Piezoelectric Cavity Pressure Telemetry in Injection Molded Parts
Wireless piezoelectric cavity pressure telemetry eliminates platen cabling, providing real-time process monitoring for active part quality containment.
Polymer Melt Compressibility
Meaning
Volumetric reduction of a thermoplastic material under high pressure and temperature defines the physical behavior of the molten resin inside the injection barrel and mould cavity. This polymer melt compressibility influences the required injection stroke and determines how much material can be packed into the mould before gate freeze. The property is characterized by the pressure-volume-temperature relationship of the specific polymer grade.
Physical Property
Molten resins behave as compressible fluids under the extreme pressures of the injection molding process, compressing up to ten percent of their unpressurized volume. This polymer melt compressibility varies with both the temperature of the melt and the structure of the polymer chains. Amorphous resins typically show greater volume change under pressure than semi-crystalline materials.
Volumetric Effect
High compressibility demands a larger injection volume from the screw to achieve a complete fill of the cavity. If the machine does not account for this volume loss, the part will suffer from low density and poor surface finish.
Cushion Variation
Maintaining a consistent cushion during the holding phase becomes difficult when polymer melt compressibility shifts due to variations in melt temperature or raw material consistency. Small thermal fluctuations in the barrel can change the compressed volume, causing the actual mass of plastic injected to vary from shot to shot. In high-precision molding, this variation leads to weight inconsistencies and dimension issues, which forces the process engineer to adjust the holding pressure dynamically to maintain part quality.