DE3216463A1 - Process for producing a flexible district heating pipe - Google Patents

Abstract

The invention relates to a process for producing a flexible district heating pipe having a media pipe (1) of metal and a foam insulation (2) in a plastic jacket (3), the latter being formed continuously around the media pipe. It achieves the object of providing such an endless production process which permits the continuous production of pipes of this type with or without spacers (4) and outstandingly meeting all modern quality requirements in one cycle and with relatively little expenditure. For this purpose, it is envisaged that the plastic jacket (3) is extruded as a tube concentric to the media pipe (1) and, directly thereafter, is cooled intensively, the foam insulation (2) being enclosed by the said tube or formed in it. <IMAGE>

Description

Method for producing a flexible district heating pipe

The invention relates to a method for producing a flexible District heating pipe with a central media pipe made of metal, preferably a stainless steel, and with a foam insulation in a plastic jacket, according to the preamble of claim 1.

District heating pipes of this type are, for example from DE-GM 1 987 451 known. So far they have been manufactured in such a way that a layer of a foamed plastic, e.g. made of polyurethane, in the form of a prefabricated Foam strip was applied, which was either laid around the pipe axis or wrapped around the pipe and then glued or welded to one to form a hose that encloses the metal pipe in a thermally insulating manner. About it was customary a separating film made of polyterephthalic acid ester enclosing these is applied, the Overlap edges. And finally it was done with a separate operation in a screw press then the outer jacket, e.g. made of polyvinyl chloride as seamless hose applied and possibly corrugated. This known manufacturing method requires a series of separate operations one after the other, namely hanging up or winding the separately prefabricated foam strip onto the metal tube, the subsequent welding of the edges of the foam strip, the application the release film and finally extruding the plastic jacket as well as its corrugation to achieve the necessary transverse compressive strength. Further Disadvantages are the difficulty between the pipe and the plastic outer jacket To arrange spacers, which at the same time act as a support from in addition within the thermal Insulation arranged electrical wires, e.g.

Moisture alarm cores or the like., Are used. The arrangement of spacers however, it is also preferred in many cases because it is unaffected the flexibility of such an endlessly manufactured cable - its strength, especially crush resistance - increase, so that the subsequent corrugation process of the outer jacket and less rigid foams less mechanical Strength, however, greater thermal insulation capacity can be used.

Another method of making such district heating pipes is known from DE-PS 15 04 632, which is used to produce a heat-insulating Cover made of a flexible foam, e.g. made of polyvinyl chloride on a bare bendable metal tube provides that the withdrawn from an unwinding drum and possibly straightened metal pipe, after applying a release agent introduced into an extruder, and in this with a foamable plastic is sprayed.

Depending on the temperature in the extruder, this foams out after it exits this on by itself or is caused to foam up by the supply of heat. Finally, the outer surface is applied to the metal pipe by extrusion Foam layer covered with a lubricant, and its pores will be in a Calibration device closed, whereupon the encased tube is cooled in the flow and fed to a winding drum by means of a special take-off device will. However, it can be before or after the cooling process by a further extruder are passed through, the additional insulating jacket on the already generated with the foam jacket covered pipe. Also with this known method are several separate work steps for the pipe production necessary, whereby the manufacturing cost increases. But the same is also true This method is particularly useful for district heating pipes with a larger diameter particularly useful arrangement of spacers neither provided nor readily to accomplish. The process temperature parameters are also particularly difficult here to be coordinated so that the foamable Plastic at the desired time after exiting the extruder through further Heat supply to the extent necessary to create a sufficiently dense closed-cell Forming foam insulation that meets modern requirements, such as they are, for example, in worksheet Q 167 of the Arbeitsgemeinschaft Industriebau eV (AG), Cologne for buried jacket pipe systems, which are factory-made with PUR rigid foam have produced thermal insulation, are indicated.

Finally, DE-OS 28 03 708 also describes a system for production a flexible multilayer insulating tube with one preferably made of plastic smooth inner tube, a plastic outer tube and an insulating layer made of foamed Plastic between the inner and outer pipe has become known, the core of which is a special trained coextrusion head of a double extruder, each with a special extruder for the preparation of the foam or plastic material for the outer tube as well as a take-off pipe-forming machine with a hollow form, which is directly lined up behind this are, in which the injection mouth for the extrusion of the outer tube and - even further preferred - which also forms a guide for the inner tube to be overmolded The injection mouth for the foam insulation protrude. Furthermore, according to the teaching this document before the double extruder an inner tube screw extruder for continuous Manufacture of a plastic inner tube, a calibration device for this and a push-through device feeding this to the twin extruder is arranged, as well as A winder is parked behind the take-off pipe forming machine.

