EP0570738B1 - Method and device for coating hollow bodies - Google Patents

Description

The invention relates to a method and a device for coating cans with an opening, in particular beverage cans.

The dip process, the flood process or a spray process can be used for painting such cans. Each of these methods has certain advantages and disadvantages. Depending on the size of the parts to be coated and the required throughput, the largest possible dipping basin is used in the dipping process. If cans are to be coated in the immersion process, the problem arises that the cans have to be completely filled with the lacquer when immersed and without air bubbles and therefore have to be introduced into the immersion bath with the opening facing upwards, while after the treatment, that is to say when they emerge emptied the immersion bath again, ie must be turned with the opening downwards. This requires correspondingly complex transport devices for the cans. Such a method is e.g. B. in the European Patent application 0 118 756 described.

In the electrophoresis flooding process, a coating is achieved by simply flooding or sprinkling an object with the aid of an electrophoresis lacquer. It should be noted here that the speed of the overflowing lacquer is limited so as not to interfere with the formation of the coating. Furthermore, only a one-sided coating can be achieved with this, in the case of cans only the outside.

In order to also reach the inside of cans, it has also been proposed according to German Auslegeschrift 26 33 179 to insert a nozzle tube into the cans that are guided above a collecting basin and to flow the liquid electrophoretic coating material through the nozzle tube onto the inner surface of the can to let, this can is rotated about its axis. This method requires a particularly complex mechanism, since the cans have to be held in a corresponding device and rotated about their own axis, and the nozzle tubes have to be inserted axially into the cans and moved out of them again. Furthermore, in the flooding and nozzle pipe processes, both of which require a catch basin, substantial foaming occurs, either by mechanical means, which is significant Require space or must be countered with chemical agents that interfere with the properties of the electrolyte.

From Japanese patent application 59 118 885, published as a summary in Patent Abstracts of Japan, Vol. 236 (C-249) (1673) dated October 30, 1984, it can be seen that it is possible to remove air in body cavities by means of robot-guided nozzles, which is to extract the air from flat cavities in the area of the wheel cutouts, under which To sell the roof or the engine and trunk hood.

From Japanese patent application 22 85 095, the summary of which is given in Patent Abstracts of Japan, Vol. 56 (C-0804) published February 8, 1991, it is furthermore known to immerse a housing for an electrical appliance with the opening upwards in a coating bath and to flood it, to rotate it by 180 ° before it emerges, so that the The opening points downwards and, when exiting the bath, blow air into the housing through air nozzles to make it easier to remove the housing from the immersion bath.

The invention has for its object to a method and an apparatus for coating cans in the immersion process create, it is not necessary to turn the cans when inserting or leaving the immersion bath and it is possible to coat the outer and inner surfaces of the cans evenly and in one operation without causing adverse foaming.

On the basis of this task, it is proposed in a method of the type mentioned at the outset that, according to the invention, the cans are completely immersed with the opening facing downwards in a dip bath with a lacquer, with the openings brought into the area of nozzles for the lacquer arranged in the dip bath below the liquid surface The air enclosed in the cans immersed in the immersion bath is at least partially displaced by the paint emerging from the nozzles and air nozzles are arranged in the immersion bath following the paint nozzles, the air in turn displacing the paint from the cans.

By completely immersing the cans in the immersion bath, the outer surface is completely wetted so that the coating takes place immediately after immersion. In order to also cover the inner surface with the paint in an uninterrupted layer, the paint is injected into the cans by means of the nozzles arranged in the immersion bath under the liquid surface, at least displacing the trapped air partially and fills the cans. The inner surface is completely covered with a layer of lacquer, so that a complete, non-porous coating is also obtained here. In view of the fact that the nozzles open practically at the liquid interface with respect to the interior of the cans, a sufficiently powerful liquid jet is created which rises to the bottom of the inner surface and displaces the trapped air.

When taking them out of the immersion bath, the cans run completely empty very quickly due to the air injected from below, with the openings still pointing downward, unnecessary paint drips off, after which the coated cans undergo a further, conventional treatment, eg. B. Rinse and dry.

If you want to completely displace the air enclosed in the cans immersed in the immersion bath, it is advantageous to first guide the cans after immersion in the immersion bath into an area with a first nozzle group and then into an area with a second nozzle group. The liquid jets generated by the second group of nozzles not only cause a complete displacement of the enclosed air, but also such a flow and turbulence in the cans that a quick coating is ensured.

On the basis of the aforementioned task, a device of the type mentioned at the outset is further proposed, which comprises a dipping bath containing a lacquer, a transport device which completely dips the cans with the opening downward and leads away therefrom, arranged in the dipping bath below the liquid surface has the openings of the cans immersed in the immersion bath for paint and below the liquid surface in the openings of the cans immersed in the immersion cans for gas, preferably air, following the nozzles for the paint.

