Description

Tubular member and method and apparatus for producing a tubu ^¬ lar member

The present invention relates to a method for producing a tu ^¬ bular member according to claim 1, to a tubular member according to claim 10 and to an apparatus for producing a tubular member according to claim 17.

A holdout is a tubular member that serves to maintain a shrinkable tubular member in an expanded state. The shrink- able tubular member may for example comprise a heat-shrinking material or a cold-shrinking material. In order to shrink the shrinkable tubular member, the holdout is removed step by step along its longitudinal direction by unsewing the holdout along a weak line arranged in spiral windings.

In the state of the art, holdouts are conventionally made by bonding a strand in spiral windings. The strand is extruded in a first processing step and spooled onto a coiler. In a later second processing step, the strand is bonded in spiral windings to form the holdout. In an alternative production method according to the state of the art, the holdout is formed as a continuous tubular member in a first production step. In a second production step, weak lines are cut into the tubular member along spiral windings using a turning machine. In the state of the art, holdouts are joined with shrinkable tubular members in a later manufacturing step.

It is an object of the present invention to provide a method for producing a tubular member. This objective is achieved by a method for producing a tubular member according to claim 1. It is a further object of the present invention to provide a tubular member. This objective is achieved by a tubular mem ^¬ ber according to claim 10. It is a further object of the pre ^¬ sent invention to provide an apparatus for producing a tubu- lar member. This objective is achieved by an apparatus ac ^¬ cording to claim 17. Preferred embodiments are disclosed in the dependent claims.

A method for producing a tubular member that is composed of a strand arranged in helical windings comprises extruding a strand with an extrusion die and directly bonding said strand to a longitudinal end of a tubular member. Advantageously, this method does not require to spool the strand on a coiler before bonding the strand to form the tubular member. This allows to perform the method in a cost-efficient and time- saving manner.

In an embodiment of the method, the strand is bonded to the tubular member before the strand crystallizes. Advanta- geously, the uncrystallized material of the strand allows to form an integral bond between the helical winding of the tu ^¬ bular member. Advantageously, no further processing is necessary for forming the bonds. According to an embodiment of the method, the strand is ex ^¬ truded in a tangential direction relative to the tubular mem ^¬ ber. Advantageously, this extrusion direction allows for di ^¬ rectly bonding the extruded strand to the tubular member. According to an embodiment of the method, two strands are ex ^¬ truded simultaneously. The two strands are arranged in the tubular member in alternating helical windings. Advantageously, a weak line of the tubular member may be arranged between the helical windings of the two alternating strands or inside one of the strands forming the tubular member. The weak line may form a seam th t is unsewn while unwinding the tubular member.

According to an embodiment of the method, the two strands comprise different materials. These materials may comprise a similar polymer base. The different materials of the two strands may serve for forming a weak line of the tubular mem ^¬ ber along the bonding line between the two strands forming the tubular member. Alternatively, one of the two different materials may be more brittle than the other material to form a weak line in the strand made of that material. The brittle material may for example comprise a high amount of fillers. One of the two different materials may also be less tear re ^¬ sistant or have less tensile strength.

According to an embodiment of the method, a further tubular member is co-extruded concentrically to the tubular member. This further tubular member is connected to the tubular member. Advantageously, this allows to produce a holdout di ^¬ rectly together with a shrinkable tubular member.

According to one embodiment of the method, the further tubu ^¬ lar member is co-extruded to an outer face of the tubular member. The further tubular member may be a shrinkable tubular member. The inner tubular member may form a holdout that withstands a radially inward-oriented force exerted by the further tubular member. In this case there may or may not be a connection between the holdout and the further tubular member . According to another embodiment of the method, the further tubular member is co-extruded to an inner face of the tubular member. Advantageously, the inner further tubular member may be a shrinkable tubular member, while the outer tubular mem- ber is a holdout that withstands and inward-oriented force exerted by the inner further tubular member.

According to an embodiment of the method, the method com ^¬ prises a further step of radially expanding the tubular mem- ber and the further tubular member. Advantageously, the pre- expanded further tubular member may later shrink again by removing the tubular member or after removal of the tubular member e.g. by application of heat. A tubular member according to the invention comprises a holdout. The tubular member comprises a first material and a sec ^¬ ond material. Advantageously, the two materials of the tubu ^¬ lar member may serve to fulfil two different functions of the tubular member.

According to one embodiment of the tubular member, the tubu ^¬ lar member comprises an inner tube and an outer tube. The inner tube comprises the first material and the outer tube com ^¬ prises the first material, the second material and/or a third material. Advantageously, either the inner tube or the outer tube of the tubular member may form a holdout while the other tube of the tubular member may form a shrinkable tubular member . According to one embodiment of the tubular member, the inner tube is a holdout and the outer tube is an elastomeric member or a coldshrinkable member or a heatshrinkable member or a member that combines coldshrinkable and heatshrinkable prop- erties. Advantageously, the inner tube may serve to withstand a radially inward-oriented force exerted by the outer tube.

According to another embodiment of the tubular member, the outer tube is a holdout and the inner tube is an elastomeric member or a coldshrinkable member or a heatshrinkable member or a member that combines coldshrinkable and heatshrinkable properties. Advantageously, the outer tube may serve to exert a radially inward-oriented force exerted by the inner tube.

