EP1068022B1 - Atomising bowl and electrostatic rotary sprayhead unit equipped therewith - Google Patents

Abstract

The invention concerns an atomising bowl (4) for coating product electrostatic rotary sprayhead unit (1), said bowl comprising a bell (7) for distributing the product made from a conductive material and arranged to be brought to high voltage when the sprayhead unit is in operation, so as charge electrostatically said product by contact. The invention is characterised in that said bell is electrically connected to at least one corona discharge element (22, 25, 28) from one tapered end (22a, 25a, 25b, 28a), said tapered end being arranged in the proximity of said bowl outer surface (20a, 9a). The bowl is electrically connected to a generator capable of detecting variations in the glow currents passing through the discharge elements (22, 25, 28) or the bowl tips.

Description

The invention relates to a spray bowl and a electrostatic rotary coating product sprayer equipped with such a bowl. A bowl according to the preamble of claims 1 or 9 is known from document EP-A-094 796.

It is known to equip a rotary product sprayer for coating a bowl or bell integral with the rotor of a rotational drive turbine, to form a cloud of sprayed coating product, this cloud being entrained by a electrostatic field and possibly by a flow air, towards an object to be coated. There are basically two types of spray bowls, namely bowls spraying material electrically conductor and the spray bowls made in a electrically insulating material.

Bowls made of insulating material do not allow do not electrostatically charge the coating material, so that additional means of charging must be provided coating product by Corona landfills or corona. The coating product load obtained is less effective, so that the effect of the electrostatic field on the particles of coating is lower, the deposit yield obtained being relatively small.

Bowls made of a conductive material allow electrostatically charge the coating product when its flow in contact with the surfaces of the bowl which is brought to high voltage by any appropriate means. These bowls feature generally the disadvantage of building up capacities electrical hazards, potentially dangerous to a user and likely to create arcs suitable for starting a fire in the explosive atmosphere a coating booth.

In addition, electrostatic coating materials and their devices are subjected to security tests pushed to ensure that they are not likely to cause an electric shock whose energy would greater than a predetermined threshold value. Some standards provide for example that the breakdown energy or discharge, between a part of the sprayer raised to high tension and a sphere of small radius arranged at a distance on the order of a centimeter, must be less than 0.24 mJ. A such value cannot be respected with a known bowl made of electrically conductive material because the edges and the flat surfaces which it comprises, in particular near the edge of the coating product, are likely to give rise to much higher energy discharges.

It is to these disadvantages that we hear more particularly remedy the invention, by proposing a spray bowl allowing a contact charge of the coating product and for which the discharge or "breakdown" energy is maintained at a level lower than that imposed by the standards more restrictive.

In this spirit, the invention relates to a spray bowl for electrostatic rotary projector of product of coating according to claim 1 or 9.

Thanks to the invention, the flange, which constitutes the part central bowl, authorizes a contact charge of the product coating in progress. The element (s) of discharge create privileged scent paths between the flange and the outside of the bowl, so that no build-up of energy is only possible at a level such as the energy of breakdown would exceed the allowable values.

Also, by taking the modeling of an object to ground which approaches the bowl, the approximation of the object leads to an increase in the corona current resulting in a drift of the current consumed, this drift can be detected by a high voltage generator used for power in high voltage of the bowl flange. Indeed, the generators known, such as in particular from patent application EP-A-0 219 409 in the name of the Applicant, are capable of reacting to a abnormal current variation. So the current variations generated by the discharge element (s) during the approach of an object to ground are detected early enough by the generator so that the security function of it removes power before a discharge potentially dangerous energy is possible.

According to a first advantageous aspect of the invention, the bowl includes several regularly distributed discharge elements around its axis of rotation. This multiplicity of elements discharge allows to obtain, when powering the bowl, the desired effect with a symmetry of revolution around of the axis of rotation of the bowl, including in the absence of setting rotation. In addition, this distribution avoids an imbalance dynamics of the bowl, i.e. an unbalance not admissible to rotational speeds considered.

