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In this project a new method for online thickness measurement and depth profile analysis of the zinc coating of galvanised sheet steel based on laser-induced breakdown spectroscopy (LIBS) is developed and evaluated. The method allows for characterising the coating with a series of single laser bursts irradiating the sheet steel in motion. Depth resolution is achieved by tuning the burst energy in small increments and by evaluating line intensity ratios of iron (substrate) and aluminium (coating) referenced to a line intensity of zinc (coating). The impact of the LIBS craters on the sheet steel quality is minimised by using burst energies below 3 mJ. The obtained craters were analysed in corrosion and visual tests and WDX. It was found that the craters did not influence the corrosion behaviour and were invisible to the naked eye. A demonstrator was built consisting of a transportable measuring unit and a rotary stage to simulate the sheet steel velocity in the plant of up to 2 m/s. LIBS measurements on rotating sheet steel discs were performed and evaluated. The depth resolution with optimised parameters was determined to about 140 nm by using well characterised industrially coated sheet steel of coating thicknesses in the range of 3.2 to 11.2 µm. The measurement time for the coating thickness is estimated to about 100 ms and for the monitoring of the Al depth profile to about 5 s. With these results a method for a fast online characterisation of galvanised sheet steel is now available.

Additional information

Authors: BALZER H, Fraunhofer Institut für Lasertechnik, Aachen (DE);NOLL R, Fraunhofer Institut für Lasertechnik, Aachen (DE);STURM V, Fraunhofer Institut für Lasertechnik, Aachen (DE);HOEHNE M, Fraunhofer Institut für Lasertechnik, Aachen (DE);VITR G, Fraunhofer Institut für Lasertechnik, Aachen (DE);WISSENBACH, Fraunhofer Institut für Lasertechnik, Aachen (DE);DILLEN H, Arcelor (OCAS), Zelzate (BE);LEUNIS E, Arcelor (OCAS), Zelzate (BE);SANCHEZ P, Fundacion ITMA, Coruno-Llanera (ES);HEMMERLIN M, Arcelor Reseacrh (IRSID), Maizières-lès-Metz (FR);RAULF M, ThyssenKrupp Stahl, Dortmund (DE);JANSSEN S, ThyssenKrupp Stahl, Dortmund (DE)
Bibliographic Reference: EUR 22827 EN (2007), 138 pp. Euro: 25
Availability: (Catalogue Number: KI-NA-22827-EN-S)
ISBN: ISBN: 978-92-79-05442-6
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