Patent Description:
In this context, plenum means a ceiling or upper wall that is able to distribute an airflow entering into the closed space of the booth while the painting takes place. Fans force air into the booth, the fans being able to be adjusted in order to vary the speed and the quantity of air input into the spray booth in a time unit. The distribution of air must be as uniform as possible and the speed of air must be controlled. In some points of the plenum the airflow can vary, while it must be constant over time in that specific point. The adjustment of inlet fans is intended to compensate the pressure drop, so that the distribution of air to said plenum is maintained inside optimal pre-set limits.

Spray booths are known that through automatic devices (reciprocators, carousels, rotating arms) spray paint onto products parts to be painted.

Spray paint application entails that not all the sprayed paint hits the product; the paint that is not applied to the product partly finishes on the product conveying system, and partly hovers in the air inside the spray booth itself. This last portion of sprayed paint is called overspray, and is partially intercepted by the spray booth suction system.

Non-intercepted overspray tends to contaminate spray booth internal walls, gathering on them up to the point of compromising manufacturing quality and leading to major waste of painted products. Therefore, costly maintenance and cleaning of the spray booth itself become mandatory.

The overspray intercepted by the suction system is conveyed towards spray booth filters, thanks especially to an airflow generated by the suction system itself. In this path, the overspray is controlled in a more proper way thanks to the emission of an airflow from the plenum.

<CIT> discloses a mobile roof for a spray painting booth. The booth is designed for the manual painting of motor vehicles, performed by a human operator. Said roof, which is a filtering ceiling, not a plenum in the sense explained above, has three portions, a central portion <NUM>, and two side sectors <NUM> and <NUM> which go upwards in an upper direction: in other words, overall the roof has a convex shape. Said ceiling can move vertically, i.e. rise and lower, according to the pressure conditions inside the booth itself, in order to prevent explosions due to the paints and fuel of the motor vehicle painted inside the booth.

<CIT> of the same applicant shows a spray painting booth, also equipped with a plenum, a transport system for advancing panels, at least one device for spraying the paint and at least one suction system. The plenum of the application <CIT> also has a broken line profile, however different from that of the present invention. The plenum of <CIT>, also equipped with a symmetrical shape, has the following profile, proceeding from the periphery towards the center of the cabin:.

<CIT> and <CIT> disclose a rotating support for spray guns. The rotating support is moved along two parallel, rectilinear tracts joined by two half-circles. This allows a plurality of guns spraying at the same time in a direction perpendicular to the parts to be painted in transit.

The present invention seeks to provide a spray booth having a plenum provided with an improved air circulation in the booth, in order to control as much as possible the phenomenon of overspray. This can be obtained by generating an airflow more similar to the geometry of the vortex generated by the combined effect of the jets of the spray guns and of the suction.

This aim is obtained with an apparatus having the features of the independent claim.

Advantageous embodiments and refinements are specified in claims appended thereto.

The object is obtained with a spray booth according to the present invention, which is provided with an M-shaped plenum, i.e. a plenum the central portion of which is lower than the immediately adjacent lateral portions; more peripherally, the plenum is lower again, reaching two ends that are lower than the central portion.

In the preferred embodiment of the spray booth, in the spray booth there is moreover a rotating device in which the spray guns follow an oval closed path provided with two parallel sides and two arcs. This device supports spray guns, and can be moved vertically, moving the spray guns to/from the part to be painted. Each gun support is provided with a distributor block supplying the gun; said distributor block allows the painting product to be recirculated.

The M-shape of the plenum forms two expansion chambers, in which the kinetic energy of the paint supplied by the gun is spontaneously and progressively reduced: this allows the suction system to intercept the overspray.

The apparatus according to the present invention has very high productivity combined with a quality of painted parts that is just as high. Indicatively, the speed of transit of the parts to be painted can range from <NUM> to <NUM>/min, while the weight of paint applicable to said parts ranges <NUM> to <NUM>/m<NUM>. The apparatus can work over three work shifts, i.e. <NUM>/<NUM>.

