The invention relates primarily to a method for producing, e.g. continuously, panels formed of two outer sheet metals and an inner layer of insulating material (e.g. glass wool or foamed synthetic material).

WO 2010/029587 describes a well-known plant for the production of these panels. The production lines allow manufacturing very long panels (up to 25 m long) but not very wide ones (1100 mm at most). Often the area to be covered is so large that the panels have to form a tessellation when placed on site. To ensure continuity of coverage between a panel and the adjacent one, one of the two sheet metals protrudes from the panel by a certain length, and this overhang is used to overlap the adjacent panel. See e.g. EP1371483 for general information.

To make the panel with protruding sheet metal, two adjacent cut ends of sheet metal are overlapped in line and a tape is laid over them to splice them. A typical splicing machine can be seen in figs. 6a÷6c of EP1371483.

The various overlaps impose an additional consumption of sheet metal, which on a production scale of millions of panels results in considerable quantities of sheet metal to be used. Moreover, the laying of the panels costs a lot in terms of number and time of manpower. It would then be preferable to produce panels of greater width, but the problem remains of how to find coils of such wide sheet metal.

Proposing a solution to this problem is the main object of the invention, which is defined in the appended claims, wherein the dependent claims define advantageous variants. In the method, insulating panels are produced in-line, and preferably continuously, having two outer sheet metals made from a continuous foil of sheet metal and an insulating layer between them, and the foil of sheet metal is formed by the union of a first and second foil of sheet metal. This method is advantageous because it allows for the production of larger panels than the known ones, so the installation of such panels drastically reduces not only the number and time of manpower but also the application aids such as gaskets and fasteners. A larger panel allows for fewer overlaps between panels for the same covered area, which means less likelihood of rainwater infiltration. The joining of the first and second foil of sheet metal may be done in various ways, e.g. by welding.

In order to achieve an efficient splice between the two foils, a preferred variant of the method envisages that the first foil of sheet metal comprises a first edge that extends along a first longitudinal axis, the second foil of sheet metal comprises a second edge extending along a second longitudinal axis, wherein a free end of the first edge is inserted into a concavity formed by a U- shaping obtained by bending the second edge about its longitudinal axis.

This mutual connection between the two edges ensures solidity, ease of joining and good waterproofness.

To improve the adhesion and strength of the joint between the two foils of sheet metal, preferably both edges are U-shaped and have one free end (of the U) contained in a concavity formed by the U-shaping of the other edge.

The edges may both be U-shaped first and then connected to each other.

Or, the first edge is bent about its longitudinal axis to shape it into a U and form a concavity with the U, a free end of the second edge is inserted into the concavity of the first edge, and the edges are flattened on top of each other so that both edges end up U-shaped and have one free end contained in a U-shaping of the other edge.

At the end of the mutual connection, the two foils of sheet metal end up joined along a splicing strip and form a composite foil.

The composite foil of sheet metal formed by splicing the first and second foil of sheet metal can be used to produce the foil of sheet metal from which only one of the outer sheet metals, or both, is/are obtained.

With the composite foil, flat or corrugated (fretted) panels may be produced.

For corrugated panels, one of the two outer sheet metals preferably undergoes in line a cold profiling to shape it according to a corrugation. The profile of the corrugation usually comprises, e.g. flat, troughs and crests joined by inclined, e.g. flat, planes. Compared to an all-flat panel, the waving of the corrugation increases the length of the outer sheet metal required to produce the corrugated side of the panel. Usually, instead, the outer sheet metal opposite the corrugated one, is flat.

The method can be applied to either one or each of the two aforementioned outer sheet metals. However, since the corrugated sheet metal is the one with the longest length, the advantages of the method are more pronounced when applied to the sheet metal on which the corrugation is eventually to be made.

It is convenient that the composite foil of sheet metal comprising the corrugation has a profile that develops orthogonally to the direction of the splicing strip.

Although the point on the profile of the corrugation where the splicing strip is placed could be any, in practice it is convenient to choose it appropriately. Preferably, then, the composite foil is profiled so that the splicing strip is located on the corrugation at an inclined plane connecting a trough and a crest of the profile.

So no water stagnation occurs and rainwater - in use - will slide off the splice.

To improve the contrast to water stagnation and the rainwater drain, preferably the composite foil is profiled and/or oriented so that the composite foil at the splicing strip, going from the side corresponding to the outside of the panel to the side corresponding to the interior of the panel, comprises the overlap of a portion of the U-shaping of the foil of sheet metal forming the nearest crest, the free end of the U-bent foil of sheet metal forming the next trough, the free end of the U-bent foil of sheet metal forming the nearest crest, a portion of the U-shaping of the foil of sheet metal forming the next trough.

