Abstract:
The bowl according to the invention is equipped with first magnetic coupling means adapted to cooperate with second complementary magnetic coupling means fixed on a non-rotary part of a sprayer, these first and second coupling means being adapted to exert an at least partially axial effort inducing the coupling in rotation of the bowl with a corresponding drive member. The radial width of an annular or truncated surface defined by the first coupling means is greater than the total radial width of the coupling means borne by the non-rotary part.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a spraying bowl for a rotary sprayer spraying coating product. The invention also relates to a coating product sprayer comprising such a bowl, as well as to an installation for spraying coating product incorporating such a sprayer.  
       BACKGROUND OF THE INVENTION  
       [0002]     In a coating product spraying installation, it is known to spray the product by means of a rotary element, called a bowl or dish, supplied with product and rotating at a speed usually included between 2,000 and 120,000 rpm. At the speeds in question, the bowl must be as light and balanced as possible in order to avoid unbalance to a maximum, particularly if its means for driving in rotation comprise an air and/or magnetic bearing turbine.  
         [0003]     It is known, for example from WO-A-94/12286, to connect a bowl to a rotor by means of a fitting ring capable of radial expansion. It is also known, for example from WO-A-01/62396, to use magnetic coupling means between a bowl and the rotor of a turbine. These coupling means comprise permanent magnets which are relatively complex to assemble on the bowl or on the rotor of the turbine, particularly in order to avoid these magnets bursting under the effect of the centrifugal force. Such assembly most often prevents a rapid replacement of the magnetic coupling magnets. In addition, the balance of the rotating parts must be as perfect as possible in order to limit the effect of the forces of inertia. The or each magnet used must therefore be balanced in rotation, which is delicate to effect, as the material constituting the magnet or magnets does not have an isotropic density and because such a material is brittle, therefore difficult to machine.  
         [0004]     It is a particular object of the invention to overcome these drawbacks by proposing a spraying bowl which may be easily driven by a rotor provided to that end thanks to an efficient magnetic coupling, without requiring the assembly of permanent magnets on a rotating part of the sprayer.  
       SUMMARY OF THE INVENTION  
       [0005]     In that spirit, the invention relates to a spraying bowl for a rotary sprayer spraying coating product, which is characterized in that it is equipped with first magnetic coupling means adapted to cooperate with second complementary magnetic coupling means fixed on a non-rotary part of the sprayer, these first and second coupling means being adapted to exert an at least partially axial effort with respect to the axis of rotation of this bowl, this effort inducing the coupling in rotation of the bowl with a corresponding drive member.  
         [0006]     Thanks to the invention, the effort resulting from the magnetic coupling makes it possible to connect the bowl and its drive means, particularly the rotor of a turbine, even if the magnetic coupling occurs between the bowl, which is rotary, and a non-rotary part of the sprayer. It may therefore be provided to mount the or each coupling magnet on this non-rotary part, said magnet(s) in that case not having to be balanced.  
         [0007]     According to advantageous but non-obligatory aspects, a spraying bowl may incorporate one or more of the following characteristics: 
        The coupling means borne by the bowl are disposed so that the effort of coupling is essentially axial.     A male part, whose external shape is globally truncated, is adapted to be engaged in a central housing of corresponding shape made in the member for drive in rotation, the bowl being able to be connected in rotation with this member by adherence between the aforementioned male part and housing, by reason of the axial effort due to the coupling means. In a variant, the bowl defines a globally truncated housing, while a male part of corresponding shape, fast with the drive member, is provided to be engaged in this housing and allows a connection in rotation of the bowl and the drive member by adherence, due to the aforementioned axial effort.     The first magnetic coupling means define an annular or truncated surface which delimits an air gap between the magnetic coupling means, while the radial width of this surface is greater than the total radial width of the second coupling means. Thanks to this aspect of the invention, the magnetic coupling effort in the air gap remains substantially axial, including in the case of radial offset between the coupling means, this avoiding the magnetic coupling effort exerting on the bowl an unbalanced effort which might lead to a contact between a rotary part and a non-rotary part of the sprayer.     The first magnetic coupling means are formed by an annular element made of magnetic material fitted or screwed around the principal body of the bowl and defining an annular or truncated surface defining the air gap with the second coupling means.        
 
         [0012]     The invention also relates to a rotary sprayer spraying coating product, which comprises a bowl and a member for driving this bowl in rotation, this sprayer being characterized in that it also comprises means for magnetic coupling between the bowl and a non-rotary part of the sprayer, these means being adapted to exert an at least partially axial effort with respect to the axis of rotation of the bowl, this effort inducing the coupling of the aforementioned bowl and member in rotation.  
