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topic 57561

CED coating over Zinc plating has pinholes

A discussion started in 2011 & continuing through 2017 . . .

June 21, 2011

Q. I am a job CED coater. Recently a Zinc plated job has come to me for coating. After coating, all jobs were rejected due to PIN HOLE problem.
Can you help me?

Avinash vidhate
Plating shop employee - Nasik, Maharashtra, INDIA

June 26, 2011

A. CED Can be done on hexavalent yellow passivated part. If it is as plated or trivalent passivated, carry out tricationic phosphating then go for CED Coating.

Nithin reddy
- Bangalore, India

July 10, 2011

Q. By phosphating Zn plated part in my bath will lead to increase in Zn content in it. Won't that matter?

Avinash Vidhate
- Nasik, Maharashtra, INDIA

Pin holes on e-coat bottom surface

August 16, 2011

Q. Hi Sir,
I'm an employee of a plating house. Recently my company newly fabricated a 2.5 tonne e-coat tank to relieve some production capacity. Unfortunately, every model go through e-coat surely will have plenty of pin holes at bottom surface. Please be kind enough to give me some idea what setting gone wrong in my tank. Thanks

57561-1  57561-2

KC Tan
plating shop employee - Ulu Tiram, Johor, Malaysia

August 17, 2011

A. Maybe it's the angle from which the photo was taken... but I can't see a weir to remove the surface foam being produced by the coating process?

Terry Hickling
Birmingham, United Kingdom

August 19, 2011

A. Bubble on top of coat bath. You need a weir box to roll the top of the tank to. You also need to determine where the air bubbles are coming from.

Adam Adkisson
- Mission Texas

Handbook of Electropainting Technology

Electrocoating: a Guidebook for Finishers

simultaneous August 22, 2011

A. Bubbles can be produced by cavitation in the main tanks pumping system.

Where a side tank is used for both collection of the e-coat tanks surface bubbles and the addition and mixing of new tank material, a bubble producing problem is possible if the weir shoot tank is:
a)Too small.
b)The rpm of the internal mixing system (normally a stirrer) is too fast.
c)Blades of stirrer are too low.

Terry Hickling
Birmingham, United Kingdom

August 23, 2011

Q. The foam issue is already resolved, mainly due to circulation pump choked by some cleaning cloth. However, the problem I'm facing is some pinholes due to gassing at bottom surface of raw parts.
Parameter of ED in spec; just pH slightly acidic (pH 4.5 - 5.0). What I'm curious is just whether tank either circulation is not enough or maybe in tank setting something has been neglected...Maybe I'm wrong, kindly advise any eval'n that I can find out more.

KC Tan [returning]
- plating shop employee - Ulu Tiram, Johor, Malaysia

October 30, 2011

A. Most important to avoid pitting at the bottom - clearance of work piece to bottom sparge pipes should be minimum 200 mm!

sara michaeli
sara michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel

November 1, 2011

A. Hi KC.
I once had the opportunity to look at an ED film ( 40 X I think) before the curing process and 'lo and behold ', they were full of pin holes! It is only through the curing process, the higher temperature makes the film more 'fluid', those pin holes were closed up, so to speak.
It may be possible, your pin holes problem are curing oven related rather than ED tank related??

SK Cheah
- Penang, Malaysia

November 27, 2011

A. First ensure that all the bath parameters are within specification and pH meter, Current-voltage meters are working properly.
Pinholes at the bottom of tank may be due to excessive gassing, i.e., due to high current density which further may be due to high solids content or suspended particles or too low pH.
Also, get solvent content tested by your paint supplier.

manoj kushwaha
Manoj Kushwaha
plating & painting - Rampur, India

January 25, 2012

A. Check your solvent (BC) content. If it is on higher side it will definitely create pin holes. Check also ramp up time for rectifier voltage.

Manish Dhyani
- Noida, India

February 1, 2012

A. Kindly provide details of the pre-treatment process that is done prior to E-coat.

Have you checked the component after pre treatment and before E-coat for presence of oil on its surface?

Gurvin Singh
Coatec India
supporting advertiser
Mohali, Punjab, India
coatec india

March 21, 2012

thumbs up signHi Folks,
Thanks for your advice. I already went through all recommendations but it was not root cause. Thereafter, I changed existing circulation pump from Vertical to horizontal centrifugal type. Surprisingly, it resolved all those pin hole defects.
Anyway, thanks for ideas from all.


