CORROSION PROTECTION
CORROSION PROTECTION
(OP)
Hello,
I'm looking for information about clear chromate and yellow dischromate coating. Full text about corrosion protection attached:
CORROSION PROTECTION: ZINC PLATED 0.0003 MIN THICKNESS PLUS A CLEAR CHROMATE OR YELLOW DISCHROMATE DIP WHICH MUST WITHSTAND 96 HOURS UNDER ASTM B-117 SALT SPRAY CONDITIONS WITHOUT ANY CORROSION
Any help is gratefully received.
Greg
I'm looking for information about clear chromate and yellow dischromate coating. Full text about corrosion protection attached:
CORROSION PROTECTION: ZINC PLATED 0.0003 MIN THICKNESS PLUS A CLEAR CHROMATE OR YELLOW DISCHROMATE DIP WHICH MUST WITHSTAND 96 HOURS UNDER ASTM B-117 SALT SPRAY CONDITIONS WITHOUT ANY CORROSION
Any help is gratefully received.
Greg





RE: CORROSION PROTECTION
RE: CORROSION PROTECTION
Historically, hexavalent chromate films have been used most often. The color of the hexavalent chromate starts out clear, with a blue tint (often called blue bright). As thicker films are deposited, the color changes to an iridescent yellow/gold/bronze, and then to an opaque olive green or brown. The thicker the chromate, the better the corrosion resistance, as the chromate delays the onset of white rust (corrosion of the zinc layer).
The following articles provide a great deal of information about chromate coatings:
http://www.pfonline.com/articles/pfd0020.html
http://www.pfonline.com/articles/pfd0323.html
http://www.pfonline.com/articles/020102.html
RE: CORROSION PROTECTION
*I presume thickness units are inches, so for 0.0003" use 8 microns of electroplated zinc (presumably on steel or iron).
Type II indicates colored chromate giving a corrosion resistance of 96 hrs (to white 'rust'). Best to specify yellow chromate.
Also, you must specify whether corrosion testing is to be done; it can be on actual part if reasonable geometry or on a test coupon coated at the same time. Note: ASTM B117 gives the test equipment & salt spray; B633 gives the applicable length of time.
Testing is often just done on the first lot; saves $ & time.
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RE: CORROSION PROTECTION
RE: CORROSION PROTECTION
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: CORROSION PROTECTION