Spray bowl for liquid coating product, rotary spray coater comprising such bowl and method for applying coating product with such spray coater

Abstract

A spray bowl for a liquid coating product, a rotary spray coater comprising such a bowl and a method of applying a coating product with such a spray coater. The invention relates to a spray bowl (6) for a liquid coating product intended to be mounted in a rotary coating product sprayer and comprising a body (60) centered on a longitudinal axis (X6), defining a radially inner surface (61) for dispensing the coating product to a circular spray edge (63) centered on the longitudinal axis, the circular spray edge is provided with a plurality of grooves (66i) formed in the radially inner distribution surface (61) and uniformly distributed around its circumference. The linear density (DL66) of the grooves (66i) along the circular sprayed edge (63) is greater than or equal to 4 grooves per millimeter. The opening angle (alpha66) of each groove (66i) is less than or equal to 45 degrees.

Description

TECHNICAL FIELD

[0001] The invention relates to a spray bowl for liquid coating products for mounting in a rotary coating spray machine. The invention also relates to a rotary spray machine comprising such a bowl, and to a method of applying a coating product using such a rotary spray machine. BACKGROUND

[0002] In the field of spraying liquid coating products, it is known to use a rotary spray machine provided with a spraying member, usually called a bowl, which defines a dispensing surface for dispensing the coating product up to a circular spraying edge from which the droplets of the coating product are sprayed.

[0003] Such a spray bowl is known, for example, from document WO 03 / 074187 Al. Such a bowl can be grooved near its circular spraying edge. This grooving method homogenizes and refines the droplets leaving the circular spraying edge of the bowl.

[0004] Another spray bowl is known from document US 4 519 549 A. The bowl has a cut along its circumferential edge, thereby forming a sawtooth structure.

[0005] With the known grooved bowls, i.e. the bowls provided with grooves near or along their circular spraying edge, the atomization of the paint droplets and their homogeneity are relatively well controlled. The rotation speed of the bowl refines the droplets of the coating product even more. The higher the speed, the finer the droplets.

[0006] On the other hand, when the rotation speed of the bowl is higher, the droplets of the coating product leave the bowl edge with more kinetic energy. However, the direction in which the droplets of the coating product are sprayed from the bowl edge is usually perpendicular to the rotation axis of the bowl. Therefore, the droplets of the coating product have to be directed towards the object to be coated, for example a motor vehicle body. In this case, it is known to use a shaping skirt provided with shaping air outlet holes which have an aerodynamic effect directed in a substantially axial direction with respect to the rotation axis of the bowl, thereby being able to force the paint droplets back towards the object to be coated. Furthermore, in the case of an electrostatic spray machine, an electrostatic charge applied to the coating product before or after spraying is able to use the electrostatic effect to direct the droplets of the coating product towards the object to be coated. The higher the rotation speed of the bowl, the more kinetic energy the droplets leaving the bowl edge have to be compensated for by the shaping air and possibly the electrostatic effect in order to force the droplets of the coating product back towards the object to be coated.

[0007] A recurring problem with rotary coating product atomizers is that it is aimed 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 layer of coating product deposited.

[0008] In this case, the rotation speed of the bowl can be reduced in order to reduce the kinetic energy of the droplets leaving its edge. However, in this case, even with a fluted bowl, there is a risk of reducing the uniformity of the cloud of droplets leaving the edge of the bowl and increasing the size of these droplets, which can reduce the quality of the layer of coating product applied. SUMMARY

[0009] The present invention is particularly aimed at these problems, and proposes a new type of spray bowl for liquid coating products, which makes it possible to apply coating products efficiently and with high quality, even at relatively low rotation speeds of the bowl.

[0010] To this end, the present invention relates to a spray bowl for liquid coating products, intended to be mounted in a rotary coating product spraying machine, the spray bowl comprising a body centered on a longitudinal axis, the body defining a radially inner distribution surface for distributing the coating product to a circular spraying edge centered on the longitudinal axis, the circular spraying edge being equipped with a plurality of flutes formed in the radially inner distribution surface and uniformly distributed around the circumference thereof. According to the invention, the linear density of the flutes along the circular spraying edge is greater than or equal to 4 flutes per mm, and the opening angle of each flute is less than or equal to 45°.

