EP2836309A1 - Rotating projector and method for spraying a coating product - Google Patents

Abstract

Said rotating projector (10) for a coating product includes a spraying device (20) having at least one circular spraying edge (23), the driving means for driving the spraying device around a rotational axis (X30), a body (30) which includes primary openings (34) arranged on a primary contour surrounding the rotation axis and intended for ejecting the primary air jets (J34) in a primary direction (∆34) having, with respect to the rotational axis, an axial component (A34) and an orthoradial component which are not equal to zero. The primary direction (∆34) has a radial component (R34), which is not equal to zero and centrifugal relative to the rotation axis (X30), and each primary jet (J34) extends, at the spraying edge (23) along the rotational axis (X30), at a distance (d34) from the rotational axis, which is strictly greater than the radius (R20) of the spraying edge. The body (30) includes secondary openings (36) arranged on a secondary contour and used for ejecting the secondary air jets (J36) in a secondary direction (∆36) having the axial components (A36) and a centripetal radial component (R36), such that the secondary jets (J36) hit an external surface (24) of the spraying device. The primary contours and the secondary contours coincide with a circle (C30) centered about the rotation axis.

Description

 ROTARY PROJECTOR AND METHOD FOR SPRAYING A PRODUCT

 COATING

The invention relates to a rotary coating product projector which comprises, inter alia, a spray member adapted to be rotated about an axis of rotation. The invention also relates to a method of spraying coating product on a surface of an object to be coated, using a rotating projector as mentioned above.

 Conventional spraying by means of rotating projectors is used to apply to objects to be coated, such as motor vehicle bodies, a primer, a base coat and / or a varnish. To do this, a rotating projector is used which comprises a spraying member rotating at high speed, under the effect of rotary drive means, such as a compressed air turbine.

 Such a spraying member generally has the shape of a rotationally symmetrical bowl and comprises at least one spraying edge from which a jet of coating product is formed. This coating material jet has a generally frustoconical shape which depends, inter alia, the rotational speed of the spray member and the flow of coating product. To control the shape of this jet of product, it is known to equip a rotary projector with orifices for emitting air jets together forming a conformation air skirt.

 JP-A-8071455 discloses a rotating projector provided with primary orifices intended to emit primary air jets inclined with respect to the axis of rotation of a bowl, in a primary direction having an axial component and a non-orthoradial component. zero. The primary air jets thus generate a swirling airflow, sometimes referred to as a "vortex" around the axis of rotation of the bowl.

 WO-A-2009/010646 teaches simultaneously using primary air jets constituting a vortex or vortex skirt and secondary air jets that strike an outer surface of the spraying member, allowing a fine adjustment and uniform spray of product sprayed from the spray edge.

WO-A-2010/037972 provides for mixing primary air jets and secondary air jets for the formation of combined jets, in an intersection region of these jets upstream of the edge of a spraying member. This makes it possible to obtain relatively high deposition efficiencies as well as good robustness of the impacts of coating product on the surfaces of the objects to be coated. EP-A-2,058,053 teaches the use of air jets emerging from orifices formed on two concentric and distinct circles and which are oriented in directions which are all either centrifugal or centripetal, with respect to an axis of rotation of a bowl.

 WO-A-2009/1 12 932 provides for the use of jets emerging from orifices located on a first circle of small diameter, in a divergent direction and without interaction with a bowl, as well as jets extending in a parallel direction to the axis of rotation of the bowl in a radial plane to this axis.

With known sprayers, it is difficult to obtain a coating product jet that is both wide and stable. Indeed, the performance of a sprayer is characterized by its efficiency of application (in English Transfer Efficiency of Application or "TEA") which is the product of the pitch of the trajectory of the center of a sprayer, compared to a surface to be coated, by the speed of movement of this sprayer on this trajectory. This application efficiency corresponds to the area swept by the projector per unit time, this area being expressed in m ² / min. In practice, the pitch and speed of movement of a projector are chosen so as to ensure a good application of the coating product, meeting the required quality specifications.

 The width of impact of a coating product jet is defined as equal to the width of a layer of coating product applied under the effect of this jet, measured in an area where this layer has a thickness equal to half of its maximum thickness. For economic reasons, high application efficiencies are sought in order to optimize the number of projectors, the number of robots supporting these projectors and the length of the projection booths.

