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topic 32574

Misc. problems in CED (cathodic electrodeposition) coating

This thread covers many CED problems, but --

• Pinhole problems have been moved to Topic 57561

Current questions, newest first:

March 6, 2021

Q. We are facing problem of shade variation in electrocolour (black colour). A little brownish colour obtained in every lot at same place (bottom side of bath) every time. what are possible reasons and solutions?

sandesh Raj
- aurangabad maharashtra india
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adv.   coatec india banner

April 11, 2021

Dear sandesh
check DFT on both surface. Brownish shade will give less DFT.
Shade variation depends on:
1. Non volAtile material concentration. add Resin & pigment as per ratio. Ask supplier for ratio.
2. Set Voltage- Increase voltage & observe current.
3. Number of Parts loading, shape & loading position - change loading position ,if more parts loaded then Decrease parts quantity.
4. Number of anode working. Confirm anolyte circulation.
5. Ensure properly burned jigs used for good contact.

vishal ghawate
- Pune ,India
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March 5, 2021

Q. Hello I am Amar I am currently doing Cathodic electro coating (Ecoat)
Clear and Coloured one for jewelry and other mid sized items but the issue is I am getting wire marks on the product which seems to get rejected by the customer even though it's a small line
Currently using 0.3mm wire with typical coating spec 30 V 60 SEC 150 ° oven (have change a few specs but no positive so far) . Would really appreciate some advice on how to not get the mark.
Thank you

Amar joshi
- Noida India
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December 28, 2020

Q. Dear Sir

We are having a problem with CED coating. Our coating supplier always said the problem is coming from the material. However, it is not happening for 1 type of material but it happened in different material such as S55C and SPFH. We also unable to identify the actual defect on this CED coating. I am involving in metal stamping for automotive part. Hopefully, any expert in this finishing industry can help me to solve this problem. This defect really affects my production productivity.

32574-8a   32574-8b

32574-8d   32574-8c


Sulaini A. Rahman
- Selangor, Malaysia
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March 5, 2021

A. Is this defect seen right after coating or after baking?
It might be due to temperature if it's after baking.

Amar Joshi
- noida india
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Previous closely related Q&A's, oldest first:


Q. I am getting the problem of half-coating and no-coating in CED. Defect rate is low. I have checked the contact points and there seems no problem with that. Defect rate might be around 1 in 100.

Madhukesh Jamadagni
painting shop - Mysore, Karnataka, India
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A. Check CED bath parameters. Check for bath and anolyte conductivity.

Manish Dhyani
- New Delhi
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Q. Please send me the information of the defects of CED COATING, and provide the answers for the questions relating to the topic. I will be grateful to you.

- Faridabad, Haryana, India
^- Reply to this post -^

affil. link
Electrocoating: a Guidebook for Finishers
by Electrocoat Association
from Abe Books

affil. link
"Handbook of Electropainting Technology"
by W. Machu
from Abe Books

A. Hi cousin Manmohan. If you are having a specific problem or problems, please try to detail your situation. We have numerous Q&A's about CED in this forum and I am confident that someone here can help you. Regarding the general issue of possible defects and solutions, at least two full books have been written on electrocoating, and we can suggest that you try to get access to one or both of these =>

Luck and Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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Dirt in Coating


Q. We are facing dirt/impurities problem on parts after CED coating.

Kalidas Suryawanshi
- Pune, India
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? Hello, cousin Kalidas. if you can give us some info, I think our readers can help! Send some pictures, and tell us what you can. If you lack sufficient data, the paint vendor, system vendor, or an e-coating consultant may be able to help. Good luck!

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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A. Dirt can come due to improper cleaning in the pre treatment line. It can be due to dirt in the E-coat tank. It could be due to dirt in the rinse tanks after E-coat. It could be due to dirt being blown around in the oven with the forced circulation. It could be because of one or more than one of the reasons above. And the reasons above could also be due to improper housekeeping or ingress of dirt and dust in your E-coat shop.

Test each and eliminate. I assure you this does not require NASA technology.

Gurvin Singh
Coatec India
supporting advertiser
Mohali, Punjab, India
coatec india
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January 14, 2018

A. Check for sludge material in phosphate bath ... if it is high, then desludge it immediately. This will solve your problem.

Baljeet Singh
- Ludhiana, punjab, India
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Ra value of CED coating

May 20, 2009


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June 2, 2009

A. Ra is checked by roughness gauge.
Better you ask your paint supplier for Ra Parameters.


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July 23, 2009

A. Hi,

Normally Ra value can be checked with use of Perthometer. try it.


