The authoritative public forum
  for Metal Finishing since 1989
-----

Foam layer growing on Anodizing & Electrocolouring baths

I am Masood khan production supervisor working for Anodizing plant in Riyadh K.S.A.

we notice a foam layer in anodizing & colouring bath when the bath is not in use for 8hrs.when we process material in colouring some inner surface is not coloured due to this foam entrapment.

This type of foam is not seen any time in past eight years.

Masood khan
Employee - Riyadh, Saudi Arabia.
July 17, 2008

---

July 20, 2008

Hi,

Am I correct in assuming that you use air agitation on the anodizing bath and that when it is in use there is no excessive foaming?
I suggest that you look in three areas.
1) Are you using a cleaner and that foam from this is being carried down the line on the racks?
2) Are you using a alkaline etch and using surfactants to suppress spray/mist? Or maybe oils and greases on the aluminium are being emulsified or saponified (made into soaps). Again foam from any of these causes could be carried into the anodizer.
3) Have you started to use a spray/mist suppressant on the anodizing bath? This can result in debris on the sides on the tank being clean off and causing "scum" on the surface of the tank.
Actions on (1) and (2) may need higher level of water in the rinses or the use of water sprays.
The stable foam on the anodizing bath will tend to act as a floatation medium for oil, grease and other soiling. It is likely that it is this suspended matter that coats the anodic film during transfer to the coloring tank and causes your problem.
If you cannnot indentify and prevent the cause of the foam, then you are left to skim it off from the surface of the bath.

Harry Parkes
- Birmingham, UK