The invention relates to pipes, in particular ventilation pipes, and manufacturing thereof. In particular, the invention relates to polymer pipes, which are provided with thermal insulation.

Background of the Invention

Insulated pipes are needed e.g. in construction works. Typical usage areas for insulated pipes include ventilation channels. Insulation is needed depending on the application area for example to prevent thermal losses and condensated water forming on outer surfaces of pipes. A large portion of pipes used by the construction industry is manufactured from metal and polymer material.

Pipes can be insulated by means of an insulating material layer arranged around the outer surface thereof. The insulating material can be e.g. wool, foamed plastic, cardboard or asbestos. In addition, gas- or vacuum-insulated pipes are known. For example, publication US 2003/0012918 discloses an insulating sheath of a pipe that consists of adjacent channels that are filled with gas. After filling the channels, the sheath is arranged around a pipe like other insulating materials referred to above, for example using fastening straps, whereby the thermal insulation capability of the pipe increases. Publication GB 1283329 presents a solution, in which between two metallic pipes, there is arranged an also metallic cell structure in order to achieve a pipe with increased insulation value. Such solutions are also known in which a wall of a pipe comprises protrusions on top of which is wrapped an additional layer in order to form an insulating air gap on the surface of the pipe. Such structure is described in publication GB 762800 A.

In known solutions, the insulating material can be arranged to the pipe before or after installation of the pipe. In both cases, insulating is formed by a separate stage of work. In the first case, the insulation makes the installation of the pipe more difficult, in particular making joints, and often one needs to repair insulation after installation. In the latter case the installation of the insulation is particularly laborious, because pipes typically comprise turns, branches, and joints and are located in tight spaces. In both cases ensuring the insulation in the final installation requires special caution in order to achieve tight insulation. Bad quality or wrong installation can lead to condensation or freezing problems or extra heat loss, depending on the application area.

In summary, it can be said that traditional insulation solutions are relatively difficult and time-consuming to install. The insulation material and its installation also raise the cost of the pipe product and/or the installation work. EP 2466185, CN 202660161U and CN 102889435 A disclose pipes comprising insulating rods and cavities in the axial direction of the pipe. In WO 2005/120805A1, the cavities have been arranged helically. KR 101547967B 1, KR 1020070102975, US 3495628, US 4531551 and US 5727598, for example, disclose solutions in which the pipe or its separate insulating sheath are formed by winding long cavity element helically into pipe form. A drawback of these solutions is relatively difficult manufacturing process, difficulty of ensuring the tightness of the pipe wall, the need of adhesive materials and/or that when the pipe is cut, the cavity structure is opened and the insulation capability of the pipe decreases significantly.

Thus, there is a need for improved insulated pipes. Summary of the Invention

It is an aim of the invention to solve abovementioned problems. A specific aim is to achieve an insulated pipe, in particular a ventilation pipe, which is simpler to install than known insulated pipes and which maintains its insulating capability when installed. An aim is also to achieve an insulated pipe, which can be manufactured from few raw materials, even from a single raw material.

An aim of the invention is additionally to achieve a method of manufacturing such pipe.

The aims are achieved by the solutions according to the independent claims. The insulated ventilation pipe according to the invention comprises a wall structure arranged into pipe form, the wall structure comprising cavities arranged into multiple layers in a radial direction of the pipe. The cavities are formed from thermoplastic polymer arranged as a unitary structure. The cavities are entirely closed and arranged into elongated form and to run tangentially, i.e. perpendicular to the longitudinal direction (and also the radial direction in the case of a circular pipe) of the pipe, around the longitudinal axis of the pipe. Due to the unitary structure and multi-layered tangential closed cavity structure, the wall structure forms a self-supporting bar and at the same time serves as a structure forming the actual air flow channel and as a thermal insulator. In the method according to the invention, softened thermoplastic polymer is extruded into pipe form, whereby the wall structure is in the extrusion provided with elongated cavities in the tangential direction of the pipe in multiple layers in the radial direction of the pipe so as to form a self-supporting wall structure.

