Got your cartridge heater stuck in the die? See how you can remove them out.

If you are in the maintenance department, in a plastic processing factory, you may have came across the stated Problem. In this article, let’s try to address this issue with a practical point of view.
Cartridge Heater seems the only viable source of concentrated heat in the dies. These heaters have a relatively short life as compared to other similar heater used in industry. The problem even gets worse, when these heater get stuck in the dies. The Reason for it is that, when the heater starts heating, due to thermal expanding, the circumference of the heater expands and thus the heater fits the bore size very tightly. While this property of expansion is beneficial, as it results in getting rid of air pockets, that remains in between the bore and heater body, It become a headache for the service personnel to remove the heater after its failure.

Some urge the concept, that, while heating the heater expands, on the other hand why does not it shrink on cooling. The reason for that is, after some time of operation, Scaling on the sheath surface occurs. This Scaling have large surface area than that of the original sheathing surface area. Thus Heater get stuck.

Now comes the solution. The heater size(or diameter)  of the heater is made small, So that sucking is avoided. But there is a problem with that too. A small diameter of the heater means loose fit. As these heaters have fairly high watt density, any left over air spot will cause resistance to heat flow and thus would eventually lead to heater failure. So in order to decide on the size of diameter, Thermal properties of the sheath material can be obtained from the manufacturer. If Your heater still got stocked in the die, the only option leftover is drilling and boring to size.
The Other option that is prevailing in market is that of split type cartridge heater. In a split type cartridge heater, the heater is made into two halves with D shape. This is then bent at 180 degree to form a full circle, a combination of two D forms an O. However, the reliability of these heater is still under consideration.

Another way to get in check, is to control the temperature of the cartridge heater itself. Please remember that, Temperature Control of the process is different than that of heater. Heater temperature control is made preliminary for controlling energy input to the heater, so that the heater do not fail prematurely with an high increase in temperature. To accompany this task, thermo sensors, such as thermocouple are made integral as the part of heater itself. Thermocouple works on the principle of seeback effect.  Now the temperature reading is that of the heater itself. Thus by setting the temperature at optimum level, the heater can be made to run for a long time, results in low downtime, high productivity and low frequency to which these heater needs replacement.      

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