The open mill is a kind of plastic mixing equipment that has been used earlier in plastic products production plants. On the calender production line, the open mill is in front of the calender and after the mixer, which is used to mix evenly mixed raw materials.

Extruders can be divided into single-screw, twin-screw and multi-screw extruders according to the number of screws. At present, single-screw extruders are more widely used and are suitable for extrusion processing of general materials.