Multi Cavity Mold Gate Shear Rate Evaluation Methods
Multi cavity mold gate shear rate evaluation requires Rabinowitsch-Mooney corrected velocity gradients matched against real micro-metrology tool dimensions.
Peak Shear Threshold
Meaning
Rheological material limits defining the maximum allowable shear rate during fluid processing mark the boundary where polymer chains undergo irreversible mechanical degradation. Establishing a peak shear threshold determines the processing velocity ceiling for molten resins inside hot runners, injection nozzles and extrusion dies. This parameter governs processing windows, ensuring polymer melt stays within safe viscosity ranges without chain scission.
The boundary applies to fluid flow in polymer processing, terminating at the solidification front within the mold cavity.
Rheological Boundary
High deformation rates within narrow gate channels rupture molecular bonds in long-chain polymers. Exceeding the peak shear threshold reduces tensile strength, impacts optical clarity and creates surface streaking in molded components. Medical device housings and structural automotive components require strict adherence to shear limits to ensure field safety.
Operating below critical shear limits preserves resin mechanical properties.
Viscous Limit
Frictional heating near the peak shear threshold raises local melt temperature rapidly, altering material viscosity profiles.
Processing Margin
Process engineers establish injection velocity profiles to keep shear rates safely below the peak shear threshold during filling. Relying on nominal supplier material data sheets without measuring real-time shear responses under high-speed production conditions leads to undetected structural embrittlement. Calling a process qualified based on low-speed prototype runs causes unexpected part failures when production presses operate at full capacity.
Rheological testing across operational temperature ranges establishes safe process boundaries for continuous manufacturing.