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"Reduce paint thickness in Cathodic Electrodeposition (CED) system?"

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A discussion started in 2003 but continuing through 2021


Q. Hello sirs I humbly feel that it's really a great time to interact with you wizards. In our CED process, we are encountering a major paint problem poor E'coat deposition (dipping process) defect in the sill outer panel of the car body because of "rust" in the non-coverage area of coating. This is not occurring in the sill outer panels we use which are provided with wax holes.

I'm really baffled whether the problem is with the process parameter settings or the mechanical alignment or settings. The process parameters settings we use in our CED process are :
%NVM = 18.7
pH = 5.94
P/B RATIO = 0.16-0.25
MAIN BUS = 235 V
CURRENT = INLET = 0/350 amps
MAIN = 950 amps

When we change the inlet voltage, paint defect "hash marks" start appearing in the car bodies. We are planning to increase the %NVM or the inlet voltage -- WILL IT SOLVE THE PROBLEM?
Generously give me your valuable suggestions .
Looking forward with great regards ,

C Nanda K [last name deleted for privacy by Editor]
- Chennai, India

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March 17, 2011


YASEER charolia
plating shop - MUMBAI INDIA

February 27, 2012

Q. Dear sir,
How to increase MEQ if bath pH is already lower side?

Digamber sidar
- Greater noida

March 1, 2012

Q. I am a technician at a factory in Shah Alam. I run the factory's CED process. I have a problem with the quality of the paint. Each item of the CED process is bubbled on the surface of part. Why did it happen?

Khairul Abidin Mohamed
- Shah Alam, Selangor Darul Ehsan, Malaysia

June 7, 2012

A. Check suction of circulating pumps after shutting the pumps.
See if there is any leakage.

Avinash Vidhate
- Nasik, Maharashtra, India

July 10, 2012

Q. I have been given a project to optimize the DFT of e coat. I need to know the exact chemistry behind e-coating plus how much it varies according to the pH, NVM. I know how it varies I just want to know how much it varies. For example, at 21% nvm at my current bath conditions I'm getting about 19 microns and for 18% I'm getting 16 microns DFT. Please help ASAP.

Harsh Bhatia
paint shop, prod. - Pune, Maharashtra

September 14, 2012

Q. I have recently been given to work on DFT optimization of paints in top coat line and on CED DFT optimization. Please suggest me any ideas on how to proceed with this project?

Vikrant Patnaik
- Ahmedabad, India

April 11, 2013

Q. What will be effect of higher DFT on CED coated part (40-45 micron against specification of 18-22 micron) on product quality?

Application : Wheel rims
Coating: CED + Top coat (white /silver)

Majid Siddiqui
- Bhoapl, India

May 20, 2013

A. It leads to peeling off.

Vijay Bhadwaj
- Ludhiana, Punjab, India

May 23, 2013

Q. Hi, I wanted to have input from you all ED experts out there!
We have a car production line with different models, surface area of which differs.
End result is that the largest body gets the required DFT with voltage of 360V, however our challenge is to optimize the energy requirement for all models. We are thinking of a Variable Voltage Rectifier, i.e., to vary the voltage to meet required DFT for DIFFERENT surface areas.
Is having this system a good idea? Can you share some more ideas of optimizing for different models? THANKS.

Sohail Pasha
- Lahore, Pakistan

July 29, 2013

A. The voltage can be controlled automatically so that the DFT remains the same even when the surface area changes.

Gurvin Singh
Coatec India
supporting advertiser
Mohali, Punjab, India

coatec india

December 20, 2013

Q. Hi, I have a cathodic electrodeposition painting system for painting motorcycle frames and other fabricated items. But now I am getting some coarse and nonuniform film on the part. Film thickness is not uniform and on some flat surfaces the film is coarse like deep orange peel. Thickness in some places is 25 microns and some places 70-100 microns. Condition of CED bath and other stages are almost the same as when no problems occur. What may be the cause of this problem and what is the remedy?

film on electrodeposition

Please do a favor to me by giving me the proper solution to this problem.
Thank you.

Fazlul Hoque
- Gazipore, Dhaka, Bangladesh

February 23, 2016

A. To reduce the thickness of the coated film you have to add hydrogen peroxide to the bath in the range of 1-10%; it acts as a hydrogen scavenger. Hydrogen gas evolves making defect in the deposited film like pits and makes the surface non uniformly covered -- the problem is in the hydrogen gas evolved, you can use other scavengers like nitroethane.
I think this is the method to get uniform and reduced thickness.


ahmad abo awf
- cairo egypt

January 23, 2014

Q. The data parameter from my process are :

1. NV 14.54% range 13-15
2. Coating voltage is 140 V (range 130 to 300 V)
3. pH is 6.33 (range from 5.8 to 6.4)
4. Conductivity is about 1630 micro Siemens/cm. (standard is 1100 to 1600).
5. Ratio F1 to F2 is 1:10
6. MEQ 32.7 range is 28-32
7. Solvent content 1.2 range 1.1-1.4
I found abnormal surface finish now like sagging is occur and in some point no paint is adhere to the metal. also in some area DFT is abnormally high. what to do now ?
More clearly I want to know:
1. how can I reduce conductivity of ED chemical and
2. how can I reduce pH or ED if it goes higher than the range?
3. how can I reduce MEQ ?