[0011] Thanks to the invention, the combination of flute characteristics obtained with the flutes distributed around the circumference of the circular edge, whether in terms of linear density or opening angle, has the effect that a relatively large amount of coating product can be sprayed from the edge of the bowl with good droplet uniformity, the droplets being fine, i.e. the droplet size being suitable for forming a layer of coating product, while at the same time the rotation speed of the bowl can be relatively low. In particular, the above-mentioned flute characteristics are contrary to the habits of the person skilled in the art, who tends to use flutes with a large opening angle of around 90° or more, considering that this allows the creation of a large cross-section passage for the flow of threads of coating product within the flutes of the bowl. The present invention, on the contrary, adopts the opposite approach, in which the number of flutes is greatly increased compared to the flutes of known bowls, while at the same time the opening angle of each flute is reduced.

[0012] According to an advantageous but non-mandatory aspect of the invention, such a bowl can incorporate one or more of the following features, taken in any technically feasible combination:

[0013] - the maximum depth of each flute, measured in the radial direction with respect to the longitudinal axis, is greater than or equal to 0.1 mm, preferably greater than or equal to 0.2 mm.

[0014] - all the flutes are straight and parallel to each other.

[0015] - the diameter of the circular spraying edge is less than or equal to 80 mm, preferably equal to about 65 mm.

[0016] - the opening angle of each groove is less than or equal to 30°, preferably equal to about 20°.

[0017] - the radial thickness of the circular spray edge, measured perpendicularly to the longitudinal axis between the bottom of the groove and the radially outer surface of the bowl, is between 0.2 and 0.5 mm, preferably between 0.3 and 0.4 mm.

[0018] According to a second aspect, the application relates to a coating product spray machine comprising a main body defining a rotation axis; a coating product spray bowl rotating around the rotation axis; a turbine for rotating the bowl around the rotation axis; and an air skirt equipped with a shaping air outlet orifice. According to the application, the coating product spray bowl is a spray bowl as described above, the longitudinal axis of which is aligned with the rotation axis.

[0019] According to a third aspect, the application relates to a method for applying a liquid coating product using a spray machine as described above, wherein the bowl is rotated around the rotation axis by the turbine at a rotation speed less than or equal to 40 000 revolutions per minute, preferably 30 000 revolutions per minute, and the shaping air is supplied to the shaping air outlet orifice at a flow rate between 250 and 500 liters per minute, preferably between 300 and 450 liters per minute.

[0020] Advantageously, the spray machine comprises means for applying a high voltage to the coating product being applied, and wherein the high voltage applied is between 40 and 85 kilovolts, preferably between 45 and 60 kilovolts.

[0021] According to another advantageous aspect, the product applied according to the method of the application is a primer or a varnish. BRIEF DESCRIPTION OF DRAWINGS

[0022] The application will be better understood and other advantages thereof will become more apparent on consideration of the following description, given by way of example only, and with reference to the appended drawings, in which:

[0023] - Figure 1 is a partial longitudinal section view of the principle of a rotary coating product spray machine according to the application, the spray machine comprising a bowl according to the application as well; and

[0024] - Figure 2 The spray machine bowl of Figure 1 is shown in two partial views on two illustrations A) and B), in which illustration A) corresponds to the detail II in Figure 1 , on a larger scale, while illustration B) corresponds to a partial section along the line B-B on illustration A), also on a larger scale. DETAILED DESCRIPTION

[0025] The front of the rotary liquid coating product spray machine 2 is shown inFigure 1 As illustrated in the cross-section in FIG. 1, the spray machine 2 comprises a turbine 4 for rotating a spraying member 6, hereinafter referred to as a bowl, about an axis X8 defined by a body 8 of the spray machine 2.

[0026] The spray machine 2 is of the electrostatic type and comprises means (not shown) for applying a high voltage to the paint product being sprayed with the spray machine 2, for example a high-voltage cascade and an electrical connection between the cascade and the bowl 6.

[0027] Alternatively, the spray machine 2 is of the non-electrostatic type.

[0028] The bowl 6 is supplied with liquid paint product through an axial duct 10 centred on the axis X8, which opens into a hub 62 of the bowl 6. The bowl comprises a one-piece body 60 defining an inner radial surface 61 and an outer radial surface 65 with respect to a longitudinal axis X6 of the bowl, which coincides with the axis X8 when the bowl 6 is mounted on the turbine 4. The bowl 6 is fitted with a distributor 64 which, during operation of the spray machine 2, directs the paint product from the duct 10 towards the inner radial surface 61, on which the product is distributed, the downstream end of which forms a circular spraying edge 63 for spraying a cloud N of droplets of paint product. The surface 61 centred on the longitudinal axis X6 has the effect of distributing the paint product from the duct 10 uniformly with a thickness that decreases gradually along the axis X6 as it approaches the circular spraying edge 63.

