Life Factor # 5
Heat Sink Material
One factor contributing to the life of a cartridge heater is the ability to pull the heat away
from the heater into the heat sink. We already start with a big advantage in that the split
sheath heater will expand and make contact with the walls of the bore for superior heat
transfer. But if the heater is inserted into a bore in ceramic insulation, little heat moves
away from the heater and the heat build-up will cook the heater unless the watt density
is extremely low.
Thermal conductivity is the intensive property of a material that indicates its ability to
conduct heat. Copper has an extremely high thermal conductivity and will literally
draw the heat away from the heater and distribute it quickly and evenly about its mass.
Aluminum is about half that of copper, but still extremely effective in drawing and
distributing heat. Cast and wrought iron and mild carbon steel, commonly used in
tooling and platens are fair. Worse yet, stainless steel is quite low in thermal conductivity. 
Higher watt densities can be tolerated by heat sink material with higher thermal
conductivity and, as the watt density climbs, the heat sink begins to factor in the
decision of tolerable or even warrantable wattage. If watt density is high, give us
a call at Dalton and we’ll talk about the application..