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What is Your Stainless Finishes IQ?

RMS (Root Mean Square) is a standard used to diagnose machining operations and surface finish.  The fineness of the finish and ultimate success of sanitation effectiveness is called RA, the roughness average, measured by height in millionths of an inch or microinches. 

A profilometer device determines RA values of small surface variations and calculates their average to determine roughness.

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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