Methods and devices for manufacturing biaxially oriented tubing.

专利摘要:
The production of a biaxially oriented tube from thermoplastic material, wherein a tube in preform condition is extruded from thermoplastic material using an extruder having an extruder die head with an inner die member that forms a lumen in the tube in preform condition. The tube in preform condition is subjected to a temperature conditioning. Use is made of a expansion device comprising a non-deformable expansion part having a gradually increasing diameter to a maximum diameter, which expansion part is contacted by the tube and exerts an expanding force so as to bring about expansion of the tempered tube in circumferential direction. The method comprises drawing the tempered tube over the expansion device using a drawing device, in such a manner that said tube is transformed from a tube in preform condition into a biaxially oriented tube with thermoplastic material which is oriented in axial direction and in circumferential direction of the tube.
公开号:NL2007592A
申请号:NL2007592
申请日:2011-10-13
公开日:2012-04-19
发明作者:Jan Visscher；Klomp Hendrik Jan Carel Jansen；Jan-Mark Bosch
申请人:Rollepaal Holding B V；
IPC主号:

专利说明:

METHODS AND DEVICES FOR MANUFACTURING BIAXIALLY ORIENTED TUBING
The present invention relates to methods and devices for manufacturing biaxially orientedtubing of thermoplastic material.
The invention relates in general to the issue of establishing production processes andproduction installations that allow to produce biaxially oriented tubing of thermoplasticmaterial, the oriented tubing having a desired uniformity of the final dimensions of theoriented tubing as well as good strength properties, e.g. as the production of rigid pipes, e.g.pressure pipes for transportation of water or gas is envisaged.
When producing biaxially oriented tubing of thermoplastic material, e.g. pipes ofpolyvinylchloride, it has proven to be difficult to produce tubing with uniform final dimensions.Such uniformity is desirable, e.g. as biaxially oriented tubing elements, e.g. pressure pipes,e.g. for transportation of water, are interconnected end-to-end, e.g. via socket connections.
The invention relates to a method for producing a biaxially oriented tube from thermoplasticmaterial, wherein a tube in preform condition is extruded from thermoplastic material usingan extruder which is provided with an extruder die head having an inner die member, theinner die member forming a lumen in the tube in preform condition, wherein the tube inpreform condition is subjected to a temperature conditioning, so that a tempered tube inpreform condition is obtained having an orientation temperature which is suitable for thethermoplastic material, and wherein use is made of an expansion device in the lumendownstream of the extruder, said expansion device comprising: - a non-deformable expansion part having a gradually increasing diameter to amaximum diameter at a downstream end thereof, which expansion part is contacted by thetube and exerts an expanding force on the tube so as to bring about an expansion of thetempered tube in preform condition in circumferential direction, - a run-on part which is located upstream of the expansion part, said run-on parthaving an upstream nose end.
The method comprises drawing the tempered tube over the expansion device using adrawing device which is arranged downstream of the expansion device and acts on the tube,in such a manner that said tube is transformed from a tube in preform condition into abiaxially oriented tube with thermoplastic material which is oriented in axial direction and incircumferential direction of the tube. The biaxially oriented tube is cooled.
In the method use is made of an expansion device having one or more fluid supply ducts.
The one or more fluid supply ducts have a port in the outer surface of the run-on part and/orthe expansion part of the expansion device, and a fluid is introduced between the expansiondevice and the tube.
First some prior art approaches will be discussed here.
In EP 823 873 a method is disclosed for the production of biaxially oriented tubing. Use ismade of a rigid mandrel having an expansion part as well as a run-on part upstream of andintegral with the expansion part. Spaced upstream from the nose end of the run-on part aclosure member is held on the anchoring rod, so as to define a chamber in the lumen of thetube in preform condition. A liquid, e.g. heated water, is fed under pressure between the tubeand the mandrel device via one or more ducts that are formed in the mandrel and have a portin the outer surface of the mandrel. This liquid then flows counter to the direction ofmovement of the tube towards the chamber upstream of the nose end of the expansiondevice and is then discharged via one or more discharge ducts in the anchoring rod.
In EP 823 873 it is also proposed to provide the mandrel with a run-off part downstream ofthe expansion part. A film of cold liquid is created between the tube and this run-off part, asone or more feed and discharge ducts for said cold liquid are formed in the mandrel. Inparticular it is proposed to cause the cold liquid in said film to flow opposite to the motion ofthe tube, so from a downstream feed opening in the outer surface of the run-off part towardsan upstream discharge opening in the outer surface of the run-off part.
In EP 823 873 the tube is made to sealingly engage the mandrel at or near the transitionbetween the expansion part and the run-off part in order to avoid that the cold liquid reachesthe expansion part.
In EP 1 159 122 a method is disclosed for the production of biaxially oriented tubing. Use ismade of a rigid mandrel having an expansion part as well as a run-on part upstream of andintegral with the expansion part. The run-on part has a uniform diameter over its length. Afilm of liquid is formed between the expansion part and the tube. The liquid is supplied at thedownstream end of the expansion part and flows counter to the motion of the tube to one ormore outlets arranged in the run-on part of the expansion device. The tube in preformcondition is shown to sealingly engage on the nose end of the run-on part as the innerdiameter of the preform is less than the diameter of the run-on part.
In US6214283 a method for the production of biaxially oriented tubing is discussed withreference to figure 5 wherein a film of liquid, water, is established between the expansionpart and the run-on part of the expansion device on the one hand and the tube on the otherhand. This film is established in counter-current fashion as the liquid is supplied via one ormore liquid supply ducts that have an outlet port in the exterior surface of the expansion part.The liquid then flows counter to the tube motion towards a space in the lumen that is locatedupstream from the nose end of the run-on part and that is delimited by a sealing membermounted on the anchoring rod. From this space the liquid is discharged via a discharge ductin the anchoring rod. The liquid film serves to reduce frictional forces, thereby avoidingoverloading of the tube by tensile forces and allowing for a greater angle of the expansionpart.
The invention aims to provide measures that allow for improvements over the prior art or atleast provide for a useful alternative.
It is a further object of the invention to provide for measures that allow for a suitable internaltempering of the tube in preform condition, possibly using liquid circulated within the lumen,e.g. in combination with heating and/or cooling on the outside of the tube in preformcondition.
It is a further object of the invention to provide measures that allow for a suitable internaltempering of the tube in preform condition, possibly using liquid circulated within the lumen,as well as introducing a fluid, e.g. a liquid or a gas, between the expansion device, e.g. theexpansion part thereof, and the tube, the introduction of fluid and the internal temperingbeing independent from one another.
It is a further object of the invention to provide a method that allows for enhanced uniformityof the tubing, in particular with respect to wall thickness and cross-sectional shape both incircumferential direction and over the length of the tube.
It is a further object of the first aspect of the invention to provide a method wherein no coldliquid is conveyed through the anchoring rod to the expansion device.
It is a further object of the invention to provide a method that allows for an easy and reliablestart-up procedure.
It is a further object of the invention to provide a method that allows for an increasedmaximum diameter of the expansion part as well as significant orientation in circumferentialdirection of the tube. This allows to produce large diameter biaxially oriented tubes withoutundue traction forces having to be applied to the tube and without a problematic start-upprocedure.
In order to achieve one or more of the above objects the invention provides a methodaccording to claim 1, wherein use is made of a expansion device with a run-on part that is provided with a sealingmember that is sealingly engaged by the tube in preform condition, said sealing memberbeing arranged at a distance upstream of the expansion part of the expansion device andhaving a diameter that is greater than the run-on part downstream of the sealing member,the sealing member forming an effective seal that prevents the fluid from reaching the lumenof the tube in preform condition upstream of the sealing member, and wherein the fluid supplied to said fluid volume that is limited at one end by said sealing contactbetween the tube in preform condition and the sealing member and at another end by sealingengagement between the tube and at least a downstream portion of the expansion part is agas, e.g. air, the pressure of the gas in said fluid volume being used - during the productionof the biaxially oriented tube- to cause gradual expansion of the tube already before the tubeactually contacts the expansion part.
The gas, e.g. air, is supplied via a compressor or other pressurized gas source to the one ormore supply ducts in the expansion device. The use of a gas, e.g. air, has some advantagesover the use of a liquid, e.g. that any problems associated with liquid that is entrained withthe tube to beyond the expansion device are avoided.
The use of a gas, e.g. air, as fluid allows to perform the production method such that apressurized gas volume is entrapped between the tube on the one hand and the run-on partand the expansion part of the expansion device on the other hand, the tube in preformcondition sealingly engaging the sealing member on the run-on part as well as sealinglyengaging at least a downstream portion of the expansion part, e.g. near or at the transition tothe run-off part of the expansion device. The pressure of the entrapped gas volume thencauses internal fluid pressure on the tube and so gradual expansion of the tube already before the tube actually contacts the expansion part. The passage over at least thedownstream portion of the expansion part of the expansion device then governs a further,possibly final, stage of the circumferential orientation of the thermoplastic material. Clearlythe volume of gas causes no frictional resistance to the movement of the tube, which may beadvantageous.
The presence of the sealing member and its sealing effect allow for a significant and stablegas pressure in said fluid volume and thereby for effective use of gradual expansion byinternal gas pressure of the tube prior to contact with the expansion part. The tube, havingundergone some expansion, e.g. a selected degree of expansion as will be explained below,then contacts the expansion part and is then subjected to expansion under the influence ofthe non-deformable expansion part.
The start-up of the production installation and method according to the invention is alsogreatly facilitated by the presence of the sealing member, its sealing effect, and thepossibility to supply gas under pressure between the run-on part and the tube downstream ofthe sealing member. During start-up the tube in preform condition is made to pass over thesealing member and then to come into contact with the expansion part. Gas is then suppliedin this region between the run-on part and the tube, so that the tube expands under saidinternal gas pressure. As is preferred in this start-up procedure, the tube - in the regionbetween the sealing member and the maximum diameter of the expansion part, is made toexpand locally to a large diameter that is at least as great as the maximum diameter of theexpansion part so that upon continued progress of the expanded portion of the tube indownstream direction, said portion of large diameter passes easily over the maximumdiameter portion of the expansion device. Once the passing of the tube over the expansiondevice has stabilized in this start-up procedure, the gas pressure in this volume can berelieved so that - during normal production of biaxially oriented tube - a reduced expansion iseffected by the gas pressure and the remainder of the expansion is effected by contact withthe expansion part.
The pressure of the gas in said gas volume could be controlled by means of a pressurecontrol valve in the supply means for the gas.
Preferably the sealing member is arranged at the nose-end of the run-on part.
The sealing member can be seen as a thickened portion of the run-on part compared to theportion of the run-on part downstream of the sealing member.
The invention allows to use a run-on part of a significant length, thereby enhancing theinternal support of the tube in preform condition by the run-on part upstream of the expansionpart. This contributes to enhanced uniformity of the biaxially stretching of the tube in preformcondition. Also this arrangement allows for a reliable and stable fluid volume between therun-on part and the tube in preform condition. The sealing engagement of the sealingmember with the tube in preform condition provides a reliable barrier between the zoneupstream of the sealing member and the zone downstream of the sealing member within thelumen of the preform, so that conditions and/or actions can be performed in one of saidzones that are fully or at least largely independent from the other zone.
