In the furnishing sector, plate-like panels are known and widely used to produce pieces of furniture, such as shelves, cupboards, drawer units and the like, because they allow light structures capable of supporting heavy loads to be produced. In order to produce furniture of this type, two or more sheet-metal panels are connected to each other by different connection systems of known type.

Patent US 4.361. 098, for example, discloses a connection system for structural elements wherein the elements which constitute the system are hollow and of substantially polygonal shape. The system comprises a clamp which is fixed to a first element and which is held by compression inside a second element.

Patent US 4.917. 528 discloses a connection system for producing metal cupboards comprising a carrier element having two flanges, a base flange and an elongate flange, which are arranged so as to form a C-shaped channel. In the assembly phase, the peripheral end of a sheet-metal panel is inserted into the channel of the carrier element and fixed by a locking screw which locks the two flanges against the peripheral end of the panel.

The above-disclosed connection devices, and those of known type in general, have considerable disadvantages, in particular in the assembly phases for a piece of furniture, insofar as such operations are generally complex and involve a great deal of time, in particular for unskilled users.

In some cases, the assembly of a piece of furniture comprising sheet-metal panels has to be carried out directly during the production cycle thereof and cannot be effected at the installation location, with the obvious disadvantages that result therefrom, such as, for example, additional production costs and difficulty of transport owing to the dimensions of panels which have already been fitted together.

The objective of the present invention is to overcome the disadvantages of the devices of known type by providing a connection system for structural sheet-metal elements which allows the operations for assembling the individual elements which form a piece of furniture to be speeded up and reduced in number.

Another objective of the present invention is to allow the assembly of a piece of furniture comprising sheet-metal panels directly at the installation location by providing a connection system which can be used with a small number of simple operations and by unskilled users.

A further objective of the present invention is to provide a connection system which is simple, economic and which is durable even after prolonged use.

In order to achieve the above objectives, the present invention relates to a connection system for sheet-metal structural elements as defined in the appended claims.

One of the principal advantages of the present invention is the facility for producing modular furnishing systems and modular pieces of furniture in a simple and rapid manner by changing the known sheet-metal panels or replacing them by means of the system of the present invention.

Other advantages and characteristics of the invention will become clear from the following detailed description of a preferred embodiment which is given with reference to the appended drawings which are provided purely by way of non- limiting example and in which: Figure 1 is a perspective view of a piece of furniture comprising a connection system according to the present invention; Figure 2 is a perspective view of a retaining member of the present invention ; Figure 3 is a sectional view of the member in Figure 2; and Figure 4 is a sectional view of two panels of a piece of furniture which are connected by the connection system of the present invention.

With reference now to Figure 1, a piece of furniture, for example, a shelving unit 10, comprises a plurality of sheet- metal structural elements, such as, preferably, a base panel 12, two lateral support panels 14 and an upper panel 16, which are connected to each other so as to form a load- bearing structure. The support panels 14 comprise a principal surface 5, to which are connected a plurality of supports 18 for shelves. The base panel 12 and the upper panel 16 each comprise a principal surface 15, two lateral end portions 13 and two front end portions 17, which are bent so as to produce two channels 19. One opening 11, whose function will be more clearly appreciated from the description below, is provided near each corner of the principal surfaces 15 of the base panel 12 and of the upper panel 16, and of the principal surfaces 5 of the support panels 14.

The above-described panels are produced from a light material, preferably sheet metal having a thickness of approximately 1 millimetre, and can have different shapes and dimensions from those illustrated according to the type of furniture, without thereby departing from the scope of the present invention.

As illustrated in Figures 2 and 3, the connection system of the present invention comprises a retaining member, for example, but in non-limiting manner, a retaining plate 20 which is bent into a"C"shape and which comprises a lateral wall 21, an upper wall 23 and a lower wall 25. A pair of coaxial openings 22, arranged opposite each other, is provided at each end of the upper wall 23 and the lower wall 25. Each opening 22, which is produced, for example, but in non-limiting manner, by punching, stamping or extrusion, comprises a face 26 which is preferably of circular cross- section and which extends towards the inside of the plate 20.

Another opening 27 which is orthogonally aligned with the pair of openings 22 is further provided at each end of the lateral wall 21.

Two retaining plates 20 are fixed to the base panel 12, near the lateral ends 13 thereof, and arranged orthogonally relative to the bent front ends 17. In this manner, and as is better illustrated in Figure 4, the openings 22 provided in the upper wall 23 of the retaining plate 20 are aligned with the openings 11 of the base panel 12, and the openings 22 provided in the lower wall 23 of the retaining plate 20 are closed by the surface of the bent ends 17.

