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What causes the formation of particles underneath the e-coat

adv.   

A discussion started in 2008 and continuing through 2017 . . .

August 19, 2008

Q. We have been sending tubular mild steel that has been welded together for some time now and we have a constant problem of receiving it back with a number of the units having splotchy particle marks beneath the e-coat. They are very small little bumps that give the appearance of air bubbles. They can cover the entire unit, not just around welded joints where splatter may have occurred or oil dried from the metal. The coater says it is oxidation or rust formation and that anything beneath the surface of the e-coat indicates there was a problem with the incoming materials, not an e-coating problem. We have tried using a rust inhibitor and there was no improvement or maybe even worse.

Anybody got any answers ?

Howard Neal
supplier - Warrenton, Georgia, USA


simultaneous September 6, 2008

A. Howard:

For anyone to answer that it will be necessary to confirm that when you ship the product the finish is perfect but after some time the patches appear and the customer sends them back to you.

The above is completely different from the situation that the patches exist immediately after the coating process.




September 7, 2008

A. Particles in an e-coat are usually due to poor filtration of the e-coat liquid. However, if you have gas bubbles trapped under the coating, this could be due to using to higher voltage and inadequate solution movement in the coating process. Blistering can also occur when the part is baked too quickly or at too higher temperature. I would suggest you talk with your supplier about it.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK



July 31, 2012

Q. I am facing burrs / particles been sticking on the surface after CED coating.
How to solve this problem? I keep the environment clean, but have this problem happen.

ALFRED SIM
engineering - Malaysia


October 2, 2012

Q. Dear sir,
Recently I face an "edges" problem after CED coating.
The edge appears somewhat uneven surface / scaling / burr .
Already nearly 1 month I try to solve it but no success.
I really feel down and really have no idea to solve it.
I hope sir that can do me a favor help me how to fix it. Thanks

Alfred Sim [returning]
plating shop employee - Penang, Malaysia


October 14, 2012

Q. Dear Sir,

I had face edges problem after CED coating.
The edges appear some kind like scaling/burr/uneven surface.
This problem already make me struggling one and half month.
And I no have an idea to solve it.
Hopefully can get the answer or feedback from all CED coating professionals.
Thanks.

Alfred Sim [returning]
plating shop employee - Penang, Malaysia


November 29, 2012

Q. How to solve the edges problem after CED coating?
I had faced the edge problem during CED coating.
The edge of frame coating appears uneven, or small burr/scaling appear on the edge.
Kindly the CED expert can help me settle this problem. Thanks.

Alfred Sim [returning]
engineering & supplies - Penang, Malaysia


December 28, 2012

A. Dear Alfred,

Maybe your operating voltage is too high or phosphating is too thick. Try working with both these parameters one at a time and see which works.

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

saify logo


January 1, 2013

Q. My existing voltage is 85 volts and 2 minutes for coating...
so I need to reduce to how many volts?

Alfred Sim [returning]
- Penang, Malaysia


January 4, 2013

A. 85 volts is not high in my experience; however you might want to increase time up to 3 minutes with the same voltage and check for results.

Are you sure your phosphating is done really well, no rough grains, no sludge sticking to the edges, phosphating solution filtered crystal clean, fresh activation bath every second or third day?

khozema vahanwala Khozem Vahaanwala
Saify Ind 
Bangalore, Karnataka, India


January 4, 2013

Q. Sir, may I know what you mean phosphating high?
Does CED coating have phosphate?

Alfred Sim [returning]
- Penang, Malaysia


January 1, 2013

A. Hi Alfred. Sorry that there seems to be a bit of a language problem, but nobody used the term "phosphating high".

What are you doing for pretreatment, i.e., what do you do to the parts before they enter the CED tank? I think you need to spend some time describing what you are doing, perhaps send photographs, because 3-1/2 months later we still don't understand your question :-(

Regards,

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


January 4, 2013

Q. Sir, see the arrow pointed area.

49724

Alfred Sim [returning]
- Penang, Malaysia


January 28, 2013

A. Hi Alfred. I think you are repeating the question but giving us little data to try to help you. After seven postings we don't even know whether the article is made of steel or aluminum (or something else).

Maybe you feel that this problem has just one possible cause and that by describing one incidence of it we should lead you to that single cause, but it usually doesn't work that way. Every cough is not lung cancer, every belly ache is not appendicitis, and there is more than one possible cause for roughness along an edge.

We don't know whether you chromate it or phosphate it, or something else.
We don't know if this happens on every part, or just on one part out of a hundred.
We don't know if it's a new problem and you used to successfully e-coat, or you have never achieved success yet.
We don't know if this happens on top edges, bottom edges, or vertical edges, or everywhere on the part; and we don't know if it happens on the topmost row of parts on the rack or the bottommost, or everywhere.
Are you sure that there are no burrs until the moment the parts enters the e-coat tank?

Good luck.

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


January 30, 2013

Q. Sorry if my language is poor.
Our part material is stainless steel; we have several models of stainless steel parts. Thickness is between 0.1 mm to 0.15 mm. 1 strip has 4 pieces. This edge problem already appears since august 2012, before that there is no such edges problem. Usually we're hanging the part vertically, one time hanging about 42 strips, 2 strips in 1 row. And normally, the edges problem occurs at upper and lower sides, and it happened edge problem all jigs or 80% of the jig. There confirmed is not a burr.
Last, not all model have this happen, but existing 2 models have this problem.

Alfred Sim [returning]
- Penang, Malaysia


A. Hi again, Alfred. If some models come out fine, it sounds very unlikely that there is a chemistry problem in your CED tank, assuming those other parts are stainless steel as well. I suspect that the other models which coat properly do not have quite the same sharp edge. Even the vertical edge of this part may be different if it doesn't have the problem. Unfortunately, we're not helping you much.

What process do you do immediately before electrocoating? Is it zinc phosphatization? Phosphating of stainless steel is problematic. I would suggest you try blasting a couple of samples before CED coating and tell us what happens at the edge in this case. Good luck.

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



E coating part edge corrosion

January 16, 2017

Q. Hello, I am currently trying to qualify a part that requires e-coating. Two rounds of samples have failed our hydrochloric acid test due to significant corrosion and flaking had happened at the edge - substrate is zinc alloy.

My engineering and I am leaning towards to believe that the edge did not get enough coating due to it is fairly sharp - our print does not allow radius but can accept to a degree.

I am wondering what solutions are out there to solve this problem? Add small radius to the edge or if there are things that can be controlled during the e coating process without modifying the tools.

Thanks!
Jade

Jade Goard
- Milwaukee, Wisconsin
  ^- Privately contact this inquirer -^


January 2017

A. Hi Jade. I don't think there is any additive coating process which does not benefit from a bit of radius. A sharp corner is a knife edge trying to slice through or at least slice into the coating as it cures.

You say the substrate is zinc alloy. Is it a diecasting, yet has a sharp corner?

Regards,

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


January 17, 2017

Q. Hi Ted, thanks for your reply. Yes it is zinc die casting part. The vendor I am qualifying is the 2nd source and when I compared their sample to the existing part the difference is very obvious. It felt quite rough.

Jade Goard [returning]
- Milwaukee, Wisconsin


January 2017

A. Hi again. I believe it's conventional to mass finish die castings (vibratory tub, for example) before coating, which should remove the roughness and relieve any sharp corner.

Regards,

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

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