Pipe with flame-retardant layer

Abstract

The invention relates to a pipe (1) comprising a flame-retardant layer (2) and an outer layer (3), where the outer layer (3) surrounds the flame-retardant layer (2), where the flame-retardant layer (2) comprises a thermoplastic and expanded graphite particles, where the expanded graphite particles are configured to expand above a starting temperature, where the expanded graphite particles are in an unexpanded state, and where the expanded graphite particles are in a non-expanded state. Wherein the outer layer (3) comprises a thermoplastic, characterized in that the outer side of the pipe (1) or the outer side of the outer layer (3) has an average roughness Ra of at most 200 or 100 or 50 [mu] m.

Description

Technical Field

[0001] The present invention relates to a pipe, comprising a flame retardant layer and an outer layer, wherein the outer layer surrounds the flame retardant layer, wherein the flame retardant layer comprises thermoplastic plastic and expanded graphite particles, and wherein the outer layer comprises thermoplastic plastic. The present invention also relates to a fluid pipeline having such a pipe and the use of the pipe or the fluid pipeline. Background Art

[0002] A pipe of this type is known from EP 3 271 170 B1, wherein, according to an embodiment, the flame retardant layer or reinforcing layer is the outermost layer. The reinforcing layer contains fibers, which can consist of aramid, for example, or can be glass fibers. The fibers are connected to each other to form a fabric and thus a non-uniform layer, which protects the flame retardant layer located below it. The flame retardant layer prevents the pipe from catching fire or heating up for a period of a few seconds or minutes. The flame retardant layer is about 1.5 mm thick and contains expanded graphite, the average particle size of the particles of which is 0.2 mm to 0.4 mm. The pipe is plugged onto the pipeline connection by force locking.

[0003] However, a disadvantage of the known pipes is the ability to provide a particularly durable fluid connection. It has been found that the mechanical connection between the known pipes and the associated line connections, in particular in demanding environments such as in land vehicles, still needs to be improved. In particular, vibrations of land vehicles can loosen the force connection between pipe and line connection over the years. The increasing embrittlement of the pipe material is also a factor leading to loosening, which can also significantly weaken the force connection after a few years. In addition to the usual material aging, high temperatures or temperature fluctuations acting on or in land vehicles on the pipes can also lead to embrittlement. Finally, land vehicles are exposed to moisture and therefore to deicing salts, etc., which can also have an adverse effect on the force connection between pipe and line connection. Summary of the invention

[0004] The invention is therefore based on the object of providing a pipe which - even under unfavorable conditions, in particular in the case of land vehicles - enables a particularly durable or secure connection to a line connection and which is heat-resistant for as long as possible in the event of a fire.

[0005] This object is achieved by a pipe, comprising a flame retardant layer and an outer layer, wherein the outer layer surrounds the flame retardant layer, wherein the flame retardant layer contains a thermoplastic and expanded graphite particles, wherein the expanded graphite particles are configured to expand above a starting temperature, wherein the expanded graphite particles are in an unexpanded state, wherein the outer layer contains a thermoplastic, wherein the outer side of the pipe or the outer side of the outer layer has an average roughness Ra of a maximum of 200 or 100 or 50 μm.

[0006] The invention is based firstly on the recognition that welding a pipe to a pipeline connection allows a significantly better or more permanent connection between the two components. It has been found that flame-retardant layers with expanded graphite are not suitable for welding to pipeline connections, and textile layers and thus inhomogeneous layers are even less suitable for welding to pipeline connections.

[0007] The invention is also based on the recognition that known flame retardant layers with expanded graphite have too high a surface roughness or too high an average roughness. Since the particles of expanded graphite cause a great deal of roughness, this significantly increases the scrap rate, especially in the preferably filigree laser welded connections between pipes and line connections. It is therefore very advantageous for laser welded connections if the surfaces that meet one another form a substantially ideal positive fit, so that the circumferential weld seam is virtually continuous in the entire connection between pipe and line connection as far as possible.

[0008] Furthermore, it has been found that for laser welding connections, the material of the line connector or the material of the pipe should be substantially transparent to the laser radiation, while the material of the components located inside in each case absorbs the laser radiation to a large extent. At the same time, automobile manufacturers often require line connectors and pipes that are dyed black. Special dyes meet the requirements of transparency to the (near infrared) laser beam on the one hand and the requirement of appearing black in the visible spectrum on the other hand. However, these special dyes are relatively expensive, so they are mainly used for line connectors. Therefore, the amount of material used for line connectors is usually less than that for pipes.

