GB2130679A

GB2130679A - Process for producing thermally insulated piping

Info

Publication number: GB2130679A
Application number: GB08330022A
Authority: GB
Inventors: Friedrich Ebeling; Gerhard Klein; Peter Rohrig; Hans Martin Schmidtchen
Original assignee: KM Kabelmetal AG
Current assignee: KM Kabelmetal AG
Priority date: 1982-11-13
Filing date: 1983-11-10
Publication date: 1984-06-06
Also published as: AT399123B; KR840006522A; NL192216C; FI78774C; FI833951A0; FI78774B; ES527141A0; ATA369783A; FI833951A; ES8406111A1; GB2130679B; GR79618B; CH665167A5; IT8349307A0; IT1168225B; FR2536007A1; FR2536007B1; KR920004612B1; NL8303743A; GB8330022D0

Abstract

In a process for producing thermally insulated piping comprising a metal tube (2), a foamed plastic insulating layer, and an outer sheath (9), the latter is formed from a flexible strip in order to obtain a pipe which can readily be bent for installation, the overlapping edges of this strip being joined by adhesive-bonding. The outer sheath composed of the flexible plastic strip is supported from the outside during the production of the insulating layer. A flexible, closed-cell polyurethane foam is introduced from a nozzle (10). A spacer-helix (7) is applied around the tube (2) before the sheath (9) is added. <IMAGE>

Description

SPECIFICATION Process for producing thermally insulated piping This invention relates to a process for producing thermally insulated piping, wherein: a spacer-helix is applied around a tube of copper or other metal; the metal tube carrying the spacer-helix is sheathed by means of a polyvinyl chloride or other plastic strip which is fed longitudinally beside the metal tube, bent round into the form of a slit tube, and joined at its longitudinal edges; and a self-foaming plastic foam forming mixture is deposited in the bentround plastic strip, before its longitudinal edges are joined, this mixture being polyurethane-based, and, when the longitudinal edges of the strip have been joined, foaming to fill the annular space between the metal tube and the plastic strip.

German Offenlegungsschrift 1,960,932 has disclosed a process as just mentioned. However, this known process is suitable only for producing rigid thermally insulated piping. The reason for this is that a stiff plastic strip is used to form the outer sheath. Since this plastic strip also forms the mould for the foam as it is developing, it must be sufficiently stable in itself to be able to withstand the pressure generated as it becomes filled with foam. For this reason, it was considered necessary to use a comparatively thick strip, composed of rigid polyvinyl chloride. This material was very suitable as a mould for the foam and even remained dimensionally stable despite the heat generated as the foam develops.

It is an object of the present invention to provide a process capable of producing flexible thermally insulated piping, including piping which can be coiled to form circular coils approximately 1 m in diameter, and which, in the course of installation, can also be laid in a bent state, that is to say without using special components affording pipe-bends.

According to the present invention, a process as first mentioned herein is characterised in that: (a) a pliable plasticised polyvinyl chloride strip or other pliable plastic strip is used as the plastic strip; (b) the strip is so bent round that its longitudinal edges overlap, and these edges are joined by adhesive-bonding; (c) the thickness of the plastic strip between 0.08 and 0.40 mm, (d) the assembly comprising the metal tube, the spacer-helix and the plastic strip which has been bent round into the form of a slit tube and adhesive-bonded at its overlapping longitudinal edges is supported from the outside along the region along which foaming is taking place; and (e) a flexible, closed-cell polyurethane foam is used as the foam.