It is preferred to have - in addition to said one or more supply ducts - one or more gasdischarge ducts that are formed in the expansion device, said one or more discharge ductshaving one or more inlet ports in the exterior surface of the expansion part of the expansiondevice, an inlet port being open or closed or partly closed dependent on whether or not theinlet port is covered and closed by the tube or to which portion of the inlet port is closed bythe tube. A gas discharge duct then provides for the relief of gas pressure from the fluidvolume when the one or more corresponding inlet ports are at least partly open, and thusestablishes a control of the expansion of the tube that is caused by internal gas pressure. Inthis embodiment the tube itself basically acts as valve in combination with a simple inlet portor inlet ports (e.g. distributed in circumferential direction) and allows to dispense with acomplicated gas pressure control valve arrangement. This embodiment also allows for a fail¬safe operation of the installation as the gas pressure in said fluid volume can never becomeexcessive. A simple open-close valve may be provided for the discharge duct, e.g. to close adischarge duct during start-up of the method as increased expansion of the tube by internalgas pressure may then be used advantageously as explained above.
In a further preferred embodiment multiple inlet ports, each associated with a correspondingdischarge duct, are provided at differing diameter positions in the exterior surface of theexpansion part, said differing diameter positions having different radial distances from thecentral longitudinal axis of the expansion part. One or more operable valves, e.g. open-closevalves, are associated with the discharge ducts, so that a selected inlet port and associateddischarge duct can be made effective to allow for relief of gas pressure when the tube doesnot fully cover and close said inlet port. At the same time the other non-selected inlet portsand associated discharge ducts are then made ineffective by closing the associated valve orvalves. This embodiment allows to control the internal diameter of the tube as it is effectivelyexpanded by the internal gas pressure in the fluid volume and reaches the expansion part ofthe expansion device. This allows for a simple selection of the degree of expansion to be obtained via the internal gas pressure versus the remaining expansion via contact with theexpansion part.
In an advantageous embodiment of the method of the invention use is made of one or moreexternal heat exchange devices that are adapted and operated to influence the temperatureof the tube in preform condition, wherein said external heat exchange devices are used toinfluence the sealing engagement between the tube in preform condition and the sealingmember of the run-on part of the expansion device.
In a practical embodiment a first heating device is used that is adapted for controlled externalheating of the tube in preform condition, and a second heating device is used that is adaptedfor controlled external heating of the tube in preform condition, wherein the first and secondheating device are independently controlled, and wherein the first heating device is arrangedupstream of the sealing member of the run-on part, and wherein the second heating device isarranged downstream of the sealing member. This embodiment allows to use the firstheating device for controlling the sealing engagement with the sealing member, and thesecond heating device in order to influence the tube directly upstream of and/or during thepassage of the tube over the expansion part of the expansion device. One or more of theseheating devices may include multiple heating elements distributed around the path of thetube, e.g. multiple infrared heating elements.
In a possible embodiment of the method - for temperature conditioning of the tube in preformcondition- a liquid circulation compartment is formed in the lumen of the tube between aclosing member that is arranged at a distance upstream from the nose end of the run-on parton the one hand and the sealing member on the other hand, wherein a liquid is circulatedthrough said liquid circulation compartment. This method allows to establish an effectiveinternal temperature conditioning of the tube in preform condition directly upstream of theexpansion device. In practice said internal temperature condition may be effected with hotwater, e.g. close to the orientation temperature, e.g. close to the boiling temperature ofwater. The closing member is located such that a suitable length of the liquid circulationcompartment is obtained. The closing member may be arranged at the die head or close tothe die head, e.g. as shown in W095/25626, figure 3. In another arrangement the closingmember is arranged between the die head and the expansion device, or it can be envisagedto employ multiple liquid circulation compartments between the die head and the expansiondevice by means of multiple closing members and associated liquid circulation ducts.
When the method of the invention is performed such that an upstream tempering from withinthe tube in preform condition is performed or enhanced by an internal liquid circulation compartment upstream of the expansion device, and such that a fluid volume is establishedbetween the expansion device and the tube by fluid that is supplied via one or more fluidsupply ducts in the expansion device, then the sealing member and the sealing engagementthereof with the preform act to prevent a loss or instability of the pressure in the fluid volume- which pressure will be preferably a higher pressure than the pressure of the liquid in theinternal liquid circulation compartment.
In an embodiment the sealing member is an annular sealing member fitted on the run-on partof the expansion device, said sealing member including a conical run-on surface for the tube,gradually increasing in diameter in downstream direction.
The sealing member preferably is a non-deformable member, e.g. a metallic member.Preferably there is no provision to supply a lubricant directly to the outer surface of thesealing member. In more complex embodiments however the sealing member may beadapted to control the frictional engagement thereof with the tube in preform condition, e.g.provided with an integral and dedicated lubrication device, e.g. allowing a gas, e.g. air, to befed directly between the sealing portion and the preform. In another embodiment the sealingmember may be construed to have a variable diameter with an associated control means,e.g. with an outer metallic skin, e.g. expandable under hydraulic or pneumatic pressure, soas to control the sealing engagement with the tube in preform condition.
In a possible embodiment a force monitoring device is associated with the sealing member,adapted to monitor the axial force on the sealing member, e.g. including one or moreelectronic force sensors, e.g. strain gauges. Said monitoring device may be coupled to, whenpresent, one or more external heat exchange devices that are used to influence the sealingengagement of the tube in preform condition with the sealing member.
In a possible embodiment one or more temperature sensors are provided on the expansiondevice, preferably at or near the sealing member, most preferably at the sealing member andin direct contact with the inner face of the tube, preferably allowing to measure thetemperature of the preform in said region, e.g. said one or more sensors being coupled to thefirst and/or second external heat exchange devices that are used to influence the sealingengagement of the preform with the sealing member in order to assist in suitable operationthereof. Said one or more temperature sensors sense the temperature of the inner face ofthe preform. The intimate contact between the tube in preform condition and the sealingmember is beneficial for the reliability and accuracy of the temperature sensing when saidone of more sensor are integrated in the sealing member.
In combination with one or more temperature sensors (e.g. multiple at circumferentiallyspaced apart positions) that sense the temperature of the outer face of the preform anindication is obtainable of the temperature profile within the wall of the preform, e.g. in orderto set and/or to maintain a desired temperature profile within said wall. This may well beadvantageous for achieving the desired biaxial orientation of the plastic material, as suchresult depends also on the actual temperature of the plastic material within the wall whensubjected to orientating stresses in the process.
For example the one or more temperature sensors on the inside of the tube in preformcondition may be linked to an output control of the extruder and/or a control of a coolingdevice that cools the extruded tube in preform condition (e.g. an internal cooling device) inorder to influence the temperature profile in the tube wall.
It is preferred for said one of more temperature sensors for the inner face of the tube to beintegrated in the sealing member, or to be located upstream thereof on the anchoring rod,e.g. within a distance of at most 2 meters from the sealing member.
It may be envisaged to have multiple temperature sensors for the inner face of the preform,each sensing the temperature of a sector of the inner face when seen in circumferentialdirection of the inner face.
Preferably said one or more temperature sensors for the inner face of the preform are indirect contact with said inner face.
The one or more sensors that sense the inner face temperature may be wired to one or moreassociated control units or may be of the wireless communication type.
In a possible embodiment the anchoring rod may be embodied as a chain or a cable.
Possibly one or more fluid supply conduits are embodied as hose or tubes, e.g. connected tothe chain or cable at intervals.
In a possible embodiment the expansion part has a first conical surface increasing indiameter in downstream direction, adjoined at its downstream end by a cylindrical surface ofa first diameter, adjoined at its downstream end by a second conical expansion surfaceincreasing in diameter in downstream direction, and wherein preferably the diameter of thesealing member on the run-on part is greater than the first diameter of the expansion part.
In a preferred embodiment use is made of an expansion device having a run-off partdownstream of the expansion part.
In a preferred embodiment the run-off part has a reduced diameter section having a smallerdiameter than the maximum diameter of the expansion part, and use is made of at least one outer diameter ring member that is arranged around saidreduced diameter section, wherein the outer diameter ring member is arranged such that theoriented tube passes through the ring member while being in contact with said ring member,the outer diameter ring member and the reduced diameter section being dimensioned suchthat seizing of the oriented tube between the run-off part and the at least one outer diameterring member is avoided, preferably the inside of the oriented tube being radially spaced fromthe reduced diameter section, preferably the expansion device having one or more fluidsupply ducts having one or more ports in the reduced diameter section, a gas being suppliedbetween said reduced diameter section and the oriented tube to establish a second fluidvolume there between.
As is preferred use is then made of a first external cooling device that is adapted andoperated to cool the oriented tube externally while passing over the run-off part.
It is envisaged that the outer diameter ring member, or the upstream outer diameter ringmember if use is made of two spaced apart ring members, could be employed to contributeto the sealing engagement of the tube with the expansion device in the region of thetransition from the expansion part to the run-off part, e.g. to maintain a reliable sealingcontact in said region. Said outer ring member could be construed to exert a constrictiveforce on the tube to obtain or improve this effect.
The inventors envisage that a gradual expansion of the tube by internal gas pressure, incombination with a non-deformable expansion part can be achieved with high reliability andstability during production, as the sealing member arranged at or near the nose end of theexpansion device secures a reliable seal of said gas volume at the upstream end thereof andwith an outer diameter ring member in combination with a reduced diameter section to assistin securing a highly reliable seal at the downstream end.
The invention also relates to an installation as described in claim 9 and in subclaims 10-15.
In an embodiment the expansion device has a run-off part which is downstream of theexpansion part, preferably a run-off part which has a reduced diameter section having asmaller diameter than the maximum diameter of the expansion part.
In an embodiment use is made of at least one outer diameter ring member that is arranged atthe location of the reduced diameter section and around said reduced diameter section,and wherein the oriented tube passes through the outer diameter ring member while being incontact with said outer diameter ring member, the outer diameter ring member and the reduced diameter section being dimensioned such that seizing of the oriented tube betweenthe expansion device and the at least one outer diameter ring member is avoided, preferablythe inside of the oriented tube being radially spaced from the reduced diameter section, and wherein the oriented tube is cooled externally while passing over the run-off part by afirst external cooling device.
The non-deformable expansion part only causes a part of the total expansion of the tube.
The other part of the desired expansion is caused by forming a gas filled fluid volumebetween the expansion device and the tube, e.g. upstream and/or downstream of the regionwherein the tube contacts the expansion part. These one or more fluid volumes, gas filled,are then operated to exert an internal fluid pressure on the tube that causes the other part orparts of the expansion of the tube.
In a preferred embodiment the maximum diameter of the non-deformable expansion partgoverns the final stage of expansion in circumferential direction of the tube. In thisembodiment any part of the expansion device - other than the reduced diameter section -downstream of said maximum diameter has a diameter at most equal to the maximumdiameter of the expansion part.
