MXPA99002885A - Rotary atomizer for particulate paints - Google Patents

Abstract

A rotary atomizer applies particulate paints with good color matching reducing the paint droplet size deviation and then optimizing the other paint spraying parameters. The droplet size parameters of paint are reduced using a bell having reduced flow deviations, including an overflow surface having a generally constant angle between a baffle and an atomized edge.

Description

ROTARY ATOMIZER FOR PARTICULATE PAINTS BACKGROUND OF THE INVENTION The present invention relates generally to rotary atomizers and more particularly to a rotary atomizer with better performance for particulate paints. Many paints are applied today with rotary atomizers to work pieces, such as car bodies. Rotary atomizers include a rotating bell having a generally conical overflow surface between a radially inward central axial bore and a radially outwardly spraying edge. At or near the atomizing edge, the angle of the overflow surface relative to the axis of the bell sharply decreases to form a lip next to the atomizing edge. The purpose of this lip is to generally direct the sprayed paint more axially forward and reduce the radial dispersion. The bells of known atomizers further include a deflector, also of generally rotational symmetry, disposed in front of the central axial bore. The paint that enters the bell through the central axial hole contacts the rear surface of the deflector and is sent radially outwards towards the overflow surface. In the bells of the known atomizers, the paint follows a tortuous, turbulent path, from the nozzle to the atomizing edge. As a result, the flow of paint to the atomizing edge is turbulent and fluctuates cyclically. As a result, the paint from the atomizer is atomized into paint droplets of a wide variety of sizes. Paint droplets can vary up to 100 microns or more. Current rotary atomizers are unable to obtain good color matching when applying paints with particles, such as mica. In general, mica includes particles of the order of 3 micras per 200 micras. When this paint is applied with rotary atomizers, the mica particles are oriented generally perpendicular to the application surface. As a result, the paint has a different tint or color than desired, that is, the mica particles are flat. To correct this problem, a second coating of the paint is typically applied with atomized air spray guns rather than with rotary atomizers. This second coating provides the right color; however, atomized air spray guns have low transfer efficiency (approximately 50%) compared to rotary atomizers (approximately 80%). Therefore, atomized air spray guns increase the amount of paint lost, increasing the cost of the paint process, and cause environmental problems related to the waste of lost paint.