According to an embodiment of the tubular member, the first material and the second material are arranged in alternating helical windings along a longitudinal direction of the tubu ^¬ lar member. Advantageously, a weak line of the tubular member may be arranged between the alternating helical windings or inside the helical winding made of either the first material or the second material.

According to one embodiment of the tubular member, the tubu- lar member is at least partially composed of a strand ar ^¬ ranged in helical windings. Each cross-section surface of the strand comprises the first material and the second material. Advantageously, a weak line of the tubular member may be ar ^¬ ranged inside the strand of the tubular member. The weak line may be formed by either the first material or the second ma ^¬ terial .

According to one embodiment of the tubular member, the first material is more brittle or less tear resistant or has less tensile strength than the second material. Advantageously, the first material may serve to form a weak line of the tubu ^¬ lar member. An apparatus according to the invention is designed for pro ^¬ ducing a tubular member that is composed of a strand arranged in helical windings. The apparatus comprises an extrusion die for extruding a strand. The apparatus further comprises means for bonding said strand to a longitudinal end of the tubular member. Advantageously, the apparatus allows for extruding the strand and bonding the strand to form the tubular member in one combined production step. Advantageously, this elimi ^¬ nates a need to spool the strand onto a coiler prior to bond- ing the strand to form the tubular member.

According to an embodiment of the apparatus, the apparatus is designed to feed the strand from the extrusion die directly to the means for bonding the strand. Advantageously, the strand may be bonded to the longitudinal end of the tubular member or any other area of the strand meant to allow for a connection. This allows for an integral connection between the helical windings of the strand of the tubular member. According to an embodiment of the apparatus, the extrusion die is provided to extrude the strand in a tangential direc ^¬ tion relative to the tubular member. Advantageously, this ar ^¬ rangement allows the extruded strand to leave the extrusion die such that it may be bonded directly to the longitudinal end of the tubular member or any other area of the strand meant to allow for a connection.

According to an embodiment of the apparatus, the extrusion die is fixed relative to the apparatus. The apparatus is de- signed to rotate the tubular member around the longitudinal axis of the tubular member during production of the tubular member. Advantageously, this allows for a simple construction of the apparatus . According to another embodiment of the apparatus, the extru ^¬ sion die is designed to rotate around a longitudinal axis of the tubular member during a production of the tubular member. Advantageously, this may reduce a friction between the pro ^¬ duced tubular member and the apparatus.

According to an embodiment of the apparatus, the apparatus is designed to produce a tubular member comprising an inner tube and an outer tube. The inner tube and the outer tube are co- extruded. Advantageously, either the inner tube or the outer tube of the tubular member may form a holdout, while the other tube of the tubular member may form a shrinkable member. The apparatus advantageously allows for a time-saving and cost-efficient simultaneous production of the two tubes of the tubular member.

According to an embodiment of the apparatus, the apparatus comprises two extrusion dies for simultaneously extruding two strands. The apparatus further comprise a means for bonding said two strands to a longitudinal end of a tubular member in alternating helical windings. Advantageously, the two strands may comprise two different materials. The two strands may serve to form a weak line of the tubular member. The weak line may either be arranged between the alternating helical windings of the two strands or inside one of the two strands of the tubular member.

According to an embodiment of the apparatus, the extrusion die designed to extrude said strand with a profile that com ^¬ prises a trench. Advantageously, the trench may form a weak line of the tubular member. According to an embodiment of the apparatus, the apparatus is designed to extrude said strand from a first material. The apparatus further comprises means to fill said trench with a second material. Advantageously, the trench filled with the second material may serve to form a weak line of the tubular member .

The invention will now be explained in more detail with ref ^¬ erence to the Figures, in which:

Figure 1 schematically shows a strand of a tubular member;

Figure 2 schematically shows two strands arranged in alter ^¬ nating helical windings and designed for forming a tubular member ;

Figure 3 schematically shows a tubular member;

Figure 4 schematically illustrates a method of forming a tu ^¬ bular member in a combined extrusion and bonding step;

Figure 5 schematically shows a first apparatus for producing a tubular member;

Figure 6 schematically shows a second apparatus for producing a tubular member;

Figure 7 schematically shows a third apparatus for producing a tubular member;

Figure 8 schematically shows a fourth apparatus for producing a tubular member; Figure 9 schematically shows a fifth apparatus for producing a tubular member;

Figure 10 schematically shows a first strand profile;

Figure 11 schematically shows a second strand profile; Figure 12 schematically shows a third strand profile; Figure 13 schematically shows a fourth strand profile;

Figure 14 schematically shows a fifth strand profile; and Figure 15 schematically shows a sixth strand profile.

Figure 1 shows a schematic perspective view of a first strand 100. The first strand 100 comprises the shape of an elongate strip with an rectangular cross section 110. In alternative embodiments, the cross section 110 may comprise a shape that is different from a rectangular shape.

The first strand 100 comprises an outer face 111 and an inner face 112 composed to the outer face 111. The first strand 110 further comprises a first side face 113 and an opposed second side face 114.

