Extrusion International 6-2024-USA

44 Extrusion International 6/2024 EXTRUSION TECHNOLOGY is minimising the energy input into the polymer during plasticising, increasing melt homogeneity with an op- timum temperature profile and maintaining the poly - mer's property profile. "A fundamental understanding of the processes in the feed zone of the extruder where the polymer granulate is still solid is essential for correct design," explains Josef Dobrowsky, who has acquired his knowledge with partners during many years of process consulting and screw design. Based on the desired spe- cific output, the ratio of motor power to screw speed is first defined. The aim is to keep the specific output constant regardless of the melt pressure. "We use a calculation model and take the results to define the motor power, the screw speed and the design of the feed zone. These are either smooth, grooved or spiral- grooved." Once the choice has been made, further parameters such as the L/D ratio and the geometry of the barrier section as well as a calculation of shear energy, rate and length of the maddock section is done. The short- est possible mixing section with the option of dynamic mixing must also be determined. "Optimising the pro- cessing unit is never just one big development step, but rather the combination of many small steps to achieve the optimum process." It goes without saying that each processing unit is tested before delivery using a defined method that delivers comparable and reproducible re- sults. CONEXTRU uses a test tool with a valve to adjust back pressure and simultaneously extrude a flat profile. Output, energy consumption, linearity at low and high back pressure over screw speed and melt quality of the extrudate are recorded. The test results are document- ed in diagrams which give input for further changes - if needed. Another use of individual design is the con- struction of screws as an exchange for the original screw supplied by a third-party extruder. This can improve the output and melt quality. Customised wear protection as a matter of course Advising a customer on extruder design also includes size advice and ultimately the level of investment. Here Josef Dobrowsky is eager to clear up some misconcep- tions: "It is neither correct that the next largest extrud- er model should be selected at higher speeds, nor is it the case that a longer processing unit consumes more energy." For example, a 40D machine requires less en- ergy than a 37D extruder with the same screw diame- ter. CONEXTRU helps customers make exactly the right choice for each specific task. If a high-speed extruder is required, CONEXTRU has a solution: their high-speed extruder with a screw diame- ter of 65 mm, achieving 600 rpmwith an output of 1,200 kg/h. Last but not least, extruder choice includes the ap- propriate wear protection, orientated towards the task at hand. If only virgin materials and few regrind and co- lour batches are used, standard equipment suffices; if more abrasive materials are used, different setups are possible. For high regrind content and highly filled poly -