[0009] The invention is therefore based on the recognition that the pipe is particularly preferably inserted into the line connection so that the outer surface of the pipe is preferably welded to the inner surface of the line connection. It has been found that a relatively low average roughness of the outer side of the pipe enables a particularly good connection, in particular a welded connection and very particularly a laser welded connection. This is preferably achieved in that the outer layer always contains small particles and / or the thermoplastic plastic of the outer layer is preferably formed uniformly. Plastics with non-uniform formations are, for example, textile layers or foam materials. The layer arrangement of the pipe according to the invention thus makes it possible to achieve a heat-resistant pipe that enables a particularly durable connection to the line connection. As a result, the objects mentioned at the beginning are achieved.

[0010] The term “average roughness” preferably refers to the arithmetic mean roughness according to DIN EN ISO 4287:2010 and DIN EN ISO 4288:1998. To detect the measuring section, the measuring device is guided in the circumferential direction of the tube, optionally making a plurality of axially offset revolutions or a helical run.

[0011] According to a very preferred embodiment, the outer layer has particles or cavities or filled cavities with a radial average size of at most 200 or 150 or 100 or 50 μm in the cross section of the tube (1), or no particles or cavities or filled cavities at all. This contributes to a low average roughness. For determination, for example, a 10 mm long tube section can be examined, in particular by μCT. If fewer than 100 or 50 or 20 or 10 particles / cavities / filled cavities with a radial size of at least 5 or 2 or 1 μm are found, the criterion of "no particles at all" is considered to be met.

[0012] According to a very preferred embodiment, the thermoplastic of the outer layer is formed uniformly over the entire cross section of the outer layer. This improves the weldability of the outer layer. The term "uniform" preferably refers to a structure having only one internal and only one external, completely intentionally produced interface in the cross section. For example, individual, also very small shrinkage holes (e.g. sub-millimeter) are not produced completely intentionally. In contrast, foam materials have completely intentionally produced bubbles and therefore have internal interfaces. Similarly, additive particles are particles that are added completely intentionally, so that in the case of additive particles a large number of intermediate interfaces can also be found between the internal interface and the external interface of the layer. Similarly, if the thermoplastic of the outer layer has the form of a fabric or a fabric layer, it is also not formed very uniformly over the entire cross section of the outer layer.

[0013] The same situation applies to the case where the outer layer in the form of a fabric is additionally impregnated with another plastic. The fabric layer impregnated in this way may not have any particles or cavities or filled cavities, as long as the cast material and the fabric material are regarded as a coherent plastic structure, relative to which the particles or cavities or filled cavities are defined. The particles or filled cavities may be composed of materials different from the plastic. The particles may be mineral in particular, and the filled cavities may contain gas, especially air. However, if there is a complete lack of particles or cavities or filled cavities, a porous plastic layer filled with another plastic may still exist. This includes in particular a fabric layer impregnated with a thermoplastic. However, these layers do not contain a thermoplastic uniformly formed over the entire cross section of the outer layer. Preferably, if a maximum of 100, 50, or 20 structures are found inside a 10 mm long pipe section, the size of which is preferably at least 5, 2, or 1 μm (preferably according to a μCT image), the thermoplastic is uniformly formed.

[0014] It is particularly preferred that the pipe is of one-piece construction. Preferably, the outer layer is irreversibly connected to the flame-retardant layer directly or indirectly via one or more layers connected in between. The individual layers of the pipe are thus firmly connected to one another and ensure corresponding mechanical stability. In order to check the irreversible connection of the individual layers of the pipe, it is advantageous to check the middle section of the pipe after separating and removing any pipeline joints. For example, if the outer protective tube can be pulled out of the pipe, the layer or layers of the protective tube do not belong to the pipe or inner pipe located therein. For example, it is possible to connect the pipe or inner pipe to the pipeline joint in a material-locked manner, while the outer protective tube is not connected to the pipe in a material-locked manner, but to the pipeline joint. In these cases, the outer protective tube and the pipe or inner pipe can in principle also be indirectly connected to one another in a material-locked manner via the one or more pipeline joints. In the context of the invention, a pipe is one-piece only if, when separating the intermediate section of the pipe which is detached at will when removing the line connection, the layers can only be separated from one another irreversibly and thus in a destructive manner. For example, if a pipe or an inner pipe with an outer protective tube is cut off from these line connections, the pipe is not one-piece in any case if the protective tube can be pulled out of the pipe or inner pipe by hand and preferably also pushed back on.

