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With different electrical termination styles, clamping mechanisms and the ability to accommodate holes and cutouts, mica-insulated band heaters are used successfully in many applications, particularly plastics.
Loss Prevention for Band Heaters
Most band heaters with heating plate do not “burn out”; instead, environmental factors create a short, cause hot spots to develop, or simply push the heater beyond its normal operating temperature. All of these factors cause a heater to fail prematurely and require replacement. Obviously, minimizing these environmental factors can reduce the frequency of replacing band heaters in your operation.
Contamination.By far, the most frequent culprit of band heater failure is contamination.
Retightening the band at an elevated temperature will account for the heater’s thermal expansion. (Remember, ceramic band heaters are radiant heaters and should not be tighten in this manner.)So, in cases where one heater design will not work -- for example, a machine setup that requires stretching the band over the end of the machine barrel, which would damage a mica band heater -- use a heater that is better suited to application such as a two-piece mica or a one-piece expandable band. Runaway Temperatures.Heaters, like finned heaters, are extremely obedient entities. If a controller tells them to produce temperatures beyond their limitations, they will do so -- until their demise. When possible, it also is good practice to specify strap-style clamping devices to hold the heater in place. These devices have a lower thermal expansion rate than the heater, so they can help hold the heater, or the defrost heater, tightly against the barrel during operation.
The durability and performance of a heater depends on selecting the appropriate wattage by using resistance thermometer.The safe heating pattern,and heating elelment of the material heated, thermal conductivity and coefficient of expansion of the cylinder are other factors that should be taken into consideration while deciding wattage.A cartridge heater consists of resistance coil wound around a ceramic core that is surround by dielectric and encased in a metal sheath. Powered heat transferred through the coil to the sheath causes the sheath to heat up. This heat is then transferred to the inside metal part requiring heat.
To fit a cartridge heater in a low or medium temperature application (600°F or less), general purpose drills are usually adequate for drilling holes. Holes can be drilled .003” to .008” over the nominal size of the drill, resulting in fits of .009” to .014.” While this fit is slightly looser than would permit optimal heat transfer, it aids in the installation and removal of the cartridge heaters with heating cable, especially those with long sheaths.
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