GB2111164A

GB2111164A - Method of producing a composite pipe

Info

Publication number: GB2111164A
Application number: GB08232560A
Authority: GB
Inventors: Herbert Vogelsang; Gerhard Ziemek; Hermann-Uwe Voigt; Eckhardt Schleese
Original assignee: Kabelmetal Electro GmbH; KM Kabelmetal AG
Current assignee: Kabelmetal Electro GmbH; KM Kabelmetal AG
Priority date: 1981-11-16
Filing date: 1982-11-15
Publication date: 1983-06-29
Also published as: IT8224035A0; FR2516443A1; IT1153344B; ES8308254A1; SE8206476D0; GR76538B; SE8206476L; GB2111164B; ES517359A0; NL8204208A; DK448782A

Abstract

In a method of producing a composite pipe for the transport of liquid or gaseous media, particularly for use in floor heating systems, an inner pipe (1) is first extruded from a thermoplastic synthetic resin material, this pipe (1) is then surrounded by a longitudinally-fed metal foil (2) coated on both sides with an adhesive, e.g. a copolymer, the edges of the strip overlapping or being welded together, and finally an outer pipe (4) is extruded onto the metal foil (2), the metal foil (2) thus being caused to adhere both to the inner pipe (1) and to the outer pipe (4). <IMAGE>

Description

SPECIFICATION Method of producing a composite pipe The present invention relates to a method of producing composite pipes for the transport of liquid or gaseous media, comprising an inner pipe made of synthetic resin, a metal foil which is arranged coaxially with the inner pipe with an overlapping seam, and an outer casing in the form of a pipe made of a thermoplastic synthetic resin.

Both metal pipes and synthetic resin pipes are used in the field of hot-water floor-heating installations. Metal pipes, particularly pipes made of copper, have proved to be advantageous in particular with respect to durability. However a disadvantage of such pipes is that, particularly in large rooms, it is not possible to use a single length of pipe, but the installed piping coil actually consists of several lengths of pipe which must be connected to one another at their adjacent ends.

In comparison with metal pipes, synthetic resin pipes have the advantage that they are available in longer lengths which has been found to be advantageous as regards the installation of the piping. However, a disadvantage of synthetic resin pipes is that they are less impervious to gas than are metal pipes. This can lead, for example, to oxygen diffusing through the walls of the synthetic resin pipe and reaching the water of the heating installation. However, oxygen is undesirable in the heating water since it is likely to lead to the corrosion both of the radiators and the heating boiler system.

It is accordingly an object of the present invention to provide a method by means of which it is possible to achieve an economical production of a composite pipe made of synthetic resin material, in which the admission of gases, in particular oxygen, into the heating water is avoided and which pipes are extremely flexible.

According to the invention, there is provided a method of producing a composite pipe comprising the steps of forming an inner pipe by extrusion of a thermoplastic synthetic resin material, longitudinally feeding a metal foil coated on both sides with an adhesive to surround said inner pipe, the longitudinal edges of said foil being overlapped or welded together, and extruding an outer pipe of thermoplastic synthetic resin material onto the metal foil to form a casing, said metal foil thereby being caused to adhere to both the inner and the outer pipe.

The metal foil in the pipe structure serves as a diffusion blocking layer, or as a permeation barrier.

The double-sided coating of the foil with an adhesive, such as a copolymer adhesive, and its adherence to the inner and outer pipes produces a composite arrangement which does not substantially reduce the flexibility of the pipe.

Tearing of the foil is to a large extent avoided as a result of its adhesion to the inner and outer pipes.

Expediently, the inner pipe is of cross-linked material, in order to increase its heat resistance. In order to ensure that the penetration of gases is largely eliminiated, the metal foil is stuck together by means of an adhesive in the overlap region. In order to increase the resistance to UV rays (which is important in the case of open-air installations) a blackening substance, preferably soot, is added to the mixture used to produce the outer pipe.

To particular advantage, the inner pipe and possibly also the outer pipe, may be produced from a synthetic resin material which can be cross-linked by the presence of moisture. Such cross-linking does not substantially reduce the flexibility of the pipe, whilst the heat resistance is substantially increased. In a preferred design of pipe, the ratio of the wall thickness of the inner pipe to the thickness of the foil is in the range of 5:1 to 10 :1, whilst the ratio of the wall thickness of the outer pipe to the thickness of the foil is in the range of 2.5:1 to 7 :1. Such dimensions ensure the requisite compression resistance, together with a very high degree of flexibility.

