DESCRIPTION

The present invention relates to a plant for the anodic oxidation of aluminum profiles having a high vertical development, in particular aluminum section bars, by means of static immersion of said manufactured products hanging on an overhead conveyor in a treatment liquid.

As known, aluminum profiles are generally subject to surface treatment processes adapted to impart predetermined surface properties to said profiles.

A particular type of treatment is anodic oxidation (or anodizing) through immersion in a tank which, besides being a final aesthetic finishing process, may be inserted in the pre- treatment cycle of aluminum section bars in painting systems with powder or liquid paints.

The anodic oxidation treatment substantially consists in an electrochemical transformation of the surface of an object made of aluminum or alloys thereof. Such transformation allows the generation of a hard surface oxide layer in general highly resistant to chemical aggressions and in particular to atmospheric agents. The anodic oxidation of aluminum has therefore taken on an increasing importance, both for the exceptional hardness and for the anticorrosion properties also valid for small thicknesses. Moreover, the anodic oxidation of aluminum alloy section bars has proved to be very suitable for anchoring a subsequent finishing painting.

For this reason, as known, extruded bars for doors and windows, sheets and various other parts intended for outdoor architectural exposure are usually anodized and such technology is increasingly requested on the market. Moreover, the anodic oxidation allows the maximum result to be achieved in terms of performance among known types of pre-treatment, which must usually undergo painting.

According to the prior art, the anodic oxidation carried out on parts immersed in a tank both in horizontal and in vertical position is carried out by the known traditional method of static immersion from above into a tank usually containing an electrolyte, for example a sulphuric acid solution.

In this tank, the aluminum objects to be oxidized are connected to one pole (for example, the anode) of a current generator. The other pole of the generator is connected to electrodes (for example, cathodes) immersed in the electrolytic bath. A strong passage of current thus occurs through the electrolyte, generating the oxide layer forming process on the surface of the parts.

The anodizing process by immersion in a tank is universally used. However, while it has reached a satisfactory functionality, it is not free from defects. In the case of vertical positioning of parts having a high unidirectional development, such defects become considerably stronger.

Moreover, the tank immersion system, for its nature, is of the discontinuous type and requires elaborate handling of the pieces to be treated. In fact, in order to immerse the parts into bath it is necessary to lift them in vertical direction from the bottom upwards, horizontally translate them and then immerse them in the tank with a vertical movement from the top downwards (and vice versa in the emersion step).

Systems of this type have been made for aluminum section bars, which have been inserted in the pre-treatment-drying-painting-baking line. Such system allows for production continuity but implies a great design complexity and a possible limitation of productivity.

At present, such types of systems require very expensive ancillary equipment of the mechanical, electronic, hydraulic, pneumatic and computer type which are difficult to install and manage. Moreover, they require the use of very large bridge cranes, capable of quick movements with strokes of tenths of meters, operating at prohibitive heights. Moreover, such equipment has a very large weight which added to the weight of the hanging parts, creates problems of oscillations and vibrations. The inertia forces involved in start-ups and stops (which must be very frequent to keep an acceptable production rate) are so high to overstress the sturdy bearing structure.

On the other hand, the reduction of the operating speed for keeping the structure oscillations within values compatible with the process and safety requirements unfavorably affects the working rate.

The most remarkable drawback of all possible types of systems (pre-treatments, electrophoresis, immersion painting, anodic oxidation, cataphoresis, anaphoresis, autophoresis, acid or alkaline pre-treatment, chromate treatment, nano -techno logical pre- treatments, non chromium conversions, liquid painting or similar treatments which may or may not require the use of electrical current), based on the typical tank immersion systems relates to the height of the building needed to contain the system. This is truer for higher parts to be treated, in the case of vertical hanging.

To make a typical example referred to the tank immersion of aluminum section bars having an average height of 7 m, the tank zone must have a free working height of at least 18 m. Such height results from doubling the part height plus the height required to install the various horizontal and vertical handling pieces of equipment. In short, the systems of this type require a unusual useful height of the building. For example, the building should have a single elevation of at least 18 m from the ground, or an elevation of about 10 m from the ground and depth of at least 8 m.

In addition to the very high cost of similar building works, it is easy to imagine all the technical, environmental, ecological, aesthetic, and bureaucratic administrative problems resulting from the installation of a system of this type.

