Galvanized vs Cadmium Zinc Plating 4

[TravisMack]

Is there a significant difference between Galvanizing and Cad Zinc plating? We have an installation where the contractor did Cad plated rod and other trades did galvanized. The owner's rep is inquiring if there is a reduced life for Cad Plated vs Galv.

This is way out of my realm, but I am just trying to help them out with locating information.

Scott - this job is in Phx.

T

 

[cdafd]

http://www.burbankplating.com/salt.php#middle

http://www.burbankplating.com/faq.php

 

[stookeyfpe]

When I previously regulated the metal plating industry, I wsa afforded the opportunity to learn some basic metallurgy and why certain components are plated with metals. For all thread rod and many threaded fasteners, cadmium is used because it is a soft metal and limits the threat of the threads galling when the hangers are screwed onto the ATR. Cadmium also offers corrosion resistance, as well as galvanizing.

I would say its a non issue, especially if the ATR is being installed in a corrosive atmosphere.

 

[TravisMack]

Stookey-

Thanks for the help. I would give you more MVP stars if I could!!!

Travis

 

[kenvlach]

Some elaboration on the plated threads issue mentioned by stookeyfpe. Cadmium's advantage over zinc is in moist or corrosive conditions. The corrosion of zinc-plated threads creates such a volume of zinc hydroxide that the fastener is effectively cemented in place that the steel bolt (capscrew) may snap when trying to unscrew. The same thing happens with a steel bolt in aluminum -- aluminum corrosion seizes the bolt so tightly that it will break when trying to undo. Cadmium's corrosion product is weak & doesn't cause problem --that is the main reason it is used on critical aircraft applications.

Having said all that, note that hot-dip galvanizing may outlast cadmium plating simply because the galvanizing may be 3-8 times thicker. In the links given by cdafd, the comparison is with electroplated zinc -- typically much thinner than galvanized. In Phoenix, galvanized life indoors may be 300 years vs. 50 for cadmium.

But, the major problem with cadmium is toxicity -- it is already banned from automobiles, electronics & government proects (except for a few critical exclusions, mostly on aircraft). Any employee handling camium plated parts must wear gloves (which should be kept segregated), and you must avoid creating vapor or dust (no welding or brazing, limited soldering, no abrasive blasting, limited machining, etc.). So, EPA, OSHA, European Union, China, California, etc. have restrictions.