It is of further advantage if the pipe is wound to form an annular coil, whereafter the inner pipe and possibly also the outer pipe are cross-linked. if a synthetic resin is used which can be cross-linked by moisture, the fundamental advantage is achieved that the pipe can be cross-linked after installation at the point of use, by allowing a moist heated medium to flow through it. If, for example, heated water is conveyed through the inner pipe, the inner pipe becomes cross-linked as a result of the increased temperature and the presence of the water. However, it is also possible to cross-link the inner pipe actually in the manufacturing plant by using water which has been heated for the sealing test which has in any case to be carried out.The outer pipe is cross-linked as a result of the heating and atmospheric moisture; it should be noted that this process takes somewhat longer than does the cross-linking of the inner pipe. It is possible to accelerate the cross-linking of the outer pipe by increasing the amount of a catalyst which initiates the cross-linking in the outer pipe.

According to a further aspect of the invention, apparatus for carrying out the method comprises an extruder, which is preceded by a guide means which serves to feed the inner pipe to the extruder, and which is also preceded by a forming device by means of which a strip which is provided on both sides with an adhesive coating and which can be drawn off from a feed reel is fed to the inner pipe in the longitudinal direction and caused to embrace the pipe, so as to form a metal covering which is closed to form a tube and which is supported on the inner pipe, and which extruder is followed by a take-up reel to take up the pipe formed.

Such apparatus allows a pipe in the walls of which a metal layer is arranged to be produced in a single process step. It is immaterial whether the inner pipe has been premanufactured or, in accordance with a further feature of the invention, has been produced in the same process step as the production of the composite pipe itself by means of an extruder. The individual items of production equipment which are used in the apparatus are known per se, so that no substantial outlay is needed for the production of the composite pipe. The combination of the various items of equipment in a single apparatus ensures that the composite pipe can be produced in a particularly economic way.

The invention will now be further described with reference to the drawings, in which:~ Figure 1 is a schematic perspective view of part of a composite pipe produced by a method according to the invention; Figures 2 and 3 are respective schematic endsectional views of two further forms of composite pipe produced by a method according to the invention; Figure 4 is a schematic perspective view in section and partly cut away, of a floor-heating system employing a composite pipe produced in accordance with the invention; Figure 5 is a schematic side view of one form of apparatus for carrying out the method of the invention; and Figure 6 is a schematic side view of a modified form of the apparatus of Figure 5.

As shown in Figure 1, a composite pipe produced by the method of the invention consists of an inner pipe 1 having a wall thickness of about 1 mm, a metal foil 2 having a thickness of 0.5 to 0.2 mm (possibly even thinner), having an overlapping seam indicated at 3, and which is coated on both sides with an adhesive. On the foil 2, which preferably consists of an aluminium foil coated on both sides with a copolymer adhesive, there is arranged an extruded outer casing in the form of a pipe 4 made of a thermoplastic material having a wall thickness of between 0.5 and 0.8 mm. The outer casing 4 is coloured black by the addition of soot.

The pipe illustrated in Figure 1 can be produced in one process step by the extrusion of the inner pipe 1 , the longitudinal covering of the inner pipe 1 with the overlapped foil 2, and the subsequent extrusion of the outer pipe forming the casing 4.

The inner pipe is advantageously formed by the extrusion of a mixture of 100 parts by weight of a polyethylene of average density (0.93-0.95 g/cm3), 1-1.5 parts by weight of silane, 0.05-0.1 5 (preferably 0.06-0.10) parts by weight of 1 .3-bis-(tert-butyl-peroxi-isopropyl)benzene, 0.03-0.10, preferably 0.06-0.08, parts by weight of dibutyl-tin-dilaurate as catalyst, and possibly an anti-aging agent.The outer pipe forming the casing is extruded from a mixture of 100 parts by weight of polyethylene, 2-4, preferably 2.5-3 parts by weight of soot (an acetylene soot preferably being used), 1-1.5 parts by weight of silane, 0.05-0.1 5, preferably 0.08-0.10, parts by weight of 1 .3-bis-(tert-butylperoxi-isopropyl)-benzene, 0.03-0.20, preferably 0.08-0.10, parts by weight of dibutyl-tindilaurate and an anti-aging agent. In the mixture used to form the outer casing 4, the amount of the catalyst dibutyl-tin-dilaurate is selected to be somewhat higher than in the mixture used to form the inner pipe, so that in the case of cross-linking of the outer pipe after installation, this takes place virtually simultaneously with the cross-linking of the inner pipe 1.

Figures 2 and 3 illustrate two further exemplary embodiments of a composite pipeline produced by the method of the invention. In these embodiments, two inner pipes 5a and Sb, each of which, as described above, is surrounded by a metal foil 7a or 7b respectively, are encased by a common outer pipe 6. In the exemplary embodiment shown in Figure 2 the outer pipe 6 has an oval cross-section so that adhesion to the inner pipes 5a, 5b via the metal foils 7a, 7b is effected only in the contact zone.

