In terms of material used in food processing and commercial equipment, here is the list of stainless materials from smoothest to the roughest RA range.
Electropolished surfaces range from 6 RA – 14RA microinches. Electropolishing can change RA values up to 50% smoother, depending on the material being treated.
2B Mill Finish – This is a widely used stainless steel finish, common in industrial, chemical and food applications. It is corrosion resistance and has a typical range from 15RA (16 gauge) – to 40 RA (7 gauge) microinches.
No. 4/Dairy Finish – For processing industries, the Dairy finish is required to meet the basic 3-A standards. It uses a 180 grit and has an RA range of 18-31 microinches.
No. 4 Finish – This finish uses a 150-grit abrasive creating a polished brushed surface. The RA range is 29-40 microinches.
No. 3 Finish – The No. 3 finish uses a 120 grit abrasive. It has a semi-polished finish with an RA range of 36 – 58 microinches.
Bead Blasted surfaces have a soft satin appearance and low reflection. The process of bead blasting utilizes bead material such as glass or ceramic beads to produce a non-directional, textured surface. The finer the blasting media, the more corrosion resistance the surface performance. The RA values are typically higher than 45RA microinches, but are dependent on the blasting process and the stainless material.
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In the photo are samples that we provide to customers to show the different types of finishes available in the design and manufacturing of equipment for industries that require a high degree of sanitation.
From the left:
2B Finish: Has common corrosion resistance properties, heat resistant, smooth (not brushed) steel. The RA (roughness average) is 36 to 15 depending on the gauge of the material.
#4 Finish: Is Characterized by short, polished brushed lines and is suitable for caustic wash down procedures. The RA is from 29 – 40 depending on the gauge of the material.
Pickle Passivation: A treatment also referred to as descaling, pickle passivation removes the scale and leaves a matte finish that is free from contamination. Apache’s tests have proven an increase in RA smoothness up to 25%, compared to measurements before the material was pickle passivated.
Bead Blast: Bead blasting utilizes material such as glass, ceramic beads to produce a non-directional, textured surface with a satin appearance and low reflectivity. The finish is not necessarily smooth, depending on the process and blasting medium. RA readings are typically greater than 45.
Electropolish: Surface metal is dissolved, removing all embedded contaminants, which creates a smooth, mirror-like finish. Apache’s tests have proven to increase smoothness up to 50%, compared to measurement before the material was electropolished.
For detailed information about these finishes and processes, download our white paper “Leveraging Stainless Steel Finishes on Sanitary Equipment”.
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