[0015] According to a preferred embodiment, the outer layer is the outermost layer of the pipe, in particular the outermost layer of a one-piece pipe. It is possible that a one-piece pipe or inner pipe has an outer layer and is simultaneously surrounded by a protective tube pushed on. The outer layer of the pipe or inner pipe is then also the outermost layer of the one-piece pipe or inner pipe, since the protective tube can be pulled out of the pipe or inner pipe when the line connection is separated and removed.

[0016] It is particularly advantageous if the flame retardant layer has a layer thickness of at most 1.5 or 1.0 or 0.7 or 0.5 mm. This prevents the pipe from becoming too thick and therefore too inflexible during the bending to be performed. It is advantageous if the flame retardant layer has a layer thickness of at least 0.05 or 0.07 or 0.10 mm. This prevents the layer from tearing.

[0017] Very preferably, the outer layer has a layer thickness of at least 0.06 or 0.08 or 0.10 mm. Otherwise, the following situation may occur, that the flame retardant layer may tear due to the expanded graphite particles during the extrusion process, with the result that the flame retardant layer is not configured to cover the surface. Advantageously, the layer thickness of the outer layer is at most 1.0 or 0.8 or 0.6 mm. This avoids the pipe from becoming too thick and therefore too inflexible when bending to be performed. Very preferably, the layer thickness of the outer layer is configured so that it compensates for the unevenness of the flame retardant layer located below it. Preferably, the superimposed layer thickness of the outer layer and the flame retardant layer is at least 0.15 or 0.2 or 0.25 or 0.3 mm. Suitably, the superimposed layer thickness obtained by the layer thickness of the flame retardant layer and the layer thickness of the outer layer totals a maximum of 2.0 or 1.5 or 1.0 mm.

[0018] Advantageously, the weight proportion of expanded graphite particles based on the flame retardant layer is at least 1 or 3 or 5 or 7 or 9 weight %. Conveniently, the weight proportion of expanded graphite particles based on the flame retardant layer totals a maximum of 50 or 40 or 30 weight %. It has been found that an excessive weight proportion of expanded graphite particles leads to excessive unevenness or excessive brittleness.

[0019] According to a preferred embodiment, the expanded graphite particles in the flame retardant layer have a radial average height of at most 200 or 150 or 100 or 70 μm in the cross section of the tube. This ensures that the average roughness on the outside of the tube or on the outside of the outer layer does not become too large. Advantageously, the expanded graphite particles in the flame retardant layer have a radial average height of at least 10 or 20 or 30 μm in the cross section of the tube. This ensures that the expansion rate of the expanded graphite particles does not become too small.

[0020] Advantageously, the expanded graphite particles of the flame retardant layer have a starting temperature of at least 130 or 150 or 170 or 190 or 210 or 230° C. Suitably, the starting temperature of the expanded graphite particles is particularly matched to the melting temperature of the thermoplastic of the flame retardant layer. Preferably, the starting temperature of the expanded graphite particles is at least 10 or 20 or 30° C. higher than the melting temperature of the thermoplastic of the flame retardant layer.

[0021] Preferably, the expansion rate of the expanded graphite particles of the flame retardant layer is at least 10 or 20 or 30 cm 3 Advantageously, the expansion rate of the expanded graphite particles of the flame retardant layer is at most 350, 250, 200 or 150 cm 3 / g. It has been found that the very large expansion rate of such expanded graphite particles requires a size of the expanded graphite particles that is too large for the layer thickness of the tube. The invention is based on the recognition that, on the one hand, in particular 100 cm 3 An expansion ratio of about 1000 Å / g is sufficient for expansion, and on the other hand, sufficiently small expanded graphite particles can be achieved.

[0022] Preferably, the pipe contains an auxiliary flame retardant, wherein the auxiliary flame retardant preferably acts as a diluent gas or diluent oxygen, wherein the auxiliary flame retardant is preferably an inorganic flame retardant. It can be achieved that the flame retardant layer is accordingly supported additionally or even synergistically by the auxiliary flame retardant. It is particularly preferred that the auxiliary flame retardant is ammoniacal and, for example, contains ammonium phosphate, ammonium sulfate and / or ammonium polyphosphate. It is possible that the auxiliary flame retardant is located in the flame retardant layer and / or the outer layer. It is particularly preferred that the auxiliary flame retardant is contained only in the flame retardant layer.

[0023] Suitably, the pipe comprises at least one further layer, preferably an inner layer. This allows for a complex pipe structure. It is possible that the pipe has a plurality of further inner layers. Preferably, the flame retardant layer surrounds the at least one inner layer. It is possible that the flame retardant layer rests against the at least one inner layer. The at least one further layer, preferably the inner layer, can be connected to the flame retardant layer in a material-locked manner. The inner layer can be the innermost layer. It is possible that one or more further layers are arranged between the innermost layer and the flame retardant layer. Advantageously, an isolation layer is arranged between the innermost layer and the flame retardant layer, wherein the isolation layer is preferably used for spatial decoupling of the flame retardant layer and the innermost layer.

