EP2803420A2

EP2803420A2 - Improved booth for powder coating articles.

Info

Publication number: EP2803420A2
Application number: EP14165777.5A
Authority: EP
Inventors: Dario Amedeo ZUCCHETTI; Giovanni Giardini
Original assignee: Trasmetal SpA
Current assignee: Trasmetal SpA
Priority date: 2013-04-24
Filing date: 2014-04-24
Publication date: 2014-11-19
Also published as: ITBG20130015U1; EP2803420A3

Abstract

A booth (100) for powder coating articles (20), comprising:
- a supporting structure (105),
- one or more lateral walls (110, 120, 130) defining an interior (140) of the booth (100),
- a front wall (101) from which powder coating dispensing means (160, 170) face the interior (140) of the booth (100),
- suction means (210, 220) for drawing air from the interior (140) of the booth (100),
- overhead conveyor means (300) positioned in the upper part of the booth (100) and adapted to convey the articles (20) to be coated into the interior (140) of the booth (100), and
- air blowing means (500) positioned in the upper part of the booth (100).

Description

The present invention relates to a booth for powder coating articles and to a system for powder coating articles that uses this booth. In particular, the present invention relates to a booth for powder coating particularly tall parts, such as aluminum profiles hanging vertically from an overhead conveyor that moves them through said booth.
As is known, in order to powder coat particularly tall parts, such as aluminum profiles positioned vertically, there are commonly used booths characterized by lateral walls that extend vertically, generally consisting of sheets closed in to loop. With reference to the attached Figs. 1 and 2, which show an example of a prior art booth 1, each loop is normally rotated, continuously or more preferably with a reciprocating motion, between two rollers positioned in proximity of the base and of the upper end of the booth. This rotation allows the application of suction systems to each sheet/wall, capable of removing the excess powder emitted by powder emitting devices, for example discs or electrostatic guns and which does not reach the parts to be coated (overspray).
In this way, on the one hand the excess powder is conveyed into specific cyclones that recover it and return it into circulation, and on the other the walls are suitably cleaned in a completely automatic manner.
This is particularly advantageous and economical considering that the height of the walls makes manual cleaning difficult. In the case of aluminum profiles, which are normally marketed in lengths in the order of 6-7 meters, the standard height of a wall is in fact around 9 meters, with considerable complications in relation to access to clean the full height.
The base of booths is also often produced by reproducing the same technique used for the lateral walls horizontally, i.e. using one or more sheets that can be cleaned automatically. Therefore, a typical booth with electrostatic powder spray guns for the vertical coating of profiles normally consists of a movable base sheet and two or more movable vertical sheets. In the case of two vertical walls, the booth will have a triangular floor plan, while in the case of three walls the booth will have a square, rectangular or trapezoidal floor plan. In the example represented in Figs. 1 and 2, the booth consists of three lateral walls 11, 12 and 13. In any case, one side of the booth (in the example of Fig. 1 and 2, side 10) is normally left open and forms the front wall from which the spray guns face the inside of the booth.
At the join between the walls there is normally positioned one or more vertical suction ducts (in the example in Figs. 1 and 2, the ducts 21 and 22) connected to a cyclone 23 for collection of the powders. On the open side 10 of the booth, i.e. on the side without the movable sheet, there is positioned a reciprocator 15 on which there are mounted numerous spray guns (for example even in excess of twenty-four) normally arranged in two banks 16 and 17, one on the left and one on the right of the reciprocator 15. Each bank normally consists of two or more rows of spray guns positioned one above the other, all oriented toward the parts 20 to be coated.
An overhead conveyor 30, on which transferable rotating hooks are hung, travels between the spray guns and the walls. The ability to transfer the hook is necessary as coating systems often have more than one coating booth, and therefore the parts to be coated must be sent alternatively to one or other booth. Perforated plates are normally fixed under the rotating hooks, on which the parts 30 to be coated are hung using metal hooks.
The overhead conveyor, with the parts hanging as described above, enters the booth from one end of the open side at the side of a bank of spray guns, and proceeds for a length toward the opposite wall or, in the case of triangular booths, toward the angle opposite the spray guns, until reaching the optimal distance for application with respect to the nozzles of the spray guns.
At this point, the conveyor curves so that the parts travel for a length of linear path in front of the first bank of spray guns which, moved from top to bottom and vice versa by the reciprocator, coat the face of the parts exposed thereto. After exposure to the first bank of spray guns, the hooks are rotated so that the face still to be coated is exposed to the second bank.
The conveyor continues its linear travel to the end of exposure to the second bank and then curves to reach the exit at the end opposite the open side at the side of the second bank of spray guns.
The prior art booths described above, although widely used to date, have numerous problems and drawbacks.
A typical problem is represented by the stack effect generated inside the booth.
Given the considerable height of these booths and the natural tendency for thermal stratification inside, a noteworthy stack effect occurs therein, i.e. a rising current of electrostatically charged powder that deposits on and soils the metal structures of the upper part.
