A. Concerning dents from a sink roll - We have a sink roll scraper, which is a tool we made in-house. I believe and it has a long handle and a blade at the end to scrape the sink roll while it is rolling in the pot. When there is an accumulation on the roll you can feel vibrations in the handle of the scraper. We use it once or twice during the day. Other thing I can think of is a problem with your coating or bath temperature too low or grooves on the surface are plugged so that there is now flow of zinc.

I hope this helps!

A. Several suggestions to your problem:

1. After removing your sink roll, you need to re-machine the surface.
2. If you are using a grooved roll, make sure the edges of the grooves are bevelled (or chamfered) with a "soft" edge.
3. Our experiences with a scraper isn't that great. It works if you catch the build-up soon after it's formed, but they're difficult to remove if it's had time.
4. Also, drill "drain holes" in the trough of the grooves at some periodic distance.

Sink roll grooving is important and chamfering is recommended. you have not mentioned size of roll.
In one case we coated sink roll with HVOF carbide and the reported life is 2 1/2 months.

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 .

Hi, Adarsh. The manufacturing process for specialty machinery parts "in detail" probably won't be offered to you, as free public forum responses from readers tend to be only a paragraph or two :-)

If you can't find the details in a book, please consider retaining a galvanizing consultant for this project, or contact a manufacturer of galvanizing equipment for their advice. Best of luck.

Regards,

A. Check your sink roll Arms. Change them if using it for a long time.

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.


Best regards

Voo

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,

A. Better provide a photo of pit marks for analysis.

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Ed. note: Photos should be attached to e-mail to mooney@finishing.com for posting here.