Surface roughness values

When talking about stainless steel finishes, we often refer to surface roughness values or Ra. Some applications call for a low surface roughness because the surfaces have to be easy to clean, because a good flow of product must be guaranteed, or because no bacteria or dirt should be able to collect on the stainless steel. The lower the surface roughness, the lower the chance of corrosion occurring.

If there are particular requirements in this area, these should be indicated on the drawing and represented in terms of Ra values. This is the average deviation of the surface profile in relation to a reference line over a specified (standard) measured length. Other notations for roughness are Rz and Ry. Of course low surface roughness values have price consequences. The roughness value is expressed in µm (microns).

Commonly specified values are: - Ra < 3.2 µm = very rough finish possible - Ra < 1.2 µm = a relatively easy to achieve finish - Ra < 0.8 µm = a fairly fine finish; I think this is the most common limit in practice to indicate a maximum Ra value. - Ra < 0.5 µm - very fine Ra values of Ra 0.1 µm or even 0.05 µm are the lowest values Alinco offers.

It goes without saying that a low Ra value requirement has price consequences.