According to a first embodiment of the invention according to claim 1, the flange is bordered at its periphery external, by a generally annular part produced in an electrically more insulating material than the material of the flange and forming a spray edge or edge of the bowl and the current discharge element is formed by an insert made of an electrically more conductive material than the annular part and arranged in this annular part, in electrical contact with the flange, this insert extending to the vicinity of an external surface of the annular part. The annular part located at the periphery of the flange avoids risk of electric breakdown between flat surfaces brought to high voltage and a neighboring object brought to ground. The inserts, which are advantageously but not necessarily metallic, constitute particularly discharge elements effective through the insulating or semiconductor layer produced by the annular part around the flange.

According to another advantageous aspect of the invention, the insert is partially received in a hole in the flange driver. This particularly simple construction ensures effective electrical contact between the flange and the insert, while ensuring its positioning in relation to others constituents of the bowl.

According to another advantageous aspect of the invention and in the case of a bowl comprising a deflector of the product flow covering placed opposite a surface, called the front face, of the flange, the deflector carries at least one discharge element extending to an external surface, called the front face, of the deflector. The presence of this discharge element in the deflector also prevents the accumulation of charges electrostatic in this deflector and in the product of coating in the course of flow around this deflector. Advantageously, the discharge element is an insert disposed along the axis of rotation of the bowl.

According to another advantageous aspect of the invention, the one or more inserts are or are needle shaped and have at least one tip-shaped end, this end being flush to the external surface of the annular part or the deflector. In this case, it is advantageously provided that at least one insert carries a collar capable of cooperating with an internal shoulder a housing for receiving the insert.

According to an advantageous alternative embodiment of the invention, at least one insert has two shaped ends point, these ends being flush with two surfaces external of the annular part, these external surfaces being oriented respectively towards the axis of rotation and towards the outside of the bowl. This particular arrangement allows limit the value of the discharge energy both towards the central area of the bowl and outwards.

According to another advantageous aspect of the invention, the end of the insert close to the outer surface of the bowl is arranged near the spray edge. This provision is particularly advantageous, because it is near the spray edge that there is more risk than getting has an obstacle to ground, such as a hatch or door not closed on a motor vehicle body in progress coating.

According to another embodiment of the invention according to claim 9, the discharge element is formed by a point shaped on the external surface of the flange. This aspect of the invention enables a bowl to be produced entirely conductive, particularly efficient for charging by coating product contact, while avoiding problems aforementioned discharge with potentially energy levels dangerous. Indeed, the spikes formed by the elements of discharge are supplied with high voltage by the mass of the flaccid and constitute as many privileged points of discharge by scents. Advantageously, the point or points are formed in a single piece with the flange.

The invention also relates to an electrostatic headlamp. coating product which includes a bowl such as previously described and electrical connection means of the flange of this bowl to a high voltage generator, this generator being able to detect variations in the corona current passing through the bowl discharge element (s). This projector meets the most demanding standards in terms of security, which corresponds to a very high dependability.

• la figure 1 est une représentation schématique de principe d'un projecteur rotatif électrostatique d'un produit de revêtement conforme à l'invention ;
• la figure 2 est une vue de face à plus grande échelle du bol utilisé avec le projecteur de la figure 1 ;
• la figure 3 est une coupe selon la ligne III-III à la figure 2 ;
• la figure 4 est une vue à plus grande échelle de deux détails IV de la figure 3 ;
• la figure 5 est une vue analogue à la partie supérieure de la figure 4 pour un bol conforme à un second mode de réalisation de l'invention et
• la figure 6 est une coupe analogue à la figure 3 pour un bol conforme à un troisième mode de réalisation de l'invention.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of three embodiments of a spray bowl and of a projector on which it can be mounted, in accordance with its principle, given solely by way of example and made with reference to the appended drawings in which:

• Figure 1 is a schematic representation of the principle of a rotary electrostatic projector of a coating product according to the invention;
• Figure 2 is a front view on a larger scale of the bowl used with the projector of Figure 1;
• Figure 3 is a section along line III-III in Figure 2;
• Figure 4 is an enlarged view of two details IV of Figure 3;
• FIG. 5 is a view similar to the upper part of FIG. 4 for a bowl according to a second embodiment of the invention and
• Figure 6 is a section similar to Figure 3 for a bowl according to a third embodiment of the invention.

