Hot-dip galvanizing is a process of applying a protective zinc coating by dipping product in bath of molten zinc. Galvanizing is a favored method of protective coating due to its low cost, ease of application, and long maintenance-free service life. Generally applied at 830 to 870 degrees, the zinc will bond with the steel. It is the most common outdoor protective coating in use. When used on bolts, due to the thickness of the zinc coating, all galvanized nuts must be tapped oversize.
Zinc plating or electroplating is a process where zinc is applied by using a current of electricity. It is a thinner coating than hot-dip galvanizing making it unsuitable for outdoor applications. Its advantages are its brightness and uniform color making it more aesthetically appealing.
The ASTM specification covering hot-dip galvanized fasteners is F2329, while the specification covering zinc plated fasteners is F1941.
I am getting iron railings for indoor stairs . Some of the spindles have a little rust on them ( I had them for a while ) . I want to put good protective coating on the railings . The place that will do the coating offers both Zinc dichromate plating or galvanizing and then powder coating . Which one would be better ?
@Ted- For an indoor application, I wouldn’t think it would matter all that much. Once you get the current rust off, if they are indoors they should not continue to rust, and either plating would likely do a sufficient job.
How can we differentiate between a Hot dip galvanized and zinc electroplated bolt when examining physically.
@Alex- Sometimes it can be tricky, but typically the electro zinc is more shiny and more even. The hot dip galvanizing is typically more gray and dull and a bit uneven.
Another issue is that there is a possibility of shape distortion due to hot dipping on the sheet metal of the manufactured cabinet. What is the minimum sheet thickness in order not to have any distortion problem?
Thanks for your help.
@Abdullah- We do not typically galvanize large objects like your cabinet, so I really can’t be certain. You might need to contact a large kettle galvanizer who is more familiar with objects like this.
What is the minimum thickness for hot-dip galvanizing? We need an outdoor cabinet for about 25 years and dont want to renew it. We thought that building it with galvanized sheet metal is meaningless because zink will be gone from the welding points. Is it the best; hot-dip galvanizing after building the whole cabinet?
Thanks for help
@Abdullah- The minimum thickness for hot dip galvanizing of bolts and hardware, which is what we do, is 2.0 mils. For structural members the thickness can vary from 1.4 to 3.9 mils, depending on the class of galvanizing specified. There are different standards for sheet metal, and I am less familiar with what those requirements are. Galvanizing the cabinet after fabrication might be a good idea, but you would need to discuss dimensions and details with your galvanizer and make sure it is within their capabilities.
IS BICROMATED COATING SAME AS HOT DIP GALVANIZED.
@Khozema- No, hot dip galvanizing is a completely different coating than a zinc chromate. Chromates are simply a sealer on top of the metallic coating, whereas hot dip galvanizing actually bonds with the steel in order to protect it.