To start things off, we thought we would ask him a few of our most common customer questions...
Q. Why would someone choose mercury relays over solid state relays? Is there an advantage to one over the other?
A. Mercury relays are extremely reliable. They rarely fail even in glass schools that fire kilns every day on long annealing cycles. Solid-state relays are just as reliable. But they produce heat, which must be dissipated, or they will fail. To prevent overheating, solid-state relays are mounted in the control panel of the kiln as far away as possible from the firing chamber. Or they are mounted on aluminum plates that pull the heat away from the relays. The kiln industry is moving toward solid-state relays because of state environmental regulations.
Q. Can I make a converter plug so my 240V-30 amp kiln can plug into a 240V-50 amp receptacle? Is that dangerous?
A. It isn’t dangerous. The Paragon TnF-82 is a 30 amp kiln, yet it has a 50 amp plug for a 50 amp wall receptacle. The 50 amp circuit breaker will still protect the 30 amp kiln from an electrical short. The disadvantage to a converter plug is that it adds an extra connection (the converter plug) to the circuit. If you make a converter plug, check the temperature of the cord from time to time during operation.
Q. My kiln temps keep bouncing 10F degrees up and 10F degrees down from the set temperature. I work on delicate things and proper temps are crucial, why can't the kiln be more exact?
A. The thermocouple type has a lot to do with temperature fluctuation during holds. The thermocouple reads the temperature inside the kiln. A heavy thermocouple with thick wires responds more slowly to temperature changes than a thermocouple with thinner wires. The slow response time of the thermocouple adds fluctuation to temperature holds. A sheathed thermocouple, which is the type that has a metal covering, adds more fluctuation than a thermocouple with a bare welded tip. To reduce temperature fluctuation, slow down the firing rate before the kiln reaches the hold temperature. Some controllers do this automatically.
Q. I think my kiln has a hot spot/cold spot! Why does this happen, and how can I fix it?
A. An open peephole can cause a cold spot in your kiln. For instance, if the kiln is equipped with a downdraft vent and the peephole plugs are left out, the bottom of the kiln will become cooler. A lid that rises in the front can cause a cold spot at the top of the kiln. A front-opening kiln that doesn’t have elements in the door will be cooler at the front than at the walls. The easiest way to improve heat distribution is to slow down the firing rate. You can improve heat distribution by adding more thermal mass to a hot spot and removing thermal mass from a cold spot. In a pottery kiln, add more ware to the hot area and less ware to the cool area. If the edges of a shelf in a glass kiln are getting too hot, place 2” wide strips of cordierite shelves along the hot outer edges.
Q. What's the life span of my thermocouple? How often should someone change it to keep the temps consistent?
A. The hotter the firings, the shorter the life of the thermocouple. Thermocouples in glass kilns last much longer than the ones in pottery kilns because glass is fired to lower temperatures than pottery. Recently I saw a 15-year-old glass kiln that still had the original thermocouple. Heavy, 8-gauge thermocouples last longer than 14-gauge thermocouples because the 8-gauge wire is much thicker than 14-gauge. To know how long your thermocouple lasts, look at the welded tip. A flaky tip indicates a lot of wear. Keep a kiln maintenance logbook and record the number of firings between parts changes.
Now it's your turn... Have a kiln question? No problem! All you need to do is Ask Arnold!