Considerable advantages are achieved by means of the invention. At least two

superimposed cavity layers combined with the low thermal conductivity of thermoplastic polymers offers a sufficient thermal insulation capability for many applications without cumbersome separate pre- or post-installed insulation materials. The unitary structure with its cavities makes the pipe rigid and allows for cuts and continuations with tight joints both between the inner pipes and cavity structures. Thus, it is possible to obtain a whole insulated fluid channel rapidly.

The rigid wall structure thus allows for using the pipe as such, in contrast to solutions, in which a flexible cavity insulator in arranged separately on an uninsulated pipe. Directly tangential and closed cavities on the other hand provide the advantage that the cavities remain intact when the pipe is cut, whereby its insulation capability is maintained. The insulation capability of a pipe with axial or helical is decreased along the whole length of the pipe irrespective of where the pipe is cut at.

It is possible to manufacture the whole insulated pipe from one starting material only and without separate attaching phase for an insulator material. These facts decrease both the manufacturing and installation costs of the pipe. Due to the absence of separate insulating material also disassembling and recycling of the pipe from the installation site is simpler and more inexpensive.

On the other hand, many different starting materials can be used for manufacturing the pipe, in particular in contrast to the limited selection of conventional pipe insulator materials. The material can be fresh polymer raw material or on the other hand also recycled material, or a mixture thereof. Particularly preferably at least a portion of the material is recycled material.

The present cavity structure improves not only the thermal insulation, but also acoustic insulation. Thus, is can be used in targets, where the prevention of heat losses is not necessary but in which transportation of sound along a pipeline is to be decreased.

The dependent claims are directed to selected preferred embodiments of the invention.

According to one embodiment, the cavities are arranged into at least three layers in the radial direction of the pipe. Thus, when the cross-section of the pipe is inspected in at last some, preferably all radial directions, a line drawn over the wall structure intersects with at least three different cavities. This kind of a pipe offers an insulation capability comparable to that of typical wool and foamed plastic insulations.

According to one embodiment, the cavities are arranged interlaced with each other, i.e., partly overlapping, into layers such that in the radial direction of the pipe each location of the pipe has at least one cavity, in particular at least two cavities. In other words, the separating walls of the cavities have been positioned in the axial and/or tangential directions to different places, whereby no direct polymer bridges, i.e. "cold bridges" are formed between the inner and outer surfaces of the pipe. Although polymers have a relatively low thermal conductivity compared with e.g. metals, this kind of an intermediate wall structure has been found to be significantly better compared with intermediate walls along a straight line. According to one embodiment, the cavities on superimposed layers are in a shifted position with respect to each other by half cavity dimension, which minimizes the conduction of heat through the polymer.

According to one embodiment, the pipe comprises cavities, which are closed on all sides thereof, that is, axially, radially and tangentially, closed air and water-tightly. These kind of completely closed cavities minimize heat convection inside the wall structure along the mantle of the pipe and further improves thermal insulation. Axially closed cavities are preferred, because in that case the pipe can be cut without opening the cavities, whereby the insulation level is easy to maintain in continuation and joint locations. The cross-sectional shape of the cavities can hexagonal or rectangular, for example.

In some embodiments, the pipe consists solely of the cavity structure, that is, is does not contain other layers in addition to the cavity layers forming the wall structure.

In some embodiments, the cavities have been vacuumized or filled with gas, such as air, i.e. are free from solid-state insulator materials. In some embodiments, the wall structure with its cavities is entirely manufactured form the same polymer material. The polymer material can be a mixture of several polymers and comprise fresh polymer, recycled polymer, or both.

According to one embodiment, the polymer comprises recycled plastic, typically 30 - 100 % by weight, preferably 50 - 100 % by weight of the total amount of polymer. The pipe, i.e., the wall structure with the cavities, can be manufactured by extruding one or more, preferably only one, thermoplastic polymer or polymer blend into pipe form. The extrusion process can comprise a co-extrusion process, in which at least the inner wall of the pipe is extruded in a first work stage, at least some of the cavity layers in a second work stage and uniting the inner wall and the cavity layers on top of each other in order fo form the insulated pipe.

Next, embodiments of the invention and advantages thereof are discussed in more detail with reference to the attached drawings.

