Spraying bowl for liquid coating product, rotary sprayer comprising spraying bowl, and process for applying coating product with rotary sprayer

Abstract

To provide a spraying bowl for a liquid coating product, intended to be incorporated into a rotary coating product sprayer.SOLUTION: A spraying bowl 6 comprises a body 60 centered on a longitudinal axis X6, the body 60 defining a radial internal surface 61 for distributing the coating product as far as a circular spraying edge 63, the circular spraying edge equipped with notches 66i formed in the radial internal distribution surface 61 and evenly distributed around its circumference. In the spraying bowl 6, the linear density DL66 of the notches 66i along the circular spraying edge 63 is greater than or equal to 4 notches per millimeter. An opening angle α66 of each notch 66i is less than or equal to 45°.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a spray bowl for a liquid coating product for incorporation into a rotary coating sprayer. Furthermore, the invention relates to a rotary sprayer equipped with such a bowl and to a method for applying a coating product using such a rotary sprayer. [Background technology]

[0002] In the field of spraying liquid coating products, it is known to use rotary atomizers equipped with an atomizing element, commonly called a bowl, which forms a distribution surface for the coating product up to a circular spray edge from which droplets of the coating product are sprayed.

[0003] Such atomizing bowls are known, for example, from WO 03 / 074187. Such bowls can be made with notches near their circular atomizing edge. This notching process homogenizes and refines the droplets that are emitted from the circular atomizing edge of the bowl.

[0004] Another spray bowl is known from US Pat. No. 4,519,549. The bowl is provided with notches along its circumferential edge, forming a sawtooth structure.

[0005] Known notched bowls, i.e., bowls with notches formed near or along the circular spray edge of the bowl, provide relatively good control over the atomization and uniformity of the paint droplets. The rotational speed of the bowl affects the droplet size of the coated product. The faster the rotational speed, the finer the droplet size.

[0006] On the other hand, the faster the bowl rotation speed, the greater the kinetic energy of the droplets of the coating product ejected from the edge of the bowl. However, the direction in which the droplets of the coating product eject from the edge of the bowl is generally perpendicular to the rotation axis of the bowl. Therefore, the droplets of the coating product must be directed toward the object to be coated, such as the body of an automobile. In this case, it is known to use a forming skirt equipped with a shaping air outlet orifice. This shaping air has an airflow effect directed generally axially with respect to the rotation axis of the bowl, which can push the paint droplets back toward the object to be coated. Furthermore, in the case of electrostatic sprayers, the electrostatic effect can be utilized to direct the droplets of the coating product toward the object to be coated by applying an electrostatic charge to the coating product before or after spraying. The faster the bowl rotation speed, the greater the kinetic energy of the droplets ejected from the edge of the bowl, which must be compensated for by the shaping air, and in some cases, by the electrostatic effect, in order to push the droplets of the coating product back toward the object to be coated.

[0007] A recurring problem with rotary coating product spray devices is the goal of increasing yield, i.e., the percentage of coating product that is actually applied to the object to be coated, without reducing the quality of the layer of coating product being deposited.

[0008] In this context, it may be possible to reduce the rotation speed of the bowl in order to reduce the kinetic energy of the droplets ejected from the edge of the bowl, but in this case, even with a notched bowl, there is a risk that the cloud of droplets ejected from the edge of the bowl will be less uniform and the droplets will be larger in size, which may reduce the quality of the applied coating product layer. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 03 / 074187 [Patent Document 2] U.S. Patent No. 4,519,549 Summary of the Invention

[0010] The present invention specifically addresses this problem and proposes a novel spray bowl for liquid coating products, which allows for efficient and high-quality application of the coating product even at relatively low bowl rotation speeds.

[0011] To this end, the present invention relates to a spray bowl for liquid coating products intended for incorporation into a rotary coating product sprayer. The spray bowl comprises a body centered on a longitudinal axis. The body defines a radially inner surface for distributing the coating product to a circular spray edge centered on the longitudinal axis, the circular spray edge being provided with notches formed on the radially inner distribution surface and uniformly distributed around its circumference. According to the invention, the linear density of the notches along the circular spray edge is equal to or greater than four notches per millimeter, and each notch has an opening angle of 45° or less.

