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. 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.

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 are fair and steel, and worse yet, stainless steel, are 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 get an opinion.

Friday Funnies

A co-worker returned after lunch carrying a dress from the cleaners.

"Pretty," said one of the guys. "Big date tonight?"

"I picked it up for a friend," she replied. "Do you really think I could fit in a tiny thing like this?"

He smiled and said, "Do you really think I've lived this long by answering questions like that?"