In another possible embodiment a downstream portion, e.g. an end portion, of a run-off partof the expansion device has a greater diameter than the maximum diameter of the expansionpart, and a fluid volume, e.g. gas filled, with pressurized fluid between the reduced diametersection and the tube is used to cause further expansion of the tube.
It is preferred for the run-off part to be of non-deformable design. However it is alsoenvisaged e.g. that the run-off part includes an expandable portion, e.g. an inflatable plug,e.g. at the downstream end thereof, e.g. limiting the downstream end of the reduceddiameter section.
If present, a reduced diameter section of the run-off part preferably has a diameter that is atleast 4 millimetres less than the maximum diameter of the expansion part. Preferably thediameter of the reduced diameter section is about twice the wall thickness of the tubepassing over the run-off part of the expansion device less than the maximum diameter of theexpansion part. Preferably the reduced diameter section has a diameter of at least 80% ofthe maximum diameter of the expansion part.
In an embodiment an outer diameter ring member is arranged around the reduced diametersection, with the radial spacing between said ring member and the reduced diameter sectionbeing more than the projected wall thickness of the tube at said location, so that radial playremains that allows for a possible variation in the wall thickness of the tube during theproduction process at said location, e.g. to minor disturbances in the process, without the riskthat said tube becomes stuck between the ring member and the reduced diameter section ofthe run-off part. Preferably a radial spacing is maintained between the reduced diametersection and the inside of the oriented tube.
Preferably each outer diameter ring member is non-deformable, at least as the diameter ofits opening through which the tube passes is concerned, under the influence of the contactwith the tube passing through the opening of the ring member. E.g. the ring member is madeof a rigid material, e.g. a metal or other thermally conductive material.
In a practical embodiment each outer ring member has an axial dimension less than thediameter of the opening therein for the tube. E.g. a ring member has an axial length ofbetween 0.5 and 5 centimetres. It is however also possible that a ring member is formed asan elongated sleeve, e.g. having a length greater than the diameter of the opening therein forthe tube.
In a possible embodiment an outer diameter ring member includes one or more internalconduits, e.g. annular internal conduits, through which a cooling fluid is passed, e.g. coolingwater, to effect a cooling of the contact surface with the oriented tube. In a possibleembodiment the first external cooling device is integrated with the one or more outerdiameter ring members, as each ring member has one or more internal conduits throughwhich cooling fluid is passed, e.g. a single outer diameter ring member being used having alength greater that the diameter of the opening therein for the tube, e.g. between 1 and 2times said diameter.
The external cooling of the tube by the first external cooling device while passing over therun-off section is preferably performed in the absence of internal cooling of the tube whilepassing over the expansion device, or even more preferably also in the absence of anyinternal cooling downstream of the expansion device.
In this regard referral is made to EP 823 873 wherein not only an external cooling of theoriented tube is performed, but also an internal cooling of the tube is performed by a coolingliquid film between the tube and the run-off part in combination with the passing of the tubethrough an outer diameter calibrating ring member downstream of the expansion device. It has been found that supplying the cooling liquid to the expansion device is problematic inview of obtaining a uniformly tempered tube in preform condition as the cooling liquid issupplied via a cooling liquid duct in the anchoring rod of the expansion device. It has alsobeen observed that this particular prior art approach may cause deformation of the rathercold inner side of the oriented tube due to the passing through the downstream calibratingring member, which deformation in cold condition is considered by the present inventors tohave a negative effect on the strength of the finally obtained tube.
In a preferred embodiment use is made of an upstream outer diameter ring member and adownstream outer diameter ring member, said ring members being arranged in series andspaced apart. Through these ring members the oriented tube passes at the location of thereduced diameter section of the run-off part. By providing multiple, preferably two, ringmembers at spaced apart axial locations along the reduced diameter section of the run-offpart, various possibilities are provided for the operator to influence the production processand the finally obtained tubing.
Preferably the first external cooling device cools the oriented tube between the upstream anddownstream outer diameter ring members. Preferably an intense external cooling is effectedhere, preferably by the outer surface of the tube being exposed, so not covered by the one ormore ring members, and subjected to sprays or jets of cooling liquid, e.g. water.
In a preferred embodiment at least one outer diameter ring member, e.g. both an upstreamand a downstream ring member, is embodied as a constrictive outer diameter ring member,said ring member exerting a radial constrictive force on the oriented tube passing therethrough during the production process, thereby reducing the outer diameter of the orientedtube, at least over a short axial length. In a preferred embodiment the upstream outerdiameter ring member exerts a constrictive force on the oriented tube which contributes to asealing engagement of the oriented tube with the expansion device at the transition betweenthe expansion part and the run-off-part. As will be explained in more detail below thisapproach is e.g. favourable when a fluid, that is a liquid or a gas, is introduced between oneor more parts of the expansion device on the one hand and the tube on the other hand.
In a preferred embodiment at least one outer diameter ring member, e.g. an upstream ringmember, is displaceable in axial direction. By suitable selection and/or adaptation of the axialposition of the one or more outer diameter ring members with respect to the run-off part, e.g.the snap-back effect can be influenced and thus the final dimension of the oriented tubecontrolled. In particular it is envisaged that the axial displacement of one or more outer diameter ring members is effected in combination with a control, and - possibly automatic -adjustment, of the cooling effect of the first external cooling device.
In a very practical embodiment the first external cooling device operates with one or morenozzles emitting sprays or jets of cooling liquid, e.g. cooling water.
In a preferred embodiment the first external cooling device is adapted and operated to adjustthe length and/or location with respect to the expansion device of the stretch of the orientedtube that is affected by the first external cooling device. It has been found that by suitableselection of the length, and preferably also the location, of the affected stretch with respect tothe expansion device, the occurrence of the snap-back effect can be influenced, and so thediameter of the tube, without needing to use an outer diameter calibration downstream of theexpansion device.
In a preferred embodiment the first external cooling device comprises an upstream shieldmember and a downstream shield member, said shield members delimiting the stretch oforiented tube that is affected by the first external cooling device, e.g. the sprays or jets ofcooling water. Preferably the outer surface of the tube is exposed between said shieldmembers, the device having nozzles spraying or jetting cooling liquid directly onto saidexposed surface.
Preferably the first external cooling device is effective directly downstream of the transitionbetween the expansion part and the run-off part, in particular when no internal cooling isperformed as is preferred.
Preferably at least one of the shield members of the first external cooling device, preferablyboth, is displaceable in axial direction, thereby allowing to adjust the length and/or thelocation of the stretch of tube that is affected by the spray of cooling liquid. It will beappreciated that by controlling the length and/or position of the shield members during theproduction process, e.g. automatically or operator controlled, possibly by hand, the cooling ofthe oriented tube can be controlled, even more when - as is common - the intensity of thecooling spray can be controlled as well.
It will be appreciated that the one or more displaceable shield members could be construedfor a manual adjusting of the axial position thereof. However in a more advancedembodiment - as is preferred - a motorized drive assembly, e.g. including one or more screwspindles, is provided for said one or more displaceable shield members.
In a very practical embodiment an outer diameter ring member is integral with a shieldmember, more preferably the upstream and downstream ring member each being integralwith the upstream and downstream shield member. As a result the first external coolingdevice is effective over the stretch of oriented tubing between both ring members, preferablyat least one thereof being movable in axial direction.
In a preferred embodiment a run-off part of the expansion device comprises an increaseddiameter portion, preferably non-deformable, downstream of the one or more outer diameterring members and delimiting the downstream end of a reduced diameter section, saidincreased diameter portion having a greater diameter than said reduced diameter section.The method is then performed such that the oriented tube, preferably in a sealing manner,engages or contacts the increased diameter portion. The increased diameter portion thenacts as an internal support for the oriented tube, and in a non-deformable embodimentcontributes to the uniformity of the dimensions of the tube.
The presence of an increased diameter portion is advantageous when a fluid is introducedbetween one or more parts of the expansion device on the one hand and the tube in preformcondition and/or oriented tube on the other hand.
The increased diameter portion can have a diameter that is the same as the maximumdiameter of the expansion part, or a smaller diameter. However, as indicated above, it is alsopossible for the increased diameter portion to have a larger diameter than the maximumdiameter of the expansion part, preferably a pressurized gas volume being then delimited atits downstream end by said increased diameter portion and the internal gas pressure causinga final stage of circumferential expansion of the tube. During normal production the tube willthen also contact the expansion part of the expansion device, thereby effecting an earlierstage of expansion of the tube, possibly preceded by yet another expansion stage effectedby internal fluid pressure caused by an upstream fluid volume.
In a highly preferred embodiment a run-off part of the expansion device has a single reduceddiameter section, and an upstream and downstream outer diameter ring member arearranged at the location of said single reduced diameter section and around said singlereduced diameter section. The upstream outer diameter ring member may contribute to oreffect a sealing engagement or contact of the tube with the expansion device in a region at ornear the maximum diameter of the expansion part. The downstream outer diameter ringmember exerts a constrictive force on the tube which may contribute to or effect a sealingengagement of the tube with a downstream located increased diameter portion of theexpansion device. This method is highly advantageous when a fluid is introduced betweenthe run-off part and the tube. The fluid e.g. is a pressurized gas, such as air, the sealing engagement of the tube at both axial locations of the run-off part avoiding an uncontrolledescape of fluid and thus uncontrolled fluctuation of the fluid volume, be it a thin film (e.g.when a liquid is used, e.g. heated water, is used) or an annular volume with significant radialthickness, e.g. an air volume, e.g. for causing some additional circumferential expansion.
Downstream of the expansion device, preferably in close vicinity to the expansion device, afurther external cooling of the tube is advised to cool down oriented tube to a further degree.For this reason a second external cooling device is arranged, preferably relative close,downstream of the expansion device and is adapted and operated to externally cool theoriented tube. The second external cooling device is controllable independent from the firstexternal cooling device arranged at the location of the run-off part. Preferably the secondexternal cooling device is arranged spaced a distance downstream from the first externalcooling device.
When the run-off part comprises an increased diameter portion at the downstream end of asingle reduced diameter section, it is preferred for a possible second external cooling deviceto be arranged downstream thereof.
Preferably the second external cooling device comprises one or more cooling liquid spraynozzles adapted and operated to spray or jet cooling liquid, e.g. water, onto the exterior ofthe oriented tube.
Preferably the second external cooling device is arranged such that the cooling effect thereofstarts at the position where the snap-back effect - wherein the diameter of the tube reducesdownstream of the expansion with no more internal support of the oriented tube - takesplace.
Preferably a dry zone is created between said first and second external cooling device. Thisis considered to avoid or at least reduce the formation of visual effects, e.g. rings, on theoutside of the tube by cooling water.
Preferably the second external cooling device is movable in axial direction, e.g. to adjust itsposition, primarily of the upstream end thereof, to the occurrence of the snap-back effect.Preferably a displacement device, preferably motorized, is associated with the secondexternal cooling device to effect such a motion.
