# bubbles and falling poured bar



## DensityRules (Mar 31, 2018)

Hello

I can pour half ounce bars with no issues at all. Tops look a little frosty but I polish it off

I've been trying to pour a 50 gram bar and I keep getting bubbles as it cools and the centre of the bar falls into the cavity formed by the bubbles. I'm using a soapstone mold.


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## jimdoc (Mar 31, 2018)

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=39&t=26126


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## DensityRules (Mar 31, 2018)

Thats a pretty good read

I'm using mapp gas and melting 999.

In the photo I posted I did my best to make a controlled slow cool by heating the top of the pour and warmed the mold first.

Any first hand experience?

My little half ounce bars dont have this problem. only the 50g I dont have a setup for larger pours.


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## DensityRules (Apr 1, 2018)

anyone? please


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## denim (Apr 1, 2018)

I would love to help you out on this but I have never dealt with silver, only gold. I use oxy-acetylene when I melt. Sorry I don't have any/better advice.

Dennis


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## Palladium (Apr 1, 2018)

Looks like a cold pour. Are you using Mapp as in the premixed store bought bottles?
You need more btu's. As the pours get larger in size it takes more btu's to keep the silver fluid and molten. You have just enough heat input to transition from a solid to a liquid phase. In other words the melting temperature. What you want to do is throw enough btu's to it that the mass will store enough so that when you pour it has heat in reserve. The silver will then release that stored energy in the form of heat in a more uniform way allowing time for the mass to become homogeneous and solidify in uniform way. Mapp burns at 3670 F so you problem is not so much temperature as it is btu's. In this case as ingot size increases their is not enough btu's to get the mass much above the melting temp because of the radiation in the form of heat loss. Again BTU'S !!!! Get a bigger orifice size or better insulate your dish with Kawool.


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## Palladium (Apr 1, 2018)

What type of dish are you melting in? You didn't mention that.
Please tell me it's not graphite!


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## ION 47 (Apr 2, 2018)

If it comes out of the melt oxygen, it will help charcoal. I'm in the crucible with the molten silver sprinkled on top of the pieces of charcoal, he took away the oxygen from the silver, and the ingot solidified smooth. Useful to place on cooling in the form of a silver torch restorative (red) flame propane torch.


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## DensityRules (Apr 2, 2018)

Palladium said:


> Looks like a cold pour. Are you using Mapp as in the premixed store bought bottles?
> You need more btu's. As the pours get larger in size it takes more btu's to keep the silver fluid and molten. You have just enough heat input to transition from a solid to a liquid phase. In other words the melting temperature. What you want to do is throw enough btu's to it that the mass will store enough so that when you pour it has heat in reserve. The silver will then release that stored energy in the form of heat in a more uniform way allowing time for the mass to become homogeneous and solidify in uniform way. Mapp burns at 3670 F so you problem is not so much temperature as it is btu's. In this case as ingot size increases their is not enough btu's to get the mass much above the melting temp because of the radiation in the form of heat loss. Again BTU'S !!!! Get a bigger orifice size or better insulate your dish with Kawool.



Yes I was using store bought mapp gas. Which after some research I understand is enriched with oxygen.

I switched torches. I used a turbotorch32 with acetylene and kept the heat on the pour as it cooled.
You're right. Deffos go big on btu. 

ALso once I began to heat the silver I kept the metal immersed in flame to prevent and o2 absorbtion as ive read liquid silver has an affinity for the stuff. 

I'll get a pic up soon


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## Palladium (Apr 2, 2018)

Good deal sir!


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