Zinc Yellow Chromate or Zinc Cobalt coating on hardware? 1

[jonesy01]

I am not familiar with these coatings but I am working with hardware that may require it according to the customer.

Hardware:
NUT, HEX, M20 X 2.5 THREAD, A194 2H
WASHER,LOCK,1/2,F436 TYPE 3
BOLT,HEX,1/2-13NC X 2 1/2, A320 GRADE L7

-What's the purpose of this coating?
-Which one should be applied?
-Difference b/w the two?

Any help or reference material is much appreciated.

 

[TVP]

A194 2H means ASTM A 194 Grade 2H
F436 TYPE 3 means ASTM F 436 Type 3
A320 GRADE L7 means ASTM A 320 Grade L7

ASTM standards can be downloaded from ASTM International (

http://www.astminternational.org).

Regarding the purpose of the coatings, it is to provide corrosion protection on steel fasteners that are not inherently resistant to corrosion. The decision on which coating to use depends on all of the usual factors, such as end use requirements, cost, availability, etc. Zinc plating is less expensive than zinc alloy plating (zinc-cobalt is an alloy), but zinc is less corrosion resistant than zinc-cobalt. Corrosion resistance of zinc plating + yellow chromate can be improved by using topcoats and sealers, perhaps even to achieve similar performance to zinc-cobalt at lower cost, so you may want to consider this as well. The following links provide more background on zinc and zinc alloy plating:

http://www.pfonline.com/articles/pfd0019.html

http://www.pfonline.com/articles/039902.html

http://www.pfonline.com/articles/pfd0313.html

http://www.pfonline.com/articles/020102.html

http://macdermid.com/industrial/pdf/SAEreport.PDF

http://www.hazmat-alternatives.com/...r_Enthone - Hex-Cr Free Zn and Zn alloy T.PDF

 

[jonesy01]

Thanks for the info.........very helpful

 

[IceStationZebra]

Be aware that some coatings are being discontinued for use in Europe. Off the top of my head I believe it is the chromate, but do some research if need be.

ISZ