Method for manufacturing an insulated pipe using a bag

[0001] In the district heating / cooling network sector, it is known to produce an insulated pipe that includes an inner pipe surrounded by a layer of insulating material, which in turn is covered by a sheath. The inner pipe and sheath can be made of materials based on polymers and metals. Typically, however, insulating pipes are made using an internal metal pipe, a closed-cell thermal insulation layer and / or solidified (insulating material) and a polymer-based sheath.

[0002] Examples of methods for producing insulated pipes, comprising an inner pipe surrounded by a layer of insulating material, which in turn is covered by a sheath, can be found in US 2007/0074778, in which the insulating material is injected into a cavity between the inner pipe and the outer pipe, and in US 3705221, which relates to the isolation of pipelines in the field.

[0003] It is known to produce insulating material on an inner pipe using a mold. According to this method, a mold is used which typically comprises two half parts. The inner tube is placed centrally inside the mold, creating a cavity between the outer surface of the inner tube and the inside of the mold half parts. When the two half portions are closed around the inner tube, liquid insulation material is injected into the mold cavity. The liquid insulation material foams until it reaches the wall of the mold cavity and then solidifies. After solidification, the half mold parts are opened and the insulated pipe is ready for covering. As mentioned, the sheath is usually polymer-based and is extruded onto the insulating material.

[0004] This known production method, however, suffers from a number of disadvantages. One of them is that the insulation material may tend to stick to the wall of the mold cavity. Therefore, it can be difficult to open the mold without damaging or tearing off parts of the solidified insulating material. In addition, the remaining solidified insulation material must be removed from the wall of the mold cavity before a new molding process can be started.

[0005] Another disadvantage of this production method is that it can be difficult to achieve sufficient clinging to the insulating material. This problem arises as a direct result of the use of known molding technology. Basically, half mold parts are needed to ensure that the insulated pipe produced will have the required dimensions and tolerances. To maintain these dimensions and tolerances, the mold cannot be opened until the injected liquid insulation material has expanded and solidified. Foaming insulation material is sticky, while solidified insulation material is not. Attempting to stick the sheath material to the solidified insulating material is therefore very difficult, if not impossible. After removing the insulated pipe from the mold, it is therefore necessary to add glue to the solidified insulating material to ensure the connection between the solidified insulating material and the sheath.

[0006] An alternative to the closed-molding technology described above is to use the open-molding technology. Traditionally, the half parts of the mold are hinged to each other in the lower part, whereby the mold opens in its upper part, symmetrically with respect to the vertical axis. Using the molding technology in open molds, it is possible to check the foaming process (expansion) of the insulating material, and thus control the foaming process. However, this manufacturing technology requires high precision in selecting the closing time of the mold - primarily to keep the foaming insulation material inside the mold. According to a known solution, to prevent the pieces of insulation material being torn off when the mold is opened after foaming and the solidifying material solidifies, a piece of foil is inserted into the mold together with the inner pipe.

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A piece of foil is located on the inner wall of the mold and protrudes outside the mold at the place of its opening. Then the liquid insulation material is injected or poured onto the foil. Regardless of whether a film is used, it is known that this manufacturing technology produces insulated pipes of varying quality, which is generally undesirable.

SUMMARY OF THE INVENTION [0007] The present invention relates to a method for producing an insulated pipe comprising an inner pipe, insulating material and a sheath according to claim 1. The production method relates to a process for forming an insulating material on an inner pipe, wherein the inner pipe is covered with a closed sleeve having open ends, and then inserts get into shape. Then liquid material is injected into the mold between the inner pipe and the sleeve. The liquid insulation material, after injection, will start foaming and eventually solidify. During these processes, the sleeve is pressed against the inner wall of the mold. Thus, the expanded and solidified insulation material will be covered with a sleeve from the inside wall of the mold.

[0008] The production method according to the present invention is advantageous because the insulated pipe can be removed from the mold without peeling off pieces of insulating material. This significantly increases production efficiency. In addition, the production method effectively eliminates leaks or losses of insulating material. Thus, the manufacturing method of the present invention is both simple and reliable and also ensures uniform product quality in all insulated pipes produced.

[0009] In addition, the sleeve-insulated material provides additional features beneficial to the process of applying the sheath to the insulated pipe. The sleeve provides sufficient adhesion between the insulating material and the cover. The quality of the finished insulated pipe is therefore much higher due to the connection that is obtained between the insulating material and the sheath. The long-term insulation values ​​of the finished insulated pipe can be improved, for example, by using a diffusion barrier sleeve that prevents oxygen from entering the insulation material. As you know, oxygen combined with high temperatures intensifies the aging process of the insulation material, which significantly reduces the efficiency of the insulation.

BRIEF DESCRIPTION OF THE DRAWINGS [0010] In the following, the invention will be described with reference to the figures in which:

Fig. 1 shows an insulated pipe known from the prior art;

figures 2a and 2b show a closed mold around the inner tube and a cross section thereof, the sleeve being partially positioned around the inner tube; figures 3a and 3b show the mold closed around the inner pipe after expansion and solidification of the injected insulation material.

DESCRIPTION OF EMBODIMENTS [0011] Fig. 1 shows an insulated pipe 100 known from the prior art, comprising an inner pipe 101 surrounded by a layer of insulating material 103, which is in turn covered by a sheath 102. Inner pipe 101 and sheath 102 may be made of materials based on polymers and metals. In the context of the present invention, the insulated pipe 100 is made using an inner tube 101 of metal or polymer, a closed cell and solidified thermal insulation layer 103, as well as a polymer-based sheath 102.

