Patent Publication Number: US-2021162434-A1

Title: Electrostatic rotary projector for coating product and spraying installation comprising such a projector

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of French Patent Application No. 19 13624, filed on Dec. 2, 2019. 
     FIELD OF THE INVENTION 
     The present invention relates to an electrostatic rotary sprayer for a coating product that includes a spraying cup, a body and a turbine assembled in this body configured to rotate the spraying cup about an axis defined by the body. 
     BACKGROUND OF THE INVENTION 
     It is known to charge a coating product leaving the spraying edge of a spraying cup by Corona effect using electrodes positioned on the body of a sprayer and brought to high voltage. The sprayers thus designed are conventionally used to coat easily accessible surfaces, such as the outer surfaces of a body of a motor vehicle. 
     In this case, as considered in EP-A-2,859,954, the electrodes, a sprayer body and a conformal air discharge skirt can be protected using a cover, so as to prevent them from becoming dirty. The positioning of the electrodes with a configuration diverging toward the front of the sprayer requires the cover to be relatively bulky, which makes the sprayer bulky, to the point that its use must in practice be limited to the outer surfaces of an object, such as a vehicle body. 
     Furthermore, it is known from US-A-2004/0255849 to assemble electrodes and resistances inside a ring immobilized on the outside of the body of an electrostatic rotary sprayer. This ring equipped with the electrodes tends to become dirty and must therefore be subject to regular disassembly and cleaning operations, which leads to relatively lengthy interruptions in the operation of a spraying installation including such a sprayer. This therefore limits the effective usage duration of such an installation. 
     These phenomena are even more significant when the sprayers used to coat the inner surfaces of an object, such as the inner surface of a body of a motor vehicle, are highly subject to “overspray”. These sprayers therefore tend to become dirty quickly, in particular at their electrodes. 
     SUMMARY OF THE DESCRIPTION 
     The invention more particularly aims to address these drawbacks by proposing a new electrostatic sprayer for coating product that can be used to coat inner surfaces and that can be cleaned easily and quickly, when necessary. 
     To this end, the invention relates to an electrostatic rotary sprayer for coating product that includes:
         a spraying cup;   a body;   a drive turbine assembled in the body and configured to rotate the spraying cup about an axis of rotation defined by the body; and   electrodes for charging the coating product sprayed by the spraying cup, these electrodes being assembled on a ring attached on the body and each supplied with voltage through a resistance.       

     According to the invention, each resistance extends axially outside the ring and is equipped, at its end opposite the electrode that it supplies, with a first electrical connection plug for connection on a second plug of corresponding geometry provided on the body of the sprayer, with a movement parallel to the axis of rotation, while the ring is configured to be assembled and connected on the body, or disassembled or disconnected from the body, while being equipped with electrodes and resistances. 
     Owing to the invention, the ring, equipped with various electrodes and resistances that protrude axially outside the ring, toward the rear of the sprayer, can be disassembled easily from the sprayer when this ring has a level of dirtiness that requires a cleaning operation, which can be done outside the sprayer, in particular during a later coating phase, that is to say during hidden time relative to the usage periods of the sprayer. Since the ring equipped with electrodes and resistances can be assembled/disassembled in a unitary manner, the assembly/disassembly of the ring takes little time, which makes it possible to consider a quick exchange of a ring equipped with dirty electrodes with a ring equipped with clean electrodes, without delaying a production line implementing the sprayer of the invention. 
     According to advantageous but optional aspects of the invention, such a sprayer may incorporate one or more of the following features, considered in any technically allowable combination:
         Each resistance is mounted in a sleeve equipped, at a first end, with an electrode, and at a second end opposite the first end, with the first electrical connection plug.   The sleeve is screwed on the ring.   Part of the electrode is received inside the sleeve and another part of the electrode protrudes outside the sleeve and passes axially through an orifice arranged to that end in the ring.   The body of the sprayer is equipped with sheaths each receiving a sleeve and in that a second plug is aligned, along a direction parallel to the axis of rotation, with each sheath, on the side of this sheath facing toward the rear of the sprayer.   The ring is snapped on the body of the sprayer and/or immobilized on the latter with interposition of a seal.   The body of the sprayer is equipped with a first peripheral snapping relief, while the ring is equipped with a second peripheral snapping relief and, in the assembled configuration of the ring and the electrodes on the body, the first and second snapping relief cooperate in order to immobilize and center, radially to the axis of rotation, the ring on the body of the sprayer.   The first plug or the second plug is of the male plug type with resiliently deformable blades.   All of the resistances and all of the first plugs extend axially on a same side of the ring, facing toward the rear of the sprayer.   The number of electrodes and resistances is inclusively between 13 and 20, preferably between 14 and 18, and preferably equal to 16.   The sprayer also includes a skirt for discharging air around the cup, while an annular slit is defined radially between the ring and the skirt, with its outlet oriented toward the front of the sprayer.   The sprayer also includes a skirt for discharging air around the cup, while the ring equipped with electrodes and resistances is configured to be assembled and connected on the body, or disassembled and disconnected from the body, without disassembly of the cup, and preferably, without disassembly of the skirt.       

