Determination of cure mechanism inside die for a part manufacturing during large-scale pultrusion

The cure kinetics of resin, heat capacity, and thermal conductivity of reinforcing materials of uncured mass dictate the ultimate curing of reinforced thermosets manufactured component. In this study, the degree of conversion from heat capacity by "Lumry and Eyring Model" and order of reaction by multi-regression technique using "Borchardt and Daniels Model" are calculated in finding cure kinetics (gamma) of the resin. Experimental results from differential scanning calorimetry, thermogravimetry (TGA), and rheological measurements were used to determine thermal conductivity, heat capacity, and rheological parameters of the resin through several model fitting. The calculated thermal conductivity of uncured composite from ration of (length vs. contact area) and thermal resistivity extracted from TGA data was fitted into a specific mathematical model, which predicts the thermal behavior of heated prepreg during pultrusion operation. These parameters used in a separate mathematical partial differential equation-based model equation to predict the change in temperature and resin conversion along axial distance and radial thickness. The influence of operating conditions, such as rate of heating (early and late heating) and fiber volume fraction while curing inside die were calculated and validated with experimental results. This study evaluates the extent of heat transfer and degree of conversion inside pultrusion die during scale up steady state process. It is observed that the paradigm of influencing parameters like pulling speed, die radial thickness and heater engagement (early and late heating) on heat flow from die wall to core (i.e., thickness of the part being pulled) follows the data captured experimentally.