The structure of these panels is often referred to as"sandwich"structure because it comprises at least one layer of insulating material, arranged between two outer walls at sight; the insulating material is generally a polyurethane foam or the like (but may also be rock wool or other insulating material), while the outer walls are in most cases made of sheet metal.

In order to provide the panels with a greater flexural rigidity, it is known to profile one of their outer walls with ribs, frets, undulations or the like having various possible designs; information on this argument and on the methods for manufacturing the panels may be found in European patent applications Nos.

682,159 and 995,594 or in international patent application PCT/EP95/03865, filed by the same applicant for the present application.

As is known, the flexural rigidity of the panels improves when the height of its ribs is increased, the other conditions such as the thickness of the panel and <BR> <BR> of the metal sheets, the materials used, etc. , obviously remaining unchanged; there are, however, drawbacks which prevent this height from being increased beyond certain limits.

Indeed, generally for reasons associated to the industrial manufacturing process, only one of the outer faces of the panel is deeply profiled, while the other face has only slight stiffening ribs.

This has negative effects on transportation of the panels, because when they are loaded onto lorries, trains, containers or the like, they must be stacked in

an alternate overturned condition, resting on their respective deeply profiled faces; as a consequence it follows that the empty space between one panel and the other represents a significant percentage of the entire product, that in current practice the cost of transportation of the panels depends on their volume and not on their weight.

It is evident that if, without changing the materials and thickness of the insulating layer, the height of the profiling of the panels is increased in order to improve their rigidity and their mechanical strength properties, the empty space between them in the stacked condition increases too: it follows therefore that in order to keep transportation costs down, in the practice only compromise solutions are adopted, taking into account both of these parameters.

The technical problem underlying the present invention is therefore that of providing a panel with improved rigidity obtained by increasing the height of its ribs, without however encountering the drawbacks referred to above in connection with transportation.

The idea for solving this problem consists in providing panel reinforcing sections, to be applied onto the ribs at the time of installation of the panel: these sections increase the height of the ribs and therefore the flexural rigidity of the panel, without negatively affecting the transportation costs since they are light and are mounted on the panel only for installation thereof.

In accordance with a preferred embodiment of the invention, the reinforcing sections are fixed to the ribs by means of mating shapes which prevent them from sliding in the longitudinal and transverse directions; furthermore, the sections preferably have dimensions such that they may be stored, for example, in the empty spaces present between the stacked panels during transportation.

The characterising features of the invention will emerge more clearly from the description provided hereinbelow, relating to a non-limiting embodiment thereof and to some variants illustrated in the accompanying drawings, wherein: - Fig. 1 is a perspective view of an insulating panel on which a reinforcing section according to the invention is applied; - Fig. 2 is a cross-section through the above panel and section; - Fig. 3 shows a cross-sectional view of two panels like the one above, in the stacked condition; - the pairs of figures 4-5 and 6-7 show views similar to those of Figs. 1 and 2, of respective variants of the invention.

In the first of these figures reference 1 denotes a composite insulating panel fixed to a beam 2 of a general support structure, such as, for example, the flooring of an industrial warehouse or a garret.

Panel 1 (only a portion thereof is shown in the drawings) comprises an upper face 4 made of sheet metal, profiled with projecting ribs 5 of trapezoidal shape onto which screws 6 for fixing the panel to the beam 2 are applied.

For this purpose the screws pass through, from above, the insulating layer 7 of expanded polyurethane, mineral wool or the like, and the lower sheet-metal face 8 of the panel, so as to engage in the underlying beam 2 and thus ensure the required fixing.

The sides of the trapezoidal ribs 5 of the panel are provided with impressions 10 obtained by means of pressing or other sheet metal processing operation, intended to engage with similar impressions 11 formed on a reinforcing section 12.

The latter, a part thereof has been cut away in the drawings in order to

reveal the underlying panel, is a metal section with an open cross-section which therefore has a certain degree of elasticity, so that it can be snap-engaged onto the respective rib 5 of the panel.

After assemblying of the section its impressions 11 are engaged with those 10 of the ribs 5, thereby forming an interlocking joint which prevents sliding of the section with respect to the panel, both in the longitudinal and in the transverse direction.

In the light of the foregoing description and of the Figures it is possible to understand how the section 12, together with the panel 1, solves the technical problem underlying the invention.

Indeed, once the former is mounted on the latter they become integral (i. e. form one piece) with each other, owing to their rigid engagement obtained by means of the respective impressions 10,11.

