EP2480340B1 - Method for controlling the function of a rotary atomizer, and corresponding coating installation - Google Patents

Description

The invention relates to a method for the functional control of a particular electrostatic series coating of workpieces such as vehicle bodies used in particular, e.g. mounted on a painting robot rotary atomizer and a corresponding coating system according to the preamble of the independent claims.

High-rotation atomizers of the type considered here essentially consist of a rotating bell cup as a spray-off body and its drive. As drive usually find air-bearing air turbines use. Depending on the paint material and throughputs, the atomizers with speeds between 5000 and 100000 / min. operated. The tangentially thrown off from the bell-shaped edge and atomized paint by a shaping air flow, the coaxial with the Zerstäuberachse from ring behind the bell cup arranged bore or annular gap arrangements emerges ( EP 1 331 037 B1 . WO 2008/061584 A1 , etc.), as well as deflected by electrostatic field forces on the grounded substrate to be coated and formed into a spray. With Lenkluft also an additional secondary paint atomization on the bell plate edge is effected. The directing air quantity is regulated as a function of target values.

In the industrial paint coating carried out with such atomizers, the quality criteria which are generally the most important are the layer thickness and the uniformity of the applied lacquer layer. The quality requirements are still rising with the desire for ever-increasing productivity and higher area performance without sacrificing quality and the availability of improved paint materials. The required layer uniformity has hitherto been achieved inter alia because the paint is applied in several overlapping layers. In future processes with less effort or increase in productivity due to higher coating speeds, correspondingly higher demands are placed on the quality of the layers.

The resulting layer thickness depends on the high rotation sputtering significantly from the area distribution of the paint due to the width of the spray. Since the area of the paint application decreases with a constant quantity of paint in the square ratio with reduction of the spray jet width, the layer thickness increases in inverse ratio, so that variations of the layer thickness by several 100% are possible and partly also used. In turn, the spray jet width which determines the layer formation is controlled by the direction and speed of the already mentioned shaping air flow. Incorrect air flow results in undesirable deviations from the intended layer formation. While too thick a spray layer on too small an area results in too thick a layer, the reverse case results in too low Sprühstrahleinschnürung. Furthermore, the cross-sectional shape of the applied layer is distorted by undesired shaping air flows.

In the vast majority of conventional rotary atomizer in practice, the point of impact of the paint particles on the workpiece is not on the extended axis of rotation of the bell cup, so concentric to the central axis of the air nozzles. Furthermore, the spray jet width can vary regardless of the location of the air nozzle axes and bell-shaped, because of a plurality of individual nozzles At high speed flowing steering air generated at their outer and inner surfaces a considerable friction against the static ambient air and thus moves parts of the ambient air in a direction parallel to the shaping air. While the resulting air deficits on the outer surface can be easily compensated by the influx of ambient air, forming a negative pressure inside the steering cone, which leads to deformation, ie bundling of the steering cone. This deformation then determines the spray jet width.

The spray jet width is set during the coating process by the regulated shaping air flow in accordance with the respective specifications regarding workpiece geometry and process conditions. This desired controllability of the spray jet width depends essentially on which negative pressure can be achieved within the flow cone. The higher flow velocities required for this purpose also bring about a better deflection of the paint particle stream at the bell-shaped edge. The Lenkluft internal pressure is thus a highly functional determinant of the transport and the local deposition of the paint particle stream. Normally, the internal pressure represents the directing air flow, the flow velocity and the flow geometry.

