The present invention relates to three-dimensional constructions which comprise at least one rigid plate, according to the preamble of Claim 1.

The present invention also relates to a method of producing three-dimensional

constructions, according to the preamble of Claim 20.

Typically, large basins and containers are made of metal or concrete which, in these purposes of use, have totally replaced wood-based materials. Concrete basins are often cast in situ because of their considerable weight. Concrete is cheaper than metal but it presents major difficulties when it comes to recycling the material after the containers are taken out of service. Whereas metal is susceptible to corrosion and must be coated, during a separate production stage, with polymeric materials, for instance for corrosion resistant

applications, concrete is affected by extreme changes in temperature and it is susceptible to frost damage, which over time can lead to cracks in the material and its disintegration. Metals, too, are affected by changes in temperature, a factor which should be considered, among others, when dimensioning the tube systems which are connected to tanks or wells.

There is a need for a building material which can be used in larger constructions but is more affordable than metal and less susceptible to variations in the ambient temperature than are metal and concrete.

In technical applications, thermoplastic materials have several advantages over wood and metal, particularly regarding, among other things, recycling and resistance to corrosion and decay caused by micro-organisms. To date, larger structures which are entirely or mainly comprised of thermoplastic material have not been available for construction purposes. The containers produced have had a maximum diameter of approximately 3-4 m and only cylindrical structures have been possible. However, it is very possible to construct open basins and other non-pressurised applications of rigid plates, if these plates can be joined together reliably in order to generate compact structures. Rigid plates for different structural purposes usually consist of thin solid plates which are stiffened by beams, such as beams having an L-or I-shaped cross-section or similar form. The plate constructions are made by cutting out large plates and then modifying them by means of flexurally rigid beams of the abovementioned type. A typical double wall construction therefore comprises two rigid plates arranged at a distance from each other and which form the surfaces of the construction and which are joined by intermediate, longitudinally or transversely running beams. In sandwich structures, stiffening layers of beehive structure are also used. If, in practice, you want to produce polymeric double-wall plates of substantial dimensions out of thermoplastic material by means of extrusion, it is not possible to make such double-wall constructions thick enough because only a limited amount of heat can be removed from the beams binding together the surface layers in these double-wall constructions. Because it is not possible to cool the beams quickly under controlled conditions, it is very difficult to produce rigid plates, for example, having consistent quality and thus strength specific properties. The uneven and slow dissipation of heat makes production costs uneconomic and leads to unfavourable internal stresses in the material and hence to twisted and curved plates. The purpose of the present invention is to eliminate at least some of the disadvantages associated with the prior art and to generate new solutions for basins, tanks and similar constructions.

The present invention is based on the idea that a three-dimensional construction is built by using a plate material which possesses a double-wall structure and which is comprised of elongated hollow profiles, which have essentially straight and parallel central axes and which abut each other and are joined together to form the abovementioned double-wall structure. According to the present invention, it is possible to provide such plates, which are primarily made of thermoplastic materials, but which can also be made of metal or of various thermosetting plastics.

Rigid plates made of thermoplastics offer the possibility of joining by welding, and the present invention therefore relates to a new process for the production of three- dimensional structures by joining at least two rigid plates, which are comprised of a plate- shaped thermoplastic material, formed of elongated tube profiles, each of which has an essentially straight central axis and which tube profiles abut each other and are welded together to form a double-wall structure, in which case the plates, when welded together, form a three-dimensional construction.

More specifically, the three-dimensional constructions according to the present invention are characterised by what is stated in the characterising part of Claim 1.

The method of producing three-dimensional constructions according to the present invention is characterised by what is stated in the characterising part of Claim 20.

Considerable advantages are achieved with the present invention. In principle, an almost unlimited number of these double-wall structures can be easily joined into three- dimensional constructions of a freely chosen design. If desired, it is also possible to bend the double-wall construction in order to form curved elements. The plates have a good flexural strength and are therefore suitable also for applications where, to date, concrete and reinforced metal walls have been used.

Because the plates are formed of hollow profiles, it is possible, if desired, to reinforce and anchor the construction by filling the cavities with, for instance, reinforcing bars or concrete mass. The cavities can also be utilised for electrical wiring and even as pipelines for liquid media. By using hollow profiles of different colours, striped structures can be designed.

According to a more preferred embodiment, several thermoplastic or metal plates of the present type welded together to form three-dimensional constructions, such as basins and tanks.

In addition to their having good flexural strength and being recyclable, the present thermoplastic plates - and thus also the three-dimensional constructions made from these - exhibit good resistance to corrosion, decay and also mould. Because the structures are composed of tube profiles, they are durably coloured and protected against UV. The structures are easy to repair or modify. In relation to their mechanical properties, their weight is low, especially when comparing these structures with equivalent structures made of reinforced concrete. In the following, preferred embodiments will be examined more closely with the aid of the accompanying drawings.