It follows therefore that the overall height of the panel along its ribs is increased, as can be easily seen from Fig. 2: this fact increases the flexural rigidity of the entire panel, thereby obtaining the desired effect.

In this connection it should be pointed out that the reinforcing section 12 does not operate like an ordinary covering element (of the type also called "junction cover"by persons skilled in the art) used to prevent the infiltration of rain water between the panels, but instead it co-operates with the underlying rib owing to the fact that it is locked with respect thereto in the longitudinal and transverse direction, thereby increasing the moment of inertia of the overall cross- section and hence the flexural rigidity of the panel.

This effect is achieved without negative drawbacks on panel transportation.

Indeed, for example, with reference to Fig. 3 which shows two insulating panels 1 and 1'identical to that described above and stacked overturned with respect to each other in the condition for transportation, it can be seen that the reinforcing sections 12 and 12'illustrated may be stored in the empty spaces present between them; obviously said sections are designed so that their cross- section is narrower than the height of the ribs 5 of the panels.

These ribs nevertheless have a height which is similar to that of the ribs of known panels so that from the point of view of dimensions, the invention does not cause any increase of empty spaces for transportation.

If, on the one hand, it has thus been seen how the invention solves the underlying technical problem, it must also be emphasized that this result is achieved in a simple and inexpensive manner, without additional difficulties for installation of the panels.

It is indeed evident that the snap-engagement of the reinforcing sections 12 onto the respective ribs 5, does not require particular skill and may therefore be carried out manually by any operator, including non-specialized operators.

Of course, changes in the invention are possible with respect to the example described above.

First of all it must be pointed out that the cross-section of the reinforcing sections may have a shape different from that shown in the drawings.

It is in fact obvious that within the teaching of increasing the height of the ribs for improving the panel moment of inertia and therefore its flexural rigidity, several designs for the cross-section of the reinforcing sections are possible; this will depend, among others, on the shape of the ribs which may differ from the trapezoidal profile of the example above, on their size and on the manner in which

the sections are fixed onto the panel.

For instance, Figures 4 and 6 show an embodiment where the width of the frets is much greater than that of the previous example.

It should also be emphasized that the engagement between the impressions 10 and 11 is only one of the possible solutions for fixing the sections to the panels; it may, however, be replaced by alternative solutions wherein the same result is obtained with other form-fitting arrangements, or using fixing means such as glue, adhesive tape or also welds.

The choice among these alternatives will depend on many factors, including the type of material from which the sections and the face of the panel are made.

It is of course clear that although in the example above reference has been made to metal as the material for the upper face 4 of the panel and for the sections 12, there will be cases where one or both of them are made of plastics, fibreglass or other materials.

In such cases it could therefore be convenient to use means for securing the sections to the panel, different from the engagement between the impressions 10, 11.

For example it would be possible to provide undercuts like those shown in Figs. 6 and 7, where for the sake of simplicity the preceding numbering has been used for the parts which are structurally or functionally identical to those already seen above.

In this variant of the invention the reinforcing section 12 has free edges 15 which are folded and which engage in a respective groove 17, formed longitudinally in the side of the ribs 5 of panel 1.

The groove is advantageously formed with undercuts so that any flexural deformations of the panel are also transmitted to the reinforcing section, thereby obtaining the same effects explained above as regards the overall flexural rigidity.

Since, however, in this case the folded edges 15 of the section 12 may slide longitudinally along the grooves 17 like along guides, they must be fixed in some way.

For this purpose it is possible to use rivets, screws or welds, at intervals as for example indicated by 19 in Fig. 6, or glue, bi-adhesive tapes or the like, to be applied along the grooves; all of these elements may, in case, be applied at the factory during production of the panels.

Finally it is worth to mention the possibility that the reinforcing sections be applied also in other zones of the panels, further to on the ribs; for example they may be applied along the junctions between the panels or in intermediate locations between the ribs.

In other words it may be stated that the effect of increasing the rigidity of the panel could also be obtained by applying sections according to the invention, between one rib and another; in this case the sections act as additional ribs with respect to those already present on the panels and do not have the (sole) function of increasing the dimensions thereof.

For this purpose it will therefore be necessary to provide suitable fixing means such as impressions, grooves, adhesives or any of the means mentioned above, in these intennediate zones where the sections are to be mounted.

As can be seen, many changes of the invention may be provided; all of them nevertheless fall within the scope of the following claims.