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Shrinkage Prediction for Slowly-Crystallizing Thermoplastic Polymers in Injection Molding

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Published/Copyright: June 4, 2013
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International Polymer Processing
From the journal International Polymer Processing Volume 12 Issue 3

Abstract

The prediction of shrinkage and warpage of crystalline polymers is quite difficult. This is because of the complications of the crystallization process and associated material property changes. In typical injection molding of semi-crystalline polymers, it is difficult to calculate crystallinity accurately because of its complicated dependence on temperature, time and stress. In the case of slowly-crystallizing polymers, typically the crystallinity of the polymer remains small during the process. In this case, therefore, the importance of accurate calculation of crystallinity is decreased. The difficulty in this case is the measurement of material properties under variable crystallinity because of the possible crystallization during measurement. In the present study, methods have been developed to obtain material properties which include the effect of crystallinity. The material properties measured include viscosity, thermal conductivity, heat capacity, PvT relation and crystallization kinetics.

Injection-molding experiments have been conducted to measure the shrinkage of a part using a slowly-crystallizing polymer. Shrinkage has been measured by comparing the mold cavity dimension and the dimension of the molded sample. The polymer used in this study is PET (polyethylene terephthalate).

A simulation program has been developed to analyze the injection-molding process. This program is based on quiescent crystallization kinetics. The predicted shrinkage and measured shrinkage are found to agree reasonably well.

* Mail address: Sejin Han, Cornell Injection Molding Program, Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York 14853, USA
Received: 1996-9-1
Accepted: 1996-11-29
Published Online: 2013-06-04
Published in Print: 1997-09-01

© 1997, Carl Hanser Verlag, Munich

Articles in the same Issue

  1. Contents
  2. Contents
  3. Editorial
  4. Dedication In Memorial to Konathala Himasekhar (1957–1995)
  5. Regular Contributed Articles
  6. Towards a 3-D Finite Element Model for the Gas-Assisted Injection Moulding Process
  7. Numerical Simulation of the Multi-Component Injection Moulding Process
  8. Shrinkage Prediction for Slowly-Crystallizing Thermoplastic Polymers in Injection Molding
  9. The Optimized Quasi-Planar Approximation for Predicting Fiber Orientation in Injection-Molded Composites1
  10. Modelling the PVT Behavior of Isotactic Polypropylene
  11. Extension of 2½ D Control Volume Methods for Transverse Flow at Sprues, Gates and Junctions
  12. Numerical Modelling of the Mould Filling Stage in Gas-Assisted Injection Moulding
  13. Modular Tangential Counter-Rotating Twin Screw Extrusion: Non-Newtonian and Non-Isothermal Simulation
  14. A Parametric Study of Sink Marks in Injection-Molded Plastic Parts using the Finite Element Method
https://doi.org/10.3139/217.970228

Articles in the same Issue

  1. Contents
  2. Contents
  3. Editorial
  4. Dedication In Memorial to Konathala Himasekhar (1957–1995)
  5. Regular Contributed Articles
  6. Towards a 3-D Finite Element Model for the Gas-Assisted Injection Moulding Process
  7. Numerical Simulation of the Multi-Component Injection Moulding Process
  8. Shrinkage Prediction for Slowly-Crystallizing Thermoplastic Polymers in Injection Molding
  9. The Optimized Quasi-Planar Approximation for Predicting Fiber Orientation in Injection-Molded Composites1
  10. Modelling the PVT Behavior of Isotactic Polypropylene
  11. Extension of 2½ D Control Volume Methods for Transverse Flow at Sprues, Gates and Junctions
  12. Numerical Modelling of the Mould Filling Stage in Gas-Assisted Injection Moulding
  13. Modular Tangential Counter-Rotating Twin Screw Extrusion: Non-Newtonian and Non-Isothermal Simulation
  14. A Parametric Study of Sink Marks in Injection-Molded Plastic Parts using the Finite Element Method
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