Patent ID: 7883329
Filing Date: 2011-02-08
Classification: B29C

Abstract:
1. Device for producing multilayer, coextruded, tubular preforms made of thermoplastic material, with a coextrusion head ( 10 ) with several essentially coaxially arranged flow channels (FK 1 , FK 2 ), each of which is fed from an individual inlet opening (ZF 1 , ZF 2 ) with a material melt, which is annularly distributed in a distributor ring ( 26 , 28 ) and flows along an annular conical frustum, wherein the material melts flow into a common annular flow channel ( 12 ) that widens like a funnel, with an annular accumulation chamber ( 14 ), in which a displaceable annular piston ( 16 ) can reciprocate, and with an annular discharge channel ( 18 ) that follows the annular accumulation chamber ( 14 ) and has an annular extrusion orifice ( 20 ) that can be closed, wherein, as viewed in a longitudinal section through the coextrusion head, the gap width (s 1 , s 5 ) in the respective distributor ring ( 26 , 28 ) is greater in the vicinity of the inlet opening (ZF 1 , ZF 2 ) than the gap width (s 2 , s 6 ) on the opposite side from the inlet opening (ZF 1 , ZF 2 ), and that, as viewed in a longitudinal section through the coextrusion head, the gap width (s 3 , s 7 ) in the respective flow channel (FK 1 , FK 2 ) is smaller in the vicinity of the inlet opening (ZF 1 , ZF 2 ) than the gap width (s 4 , s 8 ) on the opposite side from the inlet opening (ZF 1 , ZF 2 ), wherein each flow channel (FK 1 , FK 2 ) opens into a first cylindrical ring ( 22 , 24 ), wherein a region of quieted flow, which is formed as a common cylindrical ring ( 34 ), is provided between a mouth ( 30 ), at which several material melts come together, and a point of widening ( 32 ), at which the combined material melts enter the common flow channel ( 12 ), which widens like a funnel, and wherein the cross-sectional area (F 34 ) of the common cylindrical ring ( 34 ) is equal to the sum of the cross-sectional areas (F 22 , F 24 ) of the first cylindrical rings ( 22 , 24 ).