Meaning
Inline extrusion rheometers measure molten polymer viscosity at high shear rates during continuous processing. Extrusion laboratories utilize slit die testing to generate shear stress and viscosity curves by forcing polymer melt through a rectangular orifice of known dimensions. Pressure transducers mounted along the slit length record pressure drops to calculate wall shear stress accurately.
Unlike capillary rheometers, slit die apparatuses capture true inline melt behavior without requiring off-line sample preparation or manual material loading. Polymer compounders rely on this method to assess thermal degradation and shear sensitivity of newly formulated resin blends. Continuous data generation allows process engineers to optimize screw speed and thermal profiles during extrusion scale-up.
Rheological Measurement
Rectangular geometry provides a uniform high-aspect-ratio channel that simplifies wall shear stress calculations. Performing slit die testing across multiple volumetric flow rates constructs accurate viscosity curves for non-Newtonian polymer melts. Flush-mounted pressure transducers eliminate stagnant dead spots where polymer degradation occurs.
Real-time viscosity measurements reveal subtle resin lot variations before material reaches film or sheet casting dies.
Quality Verification
Polyolefin recyclers monitor melt viscosity continuously during compounding to detect variations in melt flow index. Slit die testing provides immediate feedback on lot consistency without interrupting production extrusion runs.
Entrance Loss
Pressure drop measurements taken within the fully developed flow region bypass complex entrance and exit pressure losses during slit die testing. Neglecting end effect corrections yields cleaner, highly reproducible viscosity data.
