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"Want to know reasons for PIT MARKS on galvanized sheet"

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Current question:

November 13, 2021

Dear sir ,
I'm working at 25 TPH Galvanizing unit running with 0.6 to 0.12 mm Thickness sheets. My query about pit marks defects are not really solved satisfyingly. So can you please give me a short but actual reason about how this defect evolves over the GP after coming out from the zinc bath?

Vijendra Das
- Dalli Rajhara
^




Closely related Q&A's, oldest first:

2006

Q. Dear sir, I'm working in continuous galvanizing line having capacity of 26TPH, producing sheet of thickness 0.12 to 0.6 mm. Sometimes pit marks are observed in galvanized sheet. What is the reason for pit marks?

Harsh postiwala
Essar - Hazira, Gujarat, India
^


2006

A. Pit marks can be formed in many ways . If your CRFH Material is good being paid off at your entry section then many of the causes can be eliminated. The number one reason for pitting in my experience is the of a build up of iron fines on the pot turn roll " sink roll " . Having a scrapper for this roll helps greatly. Other then that replacing the roll is the only other option. Masking the problem may be done by lowering the tension setpoint at the bath. Keeping a consistent bath temp is key to not allowing buildup to occur. Also skin passing your material may help but not eliminate the problem you're having .

Mark Postema
- Rancho Cucamonga, California, USA
^


September 16, 2014

Q. Hi sir. Sandip, working in steel in India in super galvanizing line. Capacity of line is 0.3 mm to 3 mm thickness and width capacity is 750 mm to 1550 mm.
I want to know about pitting defect on the sheet surface.
Please provide me full theory about this matter. Once again I ask you.
Thank you

sandip singh
- khopoli, Maharashtra,India
^


"Faults in Hot-Dip Galvanizing"
by Dietrich Horstmann
from Abe Books
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September 2014

A. Hi Sandip. "Full theory" about the defects would require a book =>
rather than a forum response, but if you can explain your current situation, and/or try to phrase your question in terms of the excellent response offered by Mark Postema, the readers can hopefully help you move forward towards less pitting. Good luck!

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^

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