Metal finishing Q&As since 1989
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Zinc phosphating bath is turning very dark green and non functional
Q. DEAR SIR , I AM MANUFACTURER OF ZINC PHOSPHATING CHEMICAL, ONE OF MY CLIENT HAS PROBLEM USING MY CHEMICAL THAT HIS PHOSPHATING BATH BECOME VERY DARK GREENISH (NEARLY BLACK TYPE)AND AFTER COATING METAL GET RUSTING. PLEASE ADVISE ME HOW TO REPAIR THIS. I AM USING H3PO4,ZNO, MNCO2,HNO3,HF40%,H2O.
NITIN PATEL- VADODARA, GUJARAT, INDIA
March 25, 2010
A. Gentlemen,
The solution will be having more of Iron. The Iron concentration in the bath shall be a maximum of 0.4 percent, if your bath is of Hot Phosphating with out accelerator. More over the thickness of the Phosphating also will be high when the Iron concentration is more. Please check.
Continuous mild dry Air agitation in the Phosphating bath helps to precipitate the Iron while processing the components for Phosphating.
All the Best.
- Bangalore KARNATAKA, India
A. I agree with Shankarnaraynan.
The remedy is if its a cold process add large quantities of accelerator and do air agitation. stop adding accelerator when the starch iodide paper starts turning violet.
allow the tank to digest for 4 hours the solution in the tank will turn clear. check total and free acid ratio and use the tank.
- Coimbatore, TAMILNADU, INDIA
It is our sad duty to pass along the information that the knowledgeable Mr.Shankar was lost to Covid/Corona.
He was awarded with honorable medal by then Indian president Ms. Pratibha Patil. R.I.P.
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