Where the
world gathers for metal finishing
Q&As since 1989


-----

SUITABILITY OF METALLIZING OVER HOT DIP GALVANIZING

2004

I have a query on the best way to deposit 120 microns of zinc on a 2mm steel fabricated structure - a ducting -. The processes to choose from is metallizing and hot dip galvanizing. Now, I have a metallizing factory whereas my client is keen on getting it hot dipped. However, I have suggested him to not get it hot dip as I presume it would lead to distortion of the fabrication. Please advise as to whethwe my stand is justified or not.

Regards,

Shantanu Newat
Metallizing - Calcutta, W.B., India

---

2004

Metallising - presumably you mean sprayed metal? Metallising is a process that does not metallurgically bond to the substrate like galvanizing does. (Galv is an alloying process not just a coating). So adhesion can be a problem. Further, metallised coatings are usually porous, and are often sealed with some organic coating. This reduces the cathodic protection afforded by metallisation. Galvanizing has pure zinc (or zinc alloy) exposed to atmosphere, electrically connected to the substrate and metallurgically bonded to it. It has better adhesion, better cathodic protection and this increased performance probably means that a thinner coating could be used.

120 microns on a thin steel substrate might not be achievable, even with shotblasting prior to dipping, but to compare 120 microns galv with 120 microns metallised is wrong.

Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK