Most plastic materials contain impurities, which can be easily and quickly removed using a screen changer installed on the polymer melt stream downstream of the extruder. The screen is a woven disc with a diameter matching that of the extruder barrel. Typically, several layers of screens with different mesh sizes are bundled together. Fine screens filter out small solid particles from the melt stream, while the outer, coarser screens are more robust and prevent larger particles from entering the inner, finer screens prematurely.

To counteract the forces caused by melt flow, a filter screen assembly is fitted with a dense-pored circular steel plate, known as a protective plate, which is inserted into the groove at the end of the extruder barrel. To replace the blocked screen liner, first remove the downstream equipment, replace the old liner with a clean one, and then reinstall it onto the production line.