Projectors for impact widths greater than 400 mm are known. This type of headlamp uses relatively low skirt air flow or conformation air, which comparatively lowers the coating material jet towards the axis of rotation of the spray member. These jets with wide impact are sometimes called "soft pattern". The projectors generating this type of jets can not be moved at a high speed relative to the surfaces to be coated, as this will "tear" the jet of coating product, that is to say to make it inhomogeneous, to the point that a substantial part of the paint droplets that make up this jet does not reach the target. In this case, the deposition efficiency drops and the amount of paint not deposited on the object to be coated pollutes the cabin and the robot moving the projector, which requires subsequent reprocessing operations. On the other hand, if the skirt airflow is increased, the coating product stream is better channeled between the edge of the spray member and the object to be coated. However, this increase in skirt air flow has the effect of tightening the impact, so that the pitch of the projector path must be reduced, which, at identical robot speed, increases the cycle time.

 Another method for obtaining a relatively wide impact is to move the projector away from the surface to be coated, taking into account that the coating material jet has generally the shape of a truncated cone. However, this approach significantly reduces the deposition efficiency since a significant portion of the paint droplets does not reach the target.

 It is to these disadvantages and limitations that the present invention more particularly aims to provide a rotary coating product projector which generates a wide and stable coating product jet, thus allowing to quickly coat relatively large surfaces, with high speeds of movement of the projector relative to these surfaces.

 To this end, the invention relates to a rotary coating product projector comprising a spraying member of the coating product having at least one circular spraying edge, means for driving the spraying member around a spindle axis. rotation and a body which defines the axis of rotation and which comprises primary orifices arranged on a primary contour surrounding the axis of rotation, each primary orifice being intended to eject a primary air jet in a primary direction having, relative to to the axis of rotation, an axial component and a non-zero orthoradial component. The primary direction has a radial component that is non-zero and centrifugal with respect to the axis of rotation, while a primary jet extends, at the level of the spray edge and along the axis of rotation, at a distance from the axis of rotation which is strictly greater than the radius of the spraying edge. According to the invention, the body of the projector comprises secondary orifices arranged on a secondary contour surrounding the axis of rotation, each secondary orifice being intended to eject a secondary jet of air in a secondary direction having, with respect to the axis of rotation, an axial component and a nonzero centripetal radial component, such that the secondary jet strikes an external surface of the atomizer member, while the primary and secondary contours coincide with a circle centered on the axis of rotation .

The invention takes advantage of the fact that the vortex or vortex skirt air can be used to conform the jet with good stability, with a sufficient flow of air skirt, and producing a relatively large impact width, thanks to the fact that the primary direction has a non-zero radial component and centrifugal. Indeed, this nonzero radial and centrifugal component of the primary direction induces that the skirt air tends to conform the jet from the spray edge with a flared shape, which induces a jet having a large impact width . This large impact width makes it possible to bring the spray member closer to the surface to be coated, which ensures a good homogeneity of the part of the coating product jet which reaches the surface of the object to be coated. Note that the invention takes the opposite of the habits in the field of spraying coating product since it is usual to use a skirt air, including vortex, to fold down the jet of coating product from the edge of the coating. spraying towards the axis of rotation of the spraying member. In contrast, according to the present invention, the skirt air is used to "expand" or "open" the coating product stream so as to obtain a broad impact. Thanks to the invention, the secondary jets lick the outer surface of the spray member, before reaching the spray edge where they interact with the coating product jet (leaving this edge).

