WO2007014814A2

WO2007014814A2 - Plant for surface treatment of products and corresponding conveying system

Info

Publication number: WO2007014814A2
Application number: PCT/EP2006/063807
Authority: WO
Inventors: Giovanni Giardini
Original assignee: Trasmetal S.P.A.
Priority date: 2005-07-29
Filing date: 2006-07-03
Publication date: 2007-02-08
Also published as: EP1910197A2; WO2007014814A3; ITBG20050041A1

Abstract

Described herein is a plant (1) for surface treatment of products comprising: a continuous overhead conveyor (2) having a conveying system (3) ; a loading station, an unloading station and one or more stations (101, 102 ;201,202,203;041, 402) for treatment of said products; and hooking means (4) designed to couple with said conveying system (3) and to support said products. The continuous overhead conveyor (2) comprises at least one first section and one second section (10,20) , in which the conveying system (3) traverses a substantially loop- shaped path, and a first and a second transferrer (11,12) for transferring the hooking means (4) . The first transferrer (11) is positioned upstream of the first section (10) and upstream of the second section (20) and is designed to transfer the hooking means (49 from a position upstream of the first section (10) to the second section (20) . The second transferrer (12) is positioned downstream of the first section (10) and downstream of the second section (20) and is designed to transfer the hooking means (4) from the first section (10) to a position downstream of said second section (20) . Also disclosed is a transfer device (9) for transferring products; said transfer device (9) being set between a first branch (71) and a second branch (72) of a chain conveyor (7) , and comprising first transfer means (91) and second (92) to transfer the products from the chain conveyor (7) to the transfer device (9) , and from the transfer device (9) tot he chain conveyor (7) respectively.

Description

PLANT FOR SURFACE TREATMENT OF PRODUCTS AND CORRESPONDING

CONVEYING SYSTEM

DESCRIPTION

The present invention relates to a plant for surface treatment of products, and in particular to a plant for painting of products, comprising a particular system for conveying said products, as well as to a system for conveying products, in particular for continuous paint plants. As is known, painting of products, for example, panels or sectional elements, is carried out in plants that envisage one or more overhead conveyors, formed in general by a chain or conveyor belt provided with hooking means, on which the pieces to be painted are hung. The conveyor performs a closed circuit the path of which, starting from a station for loading the products, traverses one or more treatment stations, such as for example, a paint-spray tunnel with corresponding drying area and hence paint booths and corresponding ovens for cross- linking/baking, and terminates at a station for unloading of the products. In order to have an adequate flexibility of production, said plants can, for example, be equipped with two or more treatment booths with corresponding ovens so as to be able to manage the production of lots of pieces that are to undergo painting treatments of different types. The overhead conveyor must consequently be designed to enable flexible management of the different production lots.

In some paint plants, there exist substantially two types of conveyors, with single conveying system (for example, chain conveyors), and with double conveying system (for example conveying systems with two parallel chains). In the first case, the different production lots must be interspersed, leaving spaces on the conveyor according to the type of treatment to which the pieces will be subjected. In the second case, the pieces are loaded on one or the other conveyor parallel to the first, always according to the type of treatment to which the pieces will be subjected, leaving in each case empty spaces on the conveyors.

It is clear that the existing solutions, albeit enabling an adequate management of the plant, are not totally satisfactory, either in terms of productivity of the plant or in terms of installation costs. The need to leave empty spaces on the conveyor leads in fact to a loss of overall productivity of the plant. Furthermore, the double-chain system leads to higher installation costs, there being necessary a double system of actuation and of control of the conveyor. It is moreover evident that, by increasing the complexity of the plant, i.e., by increasing the number of stations for treatment of the products, the problems described previously are amplified. It is also evident that the preliminary treatment steps are normally performed on the same conveyor in series to the subsequent painting step. This constitutes a constraint for the design of the various machines.

A primary task of the present invention is to provide a plant for surface treatment of products, and in particular a plant for painting of products, which will enable the problems referred to above to be overcome.

A further task of the present invention is to provide a conveying system, in particular for continuous paint plants, which will enable the problems of conveyors of a known type to be overcome.

In the framework of this task, a purpose of the present invention is to provide a plant for surface treatment of products, and in particular a plant for painting of products, which is provided with high flexibility and will enable effective management of the production of lots of a different type.

Another purpose of the present invention is to provide a plant for surface treatment that will enable the step of pre-treatment to be separated from the subsequent painting step to enable a more convenient design of the elements.

Another purpose of the present invention is to provide a plant for surface treatment of products, and in particular a plant for painting of products, which will enable maintenance of a high productivity, irrespective of the different types of products.

A further purpose of the present invention is to provide a plant for surface treatment of products, and in particular a plant for painting of products, which will enable effective management of the change of production lots.

