The most confusing thing about digital controllers is firing rate. Once you understand rate, the rest of the controller is easy to learn.
Rate is confusing because the rate on switch-operated kilns is adjusted by merely turning dials. You don’t have to think about degrees of temperature rise. Microwave ovens require that you enter only High, Medium, or Low, and time at that temperature.
A car’s speedometer measures speed in miles or kilometers per hour. To understand temperature rate, think of a speedometer that measures temperature change per hour instead of miles. This applies to both heating and cooling rate.
“Does the increase in temperature always assume a one hour time period?” someone asked. “If I need to get to 300 degrees in 30 minutes, would I set the ramp for 600 degrees per hour?”
The answer is yes. Rate is how much the temperature needs to go up or down in one hour. (Note: Degrees per hour is becoming our industry standard for controllers. A few controllers, however, use degrees per minute or number of hours to reach temperature. But once you understand rate, you can soon master any controller.)
At a rate of 100 degrees per hour, the kiln would take 10 hours to reach 1000 degrees.
Suppose you wanted to fire from room temperature to 1000 degrees in 2 hours. To figure rate, divide 1000 by 2 hours. The temperature needs to go up 500 degrees every hour. Rate = 500 degrees per hour.
If you need to be more precise, subtract room temperature from 1000 before dividing by 2 hours. If room temperature is 100, then subtract that from 1000:
1000 minus 100 = 900
900 divided by 2 = 450 rate
Here is a sample 4-segment firing:
Segment 1) Go from a room temperature of 100 to 700 degrees in 2 hours
Segment 2) Go from 700 to 1000 in 30 minutes
Segment 3) Go from 1000 to 1400 in 2 hours
Segment 4) Cool from 1400 to 1000 in 7 1/2 hours
Figuring rates for the above program:
Segment 1) 700 minus 100 = 600 divided by 2 = 300 rate
Segment 2) You are firing from a temperature of 700 to 1000 in 30 minutes. First, subtract 700 from 1000. Answer: 300.
You are raising the temperature 300 degrees in half an hour. Since rate is measured in hours, and the temperature will rise 300 degrees in 30 minutes, rate per hour is 300 x 2 = 600.
Segment 3) 1400 minus 1000 = 400 divided by 2 hours = 200 rate
Segment 4) 1400 minus 1000 = 400 divided by 7.5 hours = 53 rate
If you are like most artists, who think visually, it is easier to understand the controller by drawing the program on graph paper. You can even make a rough sketch on plain paper showing slanted lines for rates and horizontal lines for temperature holds.
To master the temperature controller, first understand rate. Then segments, target temperatures, and holds will fall into place.
Q. What is the difference in the cost to fire a kiln in a hot room compared to firing in a cold room?
A. Room temperature has almost no effect on the electrical cost of firing a kiln. However, if your kiln is under a carport that has open sides, protect the kiln from wind. Air blowing against the case can raise the electrical cost slightly. If you use a fan to lower the temperature of the switch box, position the fan so that the air blows into the switch box louvers but not onto the firing chamber case.
FROM A READER: A POINTER ON ADHESIVES FOR GLASS
Dr. Judy Fisher of Mitchellville, Maryland wrote, “E6000 is a better adhesive for glass than epoxy, because if there are spaces or gaps between the finding and the glass piece, the epoxy will have a weak bond. However, the Goop E6000 automatically fills in the spaces.
“Now that Goop has finally supplied a special tip for the E6000, one can use it more precisely than before.”
Thanks for the pointer, Dr. J. It is always good to hear from you.
FROM A READER: FORMAT OF KILN POINTERS
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Arnold Howard Paragon Industries, L.P. – Better Designed Kilns 2011 South Town East Blvd. Mesquite, TX 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 firstname.lastname@example.org / www.paragonweb.com
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