In addition, the steering internal pressure and the steering air / internal pressure characteristic, ie the course of the internal pressure of the shaping air flow as a function of the measured per unit time Lenkluftmenge, also an identification criterion for perfect condition of the shaping air nozzle assembly of the atomizer, in particular the opening cross-section, the geometric uniformity and proper mounting of the holes or slots of the shaping ring, in addition to manufacturing tolerances, damage or assembly errors such as swapping may also be affected by contamination of two existing different Lenkluftkreisen or missing or defective seals in the atomizer. The effect on the steering internal pressure, which is reduced by all such errors, is based significantly on the existing possibilities of balancing the high pressure difference between the external and internal pressure. Unequal discharge velocities and air volumes from individual shaping air nozzles mean different kinetic energy. The steering air is therefore deflected differently by the acting pressure forces, ie there are weaknesses in the steering air cone, which represent potential passages for pressure equalization. Even slight geometric irregularities of the nozzle bores also lead to weak spots in the guide cone as the distance from the bore increases. Furthermore, irregularities in the flow geometry may result in air flow and corresponding pressure equalization with effects on the spray jet width, depending on the direction of movement and velocity of the flow.

In part, the pressure difference is also compensated by air flow from the overpressure zone in front of the workpiece surface, whereby the spray cone can be wider. With reduction of the flow resistance of the workpiece surface of the overpressure and thus the mentioned air flow are reduced, so that the corresponding decreasing internal pressure leads to a "folding" of the spray and thus to much smaller beam diameters. In individual cases, a halving of the beam diameter and thus a quadrupling of the local paint deposition can be observed. Although this effect may be useful in certain cases, it is undesirable if it is incalculable.

The above effects can lead to undesirable reproducibility errors and quality defects in the commissioning of the coating system and in the production process. All previously available to avoid such deficiencies diagnostic options with area flow measuring systems are extremely complex and / or require intervention in the atomizer such as separation of the air supply for installation of a flowmeter or can be performed only by controlling individual components and individual functions. Furthermore, by subsequent errors in production, especially during maintenance and cleaning work for the function crucial changes of the atomizer are not excluded, for example, by contamination of the Lenkluftbohrungen, incorrect component assembly, etc. If wear or damage of components are not recognized for lack of clear diagnosis, the coating operation continued with quality losses. Also, a check of the assembled atomizer when commissioning the coating system by Lackierversuche is time and technically complex and bound to a number of conditions (often missing reference spray images for each paint material, sheets must be baked in a dryer and measured as possible machine, etc.). Furthermore, painted spray patterns such as brush profiles as a test method for quality control are dependent not only on the pure atomizer function, but also on a variety of varying factors such as properties and temperature of the paint material and other boundary conditions. In addition, changes due to contamination, leaks, incorrect or faulty components, etc. are detected too late and often only through complaints of coating quality.

Out WO 02/41003 A2 It is already known to measure the pressure curve within the steering cone of a rotary atomizer to obtain information about the air velocity profile of the atomizer. For this purpose, either a sensor arrangement with a series of pressure sensors is moved by movement of the atomizer or the sensor arrangement across the air cone or instead arranged a two-dimensional sensor matrix stationary in the air cone of the likewise stationary atomizer.

US 2005/241367 A1 discloses a system for measuring the pressure in the spray pattern of high pressure impingement spray devices in the form of water or air, such as for the water irradiation of rolled steel sheets.

DE 10 2007 062 132 A1 describes a test method, for example, for checking a rotary atomizer with an external test device, and according to EP 1 394 757 A2 The pressure is measured in a leading from the outside in a rotary atomizer Lenkluftleitung.

The invention aims to provide a method or a coating system with which simple, objective and reliable manner with little effort an almost holistic function control of rotary atomizers both before and during the coating operation (online) is possible.

This object is solved by the features of the claims.

The invention is based on the finding that a high and stable pressure difference between the pressure areas inside and outside the shaping air flow is a clear characteristic of a fault-free overall system of the rotary atomizer. The same applies to a steep long Lenkluft / internal pressure characteristic. It may also be sufficient to measure only the internal pressure of the shaping air flow or the pressure in the negative pressure area adjoining outside the shaping air flow, that is to say the pressure difference with respect to the known air pressure in the environment of the atomizer.