This sequence of overlapping layers of sheet metal ensures water tightness and tear resistance when the splicing strip is e.g. stressed by an expanding foam, e.g. polyurethane, injected under the corrugation (between the two outer sheet metals) to form the insulation layer of the panel.

Another aspect of the invention is a machine comprising means for performing a or each of the steps of the method.

Another aspect of the invention is a plant for producing, preferably continuously, insulating panels having two outer sheet metals made from a continuous foil of sheet metal and an insulating layer between them, comprising in line a machine or means to perform a or each of the steps of the method.

The advantages of the invention will be clearer from the following description of a preferred embodiment of the method, reference being made to the attached drawing wherein

- Fig. 1 shows a cross-sectional view of the ends of two foils of sheet metal;

- Fig. 2 shows a preferred operational step to achieve the configuration of Fig. 1 ; - Fig. 3 shows a partial cross-sectional view of a panel and a profile thereof.

For in-line production of insulating panels of the above type, a foil of sheet metal formed by the union of a first foil 10 of sheet metal and a second foil 20 of sheet metal, is used (see fig. 1). The two foils 10, 20 are, for example, unwound from two coils (not shown) and processed to be connected to each other as shown in Fig. 1. The foil 10 comprises an edge 12 extending along a first longitudinal axis X1, and the foil 20 comprises an edge 22 extending along a longitudinal axis X2.

By a machining operation according to the preferred method, each edge 12, 22 is bent about its longitudinal axis X1, X2 so as to eventually form a U-shaping. In the illustrated example, each U-shaping comprises a proximal portion 14, 24, a portion 16, 26 bent by 180 degrees, and a distal portion 18, 28, respectively.

The U-shaped edges 12, 22 are coupled to each other so that in the concavity formed by the curved portion of a foil the distal portion of the other foil is inserted. In the example of Fig. 1, in the concavity formed by the portion 16, 26 there is inserted - respectively - the distal portion 28, 18. In the example, the distal portion and the proximal portion of each edge lie on two substantially parallel planes.

The edges 12, 22 may both first be U-shaped and then connected. Or (see sequence of Fig. 2) the edge 12 is bent about its longitudinal axis X1 to shape it into a U and form said concavity with said U-shaping. In the example, the lying planes of the distal portion 18 and the proximal portion 28 are substantially orthogonal to the lying plane of the remaining portion of the foil 10.

The distal portion 28 of the edge 20 is then inserted into the concavity of the edge 12, and then the edges 12, 22 are flattened on each other (see arrow F) to achieve and make the configuration of Fig. 1. Specifically, the assembly given by the proximal portion 14, the distal portion 18, and the distal portion 28 is folded toward the proximal portion 24.

The relative position between the U-shaping and the rest of the foil 10 may also vary from that shown in Fig. 2.

As can be seen from Fig. 1 , after the mutual connection the two foils 12, 22 end up joined along a splicing strip and form a single composite foil 40. The composite foil 40 will then usually undergo cold forming. The aim is for example to shape it according to a corrugation having profile 42 (see fig. 3) that develops orthogonally to the direction of the splicing strip (direction orthogonal to the page of the figures). The profile 42 generally comprises crests 44 and troughs 46 connected by inclined planes 48.

Fig. 3 also shows a foil 90 of sheet metal that makes the other half of the sandwich panel, wherein between the composite foil 40 and the foil 90 insulation material is placed, e.g. glass wool or expanded polyurethane. Regarding the point on the profile 42 where the splicing strip is placed, preferably the composite foil 40 is profiled so that the splicing strip is located on an inclined plane 48 of the corrugation, as in Fig. 3. Thus, water stagnation does not occur and rainwater will slide on the inclined plane 48 away from the junction. In addition, if the insulation inside the panel is expanding material 50 such as polyurethane, the junction must withstand the thrust P of the expanding material 50. The mutual coupling between the two U's obtained on the edges 12, 22 ensures strong separation resistance.

In order to avoid water stagnation as much as possible and to favor rainwater drainage, preferably the composite foil 40 is profiled and/or oriented so that on the corrugation 42, in correspondence with the splicing strip, there is a particular configuration of the folded layers of the edges 12, 22. That is, going from the outside of the panel towards the inside, it is preferable that the overlapping of layers is in this order: the proximal portion 24, the distal portion 18, the distal portion 28, and the proximal portion 14.

The point on the inclined plane 48 where the junction strip is placed may be any. E.g. in fig. 3 the aforesaid point may be located also or only on the inclined plane 48 which in the drawing is the leftmost. The same type of junction in Fig. 1 and/or 2 may be used for the foil 90, which for a corrugated panel requires fewer junctions because less is needed per unit length of panel.