Ideas on corrosion protection, please.

N

NealB

Well-Known Member
Joined
19 Feb 2006
Messages
7,674
Location
Burnham on Crouch
Visit site
Last summer, I bought a lovely little Trident 24.

I've had a new rudder fabricated in 6mm mild steel, which has been welded to the stainless shaft.

The fabricator phoned yesterday to say that he'd sent it for galvanizing, but that they can't dip just the rudder....the whole, including shaft, needs to go in. A galvanised shaft will not fit into the bearings.

The fabricator suggests unwelding the blade, and getting that dipped, then rewelding. We'd then need to make good the galvanizing with zinc paint.

Does anyone have any other clever suggestions, please?

Could the stainless shaft be wrapped up in something to stop it being galvanised?

Would blasting, then epoxying, of the blade be better?

Would powder coating be a silly idea?

Anything obvious, I've missed?

Thank you for your thoughts.
 
Scrape the galv off to fit the bearings?
Epoxy would be fine. Won't last for ever, nothing does...
 
Hard work. Two bearings say 24" apart long and tedious, might be easier to chemically remove, stand shaft in a tube, Rydlyme would remove the Zinc, that's the way I would go.
 
Find your nearest Sherardizing plant. Its a vapour deposition process (with zinc). Sleeve the shaft (with a steel tube) and seal off, coat the lot then remove the protective tube. I believe there is one major processor and some others. Its not much more expensive than conventional galvanising.

If you have difficulty finding, send me a PM and I'll dig through my memory bank and archives (but I'm a bit out of touch being a few thousand miles away).

Wild thought - epoxy coating with a zinc powder filler? sort of a gal 'copper coat'

Jonathan
 
Stainless steel doesn't galvanize. It gets hot, but doesn't react the same way carbon steels do in molten zinc.
Its commonly thought that galvanizing is a single layer coating, formed by dipping things in molten zinc. It is that, but more. Its an alloying process, where suitable steel presented to molten zinc will form a series of alloy layers on the surface of that steel. The alloy is also overcoated with pure zinc as a result of being immersed in it.
The alloy layers are harder than carbon steel. (so would be hard to "scrape off" as suggested above - harder than "scraping off" some steel.
Welding after galvanizing is an option in some cases, but the welding will destroy (vapourise) the zinc of the galvanizing where the steel temp gets hot enough. (about 6-700C, so well under welding temps). Zinc rich paint is a poor substitute for galvanizing, as this is zinc particles suspended in a binder, meaning that they are not in electrical connection to each other. Being normally continuous, galvanizing is electrically connected to itself, allowing good electrolytic protection. Zinc rich paint is better than nothing though!

I can't think of a sheradizing plant in the UK that handles something as big as a rudder, but there might be one. Size will almost certainly be the limiting factor. This is an otherwise god suggestion.
Other suggestions:
* make the whole rudder blade from stainless, welded to the stainless shaft.
* Galvanize blade, weld to SS shaft, clean up the mess and then epoxycoat the whole.
Extend the shaft with saddles to accommodate a bolted connection for the rudder blade. Galvanize the blade, bolt whole together.
 
You must log in or register to reply here.

Share this page

Top