Because of the hygroscopic characteristic of the used ceramic insulation materials they absorb moisture. Therefore we send our cartridge heaters usually in air-tightly closed plastic bags. When stored unprotected in environmental air it is absolutely important to check the insulation resistance before use and – if necessary – to dry the elements (controlled start-up or drying oven). If humidity is inside the heater and 230 V is applied to it before pre-heating, it is very probable heater failure.
Bending the outside connection points (exit type N) could break the termination and must be avoided. Frequent movements of glasfibre isolated leads may cause damage and therefore has to be avoided.
The temperature stress of max. 750 °C at the sheath is not valid for the connection area. The temperatures arising in the connection area determine decisively the suitability of the available exits.
The max. temperature resistance of 750 °C at the sheath implies the assumption of a "normal" heat conduction and thus a "normal" temperature gradient to the heating wire. Installation and operation conditions with exceptional superb thermal conduction (e.g. heat exchanger applications using aluminium bodies) increase the temperature gradient considerably and thus result in a higher temperature at the heating wire. Max. temperature at the sheath in such applications must be assessed lower accordingly. This is especially important for the design of the control system (position of thermocouple, control temperature, hysteresis).
The stated nominal voltage must not be exceeded, otherwise overheat is risked.
Generally it can be said: the better heat is carried off, or flows into the work piece respectively, the higher the surface watt density on the sheath can be.
Watt densities on the cartridge sheath of up to 50 W/cm² are acceptable only controlled and in ideal thermal installation conditions. Materials with a good thermal conductivity and a narrow tolerated cartridge heater fit are therefore recommended strongly.
For our ground high density cartridge heaters we recommend H7-holes with a surface roughness as small as possible.
Form errors of the hole, crossing holes or shrinkage cavities obstruct the heat conduction and lead to heat accumulation which could partly overheat the cartridge critically.
The connection area of cartridge heaters must be protected from lubricants, detergents and solvents, because these could diffuse into the ceramic and lead to short-cuts.
In a solid combination of materials with different thermal expansion (e.g. steel and aluminium) or for extreme temperature gradients alongside the sheath of the cartridge heater heating wire and terminal pins can be exposed to heavy tensile loading and if worst comes to worst they can tear resp. break. Cause often is e. g. cracking of corrosion protective passive layers or the reduction of thermal tensile strength due to microstructural changes resp. phase transformation at certain temperature ranges. Especially at high operating temperatures and unavoidable mechanical stress alteration extensive load and endurance tests are indispensable before series start-up.
In every practice application there are working and environmental parameters which can not be calculated exactly in theory. That is why we recommend generally to test cartridge heaters in the application under real working conditions in advance.
No warranty claims can be derived from this user manual.
Chapter Cartridge Heaters
High power, little space: Contact heating of tools and machine parts. We make cartridge heaters from diameter 4 up to 31.8 mm in an unlimited number of styles.
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