Reconstituted zincs

[Bruce K]

My previous boat has a custom shaft/prop anode, a mould for the two halves came, and went with the boat. Both the PO and me cast/recycled said anode for at least 20 years with no corrosion problems for either shaft or prop. I just scrounged old anodes from the slip skip.

[wguinon]

Originally Posted by a64pilot

Besides the honestly deadly fumes etc, this is the problem, first new zincs are an alloy and not “pure” even extremely expensive gold is only .999 pure.
But as zincs get wasted the zinc is leached out leaving behind an alloy that is lower in zinc, melt it down for an anode and you have a less effective anode.

Besides, try aluminum anodes, I predict you’ll be happier with them, I know I am.

When you skim the dross from the molten zinc the puity is restored.

[wguinon]

Originally Posted by a64pilot

Besides the honestly deadly fumes etc, this is the problem, first new zincs are an alloy and not “pure” even extremely expensive gold is only .999 pure.
But as zincs get wasted the zinc is leached out leaving behind an alloy that is lower in zinc, melt it down for an anode and you have a less effective anode.

Besides, try aluminum anodes, I predict you’ll be happier with them, I know I am.

When you skim the dross from the molten zinc the purity is restored.

[RaymondR]

Originally Posted by Jono as 2234

Thanks for all the responses, I'll give away the idea. Seems too much trouble, dirty, dangerous, possibly ineffectual and bad manners.
Removing the anodes, polishing them back to solid metal would work, however I only slip annually and would not trust the remaining zinc for another year.
I already cast aluminium, so there's an idea. I just scavenge old window frames etc, however the end result is often a little honeycombed. May be an advantage as it increases the surface area.
Or maybe I just spend the $100 like always - teardrop, rudder halves and bow thruster.
Jon

Naah don't be a woos.

Go ahead and cast some from the scrap zinc and run some tests on them.

Connect the zinc to one lead of your digital multimeter and a piece of SS to the other, immerse them in sea water with the multimeter on the millivolt scale and note the voltage generated. Then switch to the milliamp scale and see how much current is being generated. Then do the same with the store bought one and compare the results. My prediction is that the volts will be the same however the current will only be the same if the two pieces of zinc being tested have the same surface area.

Let us know the results so that we can criticize your methods properly and do a good thorough nay say on them.

[Jim Cate]

I'm a chemical engineer not an industrial hygienist and no expert in any of this. Does anyone know better?

Bill, your analysis sounds far better than all the ignorant nay-saying. If done with reasonable ventilation and not 24/7, there should be no significant health hazards. The quality of the product will depend upon feed material and any further contamination of the zinc. I see no reason that the Cd and Al components will be missing from any sound material from the old anode.

I'd do it if required by lack of supply or finance... pretty low risk activity IMO.

And fwiw, none of the boatyards around here keep old anodes under lock and key... they mostly chuck them into the general waste bins. But then, I'm an ill-mannered bloke at the best of times.

Jim

[slug]

Originally Posted by Jim Cate

Bill, your analysis sounds far better than all the ignorant nay-saying. If done with reasonable ventilation and not 24/7, there should be no significant health hazards. The quality of the product will depend upon feed material and any further contamination of the zinc. I see no reason that the Cd and Al components will be missing from any sound material from the old anode.

I'd do it if required by lack of supply or finance... pretty low risk activity IMO.

And fwiw, none of the boatyards around here keep old anodes under lock and key... they mostly chuck them into the general waste bins. But then, I'm an ill-mannered bloke at the best of times.

Jim

This boat carries about 85 kg of zinc anodes ..

10 x7.2 kg pie plate anodes , 2x2.5 kg rudder anodes. 7 x .5 kg strap anodes , prop anode , plus various internal sea chest and heat exchanger anodes

The shipyard I use collects about 3 cubic meters of spent zinc anodes per year

Zinc is about 7000 kg per cubic meter

This is a substantial pile of valuable recycle metal

[cal40john]

Originally Posted by pilott

Watch out for the fumes from molten zinc - very toxic

You made me wonder how bad. This is what I found, do you have more authoritative or relevant sources?

From MSDS for die casting zinc alloy
http://www.aimedia.co/media/msds/ZINC.pdf
Potential chronic health effects
Inhalation:
AFTER INHALATION OF FUMES: Inhalation of fumes or very fine dust may lead to metal fever, a flu-like syndrome with
symptoms of fever, chills, malaise and cough. The syndrome is benign and symptoms usually disappear after a few
hours. Symptoms include: Feeling of weakness, vomiting, and nausea


This guy thinks the danger of fume inhalation comes from vaporizing zinc that occurs at much higher temperatures than the melting point, from activities such as welding galvanized steel and melting brass.
https://theodoregray.com/periodictable/zincsafety.html

[sanibel sailor]

Originally Posted by NorthernMac

There are old timers who melt lead tire weights to cast bullets.