Brief Description of the Drawings

Figs. 1 A and IB show in perspective and planar cross-sectional views the present pipe structure according to an embodiment, where the cavities are elongated and arranged to circumvent the pipe tangentially. Figs. 1C and ID show as side and end views sections of the present pipe according to one embodiment.

Figs. IE - 1G show in perspective views alternative cavity structures, in which the cavities circumvent the pipe tangentially. Fig. 2 shows schematically a hexagonal cavity structure.

Fig. 3 shows as a cross-section in the plane perpendicular to the longitudinal axis of the pipe an example of a rectangular pipe.

Detailed Description of Embodiments

"Axial direction" refers herein to the longitudinal direction of the pipe and "radial direction" to the direction(s) perpendicular to the axial direction and intersecting the centre of symmetry and/or mass of the pipe. "Tangential direction" refers to direction

perpendicular to the axial direction and parallel to the surface of the pipe, which in the case of a circularly symmetric (circular in cross-section) pipe unites with the direction perpendicular to both the axial and radial directions. "Cavity" means a limited zone defined by the wall structure, the zone being capable of being filled with gas, such as air, or vacuumized. An individual cavity is limited by polymer walls. The wall structure thus consists of walls between cavities, the inner side of the pipe and/or the outer side of the pipe. Herein, "limited" is a zone, which has been limited at least in the radial and tangential directions. Cavities, or at least part of the cavities, can be limited also in the axial direction, i.e. entirely closed. In particular at the ends of the pipe, the cavities can be open, even though typically at the latest at the installation or joining stage potentially open cavities are closed also at the ends of the pipe in order to improve the insulation capability.

In general, "cavity" means a hollow or channel formed inside plastic material, at least one dimension of the cavity being larger than an open or closed cell formed inside an expanded plastic material by means of foaming. The wall structure comprising multiple cavity layers arranged on top of each other in the radial direction of the pipe means that when inspecting an inner cross-section of the pipe in at least some radial directions, a line drawn over the wall structure intersects with at least two, preferably at least three, different cavities. In some embodiments, when the cavities are suitably interlaced with each other, this condition is satisfied in all radial directions in at least some axial locations of the pipe, preferably in most axial locations. In some embodiments, this condition is satisfied in all axial locations of the pipe.

"Elongated" cavity means a cavity, whose dimension in at least one direction thereof is at least three times, suitably 3,5-1000 times its dimensions perpendicular to this direction. According to the invention, the cavity is an elongated, in the tangential direction ring- shaped or arc-shaped cavity.

In one embodiment, the average diameter of the cavities is 0,5 - 100 mm, for example 0.75 - 50 mm or 1 - 20 mm. The diameter of the cavities can vary according to the inner diameter of the pipe, as will be discussed later in more detail. Usually the diameter of one cavity is about 1 - 25 % of the inner diameter of the pipe and the cross-sectional area of a cavity is 0.1 - 10 % of the inner cross-sectional area of the pipe.

Most suitable the total cross-sectional area of the cavities is about 10 - 500 %, for example about 30 - 200 % of the inner cross-sectional area of the pipe. "Unitary" structure of the wall structure or cavities means a structure in which at least the cavity wall-forming thermoplastic polymer is arranged as a continuous structure. Thus, no adhesives are used between different parts of the wall structure, and neither any other substances or means that hold the wall structure together, but the wall structure is substantially free from such substance or means. A unitary structure can contain zones, whose polymer compositions differ from each other, but in particular the unitary structure may comprise a polymer structure consisting of essentially homogeneous polymer material, including homopolymers, copolymers and essentially homogeneous polymer blends. "Unitary structure" does not exclude that for example the inner or outer surface of the pipe is coated with a separate material layer, which does not consist of thermoplastic polymer, but the term refers particularly to the unity of the cavity -forming structure. For example, to increase fire safety, one can arrange a metal layer, such as an aluminium foil, or other coating, around the outer surface of the pipe.

