plating, anodizing, & finishing Q&As since 1989
Excessive edge build-up in hot dip galvanized sheets/coils
May 16, 2012
Q. This problem occurs once in a while, and in batches, in our HDG line in mini mill. It occurs mainly with softer IF products.
I'm interested to learn possible root causes. if this has to do with baffle adjustments or incoming shape to CGL or non-uniform coating.
metallurgist - Columbus, Mississippi, USA
A. Dear Nipun,
I will assume that the edge build up is not severe because it appears in batches and only to soft material like IF. Based on these assumptions, here are a few pointers.
1. Is the cold rolled strip slitted? If so, look out for burrs on the edge of cold rolled strip.
2. Air knife settings. Most critical, the air knife lips must not have undershoot/overshoot. If unavoidable, reduce it as much as possible.
3. Low molten zinc temperature. Zinc freezes at the edge first and will be more difficult to wipe off.
4. If strip coming out of molten zinc have crossbow, there is a tendency for edge build up. Changing zinc bath correcting roll and sink roll position will correct or reduce the cross bow.
I am sure the same problem also affects the hard material; but due to the higher tensile strength, it does not stretch as easily as the IF at the edge.
- Karachi, Sind, Pakistan
Sink roll adjustment in galvanizing lineMay 14, 2014
Q. Dear Sir,
In MSC galvanizing line we produce galvanized strip between 750 - 1300 width and 0.4 - 2 thick and the coating is GA 100 - 270 Gr/m2.
Zinc pot is ceramic
Sink roll is 316L
Brushes Stellite 6
Problem is: difference in air knife parameter when the sink roll changes, meaning that by changing sink roll, the pass line will change but there is a stand for sink roll adjustment before installing in zinc pot.
What we did: 1- checking of calibration sensors,
2- checking of sink roll position during stop of line and tension in strip and the air knife position was the same,
3- Danially Co offered us to use ultrasonic sensors on air knife to measure directly the air knife position.
steel making employee - ashouri, Iran