A Surface Optimized For Appearance and Performance
As EPS removes scale it creates an optimized topography – a much more uniform surface which is ideal for painting and other coating processes. EPS even mitigates many common mill defects. By contrast, acid pickling does nothing to improve the strip surface and can actually emphasize certain defects like silicon streaks and pickling stains.
How It Works
As the EPS slurry interacts with the steel strip it smooths out the surface overall while imparting very regular pattern of ‘micro peaks and valleys’. The Ra value of this topography is often higher than that seen on acid pickled strip simply because there are so many micro peaks and valleys with EPS. But their pattern is very consistent and this leads to better paint performance in terms of both appearance and corrosion resistance.
“We’re launching an exciting new method of how we process our mild and stainless steel material to remove mill scale and rust. This innovative technology called ‘Eco Pickled Surface’ or EPS, creates an ideal proﬁle for paint adhesion especially on stainless steel. In addition, it preps the steel better than any acid chemicals currently available for wash systems.”
Central Moloney, Inc.
Test Results: Why The EPS Surface Is Better
The advantages of the EPS surface were demonstrated in a study using non-contact optical profilometry examination of samples of acid-pickled steel and EPS-processed steel. Scans of the bare EPS and bare acid- pickled surface showed EPS had a higher Ra, but a more uniform profile overall. After chromate pretreatment and e-coat were applied to both materials, the painted EPS surface actually had a lower Ra and much less “waviness” than the acid pickled surface, as can be seen in the topographical scans below. READ THE FULL TEST REPORT >
Seeing Is Believing
Side-by-side photographs show how EPS processing mitigates common mill defects. Click on the name of each defect below:
Coupons from a hot roll coil with significant surface rust were acid pickled or EPS processed. Acid pickling removed the rust, but left a surface covered with pitting and cavities. EPS achieved significant ‘smoothing’ of these defects, as verified by the Ra of the samples: EPS: 80.4 Ra . . . HRPO: 123 Ra.
click photo to enlarge
A coil arrived with bad pickling stains – probably a result of halting the acid pickling line as it was being processed. A closeup of the surface is shown on the left. The balance of the coil was EPS processed, which completely removed the pickling stains, as shown on the right.
click photo to enlarge
This sample is a single piece from a coil with severe silicon streaks, a problem of excess silicon in the steel depositing on the surface. The left half of the sample was masked off, then the sample was EPS processed. Removing the masking, it was apparent that the streaking was removed by EPS.
A manufacturer has coils of stainless steel EPS’d so as to ‘roughen’ the surface, which has demonstrated improved paint adherence and performance. A side benefit is the ‘wood grain’ pattern on the surface of the strip, shown in the ‘Before’ portion is eliminated by the EPS processing.
Mitigating Common Surface Defects
As EPS processing removes scale, it also ‘conditions’ the surface of the strip, mitigating common flaws and defects. Defects which are actual cavities in the surface (pitting) are not removed, but become ‘smoothed’ so they are less severe and less susceptible to trapping oil and contaminants. Flaws which reside on the surface, like silicon streaks or pickle stains are completely gone after EPS processing.
The gallery shown here features side-by-side photos of common surface defects. The left side shows a section of a strip that was not EPS processed or prior to EPS processing. The right side shows a section of that same strip, originally having the same surface defect, after it underwent EPS processing.
EPS benefits are also available to material that has already been acid pickled, but became rusted or exhibits high levels of surface flaws, like pickling stains, that makes it ‘secondary’ material. EPS processing can restore it to ‘primary’ status.