【专业英语】14MeltFlowRate.pdfVIP

Capillary Flow Measurement of Shear Viscosity In measuring viscosity it is assumed that the polymer behaves as a Maxwell model and measurements are made of an apparent viscosity that depends on such variables as temperature, pressure, stress, and time. Cogswell [17] suggested criteria for selecting a suitable test method. These included a strain rate up to 10,000 s-1, to be appropriate for engineering purposes, conveniently measured to reproducibility of better than 5%, and to use a sample of less than 100 g. The capillary rheometer was considered to meet many of the requirements. Shear stress and shear rate data can be calculated from measurements of melt pressure and volumetric flow rate from Poiseuilles law by wall shear stress N/m2 PR  s 2L -1 4Q wall shear rate S  3 R where 2 P = pressure drop (N/m ) Q = volumetric flow rate (m3/s) R = capillary radius (m) L = capillary length (m) 3 6 Capillary rheometers can usually measure over a range of shear stresses from 10 to 10 2 -1 N/m and shear rates from 0.001 to 500,000 s . These rheometers can be considered to be a form of heated syringe in which a plunger pushes polymer melted in a cylinder through a capillary die at its exit. The options for measuring pressure are Apply a load with a set of known weights. Apply an adjustable gas pressure