The present invention relates to a method of making boat hulls, vehicle bodies, containers and similar shell struc¬ tures, and a tube lattice for use in making such structures.

A well known prior art method of making boat hulls, vehicle bodies, containers and similar shell structures comprises that a lattice is made, whereafter panels are fastened to the lattice. When the article to be made is to have a cur¬ ved surface it is usual to preform the panels before they are applied. The forming usually requires the use of one or more moulds, depending on the number of different shapes which are needed. By making articles in small production volumes the use of moulds is a disadvantage from economical reasons, because the manufacture of the moulds will involve a large expence per unit of articles made.

It is also known to make articles of the above mentioned kind having panels on both sides of the lattice, thus form¬ ing hollow walls, and moreover it is known to fill the cavi¬ ties in such walls with an expansion material, for instance plastics foam. A problem which arises in filling the mat¬ erial to be expanded is to fill the correct quantity, in order to achieve complete filling of the cabities, but with¬ out filling such a quantity that an excessive pressure is created in the cavities.

An object of the present invention is to find a method which makes it possible to achieve filling of the cavities with an exact amount of expansion material. According to the

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invention this is achieved by placing one component of an insulating expansion material, in an amount apportioned to the volume of the cavities, in each cavity prior to closing the cavities by means of the panels, and that an activating component of the expansion material is injected into the thereafter closed cavitites in order to cause expansion, by use of at least some of the tubes as distribution channels for said second component.

The quantity of the first component placed in each cavity can be calculated on basis of the volume of the cavity, which can of course be calculated for instance from the constructio drawings, for instance by use of a computer. The amount of the second component, which is injected, is not critical. It may for instance be used a first component which cures by the presence of moisture. Thus, curing may be effected by the injection of water or water vapour. Preferably a poly urethane is used as the first component, or another material, which increases in volume during the foaming. This ensures that the cavities are completely filled with expansion mat¬ erial.

The water or water vapour may be supplied under such pressure that the expansion material is prevented in penetrating into the apertures in the tube walls. Thereby is prevented that the tubes are filled with expansion material, and the tubes, or at least some of the tubes, may be utilized as guiding or flow channels, for instance for electric wiring, cables or wires, conduits for fuel or other fluids, or the tubes may constitute buoyancy chambers in boat hulls. For instance liner tubes or hoses may be inserted in the lattice tubes after the expansion or foaming of the expansion material has taken place, in order to prevent that for instance fuel leaks through the apertures in the lattice tubes and into the expan-

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sion material. For the purpose of inserting such liner tubes or hoses the lattice tubes may for instance be perforated at their end's. Prior to and during the injection of the activating component of the expansion material the lattice tubes should be closed at their ends, in order to efficiently lead the activating component into the cavitites.

It is possible to use small panel elements. The panel ele¬ ments are placed in such a manner that their edges are loc¬ ated at or near the middle of the lattice tubes. The panel elements may be situated edge to edge and secured by means of glueing or welding. It is possible to make single ^' and double curved shell structures by use of such panel elements without the necessity to preform the elements to their cur¬ ved shape by means of moulds. It is possible to calculate the necessary circumferential shape and size of each panel element in its planar state in order to cover a certain area in curved state. It is preferable that those lattice tubes which the panel elements are to be secured against have means to keep the elements in their correct position. This is in particular of importance when glue is used to fasten the elements. The lattice tubes, or at least some of the tubes, may for instance have longitudinal ribs which the edges of the panel -elements come into engagement with. The elements are given their curved shape manually simultaneously with the application, and the elements will then press against the ribs on the tubes. In stead of ribs the tubes may have grooves, and the panel elements are then folded along their edges, which are inserted in the grooves. What ever means is used, the important point is to achieve that the panel elements are secured in the curved shape.

In order to make the above method possible the panels should have a relatively small thickness. Panels made of steel or metal may for instance have a thickness of far less than 1 mm. The expansion material which is foamed in the cavities

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formed by the application of panel elements on both sides of the tubes lattice acts to stabilize the structure, because the material will adhere to the panel elements. Without such stabilization the structure may for many purposes get too little stability, i.e. resistance against deflection. Because the amount of expansion material can be apportioned with great exactness, it is avoided that the pressure becomes so large that the panel elements are deformed, and on the other hand is avoided the formation of cavities in the material which may reduce the stability.

By the utilization of the tubes in the tube lattice for the injection of the second component of the expansion material it is not necessary to make apertures in the panel elements and to couple injection equipment to an aperture of each cavity. The lattice tubes act as conduits during the inject¬ ions, and it is sufficient to supply the second component through a single aperture or a small number of apertures in¬ to the conduit system formed by the lattice tubes.

