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Single rinse tank between pickling and fluxing

Dear All,
In my company there is only one rinsing water tank is in use after pickling,due to which rinsing water usually gets acidic in nature up to pH=2. Sir I want to know that how it will affect the GI process and will it also affect the fluxing solution or zinc coating over iron.

Nitin Gaur
telecom - Kolkata, West Bengal, India
March 3, 2010

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March 5, 2010

There are several possible outcomes from having two rinses between acid and flux.
You might have lower acid carried over on the steel into the flux, and this will help the flux pH not to reduce below the desired 4.5 or so. There might also be less FeCl2 carried over, which upsets the balance of the flux chemistry.
And not having low pH in the flux means less pickling in the flux.
Having two rinses might mean that your crane needs to travel further, and making that extra dip in the 2nd rinse takes time and so throughput might be reduced a little.
If you install a 2nd rinse, ensure to add the fresh water only to the second, and top up the first rinse only from the second rinse, not with fresh. This way your acid content in flowing back toward the pickle tanks, and your second rinse will always be the cleanest.

Next task will be to ensure that even with two rinse tanks, that two rinses are actually done! (supervision)

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK

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March 23, 2010

Sir:

Geoff is quite right that the build-up of iron+2 in the flux tank can be delayed by having two rinses after the pickle tanks. He also described well how to move the rinse waters toward the pickle tanks. If your pickle tanks are warm (e.g. 80 F) then the rinse waters can be moved more quickly toward and into these tanks helping keep the rinses cleaner. If you do have 80 F pickle tanks then you very much need a very good inhibitor in the correct amounts. Also there are necessary rinsing METHODS that are in my publications in METAL FINISHING that you need to follow to get good results.

If you do not have space for a second rinse tank or time to put the steel into a second rinse tank then the recently available rinse purification machine could solve your rinsing needs. It is equivalent to flowing rinse water at 7 gallons/minute.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA