Screen changer with pre-fill screen blocks

Abstract From the Canadian patent

A screen changer mounted between a flowable plastic extruder and a die has a clamp frame movable rectilinearly across the extrusion passage by fluid piston and cylinder means to successively position one of four screen blocks across the passage. A used block is removable from the frame at one end, whereupon latch mechanism retains three blocks while the frame retracts to receive a fresh block. Each block contains a filter recess a purge re-, cess and a pre-fill groove in the upstream face so that the incoming block, is pre-filled with plastic and purged while moving into position across the passage.