It is advisable that a soft-annealed tube should be used. The process may thus start with a soft annealed tube, supplied in coil form; or alternatively, the tube may be annealed in the course of the process, passing through an annealing unit continuously, immediately before the spacer is applied. It is normally necessary to straighten the metal tube before it runs into the equipment in which the present process is carried out. As a pliable plastic strip is used, the thermally insulated piping can readily be bent, without causing the plastic strip to tear. The adhesivebonding of the overlapping edges of the strip is intended to ensure that they are securely joined, so that the seam does not tear open, even in the event of bending.The thickness of the plastic strip, as specified above, is between 0.08 and 0.40 mm, the particular value chosen depending on the outer diameter of the foam layer. To ensure that the comparatively soft plastic strip does not deform while the foam forming mixture is foaming, the plastic strip which has been bent into the form of a slit tube is supported from the outside until foaming is completed. In contrast to the known process, in which, for insulating reasons, a rigid polyurethane foam was used, a flexible, closed-cell polyurethane foam is used here, which further enhances the flexibility of the piping, without the foam crumbling or tearing on being bent.The piping produced by the process of the invention can be wound on to coils of less than 1 metre diameter without difficulty, that is to say without the outer sheath tearing, or the foam layer deforming in an impermissible manner, and it can also be laid after having been bent, again without difficulty.

In the above-mentioned adhesive-bonding, the edges of the strip may be adhesive-bonded by means of a solvent, or solution-type adhesive, based, for example, on cyclohexanone and/or tetrahydrofuran. These adhesives have proved exceptionally suitable, and make possible a secure adhesive-bonded seam. However, a hotmetal adhesive can instead be used with advantage.

The piping (i.e. the sheathed metal tube) may be led through a sizing device, for example a tube, a helix, or a series of two or more perforated discs, in which the comparatively soft plastic strip is supported. The inside diameter of the sizing device will naturally correspond to the desired outside diameter of the finished thermally insulated piping. In addition to ensuring dimensional stability, the external support thus provided can ensure that the overlap-seam is adhesive bonded in the optimum manner. The pressure of the foam, pressing against the seam from the inside, is contained by the sizing device, causing the overlapping edges of the strip to be firmly pressed against each other.In order to keep the frictional forces at the outer periphery of the piping as low as possible as it passes through the sizing device, the piping (strictly speaking, its plastic sheath) may be externally lubricated as it passes through the sizing device. Suitable lubricants are of course those which do not attack the polyvinyl chloride or other plastic of the pliable strip, e.g. water, to which it is possible, if required, to add anti-friction agents, e.g. soaps, or alternatively oils or the like.

In accordance with a preferred feature of the invention, the plastic strip which has been bent round into the form of a slit tube is surrounded, during the foaming of the foam forming mixture, by a temporary outer supporting sheath formed from a strip of paper or other material having the requisite mechanical strength fed longitudinally beside the piping and adhesive-bonded at its edges, which can be removed from the finished piping, preferably after the foam has cured. This temporary sheath material, e.g. paper, is normally applied, in the form of a strip fed longitudinally beside the piping, around the plastic strip with a substantial overlap of its edges so that, after the strip of (e.g.) paper has been bent into the form of a slit tube, its edges can readily be joined by means of a suitable adhesive.The inside diameter of the tube of (e.g.) paper formed in this way corresponds to the outside diameter of the finished thermally insulated piping. This external support by a temporary sheath serves, on the one hand to protect the pliable plastic strip from being undesirably deformed, and in addition, to ensure that the overlap-seam of the pliable plastic strip is properly adhesive-bonded. The pressure of the foam, bearing against the overlap-seam from the inside, is contained by the temporary outer sheath, so that the overlapping edges of the plastic strip are firmly pressed against each other.

When the above-mentioned preferred feature of the invention is adopted, it is advantageous to arrange for the introduction of a textile thread, for example a nylon thread, running longitudinally between the temporary supporting sheath and the plastic strip which has been bent round into the form of a slit tube, this thread being employed as a tearing thread in removing the temporary sheath. This tearing thread allows the temporary supporting sheath to be removed without difficulty. However, the temporary supporting sheath can remain on the piping as a protection during delivery and be removed only on arrival at the point of installation.

