DE3390205T1 - Process for the production of a preferably flexible, thermally insulated pipe - Google Patents

Description

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Process for the production of a preferably flexible, thermally insulated pipe.

The invention relates to a flexible, thermally insulated pipe, preferably for underground district heating systems, in which it can be advantageous to use flexible pipes as small connecting pipes and the like to facilitate assembly. . ■■,,

The flexible pipes commonly used for such purposes consist of an inner thin-walled pipe made of steel or copper, a surrounding insulation in the form of polyurethane foam, and an outer protective jacket tube made of suitable plastic, mostly a corrugated polyethylene pipe. For flexible pipes, a soft polyurethane foam is usually used as the insulation material, while otherwise a rigid foam is used for district heating pipes, whereby the disadvantages must be accepted that the specific The weight of the soft foam is considerably higher than that of the hard foam, and last but not least that the soft foam is extremely hygroscopic.

Some manufacturers have therefore gone over to the To use hard polyurethane foam, another disadvantage must be taken into account, namely that the foam material breaks when the pipe is bent and this is of various types Reasons disadvantageous.

The purpose of the invention is to create a flexible pipe which does not show these disadvantages.

The invention is based on the knowledge that spe-_ special foams have been developed that are particularly good as

lation material for the present connection of soft and light materials are suitable, which have closed cells, and which are also sufficiently heat-resistant. In particular reference is made to a material known under the trademark FRELEN, a foam made of so-called "crosslinked" Is polyethylene and is manufactured in panels. The panels are semi-soft and resilient, and they can be rolled up be brought into tubular shape, with the opposite end faces the plate can be connected in a radial plane by gluing or the like.

Such foam tubes are suitable as insulation on or in flexible tubes, and this alone is used in relation to hard and soft polyurethane foam achieved an improvement. However, the invention goes a step further by specifies a method for producing the insulated pipe with which a particularly advantageous product is obtained.

This method according to the invention is characterized in that the insulating foam tube is attached in such a way that that it surrounds the iron or copper pipes tightly, and that the pipe then until the beginning of the melting of the inside of the Foam tube is heated so that the foam tube inside is connected to the outside of the inner tube. Such a connection could at least be achieved using the above crosslinked polyethylene can be achieved.

The process has the great advantage that the innermost layer of the non-hygroscopic foam is made into a rigid one Coating is transferred to the inner tube, in which case it is not important in practice if small leaks occur in the inner tube, e.g. cracks caused by bending the thin-walled pipe. Such a leak is in advance through the innermost Layer of building material sealed so that in case of liquid pressure is reasonably low in the inner tube, the medium is not in the foam because of the closed cells, and because of the

adhesion of the foam to the pipe surface in the area of the Leaks do not flow along the outside of the inner tube

An outflow of a medium from pipes covered with polyurethane foam are isolated can hardly be prevented, and especially not with the flexible foam types; with the hard foam types the outflow takes place more slowly, but cannot be prevented, i.e. the insulating capacity of the foam will decrease in a gradually expanding zone and because of the cracks in the foam caused by bending the tube there will quickly be a local decrease in the insulation capacity of the flexible pipes. With the invention you can so frequent, necessary and laborious repairs are complete be avoided. Another perspective of the invention is that it is realistic to have a relatively cheap inner tube use e.g. a pipe with reduced wall thickness and thus a pipe with increased flexibility. ,.

Another aspect of the invention is the possibility in principle desirable. way a firm connection between the outside of the foam tube and the inside of the produce outer jacket pipe. The jacket pipe is usually made of extruded polyethylene pipe, and precisely then, even if the foam tube is made of polyethylene, a Such a solid connection can be achieved by direct extrusion of the jacket tube around and along the foam tube, so that the foam tube is automatically heat-welded to the inside of the jacket tube. This welding is even then achieved when the jacket pipe is immediately after emerging from the extruder gland around the foam pipe by special tools is treated to achieve the corrugated shape.

The invention is described in more detail below with reference to the drawings. Show in it:

-IT'S-

Fig. 1 + 2 different stages in the production of an inventive Pipe,

3 shows a longitudinal section through part of the tubular element produced,

4 shows a side view to illustrate a further method step.

5 shows a longitudinal section showing the manufacture of the outer jacket in connection with the tubular element ¹ and

Fig. 6 is a perspective view of a modified one Manufacturing process of the insulated pipe.

In Fig. 1 it is shown how an elongated flexible Metal pipe 2 at one end, on the right, is connected to a compressed air source 4, while its other end is connected to an end piece 6 a foam tube 8, is enclosed, the other end 10 is tightly closed, the end piece 6 against the outside ' des- 'metal tube 2 is clamped.

By the natural inner diameter of the foam tube 8 is slightly smaller than the outer diameter of the metal pipe 2, but because of the air pressure from source 4 this becomes elastic Foam tube 8 widened slightly so that it can easily be over the Metal tube 2 can be drawn, the foam tube behind the end piece 6, where it is clamped against tube 2, inflated sen remains.