COMPENDIUM OF THE INVENTION The present invention provides a rotary atomizer that provides better color equalization. In general, the improved atomizer provides a more uniform paint droplet size, which, in turn, facilitates the control of the particles to ensure proper orientation of the particles and to obtain good color matching. The rotary atomizer hood according to the present invention provides several novel features aimed at reducing the deviation of the paint droplet size. First, the bell includes a generally conical overflow surface having a generally constant flow angle between a baffle and the atomizing edge. In addition, the exposed surface area of the overflow surface is increased by decreasing the size of the baffle relative to the previous bells in order to produce solvent evaporation from the paint on the overflow surface. The diameter of the atomizing edge is also increased, thereby reducing the thickness of the paint film on the atomizing edge. The hood is designed to reduce the flow deviation of the paint as it moves from the axial bore to the spray boundary in order to provide for the laminar flow of the paint through the overflow surface and the atomizing edge. The bell becomes hollow to reduce the weight of the bell. A rear cover is fixed to the back of the bell body, which encloses an annular cavity. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing, as well as other advantages of the present invention, will be readily apparent to those skilled in the art from the following detailed description of a preferred embodiment considered in light of the following scale drawings, in which: Figure 1 is a scale drawing of the atomizer of the present invention. Figure 2 is a cross-sectional scale drawing of the atomizer of Figure 1. Figure 3 is a front view in scale drawing of the bell of Figure 2. Figure 4 is an enlarged view of the deflector of Figure 2. Figure 5 is a cross-sectional view to scale of an alternative bell. Figure 6 is an enlarged view of the baffle in the bell of Figure 5. Figure 7 is a bottom-scale view of the bell of Figure 5. And Figure 8 illustrates a possible configuration for applying a base coat with the atomizer of figure 1 and the bell of figure 2 or 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 illustrates a rotary atomizer 20 and a bell 22 according to the present invention. The atomizer includes a shaping air ring 23 which preferably includes 30 nozzles generally parallel to the axis of the atomizer. The forming air ring 23 supplies forming air, preferably at 100 liters per minute. With the reduced number of holes from the known conformal air ring (typically 40), the forming air produces increased turbulence. The bell 22 is shown in more detail in Figures 2-3. The bell 22 includes a central axial hole 24 in the base of the bell 22. The central axial hole 24 includes a coaxial passage on a front surface 26 of the hood 24. The front surface 26 of the hood 22 includes a flat central portion 28. generally perpendicular to the axis of the bell 22 and a generally conical overflow surface 30 from the perpendicular portion 28 to a spray edge 32. Between the perpendicular surface 28 and the spray edge 32, the overflow surface 30 has a smooth continuous surface of a constant flow angle a with respect to the annular spray edge 32, preferably 5-40 degrees, more preferably 26-30 degrees and more preferably 28.25 degrees. The diameter of the annular spray edge 32 is preferably 63-75 mm, and most preferably 64.6 mm. An annular hub 33 extends rearwardly from the bell 22 and includes an externally threaded portion 34. A frusto-conical rear cover 35 is threaded onto the threaded portion 34 of the annular hub 33 and welded or glued to the rear of the hub. bell 22 behind the spray edge 32. As a result, the body of the bell 22 behind the overflow surface 26 is hollow, reducing the weight of the bell 22. A concentric interior hub 36 extends rearward from the bell 22 and is threaded on the outside to mount it on the atomizer 20. Other means can also be used to join the bell 22 to the atomizer 20. The spray edge 32 forms a sharp edge between the overflow surface 30 and a small bevel 38 which leads to the outer rear surface of the bell 22. If the atomizer 20 is to be used to apply a base coat, the bell 22 preferably includes a titanium alloy, preferably TÍ-6A 1-4V. If the atomizer 20 is to be used to apply a clear coating or first coat, the bell 22 is preferably made of aluminum, most preferably 6A1-4V, GAl-25N-4Zr-2M0. If the bell 22 is made of titanium, the rear cover 35 is preferably welded to the rear part of the hood 22 behind the spray edge 32. If aluminum is used, the rear cover 35 is preferably glued to the rear part of the cover. bell 22 behind the spray edge 32. Small indentations may be formed on the surface 26 at the spray edge 32 to spray a clear coating. Said indentations are known and used in the art. At the front of the central axial hole 24 is placed a deflector 40 which includes a rear surface 42 generally parallel to the perpendicular surface 28 of the bell 22 and a conical rear surface 44 which is generally parallel to the overflow surface 30 of the bell 22. Baffle 40 preferably has approximately 22, 3 millimeters in diameter, and preferably about 1/3 of the diameter of the spray edge 32. More particularly, the diameter of the baffle is less than 40 percent, and more preferably about 34.5 percent of the diameter of the edge 2. The baffle 40 is shown in more detail in FIG. 4. A passage 50 extends from the rear surface 42 to a front surface 52 of the baffle 40 and includes four tubular passages 54 (shown two) leading from the surface rear 42. The baffle 40 is retained in the hood 22 with a plurality, preferably 3, of crimped, snap-fit connectors 56 having spacers 58 preferably 0.7 millimeters wide. The