| 摘要 |
<p>The head for the extrusion or coextrusion of tubular thermoplastic preforms, particularly for machines that produce containers by the blowing technique, is composed of superposed plates or discs, in whose superposed faces there are formed, by operations of for example drilling, turning and milling, the symmetrical parts forming the chambers that are to carry the stream of plastic coming from the extruder, which is fed to the head through a radial hole and which must arrive with a uniform distribution in terms of flowrate and pressure in the downward tubular coaxial channel (C), of the said head. The stream of plastic coming from the extruder is fed to the intermediate part of a chamber (6) having in plan view the shape of the sector of a circle with an angular amplitude suitably greater than 180°, with its centre on the axis of the extrusion head, and having at its opposite ends identical openings (9, 9') 180° apart from each other which open at the base of a first annular and cylindrical chamber (8) that is likewise coaxial with the extrusion head and is of suitable height, where the plastic rises without meeting any obstacle and at the end of which first chamber the plastic follows a hairpin bend and enters a second annular and cylindrical chamber (14) coaxial with and internal to the previous chamber and likewise free of obstacles, the lower mouth of which directly or indirectly feeds the down channel (C) of the head. The distance between the walls of the said last chamber (14) is less than the distance between the walls of the upstream chamber (8).
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