Process for the continuous production of a thermally insulated corrugated pipe and thermally insulated corrugated pipe obtained thereby

Abstract

The present invention relates to a method for the continuous production of a thermally insulated corrugated pipe (1) comprising a multi-layer corrugated pipe outer casing (10) comprising a corrugated outer layer (12) and a foil layer (14), at least one media pipe (20) for conducting a fluid, and at least one foamed thermal insulation (30) arranged between the at least one media pipe (20) and the corrugated pipe outer casing (10), the method comprising the following steps: (a) introducing the at least one media pipe (20) into a film (15) forming the film layer (14) and introducing the foam-forming components (31) into the film (15) to form the foamed thermal insulation (30); (b) extruding the outer layer (12) in ring form using an extrusion device (104) through which the at least one media pipe (20) with the film (15) and the foam-forming components (31) is passed to form the foamed thermal insulation (30); (c) generating the waveform of the outer layer (12) in a corrugator (106); and (d) forming the foamed thermal insulation (30) by reaction of the foam-forming components (31) in the film (15); wherein the method is characterized according to the invention in that upon entry into the corrugator (106), the material of the outer layer (12) is in a molten state and the reaction of the foam-forming components (31) in the film (15) has reached the thread-drawing time. Furthermore, the present invention relates to a thermally insulated corrugated pipe (1) obtained by a method according to the invention.

Description

The invention relates to a method for continuously producing a heat-insulated corrugated pipe, which comprises a multilayer corrugated pipe outer jacket which comprises a corrugated outer layer and a film layer, at least one media pipe for guiding a fluid, at least one foamed thermal insulation arranged between the at least one media pipe and the corrugated pipe outer jacket, wherein the method comprises the steps of (a) introducing the at least one media pipe into a film forming the film layer and introducing the foam-forming components to form the foamed thermal insulation into the film; (b) extruding the outer layer in ring shape using an extrusion device through which the at least one media pipe with the film and the starting material is passed to form the foamed thermal insulation; (c) generating the waveform of the outer layer in a correlator and (d) forming the foamed thermal insulation by reaction of the foaming components in the film. Moreover, the present invention relates to a heat-insulated corrugated pipe obtained by such a method.Heat-insulated corrugated pipes are known in the prior art and are used in particular in short-range and district heating networks. A basic method for the continuous production of such heat-insulated corrugated pipes is disclosed in EP 0 897 788 A1. According to the method described therein, at least one medium pipe is first introduced into a film tube. Subsequently, a starting material for forming the thermal insulation is introduced into the film tube, from which the thermal insulation is formed by foaming, and using appropriate forming jaws, the corrugated structure for the outer layer is produced, which is subsequently extruded onto the corrugated surface of the film tube. In order to improve the windability of the heat-insulated corrugated tubes, which facilitates the transport of the heat-insulated corrugated tubes and enables them to be laid with small radii, it is proposed in WO 2014 / 122278 A1 to extrude the outer layer directly onto the still expanding composite made of film tube and the heat insulation and to generate the wave shape as the expansion process proceeds in a correlator by the material of the outer layer being pressed into the depressions of the correlator by the expansion of the heat insulation. Finally, WO 2019 / 214954 A1 discloses a method according to which the outer layer is guided into the correlator separately from the medium pipe with the film tube surrounding it and is provided therein with the wave shape, wherein the foaming of the thermal insulation takes place in the already wave-shaped outer layer. It is considered disadvantageous in the described methods that in the event of damage to the outer layer of the pipes obtained thereby, water, for example in the form of rainwater or groundwater, can enter the interior of the corrugated pipe and flow therein along the line. It would therefore not be ensured that a heat distribution system comprising such a corrugated tube outer jacket does not run partially or completely through water and becomes unusable in this way, which can only be eliminated with great effort and is associated with high costs. Particularly high costs for rehabilitation occur especially when large quantities of water enter a building in an uncontrolled manner due