Cartridge Heaters

Styles of Cartridge Heaters

A cartridge heater is a cylindrical electric heating element constructed by tightly winding nichrome wire around a ceramic bobbin, and inserting the wound bobbin into a metallic tube (sheath). The tube is then backfilled with magnesium oxide (MgO) powder to electrically insulate the nichrome wire from the sheath. The heater diameter is then reduced (swaged) to compact the magnesium oxide for better dielectric, while at the same time improving thermal conductivity.

Cartridge heaters come in many diameters and lengths. They vary in voltages, wattages and watt densities. Sheath materials are typically Stainless Steel of Incoloy 800. The electrical leads terminate from one end of the heater and vary in length and insulation material, depending on application and operating temperatures.

Most cartridge heaters are used in some form of die or platen heating. A close tolerance hole is drilled into a metal block, and the proper diameter heater is then inserted in to the hole. It is best to make sure the diameter of the heater is just a few thousands of an inch less than that of the hole, so that maximum surface contact, thus thermal conductivity, can be achieved. A loose fit will cause the internal temperatures of the cartridge heater to climb and the heater will fail prematurely.

Common die heating, or platen heating, applications are:

• Injection mold platen heating
• Heating medical equipment components
• Compressor sump heating
• Bolt heating
• Extruders
• Packaging equipment
• Sealing equipment
• Analytical equipment

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