The lattice tubes of course are very important to the strength and stability of the structure and must therefore be dimen¬ sioned and designed in accordance with the strain which occurs during the use of the structure.

In structures having more or less sharp corner edges, such as in the transition between a boat hull and the deck, in a boat bow or the transition between walls and between the walls and the top or bottom of a box shaped structure, such as a bus body or a caravan, the panel elements do not have to extend around the lattice tube which lies in such a corner edge. The tube may be exposed on the outside along the edge, whereby the panel elements may extend approximately to the tangential line between the elements and the tube. Thus,

the panel elements do not have to be bent to give the cor¬ rect cross sectional curvature of the corner edge, because this curvature is formed by a part of the tube surface. In for instance a boat bow may be used a tube having for in¬ stance a triangular or circular cross section, and the panel elements may, as previously mentioned, end at or near the tangential line, in such a manner that the desired corner angle is formed, and the tube may have ribs or grooves along the tangential lines. In such corner areas the tubes of course have apertures for the injection of the second com¬ ponent in those wall parts which are facing the cavities.

By the method according to the invention is first of all achieved an exact apportioning of expansion material in the cavities _^ also when the walls being made are not of even thickness. Curing of the- expansion material is achieved by means of a second component which may be supplied by use of the conduit system formed by the tube lattice. More¬ over, the exact apportioning of the amount of material makes it possible to make the panel wall by means of more or less small panel elements and which do not have to be given their desired curvature before they are applied, because it is possible to apply the elements in a condition of ten¬ sion, in which condition the elements have the desired cur¬ ved shape. Thereafter the shape of the panel elements is stabilized by means of the expansion material. It is of course not necessary that all the panel elements are curved.

In addition to the above described method the invention also relates to a tube lattice for use in making shell structures of the type disclosed above. A tube lattice in accordance with the invention comprises several tubes, of which some may extend in the entire length, width or -height of the stru-

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cture. At least one of the tubes which define each of the cavities which are formed when the panels or panel elements have been applied on both sides of the tube lattice have at least one aperture in the wall section which faces the cavity, adapted for injection of a second component of an expansion material which is to be made by in situ expansion of a first component, said first component being placed in each of the cavities prior to the closing of the cavity.

The tubes of the tube lattice may be interconnected by means of any known means, such as welding, which may be done both for steel tubes and plastics tubes. Also separate joining ele¬ ments may be used to interconnect the ends of the tubes in the lattice.

The invention is illustrated .on the annexed drawing, which shows a cross section through a wall of a shell structure made in accordance with the invention. In the drawing is shown inner panels 1 and 2 outer panels 3 and 4, a tube 5 forming a part of the tube lattice and expansion material 7 in the cavities on both sides of the tube 5. The tube 5 has apertures 8 in the wall parts which face the cavities filled by expansion material. The tube 5 is provided with ribs 9 on the outside. These ribs act as contact surfaces for the edges of the panels 1, 2, 3, 4 and the primary pur¬ pose of the ribs is to keep the panels in their correct posi¬ tion until the panels have been properly fastened to the tubes. This is particularly important when the panels are to be curved, without being preformed with respect to cur¬ vature. All those tubes along which edges of curved panels are to be situated have ribs. The ribs 9 contribute to keep the panels in place and to keep the panels curved, at least until the panels have been secured to the tubes, for instance by glueing or welding. The ribs may have a height corre-

sponding to the thickness of the panels, whereby the sur¬ face of the finished product will be substantially smooth.

In stead of ribs the tubes may have longitudinal grooves, adapted for the insertion of bent edges on the panels. The purpose of such grooves will be the same as for the ribs, and will not be explained further.

It will be understood that only those tubes along which the edges of panels or panel elements are to be situated need to have ribs or grooves.

Within the scope of the invention it is also possible to delete ribs or grooves. The panels or panel elements may for instance be welded to a tube along one edge, whereupon the panels or panel elements -are'held, by use of suitable tool means, in the desired curved shape and welded to the tube along the other edges.

By use of the method and the tube lattice in accordance with the present invention it is possible to cause foam¬ ing of the expansion material in each cavity by introduc¬ ing av activating component, which may be water or water vapour, into the conduit system formed by the tube lattice, whereby the activating component will be distributed through the lattice and into all the cavities, in which expansion of the material will take place. The activating component can be introduced in the lattice through a single aperture, or through a small number of apertures.

It will also be understood that the invention is not restri¬ cted to filling all the existing cavities between the lattice tubes with expansion material. Some of the tubes may of co¬ urse make frames for windows or doors, such as in a bus or a cara¬ van, and are not covered by panels.

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