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How To Fire An Old Olympic Electric Kiln With A Hold In The Firing Schedule


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#1 Pots by Char

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Posted 08 June 2014 - 11:20 AM

I know that with the newer digitally controlled kilns out there it is simply a matter of pushing a few buttons to set the program to a specific hold time for an given firing schedule.  But how do you achieve the same outcome with an old fashioned electric, manual switch kiln?  The most modern concept about this kiln is the kiln sitter which auto shuts the kiln down when temp is reached. So if you want to hold the temperature at a certain degree, how would you go about doing that? Also how do you tell at what rate per hour your manual kiln is climbing at the various temperatures?  I do not have a pyrometer on it either.



#2 Mark C.

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Posted 08 June 2014 - 11:42 AM

First you will need an more acurate digital pyromenter to know what is going on more easy.There are very cheap especially if you are firing under 1999.

From there I will step aside and let the electric folks answer

Mark


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#3 CarlCravens

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Posted 09 June 2014 - 03:55 PM

You can't do it without a pyrometer.  And I just did this for the first time with my new pyrometer over the weekend.

 

Rate of climb (or fall) is a function of temperature change over time... so you make out a time chart with entries for every so many minutes and check your pyrometer at each interval and record the temperature (and the switch settings for reference).  Then you can calculate the rate of change over any time period.

 

But here's the thing... rate of change is not constant when your dial settings are constant.  As the kiln gets hotter, it starts shedding more heat and the slower the temp climbs.  So you can't equate a dial setting to a rate of change... rate of change depends on the current temperature and the mass of the kiln load.

 

My concern was cooling no faster than -150°F/hr over a certain range.  The cooler the kiln got, the slower the rate of change... so I was having to do calculations as I went and turn the dials down every so often.  It was informed guess-work, but now I have a "rough draft" of a plan for the next firing, where I'll fine-tune it.  Another two or three firings and I should have a rough manual cooling schedule that looks like "Shut off the kiln at cone 6, should hit 1900°F in about 20 minutes.  Turn back up to 3 for 1 hour, then down to 2.5 for 1 hour..." and so on.


Carl (Wichita, KS)

#4 Pots by Char

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Posted 09 June 2014 - 11:44 PM

 sounds like I definitely need to get a pyrometer.  Can some one recommend a reliable inexpensive one?



#5 Babs

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Posted 09 June 2014 - 11:59 PM

Because cone and temp don't always go hand in hand, I allow the kiln sitter to fall, set it up again with a weight on it and then fire down.

A detailed log of every firing is a great practice so that when things go differently, you can sometimes work out a reason or 3.

It is a matter of playing with the input dial and recording what happens. Going up at 150 deg/hr and want to hold, turn back the input a bit and record what happens, and fine tune from there.

A bank of cones at the spy hole as well as in the sitter is a great help too.

A pyrometer is, as  above, a must, unless, like some, you can read the temp from colour of inside of kiln  

Kiln logs are a valuable document.



#6 CarlCravens

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Posted 10 June 2014 - 01:19 PM

Char,

 

I can't say anything with authority, but my DP-902F from K2 Products seems accurate enough from my first firing.  Cones went down in the expected temp range based on my rate of climb.  (Can't say anything about durability, having just got it.)  You can get detailed information from K2's web page.  (Something that you might not get from an eBay special.)

 

$75 from Clay King.  Their part number is "DT2-7".  Mine came with a metal stand not shown in the photo.  (The photo of the unit shows a max temp of 1999°F.  Current models go to 2372°, around cone 13.  I haven't tested the upper end, but I did fire to over 2200°F, to cone 6.)

 

There are certainly better and more expensive pyrometers out there, and I'll not say anyone *should* buy a cheap pyrometer, but this one's doing the job I need it to so far.  Having a cheap one made for a much better experience than not having one at all.


Carl (Wichita, KS)

#7 Babs

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Posted 10 June 2014 - 05:44 PM

The age of elements a nd the loading of the kiln can call for a different firing schedule so you still have to log and think.






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