The presence of the overhead conveyor at the top precludes the possibility of producing a roof with the same technique used for the walls and for the base. In fact, in this case a hypothetical movable top sheet could not be placed over the conveyor which, as it is necessarily made of metal, would catalyze all the overspray, making cleaning of the movable sheet pointless. Moreover, the use of a fixed roof would add a further problem to the above, as it would become soiled and could not be automatically cleaned.
For these reasons, in the prior art booths described above, the roof almost always consists of a simple metal grille to which the conveyor is fastened. In this way, the stack effect is not contained and the conveyor catalyzes only a part of the overspray. Unfortunately, the rest of the overspray, besides accumulating on the grille and on the conveyor, escapes into the production department with consequent health and safety problems for operators. Moreover, accumulations on the grille and on the conveyor, which consist of powders of different colors, periodically and unpredictably drop into the booth, contaminating the parts below.
A further problem of prior art booths is represented by the fact that the rotating hooks, just as the conveyor, also tend to become soiled with powder.
As mentioned above, they are normally transferable from one conveyor (for example the general conveyor of the coating system) to another (for example a secondary loop dedicated to a specific coating booth). After returning to the main conveyor they end up in the same oven used for polymerization of the powder on the parts to be coated. Inevitably, the powder that has deposited on the hooks also polymerizes, in this way causing serious malfunctions of these hooks over time. The same problem of polymerization of the powder deposited also occurs for the conveyor, if the booth is served directly by the main conveyor.
Moreover, when the rotating hooks travel through the whole system, including the loading and unloading areas, a further drawback is represented by the possibility of random axial coupling not always in the optimal position for coating.
Further, the rotating hook permits a certain degree of freedom of the articles hanging therefrom, so that with parts of considerable length and in other sections of the system, for example inside the treatment tunnel and under the effect of the spray jets, despite optional upper guides, the part tends to rotate with the risk of becoming jammed between the ramps and/or fixed parts of the system.
Yet another problem derives from the need to maintain a concentration of powders below a given value inside the booth.
The efficiency and safety of a coating booth are closely linked to the velocity at which the suction system moves the air inside the same booth.
From the viewpoint of safety, it is essential that the velocity at which air is fed into the booth is not below that capable of maintaining a concentration of powder equivalent to a fraction of the lower explosion limit (L.E.L). From the viewpoint of efficiency, it is important for the air velocity to be high enough to prevent powder from escaping from the booth but not so high as to limit application efficiency.
In prior art booths, the air velocity is in general basically lower that desirable unless said booths are equipped with considerably oversized suction systems, which result in increased installation and running costs of the system.
Another problem encountered in prior art booths is represented by the accumulation of powder inside the cyclone.
During operation of the booth, all the overspray travels through the cyclone and a high percentage thereof is collected and recovered. Practically all the traveling powder is removed, but a minimum percentage remains adhering to the inner surfaces of the cyclone and this is not compatible with the requirements of cleanliness necessary for color changes.
Various systems have been applied to perform cleaning which, although effective, have not solved the problem relating to cleaning the accumulation of powder on the outer surface of the central truncated cone of the cyclone, necessary for delivery of the air.
Therefore, it is evident that prior art booths have a certain number of drawbacks.
An object of the present invention is therefore to provide a booth for powder coating articles that overcomes the problems and drawbacks of prior art booths.
In particular, an object of the present invention is to provide a booth for powder coating articles that prevents problems related to the deposition of powders on the structure of the booth and/or on the conveyor system.
A further object of the present invention to provide a booth for powder coating articles that prevents or reduces to a minimum the escape of powders into the environment surrounding the booth.
Yet another object of the present invention is to provide a booth for powder coating articles that optimizes the supply speed and movement of the air in the booth, without oversizing of the suction equipment.
One more object of the present invention is to provide a booth and a system for powder coating articles that solves problems linked to deposition and polymerization of the powder on the rotating hooks and on the conveyor.
A further object of the present invention is to provide a booth for powder coating articles which prevents the phenomena of deposition and accumulation of powder in the separator cyclones making resulting in the need to clean these cyclones.
One more object of the present invention is to provide a booth for powder coating articles that is easy to install and has competitive production and running costs.
The aforesaid and other objects and advantages of the invention, which will be apparent from the following description, are achieved with a booth for powder coating articles, characterized in that it comprises:

a supporting structure,
one or more lateral walls defining an interior of said booth,
a front wall from which dispensing means of powder coating face said interior of said booth,
suction means for drawing air from said interior of said booth,
overhead conveyor means positioned in the upper part of said booth and adapted to convey the articles to be coated in the interior of said booth,
air blowing means positioned in the upper part of said booth.

