EP0951942A2 - Method and rotary sprayer for coating series or workpieces - Google Patents

Abstract

The method involves using electrostatic rotation atomizers with a rotating bell plate (22) on whose end surface the paint is fed over a flow surface (30) to a spray edge (32), from which the sprayed droplets containing the effect particles pass to a work piece. The paint material is fed to the spray edge on the flow surface in a surface region bounding on the edge in a direction at an essentially constant angle to the rotation axis. An Independent claim is also included for a rotation atomizer for series coating of work pieces.

Description

The invention relates to a method for serial coating of workpieces such as motor vehicle bodies with paint material containing effect particles and one for this electrostatic rotary atomizer to be used.

As is known, for the series coating of motor vehicles electrostatic rotary atomizer with bell cups used whose facing the workpiece to be coated End face from a central opening continuously to Spray edge or at least in the area in front of the spray edge is concave (EP 0 294 606, EP 0 463 742, DE-G 93 19 555, DE 43 06 800). One purpose of this change of direction is to enlarge it the axial component of the spray direction and one Reduction of the radial component. Over which the coating material feeding center opening of the bell plate sits a deflection part, also known as a distributor disc, that divides the material flow into partial flows, one of which directly onto the overflow surface of the Bell plates arrives while the other partial flow passes through central Openings of the deflecting part on the front and first from there flows onto the overflow surface of the bell cup. Of the Material flow to the trailing edge is due to relatively strong deflections more or less turbulent in the area in front of the spray edge, what u.a. considerable differences in the size of the paint droplets of the sprayed and atomized coating material for Consequence. The differences can be more than 100 µm.

Electrostatic rotary atomizers are characterized by high Application efficiency (ratio of the amount sprayed to the applied amount) of about 80% and have to be applied normal paint materials have been tried and tested for a long time. On the other hand was a satisfactory coating with effect particles Paint material (e.g. metallic paint) with exclusive Not possible to use the known rotary atomizers. A The reason for this is that the relatively large effect particles tend to look in the very different sized paint droplets aggregate and focus on hitting the to erect or "float" the coating surface. The result is a significant deterioration in the target Surface effects that form the nests of the effect pigments as well as different brightness depending on the viewing angle ("Flip-flop") and changes in hue at different angles Viewing angles becomes visible. Therefore, there was a double so far Color application usual and necessary, in which only the first layer was applied with electrostatic rotary atomizers, while for which the effect and color tone formation is decisive determining second order used pneumatic spray guns were. However, this had the fundamental disadvantages of pneumatic spray guns such as those known as cloud formation unwanted areas of uneven coating in the applied lacquer film and especially one in comparison with rotary atomizers much lower application efficiency Often only 30 to 35% are accepted. The related Paint losses are not just for economic reasons undesirable, but above all mean a significant environmental impact.

Accordingly, the object of the invention is a method or to specify a rotary atomizer that has a qualitative flawless, especially cloud-free application of effect paints with a much higher application efficiency enable than before.

This object is solved by the features of the claims.

The invention provides a qualitatively optimal effect painting enabled with the greatest possible application efficiency. This does not only involve extensive separation of the effect pigments and their very even distribution in the paint film achieved, but above all a flat orientation of the Effect particles on the coated surface.

What is essential for this is the knowledge that the applied A droplet (measured after spraying and before impact) Do not exceed a droplet diameter of 60 µm and if possible should be between 10 to 60 µm and one to should contain two effect pigments to make a cluster to avoid the effect pigments. The applied droplets should be as high as possible when hitting the object Solid content have reached uprighting or floating to avoid the effect pigments.

It was found that the droplet size was not only of depends on the dynamic viscosity of the paint, but influenced becomes constant by the size of the along the overflow surface permanent color flow angle of the bell cup and diameter and geometry of the spray edge and also by the amount of paint discharge and the bell plate speed. Changes and agglomerations the effect pigments are protected by paint Paint flow prevented. The desired high solid content applied droplet is mainly due to solvent loss when flowing over the bell plate and on the way to Workpiece reached.

