Andrew Holden ‘power kiln’ issues

[Shez]

Ok - thanks everyone for your comments and advice. I’ll try that next and let you know how I get on.

(probably later this month when the day job decides to allow me back into the pottery!)

[neilestrick]

8 hours ago, Shez said:

i have been shutting this primary air off completely as I start reduction. I wonder if this means that the resulting lazy, yellow flame doesn’t have enough pressure to drive circulation through the kiln?

That is likely a big part of the problem. Typically with venturi burners the air is not adjusted during the firing, rather the damper is used to control reduction. So you'll have to figure out a setting on the primary air that works for that. Compared to most setups we see here,I would say that your primary is open too far.

Run a heavy reduction for about 45 minutes where the temperature stalls out (or nearly), then proceed in a neutral atmosphere for the remainder of the firing. Pressure in the kiln will help with evenness as well as getting an even reduction throughout.

[Bill Kielb]

10 hours ago, Shez said:

I guess that I could try leaving the primary air open and managing the reduction by restricting the flue during firing. (I do that already but assumed that management of the primary air would be essential).

Yep, adjust these for best oxidizing most  efficient flame (bluest/ whitest) And lock their position with the screw. Start your reduction by closing the damper. If your site ports don’t have a healthy jet increase gas pressure, might need to back off damper a touch, never a need for sooty high carbon environment, it will decrease your reduction and waste fuel.  You should end up with a nice strong jet at bottom sight port which shows your kiln is reasonably pressurized.

Doing this will decrease the amount of secondary air coming in from around the perimeter around the burners. This air actually Helps cool the bottom of the kiln in your case which is something you are currently struggling with. For Venturi burners, set the primary air for best cleanest combustion and don’t touch them after.

A neat way to get these tuned is at body reduction time close your damper to slightly pressurize the kiln. Adjust the primary air on one burner very slowly to get your best temp rise watching a pyrometer and count seconds per degree. Do this maybe 1/2 turn at a time, you should find a relative best spot and then match your burners by turn count to tune the other and lock them in. If you have an o2 probe this is super simple to do, or use a mirror to visually tune. Infrared hazard though, even with the mirror. Protect your eyes appropriately.

nice full Reduction jet below, no soot.