Field of application

The invention relates to the field of metal construction and cladding materials.

More in detail, the invention relates to a process for producing a composite metal panel particularly suitable for covering or forming the walls of manufactured articles, and more particularly of lift and freight elevator cabins, and to a panel obtained with this process.

Prior art

Composite metal panels of the “sandwich” type are known, obtained by coupling a semi-finished double skin panel, acting as a structural core, with a stainless steel plate characterized by a particular surface finish.

The use of prefabricated composite metal panels is becoming more and more widespread for rapid cladding or the construction of walls of manufactured articles where the use of panels provided with a structural capacity and at the same time with a particular aesthetic finish is required.

Known composite metal panels substantially comprise:

- a filling metal plate (core) comprising stiffening ribs, obtained for example with a honeycomb or corrugated pattern;

- a first and a second metal sheet, made of aluminium or galvanized steel, acting as a covering skin for said filling metal plate;

- a stainless steel finishing plate applied to one of said skins, characterized by a particular surface machining, adapted to impart a prestigious aesthetic effect to the panel.

Currently the production processes for these types of panels provide for successive and independent machining steps, with the production of a first semi-finished metal panel and the preparation of the stainless steel finishing plate, to be coupled together, by gluing, only subsequently.

In detail, the production steps are as follows:

- providing a filling metal plate, for example in honeycomb or corrugated aluminium with two main faces;

- providing a first and a second metal sheet adapted to act as a covering skin for the two main faces of said filling metal sheet;

- spreading an adhesive on said main faces of said filling metal plate;

- coupling, by gluing, said sheets to said main faces to form a semifinished metal panel;

- providing a stainless steel plate having a face adapted to be turned outwards, comprising a surface finish suitable for the purpose;

- carrying out machining of the mechanical type required for the field of application of the panel on said stainless steel sheet;

- spreading a further layer of adhesive on one of said metal sheets coupled to said filling metal plate, or on said stainless steel plate;

- coupling, by gluing, said pre-machined stainless steel plate to one of said metal sheets, so as to form a composite metal panel.

The adhesive used to bond said semi-finished metal panel and said stainless steel plate is a fast-setting neoprene glue. To promote such gluing, the composite metal panel is generally pressed by rapid passage in a roller press.

As far as the mechanical machinings to be performed on the composite panel are concerned, according to the prior art one proceeds with separate machinings on said stainless steel plate by means of laser cutting and on said semi-finished panel by means of a machining centre or tools, then paying attention to the centring of the mechanical machinings during the coupling of the sheet to the panel.

Alternatively, it is possible to machine the composite panel when it is already assembled, by carrying out machining operations of a mechanical type on said composite metal panel which involve only the layers of said semi-finished panel, and therefore said sheets acting as skin and said filling plate.

Such a production process has limitations and drawbacks, as does the directly obtained panel.

Three gluing operations are required to assemble the entire panel, with the consequent use of a considerable quantity of glue: a layer of glue between each metal sheet and said filling metal sheet and a layer of glue between one of said metal sheets and the finishing plate in stainless steel.

The weight of the finished composite metal panel is significant, since the weight of the finishing plate and the adhesive is added to the weight of the semi-finished metal panel with two skins.

The mechanical machinings to be carried out on the semi-finished metal panel, when already coupled to the stainless steel plate, require very expensive technologies and must involve all the layers of the panel itself, i.e. two aluminium/galvanized steel skins and the honeycomb and/or corrugated layer, with consequent high consumption of energy, tools and material.

One of the technologies that can be used is water jet technology, which is disadvantageously non-economic and carries the risk of polluting the finished composite panel.

Alternatively, the drilling of the semi-finished metal panel can take place before gluing the already pre-drilled stainless steel plate and must provide for the mechanical machinings of both skins and the honeycomb or corrugated metal sheet with care to then make this machining coincide with the pre-drilling already present on the finishing sheet.

The production process is therefore generally complex and slow.

Disclosure of the invention

The invention aims to overcome these limits by defining a production process of a composite metal panel aimed at obtaining a resistant panel, but at the same time light, and having any type of aesthetic finish within the known treatments of stainless steel plates.

The main object is therefore to propose a fast and cost-effective process, which facilitates the machinings and reduces the raw materials used.

Such objects are achieved with a production process of a composite metal panel characterized in that it comprises the steps of:

- providing a filling metal plate comprising stiffening ribs arranged between a first and a second main face of said filling metal plate;

- providing a metal sheet adapted to act as a skin for said filling metal plate;

- spreading a first adhesive means on said first main face of said filling metal plate;

- coupling, by gluing, said metal sheet to said first main face of said filling metal plate provided with said first gluing means to make a semi-finished metal panel with a single skin;

- providing a stainless steel plate having a face adapted to be turned outwards;

- performing a surface finishing process on said face to make it suitable for use; - spreading a second adhesive means on said stainless steel plate or alternatively on said second main face of said filling metal plate;

- coupling, by gluing, said stainless steel plate provided with said second gluing means to said second main face of said filling metal plate of said semi-finished metal panel, so as to make said composite metal panel.