As already explained, the shaping air flow here means the gas flow generated in a manner known per se by the atomizer with an arrangement of shaping air openings or nozzles of the atomizer, wherein instead of air theoretically another gas could also be used. It is therefore the flow (more or less cone-shaped in the typical case) outside the atomizer at the front end, with which the coating material sprayed off from the rotating bell cup of the atomizer is applied.

The respective pressure can be measured with the help of possibly only one, but in any case less pressure measuring devices and correspondingly little effort, preferably with pressure sensors that can be permanently installed inside and / or outside of the atomizer or movable outside the atomizer. In the case of external sensors, the rotary atomizer or the pressure sensor can be brought into a predetermined defined measuring position, wherein the rotary atomizer is positioned for example by the painting robot to which it is mounted, while a movable sensor, for example manually or by a particular automatically controlled handling device or auxiliary robot can be positioned.

To measure a Lenkluftströmung with defined amounts of air per unit time or, with several simultaneously generated different Lenklüften generated with defined air flow combinations. The resulting pressure values in the outer and / or inner negative pressure area are compared with associated stored desired values for perfect condition and evaluated accordingly. In addition, several different air volumes can be set to control.

A particular advantage of the vacuum measurement according to the invention is that it can characterize the essential atomizer functions such as Lenkluftmenge, geometry of Lenkluftdüsen and real error situation without simultaneous Lackzerstäubung, so without being affected by the properties of the coating material and without corresponding disadvantages such as contamination, cleaning, disposal, etc. It is also important that the measurement can be done manually or preferably fully automatically without intervention in the atomizer and in the supply line system. Also, the measurement information is always available without delay, so immediately initiated appropriate measures in the event of a fault and consequently, for example, for manufacturing control during commissioning of the coating system and especially in the ongoing production process (online) quality defects coated Workpieces and corresponding costs can be avoided by malfunction. The quality of production is therefore supported preventively, and indeed much more objectively than in previous practice, in particular independent of subjective factors such as qualification and availability of skilled personnel. The measured values are also independent of a special test setup and test location and thus objectively and with each other comparable.

In addition, there are other advantages such as the possibility of rapid fault assignment by varying test conditions such as creating characteristics, switching the two existing steering joints, etc. Furthermore, immediately defective components of the atomizer can be detected and replaced.

Fig. 1

das Strömungsfeld an der Stirnseite eines Rotationszerstäubers;

Fig. 2

mögliche Orte für die Positionierung von Drucksensoren in dem Rotationszerstäuber und außerhalb in den Unterdruckgebieten seiner Lenkluftströmung;

Fig. 3

Beispiele für die Positionierung von Drucksensoren außerhalb des Rotationszerstäubers.

On an embodiment shown in the drawing, the invention will be explained in more detail. Show it:

Fig. 1

the flow field at the front of a rotary atomizer;

Fig. 2

possible locations for the positioning of pressure sensors in the rotary atomizer and outside in the negative pressure areas of its Lenkluftströmung;

Fig. 3

Examples of the positioning of pressure sensors outside the rotary atomizer.

In Fig. 1 schematically shows the coating of the workpiece facing frontal part of a rotary atomizer 10, consisting essentially of the bell cup 11 and a guide air ring not shown in detail, whose concentric to the axis of rotation arrangement of Lenkluftdüsen generates the shaping air flow 12 in a conventional manner. The illustrated shaping air cone corresponds to the shape of the tracks of the sprayed tangentially from the bell cup 11 paint particles, so the spray jet. The rotary atomizer 10 may be of any known type and, in particular, for the vehicle body painting type (cf., for example, the already mentioned WO 2008/061584 A1 ) and therefore needs no further description.

As has already been explained, forms an outer air friction region 13 and on its inner surface an inner air friction region 14 due to the friction between the fast-flowing shaping air and the previously stationary ambient air on the outer surface of the Lenkluftströmung 12, thereby outside the Lenkluftströmung in the Close to an outer negative pressure area 17 and within the Lenkluftströmung required for the desired bundling of the flow inner negative pressure area 18 are formed. Partial pressure equalization is effected by an outer compensating flow indicated at 15 and an inner compensating flow 16.

