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Blown Film Extrusion machine multilayer plant monolayer line

June 7, 2014 • Mrunal Ramanuj

Blown Film Plant Extrusion machine

Blown Film Extrusion machine multilayer plant monolayer line



One of the most common methods of film manufacture is Blown  (also referred to as the Tubular Film) Extrusion. The process involves extrusion of a plastic through a circular die, followed by “bubble-like” expansion. The principal advantages of manufacturing film by this process include the ability to:

  • Produce tubing (both flat and gussetted) in a single operation
  • Regulation of film width and thichness by control of the volume of air in the bubble, the output of the extruder and the speed of the haul-off
  • Eliminate end effects such as edge bead trim and non uniform temperature that can result from flat die film extrusion
  • Capability of biaxial orientation (allowing uniformity of mechanical properties)
  • Blown Film Extrusion can be used for the manufacture of co-extruded, multi-layer films for high barrier applications such as food packaging.


The Process

Plastic melt is extruded through an annular slit die, usually vertically, to form a thin walled tube. Air is introduced via a hole in the centre of the die to blow up the tube like a balloon. Mounted on top of the die, a high-speed air ring blows onto the hot film to cool it. The tube of film then continues upwards, continually cooling, until it passes through nip rolls where the tube is flattened to create what is known as a ‘ lay-flat’ tube of film. This lay-flat or collapsed tube is then taken back down the extrusion ‘ tower’ via more rollers. On higher output lines, the air inside the bubble is also exchanged. This is known as IBS (Internal Bubble Cooling).

The lay-flat  is then either kept as such or the edges of the lay-flat are slit off to produce two flat film sheets and wound up onto reels. If kept as lay-flat, the tube of film is made into bags by sealing across the width of film and cutting or perforating to make each bag. This is done either in line with the blown film process or at a later stage.

Typically, the expansion ratio between die and blown tube of film would be 1.5 to 4 times the die diameter. The drawdown between the melt wall thickness and the cooled film thickness occurs in both radial and longitudinal directions and is easily controlled by changing the volume of air inside the bubble and by altering the haul off speed. This gives blown film a better balance of properties than traditional cast or extruded film which is drawn down along the extrusion direction only.

Layer Die Head Film Bubble Going Into Collapsing Frame
3 layer die head with air ring and internal bubble cooling Film bubble going into a collapsing frame
 Control Panel From Blown Film Line  Taking An Edge Trim From Film Web
 Control panel graphic from an automated blown film line  Taking an edge trim from film web
 Layflat Tube  Blown Film Line In Action
 The layflat tube is separated into 2 single sheets  Blown Film Line In Action


Polyethylenes (HDPE, LDPE and LLDPE) are the most common resins in use, but a wide variety of other materials can be used as blends with these resins or as single layers in a multi-layer film structure. these include pp, pa, evoh. In some cases, these materials do not gel together, so a multi-layer film would delaminate. To overcome this, small layers of special adhesive resins are used in between. These are known as “tie layers”.


Blown film can be used either in tube form (e.g. for plastic bags and sacks) or the tube can be slit to form a sheet.Typical applications include Industry packaging (e.g. shrink film, stretch film, bag film or container liners), Consumer packaging (e.g. packaging film for frozen products, shrink film for transport packaging, food wrap film, packaging bags, or form, fill and seal packaging film), Laminating film (e.g. laminating of aluminium or paper used for packaging for example milk or coffee), Barrier film (e.g. film made of raw materials such as polyamides and EVOH acting as an aroma or oxygen barrier used for packaging food, e. g. cold meats and cheese), films for the packaging of medical products, Agricultural film (e.g. greenhouse film, crop forcing film, silage film, silage stretch film). Blown Film Examples

Applications made from Blow Film

The Extrusion Dies

Here are some cross section diagrams of blown film extrusion dies. Each layer in this 5 layer die is shown in a different colour dies are precision made and as such are expensive but their service life is considerable. Each die head will have a working range of die inserts at different diameters to suit the required application. Different die gaps can also be specified depending on the material being extruded.

