There are a number of factors that have to be considered when evaluating a stainless steel item for surface finishing. These include the type of material, product application and customer expectations. In this blog, we’ll take a look at three primary types of finishes: sanitary, fine, and mirror.
Understanding Roughness Average (Ra)
Before we jump into stainless steel finishing types, a key point to understand prior to making any decisions regarding product finishing is the abbreviation “Ra,” which stands for “roughness average” as determined by an algorithm. It is expressed in the measurement unit of microinches and is the most common way customers specify surface roughness (at least in the United States, where EVS Metal is located). A profilometer is used to assess the finished surface and calculate its Ra. When you know what Ra the customer wants, it will be easier to ensure the right finish is used on the end product that will meet their specifications.
Sanitary Metal Finishes for Stainless Steel
We’ll start by looking at sanitary finishes. This is the number one finish for products that will need to be used in a food-grade capacity, and requires an Ra of 30 to 35. If a product will be used in this manner, it’s absolutely essential that there are no scratches or nicks of any sort, as they can allow food particles to be trapped and therefore hold the potential to allow bacteria to flourish. This would obviously be a major liability for any company in the food-service industry, therefore it’s imperative that when this finish is specified, the result is exactly as the customer requires.
Fine Metal Finishes
Fine finishes, on the other hand, are even smoother than sanitary finishes. These are extremely common in medical, pharmaceutical and clinical environments. The Ra of 12-16 microinches means that even the smallest particles or other contaminants won’t end up caught on tiny scratches or imperfections on the product. The aerospace industry will also commonly request a fine finish on certain parts, as this finish can help reduce the chance of corrosion while enhancing the product’s durability.
Mirror Metal Finishes (Including #8)
The smoothest finish — and the one that often gives finishing specialists nightmares — is a mirror finish. In particular, the #8 mirror finish. This is by far the most complicated kind of finish, and it is most commonly requested by customers utilizing the end product in a decorative or architectural product. As the name states, mirror finishes are highly and clearly reflective with almost no haze, and require that every surface defect is removed in order for it to be achieved. A true mirror finish is so smooth, in fact, that not every metal can be finished in this manner — it’s just not possible. Stainless steel is the most common material to finish in this manner.
At EVS Metal, we have the technology and tools to achieve any desired metal finish, whether our customers require a #3 graining or a #8 mirror. Our four ISO 9001:2015-certified locations comprise over 250,000 square feet of vertically-integrated manufacturing space and feature the most modern equipment available, from welding robots and laser cutting solutions to automated powder coating lines. We serve a diverse customer base across North America, providing a range of services from quick-turn prototypes to high-volume production runs. Request a personalized metal fabrication quote online, or call (973) 839-4432 to speak with a specialist today.