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topic 38226

DACROMET vs. Zinc Plating



A discussion started in 2005 & continuing through 2017

(2005)

Q. How exactly does DACROMET 320 compare to Zinc Plating per ASTM B633 [link by ed. to spec at TechStreet] -85 spec, FE/ZN 5 with yellow chromate conversion coating?

Jonathan Pryor
R&D - Gainesville, Georgia, USA


(2005)

A. Hello, Jonathan. Dacromet is one of many brand names for zinc-rich dip-spin coating systems. From a corrosion resistance viewpoint, dip-spin coatings are usually superior to zinc electroplating, primarily because they are thicker (especially in your case where you are spec'ing a 5 µm plating, whereas up to 25 µ is covered by that spec). If the component in question is high strength steel, another factor is that here is also no hydrogen embrittlement in the coating system per se (although pretreatment electrocleaners and acid dips can introduce it).

On the other hand, dip-spin coatings are more expensive, thicker (which could be an issue on tiny precision parts), probably not as aesthetically pleasing, and can only be applied to parts of certain shapes (for example, large sheets can't be dip-spun).

Please try to post your situation so we can make the responses less abstract for you. Thanks!

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


January 20, 2011

Q. As a follow-up question to Dacromet vs. Yellow Zinc Dichromate:
What are the advantages / disadvantages that should be considered when considering changing from yellow zinc to Dacromet. As an agricultural equipment supplier we have been considering the Dacromet plating as a cost savings (specifically with contact washers - belleville washers).

P. Yucuski
- Chicago, Illinois, USA

Zinc Plating
by Geduld

January 21, 2011

A. Hi, P.

Dacromet is a proprietary zinc-rich water-based paint system, including a chromate top coat, applied by dip-spin coating. "Yellow zinc dichromate" would be zinc electroplating followed by a chromate conversion coating of a yellow color.

I'm very surprised that you are finding Dacromet to be less expensive than zinc plating because I've only heard to the contrary. But you haven't given us a thickness spec. yet, and perhaps you are specifying a thickness that is too high (say over about .0007") for economical electroplating?

For a belleville washer my concern would probably be whether paints can adhere sufficiently for the actual duty cycle. Such washers on a rarely flexing part, or used just for a static preload, sound like they would be ideal, whereas a stack of Dacromet belleville washers used as a jackhammer spring might be less so, although dip-spin coatings are in fact applied to some automobile springs and suspension components.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


October 16, 2013

Q. We are going to supply a kind of outdoor elevator component with Dacromet treatment to our client. Would you please provide the technical details of how it works?

Wang Feng
machinery - Zhangjiagang, Jiangsu, China


October 17, 2013

A. Hi Wang. Dacromet is one of several brand names of zinc-rich dip-spin coatings. The way it is applied is by dipping followed by centrifuging to fling off the excess, and curing, and a post-treatment. The way it functions is that it contains zinc (some types additionally contain aluminum), which protects the steel components galvanically.

For detailed information, inquire of the manufacturer, Metal Coatings International, for this particular brand, or of other manufacturers for other brands of dip-spin coatings. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Silver Delta Seal vs. Zinc Plating

June 2, 2009

Q. What is the difference between Delta Seal (Delta Tone) and zinc plating? Will they both provide corrosion resistance? And to what level? I am looking to replace a Delta Seal screw on a pump with a zinc plated one. Thank you in advance for your input.

Brandt Willingham
Pump Engineer - Fresno, California, USA


June 2009

A. Hi, Brandt. Delta Seal / Delta Tone is not a name for a generic process, but rather a trade name of, I believe, Doerken, for a zinc-rich dip-spin coating. Generally, dip-spin coatings are thicker than electroplated zinc coatings, and therefore they are more corrosion resistant. If the screw is very high strength steel, electroplating may introduce hydrogen embrittlement whereas the dip-spin coating per se will not.

