Melt Flow index is the imperative property of the polymer granules that are used for determining the quality of plastic. Also, it is used for determining the suitability of the granules in extrusion process. To get all the testing process right, the foremost thing is to consider the quality of the machine that is being used to determine the MFI of the test materials. In this post, we are going to highlight some features that defines the quality of a good melt flow index tester.
Standardised – The foremost thing to consider is the standards the machine is following. Is it complying to the different parameters defined under a test process. The dimensions of the barrel, the diameter of the die or orifice, etc. are some common things to consider.
Levelling of the machine – Alignment is an important factor that can lead to inaccurate test results. If the machine is not standing on a straight platform, it may lead to improper flow of the molten plastic. This improper flow may lead to the inaccurate test results.
Temperature controlled barrel – There should appropriate measures to control the rising temperature of the barrel. Continuous increase in temperature may lead to damage of heating elements plus chances of injuries to the operator may increase.
Placement of cutter – Advance models of MFI testers has automatic cutter, that immediately cuts the strand of molten plastic after the period of test process is complete. In certain machines, the cutter runs once before the test and after the test.
- The MFI testing methods to be followed to ensure accuracy in the process:
- The sample should be in granulated form. No other form or final product can be tested.
- The granules are charged in the hot barrel. It has to be made sure that there is no space within the granules in the barrel.
- Using a piston, dead weight is applied on the granules to create a pressure and to make the flow of the granules non-stop.
- As the temperature of the barrel starts to increase, the sample starts to melt.
- This molten plastic starts to come out from the orifice. There is an automatic cutter incorporated into the machine to cut the string of the plastic that is coming out from the orifice.
- This cutter runs twice. One, before starting the test and once after 10 minutes, which is the standard test time.
- This molten plastic is taken and weighed. The weight in grams is divided by 10 minutes to get the actual MFI value.
*Orifice: Orifice is an opening/die of predefined shape and dimension.
MFI tester can determine properties like viscosity, molecular structure and mechanical properties at shear stress.
Precaution to be taken to ensure precise handling:
• There has to be minimum human interference while the test is going on.
• The barrel is cleaned thoroughly before charging, else there would be mixing up of sample with previously charged sample
• Charge the samples carefully, do not leave free space in the barrel
• Piston requires extensive care, chipping off or dent may lead to inappropriate pressure
• The machines should be placed on a leveled surface, else it may lead to the disparity. Plumbline can be used for leveling.
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