Methods and installations for producing a biaxially oriented tube from thermoplastic material

A method for starting up a production process in which a biaxially oriented tube from thermoplastic material is produced, in which production process a tube in preform condition is extruded from thermoplastic material using an extruder that is provided with an extruder die head having an inner die member, the inner die member forming a lumen in the extruded tube in preform condition, wherein the extruded tube in preform condition is subjected to a temperature conditioning, so that a tempered tube in preform condition is obtained having an orientation temperature that is suitable for the thermoplastic material, and wherein use is made of an expansion device, the expansion device comprising:

• a non-deformable expansion part having an outer surface comprising a conical outer surface portion with a gradually increasing diameter, the non-deformable expansion part having a maximum diameter at a downstream end thereof;
• a run-on part that is located upstream of the non-deformable expansion part, the run-on part having an upstream sealing member;
• a run-off part downstream of the non-deformable expansion part, adjoining the non-deformable expansion part at a transition;
• and
• one or more first gas supply ducts, the one or more gas supply ducts having an outlet port in the outer surface of the expansion device;
• in which production process a first gas volume is limited at an upstream end thereof by sealing contact between the tempered tube in preform condition and the upstream sealing member and at a downstream end thereof by sealing engagement between the tempered tube in preform condition and at least a downstream portion of the non-deformable expansion part;
• in which production process, via the one or more first gas supply ducts, a pressurized gas is supplied to the first gas volume, wherein the pressure of the gas in the first gas volume causes gradual expansion of the tempered tube in preform condition already before the tempered tube in preform condition actually contacts the non-deformable expansion part;
• wherein the production process further comprises:
• drawing the tempered tube in preform condition over the expansion device in an axial direction using a drawing device that is arranged downstream of the expansion device and acts on the tempered tube in preform condition, in such a manner that the tempered tube in preform condition is transformed into a biaxially oriented tube with thermoplastic material that is oriented in axial direction and in circumferential direction of the biaxially oriented tube;
• and
• cooling the biaxially oriented tube;
• wherein the conical outer surface portion with the gradually increasing diameter of the non-deformable expansion part is provided with raised annular lands, the raised annular lands being spaced axially from one another and each extending circumferentially about the non-deformable expansion part, the raised annular lands each being raised relative to one or more recessed surface portions in adjoining annular zones of the conical outer surface portion, which annular zones each extend between successive raised annular lands;
• wherein in an initial phase of starting up of the production process, the extruded tube in preform condition emerges from the extruder and is pulled ahead by a start-up pulling device arranged downstream of the expansion device and is longitudinally slit at a location upstream of the expansion device, at least upstream of the non-deformable expansion part;
• wherein the slitting of the extruded tube in preform condition is terminated at the end of the initial phase;
• wherein the initial phase of starting up of the production process is followed by an operative phase of starting up of the production process wherein the operation of the extruder and of the start-up pulling device is continued so that a non-slitted leading portion of the extruded tube in preform condition advances towards the non-deformable expansion part and engages on the conical outer surface portion of the non-deformable expansion part so that at least one of the raised annular lands sealingly engages the extruded tube in preform condition;
• wherein during the operative phase of starting up of the production process, downstream of the upstream sealing member, a pressurized gas is supplied between the non-deformable expansion part and the extruded tube in preform condition, so that the pressurized gas is hindered from escaping by the sealing engagement between the upstream sealing member and the extruded tube in preform condition, and the sealing engagement between the non-slitted leading portion of the extruded tube and at least one of the raised annular lands, the pressurized gas assisting in reducing the resistance to which the non-slitted leading portion is subjected while advancing over the non-deformable expansion part in the operative phase of the starting up of the production process.

