Application hints cartridge heaters
The ideal way to install a cartridge heaters is to place them into a separate pocket.
In the case of a watt density of the cartridge heater up to 20 W/cm2, a cylindrical hole with the precision according to H7, with the roughness of the surface max. Ra0.8 can be used. If possible, the hole must be passable for easy replacement of the cartridge heaters.
Manufacturing of the hole with precision H7 is done using a reamer. The diameter of the drilled hole before reaming should be produced with the tolerance -0.2 mm/-0.3 mm for steel parts and -0.3.mm/- 0.4 mm for brass, bronze or aluminium parts. If more cartridge heaters are located in a series, then the ideal distance between them, from the viewpoint of the service life of the cartridge heaters and the proportional allocation of temperature, should be equal to the size of the diameter of the cartridge heater.
Leads and the point of entrance into the cartridge heater must not be affected by vibrations, movement, mechanical stressing, contamination by liquids of all kinds, fats, non-inert gases, etc. If it cannot be prevented, it is necessary to choose the appropriate method for the termination of cartridge heaters, see “Terminal options of cartridge heaters”.
If the termination of cartridge heater is not waterproof (this can only be achieved at low working temperatures, see “Termination options for cartridge heaters (leads)”) or if the cartridge heater is not located in premises with maximum air humidity up to 70%, during the first use and after each shutdown, it is necessary to measure the insulation resistance. If the value under cold conditions at 500 V – DC is lower than 200 MΩ, it is necessary to dry the cartridge heater at the temperature 105 °C – 200 °C (according to leads of the cartridge heater) after 2-3 hours. This can be done in a furnace by operating the cartridge heater at 1/3 of the nominal input power.
Leads and termination of cartridge heaters must not be inserted into the heated board. If there is a problem with the service life of the cartridge heaters in the part of leads, it is necessary to check any influences that may be a reason (vibrations, chemicals, movement, temperature) and to choose a suitable form of electric connection.
If the cartridge heaters are not fitted with a ground conductor, the heated metal part must be grounded.
The decisive and mutually influential factors of contact heating of metal parts by cartridge heaters are: working temperature, watt density of the cartridges (W/cm2 of metal) and the maximum actual gap between the cartridge heater and the hole. In the case of suitably chosen other parameters, the working temperature may be up to 750 °C.
For more information and help to solve specific heating issues regarding any new or untested cartridge heaters, please contact us.