Plastic Film Extrusion
Plastic film extrusion is one of the most essential processes in industry and it is only made possible with the application of heating elements. Without it, everyday goods such as your daily loaf of bread to your new roll of carpet would be without the protective packaging that ensures the goods are received by the consumer in pristine order (plastic film extrusion accounts for around a quarter of all thermoplastics consumed and the film extruded is almost entirely for consumption in packaging).
In simple terms, the process involves forcing molten polymer (heated in barrels using heating elements such as band and cylinder heaters) through a circular or slot die. This continuous process enables the production of a consistent high quality product to extremely accurate gauge. For most thin gauge films, the film extrusion process takes the form of blown or cast extrusion. Plastic bags and sacks are made by the blown film process which is a form of film extrusion. Blown film is created when the molten plastic material (or melt) is extruded through a ring-shaped die to form a continuous tube of plastic which is simultaneously inflated with air to form a plastic bubble. Despite the highly developed technology for controlling the average film thickness of blown films produced by the blown film extrusion process, thick and thin points within a range of tolerance cannot be avoided. Heating elements are used during the process to help control the measured thick and thin spots of the blown film, by means of which the measured thick spots are heated and/or the measured thin spots are cooled so that the result is an adjustment and approximation of the average film thickness.
Once the film has been cooled at the desired thickness or gauge, the tubing is then guided by pinch rolls to become ‘Lay Flat’ film which is wound, slit and trimmed automatically before being converted into a wide range of film and bag products – often involving printing and sealing. Today, manufacturing technologies and processes have advanced to help create machinery capable of automatically combining the complicated series of processes needed to produce the widest variety of shapes and sizes from large bags to smaller pouches. Whilst these processes are often supported by computerised methodologies that precisely control every step of manufacture, they are always supported by heating element technologies at a number of stages through the process.