     According to another aspect, the invention relates to an installation for electrostatic spraying of coating product on objects to be coated, which includes at least one sprayer as mentioned above. 
     Such an installation procures the same advantages as those mentioned above regarding the sprayer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood, and other advantages thereof will appear more clearly in light of the following description of one embodiment of an installation and a sprayer according to its principle, provided solely as a non-limiting example and done in reference to the appended drawings, in which: 
         FIG. 1  is a basic perspective illustration of an installation and a sprayer according to the invention; 
         FIG. 2  is a partially exploded perspective view of the sprayer shown in  FIG. 1 ; 
         FIG. 3  is a longitudinal sectional view of the sprayer of  FIGS. 1 and 2 , in plane III of  FIG. 1 ; 
         FIG. 4  is an enlarged view of detail IV in  FIG. 3 ; and 
         FIG. 5  is a larger scale view of detail V in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     The installation  2  shown very schematically in  FIG. 1  is used to coat objects O, which, in the example of the figures, are boxes of electrical cabinets or air-conditioning systems that have openings O 1  and O 2  and that each define an inner volume VO. These objects O are moved by a conveyor  4 , in a conveying direction shown by an axis X 4  in  FIG. 1 . Conveyor  4  includes several cradles  42  that each make it possible to support an object O to be coated and to move it along axis X 4 . 
     Installation  2  also includes an electrostatic and rotary sprayer  10  that is shown, in  FIG. 1 , on a larger scale than the other components of installation  2 . Sprayer  10  is assembled on a handle  62  of a multiaxial robot  6  that also belongs to installation  2 . It is supplied with coating product to be sprayed, high voltage and pressurized air through ducts that are not visible in  FIGS. 1 and 2  and that circulate through handle  62 . 
     Sprayer  10  in particular makes it possible to apply a coating product on the inner surfaces of an object O supported by conveyor  4 , which delimit its inner volume VO. Sprayer  10  is compact enough to engage in inner volume VO through one of openings O 1  or O 2 . 
     Sprayer  10  incudes a body  102  on which a turbine  104  is assembled for rotating a cup  106 , about an axis of rotation A 100  defined by body  102 . Cup  106  is secured to the rotor of turbine  104  by any suitable means, in particular by screwing or by magnetic assembly. 
     Body  102  is assembled on a plate  108  that constitutes the distal face of a bent part  110  of sprayer  10 , which makes it possible to off-center axis A 100  relative to a central axis A 62  of handle  62 . 
     Inside bent part  110 , a cable  112  circulates for supplying sprayer  10  with high voltage, for example, a voltage inclusively between −40 and −100 kV, in particular equal to −60 kV. A ground cable  114 , a pipe  116  for supplying liquid coating product and a pipe  118  for supplying pressurized air, with an absolute pressure inclusively between 1 and 6 bars, also circulate in bent part  110 . 
     An injector  120  is positioned at the center of turbine  104  and makes it possible to inject liquid coating product into cup  106 . The connection between supply pipe  116  and injector  120  is not visible in  FIG. 3  because it takes place in a different plane from that of this figure. 
     As shown in  FIGS. 3-5 , body  102  is formed by an inner part  1022  and an outer part  1024  that are both assembled on plate  108 , in addition to being assembled together. 
     The front of sprayer  10  is defined as the side of the sprayer facing toward the objects O to be coated when sprayer  10  is operating. Cup  106  is assembled to the front of sprayer  10 . The front of sprayer  10  faces toward the right in  FIGS. 1-5 . The back of sprayer  10  is defined as the side opposite the front, the back of sprayer  10  facing toward the left in  FIGS. 1-5 , moving away from the objects O relative to cup  106 . 
