How to Prevent Outgassing of Iron Castings – Products Finishing

Verney Denerville of TIGER Drylac outlines the procedure used to mitigate the outgassing of iron castings.
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If gasses are not expelled from metal prior to powder coating, problems such as bumps, bubbles and pinholes can occur.
Photo Credit: TIGER Drylac
Q: How do I prevent defects caused by outgassing of iron castings?
Cast metal surfaces such as iron, steel and aluminum are not always forgiving in the powder coating world. These metals trap pockets of gasses, air and other contaminants within the metal during the casting process. Shops must expel these gasses and impurities from the metal before powder coating.
The process of releasing entrapped gasses or contaminates is called outgassing. If a shop does not properly outgas, problems such as bumps, bubbles and pinholes will lead to intercoat adhesion loss and rework. Outgassing takes place when heating the substrate, which causes the metal to expand and expel the trapped gasses and other impurities. It is essential to note that entrapped gasses or contaminants within the substrate are released during the powder coating curing process as well. In addition, gasses can release during the process that was used to cast the substrate (sand pouring or die type).
The industry uses the following steps to mitigate outgassing from iron casting:
In addition, there are products, such as an OGF additive that can be dry blended in with powder coatings on site to assist with this phenomenon. When it comes to powder coating cast metals, these steps can be tricky and will take some additional time. However, this little bit of extra time amounts to a fraction of the time it would take for rework and starting the entire process over again. While not a foolproof solution, using this process along with specially formulated primers and topcoats can help mitigate outgassing problems.
The processes, chemicals and equipment, plus control and troubleshooting.
Powder coating is one of the most durable finishes that can be applied to industrial manufactured products, and offers excellent corrosion protection and is very safe because of its lack of volatile organic compounds. To understand the powder coating process you should start with the fundamentals. 
My company fabricates aluminum and steel pedestrian bridge railing among other bridge parts. We recently got an aluminum railing job that called for “Type I” anodizing per MIL-A-8625. There was no anodic coating thickness called out. We are not anodizers and we are at a loss as to how to write up a meaningful anodizing specification for this railing.
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