EP0421866B1 - Device for projecting a coating product with a rotary spray element - Google Patents

Description

The invention relates to a device for spraying a coating product with a rotary spraying member, such as for example a spray bowl rotating at high speed, commonly used in the automotive industry, in particular; it relates more particularly to an improvement making it possible to ensure rapid and effective cleaning of all the parts of the rotary member with a relatively low consumption of cleaning product.

In the field of electrostatic painting, rotary members are often used for spraying the coating product, in particular in the form of a bowl. Such a rotary member is driven at high speed by a turbine (commonly rotating between 20 and 30,000 revolutions per minute) and is brought to a high voltage. The shape of such a bowl is relatively complex, which poses cleaning problems. However, in the automotive industry, cleaning for a change of coating product must be rapid. It is generally carried out by spraying cleaning product (solvent) on the various parts of the spraying member rotating at high speed. We then come up against different problems. One of them is to clean the front of the spraying member, which makes it necessary to use a nozzle for spraying a mobile cleaning product, to reach this front part, because there is no question that such a nozzle remains in the spray of sprayed coating product, after a cleaning operation. It is therefore necessary to provide a cylinder and the corresponding control system to make this nozzle retractable as well as a Venturi vacuum cleaner intended to collect the drops of cleaning product which could flow during spraying. The functioning of such a mechanism is never completely satisfactory because, in a coating product spraying installation, the mechanisms which only move from time to time are unreliable, due to contamination of the interfaces by parasitic projections. Another problem is that of splashing when the cleaning product is projected onto the rotating bowl at high speed. To prevent these splashes from reaching neighboring elements and in particular objects to be covered, it has been proposed in French patent FR-A-1 245 081, to carry out cleaning inside an interceptor, a kind of mobile housing, which moves axially by means of jacks to completely surround the spraying member while the latter is subjected to the action of several jets of cleaning product coming from nozzles, some of which are movable with the interceptor. The latter is provided with suction means for recovering and evacuating the cleaning product causing the residues of coating product. The equipment is bulky and expensive. Its operation is unreliable for the same reasons as indicated above.

Document DE-U-8607841 describes a rotary bowl projection device in which the frustoconical outer surface of the bowl can be cleaned by diverging jets of solvent from nozzles located in the support housing the drive means of the rotary bowl. Given the characteristics of liquids, this divergence can only be obtained by a jet sprayed in droplets. These are driven by the air rotated by the bowl, which results in a loss of efficiency. According to the teaching of this document, the sprayed solvent which meets the surface to be cleaned over substantially the entire axial length thereof is then ejected radially by centrifugal force, which causes significant splashing.

Furthermore, document EP-A-0 243 043 describes another projection device with a rotating bowl made of insulating material in which a nozzle of cleaning product is disposed near the outside surface of the bowl facing a semiconductor zone.

The invention provides an arrangement comprising no cleaning nozzle and / or mobile interceptor and operating without splashes. The equipment is therefore less expensive and its operation is much more reliable. The amount of cleaning product used is also lower. The invention stems from the surprising observation that the splashes of cleaning product due essentially to the cleaning of the generally convex parts of the projection member could be eliminated (despite the centrifugal acceleration of several tens of thousands of m / s² which tends to eject the coating product radially), bringing into play, other phenomena tending to maintain the film of coating product on the surface such as, presumably, the surface tension and the Coanda effect.

The invention therefore relates to a device for spraying a coating product with a rotary spraying member, comprising at least one nozzle for ejecting a cleaning product, fixed relative to the support of said rotary member and directed towards a generally convex surface of the latter. ci, said nozzle being arranged near said generally convex surface, characterized in that this nozzle is disposed in the immediate vicinity of said generally convex surface and oriented with a significant incidence so that its jet reaches said surface behind that by allowing the cleaning product to keep its jet shape without spraying up to its point of impact on said generally convex surface.

