Quick Article Nav
Welcome to extrusion.plastics.com
What is Extrusion...[continued]
Extrusion Forming processes
Film and sheet extrusionPlastic films, typically defined as less than 10 mil (0.01 inches or 0.25 mm) thick, are produced by blown or cast film extrusion using a single screw extruder. In blown film extrusion, the polymer is fed to an annular die to form a tube that is closed at one end to make a “bubble”. The molten polymer is drawn down to a thin film in the machine direction, as well as expanded outward in the transverse direction. The “blow-up-ratio” is the ratio of the bubble diameter to the blown film die diameter. The bubble is cooled with air and collapsed into a flat tube.
The blown film tube can be used to make all kinds of bags, or the tube can be slit to form a flat sheet. In cast film extrusion, the molten polymer is fed to a flat die, the melt is drawn in the machine direction into a thin film, and the flat web is rapidly cooled by passing over one or more chilled rollers. As in all types of extrusion, the cooling rate and the draw-down rate affect molecular orientation, which affects physical properties of the end product. Both blown and cast films are used in many kinds of applications. A walk through the grocery store reveals a myriad of highly engineered film packages, from fresh-produce bags and wraps for meat to candy wrappers, cereal bags, stand-up pouches, and bags for frozen food. Films are also used in stretch and shrink wrap for bulk packaging. Outside of packaging, films are used in bags, agricultural covers for fields or greenhouses, and nonwoven products for healthcare or personal care like baby diapers, to name just a few.
Plastic sheet is usually defined as greater than 10 mil thick. Sheet is typically extruded with a single-screw extruder, although direct extrusion might use a twin-screw extruder. Like cast film, sheet is extruded through a wide, flat die, pulled through rollers, and cooled with air or water.
Sheets may be used in sheet-form for applications such as pond or landfill liners, or go to a thermoforming process to be made into a variety of containers or other parts.
Profile extrusionPlastic films, typically defined as less than 10 mil (0.01 inches or 0.25 mm) thick, are produced by blown or cast film extrusion using a single screw extruder. In blown film extrusion, the polymer is fed to an annular die to form a tube that is closed at one end to make a “bubble”. The molten polymer is drawn down to a thin film in the machine direction, as well as expanded outward in the transverse direction. The “blow-up-ratio” is the ratio of the bubble diameter to the blown film die diameter. The bubble is cooled with air and collapsed into a flat tube.
The blown film tube can be used to make all kinds of bags, or the tube can be slit to form a flat sheet. In cast film extrusion, the molten polymer is fed to a flat die, the melt is drawn in the machine direction into a thin film, and the flat web is rapidly cooled by passing over one or more chilled rollers. As in all types of extrusion, the cooling rate and the draw-down rate affect molecular orientation, which affects physical properties of the end product. Both blown and cast films are used in many kinds of applications. A walk through the grocery store reveals a myriad of highly engineered film packages, from fresh-produce bags and wraps for meat to candy wrappers, cereal bags, stand-up pouches, and bags for frozen food. Films are also used in stretch and shrink wrap for bulk packaging. Outside of packaging, films are used in bags, agricultural covers for fields or greenhouses, and nonwoven products for healthcare or personal care like baby diapers, to name just a few.
