The present invention relates to a wall structure, for example for vessels, tanks, washing towers, tubes, ships ¹ hulls etc. The invention also relates to a wall element for use in such a structure, and a method of making the wall struc¬ ture.

From Norwegian Patent Specification No. 132 417 there is known an apparatus for the manufacture of sectional products of expanded plastic by extruding in such a manner that only part of the surface of the sectional product has a substanti¬ ally non-expanded surface skin, whereas the remaining part of the surface of the product has substantially the same cell characteristics as the interior of the product.

The wall element used in the wall structure according to- the invention has certain features in common with such an extruded section, but a difference resides in that the wall element according to the invention is not a final product, but only an intermediate product for the manufacture of a greater wall structure, whereas according to Norwegian Patent Specification No. 132 417 it is a question of making ledge- formed product to be used as such. Another difference resides in that the wall element according to the invention consists of a relatively thick (about 1-10 mm) layer of solid material at the surface with a sharp transition to the expanded core, whereas according to Norwegian Patent Specification No. 132 317 it is a question of an expanded plastic which is extruded in such a manner that a relatively thin surface skin is ob¬ tained, which is practically not expanded. Here there is there¬ fore obtained a gradual transition between the surface skin and the expanded core.

The object of the present invention is to provide a continuous wall structure for vessels-, tanks, washing towers, tubes, boat hulls etc., which is strong and simple in manufac¬ ture, the structure also readily lending itself to be given

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the shape of a double-curved surface and comprising an outer weather- resistant layer of reinforced plastic.

The wall structure according to the invention is compose of closely adjacent wall elements consisting of a core of rigid plastic foam which on a first side not facing adjacent elements is covered with a layer of non-expanded plastic which adheres to the core and preferably is of the same type as the latter, whereas the core is exposed on the opposite side, and of a continuous layer of reinforced plastic which covers the said opposite side and_ adheres to the exposed core, the elements engaging each other with matching shapes and being in addition connected to each other by welding and/or gluing.

A wall structure composed in this manner may be curved in two planes, the wall elements being capable of being bent relatively easily to desired shape, since they do not have any layer of non-expanded plastic which surrounds the entire core. After the elements have been mutually connected, the side of the wall elements not to be coated with reinforced plastic, can easily be ground or otherwise machined for obtai¬ ning a smooth and even surface on which the reinforced plastic i.e. the plastic material and the reinforcement in the same, can be applied in a simple manner for obtaining an even and smooth exterior surface.

The wall elements are preferably elongated plank-like elements having side edges of a groove- and tongue-like shape for mutual engagement of the elements. Preferably the elements may consist of a core of expanded PVC having a coating of non-expanded PVC on three sides. The reinforced plastic layer is preferably glass fibre reinforced polyester or epoxy resin.

As mentioned above the wall elements are preferably of elongated plank-like shape. They can easily be manufactured by co-extrusion.

In the manufacture of a wall structure as specified above the wall elements are assembled into desired shape, if desired by means of templets, frames, shutterings, suppor¬ ting walls or the like, the elements being glued or welded together so that the composite wall structure is preferably self-supporting, whereafter the side of the wall structure

which is formed by the exposed cores of the elements, is covered with a reinforcement and a plastic mass which sets into a continuous layer, if desired after the wall structure has been ground or otherwise machined for smoothing out irregu¬ larities, especially edges at the joint between the wall elements.

The invention will now be described in more detail with reference to the drawing, which as an example shows an embodi¬ ment of a wall element and a wall structure made of such ele¬ ments, as well as examples of a tubular and a double-curved wali structure that can be made in accordance with the in¬ vention.

Fig. 1 is a cross-sectional view of a plane wall structure consisting of several assembled plank-like wall elements and a layer of glass fibre reinforced polyester.

Fig. 2 shows how it is possible in accordance with the invention to make a continuous tube having a tube wall in accordance with the invention.

Fig. 3 shows how the wall elements according to the invention can be used for making a boat hull.

