I was recently sent some documentation on a small electric furnace for melting and heat treating metal which is of a good size for hobbiests but still a lot more expensive than building your own charcoal furnace.
One of the comments in the document said:
You must be aware of the melting and pouring temperature for the metal that you want to melt.
The melting temperature of aluminium is well documented at 660°C but I’d not really heard much about the pouring temperature. So I thought I’d research a little into what pouring temperature was recommended for aluminium. I’d like to point out at this point that my charcoal furnace does not have any temperature control and I don’t have a way of measuring the temperature at the moment.
Bronzecasting.co.uk suggests that:
The optimum pouring temperature of the alloy is also partially determined by the mould’s size and capacity (ie the anticipated wall thickness of the cast). A lower pouring temperature is usual for thick walled or solid casts, with higher temperatures preferred for thin walled designs.
The “Handbook of foundry practice, Fachverlag Schiele & Schön, Berlin” provides some numbers for this with temperatures between 620°C for thick walled upto 730°C for thin walled. Thanks to Dr. Stephan Rudolph for the providing the table of numbers.
Mohammad B. Ndaliman and Akpan P. Pius from the Federal University of Technology, Minna, Nigeria did a good study back in 2004 into casting temperature of aluminium alloys and recommend a temperature of 680°C – 700°C to get the best surface finish and found that temperatures over 750°C increased the risk of problems with blowouts and casting defects.
ForestWeb suggests that charcoal can burn upto 1100°C but I suspect that my little furnace does not get the metal to those temperatures but it would be good to know a bit more about what’s going on so I can get the best results from my infrequent casting sessions.