The advantages of the present invention are linked to the improvement in the control of overspray flow. This has several consequences:.

With respect to the rotating spray gun support with an oval shape with two parallel sides, the advantages are linked to the following features:.

The present invention will be disclosed below with the help of the following figures, which show:.

<FIG> shows an apparatus <NUM> according to the present invention. The direction of the parts to be painted is shown by the arrow in bold print. A spray booth <NUM>, a series of chambers generically indicated with <NUM> that are above said spray booth <NUM>, two air inlet units <NUM>, and two air inlet hoods <NUM> are visible. The booth <NUM> has transparent protections <NUM>, which can be opened to access the spraying area, and a tower <NUM> for cleaning air, in order to separate the overspray from the air crossing the apparatus. Said tower <NUM> has two suction fans <NUM> releasing the air coming from the spraying booth <NUM> into the environment through an exhaust stack <NUM>. The portion of the apparatus <NUM> in which the paint spraying occurs (spray booth <NUM>) is at said protections <NUM>.

It is worthwhile noting that, for particular applications, the air inlet units <NUM> can be absent, in this case, they are replaced by alternative units having the same function but which supply hyperfiltered air.

<FIG> shows a lateral section of the apparatus <NUM> according to the present invention. In the preferred embodiment, a rotating device <NUM> follows its oval closed path under the central parallel portion <NUM>, while the guns <NUM> move closer to and away from the observer positioned at the side of the apparatus <NUM>. In other words, the short oval side is observed from apparatus <NUM> side. The longer (longitudinal) axis of the oval is perpendicular to the feeding direction of the parts to be painted.

<FIG> also shows a lateral section of the apparatus <NUM> according to the present invention, too, but in a simplified version. The grey highlighting allows the M-shape of the plenum <NUM> to be appreciated, in the centre of which there is the rotating device <NUM>. Moreover, <FIG> allows the overspray movement to be appreciated, which is indicated by the two spiral arrows under the M-shaped plenum.

From the periphery of the apparatus to the centre, said plenum <NUM> has two first external descending portions <NUM> tilted towards the periphery, which do not touch a belt <NUM> for conveying the products to be painted. After said portions <NUM> there are two lateral surface portions <NUM>, parallel to the belt <NUM> conveying the parts. Two central tilted surface portions <NUM> follow that descend towards the rotating device <NUM> (that therefore have a tilt opposite the first portions <NUM>). The two central descending surface portions <NUM> are connected through a parallel central surface portion <NUM>, which is parallel to the conveying belt <NUM>, which is placed lower (i.e. nearer the conveying belt <NUM>) than the parallel lateral surface portions <NUM>. The M-shaped plenum <NUM> is symmetric, and the the two sides of the structure of the portions <NUM>, <NUM>, <NUM>, <NUM> that has just been disclosed is identical. The various surface portions <NUM>, <NUM>, <NUM>, <NUM> will from now on be referred to only as "portions".

It should be pointed out that the air exiting the various portions <NUM>, <NUM>, <NUM>, <NUM> of the plenum always exits perpendicularly to each surface <NUM>, <NUM>, <NUM>, <NUM>.

The speed at which the air exits the descending external portions <NUM> is such as to contrast the residual kinetic energy of the paint dispensed by spray guns <NUM>, so that the overspray tends to recirculate towards the lateral parallel portion <NUM>, to then be suctioned by the filtration system.

In the portions <NUM> and <NUM> of the plenum the speed of air exiting the surface of said plenum can be lower than that of the air exiting the portion <NUM>, because they are in area zone in which the kinetic energy of the overspray is lower. The reduction of speed of the inlet air in the zones underneath the portions <NUM> and <NUM> of the plenum allows to an overall airflow to be obtained that is lower than in the apparatuses where the speed of the air exiting the plenum is homogeneous for all the sections <NUM>, <NUM>, <NUM>, the air speed being equal to the air speed of the portion <NUM>.

