METHOD FOR PRODUCING A CYLINDRICAL, STRAND-SHAPED PART

Description

[0001] The invention relates to a method for producing a cylindrical, strand-shaped part. In particular, the invention relates to the production of metal-plastic composite pipes, such as those used in the plumbing and heating sectors.

[0002] Plastic-metal composite pipes are becoming increasingly popular because they combine the advantages of plastic deformability of metal pipes with the advantages of corrosion resistance of plastic pipes.

[0003] Such plastic-metal composite pipes can be manufactured in various ways. For example, it is known to produce the metal layer of such a composite pipe by forming a metal strip, with the longitudinal edges of the metal strip overlapping and being welded or glued, or the longitudinal edges of the metal strip being butt-welded. A single- or multi-layer plastic pipe is then extruded into the interior of the thus formed metal pipe. Examples of such manufacturing processes can be found in DE-A-30 16 134, EP-A-0 353 977, EP-A-0 581 208, EP-A-0 920 972, WO-A-88 / 03084, and WO-A-01 / 85430.

[0004] It is also known to form the metal pipe on a previously manufactured single- or multi-layer plastic pipe. An example of such a manufacturing process is described in EP-A-0 691 193. Further examples can be found in DE-A-43 10 272, DE-A-44 04 492, and DE-C-195 36 689.

[0005] Finally, it is also known to apply the metal layer of a plastic-metal composite pipe directly to an already manufactured plastic pipe by extrusion. EP-B-0 125 788 describes extruding a metal pipe onto a prefabricated plastic pipe at a radial distance from the prefabricated plastic pipe. The metal pipe is then reduced in diameter by a drawing or similar diameter reduction process in order to fit tightly against the plastic pipe. US-A-5 222 284 discloses reducing the diameter of a prefabricated plastic pipe and then extruding a metal pipe around the plastic pipe (by extrusion). After this, the pipe with the reduced diameter expands again using the memory effect to thereby fit tightly against the metal pipe from the inside.Finally, DE-A-21 39 388 discloses the pressing of a seamless metal pipe onto a prefabricated plastic hose using a metal jacket press. The problem here is the temperatures generated in the metal jacket press by the extrusion of the metal, which affect the plastic hose.

[0006] Further plastic-metal composite pipes can be found in AU 2690971 and US 4304713.

[0007] The object of the invention is to provide a method for producing a cylindrical, strand-shaped plastic-metal composite part which is characterized by high dimensional stability.

[0008] To achieve this object, the invention proposes a method for producing a strand-shaped part, in which a hollow profile made of metal is extruded, the extruded hollow metal profile cools or is cooled and a single-layer or multi-layer plastic strand is extruded into the extruded hollow metal profile after or during its cooling, wherein the plastic strand passes an output tool of an extruder which is inserted into the hollow metal profile and exposed to the heat of the extruded hollow metal profile, which has an output opening which is arranged within a region of the hollow metal profile in which it has cooled compared to its temperature during extrusion, and the output tool is thermally coupled to the hollow metal profile and is tempered by it, and the output tool uses the heat from the extruded hollow metal profile without an external heat source when the output tool is inserted into the hollow metal profile.

[0009] In the method according to the invention, the metallic layer or layer of the cylindrical strand-like part is first extruded, i.e., produced by continuous extrusion, with a single- or multi-layer plastic strand then being extruded into the metallic layer or layer at the same time. This procedure has the advantage that the external dimensions of the cylindrical strand-like part are defined by the extrusion process of the metallic layer or layer, i.e., by the extrusion process for the metal tube. Post-processing of the produced strand-like part for the purpose of reducing its diameter or for the purpose of reducing the diameter of the metal tube is not necessary.

[0010] The metal pipe heated after the extrusion process, together with the heated single- or multi-layer plastic melt, has a positive effect on intimate adhesion to the metal pipe.