Yet a further purpose of the present invention is to provide a plant for surface treatment of products, and in particular a plant for painting of products, which will enable minimization of the number of conveying systems required.

Not the least important purpose of the present invention is to provide a plant for surface treatment of products, and in particular a plant for painting of products, which will present high reliability, and will be relatively simple to produce at competitive costs. This task, as well as the above and other purposes that will appear more clearly hereinafter, are achieved by a plant for surface treatment of products, and in particular a plant for painting of products, which comprises: a continuous overhead conveyor provided with a conveying system; a loading station, an unloading station and one or more stations for treatment of said products; and hooking means designed to couple with said conveying system and to support said products. The plant according to the invention is characterized in that the continuous overhead conveyor comprises at least one first section, one second section and one third section, in which said conveying system traverses a substantially loop-shaped path, and at least one first transferrer, one second transferrer and one third transferrer for transferring said hooking means. The first transferrer is positioned upstream of said first section and upstream of said second section and is designed to transfer said hooking means from a position upstream of said first section to said second section; the second transferrer is positioned downstream of the first section and upstream of the third section and is designed to transfer said hooking means from said first section to said third section; the third transferrer is positioned downstream of the second section and downstream of the third section and is designed to transfer said hooking means from said second section to a position downstream of said third section.

It has, in fact, surprisingly been found that the appropriate structure and configuration of the overhead conveyor, with the conveying system and transferrers associated thereto, enables extremely effective management both of the production of lots of different types and of the global productivity of the plant. In the plant according to the invention it is, in fact, possible to have any number of treatment stations and handle the change of production lots without there being any substantial loss of productivity of the plant in so far as it is possible to perform lot change without leaving empty spaces on the overhead conveyor.

The present invention moreover relates to a continuous conveyor of products comprising: a supporting structure; a chain conveyor having at least one first branch and one second branch, in which said conveyor moves in opposite directions; hooking means for said products; and a transfer device for transferring said products. The conveyor according to the present invention is characterized in that said transfer device is set between said first branch and said second branch and comprises first transfer means designed to transfer the products from the chain conveyor to said transfer device and second transfer means designed to transfer the products from the transfer device to said chain conveyor.

Further characteristics and advantages of the present invention will emerge more clearly from the description of preferred, but non-exclusive, embodiments of a plant for surface treatment of products, in particular a plant for painting products, illustrated in the attached plate of drawings, in which:

Figure 1 is a schematic illustration of a first embodiment of a plant according to the invention; Figure 2 is a schematic illustration of a second embodiment of a plant according to the invention;

Figures 3A-3E are schematic illustrations of a possible sequence of operation of the plant of

Figure 1;

Figures 4A-4D are schematic illustrations of a possible sequence of operation of the plant of

Figure 2;

Figure 5 is a schematic illustration of a third embodiment of a plant according to the invention;

Figure 6 is a schematic illustration of a fourth embodiment of a plant according to the invention;

Figure 7 is a top plan view of a possible embodiment of a transferrer used in the overhead conveyor of a plant according to the invention;

Figure 8 is a top plan view of a detail of the transferrer of Figure 5;

Figure 9 is a first top plan view of a detail of a first embodiment of a conveyor according to the invention;

Figure 10 is a first cross-sectional view of the conveyor of Figure 9;

Figure 11 is a second cross-sectional view of the conveyor of Figure 9;

Figure 12 is a second top plan view of a detail of a first embodiment of a conveyor according to the invention;

Figure 13 illustrates a first embodiment of a first detail of a hooking device of a conveyor according to the invention;

Figures 14a- 14c illustrate a first embodiment of a second detail of a hooking device of a conveyor according to the invention; and

Figure 15 illustrates a first embodiment of a third detail of a hooking device of a conveyor according to the invention.

The invention will now be described with reference to the figures referred to above, in which the same reference numbers designate elements that are the same as one another, without wishing in any way to limit the sphere of application.

With reference to Figure 5, a detail of a possible embodiment of the plant according to the invention is described. The plant 1 for surface treatment of products comprises a continuous overhead conveyor 2, just one part of which is represented, having a conveying system, constituted, for example, by at least one chain or by a closed-circuit continuous conveyor belt, actuated by appropriate actuation means, not represented in the figure. The plant 1 further comprises a station for loading and a station for unloading of the products (not represented in the figure), and one or more treatment stations 101, 201, 301 for treating said products. The conveying system moves along the entire overhead conveyor, for example in the direction indicated by the arrows 50, traversing the aforesaid treatment stations. The plant further comprises hooking means, not represented in the figure, which are designed to couple with the conveying system and to support said products. The peculiarity of the plant according to the present invention lies in the fact that the continuous overhead conveyor 2 comprises at least one first section 10 and one second section 20, in which said conveying system 3 traverses a substantially loop-shaped path, and at least one first transferrer 11 and one second transferrer 12 of said hooking means 4. The first transferrer 11 is positioned upstream of the first section 10 and upstream of the second section 20 and is designed to transfer the hooking means 4 from a position upstream of said first section 10 directly to said second section 20, hence by-passing the first section 10. The second transferrer 12 is positioned downstream of the first section 10 and downstream of the second section 20 and is designed to transfer the hooking means 4 from said first section 10 directly into a position downstream of the second section 20, hence bypassing said second section 20.