An installation for producing a biaxially oriented tube from thermoplastic material comprising:

• an extruder with an extruder die head having an inner die member adapted to extrude a tube in preform condition from thermoplastic material, the inner die member forming a lumen in the extruded tube in preform condition;
• one or more tempering devices for temperature conditioning the extruded tube in preform condition, so that a tempered tube in preform condition is obtained having an orientation temperature that is suitable for the thermoplastic material;
• an expansion device downstream of the extruder comprising:
• a non-deformable expansion part having an outer surface comprising a conical outer surface portion with a gradually increasing diameter, the non-deformable expansion part having a maximum diameter at a downstream end thereof;
• a run-on part that is located upstream of the non-deformable expansion part, the run-on part having an upstream sealing member;
• a run-off part downstream of the non-deformable expansion part, the run-off part adjoining the non-deformable expansion part at a transition;
• and
• one or more gas supply ducts, the one or more gas supply ducts having an outlet port in the outer surface of the non-deformable expansion part allowing a first gas volume to be formed between the expansion device and the tempered tube in preform condition;
• a drawing device that is arranged downstream of the expansion device and is adapted to act on the tempered tube in preform condition, in such a manner that the tempered tube in preform condition is transformed into a biaxially oriented tube with thermoplastic material that is oriented in axial direction and in circumferential direction of the biaxially oriented tube;
• and
• a cooling device that is adapted to cool the biaxially oriented tube;
• wherein:
• the conical outer surface portion with the gradually increasing diameter of the non-deformable expansion part is provided with raised annular lands;
• the raised annular lands are spaced axially from one another;
• each of the raised annular lands extend circumferentially about the non-deformable expansion part;
• each of the raised annular lands raised relative to one or more recessed surface portions in adjoining annular zones of the conical outer surface portion;
• and
• each of the annular zones extend between successive raised annular lands.

A production process for production of a biaxially oriented tube from thermoplastic material, in which production process a tube in preform condition is extruded from thermoplastic material using an extruder that is provided with an extruder die head having an inner die member, the inner die member forming a lumen in the extruded tube in preform condition, wherein the extruded tube in preform condition is subjected to a temperature conditioning, so that a tempered tube in preform condition is obtained having an orientation temperature that is suitable for the thermoplastic material, and wherein use is made of an expansion device comprising:

• a non-deformable expansion part having an outer surface comprising a conical outer surface portion with a gradually increasing diameter, the non-deformable expansion part having a maximum diameter at a downstream end thereof;
• a run-on part that is located upstream of the non-deformable expansion part, the run-on part having an upstream sealing member;
• run-off part downstream of the non-deformable expansion part, the run-off part adjoining the non-deformable expansion part at a transition;
• and
• one or more first gas supply ducts, the one or more first gas supply ducts having an outlet port in the outer surface of the non-deformable expansion part;
• in which production process a first gas volume is limited at an upstream end thereof by sealing contact between the extruded tube in preform condition and the upstream sealing member and at a downstream end thereof by sealing engagement between the extruded tube in preform condition and at least a downstream portion of the non-deformable expansion part;
• in which production process, via the one or more first gas supply ducts, a pressurized gas is supplied to the first gas volume, wherein the pressure of the gas in the first gas volume causes gradual expansion of the extruded tube in preform condition already before the extruded tube in preform condition actually contacts the non-deformable expansion part;
• wherein the production process comprises:
• drawing the tempered tube in preform condition over the expansion device in an axial direction using a drawing device that is arranged downstream of the expansion device and acts on the tempered tube in preform condition in such a manner that the tempered tube in preform condition is transformed into a biaxially oriented tube with thermoplastic material that is oriented in axial direction and in circumferential direction of the biaxially oriented tube;
• and
• cooling the biaxially oriented tube;
• and
• wherein the conical outer surface portion with the gradually increasing diameter of the non-deformable expansion part is provided with raised annular lands, the raised annular lands being spaced axially from one another and each extending circumferentially about the non-deformable expansion part, the raised annular lands each being raised relative to one or more recessed surface portions in adjoining annular zones of the conical outer surface portion, which annular zones each extend between successive raised annular lands.

An expansion device for use in an installation for producing a biaxially oriented tube from thermoplastic material, the expansion device comprising:

• a non-deformable expansion part having an outer surface comprising a conical outer surface portion with a gradually increasing diameter, the non-deformable expansion part having a maximum diameter at a downstream end thereof;
• a run-on part that is located upstream of the non-deformable expansion part;
• and
• a run-off part downstream of the non-deformable expansion part, the run-off part adjoining the non-deformable expansion part at a transition;
• wherein the conical outer surface portion with the gradually increasing diameter of the non-deformable expansion part is provided with dimples forming recessed surface portions.