|Monthly Tech-Tip |
People refer to the extent of cone-fall as numbers-on-the-clock or degrees. This cone is at 5 oclock or 80 degrees. Notice that from start-to-finish is 35 degrees F (not all cones have this same 35 degree fall). As you can read on the temperature scale, 25+ degrees happen before it reaches 2 o'clock! From 5 to 6 o'clock is only 1 degree! This is a standard cone that requires a plaque, notice that the down-touching position is when it hits the top of the plaque. It follows from this that one can convert cone-bend to equivalent temperature. That being said, remember that cones measure heat-work, so the conversion is only valid for a 60F/hr rate-of-rise.
Orton says “90 angular degrees is considered the endpoint of cone bending”. First, let's assume the normal: Examination of cones on kiln-opening to verify controller operation. Consider the cone on the left: The tip is touching. But it is also beginning to buckle, that means it was touching for a while before the firing ended . Who knows how long! The second one is not touching, but has still fallen a little too far. Why do we say that? The third one, positioned on the Orton guide, has reached the recommended 90 degrees. This demonstrates a good reason why self supporting cones are much better than standard ones: They are not touching when considered done. And standard cones, when sent in a 3/4" plaque, have a less consistent bending behaviour.
Devices that melt and bend in a ceramic kiln at specific temperatures when subjected to specific up ramps. Today, cones are used to calibrate controllers.