In FIG. 1, an electrostatic rotary projector 1 of coating product comprises a rotor 2 driven in rotation by any suitable means and, in particular by an air turbine or a electric motor. The rotor 2 carries an elastic ring 3 which may conform to the technical teaching of EP-A-0 697 917. The elastic ring 3 makes it possible to make a bowl of spraying 4 of the rotor 2. The rotor 2 is crossed by a fixed duct 5 for supplying coating product to vicinity of a central orifice 6 for supplying the bowl 4 formed in a flange 7 extending generally perpendicular to the axis of rotation XX ′ of the rotor 2, of the ring 3 and of the bowl 4.

The rotor 2 is made of a material electrically conductor, for example metallic, and connected by any means suitable for a high voltage generator 8. The ring 3 and the flange 7 are also made of materials electrically conductors, so that the high voltage from the generator 8 is transmitted to the flange 7. The flange 7 is therefore able to charge electrostatically, by contact, the coating product which flows on its surface when it is supplied with high voltage by generator 8 during operation of projector 1.

The bowl 4 also includes a deflector 9 disposed opposite the outlet orifice of the conduit 5 relative to the flange 7, that is to say facing a surface 7 a , called the front face, of the flange 7. The deflector 9 is pierced with four conduits 10 allowing, during the cleaning phases of the bowl, the flow of a part of a solvent coming from the conduit 5 on its surface 9 a directed towards the outside and called the face before. The deflector 9 is immobilized with respect to the flange 7 by screws 11 passing through the flange 7 and penetrating into the rear bosses 9 b of the deflector 9.

A generally annular part 20, made of an electrically insulating plastic material, is arranged around an external radial part 7b of the flange 7 and defines an edge or spraying edge 21 of the coating product during the rotation of the bowl 4. The piece 20 is advantageously glued to the flange 7. It is also noted that the respective shapes of the pieces 7 and 20 contribute to immobilization of the piece 20 on the flange 7 by cooperation of shapes.

Needle-shaped metal inserts 22 are housed in eight blind holes 23 formed both in the part 20 and in the flange 7. Each insert 22 comprises a first end 22 a , in the shape of a point, disposed flush with the surface external 20 has the part 20 close to the spraying edge 21. the second end 22 b is inserted into the bottom of the hole 23 which is formed in the portion 7b of the flange 7.

Thus, the inserts 22, which are metallic, are in permanently brought to the same electrical potential as the flange 7.

When an object with mass, represented by a sphere S in dashed lines in Figure 4, is approached from the spray edge 21, a discharge line L is created as shown in dotted lines. The inserts 22 therefore constitute as much discharge elements by emanation from the bowl 4. The line of L discharge results in a current consumption which can be detected by the generator 8 according to known techniques, in particular from EP-A-0 219 409. The generator is then able to react to this surge in current by cutting feeding the bowl to prevent the energy level potentially reached during a spark discharge does not is greater than an imposed value.

We understand that the fact that the bowl includes several inserts 22 distributed around the axis XX 'allows to multiply the effect described above and to ensure symmetry around it this axis.

In addition, and as appears more particularly from FIGS. 3 and 4, a second series of eight inserts 25 is arranged through the part 20 and the external radial part 7 b of the flange 7, each insert 25 comprising a first end 25 a in point shape arranged in the immediate vicinity of the external part 20 a ₁ of the external surface 20 a .

The spikes 25 are inserts 25 are directed towards the rear of the bowl 4, in the direction of a cover outer surface 12 of the projector 1 shown in phantom in Figure 1. In fact, any object to ground can not be approached tips 25a through the hood 12 which is insulating, so that the cover limits the potential approach area of a ground object.

As before, when approaching a grounded object, represented in phantom by a sphere S, a discharge line L ′ is created from the tip 25 a of the insert 25.

Each insert 25 carries, at its second end 25 b , a head or flange 25 c capable of cooperating with a shoulder 26 a of a receiving hole 26 of the insert 25. This makes it possible to position the first end with precision 25 has the insert 25 relative to the external surface 20 a ₁ of the part 20. A glue or resin plug 27 is advantageously disposed in the part of the bore 26 opposite the point 25 a , so that the part 20 a ₂ of the external surface 20 a directed towards the axis XX 'does not have any irregularities in which the coating product could accumulate.

The positioning of the inserts 25 through two parts 20 b and 20 c of the part 20 arranged on either side of the external part 7 b of the flange 7 makes it possible to improve the relative immobilization of the parts 7 and 20.

