Bell cup for spraying a liquid coating product, rotary sprayer comprising such a bell cup and method for applying a coating product with such a rotary sprayer

Abstract

The present invention relates to a liquid coating product spray bowl (6) for integration into a rotary coating product sprayer. The bowl comprises a body (60) centered on a longitudinal axis (X6) and defining an internal radial surface (61) for distributing the coating product to a circular spray edge (63) centered on the longitudinal axis and equipped with notches (66i) formed in the internal radial distribution surface (61) and regularly distributed around its circumference. The linear density (DL66) of the notches (66i) along the circular spray edge (63) is greater than or equal to 4 notches per millimeter. The opening angle (α66) of each notch (66i) is less than or equal to 45°.

Description

[0001] The present invention relates to a liquid coating product spray bowl, intended for integration into a rotary coating product sprayer. The present invention also relates to a rotary sprayer comprising such a bowl, as well as a method for applying the coating product using such a rotary sprayer.

[0002] In the field of liquid coating product spraying, it is known to use a rotary sprayer equipped with a spraying element, most often called a bowl, which defines a distribution surface of the coating product up to a circular spraying edge, from which drops of coating product are sprayed.

[0003] Such a spray bowl is known, for example, from WO03 / 074187A1. This bowl can be equipped with notches near its circular spray edge. These notches homogenize and refine the droplets leaving the bowl's circular spray edge.

[0004] Another spray bowl is known as US4519549A. This bowl includes cutouts along its circumferential edge, which form a sawtooth structure.

[0005] With the well-known serrated bowls—that is, bowls equipped with notches that form a serration near, or along, their circular spraying edge—the atomization and homogeneity of the paint droplets are relatively well controlled. The bowl's rotation speed allows for finer application of the coating product droplets. The higher the speed, the finer the droplets.

[0006] On the other hand, a droplet of coating product leaves the edge of the bowl with kinetic energy that is directly proportional to the bowl's rotational speed. However, the ejection direction of the coating product droplets from the bowl's edge is generally perpendicular to the bowl's axis of rotation. The coating product droplets must therefore be directed towards the object to be coated, for example, a car body. In this case, it is known to use a conforming skirt equipped with conforming air outlets. This conforming air has an aerodynamic effect directed along a generally axial direction relative to the bowl's axis of rotation, thus directing the paint droplets towards the object to be coated.Furthermore, in the case of an electrostatic sprayer, an electrostatic charge applied to the coating product before or after spraying allows the electrostatic effect to be used to direct the coating droplets towards the object to be coated. The higher the rotational speed of the bowl, the more the kinetic energy of the droplets leaving the edge of the bowl must be compensated, using conforming air and possibly the electrostatic effect, to deflect the coating droplets towards the object to be coated.

[0007] A recurring problem with rotary coating product sprayers is that the aim is to increase the yield, i.e. the proportion of coating product actually deposited on the object to be coated, without reducing the quality of the coating layer deposited.

[0008] In this context, reducing the bowl's rotation speed could be considered to decrease the kinetic energy of the droplets leaving its edge. However, even with a notched bowl, this approach risks reducing the homogeneity of the droplet cloud and increasing the size of the droplets, which could degrade the quality of the applied coating layer.

[0009] It is these problems that the invention intends to remedy in particular by proposing a new liquid coating product spray bowl which allows an efficient and good quality application of coating product, including with relatively low bowl rotation speeds.

[0010] To this end, the invention relates to a liquid coating product spray bowl, intended for integration into a rotary coating product sprayer, comprising a body centered on a longitudinal axis and defining an internal radial surface for distributing the coating product up to a circular spray edge centered on the longitudinal axis and equipped with notches formed in the internal radial distribution surface and regularly distributed around its circumference. According to the invention, the linear density of the notches along the circular spray edge is greater than or equal to 4 notches per millimeter, and the opening angle of each notch is less than or equal to 45°.

