# Can You Melt In Mold



## Anonymous

What is the advantage to pouring molten metal into a mold 
as opposed to melting casting grain in a graphite mold?


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## nickvc

Generally speaking the use of graphite moulds to melt in is not advisable due to the wear on the mould from the flame and the gassing and corrosive action of any fluxes used.Although graphite moulds are used in continuous casting they wear very quickly and the costs starts to mount fairly quickly.My advice would be to use a salamander crucible to melt in and pour into a pre warmed ( important ) cast ingot mould sprayed with wd40 or similar to ease removal,if using flux keep it and re run it when the quantities make it worth while to remove any tiny beads included.


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## Harold_V

Yep---what nickvc said. If they were intended to be crucibles, they most likely wouldn't be called molds. 

Graphite, when heated, burns, no different from charcoal, although slightly harder to ignite. If you attempt to melt in a mold, the form is changed rapidly. 
Perfectly acceptable results can, and will, be attained by using molds made of cast iron. Ductile is preferred, for it has far superior tensile strength and thermal shock resistance.

Molds should be preheated, then coated with a smoky acetylene torch for best performance. A mold so prepared eliminates any risk of soldering of values to the mold, and will easily discharge the ingot, simply by inverting the mold after the metal solidifies. 

Harold


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## goldsilverpro

The melting in the mold thing has been answered several times before. I think that several people have ruined their molds by trying it. Like Harold said, they are called "molds" for a reason.

Like nickvc said, WD-40 can be used as a mold release in the cast iron molds. I used to preheat the molds and then drizzle a little motor oil in. The oil was spread with a cheap paint brush to totally coat the inside of the mold. This was done quickly to keep from burning the brush. Don't use so much oil that it puddles. When the molten metal is poured into the mold, the oil burns and this produces a carbon coating. Same with WD-40. I didn't use acetylene unless the bar was being sold. Acetylene produces prettier bars.

If I remember right, the Salamander crucibles are a higher quality clay/graphite and are expensive. I most always used the silicon carbide ones and only bought the regular clay/graphite ones when they were out of SiC. In my experience, the SiC ones lasted longer. I don't remember if I ever tried the Salamanders.


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## Lou

Salamander/Vesuvius are the best brand. They last forever and are really quite durable. I don't remember ever seeing proper crucible care mentioned on this board:

1.) When your new crucible arrives, make sure that it is free of cracks. A light rapping with a wooden dowel rod should make a ringing noise like a bell, it should not "thunk" (there may be voids in it/hollow spots).
2.) Bake the crucible slowly to remove any moisture that may be present in it. Most crucibles have not had their glaze set yet. Heat to 100*C over an hour, then 20*C/hr for the next 5 or so hours, after the water is driven off, you may go faster. Don't do it in a domestic oven, the glaze stinks at higher temperatures!!
3.) Take it to its expected operating temperature, hold it, then let it cool in the furnace. It may then be used. Remember to put a piece of cardboard in between the crucible and the plinth it sits upon, lest the crucible stick!
4.) Store all crucibles in a dry, cool place. Do not keep them in a humid environment. Technically, you should always heat them slowly at first. SiC crucibles are long-enduring and a great investment, despite their higher price. They are far less prone to thermal and mechanical shock when compared to clay-graphite. They don't oxidize as easily and they are wonderful for gold and silver but do not use for the PGMs for the same reason why one should avoid graphite: carbide formation.


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## Noxx

http://www.budgetcastingsupply.com/Crucibles.php


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## Anonymous

Besides the wearing on the mould are there any other drawbacks from melting in a graphite mould? I would like to make some 1 grain ingots but can only find graphite moulds and don’t fancy pouring into such small cavity’s. I would be using a small furnace to do so, does this make any difference?


nickvc said:


> Generally speaking the use of graphite moulds to melt in is not advisable due to the wear on the mould from the flame and the gassing and corrosive action of any fluxes used.Although graphite moulds are used in continuous casting they wear very quickly and the costs starts to mount fairly quickly.My advice would be to use a salamander crucible to melt in and pour into a pre warmed ( important ) cast ingot mould sprayed with wd40 or similar to ease removal,if using flux keep it and re run it when the quantities make it worth while to remove any tiny beads included.


