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AssigneeAlphacan
InventorBernard Prevotat
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The invention relates to a method for continuously producing plastic tubes by biaxial drawing consisting in producing a blank (E) by extrusion, heating said blank to a molecular condensation temperature, radially dilating it by the internal pressure of a fluid applied between two axially distant obturator rings (7, 11) and in carrying out a calibration (8) and cooling (9) associated with an axial tension produced on a tube at the output thereof. A pressure opposite to the internal pressure is applied to the blank wall from the outside in at least one area which is exposed to the radial dilation. Said opposite pressure is selected such that it is lower than the internal pressure, thereby preventing a coanteraction to said dilation and remaining sufficient in order to control the dilation growth in such a way that it is possible to assure a substantially constant material thickness on the same circumference.
A method for the continuous production of plastic tubes with biaxial drawing, whereby a blank (E) is produced by extrusion, this blank is brought to molecular orientation temperature, it is made to undergo radial expansion by subjecting it to an internal fluid pressure applied between two axially distant obturators (7, 11), and is sized (8) and cooled (9) while at the same time exerting axial tension on the exiting tube, characterized in that a pressure antagonistic to the internal pressure is applied (13) from the outside against the wall of the blank in at least one region subjected to the radial expansion, this antagonistic pressure being lower than the internal pressure so as not to impede the expansion, but being high enough to ensure a controlled increase in the expansion, with a more or less constant material thickness over the same circumference.
Dependencies are inferred from the claim text.