Returning to Figures 2 and 3, we note that an insert 28 is disposed in. the deflector 9 and comprises a first end 28 a , in the shape of a point, disposed flush with the front face 9 a of the deflector 9. If the deflector 9 is made of electrically conductive material, the insert 28 is brought to the same potential electrostatic than the flange 7, so that it is capable of generating a discharge line, as explained above with reference to the inserts 22 and 25. It should here be noted that, even if it is disposed within an electrically surface conductive raised to the high voltage through the bosses 9b, the tip of the insert 28 constitutes a privileged zone of discharge relative to the surface 9a of the deflector 9.

As indicated previously with reference to the inserts 22, the scent generated at the tips of inserts 25 and 28 are detected by the generator 8.

It is also possible to provide that the deflector 9 is made of electrically insulating material, in which case the insert 28 is brought to a floating potential. In this case, the tip 28 a is also used for the effluvium of the electrostatic charges drained by the insert 28 on the surface of the deflector 9.

Whatever the materials used for the deflector 9, the insert 28 prevents the electrical capacity of the conduit 5, of its support and of the turbine associated with the rotor 2 from being discharged through the conduits 10 for flushing the front face 9 has deflector.

In the second embodiment of the invention shown in Figure 5, elements similar to those of the embodiment of the previous figures bear identical references. This embodiment differs from the previous one essentially in that the inserts 25 include a tapered tip at each end 25 a or 25 b . This also makes it possible to create a discharge line L "on the side of the surface 20 a ₂ of the part 20 when a sphere S, at earth potential, is approached in the direction of the point 25 b . The ends in point 25 b avoid the creation of electric arcs or high energy discharges between the front circular edge 9 c of the deflector and an object grounded in the position of the sphere S in FIG. 5.

In the two embodiments envisaged, the presence of the flange 25 c and the shoulder 26 a guarantees that the inserts 25 are not likely to be ejected from the bowl under the effect of the intense centrifugal forces which they undergo due to high rotation speeds of the spray bowl which can reach, or even exceed, 80,000 revolutions per minute.

The material used for the manufacture of the flange 7 is advantageously based on aluminum, which allows it to have good dimensional stability, this property being essential when rotating the bowl at speed high. The material used for part 20 can be a resin based on polyoxymethylene. Finally, inserts 22, 25 and 28 can be made of steel or aluminum.

The annular part 20 can also be produced in a semiconductor material, because it suffices that the part 20 has a higher resistivity than that of inserts 22 or 25 so that these constitute privileged routes of discharge. according to another alternative and when part 20 is made in an electrically insulating material, provision may be made for the inserts 22 and 25, or even insert 28, are produced in a semiconductor material.

In the third embodiment of the invention shown in Figure 6, elements similar to those of the embodiment of Figures 1 to 4 bear identical references increased by 50. The bowl 54 shown in Figure 6 can be mounted on the projector shown schematically in Figure 1. This bowl essentially comprises a flange 57 made of an electrically conductive material on which is fixed one. deflector 59 by means of several screws 61. This bowl differs from those of the previous embodiments essentially in that it does not include an annular piece more insulating than the flange 57, but on the contrary in that the flange 57 extends radially to the outside so as to form the spraying edge 71. Note 57c the outer peripheral surface of the flange 57. on this surface 57 c are provided several pins or spikes 75 is formed integrally with the flange 57 Similarly, several points 72 are provided on the spraying edge 71. Finally, points or pins 75 b are arranged on an internal surface 57 d of the flange 57 directed towards the deflector 59.

As before, the points 72 to 75 a and 75 b constitute as many privileged zones for discharging by corona the electrical capacity constituted by the flange 57 as a whole. The variations in current consumption induced by the emanations, during the creation of a discharge line, in particular by approaching an object of ground, can be detected by the generator 8 mentioned with reference to the first embodiment.

The points or pins 72, 75 a and 75 b have a height h relative to the spraying edge 71 or to the surfaces 57 c and 57 d of the order of 1 to 2 mm, which allows them to create zones discharge by fragrance without being dangerous for a user who handles the bowl 54.

