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topic 12510



Need information about DROP test of chromate conversion coating to validate the existence of coating on a part. One of the specification says DROP TEST MAY BE CONDUCTED USING ARP 70A and 70B per instruction of Macdermid Bulletin ARP 70.

Quamrul Mazumder
Honeywell - Tulsa, Oklahoma


Golly gee whiz, the finest source for that information, to insure that it is correct, would be Macdermid. They have a tech service dept. that can provide that info quite rapidly.

James Watts
- Navarre, Florida


The "ARP" sounds like an "Aerospace Recommended Practice" available from the Society of Automotive Engineers (SAE). Check their website.

Doug Hahn
Performance Review Institute - Mason, Ohio


Didn't anyone else read The World According to Garp?! ARP is EXACTLY what Garp was saying.

pooky tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania


Macdermid is the best source for the final word, so I will defer to them...but I think it is a common misconception that ARP 70 checks for chromate...rather the chemical reacts to aluminum instead. So, if the chemical reacts and turns blue, it means that aluminum is present. The thicker the protective coating, the longer it takes to turn blue. ARP 70 has nothing to do with chromate, it is just a handy way to determine if your aluminum is coated. Beware of assuming what the coating is!

Jeff Beseth
Electronics manufacturer - Olathe, Kansas

March 3, 2011

I could not find the reference to APR 70, but did find ASTM B449-93 [link by ed. to spec at TechStreet], Standard Specification for Chromates on Aluminum and ISO 10546 (don't have title, but should be similar).

Appendix IX does detail tests to detect presence of chromate and details tests to filter out other potential metals (verify chromate is in the coating and nothing else). FYI - You'll have to pay to see this standard through ASTM or ask if your employer has a subscription.

Jon Lazarus
- Salem, Oregon

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