How The EPS Surface Is Better
The EPS process actually creates a new surface as it removes scale. This surface is characterized by micro 'jagged' peaks and valleys, and is more uniform overall than a typical acid-pickled surface, as shown in the measured surface 'micro profiles' shown below:
These two surface profiles actually have similar Ra values, but notice how the acid-pickled surface exhibits larger deviations from the (red line) average and a very irregular surface. The left part of the profile is relatively smooth, which is a detriment to paint adherence, whereas the right part of the profile is more irregular. Having these two different topographies in the same area makes it more difficult to get a consistent paint finish.
The EPS surface does not have extremes of peaks and valleys – it's more uniform across the profile. Its topography is also more 'jagged' which is better for holding paint and other coatings, resulting in better adhesion.
Optimized Surface Finish
With EPS, you can specify the desired surface finish, in terms of Ra, for your processed material. The EPS Alpha line offers these 3 distinct ranges of surface Ra:
- R130: 125 - 145 microinches
- R110: 100 - 125 microinches
- R90: 80 - 100 microinches
The ability to specify surface finish opens up possibilities for you (or your customer) to enhance paint performance. For instance, paint will adhere better to a rougher surface. The EPS R110 or R130 finish can improve paint adhesion, an important factor in corrosion resistance as demonstrated by salt spray test results. But since EPS' surface is so uniform (see right ») this higher Ra level does NOT compromise the appearance of the finished painted surface.
Other applications, like stamping, drawing and cold rolling benefit from a smoother surface that can reduce tool wear and allow the lubricant to work more effectively. These users will prefer an R90 or R70 surface.
With EPS, you no longer just accept whatever finish was on the steel when acid pickling removed the scale – you can actually specify the surface finish best suited to your needs.