As in the first embodiment of the invention, the deflector 59 can be equipped with a discharge insert by corona, or even provided, in its central part, with a point of the type of tips 72.

Claims (13)

1. Atomising bowl (4) for a rotary electrostatic spray unit (1) for a coating product, the said bowl comprising a flange (7) for distribution of the product, which flange is made of an electrically conductive material and is designed to have high voltage applied to it when the spray unit is functioning, such as to charge the said product electrostatically by contact, characterised in that the said flange is edged on its outer periphery (7b) by a globally annular part (20) which is made of an electrically insulating material, and forms an atomising ridge or edge (21), in that at least one electrically conductive insert (22, 25) with current discharge by means of corona discharge from one end (22a, 25a, 25b) is disposed in the said annular part, in electrical contact with the said flange (7), and in that the said end (22a, 25a, 25b) of the said insert is in the form of a tapered point, and extends as far as the vicinity of an outer surface (20a) of the said annular part.
2. Atomising bowl according to claim 1, characterised in that the said insert (22, 25) is partially accommodated in a bore (23, 26) provided in the said conductive flange (7).
3. Atomising bowl according to claim 1 or claim 2, comprising a deflector (9) for the flow of coating product disposed opposite a surface (7a), known as the front surface, of the said flange (7), characterised in that the said deflector supports at least one discharge element (28) which extends as far as an outer surface (9a), known as the front surface, of the said deflector.
4. Atomising bowl according to claim 3, characterised in that the said discharge element is an insert (28) which is disposed according to the axis of rotation (XX') of the said bowl (4).
5. Atomising bowl according to any one of the preceding claims, characterised in that the said insert(s) (22, 25, 28) is or are in the form of a needle, and is or are provided with at least one end (22a, 25a, 28a) in the form of a point, the said end being flush with the said outer surface (20a, 20a ₁, 20a ₂, 9a) of the said annular part (20) or of the said deflector (9).
6. Atomising bowl according to claim 5, characterised in that at least one insert (25) supports a collar (25c) which can co-operate with an inner shoulder (26a) of a receptacle (26) to accommodate the said insert.
7. Atomising bowl according to claim 5, characterised in that at least one insert (25) is provided with two ends (25a, 25b) in the form of a point, the said ends being flush with two outer surfaces (20a ₁, 20a ₂) of the said annular part (20), the said outer surfaces being oriented respectively towards the axis of rotation (XX') of the bowl (4) and towards the exterior of the bowl.
8. Atomising bowl according to any one of the preceding claims, characterised in that the end (22a) of the said insert (22) which is close to the outer surface (20a) of the said bowl is disposed in the vicinity of the said atomising ridge or edge (21).
9. Atomising bowl (54) for a rotary electrostatic spray unit (1) for a coating product, the said bowl comprising a flange (57) for distribution of the product, which flange is made of an electrically conductive material and is designed to have high voltage applied to it when the spray unit is functioning, such as to charge the said product electrostatically by contact, characterised in that the said flange is provided, on an outer peripheral surface (57c) relative to the axis of rotation of the bowl, with an element for current discharge by means of corona discharge in the form of a tapered point (75a) which is integral with the said flange, and extends according to a direction substantially at right-angles to the said outer peripheral surface.
10. Atomising bowl according to claim 9, characterised in that it comprises discharge points (75b) which are provided on an inner surface (57d) of the said flange (57), facing towards a deflector (59) of the said bowl (54).
11. Atomising bowl according to claim 9 or claim 10, characterised in that it comprises points (72) which are provided on an atomising ridge (71) of the said bowl, the said points having a height (h) relative to the said ridge which allows them to create areas of discharge by means of corona discharge.
12. Atomising bowl according to any one of the preceding claims, characterised in that it comprises a plurality of discharge inserts or elements (22, 25; 72, 75a, 75b) which are distributed regularly around the axis of rotation (XX') of the said bowl (4; 54).
13. Rotary electrostatic spray unit (1) for a coating product, characterised in that it comprises a bowl (4; 54) according to any one of the preceding claims, and means (2, 3) for electrical connection of the flange (7; 57) of the said bowl to a high-voltage generator (8), the said generator being able to detect variations of the corona discharge current which passes through the said discharge inserts or elements (22, 25; 72, 75a, 75b) of the said bowl.

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