The transport device can consist of a wheel immersed in the immersion bath with holders for the cans, the cans are clamped onto the holders outside of the immersion bath by hand or by means of automatic devices and, when the wheel is turned further, are immersed into the immersion bath with the opening facing downwards. When the cans pass the nozzles, the air is at least partially displaced from the cans and the inner surfaces of the cans are covered by the nozzles in an uninterrupted layer. When emerging from the immersion bath, the cans run empty and can then be removed from the wheel and sent for further treatment.

The transport device can preferably consist, at least in some areas, of a guide channel for cans arranged in a loose bond, at least on the underside and guided in some areas below the liquid surface. This guide channel holds the cans together and leads them to below the surface of the liquid. B. can be pushed through the guide channel by means of a pushing device arranged outside the immersion bath.

Furthermore, it is possible in the direction of movement of the cans in front of the nozzles already mentioned to arrange further nozzles for the lacquer which are directed into the openings of the cans immersed in the immersion bath and which essentially serve to displace the majority of the air enclosed in the cans , while only then is the complete displacement and intensive movement of the lacquer introduced into the cans, with the support of further nozzles, in the area of the transport device which is deepest immersed in the immersion bath.

In order to achieve this, the guide channel can consist, at least in the deepest area immersed in the immersion bath, of a pair of conveyor belts which grips the cans between their top and bottom sides, at least in the area of the bottom sides of the cans with the openings, whereby at least some of the nozzles can be arranged in the area below the conveyor belt gripping the undersides of the cans. Here, the paint jets emerging from the nozzles penetrate the broken conveyor belt and penetrate into the cans gripped between the pair of conveyor belts and support the coating.

Fig. 1

einen Querschnitt durch ein Tauchbad zur Beschichtung von Getränkedosen und

Fig. 2

einen Querschnitt durch einen Führungskanal für im Tauchbad zu beschichtende Getränkedosen.

The invention is explained below with reference to an embodiment shown in the drawing. The drawing shows:

Fig. 1

a cross section through an immersion bath for coating beverage cans and

Fig. 2

a cross section through a guide channel for beverage cans to be coated in the immersion bath.

From a system for coating, only one immersion bath 1 filled with lacquer, which is located in a tub 2, is shown.

Devices for cleaning, rinsing and possibly drying the objects to be treated are usually arranged in front of the immersion bath 1.

Likewise, 1 device for Drying the coated containers arranged. This is a known technique that need not be described in detail.

In the immersion bath 1, cans are to be coated on the inside and outside, which in the example shown consist of beverage cans 8. These beverage cans 8 are guided with their underside 9 upwards and their top side 10, which forms the upper edge of the beverage can 8 and has an opening 11, in a guide channel 12 below the liquid surface 26 of the immersion bath 1.

The guide channel 12 consists of an area leading into the immersion bath 1 and from the immersion bath 1, which is formed from parallel upper and lower longitudinal bars 13 and side guide bars 14, which are connected to one another by means of spacers 15 and form a closed channel.

In the area immersed in the immersion bath 1, the guide channel consists of a pair of link belts 16. Each link belt 16 is guided endlessly via a pair of guide rollers 17, which are connected to a drive 18. The lateral limitation of the guide channel in this area is given by side guide rods 19. The beverage cans 8 are guided in a loose connection through the guide channel 12, wherein they are pushed into the guide channel part immersed in the immersion bath 1 and then from the Link belt pair 16 are detected. The all-round guidance of the beverage cans 8 ensures that they are immersed in the paint of the immersion bath 1 without floating.

In order to coat the interior of the beverage cans 8, the air enclosed in the beverage cans 8 when immersed in the paint of the immersion bath 1 is first displaced by means of paint by spraying paint jets between the longitudinal bars 13 and the nozzles 23, which are arranged on a distributor housing 24 Spacers 15 are directed against the openings 11 of the beverage cans 8. The paint is drawn in by a circulation pump 25 in the immersion bath 1 and supplied to the distributor housing 24 under pressure. The outlet openings of the nozzles 23 are arranged as close as possible in the area of the openings 11 of the beverage cans 8 in order to introduce the paint into the interior of the beverage cans 8 with the greatest possible energy and to at least partially displace the enclosed air.

Paint jets are again directed into the beverage cans 8 from below via further nozzles 20 arranged on a distributor housing 7. For this purpose, the distributor housing 7 with the nozzles 20 is arranged below the lower link belt adjoining the beverage cans 8, which has so many openings for the paint jets that they pass through the link belt 16 essentially unhindered can and can reach the bottom 9 of the beverage cans 8.

The air from the interior of the beverage cans 8 is more or less completely displaced by the paint jets emerging from the nozzles 20 and 23, and any remaining air bubbles do not interfere with the coating, since the inner surface of the beverage cans due to the strong movement of the paint in the interior of the beverage cans 8 the jet effect of the nozzles 20 is always covered in an uninterrupted layer.

