Extrusion Processes

Extrusion is the process where a solid plastic (also called a resin), usually in the form of beads or pellets, is continuously fed to a heated chamber and carried along by a feedscrew within. The feedscrew is driven via drive/motor and tight speed and torque control is critical to product quality. As it is conveyed it is compressed, melted, and forced out of the chamber at a steady rate through a die. The immediate cooling of the melt results in resolidification of that plastic into a continually drawn piece whose cross section matches the die pattern. This die has been engineered and machined to ensure that the melt flows in a precise desired shape. Examples of extruders products are blown film, pipe, coated paper, plastic filaments for brush bristles, carpet fibers, vinyl siding, just about any lineal shape, plus many, many more. There is almost always downstream processing equipment that is fed by the extruder. Depending on the end product, the extrusion may be blown into film, wound, spun, folded, and rolled, plus a number of other possibilities. This article limits any equipment discussion to the extruder itself.