EP1923138A1 - Method and atomiser for serial coating of workpieces - Google Patents

Abstract

The method involves controlling the spray jet of the sprayer of the spray cones of the sprayed coating material by limiting adjustable gas flow that is encircled circularly. Two independently adjustable gas flows are generated that emerge in different radial distances from the spraying cone axis and are set as a function of the workpiece areas that are to be coated. An independent claim is also included for sprayer for serial coating.

Description

The invention relates to a method for coating a workpiece and an atomizer for the series coating of workpieces with outlet openings for a gas flow confining the spray cone according to the preamble of the independent claims. In particular, it is the control of the shaping air of electrostatic rotary atomizers, as used for the serial coating of workpieces such as e.g. Vehicle bodies are common. But it can also be other types of atomizers. The invention is suitable for any coating material including wet paint and powder paint.

In conventional rotary atomizers ( DE 4306800 ), which atomize the coating material by the action of a bell rotating at more than 40,000 rpm, is known to be directed from the atomizer to the conical bell outer face directing air, which not only causes the paint particles radially sprayed on the bell-plate rupture edge in addition to the electrostatic forces gives an impulse towards the workpiece, but serves for spray jet forming and partly also for assisting in atomizing. The shaping air exits from a ring of bores in the end face of a shaping air ring arranged at the front end of the atomizer housing. The number, diameter, shape and direction of the holes may be different for optimizing air velocity, air flow and spray jet width. The respective desired Lenkluftmenge, which also results in the spray jet width is specified as a parameter of the coating process and controlled in a closed loop.

Instead of holes and annular gap-shaped Auslassöffnungsanordnungen can be provided for the shaping air. At one of the EP 0092043 Known rotary atomizer, an outer annular gap is provided in addition to a radially inner annular gap for the actual steering air, which is fed by the same source of compressed air as the inner annular gap. The gap width of one or both annular gaps is adjustable. The supplied by the additional annular gap outer air jacket has the task to compensate for the resulting from the color cloud in cooperation with the inner air jacket edge turbulence and due to the color particles breaking out into the cloud.

Rotary atomisers are also known in which, in addition to radially inner air openings, radially outer auxiliary air outlet openings are provided to prevent backward movement of the paint particles into the atomizer.

In general, there is the problem with atomizers that different width spraying cones are required for different workpiece areas. Known high-speed Rotationszerstäubungssysteme, for example, for the painting of vehicle bodies are preferably designed so that used for areas of surface coating bell cup with a larger diameter and spray jet widths (defined as "SB 50%", ie as width at 50% of the maximum layer thickness of the single profile) of approx 300 to 550 mm. For the detail and interior painting as well as for attachments and small parts such as mirrors, strips and bumpers, however, smaller bell plates and jet settings of 180 - 300 mm are more expedient. In the case of smaller or narrower spray patterns, the coating application efficiency defined as the ratio between the sprayed material and the precipitating material is higher than with wider spray patterns, as a result of which considerable paint and cost savings are achieved.

From the EP 1114677 are interchangeable bells known nebulizers, which differ in diameter, spray direction and Lenkluftmenge and should be selected depending on the shape of the object to be coated and the color used, etc., for example, large diameter for outer surfaces and small diameter for interior surfaces of vehicle bodies.

In practice, the interior surfaces of vehicle bodies such as e.g. Door entry areas, door rabbets, trunk, engine compartment and lid or hood inner sides, etc. so far, however, not coated with rotary atomizers, but usually with spray guns that atomize the paint not by rotation, but with compressed air. These spray guns produce an elongated, relatively sharply focused spray pattern, which is better for coating the narrower surfaces indoors than the conventional large-area circular spray patterns of the rotary atomizers. Especially in the interior painting with powder, these spray guns but can cause coating defects by Pulveransinterungen (so-called spit), which must be reworked consuming. Apart from the quality of the coating, the application efficiency of the spray guns is also worse than with rotary atomizers.