The invention will be explained in more detail by reference to the accompanying diagrammatic drawings, in which each of Figures 1 and 2 is a side elevation of equipment employed in a process according to the invention.

In the case of Figure 1, a seamless, drawn copper tube 2 is pulled from a coil 1 and is continuously straightened by means of a set of straightening rollers 3. The straightened tube 2 is then led into a continuous-type annealing unit 4, in which it is soft-annealed by resistanceannealing. The annealed copper tube 2 is then restraightened by means of a further set of straightening rollers 5. This soft copper tube 2, prepared in this way, is furnished, by a tangential applicator 6, with a spacer-helix 7, which can be, for example, a paper-based twine or, alternatively, a strand of foam material. A plastic strip 9, pulled from a stock reel 8, is positioned around the spacer-helix 7 and is gradually bent round into the form of a slit tube. This plastic strip 9 is preferably composed of plasticised polyvinyl chloride, and has a thickness of approximately 0.2 mm.Before the plastic strip 9 is formed into a closed tube, a plastic foam forming mixture, usually comprising a polyol and an isocyanate, is sprayed on to the plastic strip 9, by means of a spraying device 10.

An adhesive is applied, by means of a metering device 11, to the longitudinal edges of the plastic strip 9, and the edges of the s#trip are firmly pressed against each other. The assembly comprising the plastic strip 9 which has been formed into a tube, the copper tube 2, which is centered by the spacer 7, and the foam forming mixture present in the annular space between 2 and 9 is now run into a supporting and sizing device 12, which can comprise, for example, a sizing tube, a series of two or more perforated discs, or, alternatively, as actually represented in the Figure, an elongate wire helix. The inner diameter of the wire helix 12 corresponds to the outer diameter of the finished, thermally insulated piping 13. The wire helix 12 is intended to prevent the plastic strip 9 from deforming, in an undesirable manner, as a result of the pressure generated by the foam.For this reason, the wire helix 12 is made sufficiently long, in the axial direction, to ensure that the foaming process is complete at the end of the wire 12. A closed-cell polyurethane foam is used as the foam, and the formulation and conditions of use of the foam forming mixture adjusted so as to produce a foam sufficiently soft to enable the entire thermally insulated piping 13 to bend easily. A lubricant, for example water containing an anti-friction additive, is applied to the thermally insulated piping 13 as it passes through the wire helix 12, this lubricant being supplied from a wetting appliance 14. The essential function of the lubricant is to reduce the friction between the plastic strip 9 and the wire helix 12, but it can serve in addition to produce a certain degree of cooling during the foaming process.A caterpillar pull-off device 15, positioned downstream of the wire helix 12, grips the finished thermally insulated piping 13. This caterpillar pulloff device 15 is operated synchronously with the sets of straightening rollers, 3 and 5, which like it are power-driven. The finished thermally insulated piping 13 is then wound into circular coils by means of a winding unit 16, and is cut off in desired lengths.

In the case of Figure 2, which represents a modification of that of Figure 1, the assembly comprising the plastic strip 9 which has been formed into a tube, the copper tube 2, which is centered by the spacer 7, and the foam forming mixture present in the annular space between 2 and 9, is surrounded by a temporary supporting sheath. For this purpose, a strip 18 of strong paper, supplied from a stock reel 17, is bent round the said assembly, being gradually formed into a tube. In the course of this shaping operation, a strong textile thread 19, supplied from a stock reel 20, is run in between the plastic strip 9 and the paper strip 18, in the longitudinal direction of the pipe. The temporary supporting sheath formed from the paper strip 18 is securely adhesive-bonded at its edges, by means of an adhesive-bonding device 21.The inner diameter of the temporary supporting sheath corresponds to the outside diameter of the finished thermally insulated piping 13. The temporary supporting sheath is intended to prevent the plastic strip 9 from deforming, in an undesirable manner, as a result of the pressure generated by the foam. For this reason, the temporary supporting sheath remains on the plastic strip 9 until the foaming process is complete. A closed-cell polyurethane foam is used as the foam, which is arranged to be sufficiently flexible for thermally insulated piping 13 to be bent easily. Further downstream there is a caterpillar pull-off device 1 5 which grips the complete assembly comprising the thermally insulated piping and the temporary supporting sheath. This caterpillar pull-off device 15 is operated synchronously with the straightening rollers, 3 and 5, which like it are power-driven.

