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Anonymous
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What is the advantage to pouring molten metal into a mold
as opposed to melting casting grain in a graphite mold?
as opposed to melting casting grain in a graphite mold?
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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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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
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
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.
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.
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.
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.
Noxx
Well-known member
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Anonymous
Guest
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:
Barren Realms 007
In Remembrance
cdraig said:
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
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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. :?:
Barren Realms 007
In Remembrance
cdraig said:
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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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
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
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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. :?:
Barren Realms 007
In Remembrance
cdraig said:
Go for it Skippy, You can only believe what your eyes tell you if you don't beilieve the info here on the forum.
HAuCl4
Well-known member
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
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
cdraig said:
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
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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.
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.
Barren Realms 007
In Remembrance
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.
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
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
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A rolling mill is definitely the way that’s a great suggestion GSP's.
Nice 1
:lol:
Nice 1
:lol:
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That settled my curiosity. You may be on the right track with an idea, but you have your terminology wrongcdraig 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.
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