         [0013]     According to advantageous but non-obligatory aspects, such a sprayer may incorporate more or more of the following characteristics, taken in any technically admissible combination: 
        The coupling means are disposed so that the coupling effort obtained is essentially axial.     The aforementioned bowl and member are respectively provided with parts, of complementary shapes, for coupling in rotation by adherence.     The magnetic coupling means comprise at least one magnet disposed in annular manner about the axis of rotation of the bowl and fixed on the non-rotary part, while the coupling means borne by the bowl define an annular or truncated surface delimiting an air gap between the coupling means borne by the bowl and this magnet and the radial width of this surface is greater than the radial width of this magnet. Thanks to this aspect of the invention and, in particular, when the aforementioned surface is annular, the magnetic coupling effort remains substantially axial, including in the case of radial offset of the annular interaction surface with respect to the magnet. In that case, the mean radius of this surface may be provided to be substantially equal to the mean radius of this magnet, and/or the magnet provided to be radially bordered, internally and externally, by two volumes of material which is amagnetic or with low magnetic permeability, while the radial width of the aforementioned surface is greater than the radial width of the magnet increased by the radial width of these volumes. These volumes of material which is amagnetic or with low magnetic permeability may be formed by air, annular rings made of aluminium based alloy or filled with glue for fixation of the or each magnet in a receiving volume fast with the non-rotary part of the sprayer. The radial widths of each of these volumes are advantageously greater than the air gap defined between the aforementioned surface and the magnet, preferably at least three times greater than this air gap, and preferably still of the order of five times this air gap. In addition, the aforementioned surface may be provided to project radially, inwardly and outwardly, with respect to the magnet and to the volumes of amagnetic material, by an overhang at least greater than the air gap between this surface and this magnet, preferably at least three times greater than this air gap, and preferably still of the order of five times this air gap.     A part of the magnetic coupling means is integrated in an annular support added on the body of the sprayer and extending it axially. This aspect of the invention makes it possible to equip an existing turbine with the annular support in question, and this in order to allow an existing sprayer to be upgraded into a sprayer according to the invention.     The air gap between those parts of the magnetic coupling means respectively fast with the bowl and the-non-rotary part is such that this axial effort has an intensity included between 5 and 20 daN.     The bowl and/or the drive member is provided with a clearance for assembly/dismantling, this avoiding a wedging of the bowl on the drive member in the event of the presence of soiling at the interface between these elements.     An air flow is provided in the air gap between the magnetic coupling means, this avoiding the accumulation of soiling in this air gap, such soiling being due to the arrival of solid or liquid particles coming from the cloud of product sprayed by the bowl.        
 
         [0021]     Finally, the invention relates to an installation for spraying coating product, which comprises at least one sprayer as described hereinbefore. Such an installation is easier to operate and maintain than those of the state of the art, particularly insofar as assembly of the bowls on the turbines, and dismantling thereof, is facilitated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The invention will be more readily understood on reading the following description of two forms of embodiment of a sprayer according to the invention comprising a bowl according to the invention, given solely by way of example and made with reference to the accompanying drawings, in which:  
         [0023]      FIG. 1  is a longitudinal section of a coating product sprayer in accordance with a first form of embodiment of the invention, incorporating a bowl according to the invention and forming part of an installation according to the invention.  
         [0024]      FIG. 2  is a view on a larger scale of detail II in  FIG. 1 .  
         [0025]      FIG. 2A  is similar to  FIG. 2  but shows only the magnetic coupling elements in an offset configuration, the offset being exaggerated in order to render the drawing clearer.  
         [0026]      FIG. 3  is a section similar to  FIG. 1 , the bowl being offset with respect to the body of the sprayer.  
         [0027]      FIG. 4  is a view in perspective with parts torn away of the sprayer of FIGS.  1  to  3 .  
         [0028]      FIG. 5  schematically shows the variation of the effort of magnetic coupling as a function of the air gap, and  
         [0029]      FIG. 6  is a section similar to  FIG. 2  for a sprayer and a bowl in accordance with a second form of embodiment of the invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]     Referring now to the drawings, the sprayer P shown in FIGS.  1  to  4  is intended to be supplied with coating product from one or more sources S and displaced, for example, with an essentially vertical movement represented by double arrow F 1 , opposite objects O to be coated inside an installation I for coating these objects. The sprayer P comprises an air turbine of which only the front end  1  has been shown, i.e. the part oriented towards the objects O to be coated. This end  1  is surrounded by a protective cover  2  and supports a bowl  3  intended to be rotated about an axis X-X′ by the rotor  11  of the turbine.  
