Cone question

Well done for putting a cone in, always wise with the first firing. I guess your controller was set to give you a fairly slow firing, which means the heatwork required to melt the cone took place before the controller shut it down. When you next fire, be there to watch the cones, note the temperature that 6 goes down at and adjust the controller to shut down at that temperature. Check it every 8 to 10 firings. If your pieces look OK then you haven't done any damage. We find that some glazes rated at a particular cone are better at the next one up the scale.

Steve Bath UK

In article , L.Mac writes

Thank you very much for your response. I will definitely follow your suggestion.

LMac

since we're talking about cones....

I test fired my new Bailey 2927-10 kiln to cone 6 yesterday. The kiln only had four shelves in it and no ware. This Bailey comes with both a controller and a kiln sitter as a backup. I used the "Fast Glaze" setting to cone 6 on the controller.

I used a cone 8 bar in the kiln sitter and two sets of witness cones inside the kiln (5,6,7). The kiln sitter shut down the kiln *before* the controller had a chance to. The witness cones indicated that temp didn't quite get up to cone 6 (bent about 90 degrees over). The preview readout on the controller said it reached 2195 F before the kiln sitter shut it down.

I'll do another test firing and use a cone 10 bar in the kiln sitter next time and watch the witness cones and controller closely to make sure they agree.

Why would the kiln sitter shut down with a cone 8 bar in it when the witness cones indicate it didn't quite get up to cone 6? Was this because the sitter cone is close to the wall and elements or what?

Thanks, David

Two factors here; The weight of the sitter bar on the mini-cone DOES have an effect. The mini-cone has a smaller mass than a standard cone, and therefore may accumulate its heat-work a little in front of a standard cone. The combination of the two sent it *down* earlier than the witness cones. The Pyrometer which governs the actions of your controller measures Temperature, the cones measure Accumulated Heatwork. The two are not the same. I fired my production kiln (55 cu.ft. gross) to cone 9 in reduction over a 17 hour period. When 9 went down (nominally 1285oC, 2345oF), the pyrometer I used to monitor progress never read more than 1220 (2228oF); I had accumulated enough heatwork over that period of time to mature my glazes without physically reaching 1285oC on the Pyrometer.

In a kiln with a sitter I habitually use one cone higher in it than any witness cones I may put in as well.

Steve Bath UK

In article , Hotmail writes

Steve Mills has noted some key factors in how temperatures and pyrometric cones relate, and some things about cones that make them different from a pyrometer reading. another factor that is in play with a kiln sitter is the nature of electric heating via kiln elements made usually from a special alloy called Kanthal A-1 (or similar alloy). Heat energy produced by a Kanthal element comes from the flow of electricity (electrons actually) along the coiled wire, and can be calculated: amperage squared times resistance in ohms, I2R. as the energy builds up, the element glows and emits radiation (electromagnetic radiation, EMR) in the infra-red and visible light range of the EMR spectrum. since heat is transferred via radiation, moreso than by convection (hot-gas flows), the radiating source has to be hotter than the ware receiving the radiation, otherwise the process would reverse. In actual practice, element wire is perhaps as much as 50 C (120 F) higher in temperature than the ware being heated (and the pyrometer probe jutting out from the kiln wall). So the space close to the element wire is hotter than elsewhere, which means the sitter's minibar (or minicone) receives more heat energy per minute/hour than does a cone pack on a shelf. if you want to fire to Cone 6 bent to 3 o'clock, then place a Cone 7 minibar in the kiln sitter's probe. for a given kiln, with unusual setup, the minbar may be Cone 8 to achieve a bent Cone 6 among the ware. There is a learning curve involved in firing a new electric kiln; one should track how the kiln behaves, and make adjustments as needed. and then trust the sitter to shut-off the kiln at the appropriate point in the firing, rather than use pyrometer readings to do the same thing if you use a PLC system (programmable logic controller). However, a different procedure will come into play if your glazes need soaking or downfiring. Then the PLC becomes the shut-off device, and the sitter's cone changed. good firing. peace. Tom Buck

Tom Buck ) -- primary address. "alias" or secondary address. tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada). mailing address: 373 East 43rd Street, Hamilton ON L8T 3E1 Canada

several years back - like around 1994 - orton re-formulated their cones so that they would all drop at the same rate. it USED to be that their cones would drop differently between cone sitters, regular cones, small cones, etc. and they used to drop at slower rates. now once they are dropping - they're down!

if you're still using up an old inventory that may explain the non-uniform dropping of the cones.

along with other reasons...

see ya

steve

steve graber