GB2081415A - Flexible thermally insulated pipe and process for its manufacture - Google Patents

Abstract

The invention is concerned with a flexible thermally insulated pipe for domestic installation, comprising a metal tube and a layer of thermal insulation carried thereby, applied during manufacture. According to the invention, the said layer comprises a corrugated flexible plastics tube, an outer plastics sheath being extruded thereover. The process of the invention for the manufacture of the pipe is characterised in that the corrugated flexible plastics tube is run off from a substantially circular coil and is slit longitudinally, the metal tube is passed into the open slit, and the outer sheath is thereafter applied by extrusion.

Description

SPECIFICATION Flexible thermally insulated pipe and process for its manufacture The invention relates to a flexible thermally insulated pipe for domestic installations, of a kind comprising a metal tube, preferably a drawn seamless copper tube, and a layer of thermal insulation carried by the tube, this layer being applied during manufacture.

Flexible copper pipes, covered during manufacture, i.e. at the factory, with a plastics sheath, have proved successful in domestic installation, e.g. as hot water pipes or supply pipes running to central heating radiators. To improve the insulating effect, a "webbed sheath" has been used, i.e. the plastics sheath has been given webs with a triangular profile, these webs extending in the longitudinal direction of the pipe and resting on its surface. In addition to giving improved thermal insulation, the plastics sheath can easily be stripped off in order to join pipes together or to branch them off. This known type of flexible pipe has the advantage also that, due to its good flexibility, it can be drawn off and laid directly from a coil, without pipe-benders or similar devices being necessary.

For cases in which energy-conservation requirements prescribe minimum insulation values, a second type of copper pipe similarly pre-insulated during manufacture has proved advantageous, the insulating layer of this pipe consisting of a polyurethane foam sleeve and an outer sheath. The polyurethane foam is similarly applied during manufacture, the outer sheath, or portions thereof, serving as a mould for the foam as it develops. The disadvantage of this construction is to be seen in the fact that only hard or hard-drawn copper pipes can be used in an economical production process. The hardness of the copper pipes and the brittleness of the polyurethane foam mean that these pipes are no longer capable of being bent. For this reason, they are preferably used for riser-pipes.

It has long been desirable that a thermally insulated pipe should be made available which not only possesses the advantages with respect to laying of the known flexible pipes described above but also has significantly improved thermal insulation properties approaching those of the second type of pipe described above.

It is an object of the present invention to provide a flexiblethermally insulated pipe which, in addition to having good flexibility, can be installed without difficulty, i.e. can easily be stripped of its sheath, and exhibits good thermal insulation properties, e.g. a minimum thermal insulation of 0.08 W/mk.

According to the invention, a pipe of the kind initially mentioned herein is characterised in that the layer of thermal insulation comprises a corrugated flexible plastics tube and an outer plastics sheath extruded over the flexible plastics tube. With this construction, it is desirable that the outer plastics sheath should not penetrate into the valleys of the corrugations of the corrugated flexible plastics tube, and that a thermally insulated pipe with a smooth surface should be produced. It is especially advantageous for the flexible plastics tube to consist of a polypropylene tube with annular corrugation.

Polypropylene is a plastics material or synthetic resin which remains mechanically stable at temperatures of up to 1 200C in typical cases. The annular corrugation has the advantage that no significant convection need occur, and that the thermally insulated pipe can be sealed to a very great extent against water-leakage in the longitudinal direction. It is often advantageous to interpose a film of a heat-resistant plastics material, preferably of polypropylene, between the metal tube and the flexible plastics tube. This film of e.g. polypropylene can lower the temperature in the region of the relevant surface of the flexible plastics tube, particularly if a polypropylene foam is employed.Another advantageous optional feature is the application of at least one layer of paper tape, preferably crepe paper, between the metal tube and the flexible plastics tube, this tape preferably being applied to the metal tube in the form of a spiral with the edges of the tape overlapping. Crepe paper tape is even more suitable for reducing temperature gradients than e.g. polypropylene film.

It is usually expedient to use a flexible plastics tube with a longitudinal slit. Flexible plastics tubes are obtainable on the market as extremely cheap products, and are readily slit longitudinally so that they can be laid around the copper tube or other metal tube. A tape, applied in the form of a spiral, can be used to close the longitudinal slit, this tape being appropriately of terephthalate polyester film.

This film tape is extremely resistant to tearing and is consequently highly suitable for a commercial production procedure. Furthermore, the interposition of this film tape as an intermediate layer between the flexible plastics tube and the outer sheath can further restrict convection in the sheath assembly.

Another advantageous optional feature is the interposition of a metal foil, preferably an aluminium foil, or a plastics foil coated with aluminium by vapour-deposition, between the flexible plastics tube and the outer sheath, this foil being applied in the form of a spiral, with overlapping. By means of this last-mentioned optional feature, the slit in the flexible plastics tube is, on the other hand, readily closed, and on the other hand a radiation barrier is incorporated, significantly increasing the thermal insulating effect of the sheath.

The outer sheath advantageously possesses internal ridges with a substantially triangular profile, these ridges having their apices pointing inwards, extending in the longitudinal direction of the pipe, and resting on the flexible plastics tube or on the film tapeorfoil surrounding the latter, if present. By the use of this ribbed sheath the areas of direct or indirect contact with the flexible plastics tube can be kept quite small; there can in fact be merely point contact. Heat conduction can be kept down to a very great extent by this point contact.