     Sprayer  10  includes a skirt  124  intended to discharge air around cup  106  when sprayer  10  is operating to coat objects O. Skirt  124  is a sub-assembly of sprayer  10  assembled around body  102  and turbine  104  and which defines air circulation channels up to the vicinity of cup  106 . More specifically, body  102  is provided with an outer thread  1021  and skirt  124  is provided with an inner tapping  1241  by which skirt  124  is screwed around body  102 . 
     Skirt  124  includes a monobloc inner part  1242  and an outer part  1244  that has two parts and that includes a front outer part  1244 A and a rear outer part  1244 B, the front outer part  1244 A being located more toward the front of sprayer  10  than the rear outer part  1244 B, i.e., closer to cup  106 . 
     Several pressurized air circulation ducts  1246  are arranged in inner part  1242  of skirt  124 . Other air circulation ducts  1247  are arranged in outer part  1244 . Ducts  1246  and  1247  open onto a front face  1248  of skirt  124 , in the form of orifices  1249  distributed around axis A 100  and cup  106 . 
     Ducts  1246  and  1247  are supplied with pressurized air from a pipe  118 , the connection between these ducts and this pipe taking place in a different plane from that of  FIG. 3 . 
     Sixteen electrodes  140  are assembled on an annular ring  160  that is in the form of a closed annulus, with a circular base in the example. 
     As emerges more particularly from  FIG. 5 , each electrode  140  incudes a body  142  and a needle  144 , the tip of which is denoted  146  and faces toward the front of sprayer  10 . 
     In practice, body  142  of each electrode  140  is housed in a sleeve  170  in which a resistance  180  is also received, through which electrode  140  is supplied with high voltage from cable  112 . Reference  184  denotes a first front end of each resistance  180  by which this resistance bears against body  142  of the electrode that it supplies. Reference  186  denotes the second rear end of each resistance that is opposite its first end. 
     More specifically, a male plug  113  positioned at the end of cable  112  is connected in a female plug  190  of corresponding shape, which is connected, by a conductive bar  192 , to one of sixteen blind housings  194  in each of which a female plug  196  is positioned. 
     Parts  1022  and  1024  of body  102  are made from an electrically insulating material, such as PTFE, and the inner surface of each of blind housings  194  is coated with a conductive powder, for example a carbon-based powder. Furthermore, the conductive layers of blind housings  194  are electrically connected to one another by conductive elements  198  embedded in body  102 . Thus, each of female plugs  196  is brought to the high voltage, from high-voltage cable  112 . 
     Body  102  is equipped with sixteen sheaths  200  each aligned with a blind housing  194  along a longitudinal axis A 200  that is parallel to axis A 100  and radially offset relative thereto. Sheaths  200  are each positioned in front of a blind housing  194 . In other words, sheaths  200  are each located in the extension of a blind housing  194 , along an axis A 200  that is parallel to axis A 100 , and a female plug  196  is aligned, along an axis A 200 , with each of sheaths  200 , on the back side of this sheath. 
     Each sleeve  170  is screwed into ring  160  using a thread  172  provided near a first front end  174  of each sleeve. Ring  160  is provided with sixteen tappings  162  allowing screwing of front ends  174  of sleeves  170 . Thus, each sleeve  170  is assembled and firmly kept in position on ring  160 , all of sleeves  170  and resistances  180  that they contain extending on a same side of ring  160 , for the most part outside the latter, toward the back of sprayer  10 , toward blind housings  194 . 
     An O-ring  202  is assembled around body  142  of an electrode  140 , inside first front end  174  of the corresponding sleeve  170 , while another O-ring  204  is assembled between first front end  174  of sleeve  170  and ring  160 . O-rings  202  and  204  ensure tightness between the inner volume of a sleeve  170  and the outside. 
     When a sleeve  170  is screwed and immobilized on ring  160 , needle  144  of electrode  140  whose body  142  is contained in this sleeve passes through an orifice  164  arranged in ring  160  and which passes all the way through it, from back to front, such that tip  146  of electrode  140  protrudes in the forward direction. In practice, each tip  146  is positioned in a depression  166  made to that end on front face  168  of ring  160  facing toward the front of sprayer  10 . Each tip  146  protrudes from the bottom of a depression  166 , toward the front. Advantageously, tips  146  do not protrude toward the front of front face  168 , which limits the risks of injury during handling of ring  160 , in particular when wiping surface  168 . 