Another drawback derives from the relatively large volume of the treatment tank which is needed in order to keep a safety distance between the profiles and the electrical contacts during immersion/extraction of the profiles into/from the tank. In turn, the relatively large distance between the contacts and the profiles leads to relatively high current values in order to effectively carry-out the treatment process in relatively short times with higher operating costs.

Moreover higher currents bring about a higher temperature increase during the treatment, with the consequent needs of more powerful cooling system thereby further increasing the installation and operating costs of the plant.

Based on these remarks, there is clearly the need of providing a plant for the anodic oxidation of aluminum profiles which allows the above drawbacks to be eliminated or minimized.

The task of the present invention therefore is to provide a plant for the anodic oxidation of aluminum profiles which overcomes or minimizes the drawbacks of known treatment systems.

In particular, within the scope of this task, an object of the present invention is to provide a plant for the anodic oxidation of aluminum profiles that allows the vertical handling of the manufactured products to treat to be prevented.

Another object of the present invention is to provide a plant for the anodic oxidation of aluminum profiles which allows the height of said plant to be minimized.

Yet another object of the present invention is to provide a plant for the anodic oxidation of aluminum profiles which minimizes the need for auxiliary equipment for handling and treating said manufactured products.

A further object of the present invention is to provide a plant for the anodic oxidation of aluminum profiles that can be operated as a stand-alone unit or can be inserted in a more complex and complete system, for example a painting system.

Yet another object of the present invention is to provide a plant for the anodic oxidation of aluminum profiles which allows the production continuity of the systems, for example painting systems, in which it might be inserted, to be maintained. A further object of the present invention is to provide a plant for the anodic oxidation of aluminum profiles which is easy to manufacture at competitive costs.

Thus, the present invention therefore relates to a plant for the anodic oxidation of aluminum profiles which characterized in that it comprises first overhead transport means of said aluminum profiles hanging on said first overhead transport means along an advance direction and at least one immersion treatment tank of said aluminum profiles adapted to contain a treatment liquid, said immersion treatment tank comprising at least a first door for opening/closing said tank and filling means and emptying means of said treatment liquid from said treatment tank, said aluminum profiles entering into said treatment tank hanging on said first overhead transport means along a substantially horizontal advance direction, said plant comprising an electric circuit with first electrical contact means for contacting a not-immersed portion of said aluminum profiles during said immersion treatment and second electrical contact means immersed in said treatment liquid during said immersion treatment, electrical insulating means being provided for insulating said profiles with respect to said first overhead transport means during said immersion treatment, said immersion treatment tank further comprising venting means for venting-off the gases produced during said immersion treatment.

In other words, as better described hereinafter, the anodic oxidation plant for aluminum profiles according to the invention comprises at least one tank provided with at least a door wherethrough the aluminum profiles enter into/exit from said tank along a substantially horizontal advance direction; filling/emptying means are further provided for filling/emptying said tank with a treatment liquid. In this way, as better described hereinafter, the handling of aluminum profiles and the immersion thereof into the treatment liquid into the treatment tank substantially takes place in horizontal direction, without the need for a vertical handling of the same which is the main cause for the need for very high production sites, as mentioned above.

In practice, the aluminum profiles enter into the treatment tank when it is empty through said first door which allows the horizontal transit of the aluminum profiles hanging on the first overhead transport means and the entrance thereof into the treatment tank. Through the filling means, once the door is closed, the treatment tank is filled with a treatment liquid in the presence of the aluminum profiles which can then be subject to the anodic oxidation treatment. To this purpose, the aluminum profiles are connected to the first electrical contact means while the second electrical contact means are immersed in the treatment liquid, and the treatment is carried out by circulating current in the electrical circuit. At the end of the treatment, the treatment tank is emptied through the emptying means and after having actuated the door for opening the treatment tank, the aluminum profiles can exit therefrom still along a substantially horizontal path. Exit from the treatment tank can take place form said first door or from a second door. In the former case, the first overhead transport means make at least a U turn or a forward-backward movement inside the treatment tank and entrance into / exit from the treatment tank takes place through said first door; in the latter case entrance into the treatment tank takes place through said first door while exit therefrom takes place through said second door.

In practice, the first overhead transport means move with a "stop-and-go" motion, the "stop" phase corresponding to the residence time of the aluminum profiles inside the immersion treatment tank, the "go" phase corresponding to the entrance/exit of the aluminum profiles into/from the immersion treatment tank.

