SPIRAL WOUND PIPE AND A METHOD FOR MANUFACTURING THE SAME

Abstract: The invention relates to a spirally wound pipe and to a method and arrangement for producing it. The method according to the invention is characterized by the following steps: a flexible, elongate profile (2) is fed through an extrusion station (20) in which the profile is coated with an outer layer (3) of a weldable thermoplastic material along its entire periphery (4); after which the profile (2) is wound in spiral turns (5, 6) to form a pipe (1) about a rotating drum (30) while the said outer layer (3) from the extrusion station maintains such a temperature that the thermoplastic material is weldable, with the profile (2) in the last-wound spiral turn (5) being welded to the profile (2) in the next spiral turn (6) in such a way that a weld seam (7) is formed along the whole of the adjoining edge surfaces (8) of the profiles (2).

Description: SPIRAL WOUND PIPE AND A METHOD TOR MANUFACTURING THE SAME TECHNICAL FIELD The present invention relates to a SDirally wound thermoplastic pipe and to a method and an arrangement for producing it PRIOR ART It is already known to produce spirally wound pipes of thermoplastic with sections running in a heiical line and overlapping each other It is also known to manufacture spirally wound thermoplastic pipes from helical hollow profiles Spirally wound pipes for water drainage or thermoplastic pipes of the type described here can advantageously be used, for example, as manholes for large pipe systems or as ventilation pipes, for example for parking decks and airports One advantage of spirally wound thermoplastic pipes is that their manufacture entails low investment costs compared to other production methods, as a result of which the pipes can also be manufactured in small series while maintaining profitability European Patent Specification EP-0 429 506 B1 describes a spirally wound pipe manufactured from thermoplastic hollow profiles which, by means of a material added between the profiles, are welded together to form a pipe A problem with the spirally wound pipe in EP-0 429 506 B1 is that, from the point of view of leakage, it is very sensitive to inaccuracies in the weld seams The weld seam only needs to have pores or other inaccuracies at a single location for leakage to occur Such inaccuracies in the weld seams can also be difficult to detect in sealing tests carried out before delivery since the weld seams may burst under the stresses which arise only when A known method for solving the above sealing problem arising in pipes of the type described in EP-0 429 506 B1 is described in European Patent Specification EP-0 333 061 B1 According to this patent specification the hollow profiles are wound spirally around a conventional, non-spirally- wound thermoplastic pipe Since the inner thermoplastic pipe does not have any weld seams, a sealed pipe is obtained which retains its seal irrespective of any slight inaccuracies in the weld seams between the spirally wound hollow profiles However, a disadvantage of the pipe according to EP-0 333 061 B1 is that the benefit of lower investment costs which is achieved in spirally wound thermoplastic pipes is partially lost through the addition of the conventional inner pipe which itself requires to be made in larger series to give good profitability A method for manufacturing spirally wound thermoplastic pipes of the type in question here is described in Finnish Patent Application No 921967 The latter describes a welding method in which a thermoplastic hollow profile of rectangular cross section is wound helically on a weld drum at the same time as the profile surfaces which are to be welded together are heated to the desired temperature with hot air, after which welding material is extruded via an extruder nozzle situated in immediate proximity to the weld point onto the heated profile surfaces in two beads along each edge of the profile surface The hollow profile sections coated with welding material are then pressed together with the aid of a press roller situated adjacent to the welding drum, so that a double seam is formed between adjoining hollow profile turns A disadvantage of the method according to Finnish Patent Application No 921967 is that it requires an intricate and therefore expensive extruder nozzle in order to be able to discharge the necessary weld material at the right place in the narrow space situated immediately before the point where the profiles are welded together A further disadvantage of the method is that the double seam which is formed between adjoining hollow profile turns entails increased risk of leakage in the pipe since the profile surfaces lying against each other are not welded to each other in their entirety DESCRIPTION OF THE INVENTION The invention solves the above problems by providing a spirally wound thermoplastic pipe according to Patent Claim 1 1 , a method for producing the said pipe according to Patent Claim 1 and an arrangement for producing the said pipe