Description

Composite structural panel and relative method, of production

Technical Field

The present invention relates to a composite structural panel, with a honeycomb cellular structure, containing a filling material designed to give at least thermal resistance, acoustic resistance and fire resistance properties. The invention also relates to a method for production of the panel .

Background Art

The technology for construction of composite structural panels already includes light panels for structural and covering purposes, produced with an aluminium inner honeycomb structure; panels designed for specific uses in the aviation and space sector, but more recently also used in sectors other than the sector of origin.

Such panels basically comprise a thin aluminium honeycomb central core, on the opposite faces of which plastic resins are used to glue thin aluminium sheets, or layers of fabric or even plastic laminates.

Such panels have very high levels of stiffness and planarity relative to their mass. The density of such panels - due to the presence of a central core with empty cell structure - is very low, being between 30 and 80 kg/m ³ .

However, despite such advantageous properties, the panels also have very disadvantageous thermal insulation, acoustic insulation and fire resistance properties, which greatly limit their possibilities for use in application sectors other than those for which said panels were originally designed.

Moreover, the above-mentioned negative properties are further aggravated by the reduced thermic inertia and acoustic mass possessed by such panels, to which one must also add a high capacity for emitting black smoke in the event of a fire.

Further application limits for said panels are also represented by some poor mechanical and structural properties, which may be attributed for example to: their relatively low load- bearing capacity; a limited capacity for withstanding pressure and/or vacuum loads,- a limited resistance to peeling or, more generally, abrasive actions on their surfaces.

Other application limits are represented by their limited resistance to bad weather and chemical attacks, even of the atmospheric type.

Disclosure of the Invention

The aim of the present invention is therefore to overcome the above-mentioned disadvantages with a composite structural panel which, although maintaining a basic structure that can be traced back to a prior art type, is able to extend the spectrum of intrinsic features of such a basic type, to combine them in various ways and to modulate them quantitatively depending on the specific requirements of the possible and different intended application sectors . The invention also has for an aim to provide a method for production of the above-mentioned panel.

The technical features of the present invention, in accordance with the above aim and concerning the panel, are clear from the content of the claims herein, in particular claim 1, and from any of the claims directly or indirectly dependent on claim 1.

The technical features concerning the method of production are clear from the content of claim 19 and any of the claims directly or indirectly dependent on claim 19.

Brief Description of the Drawings

The advantages of the present invention are more apparent in the detailed description which follows, with reference to the accompanying drawings which illustrate preferred, non-limiting embodiments of the invention, in which: Figure 1 illustrates a composite structural panel as a whole;

Figure 2 is an exploded perspective view of the panel of Figure 1;

Figure 3 is a side view of a possible alternative embodiment of the panel illustrated in the previous figures;

Figures 4a - 4f are diagrams of the steps of a first method for production of the panel of Figure 1; Figure 5 is an exploded view of the panel of Figure 1 illustrated in a characteristic forming step belonging to an alternative method of production;

Figure 6 is a cross-section of a detail of the panel obtained using the alternative method illustrated in Figure 5.

Detailed description of the Preferred Embodiments of the Invention

With reference to Figures 1 and 2 of the accompanying drawings, the numeral 1 denotes as a whole a composite structural panel, basically comprising a three-dimensional stratiform element 2 with a honeycomb structure, having a plurality of open cells 3 arranged in an orderly fashion, containing a filling material 4.

The panel 1 also includes two covering sheets 5, glued to the three-dimensional stratiform element 2, substantially forming two opposite faces of the panel 1. The panel 1 generally has a density which may substantially vary between 30 and 1500 kg/m ³ , depending on the materials used and the performance properties required of the panel 1 by the applications for which it is intended; properties which by way of example, but without limiting the scope of the invention, include: thermal resistance; acoustic resistance; and fire resistance, considered both individually and in various combinations and if necessary also with other additional performance properties.

The filling material 4 may be obtained in various structural forms, in particular concerning the state of aggregation of the material, and the physical/chemical compositions. The filling material 4 may include: mineral aggregates expanded, agglomerated, or in the loose state; vegetable fibres; and/or amorphous silicate resins mixed with expanding agents, which are inserted in the cells

3 then expanded directly in position using suitable treatments at suitable temperatures and if necessary pressures.

The filling material 4 may also be obtained using thermally expanded insulators, chosen from the families of phenolic resins,

polyurethane resins, acrylic resins or polyester resins.

