Metal finishing Q&As since 1989
-----
Can we do Iriditing of Aluminum in house?
(to hopefully help readers more easily follow the Q&A's)
Aluminum is often 'chromate conversion coated' either as a corrosion resistant final finish or as a pretreatment for painting or powder coating. As with most metal finishing, the process actually involves many steps, usually including alkaline cleaning, etching, deox/desmut, the chromate conversion step per se, and water rinses between each step.
MIL-C-5541 / MIL PRF-5541 / MIL-DTL-5541 [on DLA] is the most commonly cited specification for the process.
Alodine & Iridite are trade names of major suppliers of the process, so people sometimes refer to it as "Alodining" or "Iriditing". "Chem film" is another term for the process, used mostly in the USA.
Q. We have over 40,000 aluminum parts 2" diam. by 2" lg that will need to be Iridited. Is Iriditing something we can do if we buy the necessary chemicals? What are the short comings to doing this job ourselves? The prices we have got for Iriditing seem high to us. Can you give us any advice?
Fred Pfirrmann- Glendale, Ohio
A. You probably do not want to do this in house.
Iridite has chrome in it and thus is hazardous waste.
Also, you would need many more tanks than just the Iridite. You would need pretreat cleaning & rinse tanks.
David A. Kraft- Long Island City, New York
A. Doing an adequate job is not difficult if you follow the instructions. Waste treatment is the problem. There is considerable expense and a lot of paperwork that goes with it, not to mention having to go to school regularly for haz waste handling and shipment of haz materials (about $2000).
While not closed loop, it can be contained and treated, and shipped off twice a year, negating the expense of testing every time you go to sewer.
To do this, spend the money up front and put 4 rinse tanks back of each process tank and counter flow them with a bucket.
Initial cleaner requires heat, quite a bit. Costs more initially, but heater lasts a lot longer if you go with a derated heater. A double derated is better, but might not be worth the extra cost as well as it takes up twice as much space.
Iridite tank will require a tiny amount of heat in the winter. Final rinse tank will work better with a small amount of heat.
Big cost--hoods and exhaust system--Probably a scrubber in some locations.
15 years ago there were 20 to 30 shops around here that did Iridite type process. Now there are 4. That says a lot.
James Watts- Navarre, Florida
"The Surface
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby
on
AbeBooks
or
eBay
or
Amazon
(affil links)
A. The training and waste treatment requirements of the Iridite process usually make it not cost-effective to do it yourself. One way to cut down on the cost of having a job shop do the coating is to have it processed in bulk rather than on a rack. This lowers the cost dramatically and provides an almost identical quality level. We specialize in such bulk processing, please contact us at aanodizing@aol.com
Jim GorsichCompton, California, USA