     Ring  160  also includes a snapping member formed by a resiliently deformable tab or strip  169  that extends over the entire periphery of ring  160  and that is provided to cooperate with a complementary snapping relief  1029  provided on the outside of body  102 , with a geometry corresponding to that of tab  169 . This makes it possible to immobilize ring  160  on body  102  axially and to center it radially to axis A 100 . 
     Reference  176  denotes the second rear end of a sleeve  170  opposite its first front end  174 . 
     First front end  184  of each resistance  180  is positioned at first front end  174  of the sleeve that receives it, while second rear end  186  of the resistance is positioned at second rear end  176  of the same sleeve. 
     An electrical connector  206  is assembled in each sleeve  170 , at its rear end  176 , and it makes it possible to accommodate a male plug  208  of the “banana plug” type with resiliently deformable outer blades. The second end  186  of each resistance  180  is thus equipped, through a connector  206 , with a male plug  208  to which it is connected. All of male plugs  208  extend axially on the same side of ring  140 , toward the back of sprayer  10 , and parallel to one another. 
     The geometry of each male plug  208  allows it to cooperate by jamming with a female plug  196  positioned in one of blind housings  194 , when sleeve  170  to which it is secured is fully inserted into the corresponding sheath  200 , which is aligned with the blind housing  194 . 
     One then reaches the configuration shown in  FIGS. 1, 3, 4 and 5 , where each of electrodes  140  is supplied with high voltage through a conductive element  198 , a female plug  196 , a male plug  208 , an electrical connector  206  and a resistance  180 . 
     In this configuration, an ion flow can be emitted by each of tips  146  in order to charge the coating product leaving edge  1062  of cup  106 , when cup  106  is rotated by turbine  104  and when cup  106  is supplied with coating product through pipe  116 . The product leaving cup  106  is thus electrostatically charged by a charge phenomenon called “external” or “Corona”. 
     If ring  160  tends to become dirty, particularly at depressions  166  or front face  168 , it is possible to remove ring  160  by a simple pulling force parallel to axis A 100 , as shown by arrow F 1  in  FIG. 2 . 
     Force F 1  results in an axial movement of ring  160 , the sixteen electrodes  140 , the sixteen sleeves  170  and the sixteen male plugs  208  that are secured to ring  160 , which results in extracting the first plugs, formed by male plugs  208  and which are movable with ring  160 , from the second plugs formed by female plugs  196 , which are fixed with body  102 . 
     Movement of first ring  160 , electrodes  140 , sleeves  170  and resistances  180  takes place without it being necessary to disassemble cup  106  or skirt  124 , which remain in place on body  102 . Indeed, the inner diameter of ring  160  is strictly greater than the outer diameter of cup  106  and the outer diameter of skirt  124  over its axial length included between cup  106  and ring  160  assembled on body  102 . 
     After the removal of ring  160  and its accessories, it is possible to assemble, in place of elements  140 ,  160 ,  170 ,  180  and  208  previously disassembled, a new sub-assembly including a second ring  160 , electrodes  140 , resistances  180  and sleeves  170  equipped with male plugs  208  by inserting first male plugs  208  into second female plugs  196 , with an axial force, parallel to axis A 100 , as shown by arrow F 2  in  FIG. 2 . 
     This placement movement of second ring  160  and the various elements that it supports here again takes place without it being necessary to act on cup  106  or skirt  124 , which therefore do not need to be disassembled or reassembled relative to the rest of sprayer  10 . 
     Once second ring  160  and its accessories  140 ,  170 ,  180  and  208  are placed, sprayer  10  is once again functional and may be used to coat the objects O, while the first ring, which has been disassembled, may be cleaned during hidden time. The interruption of the operation of installation  2  is therefore limited to the time necessary for disassembly and connection of first ring  160  relative to plugs  196  and assembly of second ring  160  and its connection on plugs  196 , these operations taking place by simple axial translation, in the direction of the arrows F 1  and F 2 . 
