Patent Description:
As is also well known, painting by spraying is one of the most important leather finishing operations in the processing cycle of the tanning industry, which envisages ample available space in the factory, due to the extension of the plants with which it is carried out.

Basically, in the tanning field, painting leathers consists of covering the grain side (i.e., the noblest and most valuable side of the leather) with one or more layers of painting, covering and/or coloring material, in the form of an elastic, thin and uniform film, applied by spraying and in a lesser or greater amount, depending on the covering capacity to be obtained.

The main risk also associated with painting leathers is obviously the environmental pollution which it causes in the workplace; to eliminate or at least reduce this risk, special industrial spray booths must be used, which can essentially be of two types:.

A further classification of the industrial spraying booths used in the tanning industry derives from the type of spraying that is carried out therewith, which can be manual (less and less widespread) or automatic (without the intervention of personnel).

A typical known system for spraying leathers generally comprises a conveyor belt for advancing leathers along a given linear direction, a closed industrial booth within which, by means of relative spray guns, the deposition of the covering products occurs, and a fume suction and abatement system, by means of which the exhalations of the covering products which are deposited on the leathers are sucked and filtered.

The known systems for painting or spraying leathers use, in particular, a fume extraction system deriving from the paint suspended in the air in the industrial booth which can be further classified as rotary-type (in the circular or so-called, improperly, elliptical variant) or alternating-type.

Specifically, a common circular rotary booth, visible in <FIG> where it is indicated with C and also in the prior art document published with <CIT>, has a central shaft N, arranged inside the spraying chamber S and operatively connected to motorization means M, having the function of distributing the covering fluid material (color, paint or anything else, in mixture), useful for spraying on the leather, to the spraying means to which the compressed air ducts necessary for the operation of the spraying means themselves refer.

The circular rotary spray booth C of the known type further comprises a plurality of load-bearing arms B (usually in the number of eight or twelve), arranged radially and integral with the motorized central shaft N from which they thus take the rotation movement, while the spraying means generally comprise a plurality of fixed guns F which are installed at the ends of the load-bearing arms B and spray the fluid covering material in a nebulized form on the surface of the leather P to be treated which, in turn, is placed on the upper surface of a conveyor belt T, generally made with parallel and close nylon threads, which has a width G and advances along a preset linear direction W by means of the use of an inverter, at a preset speed (usually between <NUM> and <NUM> meters/minute).

At the end of each load-bearing arm B, one, two or sometimes three fixed spray guns F can be installed, each of which also has a supply circuit thereof for the fluid covering material which is sucked by a pump arranged on the side of the rotary booth C, while the compressed air circuit provides for a correct nebulization of such fluid material.

Furthermore, there is a reading bar installed upstream of the industrial rotary booth C, which has the function of determining the position of the leather P, the surface thereof and the contour thereof, so that an electronic control system, which stores the size and shape of the leather P itself, is capable of determining the opening and closing of the spray guns.

The known circular rotary booths are preferable for the effectiveness and efficiency with which they allow carrying out the spraying treatment of the leathers since each of the spray guns, performing precisely a circular motion along a circumference of a given radius "r" and center O integral with that of the central shaft N rotating around a vertical axis, applies the fluid covering material on the leathers according to an articulated arcuate design, so-called crossed rows to form a net which, due also to the number of spraying passages performed on the leathers by the dispensing guns F, makes substantially imperceptible to the human eye and compensates for any treatment imperfections due to uneven operations of the spray guns F and thus avoids stopping the operation of the rotary booth C or at least limits the frequency of machine stops.

Faced with these advantages, however, circular rotary booths have the disadvantage of requiring significant spaces in the factory, not always available or conceivable by the entrepreneur.

For this reason, alternative industrial booths are sometimes used, which have been available on the market for some time, which have smaller dimensions; they comprise one or two guides, which are transverse with respect to the translation (or advancement) movement of the leathers on the conveyor belt and on each of which a gun-carrying carriage runs; special motors, adjustable with inverter and related chains or drive belts, determine the alternative linear movement of the carriages, as well as appropriate tubes carry both the compressed air and the fluid covering material (generally color) necessary for the operation of the spray guns and the treatment of the leathers therewith.

In industrial spray booths of the alternative type, whenever the carriage moves in a transverse direction, the spray guns apply the covering material, on the advancing leather, according to a design or pattern which is easily perceptible by the human eye and which, inevitably, affects the final quality of the product, to the point that such industrial booths are used sporadically and only for certain spraying steps.

