Patent Application
20190336990
The disclosure concerns a print head for the application of a coating agent to a component, in particular for the application of a paint to a vehicle body component.
Rotary atomizers are usually used as application devices for the series painting of vehicle body components, but these have the disadvantage of limited application efficiency, i.e. only part of the applied paint deposits on the components to be coated, while the rest of the applied paint has to be disposed of as so-called overspray.
A newer development line, on the other hand, provides for so-called print heads as application devices, as known for example from DE 10 2013 002 412 A1, U.S. Pat. No. 9,108,424 B2 and DE 10 2010 019 612 A1. In contrast to the known rotary atomizers, such print heads do not emit a spray of the paint to be applied, but rather a paint jet that is spatially narrowly confined and which is almost completely deposited on the component to be painted, so that virtually no overspray occurs.
In this case, numerous nozzles are usually arranged in a nozzle plate of the print head, whereby the individual nozzles can each be opened or closed by a movable valve element. The movable valve element is usually a valve needle with an elastomer insert as seal. Here the valve needle with the elastomer insert can be moved between a closed position and an opened position, whereby the elastomer insert seals the nozzle in the closed position of the valve needle, whereas the elastomer insert is lifted off the nozzle in the opened position and thereby releases the fluid flow (usually ink according to the state of the art) through the nozzle.
A disadvantage of this well-known type of sealing between the movable valve element (e.g. valve needle) and the nozzle is first of all the complex manufacturing process involved in manufacturing the elastomer insert.
Another disadvantage is that the valve needle with the elastomer insert can only be miniaturized within certain limits, so that the nozzle spacing between the adjacent nozzles cannot fall below a lower limit.
Furthermore, the manufacturing precision of the elastomer insert is limited, so that large fluctuations occur with regard to the required valve stroke.
The technical background of the disclosure can also be found in DE 36 34 747 A1, DE 10 2014 012 705 A1, DE 41 38 491 A1.
The term “print head” used in the context of the disclosure is to be understood in general and only serves to distinguish from atomizers (e.g. rotary atomizers, disc atomizers, airless atomizers, air-mix atomizers, ultrasonic atomizers) that emit a spray of the coating agents to be applied. In contrast, the print head according to the disclosure emits a spatially limited jet of coating agent. Such print heads are known from the state of the art and are described for example in DE 10 2013 092 412 A1, U.S. Pat. No. 9,108,424 B2 and DE 10 2010 019 612 A1.
It should also be mentioned that the print head according to the disclosure is preferably used for the application of a paint (e.g. base coat, clear coat, water paint, solvent-based paint). However, the print head according to the disclosure can alternatively be designed for the application of other coating agents, such as sealants, insulating materials, adhesives, primers, etc., to name just a few examples.
In accordance with the state of the art, the print head according to the disclosure has a nozzle plate which contains at least one nozzle for dispensing the coating agent. Preferably, this nozzle emits the aforementioned coating agent jet onto the component to be coated. There is, however, also the possibility that the nozzle is arranged inside the print head and only passes the coating agent on to the outer outlet nozzle, which then applies the coating agent jet to the component.
In addition, in accordance with the state of the art, the print head according to the disclosure has a valve element that controls the release of coating agent through the nozzle. This valve element is movable relative to the nozzle plate, with the valve element closing the nozzle in a closed position, whereas the movable valve element releases the nozzle in an opened position.
Preferably, the movement of the valve element between the closed position and the opened position is a linear movement (displacement movement), however, within the scope of the disclosure there is basically also the possibility of other movements of the valve element between the opened position and the closed position. A rotary movement, a swivel movement or a combined rotary and linear movement of the valve element are just a few examples.
Furthermore, the print head according to the disclosure includes a seal to seal the nozzle against the movable valve element in the closed position of the valve element.
However, in the case of the print head according to the disclosure, this seal is preferably not designed as an elastomer insert on the valve element, as this is associated with the problems described above.
For example, the seal can be arranged on the nozzle plate, i.e. not on the movable valve element, as is the case with the known elastomer inserts. Alternatively, it is also possible that the seal according to the disclosure is attached to the movable valve element, i.e. not to the nozzle plate. In addition, it is also possible to combine these two alternatives, whereby a seal is attached to both the movable valve element and the nozzle plate, in this case the nozzle, and the two seals then interact.
