The following story originally ran in the Nov/Dec 1996 issue of Clay Times as part 2 of a 3-part series on maintenance and repair of electric kilns. To obtain copies of parts 1 and 3, please see our back issues information page.
Before we jump into diagnosing what may be wrong with your kiln or what malady your kiln may someday fall victim to, we should make an overall assessment of the condition of your kiln and the kinds of things that can ultimately cause problems.
Cleanliness may be next to godliness, but for us, keeping the kiln clean is very important and requires more than simply not spilling hot chocolate on the lid. Dust, dirt, moisture, glaze drips, and other visible ugliness all contribute to an overall decline in your kiln's health and efficient operation. This is not just cosmetic maintenance! Regular inspection and cleaning of your kiln should be part of your schedule. Vacuum the interior as well as the upper perimeter of the kiln. Check the full interior of the kiln for dripped glaze on the bricks--or worse, on the coils. These drips should be chipped away as soon as they appear, for each successive firing will drive the glaze deeper into the brick and more permanently onto the coil. Often, glaze that drips onto a coil can be carefully loosened and taken off with a long- nosed plier. Heat up the coil first so it's not brittle, but don't heat it to the point of real softness. Turn off the current before you go to work on it. If any of the coils are popping out of their grooves, heat up the coil and carefully compress them back into their proper places. This time, heat up the coils until they are soft. The coils will have color. Again, don't forget to turn off the current before you start working.
A common cause of kiln failure is loose connections. Every 10 firings or so, turn off the current and open up the electrical boxes to inspect for loose connections, frayed wires, and corroding parts. Electrical current vibrates, sometimes causing the connection between the element and terminal to come loose. This spot can then decay rapidly. Make sure no wires are touching the element tails that come through the wall of the kiln. Vacuum these areas also. Be sure that the element tails are not coming in contact with the outside kiln jacket.
There should be a porcelain insulator protecting the jacket from an electrical connection. If your kiln is a multi-section one, there will be plugs, outlets, and sometimes electrical cord connecting each section to each other. These components do wear out and should be periodically examined. If you find a plug to be darkened, misshapen, or otherwise in less than good condition, it must be replaced. Its corresponding receptacle will most likely need replacement also. Check the cord for complete integrity. Examine the cord, plug, and receptacle that connect the kiln to your electrical service for the same kinds of weaknesses. If the lid of your kiln is on a hinge, inspect the entire hinge mechanism for corrosion, alignment, and security.
One of the most common causes of kiln deterioration is moisture. Properly ventilating your kiln with a commercial ventilation system or by locating the kiln in a well-ventilated room will contribute much to its longevity and efficient operation. Appropriate ventilation also keeps you safe from harmful effects of fumes, too.
In order to diagnose and correct your kiln's problems, you'll need some basic tools: pliers, hammer, screwdrivers, and various other common tools most of us keep around the studio. The one specialized tool that is an absolute necessity is a voltmeter. The most basic type, available from any electronics store, electrical supply, or a store like Radio Shack, will suffice. The voltmeter will have a calibration switch or dial that allows you to set it for the voltage to which it will be subjected, plus a switch for setting the meter to AC or DC voltage. Set it to AC.
Kiln problems can manifest themselves in many different ways. The most common is when all of a sudden, your kiln simply will not reach temperature and you must figure out why. At fault could be a coil (or two), a switch, the interbox plugs or outlets, the power cord, the fuse box, or any of the wiring in between. When trying to locate the source of the problem, it is best to work your way back from the recognizable symptom. In the case of the kiln failing to reach temperature, turn the kiln on high and observe whether or not all of the coils glow with color. If one or more do not, then you have uncovered a visible symptom. Just because a coil doesn't turn red, however, doesn't mean the coil isn't working, so it's best to do a simple test. Take a piece of paper and touch it to any portion of the coil. If the paper burns, you'll know the coil is intact and getting power. If it doesn't burn, the coil is either broken or something is preventing the coil from getting power. Using your voltmeter, touch the probes to each end of the coil where it enters the kiln. Does the meter register volts?If so, you'll know that since electrical power is successfully reaching the coil without causing the coil to heat up, the coil must be broken. If there is no power, you must now work your way back toward the fuse box to identify where the electrical connection is severed. Remember that you are now working with exposed connections and live current. Be extremely careful when touching the meter to connections. Often, the problem is not faulty coils at all, but may be a broken switch, loose electrical connection, or in larger, more complicated kilns, a deteriorated electrical relay or some other component.
With a common-sense, logical approach to observing the performance (or lack thereof!) of your kiln, even the most perplexing problems can be easily diagnosed. As complicated as a kiln may seem, just a limited number of things can go wrong. By using the process of elimination, you will soon become an expert at pining down those previously elusive mysteries!
In next issue's final installment of this series, we'll go over simple repair procedures. Stay tuned.
Steve Branfman owns and operates the Potter's Shop and School in Needham, MA and is a published author of pottery books.
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