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.
Is any problem while using hot dipped bolt with zinc plated galvanised nut ?
@Eldho- Hot dip galvanized nuts are tapped oversize to accommodate the coating thickness. A regular electro-zinc nut will not be tapped oversize and will therefore not properly thread onto the bolt.
Sir I want to know that galvanizing can harden the CRCA SHEET .
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@Vasim- We do not have any experience with CRCA sheet, so we are not certain of what galvanizing may or may not do. You’ll likely need to discuss with your galvanizer or the manufacturer of the sheet.
hello
i would like to ask if the electroplating stell can be welding with galvanized steel ?? if can it will effect the galvanined? or only where the welding area ?
@Robert- When welding, you typically need to remove the galvanizing either chemically or manually. The ,melting point of the zinc is lower that the temperature of the welding, so it will melt off if you don’t and can release toxic fumes. You then can weld and regalvanize.
We are having trouble meeting a specification on Department of Transportation (Idaho). They have in their spec. under 708.18 hardware for signs that Electrodeposited coatings of zinc on iron and steel meet ASTM B633.
Class No. Fe/Zn 25, Type III coating
Low or Medium Carbon Steel Externally or internally Threaded Standard Fasteners Meet SAE J429 or SEA J995 both grade 2.
All must be Domestic (Made in USA) we are using 5/16″ & 3/8″ bolts & nuts and can’t find any supplier to meet this spec. and I have heard that no one can and the spec is for bigger sized bolts. Do you know of anyway to meet this spec or some one that could tell ITD they are (nuts) :)?
@Ken- Most state DOTs are a bit nuts, sounds like Idaho is no exception. The issue you are likely running into is not that the spec covers only larger nuts, but more that the coating call out (Fe/Zn 25) is not standard. The ’25’ is a much thicker coating than usual, so what a supplier will have to do is find plain nuts and then have them plated. In my experience the only domestic nuts you will find are not grade 2, but grade 5, which is usually an acceptable substitution, but would need to be approved by the state. Another issue you may run into is that the coating thickness they are requiring may cause thread fit issues. If so, the nuts would need to be tapped oversize, but as there are no standards for tapping these, you’d be guessing as to how much to tap. We can see why you are having trouble.
Hello –
Is it possible to do hot-dipped galvanizing on top of electroplating galvanized structural bolts to increase the coating thickness? We have an issue where the supplier supplied the structural bolts with electroplating galvanizing instead of hot-dipped galvanized.
Thanks.
@Hardik- It is possible to hot dip galvanize over electro plating, however that will not increase the coating thickness above what normal hot dip galvanizing provides. During the pickling process, the electro zinc will come off, leaving the nice, clean bare steel that the hot dip zinc will to adhere to.