For their part, the common industrial rotary booths of the parallel type (improperly defined also as "elliptical") are based on the same operating principle as the alternative booths (although they are in fact rotary).

In fact, the closed annular trajectory followed by the spraying means of the so-called "elliptical" booths during the treatment consists of two straight and parallel central sections - identified exactly in the part above the conveyor belt and the leathers progressively extended thereon -, at which the spraying means work, and of two curved lateral sections (essentially two semicircles) - identified laterally and outside the conveyor belt and, therefore, definable as "dead" sections from a point of view of the spraying treatment of the leathers - which connect the aforesaid two straight sections and at which the spraying means are closed, non-operational. Parallel (or elliptical) type rotary spray booths of the prior art, an example of which is shown in the <CIT>, have a rectangular structure and a length (measured in the advancement direction of the leathers on the conveyor belt) having a value between <NUM>% and <NUM>% of the length of the circular rotary booths.

The parallel rotary booths include two gear wheels, joined together by mechanical transmission means (such as a belt or a chain) which define the aforesaid closed trajectory in parallel straight sections interspersed with arcuate sections; one of such wheels is motorized, while a plurality of spray guns, to which special air pipes and covering material to be applied are connected, are fixed to the transmission means and a central distribution shaft feeds both the air circuits and the circuits of the fluid covering material and/or dye dispensed by the spray guns.

Parallel industrial booths, in addition to being inherently rather complex from a constructional point of view, also have the disadvantage that the transverse movement of the spraying means, combined with the movement of the conveyor belt advancing the leathers, generates a linear design formed by a series of crossed strips (or lines) which, similar to the alternative industrial booths, do not provide good results; not surprisingly, these booths have a limited application in the tanning industry, usually being used to deposit the so-called "background color", on which the final color layers are then deposited with other spray booths.

Based on the operating features offered by the types of booths currently on the market, it is concluded, as already mentioned above, that circular rotary booths, although bulkier, offer the best performance in terms of surface finish of the leather by spraying treatment of a covering material and/or dye (such as a paint).

In any case, the rotary spray booths have a significant disadvantage, largely underestimated for the obvious negative effects thereof, linked to the positioning of the extraction system of the fumes and/or particulate generated by spraying the covering material on the leather, useful to prevent drops of material dispensed by the spraying means from not being deposited - for any reason, even accidental - where programmed and desired, i.e., on the leather.

In fact, although such a suction system is installed near the load-bearing arms of the spraying means, it is arranged - as it occurs in the spray booths shown in the <CIT> and in the patent application <CIT> - at a distance from the latter which is not uniform and homogeneous and, more generally and in any case, not rational.

This implies that, in the known type of rotary booths, the flow rate and direction of the continuous airflow produced by the suction means must be carefully studied and designed according to the different distance of the suction means from the spraying means, in order to try to ensure that the spraying treatment conditions of the leathers are at least sufficient and adequate for the expected result. Furthermore, if the flow rate and flow direction are not correctly sized and oriented, as sometimes occurs, there are drawbacks such as:.

In this regard, consider, for instance, the emblematic case - shown in <FIG> and <FIG> and also in the prior art document published with <CIT> - in which the suction means A are arranged in the lower part of the rotary spray booth C of the prior art, along the lateral sides of the collection plane R of the traditional substantially rectangular or in any case square shape, placed below the spraying means F inside the load-bearing structure U and provided with an upper face Ru adapted to receive by falling the particulate of the painting mixture to be sprayed on the leather P: indeed, it can be noted that the consequent distance of the suction means A from the spraying means F is not uniform and constant at least along the linear direction W, with all the complications cited above that this entails. Therefore, starting from the awareness and existence of the above disadvantages of the current state of the art, the present invention intends to remedy it.

In particular, the main purpose of the invention is to provide a rotary booth for treating leathers by spraying which allows to rationalize the airflow of the suction means inside the booth, improving it and making it more efficient than that of the prior art rotary spray booths.

As part of such a purpose, it is task of the invention to devise a rotary booth for treating leathers by spraying in which the suction means cause a dispersion of the painting material to be applied on the leather which is almost null or at least slightly less than the equivalent booths of the known type.