In view of these relationships, the flow angle between the axis of rotation and the overflow surface at least in Area between the usual distributor disc and the spray edge remain constant and preferably be between 50 and 85 °. The distributor disk diameter should preferably be less than 40% of the bell or spray edge diameter, which in comparison with the usual bell plates the exposed surface area of the overflow area Reduction of the distributor disc is increased, so as possible a lot of solvent from across the overflow area flowing paint can evaporate. Also the diameter of the spray edge is preferably larger than usual, in particular 63 to 75 mm, which increases the surface area and at the same time the thickness of the paint film reaching the spray edge is reduced. By the constant flow angle with as much as possible little deflection of the from the center opening to the spray edge flowing lacquers becomes largely laminar flow and accordingly paint-preserving color scheme achieved. For similar reasons it is advisable to make the spray edge sharp-edged with smaller Form the chamfer to the outside of the bell plate. To reduce the mass of the bell body can be divided into two parts an inner cavity and preferably made of metal less Density like Al or Ti can be manufactured.

Fig. 1

eine Schnittansicht eines Rotationszerstäubers mit einem Glockenteller gemäß der Erfindung;

Fig. 2

eine vergrößerte Ansicht des Glockenteller gemäß Fig. 1;

Fig. 3

eine Draufsicht auf die Frontseite des Glockentellers nach Fig. 2;

Fig. 4

eine vergrößerte Ansicht der Verteilerscheibe des Glockentellers nach Fig. 2;

Fig. 5

eine andere Ausführungsform eines Glockentellers gemäß der Erfindung; und

Fig. 6

eine schematische Darstellung zur Erläuterung einer Anlage zur Beschichtung von Kraftfahrzeugen mit den hier beschriebenen Rotationszerstäubern.

The invention is explained in more detail using the exemplary embodiments illustrated in the drawing. Show it:

Fig. 1

a sectional view of a rotary atomizer with a bell cup according to the invention;

Fig. 2

an enlarged view of the bell plate of FIG. 1;

Fig. 3

a plan view of the front of the bell plate of FIG. 2;

Fig. 4

an enlarged view of the distributor plate of the bell cup according to Fig. 2;

Fig. 5

another embodiment of a bell plate according to the invention; and

Fig. 6

a schematic representation to explain a system for coating motor vehicles with the rotary atomizers described here.

The rotary atomizer 20 shown in Fig. 1 can up to his bell plate 22 designed according to the invention itself be of a known type (see e.g. DE 43 06 800 C2) and must therefore insofar as not described in detail. Just a ring from distributed around the axis of rotation, the conical outer surface of the Bell plate 22 acting on axial air nozzles 23 is too mention that to form the sprayed coating material to serve. Appropriately, the order of 30 nozzles be present, the air flows with e.g. Generate 100 m / min.

2 has the rotationally symmetrical bell plate 22 a central opening 24 coaxial with the axis of rotation, through which to be sprayed from a paint tube 25 (FIG. 1) Paint material on the end face facing the workpiece of the main body of the bell plate 22 arrives. This End face consists of an adjoining the central opening 24 relatively small area 28 that is transverse to the axis of rotation runs, and a subsequent conical overflow surface 30, which is shown continuously from the area 28 smooth and with constant angles with respect the axis of rotation extends to the spray edge 32. In other words forms the overflow surface in the containing the axis of rotation 2 a straight line up to Spray edge. The constant angle of the overflow surface is in the example shown in the order of 60 °, corresponding to the illustrated angle a of approximately 30 ° with respect the spray edge.