The first strand 100 is arranged in helical or spiral wind ^¬ ings 120. The first strand 100 is wound around a winding axis 125. In the helical windings 120 of the first strand 100 the outer face 111 faces outwards away from the winding axis 125. The inner face 112 faces inwards towards the winding axis 125. The first side face 113 of one helical winding 120 of the first strand 100 faces towards the second side face 114 of a consecutive helical winding 120 of the first strand 100. In the depiction of Figure 1, the first side faces 113 of the helical windings 120 are spaced from the second side faces 114 of the neighbouring helical windings 120 of the first strand 100 for illustrative reasons. The first side faces 113 may however be bonded to second side faces 114 of consecutive helical windings 110, 120 of the first strand 100 to form a tubular member that extends along the winding axis 125. The tubular member is then composed of the first strand 100. The bond connection between the first side face 113 and the sec ^¬ ond side face 114 is preferably an integral connection.

Figure 2 shows a schematic perspective view of the first strand 100 and a second strand 200. The first strand 100 is arranged in helical windings 120 along the winding axis 125, as depicted in Figure 1.

The second strand 200 comprises the shape of an elongate strip with a rectangular cross section 210. The cross section 210 may for example be similar or equal to the cross section 110 of the first strand 100. The second strand 200 is ar- ranged in helical windings 220 along a winding axis 225 that coincides with the winding axis 125 of the first strand 100. The second strand 200 comprises an outer face 211 and an op ^¬ posed inner face 212. The outer face 211 faces away from the winding axis 225. The inner face 212 faces towards the wind- ing axis 225. The second strand 200 further comprises a first side face 213 and an opposed second side face 214. The helical windings 220 of the second strand 200 and the helical windings 120 of the first strand 100 are arranged in an alternating manner. The first side face 113 of each heli ^¬ cal winding 120 of the first strand 100 faces a second side face 214 of a helical winding 220 of the second strand 200. The second side face 114 of each helical winding 120 of the first strand 100 faces a first side face 213 of a helical winding 220 of the second strand 200. The side faces 113, 114, 213, 214 of the first strand 100 and the second strand 200 are depicted in a spaced manner in Fig ^¬ ure 2 for illustrative reasons. The side faces 113, 214, 114, 213 of consecutive helical windings 120, 220 of the first strand 100 and the second strand 200 may however be bonded to each other to form a tubular member composed of the first strand 100 and the second strand 200.

Figure 3 shows a schematic view of a tubular member 300 com ^¬ posed of the first strand 100 and the second strand 200. Con- secutive helical windings 120 of the first strand 100 and helical windings 220 of the second strand 200 form the tubu ^¬ lar member 300. A longitudinal direction 310 of the tubular member 300 coincides with the winding axis 125 of the helical winding 120 of the first strand 100 and the winding axis 225 of the helical windings 220 of the second strand 200. The first side face 113 of the first strand 100 is bonded to the second side face 214 of the second strand 200 in all helical windings 120, 220. The second side face 114 of the first strand 100 is bonded to the first side face 213 of the second strand 200 in all helical windings 120, 220 of the first strand 100 and the second strand 200. The tubular member 300 may serve as a holdout. The tubular member 300 may be disintegrated along the longitudinal direc ^¬ tion 310 by gradually unsewing a seem of the tubular member 300 that forms a weak line of the tubular member 300.

The weak line of the tubular member 300 may be formed by the bonding connection between the first side face 113 of the first strand 100 and the second side face 214 of the second strand 200 and/or by the bonding connection between the sec- ond side face 114 of the first strand 100 and the first side face 213 of the second strand 200 or by both bonding connec ^¬ tions .

Alternatively, the weak line of the tubular member 300 may be formed by either the first strand 100 or the second strand 200. In this embodiment, the first strand 100 or the second strand 200 breaks along the helical windings 120, 220 while unsewing the tubular member 300. This may be achieved by forming the strand 100, 200 that serves as a weak line from a material that is more brittle or less tear resistant or has less tensile strength than the material of the other strand 200, 100. The more brittle material may for example comprise a high amount of fillers. It is also possible that both the material the first strand 100 and the material of the second strand 200 is brittle. Both the material of the first strand 100 and the material of the second strand 200 may comprise a polymeric material. The material of the first strand 100 and the material of the second strand 200 may comprise a similar polymer base.

The first strand 100 and the second strand 200 may also com ^¬ prise of materials that differ in other properties than brit- tleness. For example, either the material of the first strand 100 or the material of the second strand 200 may be thermally or electrically more conductive than the other material. Ei ^¬ ther the material of the first strand 100 or the material of the second strand 200 may comprise other members like metal wires, eg. for heating purposes. The material of the strand 100 and the material of the second strand 200 may comprise different chemical properties. The material of the first strand 100 and the material of the second strand 200 may com ^¬ prise different appearances. The first strand 100 and the second strand 200 may also comprise different cross sections 110, 210. This may also lead to the fact that bonding is not or not only on the side faces 113, 214, 213, 114 but also in other areas of the strands 100, 200. Figure 4 shows a schematic depiction of an apparatus for pro ^¬ ducing a tubular member 400. The tubular member 400 is composed of one strand 450 that is wound in helical windings 470 around a winding axis that is parallel to a longitudinal di ^¬ rection 410 of the tubular member 400.

