Abstract: 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.

Abstract: 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.

Abstract: The invention concerns a continuous manufacturing method which consists in producing a blank (E) by extrusion, bringing said blank to a temperature for molecular orientation, passing said blank around a radial expansion mandrel (12); gauging and cooling while subjecting the blank to axial traction. The radial expansion produced on the mandrel (12) is partial so that the internal diameter (B) of the blank (E), when it leaves the mandrel, is less than the nominal internal diameter (D) of the finished tube; performing an additional radial expansion of the blank, up to its nominal diameter, by internal fluid pressure. In permanent operating conditions, the inner surface of the blank (E) is no longer in contact with the mandrel (12).

Abstract: The invention concerns a continuous manufacturing method which consists in producing a blank (E) by extrusion, bringing said blank to a temperature for molecular orientation, passing said blank around a radial expansion mandrel (12); gauging and cooling while subjecting the blank to axial traction. The radial expansion produced on the mandrel (12) is partial so that the internal diameter (B) of the blank (E), when it leaves the mandrel, is less than the nominal internal diameter (D) of the finished tube, performing an additional radial expansion of the blank, up to its nominal diameter, by internal fluid pressure. In permanent operating conditions, the inner surface of the blank (E) is no longer in contact with the mandrel (12).

Abstract: The invention concerns a method for making plastic tubes, whereby a tube blank (Te) brought to a temperature close to molecular orientation temperature is subjected to a bi-axial drawing, by radial expansion of the tube blank inside a forming shaft (2), with formation of a contraction cavity at one end of the tube, by controlled displacement of this contraction cavity to the other end of the tube, and by longitudinal drawing. The radial expansion is carried out in at least two phases, viz. a first phase during which the tube blank (Te) is inflated to an intermediate diameter (Di) determined by a double-walled envelope (21), introduced into the forming shaft (2), with circulation of a hot fluid between the two walls of the envelope (21), and then the envelope is gradually removed from the forming shaft (2) to enable, during a second phase, the radial expansion of the plastic tube up to an internal diameter of the forming shaft (2), and its longitudinal drawing.

Abstract: The invention concerns a method for treating plastic tubes, in particular PCV tubes, obtained by extrusion, whereby a tube is brought to a molecular orientation temperature, higher than room temperature, and is subjected to bi-axial drawing by radial expansion and axial elongation, to obtain a bi-oriented tube whose mechanical properties are improved. The tube (T) is cut into elements (4) of predetermined length immediately after being extruded and its temperature is higher than the molecular orientation temperature, each element constituting a blank (5); each blank (5) is placed in a chamber (E) to be cooled therein by a fluid (F) to a temperature close to the molecular orientation temperature, the dwell time of the blank in the chamber being greater than the time of its production by extrusion; and the blank (5) is then extracted from the chamber (E) to be subjected to a treatment enabling its bi-orientation.

Abstract: A distribution head having an inlet for accepting a stream of fluid plastic and an outlet for discharging the stream, two pairs of discrete channels in the distribution head extending from the input to the output for splitting the streams into corresponding discrete substreams, selected ones of the channels being of predetermined different lengths to provide lateral mixing of the stream as it passes through the head. The invention also includes a combination of the distribution head and a connected extrusion tool and the process of making homogeneous plastic articles, particularly pipes.

Abstract: A central body portion has first, second and third concentric cylinders of successively increasing diameter encircling the central body portion and each other in spaced relationship to form three concentric annular spaces for receiving molten material. Only one end of each of the first, second and third cylinders and the body portion are rigidly attached to each other so as to maintain the rigid spaced relationship. A mandrel is attached to the outer end of the central body portion and a die is attached to the outer end of the outer most concentric cylinder in spaced relationship to the mandrel to shape the molten material into a pipe having a multi-layered wall.

Abstract: The process modifies the thickness of the wall of a tube of thermoplastic material which issues at constant speed from an extruder and is driven downstream of and in the extension of the extruder by a drawing machine. The drawing machine has motorized rolling members which frictionally drive the tube and permit modifying the speed at which the tube is driven. The thickness of the wall is modified by producing a relative movement of translation between the extruder and drawing machine while maintaining the speed of rotation of the rolling members.