In the axial direction in front of the central opening 24 is a distributor disk serving deflection part 40 is arranged, which is a general parallel to the surface area 28 of the bell plate 22 Rear surface 42 and then preferably one conical rear surface running parallel to the overflow surface 30 44 has. The deflection part is provided with central openings (Fig. 4) and serves to divide the coating material emerging from the central opening 24 in Partial streams, one of which is directly between the surface area 28 and the rear surface 42 on the overflow surface 30 flows while the other partial stream flows over the front of the Deflection part 40 reaches the overflow surface 30 and there mixed with the first partial flow.

The top view of Fig. 3 shows the proportions of the Overflow surface 30 and the deflecting part 40. The diameter of the Deflection part can, for example, about 1/3 of the diameter Spray edge 32 amount. In the example shown, can the spray edge has a diameter of approximately 65 mm, the deflection part 40 has a diameter of approximately 22 mm.

The bell plate has on its back facing away from the workpiece 22 a mounting hub 31 for mounting in the rotary atomizer and a ring surrounding the mounting hub Collar part 33 with an external thread 34. On the external thread 34 is a truncated cone-shaped side wall 35 which is screwed behind the spray edge 32 on the back of the bell body e.g. can be welded or glued. As a result and as shown, the main body of the bell plate is hollow in the space 38 behind the overflow surface 30, whereby the mass the bell plate is reduced. The overflow surface forms with the outer surface of the bell plate, i.e. the side wall 35 an acute angle of less than 45 °, in the illustrated Example about 30 °. It is also essential that the between the overflow surface 30 and one to the conical outer surface the side wall 35 leading small chamfer formed spray edge 32 should be as sharp as possible.

If the rotary atomizer 20 described here for application basecoat), its bell plate 20 expediently consist of a titanium alloy, preferably one TiAl alloy. But other light metals can also be used Al-based, especially when other materials are used such as. Clear varnish should be applied. Especially for Spraying of clear lacquer can overflow surface 30 in the area before the spray edge 32 contain the usual longitudinal grooves.

The deflection part 40 is shown enlarged in FIG. 4. Be Leading like a labyrinth from the rear surface to the end surface 52 central opening system 50 contains e.g. four axial channels 54 and one across their mouths as shown transversely to Axial inner deflection element. On the main body of the Bell plate is the deflecting part 40 with preferably three even angular spacing around the axis holding pins 56 releasably attached with a press fit. The gap-like space between the deflection part 40 and the one facing it End face of the bell plate 22 (Fig. 2) is only through the middle disk-shaped spacer 58 of the holding pins 56 interrupted.

As already explained, the described bell plate ensures 22 for smaller size deviations of the sprayed paint droplets than with conventional rotary atomizers, which means a Position control of the effect particles is facilitated. If the Size of the atomized sprayed from the spray edge 32 Paint droplets are known to affect the speed of the shaping air as well as the speed of the bell plate and the color flow can be set so that the effect particles are forced to lie flat on the surface to be coated. Due to the small size differences of the paint droplets can use these parameters for a high percentage of paint material can be optimized for the desired color effect.

As has also been explained, the smaller droplet size deviation is a result of various essentials Aspects of the bell cup 22 and the deflecting part 40. First becomes larger due to the larger annular overflow surface 30 Proportion of solvent (which in the case of water-based paint is known to be largely water) evaporates, before the paint material reaches the spray edge 32. By the relatively large diameter of the spray edge 32 forms this is an advantageously thin paint film. The low ratio of the diameter of the deflection part 40 to that of the spray edge 32 ensures a more constant, laminar flow of material over the overflow surface 30 to the spray edge 32. Because the conical overflow surface 30 from the deflection part 40 to the spray edge 32 continuously and is smooth and has a constant angle a with the spray edge forms, is also the paint flow rate up to the spray edge constant, i.e. there are no oscillations. As a result this results in better control of the paint droplet size. Since also the bell plate 22 described in FIG. 2 only slight deviations in flow direction between the central opening 24 and the spray edge 32 causes, and only relatively close to the central opening 24, result more constant, in essential laminar paint flow at the spray edge 32 and therefore also smaller droplet size deviations.