[0011] The heat generated during metal extrusion is far too great to allow the plastic strand to be extruded into the hollow metal profile immediately after extrusion. This requires a location within the hollow metal profile located downstream of the metal extrusion in the machine direction. According to the invention, this is achieved with the aid of a mandrel-shaped dispensing tool that extends far into the hollow metal profile. This dispensing tool, which is essentially designed like a tube or mandrel, transports the plastic melt. In order for this plastic melt to maintain the temperature required for extrusion over the relatively long path through the dispensing tool, this dispensing tool would have to be heated.

[0012] Surprisingly, it has now been shown that the heat emanating from the extruded metal hollow profile can be used to heat or temper the dispensing tool. This achieves two effects: first, the metal hollow profile cools down by transferring its heat to the dispensing tool, and second, the dispensing tool is tempered without the use of other external heat sources.

[0013] Only by subsequently extruding the plastic melt from the inside into the seamlessly manufactured, extruded metal hollow profile can the different materials, metal and plastic, be processed with dimensionally accurate precision. This high degree of dimensional accuracy is achieved by manufacturing the metal tube seamlessly (extrusion). Pressing or extruding the metal tube onto a prefabricated plastic tube, which would also result in high dimensional accuracy, is not possible due to the high temperatures of the extruded metal hollow profile. According to the invention, the extrusion of the plastic strand into the extruded metal hollow profile is achieved by the fact that the dispensing tool is of considerable length, so that the plastic melt only comes into contact with the metal hollow profile once it has already cooled to a temperature compatible with the plastic.As already mentioned above, this takes advantage of the fact that the temperature control of the dispensing tool over its entire length is achieved by the heat dissipation of the extruded metal hollow profile.

[0014] The process according to the invention can be used, in particular, to produce cylindrical, strand-shaped hollow or solid profile parts. The process is particularly suitable for the production of multi-layer plastic-metal composite pipes.

[0015] In a further development of the invention, a single- or multi-layer plastic coating can be applied to the outside of the metal tube, preferably by extrusion. The extrusion of the outer plastic layer can be performed directly onto the extruded metal tube or after it has cooled. If multiple plastic layers are extruded, this can be achieved by tandem extrusion of the individual layers or by coextrusion.

[0016] In an advantageous embodiment of the invention, the metal tube is preferably made of aluminum or an aluminum alloy. The multilayer plastic layers that are extruded into the metal tube or can be applied to the outside of the metal tube are preferably thermoplastic materials, with the plastic layers adjacent to the metal tube comprising thermoplastic bonding agents.

[0017] The method according to the invention is particularly suitable for the production of multi-layer plastic / metal composite pipes with larger diameters (e.g., from 40 mm), in which the metal pipe, due to its wall thickness, can only be reduced in diameter after production with great effort in order to come into contact with the inner plastic strand. This diameter reduction of the metal pipe is therefore dispensed with according to the invention by extruding the plastic strand into the finished metal pipe (specifically on its inner side). The disadvantage of reducing the diameter of the metal pipe is that the deformation of the metal leads to material hardening, which in turn has a detrimental effect on the bendability of the produced metal-plastic composite pipe.In this respect, the method according to the invention also has advantages in the production of multi-layer plastic / metal composite pipes with smaller diameters (for example, up to 40 mm), since the diameter reduction of the metal pipe, which is manageable by machine for these pipe dimensions, can be dispensed with. The production of multi-layer plastic / metal composite pipes with smaller diameters is also possible according to the invention not least because the dispensing tool does not have to be heated with separate heating elements or the like for its temperature control, which would have to be part of the dispensing tool and would thus increase its diameter, since the heat required to temper the dispensing tool is provided by the heat of the extruded hollow metal profile.

[0018] The heating of the dispensing tool by the cooling, extruded hollow metal profile is advantageously achieved through thermal coupling between the two. It is particularly advantageous if the extruded hollow metal profile moves over the dispensing tool while in contact with the dispensing tool. The dispensing tool can then assume the additional function of stabilizing the shape of the extruded hollow metal profile during the phase immediately following extrusion. Alternatively, thermal coupling can also be achieved by the dispensing tool absorbing radiant heat from the hollow metal profile. In this case, the extruded hollow metal profile extends along the dispensing tool, forming an air gap.

