[TowerTalk] My Hot-Dip Galvanizing Experience (Long)

[Dr M J DiGirolamo]

Dear TT Colleagues,

Last week I had some hot-dip galvanizing done and wanted to share my experience
with all of you.  I was really intrigued by the entire process.

Some background first.  I'm following the steps to erect a 72' self-supporting,
crank up tower.  I purchased it from the estate of a SK and, though it's only 6
years old, the "T" shaped base mounting bracket showed some areas of rust.  It
came painted black from the factory but, being previously mounted in a lush back
yard next to sprinklers, oxidation found its way through the paint.  Also, I've
ordered new anchor bolts from the factory, which are 1" x 27" long with a
standard 8tpi thread.  To my surprise the bolts were not galvanized!  This
astounded me.

First, I took the "T" mounting bracket to be sandblasted to remove the old
paint.  This turned into a horrendous job.  Shortly after the job had begun, I
received a phone call saying the paint was nearly "bullet proof."  What was
supposed to be a $20 sandblasting job ended up costing me $85 due to grinding
and sanding needed prior to the sandblasting. Okay, that finished the job.  Now,
loaded with the new anchor bolts in the car, I picked up my nice shiny t-plate
and headed straight to the galvanizing plant.  I knew if I waited a day or two
that rust would immediately begin to form on this naked metal.

The plant was a fascinating place to visit.  In this long building there were
several 40 foot long tanks, some 5 feet wide and 4-5 feet tall, an overhead
crane, running on rail tracks, from one end of the building to the other.  The
crane was used to raise and lower items into the various tanks.

My items first went into a vat containing a caustic solution to remove grease
and dirt.  From there they went into a vat of hydrochloric acid to remove scale
and rust.  Then to rinse vat and then into a vat of ammonium chloride solution,
which acted as a flux.  The final step was to dip the items into a vat of molten
zinc at 850F.  WOW, when these items hit, molten zinc spitted and splattered all
over the place!  The workers all knew what to expect and stayed clear.
Experience tells these folks how long to leave items in the zinc vat.

 The entire process took about 1 hour for the T-plate but an additional 2 hours
for the anchor bolts because they needed more cleaning time in the caustic and
acid tanks.  When the items came out, they really shined - wow, was I ever
impressed.

I asked what the cost would be to do a 3, 20' section of tower and was quoted
~$400.00 if it came in galvanized.  The old zinc would need to be stripped off
in the baths first.  Usually these places have a $200 minimum charge but it
doesn't hurt to talk to the owner, like I did :)

On the way home, I stopped at a shop and purchased oversize galvanized bolts to
fit my now oversize 1x8tpi threads.  The fit was perfect and the original nuts
became useless (anyone need 18 of em?).

Thought some of you would be interested in reading my experience - hope I
haven't bored you all to death!

73,

Mike DiGirolamo, W4XN
Charlottesville, VA