KC Tan [returning]
- Ulu Tiram, Johor, Malaysia

June 18, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We have pinholes after applying the electrodeposition coat.
We think we have a problem in the activation process in pretreatment line. Please guide me.

M. Ashena
- Tehran, Iran

July 14, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. How to Solve Pin holes in CED paint plant. Please give detailed answer.

Senthil Kumar
- Chennai, India

Trouble in Your Tank
by Larry Durney
from Abe Books


July 16, 2012

A. Hi Ashena, hi Senthil.

As you see, we appended your inquiries to a thread which already addresses this issue and may solve your problem. If not, please give the details of your situation. Thanks!


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

November 16, 2012

Q. Dear sir,
I am working as an Automotive CED Paint plant. In our plant daily pinhole, crater and white dot issues observed after oven; every day more rejections -- all parameters are within spec. So please give some ideas to resolve this issue.

Senthil kumar [returning]
- Chennai, India


(Click thumbnail for high-rez photo)

December 29, 2015

Q. I am working as line chemist of PT [pretreatment] and CED line. I got some problems after maintaining PT line.

Sir please see and tell what is the problem and resolution. In this company we do coating of PT and CED on tractor spare parts.

Virender Singh
paint shop - panchkula haryana india

December 2015

? Hi Virender. Is that a hemicircular rust spot at about 8:00 o'clock where the recessed diameter meets the ID of the flange? What is the substrate and the pretreatment? While you may well have electrocoating problems, the pretreatment has to offer a properly prepared surface first :-)

Luck & Regards,

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

December 30, 2015

Q. Sir, I am working in paint shop which is doing PT and CED line of tractor spare parts. I am line chemist. Images of rejected components:

defective CED-4a defective CED-4b defective CED-4c

But my question is not clear. Tell me what is name of problems, cause and action plan. There is no hemicircular rust on components before PT line. Cleaning and Phosphate coating is okay. And my PT line is okay with standardized parameters. I have problems coming from CED line. Our CED line is not okay. Thanks

Virender Singh [returning]
paint shop - Panchkula,Haryana,India

March 1, 2016

? Hi Mr. Virender,
My questions:
1. Tried on other substrates or materials? same defect appeared?
2. Any solvent/oil floating on bath surface during ED process?
3. Ensure no stubborn oil & grease on part surface?
4. After rework process part proceed to ED happened same defect?
Above questions might lead you to certain idea to proceed.

KC Tan
- Ulu Tiram, Malaysia

March 20, 2016

A. The problem is in the bath composition; you have to add hydrogen scavenger to the bath like nitroethane or hydrogen peroxide in the ratio 4% -- this is because hydrogen evolves during the process making film defects and the surface of the work piece not fully painted which causes free zones that makes rust and pits in the film so you have to eliminate defects by hydrogen scavenger.


ahmad abo awf
- cairo, egypt

July 4, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Please tell me how eliminate the problem of pinhole on bars please tell me.

ganesh dede
- pune, maharashtra,and india

A. Hi Ganesh. We appended your inquiry to a thread with lots of great info on the subject. Please review it, then expand upon your question with details if this thread doesn't solve it for you. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

November 11, 2016

Q. Hi There,
I am working in a HDD manufacturing company in Cambodia; I am the e-coating manager.
Here we are facing very high fallout of hard blisters, soft blisters and pin hole voids (fish eye).
The pre treatment is a very mild etching process.
Please advise me how can I solve this problem.

Thank you

Param ramasamy

March 16, 2017

Q. Dear advisor,
I am employee of CED coating system in johor malaysia. Now I have some problem on my ED coating part surface. My ED bath pH - 5.7, NV%-10.00, PB ratio - 0.095, bath temp. 25.0 °C. BC % - 1.25, HC % - 0.890. The part before Ed I have been 100% confirm free from oil. but there is still pin hole defect ... but just one dot only. So how I can solve it? Please give me the some idea or advice. you cooperation will be high appreciated.

best regards,

Jiwan Rai
ED coating jobshop employee in johor baharu malaysia - johor baharu, malaysia

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