Meaning
Monitoring instruments integrated directly into an extrusion or injection line provide real time data on the flow properties of the polymer. An inline melt rheometer measures viscosity under actual processing conditions without the need to take samples to a laboratory. This immediate feedback allows for rapid adjustments to the process, reducing the amount of scrap produced during start up or material changeovers.
Process Feedback
Control systems use the data from the sensor to maintain a constant product quality despite variations in the feedstock. The inline melt rheometer can detect small changes in the molecular weight or the concentration of additives as the material flows through the die. This information is used to tune the screw speed or the barrel temperature to keep the melt within the target viscosity range.
Pressure Drop
Calculations of shear stress and shear rate are based on the resistance the polymer encounters as it passes through a calibrated capillary. The inline melt rheometer uses high precision pressure transducers to monitor this resistance at various flow rates. These sensors must be strong enough to handle the abrasive nature of filled polymers and the high pressures found in modern moulding machines.
Viscosity Measurement
Real time analysis provides a more accurate view of material behaviour than a single point melt flow rate test. An inline melt rheometer captures the full rheological curve of the polymer, showing how it responds to different shear levels. This level of detail is essential for complex processes like co-extrusion where the viscosity of two different layers must be perfectly matched to prevent interface instability.
By providing a continuous data stream, the instrument allows a manufacturer to detect subtle shifts in polymer quality that would be missed by hourly manual sampling.
