Abstract:
This device comprises a rotating spray element, such as a bowl, and drive means, such as a rotor, adapted to drive said element in rotation.  
     It further comprises means for magnetic coupling between the rotating element and the drive means. An air-gap is formed between the coupling means which advantageously include at least one magnet associated with a looping annulus. The magnet may be fitted on the rotor and/or on the bowl.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a device for spraying coating product comprising a rotating spray element, such as a bowl or dish, driven in rotation at high speed by drive means such as a rotor of an air turbine. The invention also relates to a rotating spray element that may be used with this device.  
         BACKGROUND OF THE INVENTION  
         [0002]    In an installation for spraying liquid or particulate coating product, it is known to spray the product by means of a bowl or a dish supplied with product and rotating at a speed of the order of 30,000 rpm. At such a speed of rotation, it is desirable that the bowl or dish be as light as possible and balanced, in order to avoid unbalance to a maximum, particularly if the drive turbine is an air-bearing and/or magnetic turbine.  
           [0003]    It is known to assemble a rotating spray element on the rotor of a turbine by means of a threaded rod extending axially with respect to the rotor and by means of an axial tapping of the rotating element or bowl, or by bolts distributed circumferentially about the axis of rotation of this element. Such a type of assembly considerably increases the weight of the rotating assembly while the operations of assembly and dismantling are long and fastidious, which is not forcibly compatible with the times available for maintenance, particularly on an automobile vehicle production chain.  
           [0004]    WO-A-94/12286 discloses a spraying device comprising a bowl connected to the rotor of a spray thanks to a radially expansible fitting crown. This system is satisfactory.  
           [0005]    U.S. Pat. No. 4,473,188 discloses spreading equipment comprising a rotating nozzle driven by an electric motor. The coupling between this nozzle and the driven shaft of the motor is effected by abutment of a metal ring fast with the nozzle on a magnet driven by this shaft. Such surface abutment pre-supposes a precise positioning of the nozzle with respect to the shaft, which limits the speed of rotation of the nozzle. In addition, if metal particles are deposited on the magnet, the surface abutment of the ring is no longer possible, which hinders the coupling between the nozzle and the shaft of the motor. Moreover, the successive positionings of nozzles on the shaft may damage that surface of the magnet intended to receive the rings of the nozzles in abutment. This device is therefore not adapted for the spraying of coating product for which the bowl must be regularly cleaned and/or changed, with subsequent re-positioning of this bowl or a fresh bowl.  
           [0006]    It is an object of the invention to propose an alternative solution to the one disclosed in WO-A-94/12286, which is particularly simple from the structural standpoint, therefore reliable and of attractive cost price, and compatible with the spraying of coating product.  
         SUMMARY OF THE INVENTION  
         [0007]    To that end, the invention relates to a device for spraying coating product of the type mentioned above, which comprises means for magnetic coupling between the rotating spray element and the drive means associated therewith, and which is characterized in that an air-gap is formed between these magnetic coupling means.  
           [0008]    Thanks to the use of magnetic coupling means, assembly and dismantling of the rotating spray element on and from its drive means are particularly rapid, since it suffices to bring the rotating element sufficiently close to the drive means for the magnetic coupling to produce an efficient effect of connection. These coupling means also allow a magnetic centering of the rotating element with respect to the rotor. As an air-gap is formed between the magnetic coupling means, there is no risk of upsetting the opposite surfaces of the coupling means, even after the bowl has been positioned several times. Moreover, a possible deposit of metal particles or of impurities on one of these opposite surfaces does not hinder operation of the couplig means. Particular precautions are therefore unnecessary for positioning a bowl.  
           [0009]    According to a first embodiment of the invention, the rotating element is equipped with at least one magnet adapted to cooperate with a magnetic looping element borne by the drive means.  
           [0010]    According to another advantageous embodiment of the invention, the drive means are equipped with at least one magnet adapted to cooperate with a magnetic looping element borne by the rotating element.  
           [0011]    According to a third embodiment of the invention, the rotating element and the rotor are each provided with a magnet, the polarities of these magnets being oriented so that a force of attraction is generated between these magnets when the rotating element is mounted on the rotor.  
           [0012]    Whatever the embodiment considered, the permanent magnet may be in the form of an annulus or a sector of annulus centred on the axis of rotation of the rotating element. In a variant embodiment, a plurality of magnets in the form of sectors of annulus or of studs are distributed about the axis of rotation. Similarly, the looping element may be a metal annulus centred on the axis of rotation of the rotating element.  
           [0013]    According to another advantageous aspect of the invention, the magnet and/or the looping element is force-fitted in a housing made in the rotating element or in the drive means.  
           [0014]    According to another advantageous aspect of the invention, the device comprises mechanical means for centering the rotating spray element with respect to the drive means. These centering means allow a pre-positioning of the magnetic coupling means during positioning of the spray element on the drive means. These centering means also contribute to the correct hold of the spray element on its drive means. In that case, the rotating element may be provided to comprise at least one truncated surface bearing against a corresponding truncated surface of the drive means. A truncated surface of the rotating element is advantageously formed substantially around the magnetic coupling means. In addition, a truncated surface of the drive means may be provided to be formed at the level of a free edge of a skirt defining a volume for partially receiving the rotating element.  
