Plastic Granule Extruder : Screw & Barrel couple is the heart of extruder machine. By means of rotating screw in the barrel; premixed compound is pushed to cutting plate while being heated-cooked in other words- at desired temperature. Rotating blades cuts extrudate into desired pellet size. Then air blown to cooling. Above is a single screw machine displayed. Granule extruder has all basic parts of an extruder : motor, reduction gear, hopper ,heating zones and cooling elements, screw and barrel and cutting plate. Twin screws, planet screws , co-rotating and planetary screws are also used for the same purpose. Screw diameter, barrel length and structure is designed according to plastic compound and desired technical specifications of the final product. Heating and cooling zones should be accurate. The angle of flyers , diameter over length ratio and zones of screw determined by extruded plastic , expected outcome, line speed, minimum and maximum diameter of final product.
It is essential to have homogenous blend. Plastic , Plasticizer and all other additives such antioxidants, UV stabilizer etc. must be mixed and blended homogenously. For this purpose a single screw extruder would not be competant. However it's initial cost is low.
In the drawing above, A basic , single screw extruder with hopper is shown. Some plastics require different types of loading such , side feeding, feeding in sheets form or feeding with and side-feeding extruder also possible.