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topic 45328

Low pH Problem in CED Bath

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A discussion started in 2007 but continuing through 2017


Q. Dear Sir

We are having the CED bath dip painting facility.Paint is supplied by Asian PPG.
Now we are facing the problem of low PH in bath Paint 4.6 and we want to bring it up to 6.2, low conductivity,and high NVM (more than upper limit).
Please suggest how can we control the pH of bath so that we can get the desired DFT.


Satyendra Sachan
Manager Paint Process - Faridabad, Haryana, India

Handbook of Electropainting Technology
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A. Dear Sachan,

pH always increases in CED Bath which could be brought back to normal range by adding "Acetic Acid" (pH Controller). But if the pH is going down then the situation is quite alarming. In your case this is happening because of damaged Membrane. Check your anode membranes for any damage.


Manish Dhyani
- Noida, India


A. Dear Mr. Satyendra Sachan,
You are facing a quite familiar problem of low pH, which can be simply be rectified by dumping of permeate.
I hope your problem be solved.

- Delhi, India

December 8, 2008

A. Dear Satyendra,

Please check the MEQ (milliequivalents). If high then reduce the MEQ by draining the fresh permeate and adding fresh DI water in bath with specific additives and increase the value of ash %.


Kuldeep Yadav
- Gurgaon, India

May 15, 2013

A. Drain permeate and add fresh DI water.
Also by increasing ASH contents... if you don't want to increase ASH then add some resin that is used in pigment making process.

Liaqat Bashir
- Lahore, Pakistan

June 25, 2017

Q. The CED bath at one of my customers is having a very low pH (5.2). I have checked all the anodes -- none have leakage. The anolyte solution is clear. Incoming DIW is good with pH 6.7, raw paint is well within spec.

What else could be the known cause for low pH? I have advised UF drain and fresh make-up, but I want to get to the root cause.

Rajesh G
Technical Service Manager - Pune,India

July 25, 2017

A. Anolyte line may get blocked due to the bacterial growth in return line & anolyte may overflow in CED tank.Please check ANOLYTE level in Anolyte tank, it might be dropping.

Avnash Vidhate
- Nashik, Maharashtra, INDIA

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