OPTICAL ONLINE SENSING OF THE CLEANLINESS OF METAL STRIPS

ARCHIOPOLI, ULISES CROSSA; MARTÍNEZ, OSCAR EDUARDO; LUDUEÑA, SILVIO JUAN

São Paulo

Seminario; Rolling and Metal Forming Seminar - 50º Seminário de Laminação, São Paulo, 2013; 2013

A new optical method which allows the remote, contactless real time measurement of the cleanliness of metal surfaces is presented. A pulsed laser is used to ablate the surface contaminant layer. The light emitted from the created plasma is quantified as a measure of the surface cleanliness. The laser power is set well below the surface damage threshold. This technique can be mounted online and measure cleanliness even on rapidly moving parts as found in strip galvanizing lines. It is demonstrated that this new laser equipment for cleanliness evaluation is suitable for a precise and automatic real time evaluation of the strip cleanliness after the cleaning section in a continuous hot dip galvanizing line. Three types of results are discussed: The laboratory tests showed that the new technique is more reliable and repetitive than the adhesive tape test and can be used to calibrate the system in the same scale as provided by the tape test. The tests made in line where performed at the input and output of the cleaning section, testing different conditions of the bath and different configuration of nozzles and brushes. The new detector design permits a more portable online system that can be easily moved within different locations (such as input and output of the cleaning section or even between plants).