| When your steel product requires a surface finish that will be corrosion-resistant, there are a number of options. Perhaps the first
coating that comes to mind is some form of zinc. But within the zinc category, you can still choose from zinc electroplating, hot-dip
galvanising, mechanical plating, and zinc flake processes, and that's without discussing zinc-rich paints. So, which is the one you want
to use?
Zinc electroplating is the most common and as a result, inexpensive. The downside is that it produces thin coatings (around 10 microns)
which won't last and hydrogen embrittlement does occur. However, this is a good option for small parts with tight tolerances, such as
small fasteners.
Mechanical plating and zinc flake can produce a similar coating thickness but without the embrittlement and with improved
corrosion-resistance. During mechanical plating, the zinc is added to a tumbling barrel in metallic powder form and 'cold welds' to the
part. The zinc flake process spins the part in a liquid suspension of zinc, which is followed by curing in a furnace. Mechanical plating
is of course limited by the size of the barrel. Mechanical plating and zinc flake coating are less well known and have been developed for
specific applications.
Hot-dip galvanising is a great option where the highest corrosion-resistance is desired and you are not worried about dimensional
variation. Coatings of over 50 microns are applied by passing the steel part through a molten bath of zinc. The strength of the steel is
somewhat reduced due to the high temperature of the liquid which is important to keep in mind in high strength applications.
To read more about zinc plating, see the following links:
|