The notion of incidence is to be considered here in the same way as in optics. It is therefore the angle made by the jet of cleaning liquid coming from a nozzle with respect to the normal to said generally convex surface, at the point of impact. The term “generally convex surface” is understood here to mean any surface of the rotary spraying member such that the radial component of the centrifugal force tends to spray a liquid located on this surface outside. surface, as opposed to a concave surface for which the radial component of the centrifugal force on the contrary tends to press the liquid on said surface. In the case where the spraying member has the general shape of a bowl, such a generally convex surface is in particular the external surface of said bowl and, optionally, an approximately conical central prominence, extending axially from a veil. perpendicular to the axis of rotation and set back from the spray edge of the bowl. In the latter case, the corresponding cleaning product ejection nozzle is located at the rear of the veil and the latter has a ring of holes made along a circular contour in the vicinity of the base of the protuberance and this nozzle is oriented so that part of its jet of cleaning liquid, not intercepted by the veil, meets the prominence under a desired incidence, for the cleansing of this prominence. The cleaning liquid intercepted by the veil, in particular by the side walls of the holes extending through it, is used for cleaning the external front face of the veil. The axis of the holes can be tilted in a sort of helix to reduce the interception time of the jet. One can also tilt the axis of the jet (according to the direction of rotation of the rotary member) to give it a speed component in the same direction as this rotation. It can also be advantageous to give the front face of the veil a very slightly concave shape because the normal component of the centrifugal force on the product improves cleaning.

• la figure 1 est une coupe partielle dans un plan passant par l'axe de rotation de l'organe tournant, d'une partie d'un dispositif de projection de produit de revêtement conforme à l'invention;
• la figure 2 est une vue frontale partielle du dispositif de projection de la figure 1, vu suivant la flèche II de la figure 1; et
• la figure 3 est une autre vue schématique du même dispositif, suivant la flèche III de la figure 1.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of a device in accordance with its principle, given solely by way of example and made with reference to the accompanying drawings. wherein:

• Figure 1 is a partial section in a plane passing through the axis of rotation of the rotary member, of a part of a coating product projection device according to the invention;
• Figure 2 is a partial front view of the projection device of Figure 1, seen along arrow II of Figure 1; and
• FIG. 3 is another schematic view of the same device, along arrow III in FIG. 1.

Referring to the drawings, there is shown the end part of a coating product projection device comprising a turbine 11 housed in a support housing 12 and the rotary shaft 11 of which projects from the housing, carries a spray 14 whose external shape is approximately that of a bowl. In operation, the bowl is brought to a high voltage. This type of spraying member has an approximately frustoconical external face 16, ending, opposite the object to be covered, by a discharge edge 17 and a veil 18, generally perpendicular to the axis of rotation x'x of the spraying member and set back relative to the discharge edge 17. This veil is connected to the internal face of the bowl and its internal face 18 a is extended axially by a fixed hub 19 mounted at the end of the shaft 11 has turbine. The outer face 18 b of the veil carries or has an approximately conical protrusion 20 (rounded at its end) whose role, known, is to limit parasitic deposits of coating product on the veil and to make the center of the front face cleanable from the back of the bowl. Holes 22 are made in the veil along a circular contour in the vicinity of the junction of this veil with the internal face of the bowl. As mentioned previously, the face 18b of the web can be slightly concave radially beyond said prominence. The deflection of the concavity can be 3 to 5mm. The coating product is deposited on the inner face of the veil by a fixed supply nozzle 24, carried by the support housing 12 and engaged in the space 26 defined between the internal surface of the bowl and the inner face of the veil. The coating product deposited on the internal face 18 a therefore propagates, under the effect of centrifugal force, towards the periphery of the web, passes through the holes 22 and continues its progression along the internal wall of the bowl to the edge. discharge 17 where it is sprayed. Furthermore, the housing-support 12 includes compressed air supply means 27, for example an annular chamber having a plurality of air ejection holes 27 is arranged along a circular contour at the rear of the rotary member 14 so as to create an "air envelope" driving the particles of coating product forward. The spraying member as described so far is known. In this type of rotary spraying member, there are two so-called "overall" surfaces convex "according to the above definition. This is the external face 16 of the bowl-shaped part and the protrusion 20. In fact, a liquid deposited on one or the other of these surfaces tends to leave said surface under the effect of centrifugal force when the spraying member is driven at high speed. The invention stems from the surprising observation that, even at very high speeds involved, this radial component of the centrifugal force could be compensated if the liquid was projected under a suitable incidence probably favoring other phenomena such as the Coanda effect or the action of surface tension, capable of keeping at least a significant part of the liquid in contact with said generally convex surface. he invention takes advantage of this observation for cleaning the rotary member, relatively without splashing.