[0012] The present invention combines the features of the notch processing (both in terms of linear density and opening angle) provided by the notches distributed around the circumference of the circular rim, resulting in the advantage that the bowl rotation speed can be kept relatively low while a relatively large amount of coating product can be sprayed from the bowl rim with good uniformity in the form of fine droplets, i.e., droplets of a size suitable for forming a coating product layer. In particular, the above-mentioned notch processing features are contrary to the practice of those skilled in the art, who tend to use notches with large opening angles, such as 90° or more, which would create a channel with a large cross-sectional area for the circulation of the thread of coating product within the bowl notches. The present invention takes the opposite approach, significantly increasing the number of notches compared to known bowl notches and reducing the opening angle of each notch.

[0013] According to advantageous, but not essential, aspects of the invention, such a bowl may incorporate one or more of the following features, in any technically feasible combination: 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; The notches are all straight and parallel to each other. The diameter of the circular spray edge is less than or equal to 80 mm, preferably about 65 mm. The opening angle of each notch is less than 30°, preferably about 20°. The radial thickness of the circular spray edge, measured perpendicular to the longitudinal axis between the bottom of the notch and the radially outer surface of the bowl, is 0.2 to 0.5 mm, preferably 0.3 to 0.4 mm.

[0014] According to a second aspect, the present 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 rotating the bowl about the axis of rotation, and an air skirt equipped with shaped air outlet orifices. According to the present invention, the coating product spray bowl has its longitudinal axis coinciding with the axis of rotation, as described above.

[0015] According to a third aspect, the present invention relates to a method for applying a liquid coating product using the above-mentioned sprayer, in which the bowl is rotated around the rotation axis by a turbine at a rotation speed of 40,000 rpm or less, preferably 30,000 rpm, and shaping air is supplied to the shaping air outlet orifice at a flow rate of 250 to 500 L / min, preferably 300 to 450 L / min.

[0016] Advantageously, the atomizer comprises means for applying a high voltage to the product to be applied, the high voltage applied being between 40 and 85 kV, preferably between 45 and 60 kV.

[0017] According to another advantageous aspect, the product applied according to the method of the invention is a primer or a varnish. [Brief explanation of the drawings]

[0018] The invention will be better understood, and other advantages of the invention will become more apparent, in the light of the following description, given by way of example only, of embodiments of a spray bowl, a rotary coating product sprayer, and an application method in accordance with the principles of the invention, with reference to the drawings in which:

[0019] [Figure 1] FIG. 1 is a partial longitudinal cross-sectional view of a rotary coating product sprayer according to the invention incorporating a bowl according to the invention. [Figure 2] Figure 2 shows two partial views (Inset A and Inset B) of the atomizer bowl of Figure 1. Inset A corresponds to detail II of Figure 1 and is shown enlarged, and Inset B is also shown enlarged and corresponds to a partial cross section along line BB of Inset A. DETAILED DESCRIPTION OF THE INVENTION

[0020] A rotary liquid coating product sprayer 2, shown in a front cross-sectional view in Figure 1, comprises a turbine 4 for rotating a spraying member 6 (hereinafter referred to as bowl) about an axis X8 formed by the body 8 of the sprayer 2.

[0021] The sprayer 2 is of the electrostatic type and comprises means for applying a high voltage to the coating product sprayed by the sprayer 2, for example a high voltage cascade and an electrical connection (not shown) between this cascade and the bowl 6.

[0022] Alternatively, the atomizer 2 is non-electrostatic.

[0023] The bowl 6 is supplied with the liquid coating product via an axial conduit 10, centered on the axis X8 and opening into the hub 62 of the bowl 6. The bowl has a one-piece body 60, which defines an inner radial surface 61 and an outer radial surface 65, relative to the 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 equipped with a distributor 64, which, during operation of the spray device 2, allows the coating product coming from the conduit 10 to be returned in the direction of the inner radial surface 61, from which the coating product is distributed. The downstream end of the inner radial surface 61 forms a circular spray edge 63 of the cloud N of droplets of the coating product. The function of the surface 61, centered on the longitudinal axis X6, is to distribute the coating product coming from the conduit 10 uniformly, with the thickness decreasing along the axis X6 as the thickness approaches the circular spray edge 63.