In this way, through the air blowing means, air is introduced into the upper part of the booth, thereby creating a sort of air cushion that pushes the cloud of powder downward and keeps it there, preventing the upper part of the booth from being soiled or the powder from escaping therefrom.
In other words, due to the presence of the air blowing means, the stack effect, which is the main cause of powder rising inside of the booth, is opposed without upsetting the coating process below.
According to a preferred embodiment of the booth for powder coating articles according to the present invention, said air blowing means comprise one or more pressurized chambers, which are operatively connected to an air supply system and which face the interior of said booth from above. Said one or more pressurized chambers advantageously have an interface wall facing the inside of said booth which is at least partially porous and which allows air to flow from the pressurized chamber(s) toward the inside of said booth.
For the objects of the present invention, the term "porous" is intended as the capacity of a wall (or more generally of a separator baffle) to allow air to flow through it.
By way of example, a microperforated metal sheet has the properties of porosity required by the present invention. Other materials/structures, such as porous baffles of various types, can in any case be used, provided that the air passage requirements are complied with. Advantageously, said air blowing means convey into said booth an amount of air adapted to oppose rising of the powder coating into the upper part of said booth. In other words, by appropriately dosing the amount of air that is sent into the booth it is possible to create a curtain that blocks rising of the powder without interfering with the spray coating operations. A preferred embodiment of the booth for powder coating articles according to the present invention, provides for positioning of said overhead conveyor means above said air blowing means. In this way, it is possible to prevent these from becoming soiled due to rising and deposition of the powder thereon.
Advantageously, said overhead conveyor means can be positioned in a housing produced inside of said one or more chambers. In this case, the lateral walls of said housing are preferably at least partially porous and allow air to flow from said one or more pressurized chambers toward said overhead conveyor means. In this way, also the overhead conveyor means can benefit from the pressurization condition determined by the blowing means.
A particular embodiment of the booth for powder coating articles according to the present invention provides for the presence of a covering in plastic material positioned above said overhead conveyor means. Therefore, the powder is prevented from escaping from the booth due to the presence of this covering. Moreover, in this case, said air blowing means comprise a plurality of nozzles that are adapted to send, for example, after receiving predefined commands, jets of air toward said covering in plastic material, preventing the accumulation of powder and thus ensuring cleanliness of the booth.
In a further aspect thereof, the present invention also relates to a booth for powder coating articles, characterized in that it comprises:

a supporting structure,
one or more lateral walls defining an interior of said booth,
a front wall from which dispensing means of powder coating face said interior of said booth,
suction means for drawing air from said interior of said booth,
overhead conveyor means positioned in the upper part of said booth and adapted to convey the articles to be coated into the interior of said booth,
means for at least partially closing said front wall of said powder coating dispensing means.

In this way, by limiting the open areas of the booth to a minimum, it is possible to determine a remarkable increase in the air velocity.
This solution is extremely effective as it prevents the escape of the overspray powder from the front without upsetting the efficiency of the electrostatic coating, also increasing the installation safety margins.
Advantageously, said means for at least partially closing said front wall comprise at least one wall that surrounds said powder coating dispensing means on the opposite side with respect to said front wall.
For example, said means for at least partially closing said front wall can comprise a back wall and a first and a second lateral wall that surround said powder coating dispensing means on the opposite side with respect to said front wall.
Moreover, to further improve the efficacy of the action to increase the air velocity, said means for at least partially closing said front wall can also comprise an upper wall of said powder coating dispensing means.
In practice, this solution can be produced by positioning in the back part, on the sides and, if required, also at the top of the powder coating dispensing means, a casing that determines a reduction of the open part of the booth to only the inlet and outlet for the parts, so as to considerably increase the air velocity given the same size of suction equipment.
A further aspect of the present invention relates to a cyclone for separating powders from a gaseous flow, characterized in that it comprises:

a suction section for inflow of a gaseous flow containing powders,
a first central cone operatively connected to said inflow suction section,
a second central truncated cone comprising a section for outflow of said gaseous flow,
means for closing said inflow suction section,
means for supplying air or other gaseous fluid to the outer surface of said second truncated cone movable between a closed position and an open position,
the lower end of said first central cone being movable between a closed position and an open position.