to the damaged heat distribution system. In addition, the water that has entered the heat-insulated corrugated pipe can wet through the heat-insulating layer and thus adversely affect the insulation properties of the heat-insulated corrugated pipe.At this point, the present invention uses the object of providing a method for the continuous production of a thermally insulated corrugated pipe which at least partially overcomes the disadvantages of the prior art. In particular, the method according to the invention is intended to produce a thermally insulated corrugated pipe unit which offers increased safety against the penetration of water when the outer layer is damaged. In addition, the flexibility of bending of a typical corrugated pipe should be maintained while at the same time providing high annular rigidity.These and other objects are achieved according to the invention by a method for the continuous production of a thermally insulated corrugated pipe having the features of claim 1 or by a thermally insulated corrugated pipe having the features of claim 10. Preferred embodiments of the method according to the invention and of the corrugated pipe according to the invention are described in each case in the dependent claims.According to the present invention, it has been recognized that an increased safety against the penetration of water in the event of damage to the outer layer is ensured when the film layer is circumferentially welded to the corrugated outer layer of the thermally insulated corrugated pipe. In this way, a so-called longitudinal water tightness of the heat-insulated corrugated pipe is achieved because water once has reached the corrugated pipe through the outer layer cannot flow in the longitudinal direction of the line formed with the corrugated pipe because of the circumferential welds. In order to ensure this circumferential welding of the film layer to the outer layer, in particular to the corrugation troughs of the corrugated outer layer, high temperatures and a certain pressure are required in order that the material of the film layer is pressed against the material of the outer layer and is joined thereto. According to the invention, this is achieved in that, on the one hand, the material of the outer layer is present in the molten state on entry into the rugator, as a result of which the required temperature is ensured, and, on the other hand, the reaction of the foam-forming components for the foamed thermal insulation in the film tube is already started before entry into the rugator, that is to say, for example, in the extrusion apparatus. Since the outer layer is then still in the liquid state, it can be easily joined to the film. With regard to the foaming process of the foaming components for insulation, various characteristic periods of time can be specified. This is, on the one hand, a starting time which extends from the beginning of the mixing to the first volume increase. Moreover, the term "rise time" is used, which is the time from the beginning of mixing of the foaming components to the completion of the volume increase of the foam, a thread drawing time during which threads can be drawn from the ascending reaction mixture by dipping a rod, and finally a holding time during which the foam volume increases even further despite the completion of the reaction. During the thread drawing time, chemical cross-linking takes place in the thermal insulation formed. The foam forming the thermal insulation loses its liquid properties and changes into a viscoelastic state. The further increase in the foam volume generates a pressure in the limited pipe volume, which pressure is used according to the invention to press the film tube against the still molten outer layer and thus to enable the welding of the two layers. Thus, according to the invention, welding pressure and welding temperature for welding the film tube to the outer layer are simultaneously ensured.Accordingly, the present invention is to provide a method for continuously producing a heat insulated corrugated pipe comprising a multilayer corrugated pipe outer shell comprising a corrugated outer layer and a film layer, at least one media pipe for guiding a fluid, at least one foamed thermal insulation disposed between the at least one media pipe and the corrugated pipe outer shell, the method comprising the steps of (a) introducing the at least one media pipe into a film forming the film layer and introducing the foaming components to form the foamed thermal insulation into the film; (b) extruding the outer layer in a ring shape using an extrusion apparatus through which the at least one media pipe having the film and the foaming components is passed to form the foamed thermal insulation; (c) generating the waveform of the outer layer in a rugator and (d) forming the foamed thermal insulation by reaction of the foaming components in the film, the method being characterized according to the invention in that, on