[0024] Along the longitudinal axis X6, the surface 65 also extends to a circular spray edge 63.

[0025] The faces 61 and 65 and the edge 63 are centered about the longitudinal axis X6.

[0026] The diameter of the circular spray edge 63 is designated D63. Advantageously, the diameter D63 is equal to or less than 80 millimeters (mm), for example, about 65 mm in the illustrated embodiment. "About 65 mm" means 65 mm to the nearest millimeter. This relatively small value of the diameter D63 means that for a given rotation speed of the bowl 6, the tangential ejection velocity of the droplets of the coating product is not very high, which means that the distribution of the droplets in the cloud N can be controlled.

[0027] In the example shown, the bowl 6, and in particular its body 60, is made of an aluminum-based alloy.

[0028] Alternatively, the bowl can be made of titanium or a titanium-based alloy. Other materials can also be used for the bowl 6, such as magnesium alloys or non-metallic materials such as thermoplastics, thermosets, or ceramics.

[0029] In this specification, upstream corresponds to the direction toward the source of coating or cleaning product being sprayed when the sprayer 2 is activated (left side of FIG. 1), and downstream corresponds to the direction toward the circular spray edge 63 in the opposite direction (right side of FIG. 1).

[0030] The rotor 42 and bowl 6 of the turbine 4 can be made to rotate together by magnetic attraction, in particular by magnets 47 integrated into the rotor and a ferromagnetic ring 67 integrated into the outer radial surface 65 of the bowl 6.

[0031] Alternatively, other means for rotating the rotor 42 relative to the bowl 6 may be used, such as threading.

[0032] The body 8 is equipped with an air skirt 86 which forms shaping air orifices 82 for directing or shaping the cloud N of droplets of the coated product emerging from the edge 63 towards an object to be coated (not shown). In Figure 1, the air jets emerging from the orifices 82 are represented by arrows F1. In practice, the orifices 82 are equally spaced about the axis X8, with angular intervals between 2° and 15°.

[0033] When the atomizer 2 is in operation, the orifice 82 is supplied with pressurized air through a duct 84 in an air skirt 86 .

[0034] The orifice 82 opens into an annular surface of the body 2, which forms a ring 88 surrounding the axis X8 and the bowl 6 when the bowl 6 is attached to the sprayer 2. The ring 88 forms the front surface of the body 8, i.e., the end surface facing the object to be coated, during operation of the sprayer 2.

[0035] The circular spray edge 63 has, on its inner side facing the longitudinal axis X66, a series of notches 661, 662, 663, . . . 66 arranged regularly around the axis X6. iThe notch 66 is formed in the portion of the distribution surface 61 that joins with the edge portion 63. i (i is a natural number) refers to one of the notches in the cutout 66.

[0036] Notch 66 i are identical to each other around the entire periphery of the edge 63.

[0037] In the inset B of Figure 2, the cutout 66 is only partially visible on the right side of the figure, allowing the left side of the dispensing surface 61 to be seen. In reality, the notch extends around the entire circumference of the circular spray edge 63.

[0038] Cutout 66 notch 66 i are all linear, parallel to the axis X6 and parallel to each other. According to a non-exemplified variant of the invention, the notches 66 i are not parallel to the axis X6, but they all have the same inclination angle with respect to the axis X6 and are parallel to each other. Therefore, in both cases, the notch 66 is not a knurling formed by intersecting notches facing in different directions. The dimensions of the notch 66 are easier to control than the dimensions of the knurling.

[0039] e 63 is the minimum radial thickness of the circular spray edge 63, and the notch 66 i The thickness e is measured between the bottom of the 63 is measured radially relative to the longitudinal axis X6. This minimum radial thickness e 63 is selected to be in the range of 0.2 to 0.5 mm, preferably 0.3 to 0.4 mm. In the illustrated example, this radial thickness e 63 is 0.35mm.