Preferably the second external cooling device comprises an upstream shield memberdelimiting the upstream end of the stretch of oriented tubing cooled by said second externalcooling device, said upstream shield member preferably being movable in axial direction.
Preferably the upstream end of the second external cooling device, e.g. the upstream shieldmember thereof, has a flexible annular lip engaging the oriented tube so that no noticeableconstrictive force is exerted by said flexible annular lip on the oriented tube.
In an advantageous embodiment use is made of a measuring device for measuring at leastone of the outer diameter of the oriented tube, the wall thickness of the oriented tube, andthe cross-sectional profile thereof, e.g. the outer diameter and the wall thickness, whichmeasuring device is arranged downstream of the expansion device. A control device isprovided to control the first external cooling device and/or the second external coolingdevice, preferably both when they are both present.
The measuring device is linked to the control device so as to control the cooling by said firstand/or second external cooling device, e.g. the intensity of the cooling, thereby controllingthe snap-back effect - wherein the diameter of the tube reduces - which takes place directlydownstream of the expansion device and thereby controlling the diameter of the orientedtube. This can then be done without the need for any further outer diameter calibrationdownstream of the expansion device, as is preferred.
In a preferred embodiment the control device is provided to control the first external coolingdevice with regard to at least the length and/or location with respect to the expansion deviceof the stretch of oriented tube that is affected by the first external cooling device.
Possibly the control device is adapted such that the length of the stretch of tube that isaffected by the first external cooling device is decreased to obtain an increased snap-backeffect and thus increased diameter reduction, and wherein said length is increased to obtaina reduced snap-back effect and thus decreased diameter reduction.
In a possible embodiment the second external cooling device, or an upstream shield memberof the second external cooling device, is movable in axial direction, and the measuringdevice is linked to a control device provided to control the second external cooling device.The measuring device is linked to said control device of the second external cooling device inorder to control the starting point of the cooling of the tube by the second external coolingdevice, e.g. via controlling the position of the upstream shield member thereof.
In a preferred embodiment a first fluid volume is present between the expansion device andthe tube at a position upstream of the maximum diameter of the expansion part, and asecond fluid volume is present between the run-off part and the tube. The sealingengagement in a region at or near the maximum diameter of the expansion part generallyprevents an uncontrolled communication between the two fluid volumes and thus e.g.instability of said fluid volumes and/or mixing of fluids, e.g. upstream pressurized air for thefirst volume and a liquid, e.g. heated water being used for the second volume.
In a possible embodiment use is made of an expansion device with a valve controlledpassage in communication with the first fluid volume and with the second fluid volume,wherein the expansion device includes at least one fluid supply conduit which introduces fluidinto the first and/or second fluid volume. As mentioned above the sealing engagement at themaximum diameter avoids an uncontrolled communication between said fluid volumes. Thevalve controlled passage however allows the operator to e.g. equalize pressure in bothvolumes, or first establish a first fluid filled volume upstream of the maximum diametersealing region and then let the fluid flow into the second volume downstream of said region.One or more pressure sensors may be provided to sense the actual fluid pressure in a fluidvolume. The valve controlled passage, including the valve, can be integrated entirely in theexpansion device in the lumen of the tube. However it is also possible for this valvecontrolled passage to be present outside of the tube and extruder, e.g. as part of the externalportion of the fluid supply device.
It is also an option that a first fluid supply duct introduces fluid into the first fluid volume and asecond fluid supply duct introduces fluid into the second fluid volume.
The methods according to the invention are for instance suitable to produce individual tubeelements that are later provided with a socket in a socketing operation, allowing tubes to beconnected end to end by inserting an end into a socketed end of another tube, the socketpreferably including a sealing ring.
The methods according to the invention may also include the further step of makingindividual biaxially oriented tubing elements by severing a tubing element from the tube thatextends from the extruder, over the expansion device, and beyond the drawing devicedownstream of the expansion device, e.g. tubing elements having a length between 5 and 15metres, e.g. 6 metres, and the step of providing a socket on an end of each individual tubingelement so that individual tubing elements are connectable via a socket connection.
The present invention also relates to a biaxially oriented tube obtained with a methodaccording to the invention. In a preferred embodiment the tube is a biaxially oriented tube ofpolyvinylchloride. In a preferred embodiment the tube obtained is a water or gas transportpipes, e.g. for potable water, e.g. of polyvinylchloride.
For example it is envisaged to produce with a method according to one or more of theaspects of the invention a biaxially oriented pipe, e.g. of PVC, having a pressure rating above8 Bar, e.g. of 12,5 Bar, at 20°C, e.g. with an outer diameter between 63 and 630 millimetres.
The wall thickness of the biaxially oriented pipe produced with a method according to one ormore of the aspects of the invention may lie in practice between, for example, 3 and 10millimetres.
The invention and preferred embodiments thereof will now be described with reference to thedrawings. In the drawings:
Fig. 1a, 1b and 1c show schematically an example of an installation for producing biaxiallyoriented thermoplastic tubing,
Fig. 2 shows schematically in longitudinal section a part of the installation of figures 1a, b, c,Figs. 3a and 3b show schematically in perspective view and in longitudinal sectioncomponents of the part of the installation of figure 2, and
Fig. 4 shows schematically in longitudinal section a portion of the components of figure 3,
Fig. 5 shows schematically in longitudinal section a portion of an installation for producingbiaxially oriented thermoplastic tubing,
Fig. 6 shows schematically in longitudinal section a portion of an installation for producingbiaxially oriented thermoplastic tubing,
Figs. 7a and 7b show schematically in longitudinal section a portion of an installation forproducing biaxially oriented thermoplastic tubing,
Fig. 7c shows a detail of a variant of the installation of figures 7a and 7b.
Figures 1 a, 1 b and 1 c are not to scale and schematically show consecutive portions of anexample of an installation for producing biaxially oriented thermoplastic tubing. Theinstallation is shown to elucidate the present invention, some aspect not being shown indetail, or being elucidated by assuming substitution of a part of this installation for anotherpart, e.g. as explained with reference to figures 5 and 6.
The installation comprises an extruder 1 having one or more extruder screws 2 by means ofwhich a flow of thermoplastic material is provided, e.g. of polyvinylchloride (PVC).
The thermoplastic material is fed to a die head 3 arranged on the extruder 1. The die head 3has an outer body 4 and an inner die member 5, which together with the outer body 4 definesan annular passage from which an extruded tube in preform condition 10 of thermoplasticmaterial emerges, as is preferred in a substantially horizontal direction. The inner diemember 5 forms a lumen or axial inner cavity in the tube in preform condition 10.
As is common in this technology a rather thick walled tube in preform condition 10 isextruded, the wall thickness later being reduced and the diameter being increased by thebiaxial orientation process.
In an alternative embodiment the die head 3 is an offset die head 3 with an inlet for theextruded material at a lateral side of the die head and with a central axial passage throughthe die head 3, essentially through the inner die member 5.
Preferably the die head 3 is provided with means for controlling and adjusting the annularpassage in order to control the wall thickness and/or cross-sectional shape of the tube inpreform condition 10 emerging from the die head 3. This type of die head 3 is known in theart. Preferably an appropriate measuring device 6 is arranged directly downstream of the diehead 3 and measures the emerging tube in preform condition 10 to provide control signalsfor the die head 3.
As is preferred an external cooling device 8 is arranged downstream of the extruder 1 andthe die head 5 to cool and temper the thick walled tube in preform condition 10, e.g. fromabout 200°C to about 100°C for PVC. The external cooling device 8 may e.g. comprise anumber of compartments behind one another through which cooling water is circulated, thetube in preform condition 10 being in direct contact with the cooling water in eachcompartment. The temperature of the cooling water may vary from one compartment toanother. If desired, it can be arranged that the cooling water circulation in each compartmentmay be switched on or off.
An outer diameter calibrating device 8a may be provided at the upstream end of the externalcooling device 8.
Downstream of the external cooling device 8 a first drawing device 15, which may also bereferred to as a preform speed-control device, is arranged. Preferably said device 15includes multiple tracks engaging on the exterior of the tube in preform condition 10, thespeed of the tracks being controlled by a suitable track drive system. Such drawing devices15 are customary in plastic pipe extrusion.
In an embodiment not shown here an external heating device for the tube in preformcondition is arranged between the external cooling device 8 and the first drawing device 15,said heating device being adapted to heat in an adjustable manner one sector of thecircumference of the tube 10, or possibly multiple selected sectors of the circumference ofthe tube 10, e.g. only a bottom section of the tube 10 and not the remainder of thecircumference of the tube 10, prior to reaching the first drawing device 15. It has been foundthat heating only a bottom section of the tube 10 at this position is beneficial for theuniformity of the wall thickness of the finally obtained tube. This external heating device couldcomprise one or more infrared heating elements.
The figure 1b further schematically depicts an expansion device 20. The expansion device20 is held in place by means of an anchoring rod 21 that is at one end fastened to theexpansion device 20. The anchoring rod 21 is connected to the die head 3.
As is preferred a force sensing assembly 22 is provided to measure the pull force on theanchoring rod 21 during operation of the installation.
As is preferred the anchoring rod 21 has one or more internal ducts, e.g. for supply anddischarge of fluid; liquid and/or gas (e.g. air); to locations within the lumen of the tube and/orthe expansion device 20. Also the anchoring rod 21 may include one or more ducts forelectrical wiring, e.g. to connect to one or more sensors (e.g. pressure and/or temperature) inthe lumen of the tube and/or the expansion device, or e.g. to control one or more valves orother electronic components, possibly housed within or at the downstream end of theexpansion device.
In general the expansion device 20 shown here includes - from upstream to downstreamend thereof - a run-on part 20a, an expansion part 20b, and a run-off part 20c. Theexpansion part 20b - as is preferred - has at least one non-deformable or rigid portion with agradually increasing diameter in downstream direction, e.g. of conical shape, e.g. with theouter surface of a truncated cone, so as to come into contact with the tube 10 and to exert anexpanding force on the tube 10 that brings about diametrical expansion of the tube 10. Theexpansion part 20b has a maximum diameter at its downstream end, the run-off part 20chere has a diameter that does not exceed said maximum diameter, in fact is preferably lessover a reduced diameter section as will be explained below.
The expansion part 20b and as is preferred also the run-on part 20a and the run-off part 20chere are of rigid, non-deformable embodiment.
The run-on part 20a here is of an elongated, generally cylindrical design. The diameter of therun-on part 20a substantially corresponds to the diameter of the lumen within the preform 10upstream of the expansion device 20. The run-off part 20c here is of a generally cylindricaldesign.
Preferred details of the expansion device 20 or parts thereof will be explained further below.
At a distance downstream of the expansion device 20, as is common in this technology, afurther drawing device 50 is arranged. This drawing device 50 is adapted to exert aconsiderable tensile force on the oriented tube 10. In general the passage of the suitablytempered tube 10 over the expansion device 20 under the influence of the tensile forceexerted by the drawing device 50 causes the tube 10 to be expanded in diameter as well asstretched in a considerable manner in axial direction, the wall thickness being significantlyreduced in the process so that an biaxially oriented tube 10 is obtained. The maximumdiameter of the expansion part 20b in this example basically dictates the orientation incircumferential to which the tube in preform condition is subjected.
