THE KÖRUNDA OUTDOOR FORGE
There is an outdoor forge next to the Iron Age House built of logs and timber. The actual hearth needed a redesign, which I helped out with. The forge was constructed during the sommer of 2000, which by the way was probably the rainiest ever. The design was put to a tough test during the Iron Age Fair in mid-August, and it all worked very well.
The basic design is very simple, and is made so that it is possible to use either bellows or fan. It would be a fairly simple task to build a table for it to get a field forge if you like. At Körunda, the "fan option pipe" is straight and not bent as in the picture below in order to be able to clean out ashes and clinkers. I used a battery operated fan in this case, since AC power is not available. The fan is originally intended for engine compartment evacuation in boats, and consumes 3A at 12V. This should give at least 2-3 full days of forging with a fully charged standard car battery. The hearth is made from a Toyota brake drum, which had the measures and material thicknesses I was looking for. All in all, this design did not require any large investments, probably way less than $100.
As can be seen in the pictures below, a piece of 2" pipe was cut open and welded to connect to the opening in the brake drum. A few bolts and some angle iron hold it all together. The tuyere, if I can call it that, is made out of some 3/8" square iron. This is kept in place between the brake drum and the rest of the assembly, and it´s easy to replace. It seems like these dimensions work pretty well. The enamelled tray is something I saved from an old stove...
When experimenting with the bellows, it turned out that a suitable outlet pipe dimension should not be less that one inch. The Y-pipe leading into the brake drum is welded from 1" tubing, and at first I just put it together and tested it. When blowing through one inlet, a large portion of the air would go back to the other inlet instead of into the hearth. This was solved by cutting the pipe leading into the hearth open lengthwise, and welding in a strip of sheet metal along the whole tube. By doing this, each bellows has its own inlet. In addition, you get a smaller crossectional area for the airstream before entering the hearth, which increases the airspeed significantly.
The existing forge is build of sturdy logs, and the new hearth rests on a setting of fireproof bricks and stone. I´m pretty confident this will be around for many years to come.
|The hearth from above. The bent pipe is now replaced by a straight one.||This is how it looks from below. The Y-tube is secured by a bent threaded bolt.||This is how the completed forge looks today. The new firepot is completely hidden, only the coke and stones are visible.|