[0040] Radial thickness e 63 The value of e gives the bowl 6 good geometric stability even when the turbine 4 rotates the bowl 6 about the axes X6 and X8 and a relatively high centrifugal force acts on the bowl 6. For this reason, the radial thickness e 63This makes it possible to ensure the dimensional stability of the notch processing 66 and thus the uniformity and regularity of the paint droplets emitted from the circular spray edge 63 even when the rotation speed of the bowl 6 fluctuates.

[0041] The length L63 of the circular spray edge 63 is determined by the radial thickness e 63 is equal to the value obtained by subtracting two times the value of π multiplied by π. The following relationship holds: L63=(D63-2*e 63 )*π (Equation 1)

[0042] When the diameter D63 is 65 mm, the length L63 of the circular spray edge 63 is about 204 mm.

[0043] In the illustrated example, the notch 66 i The number is 1,200.

[0044] Notch 66 along circular spray edge 63 i Linear density DL 66 The notch 66 is a notch 66 per 1 mm around the edge 63. i is defined as the number of

[0045] In this example, the notch 66 i Linear density DL 66 is as follows: DL 66 =1200 / 204=5.88 notches / mm (Equation 2)

[0046] For bowls with a circular spray edge diameter of about 65 mm, successful tests were performed using a cutout 66 with a number of notches of 1050 or more. 66 is at least 4 notches per mm, satisfactory results can be obtained with regard to the distribution and fineness of the droplets in the cloud N.

[0047] In fact, the notch 66 in the cutout 64 i Linear density DL 66 66 notchesi The number of nozzles and the diameter D63 of the nozzle 63 can be controlled by varying the number of nozzles in the various spray bowls, but the DL 66 The condition of ≥ 4 notches / mm must be met.

[0048] Notch 66 i Opening angle α 66 This notch 66 i The angle between the two planes that make up the sides of the notch is defined as 66. i is the same around the entire edge 63, so the angle α 66 is constant on this circumference.

[0049] In a variant not shown, notch 66 i The surface constituting the side of the notch is not flat. In this case, the opening angle α 66 is defined as the average angle between such planes.

[0050] In the illustrated example, the angle α 66 is approximately 20°, i.e., 20° to the nearest 0.5°. This angle α 66 The value of notch 66 i This allows for a high linear density of coating material to be distributed from edge 63 at a sufficient flow rate to ensure effective coating by bowl 6.

[0051] Separately, the angle α 66 may be greater than 20° and less than or equal to 45°, preferably less than or equal to 30°.

[0052] As can be seen in inset A of Figure 2, notch 66 i The radial depth of varies along a length parallel to the longitudinal axis X6. 66 66 notches i is the maximum depth of the axial length of the septum measured perpendicular to the longitudinal axis X66.

[0053] This maximum depth p 66 is selected to be 0.1 mm or more, preferably 0.2 mm or more.66 provides each notch with a volume sufficient to receive the amount of coating product required to produce cloud N during application.

[0054] Notch 66 i The shape of the notch 66 is a notch 66 distributed along the circular spray edge 63. i Linear density DL 66 But such a notch 66 i Opening angle α 66 Insofar as the opening angle α is relatively small, yet allows for the dispensing of a relatively large flow rate of the coating product, it is suitable for the application of coating products under industrial conditions. In this respect, the present invention contradicts the standard reasoning of those skilled in the art. Those skilled in the art will appreciate that the opening angle α can be adjusted to increase the flow rate of the coating product dispensed at the circular spray edge 63 to generate the droplet cloud N. 66 There seems to be a tendency to increase

[0055] The above-described configuration of the notches 66 in the bowl 6 means that the notches 66 can be used as part of a coating application process in which the bowl 6 is rotated by the turbine 4 about axes X6 and X8 at a relatively slow speed, e.g., up to 40,000 revolutions per minute (rpm), preferably 30,000 rpm. This ensures that the droplets of coating product ejected from the circular spray edge 63 have adequate kinetic energy. In this case, the aerodynamic forces of the shaping air and, if necessary, the electrostatic forces of the electrostatic field, more effectively deflect the coating droplets toward the area to be coated.

