Saturday, March 04, 2006

The Firing Chamber

With the firebox complete, I need to finish the work on the firing chamber of the raku kiln. There are two sets of holes that I need to create.

The hole in the side of the firebox is called a burner port, and is four inches in diameter. It is sized for an MR100 Venturi Burner. I had to compute the volume of the firing chamber and firebox, then, based on the materials and thickness of the walls of the kiln, I could determine the number of BTUs required by the burner, using propane. The kiln was at the top range recommended for the MR750, so I opted for the larger burner. We could always line the kiln and firebox with ceramic fiber to improve the firing qualities of the kiln, but I'll wait until we have used it a bit to make that decision (and hopefully have sold a few pieces).

The first hole in the firing chamber is a vent in the lid of the old Sno Industries kiln we are using. The rule of thumb is that it needs to be at least as big as the burner port in the firebox. If the hole is smaller than the burner port, then it becomes difficult to shove flame into the firebox, due to pressure building up in the kiln.

The second set is a series of holes in the floor of the kiln that we are using. These will allow the flames and gases to rise out of the firebox and into the firing chamber. It seems obvious that the area of these opening need to exceed the area of either the burner port or the vent hole; I want the flow of heat, flames and gases to be controlled by the burner and vent ports, not by the opening connecting the firebox to the firing chamber. I imagine that the bigger the better, and, worst case, I could cut out the entire bottom of the kiln, and just prop up a kiln shelf on stilts or fire bricks.


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