As may be seen from Figure 1, in the plant according to the invention, the first transferrer 11 and the second transferrer 12 are set between two segments of the overhead conveyor 2, in which said conveying system 3 moves in opposite directions. Figure 6 describes an alternative embodiment of the plant characterized by a different lay-out of the conveyor and by a different positioning of the transferrers 10 and 20, the principles of operation being the same. With reference to Figure 1, a detail of a particularly preferred embodiment of the plant according to the invention will now be described. The plant 1 comprises the continuous overhead conveyor 2, of which just one part is represented, having a conveying system, constituted preferably by at least one closed-circuit continuous chain, actuated by appropriate actuation means, not represented in the figure.

The plant 1 further comprises a station for loading and station for unloading of the products (not represented in the figure), and one or more treatment stations 101, 102, 201, 202, 203 for treatment of said products. The conveying system moves along the entire overhead conveyor, for example, in the direction indicated by the arrows 50, traversing the aforesaid treatment stations. The plant further comprises hooking means, not represented in the figure, which are designed to couple with the conveying system and to support said products. The peculiarity of the plant according to the present invention lies in the fact that the continuous overhead conveyor 2 comprises at least one first section 10, one second section 20, and one third section 30, in which said conveying system traverses a substantially loop-shaped path. By the term "loop-shaped path" it is meant that said sections define a given area that comprises a point of entry into and a point of exit from said area of the conveying system, the point of entry being contiguous to the point of exit, it being possible for the path of the conveying system within said area to be of any type; i.e., it may comprise one or more curves or U-bends and may not necessarily be a circular path.

The continuous overhead conveyor 2 further comprises at least one first transferrer 11, one second transferrer 12 and one third transferrer 13 for transferring said hooking means 4, said transferrers being of a rotary type. The first transferrer 11 is positioned upstream of said first section 10 and upstream of said second section 20 and is designed to transfer said hooking means 4 from a position upstream of the first section 10 directly to said second section 20; the second transferrer 12 is positioned downstream of the first section 10 and upstream of the third section 30 and is designed to transfer said hooking means 4 from the first section 10 to the third section 30; the third transferrer 13 is positioned downstream of the second section 20 and downstream of the third section 30 and is designed to transfer said hooking means 4 from the second section 20 to a position downstream of the third section 30.

In practice, once the system is actuated, in the loading station the products are loaded on the overhead conveyor 3, for example, by hanging them on the hooking means associated to the conveying system. The conveying system moves along the entire path of the conveyor 3, whilst the products, hanging from the hooking means, follow a path that can envisage transfer from one section to the other according to the type of treatment that they are to undergo. For example, in the case where the products are to be treated only in the stations 201, 202 and 203 of the second section 20, they can be transferred from a point upstream of the first section 10 directly to the second section 20, via the first transferrer 11, thus by-passing the first section 10. Likewise, the products coming out of the second section 20 can be transferred directly downstream of the third section 30 via the third transferrer 13, thus by-passing the third section 30. In the unloading station the products are unhooked from the hooking means, at the same time maintaining continuity of motion of the conveying system and without substantial loss of hooking points thereon (i.e., leaving only a very limited number of empty spaces on the conveying system during loading of the products). More detailed examples of the operation of the plant, particularly according to the change of production lot, will be illustrated hereinafter. Advantageously, the first, second, and third sections 10, 20 and 30 of the overhead conveyor have substantially the same length so as to be able to handle in an optimal way transfer of the products between the various sections without reducing the overall productivity of the plant. Furthermore, the hooking means can be positioned on the conveying system in hooking stations set at a fixed and pre-set distance from one another, i.e., in such a way that, as a consequence of the substantially equal length of the various sections, said sections will be able to house the same number of products hanging from the aforesaid hooking means. Preferably, the plant 1 according to the invention comprises at least one treatment station 101 in said first section 10, and at least one treatment station 201 in said second section 20. With reference to Figure 2, according to a further embodiment of the invention, the overhead conveyor 2 comprises a fourth section 40, in which the conveying system 3 follows a substantially loop-shaped path, and a fourth transferrer 14 for transferring said hooking means. The fourth transferrer 14 is positioned downstream of the third section 30 and downstream of the fourth section 40 and is designed to transfer the hooking means from the third section 30 directly to a position downstream of the fourth section 40, by-passing the fourth section 40. Further embodiments of the plant 1 are obviously possible, in which the overhead conveyor 2 comprises further sections, in which said conveying system 3 traverses a substantially loop- shaped path, and corresponding further transferrers for transferring said hooking means. The plant according to the invention can be structured in a modular way, dividing the overhead conveyor into a suitable number of sections according to the number and type of treatment stations that are to be installed, and associating to each of said sections a transferrer that will enable the corresponding section to be by-passed.