         [0031]     The rotor  11  makes it possible to drive the bowl  3  at a speed of several tens of thousands of revs per minute, for example 80,000 rpm, with the result that the coating product coming from the source S through an injection tube  18  is sprayed in the direction of an object O, as represented by arrows F 2 .  
         [0032]     According to an advantageous aspect of the invention which has not been shown, the sprayer P may be of electrostatic type, i.e. comprise means for electrostatically charging the coating product before or after the latter has been discharged from the edge  31  of the bowl  3 . As shown partially in the Figures, the bowl  3  may be provided with a notch  32 .  
         [0033]     The bowl  3  comprises a two-part hub  33  as well as a body  34  forming dish and defining a surface  35  for flow and distribution of the coating product in the direction of the edge  31 . The hub  33  is hollow and defines a longitudinal channel  36  which is centred on an axis X 3 -X′ 3  merged with axis X-X′ when the bowl  3  is mounted on the rotor  11 . The axis X 3 -X′ 3  is an axis of symmetry of the body  34  which is, for example, made of titanium.  
         [0034]     A ring  4  made of ferromagnetic material, for example magnetic stainless steel, is mounted around the body  34 . The ring  4  is in one piece and comprises an annular skirt  41  provided with an inner tapping allowing the fixation of the ring  4  by screwing on an external thread  37  of the body  34 . In a variant, the ring  4  may be fitted by force around the bowl  3 . According to another variant, the ring  4  may be in one piece with the body  34 .  
         [0035]     The ring  4  comprises a part  42  globally perpendicular to the skirt  41  and which defines an annular surface S 42  perpendicular to axis X 3 -X′ 3 . l 42  denotes the radial width of the surface S 42 , this width being measured in a radial direction with respect to axis X 3 -X′ 3 .  
         [0036]     The body  34  forms a male part  38  intended to penetrate in a central housing  12  of the rotor  11 . The external surface  38   a  of the part  38  is globally truncated and convergent towards the rear of the bowl  3 , i.e. opposite the edge  31 . The surface  12   a  of the housing  12  is also truncated and divergent in the direction of the front face  13  of the rotor  11 . α denotes the semi-vertex angle of part  38  and β the semi-vertex angle of the housing  12 . The angles α and β are substantially equal, this allowing a surface abutment of the surfaces  38   a  and  12   a . Such a surface abutment allows a connection of the elements  11  and  3  in rotation by adherence.  
         [0037]     According to a variant of the invention (not shown), the bowl may be provided with a globally truncated housing similar to housing  12 , while the rotor is equipped with a likewise truncated male part similar to part  38 , these elements in relief also allowing a connection of the elements  11  and  3  by adherence.  
         [0038]     In order to avoid a wedging of the part  38  in the housing  12 , a first clearance  38   b  is formed at the junction of the surface  38   a  and of a surface  34   b  for connecting the body  34  to the surface S 42 . A second clearance  12   b  is provided in the bottom of the housing  12  in the form of a radial groove. The clearances  38   b  and  12   b  are intended to be disposed, when the bowl  3  is mounted on the rotor  11 , respectively opposite an entrance bevel  12   c  of the housing  12  and the end edge  38   c  of the part  38 . These clearances avoid soiling wedging the part  38  in the housing  12 .  
         [0039]     A body  15  of the turbine surrounds the rotor  11  and, in practice, constitutes the stator of the turbine. This body  15  is not mobile in rotation. A support  5  made of magnetic material, for example magnetic stainless steel, is mounted on the front face  16  of the body  15 , this support being provided with an annular groove  51  centred on axis X-X′ and in which a likewise annular magnet  52  is disposed. The magnet  52  is maintained in place in the groove  51  by two layers of glue  53  and  54  which extend radially on either side of the magnet  52 . The layers of glue  53  and  54  thus form two substantially annular washers disposed on either side of the magnet  52 . Taking into account the nature of the glue, which may be glue based on epoxy resin, these washers are amagnetic.  
         [0040]     In place of one sole magnet  52 , a plurality of magnets may be disposed in the groove  51 , jointly forming a ring. The or each magnet may be made of ferromagnetic metal or of synthetic resin laden with particles of ferromagnetic metal injected so that these particles are oriented in the same overall direction.  