In principle, arbitrary measuring devices can be used per se for measuring the pressure values in the vacuum regions 17 and / or 18 according to the invention. Some embodiments of suitable locations for positioning of pressure sensors are shown in FIG Fig. 2 shown. Accordingly, it may be appropriate to permanently install in the rotary atomizer 10 a pressure sensor 21 for measuring the external negative pressure and / or a pressure sensor 22 for measuring the internal negative pressure of the shaping air flow 12. Here, the sensors with the negative pressure areas 17 and 18 through corresponding pressure measuring channels 21 'and 22' are connected, of which the channel 21 'as shown in the vicinity of the bell cup in the Peripheral surface of the atomizer housing can open, while the channel 22 ', for example, open centrally in the workpiece facing end surface of the bell cup and there can match in particular with the Lackaustrittsweg through which preferably no paint flows in the pressure measurement. In addition to the pressure sensors 21 and 22, or instead of the rotary atomizer 10 external pressure sensors 23 and 24 can be arranged directly in the negative pressure areas 17 and 18 for measuring the respective pressure there.

The pressure values measured by the sensors 21 - 24 can be supplied in the form of suitable signals to a measuring system 26 shown schematically, evaluated and compared with predetermined reference values for error-free atomizer functions. For problem-free transmission from the high-voltage region of the electrostatic rotary atomizer 10, in particular the measured values of the pressure sensors 21 and 22 can be transmitted to the measuring system 26 as pneumatic signals.

Various options for the arrangement of external pressure sensors 23 or 24 ( Fig. 2 ) in the mentioned negative pressure areas are exemplified in Fig. 3 shown. As a first example, the representation 3A shows a pressure sensor 24a, which can be installed in particular for measuring the external negative pressure with a spacer 25a fixed to the wall 30 of the spray booth or other stationary and defined in terms of its position component of the coating system considered here. For measuring the pressure value, the rotary atomizer can be automatically brought by its painting robot into the correct measuring position relative to the defined position of the pressure sensor 24a.

The illustration 3B shows an external pressure sensor 24b, which is also in particular for measuring the external negative pressure firmly and expediently can be installed with a spacer 25b on a part 31 of the painting robot itself, ie in particular on a part of the robot with the forearm and wrist reachable part defined position.

On the other hand, the representation 3C shows a manually movable and preferably transportable pressure probe 24c, which can be introduced into the shaping air flow, for example for measuring the pressure in the inner negative pressure region of the shaping air flow. As already mentioned, however, a preferably automatically controlled handling device could also be used for this purpose.

It is expedient to protect the pressure probes from the direct dynamic pressure effect of the high flow velocities of the shaping air. A suitable possibility for this purpose is, for example, the sheathing of the pressure sensors with air-permeable, but flow-breaking sintered bodies made of metal or plastic. Incidentally, known and customary pressure probes can be used.

A typical application example of the invention is a regular contamination control in the production process. Contamination with firmly dried paint mist can change the opening cross section of shaping air nozzles so that a weakening or change in direction of the air outlet takes place. The weakening of the desired shaping air flow causes a reduction of the negative pressure in the interior of the shaping air flow, whereby the bundling of the paint flow in the direction of the workpiece is weakened and thus the spray jet width is reduced. As a result, the distribution of the paint deposit on the workpiece widens with a correspondingly smaller layer thickness. In edge regions of the workpiece occur higher edge losses of paint material, because parts of the drop stream miss the surface. To diagnose such malfunctions, the atomizer at regular time intervals, for example, by the painting robot to a fixed pressure sensor such as 23 in Fig. 2 be introduced so that the internal pressure in the shaping air flow can be measured. Having previously measured and stored the proper atomizing function setpoints, it is possible to compare later with the current conditions to be tested, and thus to detect faults and initiate appropriate troubleshooting procedures, in the example considered for cleaning the shaping air nozzles.

