A recent ‘high-tech’ evaluation of comparable samples of EPS processed steel and acid-pickled steel produced convincing visual evidence of how the EPS surface texture produces a smoother, more consistent paint finish.

The evaluation employed a Wyko non-contact optical profilometer to scan samples of EPS-processed steel and acid-pickled steel. Scans were performed of the clean, bare steel, then of samples that had been chromated in preparation for painting and, finally, of samples that had been chromated and painted by e-coat. Not only did the Wyko instrument capture the customary parameters of Ra, Rq and Rt, it also captured 3D topographical ‘maps’ of the surface of each sample (see image at left.)

The bare EPS samples showed a higher average roughness value, Ra, than the bare acid pickled steel samples. This is expected, as EPS processing is designed to produce a rougher, but very uniform, surface finish that yields better paint adherence. However, as successive coatings were applied – first the chromate and then the paint – the Wyko scans showed the EPS painted surface becoming markedly more uniform than the painted acid-pickled samples. The conclusion reached is that although the EPS surface may be considered ‘rougher’ than typical acid-pickled, as measured by Ra, it is ‘topographically’ more uniform and this provides a better paint (e-coat) appearance.

You can read the full report, EPS Surface Texture Analysis and Comparison to Acid Pickled Surface, in the compiled booklet of all EPS laboratory and application testing – EPS End Use And Application Test Report.