according to Patent Claim 0 Thus, a method is made available for producing a spirally wound thermoplastic pipe, which method is characterized in particular in that - a flexible, elongate profile section is fed through an extrusion station in which the profile, while being heated, is coated with an outer layer of a weldable thermoplastic material along its entire periphery, after which - the profile is wound in spiral turns to form a pipe about a rotating drum while the said outer layer from the extrusion station maintains such a temperature that the thermoplastic material is weldable, with the profile in the last-wound spiral turn being welded to the profile in the next spiral turn in such a way that a weld seam is formed along the whole of the adjoining edge surfaces of the profiles In one advantageous embodiment of the invention, the extrusion station is situated at a distance from the said drum The pipe profile is advantageously an extruded hollow profile of rectangular or rhomboid cross section. According to a further advantageous embodiment of the method according to the invention, a band-shaped sealing film of thermoplastic material is wound spirally between the drum and the spirally wound profiles in such a way that the sealing film overlaps the weld seams which are formed between the profiles during the spiral winding A number of layers of the said sealing film are preferably wound spirally between the drum and the spirally wound profiles The number of layers can be between two and six, preferably four During the spiral winding, the sealing film is advantageously welded to those surfaces of the profile sections facing towards the centre of the pipe, by means of the sealing film being heated to a weld temperature by a heating arrangement situated in close proximity to the said drum The invention also includes an arrangement for producing a spirally wound thermoplastic pipe according to the method described above The arrangement is characterized in particular in that the extrusion station comprises an extrusion machine whose feed direction is angled in relation to the feed direction of the profile, and a crossnead comprising an extrusion tool adapted for material coating of all the outer surfaces of the profile In an advantageous embodiment of the invention, the feed direction of the extrusion machine is essentially at right angles to the feed direction of the profile The invention also includes a spirally wound thermoplastic pipe produced according to the method described The pipe comprises a spirally wound profile (preferably an extruded hollow profile of rectangular or rhomboid cross section), in which the spiral turns of profiles of the pipe are joined together by a weld seam The pipe is additionally characterized in particular in that the weld seam covers the whole of the adjoining edge surfaces of the profiles, and in that a spirally wound, band-shaped sealing film bears against those surfaces of the profiles facing towards the centre of the pipe in such a way that the sealing film overlaps the weld seam between the profiles The sealing film is preferably welded to those surfaces of the profiles facing towards the centre of the pipe The width of the sealing film is preferably greater than or equal to the width of the profiles in the longitudinal direction of the spirally wound pipe. Other embodiments and features of the invention are described in the following description of preferred embodiments and in the attached patent claims In summary, the invention makes it possible to produce spirally wound thermoplastic pipes more cost-effectively than in known techniques BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described below on the basis of illustrative embodiments and with reference to the attached drawings, in which Fig 1 shows a diagrammatic side view of an arrangement for producing spirally wound thermoplastic pipes according to the invention, Fig 2 shows a diagrammatic plan view of the arrangement in Fig 1 , Fig 3 shows a diagrammatic section through the crosshead of the extrusion station, Fig 4 shows a section of a cut-open spirally wound thermoplastic pipe according to one embodiment of the invention, Fig 5 shows an broken sectional view of a wall portion of the spirally wound thermoplastic pipe according to the invention, the band-shaped sealing film being wound in such a way that it overlaps itself, Fig 6 shows, in a sectional view similar to Fig 5, an embodiment in which the sealing film is wound spirally such that the edges of the film bear against each other without overlapping, Fig 7 is a sectional view of a wall portion of the spirally wound thermoplastic pipe according to the invention, in which the width of the sealing film is four times the width of the profiles in the longitudinal direction of the spirally wound pipe, and Fig. 8 is a sectional view similar to that shown in Fig 7, but in which four layers of sealing film are applied on the profiles. DESCRIPTION OF PREFERRED EMBODIMENTS An arrangement for producing