Following the pair of link belts 16, the beverage cans 8 again enter a guide channel area formed from longitudinal bars 13, side guide bars 14 and spacers 15 and are led out of the immersion bath 1. When leaving the immersion bath 1, the beverage cans 8 empty, excess paint residues drip back into the bath. This emptying is supported by the fact that air is blown into the cavities of the beverage cans 8 by means of air nozzles 27 and the paint is thereby displaced therefrom. The air nozzles 27 are arranged on a distributor housing 28 which is pressurized with compressed air by means of an air pump 29.

The beverage cans are then further processed in the usual way.

With the inventive method and the device achieved a very short coating time with a completely uniform and dense coating, especially in the interior of the beverage cans. The system can be operated in the usual way as a dip painting process with only one plunge pool. Compared to the flooding and nozzle tube process, the formation of foam is avoided or at least considerably reduced and the beverage cans or other cans can be guided in a loose connection in a simple manner without having to be taken individually when the guide channel 12 shown is used. With the device according to the invention, 2000 to 3000 cans per minute can be coated electrophoretically without any problems.

If such a high capacity for coating the inner surface of cans is not required, these cans can also be arranged on a wheel with a horizontal axis of rotation, the cans being attached to brackets on the wheel outside the immersion bath, going through the immersion bath and then being removed again for them to continue processing in the usual way.

It is crucial in the method and the corresponding device according to the invention that cans are introduced with the opening downwards into an immersion bath, through which nozzles arranged underneath the lacquer surface and directed towards the downward openings of the cans are acted upon by lacquer jets, in such a way that the in the Cans included Air is displaced, the inner surface of the cans is evenly covered with lacquer in an uninterrupted, moving layer, resulting in a uniform coating of the inner surface and that the lacquer in the cans is subsequently removed again by the air jets directed from below into the cans, while the cans are still below the surface of the paint, so that they can be removed from the immersion bath and the cans emptied quickly and easily.

Claims (7)

1. Process for coating cans with one opening, in particular drinks cans, characterised in that

   - the cans are completely immersed with the opening facing downwards in a dip tank containing a paint, and

   - their openings are brought into the vicinity of nozzles for the paint arranged under the surface of the liquid in the dip tank,

   - the air enclosed in the cans immersed in the dip tank is at least partially displaced by the jets of paint discharging from the nozzles, and

   - with their openings facing downwards, the cans are brought into the vicinity of air nozzles arranged under the surface of the liquid in the dip tank adjoining the area with the paint nozzles, and the paint in the cans is at least partially displaced by the air discharging from the nozzles.
2. Device for coating cans (8) with a wall, a base (9) and an opening (11) arranged opposite, with a dip tank (1) containing a paint, characterised by

   - a transport means (12; 16, 17, 18), which completely immerses the cans (8) with the opening facing downwards in the dip tank (1) and, without revolving them, removes them therefrom with their opening (11) facing downwards;

   - at least one nozzle (20, 23) for the paint, which is arranged under the surface of the liquid in the dip tank (1) and is directed into the openings (11) of the cans (8) immersed in the dip tank (1);

   - at least one pump (22, 25) to load the nozzle (20, 23) with paint so that the air enclosed in the cans (8) may be displaced, the cans (8) filled with paint and the inside surface of the cans (8) coated with the paint in a continuous layer; and

   - at least one nozzle (27) for gas, which adjoins the nozzle (20, 23) for the paint arranged under the paint surface in the dip tank (1) and is directed into the openings (11) of the cans (8) immersed in the dip tank (1) and through which the paint enclosed in the cans (8) is displaced when they leave the dip tank (1).
3. Device according to Claim 2, characterised in that the transport means comprises a wheel immersing in the dip tank with a horizontal rotational axis and with holding elements for the cans (8).
4. Device according to Claim 2, characterised in that at least in some areas, the transport means comprises a guide channel (12) for the cans (8) arranged in a loose pack, which is perforated at least on the underside and in some areas is directed below the surface (26) of the liquid.
5. Device according to Claim 4, characterised in that the cans (8) are pushed through the guide channel (12) by means of a pushing device arranged outside the dip tank (1).
6. Device according to Claim 4 or 5, characterised in that at least in its area immersed to the greatest depth in the dip tank (1), the guide channel comprises a pair of conveyor belts (16), which grasp the cans (8) between their upper sides and undersides (9, 10) and are perforated at least in the area of the undersides of the cans with the openings (11), and at least some of the nozzles (20, 23) for the paint are arranged in the area of the conveyor belt grasping the undersides of the cans.
7. Device according to Claim 6, characterised in that further nozzles (23) for the paint directed into the openings (11) of the cans immersed in the dip tank (1) are arranged under the guide channel (12) in the direction of movement of the cans (8) in front of the area of the guide channel which is immersed to the greatest depth in the dip tank (1).

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