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Purifying Wheel Weight Zinc

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john bunsenburner

Sun May 16 2010, 11:52AM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53

I'v been collectiong wheel weights inorder to make ZAMAK type alloys from the zinc to cast different objects, sparing me the hassel of high(er) melting points, and complex foundries. Now the weights I get are a mixture of Zinc, Lead and Iron. The Iron weights are sorted out by a magnet, and the lead can be melted away(please fill me in on the safety aspect of that). I am left untouched zinc weights, some with cast in Iron.

Now how do I melt this zinc and make it pure enough for use with ZAMAK?
What impurities are to be expected in wheel weights?

Until now I use a charcoal foundry with a cast iron crucible. I assume the Iron adds to impurities and so I will need to find a different crucible material.

Any information is highly appriciated both concerning the question I posed and overall casting of zinc alloys.

Thanks a lot.
JBB

hboy007

Sun May 16 2010, 01:43PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
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Posts: 373

I gathered that Zinc has a boiling point of 907 Â°C and can be distilled, the more common method seems to be a wet chemical purification so you get rid of other impurities and then plate the zinc onto an electrode. There seemed to be problems with mercury contamination at battery recycling plants so you may still run across zinc contaminated with mercury since wheel weights have to be cheap. I think you can't get the temperature high enough to dissolve noticable amounts of iron into the molten zinc if you go for the reduction process.
I'd rather play around with the chemicals than melting zinc in a crucible.
As for lead, if quickly forms an oxide coating which can be taken in as fine dust. Lead oxides are quite toxic but are relatively insoluble sho short-term effects won't show.

john bunsenburner

Sun May 16 2010, 03:03PM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
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Posts: 53

I really rather not distil zinc, ever...

Now the chemicals sound like something doable but I wonder weather I could just cast a zinc anode and then collect the pure zinc at the cathode.

Perhaps someone knows what alloy(s) I am working with and which impurities I am facing. Perhaps this entire hassel is a waste of time and my zinc is already relatively pure...?

Hazmatt_(The Underdog)

Sun May 16 2010, 04:30PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

why don't you just buy some zinc from a hobby chem store online?

klugesmith

Sun May 16 2010, 11:10PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Years ago, I had a fair amount of success casting Al and Zn alloys at home. Starting material was scrap Zn castings, scrap Al castings, and patio furniture tubing. Not as an expert, I think that cast zinc alloys (and wheel weights?) are relatively compatible with each other, and can be mixed in any proportion for low-tech sand-cast projects. (definitely not the case for Al and, expecially, Cu alloys). This is not to say you can make high quality thin-section die castings from random "Zinc" pot metal.

As a crucible for melting Zn I used a piece of steel pipe with a disk welded on one end, and some holes near the other end for a lifting bail made of 1/4-inch steel rod that could be sprung into place. Didn't worry much about steel inclusions, chrome plating on plumbing fixtures, etc. You can quickly melt dirty scrap and pour it through a screen to make clean zinc ingots, then dump out the steel inclusions along with the dross left in the pot. I would invest in heavy heat-resistant gauntlets and a pyrometer before getting a refractory crucible & tongs for Zn.

If you can't distinguish Pb from Zn weights by look and feel, could apply dilute muriatic acid & see which ones fizz.

How about making a pattern for some test bars with thick and thin sections, which you can bend to test strength and ductility?

One caveat: Zinc pot metal shrinks a lot as it solidifies, and loves to form a big cave at the thickest part of the casting. Put a very thick sprue or riser directly on that place or places.
And/or read some amateur foundry books -- what is Lindsay Press up to in this millenium?

Proud Mary

Sun May 16 2010, 11:20PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

If you Google for "zinc electrolytic refining" you'll see quite a few processes described.

klugesmith

Tue May 18 2010, 10:14PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Hazmatt_(The Underdog) wrote ...
why don't you just buy some zinc from a hobby chem store online?

I just found this source of cheap zinc.

They also have sheet lead, low melting alloys, bismuth, indium, ...

john bunsenburner

Thu May 20 2010, 04:46PM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53

Since I am located in central Europe most online stores will not be able to ship to me cheaply. However I found a source of pure zinc and aluminium, both cost $4.50 or Â£3.05 per KG. Is this price reasonable(I can get ingots in fixed sizes, this will have to be discussed with the producer, but they are very helpful and flexible)?

Also, as I wish to build a new foundry, any ideas on how to go about building a system of fueling which allows me to regulate temperatures, to allow me to find things such as casting temperatures and so on of my alloys? Would you recomend Waste vegtable oil(babginton burner?), propane or another fuel(denaturated alcohol, gasoline, charcoal?)?

Thank you for your input, it has been very helpful!

klugesmith

Thu May 20 2010, 05:14PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

The prices sound fair. If you get an ingot that is too big for your crucible, cutting it up can be a major chore.

I started with a charcoal furnace like the one in

and more generally

, about 25 years ago. Later upgraded to burn propane, using a simple burner made from iron pipe, with air from a hair dryer. I melted brass for one project, and 1.5 kg of copper once to see that I could do it.

My home-made pyrometer cost just a few dollars. From a clay-supply store I got some type K thermocouple wires, about 2 mm diameter and 400 mm long, and a few ceramic insulating beads with two holes. Used an oxyacetylene torch to fuse the wires at hot junction. At the other end were a low-voltage analog meter, on a wooden handle, with a series resistor to make the scale right.
You could use the freezing points of pure Zn and pure Al for calibration, but beware of getting the probe tip stuck. Which happened to me in Hawaii, when the volcano park rangers allowed a tourist to poke fresh lava with a stick.

Pictures to follow. Have fun!
-Rich

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