         [0041]     In place of the layers  53  and  54  of glue, washers of metal which is amagnetic or with low magnetic permeability, particularly aluminium, may be used. Similarly, volumes filled with air may suit, as long as the magnet is fixed in the groove  51  by another means.  
         [0042]     l 52  denotes the radial width of the magnet  52 .  
         [0043]     l 52  and l 54  denote the radial widths or the respective thicknesses of the layers or washers  53  and  54 .  
         [0044]     R 52  denotes the mean radius of the magnet  52 . R 42  denotes the mean radius of the surface  42 . Radii R 42  and R 52  are substantially equal, this corresponding to the fact that, when the bowl  3  is mounted on the rotor  11 , the surface S 42  is disposed opposite the exposed surface S 52  of the magnet  52  and centred thereon. The magnetic field due to the magnet  52  therefore recloses through the part  42  of the ring  4 , as is apparent from the representation of its field lines L in  FIG. 2 .  
         [0045]     This magnetic field makes it possible to exert on the ring  4  an effort F 3  parallel to axis X-X′, i.e. axial, and tending to apply the bowl  3  firmly on the rotor  11 , i.e. the surface  38   a  on the surface  12   a . Taking this effort into account, the surfaces  38   a  and  12   a  in contact are connected in rotation, this allowing the bowl  3  to be driven by the rotor  11 .  
         [0046]     It will be noted that the effort F 3  is parallel to axis X-X′ in the plane of  FIG. 2 , as in any plane of section containing the axis X-X′, this resulting from the fact that the surfaces S 42  and S 52  are perpendicular to axis X-X′.  
         [0047]     As the width l 42  is greater than width l 52  and, in practice, greater than the sum l′ 52  of the width l 52  and of the widths l 53  and l 54 , the magnetic field due to the bias of the magnet  52  recloses through the part  42  of the ring  4  even if the latter is slightly offset radially with respect to the magnet  52 , as shown in  FIG. 2A . This Figure corresponds to the case of the axis X 3 -X′ 3  of the bowl  3  not being aligned with axis X-X′ of the rotor  11  when the bowl is placed in position on the rotor. In that case, the effort F 3  remains substantially axial, which does not risk provoking a displacement of the bowl  3  with respect to the rotor  11  in a radial direction, such a displacement being able to lead to damage of the zones  12  and  38  in contact between these parts or to a transverse displacement of the rotor  11  capable of damaging its own drive means, for example its fins in the case of an air turbine.  
         [0048]     As long as the width l 42  has a sufficiently high value with respect to widths l 52 , l 53  and l 54 , the radii R 42  and R 52  are not necessarily equal.  
         [0049]     e denotes the value of the air gap made between the surfaces S 52  and S 42 . d 1  denotes the distance over which the surface S 42  projects radially towards the outside with respect to the layer  53 . d 2  denotes the distance over which the surface S 42  projects radially towards the inside with respect to the layer  54 . Overhangs d 1  and d 2  are different. However, they may be equal. Each of the overhangs d 1  and d 2  is greater than the value of the air gap e. In practice, these overhangs are at least three times greater than this air gap and, preferably, of the order of five times this air gap, this giving good stability of the effort F 3 , including in the event of slight radial displacement of the bowl  3  with respect to the rotor  11 .  
         [0050]     Furthermore, the thicknesses l 53  and l 54  are greater than the air gap e, preferably at least three times greater than this air gap. In practice, a choice of the thicknesses l 53  and l 54  substantially equal to five times this air gap allows a good distribution of the field lines.  
         [0051]     The support  5  is immobilized on the front face  16  of the body  15  by means of three screws  6  whose milled head  61  bears on the layer  53  and possibly on the magnet  52 , this contributing to immobilizing the coupling means  52  to  54  in the groove  51 . The support  5  axially extends the body  15  towards the front, i.e. in the direction of objects O.  
         [0052]     The fact that the magnets  52  and  54  are integrated in the support  5  makes it possible to provide adding such a support on the body  15  of a conventional turbine in which a bowl is normally immobilized on the rotor  11  by screwing thanks to a tapping  17  provided in the central bore  11   a  of the rotor  11  in which the tube  18  is disposed. In this way, the fact of mounting the support  5  on a turbine makes it possible to convert a conventional sprayer, in which a bowl is screwed on the rotor, into a sprayer according to the invention. This aspect of the invention makes it possible to envisage upgrading the existing equipment.  
         [0053]     According to a variant of the invention (not shown), the magnetic coupling means  52 ,  53  and  54  may be integrated on the body  15  directly, without using an added support.  