improved bell 22 provides a small deviation of the particle size, which in turn facilitates the control of the particles. In other words, if the size of the atomized paint particles is known from the spray edge 32, the forming air velocity, the turbulence and RPM of the bell 22 and the flow of paint can be adjusted to ensure that the particles in the sprayed air are in contact with the paint. they are ejected so that they are flat on the surface painted by the forming air from the forming air ring 23. With a small deviation of the particle size, said parameters can be optimized for a greater percentage of the paint droplets, providing thus providing a better color match. The reduced deviation of the particle size is the result of several novel aspects of the bell 22 and the baffle 40. First, the larger annular surface 30 causes more solvent (such as water) to evaporate before reaching the spray edge 32. The large diameter spray edge 32 provides a thin film of paint at the spray edge 32. The reduced ratio of the baffle disk 40 to the spray edge 32 provides a more constant laminar flow through the overflow surface 30 to the edge Spray 32. Since the conical surface 30 is continuous and smooth from the baffle 40 to the spray edge 32 and has a constant angle α, the flow rate of paint to the spray edge is constant (ie, does not oscillate). As a result, better control of the paint particle size is achieved. Further, as can be seen in Figure 2, the bell 22 of the present invention provides only three flow deviations between the central axial hole 24 and the spray edge 32, thus providing a constant, substantially laminar paint flow in the spray edge 32 and therefore a reduced deviation of the particle size. Figures 5 to 7 describe an alternative embodiment of a bell 100 having a baffle 110. Said bell 100 provides only two flow deviations between the central axial hole 112 and a spray edge 132. The conical portion 130 of the overflow surface it extends directly from the axial central hole 112 to the spray edge 132. Thus, the overflow surface 126 does not include a perpendicular portion (such as the perpendicular portion 28 of Figure 2). This further improves the laminar flow of the paint and further reduces the deviation of the particle size. The deflector 110 includes a generally conical rear surface 144 extending to a generally rounded central rear surface 142, thereby reducing the flow deviation of the paint. A passage 150 passes through deflector 110 and includes four divergent tubular passages 151. Alternatively, steps 151 may converge. The bell 100 can also be mounted on the atomizer 20 of Figure 1 in place of the bell 22. Figures 1-7 are scale drawings. Figure 8 illustrates a potential configuration of a paint spray zone 150 for applying a base coat to a vehicle body 152 using the atomizer 20 of the present invention shown in Figures 1-7. The vehicle body 152 advances in the direction 154 through the zone 150 while the atomizers 20 apply base coat paint. Zone 150 is an area of thirteen bells, two passes, which would apply a base coat with good color matching with the efficiency of the rotary atomizers. In known systems, the base coat would be applied with nine rotary atomizers and six air atomizers. The length of zone 150 could be reduced by approximately 9.144 m (30 ft), compared to 13.71 m (45 ft) for the known base coating areas. In zone 150, an upper machine 156 includes two atomizers 20 and applies a first coating to the center of the horizontal surfaces. A pair of side machines 158 pre-preferably each oscillate an atomizer 20 the full length of the vehicle doors 152 in the first pass. Each of a pair of side machines 160 may include a pair of vertically and horizontally offset sprays each mounted on arms 161. A first arm 161a provides three axes of movement to contour the pillars and paint the edge of the hood and boot. The second arm 161b is fixed with pivot and horizontal cover, to process the rocker arm. A pair of lateral machines 162 perform a second pass in the doors of the vehicle 152. A second upper machine 164 includes three atomizers 20 to perform a second pass on the horizontal surfaces. An example will be provided using the novel atomizer 20 of Figures 1-4 in the arrangement of Figure 8 for spraying M6S1SA paint based on BASF Prairie Tan Metallic Solvent in a two-pass base coat application with the following parameters: Bell rotation 22: 60,000 RPM; fluid flow: 200 cc / min in a first pass and 75 cc / min in a second pass; forming air: 200 L / min in the first pass and 50 L / min in the second pass. Preferably, the resonant frequencies of the atomizer bearing are avoided. The atomizer 20 produces a small deviation of the droplet size, typically 80% of the droplets will have a size deviation of the order of 8-50 μm. With the reduced size deviation, the other parameters can be adjusted to ensure that the mica particles are flat, thereby providing a good color match. More preferably, the reduction in particle size is reduced below 30 μm. The atomizer 20 produces better color matching compared to the previous bell zones. The colorimetric data for the example are:? L < 2.0,? A < 1.0 and ÁB < 1.0. By providing good color matching with rotary atomizers rather than air atomizers, the efficiency is greatly improved. More generally, the bell rotation speed is preferably between 60,000 and 80,000 RPM. In addition, the flow of paint fluid preferably does not exceed 250 ml / min. According to the stipulations of the patent statutes and the jurisprudence, the exemplary configurations described above are considered to represent a preferred embodiment of the invention. However, it should be noted that the invention can be carried out in a manner other than that specifically illustrated and described without departing from its spirit or scope.