They used to. Wheel weights are now made of zinc rather than lead. You can look and they are marked "Zn"

Don't know if this was a cost or health issue.

[fstbttms]

Recasting spent anodes is only going to do one thing- eat up a lot of time and effort and provide you with inferior anodes. Seriously, do you care so little about your boat that you can't be bothered to install new ones?

[a64pilot]

Originally Posted by wguinon

When you skim the dross from the molten zinc the purity is restored.

You’ll get the “trash” off, the non metallic composition that doesn’t melt at the metals melting temp, but you don’t restore the alloy.

Anodes are an alloy, they aren’t pure zinc, yet the wasting isn’t across all the alloy, just that active part wastes, leaving the inactive parts behind.
So when you recast zincs you have a higher concentration of the inactive ingredient, so your zincs will last longer, cause they are less effective.
Is this enough to matter? no idea, but it’s not worth the effort to recast to me.
We cruise, so I have had to learn to do without a lathe, drill press, oxy acetylene torch and TIG welder etc that I had before.
Carrying a good vise was not easy, but I have to have a vise.
Making a mold to cast zincs and carrying it around along with a torch capable of melting zinc just isn’t worth it.
Welding zinc or cad plated steel was always worrisome as I have gotten a little sick from doing it myself, but so long as it was stick welding outside in a breeze you could be careful and avoid the white smoke, it also left a greenish powder too.
But at my age, exposure to a toxic substance just isn’t worth it, I’m real careful with Acetone now too.

This is one of those yes you can, but why bother things.
But also I have gone over to aluminum for anodes, and don’t use zinc anymore, and wonder other than just inertia of it’s always been that way, why anyone uses zinc anymore, there seems to be no advantage to it.

[Dsanduril]

A64 Thanks for that

It lead me to this relatively interesting article about zinc vs. aluminum. From someone who sells both (and Mg as well). Will definitely have to give this some thought on next exchange.

For those discussing up-thread about re-forging scrap aluminum, read the notes about the specific alloy used for anodes - not at all your traditional construction aluminum. Also read about the cadmium required in the zinc anode in order for it to work.

[AKA-None]

Having been zinc poisoned once in the shipyard I can affirm that you do not want that. And it doesn’t take much.
Personal experience firsthand not something someone told me.

[Jim Cate]

Originally Posted by slug

This boat carries about 85 kg of zinc anodes ..

10 x7.2 kg pie plate anodes , 2x2.5 kg rudder anodes. 7 x .5 kg strap anodes , prop anode , plus various internal sea chest and heat exchanger anodes

The shipyard I use collects about 3 cubic meters of spent zinc anodes per year

Zinc is about 7000 kg per cubic meter

This is a substantial pile of valuable recycle metal

slug, you seem to live in a different environment than most regular sailor/cruisers. And you employ SHIPyards rather than the itsy bitsy little boatyards/slipways that we mere mortals employ.

Perhaps in that exalted place, folks dutifully place their enormous spent anodes into the yard's recycle pile. It hasn't been a practice in the many yards that I've used or visited over the years, and to suggest that we abrogate proper manners by failing to do so seems kinda presumptuous to me.

I'll not be doing the recasting thing myself, but don't think the job is beyond the capabilities of a regular cruiser if a restricted budget or remote location should encourage the practice.

Jim

[slug]

Originally Posted by fstbttms

Recasting spent anodes is only going to do one thing- eat up a lot of time and effort and provide you with inferior anodes. Seriously, do you care so little about your boat that you can't be bothered to install new ones?

Yah...making your own sounds like a fools game

Any impurity will retard the anode

When an anode is removed for service it should only be high pressure power washed and have its electrical contacts cleaned

The service life of the anode is determined by weight

After 50 percent weight loss the anode is replaced

Wire brushing anodes to make them “ look good “ can destroy the effectiveness of the anode by depositing metal from the brush onto the anode surface

Anodes with stainless steel fasteners must use a transition washer made of mild steel

Stainless and zinc are enemies ..a stainless to zinc interface will erode the zinc at contact, create a poor electrical connection and retard the anodes effectiveness

Serrated steel anode washer

[RaymondR]

If one was choosing anodes for a 300,000 super tanker a few percent efficiency difference between zinc alloys might make a difference. If one is knocking up a few prop shaft anodes for a comparatively miniscule pleasure vessel it matters not at all.