The plant according to the invention further comprises an electric circuit with first electrical contact means for contacting a not-immersed portion of said aluminum profiles during said immersion treatment and second electrical contact means immersed in said treatment liquid during said immersion treatment.

Preferably, said first electrical contact means are movable between a first, not- operating, position (i.e. an open position) in which they are at a distance from said aluminum profiles, and a second, operating, position (i.e. a closed position) in which they are in contact with said aluminum profiles. Cleaning means, e.g. washing means for delivering washing water, can be present for a quick washing of the first electrical contact means when they are in the open position. Advantageously, if necessary, collecting plates can be present in order to collect the washing liquid and prevent contamination of the treatment liquid with the washing liquid.

In practice, during the treatment, at least a portion of the aluminum profiles is not immersed in the treatment liquid so as to be contacted with first, anodic, contact means. Said portion is generally very small compared to the total length of the profiles and is kept in close proximity of the upper end of said profiles, most of the profiles being immersed in said treatment liquid. The electrical circuit is closed by second, catodic, contact means immersed in said treatment liquid and the surface oxidation process of the aluminum profiles is carried out by the current circulating into said circuit. Advantageously, said second electrical contact means are positioned along the lateral walls of said immersion treatment tank.

At least during the treatment process, the aluminum profiles are electrical insulated with respect to said first overhead transport means through electrical insulating means. This can be achieved, for example, by using electrical insulating support means interposed between the aluminum profiles and the first overhead transport means, such as insulating hooks, plates, bars or similar devices.

A further feature of the plant according to the invention, is given by the presence of venting means for said immersion treatment tank for venting-off the gases produced during said immersion treatment.

Advantageously, the immersion treatment tank can be closed with a cover on its upper portion for isolating it from the surrounding external environment during the immersion treatment. In such a case, it is worth noting that, differently from immersion treatment plant with vertical entrance of the profiles into the tank, the immersion treatment tank can be permanently closed with the cover.

In this way it is possible to avoid all problems, common in prior art plants with open tanks and vertical immersion, deriving from the release of dangerous gases, normally hydrogen, generated and released during the oxidation process. In addition, also the acid vapors coming out from the electrolytic treatment liquid (normally containing sulphuric acid) can be kept confined into the treatment vessel and vented-off through the venting system, thereby avoiding the corrosion problems of the equipment and of the building structures normally present in prior art processes.

Moreover, the system according to the invention does not require auxiliary equipment, such as for example bridge cranes or the like, for handling the parts and introducing them into the treatment tank.

In a particular embodiment of the plant for the anodic oxidation of aluminum profiles according to the invention, said treatment tank comprises distance means for avoiding the contact between said aluminum profiles and said second electrical contact means.

The first overhead transport means can comprise a single-rail transport device connected to supporting plates for said aluminum profiles, and the plant can be operated as a stand-alone unit or inserted in a more complete treatment plant.

When inserted in a more complete treatment plant, as a further advantage - and as better described hereinafter - with an appropriate selection of the first overhead transport means it is further possible to achieve the production continuity of the painting system in which the anodic oxidation plant of the invention might be inserted.

For instance, instead of having a single-rail transport device, said first overhead transport means can advantageously comprise a twin-rail transport device (also called "power & free" transport device), having a first rail superimposed to a second rail, the first rail being connected to motion driving means, the second rail hosting freewheel carriages for supporting said aluminum profiles. In such a case, at least in correspondence of said immersion treatment tank, said twin-rail "power & free" transport device can be split in two or more branches running in parallel into said immersion treatment tank, in order to increase the productivity. In practice the profiles, instead of entering into the immersion treatment tank aligned along a single line, enter into it along two or more parallel lines. Thus, for each treatment batch, the productivity is greatly increased, while maintaining a relatively short length of the immersion treatment tank.

In such a case, in order keep at a minimum the width of the door or doors, the branches of the transport device, in correspondence of the entrance to/exit from the immersion treatment tank, can advantageously be maintained at a minimal distance form each other and separating means can be positioned in correspondence of said door in order to avoid any interference between the aluminum profiles hanging from the branches of the transport device.

Advantageously, when a twin-rail "power & free" transport device is used, said second rail hosts a carriage driving a chain portion supporting a number of aluminum profiles. Thus, in this way, instead of having a rigid assembly, as in conventional systems where a supporting bar for the profiles hangs from one or more carriages, it is possible to have an articulated system that makes easier and safer the motion of the profiles along non-linear transport paths.

