Removing Zinc from Bronze Propeller Nut

[Snow and Sledy]

I have a project boat that previously experienced some severe electrolysis. One of the components that looks the best are the two bronze prop nuts, the bronze is great, but a bunch of the zinc from the nut-cone has transferred to the bronze. It filled in all the voids in the castle-nut like slots, around between the threads, and between the end of the shaft and crown of the "acorn".

My concern is that the tighter threads and zinc filling in the space between the end of shaft and top of acorn will bottom out before I get enough pressure on the new props I'm installing. I've picked a small amount off with a Dremel and dental pick, but it will be very slow going to clean out inside the whole thing.

Does anyone know a good way to get the zinc off, without damaging the bronze itself?

 

[C lectric]

What is the thread? If it is a standard thread you may be able to get a tap to suit and then use the tap to clean the threads.
Maybe ask at some machine shops as threading is a common job for many.
THe plugged slots could be milled out without damaging the nuts
OR
once the bulk of the zinc buildup in the threads is gone then use a drill at the end of each slot and drill through. THen use a file to finish the slots.

You might also try an acid such as Muriatic, a very dilute form of hydrochloric.

Also Barnacle Buster is known to eat brass fittings by attacking the zinc.
If the nuts are bronze then they should be immune.

Just be sure the nut is in fact real bronze and NOT Manganese bronze which is not a bronze, rather a brass with about 45% zinc.

Manganese "bronze' survives seawater immersion die to the shaft zincs.

 

[SteveK]

white vinegar cleaned up used pencil zinc nuts

 

[jleonard]

I always used muriatic acid to remove zincs.

 

[Bmarler]

Heat it with a torch. Zinc melts at around 800f. Bronze is double that.

 

[garbler]

Are you sure these whitish deposits are zinc ? Was the entire nut coated with this material ?
What did the prop look like, was it kind of shiney ?

Depending on your answers they may point to your problem. The amount and depth of the material in the slots has me confused as if this is a type of galvanic plating it should be all over the nut and not packed into the slots. When you plate metal you need a source of DC current a cathode and an anode. For this purpose zinc anodes on a boat should be negatively charged while the cathodes or your bronze or copper alloy fittings are positive. If you wanted to plate this is reversed. The zinc becomes the positive cathode and the bronze or brass is negative or the anode. To complete the electrolytic plating cell you need a good electrolyte such as saltwater for current to move through and DC current. The amount of current will dictate the speed with which plating deposits transfer but almost any amount of current will suffice. The more current the faster but a leaking constavolt or battery charger nearby could provide enough current.

Now I’m getting into deep water here and my technical knowledge is about get beached but maybe Steve A. will drop in and sort this out. I do know that there are some reliable indicators of stray current and one is a bright propeller. If you suspect your vessel is located in a hot slip or dock where there may be stray current I suggest talking with other owners to see if they have seen similar conditions. And/or get a reference cell that you can hang in the water off your boat to confirm DC stray current

Good luck
Rick

 

[Snow and Sledy]

Well, I got it all out, not sure what the stuff actually was, held a propane torch on it for about 15 minutes, got everything glowing nicely but did not melt away, then soaked in white vinegar, which seemed to soften it up but didn't remove, eventually set a punch on it and whacked away with a hammer. Ended up with a decent little pile of junk (ignore the few spruce needles from my garage floor) and an acceptably clean prop but now discolored nut. Thanks for the help.

(sorry about the upside down photo)