entering the rugator, the material of the outer layer is in the molten state and the reaction of the foaming components in the film has reached the filament draw time. Moreover, the present invention provides a heat insulated corrugated tube obtained by such a method.As used herein, the phrase "the reaction of the foaming components in the film is complete" means that at least 98% of the originally present foaming components have reacted with each other.With respect to the method of the present invention, it may be desirable that the reactivity of the foaming components to form the foamed thermal insulation is adjusted so that, depending on the speed of the manufacturing line for the corrugated pipe and the temperature conditions, the stringing time of the foaming reaction has just started upon entering the rugator. It has been found that at the time of the beginning of the thread drawing time the foam volume has reached between 70% and 80% of its final value. This has proven to be an ideal range of values in order that the film layer is pressed against the outer layer for welding, in order to ensure the welding between the outer layer and the film in the region of the corrugated tube troughs.It may also be helpful that, upon entering the correlator, the material of the outer layer is in the molten state and the expansion of the foaming components for foamed thermal insulation in the film still proceeds. These two features can also form the subject matter of an independent claim, for example in combination with method steps (a) to (d). As the expansion proceeds, the film is pressed in the region of the corrugation troughs of the outer jacket, so that the circumferential welding is ensured in this region.It has also proved to be useful if the reactivity of the starting material for forming the foamed thermal insulation is adjusted such that, depending on the speed of the production line for the corrugated pipe and the temperature conditions, the foaming reaction on entry into the correlator has taken place to such an extent that a foam volume has reached a value of at least 70% of the final foam volume. Preferably, the foam volume has reached a value of at most 90% of the final foam volume. This has proven to be an ideal range of values, so that the film layer is pressed against the outer layer for welding. A value in the range from 75% to 80% has proven to be particularly preferred.As a rule, a polyurethane foam is formed by the foaming reaction. For this purpose, a mixture is preferably used for forming the foamed thermal insulation, in particular a two-component mixture which comprises in particular a polyol component and a polyisocyanate component. In addition, blowing agents, for example pentane or cyclopentane, and also activators, stabilizers, cell regulators, fillers, reinforcing materials and other additives can also be present in the mixture. The reactivity of the mixture is adjusted in particular such that foaming is started even before it enters the rugator, for example in the extrusion device of the outer jacket, but the thread drawing time is reached when it enters the rugator. An example of a polyurethane system useful in the process of the invention is Elastopor® H 2130 / 38 (obtained from BASF SE, 67038 Ludwigshafen). Other possible foamable polyurethane systems are known from EP 0 826 706 A2, which is explicitly referred to herein in connection with the components for forming a polyurethane foam and corresponding additives and the use thereof. The adjustment of the reactivity of the foaming components, in particular their thread drawing time and pressing time, is familiar per se to the skilled worker and is preferably carried out by adding appropriate additives.The foam of the foamed thermal insulation can preferably be of closed-cell configuration. This prevents further transport of water in the longitudinal direction of the corrugated pipe in the event of damage to the corrugated pipe outer jacket according to the invention. Preferably, the PUR foam has a density (about 0.04 to 0.10 kg / l) and a low thermal conductivity (about 0.02 to 0.04 W / mK). In this way, good thermal insulation is achieved by the foam.It can also be helpful if the reaction of the foam-forming components in the film tube of the foamed thermal insulation is started in the extrusion device or has already been started. The high temperatures inside the extrusion apparatus help to achieve the fiber draw time of the polymerization reaction of the foaming components until entering the correlator.In the present invention or the method for continuously producing a thermally insulated corrugated pipe having at least one media pipe, the at least one media pipe is first produced and a film is introduced into which the foam-forming components for forming the foamed thermal insulation are subsequently also introduced. During the extrusion of the outer layer in ring shape using an extrusion device, the at least one media tube