It is another task of the present invention to indicate a rotary booth for treating leathers by spraying which, with respect to the prior art, allows to reduce the uncontrolled rebounds of the spraying paint material on the leather during the processing step inside the load-bearing structure.

It is a further task of the present invention to provide a rotary booth for treating leathers by spraying which, in the cognitive sphere of the main purpose thereof, makes it possible to obtain leathers of a higher quality with respect to those ones obtainable through the similar known spray booths.

It is further the task of the invention to specify a rotary booth for treating leathers by spraying which makes the cleaning operations which workers must periodically carry out in the spraying chamber easier than the current state of the art.

It is a further purpose of the present invention to develop a rotary booth for treating leathers by spraying which, in view of the advantages with respect to the prior art which it is intended to achieve, remains substantially unchanged in the overall dimensions.

Said purposes are achieved by means of a rotary booth for treating leathers by spraying according to the appended claim <NUM>, as hereinafter referred for the sake of brevity of disclosure.

Further detailed technical features of the rotary booth for treating leathers by spraying of the invention are reported in the related dependent claims.

The aforesaid claims, hereinafter specifically and concretely defined, are intended as an integral part of the present description.

Advantageously, the rotary booth for treating leathers by spraying of the invention allows to optimize and rationalize the airflow of the suction means inside the booth, making it better with respect to that of the rotary spray booths of the prior art.

This is by virtue of the fact that the rotary booth for treating leathers by spraying of the invention has suction means distributed according to a pattern which coincides with the spatial distribution of the spraying means in the lower part of the load-bearing structure of the rotary booth itself.

In other words, in the rotary booth of the present invention, used to treat leathers by spraying, the suction means suck at the spraying area, in the lower part of the load-bearing structure, cooperating with the primary circumferential arcs (belonging to the closed annular trajectory) along which the spraying means take the working condition in which they dispense the fluid painting mixture on the leather advancing on the conveyor belt.

In essence, therefore, the suction means and the spraying means of the rotary booth of the invention are advantageously arranged on two respective planes, generally horizontal, parallel and spaced from each other and according to the same and superimposable arcuate configuration.

What has just been highlighted in relation to the rotary booth of the invention is in no way found in the prior art documents published as <CIT> and <CIT> respectively; in fact:.

It follows that the suction efficiency, by means of an airflow, at least of the fumes produced by the spraying treatment inside the load-bearing structure is certainly better and increased in the rotary booth of the invention with respect to that of the equivalent booths of a known type more closely comparable thereto, shown in the aforesaid two prior art documents.

Still advantageously, the rotary booth for treating leathers by spraying of the invention does not require an oversizing of the suction means, as typically occurs in the known equivalent rotary booths: this is advantageously reflected, for the rotary booth of the invention, on the one hand, in a design of such a constructional unit which is simpler with respect to the prior art and, on the other hand and consequently, in an uncontrolled spreading, in the inner areas of the load-bearing structure, of the covering material to be sprayed on the leathers which is more contained with respect to the prior art.

In an equally advantageous way, the rotary spray booth of leathers of the present invention maintains, in the volume confined by the load-bearing structure, better cleaning conditions (with the same product dispensed by the spraying means) and at least satisfactory cleaning conditions for a longer time with respect to the known type of rotary booths comparable thereto.

Likewise advantageously, precisely because the cleaning of the rotary booth of the invention is better, in use, with respect to the rotary booths for treating animal leathers by spraying of the prior art, the operators are further aided when they must perform maintenance and dirt removal operations which are thus less complicated and faster with respect to what is currently necessary to implement. Equally advantageously, the rotary booth for treating animal leathers by spraying, the object of the invention, has an overall encumbrance at least equivalent to that of the common rotary booths of equal use of the prior art, while achieving the main advantages mentioned above.

Said purposes and advantages will result to a greater extent from the following description, related to preferred embodiments of the rotary booth for treating tannery leathers by spraying of the invention, given by way of indicative nonlimiting illustration, with the aid of the accompanying (in part yet mentioned) drawings in which:.

The industrial rotary booth of the invention, used to treat tannery leathers P by spraying paints, dyes or the like, is shown in a simplified and partial manner in <FIG> where it is indicated overall with <NUM>.

The innovative industrial rotary booth <NUM> described herein is comparable, albeit with the due, significant and innovative constructional differences which will be highlighted below, to the prior art industrial rotary booth C depicted in the accompanying <FIG> and <FIG> as well as in the prior art document published with <CIT>.

