CRYSTALLINE GLAZE & PORCELAIN POTTERY RESOURCE


SPIRAL


 STUDIO

How to Repair a Broken Kiln Element

And Associated Kiln Controller Information


Above: Broken kiln element.
Right: Heating one of the broken ends with a propane torch to soften it and facilitate straightening the wire. The element will become red hot almost instantly. It also cools off very quickly. It will be necessary to repeatedly re-heat the wire while working with it.


Both element ends are straightened using two needle-nosed pliers.


The straightened ends are heated and twisted together and trimmed with side-cutting pliers.


Above: As a nice finishing touch, a porcelain wire nut is screwed onto the splice. This provides mechanical strength to resist loosening of the joint caused by expansion and contraction of the repair during repeated heating and cooling of the kiln. The finished repair is re-heated one last time with the torch, and carefully tucked back into its soft-brick groove.
Right: Tools. Note the small, 1-1/2" long Kanthal wire element pin. A bunch of these come with each Skutt replacement element. I bent one into a horseshoe shape and used it to secure the finished splice in place.


A re-creation of the genesis of the problem. A folded vertical test tile decided to unbend during a firing, and came into contact with an element, transferring glaze to it. It took many, many firings before the glaze burned through the element.

Fortunately, I was paying close attention to the firing during which the element failed, and I realized that something was wrong. I compensated in mid-firing, and got perfect results. The above piece was in the failed element kiln firing.

The fact that I was able to get a successful firing, even though an element had failed, is a testament to Bartlett Instrument's SMT 700 series controllers with Zone Control. Zone Control means that each kiln section has an individual thermocouple, and each section cycles on and off independently of the other sections. My kiln is a Skutt 3-section, 10-sided model, with 6 elements and 27" of interior height. The failure occurred in the third element from the top.
I was not aware that I had an open element until I performed diagnostics after unloading the kiln. But I did know that my rate of temperature rise during the firing was unusually slow. Based on my many years of experience firing crystalline glazes, I made an educated guess as to how much heat work was being done, and I reprogrammed the kiln accordingly, in mid-firing.

 
Skutt Zone Control kilns come with Pilot lights that indicate which kiln sections are "on" at any given moment. In the above example, all three pilot lights (on the right side of the controller) are lit, which means that all three sections are firing.
The Bartlett 700 series board also is capable of indicating which zones are firing via decimal points on the numerical display. In the above photo, the decimal points to the right of the numerals 1, 3, and 4 indicate that sections one (top), Two (middle) and three (bottom), are all on. The display is reading: "1,345 degrees, Fahrenheit."		 In order to activate the decmal-point zone-indicator display, it is necessaries to momentarily press "8" on the touch pad during a firing. This is referred to as a "hot key." In the above photo, The two top pilot lights are lit, meaning that the top two kiln sections are "on." The decimal point to the left of the "6" on the display indicates that the top section is on. The decimal point to the left of the "3" means that the Middle section is on. The lack of a decimal point to the left of the "5" indicates the bottom section is "off."
The decimal point on the far right means that the display is reading in degrees Celsius. The display is reading "635 degrees, Celsius."

As previously mentioned, I knew that something was wrong, I just didn't yet know what. One indication was the pilot lights. The top two sections of the kiln were working like crazy, trying to keep up with the bottom section, which was hardly "on" at all, as indicated by the pilot lights.
A second indicator was the rate of temperature rise within the kiln. Pressing the number "5" on the Bartlett SMT 700 touchpad during a firing activates a "rate of rise" hot key. The display will momentarily read out the actual rate of temperature rise, at that instant, within the kiln. Toward the end of a firing, my normal rate of rise is about 60 degrees per hour. With the open element, I was only getting a rate of rise of about 35 degrees per hour, and I still had about 25 degrees to go to reach my usual cone 8 set point. At that point, I aborted the firing, and programmed and started a new firing schedule.
There was a third indicator. The numeral zero on the touchpad is an elapsed time hot key. At any time during a firing, pressing the zero key will cause the display to momentarily flash exactly how much time has elapsed since the firing commenced. It was clear that my firing was taking significantly longer than usual.

Yet another really cool feature of the Bartlett controller is that it has a built in amperage checker. Recording the amperage of each kiln section or zone prior to every firing is an excellent way of monitoring element health. After the firing, I used the amp-check feature to diagnose the kiln's problem. The amp test indicated that the kiln was drawing about half its normal amperage from the middle section, and I was quickly able to locate the problem.
It is even possible to perform an amperage check in the middle of a firing. This is done by momentarily pressing the number "7" on the touch pad. Each kiln section's amperage will briefly flash on the numerical display. Be aware that at very high temperatures the amperage drawn by the elements will slightly increase. Do not be alarmed if the amp readings from a hot kiln seem a bit high as compared to those from a cool kiln.

All of the above pieces were fired in the kiln with the failed element.
I am on a mission to see just how many firings I can get from one set of elements. Except for the open, there was still plenty of life left in the failed element, and I was very reluctant to replace it. In addition, I was ready to fire another load, and I didn't diagnose the problem until a Saturday. The whole repair took about fifteen minutes and cost me nothing. Procuring a replacement element would have taken several days, and it would have taken a considerable amount of time to install it.
Typically, crystalline glaze artists get about 25 firings from a set of elements. I have made significant modifications to my Skutt kiln in order to eclipse this number. As of this writing, I am at 137 cone 8 firings from the same set of elements, with very little sign of the elements slowing down.