 Advantageously, the primary direction forms, in a radial plane relative to the axis of rotation, an angle of between 0 and 30 °, preferably between 3 and 12 °,

The invention also relates to a coating product spraying method that can be implemented with a projector as mentioned above. More specifically, this method is used for spraying coating product on a surface of an object to be coated, using a rotating projector comprising a spraying member of the coating product having at least one circular spraying edge of which the diameter is between 50 and 100 mm, drive means of the spray member about an axis of rotation and a body which defines the aforementioned axis of rotation. In this method, during projection, the coating product sprayed from the circular edge is subjected to the action of primary jets each directed in a primary direction having, relative to the axis of rotation, an axial component and a non-zero orthoradial component. According to the invention, the primary direction has a non-zero radial component and centrifugal with respect to the axis of rotation. In addition, a primary jet extends at the spray edge and along the axis of rotation at a distance strictly greater than the radius of the circular spray edge. The circular spraying edge is disposed at an axial distance from the surface of the object to be coated, measured parallel to the axis of rotation, which is less than 200 mm, preferably less than 180 mm, preferably still less than 150 mm. The coating product is subjected to the action of secondary jets each directed in a secondary direction and having, relative to the axis of rotation, an axial component and a nonzero centripetal radial component, these jets striking an external surface of the spraying member. The primary and secondary jets out of primary and secondary ports which are arranged on primary and secondary contours coinciding with a circle centered on the axis of rotation of the spray member.

 Thanks to the method of the invention, a relatively tense impact, which can be described as a "hard pattern", is obtained under the action of the primary jets and the secondary jets and with a relatively large width of impact, because of the centrifugal orientation of the primary direction and centripetal orientation of the direction of the secondary jets, before they strike the outer surface of the spray member, even as the short axial distance between the spray member and the The object to be coated guarantees a good deposition efficiency since the droplets constituting the coating material jet remain under the influence of the skirt air throughout their path to the surface to be coated.

 According to advantageous but non-mandatory aspects of the invention, such a method may incorporate one or more of the following features taken in any technically permissible combination:

 - The total flow of the primary jets is between 100 and 500 liters / min.

 - The total flow of secondary jets is between 100 and 500 liters / min.

 - The flow of the primary jets, if necessary the flow of the secondary jets and the speed of rotation of the spray member are adjusted so that the speed of the droplets of coating products leaving the circular edge is greater than 5 m / s, while the speed of movement of the projector relative to the surface of the object to be coated is between 0.2 and 2 m / s.

 The invention will be better understood and other advantages thereof will emerge more clearly in the light of the following description of an embodiment of a projector according to its principle and a method of implementation. of this projector also in accordance with its principle, given solely by way of example and with reference to the appended drawings in which:

FIG. 1 is a diagrammatic representation of an electrostatic coating product projection installation comprising a rotating projector according to the invention; - Figure 2 is a partial perspective view of the projector of the installation of Figure 1;

 - Figure 3 is a partial side view of the projector of Figures 1 and 2 and;

 - Figure 4 is a front view of the projector of Figures 1 to 3.

 The installation 1 shown in FIG. 1 comprises a conveyor 2 capable of displacing O objects to be coated along an axis X 2 perpendicular to the plane of FIG. 1. In the example of the figures, the object O moved by the conveyor 2 is a motor vehicle body.

The installation 1 also comprises a projector 10 of the rotary and electrostatic type and which comprises a bowl 20 forming a spraying member and supported by a body 30 inside which is mounted a turbine 40 for rotating the bowl 20 around the body. an X-axis ₃₀ defined by the body 30.

 The body 30 also encloses a high voltage unit 50 connected to the bowl 20 by a high voltage cable 51 and a feed line 60 from the bowl 20 of spray coating material.

 A distributor 21 is secured to the upstream portion of the bowl 20 to channel and distribute the coating product, the speed of rotation of the bowl 20 in charge, that is to say when spraying product, is between 20,000 rpm and 80,000 rpm.

The bowl 20 has a symmetry of revolution about the X axis ₃₀ and has a distribution surface 22 on which the coating product spreads, under the effect of centrifugal force, to a spraying edge 23 where it is micronised in fine droplets. The set of droplets forms a jet of product leaving the bowl 20, at its edge 23 and pointing towards the object O on which it covers an impact surface S with a layer C of coating product of which The thickness is exaggerated in Figure 1, for clarity of the drawing.

The outer rear surface 24 of the bowl 20, that is to say its surface which is not turned towards its axis of rotation X ₃₀ , is turned towards the body 30.

