If ever you find yourself in downtown Chicago be sure to visit Millennium Park. There you’ll find the Cloud Gate sculpture. Locals refer to it as “The Bean” because it’s shaped much like a kidney bean, but one that’s 66 feet long and 33 feet high. The most impressive thing about the bean though, in our view anyway, is not the size but that it’s made from highly polished stainless steel – that then turns into a mirror reflecting both the Chicago skyline and the thousands who go to see it every day.
Sculpture is far from the only use for polished stainless steel. There’s one particular use we know a lot about (hint: it’s a bumper!), but we thought it might be interesting to look at some of the other uses. First though, an explanation of what makes stainless steel so useful.
No Protection Necessary
The big deal about stainless steel is that it doesn’t rust. Like regular carbon steel, it will oxidize, but the difference is that stainless contains a high proportion of chromium. (As much as 20% in the case of 304 grade stainless steel.)
Chromium is a shiny silver-gray metal mined in places like South Africa, India, Turkey and Kazakhstan. As soon as it comes into contact with oxygen an oxide layer forms on the surface. Oxygen can’t pass through that layer, so oxidation stops. Even more useful, if the surface is scratched a new oxide layer forms immediately on the exposed metal.
This behavior makes stainless steel attractive in applications from architecture to manufacturing because it doesn’t need painting. That lowers finishing and maintenance costs, which can more than offset the higher price of the material.
Stainless Steel Finishes
Stainless leaves the steel mill with a matte gray appearance called “mill finish”. Secondary operations can change that into finishes ranging from the brushed look popular on kitchen appliances to a highly polished appearance.
To make life easier for people buying stainless,finish grading systems were developed. In the US we use a series of numbers and letters ranging from 2B through 3, 4 and BA to 8. The designation relates to a surface roughness range, although it’s not a particularly logical progression.
In Europe they have a different classification scheme. This is defined in the EN 10088-2 standard and is still based on surface roughness.
The finish we’re particularly interested in here is what we call No. 8. This is a mirror finish with a roughness of 1 – 9 RA (1 – 10 RMS). It’s achieved by first grinding the surface with a fine grit, then polishing with soft cloths and special rubbing compounds. (Details are in our Tiki Talk post, “How Our Bumpers Get Their Mirror-Like Shine.”)
Uses for Polished Stainless Steel
One major benefit of a highly polished surface is that it’s very smooth. This means there’s nowhere for dirt or microbes to lodge, so it’s easily cleaned to a condition where the surface is sterile. It also means it’s more likely to stay clean. That leads to one particular set of applications.
The other benefit of course is that it reflects light very well. That leads to a different, though sometimes related, set of applications.
So with that background, here are 7 uses for polished stainless steel.
- Surfaces in clean rooms (countertops, wall panels doors, handles.)
- Enclosures in food processing, pharmaceutical and life science operations.
- Machinery that must remain sterile (medical equipment manufacturing, pharmaceutical manufacturing, food processing and brewing.)
- Reflectors and mirrors (solar energy concentrators, safety mirrors, the Cloud Gate sculpture.)
- Ornamental trim.
- Column covers (one of many architectural uses.)
- Fire truck bumpers. (This is the one we know a lot about.)
A Versatile Material
There are of course situations where you don’t want a mirror finish. You wouldn’t want to be dazzled by your refrigerator every time you go into your kitchen for example. But when cleanliness, durability and a reflective appearance are what’s needed, polished stainless steel should be your go-to metal.