[0011] Thanks to the invention, the combination of the characteristics of the notching obtained by the notches distributed around the circumference of the circular edge, both in terms of linear density and opening angle, results in a relatively large quantity of coating product being sprayed from the bowl edge with good homogeneity of fine droplets, i.e., droplets of a size suitable for creating a coating layer, even when the bowl's rotation speed is relatively low. In particular, the notching characteristics mentioned above contradict the habits of those skilled in the art, who tend to use notches with large opening angles, on the order of 90° or more, considering that this allows the creation of channels with a large cross-section for the flow of coating product within the bowl's notches.The present invention proceeds from an opposite approach, in which the number of notches is substantially increased compared to the notches of known bowls, while reducing the opening angle of each notch.

[0012] According to advantageous but not mandatory aspects of the invention, such a bowl may incorporate one or more of the following features, taken in all technically permissible combinations. The maximum depth of each notch, measured radially to the longitudinal axis, is greater than or equal to 0.1 mm, preferably greater than or equal to 0.2 mm. All notches are straight and parallel to each other. The diameter of the circular spray edge is less than or equal to 80 mm, preferably approximately 65 mm. The opening angle of each notch is less than or equal to 30°, preferably approximately 20°. The radial thickness of the circular spray edge, measured perpendicular to the longitudinal axis, between the bottom of a notch and an external radial surface of the bowl, is between 0.2 and 0.5 mm, preferably between 0.3 and 0.4 mm.

[0013] According to a second aspect, the invention relates to a coating product sprayer comprising a body defining an axis of rotation; a coating product spray bowl rotating about the axis of rotation; a turbine for driving the bowl rotating about the axis of rotation; and an air skirt equipped with shaped air outlet ports. According to the invention, the coating product spray bowl is as described above, with its longitudinal axis aligned with the axis of rotation.

[0014] According to a third aspect, the invention relates to a method of applying liquid coating product using a sprayer as described above, in which the bowl is driven by the turbine, rotating around the axis of rotation, with a rotation speed less than or equal to 40,000 rpm, preferably at 30,000 rpm, and the conforming air outlet orifices are supplied with conforming air at a flow rate between 250 and 500 l / min, preferably between 300 and 450 l / min.

[0015] Advantageously, the sprayer includes means for applying high voltage to the product being applied, and in which the applied high voltage is between 40 and 85 kV, preferably between 45 and 60 kV.

[0016] According to another advantageous aspect, the product applied according to the process of the invention is a primer or a varnish.

[0017] The invention will be better understood and other advantages thereof will become more apparent from the following description of an embodiment of a spray bowl, a rotary coating product sprayer, and an application method conforming to its principle, given solely by way of example and with reference to the accompanying drawings in which: [ Fig. 1 ] There figure 1 is a partial longitudinal section of a principle of a rotary coating product sprayer according to the invention, incorporating a bowl also according to the invention; and [ Fig. 2 ] There figure 2 represents, on two inserts A) and B), two partial views of the sprayer bowl of the figure 1 , insert A) corresponding to detail II on the figure 1 , on a larger scale, and insert B) corresponding to a partial section along line BB on insert A, also on a larger scale.

[0018] A rotary sprayer for liquid coating product 2, a front part of which is shown in cross-section at the figure 1 , includes a turbine 4 for driving a spraying element 6, referred to as a bowl in the following, rotating about an axis X8 defined by a body 8 of the sprayer 2.

[0019] Sprayer 2 is of the electrostatic type and includes means for bringing to high voltage a coating product being sprayed with sprayer 2, for example a high-voltage cascade and an electrical link between this cascade and the bowl 6, not shown.

[0020] Alternatively, sprayer 2 is of the non-electrostatic type.

[0021] The bowl 6 is supplied with liquid coating product by an axial conduit 10 centered on the axis X8 and which opens into a hub 62 of the bowl 6. The bowl comprises a one-piece body 60 which defines an internal radial surface 61 and an external radial surface 65, with respect to a longitudinal axis X6 of this bowl, which coincides with the axis X8 when the bowl 6 is mounted on the turbine 4. The bowl 6 is equipped with a distributor 64 which allows the coating product from the conduit 10 to be returned towards the internal radial surface 61 on which this product is distributed and whose downstream end constitutes a circular spray edge 63 of a cloud N of coating product droplets, during operation of the sprayer 2.The function of the surface 61, which is centered on the longitudinal axis X6, is to distribute the coating product from the conduit 10, regularly and with decreasing thickness along the axis X6, approaching the circular spray edge 63.