Claims (9)

1. A method for function checking of a rotary atomizer (10) used for the series coating of workpieces, which has a rotating spray body (11), which is driven by a motor during coating operation, and generates a directing air flow (12), which during coating operation shapes the sprayed coating material to form a spray jet and deflects the same towards the workpiece to be coated,
   one or a plurality of pressure values being measured, which hereby arise during the generation of the directing air flow (12) in a region (18) within the directing air flow and/or in a region (17) outside of the directing air flow, located in the vicinity thereof,
   characterized in that resultant pressure values are measured

   - with one or a plurality of pressure sensor means (21, 22) installed in the interior of the rotary atomizer (10)

   - and/or with at least one pressure sensor means (24b) arranged outside of the rotary atomizer (10) on a part (31) of a painting robot (31) which carries and moves the rotary atomizer (10), or on a coating robot which carries and moves the rotary atomizer (10), or on another automatic coating machine which carries and moves the rotary atomizer (10), and in that the measured pressure value is compared with a predetermined reference value for a flawless atomizer function.
2. The method according to Claim 1, characterized in that the pressure difference between the pressure within the directing air flow (12) and the pressure in the region (17) outside of the directing air flow is determined.
3. The method according to Claim 1 or 2, characterized in that the pressure or the progression thereof is evaluated as a function of the speed and/or the air quantity of the directing air flow (12) measured per unit of time.
4. The method accordin0g to any one of the preceding claims, characterized in that the pressure value is measured without coating material being sprayed by the spray body in the process.
5. A coating installation for the series coating of workpieces with at least one rotary atomizer (10), which has a spray body (11), which can be rotated by a motor, and an annular arrangement of directing air openings for generating a directing air flow (12), which during coating operation shapes the sprayed coating material to form a spray jet and deflects the same in the direction of the workpiece to be coated,
   characterized in that one or a plurality of pressure sensor means (21 - 24, 24b) are installed

   - in the interior of the rotary atomizer (10)

   - and/or outside of the rotary atomizer (10) on a part (31) of a painting robot which carries and moves the rotary atomizer (10), or on a coating robot which carries and moves the rotary atomizer (10), or on a another automatic coating machine which carries and moves the rotary atomizer,

   for measuring one or more pressure values which during the generation of the directing air flow hereby arise in a region (18) within the directing air flow (12) and/or in a region (17) outside of the directing air flow, located in the vicinity thereof.
6. The coating installation according to Claim 5, characterized in that at least one pressure sensor means (24a) is fixed for pressure sensing outside of the rotary atomizer (10) on a wall (30) of a spray booth in which the workpieces are coated or at another fixed position within the spray booth.
7. The coating installation according to any one of Claims 5 or 6, characterized in that a movable pressure sensor (24c) is provided outside of the rotary atomizer (10), which can be brought into a defined position with respect to the rotary atomizer (10).
8. The coating installation according to Claim 7, characterized in that a sensor (24c) for pressure sensing is provided which is moved manually or by an in particular automatically controlled handling device.
9. A rotary atomizer of a coating installation for the series coating of workpieces comprising a spray body (11), which can be rotated by a motor, and an annular arrangement of directing air openings for generating a directing air flow (12) which during coating operation shapes the sprayed coating material to form a spray jet and deflects it in the direction of the workpiece to be coated, and further comprising one or more pressure sensor means (21, 22) installed in the interior of the atomizer for measuring one or more pressure values in a region (18) within the directing air flow (12) and/or in a region (17) located outside of the directing air flow (12) in the vicinity thereof, said one or more pressure sensing means (21, 22) being connected to said regions (17, 18) by means of corresponding pressure measurement channels (21', 22').

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