In this way, as better described below, it is possible to create a high velocity current of air, tangential to the inner cone of the cyclone, which in particular allows cleaning of the outer surface of the central truncated cone and, more generally, all the surfaces on which the powder deposits.
A further aspect of the present invention relates to a system for powder coating articles, characterized in that it comprises:

a booth for powder coating articles;
a first overhead conveyor for movement of said articles in said system;
a second overhead conveyor serving said booth for powder coating;
said first overhead conveyor comprising first hooks associable with supporting plates of said articles;
said second overhead conveyor comprising second rotating hooks associable with said supporting plates of said articles;
said supporting plates of said articles being transferable between said first hooks of said first overhead conveyor and said second rotating hooks of said second overhead conveyor, and vice versa;
said system comprising first and second transfer means, positioned upstream and downstream of said booth, to transfer said supporting plates of said articles between said first hooks of said first overhead conveyor and said second rotating hooks of said second overhead conveyor, and vice versa.

In this way, it is possible to prevent the powder that tends to soil the rotating hooks and/or the conveyor from being polymerized, thus causing serious malfunctions to rotation of the same hooks.
In practice, in the system according to the present invention, this can be achieved by serving each booth with a loop of a secondary overhead conveyor that receives the parts from the main overhead conveyor of the system by transfer upstream of the booth and returns them to the same main overhead conveyor immediately downstream of the booth.
Contrary to the prior art, in the system according to the present invention, instead of transferring the whole rotating hook from the main overhead conveyor to the secondary conveyors serving each booth, only the fixed part below is transferred, i.e. only the perforated plate to which the articles to be coated are hung by means of specific hangers.
Each secondary overhead conveyor is thus equipped with its own rotating hooks that receive, through a transfer device positioned upstream of the booth, the perforated plates with the articles and after coating return them to the main overhead conveyor.
In this way, as the rotating part of the hooks, even if soiled with powder, never enters the polymerization oven, it is not subject to the aforesaid problems and malfunctions. Moreover, using a main overhead conveyor provided with hooks that do not rotate along the whole of the system and using rotating hooks only where necessary (i.e. in the coating booth), it is possible to hook the parts in an unequivocal position adequate for the coating system already at the time of loading. With this solution the risk of becoming jammed along the path of the conveyor is also eliminated.
Further characteristics and advantages of the present invention will be more apparent from the description of the preferred embodiment, illustrated by way of non-limiting example in the accompanying figures, wherein:

Fig. 1 is a side view of a prior art booth for powder coating articles;
Fig. 2 is a plan view of the booth of Fig. 1;
Fig. 3 is a side view of an embodiment of a booth for powder coating articles according to the present invention;
Fig. 4 is a view of a detail of the upper part of the booth of Fig. 3;
Fig. 5 is a plan view of the booth of Fig. 3;
Fig. 6a is a side view of an embodiment of cyclone separator according to the present invention, in operating condition;
Fig. 6b is a view of a detail of the cyclone of Fig. 6a;
Fig. 7a is a side view of an embodiment of separator cyclone according to the present invention, in cleaning condition;
Fig. 7b is a view of a detail of the cyclone of Fig. 7a;
Fig. 8 is a detail of an embodiment of an overhead conveyor system used in a system according to the present invention.

