Adjusting a lid cutoff safety switch takes only a few minutes.
Adjusting a Lid / Door Safety Switch
Reader Response: Pyrometric cone temperatures
Recent Q&As: Coating the lid; natural cooling rate explained; concern about light seen around the lid, between kiln sections, and peephole plugs
News: Janet Mansfield Passes
ADJUSTING A LID / DOOR SAFETY SWITCH
Some of the most vexing kiln problems are very easy to fix. Even if your kiln doesn’t have a lid safety switch, you may find this example of an easy repair interesting.
A customer’s kiln mysteriously stopped firing whenever it heated to 1400 degrees F / 760 C. After a faint click, the elements turned off. Then an alarm appeared in the controller’s temperature display window. None of the elements were burned out, and the circuit breaker had not tripped. The display window continued to show the temperature.
The problem was a safety switch that was out of adjustment. The switch is designed to turn off the heating elements when the door or lid is opened. Typically the elements stay on until the door is opened 1/4” – 1/2” or the lid is raised 1 1/2 ” – 2 1/2”. If the adjustment is too close, then the expansion of parts can turn off the switch even when the lid or door is closed.
Adjusting the lid or door takes only a few minutes. For instructions, go to www.paragonweb.com and click on Support, then Instruction Manuals from the drop menu. Publications are listed in alphabetical order. Scroll down the list of manuals to Safety Switch Adjustment.
Barry Burns wrote, “In the January 29, 2013 Kiln Pointers, ‘Firing Decals onto Jewelry and Ornaments,' you refer to pyrometric cone numbers. We have a total of 12 digital kilns in our community ceramics club, glass kiln club, and pottery club. There are different programs in each of them. When you write about cone numbers, we have no reference point. For future articles I suggest that you include next to a cone number the temperature in degrees F and C.”
Barry, thank you for your suggestion. The cone numbers from the last article:
cone 019 (1252F / 678C)
cone 015 (1456F / 791C)
cone 018 (1319F / 715C)
cone 017 (1360F / 738C).
Q. Before you apply coating to a kiln lid, does the old coating have to be sanded off? And how long does the new lid coating last?
A. If the old coating is loose, then it must be sanded off before applying the new coating. Loose coating looks like the cracks in a dried mud puddle; this is caused by applying the coating too thick. The lid coating lasts for several years.
Q. I found a glass firing schedule that says to "cool at a natural rate" from 1600 to 1020. What does that mean?
A. Cooling at a natural rate means you should turn off the heating elements from 1600 to 1020 by using a Full cooling rate. Full, during cooling, means the controller will try to cool as fast as possible. It does that by leaving the elements turned off.
Q. My kiln has three sections plus the lid. During firing I can see the red glow from the elements through the spaces between the sections and the lid, plus sometimes from the peepholes. (The peephole plugs do not have a snug fit.) Can this be considered wasted energy?
A. There is little heat loss through a loose-fitting peephole plug or the cracks between kiln sections. This is because at 1100F / 593C and higher, the air molecules are spread so far apart inside the kiln that heat no longer moves by convection. This is why you can hold a hand near an open peephole of a hot kiln without feeling heat pouring out.
One way to conserve energy is to make sure the lid lies flat against the kiln at high temperatures. If the lid rises half an inch at the front, the top section of the kiln will underfire. This could happen if the hinge binds.
To conserve energy, fire dry greenware. Moisture in the clay will slow down the firing and waste electricity. If you must fire moisture greenware, leave the kiln at 200F / 93C until the moisture has dried out.
"Laughter is the most healthful exertion." -- Christoph Wilhelm Hufeland
NEWS: JANET MANSFIELD PASSES
Australian potter Janet Mansfield passed away on February 4, 2013. She had been involved in pottery since 1964.
She had solo exhibits in Australia, Japan and New Zealand and started her own gallery in Paddington, Sydney. She edited “Pottery in Australia” (later named “The Journal of Australian Ceramics”) and even started her own publications, “Ceramics: Art and Perception” and “Ceramics Technical.” She was president of the International Academy of Ceramics for several years.
Karen Sullivan remembers Janet Mansfield. “I was teaching at Pasadena City College, and she gave a slide talk that was a remarkable survey, by country, of working artists. It gave a sense of the distinct trends in each country. I am grateful for her contributions. She was very generous and encouraging in providing the opportunity for artists to launch their career with images of their work in her magazine.”
Ivor Lewis of Redhill, South Australia wrote, “Janet Mansfield should be remembered for her capacity to enthuse interest. I regard her work as an editor and publisher of “Pottery In Australia,” “Ceramics: Art and Perception,” and “Ceramics Technical” as well as several books as being major achievements. She was also a salt glaze enthusiast. She was recognized for her services to the arts and the community by being awarded The Medal of the Order of Australia in 1987. Her citation in the Australian Honours list states, "For service to the arts, particularly in the fields of ceramics and pottery." It was a privilege to have known and worked with Janet. May she rest in peace.”
Some of the great teachers of the firing arts are passing away--Janet Mansfield, Boyce Lundstrom, Dan Fenton. They leave behind treasured memories. Just last week a friend called and told me stories about Camp Colton, Oregon, where Boyce taught seminars. On one occasion he wanted to stay up until 2 a.m. to work on glass.
With best wishes,
Arnold Howard Paragon Industries, L.P. – Better Designed Kilns 2011 South Town East Blvd., Mesquite, Texas 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 / email@example.com / www.paragonweb.com / www.facebook.com/paragonkilns
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