For this purpose, each of the rotary transferrers 11, 12, 13 and 14, (and possible further transferrers) is set between a corresponding first segment and a second segment of the overhead conveyor 2, with the motion of the conveying system that occurs in the first segment in an opposite direction with respect to the motion in the corresponding second segment. Preferably, at least one of said sections 30 of the conveyor functions as storage unit or buffer of said conveying system 3. In practice, as will be described in greater detail hereinafter, if a section 30 is left without any treatment stations, it is possible to use it as spare space for the hooking means and handle in an optimal way change of the production lots without any substantial loss of hooking positions on the conveying system.

A first example of operation of the plant according to the invention will now be described with reference to Figures 3A-3E. Said example regards a production stage that envisages treatment of a lot of products, represented by the symbol (/), in the stations 101, 102 of the first section and in the stations 201, 202, 203 of the second section, followed by the treatment of a lot of products, represented by the symbol (V), in the stations 101, 102 of the first section, in turn followed by the treatment of a lot of products, represented by the symbol (X), in the stations 201, 202, 203 of the second section.

With reference to Figure 3 A, the products (/), loaded on the conveying system via the hooking means in the loading station (not represented in the figure), follow the path of the overhead conveyor in the first and second sections 10 and 20. In this step, the transferrers 11 and 12 are not active, whereas the transferrer 13 is active and enables transfer of the products (/) from a point downstream of the second section to a point downstream of the third section 30, bypassing said third section.

The subsequent lot of products (V), which are to be treated only in the first section 10, is loaded in immediate succession, i.e., in such a way that between the last piece 29 of the first lot (/) and the first piece 31 of the lot (V) there is no substantial loss of hooking stations on the conveying system. In practice, it is sufficient to leave a number of positions free equal to the number of pieces present on the transferrer 13. With reference to Figure 3B, when the first piece 31 of the lot (V) is in a position corresponding to the second transferrer 12 at output from the first section 10, said transferrer 12 is activated and transfers the pieces (V) directly from the first section 10 to the third section 30, by-passing the second section 20. In the meantime, the pieces (/) continue to traverse the second section 20 and to exit therefrom directly downstream of the third section 30, via the third transferrer 13 (Figure 3C). Since the three sections 10, 20, 30 have the same length and house the same number of products, the first piece 31 of the lot (V) will reach the output of the third section 30 immediately after the last piece 29 of the lot (/) has been transferred from the second section 20 in a point immediately downstream of the third section (30); the piece 31 then tacks on to the last piece 29 of the lot (/), without there being any substantial loss of hooking stations on the conveyor (Figure 3D).

In the case where the lot of products (V) is to be followed by a lot of products (X) that are to be treated only in the second section 20, it is possible to load the latter onto the conveying system in immediate succession, i.e., in such a way that between the last piece 39 of the second lot (V) and the first piece 61 of the lot (X) there is no substantial loss of hooking stations on the conveying system (Figure 3B). In practice, it is sufficient to leave a number of free positions equal to the number of pieces present on the transferrer 12. When the first piece 61 of the lot (X) is in a position corresponding to the first transferrer 11 upstream of the first section 10, said transferrer 11 is activated and transfers the pieces (X) directly into the second section 20, by-passing the first section 10. In the meantime, the pieces (V) continue to traverse the first section 10 and exit therefrom directly into the third section 30, via the second transferrer 12 (Figure 3C and 3D).

Since the three sections 10, 20, 30 have the same length and house the same number of products, the first piece 61 of the lot (X) will reach the exit of the second section 20 immediately after the last piece 39 of the lot (V) has been transferred from the first section 10 to the third section 30; by de-activating the transferrer 13, the piece 61 then tacks on to the last piece 39 of the lot (V) without there being any substantial loss of hooking stations on the conveyor (Figures 3D and 3E).

A further example of operation of the plant according to the invention will now be described with reference to Figures 4A-4D. Said example regards a production step that envisages treatment of a lot of products, represented by the symbol (/), in the stations 101, 102 of the first section 10, followed by treatment of a lot of products, represented by the symbol (X), in the station 201 of the second section 20, and in the stations 401 and 402 of the fourth section 40.