[0029] Along the longitudinal axis X6, the surface 65 also extends to the circular spraying edge 63.

[0030] The surfaces 61 and 65 and the edge 63 are centred on the longitudinal axis X6.

[0031] The diameter of the circular spraying edge 63 is denoted D63. Advantageously, the diameter D63 is less than or equal to 80 millimetres (mm), for example about 65 mm in the embodiment illustrated in the figures. By “about 65 mm” is meant 65 mm, rounded to the nearest mm. This relatively modest value for the diameter D63 means that, for a given rotational speed of the bowl 6, the tangential ejection speed of the droplets of paint product is not too high, which means that the distribution of the droplets in the cloud N can be controlled.

[0032] In the example, the bowl 6, and in particular its body 60, is made of an aluminium-based alloy.

[0033] Alternatively, the bowl can be made of titanium or a titanium-based alloy. Other materials can also be used for the bowl 6, for example a magnesium alloy or a non-metallic material such as a thermoplastic, a thermoset or a ceramic.

[0034] In the present description, upstream corresponds to Figure 1The upper left side of the figure faces the direction in which the spraying machine 2 works when spraying a coating product or a cleaning product, while the lower right side of the figure corresponds to the opposite direction facing the circular spraying edge 63.

[0035] The rotor 42 of the turbine 4 and the bowl 6 can be made to rotate together by magnetic attraction, in particular by a magnet 47 integrated into the rotor and a ferromagnetic ring 67 integrated into the bowl 6 at an outer radial surface 65 of the bowl.

[0036] Alternatively, other means of causing the rotor 42 to rotate together with the bowl 6 can be used, for example by screwing.

[0037] The body 8 is equipped with an air skirt 86 defining holes 82 for the injection of shaping air intended to direct the cloud N of droplets of coating product leaving the edge 63 or to shape this cloud in the direction of the object to be coated (not shown). Figure 1 In the figure, the air jets leaving the holes 82 are represented by arrows Fl. In practice, the holes 82 are uniformly spaced at an angular pitch of between 2° and 15° around the axis X8.

[0038] When the spraying machine 2 is working, pressurized air is supplied to the holes 82 by a duct 84 in the air skirt 86.

[0039] The holes 82 open onto an annular surface of the body 2 which, when the bowl 6 is mounted in the spraying machine 2, forms a ring 88 surrounding the axis X8 and the bowl 6. The ring 88 forms the front surface of the body 8, i.e. the end face which, when the spraying machine 2 is working, faces the object to be coated.

[0040] The circular spraying edge 63 is equipped on its inner side facing the longitudinal axis X66 with a notching 66 formed by a series of notches 661, 662, 663...66 i distributed uniformly around the axis X6. The notching 66 is formed in the part of the distribution surface 61 which is connected to the edge 63. In the following, 66 i (where i is a natural number) designates one of the notches of the notching 66.

[0041] The notches 66 i are identical to one another over the entire circumference of the edge 63.

[0042] In the figure B) in Figure 2 , the notching 66 is shown on only the right-hand part of the figure, so that the distribution surface 61 on the left-hand side can be seen. In practice, the notching extends around the entire circumference of the circular spraying edge 63.

[0043] All the notches 66 i of the notching 66 are rectilinear, parallel to the axis X6 and to one another. According to a variant of the invention which is not shown, the notches 66i are not parallel to the axis X6, but all the grooves have the same angle of inclination with respect to the axis X6 and are parallel to each other. Therefore, in all cases, the groove portions 66 are not knurls formed by the intersection of grooves oriented in different directions. The dimensions of the groove portions 66 are easier to control than the dimensions of knurls.

[0044] e 63 is the minimum radial thickness of the circular painting edge 63 measured between the bottom of the groove 66 i and the radially outer surface 65. The thickness e 63 is measured radially with respect to the longitudinal axis X6. This minimum radial thickness e 63 is chosen to be between 0.2 and 0.5 millimeters, preferably between 0.3 and 0.4 millimeters. In the example, this radial thickness e 63 is equal to 0.35 millimeters.