As previously said, the treatment tank preferably also comprises a first and a second door respectively arranged at the inlet and outlet of the tank. In any case, a solution is possible wherein the aluminum profiles travel along a U path, or a forward-backward path, within the tank, with entry and exit from said tank through said first door.

Preferably, the plant for the anodic oxidation of aluminum profiles according to the invention advantageously comprises a containment tank arranged underneath said treatment tank. In this case, a particular embodiment of the plant according to the invention provides for said filling means and emptying means of said treatment liquid to put said treatment tank in communication with said containment tank.

As an alternative, said filling means and emptying means of said treatment liquid put said treatment tank in communication with one or more loading/discharge tanks of said treatment liquid.

Preferably, the treatment liquid is loaded into the treatment tank form the top thereof and is discharged form its bottom, thereby increasing the mixing of the liquid and heat dispersion therefrom. The plant for the anodic oxidation of aluminum profiles according to the present invention can be operated as a stand-alone unit or can be inserted in a more complex and complete system, for example a painting plant.

When operated as a stand-alone unit, e.g. as a oxidizing finishing coat unit for the profiles, the plant according to the invention can conveniently comprise a loading station and a discharge station for the profiles. In such a case, the loading and discharge stations can preferably comprise substantially horizontal conveyor belts onto which the profiles are positioned parallel to each other. In correspondence of the loading and discharge stations, the first overhead transport means are kept at a first level, which is slightly above the level of the horizontal belts, while in correspondence of the treatment tank they are at a second level, higher than the first, above the treatment tank, the first and the second level being connected by a raising portion of the first overhead transport means in correspondence of the loading station and by a decreasing portion of the first overhead transport means in correspondence of the discharge station. At the loading station the profiles are connected to the first overhead transport means through suitable fixing means, e.g. hooks, and are raised in a substantially vertical position when running in the raising portion of the first overhead transport means. Then, the profiles enter into the immersion treatment tank and, after treatment, they reach the discharge station after being brought in a horizontal position while running in the decreasing portion of the first overhead transport means.

Thus, when operated as a stand-alone unit, handling of the profiles to be treated is greatly simplified with respect to conventional immersion treatment systems.

When inserted in a more complex and complete system, the plant for the anodic oxidation can be connected to the entire plant by using the same overhead transport means, i.e. the first overhead transport means does not belong to the plant for the anodic oxidation only, but are shared with at least a portion of the painting plant.

Alternatively, the painting plant can comprise second overhead transport means operatively coupled to the first overhead transport means of the plant for the anodic oxidation, transfer means being provided for transferring the aluminum profiles between said second overhead transport means of the painting plant and said first overhead transport means of the plant for the anodic oxidation.

In such a case, preferably, the second overhead transport means move with a second speed and the first overhead transport means move with a "stop-and-go" motion, the "stop" phase substantially corresponding to the residence time of the aluminum profiles inside the immersion treatment tank, the "go" phase corresponding to the entrance/exit of the aluminum profiles into/from the treatment tank at a first speed, the first speed of the first overhead transport means during the "go" phase being higher than the second speed of the second overhead transport means. In this way, by suitably tuning the first and second speed of the first and second overhead transport means it is possible to achieve the production continuity of the painting system.

In practice, the second overhead transport means can be considered as the main transport line of the painting plant and in this way it is possible to maintain a continuous movement of the line, thereby maintaining the production continuity of the painting plant. The plant for the anodic oxidation is operated off-line with respect to the main transport line (i.e. the second overhead transport means) of the painting plant, the aluminum profiles being transferred from the second overhead transport means to the first overhead transport means in which they move with a "stop-and-go" motion. By maintaining the speed of the first overhead transport means during the "go" phase higher than the speed of the second overhead transport means, and by suitably tuning (synchronizing) the two speeds taking into account the residence time of the aluminum profiles into the immersion treatment tank, the aluminum profiles can be transferred back from the first overhead transport means to substantially the same position they had in the second overhead transport means. In other words, there is no interruption of the main transport line of the painting plant and there is no loss or modification of the position of the aluminum profiles on it, and this is a considerable achievement in terms of productivity.

Thus, in a further aspect, the present invention relates also to a painting plant for aluminum profiles comprising a plant for the anodic oxidation as described herein.

