April 08 2020 0Comment

How important is the finish of your stainless steel?

First impressions count – are you giving off the right impression when you protect your landscape? Here at IMS we care not only about how good the product looks but how long it is going to look that good!

The surface roughness is a measurement of the texture of the surface and is quantified by the vertical deviation of a real surface from its ideal form. It is a well recognised fact that the surface that the surface finish on stainless steel has a significant effects on its corrosion resistance. However, despite this seemingly obvious correlation, it seems that manufacturers in the stainless steel industry fall short on selecting the best and most premium finish.

Surface roughness is measured in Ra value by using an instrument whereby a stylus travels across the surface, with the movement of the stylus amplified to record the signal. The value of said Ra is normally measured in micrometres. There are three Ra values of surface finish that we’re going to give you an insight into. The industry standard is in excess of 1.8 Ra. Our standard has a maximum of 0.8 Ra, while our 2K finish has a maximum of 0.5 Ra.

The rougher the surface, the quicker and easier it is for it to corrode and show imperfections. Coarse polished finishes that have a transverse Ra of >1micron exhibit a higher level of corrosion due to the deep grooves where chloride ions can accumulate. We see this happening most frequently in coastal areas, where conditions are worse. Coastal or marine situations should realistically have a ‘maximum’ transverse surface roughness requirement of 0.5 Ra.

Our standard of surface finishing that we give no matter what is 0.8 Ra Max, which is only slightly more than the recommended requirement for longevity in coastal areas. While this will be more than ideal for inland usage, we would still go that little bit further and urge our customers to go for the 2K finish, which comes in at 0.5 Ra Max. This finish is obtained by using a finer grit belt or brushes, giving it a clean cut finish. While this finish is slightly more expensive, its longevity is incomparable.

Below you can see a bollard with a 2K finish, coming in at under 0.5 Ra – this finish will last longer than all others and will look far better.