What’s a Cartridge Heater?

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Cartridge heaters are thin tube-shaped devices used to internally heat machine and process components. They consist of a metal tube with a resistive heater element embedded in insulating compound, and are available in various sizes and wattage ratings. They are inserted into a tight-fitting hole in the material and controlled by a thermocouple or controller. Swagged or non-swagged options are available. The output is controlled by a surface mounted thermocouple or remote microcontroller.

A cartridge heater is a thin tube shaped heating device used to internally heat machine and process components such as plates, dies and molds, and welding rods. The heater consists of a hollow metal tube with a wound resistive heater element embedded in an insulating compound within it. A thermocouple or controller supplies power to the heater element via a series of wires that exit one end of the tube. The cartridge heater is inserted into a tight-fitting hole in the material and, when activated, heats it from within. Cartridge heaters are available as swagged or non-swagged and in a variety of sizes and wattage ratings.

Machines or process parts such as embossing plates, thermoplastic dies and extrusion dies require heating to function properly, and in most cases, it is best to heat them internally. Cartridge heaters are devices commonly used to accomplish this internal heating and are built directly into the body of the affected part. The cartridge heater consists of a thermally conductive metal tube, hollow in the center and closed at one end. An electrical resistance heater element is wrapped around an insulating core, typically a ceramic compound, and inserted into the metal tube. The space between the heating element and the tube is then filled with powder such as magnesium oxide which insulates the element electrically but conducts heat well.

This device can then be modeled or left as is. Swagging involves compressing the metal tube to force it against the powdered thermal conductor ensuring maximum heat transfer potential. While beneficial up to a point, swagging is expensive and many low cost cartridge heaters are not swagged. The two heater element power cords exit the open end of the tube. These cables can be axial for straight line installations or radial for applications requiring 90° cable orientation.

The cartridge heater is installed through a tight-fitting hole drilled in the body of the heated part. The pipe must fit tightly into the bore for maximum heater efficiency and with average manufacturer specifications requiring a 0.010 inch (0.25 mm) difference between pipe and bore diameter. The cartridge heater output is controlled by a surface mounted thermocouple or remote microcontroller which keeps the part at an optimum temperature. These heaters are available in a range of sizes from 1/4 inch (6.35 mm) to 1 inch (25.4 mm) diameter. Cartridge heaters are rated in units of “watt density” based on the diameter, length, and wattage of the heater.

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