with the film and the starting material is passed through to form the foamed thermal insulation. For this purpose, a corresponding guide for the film can be used in the extrusion device. The film is still open on one side and is welded in the longitudinal direction after the foam-forming components have been introduced. A film tube is thereby formed. Then, the as yet unwelled outer layer in the molten state enters a correlator in which the wave form of the outer layer is generated.In preferred embodiments of the present invention, the polymeric material of the outer layer is a polyolefin. According to the invention, the use of a polyethylene (preferably HDPE, MDPE or LDPE), a polypropylene or a crosslinked polyethylene is preferred.The corrugation of the outer layer in the corrugation device is a very easily controllable process, so that a well controllable shaping of the corrugated outer layer becomes possible, even with a large corrugation depth. For shaping the outer layer, a vacuum rugator is preferably used, in which a reduced pressure prevails between the shaped parts of the rugator and the outer layer to be shaped, by means of which the still liquid outer layer is pressed against the forming jaws and is thus shaped.It is desirable that the film of the film tube pressed on the inside by the continuing expanding foam onto the outer layer is welded to the outer layer under the action of the process heat present. This is the case with a film formed from polyethylene (PE), in particular with a film tube which comprises foamed polyethylene. In an advantageous embodiment, the polyethylene foam is laminated with a polyethylene film at least on its side facing the outer layer. Such a laminated-on film can easily be melted and welded to the outer layer. For this purpose, the thickness of the laminated-on polyethylene film is preferably 25 μm to 120 μm, in particular 40 μm to 70 μm. In order to avoid premature melting of the laminated-on polyethylene film, for example in the extrusion device, this mineral filler can comprise in a proportion of 3% by weight to 30% by weight, preferably 5% by weight to 20% by weight, in each case based on the total weight of the laminated-on polyethylene film as 100% by weight.Examples of mineral fillers which can be used are magnesium calcium carbonate hydrate, calcium carbonate, magnesium carbonate, calcium sulfate, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, aluminum oxide, aluminum hydroxide, hydrotalcite, mica, silicates, quartz, talc, titanium dioxide, wollastonite or mixtures of two or more of these. These mineral fillers can be provided with a sizing and / or an adhesion promoter or adhesion promoter system.The statements relating to the method according to the invention relating to the corrugated heat insulation tube according to the invention correspond.In preferred embodiments of the thermally insulated corrugated pipe according to the invention, the at least one media pipe is a pipe made of a polymer material, in particular of a thermoplastic, in particular of a polyolefin. The at least one medium tube is particularly preferably a tube made of a polypropylene, a polyethylene or a crosslinked polyethylene, wherein tubes made of crosslinked polyethylene are particularly preferred.It can also be advantageous if the thermally insulated corrugated pipe according to the invention comprises 2, 3 or 4 media pipes in the corrugated pipe outer jacket according to the invention. As a result, the heat-insulated corrugated pipe according to the invention can be adapted to the specifications of the customer or to the technology to be applied. In this way, in particular the transport capacity of such a thermally insulated pipe can be increased by the simultaneous transport of a high fluid volume through a plurality of media pipes and thus correspondingly also the amount of heat transferred.The thermally insulated corrugated pipe according to the invention can comprise at least one barrier layer on or in the protective layer, on or in the at least one insulating layer or on or in the at least one media pipe, which barrier layers are intended in particular to inhibit or prevent the diffusion of oxygen or water vapor or hydrocarbons. These barrier layers may contain in particular polymeric, metallic or inorganic material.All plastic materials in the heat-insulated corrugated pipe according to the invention can also be used in this case in the form of materials obtained by a recycling process.The present invention will be explained in detail below with reference to the embodiments illustrated in the figures. Figure shows FIG. 1 is a schematic partial longitudinal sectional view of a heat-insulated corrugated pipe according to an embodiment of the present invention; and FIG. 2 shows a schematic, partially cut-away illustration of an apparatus for carrying out the method according to the invention.FIG. 1 shows a detail from a schematic longitudinal sectional illustration of a