Calling on professional potters

Hey guys there is some disagreement at my local potters group about how often kiln elements need replacing. In my own kiln I replaced them after about 150 firings. The kiln began to take longer and then began to struggle to reach temp even though none of the elements were broken. I would really appreciate it if people would post how often they consider it necessary to replace the kiln elements. Thanks Annemarie

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Xtra News
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Hi Annemarie,

"When the kiln began to take longer and then began to struggle"... is the ideal time to replace the elements. If you wait until any are broken, that's too long.

As for how many firings, that's like asking "how long is a piece of string" ... depends on how high the firings are ... if you were doing glass firings, your elements could last 1000 firings ... if you were doing all stoneware, your elements might do 100 firings before the kiln slowed down. Also depends on how well designed the elements were in the first place.

Best way to tell is to time the firings, and when you aren't happy with the firing time, change the elements.

Cheers

Dave Coggins

Reply to
Coggo

Dear Annemarie,

Dave Coggins is absolutely right.

To add to what he said; every firing puts a VERY (microscopically) thin layer of oxide on the element wire, and the core of resistant wire is reduced by the same amount. In the initial life of the element this protects it from the harsh conditions in the kiln (so pre-fire new elements before putting pots in there), but ultimately as Dave said it gets slower and slower as the core reduces in size. You could also measure the amperage draw of the kiln when on full as well as time each firing to get a picture of the element(s) condition.

Steve Bath UK

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Reply to
Steve Mills

Thanks guys, this is exactly the sort of stuff I need to convince the skeptics that the elements need changing. The club kiln has got slower and the firing uneven when it used to be very even from top to bottom and because none of the elements is broken and they will still take a current it is thought that new elements are not needed. I did check and it had done well over 150 firings bisque and cone 6 mostly, but some earthenware and stoneware as well. However just looking at the elements (very brittle looking and many falling over) and looking at how the kiln is firing has convinced me that new elements are essential before they fail during a firing. More advise would be great, the more I can take the more convincing it will be :o)

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Xtra News

Hi Annemarie,

When I was repairing kilns, I had many customers who persisted in flogging their old elements to death, or only replacing a broken element rather than the whole lot at the same time, and they continued grumbling about how bad the firings were and how many pieces they lost - it's hard to convince some people.

The best way to get hard evidence that the elements need replacing is to get an electrician to measure the current drawn by the kiln using a proper current meter (clamp meter) while the elements are HOT - preferably near maximum temp. - as elements draw less power when hot. Compare the reading with the rated current on the kiln plate.

Any kiln which draws a current 10% or greater below the original value will generally fail to reach top temp, or take so long getting there that the ware will be overfired.

Also, if the element coils are falling over and touching, it's only a matter of time before one of the coils shorts out to another, and the element will burn out.

Another point you could mention is that the kiln is using so much more power because of the slow firings, also many pieces are not firing properly due to the unevenness of the kiln and have to be refired - this is wasteful of energy and money, and makes the kiln uneconomical to operate.

Having said that, the150 mixed firings you describe doesn't really seem to be a very good total - maybe the original element design was a bit light for the job and it might be worth looking at getting a heavier duty design if possible, particularly as group kilns always seem to have a hard life. A heavier duty design could dramatically increase the number of firings for a little extra money.

There is some information which may help on my website -

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Good luck!!

Dave Coggins

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Reply to
Coggo

Well, there ya go, let that be a lesson to all those nay-sayers! Of course for most folks the bottom line is still the bottom line which brings me to ask, what's it cost to fix? Can anybody make these repairs or should you call in a professional? If you have three ducks and the recipe calls for seven, oh no, wait, that's a whole other subject. Umm, where was I? Oh yeah... Whenever I work with electricity, if I see lots of sparks or my hair stands on end all by itself, I figure its time to call in a professional. ...Although the hair thing does look kinda cool. >8-)

~Kroozr

Reply to
the ''Kroozr''

Cost approx NZ$400 installed by professional electrician. Bottom line, yeah, there has been a lot of spending on glaze materials and shelves when the kiln needed fixing......

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Xtra News

NZ$400 is expensive and I can see how some would balk at spending that kind of money. 150 firings really isn't a lot of firings. I have an electric kiln and I can see its going to be costly just to keep it in proper running order. But if its the nature of the beast and rewiring gives you a better firing as well as safer use of the equipment, then its a no-brainer. Safety is a big concern, the idea of wires shorting out, that can't ever have a good outcome.

~Kroozr

Reply to
the ''Kroozr''

When you break it down it is only $2.60 per firing. There is of course a kiln fee which covers electricity, and glaze, it is also supposed to cover kiln maintenance. When you think about it, thats not really terribly much for a 6cf kiln with a club firing. However I was slightly missleading. A few months ago I counted how many firings this kiln had done and it was over

150 then. I will count again :o)
Reply to
Xtra News

I think that 150 sounds typical. It would I presume be a mixture of biscuit and glaze firings.

As you say the firings take longer and longer with more usage and at some point the firings may become so long that it becomes economic to fit a new set of elements. The higher the temperature of your firings the sooner this point is reached.

Another factor is the actual voltage of your supply. Any power supplier is allowed quite a large range within which he must stay. The nominal may be 240 volts say but the lower limit may be 210 volts. When I re-order elements I specify that they are for the lower limit and they are cut to length accordingly. This in effect gives them a longer life before the length of a firing becomes uneconomic.

David

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Reply to
David Hewitt

Thanks for your comments. I do not have much electrical knowledge, but know through experience that the elements are worn and the performance of the kiln will be fixed by the replacement of the elements. I do know that there is single phase, double and three phase electricity supply and the three phase has more power available. The supply at the rooms is three phase, whereas mine is single phase and my elements are slightly finer and therefore carry less electricity. My kilns top temp is 1250C between cone 7 and 8, which is fine for me as I fire to cone 6. The kilns at the rooms are stoneware capable. Not sure that this is really relevant though. :o)

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