In this known production plant for continuous endless production The inner pipe is made of Pernwärmeleitungsrohren of the type outlined above with the help the push-through device upstream of the extrusion head as a core through a concentric hole in the foam nozzle pushed and after leaving it Hole only fixed in position by the foam. This was based on the knowledge assumed that a flexible inner tube that can be flattened per se while maintaining it of the round cross-section with a foam plastic insulating layer and with a Outer pipe can be overmolded if only in the extrusion head arrangement and guidance of the inner tube in the manner described above. Furthermore, this is however, it is still necessary that the outer tube, which is still soft, after it has left the coextrusion head is taken directly from a hollow form, which hollow form an external calibration causes. This can be done by vacuum or internal pressure, with only one Question of the dimensioning of the volume flow for the plastic foam of the insulating layer and the setting of the pressure ratio is to ensure that there is a faultless insulating layer arises, but the inner tube does not lose its round cross-section in order to keep up with to be able to work with a plastic inner tube with a small wall thickness. same for but also for vacuum calibration or pressure calibration of the outer tube, whereby it seemed surprising that a vacuum cavity mold is capable of intervening of the foam also to hold the inner tube, as it were, and beyond the inner tube in the insulating layer made of the foam plastic surprisingly is also fixed in position concentrically. It goes without saying that the viscosity of the Foam plastic, from which the insulating layer is built, not too low may be set.

In this known production method, it is assumed that the mechanical Strength, especially compressive strength, one made solely from thermoplastic Plastics made pipe is sufficient. At for district heating pipeline purposes used Pipelines are provided, however, that these for a period of at least 50 years at a temperature up to 130 cc Should withstand a pressure of at least 16 bar. This requirement comes with a metallic inner tube better than in the manner described here.

When using a metallic that is essentially stable to transverse pressure The problems described with regard to the dimensional accuracy of the inner tube occur at the same time Foam-insulated and plastic-sheathed pipe only in to a lesser extent in relation to the outer tube or jacket.

However, the control of the temperature parameter is more problematic within the just extruded and still very hot when it emerges from the injection mouth Plastic jacket, which is around 250 oC or more at this point.

The foamable substances preferred for the stated purpose, in particular based on polyurethane, or PUR foams for short, foam exothermically, i.e. without supply of heat. Such a foam heats up by itself about 10000, which temperature range is not critical, but does not tolerate any additional Heat exposure, e.g. 150 cc for more than a very short period of about 10 seconds. It is therefore harmful if the PUR foam is exposed to external heat, as in the production method described with this known device is inevitable, much faster and more unevenly than foams by itself, because the cell distribution of the closed-cell foaming substance is uneven in contrast to the requirements, e.g. of the aforementioned worksheet Q 167 of the AGI. This is because cell walls can burst and also larger air pockets arise that - through internal heat convection - the desired high level of thermal insulation Reduce.

In addition to this disadvantage of the known method and its requirement for mechanical shaping, e.g. corrugation of the plastic outer jacket formed in this way immediately after its exit from the extruder there is also the Impossibility of simultaneous introduction of the mechanical strength the line increasing spacers as well as moisture detection wires or the like. It is therefore difficult to find a district heating pipe that meets the usual minimum requirements of the type described in this way by means of the system described.

The invention is based on the object of specifying a method which enables a district heating pipe of the type outlined above in continuous production and to be produced in one pass in such a way that it meets all the qualitative requirements, which are to be placed in such a modern line, to correspond in an excellent manner able, with both the manufacturing and the plant costs compared to the previous usual are reduced and with the help of both spacer-free and Pipelines of this type containing spacers and moisture detection wires in a simple manner and can be manufactured in a cost-saving manner. This task is carried out by the The invention shown in claim 1 is achieved.

What is essential here is the one immediately after the tubular outlet intensive cooling of the plastic outer jacket, which at the same time whose tubular shape is essentially stabilized and an essential part of it Heat is dissipated before the foam insulation is covered by the plastic jacket or is formed therein. The procedure here is preferably such that close to the Injection mouth, e.g. by means of a concentrically surrounding ring nozzle with an inner slot, a thin one which acts uniformly on it on all sides or is interspersed with it Coolant "wall" is used as spray pre-cooling, followed by further the The temperature of the plastic outer jacket gradually increases rapidly to one that is inside it complete foaming no longer impairing value reducing cooling. This basic idea applies both to the production of spacers as well as spacer-free district heating pipes of the type described.