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## Barren Realms 007

cdraig said:


> Besides the wearing on the mould are there any other drawbacks from melting in a graphite mould? I would like to make some 1 grain ingots but can only find graphite moulds and don’t fancy pouring into such small cavity’s. I would be using a small furnace to do so, does this make any difference?
> 
> 
> nickvc said:
> 
> 
> 
> Generally speaking the use of graphite moulds to melt in is not advisable due to the wear on the mould from the flame and the gassing and corrosive action of any fluxes used.Although graphite moulds are used in continuous casting they wear very quickly and the costs starts to mount fairly quickly.My advice would be to use a salamander crucible to melt in and pour into a pre warmed ( important ) cast ingot mould sprayed with wd40 or similar to ease removal,if using flux keep it and re run it when the quantities make it worth while to remove any tiny beads included.
Click to expand...



Are you sure about the size you are trying to pour? It is going to be hard to do this consistantley. IMHO  
1 gram = 15.432 grains

I think you might be better off trying to drill a series of holes in a crucible and shotting gold at a certain constant melting temp with your recieving crucible at a certain temp and then a required # of inches above a water vessel to cool the shot. Experimentaion involved here. But I bet one of the experts can give you the peramiters on the setup.


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## Anonymous

Well to be honest I wasn’t planning on pouring, I assumed you could melt in a graphite mould but then I saw the post I quoted. :?:


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## Barren Realms 007

cdraig said:


> Well to be honest I wasn’t planning on pouring, I assumed you could melt in a graphite mould but then I saw the post I quoted. :?:



Graphite is ok for a crucible. It does not work good as a vessel to melt/mold in because it absorbs heat so readily it also degrades rapidly at the temp that gold melts at. That is my understanding.


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## Harold_V

It would serve you well to understand that it borders on the impossible to pour ingots of a given size. Regardless of your best attempts, there will be errors, due in part to minute particles sticking in the melting vessel, or even to the odd spark that leaves the molten gold, taking with it a globule of gold. That is very common when torch melting. 

If you are serious about casting grain sized pieces, I will assure you, that isn't going to happen. If, by chance, you can be happy with random grain sized bits, the result of making gold shot, that does happen, but the ratio is horrible. You might generate a half ounce of such bits pouring a couple hundred ounces of shot. 

I will confess, if your objective IS to make tiny bits of gold, melting them in a dish and allowing them to solidify, removing them with a tweezers, is likely to be the most successful. 

You can NOT pour thin slabs of gold. It just doesn't happen, regardless of your attempts. For example, if you use a mold that casts a reasonably thick one ounce ingot, to pour a half ounce ingot, what you get is an incomplete ingot. 

In order to produce small bits of gold with reliability, it is generally rolled to a specific thickness, then punched. 

Are you serious about a grain sized bit? It's not very large. 

Harold


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## Anonymous

I am truly serious about making 1 grain bits. I have seen a graphite mold that has 117 x 1 grain oblong cut outs. My initial thought was you could simply melt them in the mold, but other comments seem to say it is not possible due to degrading of mold. I would be prepared to sacrifice a mold to do one or two castings. Do you think this is impossible? I would be using a furnace not a torch. :?:


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## Barren Realms 007

cdraig said:


> I am truly serious about making 1 grain bits. I have seen a graphite mold that has 117 x 1 grain oblong cut outs. My initial thought was you could simply melt them in the mold, but other comments seem to say it is not possible due to degrading of mold. I would be prepared to sacrifice a mold to do one or two castings. Do you think this is impossible? I would be using a furnace not a torch. :?:



Go for it Skippy, You can only believe what your eyes tell you if you don't beilieve the info here on the forum.