[0024] Preferably, the at least one inner layer comprises a thermoplastic. Thus, coextrusion is ensured even in the case of at least one inner layer. The thermoplastic of the at least one further inner layer may be a polyamide, a polyester, a polyolefin, a polyurethane or a thermoplastic elastomer. The polyester may in particular be polyethylene terephthalate (PET). Possibly, a barrier layer is arranged between the further inner layer and the flame retardant layer. The barrier layer may comprise, for example, ethylene vinyl alcohol copolymer (EVOH) or a fluoropolymer. Advantageously, a / the insulating layer is arranged between the barrier layer or the innermost layer and the flame retardant layer.

[0025] Preferably, the tube is produced at least partially and preferably completely by coextrusion.

[0026] The thermoplastic plastic of the flame retardant layer and / or the thermoplastic plastic of the outer layer can be polyamide, polyester, polyolefin, polyurethane, thermoplastic elastomer or a blend of the above plastics. PET is particularly suitable as polyester.

[0027] According to a very preferred embodiment, the thermoplastic of the outer layer comprises a thermoplastic elastomer, preferably a thermoplastic vulcanizate, and particularly preferably Santoprene. The thermoplastic vulcanizate comprises EPDM particles in a polypropylene matrix. Very preferably, the thermoplastic of the flame retardant layer is a polyolefin, and preferably polypropylene. According to a preferred embodiment, the pipe comprises two inner layers, and preferably only two inner layers. Advantageously, the innermost layer comprises a thermoplastic, preferably a thermoplastic elastomer, further preferably a thermoplastic vulcanizate and particularly preferably Santoprene. Very preferably, the second inner layer is arranged between the innermost layer and the flame retardant layer and is an isolating layer. Advantageously, the isolating layer comprises a thermoplastic, preferably a polyolefin and particularly preferably polypropylene. It is particularly advantageous that all layers of the pipe comprise a common plastic, preferably polypropylene. The common plastic of all layers is preferably used to protect the layer composite particularly well from delamination. Polypropylene materials are particularly suitable as barrier materials against aqueous solutions, for example water-glycol solutions, so that polypropylene composites are particularly suitable for use as heat exchanger tubes.

[0028] Preferably, the fluid pipeline comprises at least one pipe according to the present invention as described above and at least one pipeline connector. Preferably, the pipe and the at least one pipeline connector are welded together. A particularly durable fluid connection is thereby achieved. Advantageously, the pipeline connector contains a thermoplastic. It is particularly preferred that the thermoplastic of the pipeline connector is a plastic selected from the group consisting of "polyamide, polyester, polyolefin, polyurethane, thermoplastic elastomer", or a blend of two or more plastics selected from the above group. Preferably, the plastic of the pipeline connector belongs to the same plastic group as the thermoplastic of the outer layer and / or the thermoplastic of the inner layer. For example, if the thermoplastic of the outer layer is polyamide, the thermoplastic of the pipeline connector is preferably also polyamide. Very particularly preferably, the thermoplastic of the pipeline connector and the thermoplastic of the outer layer and / or the inner layer belong to the same plastic type, for example PA6 or PA11 or PA12. It is possible that the thermoplastic of the pipeline connector and the thermoplastic of the outer layer and / or the inner layer come from the same material storage container.

[0029] It is very particularly preferred that the pipe and the line connection are welded together and preferably connected to one another by laser welding. It is possible that the pipe and the line connection can be connected to one another by rotational friction welding or mirror welding. Preferably, the pipe is inserted into the connecting section of the line connection. It is possible that the pipe is sleeved onto the connecting section of the line connection. Suitably, the connecting section comprises at least one circumferential weld seam. It is possible that the connecting section has two or more circumferential weld seams. It is possible that the connecting section of the line connection comprises an inner weld seam and an outer weld seam, which connect the connecting section of the line connection to the pipe.

[0030] The pipeline joint preferably includes a coupling body. Advantageously, the coupling body is constructed in one piece, and particularly preferably integrally. The term "integrally" preferably means that it is prepared by one-shot injection molding. The coupling body preferably includes a coupling section, which is used for a mating part to be coupled to the pipeline joint. The mating part is preferably a plug-in part inserted into the pipeline joint. The coupling body is advantageously constructed so that the mating part can be (preferably reversibly) inserted into the coupling section. The coupling body preferably includes a / the connection section for connecting to the pipe. The connection section can be constructed for inserting and / or putting on the pipe. For example, if the connection section is constructed as a surrounding groove, the pipe is inserted into the surrounding groove, and the pipe is simultaneously put on the inner wall of the surrounding groove and inserted into the outer wall of the surrounding groove.

