Extrusion and granulating of different coloured plastic pellets and process equipment including a kneading extruder

摘要

A process for production of different coloured plastic pellets from molten resin employs twin granulating units(A,B) supplied by a kneading extruder(1) and involves: (a) feeding a thermoplastic resin of a first colour into the screw extruder(1) with one granulator connected to the extruder outlet(2a); (b) closing off the other granulator unit so that pellets of the first colour are produced by the connected granulator; (c) concluding pellet production in the first colour and connecting the extruder outlet directly to the outside of the equipment for pumping out residues of the first colour; (d) feeding a thermoplastic resin of a second colour into the screw extruder and kneading and melting; (e) pumping the second resin directly out of the equipment to purge any remaining material of the first colour from the extruder and subsequent passages; (f) closing off the direct outlet , connecting the extruder outlet to the second granulator and closing off the first granulator (g) feeding the thermoplastic resin of the second colour into the screw extruder for production by the second granulator. Process equipment includes a kneading screw type extruder (1) whose outlet (2a) is connected to an inlet (5a) of a passage change-over valve (5) with a first (5b) and a second (5c) outlet branching off at both sides of the front end. A spool (6) in the valve (5) can connect with either the first (5b) or second (5c) outlet or a purging passage running directly out of the equipment. A different granulator (A,B) is provided for each resin colour, the first being connected via a first output change-over valve (10) to the first valve outlet (5b) and the second connected via a second output change-over valve (20) to the second valve outlet (5c). A spool (11) in the first output change-over valve (10) can either connect the first outlet (5b) of the passage change-over valve (5) to the first granulator (A) or block the passage to the latter while opening an outlet directly out of the equipment. Another spool (21) in the similar second output change-over valve unit (20) performs the same function in the flow path from the second outlet (5c) of the passage change-over valve (5).