Abstract:
A pipe-connector molded part for pre-insulated pipe conduits consisting of plastic, whereby the pipe conduit is pre-insulated with polyurethane foam and the pipe-connector molded part is positioned so that it can be connected to the internal wall of the pipe conduits to be connected by a method for connecting pre-insulated pipe conduits consisting of plastic by way of the molded part.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a pipe-connection molded part for pre-insulated pipe conduits of plastic material, the pipe conduit being pre-insulated with polyurethane foam.  
         [0002]     In pipe conduit construction, in particular in applications in which good insulation of the medium relative to the environment is required, such as, for example, in pipe conduit systems for the transport of refrigerants, pre-insulated pipe conduit sections are being increasingly used. A readily suitable material for the insulation of refrigerant pipe conduits is foamed polyurethane. Arranged around the pipe conduit is an outer pipe or a tubular outer casing which is kept at a uniform distance from the outer wall of the pipe conduit concentrically around the pipe conduit by means of spacers. The annular space between the inner wall of the casing and the outer wall of the pipe conduit is completely filled with polyurethane foam. The polyurethane foam is injected as a reactive foam-forming liquid, and the foam produced hardens. The foam readily adheres to the surfaces of the pipe conduit and the outer casing and also gives the pipe conduit pre-insulated in this way greater rigidity.  
         [0003]     If a plurality of such pipe conduit sections have to be connected to one another, the effort required for preparing and producing the pipe conduit connection is relatively large. The pipe conduit itself must be exposed, cleaned of foam and connected to the next pipe conduit section by means of a sleeve. The outer casing must be made continuous again by means of a heat-shrinkable tube around the connection point, and the annular intermediate space between outer casing and the point connected to the sleeve must be filled with new foam.  
         [0004]     EP182604 B1 discloses an arrangement and a method for connecting pipe conduits pre-insulated with polyurethane foam. In the insulating material in the intermediate space between pipe conduit and outer casing, an annular space is formed at the connection point. A special annular element which shrinks under the action of heat is introduced in this annular space. The special element consists of a nickel-titanium alloy. After the shrink-fit operation, the annular element exerts such a high force on the connection point between the two pipe conduits that no further connection of the pipe conduits is necessary.  
         [0005]     Instead of the special element, a commercially available sleeve or adhesive sleeve may also be used. To this end, the polyurethane foam must also be removed from the connection region before the connection is produced. In order to obtain a sound connection between sleeve and pipe, the outside of the inner pipe must be peeled with a special peeling implement and cleaned.  
         [0006]     Based on the prior art, the object of the invention is to provide a pipe-connection molded part for pre-insulated pipe conduits which permits a medium-tight, cost-effective and environmentally safe connection between two pipe conduit sections at any desired point of the pipe conduit.  
       SUMMARY OF THE INVENTION  
       [0007]     The foregoing object is achieved by providing a pipe-connection molded part for pre-insulated pipe conduits of plastic material, the pipe conduit being pre-insulated with polyurethane foam, and the pipe-connection molded part being arranged in such a way that it can be connected to the inner wall of the pipe conduits to be connected.  
         [0008]     Preferred developments of the invention follow from the dependent claims.  
         [0009]     It is advantageous that no insulating material and no outer pipe material has to be removed and disposed of for the connection of the pipe conduit sections. This is achieved by the pipe conduit sections pre-insulated with polyurethane foam being arranged in the connection region in such a way that they can be pushed into position on a nipple matching the inside diameter of the inner pipes.  
         [0010]     It is also advantageous that no additional preparatory effort and no tools, such as, for example, peeling tools for the outside of the inner pipe, are required for the connection. In the connection region, the inner surfaces of the pipe conduit and the nipple which are to be connected to one another are not treated by the insulating process or contaminated with foam residues.  
         [0011]     It is also advantageous that, in the connection region between the pipe conduit and the pipe-connection molded part, the connecting conditions are matched to one another and can be reproduced. This is achieved by the pipe inside diameter and the nipple outside diameter being precisely definable in the connection region.  
