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Craters in contaminated electrophoretic lacquer bath

I am having problems with a freshly made EP Lacquer bath having uncountable craters, supposedly due to oil contamination from the unclean tank.
The higher the coating/DFT more are the no of craters.
Craters are up to 80% lesser when the bath is left still overnight.
Pre cleaning process has been re checked, UltraFilter permeate drain hasn't helped either.
We have tried using the USF Absolute Filter 0.2 microns, but failed.
please suggest any other technique/process to rectify this asap.

Mohit Sabharwal
Distributor / service provider - New Delhi, India
September 9, 2008

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September 11, 2008

Hi,

As there is a considerable improvement when the bath is left standing overnight, it sounds like gas bubbles. These can be due to:

Air being entrained in weirs and subsequently beaten into tiny bubbles as it passes through pumps. The air may be taken in as a result of too fast a rate of flow into the weir or large bubbles produced by splashes of electrolyte as the work is removed from the bath. Keeping the liquid level in the weir high and controlling rate of flow will cure/minimize the problem.

Gas from the counter electrodes not being properly exhausted and entering the electrolyte.

Air sucked in through pump glands. Sometimes there are tell-tale signs of resin seeping through the glands when the pump in not in operation.


Harry Parkes
- Birmingham, UK