Beyond the caterpillar pull-off device 1 5, the temporary supporting sheath is cut open, in the axial direction, by means of the tearing thread 19, is stripped off, and is removed in pieces, shown at 22. The finished thermally insulated piping 13 is then wound into circular coils, by means of a winding unit 16, and is cut off in desired lengths.

By the use of a soft-annealed copper tube, a flexible polyurethane foam, and a plastic strip 9, the latter being composed of plasticised polyvinyl chloride, a successful process has been provided for the production of flexible factory-preinsuiated piping; the problems arising in respect of the manufacturing procedure have in fact been solved in an advantageous manner.

Claims

1. A process for producing thermally insulated piping, wherein: a spacer-helix is applied around a tube of copper or other metal; the metal tube carrying the spacer-helix is sheathed by means of a polyvinyl chloride or other plastic strip which is fed longitudinally beside the metal tube, bent round into the form of a slit tube, and joined at its longitudinal edges; and a self-foaming plastic foam forming mixture is deposited in the bentround plastic strip, before its longitudinal edges are joined, this mixture being polyurethane-based, and, when the longitudinal edges of the strip have been joined, foaming to fill the annular space between the metal tube and the plastic strip: characterised in that (a) a pliable plasticised polyvinyl chloride strip or other pliable plastic strip is used as the plastic strip; (b) the strip is so bent round that its longitudinal edges overlap, and these edges are joined by adhesive-bonding; (c) the thickness of the plastic strip is between 0.08 and 0.40 mm, (d) the assembly comprising the metal tube, the spacer-helix and the plastic strip which has been bent round into the form of a slit tube and adhesive-bonded at its overlapping longitudinal edges is supported from the outside along the region along which foaming is taking place; and (e) a flexible, closed-cell polyurethane foam is used as the foam.

2. A process according to claim, characterised in that the overlapping bent-round edges of the strip are adhesive-bonded by means of a solvent, a solution-type adhesive based on cyclohexanone and/or tetrahydrofuran, or another solution-based adhesive.

3. A process according to claim 1, characterised in that the adhesive-bonding of the overlapping bent-rodnd edges of the strip is effected by means of a hot-melt adhesive.

4. A process according to claim 1, 2 or 3, characterised in that the piping is led through a sizing device in the form of a tube, a series of two or more perforated discs, or a helix.

5. A process according to claim 4, characterised in that the piping is externally lubricated as it passes through the sizing device.

6. A process according to claim 1, substantially as described with reference to Figure 1 of the accompanying drawings.

7. Insulated piping produced by a process according to any of the preceding claims.

8. A process according to any of claims 1 to 5, characterised in that, during the foaming of the foam forming mixture, the plastic strip which has been bent round into the form of a slit tube is surrounded by a temporary outer supporting sheath formed from a strip of paper or other material having the requisite mechanical strength fed longitudinally beside the piping and adhesivebonded at its edges, which can be removed from the finished piping.

9. A process according to claim 8, characterised in that the temporary sheath is removed from the finished piping after the foam has cured.

10. A process according to claim 8 or 9, characterised in that a longitudinally running thread is introduced between the temporary supporting sheath and the plastic strip which has been bent round into the form of a slit tube, this thread being employed as a tearing thread in removing the temporary sheath.

1 A process according to claim 8, 9 or 10, substantially as described with reference to Figure 2 of the accompanying drawings.

12. Insulated piping produced by a process according to claims 8, 9, 10 or 1 1.