Patent ID: 7008577

Claim:
Extrusion head for manufacture of tubes comprising at least one layer of expanded plastic by extruding a stream of molten plastic containing a blowing agent through an annular passage cross section made in the extrusion head and in which the stream of molten plastic containing the blowing agent spreads out circumferentially and welds itself to itself by recombining of two stream fronts, wherein the extrusion head is equipped with a special-purpose thermal regulation device allowing the molten plastic containing the blowing agent to be heated or cooled after the two stream fronts have recombined, wherein the annular passage cross section is preceded by an equalizing device which lies after a feed opening of the extrusion head and which is in a form of a toric groove, and the special-purpose thermal regulation device is configured to not cool the stream of molten plastic until after the stream of molten plastic has passed through the toric groove.