The industrial rotary booth <NUM> comprises, according to what has already been learned in the state of the art and can be found in part in <FIG>:.

According to the invention, the suction means <NUM> suck directly at the spraying area and in the lower part of the load-bearing structure <NUM> and are distributed according to an arcuate configuration substantially superimposable and equal to an arcuate spatial distribution of the primary circumference arcs <NUM>, <NUM> (belonging to the closed annular trajectory T) along which the spraying means <NUM> take the working condition in which they dispense the fluid painting mixture on the leather P advancing on the conveyor belt <NUM>.

The suction means <NUM> are of the type known per se to the person skilled in the art, for example comprising one or more fans, not depicted in the following figures, which maintain the flow in the rotary booth <NUM> and can be positioned on the top of the booth <NUM> itself or on external units connected to the booth <NUM> with appropriate air conveying channels.

In a particular and advantageous manner, although not essential, the suction means <NUM> are arranged at the same and constant distance from the spraying means <NUM> themselves and suck when the spraying means <NUM> take the aforesaid working condition.

Furthermore, the suction means <NUM> suck below:.

Even more in particular, as diagrammed in <FIG>, the suction means <NUM> communicate by means of an air channeling system with the lower area 2a of the load-bearing structure <NUM>, below the conveyor belt <NUM> and in which, as known, the fumes Q produced by the spraying treatment of the leathers P most accumulate, in order to put such a lower zone 2a in depression and thus allow a greater suction efficiency of such fumes Q.

Preferably but not necessarily, the suction means <NUM> communicate directly, but only in this specific case, with a storage tank <NUM> arranged inside the load-bearing structure <NUM> and below the conveyor belt <NUM>, adapted to receive by falling the particulate L and the fumes Q produced by the spraying treatment performed by the spraying means <NUM> on the leather P.

<FIG> highlights that the rotary booth <NUM> of the invention further comprises a collection plane <NUM>, contained inside the load-bearing structure <NUM> and arranged below the spraying means <NUM> and the conveyor belt <NUM> and provided with an upper face 12c, adapted to receive by falling at least the particulate (or the residue or the residual particles) L of the fluid painting mixture used during the spraying treatment of the leathers P.

In a particular and innovative manner, the collection plane <NUM> is also provided with a convex profile <NUM>' along two opposite side edges 12a, 12b which, as can be better understood from <FIG>, correspond in projection (or in height), to the primary circumference arcs <NUM>, <NUM> of the closed annular trajectory T followed by the spraying means <NUM> when the rotating unit <NUM> rotates, preferably around a vertical linear axis Y (and, for example, according to the direction given by the arrow J in <FIG>).

Also, this constructional expedient linked to the curved profile <NUM>' of the collection plane <NUM> at the two side edges 12a, 12b directly below, in vertical projection, the primary circumference arcs <NUM>, <NUM> (also called spraying arcs) contributes to optimizing and rationalizing the airflow of the suction means <NUM> inside the rotary booth <NUM> of the invention, sensitively improving it with respect to what occurs in the equivalent rotary booths of the known type.

In fact, the particular combination of the system of cooperation of the suction means <NUM> with the spraying means <NUM> with the arcuate shape of the two side edges 12a, 12b of the collection plane <NUM> allows a uniform suction along the entire spraying path avoiding unevenness in the application path of the painting mixture due to the movement of the particulate dispersion flame L, benefitting a greater cleaning of the environment circumscribed by the load-bearing structure <NUM> of the rotary booth <NUM> of the invention with respect to that of the similar rotary booths of the prior art.

<FIG> and <FIG> show that the opposite side edges 12a, 12b along which the collection plane <NUM> has the aforesaid convex (or curved or arcuate) profile <NUM>' are contained in the transverse dimension, orthogonal to the linear direction W, of the conveyor belt <NUM>.

Advantageously, in order to better achieve the preset objects of the invention, each of the opposite side edges 12a, 12b of the collection plane <NUM> has a radius of curvature K substantially equal to the radius of curvature of the primary circumference arcs <NUM>, <NUM> of the closed annular trajectory T travelled by the spraying means <NUM>.

