A Surface Optimized For Appearance and Performance
WHY THE EPS SURFACE IS BETTER
As it removes scale, EPS creates a new surface characterized by 'micro
jagged' peaks and valleys. It's more uniform than a typical acid-pickled
surface and facilitates paint performance that is superior to a typical acid pickled surface.
This was 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 more uniform profile. 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.
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With acid pickling, you get the surface that was on the steel when it left the hot strip mill. That may be fine for some purposes, but less-than-optimum for many others. With EPS pickling, the strip surface is much more uniform and optimized for painting and other coating processes.
The typical EPS surface roughness, quantified by Ra, is higher than that usually seen on acid pickled strip. But while the average roughness of EPS may be higher, the extremes of amplitude (peaks and valleys) are less and the surface is much more consistent overall (see explanation on the right ). This leads to better paint performance in terms of both appearance and corrosion resistance.
This better paint performance has been substantiated through exhaustive testing of painted EPS samples in accredited testing laboratories. Just as important, it has been proven out in real world applications by the hundreds of fabricators and manufacturers who are now producing parts from EPS-processed steel and enjoying the benefits of this 'engineered' surface.
With EPS, you no longer have to accept whatever surface was on the steel when acid pickling removed the scale. Instead, you can now receive a surface texture that, experience has shown, is usually better for how you or your customers will ultimately use the steel.
Mitigating Common Surface Defects
As EPS processing removes scale, it also 'conditions' the surface of the strip, mitigating common flaws and defects. This results in steel with a more uniform, higher quality appearance.
Defects which are actual cavities in the surface (pitting) are not removed, but become 'smoothed' so as to be 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 on the left shows 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 processing), while 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 that makes it 'secondary' material. EPS processing can restore it to 'primary' status and, in the case of processing on an EPS Coil Line, improve the material's shape by tension leveling.