Yes, the chap's largest Aluminium casting is 20g, and I think Brass was an 80g casting failure. Low melting point metals are faster than than high, so perhaps 10 to 20 minutes for the Aluminium. Double or more for cast-iron. He also preheats the metal and crucible with a blow torch before microwaving them.

Stewing is definitely a problem with Brass, because he asks for advice. Zinc loss always happens when melting Brass, and I think heating slowly to melting point would make it worse. Zinc fumes are toxic too.

Overall I was impressed and there was some good problem solving done to get it working. As an electronics buff, my main beef is cruelty to magnetrons! Domestic microwaves rarely run flat out for that long!

Main advantage I thought was melting metal indoors by plugging a cheap domestic item into the mains.

Dave

Back in the 1970’s we had a 3kW microwave oven which was used for drying samples. Not the best, because nearly dry samples did not absorb much microwave energy! Not the only poor devision when they initially changed form chemical analysis to X-ray fluorescence. They later went back to drying over a hot-plate heater.

However one, or more, of the ‘clever’ shift workers included steel nibs in the samples (on purpose, of course). I can’t remember if they got hot enough to melt, but the ceramic dishes, silica sheets, etc, were certainly annihilated or seriously damaged.

Edited to add that with exceedingly good insulation, there is not actually much heat power needed to melt some metals.  It is cumulative!

Edited By not done it yet on 19/05/2023 20:57:45