november 16, 2021

Rácz Aranka

25 komment

Melt temperature measurement – ingot


We expect there will be significant difference between the longest and shortest nozzles, at same settings the end of the long nozzle is colder, as well as the dosed material. The goal is to show that with a thin thermocouple 20-30 degree more can be measured than with a thick one, so it does not cheat us during the measurement of the injected into the open or dosed ingot.
The thermocouple is a temperature measuring device. It contains two metals with different properties, which are connected to each other by their end. This voltage is measurable and can be used to measure temperature.
There are thermocouples with different pairs of metals. The four most commonly used types are J, K, T, and E.
Every type is applicable in different temperature interval and at different environmental conditions, but the maximum temperature is mostly determined by the diameter of the applied metal fiber.

Some thermocouple compositions:
     J – Iron – Constantan
     K – Chromega – Alomega
     T – Copper – Constantan



Preparation and steps of the measurement

Set cylinder temperature in both zones: 235°C
Used material:     PE Hostalen GC7260

We need 3 pieces of thermocouples with different thickness, thermometer, and thermal imager.

Thickness and type of thermocouples:    0,5 mm (J)
                                                               1 mm (K)
                                                               1,5 mm (K)


Figure 1. Equipment required for the measurement



Perform measurement

During the measurement, from the heated and dosed cylinder we inject into the open or dose the melt on a piece of cardboard or into a plastic jar made for this purpose.
We push the end of the thermocouple into the melt and make a circular motion with it. This is recommended because the thicker thermocouple could quickly cool down the melt therefore impairing the accuracy of the measurement.
We repeat this process at least three more times to avoid scatter.
In our case we performed the measurement with three thermocouples with different diameters.


Figure 2. Perform measurement







The gotten results show that with the thinner thermocouple (0,5 mm) the ingot temperature can be measured more accurately than using the thicker one.
This is due the fact that the thermocouple warms up slower and meanwhile the melt can cool down. It is also due that the thicker thermocouple cools down the melt more.
It also can be seen that in case of longer nozzle we got higher values, which is logical since the melt is subjected to higher shear.