         [0012]     Overall, considerable material and time are saved by the connection on the inside of the inner pipe. The removal of the outer pipe and of the polyurethane foam, the environmentally compatible disposal of the polyurethane foam residues and the complicated cleaning of the outside, contaminated with polyurethane foam, of the inner pipe are dispensed with. It is not necessary to procure a special peeling implement for the outside of the inner pipe. The pipe conduit sections of the pipe conduits pre-insulated with polyurethane foam, which are relatively expensive, can be processed virtually without waste and losses. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     An exemplary embodiment of the invention is described with reference to the figures, wherein:  
         [0014]      FIG. 1 : shows a section through a prior art connection between two pipe conduit sections pre-insulated with polyurethane foam; and  
         [0015]      FIG. 2 : shows a section through a connection between two pipe conduit sections pre-insulated with polyurethane foam and having a connector according to the invention.  
     
    
     DETAILED DESCRIPTION  
       [0016]     A known connection between two pipe conduits for temperature-sensitive media, for example for refrigerants in industrial cooling line systems, is shown sectioned in  FIG. 1 . The pipe conduits consist of an inner pipe  1 ,  2 , are pre-insulated with a layer  3  of polyurethane foam and are encased with an outer pipe  4 ,  5 . The inner pipes are made of an acrylonitrile-butadiene-styrene (=ABS) and the outer pipes are made of a high-density polyethylene (=HDPE). Polyurethane foam (=PUR) is best suited for cold insulation. The pipe conduit is connected in a conventional manner using an adhesive sleeve  6 . The pre-insulated pipe conduits are obtainable in nominal diameters of 16 to 225 mm.  
         [0017]     The prior art connection is produced as follows: the pipe conduits are severed in the connection region in order to expose the ends of the inner pipes  1 ,  2 . The outer pipe  4 ,  5  and the polyurethane foam layer  3  are removed from the connection region. After the layer  3  has been removed, the outside of the inner pipe  1 ,  2  must be cleaned and prepared for the connection. The polyurethane foam forms a permanent connection with most surfaces. The outside of the inner pipe  1 ,  2  must be peeled with a special peeling implement. In the process, care must be taken to ensure that not too much material is removed, since otherwise a gap which is too large would be produced between the inner wall of the sleeve  6  and the outer wall of the inner pipe  1 ,  2 , and this gap can only be connected correctly and in a medium-tight manner with difficulty.  
         [0018]     After both pipe conduit sections have been prepared in this way, an adhesive connection or a welded connection to the sleeve  6  is produced. On the inside of the inner pipe, the adhesive forms a bead  7  at the point where the two inner pipes are pushed into the adhesive sleeve  6 . Beads  7  of molten plastic material can also be produced during the “sleeve welding process”. The space which is left between the sleeve  6  and the outer pipe  4 ,  5  is then filled again with polyurethane foam.  
         [0019]     What are referred to as half shells, or half-ring-shaped elements of polyurethane foam, which are obtainable on the market are used for this purpose. The half shells have a length which corresponds to the length of the connection region. The length of each half shell is slightly greater than twice the length of the polyurethane foam layers  3  which have been removed at both pipe conduit sections in order to expose the ends for the adhesive bonding. Finally, the pipe connection point, by means of a heat-shrinkable tube  8  of polyethylene and a sealing agent or an adhesive tape  9 ,  10 , is sealed off again against the ingress of air or moisture.  
         [0020]     A novel connection, in accordance with the present invention, between two pipe conduits for temperature-sensitive media, for example for refrigerants in an industrial cooling line system, is shown sectioned in  FIG. 2 . From the inside to the outside, the pipe conduits are composed of: an inner pipe  11 ,  12  of plastic, for example of an acrylonitrile-butadiene-styrene, a layer  13 ,  14  of insulating foam, for example polyurethane foam, and an outer pipe  15 ,  16 , for example of high-density polyethylene. In order to keep the outer pipe  15 ,  16  at a uniform distance concentrically around the inner pipe  11 ,  12  during the introduction and curing of the polyurethane foam, plastic spacers  17 ,  18  are arranged between the inner pipe  11 ,  12  and the outer pipe  15 ,  16  at regular intervals in the longitudinal direction of the pipe conduit. The differences in diameter between the inner pipe and the outer pipe, which lead to intermediate spaces of different size for the foam layer  13 ,  14 , are automatically compensated for through the use of the spacers  17 ,  18 .  
