Coating processes – Pretreatment – per se – or post-treatment – per se
Patent
1995-10-20
1998-07-28
Bareford, Katherine A.
Coating processes
Pretreatment, per se, or post-treatment, per se
427 8, 427348, 427349, 4274342, 427435, 118 63, 118672, 118673, 118712, B05D 304, B05C 1106
Patent
active
057860360
DESCRIPTION:
BRIEF SUMMARY
This is a national stage application of International Application PCT/EP94/00560, filed Feb. 25, 1994.
BACKGROUND OF THE INVENTION
The invention relates to an apparatus and a method for blowing off surplus coating material in the continuous coating of a metal band, in particular in the zinc coating of steel bands, with a pair of blow-off nozzles, between whose nozzle bodies, which are chargeable with a blow-off medium, in particular compressed air, the metal band is guided at a distance from the nozzle orifices extending transversally to the running direction of the band.
In the continuous coating of metal bands, e.g. in zinc coating steel bands, the band is guided with roller guiding means from the coating material bath in such a way that it extends as axially as possible between the opposed stationary nozzle bodies of the blow-off nozzles which are each arranged on one side of the metal band. If this axial course is impaired, inhomogeneities of the pressure profile in the blow-off nozzles and accordingly uneven coating layers will occur.
An apparatus of the kind mentioned above is known from the European Patent 0 249 234. In this apparatus the nozzle orifice is formed by two mutually adjustable nozzle lips, so that the pressure of the blow-off medium exerted on the surface of the metal band is adjustable. Sensors are provided in this apparatus for measuring the layer thickness of the coating on the metal band. The sensors are connected with a computer whose output controls regulating valves. The quantity of the blow-off medium with which the nozzle orifice is charged can be varied with the regulating valves. In this way the coating thickness can be adjusted to the desired set value. If in this apparatus deviations occur in the course of the band from the axial position, then inhomogeneities will occur in the coating as a result of the uneven charging of the band surface with the blow-off medium along the band width.
Another apparatus of the kind mentioned above is known from WO 92/02656 in which the nozzle body is arranged as a nozzle strip, this being so in such a way that along the direction of the nozzle orifice there are provided several mutually sealed partial nozzles which can be separately charged with the blow-off medium. In this way it is possible to correct unevennesses of the band to be coated because the pressure conditions along the width of the nozzle orifice are variable owing to the division into partial nozzles.
The invention is based on the object of further developing an apparatus and a method of the kind mentioned above in such a way that the axial guidance of the metal band between the nozzle bodies is improved.
This object is achieved in respect of the apparatus in such a way that at least one of the two nozzle bodies adjustable relative to the metal band carries an optical measuring device which is movable parallel to the nozzle orifice over at least the zone of one edge of the metal band and that the opposed nozzle body is provided with a reflector towards which the optical axis of the measuring device is directed in its position outside of the edge of the metal band.
The invention is characterized in that it enables a precise measurement of the distance both with respect to the mutual distance between the nozzle bodies as well as the distance of one of the nozzle bodies to the metal surface facing it. The relevant aspect is that the optical measuring device comprises two distance ranges, namely the one within the width of the metal band and the one outside thereof. Whereas the distance between nozzle and band is determined within the edge of the metal band, the distance between the nozzles arises in the zone outside of the edge. As a result of these two measured signals it is possible that the positioning of the nozzle bodies can be made in such a way that both nozzle bodies can be moved to a defined distance with respect to the metal band, and in particular that both nozzle bodies can be arranged symmetrically with respect to the band.
In a preferred embodiment of the inventi
REFERENCES:
patent: 4078103 (1978-03-01), Thornton et al.
patent: 5614266 (1997-03-01), Cox et al.
JP 62-30865 (Feb. 1987) (Abstract).
Jabs Ronald
Pannenbecker Heinrich
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