The single screw extruder is the workhorse for many extrusion processors. It is relied upon daily to keep pumping out the extruded plastic products. They lead the way for those on time shipments to meet your hard-earned customer demand. Therefore, it is important for extrusion processors to consider and maintain their extruder’s output.
First, this requires an understanding of material conveyance within these machines. Here surface friction plays an important role. Having high friction along the barrel and low friction along the rotating screw allows for forward material motion. Under these conditions, the polymer slips past and over the screw (rather than rotating with it). This further melts and mixes along at each zone. It then exits the barrel at an output rate to support the required line speed.
Please also consider your grooved barrel feed sections, and highly-polished, low friction coated extruder screws. They supplement opposing frictional forces, providing for more consistent extruder output and improved metering of materials.
Negatively altering the required friction characteristics will also have a direct effect on extruder output. It is possible to lose output and ultimately lose operating efficiency over time. As residue builds up, a layering effect on surfaces can set in. Left unchecked, this is a progressively worsening condition. It can vary from everything from material hang up or wrap, all the way up to a total loss of output.
This happens because of improperly maintaining the screw and barrel surfaces. Simply put, overlooking or underestimating the need for a clean machine is costing you! This problem is especially common with dedicated extruders, where one material and color consistently runs. It often provides a false sense that there is no need to purge—because no “real” changeovers take place. But reduced extruder output and increased operating cost will quickly begin to erode any perceived savings with this notion.
Under all extruder-operating circumstances, it is important to keep the condition of the extruder screw and barrel surfaces in mind. Having a clean machine, by including regular screw and barrel purging with a commercial purging compound, will keep your workhorse up and running at its best. Keep barrel friction high and screw friction low for optimum performance. That’s what it takes to maintain output of your single-screw extruder!
Learn about the importance of implementing proper purging procedures by downloading this free industry guide.