Zinc Plating vs. Zinc Flake Dip-Spin Coating

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,

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,

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!

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,

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,

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,

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

Regards,

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,

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!

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,

 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