It should also be mentioned that the seal is preferably flat and, in the closed position, creates a flat contact between the moving valve element and the seal. For example, flat sealing plates or sealing layers can be applied to the inside of the nozzle plate for this purpose.
Furthermore, in an embodiment of the disclosure, there is the possibility that the shape of the movable valve element is complementary to the shape of the nozzle and projects into the nozzle in the closed position. For example, the nozzle can narrow conically in the direction of flow. The movable valve element should then also taper conically towards its free end, preferably with the same cone angle as the nozzle, so that the valve element and the nozzle then form a corresponding form fit, which improves the sealing effect. Alternatively, it is also possible, for example, for the nozzle to have a hemispherical inner contour, so that preferably the movable valve element also has a hemispherical outer contour.
It should also be mentioned that the seal can be applied to the inner flanks of the nozzle. If the inner contour of the nozzle is tapered, the seal will preferably cover the inner flanks of the nozzle.
In another embodiment of the disclosure, the print head has a flexible sealing diaphragm, whereby the flexible sealing diaphragm forms the movable valve element and closes the nozzle in its closed position and releases it in its opened position. This sealing diaphragm is deflected by a valve actuator between the closed position and the opened position. On the one hand, the flexible sealing diaphragm thus seals the nozzle in the closed position. On the other hand, the sealing diaphragm also separates the coating agent supply from the valve actuator so that the valve actuator does not come into contact with the coating agent. This is particularly advantageous when coating agents of different colours are to be applied one after the other and the print head must therefore be rinsed with a flushing agent. The flexible sealing diaphragm prevents coating deposits in the valve actuator and, due to its smooth surface, also allows good flushing properties.
In addition, the sealing diaphragm can also be elastic and then performs the function of a return spring, which pushes the sealing diaphragm into its rest position, in particular into the closed position. The valve actuator then preferably deflects the sealing diaphragm into the opened position, whereas the sealing diaphragm is pressed into the closed position without being actuated by the valve actuator due to its spring elasticity. However, within the scope of the disclosure, there is also the possibility that the sealing diaphragm may be pressed into the opened position due to its spring elasticity, whereby the valve actuator then presses the sealing diaphragm into the closed position.
To move the movable valve drive, the print head preferably has a valve drive. In an example of this disclosure, the valve drive comprises a flexible drive diaphragm which is mechanically coupled to the movable valve element and can be supplied with a drive fluid (e.g. hydraulic fluid, compressed air) in order to deflect the drive diaphragm and thereby move the valve element.
There is also the possibility that the actuator membrane can be acted upon by the coating agent itself. Alternatively, the drive fluid can consist of a part of the paint, e.g. binder, solvent, Mesamol™ or similar. If the diaphragm breaks, this would not be a chemical reaction or incompatibility.
This variant of the valve actuator is particularly advantageous in combination with the flexible sealing diaphragm mentioned above, as there are then two seals between the nozzle and the actuator fluid, one being the seal through the actuator diaphragm and the other the seal through the flexible sealing diaphragm. In this way, leakage of the actuator fluid (e.g. hydraulic fluid) through the nozzle can be prevented with double safety.
Within the scope of the disclosure, however, other designs of the valve drive are also possible. For example, the valve drive can be designed as a solenoid actuator with a coil and a movable armature in the coil, whereby the armature is mechanically coupled to the movable valve element and is shifted between the opened position and the closed position depending on the current supplied to the coil.
In an embodiment of the disclosure, the valve element (e.g. tappet) is fixed in the print head, while the nozzle plate is elastically flexible and can be bent by the valve actuator. In the closed position, the valve drive then preferably exerts no force on the nozzle plate, so that the nozzle plate is flat and rests sealingly with the nozzle on the free end of the movable valve element (e.g. tappet). In the opened position, on the other hand, the valve drive bends the nozzle plate so that the nozzle is lifted from the free end of the valve element with a certain stroke, so that coating agent can escape from the nozzle. The stroke of the nozzle plate in the area of the nozzle between the closed position and the opened position is preferably about 30 μm.
It was already mentioned briefly at the beginning that the seal can be flat. For example, the seal can have a sealant layer which, for example, is vulcanised onto the nozzle plate, evaporated, applied by a layer-forming process or printed on.
Alternatively, it is also possible for the seal to have a film which can, for example, be glued, laid on, bonded or laminated to the nozzle plate.