Claims (23)

1. A rotary atomizer hood having a generally conical overflow surface between a central axial bore generally inwardly and an atomizing edge radially outward, the generally conical overflow surface having a generally constant flow angle relative to the atomizing edge.

2. The rotary atomizer hood of claim 1, further comprising a baffle having a generally rotational symmetry deflection surface disposed in front of said central hole, said overflow surface defining said generally constant flow angle relative to the axis from the deflector to the atomizer edge.

3. The rotary atomizer hood of claim 2, wherein the overflow surface defines a generally constant flow angle relative to the axis from the central axial hole to the atomizing edge.

The rotary atomizer hood of claim 2, wherein the deflector includes at least one entrance in the deflection surface, the deflection surface having a generally constant angle with respect to the axis from the at least one entry to an edge radially outside.

5. The rotary atomizer hood of claim 2, wherein the flow angle is greater than 60 degrees at all points between the baffle and the atomizing edge.

6. The rotary atomizer hood of claim 2, wherein the deflector has a diameter of less than 40% of that of the atomizing edge.

The rotary atomizer hood of claim 1, wherein the flow of paint along the overflow surface between the baffle and the atomizing edge is substantially laminar.

8. The rotary atomizer hood of claim 1, wherein the paint atomized by said rotary atomizer has a particle size deviation of less than 50 microns.

9. A rotary atomizer having the bell defined in claim 1, the rotary atomizer rotating the bell around its axis and supplying paint to the bell through the central axial hole.

10. The rotary atomizer of claim 1, further including forming air holes that supply forming air.

11. A rotary atomizer hood comprising: a bell body including a generally conical re-bossing surface between a radially inward central axial bore and a radially outwardly spraying edge; a baffle having a generally rotational symmetry deflection surface disposed in front of said central hole; a back cover affixed to a rear surface of the bell body, a generally annular cavity formed between the back cover and the overflow surface.

12. The rotary atomizer hood of claim 1, further comprising an annular hub extending rearwardly from the bell body, said back cover being secured to said annular hub.

13. The rotary atomizer hood of claim 12, wherein said annular hub includes a threaded portion, said back cover being threaded onto said threaded portion of said annular hub.

14. The rotary atomizer hood of claim 13, wherein said back cover is welded or glued to the rear part of the bell body behind the spray edge.

15. A paint spraying zone for applying a particulate paint with particles, including: a plurality of first paint sprays, each having a rotary atomizer, the first paint sprays atomizing a first coating of the particulate paint onto a surface; and a plurality of second paint sprays each having a rotary atomizer, the second paint sprays atomizing a second coating of the particulate paint to said surface on said first coating.

16. The paint spray zone of claim 15, wherein the transfer efficiency of the paint spray zone is greater than 75%.

17. The paint spraying zone of claim 15, wherein the first paint sprays and the second paint sprays are intermixed.

18. The paint spray zone of claim 15, wherein said atomizers apply said particulate paint to the surface and cause said particles to be flat on the surface.

19. The paint spray zone of claim 15, wherein the atomizers atomize the particulate paint into paint droplets having a paint drop size deviation of less than 50 microns.

20. A method for rotating atomization of a particulate paint, including the steps of: a) atomizing liquid paint with particles into paint droplets having a paint droplet deviation of less than 50 microns; and b) adjust the paint spraying parameters to ensure proper color matching. The method of claim 20, wherein said step a) further includes the step of providing a substantially laminar flow of said paint through an overflow surface of a rotary atomizer hood. The method of claim 21, wherein said step a) further includes the step of providing for less than four flow deviations of said paint between an axial hole in a base of the hood and an atomizing edge of the hood, the surface being of overflow between the axial hole and the atomizing edge. The method of claim 22, wherein said step a) further includes the step of atomizing said paint into paint droplets having a size deviation of less than 30 microns.