According to the invention, at least one cleaning product ejection nozzle is provided, fixed relative to the support 12, that is to say carried by it and directed towards such a so-called "generally convex" surface with an orientation such that its jet of cleaning liquid meets this surface with a significant incidence.

Thus, a cleaning product ejection nozzle 28 is provided, situated at the rear of the spraying member and oriented towards the surface 16 so that the angle of incidence a ₁ defined above is significant. In practice, a suitable operation is observed for an angle of incidence at least approximately equal to 20 °. However, this value does not constitute an absolute lower limit. With such an incidence and a sufficient speed of ejection of the cleaning product and also due to the fact that the nozzle 28 is located in the immediate vicinity of said generally convex surface (a few millimeters), at the rear thereof, a progression towards the front of the cleaning product is observed, on the external surface 16. The cleaning product retains its jet form, without spraying, up to its point of impact on the external surface 16.

Independently of the angle of incidence a ₁, it is also possible to orient the nozzle 28 so that its jet of cleaning liquid is contained in a plane containing no axis of rotation. The angle a ₂ between this plane and the axis x'x is such that the jet of liquid meets the external surface 16 in a slightly oblique fashion and according to the direction of rotation R of the bowl, as is clearly shown in FIGS. 2 and 3. The jet from this nozzle therefore has a speed component in the same direction as that of the bowl.

In addition, the air blowing means 27 are arranged so that the orifices 27 a are located at a radial distance from the axis of rotation x'x greater than the radial distance at which the nozzle 28 is located. In other words , the jet of cleaning liquid from the nozzle 28 is located inside the air envelope created by the air blowing means 27. This arrangement has particular advantages. Indeed, as indicated above, part of the cleaning liquid progresses towards the discharge edge 17 while remaining on the surface 16 as long as the effects of the centrifugal force are compensated for by the other phenomena mentioned above. It can be estimated that a part S1 of the surface 16 is thus directly cleaned by the cleaning liquid coming from the nozzle 28. Beyond this, the cleaning liquid tends to leave the surface 16 but it is returned to the part S2 closest to the edge 17, by the air envelope created by the air blowing means 27. Similarly, at the point of impact X of the cleaning product on the bowl, a certain part of the liquid s' escapes into coarse drops of the surface 16. These low spatter are sprayed into droplets much finer by meeting the envelope from air holes 27a and the cleaning air-product mixture is found precipitate on the part S2 of the bowl, thus contributing to its cleaning.

Finally, it should be noted that the nozzle 28 is located in a vacuum zone due to the proximity of the rotating bowl and the air envelope. If a drop of cleaning product escapes during the application of the coating product, it is picked up by the bowl and sprayed without causing any apparent defect on the object.

