Meaning
Mathematical relationship describing the temperature dependence of relaxation times in amorphous polymers defines this empirical model. The williams-landel-ferry equation relates the shift factor of a material to its glass transition temperature and two material-specific constants. It provides a reliable way to predict how the viscosity and stiffness of a resin will change as it is heated or cooled.
Constants Application
Universal values for the coefficients are often used, although grade-specific constants provide more precise results for high-performance resins. These numbers determine the shape of the curve that describes material softening.
Relaxation Threshold
Model accuracy is highest when the material is between the glass transition temperature and roughly one hundred degrees above it. In this range, the free volume of the polymer changes linearly with temperature, which the equation captures with high fidelity. Outside this window, different physical mechanisms take over and the model loses its predictive power.
Calculation of the processing window relies on this equation to ensure the melt remains stable and flowable.
Moulding Control
Temperature sensitivity explains why tight barrel control is necessary to maintain consistent part dimensions and surface finish. Predicting how viscosity drops with temperature helps in setting the correct injection pressure for complex cavities. A small change in temperature near the glass transition has a massive effect on the relaxation time of the chains.
