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AssigneeAlphacan
InventorBernard Prevotat
Estimating the term…
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 counteraction to said dilation and remaining sufficient in order to control the dilation growth in such a way that it is possible to ensure a substantially constant material thickness on the same circumference.
In a method for the continuous extrusion of a plastic tube with biaxial drawing, whereby a tubular blank (E) is produced by extrusion through a die, said tubular blank is brought to molecular orientation temperature, 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 resulting in a tube having a larger diameter than the extruded blank, the improvement comprising applying a counterpressure against the exterior wall of the tubular blank in at least one region subjected to the radial expansion and only to the localized regions most susceptible to an uncontrolled increase in the absence of counterpressure, said counterpressure 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, resulting in a substantially uniform peripheral thickness of the wall throughout the length of the resultant tube.
A method for the continuous extrusion of a plastic tube with biaxial drawing, whereby a tubular blank (E) is produced by extrusion through a die, said tubular blank is brought to molecular orientation temperature, 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 resulting in a tube having a larger diameter than the extruded blank, the improvement comprising applying a counterpressure against the exterior wall of the tubular blank in at least one region subjected to the radial expansion, said counterpressure 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, resulting in a substantially uniform peripheral thickness of the wall throughout the length of the resultant tube, and wherein the counterpressure is exerted by a mechanical contact pressing directly against the exterior wall of the blank.
In a production line for the continuous extrusion of a continuous tube with biaxial drawing comprising:
Dependencies are inferred from the claim text.