With reference to Figure 4A, the products (/), loaded on the conveying system via the hooking means in the loading station (not represented in the figure), follow the path of the overhead conveyor in the first and third sections 10 and 30. In this step, the transferrers 11 and 13 are not active, whilst the transferrers 12 and 14 are active and enable transfer of the products (/) respectively from the first section 10 to the third section 30, and from the third section 30 to a point downstream of the fourth section 40, by-passing the second and fourth sections 20, 40. The subsequent lot of products (X), which are to be treated in the second and fourth sections 20 and 40, is loaded in immediate succession, i.e., in such a way that between the last piece 79 of the first lot (/) and the first piece 81 of the lot (X) there is no substantial loss of hooking stations on the conveying system. In practice, it is sufficient to leave a number of positions free equal to the number of pieces present on the transferrers 12 and 14. With reference to Figure 4B, when the first piece 81 of the lot (X) is in a position corresponding to the first transferrer 11 upstream of the first section 10, said transferrer 11 is activated and transfers the pieces (X) directly into the second section 20, by-passing the first section 10. In the meantime, the pieces (/) continue to traverse the first and third sections 10 and 30 and exit therefrom directly downstream of the fourth section 40, via the second and fourth transferrers 12 and 14.

When the first piece 81 of the lot (X) reaches the exit of the second section 20, the third transferrer 13 is activated and enables transfer of the pieces (X) from the second section 20 directly to the fourth section 40. In the meantime, the last piece 79 of the lot (/) has left the first section 10 and is traversing the third section 30 (Figure 4C).

With reference to Figure 4D, since the four sections 10, 20, 30 and 40 have the same length and house the same number of products, the first piece 81 of the lot (X) will reach the exit of the fourth section 40 immediately after the last piece 79 of the lot (/) has been transferred from the third section 30 in a point downstream of the fourth section 40; by de-activating the transferrer 14, the piece 81 of the lot (X) hence tacks on to the last piece 79 of the lot (/), without there being any substantial loss of hooking stations on the conveyor. It may thus be seen how the plant according to the invention enables optimal management of the productivity of the plant. In practice, the overhead conveyor 2 is traversed continuously, throughout its length, by the conveying system. Via the transferrers 11-14, it is possible to transfer the hooking means from one point to the other of the conveying system, by-passing one or more sections. The plant is continuously fed, with a minimum loss of hooking stations, hence maximizing its productivity without having to undergo any slowing down or stoppage at points where the type of treatments that are to be carried out on the products vary. Furthermore, the conveying system is thus made up of a single conveying chain or belt, at the same time maintaining a high flexibility of use and a high production capacity, which cannot be achieved with conventional single-chain systems and which can be achieved only partially, but with higher costs, with double-chain systems.

With reference to Figures 5 and 6, a possible embodiment of a transferrer 11, 12, 13 and 14 to be used in the plant according to the invention will now be described. According to this embodiment, the transferrer comprises a transfer wheel 45, which is sets between a corresponding first segment and a corresponding second segment of the overhead conveyor 2, with the conveying system, constituted by a chain or conveyor belt 3, which moves in mutually opposite directions within each segment, as indicated by the arrows 55. The transferrer further comprises a transfer device 41 designed to transfer said hooking means 4 from said first segment to said transfer wheel 45, and from said transfer wheel 45 to said second segment. Preferably, according to a particular embodiment, the transfer device 41 comprises a first guide 411, actuated by a first piston 421, and a second guide 412, which is fixed. The first guide 411 enables uncoupling of the hooking means 4 from the conveying system 3 in a position corresponding to the first segment and their coupling with the transfer wheel 45, whilst the second guide 412 enables uncoupling of the hooking means 4 from the transfer wheel 45 and their coupling with the conveying system 3 in a position corresponding to the second segment. In particular, said first and second guides 411 and 421 can each comprise a cam surface, which interacts with the hooking means 4 with their consequent displacement from the conveying system 3 to the wheel 45, and vice versa.

The plant according to the invention finds convenient application in industrial painting processes, in which said treatment stations are constituted by one or more paint booths, whether for powder painting or liquid painting, and by corresponding cross-linking/baking stations, using hot air, IR or UV. Other treatment stations can obviously be envisaged, according to the type of product and treatment which must be performed.

The present invention moreover relates to a conveyor, which will be described with reference to the annexed Figures 9 to 15. In particular, the continuous conveyor 5 of products according to the present invention comprises a supporting structure 6 and a chain conveyor 7, which has at least one first branch 7 land one second branch 72, in which said conveyor 7 moves in opposite directions. The conveyor further comprises hooking means 8, which are designed to support said products, and a device 9 for their transfer.