[0031] The pipeline joint can have a clamping part in particular. The clamping part can be constructed in a roughly U-shaped manner and have a U base and two U legs, for example. According to one embodiment, the clamping part can be constructed completely around the pipe. The fitting can have a locking element, which is constructed, for example, as a surrounding flange or a surrounding groove. Advantageously, during the process of inserting the fitting into the pipeline joint, the locking element of the fitting or the plug-in part is locked with the clamping part of the pipeline joint. According to one embodiment, the coupling body can be designed as a two-piece and have a connecting part and a coupling part. It is possible that the connecting part and the coupling part are connected to each other by a locking connection or by a threaded connection. The pipeline joint suitably includes a sealing part. For example, the sealing part can have one or two sealing rings made of an elastic material.

[0032] The purpose mentioned at the beginning is achieved by the use of the pipe according to the invention or the fluid pipeline according to the invention in a land vehicle and in particular in an electric vehicle. The pipe or fluid pipeline is preferably used for cooling, particularly preferably for cooling the battery of the electric vehicle drive. It is particularly preferred that the pipe or fluid pipeline is used to guide an aqueous solution and in particular a water-glycol solution. The pipe or fluid pipeline can be used, for example, as an introduction pipeline for a pipeline system leading to the battery of the electric vehicle drive. It is very particularly advantageous that the pipe or fluid pipeline is configured to further maintain the cooling time of the battery of the electric vehicle drive by a few seconds or minutes compared to a conventional pipe or fluid pipeline without a flame-retardant layer, thereby correspondingly reserving more escape time or rescue time for the vehicle occupants. Here, the cooling of the battery of the electric vehicle is particularly critical, because excessively high battery temperatures can cause the battery to catch fire more quickly.

[0033] The pipe according to the invention or the fluid line according to the invention is schematically illustrated below with reference to the drawings of exemplary embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In the figure:

[0035] Figure 1 shows a cross-sectional view of a tube according to the invention,

[0036] Figure 2 A longitudinal section through a fluid line according to the invention is shown, the fluid line comprising Figure 1 Pipes and pipeline connectors with inserted fittings,

[0037] Figure 3 A front view showing the clamp of the pipeline joint, and

[0038] Figure 4 A to 4C show three further variants of fluid lines, each of which shows a connecting section in longitudinal section. DETAILED DESCRIPTION

[0039] according to Figure 1 According to the embodiment shown in , the tube according to the present invention may include four layers 2, 3, 26, 27, which surround the inner cavity (Lumen) 8 of the tube. The tube 1 has a flame retardant layer 2 and an outer layer 3, and may also include two inner layers 4. In this embodiment, the flame retardant layer 2 is connected to the outer layer 3 and the inner layer 4 in a material-locked manner by coextrusion. In this embodiment, the inner layers 4, 26 form the innermost layer 26 of the tube 1, which is separated from the flame retardant layer 2 by a preferred isolation layer 27. Figure 1 A possible protective tube is not shown, which is designed, for example, as a corrugated tube and surrounds the pipe 1 without being directly connected to it in a materially bonded manner. In the present embodiment, the outer layer 3 is the outermost layer of the integrally designed pipe 1.

[0040] Advantageously, all layers 2, 3, 26, 27 of the pipe 1 contain thermoplastics. It is possible that the flame retardant layer 2 contains polypropylene, in particular isotactic polypropylene. In the present embodiment, the barrier layer 27 contains polypropylene, and preferably isotactic polypropylene. In the present embodiment, the outer layer 3 and the innermost layer 26 can contain thermoplastic vulcanizate, in particular Santoprene. Preferably, the material of the innermost layer 26 comes from the same material storage container as the material of the outer layer 3.

[0041] Since thermoplastic vulcanizates also include polypropylene, all layers of the tube 1 of the present embodiment contain polypropylene, so that a good material connection is achieved between the four layers 2, 3, 26, 27 of the tube 1. In addition, the polypropylene composite of the tube 1 is particularly well suited for conducting aqueous solutions, in particular water-glycol solutions. Polypropylene absorbs little water and is therefore more resistant to water than, for example, more expensive polyamides. The tube of the present embodiment can be, in particular, an inlet line of a line system leading to a drive battery of an electric vehicle.