     The separating movement of ring  160  and body  102  takes place against the snapping force exerted by elements  169  and  1029 . The snapping force may be overcome by an intense enough force F 1 . In order to facilitate application of this force, ring  160  is provided with a peripheral groove  165  in which the jaws of a tool, not shown, may be engaged, which makes it possible to clamp ring  160  radially, then to exert the pulling force in the direction of arrow F 1 . Such a tool may, for example, have three jaws, which are distributed radially around axis A 100  and which are engaged and clamped in peripheral groove  165  using an annulus that tightens these jaws. 
     The assembly and connection force of ring  160 , in the direction of arrow F 2 , is a pushing force exerted on front face  168 . 
     During placement of a new ring  160  or replacement of a previously cleaned ring, movement in the direction of arrow F 2  continues until snapping members  169  and  1029  engage with one another, which takes place during connection of the first and second plugs  208  and  196 . 
     Cooperation of first and second plugs  208  and  196  makes it possible to center ring  160  and electrodes  140  that it bears relative to body  102 , cup  106  and axis A 100  due simply to placement of ring  160  around body  102 . 
     Electrodes  140 , sleeves  170 , plugs  196  and  208 , and sheaths  200  are identical. Thus, ring  160  may be assembled on body  102  with any angular orientation around axis A 100 , with a pitch equal to 360°/16=22.5°. 
     The assembly and disassembly mode of ring  160  equipped with electrodes  140  and resistances  180  on body  102 , which takes place according to two axial translational movements in the direction of arrows F 1  and F 2 , makes it possible to consider an automatic assembly and disassembly of ring  160  on body  102 , using a robot. This procures advantages in terms of saved time, repeatability, and reliability of the assembly. This avoids human interventions in a spraying booth, and therefore the associated constraints in terms of equipment, tools and safety conditions to allow access thereto. 
     Furthermore, a duct  220  is arranged in inner part  1022  of body  102  and opens out near rear rim  1245  of rear outer part  1244 B of skirt  124 . More specifically, an annular volume V 102  is arranged between parts  1022  and  1024  of body  102  and rear outer part  1244 B of skirt  124  extends partially in annular volume V 102 , with its rear edge  1245  engaged in a peripheral groove  1024 A formed by part  1024  of body  102  and which constitutes the rear portion of the annular volume V 102 . An O-ring  222  delimits annular volume V 102  in the forward direction. O-ring  222  is positioned between rear outer part  1244 B and inner part  1022  of body  102  and bearing against these parts, which prevents circulation of the air emerging from duct  220  into annular volume V 102  toward the front of sprayer  10 , between parts  1244 B and  1022 . Groove  1024 A forms a baffle around rear rim  1245  of skirt  124 . Air leaving duct  220  must therefore flow into volume V 102 , in the direction of arrows F 3  in  FIG. 4 , first toward the rear, then toward the front, going around rear rim  1245 . Thus, volume V 102  constitutes a pressurized air flow chamber, between body  102  and skirt  124 , this chamber being delimited in the forward direction by O-ring  222 . 
     In practice, volume V 102  is an annular volume, which surrounds certain portions of parts  1022  and  1024  of body  102 , and several ducts of the type of duct  220  are provided, which emerge in volume V 102  in several locations distributed around inner part  1022  of body  102 , which indeed makes it possible to distribute air coming from pipe  118  in volume V 102 , around axis A 100 . 
     Air which flows in the direction of arrows F 3  within volume V 102 , arrives in a first chamber  224  defined between body  102  and skirt  124 , which has, in radial section, a globally triangular shape and which is connected to a second chamber  226  by channels  228 , the number of which is inclusively between 30 and 90, preferably between 45 and 75, preferably equal to 60. Second chamber  226  is annular and defined between skirt  124  and ring  160 . Second chamber  226  is used to distribute air coming from channels  228  radially around axis A 100 . Channels  228  have an inner diameter d 228  inclusively between 1.5 and 2.5 mm, preferably equal to 2 mm. If the channels have a non-circular section, it is the smallest dimension of their cross-section that is inclusively between 1.5 and 2.5 mm, preferably equal to 2 mm. In the case of channels  228  with a circular section, as shown in the figures, their diameter d 228  is the smallest dimension of their cross-section. 
