WO2002073083A1

WO2002073083A1 - A process for the manufacture of foam-insulated pipes

Info

Publication number: WO2002073083A1
Application number: PCT/DK2002/000172
Authority: WO
Inventors: Lars Valentin Nielsen; Per Poulsen
Original assignee: Alstom Power Flowsystems AS
Current assignee: Logstor AS
Priority date: 2001-03-14
Filing date: 2002-03-14
Publication date: 2002-09-19
Anticipated expiration: 2003-09-14
Also published as: EP1397609A1

Abstract

A foam-insulated and polyethylene-cased pressure pipe, e.g. for use in district heating, is manufactured in a continuous process by foaming between a diffusion barrier tube and the pressure pipe. The foaming quality is intermittently checked by inspection of the foam itself through a transparent part of the diffusion barrier tube, which is subsequently given diffusion barrier properties by means of a strip of aluminium laminated adhesive foil.

Description

A process for the manufacture of foam-insulated pipes.

The invention relates to a process for the manufacture of foam-insulated pipes of the kind which comprises an inner pressure pipe, a foam coat, at least one diffusion barrier comprising aluminium which is formed in tubular shape, and a plastic outer casing extruded around said components.

The invention furthermore relates to a foil material which is suitable for performing the process.

Such foam-insulated pipes are manufactured in great quantity for the use in district heating, and their good insulating properties are to a large extent caused by the gas which is present in the small cells of the foam and which has been used in the foaming process. Due to diffusion, with time there will be an exchange of this gas for atmospheric air which has a considerably lower thermal insulation, or water vapour may appear in adverse conditions. This exchange takes place over a period of years, but it is still a short time compared to the lifetime expected for a district heating installation.

Constructions are known, which have an integrated diffusion barrier in a foam- insulated pipe of this kind, e.g. described in EP 84 088 and DE 33 07 865. The diffusion barrier consists of aluminium laminated with plastic.

In known constructions the manufacture is continuous, in that the inner pressure pipe is taken through a number of stations where the various layers are created. It is desired that there shall be a good adherence between the pressure pipe and the foam, between the foam and the diffusion barrier, and between the diffusion barrier and the outer casing. In practice, the foaming is performed continuously by the supply of raw materials from a mixing station (e.g. isocyanate/polyol and catalyst), in order that the foaming occurs between the pressure pipe and the diffusion barrier which is held in a tubular shape with overlapping. In the present procedure the diffusion barrier is provided in the form of a strip which has a width corresponding to the inner perimeter of the outer casing, with additional material for overlapping, and it is formed axially. In other procedures the diffusion barrier is wound helically. The diffusion barrier consists of aluminium foil which is laminated to plastic on at least one side. After the foaming the foam-filled tubular diffusion barrier with the insulation and pressure pipe inside are taken through a station for extrusion of the outer casing.

Control of the quality of the foaming may occur in several ways, e.g. by means of ultrasound, but this can only be performed further along the manufacturing process, where the foam has hardened, which means that fast-acting control to obtain correct pore dimensions and foam adherence is impossible. This is a problem which may i.a. cause rejection and cutting of pipe lengths in unsuitable locations, because sections of insulated pipe with a lower quality must be rejected.

According to the invention a solution to this problem has been found, which is suitable for continuous manufacture and which permits a quick start of a batch production without causing rejects. The result is obtained in that the diffusion barrier is a layer of aluminium laminated to plastic, in which the aluminium layer at regular intervals has been given a shape so that a transparent area is generated in the formed diffusion barrier tube, said area permitting inspection of the foaming process inside the diffusion barrier tube. The transparent areas permit the inspection of the foaming process, either by means of the experienced eye of the operator, or by means of image analysis performed on a video image of the process. The result is used for controlling the supply of foam per unit of time. Thereby a considerable certainty for correct pore dimensions and strength of the foam is obtained, particularly in connection with the start of production. By means of the invention it is possible to obtain a transparent area of optional dimensions along the pipe, only dependent upon the layout of the aluminium layer. Using helical winding of the diffusion barrier according to the prior art would make it very difficult to obtain a longitudinal dimension that exceeds the width of the strip which is wound helically.

According to an embodiment of the invention the overlapping in the tubular diffusion barrier is provided with a further aluminium-covered adhesive foil which provides the requisite diffusion barrier action at least in the transparent area. The foil may e.g. obtain its adhesion by welding of the laminated plastic layers.

According to an advantageous embodiment of the invention the inspection occurs by means of a video camera which provides an electronic image of the foaming. The image is analysed in an image analysis unit and sorted into a classification for foaming quality according to pre-defined criteria. A foaming qualtity moving towards a reduction of quality causes a regulation of the amount of foam per time unit until the desired quality is reached. By the use of learning algorithms the system's ability to classify foam correctly increases, and the increase in throughput of relevant image data will enable the use of an axially shorter transparent area in the diffusion barrier.

According to a further embodiment of the invention the diffusion barrier has a longitudinal three-layer construction with an aluminium foil in the middle, with a thermoplastic layer which is adapted to weld to the surrounding outer casing during its extrusion, and a thermoplastic layer which is adapted to adhere effectively to the foamed material, whereby the aluminium has a full width regularly interrupted by areas having a reduced width.

The invention will be described in greater detail in the following with reference to the drawing, in which

Fig. 1 schematically shows a plant for continuous manufacture of insulated pipes,

Fig. 2 schematically shows the foaming along a pipe during production,

Fig. 3 a and 3b schematically show the generation of a window by means of a transparent area, and

Fig. 4 shows inspection by means of video and image analysis.

