Meaning of Surface Quality

In order to provide favourable conditions for sterile production, the surface must be smooth and non-porous down into the microscale range. Overlapping areas,
or material laminations, must be avoided as far as possible on account of the dead spaces that result, since these areas are diﬃcult or impossible to clean and therefore represent ideal breeding grounds for germs and bacteria.
Moreover, the dimensions (including height!) must be kept as small as possible to minimise the inﬂuences of the surfaces in contact with the product. Such surfaces can be obtained by means of electropolishing.

Technologies Details

In the pharmaceutical sector, but not only there, the quality of the surface is generally defined in terms of the “Ra”-roughness. A surface with Ra ≤ 0.8 μm is normal, in special cases also Ra ≤ 0.6 μm and even Ra ≤ 0.4 μm.
All these qualities can be achieved by machining appropriately good quality steels and electropolishing them for a suﬃciently long period of time. Ra is the rithmetic average of all protuberances on the surface y over a certain measurement distance L in the x-direction.