[0045] The value of the radial thickness e 63 allows the bowl 6 to have good geometric stability, even when the bowl is subjected to relatively high centrifugal forces when the turbine 4 rotates the bowl 6 around the axes X6 and X8 together. Therefore, the radial thickness e 63 allows to guarantee the dimensional stability of the groove portions 66, thus guaranteeing the uniformity and regularity of the paint droplets that exit the circular painting edge 63, even in the case of variations in the rotation speed of the bowl 6.

[0046] The length L63 of the circular painting edge 63 is equal to this diameter minus twice the radial thickness e 63 multiplied by π. The following relationship is obtained:

[0047] L63 = (D63 - 2 * e 63 ) * π (Equation 1)

[0048] If the diameter D63 is 65 millimeters, the length L63 of the circular painting edge 63 is approximately 204 millimeters.

[0049] In the example shown in the attached figures, the number of grooves 66 i in the groove portions 66 is 1200.

[0050] The linear density DL i of the grooves 66 66 along the circular painting edge 63 is defined as the number of grooves 66 i of the groove portions 66 per millimeter of circumference of the edge 63.

[0051] In this example, the linear density DL i of the grooves 66 66 of the groove portions 66 is:

[0052] DL66 =1200 / 204 = 5.88 grooves / mm (Equation 2)

[0053] For a bowl with a circular sprayed edge diameter of approximately 65 mm, satisfactory tests were conducted using a groove portion 66 comprising 1050 or more grooves. Therefore, a linear density DL of at least 4 grooves per millimeter was achieved. 66 Satisfactory results can be obtained in terms of droplet distribution and fineness in cloud N.

[0054] In fact, the groove 66 of the groove portion 66 can be changed in a series of spray bowls. i The quantity and the diameter D63 of edge 63, simultaneously satisfying DL 66 The groove 66 of the groove portion 64 is controlled by a condition of ≥4 grooves / mm. i linear density DL 66 .

[0055] Groove 66 i The opening angle α 66 Defined as constituting the groove 66 i The angle formed between the two flat surfaces on the side. Due to groove 66 i It is the same across the entire circumference of edge 63, therefore the opening angle α 66 It is constant on that circumference.

[0056] In a variation not shown, a groove 66 is formed. i The side surface is not flat. In this case, the opening angle α of the groove is... 66 It is defined as the average angle between these surfaces.

[0057] In the example, the opening angle α 66 Approximately 20°, meaning rounded to the nearest 0.5°. Opening angle α 66 This value allows for the arrangement of grooves 66 with high linear density. i This allows for sufficient flow of paint product to be dispensed from edge 63 to ensure effective coating with bowl 6.

[0058] Alternatively, the opening angle α 66 The value can be greater than 20°, while keeping it less than or equal to 45°, preferably less than or equal to 30°.

[0059] from Figure 2 As can be seen in illustration A), groove 66 i The radial depth along the longitudinal axis X6 has a variable length. 66 It is the groove 66 in the groove portion 66 i The maximum depth measured perpendicular to the longitudinal axis X66.

[0060] This maximum depth p 66 is chosen to be greater than or equal to 0.1 millimeter, preferably greater than or equal to 0.2 millimeter. This maximum depth p 66 provides each recess with a volume sufficient to receive the amount of coating product required to generate the cloud N during application.

[0061] The recesses 66 i have a geometry compatible with the application of the coating product under industrial conditions, since the recesses 66 i of the recess portion 66 66 are distributed along the circular spraying edge 63 with a linear density DL i that makes it possible to dispense a relatively large flow of coating product, even though the openings a 66 of these recesses 66 66 are relatively small. In this respect, the application contradicts the standard reasoning of the person skilled in the art, who tends to increase the opening angle a

[0062] The structure of the recess portion 66 on the bowl 6 described above means that it can be used as part of a coating product application method during which the bowl 6 is rotated together around the axes X6 and X8 by the turbine 4 at a relatively low rotational speed of less than or equal to 40,000 revolutions per minute (rpm), preferably 30,000 revolutions per minute. This ensures that the coating product droplets that leave the circular spraying edge 63 have a moderate kinetic energy. In this case, the coating droplets can be made to fold more effectively toward the part to be coated, thanks to the aerodynamic forces generated by the shaping air and, if necessary, the electrostatic forces generated by the electrostatic field.