With reference to Figs. 3 to 5, in its most general embodiment, a booth 100 for powder coating articles 20 according to the present invention comprises a support structure 105 and one or more lateral walls defining an interior 140. In the embodiment illustrated, the booth 100 has a trapezoidal plan and comprises three lateral walls 110, 120, 130 defining the interior 140 of said booth 100 in which the operation to coat the articles 20 takes place.
A fourth side is left open and forms the front wall 101 from which powder coating dispensing means face the interior 140 of the booth 100.
In particular, in the case illustrate in Figs. 3-5, on the open side 101 of the booth there is placed a reciprocator 150, on which there are mounted two banks of spray guns 160 and 170, respectively one on the left and one on the right of the reciprocator 150. In this case, each bank 160, 170 consists of several rows of spray guns positioned one above the other, all oriented toward the parts 20 to be coated.
The booth 100 according to the present invention also comprises suction means 210, 220 for drawing air from the interior 140 of the booth 100, consisting of suction manifolds positioned respectively at the join between the walls 110,120 and 120,130. These suction ducts 210 and 220 are connected to a cyclone 230 for powder collection.
The booth 100 according to the present invention is also provided with overhead conveyor means 300, for example a rail conveyor, positioned in the upper part of said booth 100. These overhead conveyor means 300 are adapted to support the articles 20 to be coated, for example aluminum profiles, vertically hung from these through appropriate supporting means, and to convey them into the interior 140 of said booth 100.
In the embodiment illustrated in the aforesaid Figs. 3-5, the overhead conveyor 300, with the articles 20 hung for example through suitable rotating hooks, enters the booth 300 from one end of the open side 101 positioned between the bank of spray guns 160 and the lateral wall 110. Inside the booth 100, the overhead conveyor 300 proceeds for a stretch toward the wall 120, opposite the open wall 101, until reaching an optimal operating distance with respect to the dispensing spray guns.
At this point the overhead conveyor 300 curves so as to convey the articles 20 for a stretch of linear path in front of the first bank of spray guns 160, which, moved with reciprocating motion from top to bottom by the reciprocator 150, coats the face of the articles 20 exposed thereto. After exposure to the first bank of spray guns 160 the hooks are made to rotate in a known way so as to expose the face still to be coated to the second bank 170.
The overhead conveyor 300 then continues its linear travel until the end of exposure to the second bank of spray guns 170, and then curves to move toward the exit of the booth positioned at the end of the open side 101 between the bank of spray guns 170 and the lateral wall 130.
One of the main features of the booth 100 according to the present invention is represented by the fact that it comprises air blowing means 500 positioned in the upper part of said booth 100.
In this way, it is possible to generate an air "cushion" in the upper part of the booth 100, so as to oppose the stack effect that is generated therein, preventing or reducing to a minimum deposition of powder coating on the upper part of the structure and/or on the overhead conveyor means, and the escape of powder coating from the booth 100 into the surrounding work environment.
In other words, the air blowing means 500 convey into said booth 100 and in the upper portion thereof an amount of air adapted to oppose rising of the powder coating into the upper part of said booth 100.
With particular reference to the Fig. 4, said air blowing means 500 comprise one or more pressurized chambers 501, operatively connected to an air supply system, and which face the interior 140 of said booth 100 from above.
The pressurized chamber (or chambers) 501 have an interface wall 502 facing the inside 140 of said booth 100; this interface wall 502 is at least partially porous and allows air to flow from the pressurized chamber 501 toward the interior 140 of the coating booth 100. Advantageously, the interface wall 502 is produced at least partially with a microperforated metal sheet or with a porous baffle or with other equivalent materials from the viewpoint of permeability to air.
In other words, in the booth according to the present invention there is produced a horizontal plenum, consisting of a series of closed ducts in the part facing the inside of the booth 100, or of equivalent materials (for example, microperforated metal sheets and the like). Air is blown into the ducts and exits from the porous baffle to create a sort of air cushion that pushes the cloud of powder coating downward, preventing the upper part of the booth 100 and the devices contained therein (for example the overhead conveyor 300) from being soiled and opposing the stack effect without upsetting the coating process below
Preferably, the overhead conveyor means 300 are positioned above said air blowing means 500, in order to prevent the powder coating rising inside the booth 100 from reaching them and being deposited thereon.
In particular, with reference to Figs. 3-5, said overhead conveyor means 300 can be positioned in a housing 305 obtained inside said one or more pressurized chambers 501.
In this case, the lateral walls of said housing 305 are at least partially porous and allow air to flow from said one or more pressurized chambers 501 toward said overhead conveyor means 300. In this way, the overhead conveyor means 300 and at least part of the rotating hooks fixed thereto can benefit from the pressurization condition determined by the air cushion created by the air blowing means 500. A solution of this kind prevents powder from escaping from the upper part of the booth 100, ensuring that both the ceiling thereof and the overhead conveyor means 300 are not soiled by the powder coating and decreases the open part of the booth 100 so as to increase in the air velocity therein.
An alternative embodiment of the booth 100 for powder coating articles 20 according to the present invention, not shown in the accompanying figures, provides for the presence of a covering in plastic material positioned above said overhead conveyor means 300. In this case, the air blowing means can, for example, comprise a plurality of nozzles, air blades or similar devices, adapted to send, after receiving predefined commands, jets of air toward said covering in plastic material so as to perform cleaning thereof and prevent the accumulation of powder coating thereon.
In a particular aspect thereof, the booth 100 for powder coating articles 20 according to the present invention can comprise, in place of or in addition to the air blowing means 500 positioned in the upper part thereof, means 600 for at least partially closing the front wall 101 of said powder coating dispensing means.
In other words, according to this embodiment, it is possible to limit the open area of the booth 100 to a minimum, so as to determine a remarkable increase in the air velocity therein. In this way, most of the powder dispersed not used for coating is directed toward the suction ducts 210, 220, preventing it from being drawn upward and escaping from the front part 101, or reducing this, as a result of the stack effect. In particular, said means 600 for at least partially closing said front wall 101 can comprise at least one wall that surrounds said powder coating dispensing means on the opposite side with respect to said front wall 101.
Preferably, said means 600 for at least partially closing said front wall 101 comprise a back wall 601 and a first 602 and a second 603 lateral wall that surround said powder coating dispensing means on the opposite side with respect to said front wall 101.
Advantageously, said means 600 for at least partially closing said front wall 101 can also comprise an upper wall 604 of said powder coating dispensing means.
In practice, this embodiment can be implemented by positioning in the back part, on the sides and, if necessary, also at the top of the reciprocator 150, a casing that determines limiting the open wall 101 of the booth 100 only to the inlet and outlet for the parts, so as to considerably increase the air velocity given the same size of suction equipment.
