William Brouillard on thu 29 apr 99
Some thoughts on electric kiln insulation
The construction of many commercial electric kilns is determined by
factors like costs of materials and market targeting. Making electric
kilns that are inexpensive and lightweight for the home market has
resulted in designs that are less than energy efficient. Safety is
important and manufactures have to meet some federal requirements.
Placement and wiring are regulated by local ordinances and sometimes at
the mercy of the consumer and the electrician who makes the
instillation.
Popular electric kiln designs are I.M.H.O. poorly insulated. The
refractory lining of many electric kilns have at the most three-inch
thickness of brick and the possible addition of some fiber insulation
between the brick and the metal outer cover. The elements are placed in
groves cut into the brick lining. a practice that effectively reduces
the thickness of that lining to as little as 1&3/4" on some models.
Many electric kilns are advertised as being capable of high temperature
firings, C/8-C/10. Imagine the skin temperature of the kiln when peak
temperature is reached. An old table of heat transmission values from
USS, titled ,Heat Transmission through Furnace ,walls gives me a
value of 520 degrees as a cold face temperature if the hot face is 2350
degrees F.. That figure is for a two-inch wall thickness with a
conductivity value of K-2. When you consider that the elements are only
an inch and 3/4'' from the outside wall and that the elements are
usually 25 to 50 degrees hotter than the internal temperature of the
kiln the 520 degree figure would be conservative. It gives that old
Movie title F. 451 a whole new meaning. The point has been made that
heat saturation of the brick wall is never achieved during a short
firing. It is my experience that C/9 firings in poorly insulated
electric kilns are seldom of short duration and that the outer surface
of the kiln does reach very high temperatures.
Suggestions:
Buy the most insulation that you can afford. There are energy savings
and firing advantages to be had with well insulated kilns.
Placement of all high temperature furnaces is critical. Make sure that
that the surrounding walls and floors are not exposed to temperature
high enough to case ignition of paint or plasterboard. Make sure that
the kilns are isolated from people and pets that might be burned by
accidental contact with the hot surfaces
Make sure that you wiring is up to the kiln maker's specs and is up to
local electrical codes.
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