If in the overall painting of a workpiece for high order efficiency and uniform overall coating both wide and narrow spray jet settings are necessary and the coating operation should not be interrupted by a Sprühkopfwechsel, you have the lack of the possibility to set the spray sufficiently small, compromises between bell plate size with appropriate Lenkluftzuführung and Beam width regarding efficiency, paint consumption and color. Reducing the speed will allow you to achieve a better constriction of the spray jet, but will result in lower atomization fineness and degradation the coating quality accepted. Since it has hitherto not been possible to use the shaping air of a given atomizer to set the spray jet in both the width ranges mentioned above for optimum operation, considerable disadvantages arise in practice, such as insufficient or impossible interior or detail painting, increased Overspray (the proportion of paint sprayed past the object), low application efficiency, increased paint consumption and unsatisfactory coating quality.

The invention has for its object to avoid the disadvantages and to provide a method or a nebulizer, which allows the adjustment of the spray jet width without mechanical control of Auslassöffnungsanordnung in a much wider range than previously and yet optimal coating operation with good order efficiency and good Lackierqualität guarantee.

This object is solved by the features of the claims.

In a first embodiment of the invention, this is also possible without changing the spray head and without mechanical change of Auslassöffnungsanordnung. In a second embodiment, however, it may be appropriate, depending on the areas to be coated to change the atomizer bell and / or the Auslassöffnungsanordnung for the shaping air flows.

In the first exemplary embodiment, the at least two shaping air flows (or other gas flows having the same purpose) which are regulated in the closed loop are normally not generated simultaneously, but are optionally used as a function of the workpieces or workpiece areas to be coated. It is also the simultaneous one Combined use of both separately from the other separately regulated air currents possible.

The invention enables the painting of complex workpiece geometries and especially of complete bodies including interior, exterior and detail painting with the same rotary atomizer with maximum achievable paint application efficiency by specifically set spray jet widths throughout the required range. By means of two separately controlled steering joints, the spray jet widths can each be optimally adapted to the object to be coated.

Due to the optimally adapted spray jet, overall less overspray is produced than previously, resulting in higher application efficiency and lower paint consumption. This optimization also improves the quality of the painting.

Fig. 1

einen Rotationszerstäuber mit einem erfindungsgemäßen Lenkluftring;

Fig. 2a

einen Schnitt durch den Lenkluftring des Zerstäubers nach Fig. 1;

Fig. 2b

eine Draufsicht auf den in Fig. 2a von links gesehenen Lenkluftring;

Fig. 3

einen Rotationszerstäuber für Pulverlack; und

Fig. 4

eine schematische Frontansicht des Zerstäubers nach Fig. 3.

At the embodiment shown in the drawing, the invention is explained in detail. Show it:

Fig. 1

a rotary atomizer with a shaping air ring according to the invention;

Fig. 2a

a section through the shaping air ring of the atomizer after Fig. 1 ;

Fig. 2b

a top view of the in Fig. 2a from the left seen

Fig. 3

a rotary atomizer for powder coating; and

Fig. 4

a schematic front view of the atomizer after Fig. 3 ,

Apart from the steering air control of the spray steel described here, the in Fig. 1 illustrated electrostatic high-speed rotary atomizer correspond to the prior art, for example, according to the already mentioned DE 4306800 , In the on In the known manner sits on the bell cup 1 facing the front end of the atomizer 2 coaxially with the Zerstäuberachse 3 a shaping air ring 4. In the radially extending end face 5 of the shaping air ring 4, which faces the bell cup 1 and thus the spray cone formed by the sprayed coating material, open the bores 12, 13 described below for the leaving air for adjusting the spray jet width. Due to the uninterrupted continuous outer shape of the entire Zerstäuberumfangs Luftverwirbelungen be avoided around the atomizer and undesirable influence of Absprühvorgangs on the bell cup 1 and contamination of the atomizer housing ,

The end face 5 of the shaping air ring 4 can be located axially behind the bell cup 1 as in the illustrated embodiment, wherein it can extend as shown radially inwardly to close to the hollow shaft of the bell cup driving air turbine. The shaping air ring could also be inserted completely into the open front end of the atomizer housing. In other embodiments, however, the shaping air ring may also extend with its outlet opening arrangement axially further forward beyond the bell cup.

