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Updated: Jun 19

In order to understand the differences between GRIT and RA, it is important to mention that there are standards for the surface finishes of the stainless steel used in sterile and sanitary facilities, which can be grouped as follows:

  • Food and beverage: ASTM, 3-A, 304 and 316L Standards

  • Pharmaceutical, cosmetic and electronics: ASME BPE Standard

Considering the surface is what contains and moves the product, the finish specifications becomes a critical and fundamental element, as it defines the use that will be applied to any given product.

For many years, the above-mentioned industries analyzed the surface in an inaccurate way to decide whether they accepted or rejected a piece of equipment or an installation, since the analysis was based on the size of the abrasive grain used in their production, described by the term “GRIT”.

It was not until the arrival of the “Roughness Meter” that the method of analyzing surfaces became more exact, since this instrument scans the surface to be analyzed and using a needle, measures the height/depth of the irregularities, providing us with an arithmetic average.

So, we have two options to evaluate the surface finish:

  • GRIT: With the help of magnifying glasses, lenses, cameras or microscopes, the surface of the manufactured/purchased part is compared with the surface of an already polished and calibrated sample, to decide if it is accepted or rejected. With this method there is no objectivity, nor an exact measurement, nor any record, since you can obtain different finishes depending on variables such as: The eye and judgement criteria of the inspector, the roughness of the sandpaper, the abrasive and method of application, the lubricant used, etc.

  • RA (ROUGHNESS AVERAGE) PREFERRED BY OGMAN: Using the Roughness Meter as a measurement instrument, that based on the signal generated by the movement of the needle, provides measurements, graphs, differential and arithmetic calculations, etc.

In conclusion, using the roughness meter and taking into account the maximum RA allowed for a particular product, we can correctly and objectively determine whether the surface finish should be accepted or rejected.

At OGMAN Tuberías Inoxidables, we use the Roughness Average (RA), which is a measurement of the imperfections of a surface and is measured in micrometers or microinches, in order to guarantee the quality of the finishes of our products and services, depending on each customer's needs.

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