The body 30 has primary orifices 34 and secondary orifices 36 disposed on the same circle C ₃₀ centered on the axis X ₃₀ . These primary and secondary orifices 34 are intended to emit, respectively, primary air jets J ₃₄ and secondary air jets J ₃₆ which extend, at the outlet of orifices 34 and 36, in their respective directions Δ ₃₄ and Δ ₃₆ . The orifices 34 and 36 are arranged alternately along the circle C ₃₀ . In other words, each orifice 34 is disposed along the circle C ₃₀ between two orifices 36, and vice versa. The orifices 34 are arranged in a primary contour, while the orifices 36 are arranged in a secondary contour, these primary and secondary contours coinciding with the circle C ₃₀ . Due to the fact that the first and second contours are combined, the front face of the body 30 in which are formed the orifices 34 and 36 may have a small radial width. Its area is therefore small, while it is the part of the projector most exposed to soiling. In addition, the less this front face is thick radially, the less the area in which is created in front of this face, a depression Venturi effect, is important.

Along the X axis ₃₀ , the edge 23 is at an axial distance from the circle C which is here substantially 10 mm. The distance thus represents the passing of the bowl 20 out of the body 30.

The primary directions Δ ₃₄ and secondary Δ ₃₆ are respectively determined by the inclinations, with respect to the axis X ₃₀ , of primary channels 340 and secondary channels 360 defined in the body 2. These channels 340 and 360 are straight and open respectively on the primary and secondary orifices 34 and 36. Upstream, the channels 340 and 360 are connected to two known independent sources of compressed air supply and to form the jets J ₃₄ and J ₃₆ . These sources, as well as the air supply means of the channels 340 and 360 are not shown, for clarity of the drawing. They may be of the type shown in FIG. 4 of WO-A-2009/010646.

 In operation of the projector 10, the channels 340 are supplied with a pressure and a flow of air such that the total flow of the primary jets is between 100 and 500 liters / min. In operation, the channels 360 are supplied with a pressure and a flow of air such that the total flow of the secondary jets is between 100 and 500 liters / min.

The direction Δ ₃₄ has, relative to the axis X ₃₀ , an axial component A ₃₄ visible in Figure 3 which is non-zero and corresponds to the fact that the air out of the primary orifices 34 towards the front of the projector, c that is to say towards the object O to be coated. This primary direction Δ ₃₄ also has a radial and centrifugal component R ₃₄ which corresponds to the fact that the radial direction diverges from the X axis ₃₀ away from a primary orifice 34.

The relative values of the components A ₃₄ and R ₃₄ are chosen such that an angle a, defined in the plane of FIG. 3 which is radial to the axis X ₃₀ , between these components has a value comprised between 0 and 30 °, preferably between 3 and 18 °. The direction Δ34 also has an orthoradial component 0 ₃₄ visible in Figure 4 which corresponds to the fact that the primary air jets 34 form a swirling skirt or "vortex".

D ₂₀ denotes the nominal diameter of the bowl 20, that is to say the diameter of the spray edge 23.

It is noted D ₃₀ the diameter of the circle C on which are distributed primary and secondary ports 34 and 36. The diameter D ₃₀ is greater than the diameter D _20. Thus, taking into account this difference in diameter and the fact that the direction Δ ₃₄ has a radial and centrifugal component, a primary air jet J ₃₄ which extends along a direction Δ ₃₄ passes, at the level of spraying edge 23 along the X axis ₃₀ at a radial distance d ₃₄ which is greater than the radius R ₂₀ of the bowl 30, i.e. half the diameter D ₂₀ . With this orientation of the direction Δ ₃₄ , a primary air jet can freely cross the region in which the edge 23 is located.

In other words, the components A ₃₄ , R ₃₄ and O ₃₄ of the direction Δ ₃₄ of a primary jet J ₃₄ make it possible for this jet to flow at a non-zero radial distance of ₃₄ from the edge 23, this radial distance corresponding to the difference between the radial distance d ₃₄ and the radius R ₂₀ . This radial distance of ₃₄ can be between 0 and 25 mm and depends, among other things, on the value of the axial distance L1.

Each secondary air jet J ₃₆ is inclined, at the outlet of a secondary channel 36 and with respect to the axis of rotation X ₃₀ , in a secondary direction Δ36 which has an axial component A ₃₆ and a radial and centripetal component R ₃₆ . These axial and radial components are determined in such a way that the direction Δ36 strikes the rear surface 24 of the bowl 20, as is apparent from FIG.

