Postby mm5aho » Fri Dec 11, 2015 1:52 pm
I'm in Moray today, but should be no problem to add your chain to the batch.
To answer the question:
Re-galvanizing isn't any different to the first galvanizing the chain got really, only that the old remaining zinc must be removed first.
To get the surplus zinc off and prevent the links welding to each other, requires movement during the couple of minutes while the zinc cools from dipping temp of 450C down to 419C the freezing point.
We have two ways to do this, one is centrifuging it - its dipped inside a perforated basket which is rotated at speed on withdrawl from the zinc. This centrifuges the surplus off. The downside of this is that the coating is thinner and so doesn't last as long.
The other is to have enough people present at that moment and to "rattle" the chains as they emerge, and keep them moving. Freezing happens quickly, so it doesn't take too much for this.
As Alistair has said, hammering any frozen ones afterward will loosen any individual links. Zinc is quite soft, and so "breaks" easily though the zinc closest to the steel is harder as that's alloy of zinc and iron. This means it doesn't break the full thickness of the coating off.
But its a job that galvanizers don't like generally - hence the arrangement to get it done being supervised by someone used to suffering the downsides of it not being done well, and knowing exactly what to look for!
Not being a "nice" job is why many galvanizers just decline to do it as too much trouble.
Geoff.
"Contender" Rival 32: Roseneath in winter, Mooring off Gourock in summer.
