National Physical Laboratory

Capillary and slit die extrusion rheometry

Capillary and slit die extrusion rheometers are used predominantly to determine the shear viscosity of molten materials.

The principle is to measure the pressure drops across one or more dies for various volume flow rates, from which shear viscosity is calculated. Corrections can be applied to the data to take into account errors in the measurement procedure and for that reason various "hear viscosities"- end-corrected and Rabinowitsch corrected - exist.

The method can also be used to determine entrance pressure drop values as a function of flow rate. These values can be related to the extensional viscosity of the material. Such values, particularly when comparing similar types of material, are considered to be qualitatively valuable, for example in ranking materials. Through modification the method can also be used to determine the pressure dependence of viscosity.

The method is suitable for generating quantitatively accurate data for modelling as well as for quality control.

NPL Facility: Two capillary extrusion rheometers, suited for molten polymers, covering a wide range of temperatures and shear rates using dies from 0.5 mm to 2 mm in diameter. Capability to measure pressure dependence of materials.

Last Updated: 18 Aug 2016
Created: 1 Sep 2008


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