Do these kiln elements need replacing?

This 12 inch test kiln has done 910 firings. The element loops are laying down and nearly touching each other. If they are not changed soon the coils will touch the kiln will have hot spots. And the coils are expanding and getting tighter in the grooves, the longer we wait the more the grooves will be damaged when removing them. Although elements seem expensive, when costed on a per/firing basis they can be surprisingly inexpensive. Most hobby kilns service two elements with each relay and relays generally need to be replaced more often than elements. Consider, for example, replacing the elements on a Skutt 818. Being a smaller kiln it is well-powered in relation to size and elements can last up to 1000 firings (assuming 50:50 bisque and cone 6 firings). It has 4 elements and 2 relays (relays cost $65/ea, elements $95 each). The labor to replace is ~4 hours or $250 - total cost is about $750 (that is ~75¢ per firing or 32¢ per ft³). How about a larger kiln? An 8 ft³ Model 1222 has 5 elements and 3 relays and replacement is ~$1100. But its elements are only likely to last 200 firings. That yields a per firing cost of ~$5 and per ft³ of 65¢. But there is a much greater cost to consider: Old elements increase power consumption. An 818 uses 6.4 kwH and a 1222 uses 11.5 kwH - at our electricity cost of 14¢/kwH a firing costs ~$7 for the small kiln and ~$13 for the large one. But that is the cost when elements are new. When they need changing those numbers can more than double! An additional cost of old elements is ware consistency, the kiln cannot execute the firing schedule in the time programmed and this will likely affect the appearance of bodies and glazes.

Related Pictures

Pushing kiln elements back into the groove

Over time kiln elements can sag out of the channel. With each firing the problem gets worse. The elements are far too brittle to simply bend and push back in. As long as they are still in good condition this is the way to do it: Heat them with a plumbers torch and they will be pliable enough to move without breaking.

Old-style hobby kilns with a sitter are usable if you become "the controller"!

Yes. This kiln has a Dawson LT-3 kiln sitter (new ones have electronic controllers). It is a mechanical device with a safety timer and triggered latch on the external housing. A ceramic tube extends into the chamber where a pyrometric cone sits on supports with a rod on the top center. As the cone softens and bends the rod drops with it and eventually releases the shut-off latch. The utility of this depends on careful placement of the cone, sitter adjustment and keeping the rods and supports in good condition. Although not shown, these kilns had a pyrometer and one or more thermocouples (temperature gauge and heat sensing probes). Is a kiln like this useable today? Yes - if you become "the controller"! Learning to use a kiln like this involves monitoring cones on each shelf (self-supporting cones are recommended). By "babysitting" the switch settings (low, medium, high) during firings and creating paper logs (and graphs) to track the kiln's temperature against time over multiple firings you can evolve a schedule of switch-setting, from low-to-medium-to-high. It is possible to get the desired climb, even heat distribution, achieve the final temperature accurately and even implement drop-and-hold and slow cool firings. Vigilance of changes in the firing speed can be balanced by adjustments to the switch-change times.

This electric kiln thermocouple needs replacement

The old one inside is in bad condition (a new one is sitting on top ready to install). In 2022 these cost about $35 CDN. The temperature-measuring part of a thermocouple is the join of two dissimilar metal wires, these are 8 gauge. The junction produces a temperature-dependent voltage that a pyrometer or controller can convert to a reading. Thermocouples can degrade into pretty poor condition yet still work, notice the one in this kiln is separating in two. Thermocouples generally need replacement more often than elements, they generally last about 150 firings (cone 04-06) and 50 firings (cone 6). Replacing these does not require electrical expertise.

Links

Articles	Electric Hobby Kilns: What You Need to Know Electric hobby kilns are certainly not up to the quality and capability of small industrial electric kilns, being aware of the limitations and keeping them in good repair is very important.
Articles	Working with children Go in with both eyes open if you are planning to work with clay with a group of children! A lot can go wrong but it can be unforgettable for them when it goes right.

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