As is preferred an external cooling of the oriented tube 20 is effected soon after thediametrical expansion of the tube 10 has been brought about, preferably -as here - whilstthe tube 10 passes over the run-off part 20c, most preferably starting close to, yet not on, theexpansion part 20b. For this reason a first external cooling device 60 is provided. This firstcooling device 60 preferably includes one or more nozzles spraying or jetting cooling wateronto the exterior surface of the oriented tube, preferably with a significant cooling capacity toarrive at an intense external cooling. Other preferred details will be explained below.
As is preferred at least one further or second external cooling device 70 is arranged at arelatively short distance downstream of the expansion device 20. This second externalcooling device 70 preferably includes one or more nozzles spraying or jetting cooling wateronto the oriented tube 10.
As is preferred yet another or third external cooling device 80, preferably embodied with oneor more compartments as described with reference to cooling device 8, is arrangeddownstream of the device 70 and upstream of the drawing device 50 to cool the orientedtube 10 to a final, e.g. ambient, temperature.
Downstream of the drawing device 50 the oriented tube 10 may e.g. be cut to individual tubeelements with e.g. a sawing, cutting or milling device or the tube, when appropriate may bespooled onto a reel. This equipment is known in the art.
It is envisaged, in a preferred embodiment, that no calibration of the outer diameter of thebiaxially oriented tube by passing the tube through a sizing opening of a calibration device iseffected downstream of the expansion device 20. This is considered to avoid a loss ofstrength of the finally obtained tube due to the impact of the sizing device on the tube.
Here, use is made of an expansion device 20 with a run-on part 20a that is provided with asealing member 30 that is sealingly engaged by the tube in preform condition 10. The sealingmember 30 is arranged at a distance upstream of the expansion part 20b of the expansiondevice 20. As is preferred the sealing member 30 is arranged at or in the close vicinity of thenose-end of the run-on part 20a.
As is preferred, there is no external part of the installation at the height of the sealingmember 30 that presses the tube in preform condition 10 onto the sealing member 30 as thiswould cause a risk of damaging the tube in preform condition, of disturbing the expansionand also entail a risk of seizing of the tube in preform condition between the sealing member30 and any external part.
This sealing member 30 and the sealing engagement thereof with the tube in preformcondition 10 during the production process is advantageous as it provides a barrier betweenthe zone upstream of the sealing member 30 and the zone downstream of the sealingmember 30 within the lumen of the tube in preform condition 10, so that conditions and/oractions can be performed in said zones that are fully or at least largely independent from oneanother.
As is advantageous for temperature conditioning of the tube in preform condition 10 a liquidcirculation compartment 25 is formed in the lumen of the tube in preform condition 10between a closing member 26 at a distance upstream from the nose end of the run-on part20a on the one hand and the sealing member 30 on the other hand. A liquid of controlledtemperature, e.g. water, is circulated through said liquid circulation compartment in directcontact with the inside of the tube in preform condition 10. This allows to establish aneffective internal temperature conditioning of the tube in preform condition directly upstreamof the expansion device. In practice said internal temperature condition may be effected with hot water, e.g. close to the orientation temperature, e.g. close to the boiling temperature ofwater when producing biaxially oriented PVC tubing.
The closing member 26 may be arranged on the anchoring rod 21, but here is arranged onthe inner member 5 of the die head 3. By choosing the location of the closing member 26 theeffective length of the compartment 25 can be established.
The water to be circulated through the compartment 25 is supplied from a water source,preferably including a pump and a water heater, via one or more ducts in the rod 21. Thereturn flow of water leaving the compartment 25 is discharged via one or more other ducts inthe rod 21.
Here, use is made of an expansion device 20 having one or more fluid supply ducts 27 (aportion of which is schematically depicted) to form a fluid volume between the expansiondevice 20 and the tube 10. The fluid is a gas, e.g. compressed air. The use of a gas willavoid any problems associated with the presence of water residue on the inside of the tubedownstream of the expansion device.
It is noted that in figure 2 the presence of a water film between the run-on part 20a and theupstream portion of the expansion part 20b on the one hand and the tube 10 on the otherhand is suggested, which is not according to the present invention. However the thickness ofthe water film relative to the wall thickness of the tube in preform condition and the diameterof the expansion device is exaggerated.
The one or more supply ducts 27a here have a port in the outer surface of the run-on part20a and/or the expansion part 20b of the expansion device. Possibly fluid is suppliedbetween the tube and the expansion device directly downstream of the sealing member 30.
In this example of figure 2 a discharge duct 27b is provided to discharge the water beingentrained with the moving tube 10.
As is preferred the first or upstream fluid volume is established over the entire length of therun-on part 20a downstream of the sealing member 30, more preferably also over theupstream portion of the expansion part 20b. Also a second or downstream fluid volume ispreferably formed over at least a portion of the run-off part 20c, preferably a sealingengagement of the tube with the expansion device in a region at or near the maximumdiameter of the expansion part forming a barrier with an upstream fluid volume.
The first or upstream fluid volume, in conjunction with the presence of the sealing member30, allows to have a relatively long run-on part which is beneficial for the stability of the tube10 when leading up to the expansion part, the fluid preventing any or at least any excessivefrictional contact between the tube in preform condition and the run-on part, more preferablyas said contact is concentrated solely on the sealing member 30.
In a practical embodiment the sealing member 30 could have a diameter that is between 4and 20 millimetres greater than the diameter of the downstream located portion of the run-onsection.
The sealing member 30 forms an effective and reliable seal that prevents the fluid, which issupplied at an elevated pressure that is sufficient for the formation of a fluid volume, fromreaching the lumen of the tube in preform condition 10 upstream of the sealing member 30.When the production is performed with the presence of compartment 25, and with - as ispreferred - a relatively low pressure of the water in said compartment, it is understandablethat the fluid will try to reach said lower pressure zone upstream, the sealing memberreliably avoiding this effect. This allows for a stable fluid volume between the expansiondevice, preferably both the run-on part and the expansion part, and the tube, as any escapeof fluid to upstream of the sealing member 30 will cause a pressure drop in the volume andthus instability.
In an embodiment according to the invention the fluid is a gas, e.g. air, supplied via acompressor or other pressurized gas source to be introduced between the expansion deviceand the tube. Herein expansion of the tube is to be caused, at least partly, by the internalfluid pressure caused by the gas.
As can be seen in the drawings - and as is preferred - use is made of at least one externalheat exchange device 110 that is adapted to influence the temperature of the tube in preformcondition 10 arriving at the sealing member 30, and thereby the sealing contact between thetube in preform condition 10 and the sealing member 30. As is preferred at least one suchheat exchange device is an external heat exchange device that is arranged between thedrawing device 15 and the location of the sealing member 30 to influence the temperature ofthe tube in preform condition 10 from the exterior thereof. Preferably said device, here device110, is arranged directly upstream of the sealing member location.
As is preferred a second external heating device 120 here is arranged downstream of thesealing member 30 location, between said sealing member 30 and the expansion part of the expansion device or even overlapping (a part of) the expansion part of the expansion device20.
In an arrangement with a first external heating device 110 directly upstream of the sealingmember location and a second external heating device 120 downstream of the sealingmember location, each heating device 110,120 being controllable independently, the firstheating device 110 can be used primarily for controlling the sealing engagement with thesealing member 30, and the second heating device 120 in order to influence the tube 10directly upstream of and/or during the passage of the tube over the expansion part of theexpansion device. The heating devices 110,120 may each include multiple heating elementsdistributed around the path of the tube, e.g. multiple infrared heating elements.
A control device, e.g. electronic, preferably is provided to control the operation of eachexternal heating device 110,120. For the external heating device 110 the control may bebased on a feedback signal representative of the actual sealing engagement of the tube inpreform condition 10 with the sealing member 30, e.g. obtained via a force monitoring devicethat is adapted to monitor the axial force on the sealing member 30 (e.g. with a strain gauge)or obtained via a monitoring device that is adapted to monitor a local deformation in themoving tube caused by the sealing member 30, e.g. a local bulging of the tube as indicatedin figure 2, e.g. by measuring the diameter of the preform upstream, at, and downstream ofthe sealing member.
The sealing member 30 is a member 30 having a diameter that is larger than thedownstream portion of the run-on part 20a. As is preferred the run-on part 20a has a uniformdiameter between the sealing member 30 and the expansion part 20b.
As is preferred the sealing member 30 is a separately manufactured annular member fittedon a tubular member of the run-on part.
As is preferred the sealing member 30 is a metallic member with no provision to supply alubricant to the outer surface thereof. In more complex embodiments however the sealingmember may be adapted to control the frictional engagement thereof with the tube in preformcondition, e.g. provided with a lubrication device, e.g. allowing a gas, e.g. air, to be fedbetween the sealing portion and the tube in preform condition. In another embodiment thesealing member may be construed to have a variable diameter and an associated controlmeans, e.g. with an outer metallic skin that is expandable under hydraulic pressure, so as tocontrol the sealing engagement with the tube in preform condition.
The run-off part 20c, which is downstream of the expansion part 20b, has a reduceddiameter section having a smaller diameter than the maximum diameter of the expansionpart 20a. Possibly the reduced diameter section directly adjoins the maximum diametercross-section, so that a diameter reduction step occurs directly behind said maximumdiameter position. This can be clearly seen in figures 2 and 4.
Use is made here of at least one outer diameter ring member, here - as preferred - two ringmembers 90,91, through which the tube 10 passes at the location of the run-off part of theexpansion device, here at the location of the reduced diameter section of the run-off part 20c.As is preferred the ring members 90, 91 here are each embodied as a constrictive outerdiameter ring member, which means that each ring member 90, 91 exerts a radialconstrictive force on the tube 10 passing there through, thereby reducing the outer diameterof the tube 10, at least over a short axial distance. In practice this means that the openingwithin each ring member 90, 91 has a diameter which is less than the projected outerdiameter of the oriented tube 10 at said location during the normal production process.
The reduced diameter section here is dimensioned so as to avoid a problem of seizing of thetube between the expansion device 20 and the at least one outer diameter calibrating ring90, 91.
The reduced diameter section preferably has a diameter that is at least 4 millimetres lessthan the maximum diameter of the expansion part 20b of the expansion device 20.
Preferably the diameter reduction is about twice the wall thickness of the tube passing oversaid section.
By providing the reduced diameter section the outer diameter ring members 90, 91 can bearranged around said reduced diameter section, with the radial spacing between said ringmembers 90, 91 and the reduced diameter section being more than the wall thickness of thetube 10 desired during the production process at said location, so that some radial playremains that allows for possible variations in the wall thickness of the tube during theproduction process, without the risk that said tube becomes stuck between a ring member90, 91 and the reduced diameter section of the run-off part of the expansion device.
