Furnace Part Two: Finishing and using the mobile furnace

After a long break on working on the furnace we got back to it as the pandemic started.

The furnace had the bottom welded together and the top welded together but we needed refractory.

After several conversations with Larkin refractory we purchased a  9 bags of econocast 30 which is a high temp  refractory that is rammable castable, 2 large fiber boards and a shelf made of a harder castable for the furnace.  We also borrowed a cement mixer to be able to mix the castable as it a very thick castable and needs something to mechanically mix it.

We started with the bottom which we had already lined with bricks. We mixed the castable and put some around all the bricks then we invested the crucible in the castable and continued to fill the sides of the crucible with castable. We put sand bags in the crucible so it did not float up in the castable and covert he top of the crucible with news paper and paper tape so that we could put finish filling the bottom outside of the crucible with castable material.

We then build a small frame to be able to put refractory on the side of the bricks which are in the middle of the furance, we also placed the shelf to gather.

Look at the top we wanted to end up with a domed top. So first we made a mold out of wood a cardboard.   With the top being all castable it would be very very heavy so we decided to use fiber board to insulate but also to take up space and it was lighter.

First, we lined the top with fiber board, then mixed and casted the domed top.  The castable need to adhere to the sides as well as being under the mold.  So we put a good covering over the fiber board before putting the mold in to the frame and then rammed the castable under the mold and attached it to the sides of the top.

Once the castable had dried a little about 48 hours we flipped the top on to the bottom and bolted it together To flip the top because of the weight we used an engine hoist and a pulley system. 

We then worked on casting the doors, we used a piece of circular card board to make the opening of the door. we put a piece of heavy plastic as a way to keep the doors as one piece while we were working with them and so they stayed together until we cut the metal apart.  The doors are mostly fiber board with little castable around the opening since I predicted that I would get glass on the doors at the opening more than on the sides.  The doors are on a caster set at the top of the door.  The doors were hung before we cut the opening and the separated the doors to make it easier to hang the doors so that they closed. 

Once it was complete assembled and we let the whole furnace dry for a week or so with a heat lamp in it as well as being in the 90degree plus weather of NC in late spring. 

Once we got a time to light the furnace up it took about 4 hours to get up to blowing temps and to have the bumba glass to get to be able to blow. The furnace took a while to heat up for 2 reasons the first it that we were still driving off water for the first 1.5 hours of the heating since the furnace whistled and sang. once it stopped whistling the furnace heated quickly.  The second issue was that the burner did not have the top of the burner actually burning. we decided to re-build the burner after the first burn to be able to control the burner better 

We did get up to temps of 2500 F  plus which is the upper end of the infrared thermometer we have. 

Once we finished blowing we decided to re-do the burner. the glass was a little bubbly. We are still working on dialing in the propane usage as well as tweaking different things.