Preferably but not bindingly, in order to limit the overall dimensions of the rotary booth <NUM> of the invention and, by way of reference, to safeguard space in the factory, the profile <NUM>' of the collection plane <NUM> is linear at two opposite side joints 12d, 12e of the collection plane <NUM> itself connecting the opposite side edges 12a, 12b to each other and being below the secondary circumferential arcs (or non-spraying arcs) <NUM>, <NUM> of the closed annular trajectory T travelled by the spraying means <NUM> during a normal processing cycle, when the rotating unit <NUM> rotates around the vertical axis Y: such a constructive detail is best seen in <FIG>.

In particular, the opposite side joints 12d, 12e of the collection plane <NUM> are appropriately although not necessarily arranged laterally external to the conveyor belt <NUM>, in particular, from symmetrically opposite parts with respect to the longitudinal axis X of the conveyor belt <NUM> and along a longitudinal direction orthogonal to the linear direction W.

According to the preferred embodiment of the invention described herein, the collection plane <NUM> is arranged according to a pair of inclined planes <NUM>, <NUM> of an acute angle α with respect to a horizontal reference plane <NUM> (diagrammed with a drawing end line in <FIG>), diverging downwards from opposite parts starting from a common transverse central axis Z, so that the collection plane <NUM> also becomes a sliding plane which conveys the particulate L produced by the spraying treatment of the leathers P downwards, in particular towards the storage tank <NUM>, in this specific example in the description.

In fact, in the constructional solution of the rotary booth <NUM> of the invention referred to in <FIG>, the collection plane <NUM> is operatively connected to a hydraulic system, not indicated, which creates a constant layer of water on the upper face 12c, facing below the conveyor belt <NUM>, of the collection plane <NUM>: such a layer of water is used to continuously capture and dispose, downwards, the particulate L of fluid painting mixture dispensed by the spraying means <NUM> which falls by gravity on the collection plane <NUM> without affecting the leather P.

Consequently, in this specific embodiment described, the storage tank <NUM> receives by falling the water D coming from the collection plane <NUM> and dragging therewith the particulate L of the fluid painting mixture, as shown in <FIG>.

In this case, the particular combination of the cooperation system of the suction means <NUM> with the spraying means <NUM> with the arcuate shape of the two side edges 12a, 12b of the collection plane <NUM> also allows limiting the swirling of the water collected in the accumulation tank <NUM>, which greatly contributes to or improves the cleaning conditions within the space defined by the load-bearing structure <NUM> of the rotary booth <NUM> of the invention.

It is understood that in other embodiments of the rotary booth of the invention, not shown below, the collection plane can be arranged according to a single plane which is inclined with respect to a horizontal reference plane, while maintaining a curved profile at the two opposite side edges lying directly and only below the conveyor belt.

As far as the closed annular trajectory T travelled by the spraying means <NUM> is concerned, in this specific example it has a substantially circumferential profile in plan view, so that the rotary booth <NUM> of <FIG> and <FIG> can be defined as circular.

However, other embodiments of the rotary booth for treating leathers by spraying of the present invention, not accompanied by reference drawings, could provide that the closed annular trajectory presents a substantially ellipse-shaped profile in plan.

In the latter case, in particular, the radius of curvature of the primary circumference arcs will be greater with respect to the radius of curvature of the secondary circumference arcs.

Furthermore, always in the case where the profile of the closed annular trajectory is substantially elliptical, the origin of the radius of curvature of the primary circumference arcs lies on the minor semi-axis of the ellipse where it coincides with a point distinct from the center of the ellipse itself, so that the length of the radius of curvature of the primary circumference arcs is greater than the minor semi-axis of the ellipse.

For its part, the origin of the radius of curvature of the secondary circumference arcs lies on the major semi-axis of the ellipse and coincides substantially with one of the foci of the ellipse itself, so that the length of the radius of curvature of the secondary circumference arcs is less than half of the major semi-axis of the ellipse.

Preferably but not necessarily, the aforementioned radius of curvature K of the primary circumference arcs <NUM>, <NUM> has a value in the range <NUM>÷<NUM> times the width of the conveyor belt <NUM>.

Particularly, the value of such a radius of curvature K of the primary circumference arcs <NUM>, <NUM> is equal to <NUM> times the width of the conveyor belt: this specific value is nominal and, basically, allows the rotary booth <NUM> of the invention to limit the space occupied thereby in factory as much as possible, keeping appropriate constructive features, and to further distinguish from the rotary booths of the prior art.

With regard to the rotating unit <NUM>, it preferably comprises a plurality of load-bearing arms <NUM> which:.