According to a first aspect of the invention, said process comprises, before the step of coupling said stainless steel plate to said semi-finished metal panel, the step of performing mechanical machining on said stainless steel plate.

According to possible alternative variants, said process comprises the step of carrying out on said semi-finished metal panel the same machining operations of a mechanical type performed on said stainless steel plate and the step of making said mechanical machining coincide during the gluing step, or the step of performing on said composite metal panel machining of a mechanical type involving only said semi-finished metal panel when it is already coupled to said stainless steel plate, at the machining already performed on said stainless steel plate.

According to possible embodiment variants, the surface finish of said face of said stainless steel plate is of the satin, polished, mirror polished, electro-coloured, PVD-coloured, shot-peened, printed, embossed, rigid type provided with patterns, geometric textures, filigree, silk-screen engravings, etc.

Preferably, said filling metal plate is made of honeycomb or corrugated aluminium, and said metal sheet adapted to act as a skin is made of a material selected from aluminium, galvanized steel, stainless steel. In embodiment variants, said mechanical machinings, performed on said stainless steel plate and said semi-finished metal panel, comprise punching, notching, milling, bending, drilling.

According to a further aspect of the invention, said coupling steps by gluing alternatively comprise the use of roller presses, platen presses, vertical presses.

Advantageously, said step of spreading said first adhesive means on said first main face of said filling metal plate only affects the crests of said stiffening ribs.

In a particularly embodiment of the invention, said process, after the steps of making a semi-finished metal panel, in place of the step of providing a stainless steel plate having a face adapted to face outwards, comprises the steps of:

- providing a stainless steel plate with a plan dimension greater than said semi-finished metal panel and with free perimeter edges;

- notching and folding said free perimeter edges of said stainless steel plate to define a box-like structure adapted to accommodate said semifinished metal panel;

- spreading said second adhesive means on said stainless steel plate also at said folded free perimeter edges.

Another object of the invention is a composite metal panel comprising a stainless steel plate, a filling metal plate and a metal sheet adapted to act as a skin, obtained by the process described above.

The composite metal panel made according to the invention has numerous advantages, mainly due to the number and nature of the layers which constitute it and to the production technique used.

First of all, there is a lower use of material resources: compared to traditional composite metal panels, an aluminium or galvanized steel sheet acting as a skin and a relative layer of glue usually used to glue said metal sheet to the filling metal plate are eliminated.

As a result, machining times are also shortened in favour of greater productivity.

The composite panel obtained has a reduced weight, estimated at about 2.5 kg/m2, which also translates into greater manageability of the panel itself, lower energy consumption to move the manufactured articles that include it, also favouring the possibility of create large format panels. This advantageously results in ease and speed of installation, and therefore short assembly times with contained costs.

Furthermore, the single-skin panel object of the invention is more workable than the double-skin panel obtained with the prior art because it can be subjected to V-cutting, a cutting technique with inclined planes with the removal of a V-shaped section of material. It is clear that the lack of a layer, made with the second plate acting as a skin, now no longer present, favours cutting operations without the risk of damaging the stainless steel plate.

Although the composite panel has a reduced number of layers, high fire resistance is always guaranteed (classification A2), above all when said first adhesive means is placed only on the crests of the reinforcing ribs of the filling metal plate.

Finally, the composite panel obtained is advantageously totally recyclable.

Even more advantageously, the spreading of said first gluing means only on the crests of said stiffening ribs of said filling metal plate allows to further save material (in this case glue) and speed up the subsequent production steps of the panel, for example the drying step after gluing.

Brief description of the drawings

The advantages of the invention will become apparent from the following description, in which preferred methods of the production process of the panel are described, by way of non-limiting example and with the aid of the figures, where:

- Figs. 1 and 3 show, schematically with deformed proportions for clarity of representation and in exploded axonometric views, composite metal panels according to two possible alternative variants of the invention;

- Figs. 2 and 4 show, in cross section along a vertical plane, the two composite metal panels respectively of Figs. 1 and 3;

- Figs. 5 and 6 show, again schematically with deformed proportions for clarity of representation, respectively in exploded axonometric view and in cross section along a vertical plane, two steps of the production process of a composite metal panel according to a further possible variant of the invention;

- Fig. 7 shows, in cross section, a detail of the panel of Fig. 6 assembled.

Detailed description of a preferred embodiment of the invention

With reference to Figs. 1 -4, two composite metal panels 1 obtained according to possible variants of the process object of the invention are schematically illustrated.

Said process comprises a first step of providing a stainless steel plate 2.

Said stainless steel plate 2 is sized on the basis of the final dimensions of the composite panel 1 to be obtained.

Said stainless steel plate 2 has already been previously machined and treated at least on one face, the one facing the outside of the panel, to obtain the required surface finish.

This surface finish can, for example, be selected from one or more treatments of satin finishing, polishing, mirror polishing, electro-colouring, PVD colouring, shot peening, printing, embossing, stiffening, affixing of designs, geometric textures, watermarks, silk-screen engravings, etc.

