Happy New Year to everyone!
As we clear the cob webs upon returning from our vacation I figured that I would share with you an interesting steel insight that I learned in the field (the hard way of course :)).
Take a look at these pictures:
Now compare to this:
You may have the answer to the question of “What is that horrible looking stain??” but when I first saw this I did not and when it was presented to me I panicked. This material is Galvalume (See here: http://www.galvalume.com/) which is a coated steel that has a mixed coating of 55% Aluminum / 45% Zinc. (Here is more info on this from Arcelor Mittal: http://dofasco.arcelormittal.com/~/media/Files/A/Arcelormittal-Canada/documents/galvalume-brochure-web2.pdf
Typically, Galvalume has a marked spangle with what looks like tiny fish scales. Almost like what the skin of trout fish looks like. I guess, due to the mix of Aluminum and Zinc and the way they react to each other when exposed to the elements (moisture in particular), they turn black and scare the willies out of anyone that does not know what they are seeing. Imagine having bought a load of steel that has been slit to width or cut to length for example and after a few days post delivery the material begins to show off this pretty color. 🙂 ARRRGGGHHH!!
In actually though, it simply indicates that the coating is beginning to compromise itself in order to protect the steel substrate. (Exactly why the coating was applied int he first place!!) To prevent this ugliness from occurring, often times and additional (very light / thin layer) coating of acrylic will be applied to the material as a shield and a barrier against moisture. (Remember, a block is much more effective than a coating that is meant to sacrifice itself and in doing so exhibits its own reaction to the invading outside force – think sunscreen / sunblock for your skin?).
So in truth, there is nothing really wrong or defective with the steel when it shows black rust, it just looks disgusting and can send your customers running for the exits. If the part that is being produced is not for an exposed application, for the most part, this cosmetic defect should be usable and should not be cause for a rejection.
Hope this was informative and do stay in touch.
To learn more about Premium Steel Sales, LLC and what we can do for you, check out the rest of our web site at: http://premiumsteelsales.com/
Ben Levi – Premium Steel Sales