[0022] Along the longitudinal axis X6, the surface 65 also extends to the circular spray edge 63.

[0023] Surfaces 61 and 65 and edge 63 are centered on the longitudinal axis X6.

[0024] The diameter of the circular spray edge 63 is denoted D63. Advantageously, the diameter D63 is less than or equal to 80 millimeters (mm), for example, approximately 65 mm in the embodiment shown in the figures. "Approximately 65 mm" means 65 mm to the nearest 1 mm. This relatively modest value for the diameter D63 ensures that, for a given rotational speed of the bowl 6, the tangential velocity of the coating product droplets is not too high, thus allowing good control of the droplet distribution in the cloud N.

[0025] In the example of the figures, the bowl 6, in particular its body 60, is made of aluminum-based alloy.

[0026] Alternatively, the bowl can be made of titanium or a titanium-based alloy. Other materials are also possible for bowl 6, for example a magnesium alloy, a non-metallic material such as thermoplastic, thermosetting plastic, or ceramic.

[0027] In this description, upstream refers to a direction facing the source of the coating product or cleaning product sprayed when the sprayer 2 is operating, on the left side of the figure 1 , while downstream corresponds to an opposite direction, turned towards the circular spray edge 63, on the right of this figure.

[0028] The rotational locking between the rotor 42 of the turbine 4 and the bowl 6 can take place by magnetic attraction, in particular by means of a magnet 47 integrated into this rotor and a ferromagnetic ring 67 integrated into the bowl 6, at the level of its external radial surface 65.

[0029] Alternatively, other means of rotational fastening between the rotor 42 and the bowl 6 can be implemented, for example fastening means by screwing.

[0030] The body 8 is equipped with an air skirt 86 which defines conforming air ejection orifices 82 intended to guide or conform the cloud N of coating product droplets leaving the edge 63 towards an object to be coated (not shown). figure 1 The air jets exiting the orifices 82 are represented by the arrows F1. In practice, the orifices 82 are regularly distributed around the axis X8, with an angular deviation between 2 and 15°.

[0031] When the sprayer 2 is operating, the orifices 82 are supplied with pressurized air through conduits 84 provided in the air skirt 86.

[0032] The orifices 82 open onto an annular surface of the body 2 which forms a ring 88 surrounding the axis X8 and the bowl 6 in its mounted configuration in the sprayer 2. The ring 88 forms the front face of the body 8, that is to say its extreme face oriented towards the object to be coated during the operation of the sprayer 2.

[0033] The circular spray edge 63 is equipped, on its inner side facing the longitudinal axis X66, with a serration 66 formed by a succession of notches 661, 662, 663 ... 66i ... which are regularly distributed around the axis X6. The serration 66 is formed in the portion of the distribution surface 61 which joins the edge 63. In what follows, 66i, with i a natural number, designates one of the notches of the serration 66.

[0034] The notches 66 i are identical to each other, over the entire circumference of the edge 63.

[0035] On insert B) of the figure 2 The notching 66 is shown on only part of the figure, on the right, in order to visualize the distribution surface 61, on the left. In practice, the notching extends over the entire circumference of the circular spray edge 63.

[0036] All the notches 66i of the serration 66 are straight, parallel to the X6 axis, and parallel to each other. According to a non-shown embodiment of the invention, the notches 66i are not parallel to the X6 axis, but all have the same angle of inclination with respect to the X6 axis and are parallel to each other. Thus, in all cases, the serration 66 does not constitute a knurling formed by the intersection of notches oriented in different directions. The dimensions of the serration 66 are easier to control than if it were a knurling.

[0037] Let e ​​63 be the minimum radial thickness of the circular spray edge 63, measured between the bottom of a notch 66 i and the external radial surface 65. The thickness e 63 is measured radially to the longitudinal axis X6. This minimum radial thickness e 63 is chosen to be between 0.2 and 0.5 mm, preferably between 0.3 and 0.4 mm. In the example in the figures, this radial thickness e 63 is equal to 0.35 mm.