Figures la and lb show schematically how extrusion welding of tube profiles can be carried out according to an embodiment of the present invention, in which case Figure la shows a side view and Figure lb a corresponding top view;

Figures 2a and 2b show laterally the cross-section of structures of two different embodiments;

Figure 3 indicates the welding directions of a clamped stack from the front,

Figures 4a and 4b show a welded stack having welded seams from the front (Figure 4a) and in cross-section from the side (Figure 4b), and

Figure 5 shows an open culvert which is comprised of several rigid flat plates and rigid curved plates which are welded together to form an arch-like construction, suitable for smaller tunnels under roads and railways. The present technology involves the production of new three-dimensional constructions of plates that have a double-wall structure and which exhibit a significant flexural strength. These plates are produced, in turn, by joining several hollow profiles, which are arranged side by side or stacked one upon the other in such a way that a smooth horizontal row or a vertical stack is obtained (hereinafter, "stack" is used to mean both). Preferably, the stack is arranged in an upright position.

Preferably, the hollow profiles in the plate have parallel central axes and they are so straight that they can be pressed against each other along their full length. Therefore, the stack of hollow profiles has two large, typically flat, opposite sides parallel to the central axes. The widths of the flat sides correspond to the combined width of all hollow profiles.

The plate-shaped structure is typically composed of hollow profiles made of thermoplastic material, thermosetting plastics material or metal. The accompanying drawings, which are described further in the following, first show various embodiments for production of double-wall structures. The drawings relate in particular to plates made of thermoplastic material, which represents a more preferred embodiment. Thereafter, the plates are examined more closely and, in turn, their use. The production technique is described more closely in our co-pending application titled "Method of producing a plate-like construction which has a double-wall structure".

The term "plate", as used herein, means a mainly flat object which is limited in size and of which two dimensions are essentially larger than its third dimension. In practice, this means that the side of the object is much larger than its thickness.

Typically, these plates exhibit a ratio between the area of one of its flat sides and the thickness of the plate, that is more than 50 [length units ² ] : 1 [length unit], in particular approximately 75-100,000 [length units ² ] : 1 [length unit], typically approximately 100- 50,000 [length units ² ] : 1 [length unit].

By contrast, "three-dimensional constructions" are structures that occupy a significant space. In practice, the surface of one side is least 1/10, preferably at least 1/8 of the surface of the next shorter side. Typically, the present three-dimensional constructions form or define an open or closed space in which the rigid plate or the rigid plates form at least one wall.

Typical examples of three-dimensional constructions are tanks, reservoirs, basins, cabins, huts, cupboards, drawers and containers, wells, tanks and culverts. These will be discussed in more detail in the following.

It should be noted that the following description applies mutatis mutandis to the production of three-dimensional constructions which are comprised of rigid plates having double- wall structures made also of materials other than thermoplastics, although all the advantages achieved by specifically using thermoplastics are lost by using for instance metals and thermosetting plastics. A difference to be noted is that thermoset composite profiles are usually glued, rather than welded. Reinforced thermoplastic profiles, which are also included in the scope of protection can, however, be joined together for instance by extrusion welding. Production of rigid plates

Figures la and lb show an upright stack comprised of hollow profiles. In the figures, the stack comprises six thermoplastic tube profiles each of which has a cross-section that is typically rectangular. Their reference numbers are 1 to 6.

Generally, the number of tube profiles varies freely from 2 to 100, typically 2 to 50 or 3 to 30, depending on the predetermined width of the double-wall structure.

The stack is rendered immovable, which can be achieved for instance in such a way that adjacent hollow profiles are clamped together at each end of the hollow profiles. Another possibility is to arrange the hollow profiles in a separate frame which temporarily holds them together.

According to a preferred embodiment, the welding of the stack (which stands on a support) is carried out as extrusion welding, by using welding nozzles which are arranged on opposite sides of the profile stack, and which are coupled to a source of molten thermoplastic material. This is shown in detail in Figures la and lb, where the reference numbers 7, 8 and 11, and 9, 10 and 12, respectively, relate to two welding devices