a spirally wound thermoplastic pipe according to the invention is shown diagrammatically in Fig 1 The pipe is generally designated by reference number 1 The arrangement according to Fig. 1 is shown from above in Fig 2. In the preferred embodiment of the arrangement according to the invention shown here, an extruded hollow profile 2 of rectangular or rhomboid cross section is fed from a storage reel 25 mounted about a shaft 26 As previously stated, the profile 2 is made from a thermoplastic material suitable for the purpose, for example polyvinyl chloride (PVC), polypropylene or polyethylene The said thermoplastics can be used with or without admixture of fibres or other additives The polymer chains in the plastic can be oriented in a specific direction or cross-linked, as is the case with cross-linked polyethylene (PEX) The profile is flexible enough to allow it to be wound about a drum The profile 2 is drawn from the storage reel 25 by means of a removal device 27 which, in the example shown, comprises two belt conveyors 28, 29 between which the profile 2 is fed in the feed direction 24 to an extrusion station 20. The extrusion station 20 consists of a conventional extrusion machine 22 whose feed direction 23 according to the invention is oriented essentially at right angles to the feed direction 24 of the profile 2. The extrusion machine 22 is provided with a crosshead 25. Fig. 3 shows an extrusion tool 26 included in the said crosshead 25. The view shown in Fig. 3 is a diagrammatic sectional view of the extrusion tool 26, taken along the line Ill-Ill in Fig. 1. The extrusion tool 26 has a passage 32 through which the profile 2 passes in the feed direction 24. The passage 32 is so dimensioned that a channel 33 is formed around the profile 2 as the latter passes through the tool 26. The position of the profile 2 within the passage 32 of the tool is adjusted in a known manner and with great accuracy by means of positioning devices (not shown) so that the width of the channel 33, i.e. the distance between the outer surfaces 14 of the profile 2 and the walls 34 of the passage 32, remains the same around the profile 2. While the profile 2 is being fed through the tool 26, a thermoplastic is extruded from the extrusion machine 22 in the direction of arrow 36 through a delivery channel 37 and into the channel 33 formed around the profile 2, all the outer surfaces 14 of the profile 2, i.e. its entire periphery 4, being coated with an outer layer of weldable thermoplastic material. The extent of this layer thus corresponds in Fig. 3 to the channel 33, and it can be seen clearly in Figures 5 to 8 under reference number 3. The outer layer 3 can comprise the same type of thermoplastic as the profile 2, or it can comprise another thermoplastic with suitable properties. For example, the material of the outer layer 3 can be chosen with a view to optimum weldability and resistance to wear, while the material of the profile 2 can be chosen such that the pipe 1 has optimum annular stiffness. As can be seen from Fig. 2, the feed direction 23 of the extrusion machine 22 is angled in relation to the feed direction 24 of the profile 2. In the preferred embodiment shown in the figure, the feed direction 23 of the extrusion machine 22 is also essentially at right angles to the feed direction 24 of the profile 2. After the profile 2 in the extrusion station 20 has been coated with the outer layer 3 of weldable thermoplastic material, it is wound in spiral turns 5, 6 about a rotating drum 30 to form a pipe 1. When the profile 2 reaches the - 8 - heating device 35 can heat the sealing film 9 not with warm air, but by means of microwaves, infrared heat or conventional heating elements Fig 5 shows a sectional view of part of the wall of the pipe 1 A sealing film 9 is arranged, in accordance with the above, on those surfaces 13 of the profiles 2 facing towards the centre of the pipe 1 The centre of the pipe 1 is not shown in the figure, but is taken to be situated below the lower edge of the figure As will also be seen from the figure, the sealing film 9 in a preferred embodiment is wound spirally against those surfaces 13 of the profiles 2 facing towards the centre of the pipe 1 in such a way that adjoining spiral turns 11 , 12 are made to partially overlap each other in an overlap portion 15 The overlap portion affords double security against leakage since, as has already been stated the sealing film 9 also overlaps the weld seams 7 between the profiles 2 However, Fig 6 shows an alternative embodiment where the adjoining spiral turns 11 , 12 of the sealing film 9 are made to bear against each other without overlapping, along a boundary line 16 The thickness of the band-shaped sealing film 9 is between 0 1 and 0.5 mm, preferably 0.2 mm As the sealing film 9 is therefore thin in relation to the height of the profile 2 in the radial direction of the pipe 1 , a number of layers 10 of the said sealing film 9 are preferably wound between the drum 30 and the spirally wound profiles 