Contents:
- The Plan
- The Bottle
- Cutting the Bottle
- Cutting the Holes
- Setting the Forms
- Wiring the Top
- Casting the Refractory
- The Tuyere installed
- Painting the furnace
Furnace Construction Notes
These notes are a work in progress, but should be finished this week.
The Plan:
Every shop project should have a plan. I usually try to define
my plans in terms of an objective, parts list, workflow, and a sketch of what I am trying
to accomplish. My sketches aren't very sophisticated, but they help me to visualize the
job at hand. This sketch helped me define the thickness of the refractory, where to split
the freon bottle, and where the burner would enter the furnace.
The Bottle:
This is the
bottle that I started with. My auto mechanic was generous enough to contribute the bottle
to the project.
Cutting the Bottle:
The furnace and cart were designed to work as a unit, with the cart
providing the device to lift the top of the furnace to remove the crucible from the
furnace. The cut was made low on the bottm so the tongs could grab the crucible from the
side. I used a Drag-gun plasma cutter to make the cut.
Cutting the Holes:
Cutting the hole in the top for the exhaust was a piece of
cake! I used the top from a jelly jar as a guide for the plasma cutter. Laying out the
hole for the tuyere was a bit more of a challenge. The cut had to be above the refractory
on the bottom of the furnace and had to line up with the inside wall. I visually lined up
the pipe to the proper angle and marked the side of the furnace where the tangent of the
hole would be. Once I knew the bottom and side tangents, it was a simple matter to sketch
a oval on bottle where the hole needed to be cut. You can see the ground wire for the
plasma cutter in the picture.
Wiring the Top:
At this point I had already attached tabs (angle iron) on the side of the
top. The tabs serve as shoulders for the lifting device. I wanted to make sure that the
refractory wouldn't fall out of the top so I attached reinforcing wires (coat hanger) with
crown bolts. The dome shape of the top also serves to make the refractory more stable.
Setting the Forms:
Scrap wood and sheet metal. The wood held the sheet metal
in
place until there was enough refractory in the bottom to hold the sheet metal
in place. The
center of a paper towel roll makes the hole for the tuyere. I wrapped it with tape to keep
it dry.
Casting the Refractory:
Working with refractory is a lot like working with concrete, except that
it requires less water. I mixed enough to do the top, tamping the refractory in place and
making sure that I didn't leave any voids. I let the refractory set several hours before
removing the sheetmetal. I repeated the process to fill the bottom with refractory.
Removing the sheet metal from the bottom after the refractory was set was a
major pain..... I let the top and bottom set for a couple of days then lit the furnace for
a short burn to drive off any remaining moisture. Not very scientific, but the refractory
seems to be holding up and doing the job
The tuyere installed:
Closeup in tuyere. You can see the contour cut I made on the
1 1/4" pipe. I welded it in place with a mig welder. The
burner was actually lit in this picture. The flame was a pale blue and difficult to see in
this picture.
Painting the Furnace:
The furnace was finished off with a paint job. I used 1200 degree engine enamel and didn't prep the surface except to wipe it down with a clean cloth. The paint has changed color where the outside of the furnace gets the hottest, but otherwise it seems to be holding up without peeling.