Mixing in an extruder for a cable-making process

摘要

An on-line compounding process for making a strippable screen in the manufacture of an electric power cable having insulation of an ethylene homopolymer or copolymer crosslinked via silane links comprises: feeding to an extruder (a) a preformed composition comprising an ethylene copolymer and carbon black; (b) particulate polypropylene; and (c) crosslinking agents comprising an unsaturated hyrolysable silane, a grafting initiator and a silanol condensation catalyst; mixing these ingredients and generating pressure in the resulting mixture in a first zone of the extruder at a temperature above the softening range of the copolymer but substantially below the softening range of the polypropylene so that it is dispersed in the solid state into the plastified copolymer; ```and only after the crosslinking agents at least are dispersed through the mixture raising the temperature of the mixture in a second section of the extruder above the softening range of the polypropylene and sufficient to initiate grafting of silane side-chains to the copolymer and blending to further disperse the now molten polypropylene. Insulation of the cable may be performed by coextrusion with the insulation and conductor screen in a triple extrusion head. The copolymer is EVA.