In said central parallel portion <NUM> of the plenum there is an airflow outlet from the plenum <NUM> that has the function of preventing the overspray generated by the spray guns <NUM> from dirtying the guns <NUM> themselves and the support <NUM> of said guns.

The partialization of the air speed in the different portions <NUM>, <NUM>, <NUM>, <NUM> of the plenum is achieved by controlling the airflow supplied by fans <NUM> to the booth, adjusting the airflow itself through separating baffles <NUM>, <NUM>, which bound chambers <NUM>, <NUM>, <NUM> of the plenum itself. Owing to the presence of the chambers <NUM>, <NUM>, <NUM> formed by the respective baffles <NUM>, <NUM>, just two inlet air units can be used, which are placed on the respective sides of the apparatus <NUM>. By modifying the crossing surface of the baffles <NUM>, <NUM>, the airflow in the different portions <NUM>, <NUM>, <NUM><NUM> of the plenum can be varied, so adjusting also the speed of the air entering the spray booth <NUM>.

It is worthwhile noting that two walls <NUM> bound the volume in which the air is moved. Said walls <NUM> in fact bound a volume <NUM>, containing the rotating device <NUM> is placed, and to which no air is conveyed in a forced manner.

For clarity's sake, the portion indicated with <NUM> in <FIG> comprises the chambers <NUM>, <NUM>, <NUM>, the volume <NUM> not being supplied with forced air.

In an alternative not shown embodiment, the separating baffles <NUM>, <NUM> are not perpendicular to the ground as in the Figures, but are tilted, or have a different extension, or have a different degree of permeability.

The filtration system is provided in the form of lateral suction tanks <NUM>, better observable in <FIG>. Said lateral suction tanks <NUM> collect a first portion of overspray, the one provided with lower speed, whereas the overspray vortex, indicated with the spiral arrows visible in <FIG>, which forms under the external descending portion <NUM>, lateral parallel portion <NUM> and central descending portion <NUM>, allows the progressive slowing down of the overspray, allowing the suction system to capture a second portion of slowed down overspray subsequently.

The dimensions of the plenum <NUM> and its shape represent the best compromise between the overall dimensions of the apparatus <NUM> on one hand, and on the other hand the speed and quantity of air needed for containing the overspray, preventing the generation of paint accumulation inside the apparatus. In other words, a bigger apparatus would spontaneously lead to a lower overspray accumulation, but would be too cumbersome and too expensive to find its place in a production line. Indicatively, the dimensions of the spray booth <NUM> are <NUM> x <NUM>, with a distance of <NUM> between parallel lateral portion <NUM> and conveying belt <NUM>.

<FIG> shows a top view of a section performed on a horizontal plane immediately above the conveying belt <NUM>. The Figure shows said suction tanks <NUM>, which are compliant with the prior art. Two tanks <NUM> are adjacent to the conveying belt <NUM>, having a length equal to the length of the conveying belt <NUM> itself (upper outward section). The conveying belt <NUM> is a known closed belt conveyor moved by a motorized roller and an idle roller. Said tanks <NUM> are in the form of tilted planes <NUM> on which water flows, so that surfaces are kept clean. This water falls into the channel <NUM> for air suction and water conveying. The channel <NUM> is provided with a passage section larger in the peripheral portions of the apparatus, and narrower in the central portions of the apparatus, so that the suctioning speed is kept constant at the sides of the conveying belt <NUM>.

Said tanks <NUM> are a known water filtration system. Alternatively, said water filtration system can be replaced by a dry filtration system, prior art, too, or alternatively by other filtration systems prior art.

Experimentally, the best performance of the apparatus according to the present invention is obtained by combining the M-shaped plenum <NUM> with the oval rotating carousel <NUM>, which combination is the preferred embodiment. Nonetheless, the M-shaped plenum <NUM> can also be combined with spraying devices of different shape, e.g. a rotating carousel the guns of which follow a circular path, or any configuration of a spraying device in which the spraying direction goes from the centre to the periphery of the apparatus. For example, in an alternative not shown embodiment, the same M-shaped plenum <NUM> can be used combined with spray guns placed in the centre of the apparatus that move with a rectilinear reciprocal movement along a direction orthogonal to the conveying direction of the products <NUM> to be painted, with such a direction that the paint jet goes from the centre of the apparatus to the periphery.