The embodiment illustrated in Figure 3 is an advantageous one. In this case also, the outer pipe 6 is common to two inner pipes 5a and 5b, but all round adhesion of the outer pipe 6 to the metal foils 7a and 7b is ensured. A cross piece 9 connects the two inner pipes 5a and 5b to one another. In the production of the composite pipe, the inner pipe 5 is first extruded, and the metal foil 7 which is drawn off from a feed reel is then applied to the inner pipe 5 so that the longitudinal edges of the foil overlap. The structure so formed is fed into an extruder in which the outer pipe 6 is extruded.As a result of the heat of extrusion. both the inner pipe and the outer pipe 6 are caused to adhere to the copolymer adhesive coating on the metal foils 7a and 7b, resulting in a joint between the inner pipe 5, the metal foils 7a, 7b and the outer pipe 6. Where the composite pipes as shown in Figure 2 or Figure 3 are to be produced, the inner pipes 5a and Sb are fed together to the extruder.

The advantage of the exemplary embodiments illustrated in Figures 2 and 3 is that no special installation technique is necessary to achieve a uniform surface temperature of the area to be heated. Since the inner pipe 5b may be used for the outwards flow, for example, whilst the inner pipe 5a is used for the return flow, the emission of heat is virtually equal at every point of the heated floor. After installation, the inner pipes 5a and Sb are conductively connected to one another at their ends which lie opposite the feed-in point, for example, by means of a U-shaped member.

Figure 4 illustrates the structure of a floor heating system in which a pipe as shown in any of Figures 1 to 3 has been installed. It consists of a thermal insulating layer 11, which may consist, for example, of plates of foamed material or other suitable heat insulation, a plaster flooring layer 12 which is applied on the thermally insulating layer 1 1 and in which composite pipes 14 produced in accordance with the invention are installed, preferably in serpentine form, and a separating foil 13 which serves to prevent the thermally insulating layer 11 from becoming damp when the plaster flooring layer 12 is laid.

Figures 5 and 6 schematically illustrate apparatus for carrying out the method of the invention. In order to produce a composite pipe, a synthetic resin pipe is unreeled from a storage reel 21 to serve as an inner pipe 1 by means of a supply device 23 and is fed to an extruder 24 by means of which an outer pipe 4 (as shown in Figures 1 to 3) is extruded over the inner pipe 1.

The supply device 23 may consist, for example, of a caterpillar tractor arrangement.

The extruder 24 is also preceded by a forming device 26 by means of which a metal strip 27, fed in the longitudinal direction, is formed around the inner pipe 1 to produce a tubular structure. The metal strip 27 is coated on both sides with an adhesive coating, e.g. of a copolymer adhesive, and is stored on a feed reel 28 from which it is continuously unreeled. The metal strip 27 embraces the inner pipe 1 to form a closed structure and fits snugly against the surface of the inner pipe 1. It can be placed around the inner pipe 1 with overlapping edges. However, it is also possible for the metal strip 27 to be welded to form a tube by means of a welding device 29 (indicated in broken lines), in which case the longitudinal edges are expediently bent outwards to form flanges and welded at their end faces.

Before the application of the outer pipe 4, the flanges would have to be bent over until they contacted the metal strip 27 which encircles the inner pipe 1.

In the extruder 24, the outer pipe 4 is extruded onto the metal layer formed by the metal strip 27, where, as a result of the heat of extrusion of the extruded outer pipe, the metal layer is caused to adhere both to the inner pipe 1 and to the outer pipe 4, thus producing a mechanically stable yet highly flexible pipe 31 as a combination of the inner and outer pipes. The finished pipe 31 can be wound onto a reel 32 so that a practically endless production is possible. The length of pipe which has to be considered as a unit depends upon the capacity of the reel 32.

In order further to simplify the production of the pipe 31, it is possible, as shown in Figure 6, to use a first extruder 33 which, in the same production step as the production of the pipe 31, extrudes the inner pipe 1 which then, as already described with respect to Figure 5, is fed forwards by means of the supply device 23. Thus, previous manufacture of the inner pipe 1 can be dispensed with when the apparatus illustrated in Figure 6 is used.

In order to safeguard the adhesion between the metal layer and inner pipe 1 in all circumstances, an additional heat source can be arranged between the forming device 26 and the extruder 24 in order to activate the inner adhesive layer on the metal strip 27.

It is particularly advantageous if the metal strip 27 consists of an aluminium foil which is coated on both sides with a polyethylene copolymer. This copolymer serves as a strongly-adhering adhesive when heat is supplied thereto. If the metal strip 27 encircles the inner pipe 1 with its longitudinal edges overlapping, the width of the overlap is preferably between 2.0 and 5.0 mm. In this way, gases can be prevented from penetrating at the overlap region.