thermally insulated corrugated pipe 1 according to the invention in accordance with an embodiment of the present invention, as can be produced continuously in any desired length by the production method. The outer diameter of such tubes is in particular in the range from 70 mm to 350 mm. The heat-insulated corrugated pipe 1 according to the invention comprises a multi-layered corrugated pipe outer jacket 10 which comprises a corrugated outer layer 12 and a film layer 14, a media pipe 20 for guiding a fluid, and a foamed thermal insulation 30 arranged between the media pipe 20 and the corrugated pipe outer jacket 10.According to the embodiment shown in Fig. 1, the corrugated outer protective layer 12 is made of high density polyethylene (HDPE). In the embodiment shown, the film layer 14 is a 5 mm thick foam layer 16 made of foamed polyethylene, onto which a polyethylene film 18 having a thickness of 60 μm is laminated. The polyethylene film 18 contains wollastonite as a mineral filler in a proportion of 20% by weight, based on the total weight of the laminated-on polyethylene film, as 100% by weight. According to this embodiment, the media tube 20 is formed as a tube of cross-linked polyethylene (PE-X). It comprises a lumen 51 for receiving, storing or conducting the fluid. On the outer surface of the media tube 20 a heat insulation 30 is arranged, which rests with its inner surface against the outer surface of the media tube 20. The thermal insulation 30 is formed from a foamed, closed-cell polyurethane. At this time, the thermal insulation 30 was produced by a polymerization reaction of the components 31 forming the polyurethane, foaming directly on the media pipe 20.FIG. 2 schematically shows a detail of a device 100 for carrying out the method, on the basis of which the method according to the invention for producing the thermally insulated corrugated pipe 1 is explained in detail.A non-illustrated unwinding device initially unwinds the medium pipe 20. The medium pipe 20 is guided via a guide to a corresponding station in which a film 15 forming the film layer 14 is wound around the medium pipe 20 in a known manner. In this case, the film 15 initially forms a tube which is open on one side in the longitudinal direction and surrounds the medium tube 20. From the open side, the foam-forming components 31 for forming the foamed thermal insulation 30 are introduced from a mixing head 102 into the film 15. The film 15 is then welded in the longitudinal direction to form a film tube surrounding the medium tube 20. Now, in the embodiment shown, the expansion of the foam-forming components 31 starts in the film tube formed from the film 15.An extrusion device 104 extrudes the outer layer 12 in ring shape around the media tube 20 with the film 15 and the foaming components 31 Due to the temperatures prevailing inside the extrusion device 104, the reaction of the foaming components 31 accelerates, the foam volume continues to increase. The film layer 14 does not yet melt in the extrusion device due to its proportion of mineral filler. If necessary, appropriate cooling can also be provided. The material of the outer layer 12 exits the extrusion device 104 and, in the still molten state, passes directly into the mold parts of a correlator 106. In the correlator 106, the outer layer 12 receives its desired wave form. Wave-shaped molded parts of the correlator 106 close over the still liquid material of the outer layer 12 and then form a shape which tracks the outer layer 12. A vacuum draws the extruded material of the outer layer 12 against the walls of the mold parts and thus obtains the wave shape predetermined by the mold parts.The reaction rate for the foaming components 31 is adjusted so that the reaction of the foaming components 31 in the film 15 at the time of entering the correlator 106 has reached the filament drawing time. However, the expansion of the foaming components 31 still proceeds. The reaction of the foaming components 31 then enters the so-called hold-down time during which the foam volume increases even further despite the reaction being concluded or substantially concluded. In the embodiment shown, the foaming components 31 have reached a value of 78% of their fully expanded volume on entering the correlator 106. In this case, the so-called thread drawing time of the polyurethane foam forming the thermal insulation 30 has just been reached. As a result of the continued expansion of the foaming components 31, an overpressure is generated in the limited volume. The excess pressure presses the film layer 14 against the outer layer 12. This is still in the molten state and has a high temperature. As a result, the film layer 14, in particular the laminated-on polyethylene film 18, is welded circumferentially to the outer layer 12 in the region of the corrugation valleys thereof.Depending on the length of the manufacturing apparatus 100 from the mixing head 102 to the entrance into the correlator 