In plastic industry, the plastic is chosen after assessing the melt flow of the granules. Usually, the plastic raw material is procured in granulated form. There are test procedures defined by national and international relative authorities. It is very important to follow the testing process to keep the things standardised.
Some of the common processes that are followed in the industry are;
- Melt flow rate testing
- Melt flow index testing
- ASTM D1238
- Multi-stage tests
What is Melt Flow Rate Testing?
MFR testing means the rate of flow of molten plastic is measured. But it is not as easy as it sounds. A standardised equipment is needed to get the right flow rate. The testing process, dimensions of the machine, the pressure to be applied, etc. are defined in the standards. To determine the flow rate, melt flow index tester is used. This machine tests raw materials only in granulated form. So, the sample that you are procuring must be in granulated form.
What is Melt Volume Flow Rate Testing?
This test is very similar to MFR testing, only the values obtained after the test varies. In this test, the granules are heated to a melting point having a piston transducer on the barrel. As soon the granules started to melt, the piston starts to travel downwards. The distance travelled by the piston in 10 minutes is considered as the melt volume flow rate of the granules. However, rest of the testing procedure is same as determination of melt flow index.
What is ASTM D1238
A die of height 8.00mm and a bore diameter of 2.095 mm is used for the measurement of MFR. For samples having MFR greater than 75g/10 min, the size of die becomes half-height / half bore diameter, i.e. 4.00 / 1.050 mm.
Method D – ASTM D1238: multi-stage tests
In this test, several fillings are used when simple extrusion plastometers are used. It is equipped with an automatic load change unit which can measure multiple load levels from single filling. In this test, several fillings are used when simple extrusion plastomers are used. It is more like an automatic process in which the load changes automatically. This allows the multiple load levels measurement from single filling. With many polyolefins, it is usual to state the MVR value for different load-levels and determine the flow-rate ratio (FRR).