[0038] The radial thickness e 63 ensures good geometric stability of the bowl 6, even when subjected to relatively high centrifugal forces when the turbine 4 rotates the bowl 6 around the X6 and X8 axes. The radial thickness e 63 therefore guarantees the dimensional stability of the serrations 66, and thus the homogeneity and regularity of the paint droplets leaving the circular spray edge 63, even in the event of variations in the rotational speed of the bowl 6.

[0039] The length L63 of the circular spray edge 63 is equal to this diameter minus twice the radial thickness e63 and multiplied by π. We have the following relationship: L 63 = D 63 − 2 * e 63 * π

[0040] In the case where the diameter D63 is 65 mm, the length L63 of the circular spray edge 63 is approximately 204 mm.

[0041] In the example of the figures, the number of notches 66 i of the notching 66 is 1200.

[0042] The linear density DL 66 of the notches 66 i along the circular pulverization edge 63 is defined as the number of notches 66 i of the notching 66 per millimeter of circumference of the edge 63.

[0043] In the example, the linear density DL 66 of the notches 66 i of the notching 66 is: DL 66 = 1200 / 204 = 5 , 88 crans / mm

[0044] Satisfactory tests were carried out with 66 notches comprising 1050 or more notches for a bowl with a circular spray edge diameter of approximately 65 mm. Thus, a linear density DL 66 of at least 4 notches per mm allows for satisfactory results in terms of droplet distribution and fineness of the N cloud.

[0045] In practice, the linear density DL 66 of the notches 66 i of the notching 64 can be controlled by varying the number of notches 66 i of this notching 66 and the diameter D63 of the edge 63, over a range of spray bowls, while respecting the condition DL 66 ≥ 4 notches / mm.

[0046] An opening angle α 66 of a notch 66 i is defined as the angle formed between two plane surfaces constituting the sides of this notch 66 i. The notches 66 i being identical over the entire circumference of the edge 63, the angle α 66 is constant over this circumference.

[0047] In an alternative not shown, the surfaces forming the sides of the notches 66 i are not planar. In this case, the opening angle α 66 of a notch is defined as an average angle between these surfaces.

[0048] In the example shown in the figures, the angle α 66 is approximately 20°, that is, 20° to within 0.5°. This value of the angle α 66 allows the notches 66 i to be implanted with a high linear density, which makes it possible to distribute the coating product from the edge 63 with a flow rate sufficient to ensure effective coating with the bowl 6.

[0049] Alternatively, the angle α 66 can have a value greater than 20°, while remaining less than or equal to 45°, preferably less than or equal to 30°.

[0050] As visible on insert A) of the figure 2, the radial depth of a notch 66 i is variable over its length, taken parallel to the longitudinal axis X6. We note p 66 a maximum depth of a notch 66 i of the notching 66, this depth being measured perpendicular to the longitudinal axis X66.

[0051] This maximum depth p 66 is chosen to be greater than or equal to 0.1 mm, preferably greater than or equal to 0.2 mm. This maximum depth p 66 gives each notch sufficient volume to accommodate, during application, the quantity of coating product necessary to create the N cloud.

[0052] The geometry of the notches 66i is compatible with the application of coating products under industrial conditions, since the linear density DL66 of the notches 66i of the notching 66, distributed along the circular spray edge 63, allows for the distribution of a relatively high flow rate of coating product, even though the opening angle α66 of these notches 66i is relatively small. In this respect, the invention contradicts standard reasoning for those skilled in the art, which would tend to increase the opening angle α66 to allow for the distribution of a higher flow rate of coating product at the circular spray edge 63, in order to create the droplet cloud N.

[0053] The serration structure 66 of the bowl 6 mentioned above allows it to be used in a coating application process in which the bowl 6 is driven by the turbine 4, rotating about the axes X6 and X8, at a relatively low rotational speed of 40,000 revolutions per minute (rpm) or less, preferably 30,000 rpm. This ensures that the coating droplets leaving the circular spray edge 63 have moderate kinetic energy. In this case, the aerodynamic force due to the conforming air and, where applicable, the electrostatic force due to the electrostatic field, allow the paint droplets to be more effectively directed towards the part to be coated.

