How Cartridge Heaters are Made and Why They Fail
There are two methods of manufacturing cartridge heaters to ensure a useful life and not have them fail prematurely. The first is a standard cartridge heater and the second is a swaged cartridge heater. Even though both cartridge heaters might look identical on the outside, they are constructed very differently. Standard cartridge heaters are the most commonly used, but if you need to operate at higher temperatures and vibration applications, then you will need a swagged cartridge heater.
A standard cartridge heater has nichrome wire heater coils that are weaved through holes in the ceramic tubing. Pure magnesium oxide filler is vibrated into the holes, heating the coils to allow maximum heat transfer to the stainless-steel sheath.
A swaged cartridge heater’s nichrome wire is wound tightly around a ceramic core, to situate it in close proximity to the heater sheath. Pure magnesium oxide is vibrated in and the heater is swaged to a specific diameter. This compresses the magnesium oxide so it becomes an improved conductor of heat from the wire while maintaining its dielectric properties. This is why it works so well with high temperatures.
The useful life of a cartridge heating element is determined by how quickly the heat generated in the resistance wire can be dissipated to the outside sheath. So why do cartridge heaters fail and sometimes prematurely? The reasons include improper fit, moisture, watt density is too high or if you are using the incorrect voltage.
Improper fit is the most common cause of cartridge heater failure. If the cartridge does not fit into the hole it is inserted, then the heater cannot dissipate the heat being generated by contact with the sheath. So, in effect, the temperature inside the heater will continue to rise until the magnesium oxide or resistance wire breaks down and the heater fails.
If moisture or impurities are present they can be drawn into the heater. Because magnesium oxide is hydroscopic, every time power to electric heaters is eliminated, an internal vacuum occurs which draws in air from the surrounding area. This vacuum can cause a short circuit.
Finally, make sure that the wattage density isn’t too high and that you are using the correct voltage. Either of these issues can a cartridge heater to fail.
If you have any other questions about your cartridge heaters, please call us at (561) 272-5442 and one of our technicians can help you diagnose any cartridge heater problems.