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## HAuCl4

Warning: Way out of the box suggestion/idea :

Melt with an induction furnace in mid-air (levitation) and drop into mold?. Never done it, never have seen it done. But I believe it is possible!. :lol:

http://www.youtube.com/watch?v=_uHoZI-ZWyE

http://www.youtube.com/watch?v=qJkc0N6Wbco

http://www.youtube.com/watch?v=PVtcp4JZ8FA


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## goldsilverpro

cdraig said:


> I am truly serious about making 1 grain bits. I have seen a graphite mold that has 117 x 1 grain oblong cut outs. My initial thought was you could simply melt them in the mold, but other comments seem to say it is not possible due to degrading of mold. I would be prepared to sacrifice a mold to do one or two castings. Do you think this is impossible? I would be using a furnace not a torch. :?:



May I ask your purpose in wanting to produce these? If I am picturing it correctly, gold from that mold would have somewhat of a wire shape. Why not just buy or roll thin 24K gold wire and cut it to 1 grain lengths. If my math is right, .02" dia (about 24 gauge) gold wire, about .65" long, would weigh a grain. Wire of .03" dia (about 20-21 gauge) would be about .288" long. Or, maybe, buy or roll thin sheet and use a hand punch to make discs, like these:
http://cgi.ebay.com/ONE-Troy-Grain-GOLD-BULLION-ROUNDS-BARS-9999-PURE-/220608619916?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item335d4c658c

I would think either of these methods would be more accurate than trying to cast the "bits" from powder.


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## Anonymous

Fascinating stuff HAuC14 thanks for that. 
Barren Realms I was not suggesting I did not believe what I have read on the forum. It is just that the sum of what has been written on graphite moulds is not clear and some things seem to suggest it is possible but not economical. Maybe if some one could point out why they sell graphite moulds for single grain bars in the first place? I am a learner and don’t know a lot about casting it is one of the things I am here to learn about. Many thanks.


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## Barren Realms 007

cdraig said:


> Fascinating stuff HAuC14 thanks for that.
> Barren Realms I was not suggesting I did not believe what I have read on the forum. It is just that the sum of what has been written on graphite moulds is not clear and some things seem to suggest it is possible but not economical. Maybe if some one could point out why they sell graphite moulds for single grain bars in the first place? I am a learner and don’t know a lot about casting it is one of the things I am here to learn about. Many thanks.



A graphite mold works great for the aplications that are used here on the forum. They work fine as a crucible but get degraded by use and loose thier shape and structure. The fluxes also attack them. Maybe I gave to short of an answer. It is hard to adapt this type of mold for both applications and get consistant results.


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## lazersteve

I cast into graphite molds regularly. I simply preheat the mold by resting the melting dish on top of the mold while the gold is melting. Then I lift the dish and pour the gold into the mold. 

The bars do not come out the same size every time for all of the obvious reasons previously mentioned. 

I like GSP's idea of cutting 24K gold wire to the right length. You can make your own wire by casting a rod of 24k gold, then using a draw plate or rolling mill to stretch the rod into the desired diameter wire.

Steve


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## Anonymous

A rolling mill is definitely the way that’s a great suggestion GSP's.
Nice 1
:lol:


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## Harold_V

cdraig said:


> I am truly serious about making 1 grain bits. I have seen a graphite mold that has 117 x 1 grain oblong cut outs.


That settled my curiosity. You may be on the right track with an idea, but you have your terminology wrong

There is no such thing as a 117 x 1 grain oblong cut. Grains are units of measure of weight, not lengths. You can not describe a cut as you have, so we have no idea what you really want. 



> My initial thought was you could simply melt them in the mold, but other comments seem to say it is not possible due to degrading of mold. I would be prepared to sacrifice a mold to do one or two castings. Do you think this is impossible? I would be using a furnace not a torch. :?:



Sure, you could do it in a mold, assuming the mold was considered disposable. You might even be able to use it more than once---but each time you use it, it will have changed size, and it may degrade in such a way that the resulting ingot of gold keys to the mold, so you'd have to break the mold to recover the gold. 

You can avoid that problem by melting in an inert atmosphere. You'd have to use a graphite mold, to insure there'd be no gold soldering to the mold---and you'd have to start with once melted gold to insure it melted without any activity, or loss of weight. 

I still question your objective, however. There are easier ways to accomplish the same end, and they're reliable, although not cheap. Nor would be melting in an inert atmosphere, however. 

