Metal finishing Q&As since 1989
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CED coating has pinholes
Q. Hi sir,
I am working PTED line and I am facing first time PINHOLE issue in full body. And then finding a root cause is ED Path problem. And how to solve this problem please give me an idea.
Thank you sir.
Production associate team leader (trainee) - Chennai, India
July 2, 2021
by Larry Durney
on Amazon
(currently UTL
on AbeBooks & eBay)
(affil links)
A. Hi cousin Govind.
There's obviously nothing wrong with seeking a "root cause", but that doesn't mean that there is only a single possible cause for pinholes, or that there is one thing we can change that will fix it even if other things are wrong :-)
As Larry Durney tells us in "Trouble in Your Tank", if a process used to run properly, something has changed -- and figuring out what it is that has changed is always a much faster route to the fix than theoretical studies. So the key to troubleshooting when something used to work is usually a simple 1-2-3:
• Walk the Line
• Look at the Records
• Obey the Letter of the Law
But there are hints on this page as to the possible causes of pinholes if you are able to determine that none of the parameters that you monitor has changed. Good luck!
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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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?
Plating shop employee - Nasik, Maharashtra, INDIA
June 21, 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
Q. Phosphating Zn plated part in my bath will lead to increase in Zn content in it. Won't that matter?
Avinash Vidhate [returning]- Nasik, Maharashtra, INDIA
Hi Avinash. Nithin has suggested that you should take different routes depending on whether you are hexavalent chromating, trivalent chromating, or processing parts with no chromate. Please answer Nithin's implied question of which you are working with so we don't have to deal with all the ifs-ands-&-buts of three different scenarios and which aren't applicable. Thanks!
Luck & Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Pin holes on e-coat bottom surface
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 going through e-coat surely will have plenty of pin holes at bottom surface. Please be kind enough to give me some idea what setting has gone wrong in my tank. Thanks.
plating shop employee - Ulu Tiram, Johor, Malaysia
August 16, 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 HicklingBirmingham, United Kingdom
A. Bubbles on top of coating 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
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.
Birmingham, United Kingdom
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.
Thanks
- plating shop employee - Ulu Tiram, Johor, Malaysia
August 23, 2011
A. Most important to avoid pitting at the bottom - clearance of work piece to bottom sparger pipes should be minimum 200 mm!
Sara Michaeli
Tel-Aviv-Yafo, Israel
A. Hi KC.
I once had the opportunity to look at an ED film (40X, 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?
- Penang, Malaysia
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
plating & painting - Rampur, India
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
? 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?
Mohali, Punjab, India
February 1, 2012
Hi 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.
Regards
- Ulu Tiram, Johor, Malaysia
March 21, 2012
[editor appended this entry to this thread which already addresses it 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.
Thanks
- Tehran, Iran
June 18, 2012
[editor appended this entry to this thread which already addresses it in lieu of spawning a duplicative thread]
Q. How to Solve Pin holes in CED paint plant. Please give detailed answer.
- Chennai, India
July 14, 2012
A. Hi Ashena, hi Senthil.
As you see, we attached your inquiries to a thread which already addresses this issue and it will hopefully solve your problem. If not, please give us the details of your situation which make it different. Thanks!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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.
- Chennai, India
November 16, 2012
Hi again cousin Senthil. 8 readers previously offered specific suggestions on what needs checking regarding pinholes, so saying that "all parameters are within spec" probably won't help resolve your problem. Please try to comment directly regarding those previous suggestions. Thank you!
Luck & Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. I am working as line chemist of PT [pretreatment] and CED line. I have 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.
paint shop - Panchkula haryana India
December 29, 2015
? Hi Virender. Is that a semicircular rust spot at 8:00 o'clock where the recessed diameter meets the ID of the flange? If it is, although you may well have electrocoating problems, the pretreatment system has to offer a properly prepared surface first. What is the substrate and the pretreatment please? Thanks!
Luck & Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Sir, I am working in paint shop which is doing PT and CED line of tractor spare parts. I am a line chemist. Images of rejected components:
But my question is not clear. Tell me what is name of problems, cause and action plan. There is no rust on components before PT line. Cleaning & 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
December 30, 2015
? 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 ideas to proceed.
Thanks.
- Ulu Tiram, Malaysia
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.
Thanks
Ahmad abo awf
- cairo, egypt
[editor appended this entry to this thread which already addresses it 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
July 4, 2016
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 additional or differing details if this thread doesn't solve it for you. Good luck.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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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
- JOHOR BAHRU
November 11, 2016
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 pinhole defect ... but just one dot only. So how I can solve it? Please give me some idea or advice. Your cooperation will be highly appreciated.
best regards,
Jiwan RaiED coating jobshop employee - johor baharu, malaysia
March 16, 2017
Q. How important is it to drain permeate? Here where I'm working, no one drains it even a bit. And we frequently face the problem of pin holes on Cathodic electro deposited automobile bodies. My senior says it's due to high MEQ. Please shed some light on this for me.
Kasi Viswanath Boddeti- Andhra Pradesh, India
July 13, 2018
Pin hole on CED components on the bottom of the substrate
Q. Dear sir
I am employee of the CED Coating system in Chennai india. I have some problems on my CED coating pin hole issue getting on only bottom and curve of the components for all components where ever jigging. All the parameters are within spec and having sufficient agitation. Kindly guide me to resolve this issue and explain the root causes and action plan sir. We tried all trials as far as we know in all aspects.
Please find attached photos for your reference.
