As known, there are different types of systems for painting aluminum sections while those commonly used are of three types, to wit: - Vertical systems using the technique of vertical suspension of the aluminum sections. These systems have the advantage of high productivity with limited labor but the disadvantage of high cost, high energy consumption, much maintenance and difficult control of pretreatment before painting because the inline oven with two input-output mouths loses much heat with high energy consumption; - Horizontal systems using the horizontal suspension technique for the aluminum sections. These systems have fair productivity (up to 25 hangers per hour), allow pretreatment off the line and are thus easy to control and display easy loading and unloading of the parts with accumulation zones. The disadvantages of such systems is in the use of an inline or accumulation oven which, having two input-output mouths, loses a large amount of heat with high energy consumption. In addition, for color change it is necessary to keep two or three empty hangers for translation of the two booths or, with fixed booths, it is necessary to have an additional space for the two-rail

conveyor. The space occupied by the system is very great in relation to productivity; and - Compact systems (Italian Patent No. 01244788 of 29th August 1994) which are equipped with two parallel conveyors on which are fixed the hangers which carry the aluminum sections fastened horizontally. These systems have the advantages of occupying limited space, having a bell oven that consumes little energy, and one or two small painting booths. In this case the disadvantages are very low productivity, difficulty of loading and unloading parts, and having to work with the oven positioned over the heads of the operators and the poor safety for the operators who have to work in an environment with hanging bars which could fall during handling. The parts must be unloaded from the hangers while they are still very hot with clearly unfavorable working conditions for the operators. In addition, as the hangers are mounted on the overhead conveyors at the same pitch for all and it is not possible to have a small wheelbase because allowance must be made for passage of the booth for painting and space for the loading and unloading operators, a limited number of hangers can stay in the oven (usually 3 or 4) without optimizing use of the oven; these systems are thus suited for production of small lots since they can produce a maximum of 12 hangers per hour.

The general purpose of the present invention is to remedy the above mentioned shortcomings by making available a system and method for electrostatic painting of metallic manufactured articles with powders, which system and method would allow

high hourly production (25 hangers per hour similar to or higher than a horizontal system) with a small system (similar to a compact system), and with limited used of labor while operating under optimal environmental conditions.

In view of this purpose it was sought to provide in accordance with the present invention a system for electrostatic painting of metallic manufactured articles comprising a conveyor system for a plurality of hangers designed to carry the metallic manufactured articles and a painting device for the manufactured articles and an oven traversed by said conveyor system for the processing of the manufactured articles and characterized in that the conveyor system comprises the following items: - A first conveyor for accumulation outside and upstream of the oven for loading of the hangers; - A second conveyor for accumulation outside and downstream of the oven for unloading of the hangers; - A third conveyor for accumulation inside the oven; and - A fourth conveyor connecting the above mentioned first three conveyors for transfer of the hangers among the conveyors.

Again in accordance with the present invention it was sought to realize a method for electrostatic painting of metallic manufactured articles by making use of the above mentioned system and comprising the steps of: - Loading the metallic manufactured articles on hangers on the loading conveyor; - Spraying the metallic manufactured articles with electrostatically charged powders;

- Transferring the painted manufactured articles onto the conveyor inside the oven; - Heating the metallic manufactured articles to complete polymerization; - Transferring the polymerized manufactured articles onto the unloading conveyor; - Unloading the manufactured articles from the hangers of the unloading conveyer; and - Transferring the hangers unloaded from the unloading conveyor to the loading one automatically by means of the transfer conveyor.

To clarify the explanation of the innovative principles of the present invention and its advantages compared with the prior art there is described below with the aid of the annexed drawings a possible embodiment thereof by way of non-limiting example applying said principles. In the drawings: FIG 1 shows an overall side view of a realization of the system in accordance with the present invention; FIG 2 shows a plan view of the painting device; and FIG 3 shows an overall side view of an alternative realization of the system in accordance with the present invention.

With reference to the figures, FIG 1 shows a preferred embodiment of the electrostatic-painting system 10 comprising the overhead loading conveyor 11, the overhead heat-treatment conveyor 12, the unloading overhead conveyor 13, the overhead transfer conveyor 14, the hot air bell- oven 15, the painting device 16 and the supporting

structure 17. The conveyors 11,12, 13, and 14 consist of two parallel chains (not shown) handled at the same speed.

To the conveyors 11,12, 13 and 14 are hooked a plurality of hangers 18 designed to support the manufactured metallic articles 19 to be painted. The loading conveyor 11, the unloading conveyor 13 and the heat-treatment conveyor 12 are accumulating conveyors that allow accumulation of a plurality of hangers in the loading zone, the unloading zone and the oven 15 respectively. The conveyor 12 is placed in the oven 15 while the unloading conveyor 13 and the loading conveyor 11 are outside the oven 15 near the outlet 21 and inlet 20 openings respectively of the oven.