[0012] Fig. 2a shows a longitudinal section of a mold 104, 105 closed around the inner tube 101, wherein a sleeve 106 is disposed around the inner tube 101. The sleeve 106 has a tube-like shape

EP 2 590 792 with open ends. It is slid onto the inner tube before being inserted into the mold 104, 105. Fig. 2b is a cross-sectional view taken along the line aa indicated in Fig. 2a. The mold includes the upper half of the mold 104 and the lower half of the mold 105. The two half halves of the mold have horizontally directed sealing surfaces. At the ends of the inner tube 101, end tools 108 are placed surrounding the inner tube 101, and a sleeve 106 extends around the outer perimeter of the end tool 108. When the mold 104, 105 surrounds the end tools 108, a cavity forms between the mold 104, 105 and the inner tube 101. The surface of the end tools 108 facing the cavity can have different geometries depending on the type of insulated pipes produced. Thus, the surface of the end tools 108 facing the cavity can be, for example vertically straight, inclined or parabolic with the tip facing the end of the inner tube 101. The contact surfaces between the inner tube 101, end tools 108 and the mold 104, 105 are preferably hermetically sealed before molding process. The closed mold 104, 105 shown in the figure is therefore ready to start the molding process, with the liquid insulating material 103 being directed into the cavity formed by the inner tube 101 and sleeve 106 through the inlet 110. When the liquid insulating material 103 enters cavities, it begins to foam and then solidify. The foaming process gradually presses the sleeve 106 against the inner walls of the mold 104, 105. To allow for proper expansion of the insulating material 103 in the liquid state, the end tools 108 as well as the top of the mold 104 include ventilation openings 112, 114.

[0013] To avoid squeezing or damaging the sleeve 106 when handling the mold 104, 105 or closing it, a vacuum can be applied through the inlet opening 110 or the vent opening 112. This will allow the sleeve 106 to fit snugly around the inner tube 101 and end tools 108. The sleeve 106 may be made of a wide variety of materials and may be, for example, single or multi-layer. The inner surface of the sleeve 106 may advantageously be subjected to corona treatment to improve its adhesion to the insulating material 103. This will provide a better connection between the sleeve 106 and the insulating material 103. Sleeve 106 may also include a layer that acts as a diffusion barrier. In addition, after closing the mold around the inner tube, the cavity between the inner tube and the sleeve can be filled with compressed air or other gas, for example inert gas.

[0014] Fig. 3a shows a longitudinal section through a mold 104, 105 closed around the inner tube 101 after a molding process in which the insulating material 103 has been formed on the inner tube 101. The inner tube 101, which is covered with solidified insulating material 103, is therefore ready to leave the mold 104, 105. As also seen from the cross-section in Fig. 3b along the line bb marked in Fig. 3a, the sleeve 106 has been pressed against the inner wall of the mold 104, 105 due to the foaming and solidification of the insulating material 103 which has been injected into the mold in a liquid state (see Figs. 3a-b). At this stage, the sleeve 106 thus forms the outer layer of the insulated inner tube 101. The insulated inner tube (101) is then ready to leave the mold 104, 105. The insulated inner tube 101 is ready to be covered by a sheath 102 to protect the insulating material. As described, sleeve 106 allows better adhesion between the insulating layer 103 and the sheath so that these two layers (insulating material 103 and sheath 102) will be joined together.

[0015] Sleeve 106 may be:

- a monolayer polymer film, such as polypropylene or polyethylene;

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- multi-layer sandwich type film, in which each layer has its function, one of which may be a diffusion barrier. The multilayer film can thus be a sandwich film in which the metal layer is covered with a polymer-based material on both sides.

[0016] The dimensions (e.g. diameter, thickness) of the sleeve 106 may vary depending on the type of sleeve 106 (depending on material and mechanical properties), the amount of insulation material 103, its foaming and solidification speed, and pressure and / or process temperatures.

[0017] In one embodiment, the diameter of the sleeve 106 may be smaller than the diameter of the mold 104, 105. This requires that the elasticity of the sleeve 106 allows it to stretch.

[0018] In one particular embodiment, the sleeve material is LDPE (Low Density Poly Ethylene) and 150 micrometers thick. In addition, the sleeve diameter is about 2% smaller than the inside diameter of the mold. [0019] The insulating material 103 covered with the foil sleeve 106 has a number of advantages, mainly in relation to applying the sheath 102 to the insulating layer 103. Thus, when the polymer-based sheath 102 is applied (e.g. extruded) to the film-covered surface (sleeve 106) of the insulation material 103, the temperature of the sheath increases, resulting in a strong adherence and thus a connection of the sheath and the insulating material together.

[0020] End tools 108 may include at least one injection port and at least one vent port. In an alternative embodiment, the sleeve 106 is applied to the entire inner tube 101 so that it is between the inner tube 101 and the end tool 108. The liquid insulating material 103 can then be injected through a tube or similar element having one end connected to the sleeve 106 . In this way, the liquid insulating material 103 can be injected into the cavity between the inner tube 101 and the sleeve 106 through this tube. As a result, all insulation material will be covered with sleeve 106 during the molding process.

[0021] The above is an example in which a two-part mold was used for forming. In addition, it was mentioned that the mold is positioned so that its sealing surface is horizontally oriented. Obviously, you can use any form set up in different ways.