     In a plane radial to axis A 100 , like the plane of  FIGS. 3-5 , channels  228  are inclined relative to axis A 100 , converging forward toward axis A 100 , which facilitates their production by piercing of rear outer part  1244 B of skirt  124 , after machining of chambers  224  and  226  in skirt  124 . Channels  228  are oriented toward a wall  227  of the annular chamber that is inclined in the forward direction toward ring  160 , i.e., divergent in the forward direction relative to axis A 100 . 
     The channels are each parallel to a plane radial to axis A 100 . 
     In parallel to channels  228 , a gap  230  connects chambers  224  and  226 . Gap  230  is defined between outer radial surface S 124  of skirt  1244  and inner radial surface S 160  of ring  160 . In other words, between chambers  224  and  226  along axis A 100 , skirt  124  and ring  160  are not in contact, such that radial gap  230  is formed, with a nonzero radial thickness e 230 . Radial thickness e 230  is smaller than the smallest dimension of a cross-section of a channel  228 . In practice, radial thickness e 230  of a gap  230  may be chosen between 0.1 and 0.3 mm, preferably equal to 0.2 mm. 
     Second chamber  226  opens out in the downstream direction, along outer radial surface S 124  of skirt  124 , by a slit  232  that is annular and the thickness of which is denoted e 232 , measured radially to axis A 100 . Radial thickness e 232  is chosen between 0.25 and 2 mm, preferably between 0.5 and 1.5 mm, also preferably equal to 1 mm. 
     At slit  232 , outer radial surface S 124  is frustoconical and converges toward the front of sprayer  10 , toward axis A 100 . Reference α 124  denotes the half-cone angle of surface S 124  at slit  232 . Still at slit  232 , inner radial surface S 160  of skirt  160  is also frustoconical and converges toward the front toward axis A 100 . Reference β 160  denotes the half-cone angle of surface S 160  at slit  232 . Angles α 124  and β 160  have the same value. In other words, inner radial surface S 160  of ring  160  locally marries the outer shape of skirt  124 . Thickness e 232  is thus constant over the length of slit  232 . 
     In practice, radial thickness e 232  is chosen to be strictly less than the smallest dimension of a cross-section of a duct  228 , therefore than its diameter d 228  in the case of a duct  228  with a circular section. Thus, flow of air in second chamber  226  accelerates in passing through ducts  228  to slit  232 . 
     Furthermore, since the channels are oriented toward surface  227 , air is distributed effectively around axis A 100 , in circulating along this surface, before reaching slit  232 . 
     Air opens out from slit  232  by an outlet  234  oriented toward the front of the sprayer, which sends air along the outer surface S 124  of skirt  124 , as shown by arrow F 4  in  FIGS. 3-5 , with a sufficient speed to travel along surface S 124 , into the vicinity of front face  128  of skirt  124 . Preferably, the geometry of surface S 124  and that of inner radial surface S 160  of ring  160  are chosen such that thickness e 232  is constant along slit  232 . Outlet  234  of slit  232  then also has radial thickness e 232 . 
     This tends to facilitate the fact that air flow leaving slit  232  follows surface S 124  by Coanda effect. Preferably, in order to facilitate this Coanda effect, the convergence angle toward the front of surface S 124  toward axis A 100  is chosen to be less than or equal to 7°. 
     Thus, slit  232  makes it possible to orient, through its outlet  234 , an air flow shown by arrow F 4  toward the part of the sprayer located in front of ring  160  and electrodes  140 . Air flow F 4 , which can be described as an air knife, preferably flows continuously when the sprayer is operating and it sweeps over the outer surface of sprayer  10 , in particular outer surface S 124  of skirt  124 , which prevents or greatly limits the deposits of coating product on this surface. Sprayer  10  is less inclined to become dirty and the cleaning operations may be more spread out over time than with known sprayers. 
     The air flow rate exiting through slit  232 , in the direction of arrow F 4 , is preferably less than the total skirt air flow rate discharged through orifices  1249 . As an example, for a skirt air flow rate inclusively between 300 and 800 liters per minute (l/mn), the air flow rate discharged by slit  232  may be on the order of 300 l/mn. In practice, in this case, the air flow rate discharged by slit  232  may be chosen to be between 100 and 500 l/mn, preferably between 200 and 400 l/mn, the value of 300 l/mn having proven to be particularly effective. 
