Steven Branfman on sat 12 aug 00
Frances,
You posted a detailed account of your raku kiln probelms. (Aug 8). It
appears to me that the problem is not enough air. The kiln is suffocating.
Based on your description of the kiln before and after it was reconfigured,
the problems are that her kiln is very tight (2 overlaping layers of fiber),
the flue is too small (5") for the size of her chamber (24"x24"), the brick
base is very tight (not allowing any air to enter the firebox), and the size
of the burner ports are too small. All these factors are contributing to a
kiln that can't breath and a combustion system that is starved for air. You
said "What I have observed is that prior to lowering the cover (fiber kiln
chamber) , the burners burn blue right back to the nozzle. As I close the
cover, the blue flame separates from the nozzle, fluttering approximately 3 -
4" in front of the nozzle and frequently going out. " This certainly sounds
to me like not enough air. It is puzzling though that you report using forced
air burners that seem to blow the flame out. This would indicate a poor
balance between the force of your blower and gas flow. You should be able to
start the firing with the air off. A forced air system all but nullifies the
need for natural secondary air sources although you do need enough air to
light the burner and keep it going in the early stages of the firing before
you kick in with the forced air.
Of course without knowing more details about the kiln, burners, gas pressure,
etc. it's hard to make a definitive diagnoses but I'll go out on a
limb..................Solution? Enlarge the flue to about 7"x7" or even
larger, enlarge the burner ports so you have about 2" space around, open some
peep holes in the kiln chamber and fire away!!
Steven Branfman
| |
|
