Victoria E. Hamilton on mon 21 apr 08
Hello all -
My team and I (there are 3 of us) fire our 40+ year old Alpine updraft kiln
about once a week. It is about 20 cuft in size. It is forced air with 2
burners and fired with propane. Our bottom shelf consists of 2 12"x28"x1"
old high alumina shelves. The rest of our shelves are St. Gobain Advancers.
We love them and we know that we are fortunate to have them.
The current set of dampers consist of 2 pieces of the old high alumina
shelves fixed to metal rods so we can open and close them. Up until 3
firings ago when we replaced the dampers, we were using a couple of very old
silicon carbine shelves as dampers. We replaced them because they were
finally warping and cracking.
The firings for the last 5 years have been pretty great and have averaged
10-12 hours per firing including a 20-30 minute soak at the end with nice
reduction and lovely carbon trapping with our studio orange shino glaze.
Since we replaced the dampers 3 firings ago, the firings are now averaging
6-7 hours, probably because the new dampers are keeping more of the heat in
the kiln.
Also, since we replaced the dampers, there is a situation that arises near
the end of the firing time (air at about 45, gas at about 1.2-1.4, dampers
at 1") where the kiln shuts off. Sometimes we are successful in relighting
it, sometimes not. This last firing, we tried to get it relit 3 times to no
avail. So, we cannot do a soak, and a few pots are coming out with small
blisters. Also, reduction seems to be very spotty.
Well, I can see I'm starting to babble here. What's my point? My question
really revolves around the kiln shutting off.
Does anyone out there have any ideas or suggestions? We're open to
anything, really.
This is a unique and generous group. Thank you so much.
Vicki Hamilton
Millennia Antica Pottery
Seattle, WA
stephani stephenson on mon 21 apr 08
Vicki
have you noticed any difference in the amount of back pressure at the top and bottom peeps?
Does your ALpine have the old fire eye sensors/shutoff system?
do you have about 3" back pressure at the lower and 6" at the upper, both with that green/blue tinge,,, and an even level of the same color front to back emerging from the damper, indicating a neutral flame?
i don't know why changing the shelf might matter, but if it is affecting the firing time, it may have caused changes in other dynamics inside the kiln...
it's important not to overdamper the Alpines..
have you checked to see what happens if you hold a small torch/match to the auxiliary draft ports around the burner? the kiln should neither draw the flame up and out or blow it back...indicating neutral pressure...these conditions should give enough turbulence for good firing.
the ALpines i use to fire could be quite sensitive to over dampering and would shutoff when over reducing occurred.
ALpine gives the following reasons and solutions for kiln shutting off before reaching temp.
1. scanner does not have a good view of both pilot and main flame (raise or lower burner to correct position.)
2. dampering too much during reduction causing loss of flame at scanner pick up point (open up dampers to lessen back pressure at burner ports)
3. scanner or scanner wiring burned due to excessive reduction flames at burner port (replace)
4. weak photocell in West controller (change bulb first, change photocell if trouble continues)
5. scanner is weak.(check both scanners for voltage at test plugs under cover of fire-eye. voltage should read 4 volts minimum. make sure scanner lens is clean and unobstructed)
Stephani Stephenson
Encinitas CA
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