Further features and advantages of the present invention will be more clear from the description of preferred but not exclusive embodiments of plant for the anodic oxidation of aluminum profiles according to the invention, shown by way of an example in the accompanying drawings, wherein:

Figure 1 is a plan view of a particular embodiment of a plant for the anodic oxidation of aluminum profiles according to the invention;

Figure 2 is a section view of the embodiment of Figure 1;

Figure 3 shows a detailed view of the entrance/exit system used in the embodiment of Figure 1;

Figure 4 shows a detailed view of the upper portion of the plant of Figure 2, with the first contact means in the open position;

Figure 5 shows a detailed view of the upper portion of the plant of Figure 2, with the first contact means in the closed position;

Figure 6 shows a schematic view of a first general embodiment of a plant for the anodic oxidation of aluminum profiles according to the invention;

Figure 6a shows a detail of the first overhead transport means used in the embodiment of Figure 6;

Figure 7 shows a schematic view of a second general embodiment of a plant for the anodic oxidation of aluminum profiles according to the invention;

Figure 7a-7d show details of the first and second overhead transport means used in the embodiment of Figure 7;

Figure 8 shows a schematic view of a third general embodiment of a plant for the anodic oxidation of aluminum profiles according to the invention;

Figure 8a-8d show details of the first and second overhead transport means used in the embodiment of Figure 8;

Figure 9 shows a schematic view of a fourth general embodiment of a plant for the anodic oxidation of aluminum profiles according to the invention;

Figure 9a-9d show details of the first and second overhead transport means used in the embodiment of Figure 9;

Figure 10 shows a preferred embodiment of the first overhead transport means of a plant for the anodic oxidation of aluminum profiles according to the invention.

With reference to the attached figures, a plant 1 for the anodic oxidation of aluminum profiles 10, in its more general definition, comprises first overhead transport means 11 for conveying aluminum profiles 10 hanging therefrom along an advance direction. The plant 1 further comprises at least one immersion treatment tank 2 of said aluminum profiles 10, which is adapted to contain a treatment liquid. The treatment liquid is normally an electrolyte, for example a 20% solution of sulphuric acid.

The immersion treatment tank 2 comprises at least a first door 21 for opening/closing said tank 2, and filling means 3 and emptying means 4 of said treatment liquid to/from said immersion treatment tank 2. The filling means can be for example one or more pumps 300 that convey the treatment liquid from a storage tank into the immersion treatment tank 2 while the emptying means 4 can be one or more valves positioned on the bottom of the immersion treatment tank 2 and connected to liquid discharge pipes, in turn connected to a liquid collection tank that can be the same storage tank mentioned above.

As shown in Figures 1 and 2, the storage/liquid collection tank 9 can be conveniently arranged at a level below said immersion treatment tank 2, said filling means 3 and emptying means 4 of said treatment liquid placing said immersion treatment tank 2 in communication with said storage/liquid collection tank 9.

An overflow system 90, for discharging excess treatment liquid from the treatment tank 2 and keeping a constant level of treatment liquid into it, can be foreseen.

Thus, differently from prior art processes, the aluminum profiles 10 enter into said immersion treatment tank 2 hanging from said first overhead transport means 11 along a substantially horizontal advance direction, without any need of vertical movement thereof.

In the embodiments of the plant 1 according to the invention represented in the attached figure, said treatment tank 2 comprises a second door 22 for opening/closing said tank 2. Preferably the door 21 (and 22 when present) opens inwardly with respect to the immersion treatment tank 2, so that the hydrostatic pressure of the liquid inside the tank 2 helps keeping the door closed and sealed during treatment.

The plant 1 further comprises an electric circuit with first electrical contact means 51 for contacting a not-immersed portion of said aluminum profiles 10 during said immersion treatment and second electrical contact means 52, 53 immersed in said treatment liquid during said immersion treatment. Normally, the first electrical contact means 51 are the anodes of the electrical circuit and the second electrical contact means 52, 53 are the cathode of the circuit, a DC current being normally circulated inside the circuit.

In the embodiment of figures 1-5, the first electrical contact means 51 are movable between a first, not-operating, position (see Figure 4) in which they are at a distance from said aluminum profiles 10 (open position), and a second, operating, position (see Figure 5) in which they are in contact with a not-immersed portion of said aluminum profiles 10 (closed position). In the case represented in the above mentioned figures, the first electrical contact means 51 are positioned in the upper portion of the immersion treatment tank 2, so as to contact the upper end of the profiles 10, and are connected to the electrical circuit through an anodic bar 55.

