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"Galvanizing on threaded product is too heavy"

May 2, 2016

Q. I look for your kind assist in clarifying the maximum allowable thickness of hot dip galvanization, because we sent threaded materials to galvanization factory and after galvanizing did not ride the nuts, by measuring the galvanization layer, we found that it exceeds 1 mm.

Mahmoud Ahmed
MANARAT Steel Fabrication - Jedda, Saudi Arabia

May 2016

A. Hi Mahmood. Could you please be as descriptive as possible about the "threaded materials" you sent out for galvanizing? People may offer different corrective suggestions depending on the lengths and diameter (for example, some sort of centrifugal spinning might reduce the thickness, and might be practical for short bolts but not long threaded rods; chasing the threads might be practical for some short components, cutting the threads on the nuts after galvanizing is often practical on large sizes, etc.).

To my limited knowledge, there are no implied specs to be followed; and failure to specify what is needed is probably the largest cause of problems and contract disputes. If there was no specification involved in the galvanizing purchase order, unfortunately it is tricky and subjective to say the parts comply or fail to comply with "accepted practice". If the threads are literally drowned out by galvanizing drip, it might be reasonable to claim that "anybody would recognize this component as having lost its utility when it no longer has anything even resembling a usable thread"; but not fitting your nuts is a more dubious complaint.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

May 15, 2016

A. Mahmoud:

Most short to medium length bolts are put into a centrifuge or "spin-a-batch" while the zinc is still hot and the molten excess zinc is spun off leaving nice threads.

Some galvanizers use a steel brush on the galvanized threads while the zinc is still hot and molten.

On longer threaded products the threaded rods can be rolled down an inclined plane (while hot) and the excess zinc spins off.

Dr. Thomas H. Cook
- Hot Springs, South Dakota USA

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