But there are any number of ways to apply zinc to a surface, including hot-dip galvanizing, thermal diffusion, mechanical plating, flame spray, zinc phosphating, zinc-rich spray paints, etc. It is also possible to electroplate zinc alloys in lieu of plain zinc. It is hard to make an exact suggestion when we don't know your motivation for seeking a replacement nor its required properties, but zinc plating is surely the most common coating for screws and the least expensive corrosion resistant finish. Get back to us with more detail if you can.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Electrical conductivity of zinc flake coating?

November 24, 2013

Q. How about the electrical conductivity of zinc flake coating, ISO 10683 [link by ed. to spec at TechStreet] ? Has anyone done comparison test between electroplating and zinc flake coating from the electrical conductivity standpoint? And how about mechanical plating, ISO 12683 [link by ed. to spec at TechStreet]? Which one is best, better or bad. Thank you for your attention!thanks a million!

Li Ya Nan
- Tianjin, China



Brake calipers for a boat trailer: stainless vs. dip-spin coated

January 24, 2015

Q. I am considering installing disc brakes on a boat trailer and would like to know if Dacromet coated calipers would be as good as stainless steel calipers in a salt water environment.

bruce paddon
- Vancouver B.C. Canada


January 2015

A. Hi Bruce. They might be good enough, but they're not as good :-)

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Coefficient of friction for zinc plated vs. zinc dip-spin parts

December 30, 2015

Q. I am looking for difference in coefficient of friction between zinc plated parts and zinc coated parts. Consider same zinc thickness.

Another one, what is the difference between zinc coating and zinc flake coating?

Please provide information in this regard.

Kishanlal Agrawalla
- Angul, Odisha



March 22, 2016

Q. Is it possible for someone to give me the formula of zinc flake coating? Thank you.

Erika Suarez
- Bogota, Colombia


March 2016

ASM Metal Handbook
9th Edition, Vol. 5

Surface Cleaning, Finishing & Coating

A. Hi Erika. ASM Metals Handbook volume 5 =>
has a brief but good treatment of the subject of generic zinc-rich coatings, both organic and inorganic. And you can probably find some info in patent applications.

But the most successful coatings are proprietary and the result of significant development efforts by a number of companies in that field. If you do not want to license the coating from any of them, but to develop your own competitive offering, that is fine, but nobody can help you short-circuit the development work. We must be very careful that we don't assist in crowd sourcing the theft of industrial secrets on this somewhat anonymous site so, although we can post references to published works if anyone helps you, we can't just print formulas. Good luck!

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



Do zinc flake coatings hold up against Nitrogen?

April 1, 2016

Q. I sell a Dacromet coated roller chain to farmers with great success around Wheel lines, etc.
A customer is asking how it performs around nitrogen fertilizers? He currently uses stainless chains, as in the past steel chain does not perform well.
Your input appreciated.

Prior Quigley
- Saint George, Utah



October 17, 2017

Q. Hello,

I would like to gather ideas, and solution to the following concern: ZnNi/ZnCr3 vs. organo-metallic coating.

We have several problems every year with our coating suppliers. Our product is mainly a tube closed at one end and screws.

Beside price and time, necessary to get a fair enough result: 120 hr to Zn white 480 hr red rust corrosion. We have rust problems inside the tube, need of protective oil after treatment/prior to shipment, protective bags/VCI papers, etc.

I heard something about organometallic coating. Is this in automotive good? Will this kind of treatment meet requirement, legislations, ISOs, etc.? Also are there companies around that do this kind of treatment or is something outdated/new?

Please fill me in this topic.

Thank you!

Dipl. Eng. Szilárd Antal
STABILUS R&D Department - Brasov, Romania


October 18, 2017

A. Hello Szilárd,

Many automotive standards request zinc flake as coating. You must talk to some vendors (there are many approved by automotive terminals) for an adequate product for your use.

If the tube is closed in one side, you could have some trouble leveling thickness near the closed side in the inside, but I think you can find a process that can work.

Best of lucks!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina



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