<FIG> shows a detail of the rotating device <NUM>, seen from the entry of the products to be painted. Said device <NUM> is provided with a plurality of spray guns <NUM>, preferably twelve or twenty-four guns. Each gun <NUM> is supported by a suitable arm <NUM>, connecting the gun <NUM> to a pair of moving chains <NUM>. In this Figure, for simplicity's sake, only one pipe chain44 is shown, of which more details are given below.

<FIG> shows the same rotating device <NUM> seen from the top. This view allows the oval shape of the moving chains <NUM> to be appreciated, provided with two parallel long sides connected together by two arc portions.

The spray gun support arms <NUM> are supported by the pair of moving chains <NUM> which move along the oval movement trajectory of the guns between a pair of motorized sprocket wheels <NUM> and a pair of idle sprocket wheels <NUM> (both visible in <FIG>). The pair of motorized sprocket wheel <NUM> is moved by an electric gearmotor <NUM> through a chain transmission <NUM>.

<FIG> shows a detail of a spray gun <NUM> fixed on a spray gun support arm <NUM>, supported by two moving chains <NUM>.

Each pipe chain <NUM> contains the tubes for the delivery and return of the paint to each gun <NUM>. The two ends of each pipe chain44 are fixed:.

The two rotating supports <NUM> and <NUM>, which are constructively identical, allow the rotation of the two ends of the pipe chain44, allowing it to move always on the same plane, preventing mechanical warping which would lead to its breakage. In fact, the rotating disc <NUM> is in phase with the chains <NUM>, i.e. a full circle of the rotating disc <NUM> corresponds to a full circle of the moving chains <NUM>.

In order to understand the operation of the oval rotating device <NUM>, the three <FIG>, <FIG> and <FIG> must be considered together.

The same gearmotor <NUM>, again with a chain transmission, moves the disc <NUM> too, which moves the first end <NUM> of the pipe chain44 and a rotating joint <NUM>.

Said rotating joint <NUM> (visible also in <FIG>) is used for supplying the guns <NUM>; its operation is explained in detail in document <CIT> of the same applicant.

The rectilinear tracts of the oval rotating carousel are perpendicular to the feeding direction of the parts, indicated by the arrow in bold print in <FIG>. Said rectilinear tracts represent the working portions of the trajectory, i.e. the portions in which the guns <NUM> spray paint on the products <NUM> transiting underneath. In the two connecting arc portions, the dispensing of paint by the guns <NUM> is interrupted. This configuration of the moving chains <NUM> allows two spraying sections to be obtained in which there is a sequence of spray guns <NUM> to allow a great flow of paint to be dispensed onto the transiting parts <NUM>. In order to obtain the needed quantity of dispensed paint, arranging a suitable number of guns along the trajectory is sufficient. For the application field of the present apparatus, the optimal number of guns for applying the product is twelve: obviously, the skilled person can adjust the number of guns according to the quantity of paint to be dispensed and to the speed of the transiting parts. Obviously, the speed of translation of the guns <NUM> can be adjusted to harmonize the speed with the speed of the parts <NUM> to be painted.

Through supply pipes and a supply pump (which are not shown), the paint is sent from storage reservoirs (which are not shown), placed outside the apparatus <NUM>, to the rotating joint <NUM> placed at the centre of the rotating device <NUM>. From a not shown distributor connected to said joint <NUM> the supply pipes (that are not shown) lead away, directed to the individual guns <NUM>. In order to allow the correct movement of the pipes from the central portion of the rotating joint to the peripheral portions on which the guns <NUM> move, said pipe chains <NUM> are used. For simplicity's sake, in <FIG> only one pipe chain <NUM> is shown, but naturally each gun <NUM> is provided with its own pipe chain <NUM> when the guns <NUM> are twelve. Should the guns be twenty-four, the number of pipes is doubled and each pipe chain <NUM> supports a double number of pipes. Downstream of the pipe chain <NUM>, the pipe pairs divide and each supplies its own gun.