Fig. 2a and Fig. 2b show the directing ring 4 for themselves. In its end face 5 open onto two to the Zerstäuberachse 3 ( Fig. 1 ) and thus to the coinciding with them Sprühkegelachse concentric pitch circles 10 and 11 with different diameters each of wreaths distributed with uniform angular intervals Lenkluftbohrungen 12 and 13 respectively.

In the example shown, the bores 12 and 13 each open parallel to the axis in the end face, but are also other arrangements possible. The radially inner bores 13 are fed by an annular channel 14 within the shaping air ring 4, which is connected to a (not shown) compressed air line of the atomizer, while the outer bores 12 of the shaping air ring 4 from the end face 5 from first axially and then as shown with a rear part 16 extend approximately parallel to the peripheral surface 7 radially outwardly to an annular channel 17 which is formed with built-in shaping ring between the back and the adjacent parts of the atomizer and is fed by another compressed air line of the atomizer.

Instead of the two rings of holes 12 and 13 could also annular gap-like Auslassöffnungsanordnungen be provided in a shaping air ring or possibly also in separate components of the atomizer.

The two compressed air lines mentioned can be connected, for example, each with a compressed air connection of the atomizer for external lines, which can each lead to its own air control system. For example, If the effort for two separate air regulator is undesirable, the compressed air lines can also be connected via a switching valve controlled as a function of the workpiece area to be coated in each case to a bore 12 and 13 common air control system. The switching valve need not be located outside of the atomizer, but may also be installed in the atomizer, for example in the valve unit 18, so that then only a single external steering air connection is required. The shaping air could also be regulated within the atomizer.

In the coating of workpieces such as vehicle bodies, the first controlled shaping air is preferably obtained from the radially inner bores 13 for setting wider spray jets (for example for SB 50% from 250 to 300 mm) for exterior painting used, while with the separated separately from the first shaping air second shaping air from the holes 12 on the larger pitch circle 10 narrower spray jets (for example SB 50% from 50 to 300 mm) are set for detail and interior painting, it may be appropriate when the two areas overlap (as in the example considered). Thus, with one and the same atomizer, the spray jet width can be adjusted in the entire area required for exterior, interior and detail painting (in the example under consideration 50 to 550 mm) without interrupting the coating operation and without accepting significant disadvantages. The two steering joints can be used and controlled separately, ie while the atomizer works with one lenkluft, the other steering air can be switched off. The emerging behind the bell cup 1 first steering air from the inner bores 13 is relatively far back on the conically tapering rear peripheral surface of the bell cup 1, wherein the bell cup an air cushion generated and thereby advantageously a uniform air distribution is effected during atomization. On the other hand, the second shaping air from the outer bores 12 can be directed so that it impinges on the paint material to be sputtered or already partially atomized by the rotation at a small radial distance (for example of the order of 1 mm) outside the spray edge of the bell cup a stronger constriction of the spray is caused than by the shaping air from the inner bores so that maximum application efficiency is achieved and difficult to reach or small workpiece areas can be coated well.

