How do hold times and heatwork affect my work?

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How do hold times and heatwork affect my work?
  1. There is an option to add time to the end of the program that appears when you enter a program. Usually, there is no need for more than a few minutes of holding at the end. A hold allows the ware in the center of the kiln to achieve the same "heatwork" as the ware on the edges of the shelves. Heatwork is achieved by a combination of time and temperature (more time and/or more temp equal more heatwork... (heatwork can be thought of as the 'energy' that is given to the ware by the kiln, which ultimately bends the cone and melts the glaze). You can have too much heatwork- i.e. overfire the clay- if you have too much hold at the end, or go to too high a temperature. You can also overfire by climbing too slowly at the end of the firing. If you add more TIME by climbing slower or adding a hold, you must reduce the TEMP you are firing to... If you add more TEMP (by going to a hotter temp), you must reduce the amount of TIME by climbing up to temp faster.

  2. The nice thing is that the Easy-Fire programs (the slow bisque, slow glaze etc.) are programmed to automatically adjust the final temp when the rate of climb is faster or slower than what is prescribed. For example, the slow glaze program is set to climb at 120 degrees per hour in the last 250 degrees of the firing. If the firing is to cone 6 the kiln will shut off around 2237F. If the kiln is really fully loaded this time, it may start to climb slower than 120F per hour. If this happens, the controller automatically re-calculates a lower temp to shut off the kiln. If it did not do this the clay would overfire due to the slower rate of climb still going to 2238F
  3. Vary-Fire programs do not fire to cone numbers unless you set them to. When you program it to climb at 108 degrees F per hour to 2232F and it can only climb at 60F per hour, you will overfire the clay considerably if it still climbs all the way to 2232F.
  4. Your max hold at the end of any program should be no more than 10 minutes, unless you change the cone offset for Easy-Fire or the final temp for Vary-Fire to account for the longer hold. Even 10 minutes is about a half a cone hotter.
  5. Hold times and a lot of time at high temps are not kind on the heating elements. Kilns that are held for 20 minutes at temp typically get about half the number of firings as kilns that are not held at temp.

Additional Actions to Take

  1. Make sure you have programmed the kiln properly and it is supposed to be firing.
  2. Read the Operation instructions.
  3. Do a Program Review as soon as you start firing. (For DynaTrols - see this video)
  1. On the next firing make up "cone packs" for each thermocouple.
  2. Once the cone packs are positioned on shelves and are visible through the peepholes, fire the kiln to the middle cone's number
  3. Start watching cones near the end of firing.
  4. Keep checking the control display to make sure it does not say CPLt.
  5. If the middle cones did not go down together then immediately note the differences in each thermocouple reading from the one thermocouple the same zone as the first cone that went down. Change the final set point of your program to reflect the difference.
  6. If the kiln is firing too hot then lower the final set point.
  7. If the kiln shut itself off before bending the cones properly, reprogram it and then restart it as quickly as possible. Record the temperature at which the kiln shut down. Stop and restart the kiln. Reprogram the same program to one cone number higher. Do these steps quickly. Watch the middle cones again and note at what temperature the cones properly bend. If they bent while you were programming then just offset the temperature by 5 or 6 degrees. Shut the kiln off once you note that temperature.