Each ring member 90, 91 may be provided with cooling means for cooling the ring member90, 91, e.g. with an internal cooling fluid duct, e.g. an annular duct.
Each ring member 90, 91 preferably is composed of two semi-circular parts, allowing to placethe ring members 90, 91 around the tube 10, e.g. during the start-up phase of the productionprocess, and allowing to remove, e.g. for exchange, the ring members during the productionprocess.
Each ring member 90, 91 preferably is made of metal.
As indicated above, in order to freeze the orientation of the plastic material, the oriented tubeis cooled externally while passing over the run-off part 20c by the first external cooling device60.
The external cooling by first external cooling device 60 of the tube while passing over therun-off section 20c is here performed in the absence of internal cooling of the tube 10 whilepassing over the expansion device 20, and in fact also in the absence of any internal coolingdownstream of the expansion device 20.
In order to arrive at a biaxially oriented tube 10 with desired dimensions, as wall thicknessand cross-sectional shape, preferably without using an outer diameter calibrationdownstream of the expansion device 20, it has been found possible to rely on the use of theone or more outer diameter ring members 90, 91 and/or the external cooling of the orientedtube. This is done on the basis of the so-called snap-back effect. This snap-back effect isknown in the art and is visible as a reduction of the tube diameter directly downstream of theexpansion device 20.
In a preferred embodiment the first external cooling device 60 is adapted to adjust the lengthand/or location with respect to the expansion device 20 of the stretch of the oriented tube 10that is affected by the first external cooling device 60. It has been found that by suitableselection of the length, and preferably also the location, of the affected stretch with respect tothe expansion device, in particular the run-off part 20c, the snap-back effect can becontrolled, and so the diameter of the tube 10. Clearly the intensity of the cooling by device60 can also be controlled and will have an influence on the snap-back effect.
In a very practical embodiment the first external cooling device 60 operates with one or morenozzles emitting sprays or jets of cooling liquid, e.g. water, and comprises an upstreamshield member 61 and a downstream shield member 62, said shield members 61, 62delimiting the stretch of oriented tube that is affected by the sprays or jets of cooling liquid. Atleast one of the shield members, preferably both, is displaceable in axial direction, therebyallowing to adjust the length and/or the location of the stretch of tube that is affected by the cooling liquid. It will be appreciated that by controlling the length and/or position of the shieldmembers, the cooling of the oriented tube can be controlled, even more when - as iscommon - the intensity of the cooling spray can be controlled as well.
In an even more practical embodiment each of the shield members 60, 61 - as depicted here- is integral with a ring member 91,92.
A displacement device 65, here embodied as motorized drive assembly, for axialdisplacement of at least one of the shield members 61,61 and/or at least one of the ringmembers 90, 91 in axial direction along the run-off part 20a is provided. In this example thedevice 65 includes one or more screw spindles 66, e.g. operated by a common electricmotor.
As is preferred the ring members 90,91 and shield members 61,62, as well as theassociated displacement device 65, are mounted on a mobile support 68 (here with axiallinear guides 69) allowing to displace said components in axial direction, e.g. to a retractedposition downstream of the position of the expansion device 20, e.g. in order to allow accessto the expansion device e.g. when replacing the expansion device and/or during start-up ofthe installation.
As is preferred a second external cooling device 70 is arranged spaced downstream from thefirst external cooling device 60 and the expansion device 20. The second external coolingdevice 70 preferably comprises one or more nozzles emitting sprays or jets of cooling wateronto the exterior of the oriented tube 10.
Preferably a dry zone is created between the external cooling devices 60 and 70 on theoutside of the tube 10. This is considered to avoid or at least reduce the formation of visualeffects, e.g. rings, on the outside of the tube by cooling water.
Preferably the second external cooling device 70 comprises an upstream shield member 71delimiting the upstream end of the stretch of oriented tubing 10 affected by the externalcooling device 70. As is preferred the upstream shield member 71 is movable in axialdirection by an associated displacement device, or is coupled to an axially mobile ringmember 91 or shield member 62.
The upstream shield member 71 preferably has an easily flexible annular lip 72 engaging theoriented tube 10 so as to avoid any scratching or deformation of the oriented tube.
Here use is made of a measuring device 130 for measuring at least the outer diameter of theoriented tube 10, and preferably also the wall thickness and/or cross-sectional profile, whichmeasuring device 130 is arranged downstream of the expansion device 20, heredownstream of the second external cooling device 70.
Also use is made of a control device (not shown), e.g. an electronic device, which is linked tothe measuring device in order to obtain input signals that allow to control the first externalcooling device 60 and/or the second external cooling device 70.
For instance the device 60 is controlled with regard to at least the length and/or location withrespect to the expansion device of the stretch of oriented tube that is affected by the firstexternal cooling device 60, and/or the intensity of the cooling.
For instance the second external cooling device 70 is controlled with regard to the axialposition of the upstream shield member 71 and/or the intensity of the cooling.
By control of the external cooling of the tube by the cooling device 60 and/or device 70 thesnap-back effect can be controlled, and thus the diameter of the finally obtained tube. Thiscan then be done without the need for any further outer diameter calibration downstream ofthe expansion device.
In a practical embodiment this control device is adapted such that the length of the stretch oftube that is affected by the first external cooling device 60 is decreased to obtain anincreased snap-back effect and thus increased diameter reduction, and wherein said lengthis increased to obtain a reduced snap-back effect and thus decreased diameter reduction.
In a practical embodiment the axial position of the upstream shield member of the secondexternal cooling device 70 is chosen or adjusted to be in the region where the snap-backeffect occurs.
As is preferred provisions are made for the presence of a first or upstream fluid volumeupstream of the maximum diameter of the expansion part of the expansion device and asecond or downstream fluid volume between the reduced diameter section of the run-off part20c of the expansion device and the oriented tube 10.
In order to supply gas, more preferably air, most preferably heated, to the second fluidvolume, one or more dedicated supply ducts can be provided having a port in the run-off partexterior surface. As an alternative, or in combination therewith, a communication passagecan be made, preferably a valve controlled passage, that communicates with both the firstand the second fluid volume. Such a passage allows e.g. to equalize the pressure in the twofluid volumes when desired and/or to introduce fluid into one volume via a supply duct havinga port at the other volume. While not depicted here, the skilled person will appreciate that thepassage could extent between ports in the outer surface of the expansion device, e.g. on at the run-on part and one at the run-off part, with interposition of a valve, e.g. an electricallyoperated valve, e.g. mounted at the rear end of the expansion device.
The presence of two outer diameter ring members 90, 91 spaced apart from one another isadvantageous, even more advantageous when the run-off part 20c is embodied with anincreased diameter portion 20c1 delimiting the downstream end of the reduced diametersection. Preferably each ring member 90, 91 being mobile in axial direction relative to thereduced diameter section.
With the ring members 90, 91 both suitably dimensioned as constrictive ring members, theeffect can be obtained that the ring member 90 contributes to the sealing engagement of thetube with the expansion device in the region at or near the maximum diameter of theexpansion part 20b. This avoids uncontrolled escape or leakage of fluid from the one volumeto the other volume.
The ring member 91 contributes to the sealing engagement of the oriented tube with theincreased diameter portion 20c1. This avoids or at least limits any leakage of fluid into thelumen of the oriented tube downstream of the expansion device 20, and thus avoidsundesirable instability of the fluid volume. Most preferably the downstream ring member 91 islocated closely upstream of the increased diameter portion 20c1, thereby enhancing thesealing contact between the tube and the increased diameter portion 20c1.
Possibly the expansion device 20 has one or more discharge ducts 28 for the fluid, e.g. witha port near the downstream end of the reduced diameter section of the run-off part 20c,which is advantageous when use is made of a liquid that is entrained with the tube 10 froman upstream port of a supply duct to said discharge duct port.
In a preferred embodiment the installation is provided with both supply means for a liquidfluid to the one or both fluid volumes between the expansion device and the tube and supplymeans for gaseous fluid to one or both fluid volumes, and with an arrangement of ducts andone or more valves allowing to selectively feed fluid to one or both fluid volumes. Forinstance in a start-up phase fluid is only fed to the first volume, e.g. first heated water andlater gas, such as air. The ring members 90, 91 may be absent during the start-up phase,facilitating the first passage over the run-off part. Later the ring members 90, 91 are fitted ormade operative and a fluid is fed to the second volume, e.g. heated air.
The excellent sealing engagement in the region of the maximum diameter of the expansionpart, also allows for a reliable operation with the first fluid volume not being a film to prevent friction, but an internal pressurized zone within the tube that causes gradual expansion of thetube to an internal diameter less than the maximum diameter in order to maintain the reliablesealing engagement. The use of an internal pressurized zone to cause gradual expansion ina production process for biaxially oriented thermoplastic tubing is known in the art, e.g. fromWO 90/02644. However in the known installations operating according to this approach useis made of an inflatable plug to delimit the downstream end of the pressurized zone, whichinflatable plug presses the expanded tube against a surrounding sizing sleeve to obtain aseal that avoids pressure loss in the pressurized zone. This approach has shown to come upwith less favourable results, e.g. with regard to uniformity of dimensions of the finallyobtained tube and stability of the production process. One aspect is e.g. that the inflatableplug is deformable, and thus does not dictate the obtained orientation in the manner as thenon-deformable expansion part.
In the embodiment depicted here the expansion part of the expansion device 20 has astepped design with a first conical surface increasing in diameter in downstream direction,adjoining a cylindrical surface of a first diameter, followed by a second conical expansionsurface increasing in diameter in downstream direction. As is preferred the diameter of thesealing member 30 is greater than the first diameter of the expansion part in this steppeddesign. The expansion part could have multiple steps.
In an embodiment one or more rollers 125 are arranged below tube 10 so as to support saidtube, e.g. below the run-off part of the expansion device or, with preference, downstream ofthe expansion device e.g. to avoid interference with any of the rings 90, 91.
In this practical embodiment an upstream replaceable ring 20b1 is fitted at the transitionbetween the expansion part 20b and the run-off part 20c of the expansion device, thereplaceable ring 20b1 forming the maximum diameter of the expansion part 20b. This allowsfor relatively easy change of the maximum diameter of the expansion device as well asreplacement of ring in case of wear.
In this practical embodiment the increased diameter portion 20c1 is formed by a downstreamreplaceable ring which is fitted at the downstream end of the run-off section, the replaceablering having a diameter greater than the upstream portion of the run-off part of the expansiondevice. This allows for relatively easy change of the diameter of the expansion device at saiddownstream location as well as replacement of said zone in case of wear.
Fig. 5 shows schematically in longitudinal section a portion of an installation for producingbiaxially oriented thermoplastic tubing.
Figure 5 shows the portion wherein the thermoplastic tube is passing over the expansiondevice 100. This expansion device 100 may e.g. be integrated in the installation that isdescribed with reference to figures 1 a,1 b, and 1 c, or in an installation including at least anextruder, one or more tempering devices for the tube in preform condition, a drawing devicedownstream of the expansion device as well as a cooling device for the oriented tube. Whenseen in conjunction with figures 1a-c the expansion device 100 depicted in figure 5 thenreplaces the expansion device 20.