[0019] The dispensing tool is expediently a tube or mandrel-shaped tool having an annular space with an annular nozzle arranged at its dispensing end. The annular space, which is defined by two concentric walls or surfaces (e.g. tubes), can be stabilized by webs or the like connecting the walls. The plastic melt passing through the annular space flows around these webs, which is not detrimental to the extrusion process of the plastic strand. In the case of a multi-layer plastic melt stream, the annular space should be free over its entire length. The tubes forming between the annular spaces are then fixed to one another at one end.

[0020] The method according to the invention is also suitable, as already mentioned above, for producing solid profile parts. For example, the method according to the invention can be used to produce a cable surrounded by plastic and metal or another solid or hollow profile in an essentially non-deformable and temperature-resistant form, e.g. a metal pipe. The cable or profile is fed centrally through the annular nozzles of the extruder for the plastic strand and the metal pipe, so that during the extrusion of the plastic strand the space between the centrally arranged conductor and the metal pipe is filled with plastic material. This plastic material can, for example, be a foamable plastic material. In this case, an adhesion promoter is not absolutely necessary if it is guaranteed that the foamable plastic itself adheres sufficiently firmly to the inside of the metal pipe.

[0021] The invention is explained in more detail below using exemplary embodiments and with reference to the drawings. In detail, the drawings show: Fig. 1 shows the extrusion system components for producing a cylindrical, strand-shaped hollow profile part according to a first embodiment of the invention, Fig. 2 shows the extrusion system components for producing a cylindrical, strand-shaped hollow profile part according to a second embodiment of the invention, and Fig. 3 shows the extrusion system components for producing a cylindrical, strand-shaped solid profile part according to a first and second embodiment of the invention.

[0022] Fig. 1shows a schematic of the essential system components of a device 10 for producing a multi-layer plastic / metal composite pipe 12. The device 10 includes an extruder 14 or an extrusion unit for producing an aluminum pipe 16. The annular nozzle of the extruder 14 is shown at 18, while the metal heated for the plastic deformation process is designated by 20. The extruded aluminum pipe 16 is extruded, for example, at temperatures between 450 and 500 °C and then cools after exiting the nozzle 18 (for example, to 200 to 250 °C, which is indicated at 22).

[0023] A hollow mandrel 24 is inserted centrally through the annular nozzle 18 into the extruded metal tube 16. At one end, the mandrel has an annular nozzle 26 through which a two-layer, hollow-cylindrical plastic strand 28 emerges. The strand comprises a plastic adhesion promoter layer 30 on the outside and an inner plastic layer 32 on the inside, which later forms the base tube. Both plastic layers are extruded together into the cooled metal tube 16 via a co-extruder 34, specifically against its inner side 36. To ensure that the plastic melt remains there reliably, a gas, e.g., air, is introduced into the plastic melt tube (hollow-cylindrical plastic melt strand 28) through the mandrel 24, thereby building up excess pressure. The overpressure is maintained in the plastic pipe string 28 by a plug 38 arranged therein, which is fastened outside the extrusion components of the device 10 at 42 via a cable 40 passed through the hollow mandrel 24.Instead of the plug 38, the manufactured metal tube 16 with the plastic strand inside can be squeezed to prevent the excess pressure from escaping.

[0024] Fig. 2 shows a slightly modified variant 10' of a device for producing a multi-layer plastic / metal composite pipe 12. As far as the Fig. 2 The system components shown are identical or functionally equivalent to the system components according to Fig. 1 are provided with the same reference numerals.

[0025] In contrast to the device 10 of Fig. 1 are used in the device 10' of the Fig. 2 the metal tube 16 and the plastic strand 28 are coextruded. Otherwise, the manufacturing process proceeds as described above.

[0026] Fig. 3 shows a device 10 ", which is similar to the device 10' of Fig. 2 is built, at Fig. 3However, it is used to produce a cylindrical, strand-shaped solid or hollow profile part 44 in a substantially non-deformable and temperature-resistant form. The components and elements of the system Figures 1 and 2 similar parts are in Fig. 3 provided with the same reference symbols.