Different variants of this method are with the claims 2 to 6 indicated, of which claim 2 the production of such district heating pipes with spacers, claim 3 the application of the plastic jacket directly on the surface of the foam insulation, claim 4 the introduction of the Foam in liquid or pre-expanded form in the between the inner tube and the plastic outer jacket, which solidifies rapidly as a result of the intensive cooling formed annulus, the claim 5, the whipping of the foam a noticeable Piece behind the exit of the plastic jacket from the extruder, and the claim 6 the only slightly graded coextrusion of the foam insulation with the plastic jacket concern with subsequent vacuum calibration of the latter.

Each variant of the new process has considerable advantages and results in an excellent one made of a foamed plastic Insulating layer with thermal insulation properties, e.g. made of a PUR foam of regular, as fine as possible cells, which in the radial direction on average have one Less than 0.4 mm in diameter and uniform in color. Depending on the type of district heating pipe to be produced, namely whether its foam insulation including the outer jacket for its mechanical strength, in particular crush resistance Should contribute, or the foam insulation - as a result of periodically spacers arranged in between - remains essentially unloaded, can the composition and the total pipe density of the foam are adjusted in such a way that that they are less with an average value of about 60 kg / m3 with a load-free arrangement than 40 kg / in3, on the other hand with a load-bearing arrangement a total pipe density of more than 80 kg / m3, with a high degree of closed-cell content of more than 88 %. As noted, it is preferred to form the foam insulation PuR foams are used, which are usually composed of two components and in connection with the so-called frothing process, whereby a propellant, E.g. one known under the name FRIGENR Trichlorofluomethane, Monofluorotrichloromethane, or the like.

be added to achieve a pre-expansion of the plastic can. The so ~ cream ~ -like pre-foamed in the one formed between the jacket and the inner tube Foam introduced into the ring cavity expands there when it continues automatically the already initiated foaming reaction to fill the entire cavity at a speed that is adapted to the withdrawal speed of the pipe, at the same time all air present in the annular cavity is displaced1 and the foam surface resting against the still moderately warm wall of the plastic outer jacket firmly adheres. This has the advantage that the district heating pipe is absolutely free of gaps in this area with itself as well as increased dimensional stability and mechanical Strength of the pipe, especially when it is designed without spacers. as Sheath material is polyethylene, especially the particularly resistant and flexible high-pressure polyethylene or through the addition of silanol due to the action of moisture crosslinkable polyethylene preferred. The latter has the further advantage of that it is in the course of its cross-linking caused solely as a result of the water cooling also removes moisture from the ring cavity enclosed by it and binds it.

As described above, the foam insulation can be according to different Process variants either - slightly graded - in coextrusion at the same time with extruded the plastic outer jacket and in their further foaming of this includes or even at a distance from the extruder outlet of the plastic outer jacket are injected and formed therein.

The preferred embodiment variant in each case is essentially based according to the dimensions and the intended use of the district heating pipe to be produced, in particular whether this - without spacers - is particularly light and flexible, but with relatively lower mechanical strength or with greater mechanical strength Strength and almost as flexible with spacers arranged therein as well with one the freedom of the foam insulation from moisture and thus the efficiency the thermal insulation ensuring wet line lead is to be produced, the for metrological reasons is preferably kept at a distance from the metal tube, such as this by means of clamping slots or openings in the spacers provided for this purpose is possible.

For the production of such a spacer having district heating pipe the media pipe, which is preferably corrugated, in particular ring corrugated, is preformed before the extrusion of the plastic jacket at regular intervals with e.g. segment-shaped, equipped with spacers having passages protruding from the center, with at least one of these passages is designed as a sector-shaped cutout of the spacer is. Then, through the passages, the preferably in a smaller than the Extruder length corresponding to the mutual spacing arranged spacers at least a moisture detector or the like. drawn and the foam forming the insulation, preferably in the pre-expanded state between the spacers on the surface of the media pipe injected or extruded around it in its direction of movement, while the plastic outer jacket, which was extruded in tubular form at the same time or immediately beforehand is already being cooled intensively. But it is according to a different variant of the method also possible with correspondingly intensive cooling of the one emerging from the extruder Plastic sheath this directly onto the surface of the previously if necessary to extrude calibrated and smoothed foam insulation. If this process variant for the production of a district heating pipe with spacers is used, it may be useful in some cases to do this before extrusion of the plastic outer jacket to be wrapped in a film, e.g. paper, e.g. if made of For assembly reasons, a slight lifting or pulling off of the outer jacket at junction points or pipe ends is desired.