5 is a bell plate 100 according to another embodiment of the invention, which is also something different Deflection part 110 and even less directional deviations effected between the central opening 112 and the spray edge 132 than in the embodiment according to FIG. 2. The overflow surface 126 forming a straight, conical part of the end face the bell body extends here directly from the Middle opening 112 to the spray edge 132. The overflow area 126 therefore does not contain a part running perpendicular to the axis (as area 28 in FIG. 2). This will make the laminar Paint flow further improved and droplet size variations further decreased. The deflecting part 110 essentially has one here rectilinearly conical rear surface 144 adjacent to one central rounded rear surface part, causing changes in direction the paint flow can be reduced to a minimum. Also here the rear surface 144 of the deflection part runs parallel to Face of the bell body, and the annular gap is only detachable with axially parallel holding pins Attachment of the deflection part 110 interrupted, one of which is shown schematically at 56 '. In contrast to the labyrinthine 4 are the opening system 50 of the back to the end face of the deflecting part 110 leading Openings from simple inclined with respect to the axis of rotation Bores 154.

To explain the coating process described 6 shows a possible arrangement of the rotary atomizers used 20 (Fig. 1) in the coating zone 150 of a spray booth for coating motor vehicle bodies with basecoat shown. The body 152 moves in the direction of the shown arrow. The coating zone 150 contains, as shown 13 rotary atomizers for double color application. In comparable known systems, the basecoat applied with nine rotary atomizers and six air atomizers, so that the length of the coating zone 150 in contrast can be reduced by about 1/3. More specifically, there are one Roof machine 156 two rotary atomizers 20 for the first Paint application provided. At the first pair of side machines 158 Rotary atomizer for the first color application vertically moved up and down. The next page machines 160 each have two rotary atomizers offset vertically and horizontally, on arms 161a for triaxial contour movements or on fixed arms 161b for the coating further body parts are arranged. Another pair of Side machine 162 is particular for a second side coating the vehicle doors. Finally one worries second roof machine 164 with three rotary atomizers 20 for a second coating of the horizontal vehicle surfaces.

For some of the atomizers in a double coating system can also use conventional rotary atomizers whose application efficiency may a little higher can be as that of the atomizer according to that described here Invention. In any case, however, is the overall efficiency much higher (e.g. about 75%) than that of known systems for the application of paint material containing effect particles with even better quality.

In a practical experiment, a system according to FIG. 6 commercially available metallic paint in double coating operation applied with the following parameters. The bell speed was 60,000 rpm. Paint flow and steering air flow were 200 cc / min or 200 L / min for the first coating and 75 cc / min or 50 L / min for the second coating. It was made sure that no resonance frequencies occurred in the atomizer bearings. Deviations in the paint droplet size were small, typical are 80% of the droplets when they hit an area from 8-50 µm. The size of the droplets can e.g. with a Laser measurement process on the way between the spray edge and the Workpiece to be measured. Due to the small size deviation the paint droplets could adjust all other parameters in this way be that the effect particles when they hit flat lie on and ensure the desired good color coincidence. The droplet size deviation was successfully reduced to less than 30 µm to reduce.

Claims (17)

