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Manufacturing problems can be classified into two distinct categories: first, problems caused by equipment or process variables such as operating temperatures or pressures, screw speeds, die, screw and mold design, injection times, and so forth. The second category is problems caused by differences in the flow characteristics of resins and compounds (material variables). This paper will address the second category of material differences and show how they can be detected before processing through use of an instrument such as the automatic capillary rheometer (ACR).
The test method historically used for ensuring resin and compound uniformity has been the melt indexer or melt plastometer. The melt index test, however, is limited in relating polymer flow properties to actual processing conditions. It provides information only at low shear rates. Actual factory processes, such as calendering, extrusion, injection molding, transfer molding, and so forth, are performed under moderate to high shear rate conditions. The ACR is capable of measuring the viscosity of resins and compounds over the total range of processing shear rates thereby providing information relative to actual processing.
Use of the ACR in a quality control environment will be discussed along with data interpretation.
quality control, viscosity, rheological properties, evaluation, polymers, rheology, compounding, flow properties, polymeric materials, automatic capillary rheometer, constant pressure capillary, resin evaluation
Marketing technical service representative, Monsanto Polymer Products Co., Akron, OH