[0063] In this case, the air outlet orifice 82 is advantageously supplied with shaping air at a flow rate of between 250 and 500 liters per minute (L / min), preferably at a flow rate of between 300 and 450 liters per minute. The flow rate to the outlet orifice 82 can also be expressed in normal liters per minute (NLPM), the value of which is close to the values mentioned above. This also makes it possible to reduce the shaping air flow rate compared to known coating product application methods.

[0064] In the case where the spraying machine 2 is of the electrostatic type, as in the example shown, a voltage multiplier or any other device that applies a high voltage to the coating product being sprayed is able to apply a high voltage of between 40 and 85 kilovolts (kV), preferably between 45 and 60 kilovolts, since the distance between the circular spraying edge 63 of the bowl 6 and the surface to be coated is small, for example less than or equal to 180 millimeters, preferably less than or equal to 150 millimeters, advantageously less than or equal to 100 millimeters.

[0065] Advantageously, the coating product sprayed from the bowl 6 as part of the application method of the present application is a primer or a varnish. The composition of the primer or varnish is not disturbed by passing through a recess such as the recess portion 66, whereas the base can be. The uniformity and size of the cloud of droplets exiting the edge of the bowl 6 after passing through a recess such as the recess portion 66 is not reduced during the application of the primer or varnish, even at relatively low rotational speeds, whereas the base can be.

[0066] Any feature described in relation to one embodiment or variation of the above described embodiment can be applied to one or more other embodiments and variations, provided that this is technically possible.

Claims

1. A bowl (6) for a liquid coating product, intended to be mounted in a rotary coating product applicator (2), the bowl comprising a body (60) centered on a longitudinal axis (X6), the body defining a radially inner distribution surface (61) for distributing the liquid coating product to a circular application edge (63) centered on the longitudinal axis, the circular application edge being provided with a plurality of grooves (66 i ) formed in the radially inner distribution surface (61) and distributed uniformly around the circumference of the circular application edge, characterized in that: - the linear density (DL 66 ) of the grooves (66 i ) along the circular spraying edge (63) is greater than or equal to 4 grooves per mm; and - the opening angle (a i ) of each groove (66 66 ) is less than or equal to 45°.

2. The spray bowl of claim 1, wherein, The maximum depth (p66) of each groove (66 i ) measured in the radial direction with respect to the longitudinal axis (X66) is greater than or equal to 0.1 millimeter, preferably greater than or equal to 0.2 millimeter.

3. The spray bowl according to any one of claims 1 and 2, wherein, All the grooves (66 i ) are straight and parallel to each other.

4. The spray bowl of any one of claims 1 and 2, wherein, The diameter (D63) of the circular spray edge (63) is less than or equal to 80 mm, preferably equal to about 65 mm.

5. The spray bowl of any one of claims 1 and 2, wherein, The opening angle (α) of each groove 66 The angle is less than or equal to 30°, preferably about 20°.

6. The spray bowl of any one of claims 1 and 2, wherein, The radial thickness (e 63 ) of the circular spraying edge (63) measured perpendicularly to the longitudinal axis between the bottom of the recess (66 i ) and the radially outer surface (65) of the spray bowl (6) is between 0.2 and 0.5 mm, preferably between 0.3 and 0.4 mm.

7. A rotary paint product sprayer (2) comprising: - a main body (8) defining a rotation axis (X8); - a bowl (6) for spraying a paint product, rotating around the rotation axis; - a turbine (4) for rotating the bowl around the rotation axis; and - an air skirt (86) fitted with a shaping air outlet orifice (82), characterized in that the bowl (6) for spraying a paint product is a spray bowl according to any one of the preceding claims, the longitudinal axis (X6) of which is aligned with the rotation axis.

8. A method for applying a liquid paint product with a rotary paint product sprayer (2) according to claim 7, wherein: - the bowl (6) is rotated around the rotation axis (X8) by the turbine (4) at a rotation speed less than or equal to 40 000 revolutions per minute, preferably 30 000 revolutions per minute; and - the shaping air is supplied to the shaping air outlet orifice (82) at a flow rate between 250 and 500 liters per minute, preferably between 300 and 450 liters per minute. The rotary paint product sprayer comprises means for applying a high voltage to the liquid paint product being applied, and wherein the high voltage applied is between 40 and 85 kilovolts, preferably between 45 and 60 kilovolts.

9. The method of claim 8, wherein, The liquid paint product applied is a primer or a varnish.

10. The method of claim 8, wherein, ​

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