As mentioned above, the foam tube 8 can be rolled up of foam sheet elements, which can have a limited length and thickness, are formed. Thus, the pipe of the Lengthwise from several rolled up panel elements

what is caused by adjacent surfaces or glued joints 12 is indicated. Should the wall thickness of the foam tube be 8 An additional foam tube 14 with joints 16 can be insufficient to achieve the desired insulation of the tube 2 be attached to the outside of the foam tube 8, the attachment being carried out similarly to FIG. 2.

As shown in Fig. 3, care must be taken that the joints 12 and 16 of the two foam tubes 8 and 14 finally lie axially offset.

If the pipe 2, for example over a length of 50 m, is provided in this way with one or more insulating pipes 8, 14 has been provided, the opposite ends of the metal pipe 2 are connected to the electrical voltage of a power generator 18 connected, so that the tube 2 to the beginning of melting of the innermost surface layer of the foam 8, which the Outside of the metal tube 2 already elastically encloses, heated will. Melting the foam with the Outside of the metal pipe 2 connected.

If the foam tubes 8, 14 made of said cross-linked Are made of polypropylene, the foam is soft and elastic, so that it can be easily and without cracking together with the interior Tube 2 is bendable and it contains closed cells that prevent any spread of liquid through the material impede. If the foam is also connected to the surface of the inner tube 2, a possible leak in the pipe wall does not result in a continuous outflow of liquid into the foam or along the surface of the pipe 2 lead, at least not when the pressure in the pipe is as low as usual in district heating pipe systems.

The heat insulating tube described so far can with an outer protective jacket, e.g. simply through

Insertion into a separately produced plastic jacket pipe that is preferably designed as a corrugated pipe in order to facilitate the bending of the entire pipe.

Since the outer jacket tube is normally suitably made of polyethylene and said foam from the the same material, the invention offers the advantageous possibility of a desirable intimate connection between the adjacent surfaces of the foam and the jacket tube,. e.g. by gluing. A special possibility is a thermal fusion of these surfaces to effect, namely, to produce the jacket tube 20, as shown in FIG. 5, by extrusion, namely by an annular Nozzle 22 through and directly around the foam raw 8, 14, which is guided centrically through the nozzle; the outer hot jacket material welds to the outside of the Foam tube. The jacket pipe can be used in a known manner Corrugated jaws 24 are processed, which convert the smooth tube into an easier-to-bend corrugated tube.

For the corrugated jaws to work correctly, it can be advantageous if the soft foam tube is a little harder Has a surface layer, so the outermost foam tube element be of a higher specific gravity than the inner element or elements.

In Fig. 6 it is illustrated how it, based on a pair of strip-shaped foam sheets 26 and below Use of. Forming or guide tools 28 'is possible', a continuous molding of a foam tube 30 around the inner Execute pipe 2, the latter between the tools 28 is moved forward, thereby jn the foam board strips Form two half-shells, which then continuously when passing a pair of stationary welding mirrors 32 are welded together. Subsequent heating of the inner tube can, like in Fig. 4, by means of electric current or optionally also with

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hot oil. It is even a high frequency heating in a field next to or in front of the welding tools 32

possible. ''

The use of said special insulation material is also advantageous when the inner tube is made of plastic, and of course the connection of the outer one Jacket pipe, Fig. 5, regardless of the nature of the inner tube.

In the known heat-insulating pipes, the outer jacket pipe is used as mechanical protection and as protection against Penetration of water into the insulation material required. Thanks to the invention, the jacket pipe can be dispensed with, if no mechanical protection of the foam tube is required. It should be mentioned, however, that the possible connection the outer plastic pipe with the insulation foam Fusion welding in connection with the extrusion of the outer tube has the particular advantage that a perforation of the outer pipe does not give rise to water penetration into the outer pipe; albeit such penetrating water because of the closed cells of the insulation material cannot spread into it, on the other hand it would be possible for it to spread along the inside of the outer tube and another associated, more sensitive to water. Pipe system reached. It will stresses that the solution to this problem described is the same! is like that for preventing water from spreading along the inner pipe according to the first described aspect of the invention

Claims (1)

a- Expectations 1. A method for producing a preferably bendable, thermally insulated pipe, in which an inner metallic conduit pipe is cross-linked with a pipe made of insulating foam! Polyethylene or a corresponding thermoplastic foam, which has closed cells and is water and heat resistant up to a normal working temperature, is covered, characterized in that during or after the attachment of the foam pipe, the inner conduit pipe is overheated to such an extent that the inner surface of the SchauastoffÜberzug is glued to the outside of the inner tube by fusing. 2. The method according to claim 1, dadurc h characterized in that the heating of the inner tube is effected by introducing a heating medium or an electric current through the tube after the tube over its entire length, preferably a large production length of 50 m, for example, the foam insulation had received. 3. The method according to claim 1 or 2, characterized marked chn_et_j_ that. the foam cover is pulled over the conduit pipe as a preformed, elastic, expandable hose, the inner diameter of which in the free state is smaller than the outer diameter of the conduit pipe. - T-'AT. il. A method according to claim 3, characterized in that while the foam tube is being drawn up, compressed air is introduced into the space between the corresponding outer ends of the foam tube and the conduit pipe, these ends being temporarily closed. 5. The method according to claim 1, characterized in that the thermoplastic foam material is additionally fusion-welded to an outer plastic jacket tube, in that the latter is produced by hot extrusion directly onto the outside of the foam tube.