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Bruno Facca · 10-04-2002, 09:21 PM

Let me start by saying that the process of casting copper, mainly getting a blast furnace that can make and mantain that much heat requires months of work and a lot of trial and error. You also spent a LOT of fuel (whatever you use) to get the copper to the right temp, wich is far from 800 C, actually 800 C would be the temp for brass (I guess that is the name of that "yellow" metal in english, that is 50% copper 50% zinc or chrome I can't quite remember) . It may worth it if you want to make several blocks but if you only want to make one or two for yourself I think there are better methods, I'm not sure you'll get the same results, mainly with the roughness of the inside surface but that depends on a lot of things. If you are planning on doing a lot of them, well, you're competition for me wich is not good for business

.. I know some people (like me) just have to "do stuff themselves" instead of buying it so you'll probably do it anyway no matter what I say. I made that joke about competition but it's kind of true, I spent a lot of time and effort going after people that could teach me better casting techniques so I can make my blocks, if I were to share everything I learned my company (wich is starting out) would be dead before it's "officially born".
Copper can be a real bitch to work with in almost every way, casting it is not an exception, it's hard to cast pieces without any air in it or "smooth edges" you get when the air stays "around" the Cu mass inside the mold. There are a couple of things that can be done to avoid that: the most important are the air exits in your mold, they have to be put in the right spot and they have to be the right diameter, if they're too thin the air won't get out in time, if they're too large too much copper will escape trough them. Another thing is, copper melts at 1085 C, but at this temperature it's not completely liquid, it's kind of "sticky", you have to get it to around 1300 C, at that temperature it's as liquid as water (of course it's a lot heavier) so any air inside it just get out like it would get out of most liquids. Once the copper is totally liquified you have to "swirl" it inside the "bucket" so any impurities stay on top of it, as it's a very dense metal (8,9g per cubic centimeter), you just take out the impurities (if there are any) with a kind of spoon that is made especially for this.
I have been casting several water blocks without any air bubbles, I already took some of them and sanded them until they literally dissapear (turn into a bunch of copper dust) without finding one single air pocket. It's the result of the combination of the right temperature, appropriate air exits in the mold, pouring it at the mold at an appropriate speed (so it doesn't have time to cool down and trap any bubbles) and I guess the molding material I use. When you use steel it absorbs a big part of the heat of the melted copper as soon as you start pouring it in the mold so it may cool down too quickly, in that case the air doesn't have time to get out and you get those nasty air bubbles. I use something we call "green sand" here in my country, it doesn't conducts any heat so the copper takes some time to cool down after it's poured in the mold.

10-04-2002, 09:21 PM	#19
Bruno Facca Cooling Neophyte Join Date: Jul 2002 Location: Brazil Posts: 70	Let me start by saying that the process of casting copper, mainly getting a blast furnace that can make and mantain that much heat requires months of work and a lot of trial and error. You also spent a LOT of fuel (whatever you use) to get the copper to the right temp, wich is far from 800 C, actually 800 C would be the temp for brass (I guess that is the name of that "yellow" metal in english, that is 50% copper 50% zinc or chrome I can't quite remember) . It may worth it if you want to make several blocks but if you only want to make one or two for yourself I think there are better methods, I'm not sure you'll get the same results, mainly with the roughness of the inside surface but that depends on a lot of things. If you are planning on doing a lot of them, well, you're competition for me wich is not good for business .. I know some people (like me) just have to "do stuff themselves" instead of buying it so you'll probably do it anyway no matter what I say. I made that joke about competition but it's kind of true, I spent a lot of time and effort going after people that could teach me better casting techniques so I can make my blocks, if I were to share everything I learned my company (wich is starting out) would be dead before it's "officially born". Copper can be a real bitch to work with in almost every way, casting it is not an exception, it's hard to cast pieces without any air in it or "smooth edges" you get when the air stays "around" the Cu mass inside the mold. There are a couple of things that can be done to avoid that: the most important are the air exits in your mold, they have to be put in the right spot and they have to be the right diameter, if they're too thin the air won't get out in time, if they're too large too much copper will escape trough them. Another thing is, copper melts at 1085 C, but at this temperature it's not completely liquid, it's kind of "sticky", you have to get it to around 1300 C, at that temperature it's as liquid as water (of course it's a lot heavier) so any air inside it just get out like it would get out of most liquids. Once the copper is totally liquified you have to "swirl" it inside the "bucket" so any impurities stay on top of it, as it's a very dense metal (8,9g per cubic centimeter), you just take out the impurities (if there are any) with a kind of spoon that is made especially for this. I have been casting several water blocks without any air bubbles, I already took some of them and sanded them until they literally dissapear (turn into a bunch of copper dust) without finding one single air pocket. It's the result of the combination of the right temperature, appropriate air exits in the mold, pouring it at the mold at an appropriate speed (so it doesn't have time to cool down and trap any bubbles) and I guess the molding material I use. When you use steel it absorbs a big part of the heat of the melted copper as soon as you start pouring it in the mold so it may cool down too quickly, in that case the air doesn't have time to get out and you get those nasty air bubbles. I use something we call "green sand" here in my country, it doesn't conducts any heat so the copper takes some time to cool down after it's poured in the mold.