Appropriate laser machining 10, 11 is then performed on said stainless steel plate which will then define, for example, the means for hooking the composite metal panel 1 to the structure to be covered, or suitable holes for housing accessory elements, or the fixing or passage of system components.

Consider, for example, the lift application sector, where said composite metal panels 1 define the walls of the actual lift cabin: suitable holes in the stainless steel plate 2 are arranged to house the push-button panel with the up and down commands.

A second step of the production process of a composite metal panel 1 according to the invention is the step of providing a filling metal plate 3 having a first 3’ and a second 3” main face with discontinuous surfaces connected by stiffening ribs 6, comprising ridges extending up to said first 3’ and second 3” face.

Said filling metal plate 3 is made of a material selected from honeycomb-worked aluminium (Figs. 1 -2) or corrugated aluminium (Figs. 3-4).

Said filling metal plate 3, in addition to giving structure to the composite metal panel 1 , also has a lightening function.

A third step of the production process of a composite metal panel 1 is the step of providing a sheet 5 in metal material suitable for acting as a skin for said filling metal sheet 3.

Said sheet 5 is made of highly resistant material, whether it is aluminium, or stainless steel, or galvanized steel or pre-painted steel.

Said sheet 5 is adapted to be coupled, by gluing, to said first face 3’ of said filling metal plate 3 to form a semi-finished, double-layered, singleskin metal panel 7.

Said gluing step involves spreading a first gluing means 4 on said first face 3’ of said filling metal plate 3, superimposing said metal plate 3 on said metal sheet 5, and passing them between roller presses, flat or vertical, of a known type.

Particularly advantageous is the technique of spreading said first adhesive means 4 on said first face 3’ of said filling metal plate 3 only at said crests of said stiffening ribs 6, for example only on the ridges of the corrugated aluminium, or along the edges of the aluminium honeycomb texture. This technique saves glue, speeds up the application step and makes it easier to dry. Figures 3 and 4 specifically illustrate this variant.

Said first gluing means is advantageously a polyurethane glue.

A fourth step of the production process of a composite metal panel 1 is the step of coupling, by gluing, said stainless steel plate 2 to said second face 3” of said filling metal plate 3 of said bilayer semi-finished metal panel 7, obtaining a three-layer composite metal panel 1 .

In particular, this coupling step is anticipated by a step of spreading a second adhesive means 8 on said stainless steel plate 2.

Alternatively, it is possible to spread the second adhesive means 8 on said second main face 3” of said filling metal plate 3.

Said second gluing means 8 is advantageously a polyurethane glue.

The gluing always takes place with the overlapping of the stainless steel plate 2 on the semi-finished metal panel 7 and with their passage between flat or vertical presses of the known type, which guarantee a certain pressure time necessary for the polyurethane glue to set.

Once the stainless steel plate 2 has been coupled to the semi-finished bi-layer metal panel 7, and then the composite metal panel 1 has been assembled, the production process includes the step of carrying out the same mechanical processes 10, 11 carried out previously on the stainless steel plate 2, exactly matching with one another, involving only the layers of the semi-finished metal panel 7, i.e. only the filling metal plate 3 and said sheet 5 acting as skin. The mechanical processes 10, 11 on the stainless steel plate 2 act as a template for the subsequent mechanical processes performed on the composite metal panel 1 .

Alternatively, said mechanical machinings can be carried out on the semi-finished metal panel 7 prior to its gluing step to the stainless steel plate 2, paying maximum attention, during the coupling step, to the centring of all the portions subject to mechanical machinings.

All mechanical processes are carried out using a work centre or tools, such as drills, and can include punching, notching, milling, bending, drilling, etc.

Figures 2 and 4 illustrate finished metal composite panels 1 made with the process described above, differing only in the type of material chosen for the filling metal plate 3, in one case honeycomb-worked aluminium (Fig. 2) and in the other case corrugated aluminium (Fig. 4), and for the method of laying said first glue means 4.

Figures 5 and 6 illustrate possible additional steps of the process for producing a composite metal panel 1 according to the invention, in particular for the production of a box-type composite metal panel. As evident from Fig. 5, said stainless steel plate 2 has a larger plan dimension than the semi-finished metal panel 7 so that, when coupled together, said composite metal panel 1 comprises free perimeter edges 9 of said stainless steel plate 2. With reference to Fig. 6, said process comprises the preliminary step of notching the corners and folding the free perimeter edges 9 of said stainless steel plate 2, to thus create a box-like containment frame for said semi-finished metal panel 7.

Said preliminary folding step of the free perimeter parts 9 allows creating a structure suitable for laterally closing the semi-finished metal panel 7, giving the finished composite metal panel 1 a box-like conformation and greater rigidity.

For this purpose, on said stainless steel plate 2, the necessary mechanical machining had already been carried out to prepare the folding points of said free perimeter edges 9 to compose the final box-like structure of the composite panel 1 .

Figure 7 illustrates a detail of the assembled box-like composite metal panel 1 .