Polymer raw material is either available in granulated form or powdered form. For making high quality products, two things are very important;
1. High quality raw material
2. Right production process
Standards of production process are defined as per the requirements. However, raw material which is often procured from multiple vendors needs a close scrutiny. Usually, granulated plastic is tested for its flow properties to check its suitability for the extrusion process.
Measurement of flow properties
Melt flow index testing
is the most preferred test method to determine the flow rate of the granulated polymer. In this test, the molten plastic is made to flow through a capillary die and how much plastic is flown in 10 minutes is weighed and declared as the flow rate of the sample.
Precautions to be taken for MFI testing
1. The level of the machine is of utmost importance. The machine should be placed on a levelled surface so that pressure can be applied in right manner. A plumb line is provided along with the machine to check the levelling of the surface.
2. Cleaning of barrel is very important so that fresh sample does not mix with old samples which were tested earlier. This results in huge error of the final melt flow rate. Flat and threaded tools are provided with the machine to do the cleaning job easily.
3. Shape of piston is very important. It is designed as per the testing standards. Any chipping or dents may lead to application of inappropriate pressure on the granules. This is why utmost care is required while handling the piston.
4. Before starting the time, any excessive extruded plastic that is coming out is removed. Because granules started to flow as soon they attain melting temperature. Also, make sure, you start the timer once the plastic is molten. A lot of precision is required at this step.
5. As the barrel is operating at high temperature approx. 400°C, the operator should take appropriate measures to avoid burn injuries.
6. It is very important that granules are packed tightly in the barrel using the material charger. Any free space in the barrel may lead to formation of air bubbles in the extruded plastic. This may lead inappropriate measurements.
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