Letter 32074

Zinc curtains appear on galvanized steel coils  

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Dear sir,

Kindly we have a strange defect appears on the galvanzied steel surface coils this defect look likes a zinc curtains or you can say it look likes the waves and this defect isn't zinc pimples. We'd like to know the universal name, reasons and how to overcome this defect

We appreciate your efforts very much.

Ramy S.Ebrahim
continous galvanizing steel coils - Sharkia, Egypt

The defect that you seem to be explaining is a wash pattern . Also known as zinc runoff . Usually this occurs when your air knives are to high off of the bath surface . One quick fix for this is to lower the air knives and or increase the strip speed through the line . If this doesn't help try raising the air pressure to the knives and back them off the strip a bit. Usually this defect in apperance happens on heavier gauge , slower running speeds .

Mark Postema
- Rancho Cucamonga , CA, USA

Refering to the curtains problem I would like to know if these factors can be a cause of this Defect:

1- The incoming Pickeld oiled material ( coil breaks - overpickling- under pickling)

2- The exit strip temperature before dipping in the zinc pot

Hany Mohamed EL-Said Dabies
- Cairo, Egypt

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