The wall structure 1 shown in Fig. 1 is composed of wall elements 2 placed beside each other, and which after assembling have been coated on one side with a continuous layer 3 of reinforced plastic, for example a glass fibre rein¬ forced polyester or epoxy resin. Each element 2 has been made by co-extrusion of an expanding rigid plastic for forming a core 4 of rigid plastic foam, and a non-expanding plastic which forms a surface layer 5 on at least a first side of the wall elements 2, which does not face an adjacent element. However, in the embodiment in Fig. 1 the co-extruded layer 5 of non-expanded plastic is shaped so that it also covers the opposed faces of the wall elements 2. The material of the layer 5 shall consist of a plastic which adheres to the core 4 and preferably is of the same type as the latter. For example, the core may consist of expanded PVC, whereas the coating 5 consists of a non-expanded PVC. However, the core may also consist of polyuretane, polypropylene or another suitable plastic. The plastic material of the reinforced

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plastic layer 3 may be of a quality adhering to the material of the core 4. Further, the wall elements 3 are directly inter¬ connected, partly because their edges have been shaped for mat¬ ching mutual engagement and partly by welding and/or gluing. It will be understood that the design of the matching engagement shown in Fig. 1 and having the form of a groove and a tongue in opposed edges merely constitutes an example of a suitable matching engagement. By gluing the wall elements 2 together the adhesive may be evenly distributed throughout the opposed faces of the wall elements, whereas in the case of welding it will be sufficient to weld the wall elements together along the upper - in Fig. 1 - end of the joint between the elements. For this purpose the outer edge of the fents may be chamfered for giving room for deposit without any protrusion being formed on the surface.

Since the wall elements are rigidly connected to each other and since both the layer 5 and the glass fibre reinforced plastic 3 adhere to the material of the core 4, a wall structur is obtained which is capable of sustaining relatively great forces. The structure is preferably assembled with the rein¬ forced plastic layer 3 on the side of the wall subjected to the greatest tensional loads.

Although the wall elements 2 are preferably made by co-extrusion, it will also be possible to make them by gluing a sheet material of hard PVC into PVC foam.

An important advantage of a wall element according to the invention is that it can be shaped into both single-curved and double-curved surfaces, the same being flexible since only one flat face is coated with rigid plastic. Thus, in Fig. 2 the co-extruded wall elements 2 may be wound helically into a self-supporting tube structure 6. The non-expanded plastic layer 5 faces the interior of the tube 6. On the outer face of the tube 3 it is possible in a conventional manner to spray a plastic mass and a reinforcement for obtaining an outer coherent reinforced plastic layer. The tube 6 is rotated so that the co-extruder may remain stationary. Such rotation of the tube also permits a spraying nozzle 7 for applying

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the reinforced plastic to be stationary, whereby the manufac¬ turing machinery will be as simple as possible. After the spraying-on of the reinforced plastic the tube is passed con¬ tinuously and with continued rotation through a curing furnace. When the tube has passed through the furnace a strong tube 8 is obtained, which has an outer layer of reinforced plastic, a core of expanded plastic and an interior layer of for example PVC.

When making double-curved wall structures the elongated plank-like wall elements 2 are preferably arranged with their longitudinal direction in the direction in which the curvature of the surface is slightest. For obtaining a relatively small radius of curvature at right angles to the longitudinal direc¬ tion of the wall elements 2 these are made relatively narrow. It is then possible to assemble the elements so that they form an angle to each other in the transverse direction so as to obtain a generally curved surface composed of small chords. That face of this surface structure which is to be coated with reinforced plastic, may be ground or otherwise machined for evening out the polygonal surface into an evenly curved surface, whereafter the reinforced plastic layer may be applied. In Fig. 3 it has been indicated how r.he small plank-like wall elements 2 may be assembled into a double- curved shape on frames or templets 10 similar to ships' frames with the layer 5 facing the templets 10. The outwardly convex shape of the assembled wall elements 2 are thereafter ground into an even, smooth surface, whereafter the layer 3 of rein¬ forced plastic may be applied manually, by spraying or the like. It will be obvious that such method of manufacture is particularly well suited for the manufacture of boat vessels in small series, for examle for amateur builders or for under¬ takings wanting a diversified system of models.

Even large vessels of any desired cross-sectional shape, for example a circular cross-section with a diameter of 5- 12 m and a height of 3-12 m can easily be manufactured by applying reinforced plastic onto one face of wall elements assembled into the desired shape of the structure. The wall

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elements 2 may be built up against a shuttering, supporting wall or the like. This possibility has not been illustrated in detail by any figure, since it is held to be self-evident.

As indicated in Fig. 1, the layer 5 of non-expanded plastic may be thicker on the said one face of the wall ele¬ ments 2, whereas on the opposed faces of the wall elements it is considerably thinner in order not to stiffen the element 2 to a too great extent.

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