With regard to the choice of material within the scope of the disclosure, it should be mentioned that the movable element preferably consists at least partially of metal, plastic or silicon.
Furthermore, the print head according to the disclosure preferably has one of the following material combinations on the nozzle between the side of the valve element and the side of the nozzle:
For example, the moving valve element can be made of metal and combined with a plastic tappet.
In addition, the orifice may be made of silicon or contain a silicon orifice insert, while the movable valve element is at least partially made of steel, rubber or plastic (e.g. PTFE: polytetrafluoroethylene).
When the movable valve element moves from the opened position to the closed position, the seal usually also forms a mechanical stop which limits the movement of the valve element to the closed position. The seal therefore has two functions: firstly, the actual sealing function and secondly, the function of a mechanical stop.
In another embodiment of the disclosure, a separate mechanical stop is provided to limit the movement of the valve element to the closed position. This can be advantageous because a defined compression force acts on the seal.
The mechanical stop preferably has a material pairing between the side of the valve element and the side of the nozzle, which provides metal on both sides. The seal, on the other hand, is preferably elastic and, in the closed position, undergoes a certain material compression defined by the mechanical stop.
In another embodiment of the disclosure, on the other hand, the movable valve element is preferably designed as a valve plate which can be moved by the valve actuator via a tappet between the opened position and the closed position.
In a variant of the disclosure, the tappet protrudes through the nozzle and the valve plate lies in the closed position on the underside of the nozzle plate facing away from the valve drive. The valve plate is thus pulled into the nozzle to close the nozzle, whereas the nozzle plate is pushed out of the nozzle to open the nozzle.
In another variant, a nozzle channel runs through the nozzle plate from which at least one nozzle is fed. In its closed position, the plate-shaped valve element is in sealing contact with the upper section of the nozzle channel facing the valve drive.
It has already been mentioned above that the print head preferably emits a narrowly limited jet of coating agent in contrast to a spray mist as emitted by conventional atomizers (e.g. rotary atomizers).
It should also be mentioned that the print head can emit a jet of droplets in contrast to a coating agent jet being continuous in the longitudinal direction of the jet. However, within the scope of the disclosure, it is also possible for the print head to emit a coating agent jet that is connected together in the longitudinal direction of the jet, in contrast to a jet of droplets.
In a particular application it may be advantageous to apply high voltage (30-90 kV) to the entire print head or to individual components of the print head (e.g. to the nozzle plate 1) in order to take advantage of the additional benefits of electrostatic painting, such as higher application efficiency and/or electrostatic wrap-around at edges (the charged paint moves along electrical field lines, coating surfaces remote from the applicator near edges).
If electrostatic charging is used, a potential separation system may have to be used in the material supply when processing conductive paints. In this case, all components of the applicator must also be designed to withstand high voltages.
A particular advantage of the print head according to the disclosure is the fact that it works almost free of overspray, i.e. the print head preferably has an application efficiency of at least 80%, 90%, 95% or 99%, so that essentially the entire applied coating agent is completely deposited on the component without overspray forming.
It should also be mentioned that the print head preferably has a large areal coating capacity, so that the print head is also suitable for areal coating in the series painting of vehicle body components. The print head therefore preferably has a surface coating performance of at least 0.5 m2/min, 1 m2/min, 2 m2/min or even 3 m2/min.
The print head according to the disclosure can be guided by a multi-axis painting robot, which preferably has serial kinematics with at least six movable robot axes.
The print head according to the disclosure has a nozzle plate 1 with several nozzles 2, whereby only a single nozzle 2 is shown here for simplification.
The paint to be coated is fed from a paint feed 3 in the print head, whereby the paint feed 3 in the drawing is limited at the bottom by the nozzle plate 1 and at the top by a further plate 4.
The upper plate 4 has an opening coaxially to the nozzle 2 in the nozzle plate 1, on which a coil tube 5 is placed coaxially, whereby the coil tube 5 is wound with a coil 6.
In the coil tube 5 there is a coil core 7 which is sealed at the upper end of the coil tube 5 against the coil tube 5 by a seal 8.
In addition, there is an armature 9 in the coil tube 5, which can be moved in the direction of the double arrow, whereby the movement of the armature 9 depends on the current supply to the coil 6.
