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Understanding Phosphating...help

At work, I have previously put through some mild steel plates through a phosphating line. The plates afterwards definitely exhibited a colour change to a blue/gray finish.

I have just repeated the procedure some months later and now the plates are exhibiting a straw colour. Why the difference in colour, and what causes it ?

Stephen Sladin
- Congleton, Cheshire, England
2003

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Hi Stephen,

You don't give the specifics of your process or of the bath chemistry, so it's difficult to pinpoint an answer. But you can say for certain that your phosphating bath has changed somehow. It is well established that the phosphate coating will change appearance when the bath parameters have changed.

George Gorecki
- Naperville, Illinois
2003

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Hi,

U have not give the complete details of your process and which type of phosphating you are using?(Di-cationic or tri cationic). What are the pre-phosphating and after phosphating processes and what parameters you are maintaing there. It seems that either your bath has become contaminated or your passivation process is not working well enough.

Manish Chandra
- India
2003