Ancillary Equipment

Once the film has been blown, it is drawn off from the tower using ancillary equipment. Dependent on the end product (film or lay-flat tube) various specialist machines are used. The blown Film Process is a continuous process, as such the machinery has to be designed to cope with both the high speeds involved and be able to operate on a 24 hour basis.

The photographs below show two types of take off winder, single station, and a tandem winder and two examples of dies…

Blown Film Extrusion Die Blown Film Extrusion Die Tandem Winder Single Station Winder
Blown Film Extrusion Die Tandem Winder Single Station WInder

Blown Film Plant

 Film Extrusion is one of the most common polymer conversion processes in the world

 multilayer line pp  machine multilayer extrusion  line

  • Film is made by extruding molten plastic through a circular die, forming an inflated tubular bubble that moves through a cage as it cools, that is then collapsed and formed into rolls
  • The typical film blowing process consists of a series of stages, including extrusion, blowing, collapsing, and winding

HIPF Course Description

Course Objective

At the end of the course, the trainees will be able to:

  • Develop a working knowledge of and learn how to operate a Blown Film Extrusion machine
  • Understand the basics of blown film technology, the common material used, and some common problem solving situations
  • Analyze and solve practical blown  problems
  • Develop a working knowledge on maintaining a blown film machine

Course Outline

    1. Principles of Blown Film Extrusion
      Definition and Principle; Product and Applications;  Fabrication Process; Types of Blown  Machines
    1. Resin Materials
      Raw Materials Use for  Film Extrusion; Three Common Polyethylene Grades Used for Blown ; Suitable Grade index for
    1. Safety Education for  Operation
      Safety Guideline and SOP; Personal Protective Equipment (PPE); Safety Devices; Warning Signs; Safety Rules for Operation; Safety Instructions on Operation
    1. The Main Components of  Machine
      The Extruder; The Die Head and Die; The Bubble Cooling System; Bubble Stabilizer; The Take-Off System/Pinch or Nip Rolls; The Wind-Up System; Corona Treatment
    1. Die and Air Ring as Major Components for Blown 
      Kinds of Die for Blown Film; Details of Die and How It Works; Details of Air Ring and How It Works; Die and Air Ring Care and Maintenance
    1. Introduction to the Blown  Extrusion Machine
      BFE Process Flow; Start-Up of Blown Film Line; Quality Control for Blown Film; Scheduled Shut-Down of Blown Film Line; Emergency Shut-Down of Blown Film Line; Switching On After Emergency Stop
    1. Operating Skills for Blown  Extrusion Technology
      Checking of Machine Conditions Before Operation; Winder Preparations; Film Guide Set-Up and Importance; Blown Film Run Preparations; Die Checking and Adjustments; Parameter Setting-Up; Switching On After Emergency Stop; Changing Die; Changing Materials and Filling Procedures
    1. Die Dismantling, Cleaning and Mounting
      Die Dismantling Procedure; Die Cleaning and Care; Understand Die Assembly and Mounting
    1. Blown Film Extrusion Troubleshooting
      Types of Trouble of Blown Film Process; Unstable Bubble;  Appearance; Machine Malfunction
    1. Common Secondary Film Processing Methods
      Printing; Bag Making Process; Scrap Recycling
    1. Quality Control of Blown Film

The blow film extrusion process is made of four main stages: the polymer in form of pellets are melted together forming a viscous fluid which is continuous. In the molten state the material is forced through an annular die. Injection of air is done midway the die causing the melted extrusion to form a bubble which is uniform in thickness. This is followed by pulling upwards the bubble from the die and the film cooled from inside to give the bubble uniform diameter. The bubble is then passed through a roller in the blow film line and gets flattened making two flat films. The multilayer blow film line is suitable for food packaging and industrial products, and agricultural and technical applications. Visit –

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