# Graphite molds



## colu41 (Jul 6, 2013)

I've always used wooden molds. And they've always turned out great. Well I had to buy a new torch and it burns way hotter. Making the silver bubble in the wood mold now.

If I bought a graphite mold, if I had a secondary torch on the mold while melting, will that allow a decent pour? And not harden instantly?

I use Mapp by the way.


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## ilikesilver (Jul 6, 2013)

yes, you have to keep both hot, you dont need two torches, If you check and search the forum you will see that most people will hold there molds in insulation on fire brick after they have heated the mold for several minutes. When you pour from your melting dish, it has to be a nice even motion, while keeping it hot. Check it out, there are several real nice post on this subject. Tim


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## bswartzwelder (Jul 6, 2013)

I'm not sure if it will work, but I don't see any reason it shouldn't. When I am ready to pour my first gold bar, I am going to place a small metal baking pan with a thin layer of sand in it on top of my hot plate. The mold will be on the sand. Set the hot plate on high and allow all moisture to boil off/evaporate. Heating the mold gradually should eliminate thermal shock and even if the mold does fail when you pour the gold, the gold will be caught in the sand/metal pan underneath. Not only that, but it will be easy to make sure the mold is flat and not tilted, and the sand will provide a nice stable base. The few graphite molds I own are too precious for me to chance breaking them. Having said that, a representative from the place where I bought them says preheating is not necessary. I just don't fully trust that sentiment. They just might want to sell more molds.


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## colu41 (Jul 6, 2013)

I may look into insulating. Maybe consistent heat and insulation on the mold and crucible.


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## colu41 (Jul 7, 2013)

So I attempted a small pour into an old graphite piece I drilled out myself. It turnes out a lot better than I figure but. Can someone explain why it sort of caved in the middle? I understand the cooling lines but as far is it making an indent in the middle. Not sure how to prevent that. The bottom also came out a bit porous.


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## FrugalRefiner (Jul 7, 2013)

colu41 said:


> Can someone explain why it sort of caved in the middle? I understand the cooling lines but as far is it making an indent in the middle. Not sure how to prevent that. The bottom also came out a bit porous.


colu41,

That indent in the middle isn't a bad thing. When gold is pure, it shrinks quite a bit as it goes from a molten (liquid) state to a frozen (solid) state. The more impurities, the less this occurs.

When you pour your ingot, it begins cooling from the outside, all around, but especially around the sides and bottom where it touches the mold. The outside freezes while the inside is still molten. As it cools from the outside -> in, the outside is already frozen, so it can't shrink. As the inside freezes and shrinks, it pulls the top down, usually in the middle.

To minimize the effect, you can try to heat the top of the ingot after you pour. The more you can shift it to cooling from the bottom -> up instead of the outside -> in, the flatter your ingots will become. There is, of course, a limit to what you can achieve with simple torches, etc. I think your ingot looks great!

Dave


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## colu41 (Jul 7, 2013)

Thank you for that! I poured another 52 gram bar and the top was much smoother, but the bottom was still extremely porous. Almost like its only bubbling from the bottom while the top is smoothing out. Any suggestions on that?


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## FrugalRefiner (Jul 7, 2013)

Some "bubbling" is unavoidable. You can minimize it by sooting your mold and preheating it before you pour.

Dave


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## colu41 (Jul 7, 2013)

I do both but. Still get the sponge look on the bottoms :/


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## colu41 (Jul 7, 2013)

Here's my second one. Top came out a lot better but bottom is still bubbly. I ordered up a 2 oz kitkat mold and I'm hoping I can minimize this as much as possibly seeing kitkats the bottom of the mold is kind of the top of the bar. Ill just try so trial an error I guess when I get it. Thanks for all your help!


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## lazersteve (Jul 17, 2013)

Trapped gases and/or gases escaping from the structure of the graphite can lead to the 'bubbles' you see on the bottom of the bar. Try thoroughly heating your mold prior to sooting to drive out any moisture trapped in the graphite structure, then soot, and finally heat the mold while casting the silver.

Steve


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## samuel-a (Jul 18, 2013)

colu41,

No way around it... as long as you use a torch, some oxygen will be absorbed.
With practice you could reduce it sugnificantly, but not eliminate it completly.
Sometimes the top is freez before the bottom, thus not letting O2 escape and producing those bubbles.


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## niteliteone (Jul 19, 2013)

What type of torch are you using ???
Are you able to reduce the amount of oxygen to the flame ???

Silver is like a sponge to oxygen, which will cause many problems with pouring a good loaf.
I always use an acetylene torch with a reducing flame to limit the oxygen exposure as much as possible. If you are using a propane or mapp gas torch, try blocking some of the air holes around the nozzle and see if that helps. Just don't choke the flame completely.


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## lazersteve (Jul 19, 2013)

samuel-a said:


> colu41,
> 
> No way around it... as long as you use a torch, some oxygen will be absorbed.
> With practice you could reduce it sugnificantly, but not eliminate it completly.
> Sometimes the top is freez before the bottom, thus not letting O2 escape and producing those bubbles.



Sam,

I torch cast silver bars all the time and as long as the mold is hot and properly sooted, I never have any "bubbles" on the bottom. When I cast silver I typically cast several hundred ounces of various sized bars in a sitting and the first bar will sometimes have a bubble or two. Once the mold is up to temperature (usually after the first bar) the remainder of the bars are free of bubbles. I recast the first bar to remove any traces of bubbles from it, so that all the bars are bubble free. 

If you do not have enough silver to cast several bars, simply recast the same bar until the mold is up to temperature, or mount a second torch (propane is fine) that burns directly on the graphite mold before, during, and after casting.

Steve


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## samuel-a (Jul 19, 2013)

Steve,

This is the practice i was talking about.

Personally, i cast with a furnace+graphite crucible to a sooted and heated graphite mold with a protective flame.
The silver bar comes out oxygen free from the first pour with no 'bubbles' formation (top or bottom).


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## DylanDownright84 (Apr 23, 2017)

Finally! Just what I've been looking for! Haha! Finally getting the hang of using the search function better. Time to recast some silver. Thanks guys!


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