[0042] According to the present invention, the flame retardant layer 2 comprises Figure 1 The expanded graphite particles shown accordingly. The expanded graphite particles are preferably constructed in a flaky shape and embedded in the polypropylene of the flame retardant layer 2. In this embodiment, the expanded graphite particles account for at least 10% of the weight of the flame retardant layer 2. For example, the expanded graphite particles may have an average thickness of 25 μm. Due to the flaky shape, the surface of the expanded graphite particles basically includes a top surface and a bottom surface, which can extend along hundreds of microns in two dimensions. If the expanded graphite particles are sieved, for example, 85% of the particles can pass through a net sieve size of 180 μm (85% of the particles are finer than 80 mesh). The expanded graphite of this embodiment can expand 100 cm at 1000°C. 3 / g.

[0043] The melting temperature of the isotactic polypropylene of layers 2 and 27 may be 185° C. The melting temperature of the thermoplastic vulcanizate of the outer layer 3 and the innermost layer 26 may be 165° C. Preferably, the starting temperature of the expanded graphite particles is 210° C. This means that in this embodiment the temperature of the polypropylene melt is adjusted to about 190 to 200° C. to avoid expansion of the expanded graphite particles also during the extrusion of the pipe.

[0044] In the present embodiment, the outer side of the outer layer 3 has an average roughness Ra of 50 μm. This average roughness Ra is mainly caused by the expanded graphite particles in the flame retardant layer 2, but is partly leveled by the thermoplastic plastic of the flame retardant layer 2, because the thermoplastic plastic of the flame retardant layer 2 also serves as a filler in the flame retardant layer 2. The unevenness of the flame retardant layer 2 is further leveled by the outer layer 3, which is microscopically homogeneous in the present embodiment and in particular contains neither bubbles nor particles exceeding a maximum particle size of 1 μm. Preferably, the layer thickness of the flame retardant layer 2 is about 200 μm. The layer thickness of the outer layer 3 can be 250 μm. In the present embodiment, the layer thickness of the isolation layer 27 is 150 μm. The layer thickness of the innermost layer 26 can be 150 μm.

[0045] according to Figure 2 , Figure 1The pipe 1 shown in the figure is connected to the pipeline joint 5 by welding connections 7, 18 to form the fluid pipeline 1, 5. The pipeline joint 5 comprises a coupling body 11, which is preferably constructed in one piece and more preferably integrally and is made of thermoplastic (preferably polypropylene) by injection molding in the present embodiment. Because the thermoplastic vulcanizate of the outer layer 3 and the innermost layer 26 also contains polypropylene, a particularly good welding connection 7, 18 is achieved. The coupling body 11 suitably comprises a coupling section 14 and a connecting section 15. In the present embodiment, the welding connections 7, 18 are arranged in the region of the connecting section 15. The welding connections 7, 18 can include an outer weld 7 and an inner weld 18. In the present embodiment, both welds 7, 18 are formed by means of rotary friction welding, wherein the pipe 1 has been inserted into the pipe receiving portion 17 of the pipeline joint 5 or the connecting section 15.

[0046] The tube receiving portion 17 is suitably limited in the axial direction by the stopper 13 and is preferably designed as a circumferential annular groove. The tube receiving portion 17 can in particular have an outer wall 20 and an inner wall 21. The inner wall 21 of the present embodiment can taper in the axial inward direction and thus taper on its outer side in the direction of the tube 1, so that the tube 1 can be pushed onto the inner wall 21 particularly easily. The taper of the inner wall 21 is Figure 2 In some embodiments, the effect is relatively strong, but in other embodiments, it can be designed to be significantly weakened.

[0047] During the rotational friction welding process, the inserted pipe 1 is advantageously held in position while the line connection 5 is rotated. The rotation is sufficiently fast that the frictional heat generated in the pipe receiving portion 17 is sufficient to melt the material at the interface. This results in the outer weld seam 7 as well as the inner weld seam 18. A further weld seam, not shown here, can be formed directly at the groove bottom of the pipe receiving portion 17 or at the stop 13. It is important for clean weld seams 7, 18 that unevenness of the expanded graphite particles of the flame retardant layer 2 is compensated by the inner layer 4 and the outer layer 3.

[0048] In accordance with Figure 2 In the embodiment of the present invention, the coupling body 11 comprises a fluid channel 10, which connects the connecting section 15 to the coupling section 14. The connecting section 15 can in particular have an axial extension corresponding to the overlap of the tube 1 and the coupling body 11 in the axial direction. Figure 2 In the longitudinal section of , the fitting 9 is inserted into the line connector 5 or the coupling section 14. The fitting 9 can be the tip of another pipe (not shown) or the tip of a connecting element of a unit such as a tank / pump / valve / battery. The fitting 9 can have a locking element 23, which can preferably be configured as a circumferential flange, but can also be configured as a circumferential groove.

