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When solids, gases and fluids are to be heated by electric energy the process is generally carried out by conduction. It is only possible to transmit heat quickly by conduction if the producer of the heat (the cartridge) is in direct contact with the receiver of the heat (any solid, gas or fluid).
When heating takes place the molecules expand and move faster, producing a distribution of heat to the colder part until their temperatures level out.
If there is mould on which to drill in order to house a cartridge heater, and where the mould not to be in direct contact with the whole cartridge heater, the transmission of heat by conduction would occur, due to the fact the air molecules would not transmit the energy required to heat the mould. The heat would not be distributed but would remain within the cartridge heater, with the result of overheating of the latter, which, in turn, may bring about a reduction of dielectric strength between the heater wire, the power conductors and the weakening of the metallic protector, the result being a short-circuit. Therefore, the adjustment of the cartridge to the heater is of the most importance. Just a few drops of water particles are enough to weaken considerably the insulating capacity of magnesium oxide.
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