The present plastics outer sheath may be of e.g. a polyvinyl chloride composition incorporating filling material. Another possibility, however, is for the plastics outer sheath to be in the form of a webbed polyethylene sheath.

The invention includes a process for manufacturing a pipe according to the invention characterised in that a corrugated flexible plastics tube running from a substantially circular coil is slit longitudinally, the requisite metal tube is passed into the open slit, the slit is closed, and the requisite outer sheath is thereafter applied by extrusion. It is, however, also possible to pull off from a drum a flexible plastics tube which has already been slit longitudinally. After the pipe has been passed into the open slit, in either case, the slit can be closed by circumferential wrapping with a tape of terephthalate polyester film, aluminium foil or other metal foil, or a plastics foil coated with aluminium by vapour-deposition.

The invention is explained in more detail by reference to the accompanying diagrammatic drawing, the single Figure of which is a fragmentary perspective view of a pipe according to the invention, various portions of the different layers of this pipe having been cut away.

The pipe shown in the Figure comprises a drawn seamless copper tube 1 having a wall thickness of approximately 1 mm and an external diameter of 22 mm. The tube 1 is circumferentially wrapped with a layer 2 of crepe paper. A flexible plastics tube 3 surrounds the layer 2 of crepe paper, it being possible to manufacture this flexible plastics tube 3 by longitudinally slitting a plastics pipe provided with an annular corrugation. To produce an assembly as so far described, the copper tube 1, provided with the layer 2, is run into the flexible plastics tube 3, which is gaping open, the slit 4 of the flexible plastics tube 3 is closed, and a tape-winding 5 is applied. This tape-winding 5 may suitably consist of e.g. terephthalate polyester, or of a plastics tape which has been coated with aluminium by vapourdeposition, or even simply of metal.After the application of the winding 5, an outer sheath 6 is applied by extrusion. The outer sheath 6 possesses internal ridges 7; these project inwards and rest on the windings 5. The lines of contact of these ridges 7 with the winding 5, and the lines of (indirect) contact of the flexible plastics tube 3 with the ridges 5, these lines of (indirect) contact extending at right angles to the lines of contact of the winding 5 and ridges 7, form together bridging points whose area is so small that they very effectively reduce radial heat conduction at this stratum of the structure. The winding 5 prevents any significant convection between the cavities produced by the corrugation of the tube 3 and the cavities between the ridges 7. If the winding 5 is metallised, or if it is of metal, it will additionally serve as a radiation barrier. The temperature at the surface of the copper tube 1 can thus be kept at an acceptable value.

The insulation of the construction shown can be stripped off without difficulty, has good flexibility, and possesses a thermal insulation value of less than 0.08 W/mk.

Claims (16)

1. Flexible thermally insulated pipe for domestic installation, comprising a metal tube and a layer of thermal insulation carried by the tube, this layer being applied during manufacture, characterised in that the layer of thermal insulation comprises a corrugated flexible plastics tube and an outer plastics sheath extruded over the flexible plastics tube.

2. Pipe according to claim 1, characterised in that the metal tube is a drawn seamless copper tube.

3. Pipe according to claim 1 or 2, characterised in that the flexible plastics tube is a flexible polypropylene tube with annular corrugation.

4. Pipe according to claim 1, 2 or 3, characterised in that a film of a heat-resistant plastics material is interposed between the metal tube and the flexible a plastics tube.

5. Pipe according to claim 4, characterised in that the said film is of polypropylene.

6. Pipe according to any preceding claim, characterised in that at least one layer of paper tape is applied between the metal tube and the flexible plastics tube.

7. Pipe according to claim 6, characterised in that the said tape is of crepe paper.

8. Pipe according to claim 6 or 7, characterised in that the said tape is applied to the metal tube in the form of a spiral with the edges of the tape overlapping.

9. Pipe according to any preceding claim, characterised in that the flexible plastics tube has a longitudinal slit, and a tape of terephthalate polyestes film is interposed between the flexible plastics tube and the outer sheath, this film tape being applied in the form of a spiral.

10. Pipe according to any preceding claim, characterised in that an aluminium foil or other metal foil or a plastics foil coated with aluminium by vapourdeposition is interposed between the flexible plastics tube and the outer sheath, this foil being applied in the form of a spiral, with overlapping.

11. Pipe according to any preceding claim, characterised in that the outer sheath possesses internal ridges with a substantially triangular profile, these ridges having their apices pointing inwards, extending in the longitudinal direction of the pipe, and resting on the flexible plastics tube or on the film tape or foil surrounding the latter, if present.

12. Pipe according to any preceding claim, characterised in that the plastics outer sheath is of a A polyvinyl chloride composition incorporating filling' material.

13. Pipe according to any of claims 1 to 11, characterised in that the plastics outer sheath is in the form of a webbed polyethylene sheath.

14. Pipe according to claim 1, substantially as described with reference to the accompanying drawing.

15. Process for manufacturing a pipe according to claim 1, characterised in that a corrugated flexible plastics tube, running from a substantially circular coil, is slit longitudinally, the requisite metal tube is passed into the open slit, the slit is closed, and the requisite outer sheath is thereafter applied by extrusion.

16. Process according to claim 15, characterised in that the closing of the slit is carried out by circumferential wrapping with a tape of terephtha late polyester film, aluminium foil or other metal foil, or a plastics foil coated with aluminium by vapour- deposition.