Harold


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## goldsilverpro

> There is no such thing as a 117 x 1 grain oblong cut. Grains are units of measure of weight, not lengths. You can not describe a cut as you have, so we have no idea what you really want.



Harold, I think he may have meant that there were 117 oblong depressions, each of which held 1 grain of gold. At least, that's the way I took it.


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## shyknee

cdraig said:


> A rolling mill is definitely the way that’s a great suggestion GSP's.
> Nice 1
> :lol:


ya then use one of these to make those rounds
8)


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## Barren Realms 007

There you go one pop = a grain and then have a 1 oz bar for them to lift and sell them the grns at $5.00 a pop. Capitolism at it's best. 8)


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## Harold_V

goldsilverpro said:


> There is no such thing as a 117 x 1 grain oblong cut. Grains are units of measure of weight, not lengths. You can not describe a cut as you have, so we have no idea what you really want.
> 
> 
> 
> 
> Harold, I think he may have meant that there were 117 oblong depressions, each of which held 1 grain of gold. At least, that's the way I took it.
Click to expand...

Thanks, Chris. That does put a different slant on things. 

The problem with his idea is that you and I both know that you simply can't pour gold to a specified weight. A mold small enough to yield a consistent diameter would have to be closed faced---like the book end molds you used to use for casting silver. To assume you could have a series of scratches (for lack of a better description) that got surface poured with the expected results of individual wires, or strips, is absurd. Gold simply won't cooperate, regardless of anyone's best attempts. If it was that easy, they could produce planchets for coins by pouring. They don't. The material is rolled to a predetermined thickness, then blanked with a punch and die, which guarantees size, weight and uniformity. 

I know I sound like I'm trying to toss a bucket of water on this guy's barbeque, but there are certain absolutes that you simply must accept. This is one of them. If he has the inclination to pursue a given project, he'd be so much better served to observe discoveries that went before him instead of trying to re-engineer the wheel. 

Harold


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## Noxx

Harold, I believe he's talking about this:






By experience, I can tell that it is impossible to cast 1 grain gold bars due to gold surface tension. Even with my 5 gram ingot mold, I can't get a nice finish on the top.


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## Harold_V

Noxx said:


> Harold, I believe he's talking about this:
> 
> 
> 
> 
> 
> By experience, I can tell that it is impossible to cast 1 grain gold bars due to gold surface tension. Even with my 5 gram ingot mold, I can't get a nice finish on the top.


The problem, of course, is that you can not pour so the molten gold ends up flush with the surface. You will pour too much, or not enough, so in spite of the individual cavities, the end result is failure. I dare say that it will also fail to fill the corners of the cavities. 

An attempt to pour gold to a specific weight is wasted time. There are other means to achieve the desired end that are known to work reliably. 

Unless one is trying to reinvent the wheel, there are times when one is best served to followed accepted convention. It may not be as interesting, but it's a sure way to achieve success. 

Harold


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## MargueriteMingorance

Maybe he's a railroad modeller, and he wants _real_ miniature gold ingots for a treasure car.


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## Harold_V

MargueriteMingorance said:


> Maybe he's a railroad modeller, and he wants _real_ miniature gold ingots for a treasure car.


I get the humor, but regardless of one's intentions, that simply doesn't work. When small bits of precious metals are desired, they are generally produced by dies, not molds. 

Harold


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## MargueriteMingorance

Harold_V said:


> MargueriteMingorance said:
> 
> 
> 
> Maybe he's a railroad modeller, and he wants _real_ miniature gold ingots for a treasure car.
> 
> 
> 
> I get the humor, but regardless of one's intentions, that simply doesn't work. When small bits of precious metals are desired, they are generally produced by dies, not molds.
> 
> Harold
Click to expand...


Yep, I can see the problem of controlling the pour on something that small. You'd have problems with voids in the corners, with over- or under-pouring, with keeping the mold sharp, and with getting your parts out. Some kind of stamp would be much better, either a die you can hit with a hammer, or some sort of punch or large pliers.

And one grain is _tiny_, it is 1/480th of an ounce (troy).


