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Dacromet 500LC (A) vs. yellow chromatised (8) fasteners?

Hi , I have been searching the web for quite some time now , but don't seem to be able to choose the best option , I just don't have enough knowledge in this matter. Hoping that any of you can help me , I have the following issue at hand.

I need to connect an 8/10 steel item onto a cast iron item , previously I used class 8 yellow chromatised fasteners for this , and these have been working just fine.

Now I was advised to better use Dacromet fasteners. Gathering info , I do read many times that Dacromet is a really nice treatment. But I can't find a 1-on-1 comparison anywhere...so I am having doubts.

It is of the utmost importance that the fasteners are highly corrosion-proof , can stand operational temperatures of 300 °C , and can also stand an animal-stable well (corrosion-wise). The yellow-chromatised fasteners perform just fine in this situation.

Can anybody tell me if the Dacromet 500LC (grade A) will do just as well , or even better ? I hope so , because I am totally not sure at this moment :-)

Thanks for reading!

Marion de Graaf
buyer - The Netherlands
August 28, 2008

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Hi, Marion. Dacromet is a trade name, so let's talk about "dip-spin coatings" rather than a particular proprietary product. Dip-spin coatings are zinc-rich paint, sometimes water-soluble paint. An advantage over plating is that the painting does not cause hydrogen embrittlement (although the pretreatment process still could). These are widely used in the automotive industry, where they are highly satisfactory, but you should inquire of the supplier whether 300 °C is okay. Other ways of applying functional zinc coatings besides dip-spin and electroplating, include mechanical plating (Plating Systems and Technologies [a finishing.com supporting advertiser] can give you full details about that), thermal diffusion coatings and galvanizing.

Of all of these coatings, however, I believe that you will find zinc plating plus yellow chromating the most economical. And since you have clearly stated twice that the zinc plated fasteners have proved highly satisfactory, I don't see much reason to experiment with more costly alternatives in this particular case. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 29, 2008

adv.: Dip-spin Coating Services