The drawing shows the armature 9 in a lower closed position to seal the nozzle 2. For paint application, on the other hand, the coil 6 is energized in such a way that the anchor 9 is pulled upwards in the drawing to release the nozzle 2.
In addition, the control valve has a return spring 10 which pushes armature 9 into the closed position shown in the drawing without energising the coil 6.
At its free end, the armature 9 carries a seal 11 to seal the nozzle 2 in the closed position.
The seal 11 on the armature 9 works in the closed position together with a flat seal 12 on the inside of the nozzle plate 1.
In the closed position shown, there is a flat contact between the two seals 11, 12 on the armature 9 on the one hand and on the nozzle plate 1 on the other hand.
The flat seal 12 on the inside of the nozzle plate can, for example, consist of a sealant layer, which is vulcanised onto the inside of the nozzle plate 1, evaporated, applied by a layer-forming process or printed on.
Alternatively, there is the possibility that the seal 12 is a foil which is laid, glued or laminated on the inside of the nozzle plate 1.
Furthermore, there are various possibilities for the material pairings of the seal 11 on the one hand and the seal 12 on the other hand. For example, metal on metal, plastic on metal, metal on plastic, plastic on silicon, silicon on silicon or metal on silicon can be used as material pairings.
A feature of this embodiment is that the nozzle 2 tapers conically in the inlet area in the direction of flow and has lateral nozzle flanks. The seal 12 is therefore applied to the lateral nozzle flanks of the nozzle 2.
In addition, the seal 11 is adapted to this shape of the nozzle and therefore tapers conically towards its free end, so that the seal 11 on the one hand and the nozzle 2 on the other hand are adapted in shape, which leads to a good sealing effect.
A feature of this embodiment is a flexible sealing diaphragm 13 instead of the seal 11. The drawing shows the opened position in which the armature 9 is raised upwards and the sealing diaphragm 13 releases the nozzle. To close the nozzle 2, however, the coil 6 is disconnected from the power supply so that the armature 9 is pressed downwards by the return spring 10 in the drawing until the sealing diaphragm 13 rests on the internal orifice of the nozzle 2 in the nozzle plate 1 and thus closes the nozzle 2.
The sealing diaphragm 13, however, does not only have the function to release or close the nozzle 2. In many cases, the sealing diaphragm 13 also provides a seal between the paint supply 3 and the other components of the control valve, such as the armature 9, the coil tube 5 and the coil core 7. This is advantageous because it prevents paint deposits in the control valve and in particular in the coil tube 5. This is particularly important when changing the colour, because the control valve itself does not have to be rinsed because it does not come into contact with the paint at all.
A feature of this embodiment is the design of the valve actuator, which does not work electromagnetically—as in
The actuator diaphragm 14 and the sealing diaphragm 13 provide a double seal between the hydraulic connection 15 and the nozzle 2. This prevents hydraulic fluid from escaping through nozzle 2 in the event of a malfunction with double certainty.
A feature of this embodiment is that the return spring 10 has been dispensed with, i.e. the movement of the armature 9 is controlled both in the closed position and in the opened position solely by the current supply to the coil 6.
Another feature is that the armature 9 is connected via a tappet 16 to a valve plate 17, which can be moved in a nozzle channel 18 in the direction of the double arrow. The drawing shows the position of the valve plate 17 in the closed position, in which the valve plate 17 rests against the upper side of the nozzle channel 18 and thus seals the nozzle 2.
To open the nozzle 2, the tappet 16 with the valve plate 17 is pressed downwards in the drawing and then no longer rests against the upper wall of the nozzle channel 18. The paint can then enter the nozzle channel 18 from the paint feed and flow out through the nozzle 2.
A feature of this embodiment is that no nozzle channel 18 is arranged in the nozzle plate 1. Rather, the valve plate 17, in the closed position shown in the drawing, lies sealingly against the outside of the nozzle plate 1 in a recess.
The nozzle 2 is either sealed or released by a fixed tappet 19. The nozzle plate 1 is either not bent (
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 014 947.7 | Dec 2016 | DE | national |
This application is a national stage of, and claims priority to, Patent Cooperation Treaty Application No. PCT/EP2017/081141, filed on Dec. 1, 2017, which application claims priority to German Application No. DE 10 2016 014 947.7, filed on Dec. 14, 2016, which applications are hereby incorporated herein by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/081141 | 12/1/2017 | WO | 00 |
