Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
-----
Sandblasting galvanized steel
Q. I need some information about sandblasting galvanized steel.
Does in fact the sandblasting remove the galvanized finish, and if so what is another option for treating the steel afterwards. I have had 2 people ask me this in recent weeks, and I could not answer 1 of them but the second was right up my alley as it was pertaining to car parts and not aviation. It's more the aviation that I'm interested in.
ken neuts1998
A. Blasting with most medias will remove galvanizing. Some medias, such as plastic or corn starch may not remove the galvanize coating, but would in fact clean the galvanized metal surfaces.
Tyrone L. Caley- Jefferson City, Missouri
1998
Q. I wish to have the rusted aged appearance to corrugated roof metal for a project. Is there an environmentally friendly way to remove the galvanized surface that isn't too costly?
Bruce L. Dynes- Andover, Minnesota
2000
A. Hi Bruce. The galvanizing can be removed by sandblasting or by dipping in muriatic acid. Although some technologies may be more difficult to handle in responsible fashion, environmental friendliness is in general more a matter of attention to detail than a question of environmentally-friendly vs unfriendly technologies. Stripping in properly inhibited muriatic aid shouldn't be a big deal for a properly equipped shop.
Luck & Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Suitability of copper slag for sweep blasting of galvanized steel
Q. We have a client who is refusing to accept grey patches on galvanized steel generated because of the silicone variations on the ground that it is affecting the painting. He is using copper slag for the sweep blasting.
Rajan MathaiGeneral Manager - Abu Dhabi, UAE
May 7, 2008
A. You don't really say what the question is, but your heading suggests you want to know if Cu slag is suitable for preparing galv for painting?
Sweep blasting (light blast using low air pressure, or quick sweeps of the blast nozzle, or perhaps holding the nozzle way back from the steel) is one way to roughen the surface of the steel for painting adhesion, but perhaps not the best. The type of blast media in this case isn't all that important in my experience.
But you also mention grey patches due to silicon (It's not silicone with an E, that's something else again) content of the steel.
This is a different matter again. Some steel have higher reactivity in galvanizing and form more iron-zinc alloy, and Si is very influential in this. But this has little to do with painting, Unless your customer wants to paint to hide this variability in colour.
Such colour variation only lasts months anyway, as all galvanizing becomes dull grey after time.
Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK
May 9, 2008
Brush off blasting of Hot dip galvanized surface with stainless steel shots
June 27, 2016Q. Hi,
We are planning for brush off blasting (sweep blasting) on Hot dip galvanized substrates.The final finish is Powder coating. Can we use SS shots (fine) for getting a Ra finish of around 4 to 5. Will any galvanic reaction occur, as we have been advised not to use any steel shots for blasting (to avoid lateral corrosion)?
Alternatively what are the other medias we can use for blasting?
Thanks.
Paintshop manager - Mumbai, India
August 2020
A. Hi Sellappan. We appended your question to an earlier thread where Geoff answered it. But so that readers don't draw incorrect inferences, it must be noted that abrasive blasting of galvanizing is no substitute for zinc phosphatizing if it is going to be painted or powder coated.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q, A, or Comment on THIS thread -or- Start a NEW Thread