Thus, the first electrical contact means 51 can be moved from the open position to the closed position while filling of the immersion treatment tank 2 takes place. Elastic means, such as a spring, can be provided on the first electrical contact means 51 in order to keep the contact with the profiles 10. Once the first electrical contact means 51 are closed and the immersion treatment tank 2 is filled with the liquid, current is circulated into the electrical circuit thereby determining formation of a few um of aluminum oxide on the surface of the profiles.

In this embodiment, the second electrical contact means 52 are positioned along the lateral walls 20 of said immersion treatment tank 2. When, as shown in figures 1-5, the aluminum profiles 10 enter into the immersion treatment tank 2 along two parallel rows 61 and 62, the second electrical contact means 52 can comprise a further intermediate group of contacts 53 positioned between the rows 61, 62 of the aluminum profiles 10.

In order to insulate the profiles 10 with respect to said first overhead transport means 11, and the other part of the plant 1, during the immersion treatment, electrical insulating means 6 are provided. Said electrical insulating means 6 can be, for instance, the plates or the suspension system onto which the aluminum profiles are attached.

At the end of the oxidation process, the current is interrupted and the immersion treatment tank 2 is emptied through the discharge pipes.

In order to keep the first electrical contact means 51 clean, the plant 1 can be provided with cleaning means for a quick washing of the first electrical contact means 51 when they are in the open position. In the embodiment of Figures 1-5, the cleaning means comprise a manifold 56 positioned in correspondence of the first electrical contact means 51 in their open position and provided with holes, slots or spraying means for delivering washing water on said first electrical contact means 51. In general any washing mean suitable for cleaning/washing the first electrical contact means 51 can be used. Also, when necessary, collecting plates (not shown) can be present in order to collect the washing liquid and prevent mixing thereof with the treatment liquid.

Moreover, in order to avoid any possible contact between the aluminum profiles 10 and the second electrical contact means 52 and 53 (when present), the immersion treatment tank 2 preferably comprises distance means 25, for example insulating distance means that avoid lateral movements of the aluminum profiles 10.

In the plant 1 according to the invention, the immersion treatment tank 2 further comprises venting means 8 for venting-off the gases produced during said immersion treatment.

Preferably, the immersion treatment tank 2 can be closed with a cover 8 on its upper portion for isolating it from the surrounding external environment during the immersion treatment. In this case, the immersion treatment tank 2 can be kept always isolated from the outside with safe collection of gases and vapors developed during the treatment.

Figure 6 and 6a shows a general embodiment of a plant for the anodic oxidation of aluminum profiles according to the invention which is operated as a stand-alone unit, or which is inserted in a more complex and complete system (e.g. a painting plant) using the same overhead transport means. In the former case, the first overhead transport means 11 connect the immersion treatment tank with a loading and a discharging stations (not shown); in the latter case, the first overhead transport means 11 are shared with at least a portion of the painting plant.

In such a case, with reference to figure 6a, said first overhead transport means 1 1 preferably comprises a single-rail transport device 111 connected to supporting plates 112 for said aluminum profiles 10.

Figures 1-2, and 7-9 show further general embodiments of a plant for the anodic oxidation of aluminum profiles according to the invention which is inserted in a more complex and complete system (e.g. a painting plant) and which is operated off-line with respect to the main transport line (i.e. the second overhead transport means) of the painting plant.

In these cases, the painting plant comprises second overhead transport means 50. The first 11 and second overhead transport means 50 are operatively coupled through transfer means 511, that can be of conventional type, for transferring the aluminum profiles 10 between said second overhead transport means 50 and said first overhead transport means 11 upstream the immersion treatment tank 2. Similar transfer means (not shown) are then provided downstream the immersion treatment tank 2, for transferring back the aluminum profiles 10 from said first overhead transport means 11 to said second overhead transport means 50.

In particular, with reference to figures 7a- 7b, 8a-8b, 9a-9b, the second overhead transport means 50 can comprise a single-rail transport device 111 connected to supporting plates 112 for said aluminum profiles 10. In turn, the first overhead transport means 11 can advantageously comprise a twin-rail "power & free" transport device 12 having a first rail 121 superimposed to a second rail 122, the first rail 121 comprising motion driving means 31, the second rail 122 hosting freewheel carriages 32 for supporting said aluminum profiles 10.