According to a preferred embodiment of this method the plastic jacket is extruded just before the foam insulation is formed, and the foam forming this in the between the media pipe and the as The annulus created as a result of the intensive cooling, solidifying the plastic jacket injected. This can be done in such a way that the foam is a little behind the Exit of the plastic jacket from the extruder into the annulus created in this way is injected by means of a foam injection lance protruding into this, which is attached to the outside of the extruder, protrudes into this with its spray nozzle and is connected at its free outer end to a foam dosing device, to inject the foam in the pre-expanded state.

According to another variant of the method, in particular for the production of spacer-free district heating pipelines, which are nonetheless the have a high density, cellular structure and strength of the foam, it is intended that that the foam insulation in coextrusion with the plastic jacket almost at the same time is extruded with this, the jacket being cooled particularly intensively and vacuum calibrated while the extruded into the annular cavity guided by it around the media pipe Foam gradually foams up, and only - after displacing those contained in it Air - at one point on the plastic jacket for adhesive contact with its inner surface where it not only solidifies, but is also sufficiently cooled is.

The waiver of the corrugated metallic corrugation that was generally used up to now Outer jacket and the flexible design of the plastic jacket of a manufactured in this way District heating pipe bring not only considerable savings in production costs the advantages of lower weight, better flexibility and freedom of corrosion problems with it, for continuous operation at 100 OC and one Pressure of at least 16 bar for long-term district heating pipes this kind.

The manufacturing problem solved by the invention consisted primarily in the foam in the most elegant way possible at the same time as the tubular extrusion to bring the plastic jacket into this. This can be done both by coextrusion foaming in a double injection head specially set up for this purpose with simultaneous jacket extrusion and cooling, or by injecting the pre-expanded foam into the already Shortly before extruded and intensely cooled plastic jacket take place like this is explained in more detail below. The continuous print of one made in this way District heating pipe can be done by means of an extraction device such as is shown and described in DE-PS 22 03 474. The following is the invention with further details and advantages of the same explained in more detail with reference to the drawing.

The drawing shows: FIG. 1 in a schematic representation a for Application of a process variant set up production line, partially cut and FIG. 2 shows its end view.

The production line shown in the drawing for production a flexible district heating pipe with a central media pipe 1 made of metal and with a foam insulation 2 in a plastic jacket 3 comprises next to deq Sequence 7, not shown, take-off and unwinding devices, one for each variant of the method specially set up extruder 7, which has a spray pre-cooling 11, a vacuum calibration cooling section 10 and an after-cooling section 43 # n coupled to a heat exchanger 12 in the production direction are assigned one behind the other, the latter also serving as a pipe guide for a district heating pipe manufactured in this way is used before it is withdrawn. In a similar way A pipe guide can also be arranged upstream of or at the extruder inlet Insertion opening be attached.

This is not necessary if spacers were used beforehand at regular intervals 4 equipped media pipes 1, as with one of these the spacers 4 also at the same time the concentric support and guidance of the pipe during its passage through the extruder 7, the plastic jacket 3 being approximately at the same time concentric at a distance around the jacket tube 1 extruded tubular and in the so formed Annular space 5 between the plastic jacket 3 and the media pipe 1 a foam insulation 2 forming foam is injected. It is advantageous before the introduction of the media pipe 1 equipped with spacers 4 at least one wet line reader 6 pulled through the passages of the spacer 4 and attached to the corresponding Clamps or slots thereof attached.

The spacers 4 can be shaped differently, provided that they concentric pipe guidance and support of the media pipe 1 and at the same time free Allow the liquid or pre-expanded foam to flow through and ensure its foaming that completely fills the pipe gap.

It is essential here that the spacers 4 have at least one sector-shaped Have cutout and all cutouts are aligned so that one arranged in the extruder foam injection lance 14 of these passes unhindered can be. For this purpose, for example, they are also essentially star-shaped Suitable for spacers.

