The Mystery of the Kiln that Overfired
Recent Q&As: Can a kiln controller be repaired?
A Kiln Story: The Critter that Ate Greenware
Memorable Quote
News: The Max-119 Test Kiln
The Mystery of the Kiln that Overfired
A customer’s digital kiln fired perfectly for 20 years. Then it began to fire 150°F (83°C) hotter than normal. The customer took the kiln to her dealer, who replaced the thermocouple (which reads the temperature in the kiln), relay, and temperature controller.
Even with the new parts, the kiln still fired 150°F (83°C) too hot. The customer emailed photos of melted cones to us. (See photos 1 and 2.)
We asked the customer questions by speaker phone. “How old is the kiln? When did it start overfiring? What color are the thermocouple wires?” The wires were red and yellow, which is correct for her K-type thermocouple.
We eventually discovered through Facetime that the thermocouple wires were connected to the wrong terminals on the back of the controller. Ordinarily that will cause the temperature in the controller display to go down as the kiln heats up, and an error message. But this wasn’t happening. The temperature went up as the kiln heated.
What caused the overfiring? The thermocouple is attached to a connection block inside the kiln’s switch box. The kiln was about 20 years old, and the red and yellow paint on the connection block had faded away. The wires from the thermocouple had been connected to the wrong terminals on the block. This caused the temperature display on the controller to go down instead of up when the kiln heated.
The thermocouple wires were connected to the correct terminals on the back of the controller. But someone reversed them, because the temperature was going down instead of up. This made the temperature go up as it should, but it introduced the 150°F (83°C) error. The kiln operated normally when the thermocouple wires were reversed at the thermocouple block and the back of the controller.
Photos: 1 & 2) Pyrometric cones before and after firing.
3 & 4) The thermocouple wires must be connected to the right terminals on the back of the connection block and the controller.
Recent Q&As
Q. Can a temperature controller be refurbished?
A. If you send the control panel to the Orton Ceramic Foundation, they can evaluate it to see if it can be refurbished or repaired. The charge is around $100.00 ($90.00 for the evaluation plus parts). If the controller is not serviceable, they will not charge you anything to look at it.
A Kiln Story: The Critter That Ate Greenware
Deb Thuman of Las Cruces, New Mexico wrote, “We have a gas kiln in a metal shed. We’re in the desert, and the undeveloped land behind our house has critters and crawlies like you wouldn’t believe! When we first got the kiln, I thought it would be a great idea to keep the pieces to be bisque fired inside the kiln rather than outside on the back patio. It was a great idea . . . until we discovered there was a critter who loved eating dried clay. I never did figure out what the critter was. Jim now covers the holes where the gas flames go when the kiln isn’t being used.”
Memorable Quote
“The most important quality in the development of human character is, and always has been, self-discipline.” —Brian Tracy
News: The Max-119 Test Kiln
Last night we added the Max-119 test kiln to our website. The kiln fires to 2300°F (1259°C) on 120 volts. The walls are 4 1/2” thick, so the kiln has plenty of insulation to reach that temperature.
CLICK HERE to see the kiln.