With reference to figures 7, 7c and 7d, in an embodiment, the freewheel carriages 32 can be connected to supporting plates 112 similar to those used in the single-rail transport device 111 of the second overhead transport means 50.

Alternatively, with reference to figures 8, 8c and 8d, the freewheel carriages 32 can be connected to supporting bars 33, each capable to receive from the second overhead transport means 50 a relatively low number of aluminum profiles 10.

As a further alternative, with reference to figures 9, 9c and 9d, at least two freewheel carriages 32 of the second rail 122 can be connected to relatively long supporting bars 34, each capable to receive from the second overhead transport means 50 a relatively high number of aluminum profiles 10.

According to a particular embodiment, shown in figure 10, the second rail 122 of said "power & free" twin-rail transport device 12 hosts freewheel carriages 32 connectable to said motion driving means 31 in said first rail 121 and driving a chain portion 125 supporting a number of supporting plates 118 for the aluminum profiles 10. Such embodiment is particularly useful when the transport path is non-linear, since instead of having a rigid assembly, as in figures 8 and 9 where the supporting bar for the profiles hangs from one or more carriages, it is possible to have an articulated system that makes easier and safer the motion of the profiles 10 along curved paths.

With references to figure 1-5, when a twin-rail "power & free" transport device 12 used, it can be convenient to split it into two or more branches 61, 62 running in parallel into said immersion treatment tank 2.

In practice, with reference to figure 1, in correspondence of a point 91 upstream the immersion treatment tank 2, the twin-rail "power & free" transport device 12 is spitted into two branches 61 and 62, and a number of aluminum profiles 10 is alternatively sent to either of the branches 61 and 62, so as to form two parallel lines of profiles immediately before the immersion treatment tank 2. Then, in correspondence of a point 92 downstream the immersion treatment tank 2, the two branches 61 and 62 are brought together again in order to form the original single line of profiles 10. Thus, for each treatment batch, the productivity is greatly increased, as it is possible, for the same length of the immersion treatment tank 2, to double the number of treated aluminum profiles 10.

With reference to figures 1 and 3, in order keep at a minimum the width of the doors 21 and 22, the branches 61 and 62 of the transport device, in correspondence of the entrance to/exit from the immersion treatment tank 2, can advantageously be maintained at a minimal distance from each other, i.e. in correspondence of the doors 21 and 22 the pitch between the branches 61 and 62 is shorter than inside or outside the immersion treatment tank 2.

With reference to Figure 3, in order to avoid any interference between the aluminum profiles 10 hanging from the branches 61 and 62 of the transport device 11, separating means can be positioned in correspondence of said door(s) 21(22). The separating means can conveniently comprise a fixed separating wall 41, positioned just outside the immersion treatment tank 2 and extending at least for a portion of its height. A movable separating wall 42 can also be present, said movable separating wall 42 extending inside the immersion treatment tank 2 when the door(s) 21(22) is open and the profiles 10 are entering/leaving the immersion treatment tank 2, and being withdrawn outside the immersion treatment tank 2 when the door(s) 21(22) is closed and the treatment is carried out.

In order to avoid any deterioration of the surface coating formed on the aluminum profiles due to the acid nature of the liquid treatment (electrolyte), a washing section 70 of the aluminum profiles is conveniently positioned immediately downstream the immersion treatment tank 2. Washing can be carried out with conventional techniques, e.g. spraying, percolation of washing liquid from above, and similar procedures.

A particular embodiment of a plant 1 for the anodic oxidation of aluminum profiles 10 according to the invention, usable in combination with, e.g., a painting plant, is shown in figures 1-5. The painting plant normally comprises second overhead transport means 50 that can be considered as the main transport line of said painting plant. Transfer means 511 and 510 are provided for transferring the aluminum profiles 10 between said second overhead transport means 50 and the first overhead transport means 11 of the plant 1 for the anodic oxidation of the aluminum profiles 10.

