Wha Tto Set For A Preheat.

[Babs]

My controller does not have a preheat programme. What ramp would I set to get an equivalent?

I can programme this onto the beginning of the programmes I have entered.

Not having any real trouble without it but occasionally I fire thicker handmade pieces and I do glaze load and fire on the same day.

[MatthewV]

You don't get ramp/temp/hold with your controller?

How many points do you get?

 

Going 1°/hr from 90 to 150 would be basically the same as an hour hold.

A more realistic schedule is going 50°/hr up to 200. This would mean taking 4 hours to get to 200°. Giving enough time at the low temperatures; this will drive out moisture from walls up to about 2 cm thick.

[Joseph Fireborn]

I program preheats on my programmed firing. 80F/h to 180F hold for X minutes where X is your preheat time. Is this your question? Or are you saying you can't program holds?

[Babs]

Both above replies are where I'm asking advice. I can put in any C/hr  and hold and Desired temp reached.. Just wondering when people write of preheat what they are scheduling. At present I enter 100C/Hr to 200C for a glaze first ramp then 150C/Hr to 1080 then slow down to 80C/hr to fiinal temp. with a soak thereafter. but I noticed people wrote of preheat/..

I assumed that there was in fact a prefire program called preheat in some controllers and am trying to emulate that.

FIne tuning I guess.

[Joseph Fireborn]

There is a preheat you can press, but it only works on easy fire settings on most controllers. You program the easy fire setting then after its complete you press the preheat button and enter the time. This basically holds the kiln right under the temp where steam violently releases and drys the clay out before it ramps up. Water boils at 212F or 100C.

 

If your firing at 100C an hour as your first step your definitely not preheating. That's pretty quick. I would do something like 30C per hour to 85C then hold for X amount of time depending on how much you think you need. After that phase you can go back to your regular schedule. If your sure your pots are bone dry then you might get away with that, but I am surprised you haven't had explosions as that's to the steam phase in an hour, not very much time to dry out any moisture. 

 

EDIT: I misread what you posted. I thought you were bisque firing. Just hold at 100C for x amount of time and you will be fine for a glaze firing. 

[MatthewV]

Most of the Americans are familiar with Bartlett controllers. Preheat is just another way of saying candling or holding at a low temperature.

 

I only had three points on the controllers in New Zealand.

 

Bisque:

1. 150°C/hr to 100°, hold for 4-6 hours [some people thought I was crazy for the ramp rate; I have put wet clay in a hot oven and nothing bad happened which would be equivalent of an infinite ramp rate]

2. 80°C/hr to 600°, hold for 0.

3. 150°C/hr to 1000°, hold for 0:10 (or whatever temperature. I do like a short soak because I pack the kiln with stacks of pots)

 

∆6 glaze

1. 150°C/hr to 100, hold for 0:30 (or 1:00 if freshly glazed work is added)

2. 80°C/hr to 600, hold for 0

3. 150°C/hr to 1215°, hold for 0:15 (or final temperatures/holds that work for you)

4. 200°C/hr to 940°C, hold for 0:30 (if you want iron crystals to develop)

 

(I had to program it twice to get the 4 points!)