(extrusion welding sets) consisting of extruders with screws 7, 9 and hoppers 8, 10, which feed molten plastic mass through a nozzle 11, 13 into the seam between adjacent hollow profiles 3, 4, so as to form two welds 12, 14. The same seam is simultaneously welded from opposite directions. This solution avoids the generation of uneven heating of the material. For this purpose, the extrusion welding sets 7, 8, 11; 9, 10, 12 in Figures la and lb are symmetrically arranged on each side of the tube profile stack. Figure 3 shows a similar stack of tube profiles 31 to 36, which are horizontally stacked. The directions in which the welding moves are indicated by arrows. The relative movement between the stack and the welding apparatus can be achieved in various ways. In a first embodiment, the welding is carried out using fixed welding nozzles by moving the stack longitudinally, i.e. along the central axes of the hollow profiles. For this purpose, the stack can be arranged on a conveyor which is able to move the stack horizontally past the welding nozzles. However, it is also possible to carry out the welding by using movable welding nozzles which move longitudinally (horizontally) along the stack. In a similar way, the welding of a stack of tube profiles, which are placed in an upright position (in which case the seams between the profiles are vertical), is carried out by bringing the welding nozzles in a vertical direction or by moving the stack vertically or horizontally, in the case that the welding nozzles are fixed. After a seam is welded, the welding place is moved to the next seam. According to a preferred embodiment, in which the stack is arranged with horizontal seams between the profiles, the welding place is moved down to the next seam.

In a preferred embodiment, the seam surface is separately prepared before the welding to ensure a good welding quality This can be done for example by mechanically working the seam in an initial sweep along the stack, for instance by using (chip)cutting machining and then by adding the molten plastic mass in a second sweep. The preparation removes any dirt or oxidised surface layer from the welding surfaces. It is also possible to supply radiant heat or convection heat (e.g. by way of hot air) to the seam from a separate nozzle simultaneously with the welding of the previous seam.

Preferably, the seam is preheated simultaneously from both sides.

It is particularly desirable to separately heat the material in the seam edges prior to welding, preferably to a temperature above approximately 50 °C. For this purpose, it is possible to use an infrared heater. Suitably, the extrusion welding apparatus is equipped with a nozzle for blowing hot air onto the welding place immediately before welding.□

If the hollow profiles comprise surface layers of various materials (e.g. functional layers on one side, see below), it is appropriate to use different welding materials on different sides.

Figures 2a and 2b show the use of different profiles for forming a double-wall structure. Figure 2a shows the assembly of typically rectangular, identical profiles 21, 23, in which case plastic melt is injected into the seams 22, 24, which melt can build up welding excrescenses 24 which have more or less a wedge-shaped cross-section.

According to a preferred embodiment, the welding excrescence is shaped to the adjacent surface so as to produce a welded seam which, together with the side of the tube profile, forms an essentially flat and smooth surface of the plate.

Thus, the structures in Figure 2a show two essentially parallel, smooth surfaces. Figure 2b shows a corresponding structure in which the tube profiles 25, 26, 27 and 28 together form a flat surface on one side of the stack. The profiles are joined in the same way as above, with sealing compound in the seals 30 and melt in the excrescenses 29. Three of the hollow profiles 25 to 27 are identical, whereas one is wider 28. The wider profile gives a greater flexural rigidity in the longitudinal direction of the profiles and in the direction of the structure, and thus forms a kind of reinforcing element for the entire construction.

Generally, the present double-wall structures are produced by using hollow profiles which comprise tube profiles, preferably hollow profiles of a thermoplastic material, which comprises one or more layers.

Thermoplastic tube profiles are welded by using a thermoplastic material, suitably the same thermoplastic material which the tube profiles are composed of. The term "profile" is used interchangeably with "tube" (i.e. an elongated object that has an open cross-section).

The thermoplastic profile is composed of 1 to 5 layers. According to one embodiment it contains several layers, in which case one of these forms the inner layer of the profile, and one the outer layer of the profile. Mainly in cases where a multi-layer wall comprises functional layers, it is preferable to arrange the functional layer separately in the outer wall (e.g. a conductive layer) or in the inner wall (e.g. a layer with good wear resistance). Typically, the hollow profile comprises mainly or entirely conventional thermoplastic, such as a polyolefin, such as polyethylene, especially HD-PE, or polypropylene, polyacrylonitrile-butadiene-styrene (ABS), polyamide (PA) or another thermoplastic material.

Possible functional layers can comprise ultra-high molecular weight PE (UHMWPE) or for example antistatic material. A material of the latter type can be comprised of a thermoplastic material which has been made permanently conductive. In this case, the thermoplastic material can be the same as that which is used in the core layer of the tube profile. Having this arrangement achieves good compatibility between the layers. The cross-section of the tube profiles is typically rectangular, in which case the abutting sides of the tube profiles constitute at least 1/10 of the jacket surface of the tube profiles. The term "rectangular" also includes such cases where the cross-sections of the tube profiles are quadratic or essentially quadratic. The ratio of the width to the height of the tube profiles is preferably 1 : 1-1 : 10, in which case the ratio between the minimum thickness of the tube wall and the height of the cross- section of the tube profile is in particular approximately 1 : 100-1 :4, especially