The connection system further comprises connection members which are particularly suitable for mutual engagement to produce a stable connection. The connection members comprise, for example, but in non-limiting manner, a drum 30 of known type having a circular cross-section and an upper surface, in which is provided a slot, into which it is possible to insert the head of a screwdriver, or of a similar instrument, in order to allow rotation thereof. A plurality of openings having cam-type surfaces for accommodating the end of a connection pin are provided in the internal portion of the drum 30. The connection members further comprise a metal pin 40 of known type which comprises, at one end thereof, a threaded stem 42 and, at the other end, a frustoconical head 44. The two ends are separated by a central bell-like portion 46 in order to prevent the pin from being able to be inserted beyond a given depth inside a panel. The pin can be produced, for example, by die-casting using a metal alloy of zinc and aluminium.

A support insert is inserted inside the front ends of the support panel 14 and comprises, by way of non-limiting example, a solid insert 50 which is elongate in a preferential direction and which has a length substantially equal to the width of the panel in which it is inserted. The insert 50 can be produced from any materials of known type and is shaped so as to promote the insertion thereof inside the panel.

In use, during the assembly phases of a piece of furniture, the drum 30 is inserted inside the openings 11 and 22 in such a manner that the outer surface thereof fits closely against the internal surface of the walls 26 of the openings 22, and one end 24 thereof moves into abutment with the principal surface 15 of the base panel 12. The metal pins 40 are inserted in the openings 11 which are provided at each corner of the support panels 14, and are connected to those panels.

In particular, as illustrated in Figure 4, the threaded stem 42 of the metal pin 40 is inserted in the opening 11 of the support panel 14 and screwed to the support insert 50 which is inserted inside the panel 14.

Once the drum 30 has been engaged with the retaining plate 20 and the metal pin 40 has been fixed to the support insert 50, the base panel 12 and the support panel 14 are moved towards each other until the pins 40 are brought into correspondence with the openings 27 of the retaining plate 20 which is connected to the base panel 12. The support panel 14 is then moved towards the base panel 12 and the pins 40 are inserted inside the openings 27 thereof until the head 44 is inserted inside the drum 30. Next, a rotation of the drum 30 allows the head 44 to be locked against the cam-like surfaces and, consequently, the base panel 12 to be anchored on the support panel 14. The same operation is repeated for all of the panels which constitute the piece of furniture until it is completely assembled.

The arrangement of the pins 40 inside the support panels 14 and the arrangement of the drum 30, and consequently of the retaining plate 20, inside the base panel 12 and upper panel 16, have been described simply by way of example. In fact, it is possible to transpose or modify the above-indicated arrangement without thereby departing from the above- determined objectives of the present invention.

Another advantage of the present invention consists in the simplicity of manufacture of the retaining members which can be obtained by stamping, by bending, or by any of the methods of known type, at a very low cost. The openings used for the engagement of the connection member can further be provided in an equally simple manner by means of known techniques for machining plates.

A further advantage of the present invention is provided by the ease of engagement of the connection member which can readily be inserted, by means of the retaining member, inside the panels without any need to modify the structure of the panels. In this manner, it is also possible to use the present invention with commercially available plate-like panels.

A further advantage of the present invention consists in the ease of locating the drum inside the panel. By making use of the faces of the openings provided in the retaining member, the drum maintains a position orthogonal to the longitudinal direction of the connection pin, subsequently facilitating and speeding up the furniture assembly phases.

Finally, the alignment of the openings, provided in the retaining member, with the connection pins constitutes a further advantageous feature of the present invention which allows the disadvantages of the devices of known type to be overcome, wherein the alignment of the panels of the piece of furniture during the assembly phases involves a useless and expensive waste of time.

According to another embodiment of the present invention, the lateral ends 13 of the plate-like panel 12 also comprise a bent portion which defines a channel 19. In this case, the above-described openings 22 and 27 are produced directly in the channel 19 which is provided by the bent lateral end 13 of the sheet-metal panel 12, and the drum is directly engaged with the sheet-metal panel whose end constitutes the retaining member of the present invention. The principal advantage of this embodiment consists in the reduction of the number of components, consequently reducing production costs, and in further simplifying the operations for assembling the furniture.

Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated, without thereby departing from the scope of the present invention.