Polythene bags we manufactured using a two part process, blown film extrusion and bag conversion and this step by step guide will explain how both processes work.
Blown Film Extrusion Process
- The process begins with small plastic pellets, known as resin, which is available in different melt flows and densities to ensure the perfect material is manufactured. The various resins are blended, following specific recipes upon reaching the extrusion department.
- The blended resin is fed into the extruders which are heated to approximately 200oC, where the resin becomes molten and pliable. The molten polythene is pushed through the barrel by a turning screw.
- The molten polythene is then pushed through a fine filter to ensure any contamination is removed and then passes through a circular die gap to form a continuous tube of plastic.
- While molten, the polythene is pinched together inflated to the desired size and thickness, which is drawn vertically up a three storey tower allowing the molten bubble to cool before the film is laid flat by two rolls at the top of the machine.
- The final part of the extrusion process sends the flat tubing through a series of rollers and then winds the film onto a 3” diameter cardboard core, which the operator removes once there is the desired materials on the roll.
Bag Conversion Process
- When the film is delivered to the conversion department, the roll of film is passed onto the machine’s unwind stand and the material is threaded through the machine in a particular way, feeding it through the machines nip rollers.
- At this point, any accessories are added to the bag such as perforations or adhesive glue to ensure the bag meets the customers’ requirements.
- The operater must set the machine to the desired speed for the job. In some instances, with small bags, the machine cycle speed may produce up to 20,000 bags per hours, however on very large bags the machine may cycle at 1,000 bags per hour.
- Once the machine is running, the material is drawn through the machine to the correct length and is then heat sealed and cut off to an individual bag. These bags are then indexed on a moving conveyor belt to the operator who packs the bags into boxes.