<FIG> shows a pipe chain <NUM> in axonometric view. Each resting pipe chain has an inverted U-shape, which is highly visible in <FIG>.

During the rototranslation of guns <NUM>, substantially the inverted U is distorted, in which the two arms of the U are distanced from each other and at the same time the height of the inverted U is reduced.

<FIG> allows the shape modification to be appreciated of the pipe chain <NUM> during spraying. The pipe chain 44a is shown in a minimum extent position, corresponding to the view of <FIG>; said pipe chain44a feeds the gun that is in the position corresponding to the lesser axis of the oval. The pipe chain44b is shown in a maximum extent position; said chain 44b feeds the gun which is in the position corresponding to the greater axis of the oval chain <NUM>. The pipe chain <NUM> is shown in an intermediate extent position between the two the end positions 44a and 44b. During the movement along the oval trajectory, the two rotating supports <NUM> and <NUM>, representing the two ends of each pipe chain <NUM>, move away and closer to each other: this variation in distance is compensated by the different positions and shapes that the pipe chain <NUM> can adopt, widening and narrowing the two arms of the inverted U which form the pipe chain <NUM> itself, and undergoing a corresponding reduction/increase in height.

The moving chains <NUM> and the disc <NUM> are moved by the gearmotor <NUM> at the same time: a relative motion is generated between the two ends of the pipe chain <NUM>. During the gun movements, the rotating supports <NUM> and <NUM> move along two different trajectories: the rotating support <NUM> follows a circular trajectory on the disc <NUM>, while the rotating support <NUM> follows an oval trajectory on the chains <NUM>.

It is worthwhile highlighting that pipe chains have to move their mobile ends only and only on their working plane only, in order to function properly. Otherwise, if the mobile ends of a pipe chain <NUM> are moved on different planes, transverse loads are generated, which lead to the breakage of the pipe chain <NUM> itself. In the known art, such pipe chains <NUM> normally are used to guide the movement of pipes or cables between two mobile ends that move on rectilinear and coplanar pathways. In this case, unlike what happens in the prior art, pipe chains are used on a path provided with a rototranslation movement, with a rectilinear and a rotatory component.

It is worthwhile remembering that paint tends to settle, and therefore preferably the supply circuits of painting apparatuses are provided with a return branch to form a recirculation system keeping the paint in motion. As a consequence, the number of pipes specified above must be doubled, in order to have a paint delivery and return system.

The paint delivery branch goes from the storage reservoir (which is not shown) to a recirculating block <NUM> (visible in <FIG>), while the paint return branch goes from the recirculating block <NUM> to the storage reservoir (which is not shown) placed outside the apparatus. Each gun <NUM> is provided with its own recirculating block <NUM>;in other words, the number of recirculating blocks <NUM> is equal to the number of guns <NUM>. The end branch supplying paint, not undergoing recirculation, goes from the recirculating block <NUM> to the respective gun <NUM>. The arm <NUM> supporting the gun is placed inside the spraying area; the diameter of the pipe of this last branch has a smaller section than the rest of the circuit, so as to obtain a more compact gun support arm <NUM>, which is provided with a reduced exposed surface and therefore gets less dirty. All this reduces the possibility that paint residues detach and fall on the transiting product <NUM>.

A further feature of the rotating device <NUM> is that the device <NUM> can be moved, towards or awary from the device, and therefore the guns <NUM>, to/from the transiting products <NUM> to be painted. The whole device <NUM> is supported by two support columnns <NUM>, visible in <FIG>. These columns <NUM> are supported by two lifting jacks <NUM>, which rest on the ground through support plates <NUM>. This vertical movement occurs by working on said jacks <NUM> through a motor <NUM>. The synchronous motion of the two jacks <NUM> is achieved by a drive shaft <NUM>. In order to ensure a suitable support of the device <NUM>, the rotating carousel <NUM> is guided with guiding systems <NUM> that are anchored to the conveying system of the products <NUM> to be painted.