V. Anandaraj
- Chennai, India
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Dissolution of CED Coating

April 11, 2014

Q. Hello, could anybody help me understanding the reason for dissolution after CED coating on wheels? It mainly happens with small wheels.

ale luso
wheels - Bologna, italy
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April 2014

A. Hi Ale. Sorry, but I don't understand what you mean by dissolution after CED coating. Where, when, and under what conditions is this happening? Can you offer a synonym or expand upon your situation, please. Thanks.


Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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April 15, 2014

Q. Hello, I'm sorry, pictures were missing. We produce steel rims and it happens that a few rims (1 to 10% depending on the reference) leave the CED coating bath only half coated; more precisely only the first half on the rim is coated.

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I've attached an explicative picture. Which parameters could cause it in your opinion?
Kind regards,

ale luso [returning]
- Bologna, italy
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May 12, 2014

A. Sir,
It might be helpful to
- increase bath & anolyte conductivity,
- change the loading position.


Sp singh
- Faridabad,india
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Not getting e-coating despite proper voltage

September 25, 2014


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September 30, 2014

A. Hi,

I'm assuming that that you are using a cataphoretic resin. If it is anaphoretic then the advice still stands but swap the words "anode" and "cathode",

Your problem maybe caused by the anodes restricting the current flow. So, when you put large areas of work in the bath the cathode current density is too low to initiate deposition of resin. Suggest:

1) Increase the number of anodes
2) If you are using anode boxes make sure that that they are filled with electrolyte of the recommended conductivity.

Harry Parkes
- Birmingham, UK
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October 26, 2014

A. Increase anode area
Increase voltage
Increase solid in bath
Increase bath temperature
That is it.

Dr Halim Polat
- istanbul Turkey
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November 17, 2014

A. Reasons for poor CED coating:

1. Poor electrical contact to the job to be coated.
2. Low cathode-anode ratio. This will be considered in plant design itself. But this may vary if the anode gets corroded; in case of CED, check the anode condition.
3. If ramp up voltage is too high, some parts may get poor coating.

Since amps is showing very low, it means the rectifier to be checked.

Selvakumar.S, chennai
- chennai, Tamilnadu, India
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Finish coat cracked due to inferior E-coat under it?

January 21, 2015

Q. Working with a shop on a repair that used an aftermarket bumper cover (non steel) and when the finish coat was applied it cracked all over as it started to cure.

32574-4 32574-4t

Shop says it's inferior E-coat used by the aftermarket supplier. Your thoughts?

Phil W [last name deleted for privacy by Editor]
insurance claims - Houston, Texas, USA
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January 2015

A. Hi Phil. I would not expect a body shop to be a coatings science laboratory, fully instrumented, and able to analyze precisely why an aftermarket bumper cover was unpaintable. But I would certainly trust a body shop -- people who paint cars day in & day out -- to be able to reliably paint proper substrates, and to 'fess up if they made a mistake. Thanks for the photo, but it will surprise me if anyone is able to look at it and contradict the body shop's assertion that the bumper guard is defective (although yes, after significant testing, a coatings science laboratory might well be able to).

opinion!Why does the body shop feel it's your problem unless you told them to use aftermarket parts? If you did tell them to do so, it's on you to prove that the parts were paintable and the shop screwed it up.

All costs associated with the quality issues of inferior aftermarket parts should be 110% the responsibility of the insurance company if they specified them. Neither body shops nor insurance companies should be allowed to substitute parts which are inferior to OEM parts, and initial problems like this are just the tip of the iceberg of long-term problems the insured consumer is stuck with. Consumer Reports has written repeatedly about this problem of manifestly inferior replacement parts being specified by insurance companies, but apparently with the government not watching them, that's what they do. Good luck.


Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

February 17, 2015

Q. We are getting water spots and water or paint flow marks on the components after curing. We could identify the marks if we blow air after UF and before curing. How to eliminate these marks?

CED COATING UNIT - Hosur, Tamilnadu, India
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CED Painting Defect: 'Partial Coagulation'

August 1, 2015

Q. Please tell me about the CED painting defect of "partial coagulation" on child bicycle parts like swing arm, center stand and prop stand.

prince Kumar
- gurgaon, haryana, India
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Anodic to cathodic cell ratio in CED electrocoating

December 16, 2015

Q. Hi sir I want to know how much ratio in anodic and cathodic cell in CED bath

Sandeep kalidas raut
CED coating - Mumbai,Maharashtra, India
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March 16, 2016

Q. How to calculate the anode cell ratio in CED? Please, I am preparing for an interview and I need a clear answer.

BALA mani
private automobile company - chennai, tamil nadu, india
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CED Bath: Why/How has Sodium Increased with no other changes?

March 31, 2016

Q. Hello sir,
There is increase in the sodium content in the CED bath while all parameters of the bath are as per specification. Please suggest.

kalyani Argade
- Pune, Maharashtra India
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simultaneous April 13, 2016

A. Na content increases due to carryover of alkaline cleaners from P.T. line. Rinse parts thoroughly.
Have you added any tubular part recently in your production?
If so, check the carry over.