[0027] The metal tube 16 and the plastic strand 28 are used in the device 10" of the Fig. 3 again essentially coextruded. An electrical conductor 46 is passed through the hollow mandrel 24 of the extruder 34 for the plastic strand 28, which, after leaving the hollow mandrel 24, is embedded and enveloped by the material of the plastic strand 28, so that the plastic material is located between the inner side 36 of the metal tube 16 and the electrical conductor 46. With the device 10" of the Fig. 3For example, electrically insulated cables can be produced which have a metallic tube containing the electrical conductor 46 with an interposition of a plastic material.

[0028] Regarding the Figures 1 to 3 With regard to the devices 10, 10' and 10" shown, it should also be mentioned that these devices may additionally comprise one or more extruders or a coextruder for applying single or multi-layer plastic coatings to the outside of the metal pipe 16. These additional extruders, which are known in pipe production, are shown in the Figures 1 to 3 not shown.

Claims

1. Method for producing a strand-shaped part, in which - a hollow profile (16) made of metal is extruded, - the extruded metal hollow profile (16) cools and / or is cooled, and - a single- or multi-layer plastic strand (28) is extruded into the extruded metal hollow profile (16) after or during its cooling, characterized in that - the plastic strand (28) passes through a discharge tool (24) of an extruder (34) which is inserted into the metal hollow profile (16) and exposed to the heat of the extruded metal hollow profile (16), said extruder having a discharge opening (26) arranged within a region of the metal hollow profile (16) in which it has cooled compared to its temperature during extrusion, and - the discharge tool (24) is thermally coupled to the metal hollow profile (16) and is temperature-controlled by it, and the discharge tool (24) uses the heat from the extruded metal hollow profile (16) without an external heat source if the discharge tool (24) is introduced into the metal hollow profile (16).

2. Method according to Claim 1, characterized in that the discharge tool (24) contacts the inner sides of the metal hollow profile (16).

3. Method according to Claim 1 or 2, characterized in that a single-layer or multi-layer plastic layer is applied to the outside of the metal hollow profile (16), preferably by extrusion, tandem extrusion or coextrusion.

4. Method according to any one of Claims 1 to 3, characterized in that the single-layer or multi-layer plastic strand (28) extruded into the metal hollow profile (16) is formed as a plastic pipe and that an overpressure is generated within the plastic pipe to press the plastic pipe against the metal pipe (16).

5. Method according to any one of Claims 1 to 3, characterized in that the single- or multi-layer plastic strand (28) is formed as a solid profile and that a solid or hollow profile part in a substantially non-deformable and temperature-resistant form, in particular a single- or multi-core electrical conductor (46), is introduced into the solid profile during its extrusion.

6. Method according to any one of Claims 1 to 5, characterized in that the metal hollow profile (16) comprises a metal which is plastically deformable and extrudable below its melting point or a metal alloy which is plastically deformable and extrudable below its melting point.

7. Method according to Claim 6, characterized in that the metal is aluminium or the metal alloy has an aluminium alloy.

8. Method according to any one of Claims 1 to 7, characterized in that the plastic strand (28) has an outer layer (30) made of an adhesion promoter and a polymer material layer adjacent to the outer layer (30).

9. Method according to Claim 3 or any one of the preceding claims, as far as they refer back to Claim 3, characterized in that the plastic layer applied externally to the metal hollow profile (16) has an inner layer of adhesion promoter adjacent to the metal hollow profile (16) and an outer layer of polymer material adjacent to this inner layer.

10. Method according to any one of Claims 1 to 9, characterized in that the metal pipe and the plastic strand (28) are coextruded or produced by successively arranged extruders.

11. Method according to any one of Claims 1 to 10, characterized in that the metal hollow profile (16) is a metal pipe.

12. Method according to any one of Claims 1 to 11, characterized in that the plastic strand (28) comprises a particularly foamable plastic material which has adhesive or non-adhesive properties to the metal.

13. Method according to any one of Claims 1 to 12, characterized in that the discharge tool (24) has a mandrel with an annular space, at the axial end of which there is located an annular nozzle as a discharge opening (26) of the mandrel.