film thickness.

(3) Cooling unit

The cooling device usually consists of a cooling air ring, air duct, and blower. It cools the molten plastic extruded from the die head and rapidly solidifies it into the film.

(4) In-line thickness gauge

Determine the thickness of film bubbles and rolled products. If they do not meet the requirements, adjust the temperature, air volume, and other parameters.

(5) Bubble stabilizing frame

The bubble stabilizing frame stabilizes the film bubble and prevents it from deformation during cooling and traction.

(6) Herringbone plate

The herringbone plate is installed under the traction roller to adjust the nip angle and control the film bubble's leveling effect.

(7) Traction device

The traction device includes a traction frame, roller, and motor, which is responsible for traction and flattening the cooled film at a constant speed to form a continuous double-layer film.