On the other hand, another cleaning product ejection nozzle 35 is oriented towards the surface of the protrusion 20. It is located inside the space 26, therefore behind the web 18, but this the latter has a ring of holes 36 made along a circular contour in the vicinity of the base of said protrusion 20. The terminal part of the nozzle 35 is near the web 18 and bent so as to be oriented internally to "aim" at the surface of the protrusion, through the holes 36. In this way, part of the cleaning liquid, not intercepted by the veil, spreads on the surface of the protrusion 20 with a behavior similar to that described above. The incidence is strong, close to 90 °. The cleaning product which is intercepted by the veil makes it possible to clean the two faces 18 a , 18 b of the latter. Thus, the liquid which is intercepted by the face 18 a itself (meeting the veil between the holes 36) is evacuated by remaining on this rear face and therefore by cleaning it, before crossing the holes 22 and flowing until 'at the discharge edge 17. On the contrary, the cleaning liquid which is intercepted by the side walls of the holes 36, is discharged essentially by flowing over the front face 18b of the web. To improve the cleaning of the front face 18 b , it may be necessary to promote the flow of the liquid captured by the side walls of the holes, towards this front face. To do this, the holes in the crown made in the veil are divergent, from back to front relative to the axis x'x of rotation of the bowl. The orientation of the liquid jet remains converging due to the inclination of the nozzle 35. Furthermore, the side of the front face 18 b of the web, the holes 36 open at the bottom of a groove 38 around said prominence 20. This groove and more particularly its outer side wall 38 a which is here frustoconical, serves to homogenize the outlet of cleaning product captured by the holes. In one possible embodiment, we practiced eight cylindrical holes 36 distributed regularly in a crown (Figure 2). If we want to increase the proportion of product used for cleaning the prominence 20, we can provide oblong and curved holes, in smaller numbers, distributed along the same circumferential contour. Similarly, the axis of each hole 36 can be inclined according to a sort of helix and the axis of the jet coming from the nozzle 35 can be oriented so that the speed of the jet has a speed component in the direction of that of the rotary organ.

Claims (11)

1. A coating product spraying device having a rotatable atomisation member (14), comprising at least one cleaning product ejection nozzle (28, 35) which is fixed with respect to the support for said rotatable member and which is directed towards a generally convex surface (16, 20) thereof, said nozzle being arranged in the vicinity of said generally convex surface, characterised in that said nozzle is disposed in the immediate vicinity of said generally convex surface and is oriented with a substantial angle of incidence in such a way that its jet reaches said surface to the rear thereof, permitting the cleaning product to retain its jet form without atanisation as far as its point of impact against said generally convex surface.
2. A device according to claim 1 characterised in that it comprises such a said ejection nozzle (28) which is disposed to the rear of the bowl and which is oriented forwardly and towards the external surface (16) of said bowl.
3. A device according to claim 2 characterised in that said nozzle (28) is so oriented that the direction of the jet of cleaning product is included in a plane which does not include the axis of rotation of said rotatable member and such that the jet issuing from said nozzle has a velocity component in the same direction as that of the rotatable member.
4. A device according to claim 2 or claim 3 characterised in that it comprises in per se known manner air blowing means (27) which are arranged in an annular configuration coaxial with said rotatable member and to the rear thereof, in such a way that the blown air substantially envelopes the rotatable member, and that said ejection nozzle (28) is disposed at a radial distance from the axis of rotation (x'x) which is less than that of the orifices (27a) of said annular configuration, and that it is so oriented that the jet of cleaning liquid is within the air envelope created by said air blowing means.
5. A device according to one of the preceding claims wherein said rotatable member comprises a disc (18) which is generally perpendicular to the axis of rotation (x'x) and set back with respect to the edge (17) of said rotatable member, the central part of the external face of said disc defining a protuberance (20), characterised in that it comprises a said ejection nozzle (35) which is oriented towards the surface of said protuberance, that said nozzle is disposed to the rear of said disc and that the latter comprises a ring of holes (36) disposed along a circular contour in the vicinity of the base of said protuberance, the nozzle being oriented in order for a part of its jet of cleaning liquid to pass through said holes and meet said protuberance.
6. A device according to claim 5 characterised in that the holes (36) of said ring which are provided in the disc are divergent from the rear forwardly with respect to the axis of rotation (x'x) of said rotatable member.
7. A device according to claim 5 characterised in that the holes (36) of said ring open at the side of the front face of said disc at the bottan of a groove (38) surrounding said protuberance.
8. A device according to claim 7 characterised in that the external side surface (38a) of said groove (38) is frustoconical.
9. A device according to one of claims 5 to 8 characterised in that said external face of said disc is slightly concave radially beyond said protuberance.
10. A device according to one of claims 5 to 9 characterised in that the axis of each hole (36) of said ring is oriented in a kind of helix.
11. A device according to one of claims 5 to 9 characterised in that said second nozzle (35) is so oriented that the axis of the jet issuing from said nozzle has a velocity component in the same direction as that of said rotatable member.

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