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Author Topic: How are moulds made for metal casting, such as making a ring?  (Read 64997 times)

Offline stana

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Hey Guys,
I was wondering..could i make my own ring? Im not talking sophicated equipment. Just basic stuff like a Clay mould (Clay from the Pound shop. Or if your American, the Dollar shop) And then melt an iron bar into the mould and let it set?

A few questions..
1) Would my clay mould be able to withstand the heat of the molten iron or would it snap?
2) What temerature does iron start to melt..Cause i was thinking i could use a lighter..but i doubt that would work..I dont have a furnace or a gas cooker, so would i be able to make a makeshift furnace out of brick and use that?

Thanks
« Last Edit: 10/05/2008 10:06:19 by chris »


 

lyner

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This is a huge problem.
You can't melt iron without an Oxy Acetalene flame. If you want to  melt a metal, try silver - can be done with an air blown propane gas torch. It is very difficult without the right gear.  Jewelery is usally cast using the lost wax process
You might be able to cast something in lead - but the fumes are dangerous and I certainly wouldn't want to wear a lead ring.
Most simple jewelery is made by fabrication and not by casting. Start with, say, copper sheet and cut out a shape and then bend it. You can solder bits together with a little lead solder.
Silver can be soldered together at around 600 degrees celcius but it needs skill if you want to make a nice job.
 

Offline stana

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Thanks.

What about Solder? I was talking to a friend that is in the plumbing profession, and he said i could melt solder with a lighter or candle (I dont have propane or an oxy whatever  :D)

Another question is. What can i use to make the mould. I was thinking i could melt wax..and then make a mould out of that? But i guessed it would just burn straight through, would play dough work?

Cheers
 

Offline Bored chemist

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How are moulds made for metal casting, such as making a ring?
« Reply #3 on: 10/05/2008 17:16:23 »
"You can't melt iron without an Oxy Acetalene flame."
That's news to our "iron age" ancestors.
Clay can be used as a mold for molten metal butyou have to fire it first.
Clay that has just been left to dry still has some water in it. You need to remove that water by baking the clay to red heat (at least) before you put molten metal in.
I still have a small scar on my hand from pouring molten lead into a mold that wasn't dry- the hot metal turns the water to steam and that steam blows molten metal about. That's not something you want. Playdough will burn and plaster or cement are even more full of water than clay.

You might want to talk to your plumbing friend about borrowing a blowtorch.
With a blowtorch you can just about melt copper or silver into shape.
 

Offline stana

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How are moulds made for metal casting, such as making a ring?
« Reply #4 on: 10/05/2008 18:49:22 »
Would any clay be sufficent to be fired? or does it have to be a certain kind?

Thanks
 

lyner

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How are moulds made for metal casting, such as making a ring?
« Reply #5 on: 10/05/2008 21:37:57 »
Quote
"You can't melt iron without an Oxy Acetalene flame."
That's news to our "iron age" ancestors.
The 'you' I was refering to was stana and not 'one'. I think his neighbours would complain if he tried to make an iron age furnace in his back garden. I seem to remember seeing pictures of a reconstruction and it was quite a business.

'Melting into shape' is not a way to get a fine artifact. You need to melt it and then cast it. What might work for a fishing weight in lead is not the same as a piece of jewelery. Casting is usually done in plaster of paris; they evacuate the wet plaster mould to get rid of bubbles then, as you say, dry it thoroughly (but slowly at a reasonable temperature). The mould is made around a wax 'positive' or 'male' original which melts and flows out through vent holes in the plaster mould as the  hot metal flows in. It's usually done using a centrifuge for small objects in order to make the metal flow into all the parts of the mould.
For big, crude, castings like cylinder blocks, a special sand is used. It starts wet (sandcastle style) and is baked to get it strong and dry enough. It is essential that the mould is easily broken to get the final artifact out without damaging it.
 

Offline Bored chemist

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How are moulds made for metal casting, such as making a ring?
« Reply #6 on: 11/05/2008 15:06:44 »
Plaster of paris is the hemihydrate of calcium sulphate ground to a powder.
When you add water to the powder it takes up further water to produce gypsum- the dihydrate. In doing this it sets (it also expands slightly which permits good castings).
If this gypsum is heated to about 128C it will lose water and reconvert to plaster. Further heating to about 163C will remove the last of the water. Casting any metal in plaster that hasn't already been heated to about 170C to remove all the water will risk spattering of the metal.
Lost wax casting ususally involves at least 2 separate stages, the first melts out the wax (and drys the mold) the second is where the molten metal is poured in. You can't just pour hot metal into a mold full of wax- there's no room. Also, for a lot of metals, the temperature would be high enough to boil the wax giving the same danger as having a wet mold.
Sorry if I'm labouring the point but, as I said, I still have the scar 2 or 3 decades later. That was spatter from a plaster mold and molten lead. I don't want anyone else making the same mistake.

Modern sand casting doesn't just use sand, the stuff is held together with a little resin.

"It is essential that the mould is easily broken to get the final artifact out without damaging it."
"Easily" is a relative term. Ask the men with a jackhammer and a sledge hammer here.

 

lyner

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How are moulds made for metal casting, such as making a ring?
« Reply #7 on: 12/05/2008 16:45:44 »
You must be right about the exploding wax - it melts when the plaster is being heated, of course - silly me.
Believe me, though, I have seen the whole casting process done to produce a silver piece, using plaster of paris - it produces a very fine end product.
 

Offline Make it Lady

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How are moulds made for metal casting, such as making a ring?
« Reply #8 on: 12/05/2008 17:26:32 »
I used to work in a sand quarry. We made resin coated sand for moulds. The recipe has to be just right in order for it to stretch rather than snap. I used to do quality control and made little bone shaped moulds with it and then tested things like tensile strength. It is possible to buy the stuff from a sand quarry that makes it. I used to climb on top of a truck and fill a bag from a hopper for a local craftsman. 
 

Offline neilep

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How are moulds made for metal casting, such as making a ring?
« Reply #9 on: 12/05/2008 18:05:16 »
Did someone mention bespoke made rings at far far less than retail prices ?

www.ringsbydesign.com

(Blatant advertising that really ought to be deleted)
 

Offline Bored chemist

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How are moulds made for metal casting, such as making a ring?
« Reply #10 on: 12/05/2008 21:13:47 »
Neil,
If you were to add some background about metal casting you would probably get away with it.

For the record I have cast jewelry in plaster molds. That's how I got burned (not badly but...) and I'd rather that nobody else made the same error.
I must admit that my efforts weren't up to much, but that's down to my hamfistedness; there's certainly nothing wrong with the technique.
 

lyner

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How are moulds made for metal casting, such as making a ring?
« Reply #11 on: 12/05/2008 23:12:12 »
You need a centrifuge and careful placing of vents to get good flow of metal. With small objects there's not much to make the metal go into all the little nooks and crannies.
btw, when I talked about  breaking the mould easily, I had things like bronze figurines and silver tracery - not gigantic stuff like the U tube movie. Impressive tho'.
 

Offline Make it Lady

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How are moulds made for metal casting, such as making a ring?
« Reply #12 on: 14/05/2008 12:50:17 »
Mould envy!
 

Offline precisioncomponents

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Hi stana:

if you are talking about how are moulds made for metal casting,such as making a ring?. I think Die-Casting Molds ( NCH precision) can help you. since before when I was a project engineer we made this kind mold for them.

thanks.
 

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