2 The layers 10 are preferably between two and six in number, and in a preferred embodiment there are four layers 10 of sealing film 9 wound spirally between the drum 30 and the profiles 2 Fig 8 shows such a pipe 1 with four layers 10 of sealing film 9 The figure shows how the boundary lines 16 between different spiral turns of the sealing film 9 are placed such that the various layers 10 overlap each other. The width of the sealing film 9 is greater than or equal to the width of the profiles 2 in the longitudinal direction of the spirally wound pipe 1 This ratio can be seen from Figures 5, 6, 7 and 8 Fig 7 shows a sectional view of a pipe wall in which, in a preferred embodiment, the width of the sealing film 9 is four times the width of the profiles in the longitudinal direction of the spirally wound pipe 1 - 7 - arum 30, it is still at sucn a temperature - from the extrusion station 20 - that the thermoplastic is weldable That part of the profile 2 which has just been wound on the drum 30, i e the most recently wound spiral turn 5 is welded to that part of the profile 2 which is situated in the spiral turn 6 situated closest to the said most recently wound spiral turn 5, in such a way that a weld seam 7 is formed along the whole of the adjoining edge surfaces 8 of the profile 2 It should be noted that the weld seam 7 between the spiral turns 5, 6 arises directly upon contact between the edge surfaces 8 by means of the fact that, as has already been mentioned, the outer layer 3 of the profiles 2 retains its welding temperature from the extrusion station 20 There is therefore no addition of welding material to the weld seam 7 Fig 4 shows a spirally wound thermoplastic pipe according to the invention The pipe has been cut open to reveal the cross section of the profiles 2 As can be seen from Figures 1 and 2, the extrusion station 20 is situated at a distance from the said drum 30. As can be seen from Fig 1 the drum 30 rotates about a shaft 38 in the direction of the arrow 39. In a preferred embodiment of the invention, a band-shaped sealing film 9 of thermoplastic material is wound spirally between the drum 30 and the spirally wound profiles 2, in such a way that the sealing film 9 overlaps the weld seams 7 which are formed between the profiles 2 during the spiral winding The sealing film is fed to the drum 30 from a storage reel 40 which rotates about a shaft 41. However, in an alternative embodiment (not shown), the sealing film 9 can be fed directly from the station where it is produced. The material of the sealing film 9 is preferably one of the thermoplastics mentioned in connection with the profile 2. In the preferred embodiment, the sealing film 9 is welded, during the spiral winding, to those surfaces 13 of the profiles 2 facing towards the centre of the pipe 1 , by means of the sealing film 9 being heated to welding temperature by a heating device 35 situated in close proximity to the said drum 30 The heating device 35 is shown in Fig 1 , in which example it comprises a nozzle 42 for blowing warm air out to the sealing film 9 The warm air is indicated diagrammatically in the figure by the wavy lines 43 In the example shown the nozzle 42 also blows warm air onto the arum 30 in order to pre-heat the latter In alternative emboαiments (not snown), tne The invention is not limited to the embodiments αescribed above and shown in the attached figures, but can be freely varied within the scope of the attached patent claims. For example, the profile 2 can be fed directly from an extrusion station in which it is manufactured, instead of being fed from a storage reel 25 as shown in Fig. 1. Thermoplastic materials other than those mentioned can of course also be chosen.

Claims: PATENT CLAIMS 1 Method for producing a spirally wound thermoplastic pipe (1 ), characterized by the steps. - a flexible, elongate profile (2) is fed through an extrusion station (20) in which the profile, while being heated, is coated with an outer layer (3) of a weldable thermoplastic material along its entire periphery (4), after which - the profile (2) is wound in spiral turns (5, 6) to form a pipe (1 ) about a rotating drum (30) while the said outer layer (3) from the extrusion station (20) maintains such a temperature that the thermoplastic material is weldable, with the profile (2) in the last-wound spiral turn (5) being welded to the profile (2) in the next spiral turn (6) in such a way that a weld seam (7) is formed along the whole of the adjoining edge surfaces (8) of the profiles (2). 2 Method according to Patent Claim 1 , characterized in that the extrusion station (20) is situated at a distance from the said drum (30) 3 Method according to Patent Claim 1 or 2, characterized in tnat the profile (2) is an extruded hollow profile with rectangular or rhomboid cross section. 