Optimizing Hopper Airflow and Temperature Controls in Plastic Processing
Hopper airflow rates of 0.8 to 1.2 m3/hr per kg/hr combined with a dew point below -40 C prevent hydrolytic degradation and guarantee uniform drying.
Melt Flow Rate ASTM D1238
Meaning
Standardized test method for measuring the rate of extrusion of molten resins through a die of a specified length and diameter under prescribed conditions of temperature and load. Melt flow rate ASTM D1238 provides an indirect measure of the molecular weight and viscosity of a polymer. It is the most common metric used to characterize the flowability of thermoplastics during the sourcing and selection process.
Processing Indication
High values indicate a low viscosity material that flows easily into thin-walled moulds or complex geometries. Conversely, a low result for melt flow rate ASTM D1238 suggests a high viscosity resin suitable for extrusion or blow moulding. The value helps the moulder set the initial temperatures and pressures for the injection cycle.
Quality Control
Variations in the value between different lots of the same grade can indicate inconsistencies in the polymerisation process. It is also used to assess the degradation of regrind material compared to virgin resin. Excessive heat history during recycling typically causes the melt flow rate ASTM D1238 to increase as the polymer chains break down.
Testing Variable
Results are highly dependent on the specific load and temperature used during the test. A result for polyethylene at 190 degrees Celsius cannot be directly compared to a result for polycarbonate at 300 degrees Celsius.