           [0015]    According to another advantageous aspect of the invention, the magnetic coupling means also constitute means for self-centering the rotating element on the rotor, which makes it possible to envisage total or partial elimination of the mechanical centering means.  
           [0016]    The invention also relates to a rotating spray element or bowl capable of being used with a device as described hereinbefore and which bears means adapted to cooperate with complementary means provided on a drive member for connecting the bowl and the member in question by magnetic coupling, while the bowl is provided with a bearing surface against a corresponding surface of this member in such a position that an air-gap is formed between the above-mentioned magnetic coupling means which cooperate.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The invention will be more readily understood on reading the following description of two embodiments of a device for spraying coating product in accordance with its principle, given solely by way of example and made with reference to the accompanying drawings, in which:  
         [0018]    [0018]FIG. 1 is an axial section through a spraying device according to a first embodiment of the invention, in the course of assembly.  
         [0019]    [0019]FIG. 2 is an axial section through the device of FIG. 1, assembled, and  
         [0020]    [0020]FIG. 3 is a view similar to FIG. 2 for a device according to a second embodiment of the invention.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]    Referring now to the drawings, FIGS. 1 and 2 partially show the rotor  1  of an air bearing turbine. It is symmetrical about its axis of rotation X-X′ and forms two truncated surfaces  11  and  12  likewise centered on the axis X-X′ and widening outwardly of the turbine to which the rotor  1  belongs, i.e. towards the front of the spraying device of the invention.  
         [0022]    Taking into account its mode of drive by an air bearing turbine, the rotor  1  may attain speeds of rotation of several tens of thousands of revolutions per minute, for example of the order of 30,000 rpm, and even of 80,000 rpm for a so-called “high velocity” turbine.  
         [0023]    In the present specification, the terms “front” and “rear” are to be understood with respect to an operational configuration of the device, the front side being oriented towards the object to be coated, while the rear side is oriented away from it.  
         [0024]    The rotor  1  forms a substantially cylindrical skirt  13  centered on axis X-X′, the surface  12  being formed at the level of the free edge  13   a  of the skirt  13 , radially inside this free edge.  
         [0025]    The rotor  1  also forms a housing  14  for receiving an annulus  2  made of soft iron. The housing  14  comprises a shoulder  14   a  and an outer radial surface  14   b  against which the annulus  2  is force-fitted as represented by arrows F 1  in FIG. 1, the annulus  2  being immobilized in the housing  14  by cooperation of shapes.  
         [0026]    A bowl  3  is intended to be mounted on the rotor  1  in order to be driven in rotation at high velocity about axis X-X′. This bowl comprises a central part  31  intended to be arranged in the interior volume of the skirt  13  opposite the opening  51  of a tube  5  supplying the bowl  3  with coating product, this tube  5  likewise being centred on axis X-X′. The tube  5  allows axial supply of the bowl  3  by its rear side. The central part  31  of the bowl  3  is connected to a spray edge  32  by a web  33  over which the coating product is distributed by centrifugation. Channels  34  made in part  31  allow the coating product to flow from the rear face  31   a  of part  31  towards the front face  33   a  of the web  33 , then towards the edge  32 .  
         [0027]    A first truncated surface  35  is provided at the level of the rear edge  36  of the bowl  3 , outside it, this surface  35  being convergent in upstream direction of the tube  5 . The angle α 1  of aperture of the surface  35  about axis X-X′ is substantially equal to the angle α 2  of aperture of the surface  11  about this same axis, with the result that a surface bearing of surface  35  on surface  11  may be envisaged.  
         [0028]    The bowl  3  also forms a second truncated surface  37  likewise convergent towards the axis X-X′ in upstream direction of the tube  5  and of which β 1  denotes the angle of aperture. This angle is substantially equal to angle β 2  of aperture of the surface  12  about axis X-X′.  
         [0029]    The distance d 1  between the median zones of the surfaces  11  and  12  is substantially equal to the distance d 2  between the median zones of the surfaces  35  and  36 , with the result that a simultaneous abutment of surfaces  35  and  37  respectively on surfaces  11  and  12  may be obtained. In practice, the cooperation of the surfaces  35  and  11  on the one hand,  37  and  12  on the other hand, makes it possible, by the orientation of these surfaces, to obtain a centering of the bowl  3  on axis X-X′. A guiding or pre-positioning might also be obtained with one set of cooperating surfaces  35  and  11  or  37  and  12 .  
         [0030]    According to the invention, the bowl  3  is equipped with a permanent magnet  4  of annular shape which is mounted in a housing  38  made at the level of the rear edge  36  of the bowl  3 . The housing  31  forms a shoulder  38   a  and a substantially cylindrical radial surface  38   b  which allow a force-fit of the magnet  4  in the housing  38  as represented by arrow F 2 .  
