Extrusion die for crosslinkable polymers - using an insulated die with a high specific surface area to control heat cure development

摘要

Extrusion with a crosslinkable elastomer or resin where curing is initiated in the shaping die and material adhesion or hang-up on the tool surfaces is inhibited by a co-extruded film or non crosslinkable material, where profile is developed using a shallow material flow path between a pair of metal surfaces which are thermally insulated from the rest of the equipment and have closely controlled integral heating circuits. Pref. the shallow flow path is defined by relative coaxial movement between a concial mandrel and a convergent barrel of similar included angle with a clearance adjusted to less than the mean thickness of the extruded profile. The final profile is fixed by an ancillary die with additional heaters to complete the cure. Esp for applying crosslinked sheathing to continuous power cables or leads. Close temp. control via a high flow surface/volume ratio in turn controls the thickness and the degree of cure so that flow properties and the physical properties are optimised for production via a short final die land length and without independent post curing ovens.