 There is an annular area of the rear surface 24 which receives the secondary jets. From zone 25, each secondary air jet spreads over the part of the surface 24 located between the zone 25 and the edge 23. This makes it possible to generate a secondary air stream in the form of a relatively uniform sheet. .

Thus, the jet J 1 of coating product leaving the edge 23 is subjected, on the one hand, to the primary air jets J ₃₄ , which each extend in a direction Δ ₃₄ away from the edge 23, and, on the other hand, secondary jets J ₃₆ , which lick the surface 24 after having impacted the latter in zone 25.

Given the orientation of their directions Δ ₃₄ , the primary air jets J ₃₄ tend to expand or expand radially with respect to the axis X ₃₀ the jet of coating product J 1. On the other hand, the secondary jets J ₃₆ licking the rear surface 24 of the bowl 20 tending to fold down the jet J 1 coating product in the direction of the axis X ₃₀ . Under these conditions, the combined action of the primary jet J ₃₄ and secondary jets J ₃ 6 the effect of creating a coating material cloud between the bowl 20 and the surface S, which has a relatively uniform velocity profile, as represented by the profile P in FIG.

Thus, the axial distance L ₂ as measured between edge 23 and the surface S parallel to the axis X ₃₀ when the coating material spray can be maintained at a low value, which ensures a good transfer efficiency, while the impact width of the coating product cloud on the surface S is high.

In practice, for a diameter of bowl D ₂₀ between 50 and 100 mm, the distance L ₂ is less than 200 mm, preferably less than 180 mm. Particularly satisfactory results can be envisaged with a distance L _{2 of} less than 150 mm. This is particularly the case when implementing an electrostatic sprayer with internal charge, that is to say by contacting the coating product with the bowl 20 which is electrically conductive and brought to the high voltage. Alternatively, the invention is usable with an externally charged sprayer, with the same range of values for the distance L ₂ .

The flow rates of the primary jets J ₃₄ and secondary J ₃₆ and the speed of rotation of the bowl 20 are chosen so that the speed of a droplet of paint leaving the edge 23 is greater than 5 m / s.

The speed of movement of the sprayer perpendicular to the X axis ₃₀ , as represented by the double arrow F in Figure 1, is between 0.2 and 2 m / s. Given the "robustness" of the coating material cloud at the outlet of the bowl 20, this relatively fast movement speed is not likely to deform or make the cloud inhomogeneous, so that the coating product deposited on the surface S is regular.

The installation 1 may comprise means for determining the distance L ₂ , by measurement or by calculation, and this distance may be taken into account to adjust the value of the high voltage applied to the coating product, in particular by means of the bowl. Which is electrically conductive. More specifically, the set value of the high voltage delivered by the unit 50 can be set to a nominal value U such that the U / L ₂ ratio, which corresponds to the average electrostatic field between the edge 23 and the object O , is constant when the distance L ₂ varies.

In a completely advantageous manner, and given the relatively low value of the distance L ₂ , the nominal value of the high voltage used for electrostatically charging is selected to be less than 80 kV. Given the value relatively small distance L ₂ , the electrostatic field between the bowl 20 and the object O is intense, with the same intensity level as in conventional installations, while using voltage values lower than the accustomed and decreasing, therefore, the risk of fire since the stored capacitive energy is proportional to the square of the nominal high voltage delivered by the unit 50.

In practice, the value of the high voltage U is chosen according to that of the distance L ₂ so that the U / L ratio ₂ is approximately 3kV / cm. This value is advantageously between 1 kV / cm and 4 kV / cm.

Although it is particularly advantageous to use both J ₃₄ primary air jets and J ₃₆ secondary air jets with the projector and the method of the invention, the use of secondary air jets is optional in that, given the orientation of the direction Δ ₃₄ , the primary air jets primarily provide the conformation function of the jet J 1 coating product leaving the bowl.