The strand 450 is extruded by an extrusion die 480. The ex ^¬ trusion die 480 is arranged such that the strand 450 is ex ^¬ truded in a tangential direction 420 of the tubular member 400. The tangential direction 420 is normal to the longitudi- nal direction 410.

The extrusion die 480 comprises a cross section 490. The strand 450 extruded by the extrusion die 480 consequently comprises a cross section 460 that is similar or equal to the cross section 490 of the extrusion die 480. The cross sec ^¬ tions 460, 490 do not comprise a rectangular shape in the ex ^¬ ample of Figure 4. The cross section 460 of the strand 450 is rather such that the strand 450 comprises a ledge 465. The ledge 465 supports bonding of the side faces of the strand 450 together to form the tubular member 400.

After being extruded by the extrusion die 480, the strand 450 is directly bonded to the longitudinal end of the tubular member 400. Consequently, the strand 450 is not spooled on a coiler or stored or processed otherwise between extrusion of the strand 450 and bonding of the strand 450 to form the tu ^¬ bular member 400.

Preferentially, the strand 450 is bonded to the longitudinal end of the tubular member 400 before the material of the strand 450 has fully crystallized and/or cooled down after extrusion of the strand 450. This supports formation of an integral bond connection between the helical windings 470 of the strand 450 without requiring further treatment of the strand 450 or additional means like eg. adhesives or addi ^¬ tional processes like eg. ultrasonic or laser welding During production of the tubular member 400, the extrusion die 480 rotates around the winding axis of the helical wind ^¬ ings 470 relative to the tubular member 400. This may either be achieved by maintaining the tubular member 400 in a fixed position and rotating the extrusion die 480 or by maintaining the extrusion die 480 in a fixed position and rotating the tubular member 400 around the winding axis that coincides with the longitudinal direction 410 of the tubular member 400. The tubular member 400 of Figure 4 is composed of only one strand 450. The tubular member 400 may, however, also be com ^¬ posed of two strands like the tubular member 300 shown in Figure 3, as will become more apparent in conjunction with the further description below.

Figure 5 shows a highly schematic sectional view of a first apparatus 500 for producing a tubular member. The first appa ^¬ ratus 500 comprises an inner part 510 and an outer part 520. The inner part 510 and the outer part 520 are substantially rotationally symmetric with respect to an axis 501. The inner part 510 is at least partially arranged inside the outer part 520 with respect to the axis 501.

Arranged between the inner part 510 and the outer part 520 of the first apparatus 500 is an extrusion and bonding chamber 530. The extrusion and bonding chamber 530 is substantially rotationally symmetric with respect to the axis 501. The ex ^¬ trusion and bonding chamber 530 is provided for the extrusion of a first strand 570 and a second strand 580 that together form a tubular member 560. A first feed pipe 540 extends through the outer part 520 of the first apparatus 500 towards a first extrusion die 545 ar ^¬ ranged in the extrusion and bonding chamber 530. The first extrusion die 545 is only shown schematically in Figure 5. The first extrusion die 545 is arranged tangentially with re- spect to the tubular member 560. In the example of Figure 5, the first extrusion die 545 comprises an approximately trape ^¬ zoid cross section.

On a side of the outer part 520 that is radially opposed to the first feed pipe 540 with respect to the axis 501, a sec ^¬ ond feed pipe 550 extends through the outer part 520 of the first apparatus 500 towards a second extrusion die 555 that is arranged in the extrusion and bonding chamber 530 at a po- sition opposed to the first extrusion die 545 with respect to the axis 501. The second extrusion die 555 is also arranged tangentially to the tubular member 560 and comprises a cross section that corresponds to the cross section of the first extrusion die 541 in the example of Figure 5.

A first material 575 is fed through the first feed pipe 540 to form the first strand 570 that is extruded by the first extrusion die 545. The first strand 570 comprises a first cross section 571 that corresponds to the cross section of the first extrusion die 545. The first strand 570 is extruded into the extrusion bonding chamber 530 in a tangential direc ^¬ tion of the tubular member 560. A second material 585 is fed through the second feed pipe 550 to form the second strand 580 that is extruded by the second extrusion die 555 into the extrusion and bonding chamber 530 in a tangential direction of the tubular member 560. The sec ^¬ ond strand 580 comprises a second cross section 581 that cor- responds to the cross section of the second extrusion die 565.

The second material 585 is preferably different from the first material 575. The first material 575 and the second ma- terial 585 may however also be the same material.

The tangential extrusion of the first strand 570 and the sec ^¬ ond strand 580 in the same rotational direction with respect to the axis 501 exerts a rotational force on the tubular mem- ber 560 with respect to the axis 501. The inner part 510 of the first apparatus 500 comprises a thread 535 in the region of the extrusion and bonding chamber 530. The thread 535 comprises a twofold pitch. The rotational force exerted on the tubular member 560 sets the tubular member 560 in rotation around the axis 501. The thread 535 drives the rotating tubu ^¬ lar member 560 out of the extrusion and bonding chamber 530 along the axis 501.

At the same time, the continuously extruded first strand 570 and second strand 580 are continuously bonded to the longitu ^¬ dinal end of the tubular member 560 arranged in the extrusion and bonding chamber 530. The first strand 570 is bonded onto a longitudinal end of the tubular member 560 in a first bond ^¬ ing area 531. The second strand 580 is bonded onto a longitu ^¬ dinal end of the tubular member 560 in a second bonding area 532. The twofold pitch of the thread 535 ensures the forma ^¬ tion of alternating helical windings 565, as previously de- picted in Figure 3.

