Help! Silver Bars Won't Come Out Smooth (pic included)

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anon136

Member
Joined
May 20, 2014
Messages
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I'm at about my wits end with trying to pour nice bars. I'm not sure what im doing wrong. Every bar I pour has odd ridges and indentations on the bottom side (bottom when in the mold, top upon removal). Little imperfections i expect, ill just grind them off with my dremel, but i cant sand that sort of thing away, it would take way to much silver with it. Any information or advise you guys give will be appreciated. Thanks!

IMG_20140612_184833.jpg
 
there has been many posts on this, is this recovered silver, has it been through a silver cell, do you just pour your silver into the heated mold ? try use a secondary torch to heat the mold & silver during the pour.

never tried it but i have seen videos.

goldnscrap has posted some great videos

https://www.youtube.com/watch?v=bEGkoTc17Zw

(whats the trick to embedding youtube vids ?)
 
No I haven't tried torching my mold while pouring. I don't really have enough hands :p Maybe I can rig something up. Er or ill just have my wife do it and if it actually works THEN ill try to rig something up. Thanks for the suggestion.
 
Just a thought, but perhaps insulating the mold with a fibreglass nest might help?
 
I get it now! The bubbles are formed by oxygen. The fire consumes all of the oxygen in the area. So the fire should prevent oxygen bubbles from forming. Though it is a bit strange that, if i remember my facts from my years of government incarceration as a child, the atmosphere is like 80% nitrogen and i dont think fire consumes nitrogen. So i wonder why it forms oxygen bubbles with such a tiny percentage of the atmosphere but doesnt form nitrogen bubbles when the atmosphere is like 80% nitrogen.
 
I don't see a bit oxygen problem there, maybe a little, but i'm with Chris. It's a heat issue. Is that the bottom of the bar and how much does it weight? How are you melting it? What kind of mold? What kind of gas?
 
The flame or fire can be oxidizing or reducing depending on the air or oxygen content, so depending on the flame silver can actually gather oxygen from your torch of furnace flame, adjusting your torch to a more carbonizing flame or reducing flame can help as then the fire will take up the involved oxygen, and providing a more reducing environment for the silver.

Silver when heated to the melting point has a unique behavior with oxygen, when pure silver is melted in ambient air can absorb about ten times its volume, or about 0.3% of its weight of oxygen. On cooling to a few degrees above solidification, it abruptly releases most of its oxygen spitting out the oxygen, this oxygen can come from the air, or from your torch, starving the environment from air can help, as well as a carbon flux cover while melting.

Nitrogen does not burn, but some of it can combine with oxygen at these high temperatures forming some NOx gases.
 
goldsilverpro said:
You may be getting the silver too hot.
Click to expand...

Now thats an interesting notion! I have been trying to combat this problem by getting the silver as hot as possible! I have been pouring at about 2000F. What temperature do you recommend?
 
Palladium said:
I don't see a bit oxygen problem there, maybe a little, but i'm with Chris. It's a heat issue. Is that the bottom of the bar and how much does it weight? How are you melting it? What kind of mold? What kind of gas?
Click to expand...

Yes what you see as the top of the bar in the picture is the bottom of the bar when it is in the mold.

10 troy ounces.

electric melting furnace.

graphite.

see above.
 
butcher said:
The flame or fire can be oxidizing or reducing depending on the air or oxygen content, so depending on the flame silver can actually gather oxygen from your torch of furnace flame, adjusting your torch to a more carbonizing flame or reducing flame can help as then the fire will take up the involved oxygen, and providing a more reducing environment for the silver.

Silver when heated to the melting point has a unique behavior with oxygen, when pure silver is melted in ambient air can absorb about ten times its volume, or about 0.3% of its weight of oxygen. On cooling to a few degrees above solidification, it abruptly releases most of its oxygen spitting out the oxygen, this oxygen can come from the air, or from your torch, starving the environment from air can help, as well as a carbon flux cover while melting.

Nitrogen does not burn, but some of it can combine with oxygen at these high temperatures forming some NOx gases.
Click to expand...

Any idea how i might go about starving the inside of my electric furnace of air? Or suggestions in general for dealing with this problem while using an electric melting furnace?

Thanks so much everyone for your time and consideration.

*edit* also i cant find anything about this carbon flux cover. if you just mean sprinkling ontop the pure carbon element than that should be simple enough.

*edit2* i have an idea. i could put paper in my crucible before turning it on and then put the lid on tight and cover the hole. the paper would catch on fire and remove the oxygen, and then i believe the left over ash would be carbon, double win! maybe. what do you guys think?
 
