finishing.com -- The Home Page of the Finishing Industry
no_pop_no_spam
HomeFAQsBooksHelpWantedsForum letter 24405

Serious Education ... plus the most fun you can have in metal finishing.

Galvanizing vs. Dacromet


(2003)

Q. Dear Sirs,
1. I am writing to ask you if galvanized auto parts are poisonous for either workers or people touching them? If yes, why?
2. Between galvanizing and Dacrotizing, which is more economical?
What percent in comparative choice?

Warmest regards,

Abdolhossein Abarghouei, Tool engineer
supplying auto parts - Tehran, Iran


October 20, 2009

A. Hi, Abdolhossein. Galvanized parts are certainly not poisonous. Feed bins and watering troughs for farm animals have been made of galvanized metal for decades. Similarly galvanized roofs have long been used to collect rainwater for drinking where water supplies are limited. Although it's not considered best practice today, domestic water pipes were galvanized steel in some areas.

1. Galvanized coatings are basically zinc, which is an essential nutrient, not a toxin. However, galvanized coatings sometimes contain a small amount of lead, and galvanized components sometimes receive a final chromium quench which has some small amount of hexavalent chromium in it, and those are toxic materials.

2. The thicker the layer of deposited zinc, usually the more costly, and the more corrosion resistant. In general it proves most economical to apply thin layers of zinc by electroplating, mid thickness layers by dip-spin zinc flake coatings (Dacromet is the brand name of a proprietary coating of that nature) or mechanical plating/galvanizing, and thick layers by hot dip galvanizing. So hot dip galvanizing is substantially thicker and more corrosion resistant than dip-spin coatings. I think galvanizing more expensive but the dip-spin coatings do involve proprietary supplies, sometimes top coats, etc., so they are not cheap like zinc electroplating.

But many times the choice is not based solely on corrosion resistance and cost, but the specific needs of the component. For example thick hot-dip galvanized coatings can be a substantial problem for small and medium size fasteners because of their serious impact on thread dimensions. The fasteners may require specially cut threads, or skipping the galvanizing on the threads of nuts, etc.

Regards,

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



-- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I would like to know how the Dacronized finished steel compares to a galvanized steel in the salt environment, i.e., for deck boards along a pier or dock?

Jordan Loran
- Annapolis, Maryland


May 31, 2009

A. Hi, Jordan. I'm pretty sure you mean Dacrotized. The corrosion protection of zinc-rich coatings comes primarily from the thickness of the zinc. Hot dip galvanized zinc coatings will almost always be substantially thicker than the competing technologies, and thus more corrosion resistant.

Regards,

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


 

A. I would ask the makers of Dacral and Dacromet [Metal Coatings International].


Tom Pullizzi
Falls Township, Pennsylvania



(2005)

Q. I am a product tester for a company that makes wood products. I only test products that are non-wood though. Many of the products we receive are from overseas, and we have run across some products that are below par. For our purposes, Dacromet coating is preferred. Anyway, we have a company that suggested using galvanized metal, and spraying a "Dacromet" coating on top that they say doesn't need to be cured. Is it possible to use Dacro over galvanized metal? And if so, doesn't it have to be cured to perform correctly?

Dave Au
- Brookings, South Dakota, USA



A. Hi Dave. Yes, that does sound wrong to me. They may be talking about a solvent-based zinc-rich galvanizing touch-up paint rather than actual Dacromet.

I was about to suggest that hot-dip galvanizing by itself is the equal in corrosion resistance to any coating (75+ years proven, not conjectured life) so no worries ... but then I realized that the products they are claiming as "galvanized" may be just zinc electroplated rather than hot dip galvanized :-)

Be double careful. Good luck.

Regards,

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



October 7, 2010

Q. WHAT IS THE NATURE OF COATING IN DIP SPIN COATING PROCESS? IS IT ZINC PHOSPHATE BASE PAINT? IS IT A REPLACEMENT FOR HOT DIP GALVANISING PROCESS ZINC COATING PHYSICALLY AND QUALITY WISE?

DR.DIPANKAR SEN
RESEARCH & DEVELOPMENT- PLATING SHOP - KOLKATA, India


October 7, 2010

A. Hi, Dipankar. Dip-spin is an application method rather than a type of coating, but I do think the method is used mostly for zinc-rich (and sometimes aluminum-bearing) compounds like Magni, Dacromet, Delta-tone, etc.