In order to support the rotational movement of the tubular member 560 with respect to the fixed inner part 510, outer part 520, first extrusion die 545 and second extrusion die 555 of the first apparatus 500, a sufficient lubrication be ^¬ tween the tubular member 560 and the inner part 510 and the outer part 520 respectively may be required .

Figure 6 shows a schematic sectional view of a second appara- tus 600 for producing a tubular member. The second apparatus 600 comprises an inner part 610 and an outer part 620. The inner part 610 and the outer part 620 are essentially rota- tionally symmetric with respect to a common axis 601. The outer part 620 is at least partially arranged around the in- ner part 610. In a region between the inner part 610 and the outer part 620 an extrusion and bonding chamber 630 is arranged. Both the inner part 610 and the outer part 620 com- prise a thread 635 in the region of the extrusion and bonding chamber 630.

A first feed pipe 640 extends through the outer part 620 to- wards a first extrusion die 645 arranged tangentially to a tubular member 660 in the extrusion and bonding chamber 630. A second feed pipe 641 extends through the outer part 620 of the second apparatus 600 towards a second extrusion die 646 arranged tangentially to the tubular member 660 in the extru- sion and bonding chamber 630. The first extrusion die 645 and the second extrusion die 646 are arranged at opposed posi ^¬ tions of the extrusion and bonding chamber 630 with respect to axis 601. The first extrusion die 645 and the second ex ^¬ trusion die 646 are arranged in the same rotational direction with respect to axis 601.

A third feed pipe 650 extends through the inner part 610 of the second apparatus 600 towards a third extrusion die 655 and a fourth extrusion die 656. Both the third extrusion die 655 and the fourth extrusion die 656 are arranged in a tan ^¬ gential direction of the tubular member 660 in the extrusion and bonding chamber 630. The third extrusion die 655 and the fourth extrusion die 656 are opposed to each other with respect to axis 601. The third extrusion die 655 is arranged at the same angular position of the extrusion and bonding chamber 630 as the first extrusion die 645. The fourth extrusion die 656 is arranged at the same angular position of the ex ^¬ trusion and bonding chamber 630 as the second extrusion die 646. All extrusion dies 645, 646, 655, 656 are oriented in the same angular direction with respect to axis 601.

A first strand 670 with a first cross section 671 and com ^¬ posed of the first material 675 is extruded by the first ex- trusion die 645. The second strand 680 comprising a second cross section 681 and a second material 685 is extruded by the second extrusion die 646. A third strand 690 comprising a third cross section 691 and a third material 695 is extruded by the third extrusion die 655. A forth strand 692 comprising a fourth cross section 693 and the third material 695 is ex ^¬ truded by the fourth extrusion die 656. The first material 675 and the second material 685 may be the same material in a simplified embodiment. In the example shown in Figure 6, all cross sections 671, 681, 691, 693 comprise an approximately trapezoidal shape.

The first strand 670 and the second strand 680 are bonded to ^¬ gether to form alternating helical windings 665 of an outer tube 662 of the tubular member 660. The third strand 690 and the fourth strand 692 are bonded together to form alternating helical windings 665 of an inner tube 661 of the tubular mem ^¬ ber 660. At the same time, the inner tube 661 and the outer tube 662 of the tubular member 660 are bonded together in the extrusion and bonding chamber 630.

Extrusion of the strands 670, 680, 690, 692 exerts a rota ^¬ tional force on the tubular member 660 that sets the tubular member 660 in rotational movement around the axis 601 with respect to the inner part 610 and the outer part 620 of the second apparatus 600. The thread 635 ensures that the rota ^¬ tional movement of the tubular member 660 is attended by a longitudinal movement in a longitudinal direction of the tu ^¬ bular member 660 that coincides with the axis 601. The longi- tudinal movement of the tubular member 660 moves the tubular member 660 out of the extrusion and bonding chamber 630. Figure 7 shows a schematic sectional view of a third appara ^¬ tus 700 for producing a tubular member. The third apparatus comprises an inner part 710 and an outer part 720. Both parts 710, 720 are approximately rotationally symmetric with re- spect to an axis 701. An approximately rotationally symmetric co-extrusion and bonding chamber 730 is arranged between the inner part 710 and the outer part 720 of the third apparatus 700. The inner part 710 comprises a first extrusion die 745 and a second extrusion die 746. The first extrusion die 745 and the second extrusion die 746 are arranged tangentially to a tubu ^¬ lar member 760 at opposed positions of the co-extrusion and bonding chamber 730. The first feed pipe 740 extends through the inner part 710 to feed a first material 775 to the first extrusion die 745 and the second extrusion die 746.

The first extrusion die 745 serves to extrude a first strand 770 comprising a first cross section 771 and the first mate- rial 775. The second extrusion die 746 serves to extrude a second strand 780 comprising a second cross section 781 and the first material 775.

