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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Zinc Plating vs. Zinc Flake Dip-Spin Coating
Current question and answers:
TUTORIAL FOR NEWBIES:
For the most part, zinc and zinc-based coatings are applied to steel for sacrificial corrosion resistance (the coating not only tries to seal the iron/steel away from the environment the way paint does, but it is also anodic to the steel, so in the event of a breach in the coating, it tries to sacrifice itself to the corrosive forces instead of letting the steel rust).
There are numerous ways to apply zinc coatings to steel, from painting with zinc-rich paints, to electroplating with zinc, to mechanical plating, to thermal sprayed zinc, to diffusion coatings such as Sherardizing, to hot dip galvanizing. Although it is not 100% true or without exception, a general guideline is "zinc is zinc", with the corrosion resistance being generally proportional to the thickness of the coating.
Each method not only has minimum & maximum practical thicknesses, but economic thickness ranges as well. For example, zinc electroplating offers the thinnest coatings and lowest cost, but becomes uneconomic compared to other methods as the required thickness increases. At the other end, hot-dip galvanizing offers the thickest coatings and the most corrosion resistance but at high cost, and while the thickness can be wiped downward if necessary, that only makes sense in limited cases.
And in addition to practical and economic thickness ranges, the application methods have other advantages & disadvantages. Electroplating, for example, offers the most aesthetic finishes and close tolerances for tiny fine-thread fasteners but can cause dangerous hydrogen embrittlement in high strength components.
Another thing complicating the section of a coating method is alloying. The performance of zinc-aluminum dip-spin coatings (zinc-rich paint) is different than pure zinc; the corrosion resistance of zinc-alloy electroplatings like zinc-nickel is better than pure zinc electroplating, and hot-dip coatings of aluminum or containing aluminum are different than conventional zinc hot-dip galvanized coatings.
Q. Hello everyone,
Please give me an insight on the differences (be that functional or aesthetic) between Zn-Ni (Zinc-Nickel) and Zinc flake coatings.
I'm a bit confused.
My main concerns are not the corrosion resistance but more like the surface finish/roughness that can be achieved.
Kind regards,
Szilard
- Brasov Romania
April 13, 2021
A. Hi Szilard. Zinc flake coatings and zinc-aluminum flake coatings are essentially zinc-rich paint or zinc-aluminum rich paint, usually but not always with a topcoat of something. Being such, they may not be appropriate for extremely small fine-thread fasteners, plus the coatings are more expensive than electroplating, and they do not have the strength and adhesion of electroplated coatings, nor the aesthetic brightness. They may not be applicable to large components which don't suit the dip-spin method either.
But zinc flake coatings are very widely used for fasteners in the automotive field because they offer more corrosion resistance, generally less environmental impact, are not subject to hydrogen embrittlement. They may also be more compatible with top coatings which offer needed qualities like lubrication.
Zinc-nickel electroplating, as opposed to pure zinc plating, offers greater corrosion resistance at greater cost. The greater corrosion resistance is probably due primarily to tighter, more impervious corrosion products which slow the rate of corrosion of the coating. There are probably fasteners and small components where it is quite difficult to make a choice between zinc flake coatings and zinc-nickel electroplating.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 2021
Q. Many thanks for the insight.
In regards of surface resistance to tear/wear:
one of our application is a reciprocating, gliding of a Zn-Ni coated tube inside an ALU tube. Contact between the to: 0-ring-rubber seal ring + grease. Similar to gas struts....but no pressure inside.
Do you think that Zinc-flake coat might be damaged, or might peel off the Steel tube against the Zn-Ni coating?
Or more importantly, does the surface finish/roughness differ highly between the two, or both can be done for low roughness but maybe higher costs?
Thanks again.
- Brasov Romania
April 19, 2021
A. Hi again. I don't have actual experience in that and hope that someone who does will chime in. But my feeling is that only actual plated metal coatings, not paint-like coatings, are well suited to that purpose.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 2021
⇩ Related postings, oldest first ⇩
Q. How exactly does DACROMET 320 compare to Zinc Plating per ASTM B633-85 spec, FE/ZN 5 with yellow chromate conversion coating?
Jonathan PryorR&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, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005
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).
- Chicago, Illinois, USA
January 20, 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, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 21, 2011
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 Fengmachinery - Zhangjiagang, Jiangsu, China
October 16, 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, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 17, 2013
Silver Delta Seal vs. Zinc Plating
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 WillinghamPump Engineer - Fresno, California, USA
June 2, 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, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 2009
Electrical conductivity of zinc flake coating?
Q. How about the electrical conductivity of zinc flake coating, ISO 10683 ? Has anyone done comparison test between electroplating and zinc flake coating from the electrical conductivity standpoint? And how about mechanical plating, ISO 12683? Which one is best, better or bad. Thank you for your attention!thanks a million!
Li Ya Nan- Tianjin, China
November 24, 2013
Brake calipers for a boat trailer: stainless vs. dip-spin coated
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 24, 2015
A. Hi Bruce. They might be good enough, but they're not as good :-)
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 2015
Coefficient of friction for zinc plated vs. zinc dip-spin parts
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.
- Angul, Odisha
December 30, 2015
Q. Is it possible for someone to give me the formula of zinc flake coating? Thank you.
Erika Suarez- Bogota, Colombia
March 22, 2016
March 2016
9th Edition, Vol. 5
"Surface Cleaning, Finishing & Coating"
on AbeBooks
or eBay or
Amazon
(affil links)
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,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Do zinc flake coatings hold up against Nitrogen?
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.
- Saint George, Utah
April 1, 2016
October 17, 2017
Q. Hello,
I would like to gather ideas, and solution to the following concern: Zn-Ni/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!
STABILUS R&D Department - Brasov, Romania
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!
TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina
October 18, 2017
July 31, 2018
Q. Thank you all for all your efforts and time put to this forum.
I want to buy some brake rotors for my Jeep Wrangler, and was doing some research, as my knowledge in this particular area is practically nil.
From what I read, most good rotors are Iron casts of grade G3000, some are of grade G3500 and these claim to be of better or more premium grade. I know they are stiffer, but not sure if that is a good thing or not for Rotors.
The other main thing which I need to know is, which serves better for a Rotor, silver Zinc plated or Geomet coating, as my choices have narrowed down to choose between a G3500 zinc plated and a G3000 Geomet coated Rotors :) ?
Thanks for all your time.
Tarek
A newbie working on his Jeep and learning throughout the way.
- Dubai UAE
A. Hi Tarek. Yes G3500 is harder, and I suppose theoretically 'better' for rotors. But Geomet is more expensive and more corrosion resistant than zinc electroplating. My own experience (even as someone with some finishing experience) is that you really can't judge a product from its sales pap though. Finding out what buyers think some time down the road, perhaps combined with performance test results if published, is usually a more effective approach.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 2018
August 1, 2018
Thanks Ted,
Both manufacturers had excellent reviews.
Eventually, I closed my eyes and did an eeny, meeny, miny, moe and ended up buying the G3000 with Geomet coating.
Also down deep I was tending more towards the one I ended up buying.
I did send an inquiry email to the manufacturer before, and below was their reply:
"Yes this is the correct kit. I'm not sure what cast grade 3500 is but ours are G3000 with a high carbon content. You definitely don't want the casting too hard or there wont be adhesion for the pads. I would assume that theirs is a made up figure because to go to that grade the pads would almost need to be steel to get a decent coefficient of friction."
The brake pads offered on both Kits were carbon ceramic.
Again, thanks for your support.
Tarek
- Dubai, UAE, UAE
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