Smelting temp issue ?

[yovinny]

I'm sure it's been covered lots before, but please help a newbee smelter out.

I've been casting in the electric pot for years, but yesterday was my first time doing a large smelting with the cast iron pot-propane fish frier set-up, and I experienced something I havent seen before in the electric pot.

Using some reclaimed range lead I bought here (my first time with this also), I got it up to 650*, added some tin and stirred well. All seemed good at this point and there was just a little bit of gray dross on top. Checking the temp was still at least 650*, I then fluxed with a few tablespoons of sawdust and a little bullet lube, stirring well again.

Now my small amount of gray dross turned into 4-5 tablespoons of gray/black dross and silver metal mush.
I tried both going a little bit hotter and fluxing again, but couldent get this 'mush' reduced and back into the mix, so I skimmed it off before pouring my ingots.

Was this 'mush' zinc or ??? or am I just doing this to cool or doing something else wrong ?

TIA
Cheers, YV

[bobthenailer]

Zinc does not usually melt at 650 degrees but i guess it could get mushy ? I smelt at 600 degrees
After fluxing you will mix the lead ,antimony and tin togeather and remove the impurties suspended in the mix that rise to the surface ,skim off those impurties.

[R.M.]

If what you're smelting is range lead, I doubt you have much if any zinc. I'd run it up to 700, you might just be in the slush stage.

[shadowcaster]

Zinc starts to melt at 787 F and boils at 900 F. Range lead should not have any zinc to begin with. I smelt at 675 F as anything cooler it begins to slush up. I have often wondered if elevation has anything to do with melting temps like boiling water does.

[Jim]

From CHEMICALELEMENTS.COM (http://www.chemicalelements.com/elements/zn.html)

Name: Zinc
Symbol: Zn
Atomic Number: 30
Atomic Mass: 65.39 amu
Melting Point: 419.58 °C (692.73 K, 787.24396 °F)
Boiling Point: 907.0 °C (1180.15 K, 1664.6 °F)
Number of Protons/Electrons: 30
Number of Neutrons: 35
Classification: Transition Metal
Crystal Structure: Hexagonal
Density @ 293 K: 7.133 g/cm3
Color: bluish

[shadowcaster]

Good catch Jim... Got my C's & F's mixed up. :-)

[yovinny]

The thing was, my lead looked wonderfull at 650* and was completely melted.
I added the tin, stirred it up good, checked temp, and it still looked wonderfull, with maybe 1/4 tablespoon of fine black dross on top.

I could have quickly skimmed that little bit and poured ingots, but instead I decided to try fluxing with sawdust/bullet lube and it quickly went downhill and turned into a mess.

I use the same tin and flux with the same sawdust/bullet lube in my electric pot without issue, so I dont think it's that.

It was near freezing out and I use the electric pot inside, so maybe the top of my mix got chilled ? even though the temp said 650* down in the middle of the pot ?

I think I'll just have to try again, a little bit hotter.

[plainsman456]

I always add more sawdust when these things show up and heat it a little more.
It will mix back in.

[a.squibload]

One day my lead turned to slush like that,
my homemade burner was running big yellow flames.
Incomplete combustion made so much soot under the
pot it insulated from the weak flame. Cleaned the
outside of the pot & added air injection, fixed it.