The durability and performance of a mica band heater
depends on selecting the appropriate wattage. Exceeding the maximum
allowable watt density for the specified heater size will result in
premature mica band heater failure. While calculating watt densities, we should
remove the area of the cold section from the overall calculated surface
area of the mica band heater.
Watt density
Wattage
-------------------------
=
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(W/in2)
(3.14 X ID X Width) – (Cold section)
Construction
Cold Section
One piece
1" x width
Two piece
2" x width
Holes, Cutouts
(Size+1/2") x width
Maximum
allowable
watt densities
for mica band heaters 2” wide or less
Points to consider while selecting watt density
Select narrower Mica band heaters where possible,
as their heat transfer is superior to wide Mica band heaters. 1” to 2.5”
wide Mica band heaters are ideal.
The watt density should be selected in
accordance with the operating temperature. A table that shows the
maximum allowable watt density is provided as a guideline.
To avoid short cycling and inefficient
operation, select a wattage as close to the needed capacity as possible.
The wattage should be in accordance with
the voltage and current rating of the controls.
The safe heating pattern of the material
heated, thermal conductivity and coefficient of expansion of the cylinder
are other factors that should be taken into consideration while deciding
wattage.