An aluminium foil used as the metal strip 27 preferably has a thickness of 0.1 to 0.3 mm, preferably 0.2 mm. Such a thickness ensures a diffusion barrier with respect to gases, and ease of processing during the production of the pipe 31.

The wall thickness of the inner and outer pipes can be the same in the range of 0.5 to 2.0 mm. With these dimensions the pipe 31 still exhibits good flexibility, but is nevertheless well able to withstand the pressure of hot water prevailing in hot water heating systems. Since, with such dimensions, the aluminium foil is located in the middle of the walls of the pipe 31, it enjoys optimum protection against bending with regard to its mechanical load capacity.

In addition to the possible uses previously described, the pipe 31 (particularly, in its crosslinked form), is also suitable as a connecting line between heat exchangers, or heat adsorbers, installed outdoors, and a heat utilising apparatus, for example, a heat pump.

Claims

1. A method of producing a composite pipe comprising the steps of forming an inner pipe by extrusion of a thermoplastic synthetic resin material, longitudinally feeding a metal foil coated on both sides with an adhesive to surround said inner pipe, the longitudinal edges of said foil being overlapped or welded together, and extruding an outer pipe of thermoplastic synthetic resin material onto the metal foil to form a casing, said metal foil thereby being caused to adhere to both the inner and the outer pipe.

2. A method as claimed in Claim 1 , wherein said adhesive is a copolymer adhesive.

3. A method as claimed in Claim 1 or Claim 2, wherein said inner pipe is cross-linked.

4. A method as claimed in any one of Claims 1 to 3, wherein said metal foil is glued together in the overlap region.

5. A method as claimed in any one of the preceding Claims, wherein said outer pipe is coloured black by the addition of a colouring material.

6. A method as claimed in Claim 5 wherein said colouring material is soot.

7. A method as claimed in Claim 3, or any of Claims 4 to 6 as dependent thereon, wherein the inner pipe is extruded from a synthetic resin material which can be cross-linked in the presence of moisture.

8. A method as claimed in Claim 7, wherein said outer tube is also extruded from a synthetic resin material which can be cross-linked in the presence of water.

9. A method as claimed in any one of the preceding Claims, wherein the ratio of the wall thickness of the inner pipe to the thickness of the foil is from 5:1 and 10:1, and the ratio of the wall thickness of the outer pipe to the thickness of the foil is from 2.5:1 to 7:1.

10. A method as claimed in any one of the preceding Claims, wherein the pipe is wound to form an annular coil and is subsequently crosslinked.

11. A method as claimed in Claim 3, or any one of Claims 4 to 10 as dependent thereon, wherein the inner and/or outer pipes are cross-linked at the place of manufacture in the course of a sealing test carried out by the passage of water heated to about 800C through the pipe.

12. A method as claimed in any one of Claims 1 to 10, wherein the pipe is cross-linked after installation at the point of use by passage of a heated medium therethrough.

13. A method as claimed in any one of the preceding Claims, wherein two identical inner pipes are housed within a common outer pipe.

14. A method as claimed in Claim 13, wherein said two inner pipes are surrounded by an extruded outer pipe so that said inner pipes are interconnected in the form of a twin lead.

15. A method as claimed in Claim 3 or any one of Claims 4 to 14 as dependent thereon, wherein said inner pipe and optionally also said outer pipe, is or are extruded from a polymer which can be cross-linked after the addition of silane, by the influence of moisture.

16. A method as claimed in Claim 15, wherein said polymer is polyethylene.

17. A method of producing a composite pipe substantially as hereinbefore described with reference to the drawings.

18. Apparatus for carrying out the method of Claim 1, comprising an extruder preceded by a guide device which serves to feed said inner pipe to the extruder and by a forming device, by means of which a metal strip which is provided on both sides with an adhesive coating and which is unreeled from a feed reel is caused to enclose the inner pipe in the longitudinal direction, so as to form a closed tubular metal covering resting against the inner pipe, said extruder serving to extrude said outer pipe onto said metal covering and being followed by a take-up reel serving to take-up the composite pipe formed.

19. Apparatus as claimed in Claim 18, in which the composite pipe is produced in one operating step, wherein said inner tube guide device is preceded by an initial extruder which serves to produce the inner pipe.

20. Apparatus as claimed in Claim 18 or Claim 19, wherein said extruder is followed by means for cross-linking the synthetic resin material of said inner pipe and/or said outer pipe.

21. Apparatus as claimed in any one of Claims 18 to 20, wherein between the forming device and said extruder, there is arranged a welding device which serves to weld the metal strip along a longitudinal seam to form said metal covering.

22. Apparatus for producing a composite pipe, substantially as hereinbefore described with reference to and as illustrated in Figure 5, or Figure 6, of the drawings.

23. A floor heating system using a composite pipe as claimed in any one of Claims 1 to 1 7.