Avinash Vidhate
- Nasik, Maharashtra, India
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April 12, 2016

A. An increase in the sodium level can be due to drag out from your alkaline cleaner. Are you using a sodium hydroxide based cleaner?

Dan Mack
- Horicon, Wisconsin USA
^- Reply to this post -^

June 27, 2016

Q. Hi
What is maximum oven temperature for CED jobs?
Can we put CED & Power Coated jobs into one batch for Curing the coatings?

Please give details.
Thanks & Regards

Vivek Nirgudkar
powder coating & CED coatings - Pune, Maharastra, India
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July 7, 2016

A. Generally CED Paint cures at 150 °C / 20 minutes or 160 °C / 10 minutes Effective Metal Temperature. Oven Air temperature can be set depending on the Material thickness (Component) and time available for Oven curing.

If it is thin material may be 170 °C, 30-40 minutes more than sufficient to cure. In case of thick material like Forging or Casting we may go ahead up to 200 - 220 °C.

Logically we can bake both Powder and E.Coat in the same oven and there will be not any issue in the baking as long as if we meet the baking window criteria.

However E.Coating is a 'wet' process and it is cured in an oven to promote cross-linking. Solvent and Moisture evaporation takes place. Whereas in Powder, Curing causes the particles to melt and also serves as the catalyst for a chemical reaction that produces the desired finish. Both are different process.

During the Hot air circulation sometime loose powder particles deposits on the E.Coat surface before curing causes finish problem. Hence I would not advise Technically. Let us wait for some expert comment please.

Saravanan P.M
- Chennai, Tamilnadu, India
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July 2016

thumbs up signHi. That sounded like "expert comment" to me. Thanks!


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
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March 24, 2017

Q. How can we control roughness after CED coating? It is varying a lot. I want to maintain it to its standard.

monu mittal
- gurgaon, haryana, india
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June 14, 2017


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Anode Cell Area Calculation

October 7, 2017

Q. Can anyone please help me how to calculate the Anode cell area/ no. of Anode cells required in ED Coating process according to Area of Component or Tank size?

Also how to select the range of Rectifier?

Arunprabhu A R
Designer - India
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November 27, 2017

Q. Can anyone please help me how to calculate the Anode cell area/ no. of Anode cells required in ED Coating process according to Area of Component or Tank size? How do we know what is the capacity of anode in relation to surface area? How much surface area is covered by one anode?

We manufacture wheel rims; when we hang these on a basket after CED coating some area is unpainted where they are touching each other. What is the real cause of this

Rohit Kumar
- Faridabad haryana ,india
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Masking for CED Coating

January 22, 2018

Q. Hi
We'd like to mask the wheel rim knurling during CED process.
Please suggest any masking.

Felix prasad
- Chennai, India
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April 11, 2018

Q. Hi sir,
I am having one small doubt regarding dot contamination (like popping). This only comes at body c-zone area, that means nearby the anode location.

Note: our dip coating system.

Suresh Nataraj
NEROLAC - Bangalore, Karnataka & India ^- Reply to this post -^

Ed. note: Please forward a photo of the problem to for posting here.

CED coating defects

September 5, 2018

Q. Please explain the defects of CED coating.

sathish kumar
employee - india
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September 2018

A. Hi cousin Sathish. More words please -- are you asking a previous poster to clarify the defects they reported so that you can help them? If so, thanks -- attempting to teach is perhaps the fastest way to learn -- but please be more explicit about which posting you are replying to.

If you are looking for help yourself, you can read this thread, as well as threads 23154, 38297, 51966, and 57561. You can search the site using the term "CED defect" for many more threads on the topic.

You can also obtain the two books about CED coating which were suggested higher up on the page. I am not aware of training courses for this subject is India, but hopefully Coatec India [a finishing.com supporting advertiser] or a reader local to you will advise (please tell us your city because some areas of India probably aren't easily accessible to you). Best of luck, but be ready to invest at least a month of hard work in the study of CED defects :-)

Best of luck!


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
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September 8, 2018

A. Dear Sathish, There are lots of defects in CED coating, as it's a very broad area.
But I will explain some defects which are usefully common for all CED Coating lines.
1) Paint Bubbles or CED bubbles :-
First of all CED is a continuous process. It's a non stoppable process. Whenever your conveyor getting stop this paint bubbles will come. this is a wet on wet process i.e. after dipping in ED bath it have mist spray to keep it wet, but some location are not covered in line, which show the Paint Bubbles issue.

D. Sharma
Paint Technologist - Aligarh,U.P., India
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