The unitary structure can be achieved by polymer extrusion. Thus, typically the structure is manufactured by extrusion or a corresponding fabrication method, in which molten plastic mass is pressed through a nozzle so that the cavity structure is formed in such pressing stage. In one particularly preferred application, the structure is formed without foaming, whereby the cavities of the structure do not contain cells due to expansion of plastic. With this application one can achieve a mechanically durable structure which can form at least part of the wall structure of the pipe, in particular pressure-withstanding wall structure of the pipe. The drawings illustrate embodiments of the present technology:

Figs. 1 A - IE show a pipe structure according to one embodiment, in which the cavities run in a ring-like manner, i.e. tangentially, around an inner pipe. In more detail, the pipe comprises a wall structure 10, which further comprises an inner wall 11 and outer wall 11 oriented parallel to the mantle (cylindrically) and intermediate walls 12, 13 oriented parallel to the mantle between these. The actual fluid channel is formed inside the inner wall. In addition, the wall structure has been provided with intermediate walls 15 A, 15B, 15C in a plane perpendicular to the axial direction of the pipe. The inner and outer walls 11, 14 and intermediate walls 13, 15A, 15B, 16C together form cavities 16A, 16B, 16C between them.

The cavities 16A, 16B, 16C have in this example been arranged in three layers, each of which comprises several cavities circumventing the pipe tangentially side by side. The number of layers can however be for example 2 or 4 - 10. Typically, there are 3 - 6 layers. In this example, the cavities are rectangular in cross section, i.e. the inner, outer and intermediate walls are essentially of constant thickness and arranged at right angles with respect to each other.

To achieve as good insulation capability as possible, the cavities 16A, 16B; 16B, 16C of successive layers have been arranged such that their radial-direction intermediate walls are not situated on the same line, but shifted with respect to each other, herein by half cavity distance. This prevents formation of direct cold bridges between the inner and outer falls of the pipe, which improves heat insulation.

In the exemplary solutions according to Figs. 1 A - ID, there are provided additional cavities 18 protruding from the outer wall 14 of the pipe, which, however, do not form a full layer, but provide an uneven, "wrinkled" outer surface to the pipe. This can be desirable in some applications. At the same time, the protruding cavities 18 increase the thermal insulation value of the pipe for their part. Such protruding cavities 18 are not necessary. The outer surface of the pipe can be defined by the outermost full cavity layer, i.e., be even.

Fig. IF shows a wall structure, in which the cavities 170A, 170B, 170C circumventing the pipe in ring-like manner are circular in cross-section and polymer fills zones between the cavities.

Fig. 1G shows a cavity structure, in which the cavities 180B, 180C, 180D circumventing the pipe in ring-like manner are hexagonal in cross-section (excl. the innermost,

"incomplete" cavity layer 180A). The polymer intermediate walls are of equal thickness. In these examples too, the cavities 170A, 170B, 170C; 180A, 180B, 180C, 180D have been arranged into multiple layers, which are interlaced with respect to each other to achieve larger total cavity volume and to decrease cold bridges. Fig. 2 shows a variation, in which the cavities 36A are hexagonal in cross-section and arranged tangentially like in Figs. 1A - ID, herein into four layers.

Above, cross-sectionally essentially circular pipes are presented. However, the cross- section of the pipe can be any other too, such as elliptical, rectangular or hexagonal. Fig. 3 shows an example of an essentially rectangular cross-section pipe, whose wall structure 40 comprises two cavity layers. Herein too, the cavities 46 are elongated and extend in the tangential direction of the pipe.

The largest transverse inner dimension of the pipe, i.e. inner diameter, is typically 30 - 500 mm, in particular 50 - 250 mm, in a ventilation pipe most typically 70 - 200 mm. The thickness of the wall structure can be e.g. 30 - 150 mm, typically 40 - 100 mm. The radial dimension of a single cavity can be e.g. 1 - 30 mm, typically 3 - 20 mm.

According to one embodiment, one or both ends of the pipe comprise, as a unitary polymer structure, a joint portion, whose inner and/or outer dimension differs from the

corresponding basic dimension of the pipe. The joint portion can comprise e.g. a socket, whose inner diameter is the same or larger than a basic diameter of the pipe. The joint portion can be arranged to engage with an essentially similar or different kind of a pipe in order to achieve a pipe extension or pipe joint. Two pipes can be joined also by means of a separate joint part.

