Meaning
Thermodynamic cooling paths maintain constant specific volume during polymer solidification inside a sealed mold cavity. Executing isochoric cooling suppresses macroscopic volumetric shrinkage by maintaining high hydrostatic pressure until thermal equilibrium is achieved. Conventional isobaric cooling leads to significant dimensional reduction as polymer density increases during phase change.
Molders utilize sealed cavity systems and high injection pressures to hold molten resin at constant volume throughout crystallization.
Pressure Evolution
Maintaining fixed volume forces internal cavity pressure to decay along specific PVT state lines as temperature drops. The trapped polymer chains freeze under high hydrostatic stress, preventing macromolecular rearrangement. Pressure drops rapidly once the core temperature passes the glass transition or crystallization point.
Tool sealing integrity governs whether true constant-volume conditions persist without melt backflow through the gate.
Structural Outcome
High internal hydrostatic pressure alters chain packing geometry, creating uniform internal density distributions. Residual stress concentration increases when cooling at constant volume, requiring post-molding annealing for stress-sensitive applications. Thick wall sections resist sink mark formation because volumetric contraction is absorbed by pressure decay rather than physical wall collapse. regrind blends show altered PVT paths, changing cavity pressure decay curves.
Shrinkage Control
Constant volume solidification eliminates post-ejection sink defects in thick structural components. Precision optical elements benefit from uniform refractive index profiles generated under controlled pressure decay paths. Precise thermodynamic control guarantees tight dimensional compliance in high-tolerance applications.