         [0031]    The magnet  4  is annular, but an annulus comprising a plurality of permanent magnets might also be used in place of magnet  4 . According to another alternative, a plurality of magnets in the form of studs may be distributed to the rear of the bowl  3 , for example three magnets distributed at 120°.  
         [0032]    When the bowl  3  is mounted on the rotor  1  as shown in FIG. 2, the magnet  4  is disposed opposite the soft iron annulus  2 , an air-gap e being formed due to the bearing of the surface  35  and  37  on the surfaces  11  and  12 .  
         [0033]    Elements  2  and  4  enable an intense magnetic coupling to be effected between the rotor  1  and the bowl  3 , the annulus  2  allowing the magnetic field generated by the magnet  4  to be closed. In this way, an effort of attraction represented by arrow F 3  in FIG. 3 is obtained, this effort contributing to applying the surfaces  35  and  37  strongly on surfaces  11  and  12 , which contributes to an immobilization, axial and in rotation, of the bowl  3  with respect to the rotor  1 . The bowl  3  is immobilized in rotation with respect to the rotor  1  thanks to the forces of friction between their surfaces in contact. In addition, it is possible to envisage a blockage of the bowl  3  on the rotor  1  in rotation, by a mechanical device, for example of the key type.  
         [0034]    When the bowl  1  is positioned on the rotor  3 , it suffices for an operator to bring the bowl  3  close to the rotor  1  using the surfaces  11 ,  12 ,  35  and  36  as guiding means until the air-gap e between the magnet  4  and the annulus  2  is sufficiently small for the force of magnetic attraction between the elements  2  and  4  to apply the bowl  3  firmly on the rotor  1 .  
         [0035]    The shape of the surfaces  12  and  35  defines the width of the air-gap e.  
         [0036]    The magnetic coupling elements  2  and  4  are disposed around tube  5 . In other words, the device of the invention is compatible with an axial or central supply of the bowl with coating product, by its rear side.  
         [0037]    When the bowl  3  is to be dismantled with respect to the rotor  1 , it suffices to exert on the bowl  3  an effort of extraction substantially parallel to axis X-X′ and opposite the effort of magnetic attraction represented by arrows F 3 .  
         [0038]    No specific tool is necessary, the assembly and dismantling of the bowl  3  being particularly simple and rapid operations.  
         [0039]    In the second embodiment of the invention shown in FIG. 3, elements similar to those of the first embodiment bear identical references increased by 100.  
         [0040]    The bowl  103  of this embodiment is intended to be mounted on a rotor  101  of an air turbine. The bowl  103  is equipped with an annulus  102  of soft iron, fitted in a housing  138  made near the rear edge  136  of the bowl  103 . The rotor  101  is equipped with an annulus  104  formed by a plurality of magnets  104   a,    104   b,    104   c , . . . in the form of sectors of annulus.  
         [0041]    Annulus  104  is received in a housing  114  formed inside the rotor  101 .  
         [0042]    Like elements  2  and  4 , elements  102  and  104  have substantially the same radius, with the result that they provide an efficient magnetic coupling between the bowl  103  and the rotor  101 , an air-gap e being formed therebetween.  
         [0043]    Truncated surfaces  112  and  135  are respectively provided on the rotor  101  and the bowl  103 . They define the relative position of the elements  101  and  103  under the effect of the attraction exerted by the coupling elements  102  and  104 . In particular, the width of the air-gap e depends on the position of these surfaces.  
         [0044]    This embodiment presents the particular advantage that the annulus  104  which constitutes the active part of the means for magnetic coupling between the rotor and the bowl is housed inside the rotor  101 , with the result that it is protected against possible impurities, there being no risk of the annulus  102  attracting metallic particles or filings when it is dismantled and stored outside the spraying installation to which the device of the invention belongs.  
         [0045]    This embodiment further provides the possibility of the magnets  104   a,    104   b,    104   c,  of the annulus  104  being electromagnets controlled by appropriate means mounted on the rotor  101 . This makes it possible to activate these magnets or not, as a function of the assembly or dismantling of the bowl  103 .  
         [0046]    It is also possible to provide in this second embodiment one sole electromagnet of annular shape, similarly to what is described with reference to the first embodiment of the invention.  
         [0047]    The annuli  2  and  102  may be in one piece or made of a plurality of pieces. They are made of metal, preferably soft iron, steel or another ferromagnetic material.  
         [0048]    According to a variant embodiment of the invention (not shown), two permanent magnets may be used for effecting the magnetic coupling. One magnet is mounted on the bowl, while the second is mounted on the rotor, the polarities of these magnets being oriented in order to obtain an attraction of one magnet with respect to the other when the bowl is mounted on the rotor. In fact, in that case, the magnetic looping element which is constituted by the annuli  2  and  102  of the embodiments described, is constituted by the second magnet.  
         [0049]    Whatever the embodiment considered, the means for magnetic coupling between the bowl and the rotor, which are essentially symmetrical about the axis of rotation of the rotor and of the bowl, allow the bowl to be self-centred on the rotor.