[0056] In this case, air outlet 82 is advantageously supplied with shaping air at a flow rate of 250-500 liters per minute (L / min), preferably 300-450 L / min. The flow rate to outlet 82 can also be expressed in standard liters per minute (NLPM) at values ​​close to those values. This also allows for a reduced flow rate of shaping air compared to known coated product application processes.

[0057] In the illustrated example, when the sprayer 2 is electrostatic, the cascade or any other means for applying a high voltage to the coating product being sprayed can apply a high voltage of 40 to 85 kilovolts (kV), preferably 45 to 60 kV, since the distance between the circular spray edge 63 of the bowl 6 and the surface to be coated is small (for example 180 mm or less, preferably 150 mm or less, advantageously 100 mm or less).

[0058] Advantageously, the coating product sprayed using bowl 6 as part of the application process of the present invention is a primer or varnish, the composition of which is not disturbed by passing through a notch such as cutout 66, but may be disturbed at the base. When applying a primer or varnish, the uniformity and size of the cloud of droplets emitted from the edge of bowl 6 after passing through a notch such as cutout 66 is not reduced even at relatively slow rotational speeds, but may be reduced at the base.

[0059] Any feature described with respect to one embodiment or variant above may also apply to one or more of the other embodiments and variants described above, insofar as technically feasible.

Claims

1. A spray bowl (6) for a liquid coating product intended to be incorporated into a rotary coating product sprayer (2), comprising a body (60) centered on a longitudinal axis (X6) and forming a radially inner surface (61) for distributing said coating product up to a circular spray edge (63), said circular spray edge (63) being formed on said radially inner distribution surface (61) centered on said longitudinal axis and having notches (66) uniformly distributed along its circumference. ｉ In a spray bowl (6) having a body (60) equipped with - the notch (66) along the circular spray edge (63) ｉ ) linear density (DL ６６ ) is equal to or greater than 4 notches per millimeter, - each notch (66 ｉ ) opening angle (α ６６ ) is 45° or less.

2. Each notch (66) measured in a radial direction of the longitudinal axis (X66) ｉ ) maximum depth (p ６６ 2. Bowl according to claim 1, wherein the thickness of the periphery of the bowl is 0.1 mm or more, preferably 0.2 mm or more.

3. The notch (66 ｉ 3. The bowl of claim 1, wherein the first and second ribs are all straight and parallel to each other.

4. 3. Bowl according to claim 1 or 2, wherein the diameter (D63) of the circular spraying edge (63) is less than or equal to 80 mm, preferably about 65 mm.

5. The opening angle (α ６６ 3. A bowl according to claim 1 or 2, wherein the angle θ is less than 30°, preferably about 20°.

6. Notch (66 ｉ ) and the radial outer surface (65) of the bowl (6), the radial thickness (e ６３ 3. Bowl according to claim 1 or 2, wherein the thickness of the periphery of the bowl is 0.2 to 0.5 mm, preferably 0.3 to 0.4 mm.

7. a body (8) defining an axis of rotation (X8); a bowl (6) for spraying the coating product, rotating about said axis of rotation; a turbine (4) that rotates said bowl around said axis of rotation; - an air skirt (86) with shaped air outlet orifices (82), A rotary coating product sprayer (2) in which the bowl (6) for spraying the coating product is as claimed in any one of claims 1 to 6, characterized in that its longitudinal axis (X6) is aligned with the axis of rotation.

8. 8. A method for applying a liquid coating product using a sprayer (2) according to claim 7, comprising the steps of: - said bowl (6) is rotated around said axis of rotation (X8) by said turbine (4) at a rotational speed of less than 40,000 rpm, preferably 30,000 rpm; - A method characterized in that said shaping air outlet orifice (82) is supplied with shaping air at a flow rate of 250 to 500 L / min, preferably 300 to 450 L / min.

9. 9. A method according to claim 8, wherein the sprayer comprises means for applying a high voltage to the product to be applied, the high voltage applied being between 40 and 85 kV, preferably between 45 and 60 kV.

10. The method of claim 8, wherein the applied coating product is a primer or varnish.

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