         [0021]     The connection between the two pipe conduits is produced by means of a nipple or connector  19  of plastic which can be connected to the plastic of the inner pipe  11 ,  12 , that is to say it can be adhesively bonded or welded to said plastic of the inner pipe  11 ,  12 , and is compatible with it. The nipple  19  can be made adhesive before being connected to the pipe conduits. To this end, either those surfaces of the nipple  19  and the inner pipes  11 ,  12  which are to be connected to one another are heated by a “sleeve welding process”, or the surfaces to be connected are adhesively provided with a suitable adhesive. In the center, on the outer circumference of the nipple or connector, the nipple  19  has an annular web  20  which is directed radially outward and serves as a stop for the inner pipes  11 ,  12  during the connection. The web  20  ensures that both pipes  11 ,  12  are pushed sufficiently deep over the nipple  19 . At the start and at the end, the nipple  19  has wall regions  21 ,  22  rounded off or beveled inward. This ensures that the flow of the refrigerant through the pipe conduit is hindered as little as possible and that the pressure loss in the pipe conduit on account of changes in diameter is kept as small as possible.  
         [0022]     At the end, on the pipe inside, the inner pipes  11 ,  12  may be beveled with a “draw-in bevel” or be rounded off with a draw-in radius. In  FIG. 2 , the ends of the inner pipes  11 ,  12  have a bevel  23 ,  24 , the “draw-in bevel  23 ,  24 , directed obliquely inward. This ensures that the pipe conduits can be pushed into position on the nipple  19  as simply as possible. During the adhesive bonding, the bevel  23 ,  24  also serves to draw in excess material which is displaced when the pipe conduits are pushed onto the nipple  19 . If the inside diameter of the inner pipes  11 ,  12  is too small in relation to the outside diameter of the nipple  19 , the inner pipes  11 ,  12  must be calibrated beforehand, that is to say they must be given a matching inside diameter by a peeling or scraping operation.  
         [0023]     Before the connecting operation, the pipe conduit sections are aligned with the pipe conduit axis as accurately as possible. If the pipe conduit sections are processed on site in shorter lengths than the lengths delivered by the manufacturer, a new bevel  23 ,  24  has to be made as single preparation at the interface. No material is removed from the insulating layer  13 ,  14  or from the outer pipe  15 ,  16 . In all cases, it is not necessary to remove polyurethane foam or polyethylene if the nipple  19  is used. No polyurethane foam or polyethylene need be disposed of. The connection on the inside of the pipe  11 ,  12  is simpler, since no polyurethane residues have to be removed from the surface of the inner pipe  11 ,  12 .  
         [0024]     Before the connection is produced, a “heat-shrinkable tube”  25  is put loosely over one of the pipe conduits, that is to say a tube of plastic material which has been modified in such a way that it shrinks under the action of heat. After the curing of the connection between nipple  19  and the inner pipes  11 ,  12 , the tightness of the connection is tested.  
         [0025]     Due to the formation of the web  20 , a gap  31  is produced in the region of the web  20  between the pipe conduits, that is to say between the insulating foam layers  13 ,  14  and the outer pipes  15 ,  16 . This gap  31  can readily be inspected during a test for pressure tightness, which is carried out following the actual connecting operation and before the welding to the heat-shrinkable tube. During the pressure tightness test, it can be observed in the gap  31  whether medium is escaping from the inner pipe  11 ,  12  in the event of a leaky connection. If there were no gap  31 , the escaping test medium would be absorbed by the insulating foam.  
         [0026]     After the testing of the tightness of the connection between nipple  19  and the inner pipes  11 ,  12 , an adhesive sealing tape or a sealing adhesive tape  27 ,  28  is wound around the ends of the outer pipes  15 ,  16  in the region of the nipple  19 . In order to achieve better adhesion on the heat-shrinkable tube  25  and on the outer pipe  15 ,  16 , the adhesive tape  27 ,  28  may be a double-sided adhesive tape. Sound sealing in the region of the heat-shrinkable tube  25  is necessary in order to retain the insulating properties of the insulating foam  13 ,  14  even after the connecting. The heat-shrinkable tube  25  is then shrunk to the diameter of the outer pipes  15 ,  16  by the action of heat in the connection region.