As is preferred in combination with the expansion device 100 a first external cooling device60 is used, here, as preferred, having one or more features of the external cooling device 60as has been discussed herein before. As is preferred a second external cooling device,preferably having one or more of the features of external cooling device 70, is arrangeddownstream of the expansion device 100. It will be appreciated that a control device forthese first and/or second external cooling device, preferably having one or more of thefeatures of the control device as discussed herein before, is also present.
By suitable control of the first and/or second external cooling device the snap-back effect,that occurs at a short distance downstream of the expansion device can be controlled, andthereby the diameter of the oriented tube, this without - as is preferred - making use of anyexternal diameter calibrating device downstream of the expansion device.
The expansion device 100 is embodied to cause expansion of the tube from the preformcondition into a biaxially oriented tube based on internal fluid pressure in a relative large fluidvolume 101 inside the lumen of the tube between the tube and the expansion device.
The expansion device 100 here includes an upstream sealing portion 103 that fits sealinglyinto the yet unexpanded tube in preform condition, e.g. the sealing portion having one ormore of the features of the sealing member 30. The upstream sealing portion 103 delimitsthe volume 101 at its upstream end.
The expansion device 100 also includes a downstream sealing portion 105 that fits sealinglyin the expanded tube 10 and delimits the fluid volume 101 at its downstream end. As ispreferred the sealing portion 105 is non-deformable, e.g. of a metal.
The expansion device 100 includes one or more fluid supply ducts 106 that allow to introducepressurized gas, e.g. air, into the fluid volume 101.
The figure 5 shows the presence of a downstream outer diameter ring member 91 that isarranged a short distance upstream of the downstream sealing portion 105. The ring member91 exerts a constrictive force on the tube, thereby contributing to the sealing engagementbetween the tube and the sealing portion 105. As is highly preferred, there is no part of theinstallation at the same axial location as the portion 105 that contacts the tube on the exteriorso as to press it against the sealing portion 105. This avoids any risk of seizing of the tubebetween such a part of the installation and the sealing portion 105, as well as preventsundesirable damage to the tube.
As is preferred a further, upstream outer diameter ring member 90 is arranged at a distanceupstream of the ring member 91. As will be appreciated the ring members 90, 91 arepreferably integrated with shield members of the first external cooling device 60.
The cooling by first external cooling device 60 also contributes somewhat to the sealingengagement between the tube 10 and the portion 105. However its main purpose is to freezethe biaxial orientation, as well as to control the snap-back effect, as is preferred incombination with the use of the second external cooling device 70.
Figure 6 shows schematically in longitudinal section a portion of an installation for producingbiaxially oriented thermoplastic tubing. The figure 6 is used to elucidate the invention.
Figure 6 shows the portion wherein the thermoplastic tube is passing over the expansiondevice 200. This expansion device 200 may e.g. be integrated in the installation that isdescribed with reference to figures 1a,1b, and 1c, or in an installation including at least anextruder, one or more tempering devices for the tube in preform condition, a drawing devicedownstream of the expansion device as well as a cooling device for the oriented tube. Whenseen in conjunction with figures 1a-c the expansion device 200 depicted in figure 5 thenreplaces the expansion device 20.
The expansion device 200 is embodied to effect expansion of the tube by a hybrid process ofexpansion by internal fluid pressure and expansion caused by contact with a non-deformableexpansion part of the device 200.
In this example the expansion device includes a run-on part 200a including a sealing portion201 that sealing engages the non-expanded tube in preform condition. Downstream thereof,spaced from the sealing portion 201, the expansion device 200 has a non-deformableexpansion portion 200b with a gradually increasing diameter to a maximum diameter.Downstream of said portion 200b the expansion device 200 includes a run-off part 200c,here with an increased diameter portion also acting as downstream sealing portion 204.
An upstream or first fluid volume 210 is present between the upstream sealing portion 201and the location of contact of the tube with the expansion part 200b. This fluid volume 210 isfilled with a pressurized gas, here air, via supply duct 206 so as to effect gradual expansionof the tube due to internal fluid pressure. This expansion is such that the tube 10 is expandedfrom its preform condition to a diameter such that the tube 10 still contacts the conical face ofexpansion part 200b during normal production of the biaxially oriented tube. This contactcauses a further expansion of the tube 10 due to the forces exerted by the expansion part200b on the tube. As can be seen the tube now sealingly engages the expansion device inthe region at or near the maximum diameter of the expansion part 200b.
A downstream or second fluid volume 220 is present between the location of contactbetween the tube at or near the maximum diameter of the expansion part 200b on the onehand, and the location of contact between the tube and the downstream sealing portion 204on the other hand.
This fluid volume 220 is filled with a pressurized fluid, preferably a gas, here gas, via supplyduct 207 so as to effect gradual expansion of the tube due to internal fluid pressure. So afurther expansion is effected by said fluid pressure, generally to expand the tube so that itcan pass over the sealing portion 204 which has a greater diameter than the maximumdiameter of the expansion part 202.
As is preferred a communication passage 208 with a control valve 209 is provided in the fluidsupply device, here schematically shown, allowing to bring the fluid volumes 210 and 220 incommunication, thus allowing to equalize the pressure in both volumes on command. Asshown here the supply duct 207 is placed in series with said passage 208, however thesupply duct could also be a distinct supply duct, the passage 208 forming a controllableconnection between the duct 206 and the duct 207.
As is preferred a downstream outer diameter ring member 91 is provided, preferably suchthat said ring member 91 contributes to the sealing engagement of the tube with the sealing portion 204. Further preferred details of said ring member 91 have been disclosed hereinbefore and may be used in combination with the expansion device 200.
As is preferred an upstream outer diameter ring member 90 is also provided, said ringmember 90 being arranged downstream of the maximum diameter of the expansion portion202.
As is preferred a first external cooling device 60 is employed for cooling the tube when thetube passes between the expansion part and the downstream sealing portion 204. As ispreferred the first external cooling device includes one or more of the features of the coolingdevice described herein.
As is preferred the one or more ring members 90, 91 are integrated with one or more shieldmembers of the first external cooling device 60.
When desired the downstream sealing portion 204 can be embodied with a graduallyincreasing diameter and the tube contacting said face of the sealing portion in a manner thata further circumferential expansion is caused by said contact, thus the portion 204 acting asan expansion part to effect the final expansion of the tube.
The downstream sealing portion 204 can also be embodied as an expandable portion, e.g.an inflatable portion, e.g. as an inflatable plug as is known in the art, allowing to vary thediameter thereof, e.g. to facilitate start-up of the installation with the diameter of portion 204in the start-up phase being reduced, e.g. to at most the maximum diameter of part 200b. Incombination with an expandable downstream sealing portion, the rigid run-off part as shownin figure 6 could e.g. be of reduced axial length, e.g. just sufficient for contact with the tubedirectly downstream of the maximum diameter of the part 200b, e.g. cylindrical having thesame diameter as the maximum diameter. A slender rod could extend between theexpandable portion 204 and the non-deformable body including at least the part 200b to holdthe expandable portion in position.
In figures 7a and 7b an installation is shown that largely corresponds to the installationshown in figure 6. Parts have the same or similar structure and function have been denotedwith the same reference numerals. Figure 7c shows a detail of a variant of said installation.
In the expansion device 200 now also a gas discharge duct 250, which duct 250 has an inletport 250a in the exterior surface of the expansion part of the expansion device, as can beseen in the enlarged detail of figure 7a.
In figure 7a the situation is shown wherein the inlet port 250a is covered and closed by thetube 10, so that said port 250a is not in communication with the gas volume 210.
In figure 7b the same installation is shown, but now the tube 10 has expanded some moreunder the influence of the gas pressure in volume 210. As can be seen in the enlarged detail,the port 250a is now not covered by the tube 10 and thus in communication with the gasvolume 210.
The gas discharge duct 250 in figure 7b provides for the relief of gas pressure from thevolume 201 as the corresponding inlet port is fully or at least partly open and thereby theexpansion of the tube 10 caused by internal gas pressure is controlled.
This relief of gas pressure stops when the inlet port 250a is fully covered and closed by thetube 10 (as in figure 7a).
In practice an equilibrium situation may be reached wherein the port 250a remains partlyopen, so that a circulation of gas through the volume 210 is present.
So the cooperation of the tube 10 with the inlet port 250a achieves in a very attractivemanner a control of the degree of expansion that is caused in the tube 10 due to the internalgas pressure in volume 210. Effectively the position of the inlet port 250a on the slopingexterior face of the expansion part of the device 200 controls where the tube 10 will contactsaid face, assuming that the gas pressure in volume 210 is sufficient to cause the tube 10 toexpand.
The provision of duct 250 with inlet port 250a also provides for an automatic safety againstthe tube being expanded by gas pressure excessively, e.g. to a greater diameter that theexpansion part prior to reaching said expansion part, which situation in reality would lead to astoppage of the production.
It is noted that a group of multiple inlet ports 250a connected to a common gas dischargeduct could be arranged distributed around the circumference of the expansion part and at the same radial distance to a central longitudinal axis of the expansion part, so as to avoid thatthe tube would over-expand somewhere along its circumference.
In another embodiment, shown in figure 7c, multiple inlet ports 250a, 250b, each associatedwith a corresponding discharge duct 250, 260, are provided at differing diameter positions inthe exterior surface of the expansion part, said differing diameter positions having differentradial distances from a central longitudinal axis of the expansion part (so in axial direction ofthe expansion device one inlet port behind the other inlet port). In this embodiment it isenvisaged to provide one or more operable valves 270, 271 that are associated with thedischarge ducts 250, 260, so that a selected inlet port and associated discharge duct can bemade effective to relief gas pressure (here port 250a) when the tube does not cover andclose said inlet port, whereas one or more non-selected inlet ports (here port 260a) andassociated discharge ducts are made ineffective. This allows to provide control over theinternal diameter of the tube as it expands by the internal gas pressure in the fluid volumebefore reaching the non-deformable expansion part.
In figure 7a also a temperature sensor 280 is shown at the sealing member 201. This sensor280 allows to measure the temperature of the preform in said region. This sensor 280 maye.g. be coupled to the first and/or second external heat exchange devices that are used toinfluence the sealing engagement of the preform with the sealing member 201 in order toassist in suitable operation thereof.