If oxygen is a problem. which it probably isn't in this case, covering your silver with carbon can help, I would not expect much oxygen in a closed electric furnace.

http://www.hauserandmiller.com/reference/casting.html
 
butcher said:
If oxygen is a problem. which it probably isn't in this case, covering your silver with carbon can help, I would not expect much oxygen in a closed electric furnace.

http://www.hauserandmiller.com/reference/casting.html
Click to expand...

thanks for that great link! im using a 1100 watt element to heat up my mold. it says the temperature should be about 1000 degrees below the boiling point of silver. i know im going way off topic now. but does anyone have any idea how to measure the temperature produced by this thing?
 
anon136 said:
butcher said:
If oxygen is a problem. which it probably isn't in this case, covering your silver with carbon can help, I would not expect much oxygen in a closed electric furnace.

http://www.hauserandmiller.com/reference/casting.html
Click to expand...

thanks for that great link! im using a 1100 watt element to heat up my mold. it says the temperature should be about 1000 degrees below the boiling point of silver. i know im going way off topic now. but does anyone have any idea how to measure the temperature produced by this thing?
Click to expand...


Thermocouple and a multimeter, infrared thermometer

Eric
 
Silver has a unique property which allows it to absorb oxygen out of the air while it is molten and it spits it out while it cools down. There are different ways refiners deal with this problem.

One way is to blanket the melt and pour with argon gas, effective but it only pays for large operations.

Another is to burn a reducing flame in a torch pointing directly into the crucible for the entire melt, this flame will burn off the oxygen before it can be absorbed by the silver. When you pour a torch should remain concentrated on the molten metal and also held over the mold while the silver solidifies.

This is a pair of pouring tongs with a torch attached for this purpose.

IMG_0823.jpg

Silver is such a pain in the butt and for that reason alone I believe it should be valued at more than twenty bucks an ounce!
 
Or, the very best trick for large quantities when you're using induction not gas, and don't want to blanket it under an H2 flame (much cheaper than argon)...

a speck of lithium. A gram or so will treat several thousand ounces and eliminate the "crabby spikes".


When casting larger bars of silver, cooler metal is better, like with any casting.


You should heat your mold to a dull red heat. Pour with a steady, smooth motion (practice makes perfect). Soot your molds with acetylene, or spray the boron nitride mold release.
 
Lou said:
Or, the very best trick for large quantities when you're using induction not gas, and don't want to blanket it under an H2 flame (much cheaper than argon)...

a speck of lithium. A gram or so will treat several thousand ounces and eliminate the "crabby spikes".


When casting larger bars of silver, cooler metal is better, like with any casting.


You should heat your mold to a dull red heat. Pour with a steady, smooth motion (practice makes perfect). Soot your molds with acetylene, or spray the boron nitride mold release.
Click to expand...

Is it possible to still get a 999 pure product using this method?
 
Yes, you're adding at most a few grams to remove (and one will see it act) on many thousands of ounces--a mole of Li is very light, ~ 7 g/mol and will remove half a mol of dissolved O2 (which is quite a bit of O2). It will slag off as Li2O on the crucible walls. Li is too light to see on standard XRF, isn't looked for on ICP for good deliverable silver, and if found will never be more than tens of PPMs.

Example, 3 g of Li added to 3300 troy ounce melt lot; assuming no oxidation of Li to Li2O, and even distribution of metallic Li through melt:
3 g/(3300 try oz *31.103 g/tr oz) X 100 = 0.0029 % Li. This would knock it down to 4N5 if no other impurities were present :roll: . In practice, it has no impact.

Some even use natural gas through a stainless pipe to de-ox but the Li is safer/faster.

I don't think you have an oxygen problem--I think you have a too hot silver/too cool mold/too unsteady of a pour.
 
Lou said:
Yes, you're adding at most a few grams to remove (and one will see it act) on many thousands of ounces--a mole of Li is very light, ~ 7 g/mol and will remove half a mol of dissolved O2 (which is quite a bit of O2). It will slag off as Li2O on the crucible walls. Li is too light to see on standard XRF, isn't looked for on ICP for good deliverable silver, and if found will never be more than tens of PPMs.

Example, 3 g of Li added to 3300 troy ounce melt lot; assuming no oxidation of Li to Li2O, and even distribution of metallic Li through melt:
3 g/(3300 try oz *31.103 g/tr oz) X 100 = 0.0029 % Li. This would knock it down to 4N5 if no other impurities were present :roll: . In practice, it has no impact.

Some even use natural gas through a stainless pipe to de-ox but the Li is safer/faster.

I don't think you have an oxygen problem--I think you have a too hot silver/too cool mold/too unsteady of a pour.
Click to expand...

well thanks so much for the great information. what ever the problem be i think that i have enough information here to solve it with a little trial and error.

also are you still selling that 22l flask? if so would you take bitcoin?
 

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