Metal Casting Zone

i cut off the top of a 55 gal drum, put in a smaller metal drum (same height, just half the diameter), and poured the refractory mix between the walls of the two barrels (with the tuyere in place). now that the refractory is dry, the only way for me to get the smaller barrel out of the middle is to take an angle grinder to it and cut it out in sections.
my question is; can i leave the inside iron drum where it is, lining the inside of the refractory, or will it cause immediate problems? my prediction is that the inner barrel will expand during firings and crack the refractory... but this shouldn't be a problem, as long as the inner barrel can hold the supposedly crumbled refractory in it's place?

my plan is to fire it up, attempt a melt, and see if the inner metal lining cracks and lets little bits of refractory fall into the fire or crucible

oh and by the way, do i need refractory to line the bottom of the foundry? all i have is two layers of sheet metal (the outer drum plus the inner drum)... i expect that to hold the fire alright...

Hi svensken,

The refractory in your furnace is set but it probably is not dry. If you attempt a melt with damp refractory this can explode! there have been fatalities from uncured refractory explosions. I suggest you remove the inner drum then, if or when the refractory seems quite dry, set a small fire at the base of the furnace ( probably easier with the drum bottom removed and the furnace up on blocks). Raise the refractory temperature slowly (25-50ºC per hour) to no more than 200ºC at which temperature it should be held for one hour for every inch ( 25mm) of refractory thickness, if at any time steam is seen coming from the refractory the temperature should be held at that temperature till the steaming stops only then recommence raising the temperature. After holding the temperature at 200ºC for the required time the heating rate can be accelerated to double the preceding. The heating should be continued to a maximum hopefully equal to that at which the furnace will be used and held at this temperature for an hour. After this cover all the openings and let the furnace cool slowly.

Most information I have read on furnaces of this nature recommend a sheet metal bottom held on with screws, on top of this at least two inches (50mm) of sand clay mix ( three parts sand one part clay ). If you have a major spill or other mishap the bottom can be easily replaced.

Hope this helps.

What fuel do you plan to use?

Peter.

I reccomend removing it also, at temperature it is going to turn into nothing but rust in short order, and it will flux your refractory liner and ruin it. Iron is an aggresive flux at aluminum temps and above. I wouldn't worry about expansion so much, it probably would weaken and deform before it could exert much force on the walls. Also, that metal inner drum is nothing but a big heat sink at the moment, the liner is supposed to also reflect heat back at the melt rather than absorb it. You also want to line the bottom, if you just leave the metal bottom it will rust out after deforming, it won't hold up. I also reccomend clay-sand, you will be replacing it, and the bottom doesn't see that much heat. Hope this helps, sounds like it's a pretty good sized furnace.

thanks a bunch; sage advice is always greatly appreciated!

ill try to get most of it out, and since i have a little clay and sand left over from mixing refractory i can mix those up and line the bottom

boy, am i glad you guys straightened it out for me though, i woulda never guessed half of those factors/outcomes hehe