As another embodiment of the invention is in Fig. 3 the front part of a mounted for example on the wrist of a robot electrostatic rotary atomizer for powder coating or other powder coating material shown in longitudinal section. Like the electrostatic wet sprayer to Fig. 1 The atomizer contains a powered by compressed air drive turbine 30 for example, in the front end of the hollow shaft 31 fixed rotating atomizer 33. Through the hollow shaft 31 extends coaxially serving as a powder channel of the atomizer cylindrical tube 32 into the hub portion 35 of the bell 33 into where he presents as shown axially outside of the atomizer 36 opens. The powder tube 32 is connected in the atomizer to a powder hose (not shown) coming from an external air and powder supply. The atomizer 33 is in a known manner ( EP 1238710 ; US 5353995 ) substantially of an outer part 38 attached to the hub part 35, which has an inner conical surface 40 of the form shown, and an inner part 42 seated in the space in front of the surface 40, which faces one of the surface 40 to form a gap channel 44 Inner surface 46 and is rigidly connected to the outer part 38. The gap channel 44 is thus bounded by the two conical surfaces 40 and 46. The radially outer peripheral surface 49 of the outer and axially rear, ie the main part of the atomizer facing bell member 38 is shown extending (and in contrast to the mentioned known powder bells) only slightly conically widening forward so that they with the axis of rotation at an acute angle of preferably less than 20 °, in the illustrated example about 5 °. On its way through the tube 32 and through the gap channel 44, the coating powder can be charged to high voltage in the usual way.

As in the embodiment according to Fig. 1 Radially outside the circumferential surface 49 of the bell 33, a controllable shaping air flow 50 (or other gas flow) which surrounds or surrounds the spray cone in an annular manner acts, which can be directed approximately parallel to the axis. Radially outside the flow 50 exits a further air or gas flow 51, the exit direction also axially, but as shown against the Axial direction is inclined inwardly at an acute angle, so that it intersects the direction of the inner flow 50. The directions indicated by the illustrated arrows may be such that they do not intersect the outer surface of the bell 33, but pass close to the bell. Suitably, the radially outer gas flow 51 may be directed approximately to the powder exit point of the atomizer 33.

The radially outer flow 51 is not circular in shape here as the flow 50, but consists of separate, for example, flat upper and lower parts that flatten (ovalize) when hitting the inner flow 50 and the spray cone in an oval cross-sectional shape. The provided for this purpose outlet openings are in the schematic representation of Fig. 4 recognizable. While the annular shaping air flow 50 emerges from the ring concentrically surrounding the axis of rotation of a plurality of openings 52, two straight slots 53 and 53 'can be provided for the two planar parts of the flow 51, which are tangent to one another to the circular ring formed by the openings 52 on opposite sides of the axis of rotation are parallel. The slots 53, 53 'are so symmetrical to the axis of rotation that the perpendicular to the longitudinal direction of its mouth opening connecting its center line intersects the axis of rotation. The slots 53, 53 'are fed by compressed air lines 54 on their atomizer side. Instead of the two slots and parallel rows of each sufficiently large openings could be effective.

The shaping air openings 52 and / or the ovalization slots 53, 53 'may be located in an annular body 55 which is removably and quickly and easily fastened to another atomizing air ring with another outlet opening arrangement interchangeable with the atomizer. With the shaping air ring, the atomizing bell 33 can also be adapted to the workpiece area to be coated be replaced with another bell. The remaining part of the rotary atomizer can remain unchanged. The bells and Lenkluftringe can be changed automatically, for example by controlling the robot.

A significant advantage of the rotary atomizer described here is that the same base atomizer can be used for example in the program-controlled body painting both for the outer surfaces and for the automatic interior painting. For the interior painting, a round bar with a smaller diameter is expediently produced than in the exterior finish, which is ovalized by the air flow flowing planar from the slots 53, 53 'at the powder exit point of the atomizer bell 33.

By using a rotary atomizer for all exterior and interior areas of the workpiece, not only the automatically controlled coating sequence can be simplified, but also the quality of the coating can be improved compared to the previously customary spray guns and the coating efficiency can be increased. In addition, it is easier than previously possible to perform its work with another robot in case of failure of a robot.

In other cases, but also in the embodiment 3 and 4 the rotary atomizer coat all or at least different workpiece surfaces with the same bell and the same outlet opening arrangement, wherein only the gas flows 50, 51 are changed by means of the control circuits for adaptation to the respective workpiece areas.

