The strainer, a single axis screw extruder, removes foreign materials and metallic particles that are mixed during the mixing process. In this way it protects the calender roll. In general, it is put just in front of the calender for soft or semi rigid PVC to remove foreign materials. It continuously supply the compounding raw materials having even temperature to the calender, and normally has 5∼8 of L/D and much small compression ratio.