[TowerTalk] Rohn U-bolts
grants2 at pacbell.net
Sat Jul 29 14:43:17 EDT 2017
Zinc corrodes about 1/30 the rate of steel per year when exposed
outdoors. Add salt to the air and erosion is much faster. Zn is also
sacrificial relative to iron so small scratches in the coating has the
steel still protected.
There are two principal forms of zinc on steel - electroplating and hot
Electroplating is cheap and fast and thin enough the steel as plated
dimensions change very little. It is usually 0.0002" for spec'ed
fasteners, probably less from hardware store stuff from China, and will
protect the steel outside for a year or two.
Hot dip is usually specified around 0.005" thick so lasts about 25 times
as long. Parts are cleaned, fluxed and dipped in a molten Zn bath.
Just like soldering. The Zn is thick enough that bolts and nuts need to
be sized differently to fit together. Also, holes tend to get Zn
droplets inside when hoisted from the molten Zn kettle, so may need
filed or reamed for bolts to fit. The design of the parts to be HDG has
to consider they will be immersed in molten Zn above 800 deg F.
Ace Galvanizing in South Seattle had a minimum charge of $125, or $1.25
per pound of steel, whichever is larger, when last I was there a year
ago. Great folks, easy to work with but a very busy place with many
tons dipped per day.
On 7/29/2017 9:27 AM, Rob Atkinson wrote:
> I've heard that you have to be careful sourcing hardware for a tower,
> especially from a non-tower manufacturer. It has to do with the
> galvanizing. From what I've been told, the non-tower intended
> hardware has shall we say, "casual galvanizing" and the tower stuff is
> galvanized to be up in a hard to get to place for a long time.
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