     Air exiting from slit  232  in the direction of arrow F 4  has a driving effect by suction on the adjacent air, in particular on the air located in front of front face  168  of ring  160 . This driving effect creates an air current shown by arrow F 5  in  FIG. 3 , which facilitates cleaning of front face  168  and of the depressions  166  in the process of spraying or prevents overspray deposits, in the case where coating product residues tend to become deposited. 
     During operation, it is possible to monitor the high voltage applied to electrodes  140 , which makes it possible to detect any runaway of the electrostatic charge phenomenon or, on the contrary, a rapid decrease in this phenomenon, which could come from dirtying of electrodes  140  or of the adjacent parts of the sprayer, in particular skirt  124 . In case of drift of the voltage relative to a nominal value, for example −60 kV, the supply rate of pressurized air to volume V 102  and slit  232  may be temporarily increased, so as to quickly clean any deposit of coating product or moisture from surface S 124 . In particular, the supply rate of pressurized air to volume V 102  and slit  232  may be doubled in this case. 
     In this respect, in case of moisture risk, it is possible to consider that air conveyed to volume V 102 , therefore air discharged by slit  232 , may be hotter than the ambient air. In other words, air supplying the slit  232  may be heated relative to the ambient air around the sprayer, which improves the drying effect of surface S 124  owing to air flow leaving slit  232  through its outlet  234 . 
     According to another aspect of the invention, which can be applied in conjunction with or in place of those mentioned above, air supplying annular slit  232  may be electrically polarized. For example, electrodes, not shown, may be positioned in duct  118  or ducts  220  and in the parallel ducts in order to charge air with a polarity opposite that of the voltage applied on electrodes  140 . Under these conditions, air leaving slit  232  has the same polarity as the particles of coating product ejected by edge  1062  of cup  106 , which results in pushing these particles back toward the front of the sprayer, while limiting dirtying of surface S 124  and of ring  160 , in particular of its front face  168 . Such polarization of air discharged through slit  232  may be considered continuously or only in case of drift of the high voltage value delivered at electrodes  140 . 
     Annular slit  232  and air leaving it when the sprayer is operating facilitate cleaning of sprayer  10  within a rinsing box. In this type of equipment, it is typical to bring part of a sprayer into contact with one rim of the rinsing box, with an interposed seal. It is also typical to provide, in the rinsing box, an inner air jet and/or a device for scraping the outer surface of the sprayer. The air flow shown by arrow F 4  makes it possible to do away with this seal, inner air jet and/or scraping device because it continuously cleans the front part of the sprayer, including when the latter is engaged in the rinsing box. This provides greater freedom in the design of the outer shape of body  102  and skirt  124 . Furthermore, the air knife, which leaves slit  232  by its outlet  234 , as shown by arrows F 4 , makes it possible to confine any splashes of cleaning product and coating product to the inside of the rinsing box. In terms of the method, it is possible to provide that the chamber formed by volume V 102  is supplied with a maximum air flow rate when the sprayer is engaged in the rinsing box, which procures a maximum cleaning/drying effect during this phase of a spraying method implementing sprayer  10 . Owing to the air knife formed by the air flow leaving slit  232  through its outlet  234 , the drying time of the sprayer is decreased, which decreases the immobilization time of the sprayer in the rinsing box. Passage of the sprayer in the rinsing box makes it possible to space out the disassemblies/reassemblies of electrode  160  relative to body  102 . 
     When the sprayer is assembled, as shown in  FIGS. 1 and 3-5 , ring  160 , and in particular electrodes  140  and slit  232  are offset, along axis A 100 , toward the rear, relative to edge  1062  of the cup and relative to outlet orifices  1249  of skirt  124 . More specifically, tips  146  of electrodes  140  and outlet of slit  232  toward the outside are further from edge  1062  and orifices  1249  than skirt  124  front outer part  1244 A. Furthermore, along axis A 100 , annular slit  232  is positioned in the vicinity of tips  146 , which are also offset toward the rear relative to orifices  1249 . “In the vicinity of” means that, along axis A 100 , tips  146  of electrodes  140  are located less than 5 mm from slit  232 . 
     The invention is applicable with a liquid coating product, as mentioned above, or in a variant, with a powdered coating product. 
