The purpose of a cartridge heater is the heat metal parts by inserting them into predetermined spaces of the parts. The most common use of cartridge heaters in the hot melt industry, is for heating all automatic applicators, all hand guns, and sometimes even melters. They are very easy to install as the heaters are made slightly undersized relative to their nominal diameter.

It is recommended that the watt density of a cartridge heater only be as high as needed. Under normal applications maximum watt density is not required. Safety margins usually are rated by using less than the maximum allowed. Rather than having the highest possible wattage per heater, heaters should be selected that give a more even heat pattern.

In the hot melt equipment industry, watt densities are usually high rather than medium. In machining the applicators that receive the heaters, holes are drilled and reamed to exact tolerances. In a high watt density application, a very close fit is important. This style cartridge heater should have a hole tolerance of plus or minus .003. After holes have been properly drilled and reamed they should be cleaned and degreased to remove any remaining cutting debris.

Watt density is the heat flow rate or surface loading of a cartridge heater. It is the number of watts per square inch of a heated surface area. Watt density calculation would be as follows.

Watt Density = wattage / (pi x diameter x heated length)

The heater cartridges in hot melt systems and their components are normally controlled by a master temperature controller on the hot melt units themselves. The temperature controllers on the hot melt units read RTD sensors to control the temperature of the heaters. RTD sensors are found in all components of a hot melt system including the tank, the heated hoses, and all heated applicators.

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