These openings 20 and 21 are positioned on the lower side of the bell oven 15. The overhead conveyor 14 is a transfer conveyor connecting the three accumulation conveyors 11, 12,13 in a closed loop. The conveyor 14 has purposeful hooking and unhooking systems and at each step deposits and takes a part-carrying hanger 18 from each of the three accumulation conveyors 11,12, 13. The connection between the unloading conveyor 13 and the loading conveyor 12 passes above the oven 15 as shown in FIG 1. The supporting structure 17 holds up the oven 15 in a superelevated position above the conveyors 11 and 13 and over the painting device 16. The oven 15 has dimensions such as to contain about ten hangers 18. The painting device 16 is positioned between the loading conveyor 11 and the oven inlet 20.

FIG 2 shows in detail a plan view of the painting device 16. This device includes a booth-carrier platform 30, two

painting booths 31a and 31b, air suction means 32, a suction channel 33 and electronic translation speed control means for the booths 41 and suction intensity 40. Each booth 31a and 31b has two powder dispensers 34 for spraying metallic manufactured articles hung on the hangers 18. The booths have wheels 35 for translation from one part to the other of the booth-carrier platform 30 on a purposeful path so as to receive the hangers 18 in the booths in the space included between the two dispensers 34. The powder dispensers 34 are rectilinear in form and placed in a vertical position. They are inclined at an angle between 0° and 60° to the direction perpendicular to the booth translation direction. The translation path on the booth- carrier platform 30 is sufficiently long to allow one of the two booths, no. 31b, to stop in a rest position without interfering with the translational motion of the other booth 31a that is in the painting step. The suction channel 33 connects the suction means 32 with the entire painting booth running path along the booth-carrier platform 30 as shown in the figure. The channel 33 is normally closed on the platform 30 side and is opened at the position of the painting booth 31 so as to suck air only in the actual painting zone.

We shall now describe the painting process that uses the system 10.

The manufactured articles 19 are loaded manually onto the hangers 18 on the loading conveyor 11 that accumulates them in the inlet zone. Then the manufactured articles are sprayed with powder in the painting device 16. The painting

booth 31a, in translating from one side to the other of the booth-carrier platform 30, receives the hangers 18 and the manufactured metallic article 19 in the space included between the two dispensers 34 which spray electrostatically charged powder over the entire surface of the manufactured articles 19. A sliding device (not shown in the figure) opens the suction channel 33 normally closed on passage of the booth 31a so that the painting powders are recovered and the direction of flow of the painting powders is optimized. Said powders are sprayed at an optimal angle thanks to the inclination of the dispensers 34. While the booth 31a is in the spraying step, the other booth 31b is available for cleaning and color change. The booth translation speed control means 41 make it possible to have high speed during arrival and leaving from the spraying zone and to adjust speed during spraying depending on the type of parts. The suction intensity control means 40 allow increase of suction in the spraying step so as to optimize power consumption of the suction means 32.

After being sprayed with the powders, the manufactured articles 19 enter through the opening 20 into the oven 15 for polymerization. In the oven 15 the manufactured articles are received on the accumulation conveyor 12. The oven 15 can contain about ten hangers 18 to allow simultaneous polymerization of a plurality of metallic manufactured articles 19. Heat treatment lasts between 15' and 30'and, once completed, the manufactured articles 19 come out of the oven through the opening 21 to be received on the unloading accumulation conveyor 13. Before being

unhooked from the hangers 18, the manufactured articles 19 stop on the unloading conveyer 13 long enough to cool and allowing the operators to work under safe environmental conditions. Once unloaded, the hangers 18 are automatically carried back to the inlet conveyor 11 by means of the overhead transfer conveyor 14. The hangers can now be reloaded for another processing cycle.

FIG 3 shows an alternative embodiment of the system in accordance with the present invention. Said embodiment 110 comprises, similarly to the above described embodiment, a loading conveyor 111, a painting device 116, a heat- treatment conveyor 112, a hot-air bell-oven 115, an unloading conveyor 113, an overhead conveyor 114 for transfer of the hangers 118 hookable to the conveyors 111, 112,113, 114. The alternative embodiment comprises in addition a pretreatment system 150 for the manufactured articles. This system 150 comprises the anodizing (or chromium plating) tanks 151, the rinsing tank 152 and the drying tank 153. The pretreatment system 150 is fitted between the loading conveyor 111 and the painting device 116 as shown in the figure.

After having described two embodiments of the present invention, the numerous advantages obtained as compared with the prior art such as high hourly production, limited use of space and excellent environmental conditions for the operators appear to be evident. Indeed, considering that the bell oven can receive up to ten part-carrying hangers and that polymerization time for the metallic manufactured articles varies between 15'and 30', an hourly production

of approximately 25 to 30 hangers per hour is achieved, which is higher than the hourly production achievable with the prior art systems. Again, use of space is limited in relation to productivity since use of the bell oven is optimized thanks to the particular shape of the system embodiment realized. In addition, accumulation of the hangers leaving the oven on the unloading conveyor allows cooling of the manufactured articles painted and polymerized before intervention of the operators in the unloading zone. In this manner, the working environment is safer. The efficiency of the system is further improved by the capability of cleaning one of the two painting booths off-line without interrupting the manufacturing process which continues by making use of the other booth. Power consumption is also optimized thanks to complete utilization of the bell oven and reduced used of power for treatment of the inner atmosphere of the booth thanks to selective air suction in the spraying zone.

Naturally the above description of an embodiment applying the innovative principles of the present invention is given by way of non-limiting example of said principles within the scope of the exclusive right claimed here.