         [0054]     As is more particularly visible in  FIG. 5 , the effort F 3  is substantially inversely proportional to the value of the square of the air gap e. The air gap e is chosen so that the effort F 3  is greater than a minimum value F 3min  of the order of 5 daN corresponding to a satisfactory hold of the bowl  3  on the rotor  11 . The air gap e is also chosen so that the effort F 3  is less than a maximum value F 3max  of the order of 20 daN, and this in order to avoid the bowl  3  being applied against the support  5  without the pressurization of the air bearing of the turbine allowing detachment of the bowl and the rotor. In effect, there is a risk that the effort F 3  pushes the rotor  11  towards the left in FIGS.  1  to  3 , which would have the effect of firmly immobilizing the bowl  3 . It is therefore envisaged to obtain an effort F 3  whose intensity lies within the non-hatched zone in  FIG. 5 . In this zone, the variation of the value of the effort F 3  with respect to the variation of the value of the air gap e is less than in the hatched zone located above the value F 3max . In this way, the machining and assembly tolerances do not have too great an influence on the value of the effort F 3  or, at least, have less influence than in the aforementioned hatched zone.  
         [0055]     In practice, the effort F 3  is chosen with a value equal to about 12 daN, this making it possible to determine the value of the air gap e from the curve of  FIG. 5 . This value may vary over an area Δ e  visible in  FIG. 5  and depending on values F 3min  and F 3max . This value depends, in practice, on the inertia of the bowl, therefore on its geometry. It may be different as a function of the types of bowls used.  
         [0056]     In order to avoid the accumulation of soiling between the opposite surfaces of the part  42  of the magnet  52 , an air flow E is arranged in the air gap between these coupling means.  
         [0057]     In the second form of embodiment of the invention shown in  FIG. 6 , elements similar to those of the first embodiment bear identical references. The bowl  3  of this embodiment is equipped with a ring  4  force-fitted on the body  34  of this bowl. This ring  4  comprises an annular skirt  41  as well as a truncated part  32  convergent towards the rear of the bowl  3  and centred on the axis of rotation X-X′ of this bowl. A support  5  added on a turbine body, of the type of body  15  of the first embodiment, is equipped with a magnet  52  bordered by two washers  53  and  54  made of amagnetic material. Elements  52  to  54  are disposed in the support  5  so that their exposed surfaces are truncated and convergent towards the rear of the turbine, with a semi-vertex angle γ equal to the semi-vertex angle δ of the surface S 42  of part  42  which faces the elements  52  to  54 . S 52  denotes the exposed surface of the element  52 . The surfaces S 42  and S 52  are therefore parallel and define therebetween an air gap e of substantially constant thickness, this air gap also being truncated with a semi-vertex angle equal to γ and δ. R 42  and R 52  respectively denote the mean radii of the surfaces S 42  and S 52 , these mean radii being substantially equal.  
         [0058]     When the bowl  3  is in place on the front end  1  of the turbine, a magnetic coupling effort F 3  is exerted, this effort being substantially perpendicular to the surfaces S 42  and S 52  in the plane of section of  FIG. 6 , with the result that it has an axial component parallel to axis X-X′. As for the resultant of the unitary efforts F 3  about axis X-X′, it is substantially axial.  
         [0059]     l 42  denotes the radial width of the surface  42 . l 52  likewise denotes the radial width of the surface S 52 , and l 53  and l 54  the radial widths of the rings  53  and  54 . l′ 52  denotes the sum of the widths l 52 , l 53 and l 54 . As in the first embodiment, the width l 42  is greater than the width l′ 52 , the surface  42  projecting radially outwardly and inwardly with respect to the rings  53  and  54  by an overhang d 1  or d 2  which is, in practice, of the order of five times the thickness of the air gap e.  
         [0060]     The magnetic field lines L reclose through the part  42  of the ring  4 , this ensuring an efficient hold of the bowl in position with respect to the end  1  of the turbine.  
         [0061]     The bowl  3  is provided with a male part  38  intended to be received in a housing formed by the rotor  11  of the turbine, a connection by adherence taking place under the effect of the effort F 3 , between the external truncated surface  38   a  of the part  38  and a truncated surface  12   a  defining the housing formed by the rotor  11 .  
         [0062]     In this embodiment, an air flow E may also be arranged in the air gap e with the particular advantage that the rotation of the bowl induces an effect of “pumping” of the air from the inside to the outside of the air gap e.