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## ceritus

The reason he wants to make one grain bars is because of http://www.ebay.com/itm/New-Capricorn-Zodiac-1-Grain-999-Pure-24kt-9999-Fine-Solid-Gold-Bullion-Bar-/220989320407?pt=LH_DefaultDomain_0&hash=item3373fd6cd7
and 

http://www.ebay.com/itm/1-Grain-24k-AU-999-Solid-Gold-Bar-w-free-shipping-U-S-A-/110849573513?pt=LH_DefaultDomain_0&hash=item19cf264289

Saw some go for $8 with free shipping....


Gotta give the people what they want.


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## MysticColby

cdraig said:


> Fascinating stuff HAuC14 thanks for that.
> Barren Realms I was not suggesting I did not believe what I have read on the forum. It is just that the sum of what has been written on graphite moulds is not clear and some things seem to suggest it is possible but not economical. Maybe if some one could point out why they sell graphite moulds for single grain bars in the first place? I am a learner and don’t know a lot about casting it is one of the things I am here to learn about. Many thanks.



I believe that the people who make these molds have never used them and just make them so they can charge more money to people who really want it to work.
I've tried to do what you suggest (on a 10-gram multicavity mold I made), and the top 1/8" of the mold had crumbled away into ash by the time the silver melted.
What might be possible is sintering. put 1 grain of powdered gold in each cavity, heat with torch for short time, powder will condense into glob of gold (this doesn't actually reach the melting temp, and it's more of a bead than bar, but it'll give you 117 beads of 1 grain each  ) It only works if the amounts are small enough that they heat up much quicker than the mold.


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## Abbarue

I think that's the reason he wanted to know if the gold could be melted in the mold. 
He probably was planing on putting fine gold dust into each little mold and then heating it in a furnace. 
He did say he wanted to use a furnace and not a torch. So the whole mold gets heated at once. 

Any way! I'm a new member here! I just signed up today, and wanted to say hello to everyone! 
I'm wondering what's the best way to purify gold oxides? 
Should they be treated with a chemical like HCl or should they be heated directly in a crucible. 
I read that Digold trioxide decomposes at 150 C, but can this just be melted into a gold button in borax?


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## Geo

Abbarue said:


> I think that's the reason he wanted to know if the gold could be melted in the mold.
> He probably was planing on putting fine gold dust into each little mold and then heating it in a furnace.
> He did say he wanted to use a furnace and not a torch. So the whole mold gets heated at once.
> 
> Any way! I'm a new member here! I just signed up today, and wanted to say hello to everyone!
> I'm wondering what's the best way to purify gold oxides?
> Should they be treated with a chemical like HCl or should they be heated directly in a crucible.
> I read that Digold trioxide decomposes at 150 C, but can this just be melted into a gold button in borax?



gold oxide is soluble in hcl. gold oxide decomposes at a pretty low temperature so if it were mine, i would put it in solution and precipitate it as elemental gold before melting. im sure theres a simple redox method maybe like the silver reduction with sodium hydroxide and sugar. i dont know if sugar will work on gold oxide like it does for silver oxide but it sure would be quick and easy.


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## Irons2

I've 'Melted' Gold Oxide into a bead. One problem is if you heat it too quickly, the outgassing of Oxygen will blow particles all over your furnace. At a minimum, you will get tiny beads of Gold all over the inside surface of your crucible. It's better to warm it in a test tube to drive off the oxygen, then melt the resulting Gold Powder with a little borax for flux.
It does dissolve in HCl, which makes it handy for making Gold solutions of known concentration.


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## Abbarue

Irons2 said:


> I've 'Melted' Gold Oxide into a bead. One problem is if you heat it too quickly, the outgassing of Oxygen will blow particles all over your furnace. At a minimum, you will get tiny beads of Gold all over the inside surface of your crucible. It's better to warm it in a test tube to drive off the oxygen, then melt the resulting Gold Powder with a little borax for flux.
> It does dissolve in HCl, which makes it handy for making Gold solutions of known concentration.



Thanks! 

The oxide dust is so fine I'm afraid It will blow all over if I take a torch to it, how can I best keep it together?

I'm from Canada and was wondering if someone knows a good place in Canada to order crucibles from? 
Any other Canadians on this forum?


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