Apparatus for coating container bodies internally

Details Apparatus for coating container bodies internally Apparatus for coating container bodies internally

1997-09-09

2001-01-23

Edwards, Laura (Department: 1734)

Coating apparatus

Projection or spray type

Inside of hollow work

C118S306000, C118S308000, C118SDIG001

Reexamination Certificate

active

06176927

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a method for coating container bodies internally as they emerge in succession from a welding machine. The invention further relates to an apparatus for coating container bodies internally as they emerge in succession from a welding machine.
It is known to coat containers or container bodies internally with liquid or powder lacquers. Special problems arise in the coating of container bodies, particularly can bodies, emerging in succession from a welding machine in which the longitudinal seam of the bodies has been welded. If only the welded seam is to be covered, it is known to convey coating material through the welding machine and to apply it to the welded seam. However, if the whole of the internal wall of the container is to be coated, problems arise, as the deposition rate is only approximately 60%, which means that approx. 40% of the coating material, which is in the form of a mist of powder or liquid particles, does not remain, but escapes from the body, contaminating the conveyor line and its surroundings.
To give an indication of the level of this contamination, it can be stated as an example that in order to coat the weld seam only on the internal wall of the body of a ½ kg can 114 mm long, approximately 100 mg of powder coating material must be sprayed, of which, assuming the deposition rate to be as stated, 40 mg passes into the environment. With a daily production of 500,000 cans, this results in a considerable quantity of powder being discharged into the environment, and which, despite recycling by an external extraction system, may cause damage eg. to the bearings of the conveyor line, and even to those of the welding machine. If the container body is to be coated over its whole internal circumference, ie. over 360°, the quantity of powder involved will be increased several times more.
SUMMARY OF THE INVENTION
Accordingly the object which lies at the basis of the invention is to provide a method, which does not possess or which mitigates the drawbacks which have been mentioned, for coating the whole of the internal walls of container bodies over the entire circumference.
This is achieved, in a method of the abovementioned kind, by feeding the coating material from the welding machine end and spraying it inside the can body more or less uniformly onto the internal wall, and by extracting sprayed coating material inside the can body for return and returning of the said material via the welding machine end of the spray process.
Because extraction of sprayed material takes place inside the can body itself, contamination of the environment with the coating material can be effectively prevented, as only a small amount of material remains to be removed by the external extraction system. The quantity of material which the external extraction system fails to remove is likewise reduced, resulting in a significant diminution in external contamination. The material in question is returned and can be disposed of or reused.
Furthermore the gap between adjacent can bodies in the coating area is preferably reduced with respect to the normal conveying gap, eg. by braking the bodies in front. This additional step enables a further reduction to be made in the coating material escaping through the gaps between successive bodies.
A further object of the invention is to provide an apparatus for coating container bodies internally in which the disadvantages which have been described can be avoided or reduced. This is accomplished in the abovementioned apparatus by providing at least one coating material feed line through the welding machine and at least one coating material return line through the welding machine, and by providing a spray and suction head connected to the feed and return lines and positioned so as to act on the interior of the can body. With a more uniform application over the circumference, there is a reduction in the amount of powder to be returned. This can be produced by a rotating spray head. Also, it is possible to provide for slightly more powder to be applied at the weld seam, to ensure that the step in level is satisfactorily covered.


REFERENCES:
patent: 3422795 (1969-01-01), Smith
patent: 3516385 (1970-06-01), Walling
patent: 4869201 (1989-09-01), Takahashi et al.
patent: 5173325 (1992-12-01), Knobbe et al.
patent: 5520735 (1996-05-01), Mulder
patent: 5725610 (1998-03-01), Wilson et al.

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