权利要求:
Claims (20)
[1]
A method for producing a biaxially oriented tube of thermoplastic material, in which a tube is extruded in preform state from thermoplastic material with an extruder provided with an extruder head with an internal head element, which internal head element forms a lumen in the tube in preform condition, the tube in the preform state is subjected to a temperature conditioning by one or more tempering devices so that a tempered tube is obtained with an orientation temperature suitable for the thermoplastic material, and wherein use is made of an expansion device in the lumen downstream of the extruder, the expansion device comprises: a non-deformable expansion member having a gradually increasing diameter to a maximum diameter at the downstream end thereof, the tube making contact with the expansion member and the expansion member exerting an expansion force on the tube to allow expansion of the tempered tube in the preform state to produce the circumferential direction, a ramp part arranged upstream of the expansion part, which ramp part has an upstream nose end, the method comprising pulling the tempered pipe over the expansion device using a pulling device downstream of the expansion device is arranged and acts on the tube in such a way that the tube is transformed from a tube in preform state into a biaxially oriented tube with thermoplastic material oriented in the axial direction and in the circumferential direction of the tube, the biaxially oriented tube is cooled, wherein use is made of an expansion device with one or more fluid supply channels, which one or more fluid supply channels have a port in the outer surface of the ramp part and / or of the expansion part of the expansion device, and wherein fluid is introduced and a fluid volume is filled me between the expansion device and the tube, the method being characterized in that use is made of an expansion device with an overflow part which is provided with a sealing member on which the tube engages sealingly in the preform state, the sealing member being spaced upstream of the expansion member is arranged and has a diameter larger than that of the ramp member downstream of the sealing member, the sealing member forming an effective seal that prevents fluid in the fluid volume from reaching the lumen of the tube upstream of the sealing member, and wherein the method is characterized in that the fluid supplied to the fluid volume bounded at one end by the sealing contact between the tube in preform condition and the sealing member and bounded at the other end by the sealing contact between the tube and at least one downstream portion of the expansion member a gas o is under pressure, for example air, wherein the pressure of the gas in that fluid volume is used to achieve a gradual expansion of the tube even before the tube actually makes contact with the expansion part.
[2]
Method according to claim 1, wherein one or more gas discharge channels are formed in the expansion device, which one or more discharge channels have one or more inlet ports in the outer surface of the expansion part of the expansion device, an inlet port being open or closed or partially closed in depending on whether or not the inlet port is covered and closed by the tube or a portion of the inlet port is closed by the tube, the gas discharge channel realizing the escape of gas pressure from the fluid volume when the one or more associated inlet ports are at least partially opened and thereby reduces tube expansion caused by the internal gas pressure, which escapes from gas pressure until the one or more associated inlet ports are covered and closed through the tube.
[3]
3. Method as claimed in claim 2, wherein a plurality of inlet ports, each associated with a corresponding discharge channel, are provided at deviating diameter positions in the outer surface of the expansion part, which deviating diameter positions have different radial distances to a central longitudinal axis of the expansion part, and wherein one or more operable valves belong to the outlets so that a selected inlet port and associated outlet can be made operable to release gas pressure when the tube does not completely cover and close off that inlet port, thereby disabling one or more non-selected inlet ports and associated outlets, thereby providing control over the internal diameter of the tube as this internal gas pressure expands in the fluid volume before this tube reaches the non-deformable expansion portion.
[4]
Method according to one or more of the preceding claims, wherein use is made of an expansion device with a drain part downstream of the expansion part.
[5]
A method according to claim 4, wherein a second fluid volume is realized between the expander part of the expander and the oriented tube, preferably between a reduced diameter part of the expander part and the oriented tube, and wherein, preferably, the second fluid volume of fluid supplied is a pressurized gas, for example air, for example a heated gas.
[6]
Method according to claim 4 or 5, wherein the expander part of the expansion device has a reduced diameter part with a smaller diameter than the maximum diameter of the expansion part, and wherein use is made of at least one outer diameter ring element arranged around the reduced diameter part and wherein the outer diameter ring member is arranged so that the oriented tube passes through the ring member while the tube is in contact with the ring member, the outer diameter ring member and the reduced diameter portion being dimensioned such that the jammed of the oriented tube between the drain member and the at least an outer diameter of ring element is avoided, wherein preferably the inside of the oriented tube is at a radial distance from the reduced diameter portion, and wherein, preferably, the expansion device is provided with one or more fluid supply channels with one or more ports in the reducer a diameter section, wherein a pressurized gas is supplied between said reduced diameter section and the tube to form a second fluid volume, and wherein use is made of a first external cooling device which is arranged and operated to cool the oriented tube externally while the tube passes over the drain part.
[7]
Method according to one or more of the preceding claims, wherein one or more temperature sensors are provided on the expansion device, preferably at or near the sealing member, which one or more sensors determine the temperature of the tube in preform condition in that area, wherein, for example, the one or more sensors are coupled to first and / or second external heat exchanger devices that may be used to influence the sealing engagement of the tube in the preform state on the sealing member to assist in proper operation thereof.
[8]
Method according to one or more of the preceding claims, wherein the expansion part has a first conical surface that increases in diameter, downstream direction, connecting at its downstream end to a cylindrical surface with a first diameter, connecting at its downstream end to a second conical surface which diameter increases in downstream direction, and wherein, preferably, the diameter of the sealing member on the ramp member is greater than the first diameter of the expansion member.
[9]
Installation for producing a biaxially oriented tube of thermoplastic material, which installation comprises: - an extruder with an extruder head with an internal head element, which is adapted for hot extruding a tube in the preform state, the internal head element forming a lumen in the tube - one or more tempering devices for temperature conditioning the tube in preform state, so that a tempered tube in preform state is obtained with an orientation temperature suitable for the thermoplastic material, - an expansion device in the lumen downstream of the extruder, the Expansion device comprises: a non-deformable expansion member having an increasing diameter to a maximum diameter at the downstream end thereof, the tube contacting the expansion member and the expansion member exerting an expansion force on the tube to cause expansion of the tempered tube in the circumferential direction , - a ramp part arranged upstream of the expansion part, which ramp part has an upstream nose end, - one or more fluid supply channels, which one or more fluid supply channels have a port in an outer surface of the ramp part and / or the expansion part, so that a fluid volume can be formed between the expansion device and the tube, - a pulling device which is arranged downstream of the expansion device and is arranged to act on the tube in such a way that the tube is transformed from a tube in preform state into a biaxially oriented tube of thermoplastic material which is oriented in the axial direction and in the circumferential direction of the tube, - a cooling device which is adapted to cool the biaxially oriented tube, characterized in that the run-on part is provided with a sealing member which is adapted to be seized by the tube in a sealing manner preform state, which sealing member at a distance is arranged upstream of the expansion member and has a diameter larger than the ramp downstream of the sealing member, the sealing member forming an effective seal that prevents fluid in the fluid volume from reaching the lumen of the tube upstream of the sealing member, and characterized in that one or more fluid supply channels are connected to a source for pressurized gas, such that the fluid is supplied to the fluid volume bounded at one end by the sealing contact between the tube in preform condition and the sealing member and bounded at the other end by the sealing contact between the tube and at least a downstream portion of the expansion part is a pressurized gas, for example air, and that the installation is adapted to control the pressure of the gas in that fluid volume so that - during production of the biaxially oriented tube - a gradual expansion of the pipe is machined Even before the tube actually makes contact with the expansion part.
[10]
Installation according to claim 9, wherein one or more gas discharge channels are formed in the expansion device, which one or more discharge channels have one or more inlet ports in the outer surface of the expansion part of the expansion device, an inlet port being open or closed or partially closed depending on whether or not the inlet port is covered and closed by the tube or a portion of the inlet port is closed by the tube, the gas discharge duct - when using the installation - allowing the escape of gas pressure from the fluid volume when one or more associated inlet ports are at least partially opened, thereby reducing the expansion of the tube caused by the internal gas pressure, which escape of gas pressure continues until the one or more associated inlet ports are covered and closed again by the tube.
[11]
11. Installation as claimed in claim 10, wherein a plurality of inlet ports, each associated with a corresponding discharge channel, are provided at deviating diameter positions in the outer surface of the expansion part, which deviating diameter positions have different radial distances from a central longitudinal axis of the expansion part, and wherein one or more operable valves belong to the outlets so that - when using the installation - a selected inlet port and associated outlet can be made effective to allow gas pressure to escape when the tube does not cover and close off that inlet port, whereby one or more non-selected inlet ports and associated outlets may become ineffective which provides control over the inner diameter of the tube as it expands through fluid gas pressure in the fluid volume before this tube reaches the non-deformable expansion member.
[12]
12. Installation as claimed in one or more of the claims 9-11, wherein the expansion device has a drain part downstream of the expansion part.
[13]
Installation according to claim 12, wherein - in use - a second fluid volume is realized between the drain part of the expansion device and the oriented tube, preferably between a reduced diameter part of the drain part and the oriented tube, and wherein, preferably, the fluid supplied to the second fluid volume is a gas under pressure, e.g. air, e.g. a heated gas.
[14]
14. Installation as claimed in claim 12 or 13, wherein the drain part of the expansion device has a reduced diameter part with a smaller diameter than the maximum diameter of the expansion part, and at least one outer diameter ring element is arranged around the reduced diameter part, and wherein the outer diameter annular element is arranged such that the oriented tube passes through the annular element while the tube is in contact with that annular element, the outer diameter of the annular element and the reduced diameter portion being dimensioned so as to prevent jamming of the oriented tube between the discharge part and the at least one external diameter of the annular element, wherein, preferably, the inside of the oriented tube is radially spaced from the reduced diameter portion, and wherein, preferably, the expansion device has one or more fluid supply channels with one or more ports in the reduced diameter portion, wherein a ga s is supplied between the reduced diameter portion and the oriented tube to form a second fluid volume therebetween, and wherein a first external cooling device is provided which is adapted to cool the tube exterior as the tube passes over the drain portion.
[15]
15. Installation as claimed in one or more of the foregoing claims 9-14, wherein one or more temperature sensors are provided on the expansion device, preferably at or near the sealing member, which make it possible to determine the temperature of the tube in the preform condition in the area wherein, for example, the one or more sensors are coupled to first and / or second external heat exchanger devices that are used to influence the sealing engagement of the tube in the preform state on the sealing member to assist in proper operation thereof.
[16]
Installation according to one or more of the preceding claims 9-15, wherein the expansion part has a first conical surface which increases in diameter in the downstream direction, connecting at its downstream end to a cylindrical surface with a first diameter, connecting at its downstream end to a second conical surface that increases in diameter in downstream direction, and wherein, preferably, the diameter of the sealing member on the ramp member is greater than the first diameter of the expansion member.
[17]
A biaxially oriented thermoplastic tube obtained by the method according to one or more of the preceding claims 1-8.
[18]
18. Biaxially oriented PVC pipe obtained with the method according to one or more of the preceding claims 1 - 8.
[19]
A biaxially oriented pressure tube for water transport obtained with the method according to one or more of the preceding claims 1 - 8.
[20]
An expansion device adapted for use in a method according to one or more of the preceding claims 1 - 8 and / or an installation according to one or more of claims 9-16.

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法律状态:
2012-04-25| SD| Assignments of patents|Effective date: 20120406 |

优先权:

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申请号 | 申请日 | 专利标题

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NL2003666|2009-10-19|

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NL2003666A|NL2003666C2|2009-10-19|2009-10-19|Methods and devices for manufacturing biaxially oriented tubing.|

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NL2010050687|2010-10-18|

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PCT/NL2010/050687|WO2011049436A2|2009-10-19|2010-10-18|Methods and devices for manufacturing biaxially oriented tubing|

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