approximately 1 :50-1 : 5. In a preferred embodiment, plastic profile types are used which can also be used for manufacturing of plastic tubes by spiral winding. Such plastic profiles are described in, among others, U.S. Patents Nos. 5,127,442, 5,411,619, 5,431,762, 5,591,292, 6,322,653 and 6, 939,424. Typically, the surfaces of the tube profiles are smooth. However, part or all of the tube profiles may be rib-reinforced, in particular they may exhibit one or more longitudinal ribs on the inside or outside or on both sides of the tube profile. In the case where the tube profiles are made of a thermoplastic, reinforcement ribs, if used, are preferably made of the same material.

Ri2id thermoplastic plates

Generally, by means of a method of the type mentioned above, it is possible to produce plates whose flat surfaces have dimensions (height x length) ranging from approximately 100 mm x 100 mm to approximately 10,000 m x 20,000 m. Typical maximum dimensions of the plates are approximately 7,500 mm x 5,000 mm, especially approximately 5,000 mm x 3,500 mm, and the typical minimum size is approximately 500 mm x 1000 mm. Figures 4a and 4b show a finished plate which consists of six essentially quadratic tube profiles 41 to 46, which are welded together to form a uniform, dense plate, by using molten thermoplastic material in the seams 47. In the figures, the profiles are joined together along the narrower side walls. Astiffer but narrower structure is achieved by turning the profiles 90 degrees and joining them together along the wider side walls. The type of plate shown in Figures 4a and 4b is straight and rigid. However, it can be shaped to exhibit a curved shape, such as an arch structure, and this curved shape can be rendered permanent.

The present plate is self-supporting at span widths of up to 5,000 mm when transverse to the central axes of the tube profiles and up to 20,000 mm in the direction of the central axes.

The use of the double-wall structures A plastic plate of the type described above can be used as an element in the manufacturing of composite structures. Such a plastic plate can be cut to predetermined dimensions prior to manufacturing of the composite structure.

However, the plastic plate can be joined together with other similar plastic plates to form large uniform flat surfaces composed of several individual plastic plates.

Figure 5 shows an open culvert 51, which is comprised of four plates, 52-55, which are joined together. Two of these plates are flat/straight plates, namely 52 and 53, which, after installation, form the vertical part of the culvert, while the arched parts, 54 and 55, form the roof. The arched parts can be readily produced from rigid plates which are similar to the straight sides, 51 and 52, by bending them in a jig and, if necessary, by simultaneously heating them.

The plates are joined together at the edges by welding, for example, in the same way as are the individual tube profiles.

There are several examples of the use of either individual plates or assemblies of joined plates. Examples of these are open containers and basins, such as the process basins for treatment of water and waste water, basins for chemical processes, basins for fish care and fish farming, and catchment basins underneath conventional basins and tanks.

Naturally, these few examples are by no means exhaustive, rather, this technology can be applied to virtually all open reservoirs, basins and tanks.

Similarly, sealed containers of various types of tanks and silos for dry material, sludge, liquid and gases are exemplified. Also, cylindrical drying devices can be produced according to the present technology. Other three-dimensional examples are wells, rectangular tanks above and in the ground, open culverts, cabins, huts, cupboards, drawers and containers.

As shown in our parallel patent application "Method of producing a plate-like

construction which has a double-wall structure", elements which are essentially two- dimensional can also be produced for these three-dimensional constructions, i.e. the plates can form merely part of the construction, even though such a construction is three- dimensional, and the other sides are then comprised of conventional sides and materials.

Examples of this latter case comprise tank tops, silo bottoms, construction bases, tank ends for horizontal tanks, both horizontal and vertical partition walls of tanks, tank ends for upright tanks, which ends can be balanced and reinforced with concrete mass.

Furthermore, the plates can be used as protective barriers, protective surface structures in port facilities; shock absorbers, pylon protection, casting moulds, sliding surfaces.

Other examples of protective barriers are wall surfaces in community building - noise barriers and protection walls at roadsides.

Other examples of mainly flat constructions are floating manhole covers.

A particular field of application is heat exchangers for air/gases, and heat exchangers for water/liquids. In these applications, it is possible to take advantage of the fact that the rigid plates exhibit a large number of parallel cavities.

It is also possible to build constructions by combining the present straight plates with corresponding plates that are shaped into arched structures. An example of such constructions is an open culvert.

Another particularly interesting field of application includes straight and arched plates for boat building, decks and hulls.

In the case where the plates are made of thermoplastics, the joining of several plates to larger three-dimensional units can be achieved by welding, usually after first bevelling the edges of the sheets to be joined.