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Fundamentals of Melt Flow Testing

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Fundamentals of Melt Flow Testing

  1. 1. MELT FLOW TESTING ISO 1133, ASTM D1238
  2. 2. Both Melt Flow and Rheology Tests can be very helpful tools for QC monitoring and development of polymers. This presentation is designed to be an informative introduction and guide to Melt Flow test, and to assist with troubleshooting inconsistencies in results.
  3. 3. MELT FLOW Melt Mass-Flow Rate(MFR) The mass of material flowing through a die at a specified temperature (g/10 min) Melt Volume Rate(MVR) The volume of material flowing through a die at a specified temperature (cm3/10 min) MVR = MFR/density of material at melted state “Measure of the ease of flow of melted polymer” MELT FLOW: Typical Index for QC of thermoplastics
  4. 4. WHY MELT FLOW? • Melt Flow is a Typical Index for polymer materials • Verify incoming/entrance material • Check regular quality control of material • Compare new materials in a product development setting • Predict how a polymer will behave in a number of processing techniques Raw Material Producers Compounders Manufacturers/Convertors
  5. 5. A TRUE STORY As an example of an actual case of how Melt Flow information can be used: An injection molded polycarbonate part was found to crack when dropped. The virgin resin had an MFR of 28.5 g/10min. A sample from a known “good” lot of parts was ground up and tested in a melt flow tester. It had an MFR of 27 g/10min, well within established tolerances (±30%). But a “problem” part showed an MFR of 90 g/10min. From this evidence, it was discovered that the “bad” lot contained a large amount of regrind that had been thermally degraded in processing. Manufacturers/Convertors
  6. 6. THE EQUIPMENT MASS KNOWN/SET TEMPERATURE (variable per material) KNOWN DIE SIZE (per standard – ASTM D1238, ISO 1133) KNOWN/SET MASS (variable per material) MFR: Amount of material extruded in 10 minutes Melted Polymer
  7. 7. General standards: • ISO 1133-1,-2 (Method A, B) • ASTM D1238 (Methods A, B, C, D) Material specific standards, such as: • ASTM D3364 (for PVC) • ISO 1872-1 (for PE) MELT FLOW STANDARDS
  8. 8. ISO 1133 : 2 methods (A & B) A : Manual test, measure of mass flow (MFR) B : Encoder-assisted tests, measure of volume flow (MVR) (*) ISO 1133-2 introduced new stricter tolerances for temperature profile inside the barrel, and is dedicated for materials that are sensitive to time-temperature history and/or moisture ASTM D1238 : 4 procedures (A, B, C & D) A : Manual test, measure of mass flow (MFR) B : Encoder-assisted tests, measure of volume flow (MVR) C : For high-flow materials (special procedure, die with D= 1.048, L= 4 mm and a Die Plug Device) D : For multiple-weight tests INTERNATIONAL STANDARDS FOR MFT
  9. 9. Easy test procedure: • Preheat barrel, die, and piston at working temperature • Choose the test mass • Insert the right amount of sample • Apply the test mass to compact the sample • Measure the amount of sample flowing through the die during a fix time or for a specific piston displacement • Clean carefully piston, die, and barrel MELT FLOW: THE TEST Polymer Melt Extrudate Constant Test Temperature
  10. 10. KEY FACTORS THAT INFLUENCE RESULTS Temperature Accuracy Preparation of Sample (moisture) Sample Compacting Method Parameters Melt Density Value Manual Operations within Test Maintenance of Die and Piston Cleaning Procedures Temperature Stability Choice of Procedure Encoder Accuracy Extrudate Cutting Precision = most common
  11. 11. • Is the barrel clean? Or is the die clean? • Increased friction between the barrel & piston will reduce melt flow rates • Is the test being run at the correct temperature? • Is system temperature control accurate and consistent throughout length of barrel? • Especially critical for materials that are sensitive to time-temperature history • Has the material been pre-conditioned according to procedure? • Hygroscopic materials give unreliable test results if they are not dried in consistent manner • Moisture tends to generate bubbles and trigger degradation of sample • Is the melt density being used in the MFR calculations correct? • Was the material compacted properly (or were there air bubbles)? KEY FACTORS THAT INFLUENCE RESULTS
  12. 12. MANUAL v. AUTOMATIC TEST OPERATIONS • Controlled Compacting • Better reproducibility and less scattering of results • No physical effort required by operator (reduces risk of injury) • Post-test automatic purging • Reduces total test time • Operator is ready to run next test more quickly • Cleaning • Thorough cleaning extends life of equipment & helps maintain consistent results
  13. 13. THANK YOU FOR YOUR TIME! Please contact your local Instron® Sales Representative with any questions.