Now, my question is, when I have 6 flasks waiting to be cast, each
requiring a different amount of metal, do I melt just the small
amount of metal needed for one flask, pour, vacuum, then measure
and melt the amount needed for the next flask, and so on until each
flask has been vacuumed?
That’s right, Alma. Those graphite crucibles are slick and smooth
inside. Pouring just a little of the metal is difficult. You might
manage a single melt if you were casting large flasks with many
ounces of metal, so the crucible started with a lot of metal, and a
difference in the pour of an ounce or so would only be a different
size button, and not mess up the nest pour. But it doesn’t really
save time to do this, since then the initial large melt takes
longer, and usually, when you open the furnace lid and pour some,
there is some chilling of the crucible and metal involved, so you
often might need, even with a larger single melt, to wait at least a
little bit for the temp of the melt to again stabilize, before
pouring another flask. .
What we do is to pre-measure the metal for each flask so all the
metal is ready before getting ready to cast anything. Film cans or
other suitable size simple containers, each with a post-it note
identifying which flask it’s for get lined up near the furnace, in
decreasing order of melt temp/flask temp. Starting with hottest
metal/flask first, you can just go down the line. with the furnace
preheated, the next smaller flask size melt goes quickly enough. If
there is a step down in the flask temp, needing the burnout furnace
to cool down a bit, we usually don’t turn the melting furnace off,
but just let it idle at melting temp, unless there will be a long
wait. Cooling down the melt furnace between melts, for lower melting
metals, is easy, since the furnace will have chilled a bit while
melting and pouring the previous flask. Just set the temp down to
what the next one will need when a melt is ready to pour, and when
you then, after pouring, add the next charge of metal, it simply
won’t overheat.
Note that the above reflects our casting volume and type. We’re
usually using 2.5 inch by 2.5 inch or thereabout flasks, each with up
to about six or eight rings, or a similar volume, usually requiring
anywhere from half an ounce of gold, to a couple ounces or a bit more,
per flask. So these are fairly small pours. If you’re doing large 4x6
flasks needing ten or twenty ounces per pour, you might find a
different method would work well for you.
Try a test. Pour a few ingots of a size that reflects your casting
charge. If you find your furnace allows you to easily control how
much metal you pour for your ingot, then perhaps you can choose a
single melt method. If you find it harder to start/stop the flow
precisely, then use our method. Our melter, by the way, is one of the
Italian furnaces that use separate graphite crucibles that are lifted
out of the furnace to pour, not the type of furnace where the whole
furnace is lifted to pour the metal.
HTH
Peter