Purely preferred but not essential and not limiting, the support arms <NUM> are provided with adjustment means, not specifically indicated in <FIG> and <FIG>, adapted to vary the length of the support arms <NUM> in relation to the position of the spraying means <NUM> in the passage thereof from the primary circumference arcs <NUM>, <NUM> to the secondary circumference arcs <NUM>, <NUM> and vice versa while the rotating unit <NUM> rotates (according to the purely preferred direction given by the arrow J) around the aforesaid vertical linear axis Y defined by the central distribution shaft <NUM> (which can be inside the load-bearing structure <NUM>, as in this case, or outside, arranged in the upper part of the load-bearing structure itself).

<FIG> diagrammatically and partially shows a possible embodiment of the invention, in which the rotary booth, indicated overall with <NUM>, differs from the rotary booth <NUM> described with reference to <FIG> firstly by the fact that the collection plane <NUM> is not inclined with respect to a horizontal reference plane but coincides therewith.

In such a case, the collection plane <NUM> underlying the conveyor belt <NUM> comprises restraint means, not specifically shown, of the particulate L of the fluid painting mixture sprayed by the spraying means, overall numbered with <NUM>, and comprising for example one or more filtering bodies (coplanar and side by side or superimposed on each other, if more than one) or one or more filtering sheets (coplanar or superimposed on each other, if more than one).

Another significant technical feature differentiating the rotary booth <NUM> from the rotary booth <NUM> of the invention (both of which fall within the main object of the invention, as expressed by the appended claim <NUM>) concerns the storage tank <NUM> with which the suction means, overall indicated with <NUM>, communicate and which, in this case, mainly receives by suction the fumes Q and the particulate L coming from the collection plane <NUM> without providing any conveyor water veil.

Based on the description just provided, it is therefore understood that the rotary booth for treating tannery leathers by spraying of the present invention achieves the purposes and reaches the advantages mentioned above.

The load-bearing structure of the rotary booth of the invention extends according to a length, measured according to the preset linear advancement direction of each of the leathers on the conveyor belt, rather limited, not exceeding substantially <NUM> meters.

Claim 1:
Rotary booth (<NUM>; <NUM>) for treating leathers (P) by spraying, comprising:
- a load-bearing structure (<NUM>) which has at least one loading area (<NUM>) in which a leather (P) to be subjected to a spraying treatment is conducted within said load-bearing structure (<NUM>), and a discharge area (<NUM>) in which said leather (P) just treated is conducted outside said load-bearing structure (<NUM>);
- a conveyor belt (<NUM>; <NUM>) mainly housed in said load-bearing structure (<NUM>), adapted to advance along a linear direction (W) said leather (P) received on an upper surface (5a) of said conveyor belt (<NUM>; <NUM>);
- a rotating unit (<NUM>) coupled inside said load-bearing structure (<NUM>) and provided with spraying means (<NUM>; <NUM>) adapted to deposit in sprayed form on said leather (P), advancing along said linear direction (W) on said conveyor belt (<NUM>; <NUM>), at least one fluid painting mixture while said spraying means (<NUM>) follow a closed annular trajectory (T) under the rotation of said rotating unit (<NUM>), so that said spraying means (<NUM>; <NUM>) take a working condition along two primary circumference arcs (<NUM>, <NUM>) belonging to said closed annular trajectory (T) and defined directly above said conveyor belt (<NUM>; <NUM>), and a resting condition along two secondary circumference arcs (<NUM>, <NUM>), connecting said primary circumference arcs (<NUM>, <NUM>) and belonging to said closed annular trajectory (T), defined externally and laterally to said conveyor belt (<NUM>; <NUM>);
- suction means (<NUM>; <NUM>) operatively connected to said load-bearing structure (<NUM>) and adapted to capture by means of an airflow the fumes (Q) produced by said spraying treatment inside said load-bearing structure (<NUM>),
characterized in that said suction means (<NUM>; <NUM>) suck at the spraying area and in the lower part of said load-bearing structure (<NUM>) and are distributed according to an arcuate configuration substantially superimposable and equal to an arcuate spatial distribution of said primary circumference arcs (<NUM>, <NUM>) belonging to said closed annular trajectory (T) and along which said spraying means (<NUM>; <NUM>) take said working condition in which they dispense said fluid painting mixture on said leather (P) advancing on said conveyor belt (<NUM>; <NUM>).