Sherardizing vs Galvanising

A. The main difference between the two galvanizing techniques is in the application method. Sherardizing is a very laborious way of applying zinc to a metallic surface, especially on long sections such as those used in transmission towers. Hot-dip zinc is a much faster and more straightforward process. I believe that the galvanic couple between hot-dip zinc and steel is far stronger than with sherardized zinc, as there is a definite formation of ferro-zinc alloys when using the hot-dip process. There is also the question of the weight of deposited zinc as measured in gms/sq.metre. Hot-dip zinc is easier and more accurate to control, with a definite thickness/weight of zinc being applied. This is generally much heavier than a sherardized coating.

A. Sherardized coated bolts are cheaper; that's an advantage if you are only using the bolts in a temporary condition.

A. Hi Soumya. Washers, fasteners, etc., can be galvanized. You might also investigate zinc-rich dip-spin paint. An electroplated zinc alloy like zinc-nickel might serve, depending upon your needs. There are also, of course, organic coatings.

Regards,

Q. So Sir, as per you, galvanizing is more cost effective than sherardizing of washers, fasteners, etc.
What about quality of finish and property of the final product?

A. Hi again, Soumya. I did not say anything remotely like that -- where did that interpretation come from? :-)

In fact, Phil M claimed that Sherardizing was cheaper, and I imagine that this is often true; but I don't know that it universally is. We pointed you to five threads on Sherardizing and we have dozens of very long threads here comparing the properties and advantages of the various application methods for zinc coatings, which include sherardizing, modern proprietary tweaks to sherardizing, hot dip galvanizing (with variations like wiping or spinning to reduce thickness), electroplating (which actually offers the best appearance of all and can involve zinc alloys as well as pure zinc), mechanical plating, zinc-rich dip spin coatings, "cold galvanizing" zinc-rich spray paints, flame spraying, etc. -- and you are welcome to read them all.

But the basic issue is that all these alternate application methods would not exist if one was generally better than the other ... they all have advantages and disadvantages. And you simply can't become an expert, able to evaluate which coating method is better for every situation, based on a forum response. It can take years; at the least, you'd need to read several books, not a couple of paragraphs :-)

What the readers hopefully can do for you is help you figure out which coating may be better for a specific actual application. So please tell us the exact application with as much data and specificity as you can, like the sizes of the washers and fasteners, the exposure conditions, desired life -- and we'll try to help. Apparently you currently use Sherardized components ... what do you think of them? Thanks.

Regards,

A. Many, many structures (bridges, buildings, etc.) are painted with zinc-rich paint as an alternative to hot dip galvanizing. The Steel Structures Painting Council (http://www.sspc.org) is an excellent starting point for literature and standards.