Claims

1. - Rotating product coating projector (10) comprising  a member (20) for spraying the coating product having at least one circular edge (23) for spraying, means (40) for driving the spraying member about an axis of rotation (X ₃₀ ), - a body (30) which defines the axis of rotation and which comprises primary orifices (34) arranged on a primary contour (C ₃₀ ) surrounding the axis of rotation, each primary orifice (34) being intended to eject a primary air jet (J ₃₄ ) in a primary direction (Δ ₃₄ ) having, relative to the axis of rotation, an axial component (A ₃₄ ) and an orthoradial component (0 ₃₄ ) non-zero, the primary direction (Δ ₃₄ ) having a non-zero radial component (R ₃₄ ) and centrifugal with respect to the axis of rotation (X ₃₀ ) and a primary jet (J ₃₄ ) extending at the spraying edge (23) along the axis of rotation at a distance (d ₃₄ ) from the strictly greater axis of rotation (X ₃₀ ) at the radius (R ₂₀ ) of the spray edge, characterized in that the body (30) comprises secondary orifices (36) disposed on a secondary contour (C ₃₀ ) surrounding the axis of rotation (X ₃₀ ), each secondary orifice being intended to eject a secondary jet of air (J ₃₆ ); in a secondary direction (Δ ^) having, relative to the axis of rotation, a nonzero axial component (A ₃₆ ) and a centripetal radial component (R ₃₆ ), such that the secondary jet strikes an outer surface (24) the spraying member (20), and the primary and secondary contours of the primary (34) and secondary (36) orifices coincide with a circle (C ₃₀ ) centered on the axis of rotation (X ₃₀ ). 2. - Headlamp according to claim 1, characterized in that the primary direction (Δ ₃₄ ) forms, in a radial plane and with respect to the axis of rotation (X ₃₀ ), an angle (a) between 0 and 30 °, preferably between 3 and 12 °. 3. - Method of spraying coating product on a surface of an object to be coated, using a rotating projector (10) comprising:  - a spraying member (20) of the coating product having at least one circular edge (23) spraying means (40) for driving the spraying member about an axis of rotation (X ₃₀ ), and  a body (30) defining the axis of rotation, method in which, during projection, - The coating product (Ji) sprayed from the circular edge (23) is subjected to the action of primary jets (J ₃₄ ) out of primary orifices arranged on a primary contour, these primary jets being each directed a primary direction (Δ ₃₄ ) having, relative to the axis of rotation (X ₃₀ ), an axial component (A ₃₄ ) and a non-zero orthoradial component (0 ₃₄ ), the primary direction (Δ ₃₄ ) has a radial component (R ₃₄ ) that is non-zero and centrifugal with respect to the axis of rotation (X ₃₀ ), a primary jet (J ₃₄ ) extends, at the level of the spray edge (24) and along the axis of rotation (X ₃₀ ), at a distance (d ₃₄ ) strictly greater than the radius (R ₂₀ ) of the circular spraying edge, this method being characterized in that the diameter (D ₂₀ ) of the spray edge is between 50 and 100 mm, the circular spraying edge (23) is disposed at an axial distance (L ₂ ) from the object to be coated (O), measured parallel to the axis of rotation (X ₃₀ ), which is less than 200 mm, preferably less than 180 mm, more preferably less than 150 mm. - During projection, the coating product is subjected to the action of secondary air jets (J ₃₆ ) outgoing secondary orifices disposed on a secondary contour coincident with the primary contour and with a circle (C ₃₀ ) centered on the axis of rotation, these secondary jets being each directed in a secondary direction (Δ ₃₆ ) having, relative to the axis of rotation (X ₃₀ ), an axial component (A ₃₆ ) and a centripetal radial component (R ₃₆ ) nonzero, these jets striking an outer surface (24) of the spray member. 4. - Method according to claim 3, characterized in that the total flow of the primary jets (J ₃₄ ) is between 100 and 500 liters / min. 5. - Method according to claim 4, characterized in that the total flow of secondary jets (J ₃₆ ) is between 100 and 500 liters / min. 6. - Method according to one of claims 3 to 5, characterized in that the flow of the primary jets (J ₃₄ ), where appropriate the flow of secondary jets (J ₃₆ ) and the speed of rotation of the organ of spraying (20) are adjusted so that the velocity of the coating product droplets leaving the circular edge (23) is greater than 5 m / s and the speed of movement (F) of the projector relative to the surface of the object to be coated (O) is between 0.2 and 2 m / s.