Meaning
Material density change as a function of temperature and pressure is measured to predict polymer shrinkage during the moulding cycle. This relationship is captured in PVT data, which plots pressure, volume, and temperature for a specific resin. Processors and simulation engineers use these curves to calculate the correct cavity size and packing parameters.
These charts are typically generated using high-pressure capillary rheometers or isobaric measurement devices.
Simulation Accuracy
Injection moulding simulation software relies on material models to predict how plastic flows and shrinks in the mould. Inaccurate PVT data leads to poor predictions of part shrinkage, warpage, and gate freeze-off times. High-quality, grade-specific data is necessary for running reliable fill and pack simulations.
Shrinkage Prediction
As molten plastic cools under pressure, its specific volume decreases. Analyzing the PVT data allows engineers to determine the holding pressure needed to compensate for this thermal contraction. Proper analysis helps to minimize the formation of internal voids and sink marks in thick sections of the part.
Quality Control
Monitoring melt temperature and cavity pressure during the run allows the machine to adjust parameters to keep specific volume constant. Utilizing PVT data in this way helps to maintain consistent part weight and dimensions despite variations in raw material viscosity. Real-time correction reduces scrap rates in high-precision moulding.
