Seeing Is Believing
To see side-by-side photographs of various flat rolled steel defects (left side) and how EPS processing mitigates those defects (right side), just click on the name of each defect listed below:
| Roll Marks | ||
A coil with repeated roll marks was the source of samples that were acid pickled or EPS processed. Acid pickling did not visibly effect the roll 'scrape' mark but EPS processing left the mark barely visible, as it blends into the very uniform surface.
This sample is a single piece from a coil showing significant silicon streaks, the 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. When the masking was removed it was apparent that visible 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.
Coupons taken from a coil of hot roll all featured severe pitting. Some were acid pickled and some were EPS'd. The EPS process served to smooth out the contours of any cavities that remained on the steel (see right side above), something acid pickling cannot do.
Coupons from a coil of hot roll with significant surface rust were acid pickled or EPS processed. The acid pickled samples removed the rust, but left a surface covered with pitting and cavities. The EPS samples accomplished significant 'smoothing' of these defects, as verified by the Ra of the samples: EPS: 80.4 Ra . . . HRPO: 123 Ra.
A coil of HRPO arrived with bad pickling stains – probably a result of stopping/starting the acid pickling line as it was being processed. A closeup of a representative sample of the surface is shown on the left. The balance of the coil was EPS processed, which completely removed the pickling stains, as shown in the sample on the right.
Mitigating 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 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 your right 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 very same strip, originally having the same surface defect, after it underwent EPS processing. To get further details on these examples, refer to the EPS Research White Paper.
EPS benefits are also available to material that has already been acid pickled, but became rusted or exhibit high levels of surface flaws that makes it 'secondary' material. EPS processing can restore it to 'primary' status and, in the case of coils, improve shape by tension leveling performed during the EPS processing.