Carreau-Yasuda Model

Flow Prediction

Accuracy in predicting the filling stage of a tool relies on high-quality rheological data that covers the entire processing window. The carreau-yasuda model captures the subtle changes in viscosity that occur as the polymer enters the narrowest parts of the mould, such as the gate or a thin rib. When a melt transitions from the sprue to the gate, the shear rate climbs rapidly and the internal friction drops.

Chains begin to align under the stress, which reduces the effort required to move the material into the cavity. Molders use these simulations to determine the minimum clamp force required to keep the tool closed during the high-pressure phase. If the model underpredicts the viscosity, the machine may lack the pressure to fill the furthest parts of the part.

Overprediction leads to selecting a machine that is too large and expensive for the specific job. The equation includes five distinct variables that are calculated from laboratory measurements.

Material Characterization

Laboratory testing on a capillary rheometer provides the data points necessary to fit the curve to a specific resin grade. Scientists measure the pressure drop across a die at various speeds to calculate the viscosity across a range of shear rates. This information forms a core part of a resin datasheet and allows for the comparison of different batches.

The carreau-yasuda model allows a moulder to compare the processing window of a virgin resin against a lot that contains recycled content. Regrind often has a lower zero-shear viscosity because the previous heat history has broken some molecular bonds. Shorter chains slide past each other with less resistance at low speeds.

Simulation Precision

High-fidelity results in flow analysis software require the use of models that account for the transition region between Newtonian and power-law behavior. Within the carreau-yasuda model, the parameter known as a controls how sharply the curve bends from the plateau into the thinning phase. This level of detail is necessary for materials like polycarbonate which exhibit complex flow behaviors at different temperatures.

Precise calculations help in identifying where shear heating might cause the material to burn or degrade. The model stands as a standard for professional engineering across the plastics industry. It provides the necessary data to balance the flow in multi-cavity tools.