A particularly advantageous embodiment of the booth 100 for powder coating articles 20 according to the present invention provides for the simultaneous presence of air blowing means 500 positioned in the upper part thereof and of means 600 for at least partially closing the front wall 101 of the powder coating dispensing means.
In this embodiment the beneficial effects of opposing the stack effect and of increasing the air velocity inside the booth 100 are fully exploited and synergically strengthened, with considerable advantages in terms of containing the powder coating therein and solving the problems of soiling the upper part of the booth and of the devices contained therein.
In this case, the specific and preferred solutions of the air blowing means 500 and of the means 600 for at least partially closing the front wall 101, described above, can also be advantageously applied to this combined embodiment.
With reference to Figs. 6a, 6b, 7a, and 7b, there will now be described an embodiment of a cyclone for separating powders from a gaseous flow according to the present invention. In the aforesaid figures, the cyclone according to the present invention is illustrated in operating conditions (Figs. 6a, 6b) and in cleaning conditions (Figs. 7a, 7b).
In its most general embodiment, the cyclone 8 for separating powders according to the present invention comprises a suction section 81 for inflow of a gaseous flow 810 containing powders. The cyclone 8 also comprises a first central cone 82 which is operatively connected to said inflow suction section 81 and a second central truncated cone 83 comprising a section 830 for outflow of said gaseous flow 810.
One of the peculiar features of the cyclone 8 according to the present invention is represented by the fact that it comprises means 811 for closing said inflow suction section 81.
Another peculiar feature is represented by the presence of means 84 for supplying air or another gaseous fluid to the outer surface 831 of said second truncated cone 83. The means 84 for supplying air or another gaseous are movable between a closed position and an open position, according to an operating principle explained in more detail below.
Moreover, in the cyclone 8 according to the present invention, the lower end 821 of said first central cone 82 is movable between a closed position and an open position.
With reference to the aforesaid figures, operation of the cyclone 8 according to the present invention is as follows.
In operating conditions (Figs. 6a, 6b), the means 811 for closing the inflow suction section 81 are open, while the means 84 for supplying air or another gaseous fluid to the outer surface 831 of said second truncated cone 83 are closed, and the lower end 821 of the first central cone 82 is also in closed position. In these conditions, the cyclone 8 according to the present invention operates in the same was as a conventional cyclone, with the gaseous flow 810 containing powder entering from the suction section 81 and exiting substantially powder free from the outflow section 830.
In cleaning conditions (Figs. 7a, 7b), the means 811 for closing the inflow suction section 81 are instead closed, while the means 84 for supplying air or another gaseous fluid to the outer surface 831 of said second truncated cone 83 are open, and the lower end 821 of the first central cone 82 is also in open position.
In these conditions there is no inflow of gaseous flow 810 containing powders from the suction section 81. Maintaining suction through the outflow section 830 active, an inflow of air or other gas is created through the supply means 84 and the open lower part of the first central cone 82. This flow of air or other gas is substantially tangential to the surfaces to be cleaned, in particular to the outer surface 831 of the second truncated cone 83, thus allowing them to be cleaned automatically.
As can be noted, thanks to the solutions described it is possible to achieve, rapidly and substantially automatically, complete cleaning of the inside of the cyclone.
From a practical viewpoint, the means 811 for closing said inflow suction section 81 can be of conventional type, for example a shut-off valve or damper.
Preferably, said means 84 for supplying air or another gaseous fluid to the outer surface 831 of said second truncated cone 83 comprise, for example, one or more calibrated passages 841 positioned in the upper portion 832 of said second truncated cone 83.
Advantageously, said one or more calibrated passages 841 are operatively associated, for example, with corresponding dampers 842 for opening/closing said calibrated passages 841, said dampers 842 being activated by actuator means 843, such as actuator pistons or similar devices.
Finally, the movement of the lower end 821 of said first central cone 82 between a closed position and an open position can advantageously be produced, for example, by pivoting said lower end 821 of the first central cone 82 on the central part 822 of said first central cone 82. Naturally, other solutions that allow the movement thereof are possible.
Although the cyclone 8 according to the present invention can conveniently be applied to the coating booths 100 described previously, it can also be used advantageously in other applications, both for coating and in other technological sectors.
With reference in particular to Figs. 5 and 8, an embodiment of a system for powder coating articles according to the present format will now be described.
In its most general embodiment, the system for powder coating articles 20 according to the present invention comprises a booth 100 for powder coating said articles 20. Said booth 100 can be of the type described previously, but also of different type.
The system for powder coating according to the present invention also comprises a first overhead conveyor 90 for moving said articles 20 in said system. A second overhead conveyor 300 instead specifically serves said booth 100 for powder coating.
Said first overhead conveyor 90 advantageously comprises first hooks 91 associable with supporting plates 900 of said articles 20.
In turn, the second overhead conveyor 300 advantageously comprises second rotating hooks 92 associable with said supporting plates 900 of said articles 20.
One of the peculiar features of the system for powder coating according to the present invention is represented by the fact that the supporting plates 900 of said articles 20 can be transferred between said first hooks 91 of said first overhead conveyor 90 and said second rotating hooks 92 of said second overhead conveyor 300, and vice versa.
For this purpose, the system advantageously comprises first 301 and second 302 transfer means, positioned upstream and downstream of said booth 100, and which allow the transfer of the supporting plates 900 of the articles 20 between the first hooks 91 of said first overhead conveyor 90 and the second rotating hooks 92 of said second overhead conveyor 300, and vice versa.
In this way, the rotating hooks are only present in the coating booth 100 and do not enter the polymerization ovens located downstream of the booth.
Preferably, said first hooks 91 comprise first coupling means 911 of said supporting plates 900, while said second rotating hooks 92 comprise a rotating ring nut 920 associated with second coupling means 921 of said supporting plates 900.
In this case, said supporting plates 900 preferably comprise third coupling means 903 associable with said first 911 and second 921 coupling means.
In a specific embodiment of the system according to the present invention, said first 911 and second 921 coupling means are substantially the same as one another and comprise a hollow body 950 with an inlet groove 951.
In this case, the third coupling means 903 comprise a shuttle 931 adapted to slide inside said hollow body 950 through said inlet groove 951.
Naturally, other solutions are also possible that allow transfer of the supporting plate of articles from a fixed hook of the main conveyor to a rotating hook of the secondary conveyor serving the booth.
In the system for powder coating articles according to the present invention it is possible to use coating booths of the type described above. Nonetheless, it is also possible to use booths of different type.
The embodiments described for the invention in question are susceptible to numerous modifications and variants falling within the scope of the same innovative idea defined in the attached claims.