106, the temperature history in this range, and the manufacturing speed for the heat-insulated corrugated pipe 1 (2.5 m / min to 8 m / min), the thread drawing time of the mixture forming the heat insulator 30 needs to be adjusted. This adjustment can be effected by adding appropriate activating agents or retarding agents, as required, and is familiar to the skilled person.In the correlator 106, the material of the outer layer 12 solidifies, which is welded circumferentially to the polyethylene film 18 on the inner side in the region of the wave troughs. As a result, the heat-insulated corrugated pipe 1 obtained by the method according to the invention has a sufficient degree of longitudinal water tightness so that water once it has entered the inside of the pipe cannot be transported further in the longitudinal direction of the pipe 1. The expansion process of the foam-forming components 31 also ends to form the finished thermal insulation 30. After leaving the correlator, the finished thermally insulated corrugated tube 1 is cooled and wound onto a tube reel.It is understood that the features explained above can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the present invention.The present invention has been explained in detail by way of example with reference to the embodiments illustrated in the figures. It is to be understood that the present invention is not limited to these embodiments. Rather, the scope of the present invention will be apparent from the appended claims.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedEP 0 897 788 A1

[0002] WO 2014 / 122278 A1

[0002] EP 0 826 706 A2

[0011]

Claims

A method for continuously producing a heat insulated corrugated pipe (1) comprising a multi-layered corrugated pipe outer jacket (10) comprising a corrugated outer layer (12) and a film layer (14), at least one media pipe (20) for guiding a fluid, and at least one foamed thermal insulation (30) arranged between the at least one media pipe (20) and the corrugated pipe outer jacket (10), the method comprising the following steps: (a) introducing the at least one media pipe (20) into a film (15) forming the film layer (14) and introducing the foam-forming components (31) into the film (15) to form the foamed thermal insulation (30); (b) extruding the outer layer (12) in a ring shape using an extrusion apparatus (104) through which the at least one media tube (20) having the film (15) and the foaming components (31) is passed to form the foamed thermal insulation (30); (c) creating the wave shape of the outer layer (12) in a rugator (106); and (d) forming the foamed thermal insulation (30) by reaction of the foaming components (31) in the film (15); characterized in that on entering the rugator (106), the material of the outer layer (12) is in the molten state and the reaction of the foaming components (31) in the film (15) has reached the filament draw time.Method according to claim 1, characterised in that the reactivity of the foam-forming components (31) for forming the foamed thermal insulation (30) is adjusted in such a way that, depending on the speed of the production line for the corrugated pipe (1) and the temperature conditions, the thread drawing time of the foam-forming reaction has just begun when it enters the rugator (106).Method according to claim 1 or claim 2, characterised in that the reactivity of the foam-forming components (31) for forming the foamed thermal insulation (30) is adjusted in such a way that, depending on the speed of the production line for the corrugated pipe (1) and the temperature conditions, the foaming reaction on entry into the rugator (106) has taken place to such an extent that a foam volume has reached a value of at least 70% of the final foam volume.Method according to one of Claims 1 to 3, characterized in that the reaction of the foam-forming components in the film tube of the foamed thermal insulation (30) is started or has already been started in the extrusion apparatus (104).Method according to one of Claims 1 to 4, characterized in that the waveform of the outer layer (12) is generated in the correlator (106) using a reduced pressure.Method according to one of Claims 1 to 5, characterized in that the film tube comprises foamed polyethylene.Method according to claim 6, characterised in that the polyethylene foam is laminated with a polyethylene film at least on its side facing the outer layer (12),Method according to claim 7, characterised in that the laminated-on polyethylene film comprises mineral fillers in a proportion of 3 wt.% to 30 wt.%, based on the total weight of the film layer (14), as 100 wt.%.Method according to one of Claims 1 to 8, characterized in that the foamed thermal insulation (30) is formed from a closed-cell polymer foam, in particular from a closed-cell polyurethane foam.A heat insulated corrugated pipe (1) obtained by a method according to any one of claims 1 to 9.

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