By means of the front attached to a holder 15 on the extruder 7 and - penetrating its passage opening - foam injection lance protruding far into the space behind it 14, which is connected to a foam metering device 16 at its outer end can be, the foam preferably prefoamed by means of a propellant gas through its end nozzle so into the inside of the extruded and through intense Cooling to below the critical temperature for the foam plastic jacket 3 injected so that it fills this completely foamingly, the spacers encloses and displaces the air present in the annular cavity 5. Here are the Distances and thickness ratios as well as the take-off speed of the so manufactured Pipe so coordinated that - what the quality of the foam insulation 2 essential Importance is - the foaming is proportionate can be done slowly, calmly and evenly. For this it is necessary that the spray nozzle the injection lance 14 sufficiently deep in the manufacturing direction into the annular cavity 5 protrudes and the injection end points downwards so that the exiting Foam from below evenly and consistently with a certain slope of its able to build up the surface facing the outside air.

At the same time, the tubular extruded plastic jacket 3, first by means of the pre-cooling 11 immediately upon its exit from the spray mouth pre-cooled and then in the vacuum calibration cooling section 10, which with a special cooling device 9, e.g. a cooling coil through which the brine flows, as well as is equipped with an air pump 8, at the same time calibrated true to shape, smoothed and cooled down below 150 ° C. In this state, the outer shell thus formed becomes 3 together with its inner tube 1 and optionally the spacers 4 then passed through a post-cooling section 13 coupled to a heat exchanger 12, so much residual heat is still withdrawn from him that his internal temperature is not has more than about the temperature of 100 ° C., which is favorable for foaming. the After-cooling section 13 also serves as a pipe guide, from which the completed District heating pipe / inside which meanwhile the thermal insulation 2 their Lasting shape and consistency was achieved by means of a known pull-off device fed to a winding device, which are not shown here.

Similarly, it can - without the need for spacers 4 - such a district heating pipe can be created in a manner known per se, however, to ensure the required quality, in particular density, heat resistance, Strength and thermal insulation of the foam insulation 2 with simultaneous formation of the plastic outer jacket 3 a similar intensive and sustainable cooling of the Plastic outer jacket formed almost at the same time as the foam insulation 3 must be brought forward. This can be done in the same way as this is shown in connection with the method variant described above.

Claims (6)

Claims: 1. A method for producing a flexible district heating pipe with a central media pipe (1) made of metal, preferably a stainless steel, and with a foam insulation (2) in a plastic jacket (3), the foam insulation (2) is continuously formed around the bare media pipe (1), d ad u r c h g e k e n n n z e i c h -n e t that the plastic jacket (3) is evenly spaced concentrically around the media pipe (1) continuously as a hose made of a thermoplastic, however, after solidification or hardening, it is flexible and particularly resistant at the same time Plastic, such as high-pressure polyethylene, crosslinkable polyethylene or the like. extruded, and is intensively cooled immediately afterwards, whereby the foam insulation (2) encompassed by this or is formed therein. 2. The method according to claim 1, d a d u r c h g e k e n n -z e i c h n e t that the preferably corrugated preformed media pipe (1) prior to extrusion of the plastic jacket (3) at regular intervals with preferably segment-shaped, radially protruding passages having spacers (4) is fitted by the passages of the same at least one moisture detector (6) or the like. pulled, and the foam forming the insulation (2), preferably in the pre-expanded state injected between the spacers (4) on the surface of the media pipe (1) or is extruded around it in its direction of movement. 3. The method according to claim 1 or 2, d a d u r c h g e -k e n n z e i c h n e t that the plastic jacket (3) directly on the surface of the previously optionally calibrated and smoothed foam insulation (2) or a separating film covering this, e.g. made of paper, is extruded. 4. The method according to claim 1 or 2, d a d u r c h g e -k e n n z e i c h n e t that the plastic jacket (3) immediately before the formation of the foam insulation (2) extruded, and the foam that forms it in between the media pipe (1) and the plastic jacket that solidifies as a result of the intensive cooling (3) created annulus (5) is injected. 5. The method according to claim 4, d a d u r c h g e k e n n -z e i c h n e t that the foam is a little behind the outlet of the plastic jacket (3) is injected into the annular space (5) created here. 6. The method according to claim 4, d a d u r c h g e k e n n -z e i c h n e t that the foam insulation (2) in coextrusion with the plastic jacket (3) extruded and solidified approximately at the same time, with the jacket being vacuum calibrated will.