Claims

A booth (100) for powder coating articles (20), characterized in that it comprises:
- a supporting structure (105),

- one or more lateral walls (110, 120, 130) defining an interior (140) of said booth (100),

- a front wall (101) from which powder coating dispensing means face said interior of said booth (100),

- suction means (210, 220) for drawing air from said interior (140) of said booth (100),

- overhead conveyor means (300) positioned in the upper part of said booth (100) and adapted to convey the articles (20) to be coated into the interior (140) of said booth (100),

- air blowing means (500) positioned in the upper part of said booth (100).
The booth (100) for powder coating articles (20) according to claim 1, characterized in that said air blowing means (500) comprise one or more pressurized chambers (501), operatively connected to an air supply system, that face the interior of (140) said booth (100) from above, said one or more pressurized chambers (501) having an interface wall (502) facing the inside (140) of said booth (100), said interface wall (502) being at least partially porous and allowing air to flow from said one or more pressurized chambers (501) toward the interior (140) of said booth (100).
The booth (100) for powder coating articles (20) according to claim 2, characterized in that said overhead conveyor means (300) are positioned in a housing (305) obtained inside said one or more pressurized chambers (501).
The booth (100) for powder coating articles (20) according to claim 3, characterized in that the lateral walls of said housing (305) are at least partially porous and allow air to flow from said one or more pressurized chambers (501) toward said overhead conveyor means (300).
The booth (100) for powder coating articles (20) according to one or more of the preceding claims, characterized in that said interface wall (502) is produced at least partially with a microperforated metal sheet or with a porous baffle.
The booth (100) for powder coating articles (20) according to one or more of the preceding claims, characterized in that said air blowing means (500) convey into said booth (100) an amount of air adapted to oppose rising of the powder coating into the upper part of said booth (100).
The booth (100) for powder coating articles (20) according to one or more of the preceding claims, characterized in that said overhead conveyor means (300) are positioned above said air blowing means (500).
The booth (100) for powder coating articles (20) according to one or more of the preceding claims, characterized in that it comprises a covering in plastic material positioned above said overhead conveyor means (300), said air blowing means comprising a plurality of nozzles adapted to send, after receiving predefined commands, jets of air toward said covering in plastic material.
A booth (100) for powder coating articles (20), characterized in that it comprises:
- a supporting structure (105),