[0049] The pipeline connection 5 suitably comprises as in Figure 316 is shown by way of example in the figure. In particular in the front view, the clamping element 16 can be designed to be essentially U-shaped and have two legs 25. The legs 25 can be connected to each other via a U base, which forms the actuation section 24. The clamping element 16 can be pushed into the actuation section 24 in the radial direction by means of manual pressure. Figure 2 In the coupling body 11 or the coupling section 14. In this way, if the fitting 9 is inserted into the pipeline connector 5 in the axial direction, the locking elements 23 of the fitting 9 cause the legs 25 of the clamping part 16 to be elastically spread apart from each other. Once the locking elements 23 have passed through the legs 25 of the clamping part 16, the legs 25 will rebound under the action of the elastic restoring energy, thereby fixing the fitting 9 in the pipeline connector 5.

[0050] The pipeline joint 5 can also have a seal 12, which includes two sealing rings and a spacer therebetween in the present embodiment. The plug-in rod 22 of the fitting 9 is suitably configured to produce a force lock with the seal 12, thereby achieving fluid sealing. The seal 12 can be fixed in particular by a seal retainer 19, so that the seal 12 is also fixed in the axial outward direction. In the present embodiment, the inner wall of the coupling body 11 and the plug-in rod 22 of the fitting 9 and the connecting section 15 together with the pipe 1 connected thereto are concentrically constructed with each other and have a common central axis M. In other embodiments, the connecting section 15 and the coupling section 14 can be constructed at an angle to each other.

[0051] Figure 4 Three variants A to C of further welded connections 6, 21 between pipe 1 and line connection 5 are shown. Figure 4 In case A, the connecting section 15 of the line connection 5 comprises a pipe receiving portion 17 into which the pipe 1 is inserted. Figure 2 In contrast, the tube receptacle 17 has no inner wall but only an outer wall 20 and a stop 13. Due to the lack of an inner wall of the tube receptacle 17, no inner weld seam is formed but only a single weld seam 6. This single weld seam 6 can be produced, for example, by means of rotational friction welding.

[0052] Figure 4 B shows another embodiment of a welded connection 21 between a pipe 1 and a line connection 5. In this embodiment, the connecting section 15 comprises a pipe receptacle 17 which does not comprise an outer wall, but for this purpose comprises an inner wall 21. The inner wall 21 is designed to taper on its outer side in the axial inward direction, so that when the pipe 1 is pushed on, the tip of the pipe 1 widens increasingly and forms an increasing force connection. In this embodiment, the pipe 1 can also be pushed on up to the stop 13 of the line connection 5 or the connecting section 15 or the pipe receptacle 17. The weld seam 6 can be formed by rotary friction welding.

[0053] exist Figure 4 In FIG. 1 , the connecting section 15 comprises a tube receiving portion 17 which is substantially hollow cylindrical and closed by a stopper 13. The tube receiving portion 17 can be designed in particular such that the inner wall of the tube 1 is aligned with the inner wall of the pipeline connection 5. In the present embodiment, due to the use of a special dye additive, the material of the pipeline connection 5 or the connecting section 15 is transparent to a laser beam, in particular to a near-infrared laser beam, but is dyed black in the visible spectrum. In contrast, the material of the pipeline 1 is opaque to the same laser beam, so that the laser beam is absorbed at the interface between the outer side of the pipeline 1 and the inner side of the pipeline receiving portion 17. Since the tube 1 is also preferably colored dark or black by means of conventional pigments, a uniform color appearance of the fluid pipelines 1, 5 is achieved, while at the same time, the laser beam can only propagate in the tube receiving portion 17 as far as the tube 1.

[0054] The laser beam or beams can be directed so that a complete rotation occurs, thereby achieving a corresponding circumferential weld seam 6. Since the laser beam is relatively finely structured and only produces a force connection of suitable strength between the pipe 1 and the line connection 5, a particularly uniform surface of the outer side or outer layer 3 of the pipe 1 is advantageous. Figure 4 The average roughness of the outer side of the tube 1 of example C is particularly preferably less than 50 μm, for example 20 μm. This results in a particularly durable fluid connection between the tube 1 and the line connection 5 , while the tube 1 has particularly good flame retardancy.