The peculiarity of the conveyor according to the invention lies in the fact that the transfer device 9 is set between said first branch 71 and said second branch 72 (in which the conveyor moves in opposite directions) and comprises first transfer means 91, which are designed to transfer the products from the chain conveyor 7 to said transfer device 9, and second transfer means 92, which are designed to transfer the products from the transfer device 9 to said chain conveyor 7.

Preferably, the conveyor is of an overhead type, i.e., of the type in which the chain conveyor follows a given path at a certain height from the ground, the products hanging from said chain; there are, however, also possible embodiments in which the chain conveyor rests on the ground and the products are suitably supported on said chain.

The transfer device 9 set between the two branches 71 and 72 of the conveyor which move in opposite directions with respect to one another is preferably constituted by a rotary device, preferably of the type comprising a transfer wheel 93 provided with teeth 931 for meshing with said chain conveyor 7.

In the embodiment illustrated in the annexed figures, the hooking means 8 comprise a plurality of supporting plates 85 fixed on said chain conveyor 7, and a plurality of supporting elements

86 fixed with respect to the transfer wheel 93. A plurality of hooking devices 87 is moreover present, which are designed to couple to and uncouple from said supporting plates 85 and said supporting elements 86. With reference to Figures 13-15, said hooking devices 87 preferably comprise a T-shaped element; the horizontal branch 871 of said T-shaped element 87 is designed to couple to and uncouple from corresponding seats 875 present in the supporting plates 85 and corresponding seats 876 present in the supporting elements 86. In practice, the hooking device 87 can be transferred, with modalities that will be described hereinafter, from the supporting plate 85 (fixed with respect to the chain) to the supporting element 86 (fixed to the wheel 93), by releasing one end of the horizontal arm 871 from one of the holes 875 and inserting the other end of the horizontal arm 871 in one of the holes 876. Synchronization of transfer and correspondence in position between the supporting plate 85 and the supporting element 86 at the moment of transfer is guaranteed by the fact that the wheel 93 is always coupled to the chain 7 via the teeth 931.

With reference to Figures 9-12, the transfer means 91 comprise a first mobile guide 911, which is actuated from a first, inactive, position to a second, active, position, whilst the second transfer means 92 comprise a second guide 922, which is fixed. Via appropriate actuation means, formed, for example, by a piston 912, the first guide 911 can be actuated between said first, inactive, position and said second, active, position, in which one of the surfaces 913 of the guide 911 interacts with the vertical branch 872 of the T-shaped element 87. In practice, when the chain is moving and keeping the guide 911 in the position indicated in the aforesaid figures, the vertical arm 872 of the hooking device 87 slides against the cam surface 913 of the guide 911. Said interaction brings about exit of the horizontal arm 871 from the seat 875 in the plate 85 and its insertion into the seat 876 of the supporting element 86 fixed to the wheel 93. In the case where it is not desired to transfer the products from the chain 7 to the wheel 93, it is sufficient to bring the guide 911 back into its inactive position, moving it away from the chain 7.

Preferably, the second guide 922 is fixed and comprises a cam surface 923, which interacts with the vertical branch 872 of the T-shaped element 87 bringing about its release from the seat 876 of said supporting element 86 in which it is located and insertion into a corresponding seat 875 in one of said plates 85 fixed with respect to the chain. In practice, the second guide 922 is fixed and, when the chain is moving, the vertical arm 872 of the hooking device 87 slides against the cam surface 923 of the guide 922. Said interaction brings about exit of the horizontal arm 871 from the seat 876 of the supporting element 86 and its insertion in the seat 856 of the plate 85 fixed with respect to the chain 7. In this way, whenever a product is loaded by the branch 71 of the chain 7 onto the transfer wheel 93 as a result of the action of the guide 911, said product is automatically unloaded onto the branch 72 of the chain 7 as a result of the guide 922. As has been said previously, this is made possible thanks to the synchronization guaranteed by the coupling between the wheel 93 and the chain 7 via the teeth 931. The conveyor 5 according to the invention further comprises actuation means constituted, for example, by electric motors that can be coupled, for example, to the chain 7; in this case, the wheel 93 is driven in motion by the chain itself. Alternatively, the actuation means can be coupled to the wheel 93, and in this case the chain 7 will be driven in motion by the wheel 93. Obviously, also combinations of these two types of solution are possible. The conveyor according to the invention is suited particularly for single-chain conveying systems, but can be conveniently used in double-chain or multiple-chain conveying systems. Likewise, it is possible to configure variants in which the transferrer acts between two or more independent loops of chain, one of which, which can be defined as "primary loop", for example, presides over movement in a limited stretch of the painting plant (for example, loading, pre-treatment, drying, baking and unloading) and the other/others, which can be defined as "secondary loop or loops", ensure movement in other stretches of the same plant, for example, the one for the paint booth or booths. Said configuration proves particularly advantageous, for example, in the cases where the painting step requires rotations (of the product to be painted) that are not required in any other part of the plant. This type of rotations is generally obtained using rotary hooks, which are complex and delicate mechanical objects with a cost that is certainly higher than that of ordinary non-rotating hooks. In the configuration mentioned above, unlike what is so far known and used, it is possible to limit the use of the rotary hooks just to secondary loops. In said way, in addition to the obvious saving due to use of a far smaller number of rotary hooks, the life of the few rotary hooks used will be prolonged because these will not undergo continuous chemical attack (in the pre-treatment steps) nor repeated thermal stresses (in the drying and baking steps) to no purpose. In the case where the products are of relatively large overall dimensions, instead of using a transfer wheel having an excessively large diameter, it is possible to use two or more transfer wheels appropriately arranged and associated to one another.