In this embodiment, the first overhead transport means 11 comprises a twin-rail "power & free" transport device 12 having a first rail 121 superimposed to a second rail 122. With reference to Figure 10, the first rail 121 comprises motion driving means 31, while the second rail 122 is provided with freewheel carriages 32 driving a chain portion 125 supporting a number of plates 118 for supporting said aluminum profiles 10, said freewheel carriages 32 being connectable to said motion driving means 31. In other words, in this embodiment, the supporting and carrying device for the profiles substantially consists of a chain segment 125 supporting the profiles 10 and driven by the carriage 32, thereby realizing an articulated assembly that can easily follows the turns of the overhead transport means 11.

In correspondence of the transfer means 510, the aluminum profiles 10 are transferred from the second overhead transport means 50 to the supporting plates 118 of a first chain segment 125 which is synchronized with the second overhead transport means 50, i.e. the freewheel carriage 32 driving the first chain segment 125 is connected to first driving means 31 moving at the same speed ("second speed") of the second overhead transport means 50.

The second rail 122 of the first overhead transport means 11 is provided with a number of such chain segments 125 driven by corresponding freewheel carriages 32, and running in sequence in correspondence of the transfer means 51.

Upstream said immersion treatment tank 2, the twin-rail "power & free" transport device 12 is split in two branches 61 and 62 running in parallel, the chain portion 125 being alternatively sent to one of the two branches 61 and 62. In other words, a first chain segment 125 is sent to the first branch 61 and stopped by disengaging the freewheel carriage 32 from the first driving means 31 and a second chain segment 125 is sent to the second branch 62 and stopped by disengaging the corresponding freewheel carriage 32 from the corresponding first driving means 31.

Once the door 21 of the immersion treatment tank 2 is open, the freewheel carriages 32 of the first and second chain segments 125 engage second driving means moving with a speed (first speed) much higher than the speed (second speed) of the first driving means, thereby moving the first and second chain segments 125 inside the immersion treatment tank 2. Once the chain segments 125 are inside the immersion treatment tank 2, they are stopped by disengaging the freewheel carriages 32 of the first and second chain segments 125 from the second driving means, the door 21 is closed, the tank is filled with the treatment liquid and the treatment can be carried out by circulating the current into the electric circuit, as better explained hereinbefore.

During treatment, further chain segments are brought into the two branches 61 and 62 and stopped until the treatment is completed. At the end of the treatment, and after having discharged the treatment liquid, the doors 21 and 22 open and the freewheel carriages 32 of the first and second chain segments 125 engage said second driving means moving at said first "high" speed, while the further chain segments in the branches 61 and 62 outside the immersion treatment tank 2 repeat the entrance sequence described above.

In this way, the aluminum profiles 10 exiting the immersion treatment tank 2 can be immediately and quickly brought into the washing section 70 downstream said immersion treatment tank 2, thereby avoiding possible damages of the treated surface of the profiles 10 due to the acid nature of the treatment liquid.

During or after the washing section, in correspondence of a point 92, the two branches 61 and 62 are brought together again and the original sequence of chain segments 125 is formed. At this stage, the freewheel carriages 32 driving the chain segments 125 are connected to first driving means moving at the same speed ("second speed") of the second overhead transport means 50. Thus, the two systems are now synchronized again and in correspondence of the transfer means 510 the aluminum profiles 10 can be transferred back from the first overhead transport means 11 to the second overhead transport means 50.

In practice, in this embodiment, the first rail 121 of the twin-rail "power & free" transport device 12 is equipped with a number of motion driving means (e.g. chains) moving at different speed, i.e., at least at a first speed and at a second speed, the second speed being the speed of the second overhead transport means 50, the first speed being higher than the second speed and being at least used to transfer the aluminum profiles 10 to and from the immersion treatment tank 2. In this way, by suitably tuning the two speeds taking into account the residence time of the aluminum profiles 10 into the immersion treatment tank 2, the aluminum profiles 10 can be transferred back from the first overhead transport means 11 to substantially the same position they had in the second overhead transport means 50.

As is clear from the above description, the technical solutions adopted for plant for the anodic oxidation of aluminum profiles according to the present invention allow the proposed aims and the objects to be fully achieved.

The plant for the anodic oxidation of aluminum profiles according to the invention is suitable for carrying out the anodic oxidation as top coat but is also easily integrated as pre- treatment method in powder or liquid painting systems of aluminum profiles.

Several variations can be made to the plant for the anodic oxidation of aluminum profiles thus conceived, all falling within the scope of the present invention. In practice, the materials used and the contingent dimensions and shapes can be any, according to requirements and to the state of the art.