» Knowledge Base » A Quality Control Tool For Plastics – Melt Flow Index Tester

A Quality Control Tool For Plastics – Melt Flow Index Tester

Why melt flow rate is important?

The plastic manufacturers must check the materials for flow properly into their molds during casting. For maintaining the quality of plastic products and for the development of efficient and cost-effective manufacturing, the flow of melted plastics must be precisely measured. The melt flow index tester is used to test the melt viscosity or flow resistance of the plastic resins at a particular stress and temperature. If the polymer chains have a short length and simple geometry, it can slide past one another easily with little flow resistance, whereas the compound structure with a long chain of polymer indicates high flow resistance. The quality of resins is compared to determine the resin degradation due to storage or transit conditions. The testing also determined improper processing conditions. The MFI is the property of plastics determining the physical and chemical properties of materials. The equipment assists in the precise analysis of plastic granules. The flow property plays a significant role to check the quality of the plastics before using for manufacturing different plastic products, for example, the children’s toys must be made with best plastics for the safety purpose.

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Why is MFI prominent?

The instrument measures the amount of grams of polymers pass through a standardized capillary under a standard load more than 10 minutes. The higher melt flow index means the low viscosity of the material. The tool allows easy or rough comparison of flow characteristics of different types of plastics.

The melt flow index tester is an advanced tool and is provided with different cleaning and administrative tools. These tools help in maintaining the machine clean and attaining the precise test results. The instrument is ideal to test plastic granules being used for molding of plastic products.

Main features of MFI

  • The MFI has a high heating capacity from to 400 degree Celsius with a pre-settable digital timer to select the test cycle for sample cutting.
  • The MFI has a PID controller to control the temperature inside the chamber with accuracy. The timer can be used for setting the testing time up to 999 hours.
  • The inner body is made of stainless steel with corrosion resistance ability.
  • Both automatic and digital operations are available for test specimen

How to calculate MFI?

Prior to starting the calculation of MFI, ensure the machine is perfectly leveled using the plumb line provided.

  • Connect the main socket to a 3 pin 15 amp socket, the PID controller will show some readings on the process value (PV) and set value (SV). Set the SV value on controller and test duration timing on a digital
  • The machine has a manual operation in which manual cut button on the control panel is used to cut the granules manually with the help of the toggle switch.
  • When the temperature and timer are set, turn ON heater switch and wait until reading display in the controller to reach the SV display.
  • Once required temperature is set, add plastic granules to the barrel of the machine and poke with the plunger so any air between the granules can be eliminated.
  • Inserting granules will cause a slight decrease in PV value, thus wait until the value reaches the SV value. Preheat granules before beginning the test.
  • When PV and SV value matches, put the plunger along with the dead weights. The extrudate will come out of the die/orifice positioned at the lower end of the barrel.
  • Once the time cycle is complete, the extrudate is automatically cut by the cutter or can also be done manually.
  • Discard the first extrudate cut by a knife and consider the next one for testing. Weigh the extrudate cut from a barrel with the help of a digital balance. Calculate melt flow index of the sample using the below formula:

MFI = weight of sample in gm/10 min

The flow property of the molten polymer is crucial. During the plastic processing, material is melted and pumped through the orifice using a screw pump. This process is used for mixing operation and for making the finished objects using injection molding and film production. Stress is applied to shape the molten plastic. The pipes, sheets, profile, and film are the result of extrusion. The calibration of melt flow index tester is also crucial for the right testing procedures.


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