[0054] In this case, the air outlets 82 are advantageously supplied with conforming air at a flow rate of between 250 and 500 liters per minute (l / min), preferably between 300 and 450 l / min. The supply flow rate to the outlets 82 can also be expressed in normal liters per minute (NI / min), with values ​​close to those mentioned above. Thus, it is also possible to reduce the conforming air flow rate compared to known coating application methods.

[0055] In the case where the sprayer 2 is of the electrostatic type as in the example of the figures, the cascade or any other means of applying a high voltage to the coating product being sprayed is capable of applying a high voltage of between 40 and 85 kilovolts (kV), preferably between 45 and 60 kV since the distance between the circular spraying edge 63 of the bowl 6 and the surface to be coated is reduced, for example less than or equal to 180 mm, preferably less than or equal to 150 mm and advantageously less than or equal to 100 mm.

[0056] Advantageously, the coating product sprayed with the bowl 6 in the application process of the invention is a primer or a varnish. The composition of a primer or a varnish is not disrupted by passing through a notch such as the notch 66, whereas this could be the case for a base coat. The homogeneity and size of the droplet cloud leaving the edge of the bowl 6 after passing through a notch such as the notch 66, during the application of a primer or a varnish, is not degraded, even at relatively low rotational speeds, whereas this could be the case for a base coat.

[0057] Any feature described for an embodiment or variant in the foregoing may be implemented for one or more of the other embodiments and variants mentioned above, provided that it is technically feasible.

Claims

1. Liquid coating product spray bowl (6), intended to be integrated into a rotary coating product sprayer (2) and comprising a body (60) centered on a longitudinal axis (X6) and which defines an internal radial surface (61) for distributing the coating product up to a circular spraying edge (63) centered on the longitudinal axis and equipped with notches (66 i ) arranged in the internal radial surface (61) of distribution and regularly distributed over its circumference, characterized in that - linear density (DL 66 ) notches (66 i ) along the circular spray edge (63) is greater than or equal to 4 notches per millimeter; and - an opening angle (α 66 ) of each notch (66 i ) is less than or equal to 45°.

2. Bowl according to claim 1, wherein a maximum depth (p66) of each notch (66 i), measured along a radial direction to the longitudinal axis (X66), is greater than or equal to 0.1 mm, preferably greater than or equal to 0.2 mm.

3. Bowl according to any one of the preceding claims, in which all the notches (66 i ) are straight and parallel to each other.

4. Bowl according to any one of the preceding claims, wherein a diameter (D63) of the circular spray edge (63) is less than or equal to 80 mm, preferably equal to about 65 mm.

5. Bowl according to any one of the preceding claims, wherein the opening angle (α 66 ) of each notch is less than or equal to 30°, preferably equal to about 20°.

6. Bowl according to any one of the preceding claims, wherein a radial thickness (e 63 ) of the circular spray edge (63) measured perpendicular to the longitudinal axis, between the bottom of a notch (66 i) and an external radial surface (65) of the bowl (6), is between 0.2 and 0.5 mm, preferably between 0.3 and 0.4 mm.

7. Rotary coating product sprayer (2) comprising - a body (8) defining an axis of rotation (X8); - a coating product spray bowl (6) rotating about the axis of rotation; - a turbine (4) driving the bowl in rotation about the axis of rotation; and - an air skirt (86) equipped with shaped air outlet ports (82), characterized in that the coating product spray bowl (6) is according to one of the preceding claims, with its longitudinal axis (X6) aligned with the axis of rotation.

8. Method of applying liquid coating product using a sprayer (2) according to the preceding claim, wherein: - the bowl (6) is driven by the turbine (4), rotating about the axis of rotation (X8), with a rotation speed less than or equal to 40000 rpm, preferably at 30000 rpm; and - the conforming air outlet orifices (82) are supplied with conforming air with a flow rate between 250 and 500 l / min, preferably between 300 and 450 l / min.

9. A method according to the preceding claim, wherein the sprayer comprises means for applying a high voltage to the product being applied and wherein the applied high voltage is between 40 and 85 kV, preferably between 45 and 60 kV.

10. A method according to any one of claims 8 and 9, wherein the coating product applied is a primer or a varnish.

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