The inner part 710 comprising the first extrusion die 745 and the second extrusion die 746 rotates around the axis 701 with respect to the outer part 720 of the third apparatus 700 and the tubular member 760. The first strand 770 and the second strand 780 are extruded in a tangential direction of the tu ^¬ bular member 760 in the same rotational direction with re- spect to the axis 701. The first strand 770 and the second strand 780 can be bonded together in alternating helical windings 765 in the co-extrusion and bonding chamber 730 to form an inner tube 761 of the tubular member 760. Alterna- tively the first strand 770 and the second strand 780 are not bonded together but are both bonded to the tubular member 760. At the same time, the tubular member 760 is longitudi ^¬ nally moved out of the co-extrusion and bonding chamber 730 along a direction that coincides with the axis 701.

The outer part 720 of the third apparatus 700 comprises a second feed pipe 750 that is provided to feed a second mate ^¬ rial 795 to the co-extrusion and bonding chamber 730. In the co-extrusion and bonding chamber 730 the second material 795 is co-extruded with the first strand 770 in a first bonding area 731 and the second strand 780 in a second bonding area 732 to form an outer tube 762 that arranged on an outer face of the inner tube 761. The inner tube 761 and the outer tube 762 together form a tubular member 760.

Alternatively, the first strand 770 and the second strand 780 are not bonded together, but only bonded to the outer tube 762.

Extrusion of the outer tube 762 in the longitudinal direction of the tubular member 760 drives the tubular member 760 out of the co-extrusion and bonding chamber 730 in the longitudinal direction of the tubular member 760. The rotating first extrusion die 745 and second extrusion die 746 continuously arrange further helical windings 765 of the first strand 770 and the second strand 780 respectively on the freshly ex ^¬ truded outer tube 762. The co-extruded inner tube 761 and outer tube 762 of the tu ^¬ bular member 760 may serve to fullfill different purposes. The inner tube 761 of the tubular member 760 may serve as a holdout. The outer tube 762 of the tubular member 760 may serve as a shrinkable member. The second material 795 of the outer tube 762 may be an elastomeric material or another ma ^¬ terial, eg. a coldshrinkable material, a heatshrinkable mate ^¬ rial or a combination of coldshrinkable and heatshrinkable materials.

The inner tube 761 and the outer tube 762 of the tubular mem ^¬ ber 760 may be pre-expanded together after co-extrusion of the tubular member 760. The inner tube 761 and the outer tube 762 of the tubular member 760 may for example be pre-expanded by a factor of up to 300 %.

Figure 8 shows a schematic sectional view of a fourth appara ^¬ tus 800 for producing a tubular member. The fourth apparatus 800 comprises an inner part 810 and an outer part 820. The inner part 810 and the outer part 820 both are essentially rotationally symmetric with respect to an axis 801. A co- extrusion and bonding chamber 830 is arranged in a region between the inner part 810 and the outer part 820 of the fourth apparatus 800.

The outer part 820 comprises an extrusion die 845 that is ar ^¬ ranged tangentially with respect to a tubular member 860 in the co-extrusion and bonding chamber 830. A first feed pipe 840 extends through the outer part 820 to feed a first mate ^¬ rial 875 to the extrusion die 845 to extrude a strand 870 with a cross section 871. In the example of Figure 8, the cross section 870 comprises an approximately trapezoidal shape. The cross section 871 of the strand 870 may, however, comprise a different shape.

The inner part 810 of the fourth apparatus 800 comprises a second feed pipe 860 for feeding a second material 885 to the co-extrusion and bonding chamber 830. In the co-extrusion and bonding chamber 830, a tubular inner tube 861 is formed from the second material 885. The outer part 820 comprising the extrusion die 845 rotates around the axis 801 with respect to inner part 810 and the inner tube 861 formed in the co-extrusion and bonding chamber 830. The rotating outer part 820 arranges the strand 870 ex ^¬ truded by the extrusion die 845 in helical windings 865 around the inner tube 861, to form an outer tube 862. The in ^¬ ner tube 861 and the outer tube 862 together form the tubular member 860.

The inner tube 861 of the tubular member 860 may serve as a shrinkable member. The outer tube 862 of the tubular member

860 may serve as an external holdout for the shrinkable inner tube 861. The tubular member 860 comprising the inner tube

861 and the outer tube 862 may be pre-expanded by a factor of for example up to 300 % after co-extrusion of the tubular member 860.

The outer tube 862 may bond well to the inner tube 861. Fur ^¬ ther the windings 865 of the outer tube 862 may or may not bond to each other but allow for tearing apart.

Figure 9 shows a schematic sectional view of a fifth appara ^¬ tus 900 for producing a tubular member. The fifth apparatus 900 comprises an inner part 910 and an outer part 920. Both the inner part 910 and the outer part 920 are essentially ro- tationally symmetric with respect to an axis 901. Arranged in a ring shaped-region between the inner part 910 and the outer part 920 is a co-extrusion and bonding chamber 930. The inner part 910 comprises a third fee pipe 950 for feeding a third material 995 to the co-extrusion and bonding chamber 930. The third material 995 is extruded in the co-extrusion and bonding chamber 930 to form a tubular inner tube 961 of a tubular member 960. Continuous extrusion of the inner tube 961 drives the produced tubular member 960 continuously out of the co-extrusion and bonding chamber 930 in a longitudinal direction of the tubular member 960 that coincides with the axis 901.