Process for the serial coating of workpieces such as, for example, motor vehicle bodies with paint material containing effect particles, using electrostatic rotary atomizers (20) with a rotating bell cup (22, 100), on the front side of which the paint material flows over an overflow surface (30, 126) to a spray edge ( 32, 132) from where the sprayed paint droplets containing effect particles migrate to the workpiece,
wherein the paint material is fed to the spraying edge on the overflow surface in the surface area adjacent to the spraying edge in a direction which forms an angle which remains essentially constant with the axis of rotation in the direction of the spraying edge. A method according to claim 1, characterized in
that the constant angle between the axis of rotation and the surface area adjacent to the spraying edge (32, 132) is 50 to 85 °. A method according to claim 1 or 2, characterized in that
that the bell plate (22, 100) rotates at 60,000 to 80,000 rpm. Method according to one of claims 1 to 3,
characterized,
that the paint material flows at a maximum of 250 ml / min to the spray edge (32, 132). Method according to one of claims 1 to 4,
characterized,
that the constant angle between the overflow surface (30, 126) and the axis of rotation, the diameter of the spray edge (32, 132), the bell plate speed and the flow rate of the paint material are selected so that the applied paint droplets are at least for the most part smaller than 60 microns and the effect particles lie flat on the workpiece when they hit. Electrostatic rotary atomizer for the serial coating of workpieces such as motor vehicle bodies, the rotatably mounted bell plate (22, 100) of which on its front side facing the workpiece has a central opening (24, 112) which is coaxial with the axis of rotation and is generally conical to an annular spray edge (32, 132) extending overflow surface (30, 126) for the coating material,
characterized,
that the overflow surface (30, 126) in the area adjacent to the spray edge (32, 132) forms an angle with the axis of rotation which remains essentially constant in the direction of the spray edge. Rotary atomizer according to claim 6,
characterized,
that the length, measured in the direction of the spraying edge (32, 132), of the constant angle area adjacent to the spraying edge is substantially greater than that of the overflow surface (28) between the central opening (24) and the constant angle area
or the area of constant angle extends essentially from the spray edge (132) to the central opening (112). Rotary atomizer according to claim 6 or 7,
characterized,
that the constant angle is about 50 to 85 °. Rotary atomizer according to claim 6 or 7,
characterized,
that the constant angle is of the order of 60 °. Rotary atomizer according to one of claims 6 to 9 with a deflection part (40, 110) arranged axially in front of the central opening (24, 112),
characterized,
that the area of constant angle extends from the spray edge (32, 132) to or below the deflecting part (40, 110). Rotary atomizer according to claim 10,
characterized,
that the inner surface (42) of the deflection part (40) facing away from the workpiece runs essentially parallel to the overflow surface (28, 30) opposite it. Rotary atomizer according to claim 10 or 11,
characterized,
that the gap-shaped space between the inner surface (42) of the deflecting part (40) facing away from the workpiece and the overflow surface (28, 30) is only interrupted by axial pin elements (56) with which the deflecting part (40) is releasably attached to the bell cup (22) is. Rotary atomizer according to one of claims 10 to 12,
characterized,
that the diameter of the circular circumference of the deflecting part (40) is less than 40% of the diameter of the spray edge (32). Rotary atomizer according to one of claims 6 to 13,
characterized,
that the diameter of the spray edge (32) is about 63 to 75 mm. Rotary atomizer according to one of claims 6 to 14,
characterized,
that the overflow surface (30, 126) forms a sharp-edged spraying edge (32) with the lateral outer surface (35) of the bell cup (22) or a bevel or transition surface leading to the lateral outer surface. Rotary atomizer according to one of claims 6 to 15,
characterized,
that the generally conical outer surface (35) of the bell cup (22) with the conical overflow surface (30) forms an acute angle of less than 45 ° and the bell cup (22) contains a cavity (38) between these surfaces. Coating system for the serial coating of workpieces such as motor vehicle bodies with paint material containing effect particles using electrostatic rotary atomizers (20) with a rotating bell cup (22, 100), on the front side of which the paint material flows over an overflow surface (30, 126) to a spray edge ( 32, 132) is directed,
with two groups of a plurality of rotary atomizers (20) arranged one behind the other in a coating zone (150) in the conveying direction of the workpieces (152) and mounted on coating machines (156-164) for double coating of different areas of the workpieces (152),
wherein the atomizers (20) of one group, to which the paint material containing the effect pigment particles can be supplied, are equipped with bell cups (22, 100), the overflow surface (130, 126) of which in the area adjacent to the spraying edge (32, 132) with the axis of rotation forms an angle which remains essentially constant in the direction of the spray edge.

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