Regards,
Ganesan NallusamyShop employees - Chennai, Tamil nadu, India
August 26, 2018
Q. I am working in a e-coating plant Bangalore. Our pretreatment line is OK, but pinhole is coming in component. What shall we do? Please guide me?
Tekchand Patel- Bangalore, India
September 7, 2018
A. For the Pin hole problem:
1. check that all parameters are in range (PT line, voltage, ED temperature, pH, N/v content, conductivity, dipping time & cleaning frequency)
2. check the circulation in ED bath
3. check the hanging positions of part
4. check the proper insulation removed before part loading
To avoid this problem ... then install filtration method in ED bath.
- India, Maharashtra, pune
March 2, 2019
Q. Sir, I also encountered a pin holes issue. Our parameters are within the standard. In the end of the roof, it has many pin holes but in the front of it has nothing, it's good. And when we change the DI rinse water after phosphate, the pin holes decrease (we change when the conductivity of this tank approximate 1000, and when the conductivity of this tank is higher than 300 it has more pin holes).
So my question is why is this? can you explain this and how to solve it?
Thank you!
paint shop - Hanoi, Vietnam
July 26, 2019
A. Hi Ryan. We may be having a little bit of language difficulty because I don't understand what you mean by "roof". Are you coating discrete parts or reel-to-reel? Maybe you are saying the coating is good at the beginning of a reel, but full of pinholes by the end?
Also, we may not be agreeing on how a DI rinse water tank is supposed to function. Conventionally, you don't fill the tank with DI water and dump it when it gets too contaminated. Rather, you constantly recirculate the water from the tank through a de-ionizing unit, and back to the tank so it remains de-ionized to the same degree all the time. What you change is the DI cylinder when it becomes exhausted, not the water in the tank.
Please clarify these things for us. Thanks.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Thanks sir. Sorry about my english, it's quite bad.
About the problem, we dip a car in the tank, so "roof" that I mention is the top of car. But when dip in ED tank it's in the bottom of tank.
The second question, yes it's a lot of pinholes by the end of this roof. It just stay in it.
And about the DI water tank after phosphate tank, it has been designed. When it bad, it will be replaced, not as your mention. And the company does not allow modification, it will be in charge.
Paint shop - Hanoi, Vietnam
A. Hi again, Ryan. Thanks for the explanation about the roof, it is very clear now!
A whole pretreatment and electrocoating line is a complex arrangement of equipment and chemistry, and I cannot pretend to understand everything that is going on ...
... but if you already know that the problem gets much worse as the DI rinse gets contaminated but you cannot take the necessary measures to keep the DI tank from getting contaminated even knowing that, what can be suggested? Trying to change the electrocoating formulation or application parameters so it is more dirt-tolerant doesn't sound promising to me. Maybe another reader has an idea though.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. But I can't explain why. What is mechanism of it? So I can more understand about it. And when I change the DI water, the pin holes just decrease, not disappear. And the flow of ED tank on top is left to right and in bottom is opposite, it make a circle, and I think it not strong like swirls to put the hydrogen on in the roof of car, is this right? Because I just graduated from university so don't have much experience. Thank you!
Ryan Nguyen [returning]Paint shop - HaNoi, Vietnam
July 28, 2019
A. Hi again Ryan. Hopefully another reader will jump in because I am not an e-coating expert and I don't pretend to know exactly what is causing those pinholes. But the fact is that contamination can cause or aggravate them, and you already realize that, and have demonstrated it, and need to address that.
Why exactly a dirty DI rinse accentuates the problem may not be known now or ever; a certain amount of knowledge is simply empirical and we can't necessarily trace it all the way back to first principals: it might be dirt interfering, it might be that the higher conductivity is allowing galvanic currents, it might be a reaction with some very specific contaminant.
by Larry Durney
on Amazon
(currently UTL
on AbeBooks & eBay)
(affil links)
If you have another theory of what is causing it, and feel that a dirty rinse merely accentuates rather than causes it, that's fine. But wet metal finishing processes are quite complex and as Larry Durney writes in "Trouble in Your Tank", an important starting point in any troubleshooting exercise is "Obey the Letter of the Law". When you know that contamination in the rinse tank is aggravating the problem, you need to fix it, not ignore it :-)
Good luck!
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. Hello Ryan. Change the dip D.I. water rinse to SPRAY rinse or Add fresh D.I.water SPRAY while taking out car body from the dip rinse tank. The sludge from phosphate tank remains at flat portion and that's the reason for pin holes (What I think is those are not pin holes but are CRATERS that formed due to impurities in the water.)
Avinash Vidhate- NASHIK, Maharashtra, India
August 1, 2019
Q. Hi I'm sunny. I have a CED coating plant and want to check my CED coating bath. Please tell me how to check it.
I have a problem with casting material. Pinholes is my big problem.
Sunny patel [returning]- India gujrat in Rajkot
February 19, 2020
A. Hi Sunny. If the above discussion does not suggest to you what to do next, I think we'll need photos and more words before additional suggestions will help much. But please clarify what you mean by "casting material" -- cast iron parts, diecast zinc parts, pressure cast aluminum parts? Thanks!
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Hello all, I have some problems with painting.
I have an E-coating line almost 3 years; everything was okay until last month. Problem is with non-painted small holes on the object. I think this is not a problem of pretreatment or air bubbles or racking.
My paint supplier suggested that I add more solvent, but this did not help. Does anybody have an idea what is the cause of this issue?
Nikola Djukic- Prnjavor, Bosnia
December 23, 2020
adv.
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