When insulating properties are also to be combined with suitable fire resistance properties, the filling material may also include expanded mineral mixtures . Various choices are possible for the materials used for the covering sheets 5, including thin sheets of glass cloth; metal foils, for example aluminium, steel, copper; loose-woven synthetic cloths, all of these being materials which can form both panel 1 aesthetic surface finishing elements and elements for supporting another covering layer 6 (Figure 3) . Said covering layer 6, which can be applied to the outside of the panel 1 is designed to give the panel 1 a specific surface finish, or is even designed to give it structural and mass properties particularly useful in allowing the panel 1, for example, to have a specific inertia to some physical phenomena involved in construction or in the architectural field.

It is known that, irrespective of the greater or lesser resistance to conducting heat or transmitting sound, some construction structures must have a suitable delay in the response to thermal and acoustic transients, or even total non-flammability, or in any case deferred lighting in case of fire. Therefore, with respect both to purely aesthetic aspects and to the above-mentioned functional aspects, the panel 1 may advantageously include in its structure such a covering layer 6 which may consist of a layer of plaster; a stone material, such a marble or granite; a ceramic material; a vitreous material; a metal laminate; or even a plastic material (for example phenolic) .

It should be noticed that, depending on the material used for the covering layer 6, the panel 1 may have technical features which allow additional advantages in terms of the capacity to withstand weather, the abrasive effects of dusts carried by the wind and/or even a chemical attack ascribable for example to the acidity of meteoric water.

The materials used to make the three-dimensional stratiform element 2 may be metals, such as aluminium and/or steel alloys; or even fibreglass and/or carbon fibre materials. However, it should be noticed that the three-dimensional stratiform element 2 may also

be made from a chequered plate or even a net whose mesh forms the above-mentioned cells 3.

Figures 4a - 4f may be used to describe a method for production of a panel 1, as described above, in which the material 4 which will be used to fill the cells 3 is in a loose solid state. Said method basically comprises the steps of :

- [Figure 4a] gluing the three-dimensional stratiform element 2 with open cells 3 above a first covering sheet 5 for the panel 1;

- [Figure 4b] inserting the filling material 4 in the cells 3 of the three-dimensional stratiform element 2. Said step may be performed for example using a suitable filling material dispensing apparatus 10, under which the stratiform element 2 is fed, as indicated with the arrow 11;

- [Figure 4b] settling the filling material 4 in the cells 3 by supporting the stratiform element 2 on a vibrating table 12;

- [Figure 4c] mechanically compressing the material 4 in the cells 3;

- [Figure 4d] subjecting the material 4 contained in the cells to heat treatment, for example to activate the expanding agents, if it contains any; or to remove the liquids if the material 4 is in the mortar state, as happens in the case of water-based amorphous silicate resins; or to remove, in general, the moisture content; and/or to subject the material 4 to a temperature of between 250 and 400 ⁰ C for example to bake it. Said heat treatment may be carried out in many different ways. In the diagram in 4d it is assumed that said treatment is carried out in a discontinuous or continuous tunnel furnace 13 , through which the panel 1 being produced passes in the semi-finished state;

- [Figure 4e] gluing a second covering sheet 5 to, and above, the three-dimensional stratiform element 2 with open cells 3, to obtain an assembly in a single body forming the panel 1 [Figure 4f] .

Figures 5 and 6 may be used to describe an alternative method of production for a panel 1 as described above, an alternative particularly advantageous in cases in which a preformed panel of filling material 4 is to be used, for example a panel of relatively friable solid material. In said case, the method basically

comprises the steps of:

- gluing the three-dimensional stratiform element 2 with open cells 3 above a first covering sheet 5 for the panel 1;

- positioning the filling material 4, in the form of a preformed panel, above the cells 3 of the three-dimensional stratiform element 2; pressing the filling material 4, in the form of the preformed panel, against the three-dimensional stratiform element 2 (arrow 14) so that it is inserted in the cells 3 and cut by walls 7 delimiting the outline of the cells 3 ;

- removing the residues of filling material 4 outside the cells 3 ; and

- gluing a second covering sheet 5 to, and above, the three- dimensional stratiform element 2 with open cells 3, thus making the whole assembly a single body.

Before gluing the second covering sheet 5 it is advisable to proceed to a step of preparing the edges 8 of the cells 3. This step may comprise simple cleaning to remove even the smallest particles, which could prevent effective gluing of the second sheet 5 which must cover the entire outline of the edges 8 of the cells

3. But it may also comprise a step of mechanically upsetting the edges 8 of the cell 3 walls (Figure 6) . This would have the advantage of not only increasing the extent of the glued surface, but also gripping the filling material 4, preventing it from moving any more relative to the cell 3 walls 7, after definitive panel 1 forming.

The invention described has evident industrial applications and may be modified and adapted in several ways without thereby departing from the scope of the inventive concept. Moreover, all details of the invention may be "substituted by technically equivalent elements .