[0055] List of reference numerals:

[0056] 1. Pipe

[0057] 2 Flame retardant layer

[0058] 3 Outer layer

[0059] 4 Inner layer

[0060] 5 Pipeline connector

[0061] 6 The only weld

[0062] 7 External weld

[0063] 8 1 inner cavity

[0064] 9 Matching parts

[0065] 10 5 fluid channels

[0066] 11 5 coupling body

[0067] 12 5 Seals

[0068] 13 5 stop

[0069] 14 11 coupling section

[0070] 15 11 connection section

[0071] 16 5 clamping parts

[0072] 17 11, 15 pipe receiving portion

[0073] 18 Internal weld

[0074] 19 5 Seal Retainer

[0075] 20 outer wall

[0076] 21 Inner wall

[0077] 22 9 plug-in rod

[0078] 23 9 locking element

[0079] 24 16 actuation section

[0080] 25 16 outriggers

[0081] 26 Innermost

[0082] 27 Isolation layer

[0083] 1.5 Fluid pipeline

[0084] M Center axis

[0085] 6, 7, 18 welding connection

Claims

1. A pipe (1), comprising a flame retardant layer (2) and an outer layer (3), wherein the outer layer (3) surrounds the flame retardant layer (2), wherein the flame retardant layer (2) comprises a thermoplastic and expanded graphite particles, wherein the expanded graphite particles are configured to expand above a starting temperature, wherein the expanded graphite particles are in an unexpanded state, wherein the outer layer (3) comprises a thermoplastic, It is characterized in that The average roughness Ra of the outer side of the tube (1) or the outer side of the outer layer (3) is at most 200 or 100 or 50 μm.

2. The tube (1) according to claim 1, wherein the outer layer (3) has particles or cavities with a radial average size of at most 200 or 150 or 100 or 50 μm in the cross section of the tube (1), or contains no particles or cavities at all or filled cavities.

3. The pipe (1) according to claim 1, wherein the thermoplastic material of the outer layer (3) is formed uniformly over the entire cross section of the outer layer (3).

4. The tube (1) according to any one of claims 1 to 3, wherein the tube (1) is of one-piece construction.

5. The tube (1) according to any one of claims 1 to 4, wherein the outer layer (3) is the outermost layer of the tube (1).

6. The pipe (1) according to any one of claims 1 to 5, wherein the flame-retardant layer (2) has a layer thickness of at most 1.0 or 0.7 mm or 0.5 mm.

7. The tube (1) according to any one of claims 1 to 6, wherein the outer layer (3) has a layer thickness of at least 0.05 mm or 0.07 mm.

8. The pipe (1) according to any one of claims 1 to 7, wherein the weight ratio of expanded graphite particles in the flame retardant layer (2) is at least 1 or 3 or 5 weight %.

9. The tube (1) according to any one of claims 1 to 8, wherein the expanded graphite particles in the flame retardant layer (2) have a radial average height of at most 200 or 150 or 100 μm in the cross section of the tube (1).

10. The tube (1) according to any one of claims 1 to 9, wherein the expanded graphite particles of the flame retardant layer (2) have an onset temperature of at least 130 or 150 or 170°C.

11. The pipe (1) according to any one of claims 1 to 10, wherein the expansion rate of the expanded graphite particles of the flame retardant layer (2) is at least 10 or 20 or 30 cm 3 / g.

12. The pipe (1) according to any one of claims 1 to 11, wherein the pipe (1) comprises an auxiliary flame retardant, wherein the auxiliary flame retardant preferably acts as a diluent gas or dilutes oxygen, wherein the auxiliary flame retardant is preferably an inorganic flame retardant.

13. A pipe (1) according to any one of claims 1 to 12, wherein the pipe (1) comprises at least one further layer (4), preferably an inner layer (4), wherein preferably the flame retardant layer (2) surrounds the inner layer (4), wherein preferably the flame retardant layer (2) is in contact with the at least one inner layer (4).

14. The pipe (1) according to any one of claims 1 to 13, wherein the thermoplastic plastic of the flame retardant layer (2) and / or the thermoplastic plastic of the outer layer (3) comprises polyamide, polyester, polyolefin, polyurethane or thermoplastic elastomer.

15. A fluid pipeline, comprising at least one pipe (1) according to at least one of claims 1 to 14 and at least one pipeline joint (5), wherein preferably, the pipe (1) and the at least one pipeline joint (5) are welded together.

16. Use of a tube (1) according to any one of claims 1 to 14 or a fluid line according to claim 15 in a land vehicle, in particular in an electric vehicle, in particular for cooling, preferably for cooling a battery of an electric vehicle drive.

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