The outer part 920 of the fifth apparatus 900 comprises a first extrusion die 945 and second extrusion die 946. Both extrusion dies 945, 946 are oriented in a tangential direc ^¬ tion of the tubular member 960 in the co-extrusion and bond- ing chamber 930. The first extrusion die 945 and the second extrusion die 946 are arranged at opposed positions of the co-extrusion and bonding chamber 930 with respect to the axis 901. A first feed pipe 940 extends through the outer part 920 of the fifth apparatus 900 to feed a first material 975 to the first extrusion die 945. A second feed pipe 941 extends through the outer part 920 to feed a second material 985 to the second extrusion die 946.

The outer part 920 rotates around the axis 901 with respect to the inner part 910 and the inner tube 961 of the tubular member 960. The first extrusion die 945, rotating around the axis 901, continuously extrudes a first strand 970 comprising a first cross section 971 and the first material 975 and ar ^¬ ranges the first strand 970 continuously around the inner tube 961 of the tubular member 960, bonding the first strand 970 to the inner tube 961. At the same time, the second ex- trusion die 946, rotating around the axis 901, extrudes a second strand 980 comprising a second cross section 981 and the second material 985 and arranges the second strand 980 around the inner tube 961 of the tubular member 960, bonding the second strand 980 to the inner tube 961 and possibly also to the first strand 970. In interplay between the longitudi ^¬ nal movement of the inner tube 961 and the rotational move ^¬ ment of the extrusion dies 945, 946, the first strand 970 and the second strand 980 are arranged in alternating helical windings 965 around the inner tube 961 to form an outer tube 962 of the tubular member 960.

The first material 975 of the first strand 970 and the second material 985 of the second strand 980 may be the same mate- rial or different materials.

The inner tube 961 of the tubular member 960 may serve as a shrinkable member. The third material 995 of the inner tube

961 of the tubular member 960 may for example be an elas- tomeric material or another material, eg. a coldshrinkable material, a heatshrinkable material or a combination of cold- shrinkable and heatshrinkable materials. The outer tube 961 of the tubular member 960 may serve as an external holdout. The inner tube 961 and the outer tube 962 of the tubular mem- ber 960 may be pre-expanded by a factor of for example up to 300 % after co-extrusion of the inner tube 961 and the outer tube 962 of the tubular member 960.

Since the outer tube 962 of the tubular member 960 is com- posed of alternating helical windings 965 of the first strand 970 and the second strand 980, weak lines of the outer tube

962 may be arranged in the bonding areas between the first strand 970 and the second strand 980, or inside the first strand 970 or inside the second strand 980.

The outer tube 762 of the tubular member 760 of Figure 7, the inner tube 861 of the tubular member 860 of Figure 8 and the inner tube 961 of the tubular member 960 of Figure 9 may com ^¬ prise one or more materials that may be arranged concentric and that do not necessarily need to be continuous in the lon ^¬ gitudinal directions of the tubular members 760, 860, 960. The two or more materials may be coldshrinkable, heatshrink- able or a combination of those.

The strands 100, 200, 450, 570, 580, 670, 680, 690, 692, 770,

780, 870, 970, 980 of the tubular members 300, 400, 560, 660, 760, 860, 960 of Figures 1 to 9 have been shown with cross sections 110, 210, 460, 571, 581, 671, 681, 691, 693, 771,

781, 871, 971, 981 that comprise of only one material. It is however possible, that each cross section surface comprises of two or more materials. This may support creation of a weak line that is arranged inside a strand forming a tubular mem ^¬ ber. A strand forming a tubular member may also comprise a cross section that comprises trenches or cuts. This may also support the formation of a weak line inside the strand. Figure 10 shows a schematic view of a first strand profile

1000. A strand comprising the first strand profile 1000 com ^¬ prises an outer face 1001 and an inner face 1002 that is op ^¬ posed to the outer face 1001. The strand further comprises a first side face 1003 and a second side face 1004 that is op- posed to the first side face 1003. If the strand is arranged in helical windings to form a tubular member, the first side face 1003 is bonded to the second side face 1004. The first strand profile 1000 comprises an outer trench 1010 that extends from the outer face 1001 to an inner region of the first strand profile 1000. The first strand profile 1000 further comprises an inner trench 1020 that extends from the inner face 1002 towards an inner region of the first strand profile 1000. The outer trench 1010 and the inner trench 1020 are inclined with respect to the outer face 1001 and the in ^¬ ner face 1002. The outer trench 1010 and the inner trench 1020 are designed as essentially parallel trenches. A section between the outer trench 1010 and the inner trench 1020 may serve as a weak line of the strand comprising the first strand profile 1000. The strand comprising the first strand profile 1000 may break in the region between the outer strand 1010 and the inner trench 1020 while unsewing a tubular mem- ber formed by the strand arranged in helical winding.

A strand comprising the first strand profile 1000 may be ex ^¬ truded using an extrusion die with a cross section that essentially corresponds to a negative of the first strand pro- file 1000.

Figures 11 to 15 show further possible strand profiles. Each of these strand profiles comprises an inner trench and/or an outer trench. Strands comprising these strand profiles may be extruded using appropriately shaped extrusion dies.