Claims (20)

Method of coating a workpiece with a nebulizer,
wherein, for controlling the spray jet shape of the sprayer, the spray cone of the sprayed coating material is bounded by a controllable gas flow which surrounds it annularly and which exits the atomizer concentrically with the spray cone axis (3),
and wherein different areas of the workpiece are coated with different spray jet shapes,
in particular for the standard painting of vehicle bodies with a painting robot,
characterized in that at least two independently controllable gas flows are generated which emerge at different radial distances from the spray cone axis (3) and are used as a function of the workpiece areas to be coated. A method according to claim 1, characterized in that are coated with the one spray jet shape outer areas of a vehicle body or the workpiece and using the same atomizer or essential parts of the same atomizer with the other spray jet interior areas of this body or the workpiece. A method according to claim 1 or 2, characterized in that a high-rotation atomizer is used. A method according to claim 3, characterized in that a rotary atomizer is used, whose on the annular gas flow (50) directed radially outer gas flow (51) brings the spray cone in the coating of the inner regions in an oval or flattened shape. Method according to one of the preceding claims, characterized in that each gas flow is regulated in its own closed loop. Method according to one of the preceding claims, characterized in that a controlled gas flow is supplied to the radially outer or the radially inner outlet openings (12,13) via a switching valve controlled in dependence on the workpiece areas to be coated. Method according to one of the preceding claims, characterized in that only one gas flow is used for coating with a wider spray cone and only the other gas flow is used for coating with a narrow spray cone. A method according to claim 7, characterized in that the two areas in which the spray cone width is adjustable in each case overlap each other. Method according to one of the preceding claims, characterized in that the workpiece is coated with powdered paint. Atomizer for the series coating of workpieces with at least one first annular arrangement, concentric with its spray cone axis (3), of the spray cone-facing outlet openings (13, 52) for a gas flow delimiting the spray cone,
with at least one further arrangement of the spray cone facing outlet openings (12, 53), the other, in particular greater radial distance from the spray cone axis than the first arrangement,
and with a to the outlet openings (12,13,52,53) leading gas line arrangement which is connected to at least one control loop for the gas flow or connectable, characterized in that the radially inner and the radially outer gas flow are separately controllable. An atomiser according to claim 10, characterized in that the radially inner outlet opening arrangement (13) and the radially outer outlet opening arrangement (12) are each connected to a separate closed loop or can be connected. An atomiser according to claim 10, characterized in that the line arrangement leading to the outlet opening arrangements (12, 13) are connected or connectable to a common control circuit via a change-over valve. An atomiser according to claim 12, characterized in that the switching valve is located in the atomizer. An atomiser according to any one of claims 10 to 13, characterized in that each of the outlet port assemblies (12, 13) is connected to a gas port of the atomizer for each external gas supply conduit. Atomiser according to one of claims 10 to 14, characterized in that the two outlet opening arrangements (12, 13) in the spray cone facing end surface (5) of an annular body (4) on the spray cone facing front end of the spray head (1) of the atomizer retaining housing (2) are located. An atomiser according to claim 15, characterized in that the peripheral surface (7) of the annular body (4) is continuously aligned with the adjacent peripheral surface (8) of the housing (2). An atomiser according to any one of claims 10 to 16 or to the preamble of claim 10, characterized in that two radially outer outlet port arrangements (53, 53 ') are provided which face each other at least approximately parallel on opposite sides of the spray cone axis and at least approximately tangentially the annular Auslaßöffnungsanordnung (52) extend. An atomiser according to claim 17, characterized in that the radially outer Auslassöffnungsanordnungen from elongated slots (53, 53 ') consist. An atomiser according to any one of claims 10 to 18, characterized in that the outlet openings (52, 53) are located in a body (55) detachably and replaceably mounted on the atomiser, and that for the atomizer at least two interchangeable bodies (55) with different Outlet opening arrangements are provided. An atomiser according to any one of claims 10 to 19, characterized in that the discharge direction of the radially outer gas flow (51) extends close to the spray edge (47) of the atomizer (33) without cutting the outer surface of the atomizer (33).

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