Anyone cast zinc anodes?

V

Vegable

Well-Known Member
Joined
4 Mar 2010
Messages
284
Location
me : Pwllheli Boat : Arisaig
Visit site
Wandering around boat parks you can always see discarded zinc anodes. The temperature of molten zinc is only about 50 degrees higher than that of lead and I've done a lot of lead casting for fun.
Has anyone tried making their own anodes from discarded ones? Is there any reason why it won't work?
Mike
 
Vegable said:
Wandering around boat parks you can always see discarded zinc anodes. The temperature of molten zinc is only about 50 degrees higher than that of lead and I've done a lot of lead casting for fun.
Has anyone tried making their own anodes from discarded ones? Is there any reason why it won't work?
Mike
Click to expand...

This has been asked several times. See:
http://www.ybw.com/forums/archive/index.php/t-151873.html
http://www.ybw.com/forums/showthread.php?117545-Recycle-anodes
http://www.ybw.com/forums/showthread.php?37227-Anodes

for starters.

AFAIR, the crucial points are:

1) The mould must be bone dry, to avoid steam explosions.
2) The melting temperature is manageable with a suitable blowtorch, but as you say is hotter than for lead.
3) Be careful about selecting the material, as there are several different compositions for anodes, which are not mutually compatible. Some have Magnesium in, others have aluminium, depending on the environment for which they are designed. There isn't an easy way of telling t'other from which for people without access to an analytical chemist.
 
I've used discarded anodes to cast zinc "pencils" to machine into anodes for my engine. Not too difficult, but rather a lot of surface dross IIRC. No problem as it was subsequently cut off.
I've read here that iron contamination of the zinc is a bad thing, so probably best to use, say, a plaster mould.
Beware of the "zinc shakes", from toxicity.
 
macd said:
There was a thread a while ago in which Vyv Cox, I think, warned that unless the zinc is of very high purity it can have serious adverse electrolytic effects.
Click to expand...

Yes, the problem occurs when the iron content of the anode is increased above a tiny amount. A MIL specification covers it, referred to here http://www.boatzincs.com/use_milspec_a18001k.html Many anodes will have a steel strap cast into them. Just melting the whole thing will doubtless lead to an iron content higher than it should be. You might then assume that your anode was providing protection when it was doing no such thing, a situation that several saildrive owners have discovered to their considerable cost.
 
For the last several years, I've made my own anodes for my Autoprop. They are much more difficult to make than ordinary pear-shaped anodes, but the Autoprop anodes are hideously expensive, and it's very satisfying to make my own.
The pear-shaped ones are quite easy, but a search on the 'net comes up with some quite reasonably priced ones, so for me anyway, not worth the bother.
 
I've experimented with re-smelting old zinc for engine pencil anodes. I figured that as the melting point of any iron or steel in the process was so much higher than the zinc, contamination at a molecular level would not occur. Presumably when the steel strap is bonded into the original anode it didn't cause a problem, and I actually use a steel crucible and melt the zinc in the sitting room woodburner, which is pushing my luck on several fronts.

The anodes seem to work but that's very hard to quantify. They certainly dissolve through the course of a season.

If they were available off the shelf I'd probably get them that way as the cost of getting it wrong would be disproportionally high!
 
When I get a little time I plan to cast some anodes.
I got a bag full of pure zinc billets from a local galvaniser for a few quid.
If you seriously want cast anodes then I suggest getting some good material in a similar way.
I expect the "good bits" of old anodes have been selectively removed in service hence all the dross described above.
 
Halo said:
When I get a little time I plan to cast some anodes.
I got a bag full of pure zinc billets from a local galvaniser for a few quid.
If you seriously want cast anodes then I suggest getting some good material in a similar way.
I expect the "good bits" of old anodes have been selectively removed in service hence all the dross described above.
Click to expand...

The dross is very easily pushed off the molten metal. I melt mine in a large ladle with a spout. The ladle holds more than enough for one anode.
 
I have been making pencil anodes for several years and they work just fine.

I use a simple crucible to separate the pure zinc from the slag that forms on top. Two brass 28mm plumbing compression elbows with a short length of 28mm copper between. I then use a piece of 22mm copper about 50mm long inserted into a 28mm stop end fitting to form a mould.

Wearing gloves in a very well ventilated space with a bucket of water nearby I heat the entire crucible thoroughly with it cocked at about 30 degrees in the vice, using a turbo torch. The mould is ready nearby, clamped in another vice or mole grips.

Once the crucible is nice and hot I let the old pieces of zinc melt into the upper end of the cruible, where a lot of slag and dusty ash forms, but you then see the pure zinc running into the lower part of the crucible. When the lower part is about to overflow it is ready to pour.

Briefly preheat the copper mould, re warm the crucible again then using a large water pipe plier style wrench pick the crucible up from the vice and pour into the mould.

Forms a nice pure slug that can then be turned to final size. Once cool this knocks out of the copper tube, and one piece of copper will make up to 6 - 10 slugs, by which time it starts to mutilate.

Oh yes you also need a small lathe to turn to final size and a tap to thread the end. I initially used to cast the thread over a bolt through the base of the 28 mm stop end fitting, but found the thread strength wasn't up to much so a hand cut thread is more effective.

Sea water based marinas will almost always be littered with scrap zinc. Aluminium is obviously lighter, and magnesium is just not used on saltwater, but if you do pick one you will soon know when it bursts into flames as you try to melt it.
 
My Dad made some for his BMW engine, got the wasted steel plug and cast round that.

IIRC he used a primus for the heat, an old cast iron pan as the crucible, and zinc pellets from BDH for the zinc, a lump off an old anode would work.

Sand was used for the mould using a purchased anode as a blank.

As mentioned, zinc fumes can be nasty so it's best to do the deed in a well ventilated spot, in the garage with the doors open was sheltered but open enough.
 
You must log in or register to reply here.

Share this page

Top