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Ask Joe Powder
"Ask Joe Powder" is a question and answer column authored by Kevin Biller of
the Powder Coating Research Group. Mr. Biller has over 30 years experience
formulating and manufacturing powder coatings. He welcomes your questions
regarding powder coating technology. Please write to: email@example.com
The Powder Coating Research Group
15 W. Cherry Street, 3rd Floor
Columbus, OH 43215
Dear Mr. Joe
We are in a business to produce diesel generators with acoustic enclosures.
We apply pure polyester powder coating on these enclosure parts.
Recently we have been asked to install our generator at a place which is
surrounded by heavy chlorine gas throughout the life of all installations
over there. Please suggest suitable surface treatment and painting system
for our enclosure parts to resist such an atmosphere, and also guide us life
expectancy of such coating system and if required frequency of recoating on
site to sustain durability of coating.
Matter urgent and your guide line may help others also having similar
Super Nova Engineers ltd.
You are wise to consider using a more durable powder technology than
polyester chemistry for this hostile chemical environment. First let’s talk
about metal pretreatment. The steel must be completely cleaned and devoid of
any oxidation. The best cleaning technique would involve a high quality
alkaline cleaner followed by a water rinse. Next stage should be a high
quality iron phosphate conversion coating followed by two rinses, clean
water then a deionized water rinse. The final stage should be a seal that
can be either chromate based or an organic alternative.
The parts should then be thoroughly forced air dried in an oven and cooled
before the powder coating application. Your choice of powder will depend
upon whether it is in an indoor or outdoor environment. I would assume that
this is an indoor application from your explanation.
For indoor environments I recommend that you use a functional grade
epoxy-based powder coating. These can be either phenolic cured or amide
cured products. Either will work well. The powder coating should be applied
to a thickness of at least 75 microns, but preferably 100 to 150 microns and
thoroughly cured per the manufacturer’s recommendation. The color stability
of epoxy powders is only marginal so you can expect to see a variation of
color for lighter shades.
For exterior environments you have two choices – one is using an epoxy based
primer followed by
a polyurethane topcoat. Alternately you can consider using a single coat of
polyurethane. The two
coat system will provide the best overall durability, however you will need
to take measures to ensure acceptable adhesion of the polyurethane to the
epoxy. The best process is to slightly undercure the epoxy primer then apply
the polyurethane and fully baked the two-coat system.
Both the epoxy and polyurethane can resist chlorine gas if formulated and
applied properly. Recoating should not necessary for a long time. I strongly
recommend that you test any coating system thoroughly before committing to a
commercial process. It would make sense to coat a number of test panels
wirth the systems described above and expose them to the service environment
targeted to determine if the products will withstand the possible chemical
Please forward any questions or comments to