Extrusion International USA 5-2019

44 Extrusion International 5/2019 PELLETIZING – CASE STUDY Writer: Christian Lebert, Product Manager at Maag Automatik GmbH in Großostheim, Germany A leading manufacturer of polystyrene extruder foam (XPS) for construction and industrial applications is using a newly developed SFS-3-3000 type static cartridge filter system from Maag. With a filtration fineness of 600 µm or 800 µm, it reliably separates impurities in the form of unmelted particles or agglomerates from the melt and homogenizes them further. As a result, the melt exits the extruder die continuously with a high degree of uniformity XPS is a closed-cell, hard insulating material. In its extru- sion process, the manufacturer mixes polystyrene pel- lets with dyes and other additives to create a blend that is melted in a first extruder. After that stage, the melt is mixed with the blowing agent carbon dioxide and then passes through a second extruder, which homogenizes the melt and lowers its temperature. After exiting this through a wide-slotted die, the melt foams into an end- less strip which is subsequently calibrated to its final size. The foaming produces a large number of small closed cells. These provide the high mechanical strength of the resulting sheets cut from the webs and makes them in- sensitive to moisture. High-Performance Cartridge Filter System stabilizes XPS Extrusion Careful filtration assures productivity If the melt is not filtered - or insufficiently so - on its way through the production unit, impurities carried along in the melt can settle in the extruder die. The melt flow then divides at this point, so that instead of a continuous web, a two-part web is formed, resulting in rejects. This can be largely ruled out by using a suitable filter system between the cooling extruder and the wide-slotted die - though ensuring that the productivity of the plant is still main- tained without restriction when doing so. After conventional filter systems had proved disadvanta- geous in practice due to leakages and inadequate service life, in 2017 Maag supplied the manufacturer with a type Picture 1: View into thefilter inlet (All pictures: ©Maag)