The conveyor according to the invention finds convenient application in plants of various types, in particular in continuous paint plants. Plants comprising one or more conveyors 5 as described previously constitute a further aspect of the present invention. On the basis of the foregoing description, other characteristics, modifications or improvements are possible and evident to the average person skilled in the branch. Said characteristics, modifications and improvements are hence to be considered as forming part of the present invention. In practice, the materials used, as well as the contingent dimensions and shapes, may be any whatsoever according to the requirements and the state of the art.

Claims

1. A plant (1) for surface treatment of products comprising: a continuous overhead conveyor (2) having a conveying system (3); a loading station, an unloading station and one or more treatment stations (101, 102; 201, 202, 203; 401, 402) for said products; and hooking means (4), designed to couple with said conveying system (3) and to support said products, said plant being characterized in that the continuous overhead conveyor (2) comprises at least one first section and one second section (10, 20) in which said conveying system (3) traverses a substantially loop-shaped path, and at least one first transferrer (11) and one second transferrer (12) for transferring said hooking means (4), the first transferrer (11) being positioned upstream of said first section (10) and upstream of said second section (20) and being designed to transfer said hooking means (4) from a position upstream of said first section (10) to said second section (20), the second transferrer (12) being positioned downstream of the first section (10) and downstream of the second section (20) and being designed to transfer said hooking means (4) from said first section (10) to a position downstream of said second section (20).

2. The plant (1) according to Claim 1, characterized in that said first and second transferrers (11, 12) are set between two segments of the overhead conveyor (2), in which said conveying system (3) moves in opposite directions.

3. The plant (1) according to Claim 1 or Claim 2, characterized in that the continuous overhead conveyor (2) comprises at least one first section (10), one second section (20), and one third section (30) in which said conveying system (3) traverses a substantially loop-shaped path, and at least one first transferrer (11), one second transferrer (12), and one third transferrer (13) for transferring said hooking means (4), the first transferrer (11) being positioned upstream of said first section (10) and upstream of said second section (20) and being designed to transfer said hooking means (4) from a position upstream of said first section (10) to said second section (20), the second transferrer (12) being positioned downstream of the first section (10) and upstream of the third section (30) and being designed to transfer said hooking means (4) from said first section (10) to said third section (30), the third transferrer (13) being positioned downstream of the second section (20) and downstream of the third section (30) and being designed to transfer said hooking means (4) from said second section (20) to a position downstream of said third section (30).

4. The plant (1) according to Claim 3, characterized in that said first section (10), second section (20), and third section (30) have substantially the same length.

5. The plant (1) according to one or more of the preceding claims, characterized in that it comprises at least one treatment station (101) in said first section (10) and at least one treatment station (201) in said second section (20).

6. The plant (1) according to Claim 3, characterized in that the overhead conveyor (2) comprises a fourth section (40) in which said conveying system (3) traverses a substantially loop-shaped path, and a fourth transferrer (14) for transferring said hooking means (4), which is positioned downstream of said third section (30) and downstream of said fourth section (40) and is designed to transfer the hooking means (4) from the third section (30) to a position downstream of the fourth section (40).

7. The plant (1) according to Claim 6, characterized in that the overhead conveyor (2) comprises further sections in which said conveying system (3) traverses a substantially loop-shaped path, and corresponding further transferrers for transferring said hooking means.

8. The plant (1) according to one or more of Claims 3 to 7, characterized in that at least one of said sections (30) of said conveyor functions as storage unit or buffer of said conveying system (3).

9. The plant (1) according to one or more of Claims 3 to 8, characterized in that each of said transferrers (11, 12, 13, 14) is set between a corresponding first segment and a corresponding second segment of the overhead conveyor (2), the motion of the conveying system (3) occurring in the first segment in a direction opposite to the motion in the corresponding second segment.