In Fig. 1 is seen an industrial plant which is essentially intended for continuous production, apart from the fact that pressure pipes are brought to the plant at one end, and are welded end-to-end to unlimited length, and that foil material is brought on rolls which have to be renewed, and that plastic granules have to be provided for the outer casing. At the other end the finished insulated pressure pipes must be wound on storage devices with a limited length, which means that the unbroken pipe must be cut when a storage device is full. The plant comprises an uncoiling station 1 for an inner pressure pipe 2 which is taken through a straightening apparatus 3 with its own control system 4 for controlling the tension of the inner pipe. A foaming station 5 is provided with foam from a foam generator 6 via a foam supply line 6a, which feeds into a foil L taken from a foil supply roll 7 and folded into a tubular shape. An observation location O enables inspection according to the invention (indicated by an eye), which controls the amount of foam supplied. The pressure pipe 2 surrounded by foam in the foil tube is pulled through a foam hardening zone 8 by means of pulling apparatus 9. A strip of adhesive foil of predetermined length is supplied from a supply roll 10 and is adhered to pre-determined areas of the foil tube at F. An extuder 11 creates the plastic outer casing for the insulated pipe. This casing is cooled in a cooling zone 12, the velocity of the pipe is measured at 13, and outer markings are printed or stamped onto the casing at 14. The completed insulated pipe is pulled forward by means of further pulling apparatus 15 and passed to a rotated take-up reel 17 via a cutting station 16, which cuts the pipe when a reel is full. A new reel 17 is fitted, and the pulling apparatus 15 provides pipe to wind onto the empty reel. The plant is controlled by a central controller 18, which communicates with a control 19 for the foaming apparatus, in particular the foam generator 6.

The foaming commences immediately upon the mixing of the ingredients and it is ended when the foam has hardened. In Fig. 2 it is shown schematically, how a sloping foam front is created, because the foam is at a low level initially and expands and fills the space between the surrounding foil L and the inner pressure pipe. The foam S is supplied in a controlled manner through a supply line immediately before the overlapping between the two sides of the foil strip takes place. This overlapping is created by the guide rollers r which are shown schematically. Because the surrounding foil and the inner pressure pipe are pulled away in time with the foaming, any location along the pipe in the range of the foaming will have a particular foam level. By means of the invention it has become possible to observe the foam when it has reached its maximum expansion and to evaluate its quality immediately before it hardens. This may advantageously be performed in the area designated O. Properties, such as pore dimensions, pore unifority, and colour are evaluated. As the window used consists of two plastic layers only (polyethylene on the outside and polyester on the inside), the diffusion barrier is not sufficient in this area, and the foil tube is hence provided with a strip of adhesive foil laminated with aluminium in the areas of the windows, and with a suitable overlapping. The foil application station is shown at F in Fig. 1.

In Fig. 3 a is shown a strip which consists of a layer M of aluminium, which has a plastic foil on either side as described above. This laminate has an overlapping part K, and the aluminium layer has areas of reduced width, whereby an area P is obtained which consists of the two outer plastic layers, without aluminium. In Fig. 3b it is further seen how the foil, which is folded into a cylindrical shape, creates an oblong window N, due to the particular shape of the aluminium layer, through which window the inspection may occur. Such areas P may be provided at regular intervals in order that the production may be inspected.

In Fig. 4 is shown how a stereoscopic video camera 20 with a closeup lens focuses on an area immediately inside the foil window N, and that the video signals processed in signal processing means 21 in in order that the contrast and edge definition are improved. An image processing programme extracts information about the mean pore dimensions and the spread in a further unit 22, as well as the colour type and distribution, and as a result of this the amount of foam supplied at the input end of the foaming station is increased or decreased by providing a control signal to the foam control unit 19 or directly to the foam generator 6. Hereby the foam properties become self-regulating.

It should be mentioned that any metal-based diffusion barrier that is not transparent may be used, and the advantages of the invention obtained by means of a window will be as described.

Claims

PATENT CLAIMS

1. A process for the manufacture of foam-insulated pipes of the kind which comprises an inner pressure pipe (2), a foam coat, at least one diffusion barrier (L) comprising aluminium, which is formed in tubular shape, and a plastic outer casing extruded around said components, characterised in that the diffusion barrier is a layer of aluminium laminated to plastic, in which the aluminium layer at regular intervals has been given a shape so that a transparent area (V) is generated in the formed diffusion barrier tube, said area permitting inspection of the foaming process inside the diffusion barrier tube.

2. A process according to claim 1, characterised in that the overlapping (K) in the tubular diffusion barrier is provided with a further aluminium- covered adhesive foil which provides the requisite diffusion barrier action at least in the transparent area (V).

3. A process according to claim lor2, characterised in that the inspection occurs by means of a video camera (20) which provides an electronic image of the foaming, said image being analysed in an image analysis unit (21, 22) and sorted into a classification for foaming quality according to pre-defined criteria, whereby a foaming qualtity moving towards a reduction of quality causes a regulation of the amount of foam per time unit until the desired quality is reached.

4. A foil material for use in the process according to the above claims, characterised in that the diffusion barrier has a longitudinal three-layer construction with an aluminium foil (M) in the middle, with a thermoplastic layer which is adapted to weld to the surrounding outer casing during its extrusion, and a thermoplastic layer which is adapted to adhere effectively to the foamed material, whereby the aluminium foil has a full width regularly interrupted by areas having a reduced width.