<FIG> shows a detail of the oval rotating carousel <NUM> in a lateral view, i.e. from the short side of the oval, orthogonal to the view shown in <FIG>.

<FIG> shows a detail of the spraying device in axonometric view.

The two <FIG> and <FIG> taken together allow the presence of a cleaning device <NUM> to be appreciated. Such a device <NUM> is prior art, and has a rotating brush <NUM>, moved by a motor <NUM>. The lower half of this brush <NUM> is contained inside a tray <NUM>, containing solvent or the detergent liquid.

This rotating brush is intended for cleaning the nozzles of the guns <NUM> when it is brought into a position suitable for interfering with the gun <NUM>.

During spraying, when the spray guns <NUM> are active, said cleaning device <NUM> is in the rest position (bottom, shown in <FIG>), distanced from the guns. At the end of a spraying cycle, the cleaning device <NUM> is automatically brought into its working position (top) and can proceed to an automatic cleaning cycle of all the guns. Each gun <NUM> travels a tract of the oval path to be placed at the device <NUM>, above the device <NUM>, and subsequently the cleaning device is raised. The nozzle of each gun undergoes a brushing of a pre-set duration of a few seconds (indicatively, from <NUM> to <NUM> seconds). The duration of an automatic cleaning cycle is therefore the duration of the pre-set cleaning time multiplied by the number of guns present. In an automatic cleaning cycle, all twelve or twenty-four guns present are cleaned.

The position of the cleaning device <NUM> is defined: in order to perform the cleaning of all the guns <NUM>, the cleaning device has to be lifted to the height of the guns <NUM>. The passage of a gun <NUM> to the next occurs while the cleaning device <NUM> is in the lower rest position, while when the gun arrives at the cleaning device <NUM>, the device <NUM> is lifted to the working position. In other words, during a cleaning cycle the cleaning device undergoes a number of translations corresponding to the number of guns present. This translation movement is performed by a pneumatic cylinder <NUM>, visible in <FIG>.

Not all commercially available spray guns are identical, adjusting means is accordingly provided to allow the correct positioning of the brush <NUM> with respect to the nozzle of the specific gun <NUM>.

Finally, it is worthwhile specifying that in addition to the automatic cleaning that operates as explained above, also focused manual cleaning can be performed of the single spray gun <NUM>.

Each gun <NUM> with its respective support arm <NUM> is marked with a progressive number, e.g. from one to twelve or from one to twenty-four, which allows the gun <NUM> to be identified univocally. For example, let the case be considered in which gun number eleven sprays poorly because the nozzle thereof is clogged. The apparatus <NUM> is provided with a program allowing the apparatus <NUM> to bring the desired gun, e.g. gun number eleven, at the greater axis of the oval. A human operator can remove the corresponding glass protection <NUM> and proceed to the manual cleaning of the nozzle of gun number eleven.

Claim 1:
Apparatus (<NUM>) for painting mainly flat products comprising a spray booth (<NUM>), in turn comprising a plenum (<NUM>), a conveying belt (<NUM>) for conveying products (<NUM>) at least one device (<NUM>) for applying paint, and at least one suction plant, wherein
the plenum (<NUM>) of the spray booth has a symmetric M-shape comprising, from a
periphery of the plenum to a centre of said plenum (<NUM>) in sequential order:
- two external first surface portions (<NUM>), opposing to each other with respect to the centre ,each ascending from the periphery and tilted toward the centre;
- two lateral second surface portions (<NUM>), opposing to each other with respect to the centre, parallel to the conveying belt (<NUM>);
- two central third surface portions (<NUM>), opposing to each other with respect to the centre, each descending to the centre with a tilt opposed to that of the external first surface portions (<NUM>);
- a central fourth surface portion (<NUM>) parallel to said conveying belt (<NUM>), which is closer to said conveying belt (<NUM>) than the lateral second surface portions (<NUM>).