- one or more lateral walls (110, 120, 130) defining an interior (140) of said booth (100),

- a front wall (101) from which powder coating dispensing means face said interior of said booth (100),

- suction means (210, 220) for drawing air from said interior (140) of said booth (100),

- overhead conveyor means (300) positioned in the upper part of said booth (100) and adapted to convey the articles (20) to be coated into the interior of (140) of said booth (100),

- means (600) for at least partially closing said front wall (101) of said powder coating dispensing means.
The booth (100) for powder coating articles (20) according to claim 9, characterized in that said means (600) for at least partially closing said front wall (101) comprise at least one wall that surrounds said powder coating dispensing means on the opposite side with respect to said front wall (101), and in that said means (600) for at least partially closing said front wall (101) comprise a back wall (601) and a first (602) and a second (603) lateral wall that surround said powder coating dispensing means on the opposite side with respect to said front wall (101), and in that said means (600) for at least partially closing said front wall (101) comprise an upper wall (604) of said powder coating dispensing means.
A booth (100) for powder coating articles (20), characterized in that it comprises:
- a supporting structure (105),

- one or more lateral walls (110, 120, 130) defining an interior of (140) of said booth (100),

- a front wall (101) from which powder coating dispensing means face said interior of said booth (100),

- suction means (210, 220) for drawing air from said interior (140) of said booth (100),

- overhead conveyor means (300) positioned in the upper part of said booth (100) and adapted to convey the articles (20) to be coated into the interior (140) of said booth (100),

- air blowing means (500) positioned in the upper part of said booth (100),

- means (600) for at least partially closing said front wall (101) of said powder coating dispensing means.
A system for powder coating articles (20) characterized in that it comprises:
- a booth (100) for powder coating said articles (20) according to one or more of the previous claims;

- a first overhead conveyor (90) for moving said articles (20) in said system;

- a second overhead conveyor (300) serving said booth (100) for powder coating;

- said first overhead conveyor (90) comprising first hooks (91) associable with supporting plates (900) of said articles (20);

- said second overhead conveyor (300) comprising second rotating hooks (92) associable with said supporting plates (900) of said articles (20);

- said supporting plates (900) of said articles (20) being transferable between said first hooks (91) of said first overhead conveyor (90) and said second rotating hooks (92) of said second overhead conveyor (300), and vice versa;

- said system comprising first (301) and second (302) transfer means, positioned upstream and downstream of said booth (100), to transfer said supporting plates (900) of said articles (20) between said first hooks (91) of said first overhead conveyor (90) and said second rotating hooks (92) of said second overhead conveyor (300), and vice versa.
The system for powder coating articles (20) according to claim 12, characterized in that said first hooks (91) comprise first coupling means (911) of said supporting plates (900) and said second rotating hooks (92) comprise a rotating ring nut (920) associated with second coupling means (921) of said supporting plates (900), and in that said supporting plates (900) comprise third coupling means (903) associable with said first (911) and second (921) coupling means, and in that said first (911) and second (921) coupling means are substantially the same as one another and comprise a hollow body (950) with an inlet groove (951), said third coupling means (903) comprising a shuttle (931) adapted to slide inside said hollow body (950) through said inlet groove (951).
A cyclone (8) for separating powders from a gaseous flow (810), characterized in that it comprises:
- a suction section (81) for inflow of a gaseous flow (810) containing powders,

- a first central cone (82) operatively connected to said inflow suction section (81),

- a second central truncated cone (83) comprising a section (830) for outflow of said gaseous flow (810),

- means (811) for closing said inflow suction section (81),

- means (84) for supplying air or another gaseous fluid to the outer surface (831) of said second truncated cone (83) movable between a closed position and an open position,

- the lower end (821) of said first central cone (82) being movable between a closed position and an open position.
The booth (100) for powder coating articles (20) according to one or more of claims 1 to 11, characterized in that it comprises a cyclone (8) for separating powders from a gaseous flow (810) according to claim 14.