10. The plant (1) according to Claim 9, characterized in that said transferrers (11, 12, 13, 14) comprise a transfer wheel (45), set between a corresponding first segment and a corresponding second segment of the overhead conveyor (2), and a transfer device (41), designed to transfer said hooking means (4) from said first segment to said transfer wheel (45) and from said transfer wheel (45) to said second segment.

11. The plant (1) according to Claim 9, characterized in that said transfer device (41) comprises a first guide (411), actuated by a first piston (421), and a second guide, which is fixed, the first guide (411) enabling uncoupling of the hooking means (4) from the conveying system (3) in a position corresponding to the first segment and their coupling with the transfer wheel (45), the second guide (412) enabling uncoupling of the hooking means (4) from the transfer wheel (45) and their coupling with the conveying system (3) in a position corresponding to the second segment.

12. The plant (1) according to Claim 11, characterized in that said first and second guides (411, 421) each comprise a cam surface that interacts with the hooking means (4).

13. The plant (1) according to one or more of the preceding claims, characterized in that said conveying system (3) comprises a single conveyor belt or chain.

14. The plant (1) according to one or more of the preceding claims, characterized in that it comprises a first painting station (101) and a second painting station (201) positioned in two different sections of said overhead conveyor (2).

15. A continuous conveyor (5) of products comprising: a supporting structure (6); a chain conveyor (7) having at least one first branch (71) and one second branch (72), in which said conveyor (7) moves in opposite directions; hooking means (8) for hooking said products; and a transfer device (9) for transfer of said products, said conveyor being characterized in that said transfer device (9) is set between said first branch (71) and said second branch (72) and comprises first transfer means (91), designed to transfer the products from the chain conveyor (7) to said transfer device (9), and second transfer means (92), designed to transfer the products from the transfer device (9) to said chain conveyor (7).

16. The conveyor (5) according to Claim 15, characterized in that said transfer device (9) comprises a transfer wheel (93) provided with teeth (931) for meshing with said chain conveyor (7).

17. The conveyor (5) according to Claim 16, characterized in that said hooking means (8) comprise a plurality of supporting plates (85) fixed with respect to said chain conveyor (7), a plurality of supporting elements (86) fixed with respect to said transfer wheel (93) and a plurality of hooking devices (87), designed to couple to and uncouple from said supporting plates (85) and said supporting elements (86).

18. The conveyor (5) according to Claim 16, characterized in that said hooking devices (87) comprise a T-shaped element, the horizontal branch (871) of said T-shaped element (87) being designed to couple to and uncouple from corresponding seats (875, 876) present in said supporting plates (85) and in said supporting elements (86).

19. The conveyor (5) according to one or more of Claims 15 to 18, characterized in that said first transfer means (91) comprise a first mobile guide (911), which can be actuated from a first, inactive, position to a second, active, position, and said second transfer means (92) comprise a second guide (922), which is fixed.

20. The conveyor (5) according to Claim 19, characterized in that said first guide (911) is actuated via a piston (912) between said first, inactive, position and said second, active, position, in which one of the surfaces (913) of said guide (911) interacts with the vertical branch (872) of said T-shaped element (87), bringing about its release from a corresponding seat (875) in said plate (85), which is fixed with respect to the chain and insertion in a corresponding seat (876) in said supporting element (86), which is fixed with respect to said transfer wheel (93).

21. The conveyor (5) according to Claim 19 or Claim 20, characterized in that said second guide (922) comprises a cam surface (923), which interacts with the vertical branch (872) of said T-shaped element (87), bringing about its release from a corresponding seat (876) in said supporting element (86), which is fixed with respect to said transfer wheel (93) and insertion into a corresponding seat (875) in said plate (85), which is fixed with respect to the chain.

22. The conveyor (5) according to one or more of Claims 15 to 21, characterized in that it comprises actuation means coupled to said chain, said transfer device (9) being driven in motion by said chain.

23. The conveyor (5) according to one or more of Claims 15 to 21, characterized in that it comprises actuation means coupled to said transfer device (9), said chain being driven in motion by said transfer device (9).

24. The conveyor (5) according to one or more of Claims 15 to 23, characterized in that said conveyor is a single-chain conveyor.

25. The conveyor (5) according to one or more of Claims 15 to 23, characterized in that said conveyor is a double-chain or multiple-chain conveyor.

26. A plant comprising a conveyor (5) according to one or more of Claims 15 to 25.

27. The plant according to Claim 26, characterized in that it comprises at least one first chain loop, associated to which are non-rotary hooking means, and at least one second chain loop, associated to which are rotary hooking means.