I also used the latest technology of ED Paint, which is Acrylic CED-Lead Free

Rahul Amin
- Dhaka, Bangladesh

August 24, 2016

A. Welded area usually having spatters and gloss bleed. It will not allow CED coating/paint to stick to the surface over a period of time rust formation will happen.
It is very important to clean the weld spatters & gloss bleed before any paint coating.

For reducing ED coating (CED DFT) you may reduce the bath temperature to less than 25 (22 - 25) & voltage (140-180)

Navnith Raj S N
- Mysore, karnataka & India

July 25, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. What is the effect found on surface when pH value of bath increases or decreases?

Suman K Singh
- Jamshedpur, Jharkhand, INDIA

"Electrocoating: a Guidebook for Finishers"
by Electrocoat Association
from Abe Books

(affil. link)

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

(affil. link)

July 2016

A. Hi Suman. "Handbook of Electropainting Technology" has at least 6 sub-chapters devoted to pH; I don't have a copy of "Electrocoating -- A Guidebook", but good books on the subject are best when you are interested in the abstract science of a subject. Vendors like Coatec India [a finishing.com supporting advertiser] might be able to meet with you as well to discuss such general topics as well.

This forum handles highly specific shop problems well, as you can see, but there probably isn't much that people can do for you in a forum of this type to help with abstract theoretical discussion.

If you are having a specific problem, please carefully detail it (i.e., use more words in your question than you want in the answer), and I'm pretty sure the readers can help. Good luck!


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

December 9, 2016

Q. Hello sir,
I am rohit singh. Currently I am starting of career in CED coating so please suggest me best book, or if can be possible you provide me related material.


rohit singh
- gurgaon, haryana, india

A. Hi Rohit. The two that I just mentioned to Suman are the only books I know of; I've only read the one. Good luck.


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

September 9, 2017

Q. Sir, I am working on CED machine. On the finished product I get a thickness up to 80 mm, but only 15-20 is acceptable. So what to do for this?

Rohit kumar
- faridabad,haryana,india

November 2017

A. Hi cousin Rohit. This page is about how to reduce the thickness of CED coatings. There have been some explicit & repeated suggestions, so please try your best to cast your question in terms of the suggestions that have been offered and commenting on the proposed solutions. Thanks!


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

April 25, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Running Cathodic epoxy e-coat line. My paint thickness is through the roof. I have turned down our rectifier and still no better results.

Jason Daire
- Jackson, Michigan United States

September 26, 2018

Q. Hello friends
Please can you help me for CED coating DFT because currently I'm facing DFT problem. I'm getting high DFT 18/20 micron, as per required DFT 16 micron. So please suggest to me CED bath parameters is temp. 32 and NVM is 14.63, CED bath pH is 5.9. And anolyte conductivity is 1400, and CED bath level is 18/20. Rectifier is 200 V.

Best regards

Amit Sharma
Student - Jamesdpur, India

December 15, 2018

A. Hello jason , Hello amit,

I think you both have same problem with excess throwing; I think three ways we can decrease the DFT:
1) Decrease paint solids
2) By Decrease in pH (5.5- 5.6)
3) Addition of solvent which reduces the viscosity of tank

So by this way we can control on DFT

Chandresh Varsani
- RAJKOT, Gujarat, India

August 18, 2020 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Ed. note: Please!
No abstract questions.

Can we reduce the acrylic DFT from 25 to 20? Or how much DFT can be kept of a CED coating at the lower side, on which all the Quality properties are right? (Current Spec is 25-30 Micron).

Sunil kumar
- Haridwar Uttrakhand

August 2020

A. Hi Sunil. I don't think your concern was actually about UV resistance, so we moved your posting off of the thread where you posted it, and onto this page which is about controlling thickness, and which already offers many suggestions. It sounds like 20 to 25 micron thickness is generally readily achievable.

But if the spec says 25 to 30 microns why are you anxious to change it? What is the substrate material and its surface roughness? A thickness which is sufficient for a polished substrate may not be satisfactorily pore-free on some rough surfaces. What follows the CED? -- Powder Coating? What precedes it -- a reliable zinc phosphate? Thanks!

Luck & Regards,

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

September 16, 2020

Q. Dear Sir, I'm the PTED line Operator.
Sir I want to know how I can reduce thickness of CED paint.

Current pH = 5.8 to 5.96 while std. pH = 5.8 to 6.20
Anolyte conductivity is 800 to 810; sometimes it's 790 to 800 wile standard of anolyte conductivity 700 to 1200.
And also bath conductivity is also low as compared to before. Current bath conductivity 1550 to 1580 while temp is 28 to 28.8 while std temperature of ED is 28 to 30 while voltage is setting on 270 to 290.

First we worked on 290 voltage but now we reduce voltage to 270 to reduce thickness, but still not achieving from 40 to 25.
How can I reduce thickness? Kindly suggest ... I'll be waiting for your reply.

Munawer Ali
- Pakistan karachi

May 31, 2021

A. Dear sir,.
Please check the solvent content in bath, if it high ,
By reducing the solvent content in the bath DFT also will reduce

Sudhakar Reddy
- Hindupur, Aandra pradesh

May 2021

thumbs up sign Thanks Sudhakar! Five previous writers offered the same relationship: "lower solvent = lower DFT". It's a bit counter-intuitive because higher solvent does means lower viscosity as one responder noted ... but competing forces overwhelm that effect as confirmed by graphs in the previously mentioned W. Machu Handbook of Electropainting Technology.

Luck & Regards,

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

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