FrogBlog

Observing a Kiln During Firing... What's Normal?

  A big thank you to our friend Arnold from Paragon Kilns who helped answer these important questions about observing your kiln during firing. Gail also added some nuggets of information to help round out your knowledge! The heating elements hum when they turn on.  The sound is generated because the elements vibrate in the brick grooves due to magnetism between the coils. So, it's totally normal! The sound actually diminishes as the kiln gets hotter because the elements soften. Notes from Gail: This is also true in kilns with suspended quartz wrapped tubes, but it's harder to hear since the elements are inside the tubes. Elements that are wrapped around ceramic rods probably won't hum much at all. The clicking noise of an infinite switch-operated kiln is also normal. It is the sound of an infinite control switch cycling on and off. When the clicking turns into a popping noise, the switch is probably about to fail. Notes from Gail: This isn't happening if you only have a digital controller. But, some kilns have an infinite switch in the lid with a digital control of the body. You'll be hearing the clicking on those. Digital Relays are another source of clicking. To turn on the elements, a digital controller sends twelve volts to the relays. The relays, in turn, act as switches and send full voltage to the elements. The relays click every time they turn on. A chattering noise, however, indicates that a relay is about to fail. Notes from Gail: This is why I'm a big fan of MDRs (mercury displacement relays) and SSRs (solid state relays.) They are much quieter and worth the money to upgrade in the long run! A crackling noise followed by a loud POP from the kiln's switch box usually means that a loose electrical connection has just failed. If you hear crackling, which sounds like sparks, turn off the kiln. The loose connection creates a tiny electrical arc, which overheats and burns electrical parts. Rapid arcing causes the popping noise. Whenever you change elements or have the switch box open for any reason, check all of the wire connections. Make sure they are tight... The power must be disconnected, of course. Tug on the wires. If a wire pulls out of a terminal, replace the terminal with a new one using a good crimping tool. Remove any dust before closing the switch box. When you replace elements, make sure the connections are tight. Notes from Gail: This happens in clamshell kiln lids occasionally, since the lid is constantly being opened and closed, the element connections an get loose. Don't despair, it's an easy repair. Why is there a gap between the kiln and the lid near the hinge?  The gap under the lid of a cold kiln at the hinge is normal. As the kiln heats up, the firebricks expand, which causes the body of the kiln to grow taller and close the gap. The gap is designed to help prevent the front of the lid from rising at high temperatures. Notes from Gail: Yup! The lid on my kiln is rising at the front during firing. What is the cause?  During firing, the wall bricks expand. This pushes the lid upward. If the hinge does not have sufficient play, the lid will rise at the front. If this happens, please do not put a weight on the lid to hold it down. That will only damage the lid. Instead, check for binding in the hinge. Notes from Gail: If this is happening, call the kiln manufacturer and ask them how to mitigate the problem. They'll walk you through an easy fix for your type of kiln. If this becomes extreme, it can crack your kiln lid so, it's important to take care of this issue sooner rather than risk a messy, crumbling lid. My front-loading kiln has a gap between the door and the firing chamber. Is that normal?  There should be no gap between the door and the firing chamber at the side toward the door latch. There should be a gap, however, at the hinge side of the door. When the kiln is cold, you should see a gap of about 1/16 between the hinge side of the door and the firing chamber. As the kiln heats, the firebricks expand. Without a gap, the door will bind at the hinge and cause a gap at the side toward the latch. Notes from Gail: Some kilns have gaskets that fill the space and seal the door opening. If you have a gasket that is worn, it's easy to get a replacement from the manufacturer and should help alleviate the issue. New doors can also be purchased if needed.  I am concerned about the light that appears under my kiln lid during firing.  The light that you see under the lid is normal as long as the lid is not rising in front. The inner lid surface expands more than the outer cooler surface. Therefore, it bows inward slightly toward the firing chamber. This is normal. For this reason, you will see a thin line of light around the lid since the lid is no longer a flat surface resting on the flat firing chamber sidewalls. Surprisingly, there is very little heat loss from around the edge of the lid. Notes from Gail: If you suspect this is causing a cold spot during firing, call your manufacturer. If this becomes a serious issue, you can purchase replacement lids at reasonable prices for most top loaders.