Meaning
In the characterization of injection molding resins, the flow behavior must be measured under conditions that mimic the actual production environment. High pressure melt rheology uses specialized capillary rheometers to determine how the viscosity of a polymer changes when subjected to the extreme pressures found in a mold. Standard melt flow index tests are too slow to capture these effects.
Shear Rate
Velocity gradients within the melt become very high during the filling of thin-walled parts. Through the use of high pressure melt rheology, engineers can map the viscosity across a wide range of shear rates. This map allows for more accurate flow simulations during the mold design phase.
Injection Velocity
Pressure increases as the machine forces the plastic through small gates at high speeds. Data from high pressure melt rheology reveals if a material will thin out too much or if it will resist the flow and cause a short shot. This understanding helps in selecting the right grade of resin for a specific tool.
Tooling Influence
Friction between the melt and the metal walls generates internal heat that can change the viscosity. Using high pressure melt rheology allows a moulder to account for this viscous heating and adjust the cooling cycle accordingly.