4 Method according to one or more of the preceding patent claims, characterized in that a band-shaped sealing film (9) of thermoolastic material is wound spirally between the drum (30) and the spirally wound profiles (2) in such a way that the sealing film (9) overlaps the weld seams (7) which are formed between the profiles (2) during the spiral winding 5 Method according to Patent Claim 4 characterized in that a number of layers (10) of the said sealing film (9) are wound spirally between the drum (30) and the spirally wound profiles (2) 6 Method according to Patent Claim 5 characterized in that between two and six layers (10) of sealing film (9) are wound spirally between the drum (30) and the spirally wound profiles (2) 7 Method according to Patent Claim 5 or 6, characterized in that four layers (10) of sealing film (9) are wound spirally between the drum (30) and the spirally wound profiles (2) 8 Method according to Patent Claim 5, 6 or 7, characterized in that the sealing film (9) is wound spirally in such a way that adjoining spiral turns (11 , 12) are made to partially overlap each other 9 Method according to Patent Claim 4, characterized in that the said sealing film (9) is welded to those surfaces of the profiles (2) facing towards the centre of the pipe (1 ), by means of the sealing film (9) being heated to a weld temperature by a heating arrangement (35) situated in close proximity 10 Arrangement for producing a spirally wound thermoplastic pipe (1) according to the method specified in one or more of the preceding claims, characterized in that the said extrusion station (20) comprises an extrusion machine (22) whose feed direction (23) is angled in relation to the feed direction (24) of the profile (2), and a crosshead (25) comprising an extrusion tool (26) adapted for material coating of all the outer surfaces (14) of the profile 11 Arrangement for producing a spirally wound thermoplastic pipe according to Patent Claim 10, characterized in that the feed direction (23) of the extrusion machine (22) is essentially at nght angles to the feed direction (24) of the profile (2) 12 Spirally wound thermoplastic pipe (2) comprising a spirally wound profile in which the spiral turns (5, 6) of profiles (2) of the pipe are joined together by a weld seam (7), characterized in that - the said weld seam (7) covers the whole of the adjoining edge surfaces (15) of the profiles (2), - a spirally wound, band-shaped sealing film (9) bears on those surfaces (13) of the profiles (2) facing towards the centre of the pipe (1 ), in such a way that the sealing film (9) overlaps the weld seam (7) between the profiles (2). 13 Spirally wound thermoplastic pipe (2) according to Patent Claim 12, characterized in that the sealing film (9) is welded to those surfaces (13) of the profiles (2) facing towards the centre of the pipe (1) 14 Spirally wound thermoplastic pipe (1 ) according to Patent Claim 12, characterized in that the width of the band-shaped sealing film is greater than or equal to the width of the profiles (2) in the longitudinal direction of the spirally wound pipe. 15 Spirally wound thermoplastic pipe (1 ) according to Patent Claim 12, characterized in that the width of the band-shaped sealing film (9) is four times the width of the profiles (2) in the longitudinal direction of the spirally wound pιpe (1). 16. Spirally wound thermoplastic pipe (1 ) according to one or more of Patent Claims 12 to 15, characterized in that a number of layers (10) of the said sealing film (9) are wound spirally between the drum (30) and the spirally wound profiles (2). 17. Spirally wound thermoplastic pipe (1 ) according to Patent Claim 16, characterized in that between two and six layers (10) of sealing film (9) are wound spirally between the drum (30) and the spirally wound profiles (2). 18. Spirally wound thermoplastic pipe (1 ) according to Patent Claim 16 or 17, characterized in that four layers (10) of sealing film (9) are wound spirally between the drum (30) and the spirally wound profiles (2). 19 Spirally wound thermoplastic pipe (1 ) according to one or more of Patent Claims 12 to 18, characterized in that the band-shaped sealing film (9) is wound spirally in such a way that adjoining spiral turns (11 , 12) are made to partially overlap each other. 20. Spirally wound thermoplastic pipe (1 ) according to one or more of Patent Claims 12 to 19, characterized in that the thickness of the band- shaped sealing film (9) is between 0.1 and 0.5 mm. 21. Spirally wound thermoplastic pipe (1 ) according to Patent Claim 20, characterized in that the thickness of the band-shaped sealing film (9) is 0.2 mm. 22. Spirally wound thermoplastic pipe (1 ) according to one or more of Patent Claims 12 to 21 , characterized in that the profile (2) comprises an extruded hollow profile with rectangular or rhomboid cross section.

Inventors: FORSELL FREDRIK, HOELSOE EINO, JAERVENKYLAE JYRI, FORSELL, FREDRIK, HOELSOE, EINO, JAERVENKYLAE, JYRI
Applicants: FORSELL FREDRIK, HOELSOE EINO, JAERVENKYLAE JYRI, UPONOR INNOVATION AB, FORSELL, FREDRIK, HOELSOE, EINO, JAERVENKYLAE, JYRI
Application year: 1999
Main classification: B29C53
IPC codes: B29C47, B29C53, B29L9, B29L23, B29L31, F16L9