There are many ways to apply zinc as a coating, including electroplating, mechanical plating, sherardizing, flame spraying, hot dip galvanizing, spraying cold galvanizing compounds from a rattle can, and applying water-based zinc-rich coatings by dip-spin. The easiest way to look at it, which is somewhat of a simplification but not too far off the mark, is "zinc is zinc", i.e., the corrosion protection will be essentially proportional to the thickness of the coating. Each coating method suits different applications and thicknesses, with zinc electroplating used for the thinnest coatings, galvanizing used for the heaviest, and the others for thicknesses in between.

Good luck.

Regards,

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

November 24, 2010

A. Dear Mr. Sen,

Cost wise zinc flake coating raw material is 15 to 20 times that of Hot Dip Zinc in India. Unless there are threaded parts we are talking about for which control on the dimensions or COF requirements compel the use of Zinc Flake - I don't see any significant improvement in corrosion resistance to merit a 20 times higher manufacturing cost.

khozema
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

saify logo


thumbs up signMy trusted colleague KV has surprised me with that cost comparison. I had been under the impression that, due to the much heavier coating thickness, galvanizing was more expensive.

Regards,

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



August 16, 2011

Q. I am looking at buying a boat trailer. One supplier is offering Dacromet Finish for the Axles and Springs. Normally this is galvanised.

Is there any benefit or weakness to the application?

Joe Whittle
private customer - Sydney, NSW, Australia

August 16, 2011

A. Hi, Joe. My personal opinion is that Dacromet can be a very good corrosion resisting finish, but is not quite the equal of hot dip galvanizing (How can we actually know since accelerated salt spray testing proves nothing for zinc-based coatings, and galvanizing can last 75+ years, whereas Dacromet hasn't been around for a fraction of that time?)

I certainly would not rule out a boat trailer with Dacromet axles and springs, but I certainly wouldn't consider it an advantage over hot-dipping. Happy boating.

Regards,

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



June 2, 2013

Q. What are the visual differences between spinal hot dip galvanizing and Dacromet coating?
Thanks.

Hossein Akbari
- Tehran, Iran


June 3, 2013

A. Hi Hossein. Sorry, I don't know what you mean or intended to say with the word "spinal". Your question may be better handled by hands-on instruction, but you can see some photos on the Dacromet website. In general, Dacromet has a "paint-like" look to the finish whereas galvanizing often has the familiar mottled "frost on a window pane" look, and looks like metal rather than paint. Good luck.

Regards,

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


June 12, 2013

Q. Hi,
I am trying to find some authoritative documentation that indicates the rust proofing qualities of Dacrotizing. Does anyone know of any environmental test reports, please?
Ideally I'd like something that makes a direct comparison between Dacrotizing and HD Galvanized.
Until I am convinced that Dactotizing is at least as good as HD [hot dip] Galvanizing I can't recommend it to my customer.
Cheers,
Ian.

Ian Matthews-Golledge
- Southampton, Hampshire, UK


June 12, 2013

A. Hi Ian. Dacromet is a proprietary product, not a generic process. Therefore, I think you should contact the manufacturer of the product for case studies, test results, white papers, etc.

I think it is an excellent product, and automobile manufacturers around the world do as well. It's widely used on underbody components I understand.

In fact, though, there is nothing that can be said with 100% surety to be "at least as good as HD galvanizing" for the simple reason that we have structures in existence that were galvanized 75+ years ago. No accelerated test is truly representative, so how can any manufacturer of any coating at all claim performance at least as good as galvanizing unless it was available and applied more than 75 years ago :-)

Regards,

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


June 14, 2013

thumbs up signThank you Ted, very wise words.
I have been in contact with NOF Metal Coatings, who have forwarded some information.
Like any coating, the suitability is dependent on the product and environment in which it is to be used. Whilst I don't doubt that it's a good product, we won't be using it on this occasion.
Regards,
Ian.

Ian Matthews-Golledge
- Southampton, Hampshire, UK

ADD a Q or A to THIS thread START a NEW THREADView This Week's HOT TOPICS

Disclaimer: It is not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & DevicesUsed & Surplus


©1995-2017 finishing.com     -    Privacy Policy
How Google uses data when you visit this site.