     According to one embodiment of the invention that is not shown, disassembly of ring  160  may take place owing to a tool that exerts a pulling force not on the outside of the ring, at peripheral groove  165 , but by the inside of ring  160 . In this case, when ring  160  must be removed, skirt  124  is disassembled, while keeping cup  106  in place on turbine  104  if the diameter of the cup is smaller than the inner diameter of skirt  124 . If the diameter of cup  106  is greater than or equal to the inner diameter of skirt  124 , like in the example of the figures, cup  106  is disassembled from the turbine prior to disassembly of skirt  124  relative to body  102 . In all cases, disassembly of skirt  124  occurs by unscrewing ring  160  relative to body  102 , by disengaging tapping  1241  from thread  1021 . It is then possible to screw, on thread  1021 , the body of a tool, not shown, that is provided with resilient tabs that extend toward the rear of sprayer  10 , past a surface S 161  of the ring that is radial to axis A 100  and facing toward the rear of the sprayer. These tabs deform resiliently in order to pass radially to the center of ring  160 , between ring  160  and body  102 , to the inside of volume V 102 , during assembly of the tool on body  102 . Free ends of the resilient tabs have harpoon-shaped tips, which, when the tabs regain their non-stressed configuration, engage behind surface S 161 . The harpoon-shaped tips are distributed around body  102 , therefore able to exert an axial force on surface S 161  in the direction of arrow F 1 , this force being distributed around axis A 100  due to the multiplicity of the tabs in question. This force is exerted when, after having engaged the harpoon-shaped tips of the tabs of the tool behind surface S 161 , the tool is unscrewed relative to body  102 . This force makes it possible to disassemble ring  160  relative to body  102 , subject to the removal of skirt  124 , and optionally of cup  106 . This allows for easy disassembly of ring  160  owing to the guiding of the tool on the thread, which guarantees a pulling force, shown by arrow F 1 , which is along axis A 100 . Additionally, the force is increased by the screw pitch. 
     In a variant, the number of electrodes  140  is different from sixteen. Preferably, this number is chosen between 13 and 20, in particular between 14 and 18. The fact that the number of electrodes is strictly greater than 12 means that the angular gap around axis A 100  between two adjacent electrodes is strictly less than 30°. Thus, the portion of front face  168  of ring  160  that is exposed to overspray between two tips  146  is relatively small, which limits the area of the surfaces of ring  160  to be cleaned. In all cases, the number of sleeves  170 , resistances  180  and first plugs  208  is equal to the number of electrodes  140 . 
     According to a variant of the invention that is not shown, first plugs  208  secured to ring  160  are female plugs, while second plugs  196  secured to body  102  are male plugs. 
     According to another variant, the structure and the geometry of skirt  124  may be different from that shown in the figures. In particular, the number of component parts of skirt  124  may be different than three. 
     According to still another variant, channels  228  may have an orthoradial component, to the point that air leaving from these channels has an orthoradial component resulting in a vortex component of air leaving from slit  232 . 
     The section of channels  228  may be different than circular. 
     Furthermore, the channels may be made, in whole or in part, in body  102 , instead of in skirt  124 . 
     According to still another variant, snapping members  169  and  1029  may be replaced by a seal positioned between body  102  and ring  160 , this seal making it possible to center and jam the ring on the body. This seal is advantageously an O-ring. 
     In the example, the supply circuit supplying slit  232  with pressurized air extends at once in body  102 , in the form of ducts  220 , in skirt  124 , in the form of ducts  228 , between body  102  and skirt  124 , in the form of volume V 102 , and between skirt  124  and ring  160 , in the form of gap  230 . In a variant, this circuit extends only in one or another of these parts or only between two of them. 
     The objects O on which the coating product is applied in the installation of the invention may be objects other than boxes, in particular motor vehicle bodies. Sprayer  10  is particularly suited to application of coating product to the inside of such bodies. 
     In a variant, multiaxial robot  6  may be replaced by another type of robot, in particular a reciprocator. 
     The invention makes it possible to consider, with time, dropping the entire outer casing of the sprayer and picking up a clean casing without stopping production, at a frequency depending on the application conditions and types. According to such an approach, the cup, skirt and electrode are dropped when they are dirty. A whole clean set is taken up and cleaning of the first casing is done during hidden time. It is even possible to consider moving toward dropping/taking up all of the parts in contact with the paint cloud or with the overspray, which would be difficult, if not impossible, with the external charge electrodes of the prior art. 
     The embodiments and variants considered above may be combined with one another to generate other embodiments of the invention.