Boulters Farm Centre
Castlemorton Common
533566704
Welland Malvern
Worcestershire
MEASURING POWDER FLOW PROPERTIES – A COMPARISON OF WR13 6LE
United Kingdom
EMPIRICAL DYNAMIC MEASUREMENTS WITH
SINGLE PLANE SHEAR CELL DATA
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This paper is a comparative study of powder flowability using two techniques. The newest
is 1684
an empirical
method that measures the energy needed to establish three dimensional flow patterns
at
closely
controlled
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packing conditions. The other is the shear cell in which the powder sample is sheared across a single plane
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in order to determine its shear strength, cohesion and angle of internal friction.
The instrument used for this study is the FT4 Powder Rheometer (Freeman Technology) that conventionally
measures the dynamic flow properties of powders but can also measure shear properties using its automated
shear cell accessory. The main objective of this study is to correlate the data from the two methods,
determine levels of reproducibility and assess the sensitivity to some of the key variables that affect powder
flow properties.
Shear cell methodology is attractive because the single plane of shearing allows the shear strength to be
easily determined. However the single plane of shearing is not representative of normal flow experienced in
powder processing which is mostly three dimensional and complex. Dynamic flow assessments are
necessarily empirical but provide high reproducibility and high sensitivity to the key variables such as packing
condition, aeration, stability, moisture adsorption etc.
A number of different powder types are evaluated, including CRM-116 limestone having known shear
properties. The shear data provides yield loci for each material including the direct measurement of cohesion
– that is the shear strength at zero consolidation pressure. Penetration test data allows the determination of
the wall friction coefficient.
The dynamic assessments provide the key flowability parameters – Stability Index, Basic Flowability Energy,
Flow Rate Index, Compaction Indices and Aeration Ratio and these results are compared with the shear test
data to determine correlation.
Author: Mr Reg Freeman, Freeman Technology Ltd.
R E Freeman C Eng M I Mech E
J A Freeman
VAT No. 488-1707-11