TOPOGRAPHY ASSESSMENT OF COATED STEEL SHEET SURFACE IMPERFECTIONS IN RELATION TO APPEARANCE AFTER PAINTING

This study examined the evolution of the surface topography of imperfections in response to painting. Critically-sized imperfections on industrially produced coated sheet steel surfaces were sampled, and carefully characterized. Changes in the surface topography were measured after painting simulations, and visibility after painting was assessed. Three-dimensional optical profilometry was demonstrated to be a powerful technique for assessing imperfection topographies and their evolution during painting; several imperfections that were completely invisible through human inspection after painting were still measurable by 3-D topography. Two primer surfacer systems were used, to compare a conventional liquid system with a high-build anti-chip powder system.

While most imperfections remained visible after e-coating, the results showed that many surface imperfections are rendered invisible after final top coating, and the results provide a basis for industry to begin developing measurement-based inspection criteria for imperfection severity. The powder primer surfacer system was found to be much more effective in attenuating imperfections. A simple model was hypothesized to understand topography evolution, based on film shrinkage during paint curing, with some important implications related to painting system variables.