According to one embodiment, the joint portion is adapted to make tight both inner and outer walls of two pipes, and optionally also the intermediate walls such that both the integrity of the fluid channel and insulation capability of the wall structure is maintained at the location of the joint. This kind of sealing can be achieved e.g. by means of a diameter reduction and/or socket and a separate sealing part, such as a sealing ring. Such joint can be arranged as air tight, whereby the pipe can be steam washed, if necessary. As mentioned above, the pipe comprises a self-supporting rigid bar. The length of the bar can be e.g. 1 - 10 m.

The pipe can be manufactured from any natural of synthetic thermoplastic polymer material. Examples include polyvinylchloride in different forms thereof (PVC, UPVC, CPVC), polypropene (PP), polycarbonate (PC), polyethylene (PE), in particular in cross- linked form (PEX), polystyrene (PS), polymethylmetacrylate (PMMA), acrylonitrile butadiene styrene (ABS), polybutylene (PB), polyvinylidene fluoride (PVDF), Nylon or other polyamide, or blends or derivatives of these. In one embodiment, the pipe comprises recycled thermoplastic polymer material, which can be one or more of the abovementioned polymers. Preferably, the pipe is manufactured from hard, unfoamed plastic, in contrast to cell plastics having gas foamed therein. Thus, a tight, hard and strong, but still well heat- insulating pipe due to the cavity structure is obtained.

As additives within the polymer can be typical additives used in the art, such as UV protection agents, colorants, fillers or reinforcements.

As states above, the present pipe can be manufactured entirely in an extrusion process in one or more extrusion stages. Typically, the manufacturing process consists of coextrusion, in which the yield of two or more extruders is combined into one continuous pipe item. This makes the manufacturing of the cavity structure easier. For example, with reference to Fig. IB the inner wall 11 and first outwards-directed intermediate walls 15A can be produced with a first extruder and the first intermediate mantle 12 and second outwards- directed intermediate walls 15B with a second extruder etc. In the process, the extrudates are joined, whereby the cavity structure is formed. The number of coextruders can be e.g. 2 - 10, typically 2 - 6. According to one embodiment, the pipe is a ventilation pipe. This can be installed for example as part of a ventilation system comprising at least one heat pump and/or heat recovery machine. In such systems there is a large difference between the inner and outer temperatures of the pipe, whereby the risk of condensed water is high without heat insulation. A particular risk for condensed water damages outside the pipe is in cooling systems, in which cooler air is carried by the pipe. An insulated pipe can provide benefits also in other kinds of ventilation systems, that is, it can be used with all ventilation solutions, including cooling and heating solutions.

In ventilation pipelines in which the pressure is typically low, the pipe joint technique can be e.g. a simple socket or rubber seal joint, by which primarily the joining of the actual fluid channels (inner pipes) of the pipes air/water tightly is ensured.

Heat insulation simulations

A circular pipe comprising a wall structure consisting of hexagonal cavities ("Hex pipe") has been verified by simulations using the CFD (computational fluid dynamics) method. In this thermal analysis two pipe sizes with three and five cavity layers were simulated and results were compared to similar size rock wool pipes. Hex pipe and rock wool pipe thermal transmittances was defined with CFD. Simulation took into account pipe material thermal conductivity and air in pipe cavities with air natural convection. Rock wool thermal transmittance was also defined according to standard EN ISO 12241.

Simulation boundary and domain properties/parameters were the following:

- Hex pipe material polypropylene (PP), heat transfer coefficient 0.22 W/(m*K).

- Hex pipe cavities are filled with normal air, which is moving by natural convection. The results are shown in Table 1.

Table 1. Simulation results

The simulations suggest that three cavity layers in 50 mm thickness and five cavity layers in 100 mm thickness essentially correspond to similar thicknesses of rock wool, as concerns thermal isolation capability of the pipe.

Also simulations where pipe cavities were cut with several additional wall in the axial- radial plane to prevent air flow inside the cavities were made. It is, however, notable that adding such walls added extra path to heat flow and decreased thermal insulation. This suggests that completely ring-shaped cavities are preferred.