Surface roughness values

Surface Roughness Values

In stainless steel finishing, surface roughness values, such as Ra values, play a crucial role. For applications where surfaces need to be easily cleanable, ensure good product flow, or where bacteria and contaminants should not have a chance, a low roughness value is essential. A lower roughness value also reduces the risk of corrosion.

What are Surface Roughness Values?

  • Ra value: The average deviation of the surface relative to a reference line over a standardized measurement length. This is the most used parameter for roughness.
  • Other Parameters: Rz (average peak height) and Ry (maximum peak height) are also common roughness parameters.
  • Unit: Roughness values are expressed in micrometers (µm).

Commonly Used Ra Values

  • Ra < 3.2 µm: Very rough finish.
  • Ra < 1.2 µm: Relatively easy achievable finish.
  • Ra < 0.8 µm: Fine finish; often the most commonly used limit for a maximum Ra value.
  • Ra < 0.5 µm: Very fine finish, with values up to Ra 0.1 µm or even 0.05 µm as the lowest that Alinco can achieve.

Applications and Benefits

  • Hygiene: Lower roughness values are essential for applications in the food and pharmaceutical industries where hygiene is crucial.
  • Corrosion Resistance: A smoother surface reduces the chance of corrosion formation.
  • Cleanability: Lower roughness values make it easier to keep surfaces clean and maintain them.

Cost Implications

Roughness is measured using a calibrated roughness meter, where a stylus moves over the surface.

Specification on Drawings

Given the cost implications, it is important to carefully consider roughness requirements. Please also specify them correctly on the drawings.

How to Reduce?

Techniques to reduce roughness include:

  • Mechanical polishing
  • Electropolishing (limited)

For a good overview of roughness measurements, click here.

A Note on Ra Values

The Ra value will remain a benchmark for years to come. However, it is not 100% correct, as the microscopic topography of the surface also plays a role in cleanability and anti-adhesion of dirt.

It is evident that sharp peaks and valleys at an Ra of 0.8µm might be worse in terms of hygiene than gentle microscopic undulations at an Ra of 1.2µm. Such an undulating surface is often obtained through forms of wet blasting such as Sublimotion.