Figure 11 shows a second strand profile 1200. The second strand profile 1200 comprises only an inner trench 1220. The inner trench extends from the inner face 1002 of the second strand profile 1200 towards the outer face 1001. Between the inner trench 1220 and the outer face 1001, a strand compris ^¬ ing the second strand profile 1200 comprises a reduced mate ^¬ rial thickness. Consequently, a weak line of a strand com- prising the second strand profile 1200 is formed in the re ^¬ gion between the inner trench 1220 and the outer face 1001.

Figure 12 shows a third strand profile 1300. The third strand profile 1300 comprises an outer trench 1310 and an inner trench 1320. Again, a weak line is formed in an area between the outer trench 1310 and the inner trench 1320.

Figure 13 shows a fourth strand profile 1400. The fourth strand profile 1400 comprises an outer trench 1410 and an in ^¬ ner trench 1420. Both the outer trench 1410 and the inner trench 1420 comprise an undercut. A weak line is formed be ^¬ tween the outer trench 1410 and the inner trench 1420. The outer trench 1410 comprises an undercut that can advanta- geously be fabricated using an extrusion production method. Such undercut cannot be produced easily by extruding a sub ^¬ stantially tubular sleeve and then removing material by me ^¬ chanical treatment, eg. on a lathe. Figure 14 shows a fifth strand profile 1600. The fifth strand profile 160 comprises an outer trench 1610. A strand compris ^¬ ing the fifth strand profile 1600 comprises a reduced mate ^¬ rial thickness in an area between the outer trench 1610 and the inner face 1002. This area of reduced material thickness forms a weak line of the strand comprising the fifth strand profile 1600.

Figure 15 shows a sixth strand profile 1800. The sixth strand profile 1800 comprises an outer trench 1810 and an inner trench 1820. The outer trench 1810 comprises an undercut. A region between the outer trench 1810 and the inner trench 1820 forms a weak line. In alternative embodiments, the trenches 1010, 1020, 1220, 1310, 1320, 1410, 1420, 1610, 1810, 1820 of strands compris ^¬ ing the strand profiles 1000, 1200, 1300, 1400, 1600, 1800 may be filled with a second material. Two materials are co- extruded side-by-side such that the strand is formed of a first material and the trenches 1010, 1020, 1220, 1310, 1320, 1410, 1420, 1610, 1810, 1820 are filled with the second mate ^¬ rial. The second material may for example be more brittle than the first material.

Reference symbols

100 first strand

110 cross section

111 outer face

112 inner face

113 first side face

114 second side face

120 helical windings

125 winding axis

200 second strand

210 cross section

211 outer face

212 inner face

213 first side face

214 second side face

220 helical windings

225 winding axis

300 tubular member

310 longitudinal direction

400 tubular member

410 longitudinal direction 420 tangential direction

450 strand

460 cross section

465 ledge

470 helical windings 480 extrusion die

490 cross section 500 first apparatus

501 axis

510 inner part 520 outer part

530 extrusion and bonding chamber

531 first bonding area

532 second bonding area

535 thread

540 first feed pipe

545 first extrusion die

550 second feed pipe

555 second extrusion die

560 tubular member

565 helical windings

570 first strand

571 first cross section

575 first material

580 second strand

581 second cross section

585 second material

600 second apparatus

601 axis

610 inner part

620 outer part

630 extrusion and bonding chamber

635 thread

640 first feed pipe

641 second feed pipe

645 first extrusion die

646 second extrusion die

650 third feed pipe

655 third extrusion die

656 fourth extrusion die

660 tubular member

661 inner tube

662 outer tube

665 helical windings

670 first strand

671 first cross section 675 first material

680 second strand

681 second cross section

685 second material

690 third strand

691 third cross section

692 fourth strand

693 fourth cross section

695 third material

700 third apparatus

701 axis

710 inner part

720 outer part

730 co-extrusion and bonding chamber

731 first bonding area

732 second bonding area

740 first feed pipe

745 first extrusion die

746 second extrusion die

750 second feed pipe

760 tubular member

761 inner tube

762 outer tube

765 helical windings

770 first strand

771 first cross section

775 first material

780 second strand

781 second cross section

795 second material

800 fourth apparatus

801 axis

810 inner part

820 outer part

830 co-extrusion and bonding chamber 840 first feed pipe

845 extrusion die

850 second feed pipe

860 tubular member

861 inner tube

862 outer tube

865 helical windings

870 strand

871 cross section

875 first material

885 second material

900 fifth apparatus

901 axis

910 inner part

920 outer part

930 co-extrusion and bonding chamber

940 first feed pipe

941 second feed pipe

945 first extrusion die

946 second extrusion die

950 third feed pipe

960 tubular member

961 inner tube

962 outer tube

965 helical windings

970 first strand

971 first cross section

975 first material

980 second strand

981 second cross section

985 second material

995 third material

1000 first strand profile

1001 outer face

1002 inner face 1003 first side face

1004 second side face 1010 outer trench

1020 inner trench

1200 second strand profile 1220 inner trench

1300 third strand profile 1310 outer trench

1320 inner trench

1400 fourth strand profile 1410 outer trench

1420 inner trench

1600 fifth strand profile 1610 outer trench

1800 sixth strand profile 1810 outer trench

1820 inner trench