Curing

After getting the refractory liner in the furnace I left the furnace covered for several days. From what I have read this is ok to do, even possibly advantageous to do, as long as the refractory is not allowed to dry out. I had no issues when I finally got around to curing the refractory liner. Now, this is where having the lid ready to go is necessary because it is required to complete the curing, in fact when I made the lid I also took some of the extra refractory and made up several small bricks with the left over material and cured them at the same time by simply placing them among the coal of the fire for the duration of the lid curing process.
Curing the furnace is straight forward enough. I started with a double layer of charcoal, soaked in lighter fluid and got them fired up. I used this lower temperature heat to drive moisture out of the liner slowly and it also burned the cardboard inner form out as well.

After getting the first double layer of charcoal going good and burning out the inner form I added another double layer of charcoal and got that going strong. I kept adding charcoal layers as the last layer of charcoal was burning good until I had about 2/3's of the furnace filled with lit charcoal. Then I put the lid in place and started adding air through the tuyrere.

I used my shop-vac as an air source, which was a bit too much air. To solve this I am working on a valve system to allow a variable, more controllable flow rate. But as you can see, it worked great for the curing process.

I kept this up all through the burning of the first load of charcoal and when that had burnt down to a few inches left I added to the charcoal again to a load of about half full and kept the air going.

 

Use caution! As you can see the furnace will send out some embers, especially with a fresh load of charcoal (note how I have backed the air supply away from the tuyere to limit airflow)

I was surprised at how hot things actually got inside the furnace!

Even with the air supply shut off, it's HOT in there.

After adding that last half load of charcoal I kept the air supply running until almost all of the charcoal was consumed at which point I took the air supply away and used those small bricks I had made earlier to cover the vent and tuyere holes and allowed the furnace to cool on it's own.

After cooling, I inspected the condition of the furnace interior and other than losing a bit of refractory from the bottom lining everything held up very well.

Next I need to get started making various other components in preparation for turning my scraps into usable ingots.